Effect of deformation schedule on the microstructure and mechanical properties of a thermomechanically processed C-Mn-Si transformation-induced plasticity steel

Thermomechanical processing simulations were performed using a hot-torsion machine, in order to develop a comprehensive understanding of the effect of severe deformation in the recrystallized and nonrecrystallized austenite regions on the microstructural evolution and mechanical properties of the 0.2 wt pct C-1.55 wt pct Mn-1.5 wt pct Si transformation-induced plasticity (TRIP) steel. The deformation schedule affected all constituents (polygonal ferrite, bainite in different morphologies, retained austenite, and martensite) of the multiphased TRIP steel microstructure. The complex relationships between the volume fraction of the retained austenite, the morphology and distribution of all phases present in the microstructure, and the mechanical properties of TRIP steel were revealed. The bainite morphology had a more pronounced effect on the mechanical behavior than the refinement of the microstructure. The improvement of the mechanical properties of TRIP steel was achieved by variation of the volume fraction of the retained austenite rather than the overall refinement of the microstructure.

Utility of mitochondrial DNA sequences from four gene regions for systematic studies of Australian freshwater crayfish of the Genus Cherax (Decapoda: Parastacidae)

One of the most important requirements for systematic and phylogenetic studies is the identification of gene regions with the appropriate level of variation for the question of interest. Molecular phylogenetic and systematic studies of freshwater crayfish have made use of DNA sequences mainly from ribosomal genes, especially the 16S rRNA gene region. Thus, little information is available on other potentially useful mitochondrial gene regions for systematic studies in these animals. In this study, we look at nucleotide variation and phylogenetic relations within and between four species of freshwater crayfish of the genus Cherax from the southwest of Western Australia using four fragments amplified from the 16S rRNA, 12S rRNA, Cytochrome Oxidase I (COI), and Cytochrome b (Cyt b) gene regions. Samples of Engaeus strictifrons, Euastacus bispinosus, and Geocharax falcata were also sequenced for comparative purposes. The size of the fragments varied from 358 bp to 600 bp. Across all samples, the four fragments showed significant phylogenetic signal and showed similar proportions of variable sites (28.81–37.33%). Average divergence within species for the mitochondrial gene regions varied from 1.18% to 4.91%, with the 16S rRNA being the least variable and Cyt b the most variable. Average divergence between species ranged 7.63–15.53%, with 16S rRNA being the least variable and COI the most variable. At the generic level, average divergence ranged 17.21–23.82%. Phylogenetic analyses of the 16S rRNA, 12S rRNA, and COI regions generated four clades consistent with the presence of four species previously identified on the basis of allozyme and morphological studies. The relationships among samples were largely congruent across the data set, although some relationships remained unresolved. Not all samples could be amplified using the Cyt b primers, and some of those that were showed quite anomalous relationships, suggesting that one or more Cyt b pseudogenes were being amplified.

Effect of microstructure on the stability of retained austenite in transformation-induced-plasticity steels

Two Fe-0.2C-1.55Mn-1.5Si (in wt pet) steels, with and without the addition of 0.039Nb (in wt pet), were studied using laboratory rolling-mill simulations of controlled thermomechanical processing. The microstructures of all samples were characterized by optical metallography, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The microstructural behavior of phases under applied strain was studied using a heat-tinting technique. Despite the similarity in the microstructures of the two steels (equal amounts of polygonal ferrite, carbide-free bainite, and retained austenite), the mechanical properties were different. The mechanical properties of these transformation-induced-plasticity (TRIP) steels depended not only on the individual behavior of all these phases, but also on the interaction between the phases during deformation. The polygonal ferrite and bainite of the C-Mn-Si steel contributed to the elongation more than these phases in the C-Mn-Si-Nb-steel. The stability of retained austenite depends on its location within the microstructure, the morphology of the bainite, and its interaction with other phases during straining. Granular bainite was the bainite morphology that provided the optimum stability of the retained austenite.

