42 resultados para Hopkins, Ezekiel, 1634-1690.


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Pheromones are chemical cues released and sensed by individuals of the same species, which are of major importance in regulating reproductive and social behaviors of mammals. Generally, they are detected by the vomeronasal system (VNS). Here, we first investigated and compared an essential genetic component of vomeronasal chemoreception, that is, TRPC2 gene, of four marine mammals varying the degree of aquatic specialization and related terrestrial species in order to provide insights into the evolution of pheromonal olfaction in the mammalian transition from land to water. Our results based on sequence characterizations and evolutionary analyses, for the first time, show the evidence for the ancestral impairment of vomeronasal pheromone signal transduction pathway in fully aquatic cetaceans, supporting a reduced or absent dependence on olfaction as a result of the complete adaptation to the marine habitat, whereas the amphibious California sea lion was found to have a putatively functional TRPC2 gene, which is still under strong selective pressures, reflecting the reliance of terrestrial environment on chemical recognition among the semiadapted marine mammals. Interestingly, our study found that, unlike that of the California sea lion, TRPC2 genes of the harbor seal and the river otter, both of which are also semiaquatic, are pseudogenes. Our data suggest that other unknown selective pressures or sensory modalities might have promoted the independent absence of a functional VNS in these two species. In this respect, the evolution of pheromonal olfaction in marine mammals appears to be more complex and confusing than has been previously thought. Our study makes a useful contribution to the current understanding of the evolution of pheromone perception of mammals in response to selective pressures from an aquatic environment.

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用角膜表皮刮磨方法人工造成兔眼角膜创伤直径为10mm的圆形创面,分析小鼠表皮生长因子(EGF)对其修复的剂量关系。5个浓度EGF(100、50、20、10和0.5μm/ml)治疗的试验组痊愈时间均比对照组提前,有非常显著的差异(P<0.01),但在这5个浓度组之间,痊愈时间无显著性差异。结果表明,小鼠EGF对兔眼角膜损伤有促修复作用,实验所用的5个浓度与修复作用无剂量依赖关系。

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运用透射电镜及荧光显微技术 ,对富营养化的武汉东湖中浮游病毒丰度及多样性进行了研究。电镜观察和计数结果显示 ,东湖中浮游病毒的丰度达到 10 8个 /mL。荧光显微镜计数结果约是电镜计数结果的 2 72倍 ,差异极显著 (P <0 0 1)。在东湖超富营养区的水样中观察到了多种与各种病毒形态类似的颗粒 ,其中大部分与噬菌体和噬藻体类似 ,具多种形态的尾部和六边形头部。还有一些线状、杆状、子弹形等形态的病毒粒子。研究结果显示东湖水环境中的浮游病毒不仅丰度极高 ,而且种类丰富。提示浮游病毒在东湖水环境和水生态

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中国科学院知识创新工程重大项目 (KSCXI SW 13 0 4) ; 国家重点基础研究发展计划 (2 0 0 3CB415 10 3 )资助

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<正> 脂肪含量的测定,是鱼类能量学及营养学的重要环节。目前最常用的测定方法,是用氯仿一甲醇(2:1)混合液(下面简称C-M液)抽提。这一方法的基本步骤见图1。不同研究者采用的具体步骤有所差异。如崔奕波引用的方法系将样品用C-M液匀浆后直接离心,而Hopkins等对样品不匀浆,仅用C-M液浸泡半小时后离心。这一方法最初是用于医学检验;在生态学研究中。常需要测定大量样品,故方法的简化尤为重要。本研究的目的是探讨不同抽提步骤对测定结果的影响,以期对原方法进行简化;同时将C-M抽提法与我国常用的索氏乙醚抽提法进

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提出一种新的基于分布布拉格反射可调激光器的光外差频率响应测试系统,并给出了准确有效的校准方法来消除输出光功率和拍频线宽的波动等引起的误差,从而可以精确表征高速光探测器的频率响应特性.通过对标准高速光探测器的测试和校准,得到的结果与制造商提供的数据表相当符合,证明了该测试方法的准确性和有效性.文中也研究了系统中可能会影响频响特性测量的其他因素,如光源的边模抑制比、波长调谐速度等.

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采用RNG(renormalization group)k-ε湍流模型和近壁区的Wolfstein一方程模型对超临界压力下大庆RP-3航空煤油在水平圆管内的流动和换热特性进行了数值研究.超临界压力下,由于航空煤油在拟临界点附近热物性的剧烈变化,浮升力将引起显著的二次流动.二次流动使得水平圆管的下表面湍流强度和对流换热增强,而上表面的湍流强度和对流换热减弱.最后分析了两种水平管内对流换热受浮升力影响判别标准在超临界流体中的适用性

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以森林资源遥感分类为切入点,以黄土高原丘陵沟壑区陕西黄龙县境内的水土保持林作为对象,针对ETM+遥感影像在森林信息提取中存在的大量混合像元的问题,引入一种基于针叶林-阔叶林-灌草(C-B-G)模型的混合像元分解方法,通过这种方法,分别得到研究区针叶林、阔叶林、灌草的覆盖图像,并提取出了针阔混交林的分布情况。采用ER-DAS 9.1对分类结果进行精度评价,结果表明针阔混交林的分类精度相对于通用分类方法——监督分类的精度提高了20%,说明该方法可以改善植被信息提取的效果。

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掌握矿区土地利用变化规律,有效制定矿区土地利用政策是矿山可持续发展的重要基础。利用RS和GIS技术对土地利用变化进行检测、变化信息提取与发现以及对其进行分析,得出了土地利用变化的基本规律,为矿区土地资源的合理利用提供决策依据。结果表明:该方法效率高,成本低,技术性强,是目前一种较先进的土地利用变化监测方法。