title: Trends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers

authors: Magee, Madeline R.

abstract: The one-dimensional hydrodynamic ice model, DYRESM-WQ-I, was modified to simulate ice cover and thermal structure of dimictic Lake Mendota, Wisconsin, USA, over a continuous 104-year period (1911-2014). The model results were then used to examine the drivers of changes in ice cover and water temperature, focusing on the responses to shifts in air temperature, wind speed, and water clarity at multiyear timescales. Observations of the drivers include a change in the trend of warming air temperatures from 0.081°C per decade before 1981 to 0.334°C per decade thereafter, as well as a shift in mean wind speed from 4.44ms-1 before 1994 to 3.74ms-1 thereafter. Observations show that Lake Mendota has experienced significant changes in ice cover: later ice-on date(9.0 days later per century), earlier ice-off date (12.3 days per century), decreasing ice cover duration (21.3 days per century), while model simulations indicate a change in maximum ice thickness (12.7cm decrease per century). Model simulations also show changes in the lake thermal regime of earlier stratification onset (12.3 days per century), later fall turnover (14.6 days per century), longer stratification duration (26.8 days per century), and decreasing summer hypolimnetic temperatures (-1.4°C per century). Correlation analysis of lake variables and driving variables revealed ice cover variables, stratification onset, epilimnetic temperature, and hypolimnetic temperature were most closely correlated with air temperature, whereas freeze-over water temperature, hypolimnetic heating, and fall turnover date were more closely correlated with wind speed. Each lake variable (i.e., ice-on and ice-off dates, ice cover duration, maximum ice thickness, freeze-over water temperature, stratification onset, fall turnover date, stratification duration, epilimnion temperature, hypolimnion temperature, and hypolimnetic heating) was averaged for the three periods (1911-1980, 1981-1993, and 1994-2014) delineated by abrupt changes in air temperature and wind speed. Average summer hypolimnetic temperature and fall turnover date exhibit significant differences between the third period and the first two periods. Changes in ice cover (ice-on and ice-off dates, ice cover duration, and maximum ice thickness) exhibit an abrupt change after 1994, which was related in part to the warm El Niño winter of 1997-1998. Under-ice water temperature, freeze-over water temperature, hypolimnetic temperature, fall turnover date, and stratification duration demonstrate a significant difference in the third period (1994-2014), when air temperature was warmest and wind speeds decreased rather abruptly. The trends in ice cover and water temperature demonstrate responses to both long-term and abrupt changes in meteorological conditions that can be complemented with numerical modeling to better understand how these variables will respond in a future climate.

text: Trends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers The one-dimensional hydrodynamic ice model, DYRESM-WQ-I, was modified to simulate ice cover and thermal structure of dimictic Lake Mendota, Wisconsin, USA, over a continuous 104-year period (1911-2014). The model results were then used to examine the drivers of changes in ice cover and water temperature, focusing on the responses to shifts in air temperature, wind speed, and water clarity at multiyear timescales. Observations of the drivers include a change in the trend of warming air temperatures from 0.081°C per decade before 1981 to 0.334°C per decade thereafter, as well as a shift in mean wind speed from 4.44ms-1 before 1994 to 3.74ms-1 thereafter. Observations show that Lake Mendota has experienced significant changes in ice cover: later ice-on date(9.0 days later per century), earlier ice-off date (12.3 days per century), decreasing ice cover duration (21.3 days per century), while model simulations indicate a change in maximum ice thickness (12.7cm decrease per century). Model simulations also show changes in the lake thermal regime of earlier stratification onset (12.3 days per century), later fall turnover (14.6 days per century), longer stratification duration (26.8 days per century), and decreasing summer hypolimnetic temperatures (-1.4°C per century). Correlation analysis of lake variables and driving variables revealed ice cover variables, stratification onset, epilimnetic temperature, and hypolimnetic temperature were most closely correlated with air temperature, whereas freeze-over water temperature, hypolimnetic heating, and fall turnover date were more closely correlated with wind speed. Each lake variable (i.e., ice-on and ice-off dates, ice cover duration, maximum ice thickness, freeze-over water temperature, stratification onset, fall turnover date, stratification duration, epilimnion temperature, hypolimnion temperature, and hypolimnetic heating) was averaged for the three periods (1911-1980, 1981-1993, and 1994-2014) delineated by abrupt changes in air temperature and wind speed. Average summer hypolimnetic temperature and fall turnover date exhibit significant differences between the third period and the first two periods. Changes in ice cover (ice-on and ice-off dates, ice cover duration, and maximum ice thickness) exhibit an abrupt change after 1994, which was related in part to the warm El Niño winter of 1997-1998. Under-ice water temperature, freeze-over water temperature, hypolimnetic temperature, fall turnover date, and stratification duration demonstrate a significant difference in the third period (1994-2014), when air temperature was warmest and wind speeds decreased rather abruptly. The trends in ice cover and water temperature demonstrate responses to both long-term and abrupt changes in meteorological conditions that can be complemented with numerical modeling to better understand how these variables will respond in a future climate.

