The crystal structure and a phase transition of gadolinium orthoborate, GdBO 3 , were studied by electron diffraction and X-ray powder diffraction. GdBO 3 crystallizes in the vaterite structure (LT), in a rhombohedral space group R32 with the lattice constants of a ) 6.6357-(2) Å and c ) 26.706(1) Å. The structure of the LT phase was derived from the hexagonal YBO 3 structure and refined using X-ray powder diffraction data. The structure consists of tetrahedral polyborate group B 3 O 9 9and the gadolinium atoms, located respectively on the 3-fold screw axis and a general position. The material undergoes a first-order phase transition with a large thermal hysteresis. The high-temperature (HT) phase crystallizes in a calcite related structure with the lattice constants of a ) 4.1154(2) and c ) 8.592(1) Å, which consists of planer triangular borate group BO 3 3-. The observed large thermal hysteresis of the phase transition is mainly caused by a structural change of the borate group, from B 3 O 9 9in the LT phase to BO 3 3in the HT phase.

China has undergone enormous economic growth in the last

A series of new monomers of 2,5-bis[(4-tertbutyl-phenyl)-1,3,4-oxadiazole] styrene (M-Ct) and 2,5-bis[(4-alkoxy-phenyl)-1,3,4-oxadiazole]styrene (M−OCm, m is the number of the carbons in the alkoxy groups, m = 8, 10, 12, 14) were synthesized. Conventional radical polymerization of the monomers resulted in a series of new mesogen-jacketed liquid crystalline polymer (MJLCP) containing the 1,3,4-oxadiazole unit. The chemical structures of the monomers were confirmed by elemental analysis, mass spectrometry, 1H NMR, and IR. The molecular characterization of the corresponding polymers of P-Ct and P-OCms was performed with 1H NMR, gel permeation chromatography, and thermogravimetric analysis. Their phase structures and transitions were investigated by differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy experiments. The P-Ct formed the hexatic columnar nematic (ΦHN) phase that is typical for MJLCPs, wherein the chain molecules were rodlike. The P-OCms exhibited a well-defined smectic A (SA) phase. As the mesogenic group is laterally jacketed to the polyethylene backbone through a single carbon−carbon bond, the P-OCm molecule in the SA phase should be more or less ribbonlike with the backbone squeezed by the parallel aligned side chains on both sides. The transition of the four P-OCms follows the sequence of SA ↔ N ↔ I. The comparison between P-Ct and P-OCms indicates that the flexibility of the side-chain tails is crucial to determine the LC structures. Namely, simply changing the chemical structures of small portion of the MJLCP may greatly vary the molecular packing behavior and thus the molecular shape in LC phase structures.

The crystallization kinetics of biodegradable poly(butylene succinate‐co‐adipate) (PBS/A) copolyester was investigated by using differential scanning calorimetry (DSC) and polarized optical microscopy (POM), respectively. The Avrami and Ozawa equations were used to analyze the isothermal and nonisothermal crystallization kinetics, respectively. By using wide‐angle X‐ray diffraction (WAXD), PBS/A was identified to have the same crystal structure with that of PBS. The spherulitic growth rates of PBS/A measured in isothermal conditions are very well comparable with those measured by nonisothermal procedures (cooling rates ranged from 0.5 to 15 °C/min). The kinetic data were examined with the Hoffman–Lauritzen nucleation theory. The observed spherulites of PBS/A with different shapes and textures strongly depend on the crystallization temperatures. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3231–3241, 2005

In R. graveolens pollen removal is promoted through one-by-one movement of the stamen, which presents pollen in doses to pollinators by successive uplifting of the stamen and avoids interference of two consecutively dehisced anthers by falling back of the former stamen before the next one moves into the flower's centre. Simultaneous stamen movement at the end of anthesis probably reflects an adaptation for late-acting self-pollination.

This study presents an updated analysis of the relative generality of invasion mechanisms in invasive plants. We categorised eight invasion mechanisms into three classes, according to the ecological processes behind the invasions: physical environment mechanisms (phenotypic plasticity in environmental tolerance and evolutionary adaptation to physical environment), resource use mechanisms (resource competition, resource utilisation and allelopathy) and enemy release mechanisms (high growth ⁄ reproduction rate, evolutionarily increased competitive ability and phenotypic plasticity in resource allocation). An analysis of 133 invasive plant species in the literature showed the enemy release mechanisms are equally general as resource use mechanisms, while the physical environment mechanisms are less general. Among the eight specific invasion mechanisms, phenotypic plasticity (either in resource allocation or in environmental tolerance), allelopathy, evolutionarily increased competitive ability and high resource-use efficiency are fairly common. Furthermore, chemical defence behaviour is very common in plant invaders. Species invading through enemy release were more likely to originate from Europe and those invading through resource competition ⁄ utilisation were often native to tropical and North America and Asia. Invaders with allelopathy were more likely to be from tropical and North America and those showing evolutionarily increased competitive ability were often native to temperate regions such as Europe and North America. Collectively, phenotypic plasticity, defence strategy and native status can be used not only to predict a plantÕs invasiveness, but also for identifying the potential invasion mechanisms.

Genetic variation within and between 34 populations of Eichhornia crassipes (water hyacinth) in China was surveyed using random amplified polymorphic DNA (RAPD) markers. A total of 1009 individuals were analysed, for which 12 RAPD primers amplified 69 reproducible bands, with 22 (32%) being polymorphic. The percentage of polymorphic loci (p) within a population ranged from 4.4% to 17.4%, and the mean Nei's gene diversity (H e ) was 0.046 ± 0.0145, indicating a low genetic diversity of E. crassipes in China. Each population contained at least four RAPD phenotypes (genotypes), and the same particular genotype was invariably dominant in all the populations sampled. The mean proportion of distinguishable genotypes was 0.29. Analysis of molecular variance revealed a large proportion of genetic variation (83.9%) residing within populations and a slightly larger proportion (88.1%) within localities, indicating a low genetic differentiation of E. crassipes populations, both locally and regionally. Human-mediated dispersal, vigorous clonal growth, and a generally low level of sexual reproduction were thought to be responsible for such a pattern of genetic structure. Keywords: biological invasion, Eichhornia crassipes, genetic variation, random amplified polymorphic DNA. REN M-X, ZHANG Q-G & ZHANG D-Y (2005) Random amplified polymorphic DNA markers reveal low genetic variation and a single dominant genotype in Eichhornia crassipes populations throughout China. Weed Research 45, 236-244.

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