Phylogeny of the Australian freshwater crayfish Cherax destructor-complex (Decapoda:Parastacidae) inferred from four mitochondrial gene regions

The phylogenetic relationships among 32 individuals of Australian freshwater crayfish belonging to the Cherax destructor-complex were investigated using a dataset comprising sequences from four mitochondrial gene regions: the large subunit rRNA (16S rRNA), cytochrome oxidase I (COI), adenosine triphosphatase 6 (ATPase 6), and cytochrome oxidase III (COIII). A total of 1602 bp was obtained, and a combined analysis of the data produced a tree with strong support (bootstrap values 94–100%) for three divergent lineages, verifying the phylogenetic hypotheses of relationships within the C. destructor species-complex suggested in previous studies. Overall, sequences from the 16S rRNA gene showed the least variation compared to those generated from protein coding genes, which presented considerably greater levels of divergence. The level of divergence within C. destructor was found to be greater than that observed in other species of freshwater crayfish, but interspecific variation among species examined in the present study was similar to that reported previously.

The plasticity of professional boundaries: a case study of collaborative care in maternity services

A case study of twenty-nine midwives and nine obstetricians working in a regional, public sector Australian hospital demonstrates the plasticity of professional boundaries within a post-welfare state. Driven by new discourses of globalisation, marketisation, managerialism and consumerism, professional boundaries in health care are being blurred, reordered and reconstituted. Government policies that call for a new interdisciplinarity between maternity professionals may be seen as responses to the above pressures. However, there remain considerable barriers to achieving collaborative models including conflicting interpretations of risk, of women's bodies and of childbirth; the veto power of decision-making retained by obstetricians; questions of professional accountability; and diversity over appropriate styles of micro-interaction. Collaboration demands a new egalitarianism to eclipse the old vertical system of obstetric dominance and this means that midwives need to create a distinctive professional specialty, or new object of knowledge. Midwives' skill in 'emotion management' could provide this speciality in addition to their rational-technical knowledge and thus elevate midwifery to an equivalent professional status with obstetrics but as yet neither obstetrics nor midwifery have realised its professionalising potential

Asymptomatic hypoechoic regions on patellar tendon ultrasound : a 4-year clinical and ultrasound followup of 46 tendons

Patellar tendon ultrasound appearance is commonly used in clinical practice to diagnose patellar tendinopathy and guide management. Using a longitudinal study design we examined whether or not the presence of a hypoechoic ultrasonographic lesion in an asymptomatic patellar tendon conferred a risk for developing jumper's knee compared with a tendon that was ultrasonographically normal. Ultrasonographic, symptomatic and anthropometric assessment was completed at baseline and followup. Magnetic resonance imaging was performed on four tendons that resolved ultrasonographically in the study period. Forty-six patellar tendons were followed over 47±11.8 months. Eighteen tendons were hypoechoic at baseline and 28 were ultrasonographically normal. Five tendons resolved ultrasonographically in the study period. Magnetic resonance imaging in four of these tendons was normal. Seven normal patellar tendons at baseline developed a hypoechoic area but only two became symptomatic. Analysis of ultrasonography at baseline and clinical outcome with Fisher's exact test shows there is no association between baseline ultrasound changes and symptoms at followup. In this study there is no statistically significant relationship between ultrasonographic patellar tendon abnormalities and clinical outcome in elite male athletes. Management of jumper's knee should not be solely based on ultrasonographic appearance; clinical assessment remains the cornerstone of appropriate management.

Precipitate characterisation of an advanced high-strength low-alloy (HSLA) steel using atom probe tomography

