title: Using a permutation test for attribute selection in decision trees

authors: Frank, Eibe

subjects: computer science

abstract: Most techniques for attribute selection in decision trees are biased towards attributes with many values, and several ad hoc solutions to this problem have appeared in the machine learning literature. Statistical tests for the existence of an association with a prespecified significance level provide a well-founded basis for addressing the problem. However, many statistical tests are computed from a chi-squared distribution, which is only a valid approximation to the actural distribution in the large-sample case-and this patently does not hold near the leaves of a decision tree. An exception is the class of permutation tests. We describe how permutation tests can be applied to this problem. We choose one such test for further exploration, and give a novel two-stage method for applying it to select attributes in a decision tree. Results on practical datasets compare favourably with other methods that also adopt a pre-pruning strategy.

text: Using a permutation test for attribute selection in decision trees Most techniques for attribute selection in decision trees are biased towards attributes with many values, and several ad hoc solutions to this problem have appeared in the machine learning literature. Statistical tests for the existence of an association with a prespecified significance level provide a well-founded basis for addressing the problem. However, many statistical tests are computed from a chi-squared distribution, which is only a valid approximation to the actural distribution in the large-sample case-and this patently does not hold near the leaves of a decision tree. An exception is the class of permutation tests. We describe how permutation tests can be applied to this problem. We choose one such test for further exploration, and give a novel two-stage method for applying it to select attributes in a decision tree. Results on practical datasets compare favourably with other methods that also adopt a pre-pruning strategy.

year: 1998

title: Work hardening of quaternary powder metallurgy Ti alloys

authors: Al-hajiri, M

abstract: The concurrent addition of Al as α stabiliser and Nb and Cu or Mn as β stabilisers was used to design new powder metallurgy quaternary Ti alloys and investigate their manufacturability and consequent performance. It is found that the powder blend's compressibility decreases with the total amount of alloying elements due to the characteristics of the powders used. Consequently, the sintered density of the quaternary Ti alloys decreases and slightly higher values are achieved if Mn instead of Cu is used, despite the higher diffusivity of Cu at the sintering temperature. The quaternary Ti alloys are characterised by a lamellar microstructure comprising α grain boundaries and α+β lamellae where the amount and type of alloying elements determine the coarseness of the microstructural features. This results in stronger and harder but less ductile quaternary Ti alloys for higher alloying elements contents and for stronger β stabilisers, although of their overall elastoplastic behaviour. Because of their lamellar microstructure, the quaternary Ti alloys show similar deformation behaviour but the actual work hardening rate is governed by the fineness of the microstructure.

text: Work hardening of quaternary powder metallurgy Ti alloys The concurrent addition of Al as α stabiliser and Nb and Cu or Mn as β stabilisers was used to design new powder metallurgy quaternary Ti alloys and investigate their manufacturability and consequent performance. It is found that the powder blend's compressibility decreases with the total amount of alloying elements due to the characteristics of the powders used. Consequently, the sintered density of the quaternary Ti alloys decreases and slightly higher values are achieved if Mn instead of Cu is used, despite the higher diffusivity of Cu at the sintering temperature. The quaternary Ti alloys are characterised by a lamellar microstructure comprising α grain boundaries and α+β lamellae where the amount and type of alloying elements determine the coarseness of the microstructural features. This results in stronger and harder but less ductile quaternary Ti alloys for higher alloying elements contents and for stronger β stabilisers, although of their overall elastoplastic behaviour. Because of their lamellar microstructure, the quaternary Ti alloys show similar deformation behaviour but the actual work hardening rate is governed by the fineness of the microstructure.

year: 2024-04-01

title: Mana Wahine Geographies: Spiritual, Spatial and Embodied Understandings of Papatūānuku

authors: Simmonds, Naomi Beth

subjects: Mana wahine

abstract: This thesis is a theoretical and empirical exploration of Māori women's knowledges and understandings of Papatūānuku in contemporary Aotearoa. The primary focus of this research is on the complexities, connections, and contradictions of Māori women's embodied relationships with the spaces of Papatūānuku - spaces that are simultaneously material, discursive, symbolic, and spiritual. In doing so, I displace the boundaries between coloniser/colonised, self/other, rational/irrational and scientific/spiritual. I demonstrate that Māori women's colonised realities produce multiple, complex and hybrid understandings of Papatūānuku. 

