title: Damping properties and microstructure of magnetorheological composites based on iron sand and natural rubber

authors: Shuib, Raa Khimi

abstract: Material with high damping capability is desired from the viewpoint of vibration suppression in structures. Rubber is by far the most commonly used material for damping; here damping relies on the energy absorbed due to viscous flow that occurs during deformation in this viscoelastic materials. However, enhancement of damping through rubber modification or rubber selection to increase viscous flow, not surprisingly, generally results in a reduction in stiffness and strength [1]. More recently, a new class of damping materials, magnetorheological elastomers (MREs) have been developed such that inclusion of magnetic particles in rubber enables additional damping through magnetic particle interaction and interfacial friction. Furthermore, damping and stiffness can be varied by application of an applied magnetic field during fabrication or in service. MREs can be utilised for damping, either alone or within a composite structure such as those including steel plates.

text: Damping properties and microstructure of magnetorheological composites based on iron sand and natural rubber Material with high damping capability is desired from the viewpoint of vibration suppression in structures. Rubber is by far the most commonly used material for damping; here damping relies on the energy absorbed due to viscous flow that occurs during deformation in this viscoelastic materials. However, enhancement of damping through rubber modification or rubber selection to increase viscous flow, not surprisingly, generally results in a reduction in stiffness and strength [1]. More recently, a new class of damping materials, magnetorheological elastomers (MREs) have been developed such that inclusion of magnetic particles in rubber enables additional damping through magnetic particle interaction and interfacial friction. Furthermore, damping and stiffness can be varied by application of an applied magnetic field during fabrication or in service. MREs can be utilised for damping, either alone or within a composite structure such as those including steel plates.

year: 2013

title: Volcanic and sedimentary geology of the basaltic Karaka Volcano, South Auckland

authors: Hansen, Madison Keddie Ivy

subjects: volcano

abstract: Intraplate monogenetic volcanic fields are a common volcanic feature of the upper western North Island. There are four geographically related fields, approximately 38 km apart which young northwards from Raglan to Auckland. The South Auckland Volcanic Field (SAVF; 1.56–0.51 Ma) is older and more degraded than the Auckland Volcanic Field (AVF; active since 250 ka) to the north. Located between the two fields and overlying the Late Pliocene to Mid-Pleistocene pumiceous fluvial deposits of the Puketoka Formation, is the newly discovered Karaka Volcano. Although residents had referred to a volcanic landform in the area, it was in 2018 that evidence for a volcano based on geomorphology, a magnetic anomaly, weathered surficial deposits and water bore data was reported.

This thesis will present the recent findings of the volcano-sedimentary geology of the Karaka volcano. Evidence is based on stratigraphic analysis of two new drill cores, a complementary resistivity survey, petrography, scanning electron microscopy and geochemical investigations. One drill core intersected an upper 6 m blanket of Hamilton Ash Formation and a lower 7 m succession of interbedded, laminated dark brown organic-rich silts, and distal tephras. The lower succession is consistent with lake sediments associated with a crater lake within the geomorphic tuff ring. The second drill core, on the central high point of the volcanic landform, intersected an upper 6 m of brown and red clay. Beneath this, is a lower 9.5 m succession of volcanic ash, coarsening downwards, to a basaltic lapilli ash deposit with a lithic-rich matrix. This represents a phreatomagmatic phase in the upper part of the volcanic sequence. The resistivity survey connects the two drill holes giving an indication of extent and layering of the geology beneath the surface. No recognised volcanoes are within 5 km of this site, so it is unlikely that this pyroclastic deposit came from a distal vent, despite its isolated location outside of the predefined margins of the South Auckland and Auckland volcanic fields. 

Basalt lapilli within the pyroclastic succession are porphyritic with a trachytic to glassy groundmass with predominant phenocrysts of olivine, augite, opaque minerals and plagioclase. Geochemical analysis was conducted on whole rock samples of basalt lapilli by X-ray fluorescence spectroscopy (XRF) and on pyroxene, olivine, plagioclase and zeolites by electron probe microanalysis (EPMA). This data identified Karaka Basalt as a member of the Group B basalts of the SAVF. Lithics were fragments of the underlying sandstone and siltstone of the Waitemata Group.  The surrounding matrix comprised small basalt fragments, lithics, quartz and plagioclase.

Glass compositions of tephra by EPMA provide information that has been used to produce a tentative minimum age on the crater lake and by proxy the volcano itself. Tephra TW gives a possible correlation to the Kidnappers Ignimbrite which has been dated previously at ~0.99 Ma. The age of this tephra along with belonging to the SAVF, and a covering of Kauroa and Hamilton Ashes, gives the Karaka Volcano an approximate age range of 1.56 – 0.99 Ma.

text: Volcanic and sedimentary geology of the basaltic Karaka Volcano, South Auckland Intraplate monogenetic volcanic fields are a common volcanic feature of the upper western North Island. There are four geographically related fields, approximately 38 km apart which young northwards from Raglan to Auckland. The South Auckland Volcanic Field (SAVF; 1.56–0.51 Ma) is older and more degraded than the Auckland Volcanic Field (AVF; active since 250 ka) to the north. Located between the two fields and overlying the Late Pliocene to Mid-Pleistocene pumiceous fluvial deposits of the Puketoka Formation, is the newly discovered Karaka Volcano. Although residents had referred to a volcanic landform in the area, it was in 2018 that evidence for a volcano based on geomorphology, a magnetic anomaly, weathered surficial deposits and water bore data was reported.

