Mass transfer properties (permeability and mass diffusivity) of four australian hardwood species

Characterization of mass transfer properties was achieved in the longitudinal, radial, and tangential directions for four Australian hardwood species: spotted gum, blackbutt, jarrah, and messmate. Measurement of mass transfer properties for these species was necessary to complement current vacuum drying modeling research. Water-vapour diffusivity was determined in steady state using a specific vapometer. Permeability was determined using a specialized device developed to measure over a wide range of permeability values. Permeability values of some species and material directions were extremely low and undetectable by the mass flow meter device. Hence, a custom system based on volume evolution was conceived to determine very low, previously unpublished, wood permeability values. Mass diffusivity and permeability were lowest for spotted gum and highest for messmate. Except for messmate in the radial direction, the four species measured were less permeable in all directions than the lowest published figures, demonstrating the high impermeability of Australian hardwoods and partly accounting for their relatively slow drying rates. Permeability, water-vapour diffusivity, and associated anisotropic ratio data obtained for messmate were extreme or did not follow typical trends and is consequently the most difficult of the four woods to dry in terms of collapse and checking degradation. © The State of Queensland, Department of Agriculture, Fisheries and Forestry, 2012.

Electronic transport properties of hot-pressed B6Si

Measurements of the electrical conductivity, Seebeck coefficient and Hall mobility from -300K to -1300K have been carried out on multiphase hotpressed samples of the nominal composition B6Si. In all samples the conductivity and the p-type Seebeck coefficient both increase smoothly with increasing temperature. By themselves, these facts suggest small-polaronic hopping between inequivalent sites. The measured Hall mobilities are always low, but vary in sign. A possible explanation is offered for this anomalous behavior.

Virulence properties of asymptomatic bacteriuria Escherichia coli

In asymptomatic bacteriuria (ABU), bacteria colonize the urinary tract without provoking symptoms. Here, we compared the virulence properties of a collection of ABU Escherichia coli strains to cystitis and pyelonephritis strains. Specific urinary tract infection (UTI)-associated virulence genes, hemagglutination characteristics, siderophore production, hemolysis, biofilm formation, and the ability of strains to adhere to and induce cytokine responses in epithelial cells were analyzed. ABU strains were phylogenetically related to strains that cause symptomatic UTI. However, the virulence properties of the ABU strains were variable and dependent on a combination of genotypic and phenotypic factors. Most ABU strains adhered poorly to epithelial cells; however, we also identified a subgroup of strongly adherent strains that were unable to stimulate an epithelial cell IL-6 cytokine response. Poor immune activation may represent one mechanism whereby ABU E. coli evade immune detection after the establishment of bacteriuria.

Mechanics of Polyropylene-Seed-Coat-Fibres Composites AndPolyropylene –Wood Fibres Composites-A Comparative Study

Forestry by-products have potential applications as components of wood composites. Replacement of conventional pine radiata wood-fibres by the fibres from the seeds (SCF) of the by-products, require determining and optimizing the mechanical properties to producing highest quality products. Response to mechanical stress is an important aspect to consider towards partial or full replacement of the wood-fibres by SCFs. In the present study the critical strain energy release rate, and the fracture toughness are derived from the published data. The present work uses rules of mixture to derive the mechanical and the physical properties of the SCF and relates the performance of the composites of the wood-fibres and the SCF to chemical composition, dispersion, weight and Vf of the fibres. We have also derived the Gc, the critical strain energy release rate, KIC, the fracture toughness of the composites.

A multiscale study on the structural and mechanical properties of the luffa sponge from Luffa cylindrica plant

Cellular materials that are often observed in biological systems exhibit excellent mechanical properties at remarkably low densities. Luffa sponge is one of such materials with a complex interconnecting porous structure. In this paper, we studied the relationship between its structural and mechanical properties at different levels of its hierarchical organization from a single fiber to a segment of whole sponge. The tensile mechanical behaviors of three single fibers were examined by an Instron testing machine and the ultrastructure of a fractured single fiber was observed in a scanning electronic microscope. Moreover, the compressive mechanical behaviors of the foam-like blocks from different locations of the sponge were examined. The difference of the compressive stress-strain responses of four sets of segmental samples were also compared. The result shows that the single fiber is a porous composite material mainly consisting of cellulose fibrils and lignin/hemicellulose matrix, and its Young's modulus and strength are comparable to wood. The mechanical behavior of the block samples from the hoop wall is superior to that from the core part. Furthermore, it shows that the influence of the inner surface on the mechanical property of the segmental sample is stronger than that of the core part; in particular, the former's Young's modulus, strength and strain energy absorbed are about 1.6 times higher. The present work can improve our understanding of the structure-function relationship of the natural material, which may inspire fabrication of new biomimetic foams with desirable mechanical efficiency for further applications in anti-crushing devices and super-light sandwich panels.

Study on microwave dielectric properties of epoxy resin mixtures used for rapid product development

This paper presents a preliminary study on the dielectric properties and curing of three different types of epoxy resins mixed at various stichiometric mixture of hardener, flydust and aluminium powder under microwave energy. In this work, the curing process of thin layers of epoxy resins using microwave radiation was investigated as an alternative technique that can be implemented to develop a new rapid product development technique. In this study it was observed that the curing time and temperature were a function of the percentage of hardener and fillers presence in the epoxy resins. Initially dielectric properties of epoxy resins with hardener were measured which was directly correlated to the curing process in order to understand the properties of cured specimen. Tensile tests were conducted on the three different types of epoxy resins with hardener and fillers. Modifying dielectric properties of the mixtures a significant decrease in curing time was observed. In order to study the microstructural changes of cured specimen the morphology of the fracture surface was carried out by using scanning electron microscopy.