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.     

F10蛋白及mRNA在部分正常组织及癌组织中的表达

目的:了解F10基因在部分正常组织及肿瘤组织中的表达情况。方法:利用原位杂交和免疫组化方法对F10在部分正常组织和肿瘤组织中的mRNA和蛋白表达情况进行分析。结果:F10基因不仅在腺癌组织中表达呈阳性,在鳞癌组织中表现出较腺癌更强的强阳性,并且在正常组织中也有一定的表达。结论:F10是一个在多种组织普遍表达的细胞内蛋白,其功能可能与物质转运相关。     

离子通道递质受体大家族:每种受体所特有的变构调制中心在神经药理学中的重要性

美国飞迪亚-乔治城神经科学研究所所长、美国科学院院士E.Costa博士,1989年1月10日来北京接受北京医科大学授予名誉教授衔。Costa教授在该仪式上所作的报告指出了当前神经递质研究的新方向,具有重要的学术意义。特予介绍,以飨读者。     

甘薯杂交胚发育过程中的一些生理变化

杂交育种仍是目前甘薯（Ipomoeabatatas）育种的主要手段，而品种间不亲和性的大小和杂交结实率低是制约甘薯杂交育种效果的两个主要因素［”］。迄今已知甘薯存在着15个不同的杂交不亲和群，同群品种间杂交不结实或结实率极低（0％～5％），而异群品种间杂交给实率较高（20％～50％）［‘j。对于杂交结实率低的原因和解决途径，只有少量基干解剖学的观察［”‘’1和利用嫁接、植物生长调节剂提高结实率的报道＊－”。在生理基础方面的研究则未见报道。为此我们选择甘薯高自1号X88－3这一杂交组合（结实率为13．3士l．8％），在8月份的每天…