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Potential impacts of climate change on Welwitschia mirabilis populations in the Namib Desert,southern Africa
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作者 Pierluigi BOMBI 《Journal of Arid Land》 SCIE CSCD 2018年第5期663-672,共10页
Climate change is threatening natural ecosystems in the Earth, and arid regions of southern Africa are particularly exposed to further drying. Welwitschia mirabilis Hook. (Welwitschiaceae) is an unusual gymnosperm t... Climate change is threatening natural ecosystems in the Earth, and arid regions of southern Africa are particularly exposed to further drying. Welwitschia mirabilis Hook. (Welwitschiaceae) is an unusual gymnosperm tree that is recognized as an icon of the Namib Desert, southern Africa. Many aspects of its biology were investigated in the past, with a special emphasis for its physiology and adaptations, but nothing is known about its potential sensitivity to current climate changes. In this study, we adopted an approach based on distribution data for W. mirabilis and ecological niche models for clarifying the species-climate interactions and for predicting the potential impacts of climate change on W. mirabilis populations in three well-separated sub-ranges (northern, southern and central) in northwestern Namibia, southern Africa. We evidenced that the populations occurring in the northern sub-range have peculiar climatic exigencies compared with those in the central and southern sub-ranges and are particularly exposed to the impact of climate change, which will consist of a substantial increase in temperature across the region. These impacts could be represented by demographic changes that should be detected and monitored detailedly to plan efficient measures for managing populations of this important species on the long-term scale. 展开更多
关键词 global warming range fragmentation climatic suitability Welwitschia mirabilis ecological niche model Namib Desert
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基于ABAQUS的气动潜孔锤球齿碎岩及布齿优化
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作者 杨秋明 周兢 +2 位作者 王瑜 夏柏如 吴浩 《钻探工程》 2024年第1期40-50,共11页
为提高坚硬地层大直径潜孔锤的破岩效率与使用寿命,运用ABAQUS软件建立了球齿碎岩仿真模型,对比分析?18 mm球齿在不同钻进参数下冲击切削碎岩过程中的破碎比功、侵入深度、破碎范围与应力影响范围等曲线,优选钻进参数和布齿。分析结果表... 为提高坚硬地层大直径潜孔锤的破岩效率与使用寿命,运用ABAQUS软件建立了球齿碎岩仿真模型,对比分析?18 mm球齿在不同钻进参数下冲击切削碎岩过程中的破碎比功、侵入深度、破碎范围与应力影响范围等曲线,优选钻进参数和布齿。分析结果表明:当钻压为1.2 kN、冲击功为30 J时,对岩石的破碎效率较高,球齿入岩的位移可达0.67 mm,并对岩石进行应力界限划分,得出应力影响范围为43.4 mm;通过双齿冲击切削模拟确定了较为优秀的圈距与间距:圈距取47.4 mm,间距取43.4~51.4 mm;考虑到球齿的磨损,利用圈距与间距对?711 mm大直径潜孔锤进行了优化布齿。 展开更多
关键词 气动潜孔锤 球齿 钻进参数 布齿 应力影响范围 坚硬地层 岩石破碎 ABAQUS
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某复合增程弹底排船尾碎裂原因探析及对策
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作者 赵丽俊 毛亮 +2 位作者 赵国伟 王连义 邸建国 《兵器材料科学与工程》 CAS CSCD 北大核心 2013年第3期110-113,共4页
为探寻某复合增程弹底排船尾碎裂的原因,对回收弹体、底排船尾残骸及同批次弹体和回收的底排船尾的力学特性进行检测,复查试验用弹体和底排船尾的力学特性参数。对发射时底排药柱的受力情况进行分析,并建立药柱强度的计算方法。结果表明... 为探寻某复合增程弹底排船尾碎裂的原因,对回收弹体、底排船尾残骸及同批次弹体和回收的底排船尾的力学特性进行检测,复查试验用弹体和底排船尾的力学特性参数。对发射时底排药柱的受力情况进行分析,并建立药柱强度的计算方法。结果表明,底排船尾碎裂是由于底排药柱与船尾之间存在空隙,发射时出现受力不均而导致强度不足所致;通过填充柔性体可以解决。 展开更多
关键词 复合增程弹 底排船尾 碎裂 底排药柱
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