一类强非线性微分方程极限环的非线性时间变换法

应用非线性时间变换法研究一类强非线性微分方程的极限环,它给出极限环的近似解,当方程中的参数较小时,精确度令人满意,其特点是计算简便.     

关于（Ⅱ）_（n＝0）系统极限环的分布

本文得到了二个保证（Ⅱ）ｎ＝０系统的极限环是（１，１）分布的充要条件。     

Ground reaction forces and osteogenic index of the sport of cyclocross

Abstract

Weight-bearing activity has been shown to increase bone mineral density. Our purpose was to measure vertical ground reaction forces (GRFs) during cyclocross-specific activities and compute their osteogenic index (OI). Twenty-five healthy cyclocross athletes participated. GRF was measured using pressure-sensitive insoles during seated and standing cycling and four cyclocross-specific activities: barrier flat, barrier uphill, uphill run-up, downhill run-up. Peak and mean GRF values, according to bodyweight, were determined for each activity. OI was computed using peak GRF and number of loading cycles. GRF and OI were compared across activities using repeated-measures ANOVA. Number of loading cycles per activity was 6(1) for barrier flat, 8(1) barrier uphill, 7(1) uphill run-up, 12(3) downhill run-up. All activities had significantly (P < 0.01) higher peak GRF, mean GRF values and OI when compared to both seated and standing cycling. The barrier flat condition (P < 0.01) had highest peak (2.9 times bodyweight) and mean GRF values (2.3 times bodyweight). Downhill run-up (P < 0.01) had the highest OI (6.5). GRF generated during the barrier flat activity is similar in magnitude to reported GRFs during running and hopping. Because cyclocross involves weight bearing components, it may be more beneficial to bone health than seated road cycling.     

生命周期视角下的广东中小工业企业转型与成长探讨

分析当前经济转型中国内中小企业的状况,阐述广东省中小工业企业发展基本情况及存在的问题,包括企业创业、成长环境堪忧,资源占有少等。最后提出优化创业环境、构建企业发展核心能力等广东省中小工业企业发展对策。     

生态学长期研究促进资源高效利用和区域农业可持续发展

华北平原农业的高强度水肥投入造成严重地下水超采和氮素污染风险。中国科学院栾城农业生态系统试验站立足农田生态系统的长期生态学监测和研究,围绕农业资源高效利用和可持续发展,建立了农田土壤-作物-大气系统(SPAC)界面节水调控理论与技术,提出基于农田水平衡的休耕轮作和适水型种植制度调整思路,阐明了农田碳氮循环特征和温室气体排放及硝酸盐淋失通量,在厚包气带水盐运移和硝酸盐转化和削减机理方面取得突破性认识,研发了农田生产信息快速获取和精准管理的技术产品与平台,并与农业发展紧密结合,集成了系列农业生产技术模式,为区域农业的优质高效发展和水资源可持续利用提供了理论和技术支撑。     

一个非线性连续培养模型的极限环及其周长

用微分动力系统的定性理论研究了一个非线性连续微生物培养动力系统的极限环问题,探讨和估计了存在极限环的条件和极限环的周长。本文的模型是对本文作者之一在多年前所提出和研究过的发酵模型的推广[5],这里我们对发酵产物与基质浓度的非线性函数关系做了进一步的深入研究。这一模型最近又被Pilyugin和Wahman在生化培养的研究中再次导出的[14]。工程界对于连续发酵的非线性振荡方面的研究大多是采用从实验数据归纳出来的经验模型,很难反映过程的本质;生物数学界有关这方面的模型,其中的函数大多数是文的特例。本文的工作无论从生化的角度还是从数学的角度考虑都是有意义的。     

Tracing the Olympiad's Chronological Arc

Modern purists prone to lament the tenuous links between the Olympic Games of antiquity and today's quadrennial extravaganzas often cite the four-year Olympic cycle as a symbol of continuity and permanence. Yet the Olympiad also evinces a striking historical paradox: this benchmark of ancient calendar reckoning has emerged, in our time-sensitive age, as a source of both chronological and semantic confusion, fragmenting into contextual strands bearing little relation to time cycles, the Olympic Games or sport. In revisiting these ancient--modern links, this article holds that the Olympiad's importance has traditionally been derivational and its precision relative rather than absolute. Multiple uncertainties persist over how the ancient festival was scheduled, affixed as a four-year cycle and retro-dated to 776 bce, reflecting wider struggles to forge a universal calendar standard in a fragmented Greek world. Such knowledge gaps, and the Olympiad's obsolescence as a recognised time frame, give new perspective to the definitional flaccidity and juridical half-life now associated with it. In its post-2000 switch from games-to-games to calendar-year reckoning, the IOC belatedly modernised the Olympiad cycle amidst a downgrading of its chronological significance. Alternative applications, however, evoke unexpected elements of continuity from antique notions of agonistic competition as a societal underpinning.     

Innovation in times of crisis: National Systems of Innovation, structure, and demand

This article addresses the impact of the current economic downturn on innovation across Europe. Using micro- and macro-data, we investigate to what extent some structural characteristics of National Systems of Innovation, along with demand, affect firms’ persistency in terms of innovation investment. It emerges that the effects of the economic downturn in terms of firms’ innovation investment are not the same across European countries. The competences and quality of the human resources, the specialization in the high-technology sector, together with the development of the financial system seem to be the structural factors which are able to offset the effect of the economic downturn on innovation investments of firms across Europe. Finally, some considerations about policies during recessions are discussed.     

具有固定权集合的赋权圈的无号拉普拉斯谱半径

赋权图的谱经常用来解决网络和电路设计中的问题.本文主要研究有固定点数和正的权集合的赋权圈的无号拉普拉斯谱半径,并找出其中无号拉普拉斯谱半径最大的圈.