year: 2016

title: The Formulation of Titanium - based Metal Feedstocks and the Fabrication of Parts using the Powder Injection Moulding Process

authors: Ewart, Paul Douglas

subjects: Binder

abstract: Development of a profitable titanium industry for New Zealand will not come about without innovative technologies. Plastic injection moulding has long held a place in NZ manufacturing to produce large quantities of complex parts and holds the key to such innovation.
Titanium metal parts were fabricated by injection moulding titanium based metal powder feedstock followed by a debinding process and subsequent sintering. The fabrication process in its entirety was investigated in four distinct steps. Feedstock formulation involved combining the metal powders with various carrier components. Injection moulding enabled the shaping of the feedstock into geometries approximating the final part. Debinding being the process whereby the carrier/binder system is removed from the part to create a powder compact retaining the required geometry. Sintering being the final step where the metal powders are consolidated into a fully dense metal part of net shape.
The feedstock binder consisted of water soluble polyethylene glycol that reduced feedstock viscosity, improved particle wetting, aided greenpart shape retention and eliminated toxic solvents in debinding. Carnauba wax and bees wax aided dispersion, lubricated particles, were safe to handle and better for the environment (than petroleum waxes). Their low melt temperatures aided removal during thermal debinding and supported residue elimination.
By optimising the ratio of water soluble, wax and polyolefin binder components (3: 2: 1 respectively) for melt flow and pellet formation, greenparts defect free with uniform particle distribution were made. The optimal binder system proved suitable for titanium alloy and irregular shape pure titanium powders (hydride-de-hydride). Increasing powder loading (wP = (0.60 to 0.65)) had no appreciable effect on viscosity while enabling feedstock with good uniformity and pellet formation. Dimensional change was not affected by uniformity of the feedstock however molecular weight, volume and dispersion of binder components affected interparticular distances. Low processing temperatures reduced disruption to part geometry, benefitted particle bonding and helped retain handling strength.
The use of low temperatures for thermal debinding (t = 250 °C) enabled removal of the binder below the temperatures that facilitate interstitial diffusion and oxide/carbide formation, although part thickness, mass and overall volume effected the processing time. A strong correlation was seen between handling strength of the greenparts and defects, such as non-uniform density distribution and cracking after sintering.
Sintering was essential to produce the final part and showed that a binder free brownpart was not the only criteria for eliminating impurities. The furnace atmosphere must remain free from contamination to eliminate transfer back to the parts. This was addressed using an argon sweep gas, however, the design and efficacy of the system was considered inadequate. Decomposition products need to be removed quickly from the furnace as they evolve before impurities from the sweep gas diffuse back into the parts during the extended duration at sinter temperatures (t = 1300 °C).
The combination of an optimised titanium feedstock and the use of a low temperature thermal debinding technique produced a consolidated MIM part of relatively large dimensions. The parts were seen to have uniform microstructure throughout the cross-section with density comparable to that of MIM standards. In difference to the literature, a high powder loading (φp = 0.65) of HDH powders was used and shown to be readily mouldable. The higher powder loading also eliminate separation defects and shape distortions evident using lower amounts of powder.

