The Mitochondrial Genome of the Lycophyte Huperzia squarrosa: The Most Archaic Form in Vascular Plants

Mitochondrial genomes have maintained some bacterial features despite their residence within eukaryotic cells for approximately two billion years. One of these features is the frequent presence of polycistronic operons. In land plants, however, it has been shown that all sequenced vascular plant chondromes lack large polycistronic operons while bryophyte chondromes have many of them. In this study, we provide the completely sequenced mitochondrial genome of a lycophyte, from Huperzia squarrosa, which is a member of the sister group to all other vascular plants. The genome, at a size of 413,530 base pairs, contains 66 genes and 32 group II introns. In addition, it has 69 pseudogene fragments for 24 of the 40 protein- and rRNA-coding genes. It represents the most archaic form of mitochondrial genomes of all vascular plants. In particular, it has one large conserved gene cluster containing up to 10 ribosomal protein genes, which likely represents a polycistronic operon but has been disrupted and greatly reduced in the chondromes of other vascular plants. It also has the least rearranged gene order in comparison to the chondromes of other vascular plants. The genome is ancestral in vascular plants in several other aspects: the gene content resembling those of charophytes and most bryophytes, all introns being cis-spliced, a low level of RNA editing, and lack of foreign DNA of chloroplast or nuclear origin

Local and post-local buckling of double skin composite panels

Double skin composite (DSC) panels are constructed by filling concrete between two steel plates welded with stud shear connectors at a regular spacing. Steel plates in DSC panels used as two-way slabs or shearwalls may buckle locally between stud shear connectors when subjected to in-plane biaxial compression. This paper investigates the local and post-local buckling behaviour of biaxially compressed steel plates restrained by shear connectors and concrete in DSC panels by using the finite element modelling technique. Local buckling coefficients are obtained for steel plates with various aspect ratios, biaxial loading and boundary conditions by incorporating the shear stiffness effect of stud shear connectors. These buckling coefficients can be used to determine limiting width-to-thickness ratios for steel plates and the distribution of stud shear connectors. A geometric and material non-linear analysis is undertaken to quantify the post-local buckling strength of steel plates under biaxial compression. The initial imperfections of steel plates and non-linear shear–slip characteristics of stud shear connectors are taken into account in the post-local buckling analysis. Based on numerical results, biaxial strength interaction curves and formulae are developed for the ultimate strength design of steel plates in double skin composite construction