title: Willingness-to-Pay for prescribed fire in the Colorado (USA) Wildland Urban Interface

authors: Kaval, Pamela

subjects: prescribed burning

abstract: During the summer of 2001, survey data were collected from Colorado residents living near public lands (i.e., the wildland urban interface). Data were collected by telephone after mailing respondents a survey. These data include detailed information of respondents’ views towards wildfire management and willingness-to-pay (WTP) values for prescribed burning. Results indicate that Colorado residents living near public lands are aware that fire is a natural process in their area and are in favor of using prescribed burning for fire risk reduction. They also are willing-to-pay an annual tax for prescribed fire undertaken on the public lands near their homes. Respondents’ support for adopting a fire risk mitigation policy based on prescribed fire depended on perceived fire frequency intervals. The substantial WTP values for prescribed burning indicate that the public living in the wildland urban interface could potentially pay an annual tax, so the burden of wildfire management need no longer predominantly lie in the hands of the general taxpayers.

text: Willingness-to-Pay for prescribed fire in the Colorado (USA) Wildland Urban Interface During the summer of 2001, survey data were collected from Colorado residents living near public lands (i.e., the wildland urban interface). Data were collected by telephone after mailing respondents a survey. These data include detailed information of respondents’ views towards wildfire management and willingness-to-pay (WTP) values for prescribed burning. Results indicate that Colorado residents living near public lands are aware that fire is a natural process in their area and are in favor of using prescribed burning for fire risk reduction. They also are willing-to-pay an annual tax for prescribed fire undertaken on the public lands near their homes. Respondents’ support for adopting a fire risk mitigation policy based on prescribed fire depended on perceived fire frequency intervals. The substantial WTP values for prescribed burning indicate that the public living in the wildland urban interface could potentially pay an annual tax, so the burden of wildfire management need no longer predominantly lie in the hands of the general taxpayers.

