title: Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas

authors: Matthaeus, William H.

subjects: Science & Technology

abstract: An overview is given of important properties of spatial and temporal intermittency, including evidence of its appearance in fluids, magnetofluids and plasmas, and its implications for understanding of heliospheric plasmas. Spatial intermittency is generally associated with formation of sharp gradients and coherent structures. The basic physics of structure generation is ideal, but when dissipation is present it is usually concentrated in regions of strong gradients. This essential feature of spatial intermittency in fluids has been shown recently to carry over to the realm of kinetic plasma, where the dissipation function is not known from first principles. Spatial structures produced in intermittent plasma influence dissipation, heating, and transport and acceleration of charged particles. Temporal intermittency can give rise to very long time correlations or a delayed approach to steady-state conditions, and has been associated with inverse cascade or quasi-inverse cascade systems, with possible implications for heliospheric prediction.

text: Intermittency, nonlinear dynamics and dissipation in the solar wind and astrophysical plasmas An overview is given of important properties of spatial and temporal intermittency, including evidence of its appearance in fluids, magnetofluids and plasmas, and its implications for understanding of heliospheric plasmas. Spatial intermittency is generally associated with formation of sharp gradients and coherent structures. The basic physics of structure generation is ideal, but when dissipation is present it is usually concentrated in regions of strong gradients. This essential feature of spatial intermittency in fluids has been shown recently to carry over to the realm of kinetic plasma, where the dissipation function is not known from first principles. Spatial structures produced in intermittent plasma influence dissipation, heating, and transport and acceleration of charged particles. Temporal intermittency can give rise to very long time correlations or a delayed approach to steady-state conditions, and has been associated with inverse cascade or quasi-inverse cascade systems, with possible implications for heliospheric prediction.

year: 2015

title: Conditions for sustainment of magnetohydrodynamic turbulence driven by Alfvén waves

authors: Dmitruk, Pablo

subjects: Alfvén waves

abstract: In a number of space and astrophysical plasmas,turbulence is driven by the supply of wave energy. In the context of incompressible magnetohydrodynamics (MHD) there are basic physical reasons, associated with conservation of cross helicity, why this kind of driving may be ineffective in sustaining turbulence. Here an investigation is made into some basic requirements for sustaining steady turbulence and dissipation in the context of incompressible MHD in a weakly inhomogeneous open field line region, driven by the supply of unidirectionally propagating waves at a boundary. While such wave driving cannot alone sustain turbulence, the addition of reflection permits sustainment. Another sustainment issue is the action of the nonpropagating or quasi-two dimensional part of the spectrum; this is particularly important in setting up a steady cascade. Thus, details of the waveboundary conditions also affect the ease of sustaining a cascade. Supply of a broadband spectrum of waves can overcome the latter difficulty but not the former, that is, the need for reflections. Implications for coronal heating and other astrophysical applications, as well as simulations, are suggested.

text: Conditions for sustainment of magnetohydrodynamic turbulence driven by Alfvén waves In a number of space and astrophysical plasmas,turbulence is driven by the supply of wave energy. In the context of incompressible magnetohydrodynamics (MHD) there are basic physical reasons, associated with conservation of cross helicity, why this kind of driving may be ineffective in sustaining turbulence. Here an investigation is made into some basic requirements for sustaining steady turbulence and dissipation in the context of incompressible MHD in a weakly inhomogeneous open field line region, driven by the supply of unidirectionally propagating waves at a boundary. While such wave driving cannot alone sustain turbulence, the addition of reflection permits sustainment. Another sustainment issue is the action of the nonpropagating or quasi-two dimensional part of the spectrum; this is particularly important in setting up a steady cascade. Thus, details of the waveboundary conditions also affect the ease of sustaining a cascade. Supply of a broadband spectrum of waves can overcome the latter difficulty but not the former, that is, the need for reflections. Implications for coronal heating and other astrophysical applications, as well as simulations, are suggested.