This thesis has three main strands. The first is theoretical. I offer mana wahine (Māori feminist discourses) as another perspective for geography that engages with the complex intersections of colonisation, race and gender. A mana wahine geography framework is a useful lens through which to explore the complexities of Māori women's relationships to space and place. This framework contributes to, and draws together, feminist geographies and Māori and indigenous academic scholarship.

Autobiographical material is woven with joint and individual semi-structured in-depth interviews conducted with nine Māori women in the Waikato region. The second strand, woven into this thesis, is a critical examination of the colonisation of Māori women's spiritual and embodied relationships to Papatūānuku. The invisibility of Māori women's knowledges in dominant conceptualisations of mythology, tikanga and wairua discourses is not a harmless omission rather it contains a political imperative that maintains the hegemony of colonialism and patriarchy. I argue that to understand further Māori women's relationships to space and place an examination of wairua discourses is necessary.

The third strand reconfigures embodied and spatial conceptualisations of Papatūānuku. Māori women's maternal bodies are intimately tied to Papatūānuku in a way that challenges the oppositional distinctions between mind/body and biology/social inscription. Māori women's maternal bodies (and the representation of them in te reo Māori) are constructed by, and in turn, construct Papatūānuku. Furthermore, women's spatial relationship to tūrangawaewae, home space and wider environmental concerns demonstrates the co-constitution of subjectivities, bodies and space/place. 

My hope is that this thesis will add to geographical literature by addressing previously ignored knowledges and that it will contribute to indigenous scholarship by providing a spatial perspective.

text: Mana Wahine Geographies: Spiritual, Spatial and Embodied Understandings of Papatūānuku This thesis is a theoretical and empirical exploration of Māori women's knowledges and understandings of Papatūānuku in contemporary Aotearoa. The primary focus of this research is on the complexities, connections, and contradictions of Māori women's embodied relationships with the spaces of Papatūānuku - spaces that are simultaneously material, discursive, symbolic, and spiritual. In doing so, I displace the boundaries between coloniser/colonised, self/other, rational/irrational and scientific/spiritual. I demonstrate that Māori women's colonised realities produce multiple, complex and hybrid understandings of Papatūānuku. 

This thesis has three main strands. The first is theoretical. I offer mana wahine (Māori feminist discourses) as another perspective for geography that engages with the complex intersections of colonisation, race and gender. A mana wahine geography framework is a useful lens through which to explore the complexities of Māori women's relationships to space and place. This framework contributes to, and draws together, feminist geographies and Māori and indigenous academic scholarship.

Autobiographical material is woven with joint and individual semi-structured in-depth interviews conducted with nine Māori women in the Waikato region. The second strand, woven into this thesis, is a critical examination of the colonisation of Māori women's spiritual and embodied relationships to Papatūānuku. The invisibility of Māori women's knowledges in dominant conceptualisations of mythology, tikanga and wairua discourses is not a harmless omission rather it contains a political imperative that maintains the hegemony of colonialism and patriarchy. I argue that to understand further Māori women's relationships to space and place an examination of wairua discourses is necessary.

The third strand reconfigures embodied and spatial conceptualisations of Papatūānuku. Māori women's maternal bodies are intimately tied to Papatūānuku in a way that challenges the oppositional distinctions between mind/body and biology/social inscription. Māori women's maternal bodies (and the representation of them in te reo Māori) are constructed by, and in turn, construct Papatūānuku. Furthermore, women's spatial relationship to tūrangawaewae, home space and wider environmental concerns demonstrates the co-constitution of subjectivities, bodies and space/place. 

My hope is that this thesis will add to geographical literature by addressing previously ignored knowledges and that it will contribute to indigenous scholarship by providing a spatial perspective.

year: 2009