Effect of chemical treatments on flax fibre reinforced polypropylene composites on tensile and dome forming behaviour

Tensile tests were performed on two different natural fibre composites (same constituent material, similar fibre fraction and thickness but different weave structure) to determine changes in mechanical properties caused by various aqueous chemical treatments and whether any permanent changes remain on drying. Scanning electronic microscopic examinations suggested that flax fibres and the flax/polypropylene interface were affected by the treatments resulting in tensile property variations. The ductility of natural fibre composites was improved significantly under wet condition and mechanical properties (elongation-to-failure, stiffness and strength) can almost retain back to pre-treated levels when dried from wet condition. Preheating is usually required to improve the formability of material in rapid forming, and the chemical treatments performed in this study were far more effective than preheating. The major breakthrough in improving the formability of natural fibre composites can aid in rapid forming of this class of material system.We wish to acknowledge financial support from the Australian National University

Asymmetric Syntheses of Analogs of Kainic Acid

Kainic acid has been used for nearly 50 years as a tool in neuroscience due to its pronounced neuroexcitatory properties. However, the significant price increase of kainic acid resulting from the disruption in the supply from its natural source, the alga Digenea Simplex, as well as inefficient synthesis of kainic acid, call for the exploration of functional mimics of kainic acid that can be synthesized in a simpler way. Aza kainoids analog could be one of them. The unsubstituted aza analog of kainoids has demonstrates its ability as an ionotropic glutamate receptor agonist and showed affinity in the chloride dependent glutamate (GluCl) binding site. This opened a question of the importance of the presence of one nitrogen or both nitrogens in the aza kainoid analogs for binding to glutamate receptors. Therefore, two different pyrrolidine analogs of kainic acid, trans-4-(carboxymethyl)pyrrolidine-3-carboxylic acid and trans-2-carboxy-3-pyrrolidineacetic acid, were synthesized through multi-step sequences. The lack of the affinity of both pyrrolidine analogs in GluCl binding site indicated that both nitrogens in aza kainoid analogs are involved in hydrogen bonding with receptors, significantly enhancing their affinity in GluCl binding site. Another potential functional mimic of kainic acid is isoxazolidine analogs of kainoids whose skeleton can be constituted directly via a 1, 3 dipolar cycloaddition as the key step. The difficulty in synthesizing N-unsubstituted isoxazolidines when applying such common protecting groups as alkyl, phenyl and benzyl groups, and the requirement of a desired enantioselectivity due to the three chiral ceneters in kainic acid, pose great challenges. Hence, several different protected nitrones were studied to establish that diphenylmethine nitrone may be a good candidate as the dipole in that the generated isoxazolidines can be deprotected in mild conditions with high yields. Our investigations also indicated that the exo/endo selectivity of the 1, 3 dipolar cycloaddition can be controlled by Lewis acids, and that the application of a directing group in dipolarophiles can accomplish a satisfied enantioselectivity. Those results demonstrated the synthesis of isoxazoldines analogs of kainic acid is very promising

Partial correlation analysis indicates causal relationships between GC-content, exon density and recombination rate in the human genome

{\bf Background}: Several features are known to correlate with the GC-content in the human genome, including recombination rate, gene density and distance to telomere. However, by testing for pairwise correlation only, it is impossible to distinguish direct associations from indirect ones and to distinguish between causes and effects. {\bf Results}: We use partial correlations to construct partially directed graphs for the following four variables: GC-content, recombination rate, exon density and distance-to-telomere. Recombination rate and exon density are unconditionally uncorrelated, but become inversely correlated by conditioning on GC-content. This pattern indicates a model where recombination rate and exon density are two independent causes of GC-content variation. {\bf Conclusions}: Causal inference and graphical models are useful methods to understand genome evolution and the mechanisms of isochore evolution in the human genome

Forming Analysis of Natural Fibre Composites

Weight reduction can significantly contribute to reducing Green House Gas (GHG) emissions from vehicles. In addition to the significant increase in the demand on transportation due to the increase in global population, there is an urgent need to reduce the weight of vehicles to increase their fuel efficiency and therefore to reduce global GHG emissions. Driven by ecological and economic interests, there has been an increasing use of plant based material systems in various applications over the past decade. Currently, one of the main challenges in using these material systems for use in automotive components is to understand the forming behaviour of this class of material systems. This work is designed to answer two key questions regarding the forming of natural fibre composites. The first one is when does failure initiate in this class of material systems, and what is the most effective measure for predicting it? To answer this question, hourglass samples with varying sample widths are stretched and then formed through the stamping press machine. The ARAMIS. system beneath the press machine provides displacement and strain deformation which could be used to determine the failure behaviour of the composites. This study proposes a new FLC for woven composites, which is more effectively in predicting the failure behaviour of the natural fibre composite than the conventional method as it can successfully eliminate the path dependency effect. This innovative failure criterion has been proven to be more effective than the existing failure criterion through FEA simulations. The second question that the current work tries to answer is how to improve the formability of natural fibre composites. The approach here is to perform dome forming tests in different treatment conditions, namely preheating, water treatment, and tailored blanks. It is found that, among all treatment, the water treatment works the best, and is more effective than the conventional treatment of preheating. Woven composite with a tailored shape becomes much more formable due to its woven nature of fibre reinforcement, while such improvement is insignificant in nonwoven composites. This study lays a foundation for rapid forming of this class of material system, and will in turn lead to possible weight savings in future vehicles