寄生是生物有机体之间一种常见的互作关系,其有趣的生理、生态和进化问题日益受到关注与研究。以小红花寄生(Scurrula parasitica var. graciliflora)为研究对象,研究了该植物的开花物候、繁育系统、种子萌发特性及寄生关系的建立。结...寄生是生物有机体之间一种常见的互作关系,其有趣的生理、生态和进化问题日益受到关注与研究。以小红花寄生(Scurrula parasitica var. graciliflora)为研究对象,研究了该植物的开花物候、繁育系统、种子萌发特性及寄生关系的建立。结果表明:小红花寄生的开花高峰期为4月中下旬至5月下旬。花冠筒闭合期间与花冠筒开裂24 h后的花粉活力均> 90%,且两者之间没有显著差异(P>0.05),但花冠筒开裂48 h之后的花粉活力≤70%。柱头可授性在花冠筒闭合期间显著高于花冠开裂之后(P<0.05)。自然授粉的对照组和花蕾期套袋的实验组的座果率(分别是82.5%和83.1%)显著高于花开放之后的异花授粉的实验组的座果率(33.8%)(P<0.05),而去除雄蕊的花则未能结实。小红花寄生的种子对脱水敏感,严重脱水显著降低种子萌发率。适宜的种子萌发温度为25℃和30/20℃。仅在桂花幼树的茎顶叶腋处获得了6.25%的寄生成功率,而其他部位的人工寄生均不成功。综合分析表明,两性花的小红花寄生依赖于前自交型的自花授粉;种子萌发表现出明显的温度偏好性,但对光照没有依赖性。人工寄生成功率显示,种子依附的寄主部位直接影响小红花寄生的幼苗与寄主寄生关系的建立。展开更多
Variational modeling approach is often used to interactively design free-form curves and surfaces. Traditionally, a variational problem can be transformed to the optimization of control points. Unfortunately, as the n...Variational modeling approach is often used to interactively design free-form curves and surfaces. Traditionally, a variational problem can be transformed to the optimization of control points. Unfortunately, as the number of basis functions grows, the local support property of B-spline often makes the computation of an optimization system time-consuming. To solve this problem, wavelet basis instead of B-spline basis is used to represent the curves or surfaces. Because the wavelet basis is a hierarchical basis with multiresolution property, the coarse wavelet basis can be used to describe the overall shape of the curves/surfaces, while the finer wavelet basis used to describe the details of the curves/surfaces. Thus, the computing speed of the optimization system can be raised greatly.展开更多
With the rapid increase in the number of three-dimensional （3D） models each year, to quickly and easily find the part desired has become a big challenge of enterprises. Meanwhile, many methods and algorithms have be...With the rapid increase in the number of three-dimensional （3D） models each year, to quickly and easily find the part desired has become a big challenge of enterprises. Meanwhile, many methods and algorithms have been proposed for part retrieval. However, most of the existing methods are designed lbr mechanical parts, and can not be well worked for sheet metal part re- trieval. An approach to feature-based retrieval of sheet metal parts is presented. Firstly, the features frequently used in sheet metal part design are chosen as the ＂＇key words＂ in retrieval. Based on those features, a relative position model is built to express the different relationships of the features in 3D space. Secondly, a description method of the model is studied. With the descrip- tion method the relative position of features in sheet metal parts can be expressed by four location description matrices. Thirdly, based on the relative position model and location description matrices, the equivalent definition of relationships of two feature groups is given which is the basis to calculate the similarity of two sheet metal parts. Next, the tbrmula of retrieval algorithm for sheet metal parts is given. Finally, a prototype system is developed to test and verify the effectiveness of the retrieval method suggested. Experiments verify that the new method is able to meet the requirements of searching sheet metal parts and possesses potentials in practical application.展开更多
文摘Variational modeling approach is often used to interactively design free-form curves and surfaces. Traditionally, a variational problem can be transformed to the optimization of control points. Unfortunately, as the number of basis functions grows, the local support property of B-spline often makes the computation of an optimization system time-consuming. To solve this problem, wavelet basis instead of B-spline basis is used to represent the curves or surfaces. Because the wavelet basis is a hierarchical basis with multiresolution property, the coarse wavelet basis can be used to describe the overall shape of the curves/surfaces, while the finer wavelet basis used to describe the details of the curves/surfaces. Thus, the computing speed of the optimization system can be raised greatly.
基金National High-tech Research and Development Program of China (2009AA043302)
文摘With the rapid increase in the number of three-dimensional （3D） models each year, to quickly and easily find the part desired has become a big challenge of enterprises. Meanwhile, many methods and algorithms have been proposed for part retrieval. However, most of the existing methods are designed lbr mechanical parts, and can not be well worked for sheet metal part re- trieval. An approach to feature-based retrieval of sheet metal parts is presented. Firstly, the features frequently used in sheet metal part design are chosen as the ＂＇key words＂ in retrieval. Based on those features, a relative position model is built to express the different relationships of the features in 3D space. Secondly, a description method of the model is studied. With the descrip- tion method the relative position of features in sheet metal parts can be expressed by four location description matrices. Thirdly, based on the relative position model and location description matrices, the equivalent definition of relationships of two feature groups is given which is the basis to calculate the similarity of two sheet metal parts. Next, the tbrmula of retrieval algorithm for sheet metal parts is given. Finally, a prototype system is developed to test and verify the effectiveness of the retrieval method suggested. Experiments verify that the new method is able to meet the requirements of searching sheet metal parts and possesses potentials in practical application.
