Flexible control of the Peierls transition in metallic C60_{60} polymers

The metal-semiconductor transition of peanut-shaped fullerene (C$_{60}$) polymers is clarified by considering the electron-phonon coupling in the uneven structure of the polymers. We established a theory that accounts for the transition temperature $T_c$ reported in a recent experiment and also suggests that $T_c$ is considerably lowered by electron doping or prolonged irradiation during synthesis. The decrease in $T_c$ is an appealing phenomenon with regard to realizing high-conductivity C$_{60}$-based nanowires even at low temperatures.Comment: 3 pages, 3 figure

A molecular phylogeny of Southeast Asian Cyrtandra (Gesneriaceae) supports an emerging paradigm for Malesian plant biogeography

The islands of Southeast Asia comprise one of the most geologically and biogeographically complex areas in the world and are a centre of exceptional floristic diversity, harbouring 45,000 species of flowering plants. Cyrtandra, with over 800 species of herbs and shrubs, is the largest genus in the family Gesneriaceae and is one of the most emblematic and species-rich genera of the Malesian rainforest understorey. The high number of species and tendency to narrow endemism make Cyrtandra an ideal genus for examining biogeographic patterns. We sampled 128 Cyrtandra taxa from key localities across Southeast Asia to evaluate the geo-temporal patterns and evolutionary dynamics of this clade. One nuclear and four chloroplast regions were used for phylogenetic reconstruction, molecular dating, and ancestral range estimation. Results from the dating analysis suggest that the great diversity of Cyrtandra seen in the Malesian region results from a recent radiation, with most speciation taking place in the last five million years. Borneo was recovered as the most likely ancestral range of the genus, with the current distribution of species resulting from a west to east migration across Malesia that corresponds with island emergence and mountain building. Lastly, our investigation into the biogeographic history of the genus indicates high levels of floristic exchange between the islands on the Sunda shelf and the important role of the Philippines as a stepping stone to Wallacea and New Guinea. These patterns underlie much of the plant diversity in the region and form an emerging paradigm in Southeast Asian plant biogeography

Different photochemical behavior of bis(biphenyl)ethylenes and ethenes in solution and in the solid-state: Structurally controlled Z/E-photoisomerization in the solid-state

ArticleJOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY. 184(1-2): 44-49 (2006)journal articl

Poly(benzyl ether) dendrimers with strongly fluorescent distyrylbenzene cores as the fluorophores for peroxyoxalate chemiluminescence: insulating effect of dendritic structures on fluorescent sites

ArticleTETRAHEDRON. 61(46): 11020-11026 (2005)journal articl

Cytokinin biosynthesis ISOPENTENYLTRANSFERASE genes are differentially expressed during phyllomorph development in the acaulescent Streptocarpus rexii (Gesneriaceae)

Abstract The enzyme ISOPENTENYLTRANSFERASE (IPT) is responsible for the rate limiting step of cytokinin biosynthesis, an important plant hormone with key roles in meristem maintenance and organ development. In this study, we isolated IPT genes from the acaulescent Streptocarpus rexii, a plant that shows an unorthodox development starting with post-germination anisocotyly, in which cytokinins play an integral role. Three adenosine phosphate-IPTs and two tRNA-IPTs were isolated from S. rexii. Their expression levels and patterns in different tissues were compared by means of realtime-PCR and mRNA in-situ hybridization. We found that each SrIPT had a distinctive expression pattern. Interestingly, in vegetative tissues as well as in meristems only the adenosine phosphate-IPT SrIPT5 and the tRNA-IPT SrIPT9 were found. In addition, they were differentially affected by external hormone application, suggesting their different regulation and expression during meristem formation and maintenance and lamina growth. Our results indicate that SrIPTs are involved in shaping the architecture of S. rexii, working differentially and redundantly, and show that differentially expressed IPT genes regulate plant form

Gibberellin as a suppressor of lateral dominance snd inducer of apical growth in the unifoliate Streptocarpus wendlandii (Gesneriaceae)

