78 resultados para through pores formation


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Both scholarly literature and popular media often depict predominantly negative and one-dimensional images of boys, especially African-American boys. Predictions of these boys’ anticipated difficulties in school and adulthood are equally prevalent. This paper reports qualitative research that features case studies of nine urban boys of color, aged nine to eleven, who participated in an afterschool program where they learned to create digital multimedia texts. Drawing on an analysis of the children’s patterns of participation, their multimodal products, and their social and intellectual growth over time, the study revealed that these children demonstrated many versions of male selves, and that their digital stories narrated these identities in ways that often challenged hegemonic versions of masculinity. These enactments of identity were made possible by the ways that their afterschool social space structured their activities, as well as by the symbolic means and subject matters privileged in that space, principally digital multimodal narratives and popular culture. At a time when afterschool programs are under pressure to become extensions of the school day, this research argues for recognition of and support for the different functions such programs can serve when structured as alternative spaces for learning and identity formation.

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The main aim of this study was to investigate the critical conditions for the formation of ultrafine grain structures using hot torsion and wedge rolling techniques. In addition, the effect of thermomechanical parameters and steel composition on the critical conditions for ultrafine grain structure formation has been systematically evaluated.

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In the current study, a novel approach was employed to produce a unique combination of ultrafine ferrite grains and low temperature bainite in a low carbon steel with a high hardenability. The thermomechanical route included warm deformation of supercooled austenite followed by reheating in the ferrite region and then cooling to bainitic transformation regime (i.e. 400-250°C). The resultant microstructure was ultrafine ferrite grains (i.e. <4μm) and very fine bainite consisting of bainitic ferrite laths with high dislocation density and retained austenite films. This microstructure offers a unique combination of ultimate tensile strength and elongation due to the presence of ductile fine ferrite grains and hard low temperature bainitic ferrite laths with retained austenite films. The microstructural characteristics of bainite were studied using optical microscopy in conjunction with scanning and transmission electron microscopy techniques.

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A novel approach was used to produce an ultrafine grain structure in low carbon steels with a wide range of hardenability. This included warm deformation of supercooled austenite followed by reheating in the austenite region and cooling (RHA). The ultrafine ferrite structure was independent of steel composition. However, the mechanism of ferrite refinement changed with the steel quench hardenability. In a relatively low hardenable steel, the ultrafine structure was produced through dynamic strain induced transformation, whereas the ferrite refinement was formed by static transformation in steels with high quench hardenability. The use of a model Ni-30Fe austenitic alloy revealed that the deformation temperature has a strong effect on the nature of the intragranular defects. There was a transition temperature below which the cell dislocation structure changed to laminar microbands. It appears that the extreme refinement of ferrite is due to the formation of extensive high angle intragranular defects at these low deformation temperature that then act as sites for static transformation. © 2008 World Scientific Publishing Company.

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The development of the third sector in Australia has involved the negotiation of varying forms of state and market regulatory mechanisms. In the course of these settlements, ground-up initiatives have often found that authenticity is only the starting point on journeys that end in incorporation. Social entrepreneurship is an emerging set of ideas which attempts to hold on to the authentic and unique elements generated by grassroots actions. What are its chances of success? This article sets out to answer this question through a discussion of regulation and social capital. A four-fold model of social cap ita I formation is advanced which outlines 'defensive', 'consolidative', 'inclusive' and 'regulated' social capital. It is concluded that while social entrepreneurship has the potential to shift social capital formation from reactive to active forms, it is likely to become increasingly standardised and regulated.

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In the present study, the effect of nominal equivalent strain (between 0 and 1.2), deformation temperature (790– 750°C) and carbon content (0.06 – 0.35%C) was investigated on ferrite grain refinement through dynamic strain induced transformation (DSIT) in plain carbon steels in single pass rolling. The microstructural evolution of the transformation of austenite to ferrite has been evaluated through the thickness of the strip. The results showed a number of important microstructural features as a function of strain, which could be classified into three regions; no DSIT region, DSIT region, and ultrafine ferrite (UFF) grain region. Hence, two critical strains; dynamic strain induced transformationC, DSIT) and ultrafine ferrite formationC, UFF) were determined. These strains were increased significantly with an increase in carbon content. The critical strain for UFF formation reduced with decrease in deformation temperature. The UFF microstructure consisted of ultrafine, equiaxed ferrite grains (<2 μm) with very fine cementite particles. In the centre of the rolled strip, there was a conventional ferrite– pearlite microstructure, although ferrite grain refinement and the volume fraction of ferrite increased with increase in the nominal equivalent strain.

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The formation of ultrafine ferrite by strain induced transformation is assessed using rolling and hot torsion experiments. These experiments are used to examine the impact of thermomechanical processing conditions and steel chemistry on strain induced austenite to ferrite transformation and the formation of ultrafine ferrite. The critical strain for dynamic strain induced transformation increased with increasing carbon equivalence, deformation temperature and austenite grain size. The deformation structure in the austenite grains changes with the thermomechanical processing conditions. Drawing on these results and the current literature, the important factors for the production of ultrafine ferrite are described and a mechanism is proposed.

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The importance of effective multilateral security networks is widely recognised in Australia and internationally as being essential to facilitate the large-scale sharing of information required to respond to the threat of terrorism. Australian national security agencies are currently constructing networks in order to bring the diverse national and international security agencies together to achieve this. This paper examines this process of security network formation in the area of critical infrastructure protection, with particular emphasis on airport security. We address the key issues and factors shaping network formation and the dynamics involved in network practice. These include the need for the networks to extend membership beyond the strictly defined elements of national security; the integration of public and private ‘nodes’ in counter-terrorism ‘networks’; and the broader ‘responsibilisation’ of the private sector and the challenges with ‘enabling’ them in counter-terrorism networks. We argue that the need to integrate public and private agencies in counter-terrorism networks is necessary but faces considerable organisational, cultural, and legal barriers.