Increased fuel economy, combined with the need for the improved safety has generated the development of new hot-rolled high-strength low-alloy (HSLA) and multiphase steels such as dual-phase or transformation-induced plasticity steels with improved ductility without sacrificing strength and crash resistance. However, the modern multiphase steels with good strength-ductility balance showed deteriorated stretch-flangeability due to the stress concentration region between the soft ferrite and hard martensite phases [1]. Ferritic, hot-rolled steels can provide good local elongation and, in turn, good stretch-flangeability [2]. However, conventional HSLA ferritic steels only have a tensile strength of not, vert, similar600 MPa, while steels for the automotive industry are now required to have a high tensile strength of not, vert, similar780 MPa, with excellent elongation and stretch-flangeability [1]. This level of strength and stretch-flangeability can only be achieved by precipitation hardening of the ferrite matrix with very fine precipitates and by ferrite grain refinement. It has been suggested that Mo [3] and Ti [4] should be added to form carbides and decrease the coiling temperature to 650 °C since only a low precipitation temperature can provide the precipitation refinement [4]. These particles appeared to be (Ti, Mo)C, with a cubic lattice and a parameter of 0.433 nm, and they were aligned in rows [4]. It was reported [4] that the formation of these very fine carbides led to an increase in strength of not, vert, similar300 MPa. However, the detailed analysis of these particles has not been performed to date due to their nanoscale size. The aim of this work was to carry out a detailed investigation using atom probe tomography (APT) of precipitates formed in hot-rolled low-carbon steel containing additions Ti and Mo.

The investigated low-carbon steel, containing Fe–0.1C–1.24Mn–0.03Si–0.11Cr–0.11Mo–0.09Ti–0.091Al at.%, was produced by hot rolling. The processing route has been described in detail elsewhere [5] European Patent Application, 1616970 A1, 18.01.2006.[5]. The microstructure was characterised by transmission electron microscopy (TEM) on a Philips CM 20, operated at 200 kV using thin foil and carbon replica techniques. Qualitative energy dispersive X-ray spectroscopy (EDXS) was used to analyse the chemical composition of particles. The atomic level of particle characterisation was performed at the University of Sydney using a local electrode atom probe [6]. APT was carried out using a pulse repetition rate of 200 kHz and a 20% pulse fraction on the sample with temperature of 80 K. The extent of solute-enriched regions (radius of gyration) and the local solute concentrations in these regions were estimated using the maximum separation envelope method with a grid spacing of 0.1 nm [7]. A maximum separation distance between the atoms of interest of dmax = 1 nm was used.

The microstructure of the steel consisted of two types of fine ferrite grains: (i) small recrystallised grains with an average grain size of 1.4 ± 0.2 μm; and (ii) grains with a high dislocation density (5.8 ± 1.4 × 1014 m−2) and an average grain size of 1.9 ± 0.1 μm in thickness and 2.7 ± 0.1 μm in length (Fig. 1a). Some grains with high dislocation density displayed an elongated shape with Widmanstätten side plates and also the formation of cells and subgrains (Fig. 1a). The volume fraction of recrystallised grains was 34 ± 8%.

Transmission electron microscopy characterization of the bake-hardening behavior of transformation-induced plasticity and dual-phase steels

The effect of prestraining (PS) and bake hardening (BH) on the microstructures and mechanical properties has been studied in transformation-induced plasticity (TRIP) and dual-phase (DP) steels after intercritical annealing. The DP steel showed an increase in the yield strength and the appearance of the upper and lower yield points after a single BH treatment as compared with the as-received condition, whereas the mechanical properties of the TRIP steel remained unchanged. This difference appears to be because of the formation of plastic deformation zones with high dislocation density around the “as-quenched” martensite in the DP steel, which allowed carbon to pin these dislocations, which, in turn, increased the yield strength. It was found for both steels that the BH behavior depends on the dislocation rearrangement in ferrite with the formation of cell, microbands, and shear band structures after PS. The strain-induced transformation of retained austenite to martensite in the TRIP steel contributes to the formation of a complex dislocation structure.

