快速成型中粗糙STL模型细分算法

快速成型过程中STL模型精度直接影响成型零件的成型精度,当面对粗糙的STL模型并且没有原始模型进行重新生成或者生成精度不高时,以及逆向工程三维重建得到的STL模型精度不能满足要求时,需要对STL模型进行细分以提高其表面精度,进而提高成型零件精度。为此,提出一种新的STL模型面边点拓扑信息结构,解决了两三角形面片共享边空间插值两次带来的精度误差问题;在此基础上,应用Hermite空间插值方法近似表示三角形面片三边所对应的空间曲线段,之后依据设定的规律连接空间曲线段的中点,实现对粗糙STL模型三角形面片的细分。试验结果表明:细分算法适用于形面较为复杂以及大尺寸多三角面片的STL模型,其效率可达4~n(n是细分次数),可以快速提高给定STL三维网格模型的表面精度。     

浙江严子陵钓台文化景观变迁探析

严子陵钓台是中国隐士文化景观的重要组成部分。通过文献整理,现场调研等研究方法,探索严子陵钓台历史变迁,共分为形成之初、繁荣发展、明清与近代发展3个时期。并且以钓台测绘图为基础,结合古籍文献对盛期钓台进行复原。在此基础上,从山水形胜、文人活动、景面文心3个方面分析了严子陵钓台的景观形成与特征。为严子陵钓台文化景观的保护提供参考,也为同类型文化景观的研究工作提供了一种研究思路。     

考虑物理特征的避障路径生成算法

自然、逼真的避障路径生成算法在仿真、游戏等领域有广泛应用。避障路径与障碍物的形状尺寸、运动物体的尺寸、转弯半径等物理属性密切相关。在综合考虑上述物理属性后,提出了一种避障路径生成算法。基于三次Hermit样条曲线的优异特性,算法生成的避障路径不仅具备C2连续性,而且还能保证新路径和原路径的连接具备G1连续性。算法被应用于某三维战场仿真系统,效果良好。     

严子陵隐逸意象在唐五代诗歌中的凝定历程

严子陵钓鱼的形象已经成为文学文化史中经典的隐逸意象。唐前涉及到严子陵的诗歌并不多;盛唐时关于严子陵隐逸意象的诗歌体现了盛唐文人漫游生活与建功立业的心态;中唐时期,以大历诗人为代表的文人由于失去进取心态而在其诗歌中以严子陵的隐逸意象表达其闲适之意;唐末五代时,世道的混乱使文人们的隐逸心理渐趋稳定。严子陵式的隐逸成为文人们效仿的生活方式,严子陵的经典隐逸意象在诗歌中渐趋凝定。     

隐逸文化对文人园林的影响

传统的隐逸文化对文人园林的发展有着重要影响.本文主要通过对魏晋南北朝时期隐逸文化的产生的回顾与研究及其与文人园林的联系,初步揭示隐逸文化对文人园林的影响.     

考虑物理特征的避障路径生成算法

自然、逼真的避障路径生成算法在仿真、游戏等领域有广泛应用。避障路径与障碍物的形状尺寸、运动物体的尺寸、转弯半径等物理属性密切相关。在综合考虑上述物理属性后,提出了一种避障路径生成算法。基于三次Hermit样条曲线的优异特性,算法生成的避障路径不仅具备C2连续性,而且还能保证新路径和原路径的连接具备G1连续性。算法被应用于某三维战场仿真系统,效果良好。     

Costs of a more spacious home after remodelling by hermit crabs

Architectural creations occur throughout the animal kingdom, with invertebrates and vertebrates building structures such as homes to maximize their Darwinian fitness. Animal architects face many trade-offs in building optimally designed structures. But what about animals that do not build, and those that only remodel the original creations of others: do such secondary architects face similar trade-offs? Recent evidence has revealed that hermit crabs—animals well known for opportunistically moving into remnant gastropod shells—can also act as secondary architects, remodelling the shells they inherit from gastropods. Remodelling has only been found among terrestrial hermits (Coenobita spp.), not marine hermits. Here we investigate the potential trade-offs Coenobita compressus faces from remodelling by subjecting its remodelled and unremodelled homes to controlled engineering crush tests, which parallel the homes being crushed by predators. While remodelled homes are significantly more spacious and lightweight than unremodelled homes, we find that the homes attain these beneficial qualities at a cost: a reduced resistance to being crushed. Hermit crabs may therefore only remodel their homes to thresholds set by the bite force of their predators. Our results suggest that, like primary animal architects, which face trade-offs when optimizing architectural designs, secondary animal architects face trade-offs when remodelling such designs.     