text: The Formulation of Titanium - based Metal Feedstocks and the Fabrication of Parts using the Powder Injection Moulding Process Development of a profitable titanium industry for New Zealand will not come about without innovative technologies. Plastic injection moulding has long held a place in NZ manufacturing to produce large quantities of complex parts and holds the key to such innovation.
Titanium metal parts were fabricated by injection moulding titanium based metal powder feedstock followed by a debinding process and subsequent sintering. The fabrication process in its entirety was investigated in four distinct steps. Feedstock formulation involved combining the metal powders with various carrier components. Injection moulding enabled the shaping of the feedstock into geometries approximating the final part. Debinding being the process whereby the carrier/binder system is removed from the part to create a powder compact retaining the required geometry. Sintering being the final step where the metal powders are consolidated into a fully dense metal part of net shape.
The feedstock binder consisted of water soluble polyethylene glycol that reduced feedstock viscosity, improved particle wetting, aided greenpart shape retention and eliminated toxic solvents in debinding. Carnauba wax and bees wax aided dispersion, lubricated particles, were safe to handle and better for the environment (than petroleum waxes). Their low melt temperatures aided removal during thermal debinding and supported residue elimination.
By optimising the ratio of water soluble, wax and polyolefin binder components (3: 2: 1 respectively) for melt flow and pellet formation, greenparts defect free with uniform particle distribution were made. The optimal binder system proved suitable for titanium alloy and irregular shape pure titanium powders (hydride-de-hydride). Increasing powder loading (wP = (0.60 to 0.65)) had no appreciable effect on viscosity while enabling feedstock with good uniformity and pellet formation. Dimensional change was not affected by uniformity of the feedstock however molecular weight, volume and dispersion of binder components affected interparticular distances. Low processing temperatures reduced disruption to part geometry, benefitted particle bonding and helped retain handling strength.
The use of low temperatures for thermal debinding (t = 250 °C) enabled removal of the binder below the temperatures that facilitate interstitial diffusion and oxide/carbide formation, although part thickness, mass and overall volume effected the processing time. A strong correlation was seen between handling strength of the greenparts and defects, such as non-uniform density distribution and cracking after sintering.
Sintering was essential to produce the final part and showed that a binder free brownpart was not the only criteria for eliminating impurities. The furnace atmosphere must remain free from contamination to eliminate transfer back to the parts. This was addressed using an argon sweep gas, however, the design and efficacy of the system was considered inadequate. Decomposition products need to be removed quickly from the furnace as they evolve before impurities from the sweep gas diffuse back into the parts during the extended duration at sinter temperatures (t = 1300 °C).
The combination of an optimised titanium feedstock and the use of a low temperature thermal debinding technique produced a consolidated MIM part of relatively large dimensions. The parts were seen to have uniform microstructure throughout the cross-section with density comparable to that of MIM standards. In difference to the literature, a high powder loading (φp = 0.65) of HDH powders was used and shown to be readily mouldable. The higher powder loading also eliminate separation defects and shape distortions evident using lower amounts of powder.

year: 2015

title: HIV diagnoses in indigenous peoples: comparison of Australia, Canada and New Zealand

authors: Shea, Beverley

subjects: HIV

abstract: In industrial countries, a number of factors put indigenous peoples at increased risk of HIV infection. National surveillance data between 1999 and 2008 provided diagnoses for Aboriginal and Torres Strait Islanders (Australia), First Nations, Inuit and Métis (Canada excluding Ontario and Quebec) and Māori (New Zealand). Each country provided similar data for a non-indigenous comparison population. Direct standardisation used the 2001 Canadian Aboriginal male population for comparison of five-year diagnosis rates in 1999–2003 and 2004–2008. Using the general population as denominators, we report diagnosis ratios for presumed heterosexual transmission, men who have sex with men (MSM) and intravenous drug users (IDU). Age standardised HIV diagnosis rates in indigenous peoples in Canada in 2004–2008 (178.1 and 178.4/100 000 for men and women respectively) were higher than in Australia (48.5 and 12.9/100 000) and New Zealand (41.9 and 4.3/100 000). Higher HIV diagnosis rates related to heterosexual contact among Aboriginal peoples, especially women, in Canada confirm a widening epidemic beyond the conventional risk groups. This potential of a generalised epidemic requires urgent attention in Aboriginal communities; available evidence can inform policy and action by all stakeholders. Although less striking in Australia and New Zealand, these findings may be relevant to indigenous peoples in other countries.

text: HIV diagnoses in indigenous peoples: comparison of Australia, Canada and New Zealand In industrial countries, a number of factors put indigenous peoples at increased risk of HIV infection. National surveillance data between 1999 and 2008 provided diagnoses for Aboriginal and Torres Strait Islanders (Australia), First Nations, Inuit and Métis (Canada excluding Ontario and Quebec) and Māori (New Zealand). Each country provided similar data for a non-indigenous comparison population. Direct standardisation used the 2001 Canadian Aboriginal male population for comparison of five-year diagnosis rates in 1999–2003 and 2004–2008. Using the general population as denominators, we report diagnosis ratios for presumed heterosexual transmission, men who have sex with men (MSM) and intravenous drug users (IDU). Age standardised HIV diagnosis rates in indigenous peoples in Canada in 2004–2008 (178.1 and 178.4/100 000 for men and women respectively) were higher than in Australia (48.5 and 12.9/100 000) and New Zealand (41.9 and 4.3/100 000). Higher HIV diagnosis rates related to heterosexual contact among Aboriginal peoples, especially women, in Canada confirm a widening epidemic beyond the conventional risk groups. This potential of a generalised epidemic requires urgent attention in Aboriginal communities; available evidence can inform policy and action by all stakeholders. Although less striking in Australia and New Zealand, these findings may be relevant to indigenous peoples in other countries.

year: 2011