title: Investigation on the interface structure and thermal conductivity of hot-forged Cu/(Ti/W-coated)-diamond composites

authors: Ma, Jingnan

abstract: Effectively dissipating heat is required for the high-power electronic equipment to ensure the equipment has a safe working environment. Cu/diamond composite is considered as a new generation of heat sink materials because of its potential of achieving high thermal conductivity and tailorable coefficient of thermal expansion. The poor chemical affinity between the copper and the diamond is the main barrier for obtaining Cu/diamond composites that have high thermal conductivity. The interface layer between the copper and the diamond plays an important role in facilitating heat transfer in the Cu/diamond composites. However, it lacks deep understanding on the influence of interface characteristics on the Cu/diamond composite’s thermal conductivity.

We aim to tailor the thermal conductivity of Cu/diamond composites by modifying the interphase layer’s phase composition and microstructure, and there are three primary research parts in this thesis. The first part is the study of the Cu/Ti-diamond composite prepared by induction heating and hot forging from pre-annealed Ti-coated diamond particles. Part two is the study of the Cu/W-diamond composite prepared with the identical process that used in the part one from the pre-annealed W-coated diamond particles. The third part presents Cu/Ti-diamond composites that are fabricated by the combination of vacuum sintering and hot forging from Ti-coated diamond particles. The fabricated composites’ microstructure and the interface morphology of diamond particles that are extracted from the fabricated composites are examined by scanning electronic microscopy (SEM) and atomic force microscopy (AFM), respectively, and the phase composition of the fabricated composites is analyzed by X-ray diffraction (XRD). 

Results show that both TiC and W2C particles are easier to nucleate on the diamond-{111} facet than on diamond-{100} facet during pre-annealing, and the reaction temperature for forming TiC is 800℃ and W2C is 1050 ℃, respectively, and the higher the annealing temperature is, the more carbides nucleation and growing locations present on the diamond surface. It finds that the un-reacted diamond coating (titanium or tungsten) further reacts with the diamond to form metal carbides during the process of hot forging at 800 ℃. Ti-800-Cu/Dia composite has the highest thermal conductivity among the hot-forged Cu/Ti-diamond composites, with a value of 350W/ (mK), attributed to the formation of a continuous interface, almost no interfacial layer spallation, and a rough interface formed on the diamond particle surface. Due to a large amount of WC interface is formed after hot forging, W-1050-Cu/Dia composite shows the highest thermal conductivity (223 W/ (mK)) among the hot-forged Cu/W-diamond composites. After vacuum sintering, the Ti coating is fully reacted with the diamond to form TiC, however, the preformed TiC particles are easy to spall from the diamond surface during hot forging. This leads to weak interfacial bonding strength between the diamond and the copper. The thermal conductivity of the Cu/Ti-Dia-VS is only 46W/ (mK) because of its low relative density. After hot forging, the thermal conductivity of Cu/Ti-Dia-VSHF composite is improved to 241W/ (mK), due to the significant increase of the hot-forged composite’s relative density. It is possible to design the interface characteristics of Cu/diamond composites by changing the pre-annealing temperature of the coated-diamond particles prior processing.

text: Investigation on the interface structure and thermal conductivity of hot-forged Cu/(Ti/W-coated)-diamond composites Effectively dissipating heat is required for the high-power electronic equipment to ensure the equipment has a safe working environment. Cu/diamond composite is considered as a new generation of heat sink materials because of its potential of achieving high thermal conductivity and tailorable coefficient of thermal expansion. The poor chemical affinity between the copper and the diamond is the main barrier for obtaining Cu/diamond composites that have high thermal conductivity. The interface layer between the copper and the diamond plays an important role in facilitating heat transfer in the Cu/diamond composites. However, it lacks deep understanding on the influence of interface characteristics on the Cu/diamond composite’s thermal conductivity.

We aim to tailor the thermal conductivity of Cu/diamond composites by modifying the interphase layer’s phase composition and microstructure, and there are three primary research parts in this thesis. The first part is the study of the Cu/Ti-diamond composite prepared by induction heating and hot forging from pre-annealed Ti-coated diamond particles. Part two is the study of the Cu/W-diamond composite prepared with the identical process that used in the part one from the pre-annealed W-coated diamond particles. The third part presents Cu/Ti-diamond composites that are fabricated by the combination of vacuum sintering and hot forging from Ti-coated diamond particles. The fabricated composites’ microstructure and the interface morphology of diamond particles that are extracted from the fabricated composites are examined by scanning electronic microscopy (SEM) and atomic force microscopy (AFM), respectively, and the phase composition of the fabricated composites is analyzed by X-ray diffraction (XRD). 

Results show that both TiC and W2C particles are easier to nucleate on the diamond-{111} facet than on diamond-{100} facet during pre-annealing, and the reaction temperature for forming TiC is 800℃ and W2C is 1050 ℃, respectively, and the higher the annealing temperature is, the more carbides nucleation and growing locations present on the diamond surface. It finds that the un-reacted diamond coating (titanium or tungsten) further reacts with the diamond to form metal carbides during the process of hot forging at 800 ℃. Ti-800-Cu/Dia composite has the highest thermal conductivity among the hot-forged Cu/Ti-diamond composites, with a value of 350W/ (mK), attributed to the formation of a continuous interface, almost no interfacial layer spallation, and a rough interface formed on the diamond particle surface. Due to a large amount of WC interface is formed after hot forging, W-1050-Cu/Dia composite shows the highest thermal conductivity (223 W/ (mK)) among the hot-forged Cu/W-diamond composites. After vacuum sintering, the Ti coating is fully reacted with the diamond to form TiC, however, the preformed TiC particles are easy to spall from the diamond surface during hot forging. This leads to weak interfacial bonding strength between the diamond and the copper. The thermal conductivity of the Cu/Ti-Dia-VS is only 46W/ (mK) because of its low relative density. After hot forging, the thermal conductivity of Cu/Ti-Dia-VSHF composite is improved to 241W/ (mK), due to the significant increase of the hot-forged composite’s relative density. It is possible to design the interface characteristics of Cu/diamond composites by changing the pre-annealing temperature of the coated-diamond particles prior processing.