Effects of dietary omega-3 polyunsaturated fatty acids on brain gene expression

Polyunsaturated fatty acids (PUFA) are essential structural components of the central nervous system. Their role in controlling learning and memory has been well documented. A nutrigenomic approach with high-density microarrays was used to reveal brain gene-expression changes in response to different PUFA-enriched diets in rats. In aged rats fed throughout life with PUFA-enriched diets, genes with altered expressions included transthyretin, α-synuclein, and calmodulins, which play important roles in synaptic  plasticity and learning. The effect of perinatal omega-3 PUFA supply on gene expression later in life also was studied. Several genes showed similar changes in expression in rats fed omega-3-deficient diets in the perinatal period, regardless of whether they or their mothers were fed omega-3 PUFA-sufficient diets after giving birth. In this experiment, among the down-regulated genes were a kainate glutamate receptor and a DEAD-box polypeptide. Among the up-regulated genes were a chemokine-like factor, a tumor necrosis factor receptor, and cytochrome c. The possible involvement of the genes with altered expression attributable to different diets in different brain regions in young and aged rats and the possible mode of regulatory action of PUFA also are discussed. We conclude that PUFA-enriched diets lead to significant changes in expression of several genes in the central nervous tissue, and these effects appear to be mainly independent of their effects on membrane composition. The direct effects of PUFA on transcriptional modulators, the downstream developmentally and tissue-specifically activated elements might be one of the clues to understanding the beneficial effects of the omega-3 PUFA on the nervous system.

Investigation of deformation mechanisms involved in the plasticity of AZ31 Mg alloy: in situ neutron diffraction and EPSC modelling

In situ neutron diffraction and Elasto-Plastic Self-Consistent (EPSC) polycrystal modelling have been employed to investigate which deformation mechanisms are involved in the plasticity of extruded AZ31 Mg alloy during the tensile loading along the extrusion direction. On the basis of this study we were able to determine the relative activity of the slip and twinning deformation modes. By tuning the parameters of the EPSC model (i.e. the critical resolved shear strengths and hardening parameters), excellent agreement with the experimental data has been achieved. It is shown that the strain in the crystallographic ⟨c ⟩direction is accommodated mainly by ⟨c + a ⟩ dislocation slip on second-order pyramidal planes. The results further indicate that either slip of ⟨a ⟩dislocations occurs on {10.1} pyramidal planes or cross-slip from basal and prismatic planes takes place.

Effect of pre-straining and bake hardening on the microstructure and mechanical properties of CMnSi trip steels

The effects of pre-straining and bake hardening on the mechanical behaviour and microstructural changes were studied in two CMnSi TRansformation-Induced Plasticity (TRIP) steels with different microstructures after intercritical annealing. The TRIP steels before and after pre-straining and bake hardening were characterised by X-ray diffraction, optical microscopy, transmission electron microscopy, three dimensional atom probe and tensile tests. Both steels exhibited discontinuous yielding behaviour and a significant strength increase with some reduction in ductility after pre-straining and bake hardening treatment. The following main microstructural changes are responsible for the observed mechanical behaviours: a decrease in the volume fl:action of retained austenite, a increase in the dislocation density and the formation of cell substructure in the polygonal ferrite, higher localized dislocation density in the polygonal ferrite regions adjacent to martensite or retained austenite, and the precipitation of fine iron carbides in bainite and martensite. The mechanism for the observed yield point phenomenon in both steels after treatment was analysed.

Sex-specific developmental plasticity in response to yolk corticosterone in an oviparous lizard

Corticosterone exposure during prenatal development as a result of maternal upregulation of circulating hormone levels has been shown to have effects on offspring development in mammals. Corticosterone has also been documented in egg yolk in oviparous vertebrates, but the extent to which this influences phenotypic development is less studied. We show that maternal corticosterone is transferred to egg yolk in an oviparous lizard (the mallee dragon, Ctenophorus fordi Storr), with significant variation among clutches in hormone levels. Experimental elevation of yolk corticosterone did not affect hatching success, incubation period or offspring sex ratio. However, corticosterone did have a sex-specific effect on skeletal growth during embryonic development. Male embryos exposed to relatively high levels of corticosterone were smaller on average than control males at hatching whereas females from hormone-treated eggs were larger on average than control females. The data thus suggest that males are not just more sensitive to the detrimental effects of corticosterone but rather that the sexes may have opposite responses to corticosterone during development. Positive selection on body size at hatching for both sexes in this species further suggests that increased corticosterone in egg yolk may have sex-specific fitness consequences, with potential implications for sex allocation and the evolution of hormone-mediated maternal effects.