title: Transport of solar wind fluctuations: A two-component model

authors: Oughton, Sean

subjects: maths

abstract: We present a new model for the transport of solar wind fluctuations which treats them as two interacting incompressible components: quasi-two-dimensional turbulence and a wave-like piece. Quantities solved for include the energy, cross helicity, and characteristic transverse length scale of each component, plus the proton temperature. The development of the model is outlined and numerical solutions are compared with spacecraft observations. Compared to previous single-component models, this new model incorporates a more physically realistic treatment of fluctuations induced by pickup ions and yields improved agreement with observed values of the correlation length, while maintaining good observational accord with the energy, cross helicity, and temperature.

text: Transport of solar wind fluctuations: A two-component model We present a new model for the transport of solar wind fluctuations which treats them as two interacting incompressible components: quasi-two-dimensional turbulence and a wave-like piece. Quantities solved for include the energy, cross helicity, and characteristic transverse length scale of each component, plus the proton temperature. The development of the model is outlined and numerical solutions are compared with spacecraft observations. Compared to previous single-component models, this new model incorporates a more physically realistic treatment of fluctuations induced by pickup ions and yields improved agreement with observed values of the correlation length, while maintaining good observational accord with the energy, cross helicity, and temperature.

year: 2011

title: Light, camera, actions: characterizing the usage of IXPs' action BGP communities

authors: Mazzola, Fabricio

subjects: computer science

abstract: Border Gateway Protocol (BGP) communities, an optional message attribute, allow network operators to tag BGP announcements and act on routing decisions. Although widely used, it is so far unclear how prevalent the different types of communities are and the degree to which the different traffic engineering actions have been used. There are two major reasons for this gap: few community values have been standardised and the limited visibility at route collectors. In this paper, leveraging the fact that Internet eXchange Points (IXPs) have sets of well-documented BGP communities, we use their BGP Looking Glasses (LGs) to inspect their route servers and shed light on how IXP members are using action BGP communities. During twelve weeks, we collected and analysed routing data from eight IXPs worldwide, focusing the analysis on the four largest IXPs. We observe that i) over one-third of IXP members (>35.7%) use action communities in at least one route; ii) two-thirds (66.6%) of them are intended to avoid propagating routes, mostly to content providers (CPs); iii) nearly one-third (31.8%) are targeting Autonomous Systems (ASes) that are not present at the IXPs' route servers, resulting in no practical routing effect and only increasing processing and memory storage overheads.

text: Light, camera, actions: characterizing the usage of IXPs' action BGP communities Border Gateway Protocol (BGP) communities, an optional message attribute, allow network operators to tag BGP announcements and act on routing decisions. Although widely used, it is so far unclear how prevalent the different types of communities are and the degree to which the different traffic engineering actions have been used. There are two major reasons for this gap: few community values have been standardised and the limited visibility at route collectors. In this paper, leveraging the fact that Internet eXchange Points (IXPs) have sets of well-documented BGP communities, we use their BGP Looking Glasses (LGs) to inspect their route servers and shed light on how IXP members are using action BGP communities. During twelve weeks, we collected and analysed routing data from eight IXPs worldwide, focusing the analysis on the four largest IXPs. We observe that i) over one-third of IXP members (>35.7%) use action communities in at least one route; ii) two-thirds (66.6%) of them are intended to avoid propagating routes, mostly to content providers (CPs); iii) nearly one-third (31.8%) are targeting Autonomous Systems (ASes) that are not present at the IXPs' route servers, resulting in no practical routing effect and only increasing processing and memory storage overheads.

year: 2022-12-06

title: Learning in later life: a bicultural perspective from Aotearoa/New Zealand

authors: Findsen, Brian

abstract: This article is concerned with how learning in later life has been constructed and practised by the two most numerous ethnic groups in Aotearoa/New Zealand, Pākėhā (Europeans) and Māori (Indigenous people). It is argued that learning is heavily influenced by historic features of interaction between these two groups; Pākehā as the dominant cultural and economic group and Māori as subordinate. While contemporary perspectives are necessarily interpreted in the light of historical trends and events, fresh interpretations of what constitutes biculturalism in this country allow for more nuanced understanding of possibilities for and obstacles to older adult learning/education. Themes from lifelong learning are analysed with special reference to older people’s learning, the consequences of Māori sovereignty on pedagogy and trends identified for older adult education. Two linked case studies of Pākehā and Māori older adult education in a New Zealand university are described to illustrate complexities and tensions in provision in a bicultural context.

text: Learning in later life: a bicultural perspective from Aotearoa/New Zealand This article is concerned with how learning in later life has been constructed and practised by the two most numerous ethnic groups in Aotearoa/New Zealand, Pākėhā (Europeans) and Māori (Indigenous people). It is argued that learning is heavily influenced by historic features of interaction between these two groups; Pākehā as the dominant cultural and economic group and Māori as subordinate. While contemporary perspectives are necessarily interpreted in the light of historical trends and events, fresh interpretations of what constitutes biculturalism in this country allow for more nuanced understanding of possibilities for and obstacles to older adult learning/education. Themes from lifelong learning are analysed with special reference to older people’s learning, the consequences of Māori sovereignty on pedagogy and trends identified for older adult education. Two linked case studies of Pākehā and Māori older adult education in a New Zealand university are described to illustrate complexities and tensions in provision in a bicultural context.

year: 2016