title: Modification of sintered titanium alloys by hot isostatic pressing

authors: Bolzoni, Leandro

subjects: HIP

abstract: Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures close to ingot metallurgy products. However, residual porosity is normally present in the products produced by the PM route of powder pressing and sintering (P&S)\, and this needs to be reduced by using post-sintering process step such as hot isostatic pressing (HIP) and forging. In this study, the microstructural and mechanical property changes caused by HIP of samples of two alloys, near-α Ti-3Al-2.5V alloy and α+β Ti-6Al-4V, produced by P&S route were investigated. Two types of powders were utilised: prealloyed powders and blend of elemental titanium powder and master alloy powder. Four conditions defined by HIP temperature, pressure and time were used to HIP the sintered samples with two geometries. The results show that, independent of the HIP conditions used, HIP increased the relative density of the samples to approximately 97.5% and their hardness by 30-50 HV depending on the HIP condition. However, HIP at 1000°C changes the fracture mode of the sintered samples from ductile to brittle.

text: Modification of sintered titanium alloys by hot isostatic pressing Powder metallurgy (PM) permits to obtain titanium alloys with properties and microstructures close to ingot metallurgy products. However, residual porosity is normally present in the products produced by the PM route of powder pressing and sintering (P&S)\, and this needs to be reduced by using post-sintering process step such as hot isostatic pressing (HIP) and forging. In this study, the microstructural and mechanical property changes caused by HIP of samples of two alloys, near-α Ti-3Al-2.5V alloy and α+β Ti-6Al-4V, produced by P&S route were investigated. Two types of powders were utilised: prealloyed powders and blend of elemental titanium powder and master alloy powder. Four conditions defined by HIP temperature, pressure and time were used to HIP the sintered samples with two geometries. The results show that, independent of the HIP conditions used, HIP increased the relative density of the samples to approximately 97.5% and their hardness by 30-50 HV depending on the HIP condition. However, HIP at 1000°C changes the fracture mode of the sintered samples from ductile to brittle.

year: 2012

title: Failure resilience and traffic engineering for multi-controller software defined networking

authors: Zaicu, Nicu Florin

abstract: This thesis explores and proposes solutions to address the challenges faced by Multi-Controller SDN (MCSDN) systems when deploying TE optimisation on WANs. Despite the interest from the research community, existing MCSDN systems present limitations. For example, TE optimisation systems are computationally complex, have high consistency requirements, and need network-wide state to operate. Because of such requirements, MCSDN systems can encounter performance overheads and state consistency problems when implementing TE. Moreover, performance and consistency problems are more prominent when deploying the system on WANs as these network types have higher inter-device latency, delaying state propagation.

Unlike existing literature, this thesis presents several design choices that address all four challenges affecting MCSDN systems (scalability, consistency, resilience, and coordination). We use the presented design choices to build Helix, a hierarchical MCSDN system. Helix provides better scalability, performance and failure resilience compared to existing MCSDN systems by sharing minimal state between controllers, offloading operations closer to the data plane and deploying lightweight tasks.

A challenge that we faced when building Helix was that existing TE algorithms did not meet Helix's design choices. This thesis presents a new CSPF-based TE algorithm that needs minimal state to operate and supports offloading inter-area TE to local controllers, fulfilling Helix's requirements. Helix's TE algorithm provides better performance and forwarding stability, addressing 1.6x more congestion while performing up to 29x fewer path modifications than the other algorithms evaluated in our experiments.

While MCSDN literature has explored evaluating different aspects of system performance, there is a lack of readily available tools and concrete testing methodologies. To this end, this thesis provides concrete testing methodologies and tools readily available to the MCSDN community to evaluate the data plane failure resilience, control plane failure resilience, and TE optimisation performance of MCSDN systems.

text: Failure resilience and traffic engineering for multi-controller software defined networking This thesis explores and proposes solutions to address the challenges faced by Multi-Controller SDN (MCSDN) systems when deploying TE optimisation on WANs. Despite the interest from the research community, existing MCSDN systems present limitations. For example, TE optimisation systems are computationally complex, have high consistency requirements, and need network-wide state to operate. Because of such requirements, MCSDN systems can encounter performance overheads and state consistency problems when implementing TE. Moreover, performance and consistency problems are more prominent when deploying the system on WANs as these network types have higher inter-device latency, delaying state propagation.