year: 2001

title: Materials for enhancing denitrification performance in partially saturated vertical flow wetlands for marae

authors: Liu, Lucian XiaoRan

abstract: There are upwards of 773 marae in New Zealand which are responsible for many key events for the indigenous people, Māori, many of which are located rurally and have inadequate on-site wastewater treatment mostly comprising of a septic tank followed by land application. Māori have many strong beliefs about water and subsequently criteria surround the treatment of wastewater due to the effects it can have on people and environment. One proposed solution that meets criteria are treatment wetlands, more specifically partially saturated vertical flow wetlands which require a smaller footprint and produce better effluent than traditional wetland designs. NIWA (National Institute of Water and Atmospheric Research) has experimented with mesocosm scale versions of this design and has encountered issues with denitrification in the saturated zone.

This research is therefore directed at enhancing denitrification in the saturated zone with materials that are able to supplement organic carbon for denitrification. Several woodchip materials (Eastern Cottonwood, Mahogany, Manuka, Eucalyptus, Crack Willow, Princess Tree and Pine) along with two industry by-product materials (Brewers Spent Grain and Slum gum) and Coir (Coconut derivative) were examined for denitrification capabilities and to serve in producing a leachate for dosing the proposed system to supplement organic carbon for denitrification.

The research is split into three phases; the first examines the ability of materials to release organic carbon into water over 60 days, the second examines the same but over three 10 day cycles, and the third quantifies denitrification performance of the materials at lab scale.

Results showed that producing a suitable leachate is not possible without the use of fresh material for each batch. By-product materials had great capacity for releasing organic carbon into water and denitrification (up to 85.5% nitrate removal) but had limited lifespans as media. While woodchip materials did not exhibit as great carbon release, they achieved comparable denitrification (74.2-74.5% nitrate removal) with long lifespans. Therefore, a woodchip and industry by-product mix could be the solution. Alternatively, there are many woodchip species, some which could have better denitrification capacity or suitable industry by-products with longer useful lifespans.

text: Materials for enhancing denitrification performance in partially saturated vertical flow wetlands for marae There are upwards of 773 marae in New Zealand which are responsible for many key events for the indigenous people, Māori, many of which are located rurally and have inadequate on-site wastewater treatment mostly comprising of a septic tank followed by land application. Māori have many strong beliefs about water and subsequently criteria surround the treatment of wastewater due to the effects it can have on people and environment. One proposed solution that meets criteria are treatment wetlands, more specifically partially saturated vertical flow wetlands which require a smaller footprint and produce better effluent than traditional wetland designs. NIWA (National Institute of Water and Atmospheric Research) has experimented with mesocosm scale versions of this design and has encountered issues with denitrification in the saturated zone.

This research is therefore directed at enhancing denitrification in the saturated zone with materials that are able to supplement organic carbon for denitrification. Several woodchip materials (Eastern Cottonwood, Mahogany, Manuka, Eucalyptus, Crack Willow, Princess Tree and Pine) along with two industry by-product materials (Brewers Spent Grain and Slum gum) and Coir (Coconut derivative) were examined for denitrification capabilities and to serve in producing a leachate for dosing the proposed system to supplement organic carbon for denitrification.

The research is split into three phases; the first examines the ability of materials to release organic carbon into water over 60 days, the second examines the same but over three 10 day cycles, and the third quantifies denitrification performance of the materials at lab scale.

Results showed that producing a suitable leachate is not possible without the use of fresh material for each batch. By-product materials had great capacity for releasing organic carbon into water and denitrification (up to 85.5% nitrate removal) but had limited lifespans as media. While woodchip materials did not exhibit as great carbon release, they achieved comparable denitrification (74.2-74.5% nitrate removal) with long lifespans. Therefore, a woodchip and industry by-product mix could be the solution. Alternatively, there are many woodchip species, some which could have better denitrification capacity or suitable industry by-products with longer useful lifespans.

year: 2023