year: 2020

title: A light in the dark; an investigation of fetal visual perception

authors: Leov, Jessica Noelle

subjects: fetal vision

abstract: How does a fetus engage with their visual world? Prenatal developmental trajectories are primarily unexplored, with fetal visual perception the most poorly understood of all sensory systems. In the third trimester, fetuses not only possess the ability to process perceptual information, but recent research suggests that enough light penetrates the womb to enable a visual experience. Understanding fetal visual capabilities has the potential to reshape our knowledge of both visual and psychological developmental trajectories. This thesis sits at the intersection of developmental psychology, medical imaging, and vision science.  The overall aim of this work is to assess fetal visual function through novel experimental paradigms. We employed 2D ultrasound to visualize the fetal lens and index eye movements in response to light stimuli presented in utero. Tracking fetal eye movements in response to visual stimuli beyond light / no light has never been previously attempted. Three separate experiments explore central elements of fetal visual perception and cognition, including differential fetal responding to temporal and nasal visual fields, anticipatory gaze, and fetal sensitivity to agentive motion cues. The results of these studies demonstrate that the fetus actively engages with their visual environment exhibiting a preference for stimuli presented in their temporal visual field and the ability to perform anticipatory visual gaze, specifically that fetuses can use an auditory cue to anticipate the appearance of a light stimulus. These experiments and new methods offer new key insights into early sensory and psychological development.

text: A light in the dark; an investigation of fetal visual perception How does a fetus engage with their visual world? Prenatal developmental trajectories are primarily unexplored, with fetal visual perception the most poorly understood of all sensory systems. In the third trimester, fetuses not only possess the ability to process perceptual information, but recent research suggests that enough light penetrates the womb to enable a visual experience. Understanding fetal visual capabilities has the potential to reshape our knowledge of both visual and psychological developmental trajectories. This thesis sits at the intersection of developmental psychology, medical imaging, and vision science.  The overall aim of this work is to assess fetal visual function through novel experimental paradigms. We employed 2D ultrasound to visualize the fetal lens and index eye movements in response to light stimuli presented in utero. Tracking fetal eye movements in response to visual stimuli beyond light / no light has never been previously attempted. Three separate experiments explore central elements of fetal visual perception and cognition, including differential fetal responding to temporal and nasal visual fields, anticipatory gaze, and fetal sensitivity to agentive motion cues. The results of these studies demonstrate that the fetus actively engages with their visual environment exhibiting a preference for stimuli presented in their temporal visual field and the ability to perform anticipatory visual gaze, specifically that fetuses can use an auditory cue to anticipate the appearance of a light stimulus. These experiments and new methods offer new key insights into early sensory and psychological development.

year: 2024

title: Exploring inequity in access to medications for Type 2 Diabetes in primary care in the Waikato region: Final report

authors: Lawrenson, Ross

abstract: Type 2 diabetes (T2D) is a growing health issue in New Zealand (NZ) that disproportionately affects twice as many Māori as non-Māori and an increasing number of younger people. T2D is associated with a range of microvascular and macrovascular complications, chronic kidney disease and cardiovascular disease (CVD), the latter being the greatest cause of morbidity and mortality in this patient group. However, complications are reduced in patients that have improved glycaemic control. To achieve optimal outcomes and reduce the chance of diabetes-related complications, patients should aim to have their glycated haemoglobin (HbA1c) measurement less than 53 mmol/mol if possible.

Diabetes is primarily managed in primary care, and a number of recent publications suggest that there is considerable inequity in the management of diabetes in New Zealand, particularly for Māori. In an earlier piece of work we have shown that Maori are significantly less likely than non-Maori to be prescribed metformin, but that once prescribed it they are equally likely to have the medication dispensed. This suggests that there may be issues that can be addressed within primary care that are influencing the use of diabetes medications.
Thus, the aim of this small piece of work was to characterise diabetes medication use in a Waikato primary care population, and to report on medication adherence and association with HbA1c levels.

text: Exploring inequity in access to medications for Type 2 Diabetes in primary care in the Waikato region: Final report Type 2 diabetes (T2D) is a growing health issue in New Zealand (NZ) that disproportionately affects twice as many Māori as non-Māori and an increasing number of younger people. T2D is associated with a range of microvascular and macrovascular complications, chronic kidney disease and cardiovascular disease (CVD), the latter being the greatest cause of morbidity and mortality in this patient group. However, complications are reduced in patients that have improved glycaemic control. To achieve optimal outcomes and reduce the chance of diabetes-related complications, patients should aim to have their glycated haemoglobin (HbA1c) measurement less than 53 mmol/mol if possible.

Diabetes is primarily managed in primary care, and a number of recent publications suggest that there is considerable inequity in the management of diabetes in New Zealand, particularly for Māori. In an earlier piece of work we have shown that Maori are significantly less likely than non-Maori to be prescribed metformin, but that once prescribed it they are equally likely to have the medication dispensed. This suggests that there may be issues that can be addressed within primary care that are influencing the use of diabetes medications.
Thus, the aim of this small piece of work was to characterise diabetes medication use in a Waikato primary care population, and to report on medication adherence and association with HbA1c levels.

year: 2021-08-17