title: The role of new particle surfaces in synthesizing bulk nanostructured metallic materials by powder metallurgy

authors: Zhang, Deliang

subjects: nanostructure

abstract: The role of new particle surfaces in synthesizing bulk nanostructured metallic materials by consolidation of nanostructured powders and nanopowders is analysed by developing three simple mathematical equations for calculating the α factor for different thermomechanical powder consolidation processes such as hot pressing, high pressure torsion and extrusion. The α factor is the fraction of the area of the powder particle surfaces newly formed during consolidation over the total particle surface area which includes both pre-existing surface area and the newly formed surface area. It is demonstrated that the values of the α factor calculated using these equations can be reasonably used to predict the level of inter-particle atomic bonding that is likely to be achieved through cold-welding by the above mentioned typical thermomechanical powder consolidation processes which also include high energy mechanical milling. Based on this analysis, it is clear that uniaxial hot pressing of a powder compact in a rigid die at low homologous temperatures (<0.5Tm) is unlikely to be capable of achieving a sufficiently high level of inter-particle atomic bonding for producing a high quality consolidated material, while processes involving a large amount of plastic deformation have such capabilities.

text: The role of new particle surfaces in synthesizing bulk nanostructured metallic materials by powder metallurgy The role of new particle surfaces in synthesizing bulk nanostructured metallic materials by consolidation of nanostructured powders and nanopowders is analysed by developing three simple mathematical equations for calculating the α factor for different thermomechanical powder consolidation processes such as hot pressing, high pressure torsion and extrusion. The α factor is the fraction of the area of the powder particle surfaces newly formed during consolidation over the total particle surface area which includes both pre-existing surface area and the newly formed surface area. It is demonstrated that the values of the α factor calculated using these equations can be reasonably used to predict the level of inter-particle atomic bonding that is likely to be achieved through cold-welding by the above mentioned typical thermomechanical powder consolidation processes which also include high energy mechanical milling. Based on this analysis, it is clear that uniaxial hot pressing of a powder compact in a rigid die at low homologous temperatures (<0.5Tm) is unlikely to be capable of achieving a sufficiently high level of inter-particle atomic bonding for producing a high quality consolidated material, while processes involving a large amount of plastic deformation have such capabilities.

year: 2009

title: Is size assortative mating in Paracalliope fluviatilis (Crustacea: Amphipoda) explained by male–male competition or female choice?

authors: Sutherland, Darin Lee

subjects: amplexus

abstract: Field and laboratory studies were used to assess: (1) whether size assortative mating occurred in the New Zealand amphipod Paracalliope fluviatilis and (2) hypotheses developed to explain size assortative mating. We found that assortative mating occurred and that larger females carried more eggs, suggesting they may be more valuable as mates. Laboratory experiments were then used to determine whether: (1) male size influenced the size of the female selected (mechanical constraints hypothesis); (2) male size influenced pairing success in the presence of competition (intrasexual selection hypothesis); (3) take-overs of females occurred and whether large males were more successful (intrasexual selection hypothesis); (4) guard duration varied relative to male and female size (guard duration hypothesis); and (5) females had control over pairing success and guard duration (intersexual selection hypothesis). Although there was evidence to suggest the existence of intrasexual competition for mates (i.e. both small and large males preferred large females), there was no evidence of overt competition (i.e. takeovers of paired females). There was also no difference with respect to how long small and large males guarded females, but large females were guarded longer by both male size classes. Females handicapped by having their mobility reduced were guarded for the same duration as control females but males were more likely to pair with handicapped females, suggesting that they were easier to amplex. Given the lack of evidence for direct male–male competition or female choice, we suggest that assortative mating may be the result of: (1) indirect competition (e.g. in situ large males may be better able to access and amplex the largest females) or (2) female resistance to small males in combination with higher costs that small males may incur in securing large females.

text: Is size assortative mating in Paracalliope fluviatilis (Crustacea: Amphipoda) explained by male–male competition or female choice? Field and laboratory studies were used to assess: (1) whether size assortative mating occurred in the New Zealand amphipod Paracalliope fluviatilis and (2) hypotheses developed to explain size assortative mating. We found that assortative mating occurred and that larger females carried more eggs, suggesting they may be more valuable as mates. Laboratory experiments were then used to determine whether: (1) male size influenced the size of the female selected (mechanical constraints hypothesis); (2) male size influenced pairing success in the presence of competition (intrasexual selection hypothesis); (3) take-overs of females occurred and whether large males were more successful (intrasexual selection hypothesis); (4) guard duration varied relative to male and female size (guard duration hypothesis); and (5) females had control over pairing success and guard duration (intersexual selection hypothesis). Although there was evidence to suggest the existence of intrasexual competition for mates (i.e. both small and large males preferred large females), there was no evidence of overt competition (i.e. takeovers of paired females). There was also no difference with respect to how long small and large males guarded females, but large females were guarded longer by both male size classes. Females handicapped by having their mobility reduced were guarded for the same duration as control females but males were more likely to pair with handicapped females, suggesting that they were easier to amplex. Given the lack of evidence for direct male–male competition or female choice, we suggest that assortative mating may be the result of: (1) indirect competition (e.g. in situ large males may be better able to access and amplex the largest females) or (2) female resistance to small males in combination with higher costs that small males may incur in securing large females.

year: 2007

title: A game of slides and ladders: Māori health providers and funders

authors: Masters-Awatere, Bridgette

abstract: Devolution of government responsibility after the neo-liberal reforms of the 1980s, and the re-orientation of health services towards public health in the 1990s, created an opportunity for Māori to take control of their own health outcomes through the delivery of culturally relevant and appropriate services. By 2000 “By Maori, For Maori” service provision had burst forth as the preferred approach with Māori. While grappling with the tendency of government agencies to fund services based on pre-existing health output criteria, Māori service providers were “walking on egg shells” under the constant threat of losing their funding. Currentcontracting does not capture the extent of the work done by Māori providers to serve precariat families. Nor does it adequately acknowledge, validate or value indigenous approaches to health and wellbeing. Instead, narrow, administratively demanding and difficult to interpret contracts threaten the provision of culturally relevant services. This chapter talks about some of the creative and insightful ways Māori service providers manage contrasting cultural and contractual expectations.

text: A game of slides and ladders: Māori health providers and funders Devolution of government responsibility after the neo-liberal reforms of the 1980s, and the re-orientation of health services towards public health in the 1990s, created an opportunity for Māori to take control of their own health outcomes through the delivery of culturally relevant and appropriate services. By 2000 “By Maori, For Maori” service provision had burst forth as the preferred approach with Māori. While grappling with the tendency of government agencies to fund services based on pre-existing health output criteria, Māori service providers were “walking on egg shells” under the constant threat of losing their funding. Currentcontracting does not capture the extent of the work done by Māori providers to serve precariat families. Nor does it adequately acknowledge, validate or value indigenous approaches to health and wellbeing. Instead, narrow, administratively demanding and difficult to interpret contracts threaten the provision of culturally relevant services. This chapter talks about some of the creative and insightful ways Māori service providers manage contrasting cultural and contractual expectations.

year: 2017