year: 2006-10

title: Pressure screening studies with wood pulp

authors: Weeds, Zuben

subjects: Wood-pulp Refining Separation

abstract: Pressure screening is used in paper making to separate components of a wood pulp slurry (water, wood fibre and solid contaminant material) and to concentrate the wood fibre. The complex solid-liquid and solid-solid mechanisms involved in pressure screening are still poorly understood. This thesis reviews the literature on pressure screening mechanisms and highlights the problems in the models used to describe pressure screening. 
Two models, based on well-mixed tanks in series, are developed to describe reject thickening behaviour of long and short screens. The first model uses a single one row of tanks to model steady flow from feed to accept and from feed to reject streams of a screen. A back-flow model, which had two rows of well-mixed tanks, one for the feedside and another for the accept-side of the screen, was also developed. The passage ratio for back-flow of fibre PB was estimated numerically by deducing the passage ratio for forward-flow of fibre PF. The model showed that PB can decrease more quickly than PF when feed consistency increases, even when overall passage ratio Pp remains constant. 
A small industrial pressure screen (diameter 203 mm, length 220 mm) was used to investigate the effect of screen length Ls and feed consistency Cf on pressure screening performance. The effects of pulp type ( eucalypt for short fibre and pine kraft pulp for short fibre), feed consistency (from 0.005% to 2% compared to approximately 1 % in industrial plants), screen length and placement along the length of the screen, rotor type (bump or step), and screen hole shape (round holes or slots) were investigated. Measurements of pulp consistency in the feed, reject and accept streams under different processing conditions were used to assess the screen models developed. Screening behaviour of screens less than 220 mm was studied extensively for the first time. 
The tanks-in-series model showed that the effect of screen length on reject thickening could be described as well-mixed tanks in series with plug flow behaviour when the screen was modelled as 100 tanks. The reject thickening factor T decreased semilogarithmically when number of tanks was decreased but increased slightly when the number of tanks was increased. . Reject thickening factor decreases when a screen with 1-mm hole is shortened from 220 mm to 27 mm. This reduction can be attributed mainly to the flow regime changing from plug to mixed flow.
The maximum volumetric accept flow rate Qmax decreased by approximately 30 % when a 55-mm screen section was moved from the feed end to the reject end. 1bis decrease in Qmax was consistent with an axial decrease in relative speed ( difference between rotor tip and pulp suspension in the feed annulus), along with an estimated 33% reduction in the negative pressure pulse PNP along the screen. Overall fibre passage ratio PP also decreased when the screen section was moved to the reject end, or when pulp was accelerated in a feed chamber upstream of the feed annulus. 
The three distinct regions and two critical feed consistencies observed when Cr increased from 0.005% to 2% are postulated to indicate when fibre accumulation on the feed and accept sides of the screen produces screen plugging. The critical Cr for the accept side is about ten times greater than that for the feed side due mainly to the fact that the conical holes have a larger diameter on the accept side so more fibre must accumulate before backflow is hindered. In Region 1 ( crowding number < 1 ), reject thickening is independent of feed consistency and remains constant regardless of rotor type (bump or step) and screen type (smooth holes or contoured slots). In Region 2 (1< crowding number< 60), reject thickening decreases with feed consistency. In Region 3 (crowding number > 60), reject thickening either . decreases with feed consistency or remains constant depending on the ratio of forward to back-flushing flow exhibited by the rotor and as predicted by the two-tanks in series model. For the step rotor with a flow ratio of 2:1 reject thickening is constant with feed consistency regardless of screen type. For the bump rotor with a flow ratio of 5: 1 reject thickening decreases with feed consistency regardless of the screen type.
Fibre-length fractionation index <I> increased with increasing Cr to a maximum at about Ct=0.7% when using a 1-mm smooth-holed screen with a bump rotor or at Ct=2% for a 2.4-mm smooth-holed screen. Fractionation index then decreased with increasing Cf. 
It is recommended that the back-flow model be further developed so that the volumetric flow ratio (ratio of forward flow to back flow) can be calculated from a residence time distribution. It is also recommended that fibre-length fractionation be attempted at various positions along the screen for medium consistency pulp (Cr of 8 to 12%) using unconventionally large holes (3-5 mm).

