Sea Urchin Spines as a Model-System for Permeable, Light-Weight Ceramics with Graceful Failure Behavior. Part I. Mechanical Behavior of Sea Urchin Spines under Compression

The spines of pencil and lance urchins Heterocentrotus mammillatus and Phyllacanthus imperialis were studied as a modelof light-weight material with high impact resistance.The complex and variable skeleton construction ("stereom") of body andspines of sea urchins consists of highly porous Mg-bearing calcium carbonate.This basically brittle material with pronouncedsingle-crystal cleavage does not fracture by spontaneous catastrophic device failure but by graceful failure over the range of tensof millimeter of bulk compression instead.This was observed in bulk compression tests and blunt indentation experiments onregular,infiltrated and latex coated sea urchin spine segments.Microstructural characterization was carried out using X-raycomputer tomography,optical and scanning electron microscopy.The behavior is interpreted to result from the hierarchicstructure of sea urchin spines from the rnacroscale down to the nanoscale.Guidelines derived from this study see ceramics withlayered porosity as a possible biomimetic construction for appropriate applications.     

追溯山茱萸科植物的性状进化和生物地理学历史——方法选择的影响?

This study compares results on reconstructing the ancestral state of characters and ancestral areas of distribution in Cornaceae to gain insights into the impact of using different analytical methods. Ancestral character state reconstructions were compared among three methods (parsimony, maximum likelihood, and stochastic character mapping) using MESQUITE and a full Bayesian method in BAYESTRAITS and inferences of ancestral area distribution were compared between the parsimony-based dispersal-vicariance analysis (DIVA) and a newly developed maximum likelihood (ML) method. Results indicated that among the six inflorescence and fruit characters examined, "perfect" binary characters (no homoplasy, no polymorphism within terminals, and no missing data) are little affected by choice of method, while homoplasious characters and missing data are sensitive to methods used. Ancestral areas at deep nodes of the phylogeny are substantially different between DIVA and ML and strikingly different between analyses including and excluding fossils at three deepest nodes. These results, while raising caution in making conclusions on trait evolution and historical biogeography using conventional methods, demonstrate a limitation in our current understanding of character evolution and biogeography. The biogeographic history favored by the ML analyses including fossils suggested the origin and early radiation of Cornus likely occurred in the late Cretaceous and earliest Tertiary in Europe and intercontinental disjunctions in three lineages involved movements across the North Atlantic Land Bridge (BLB) in the early and mid Tertiary. This result is congruent with the role of NALB for post-Eocene migration and in connecting tropical floras in North America and Africa, and in eastern Asia and South America. However, alternative hypotheses with an origin in eastern Asia and early Trans-Beringia migrations of the genus cannot be ruled out.