Plastic relaxation of the internal stress induced by twinning

The back stress induced in a twin by the surrounding matrix is analysed using a simple two-dimensional finite element model of an elastic elliptical inclusion in a plastic medium. The influence of the ellipse aspect ratio, the matrix yield stress and the external loading on the internal shear stress are investigated. Comparison is made between isotropic and anisotropic yield criteria. It is seen that von Mises plasticity in the matrix (due to glide) leads to complete relaxation of the twin back stress. The closer the applied stress is to the stress required for macroscopic yielding of the matrix, the greater the relaxation of the back stress. To simulate the role of soft shear directions in the matrix, as seen for the case of easy basal slip in hexagonal close-packed metals, Hill’s anisotropic yield surface was employed. These simulations show relaxation of the back stress that is independent of the level of the applied stress. Comparison between simulations and experiments performed on a magnesium alloy reveals higher levels of relaxation in practice. This is possibly due to (i) further twinning as a relaxation mechanism and (ii) the occurrence of neighbouring grains ideally oriented for relaxation. Analytical expressions are developed to capture the trends seen in the simulation. A correction to bring these into line with experiment is proposed as a tentative means of applying the present findings in an analytical framework.     

Surface Modification of Biomedical and Dental Implants and the Processes of Inflammation,Wound Healing and Bone Formation

Bone adaptation or integration of an implant is characterized by a series of biological reactions that start with bone turnover at the interface (a process of localized necrosis), followed by rapid repair. The wound healing response is guided by a complex activation of macrophages leading to tissue turnover and new osteoblast differentiation on the implant surface. The complex role of implant surface topography and impact on healing response plays a role in biological criteria that can guide the design and development of future tissue-implant surface interfaces.     

A Comparison of Anticonvulsants in the Treatment of Impulsive Aggression.

This study compared the behavioral effects of 3 anticonvulsants in impulsive aggressive men. In a double-blind, placebo-controlled, parallel groups design, participants were randomly assigned to 1 of 4 6-week treatments: phenytoin (n = 7), carbamazepine (n = 7), valproate (n = 7), or placebo (n = 8). The efficacy measure was the average aggression score, a global severity index from the Overt Aggression Scale (J. M. Silver & S. C. Yudofsky, 1991). Analysis showed a significant reduction in impulsive aggression during all 3 anticonvulsant conditions compared with placebo. However, the treatment effect during carbamazepine administration was slightly delayed compared with phenytoin and valproate. These findings suggest that increased use of anticonvulsants could make a significant impact in the control of impulsive aggression in both mental health and criminal justice settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Na Partitioning During Thermomechanical Processing of an Mg-Sn-Zn-Na Alloy

Microstructural characterization was used to examine the changes that occur in an Mg-6Sn-5Zn-0.3Na alloy from casting to extrusion at either 623 K or 723 K (350 °C or 450 °C) followed by artificial aging at 473 K (200 °C). In particular, the partitioning of Na was examined at each step using STEM-EDS mapping. Na atoms were found to preferentially partition to the Mg-Zn phase when present. After extrusion, when no Mg-Zn was observed, the spherical Mg₂Sn particles were found to be enriched in Na, particularly at the higher extrusion temperature. Artificial aging following extrusion resulted in a change in Na partitioning, and a coarse distribution of Mg-Zn precipitate rods. Na microadditions led to a high as-extruded hardness, but a significant tension–compression yield asymmetry was still observed at room temperature. The compressive yield strength was found to decrease significantly after 1000 hours of aging.     