text: Pressure screening studies with wood pulp Pressure screening is used in paper making to separate components of a wood pulp slurry (water, wood fibre and solid contaminant material) and to concentrate the wood fibre. The complex solid-liquid and solid-solid mechanisms involved in pressure screening are still poorly understood. This thesis reviews the literature on pressure screening mechanisms and highlights the problems in the models used to describe pressure screening. 
Two models, based on well-mixed tanks in series, are developed to describe reject thickening behaviour of long and short screens. The first model uses a single one row of tanks to model steady flow from feed to accept and from feed to reject streams of a screen. A back-flow model, which had two rows of well-mixed tanks, one for the feedside and another for the accept-side of the screen, was also developed. The passage ratio for back-flow of fibre PB was estimated numerically by deducing the passage ratio for forward-flow of fibre PF. The model showed that PB can decrease more quickly than PF when feed consistency increases, even when overall passage ratio Pp remains constant. 
A small industrial pressure screen (diameter 203 mm, length 220 mm) was used to investigate the effect of screen length Ls and feed consistency Cf on pressure screening performance. The effects of pulp type ( eucalypt for short fibre and pine kraft pulp for short fibre), feed consistency (from 0.005% to 2% compared to approximately 1 % in industrial plants), screen length and placement along the length of the screen, rotor type (bump or step), and screen hole shape (round holes or slots) were investigated. Measurements of pulp consistency in the feed, reject and accept streams under different processing conditions were used to assess the screen models developed. Screening behaviour of screens less than 220 mm was studied extensively for the first time. 
The tanks-in-series model showed that the effect of screen length on reject thickening could be described as well-mixed tanks in series with plug flow behaviour when the screen was modelled as 100 tanks. The reject thickening factor T decreased semilogarithmically when number of tanks was decreased but increased slightly when the number of tanks was increased. . Reject thickening factor decreases when a screen with 1-mm hole is shortened from 220 mm to 27 mm. This reduction can be attributed mainly to the flow regime changing from plug to mixed flow.
The maximum volumetric accept flow rate Qmax decreased by approximately 30 % when a 55-mm screen section was moved from the feed end to the reject end. 1bis decrease in Qmax was consistent with an axial decrease in relative speed ( difference between rotor tip and pulp suspension in the feed annulus), along with an estimated 33% reduction in the negative pressure pulse PNP along the screen. Overall fibre passage ratio PP also decreased when the screen section was moved to the reject end, or when pulp was accelerated in a feed chamber upstream of the feed annulus. 
The three distinct regions and two critical feed consistencies observed when Cr increased from 0.005% to 2% are postulated to indicate when fibre accumulation on the feed and accept sides of the screen produces screen plugging. The critical Cr for the accept side is about ten times greater than that for the feed side due mainly to the fact that the conical holes have a larger diameter on the accept side so more fibre must accumulate before backflow is hindered. In Region 1 ( crowding number < 1 ), reject thickening is independent of feed consistency and remains constant regardless of rotor type (bump or step) and screen type (smooth holes or contoured slots). In Region 2 (1< crowding number< 60), reject thickening decreases with feed consistency. In Region 3 (crowding number > 60), reject thickening either . decreases with feed consistency or remains constant depending on the ratio of forward to back-flushing flow exhibited by the rotor and as predicted by the two-tanks in series model. For the step rotor with a flow ratio of 2:1 reject thickening is constant with feed consistency regardless of screen type. For the bump rotor with a flow ratio of 5: 1 reject thickening decreases with feed consistency regardless of the screen type.
Fibre-length fractionation index <I> increased with increasing Cr to a maximum at about Ct=0.7% when using a 1-mm smooth-holed screen with a bump rotor or at Ct=2% for a 2.4-mm smooth-holed screen. Fractionation index then decreased with increasing Cf. 
It is recommended that the back-flow model be further developed so that the volumetric flow ratio (ratio of forward flow to back flow) can be calculated from a residence time distribution. It is also recommended that fibre-length fractionation be attempted at various positions along the screen for medium consistency pulp (Cr of 8 to 12%) using unconventionally large holes (3-5 mm).

year: 2006

title: Too many Māori and Asian people are drowning – can better cultural understanding reverse the trend?

authors: Wheaton, Belinda

abstract: The article discusses the high rate of drownings in New Zealand, particularly among Māori and Asian communities. It highlights the need for culturally specific water safety education to address this issue. The Asian community, in particular, includes many first-generation migrants who may lack water skills due to their upbringing and fear of water. Overprotectiveness towards children around water is also common among Asian parents. The article emphasizes the importance of providing support and learning opportunities to help Asian migrants develop water skills and feel more comfortable in outdoor activities. Additionally, it mentions the declining water skills among New Zealand children in general and the need for better resourcing of school programs and community initiatives like ActivAsian. Culturally relevant knowledge and education are deemed crucial in changing attitudes and behaviors towards water safety. The article stresses that making New Zealand's beaches and waterways safe for all residents, including migrants, requires targeted funding and a collaborative effort to prevent tragic drowning incidents.

text: Too many Māori and Asian people are drowning – can better cultural understanding reverse the trend? The article discusses the high rate of drownings in New Zealand, particularly among Māori and Asian communities. It highlights the need for culturally specific water safety education to address this issue. The Asian community, in particular, includes many first-generation migrants who may lack water skills due to their upbringing and fear of water. Overprotectiveness towards children around water is also common among Asian parents. The article emphasizes the importance of providing support and learning opportunities to help Asian migrants develop water skills and feel more comfortable in outdoor activities. Additionally, it mentions the declining water skills among New Zealand children in general and the need for better resourcing of school programs and community initiatives like ActivAsian. Culturally relevant knowledge and education are deemed crucial in changing attitudes and behaviors towards water safety. The article stresses that making New Zealand's beaches and waterways safe for all residents, including migrants, requires targeted funding and a collaborative effort to prevent tragic drowning incidents.

year: 2022-12-20