Unlike existing literature, this thesis presents several design choices that address all four challenges affecting MCSDN systems (scalability, consistency, resilience, and coordination). We use the presented design choices to build Helix, a hierarchical MCSDN system. Helix provides better scalability, performance and failure resilience compared to existing MCSDN systems by sharing minimal state between controllers, offloading operations closer to the data plane and deploying lightweight tasks.

A challenge that we faced when building Helix was that existing TE algorithms did not meet Helix's design choices. This thesis presents a new CSPF-based TE algorithm that needs minimal state to operate and supports offloading inter-area TE to local controllers, fulfilling Helix's requirements. Helix's TE algorithm provides better performance and forwarding stability, addressing 1.6x more congestion while performing up to 29x fewer path modifications than the other algorithms evaluated in our experiments.

While MCSDN literature has explored evaluating different aspects of system performance, there is a lack of readily available tools and concrete testing methodologies. To this end, this thesis provides concrete testing methodologies and tools readily available to the MCSDN community to evaluate the data plane failure resilience, control plane failure resilience, and TE optimisation performance of MCSDN systems.

year: 2022

title: The Truth About Stories: A Native Narrative By Thomas King

authors: Douglas, Zanna

abstract: The truth about stories is that that’s all we are.” Koinei ngā kupu e tika ana hei whakamana i te āhua o te pukapuka nei nā Thomas King i tuhi. Ko te pakiwaitara tētehi āhuatanga e pupuri nei e te iwi taketake, he huarahi e mārama ai tātou ki te huringa o te ao. He taonga hoki ēnei kua take mai nō mua rā anō, kia kore e warewaretia wā tātou hītori, kia pupuri tonu hoki ki ngā kōrero ō mua, ngā kōrero e puawai ai te tuakiri o te tangata. Mō King, ka hanga te pakiwaitara i te tangata, nā koianei te pūtakenga mai o tāna aronga i roto i te pukapuka nei. Ko tāna he whakatakoto mai i ngā pakiwaitara kua rangona e ia i roto i ōna tau, me kī ko ngā hītori nō tōna iwi. Ko tētehi o ngā āhuatanga matua ka tū mai i roto i te tuhituhinga nei ko tāna kōrero mō ngā āhuatanga kua pā ki a ia i roto i tōna oranga. He huarahi pai tēnei hei whakamahana atu i te kaituhi ki te kaipānui, mā reira e āhei ana te kaipānui ki te whakawhanaunga atu ki te ngako o ngā kōrero o roto i te pukapuka.

text: The Truth About Stories: A Native Narrative By Thomas King The truth about stories is that that’s all we are.” Koinei ngā kupu e tika ana hei whakamana i te āhua o te pukapuka nei nā Thomas King i tuhi. Ko te pakiwaitara tētehi āhuatanga e pupuri nei e te iwi taketake, he huarahi e mārama ai tātou ki te huringa o te ao. He taonga hoki ēnei kua take mai nō mua rā anō, kia kore e warewaretia wā tātou hītori, kia pupuri tonu hoki ki ngā kōrero ō mua, ngā kōrero e puawai ai te tuakiri o te tangata. Mō King, ka hanga te pakiwaitara i te tangata, nā koianei te pūtakenga mai o tāna aronga i roto i te pukapuka nei. Ko tāna he whakatakoto mai i ngā pakiwaitara kua rangona e ia i roto i ōna tau, me kī ko ngā hītori nō tōna iwi. Ko tētehi o ngā āhuatanga matua ka tū mai i roto i te tuhituhinga nei ko tāna kōrero mō ngā āhuatanga kua pā ki a ia i roto i tōna oranga. He huarahi pai tēnei hei whakamahana atu i te kaituhi ki te kaipānui, mā reira e āhei ana te kaipānui ki te whakawhanaunga atu ki te ngako o ngā kōrero o roto i te pukapuka.

year: 2011-04