title: Viscous effects in planar magnetic X-point reconnection

authors: Craig, Ian J.D.

subjects: magnetohydrodynamics

abstract: The impact of viscous dissipation is considered on magnetic reconnection in closed line-tied magnetic X-points. It is shown that viscous effects can provide fast energy dissipation for disturbances which do not alter the initial X-point topology. If the X-point topology is altered, then the rate of viscous dissipation depends on both the perturbed topology and the relative magnitudes of viscosity and electric resistivity. New solutions are demonstrated, which derive from the combination of resistive and viscous effects. The solutions are characterized by monotonically decaying modes which are qualitatively different from the previously known oscillatory modes in nonviscous resistive X-point reconnection. These results suggest that viscous heating in magnetic X-points may be an important effect in solar flares.

text: Viscous effects in planar magnetic X-point reconnection The impact of viscous dissipation is considered on magnetic reconnection in closed line-tied magnetic X-points. It is shown that viscous effects can provide fast energy dissipation for disturbances which do not alter the initial X-point topology. If the X-point topology is altered, then the rate of viscous dissipation depends on both the perturbed topology and the relative magnitudes of viscosity and electric resistivity. New solutions are demonstrated, which derive from the combination of resistive and viscous effects. The solutions are characterized by monotonically decaying modes which are qualitatively different from the previously known oscillatory modes in nonviscous resistive X-point reconnection. These results suggest that viscous heating in magnetic X-points may be an important effect in solar flares.

year: 2005

title: Is Semantic Query Optimization Worthwhile?

authors: Genet, Bryan Howard

subjects: semantic query optimization

abstract: The term quote semantic query optimization quote (SQO) denotes a methodology whereby queries against databases are optimized using semantic information about the database objects being queried. The result of semantically optimizing a query is another query which is syntactically different to the original, but semantically equivalent and which may be answered more efficiently than the original. SQO is distinctly different from the work performed by the conventional SQL optimizer. The SQL optimizer generates a set of logically equivalent alternative execution paths based ultimately on the rules of relational algebra. However, only a small proportion of the readily available semantic information is utilised by current SQL optimizers. Researchers in SQO agree that SQO can be very effective. However, after some twenty years of research into SQO, there is still no commercial implementation. In this thesis we argue that we need to quantify the conditions for which SQO is worthwhile. We investigate what these conditions are and apply this knowledge to relational database management systems (RDBMS) with static schemas and infrequently updated data. Any semantic query optimizer requires the ability to reason using the semantic information available, in order to draw conclusions which ultimately facilitate the recasting of the original query into a form which can be answered more efficiently. This reasoning engine is currently not part of any commercial RDBMS implementation. We show how a practical semantic query optimizer may be built utilising readily available semantic information, much of it already captured by meta-data typically stored in commercial RDBMS. We develop cost models which predict an upper bound to the amount of optimization one can expect when queries are pre-processed by a semantic optimizer. We present a series of empirical results to confirm the effectiveness or otherwise of various types of SQO and demonstrate the circumstances under which SQO can be effective.

text: Is Semantic Query Optimization Worthwhile? The term quote semantic query optimization quote (SQO) denotes a methodology whereby queries against databases are optimized using semantic information about the database objects being queried. The result of semantically optimizing a query is another query which is syntactically different to the original, but semantically equivalent and which may be answered more efficiently than the original. SQO is distinctly different from the work performed by the conventional SQL optimizer. The SQL optimizer generates a set of logically equivalent alternative execution paths based ultimately on the rules of relational algebra. However, only a small proportion of the readily available semantic information is utilised by current SQL optimizers. Researchers in SQO agree that SQO can be very effective. However, after some twenty years of research into SQO, there is still no commercial implementation. In this thesis we argue that we need to quantify the conditions for which SQO is worthwhile. We investigate what these conditions are and apply this knowledge to relational database management systems (RDBMS) with static schemas and infrequently updated data. Any semantic query optimizer requires the ability to reason using the semantic information available, in order to draw conclusions which ultimately facilitate the recasting of the original query into a form which can be answered more efficiently. This reasoning engine is currently not part of any commercial RDBMS implementation. We show how a practical semantic query optimizer may be built utilising readily available semantic information, much of it already captured by meta-data typically stored in commercial RDBMS. We develop cost models which predict an upper bound to the amount of optimization one can expect when queries are pre-processed by a semantic optimizer. We present a series of empirical results to confirm the effectiveness or otherwise of various types of SQO and demonstrate the circumstances under which SQO can be effective.

year: 2007

title: The Critical Juncture in Aotearoa New Zealand and The Collective Future: Policy Issues in Settler/Invader Colonial Zombiism Found in “Biculturalism”

authors: Simon, Hemopereki

abstract: This theoretical Kaupapa Māori writing inquiry study seeks to explore the settler colonial nature of Aotearoa New Zealand. The research finds that biculturalism, as a neo-liberal and settler-colonial construct does not provide for either tino rangatiratanga or mana motuhake. Indeed, biculturalism fails to provide for indigenous inclusion and actively suppresses the recognition of mana motuhake. Biculturalism is found to fit Beck’s definition of Zombie Concepts. These are social concepts that are dead and yet kept alive in their use by scholars and society to describe the growing fiction of traditional social institutions and in being kept alive maintain, in this case, settler colonial and colonial power structures. The main argument is that Biculturalism is neoliberal and settler colonial public discourse, that needs to be unpacked and then discarded because it does not provide for tino rangatiranga or mana motuhake.

text: The Critical Juncture in Aotearoa New Zealand and The Collective Future: Policy Issues in Settler/Invader Colonial Zombiism Found in “Biculturalism” This theoretical Kaupapa Māori writing inquiry study seeks to explore the settler colonial nature of Aotearoa New Zealand. The research finds that biculturalism, as a neo-liberal and settler-colonial construct does not provide for either tino rangatiratanga or mana motuhake. Indeed, biculturalism fails to provide for indigenous inclusion and actively suppresses the recognition of mana motuhake. Biculturalism is found to fit Beck’s definition of Zombie Concepts. These are social concepts that are dead and yet kept alive in their use by scholars and society to describe the growing fiction of traditional social institutions and in being kept alive maintain, in this case, settler colonial and colonial power structures. The main argument is that Biculturalism is neoliberal and settler colonial public discourse, that needs to be unpacked and then discarded because it does not provide for tino rangatiranga or mana motuhake.

year: 2022