A morphology-related study on photodegradation of protein fibres

The wool fibre has a complex morphology, consisting of an outer layer of cuticle scales surrounding an inner cortex. These two components are hard to separate effectively except by using harsh chemical treatments, making it difficult to determine the susceptibility of the different components of the fibre to photoyellowing. An approach to this problem based on mechanical fibre modification is described. To expose the inner cortex of wool to different degrees, clean wool fibres were converted into ‘powders’ of various fineness via mechanical chopping, air-jet milling, ball milling or their combination. Four types of powdered wool (samples A, B, C and D) were produced with reducing particle size distributions and an increasing level of surface damage as observed using SEM. Sample A contained essentially intact short fibre snippets and sample D contained a large amount of exposed cortical materials. Samples B and C contained a mixture of short fibre snippets and cortical materials. Solid wool discs were then compressed from the corresponding powder samples in a polished stainless steel die to enable colour measurement and UV irradiation studies. ATR-FTIR studies on powder discs demonstrated a small shift in the amide I band from 1644 cm−1 for disc A to 1654 cm−1 for disc D due to the different structures of the wool cuticle and cortex, in agreement with previous studies. Similarly an increase in the intensity ratio of the amide I to amide II band (1540 cm−1) was observed for disc D, which contains a higher fraction of cortical material at the surface of the disc.

Discs prepared from sample D appeared the lightest in colour before exposure and had the slowest photoyellowing rate, whereas discs made from powders A–C with a higher level of cuticle coverage were more yellow before exposure and experienced a faster rate of photoyellowing. This suggests that the yellow chromophores of wool may be more prevalent in cuticle scales, and that wool photoyellowing occurs to a greater extent in the cuticle than in the cortex. Photo-induced chemiluminescence measurements showed that sample D had a higher chemiluminescence intensity after exposure to UVA radiation and a faster decay rate than samples A and B. Thus one of the roles of the wool cuticle may be to protect the cortex by quenching of free radical oxidation during exposure to the UV wavelengths present in sunlight.

Effects of pore morphology on the compressive behaviour of porous metals

In the present study, porous nickel foams with three different porosities (i.e. 50 %, 60 % and 70 %) were fabricated using the space-holding sintering method. Ammonium bicarbonate particles with sizes ranging from 1- 2 mm were chosen as the space-holding material. The anisotropic behaviours of the nickel foam samples were investigated by compressive testing loading at different directions, i.e., in both directions of the major and minor axis of ellipsoidal cells. Electron scanning microscopy (SEM) and Image-Pro Plus was used to characterise the morphological characteristics of the porous nickel foam samples. Results indicated that the porous nickel foam samples exhibited obvious anisotropic mechanical properties. The foam sample shows significantly higher nominal stress for loading in the direction of the major axis of the pores than loading in the direction of the minor axis of pores. The nominal stress increases with the decreasing of the porosity.

Functional morphology of the gastric mills of carnivorous, omnivorous, and herbivorous land crabs

Terrestrial decapods consume a wide variety of plant and animal material. The potential adaptations of carnivorous, omnivorous, and herbivorous terrestrial crustaceans were studied by examining the functional morphology of the gastric mill. Two closely related species from each feeding preference group were examined to identify which features of the mill were due to phylogeny and which were due to adaptation. The morphology of the gastric mill matched the diet well; the gastric mills of the carnivorous species (Geograpsus grayi and Geograpsus crinipes) possessed a blunt, rounded medial tooth and flattened lateral teeth with a longitudinal grinding groove. These features make them well suited to a carnivorous diet of soft animal tissue as well as hard material, such as arthropod exoskeleton. In contrast, the mill of the herbivorous gecarcinids (Gecarcoidea natalis and Discoplax hirtipes) consisted of a medial tooth with sharp transverse ridges and lateral teeth with sharp interlocking cusps and ridges and no grinding surface. These features would efficiently shred fibrous plant material. The morphology of the mill of the omnivorous coenobitids (Coenobita perlatus and Birgus latro) was more generalized toward a mixed diet. However, the mill of B. latro was more adapted to deal with highly nutritious food items, such as nuts and heavily calcified decapods. Its mill possessed lateral teeth with extended ridges, which sat close to the calcified cardiopyloric valve to form a flattened floor. Hard items trapped in the mill would be crushed against this surface by the medial tooth.

Passive flow through an unstalked intertidal ascidian: Orientation and morphology enhance suspension feeding in Pyura stolonifera

Passive flow is believed to increase the gains and reduce the costs of active suspension feeding. We used a mixture of field and laboratory experiments to evaluate whether the unstalked intertidal ascidian Pyura stolonifera exploits passive flow. We predicted that its orientation to prevailing currents and the arrangement of its siphons would induce passive flow due to dynamic pressure at the inhalant siphon, as well as by the Bernoulli effect or viscous entrainment associated with different fluid velocities at each siphon, or by both mechanisms. The orientation of P. stolonifera at several locations along the Sydney-Illawarra coast (Australia) covering a wide range of wave exposures was nonrandom and revealed that the ascidians were con- sistently oriented with their inhalant siphons directed into the waves or backwash. Flume experiments using wax mod- els demonstrated that the arrangement of the siphons could induce passive flow and that passive flow was greatest when the inhalant siphon was oriented into the flow. Field exper- iments using transplanted animals confirmed that such an orientation resulted in ascidians gaining food at greater rates, as measured by fecal production, than when oriented perpendicular to the wave direction. We conclude that P. stolonifera enhances suspension feeding by inducing pas- sive flow and is, therefore, a facultatively active suspension feeder. Furthermore, we argue that it is likely that many other active suspension feeders utilize passive flow and, therefore, measurements of their clearance rates should be made under appropriate conditions of flow to gain ecolog- ically relevant results.

Thermal degradation kinetics and morphology of natural rubber/silica nanocomposites

A novel natural rubber/silica (NR/SiO₂) nanocomposite with a SiO₂ loading of 4 wt% is developed by incorporating latex compounding with self-assembly techniques. The SiO₂ nanoparticles are homogenouslydistributed throughout the NR matrix as spherical nano-clusters with an average size of 75 nm. In comparison with the host NR, the thermal resistance of the nanocomposite is significantly improved. The degradation temperatures (T), reaction activation energy(E), and reaction order (n) of the nanocomposite are markedly higher than those of the pure NR, due to significant retardant effect of the SiO₂ nanoparticles.