Biodegradation of genetically modified seeds and plant tissues during composting

BACKGROUND: The increasing global market of genetically modified (GM) crops amplifies the potential for unintentional contamination of food and feed with GM plants. Methods proposed for disposal of crop residues should be assessed to prevent unintended distribution of GM materials. Composting of organic material is inexpensive and location‐independent. The objective of this study was to determine the effectiveness of composting for disposal of GM plants in terms of reducing seed viability and promoting the degradation of endogenous as well as transgenic DNA. RESULTS: Duplicate samples of corn kernels, alfalfa leaves, and GM canola seeds, meal and pellets were sealed in porous nylon bags and implanted in duplicate 85 000 kg (initial weight) feedlot manure compost piles. Samples were collected at intervals over 230 days of composing. Canola seeds and corn kernels were not viable after 14 days of composting with temperatures in the piles exceeding 50 °C. In all samples, PCR analyses revealed that plant endogenous and transgenic fragments were substantially degraded after 230 days of composting. Southern blotting of genomic DNA isolated from canola seeds identified differences in the persistence of endogenous, transgenic, and bacterial DNA. CONCLUSION: Composting GM and non‐GM plant materials with manure rendered seeds non‐viable, and resulted in substantial, although not complete, degradation of endogenous and transgenic plant DNA. This study demonstrates that composting could be effective for disposing of GM crops in the event of their inadvertent entry into the food or feed chain. Copyright © 2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd     

Investigation into the use of gaseous and liquid nitrogen as a cutting fluid when turning BS 970-80A15 (En32b) plain carbon steel using WC–Co uncoated tooling

Cutting fluids play an important role in metal cutting, but have considerable environmental impact. There is a need, therefore, to understand the role of cutting fluids within the cutting process and in this context to evaluate possible environmentally friendly alternatives. To achieve this, the cutting environment and the consequences of removing cutting fluid from the process altogether have to be assessed. This work investigates the role of cutting fluids and the implications of their use. Industrially reproducible cutting tests were devised, where BS 970-080A15 (En32b) plain carbon mild steel was turned in various cutting environments that included dry cutting. In particular, tool life is measured for both ambient and cryogenic temperature nitrogen gaseous environments and results then compared with more traditional cutting conditions. The results indicate that a 55% reduction in flank wear is achievable when turning BS 970-080A15 (En32b) steel using WC–Co uncoated tooling in a nitrogen environment, and thereby establish the suitability of nitrogen atmospheres in high speed machining applications. This work indicates that alternative, non-polluting environments should be investigated further in order to determine their viability in high-speed machining applications.     

Reactive processing of acrylic–polyurea interpenetrating networks: reaction kinetic studies

Interpenetrating networks (IPNs), comprising a crosslinked acrylic polymer as one component and either a polyurea, a segmented copolyurea or a copoly(urea–isocyanurate) as the other component, have been formed by reaction injection moulding (RIM). The effects on the processability and the formation of the IPNs of (i) the crosslinker concentration in the acrylic component, (ii) the functionality of the amine‐functionalized polyether used for the polyurea, and (iii) the weight fractions of acrylic components are evaluated. Reaction kinetics during RIM processing of the IPNs are studied using adiabatic temperature rise (ATR) measurements. The macroscopic structures of RIM materials, determined via optical microscopy, are used to assess the mixing characteristics operative during reactive processing of the various IPNs. The results are interpreted in terms of differences in the rates of polymerization and in the solubilities of the acrylic‐ and polyurea‐forming components. © 2001 Society of Chemical Industry     

Martensite/particle interactions and the shape memory effect in an Fe–Mn–Si-based alloy

The effect of carbide precipitates with a size range of 30–300 nm on the austenite to martensite transformation has been studied. Such particles are known to enhance shape memory, and it was the aim of this work to clarify how the particles exert a favourable effect on shape memory. Differential scanning calorimetry revealed that the presence of particles increases the amount of thermally induced martensite. X-ray diffraction showed that the presence of particles increases the amount of stress-induced martensite also. Surface-relief produced on a pre-polished surface by bending deformation showed that the particle-containing samples exhibited a more complex and highly tilted surface-relief indicative of the formation of a larger volume fraction of martensite. The reversion characteristics of the particle-containing and solution-treated samples were similar: both showed co-reversion of multiple variants of martensite within the same volume of microstructure. However, a higher volume fraction of martensite reverted for the particle-containing sample on recovery annealing. The increased density of nucleation sites for martensite formation and a higher volume fraction of stress-induced martensite for a given strain are therefore considered to be the main contributions of relatively coarse carbide particles to the improvement of shape memory performance.