We report on the effects of exogenously applied hormones on the lateral and apical dominance that governs morphogenesis in the unifoliate Streptocarpus wendlandii. In this phenotype, lateral dominance is extreme as the plants only retain a macrocotyledon that develops into a leaf-like phyllomorph by means of a basal meristem and do not show apical growth. Gibberellin applications suppressed the basal meristem activity of the macrocotyledon resulting in an isocotylous seedling with two microcotyledons and caused the formation of a primary phyllomorph, which suggests that the groove meristem, a shoot apical meristem equivalent, is released from apical suppression by the basal meristem. Interestingly, uniconazol, a gibberellin biosynthesis inhibitor, also caused a reduction in basal meristem activity, but without primary phyllomorph formation, suggesting that some gibberellin is required for proper function of the basal meristem. Co-application of gibberellin and cytokinin resulted in two macrocotyledons also without phyllomorph formation, which is similar to previous results for cytokinin-only applications. Thus, cytokinin may act downstream in the regulatory pathway of the basal meristem. Our results suggest that the balance between gibberellin and cytokinin in the cotyledons appears thus as key factor in the regulation of lateral and apical dominance in Streptocarpus. Their interplay may well be the primary explanation for the great diversity in growth form exhibited in species of this genus. Our work shows that small imbalances of hormones in early stages of plant development can have major effects on the final phenotype

Associations between stratospheric variability and tropospheric blocking

There is widely believed to be a link between stratospheric flow variability and stationary, persistent “blocking” weather systems, but the precise nature of this link has proved elusive. Using data from the ERA-40 Reanalysis and an atmospheric general circulation model (GCM) with a well-resolved stratosphere (HadGAM), it is shown that there are in fact several different highly significant associations, with blocking in different regions being related to different patterns of stratospheric variability. This is true in both hemispheres and in both data sets. The associations in HadGAM are shown to be very similar to those in ERA-40, although the model has a tendency to underestimate both European blocking and the wave number 2 stratospheric variability to which this is related. Although the focus is on stratospheric variability in general, several of the blocking links are seen to occur in association with the major stratospheric sudden warmings. In general, the direction of influence appears to be upward, as blocking anomalies are shown to modify the planetary stationary waves, leading to an upward propagation of wave activity into the stratosphere. However, significant correlations are also apparent with the zonal mean flow in the stratosphere leading the occurrence of blocking at high latitudes. Finally, the underestimation of blocking is an enduring problem in GCMs, and an example has recently been given in which improving the resolution of the stratosphere improved the representation of blocking. Here, however, another example is given, in which increasing the stratospheric resolution unfortunately does not lead to an improvement in blocking

The bending of cell sheets - from folding to rolling

The bending of cell sheets plays a major role in multicellular embryonic morphogenesis. Recent advances are leading to a deeper understanding of how the biophysical properties and the force-producing behaviors of cells are regulated, and how these forces are integrated across cell sheets during bending. We review work that shows that the dynamic balance of apical versus basolateral cortical tension controls specific aspects of invagination of epithelial sheets, and recent evidence that tissue expansion by growth contributes to neural retinal invagination in a stem cell-derived, self-organizing system. Of special interest is the detailed analysis of the type B inversion in Volvox reported in BMC Biology by Höhn and Hallmann, as this is a system that promises to be particularly instructive in understanding morphogenesis of any monolayered spheroid system

Stability of Ge-related point defects and complexes in Ge-doped SiO_2

We analyze Ge-related defects in Ge-doped SiO_2 using first-principles density functional techniques. Ge is incorporated at the level of ~ 1 mol % and above. The growth conditions of Ge:SiO_2 naturally set up oxygen deficiency, with vacancy concentration increasing by a factor 10^5 over undoped SiO_2, and O vacancies binding strongly to Ge impurities. All the centers considered exhibit potentially EPR-active states, candidates for the identification of the Ge(n) centers. Substitutional Ge produces an apparent gap shrinking via its extrinsic levels.Comment: RevTeX 4 pages, 2 ps figure

Strong long-period fiber gratings recorded at 352 nm

We describe long-period grating inscription in hydrogenated telecom fibers by use of high-intensity femto-second 352 nm laser pulses. We show that this technique allows us to fabricate high-quality 30 dB gratings of 300 μm period and 2 cm length by use of a three-photon absorption mechanism. © 2005 Optical Society of America