945 resultados para 1089
Resumo:
本研究初步建立了基于土壤水分平衡原理的毛乌素沙地草地种植咨询系统“ASSG”,该系统用于进行毛乌素地区沙地草地利用和种植管理咨询,并可进行更新知识库和存储有关咨询结果的操作。该系统适用于田间工作者、农场管理者、有关科研人员以及任何对生态科学和自然资源管理感兴趣者。 在文中描述了该咨询系统的开发过程,即系统的需求分析、设计、实现和运行,该系统实现了专家系统和仿真模型的结合,该模型即基于水分平衡的最佳植被覆盖率模型,有如下初步结论产生:土壤水分的平衡随植被覆盖率变化的情况(上升或下降)取决于立地条件的差异,笼统地讲“植被覆盖率越高越好”或“植被覆盖率一概不宜太高”未免失之偏颇。 在解决复杂的生态学问题时人工智能/专家系统技术的应用以及在定性模型和方法(如专家系统)的应用中使用定量模型(如仿真模型)正处于发展之中,本系统的实现是应用专家系统与仿真模型结合的方法解决实际生态学问题的又一个例子。
Resumo:
Carnivora; Caniformia; Feliformia; Phylogenetic tree; Mitochondrial DNA; Nuclear genes; 【摘要】 追溯生物界不同生物类型的起源及进化关系,即重建生物类群的系统发育树是进化生物学领域中一个十分重要的内容。食肉目哺乳动物位于食物链顶端,很多成员不仅在我国野生动物保护工作中占有重要地位,而且还是研究动物适应性进化遗传机制的重要模式生物。因而,食肉目物种作为物种资源中的一个重要类群,其系统发育学一直是国内外研究的热门课题。构建可靠的食肉目分子系统树,无疑将具有重要的进化理论意义和保护生物学价值。鉴于目前食肉目各科间系统发育关系仍然处于“广泛争论”的状态,本文将针对食肉目科水平上的系统发育学研究进展,包括来自于形态学特征、细胞学及分子生物学方面的证据,做简要概述,并提出目前研究中存在的问题。这对今后食肉目系统发育方面的进一步研究工作具有指导意义,并为以该类群作为模式生物开展适应性进化研究奠定基础
Resumo:
Just under half of all energy consumption in the UK today takes place indoors, and over a quarter within our homes. The challenges associated with energy security, climate change and sustainable consumption will be overcome or lost in existing buildings. A background analysis, and the scale of the engineering challenge for the next three to four decades, is described in this paper.
Resumo:
Just under half of all energy consumption in the UK today takes place indoors, and over a quarter within our homes. The challenges associated with energy security, climate change and sustainable consumption will be overcome or lost in our existing buildings. A background analysis, and the scale of the engineering challenge for the next three to four decades, is described in this paper.
Resumo:
Apo-14 is a fish-specific apolipoprotein and its biological function remains unknown. In this study, CagApo-14 was cloned from gibel carp (Carassius auratus gibelio) and its expression pattern was investigated during embryogenesis and early larval development. The CagApo-14 transcript and its protein product were firstly localized in the yolk syncytial layer at a high level during embryogenesis, and then found to be restricted to the digestive system including liver and intestine in later embryos and early larvae. Immunofluorescence staining in larvae and adults indicated that CagApo-14 protein was predominantly synthesized in and excreted from sinusoidal endothelial cells of liver tissue. Morpholino knockdown of CagApo-14 resulted in severe disruption of digestive organs including liver, intestine, pancreas and swim bladder. Moreover, yolk lipid transportation and utilization were severely affected in the CagApo-14 morphants. Overall, this data indicates that CagApo-14 is required for digestive system organogenesis during fish embryogenesis and larval development.
Resumo:
采用静态优先级调度的实时系统中,当任务个数多于优先级个数时,只能给多个任务分配相同的优先级·现有分配算法增大了高优先级任务的最坏情况响应时间,可能造成任务集合不可调度·利用抢占阈值的调度算法,能在提高任务集合可调度性的同时,使用较少的线程·但所用优先级个数没有减少·提出了一种优先级映射算法———阈值段间映射法(threshold segment mapping,TSM),以及与之配合的事件驱动线程框架·证明了TSM是严格排序的·仿真结果表明,在保证任务集合可调度的前提下,TSM使用了比现有映射算法更少的优先级·
Resumo:
本文讨论了太阳能游泳池的设计方法,得出了一些经验公式和一系列有用的数据,并进行了热损失计算。 本文还介绍了广东省中山市的一个太阳能游泳池的运行特性,并对复盖保温气垫膜的游泳池进行了传热分析,最后以广州地区的气象条件为例,对不同的太阳能游泳池的运行温度作了预测。
Resumo:
Relative paleointensity records from the northern South China Sea, northwest Pacific Ocean were studied in two gravity piston cores. Continuous mineral magnetic and paleomagnetic measurements were made using discrete sediment samples. Detailed rock magnetic parameters, such as thermomagnetic and high-field hysteresis data, indicate that pseudo-single domain magnetite in a narrow range of grain-size and concentration is the main contributor to the remanent magnetization. The uniform magnetic mineralogy meets the commonly accepted criteria for establishing relative paleointensity records. The relative paleointensity (RPI) curves were constructed by normalizing the natural remanent magnetization (NRM) with isothermal remanent magnetization (IRM), both in the 20-60 mT demagnetization state. Dating constraints have been provided by radiocarbon ages in the upper 400 cm of both cores. Furthermore, we have correlated our paleointensity records with NAPIS-75, S.Atlantic-1089, Sint-200 and NOPAPIS-250 to determine the chronological RPI framework for the South China Sea (SCS-PIS). Although some temporal offsets of paleointensity features between the different records have been recognized, their similar shape suggests that relative paleointensity on the 10(3)-10(4) year scale is globally coherent and can provide an age framework for sediments independent of delta O-18 ages.