Chemical attraction of hermit crabs and other attendants to simulated gastropod predation sites

Simulated gastropod predation sites were observed in the gulf intertidal near the Edward Ball Marine Laboratory, Sopchoppy, Florida,Fundulus similis, Callinectes sapidus, Melongena corona, Clibanarius vittatus, andPagurus longicarpus were attracted to the sites by small molecules released passively from the flesh of wounded or dead animals. Flesh consumers (F. similis, C. sapidus, andM. corona) were attracted to molecules released from the flesh of bivalves, gastropods, and crabs. Shell users (C. vittatus andP. longicarpus) were attracted only to small molecules from gastropod flesh, withP. longicarpus attendingP. duplicatas sites whileC. vittatus preferentially attendedM. corona, Busycon contrarium, andBusycon spiratum sites. Flesh consumers and shell users may be attracted to the sites by different sets of small molecules. The addition of proteolytic enzymes to the flesh increased the attendants at a site, indicating that the attractant molecules might be amino acids or small peptides. Flesh consumers were attracted to the sites primarily in the first 12 hr while the shell users were attracted from 2 hr to several days postinitiation. New shells were attractive to hermit crabs up to 12 hr after entry by a hermit crab. The shell species of the attendantC. vittatus were in different proportions than the generalC. vittatus population, and the shell fit of theP. longicarpus attendants was not as good as the general population ofP. longicarpus. Significantly moreC. vittatus attended than P. longicarpus, and it was speculated that there were moreC. vittatus in the area with a poor shell fit thanP. longicarpus.     

Disturbance and reattachment behavior of sea anemonesCalliactis tricolor (Le Sueur): Temporal,textural and chemical mediation

Two hermit crabs,Dardanus venosus (Milne-Edwards) andPagurus pollicaris Say, have evolved mutualistic symbiotic relationships with sea anemones,Calliactis tricolor (Le Sueur). Anemones live on gastropod shells occupied by the crabs. Both partners are thought to participate in the transfer of the anemone to the crab's shell. However, neither species invariably exhibits transfer behavior when in contact with the other symbiont. Factors influencing transfer activity ofC. tricolor were studied. Anemone attachment is stimulated by disturbance and is time dependent. Anemones attached to shells more frequently immediately after the anemone was disturbed. Assays testing surface texture and surface composition showed that attachment activity of the sea anemone is dependent upon the organic matrix of the shell and is enhanced by texture. Attachment by anemones to shells with organic matrix removed is reduced, but is stimulated by adsorption of complex odor mixtures. Anemones respond to odor mixtures that signal food to crabs and to odor mixtures that stimulate shell investigation and shell switching in crabs. Thus,C. tricolor participates in shell transfer activity after disturbance. Behavior of the anemone is cued by texture and chemicals, including chemical mixtures that cause hermit crabs to change shells.     

Volatile shell-investigation cues of land hermit crabs: Effect of shell fit,detection of cues from other hermit crab species,and cue isolation

Land hermit crab responses to volatile shell-investigation cues from land hermit crabs and from marine hermit crabs are analogous to the responses of marine hermit crabs to shell-investigation cues from marine crabs and from snails. Land hermit crabs attracted to shell cues are in worse-fitting shells and are more likely to investigate conspecifics' shells than are crabs attracted to feeding cues. Moving land hermit crabs from worse shells to better shells decreases the number of crabs investigating shells, while moving crabs from better shells to worse shells increases the number of crabs investigating shells. Gravid females have better-fitting shells than nongravid females or males. Crabs from two different populations in Panama have different shell fits and show different levels of responses to shell-investigation cues. Land hermit crabs respond to volatile shell-investigation cues from both land and marine hermit crabs, but marine hermit crabs do not respond to cues from land hermit crabs. A cue detection system for volatile cues most likely evolved in land hermit crabs during their transition from a marine to a terrestrial existence. Thus, the cues found in land hermit crabs and marine hermit crabs may be chemically similar. Volatile compounds collected from hermit crabs onto Tenax columns can be eluted with ethanol and act as shell-investigation cues in field assays.