999 resultados para 1477


Relevância:

10.00% 10.00%

Publicador:

Resumo:

利用飞秒激光散斑的信息,可以得知散射体的空间运动信息。为此提出了飞秒激光散斑相关测量技术,将散射体变化或移动前后的飞秒散斑场分别用CCD探测器记录下来并储存于计算机中,对移动前的飞秒散斑场和移动后的飞秒散斑场进行相关性运算,就可以确定出散射体的有关特性或移动量,实现对飞秒散斑场移动实时测量。结果表明,实验中散射体的位移量与用相关算法得到散射体的移动量相吻合,证实了飞秒散斑相关法测量的可行性。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

采用Ag^+-Na^+离子工艺,在K9玻璃上制备了跑道形波导谐振腔滤波器.测试得到该滤波器自由光谱范围为FSR=0.177nm,对比对为Cr=7.5dB.同时分析得到耦合器的耦合系数为κ=0.916,耦合器和环形腔的损耗因子分别为δ=0.55,γ=0.48.耦合器的两波导几乎相连、条波导边缘不规则和一次离子交换波导表面缺陷是造成该波导滤波器具有较大损耗的主要原因。通过改进工艺技术降低波导损耗,该滤波器可以用于光通信、传感等领域,也可与其它波导结构相结合实现新的功能。

Relevância:

10.00% 10.00%

Publicador:

Relevância:

10.00% 10.00%

Publicador:

Resumo:

水分条件不仅影响半干旱区群落的组成,而且在一定程度上决定了群落的功能。处于不同水分条件生境下群落的优势物种在水分利用和同化物利用效率方面的功能特征会存在差异,这些差异将导致群落对于气候变化产生不同的响应,进而影响到景观和区域尺度上对于全球变化下碳动态和格局的分析。本研究选取了锡林河流域典型草原区沿水分梯度的四个代表群落,在野外实验测定并结合长期定位研究成果基础上,利用BIOME-BGC模型对代表群落的长期净初级生产力(NPP)动态进行了模拟和模型验证。通过分析该地区1953~2005年气候变化趋势,推测了未来可能的气候变化情景,进而模拟了气候变化下四个群落长期NPP动态的响应。 野外实验分析表明,在四个群落中,净光合速率与光合有效辐射呈单峰曲线关系,与温度和蒸气压亏损(VPD)成反比,叶片氮含量和比叶面积也会影响到光合能力。四个群落由于水分与土壤条件的差别,净光合速率随VPD与温度的变化表现出不同的增减幅度。将日变化分为四个阶段,分别为大致在6:00~8:00左右的低温高湿阶段,10:00~16:00的高温低湿阶段,16:00以后的低温低湿阶段和低温高湿阶段变为高温低湿阶段过程中的适温适湿阶段。在每个阶段中,影响羊草光合速率的主导因子是不同的。在不同的水分与土壤状况下,羊草的光合特性表现出明显差异,但总体说来水分仍是光合作用的主导因子。 模型模拟结果表明,当前气候条件下,羊草群落NPP平均值为197.76 gC m-2 (SE=7.11),大针茅群落NPP平均值为198.95 gC m-2 (SE=6.41),贝加尔针茅群落NPP平均值为210.41 gC m-2 (SE=7.87),克氏针茅群落NPP平均值为144.92 gC m-2 (SE=4.64),四个群落NPP平均值为188.01 gC m-2 (SE=3.72)。 日最高温度与最低温度在1953~2005年间都明显增加,而降水变化很大。温度增加下(P0T1)NPP平均下降14.2%,降水增加下(P1T0)NPP平均增加13.2%,温度与降水都增加情景下(P1T1)NPP平均下降2.7%。在半干旱区,降水是NPP变化的主要限制因子,而温度通过影响了植物的呼吸与蒸散作用对NPP产生影响。 由于生境水分条件差别和优势物种功能特征差异,四个群落在气候变化中表现出对温度与降水不同的敏感程度,这与水分胁迫系数WSI、碳胁迫系数CSI变化密切相关。克氏针茅群落由于所处生境水分条件差,水分胁迫系数高,对降水的依赖程度最大;贝加尔针茅群落一方面处于较好的水分生境,具有相对较小的水分胁迫系数,另一方面,由于具有高碳氮比,维持呼吸消耗的光合产物比例低,碳胁迫系数远低于其它三个群落,未来气候变化下NPP较其它三个群落仍较高。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Cross-species painting (fluorescence in situ hybridization) with 23 human (Homo sapiens (HSA)) chromosome-specific painting probes (HSA 1-22 and the X) was used to delimit regions of homology on the chromosomes of the golden mole (Ghrysochloris asiaticus) and elephant-shrew (Elephantulus rupestris). A cladistic interpretation of our data provides evidence of two unique associations, HSA 1/19p and 5/21/3, that support Afrotheria. The recognition of HSA 5/3/21 expands on the 3/21 synteny originally designated as an ancestral state for all eutherians. We have identified one adjacent segment combination (HSA2/8p/4) that is supportive of Afroinsectiphillia (aardvark, golden mole, elephant-shrew). Two segmental combinations (HSA 10q/17 and HSA 3/20) unite the aardvark and elephant-shrews as sister taxa. The finding that segmental syntenies in evolutionarily distant taxa can improve phylogenetic resolution suggests that they may be useful for testing sequence-based phylogenies of the early eutherian mammals. They may even suggest clades that sequence trees are not recovering with any consistency and thus encourage the search for additional rare genomic changes among afrotheres.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The authors use simulation to analyse the resource-driven dependencies between concurrent processes used to create customised products in a company. Such processes are uncertain and unique according to the design changes required. However, they have similar structures. For simulation, a level of abstraction is chosen such that all possible processes are represented by the same activity network. Differences between processes are determined by the customisations that they implement. The approach is illustrated through application to a small business that creates customised fashion products. We suggest that similar techniques could be applied to study intertwined design processes in more complex domains. Copyright © 2011 Inderscience Enterprises Ltd.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

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.