Kinks, rings, and rackets in filamentous structures

Carbon nanotubes and biological filaments each spontaneously assemble into kinked helices, rings, and "tennis racket" shapes due to competition between elastic and interfacial effects. We show that the slender geometry is a more important determinant of the morphology than any molecular details. Our mesoscopic continuum theory is capable of quantifying observations of these structures, and is suggestive of their occurrence in other filamentous assemblies as well.Comment: This paper was originally published in PNAS 100: 12141-12146 (2003). The present version has corrected Eq. 3, A1, and A2, and some minor typo

Fruit anatomy of the genus Bupleurum (Apiaceae) in northeastern China and notes on systematic implications

The fruit anatomy of all eight species of the genus Bupleurum L. mentioned in the most recent literature from northeastern China was studied for the first time. The eight species were divided into two groups based on the shape of the mericarps in transverse section. The first group (round mericarps without prominent ribs) includes B. longiradiatum and B. komarovianum, and the second group (angular mericarps with prominent ribs) includes B. angustissimum, B. bicaule, B. chinense, B. euphorbioides, B. scorzonerifolium and B. sibiricum. The second group can be further subdivided into group 2a (large vittae, very small vascular bundles) — B. euphorbioides and B. sibiricum, and group 2b (small vittae, large vascular bundles) — B. angustissimum, B. bicaule, B. chinense and B. scorzonerifolium. This result closely supports the traditional classification system which was based on gross morphology (plant height; leaf shape and size; involucre number, size and shape). The only exception is that B. komarovianum should not be close to the second group, but close to B. longiradiatum. Group 1 corresponds with Bupleurum sect. Longifolia and group 2 with sect. Eubupleura; group 2a with ser. Ranunculoides and group 2b with ser. Falcata. Fruit anatomical characters seem to have potential for evaluating infrageneric relationships in the genus Bupleurum