This thesis will present the recent findings of the volcano-sedimentary geology of the Karaka volcano. Evidence is based on stratigraphic analysis of two new drill cores, a complementary resistivity survey, petrography, scanning electron microscopy and geochemical investigations. One drill core intersected an upper 6 m blanket of Hamilton Ash Formation and a lower 7 m succession of interbedded, laminated dark brown organic-rich silts, and distal tephras. The lower succession is consistent with lake sediments associated with a crater lake within the geomorphic tuff ring. The second drill core, on the central high point of the volcanic landform, intersected an upper 6 m of brown and red clay. Beneath this, is a lower 9.5 m succession of volcanic ash, coarsening downwards, to a basaltic lapilli ash deposit with a lithic-rich matrix. This represents a phreatomagmatic phase in the upper part of the volcanic sequence. The resistivity survey connects the two drill holes giving an indication of extent and layering of the geology beneath the surface. No recognised volcanoes are within 5 km of this site, so it is unlikely that this pyroclastic deposit came from a distal vent, despite its isolated location outside of the predefined margins of the South Auckland and Auckland volcanic fields. 

Basalt lapilli within the pyroclastic succession are porphyritic with a trachytic to glassy groundmass with predominant phenocrysts of olivine, augite, opaque minerals and plagioclase. Geochemical analysis was conducted on whole rock samples of basalt lapilli by X-ray fluorescence spectroscopy (XRF) and on pyroxene, olivine, plagioclase and zeolites by electron probe microanalysis (EPMA). This data identified Karaka Basalt as a member of the Group B basalts of the SAVF. Lithics were fragments of the underlying sandstone and siltstone of the Waitemata Group.  The surrounding matrix comprised small basalt fragments, lithics, quartz and plagioclase.

Glass compositions of tephra by EPMA provide information that has been used to produce a tentative minimum age on the crater lake and by proxy the volcano itself. Tephra TW gives a possible correlation to the Kidnappers Ignimbrite which has been dated previously at ~0.99 Ma. The age of this tephra along with belonging to the SAVF, and a covering of Kauroa and Hamilton Ashes, gives the Karaka Volcano an approximate age range of 1.56 – 0.99 Ma.

year: 2020

title: Inequities in Covid-19 Omicron infections and hospitalisations for Māori and Pacific people in Te Manawa Taki Midland region, New Zealand

authors: Whitehead, Jesse

abstract: Covid-19 impacts population health equity. While mRNA vaccines protect against serious illness and death, little New Zealand (NZ) data exists about the impact of Omicron - and effectiveness of vaccination - on different population groups. We aim to examine the impact of  Omicron  on Māori, Pacific and Other ethnicities and how this interacts with age and vaccination status in the Te Manawa Taki Midland region of NZ. Daily Covid-19 infection and hospitalisation rates (01/02/2022 - 29/06/2022) were calculated for Māori, Pacific and Other ethnicities for six age bands. A multivariate logistic regression model quantified the effects of ethnicity, age, and vaccination on hospitalisation rates. Per-capita Omicron cases were highest and occurred earliest among Pacific (9 per 1,000) and Māori (5 per 1,000) people and were highest among 12-24 year-olds (7 per 1,000). Hospitalisation was significantly more likely for Māori (OR=2.03), Pacific people (OR=1.75), over 75-year olds (OR=39.22), and unvaccinated people (OR=4.64). Length of hospitalisation is strongly related to age. Covid-19 vaccination reduces hospitalisations for older individuals and Māori and Pacific populations. Omicron inequitably impacted Māori and Pacific people through higher per-capita infection and hospitalisation rates. Older people are more likely to be hospitalised and for longer.

text: Inequities in Covid-19 Omicron infections and hospitalisations for Māori and Pacific people in Te Manawa Taki Midland region, New Zealand Covid-19 impacts population health equity. While mRNA vaccines protect against serious illness and death, little New Zealand (NZ) data exists about the impact of Omicron - and effectiveness of vaccination - on different population groups. We aim to examine the impact of  Omicron  on Māori, Pacific and Other ethnicities and how this interacts with age and vaccination status in the Te Manawa Taki Midland region of NZ. Daily Covid-19 infection and hospitalisation rates (01/02/2022 - 29/06/2022) were calculated for Māori, Pacific and Other ethnicities for six age bands. A multivariate logistic regression model quantified the effects of ethnicity, age, and vaccination on hospitalisation rates. Per-capita Omicron cases were highest and occurred earliest among Pacific (9 per 1,000) and Māori (5 per 1,000) people and were highest among 12-24 year-olds (7 per 1,000). Hospitalisation was significantly more likely for Māori (OR=2.03), Pacific people (OR=1.75), over 75-year olds (OR=39.22), and unvaccinated people (OR=4.64). Length of hospitalisation is strongly related to age. Covid-19 vaccination reduces hospitalisations for older individuals and Māori and Pacific populations. Omicron inequitably impacted Māori and Pacific people through higher per-capita infection and hospitalisation rates. Older people are more likely to be hospitalised and for longer.

year: 2023-04-24