title: Refinement of Mg alloys crystal structure via Nb-based heterogeneous substrates for improved performances

authors: Bolzoni, Leandro

abstract: Lightness and high specific strength make magnesium alloys ideal materials for the transportation industry, especially the automotive sector that is struggling to cope with the everyday more stringent regulations on emission of carbon dioxide. Wrought magnesium alloys are difficult to deform because of the few active slip systems characteristic of their hexagonal close-packed lattice. Consequently, most of the commercially available magnesium alloys are alloys based on the Mg-Al binary system used in casting processes. The improvement of the mechanical properties of these alloys cannot be achieved by means of grain refinement using Zr due to the formation of Zr aluminides. In this study we propose a novel chemical composition that can refine all types of Mg alloys as proved in the Al-containing AM50 Mg alloy. We demonstrate that Nb-B inoculation of Mg alloys promotes the formation of heterogeneously nucleated primary α-Mg grains leading to the reduction of the grain size and this is obtained over a wide range of cooling rates. We also show that the grain refinement achieved leads to the improvement of the properties of high pressure die cast Mg automotive components and has the potential to enhance the mechanical properties of cast Mg alloys.

text: Refinement of Mg alloys crystal structure via Nb-based heterogeneous substrates for improved performances Lightness and high specific strength make magnesium alloys ideal materials for the transportation industry, especially the automotive sector that is struggling to cope with the everyday more stringent regulations on emission of carbon dioxide. Wrought magnesium alloys are difficult to deform because of the few active slip systems characteristic of their hexagonal close-packed lattice. Consequently, most of the commercially available magnesium alloys are alloys based on the Mg-Al binary system used in casting processes. The improvement of the mechanical properties of these alloys cannot be achieved by means of grain refinement using Zr due to the formation of Zr aluminides. In this study we propose a novel chemical composition that can refine all types of Mg alloys as proved in the Al-containing AM50 Mg alloy. We demonstrate that Nb-B inoculation of Mg alloys promotes the formation of heterogeneously nucleated primary α-Mg grains leading to the reduction of the grain size and this is obtained over a wide range of cooling rates. We also show that the grain refinement achieved leads to the improvement of the properties of high pressure die cast Mg automotive components and has the potential to enhance the mechanical properties of cast Mg alloys.

year: 2018

title: Change detection in categorical evolving data streams

authors: Ienco, Dino

subjects: categorical data

abstract: Detecting change in evolving data streams is a central issue for accurate adaptive learning. In real world applications, data streams have categorical features, and changes induced in the data distribution of these categorical features have not been considered extensively so far. Previous work on change detection focused on detecting changes in the accuracy of the learners, but without considering changes in the data distribution.

To cope with these issues, we propose a new unsupervised change detection method, called CDCStream (Change Detection in Categorical Data Streams), well suited for categorical data streams. The proposed method is able to detect changes in a batch incremental scenario. It is based on the two following characteristics: (i) a summarization strategy is proposed to compress the actual batch by extracting a descriptive summary and (ii) a new segmentation algorithm is proposed to highlight changes and issue warnings for a data stream. To evaluate our proposal we employ it in a learning task over real world data and we compare its results with state of the art methods. We also report qualitative evaluation in order to show the behavior of CDCStream.

text: Change detection in categorical evolving data streams Detecting change in evolving data streams is a central issue for accurate adaptive learning. In real world applications, data streams have categorical features, and changes induced in the data distribution of these categorical features have not been considered extensively so far. Previous work on change detection focused on detecting changes in the accuracy of the learners, but without considering changes in the data distribution.

