对海南清澜港海南海桑(Sonneratia×hainanensis W.C.Ko,E.Y.Chen et W.Y.Chen)群落现状进行系统调查,采用Levins指数、Pianka指数、Schoener指数和方差比率(VR)等指标以及χ^(2)检验对海南海桑群落中物种生态位特征和种间联结性进...对海南清澜港海南海桑(Sonneratia×hainanensis W.C.Ko,E.Y.Chen et W.Y.Chen)群落现状进行系统调查,采用Levins指数、Pianka指数、Schoener指数和方差比率(VR)等指标以及χ^(2)检验对海南海桑群落中物种生态位特征和种间联结性进行了研究。结果显示:海南海桑群落共有14种(变种,下同)植物,隶属于8科10属,其中海南海桑的重要值(33.48%)和生态位宽度(Levins指数为14.40)在群落中均排名第1,明显高于其他物种。14种植物共组成91个种对,其中Pianka指数和Schoener指数小于0.5的种对数分别占总种对数的86.8%和92.3%,说明群落中大部分物种间的生态位重叠程度和生态位相似性较低,种间竞争不激烈。海南海桑群落物种间总体表现为不显著负联结,并有84.6%的种对联结性不显著,说明群落物种间联结性不强,具有一定的独立性。海南海桑与其他植物组成的13个种对中,显著联结种对数仅占38.5%,说明海南海桑与群落中大部分物种联结性较弱。综合分析认为,生态位特征和种间联结不是海南海桑濒危的主要因子,可从开展人工辅助育种工作、加大就地保护力度和优化迁地保护策略方面考虑海南海桑种群的保护与恢复。展开更多
Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, bu...Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, burr, poor surface quality and rapid wear of cutters. Accurate and fast pre- diction of cutting forces is important for milling C/C composite materials with high quality. This paper presents an alternative cutting force model involving the influences of the directions of fiber. Based on the calculated and experimental results, the cutting forces＂ coefficients of 2.5D CC com- posites are evaluated using multiple linear regression method. Verification experiment has been car- ried out through a group of orthogonal tests. Results indicate that the proposed nmdel is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.展开更多
文摘对海南清澜港海南海桑(Sonneratia×hainanensis W.C.Ko,E.Y.Chen et W.Y.Chen)群落现状进行系统调查,采用Levins指数、Pianka指数、Schoener指数和方差比率(VR)等指标以及χ^(2)检验对海南海桑群落中物种生态位特征和种间联结性进行了研究。结果显示:海南海桑群落共有14种(变种,下同)植物,隶属于8科10属,其中海南海桑的重要值(33.48%)和生态位宽度(Levins指数为14.40)在群落中均排名第1,明显高于其他物种。14种植物共组成91个种对,其中Pianka指数和Schoener指数小于0.5的种对数分别占总种对数的86.8%和92.3%,说明群落中大部分物种间的生态位重叠程度和生态位相似性较低,种间竞争不激烈。海南海桑群落物种间总体表现为不显著负联结,并有84.6%的种对联结性不显著,说明群落物种间联结性不强,具有一定的独立性。海南海桑与其他植物组成的13个种对中,显著联结种对数仅占38.5%,说明海南海桑与群落中大部分物种联结性较弱。综合分析认为,生态位特征和种间联结不是海南海桑濒危的主要因子,可从开展人工辅助育种工作、加大就地保护力度和优化迁地保护策略方面考虑海南海桑种群的保护与恢复。
基金supported by the National Natural Science Foundation of China(No.51105312)the Fundamental Research Funds for the Central University of China(No.3102015JCS05005)
文摘Machining of carbon/carbon （C/C） composite materials is difficult to carry out due to its high specific stiffness, brittleness, anisotropic, non-homogeneous and low thermal conductivity, which can result in tear, burr, poor surface quality and rapid wear of cutters. Accurate and fast pre- diction of cutting forces is important for milling C/C composite materials with high quality. This paper presents an alternative cutting force model involving the influences of the directions of fiber. Based on the calculated and experimental results, the cutting forces＂ coefficients of 2.5D CC com- posites are evaluated using multiple linear regression method. Verification experiment has been car- ried out through a group of orthogonal tests. Results indicate that the proposed nmdel is reliable and can be used to predict the cutting forces in ball-end milling of 2.5D C/C composites.
