Resistance in Cucurbita pepo and Cucurbita maxima germplasms to cucumber mosaic virus

Summary A total of 384 Cucurbita pepo and Cucurbita maxima accessions were evaluated in growth chambers or glasshouse tests for resistance to cucumber mosaic virus (CMV). Seedlings were mechanically inoculated at the cotyledon stage, and scored for symptoms on cotyledons and true leaves 7 and 18 days after inoculation. Significant variation in resistance was found. A limited number of accessions were free of visual symptoms of infection. One C. pepo accession and thirteen C. maxima accessions showed a high level of resistance. Generally, C. maxima may be considered more resistant to CMV compared to C. pepo. There is no close relationship between origin, fruit morphotypes and CMV resistance in either species. Some accessions (e.g., C. pepo PI 438699; C. maxima PI 176530, PI 265555, PI 368564, PI 500483) could be useful for the future breeding programmes. The C. pepo cvs. Cinderella and Defender F1, previously described as resistant, showed maximum susceptibility to the yellow strain of CMV.Abbreviations CMV cucumber mosaic virus - WMV watermelon mosaic virus - ZYMV zucchini yellow mosaic virus - CYVV clover yellow vein virus - ZYFV zucchini yellow fleck virus     

Persistence and conservation of a consumer-resource metapopulation with local overexploitation of resources

The monophagous flightless weevil Hadramphus spinipennis causes the frequent local extinction of its host plant Aciphylla dieffenbachii through overexploitation. Both species are endemic and restricted to the Chatham Islands group (New Zealand). The weevil is classified as endangered and the plant as a threatened species. As this herbivore-plant system is locally unstable long-term persistence only appears possible via a metapopulation structure in which subpopulations are connected by dispersal. This paper investigates this hypothesis using a spatially explicit model of a consumer population whose resource is patchily distributed. The parameters are adapted to the H. spinipennis-A. dieffenbachii system. Our model includes local population dynamics and dispersal of the consumer, the destruction of host plant patches due to foraging and their regeneration. The results show that the key factor for long-term persistence is the short-range dispersal of the consumer with high mortality during dispersal. Only this highly inefficient dispersal prevents the synchronisation of local dynamics while ensuring sufficient colonisation of regenerated patches. We also show that although synchronisation through spatially correlated environmental fluctuations may be critical for long-term persistence, it cannot replace the strong effects of dispersal. Thus, in a consumer-resource metapopulation with deterministic local extinction, the strength and spatial scale of consumer dispersal in relation to the spatial and temporal scales of the resource patch dynamics (patch destruction and regeneration, number, size and distance of patches) play a vital role for long-term persistence. The consequence for conservation management is that such metapopulations could in fact profit rather than suffer from decreasing connectivity of resource patches.     

交变磁场下磁纳米流冷却液强化柴油机缸盖微区域冷却

为能实现柴油机缸盖鼻梁微区域高效冷却兼顾节能化的要求,该文提出了一种通过外部施加交变磁场的方式促进磁纳米流内粒子的微运动达到强化传热的方法,并与传统乙二醇冷却液、Cu-乙二醇纳米流冷却液进行了柴油机缸盖鼻梁微区域传热效果的对比研究。结果表明:在0.17 Hz的磁场交变频率影响下,磁纳米流中加热棒温度值最大下降幅度提升了29.3%,内部粒子运动涡数增加。缸盖鼻梁微区域试验表明:相比传统乙二醇冷却液,稳态工况下,最大扭矩工况点和标定工况点处测点温度值最大下降幅度分别约为12%、14.4%,外特性工况下测点平均温度值降幅为23.7℃,约为9.4%。瞬态工况测试结果表明,采用交变磁场影响下的磁纳米流冷却液,柴油机预热时间较采用传统乙二醇冷却液和Cu-乙二醇纳米流冷却液分别缩短了9.8%和8.2%,柴油机急加速工况下能保持冷却液温度波动性小。能耗率计算结果表明,采用外部施加交变磁场加强磁纳米流冷却液高效传热的方式在达到相同冷却液温度时,可实现节能幅度为7.2%。该研究为柴油机乃至其他高温部件的节能化高效冷却提供科学参考。     

灌溉管网中变径管水力特征的试验研究与数值模拟

运用RNGk-ε紊流模型,对不同流速条件下管道中流体的流动进行了数值模拟。给出了6种常见PVC变径管件的模拟计算结果,并选取其中4组进行试验验证。对变径管件的局部能量损失机理进行了探讨,分析了灌溉管网中变径段独特的水流特性及能量耗散机理。结果表明,模拟结果与试验结果基本吻合,得到了局部阻力系数与变径管上下游管径比的拟合关系式。     

切割材料广义择厚原则数学模型

本文运用局部调整法 ,给出了切割材料广义择厚原则数学模型     

Operation and maintenance in Asian irrigation: Reappraising government and farmer responsibilities and rights

A major policy concern in irrigation development is reducing government costs of both construction and operation and maintenance. There is increasing interest in shifting some of these costs to the farmers using the irrigation facilities. This paper discusses the opportunities for reducing certain direct costs to government by collaborative arrangements with water users so that the latter mobilize more of their own resources to implement specified O&M activities. Five propositions are discussed which suggest the prerequisites for successful collaboration: (1) reexamining the processes of design and construction now being used, (2) reorienting the policies and procedures of the irrigation agency, (3) increasing farmer involvement in operations, (4) increasing local organizational capacity, and (5) creating new financial procedures.     

美国学校中政治教育的演变阶段探析

本文试析了美国学校中政治教育的演变阶段先后为:建国后、南北战争后、1900年以后和21世纪60年代后，认为随着21世纪的到来，美国学校中的政治教育又进入了一个新的发展盯段，并且尝试探析了这种划分对我国政治教育的启示。     

毛泽东与实学传统

实事求是、经世致用、史学经世是中国传统实学的重要组成部分 ,也是毛泽东与实学传统间关系最为密切的三个方面。毛泽东自青少年时代起就接受了实学传统的积极影响 ,完成世界观转变后 ,他又运用马克思主义的科学态度自觉地批判继承了这一传统 ,并实现了马克思主义的超越。毛泽东不愧为站在现代社会制高点上正确处理传统文化的一位大师