To cope with these issues, we propose a new unsupervised change detection method, called CDCStream (Change Detection in Categorical Data Streams), well suited for categorical data streams. The proposed method is able to detect changes in a batch incremental scenario. It is based on the two following characteristics: (i) a summarization strategy is proposed to compress the actual batch by extracting a descriptive summary and (ii) a new segmentation algorithm is proposed to highlight changes and issue warnings for a data stream. To evaluate our proposal we employ it in a learning task over real world data and we compare its results with state of the art methods. We also report qualitative evaluation in order to show the behavior of CDCStream.

year: 2014

title: Anō, ko te Riu ō Tāne Mahuta Possibilities and Challenges in a Ngāti Rangiwewehi Curriculum

authors: Mahuika, Rangimarie

subjects: Curriculum

abstract: This thesis considers how a curriculum might form a useful tool in meeting the needs and aspirations of Ngāti Rangiwewehi, a small, but dynamic tribe, who occupy specific territory from the north western shores of Lake Rotorua into the eastern Bay of Plenty of the North Island of New Zealand. In contemplating the potential benefits of a curriculum, this study begins by examining the epistemological frames of reference crucial to understanding how the tribe views the world around them, and their positioning within it. The thesis goes on to explore the pedagogical approaches specific to the iwi, and concludes by assessing the extent to which a curriculum is a viable means of maintaining and empowering Rangiwewehi mātauranga, and their underlying ambitions, and goals. Whether ‘curriculum’ is an appropriate framework to describe the way Ngāti Rangiwewehi view our educational processes, is an issue addressed in this study. To this extent, Rangiwewehi perspectives are intentionally privileged allowing appropriate representation of our understandings and aspirations. Eighteen people were interviewed as part of this study, yet many other voices included here were recorded during a tribal wānanga held in late 2010. Their accounts provide the core ideas and positions at work in this thesis, and are invaluable for the depth and texture they offer. An emphasis on the qualitative data collected here is important in allowing their words to take centre stage. In conveying their views and stories, three major themes emerged: these were people, place, and survival. Woven through the body of the thesis, these themes work to illustrate the key designs and patterns that were seen as fundamental to a Rangiwewehi way of viewing the world. Place and people, for instance, were affirmed as crucial to both the pedagogical and epistemological beliefs and practices maintained across generations. Similarly, the theme of survival was deemed a significant thread in comprehending the struggle and self-determination inherent in the tribe’s sense of identity and knowing. These themes reflect convictions shared across the iwi, highlighting the importance of understanding Ngāti Rangiwewehi by first listening to what they have to say about themselves and their curriculum.

text: Anō, ko te Riu ō Tāne Mahuta Possibilities and Challenges in a Ngāti Rangiwewehi Curriculum This thesis considers how a curriculum might form a useful tool in meeting the needs and aspirations of Ngāti Rangiwewehi, a small, but dynamic tribe, who occupy specific territory from the north western shores of Lake Rotorua into the eastern Bay of Plenty of the North Island of New Zealand. In contemplating the potential benefits of a curriculum, this study begins by examining the epistemological frames of reference crucial to understanding how the tribe views the world around them, and their positioning within it. The thesis goes on to explore the pedagogical approaches specific to the iwi, and concludes by assessing the extent to which a curriculum is a viable means of maintaining and empowering Rangiwewehi mātauranga, and their underlying ambitions, and goals. Whether ‘curriculum’ is an appropriate framework to describe the way Ngāti Rangiwewehi view our educational processes, is an issue addressed in this study. To this extent, Rangiwewehi perspectives are intentionally privileged allowing appropriate representation of our understandings and aspirations. Eighteen people were interviewed as part of this study, yet many other voices included here were recorded during a tribal wānanga held in late 2010. Their accounts provide the core ideas and positions at work in this thesis, and are invaluable for the depth and texture they offer. An emphasis on the qualitative data collected here is important in allowing their words to take centre stage. In conveying their views and stories, three major themes emerged: these were people, place, and survival. Woven through the body of the thesis, these themes work to illustrate the key designs and patterns that were seen as fundamental to a Rangiwewehi way of viewing the world. Place and people, for instance, were affirmed as crucial to both the pedagogical and epistemological beliefs and practices maintained across generations. Similarly, the theme of survival was deemed a significant thread in comprehending the struggle and self-determination inherent in the tribe’s sense of identity and knowing. These themes reflect convictions shared across the iwi, highlighting the importance of understanding Ngāti Rangiwewehi by first listening to what they have to say about themselves and their curriculum.

year: 2011