title: Nitrogen-15 isotope enrichment in benthic boundary layer gases of a stratified eutrophic iron and manganese rich lake

authors: Pearson, Lisa Kyle

subjects: nitrogen isotope

abstract: The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km²), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion, hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values of δ¹⁵N [N2] ranged from -1 to 0.28%₀in the epilimnion, -1.5 to 1.25%₀ in the hypolimnion, -1.8 to 12.2%₀ in the benthic boundary layer and -0.7 to 3.5% in sediment pore waters. Values of δ¹⁵ [N₂] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification. Increases in 15N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen concentrations <6.3 µM) and may be related to abundant ammonium substrate (up to 275 µM) to support denitrification. Nitrate concentrations increased up to 36 µM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ¹⁵N[N₂] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of Lake Ngapouri. The changes in δ¹⁵N [N₂] values indicate the potential use of isotope ratios to identify and quantify potential chemonitrification/denitrification in the water column and sediment pore waters of lakes.

text: Nitrogen-15 isotope enrichment in benthic boundary layer gases of a stratified eutrophic iron and manganese rich lake The applicability of the natural abundance of nitrogen gas isotope ratios was used to indicate the spatial distribution of nitrogen transformations in the water column and sediment pore waters of Lake Ngapouri, a small (area 0.19 km²), monomictic, eutrophic lake in the Taupo Volcanic Zone, North Island, New Zealand. Samples were collected from the epilimnion, hypolimnion, benthic boundary layer and at 5-cm intervals from the sediment pore waters at monthly intervals for 1 year. Values of δ¹⁵N [N2] ranged from -1 to 0.28%₀in the epilimnion, -1.5 to 1.25%₀ in the hypolimnion, -1.8 to 12.2%₀ in the benthic boundary layer and -0.7 to 3.5% in sediment pore waters. Values of δ¹⁵ [N₂] showed a strong seasonal pattern that was related to the loss of dissolved oxygen in the hypolimnion during seasonal stratification. Increases in 15N-enriched dinitrogen take place in the benthic boundary layer during the periods of anoxia (taken to be dissolved oxygen concentrations <6.3 µM) and may be related to abundant ammonium substrate (up to 275 µM) to support denitrification. Nitrate concentrations increased up to 36 µM with increasing duration of anoxia. We hypothesise that an alternative electron acceptor besides oxygen is required to support the nitrification needed for the production of nitrate. Iron and manganese hydroxides and oxides from material sedimenting out of the water column may have induced chemo-nitrification sufficient to oxidise ammonium in the anoxic benthic boundary layer. The nitrate formed would mostly be rapidly denitrified so that the δ¹⁵N[N₂] would continue to become enriched during the presence of anoxia, as observed in hypolimnion and benthic boundary layer of Lake Ngapouri. The changes in δ¹⁵N [N₂] values indicate the potential use of isotope ratios to identify and quantify potential chemonitrification/denitrification in the water column and sediment pore waters of lakes.

year: 2012

title: An electronics Threshold-Concept Inventory: Assessment in the face of the dependency of concepts

authors: Scott, Jonathan B.

subjects: assessment

abstract: The Theory of Threshold Concepts (TCs), first articulated by Land and Meyer in 2003, provides educators in many disciplines with a tool to identify those special ideas that both define the characteristic ways of thinking of expert practitioners, and cause the greatest learning difficulties for students. Concept inventories are popular assessment tools, epitomized by the widely-accepted Force Concept Inventory of Hestenes et al., introduced circa 1992. It is a natural marriage to bring these two thrusts together to produce “Threshold-Concept Inventories”. We report ongoing work to develop and verify such a TC-inspired inventory assessment tool in the field of electronics and simple circuit theory. We identify the difficulty in the development of questions targeted at assessing understanding of single threshold concepts and present results in support of a strategy to deal with this.

text: An electronics Threshold-Concept Inventory: Assessment in the face of the dependency of concepts The Theory of Threshold Concepts (TCs), first articulated by Land and Meyer in 2003, provides educators in many disciplines with a tool to identify those special ideas that both define the characteristic ways of thinking of expert practitioners, and cause the greatest learning difficulties for students. Concept inventories are popular assessment tools, epitomized by the widely-accepted Force Concept Inventory of Hestenes et al., introduced circa 1992. It is a natural marriage to bring these two thrusts together to produce “Threshold-Concept Inventories”. We report ongoing work to develop and verify such a TC-inspired inventory assessment tool in the field of electronics and simple circuit theory. We identify the difficulty in the development of questions targeted at assessing understanding of single threshold concepts and present results in support of a strategy to deal with this.

year: 2012

title: Mana Motuhake Ringa: The non-invasive neural interface based artificial hand

authors: Owen, Mahonri W.

subjects: Prosthetics

abstract: Ten million people on the earth at any given time suffer from the loss or lack of a limb. Three million of these are upper extremity amputees. No matter the cause or reason for amputation the amputees’ life is never the same again. Independence can be lost and never regained. The loss of a limb can be an overpowering event that effects the mental, social, and physical well-being of a person. Although there has been many attempts to restore hand function through neural prosthetics there is little to no credible solutions to regain it. This thesis presents methods to restore hand function based on the human grasping system and addresses key challenges in the practical application of those methods. The contribution of this work lies in improving artificial hand function by mimicking the human grasping system. The human grasping system consists of the brain, the nervous system and the hand. The methods used investigate: biomechanical design principles for artificial hands, the limitations of machine learning in non-invasive neural interfaces (NI’s) and the development of an autonomous hand control framework for artificial hand control. 

The application of the Support Vector Machine (SVM) to a non-invasive neural interface is principally limited to binary applications in the real world. In order to overcome this limitation an autonomous approach is developed to achieve better response and accuracy from NI control frameworks. In binary applications the SVM performed well with a classification accuracy of around 80% accompanied by a response time of just under 5 seconds. When applied to multiple classifications the SVM decreased in accuracy and response dramatically. The accuracy of the autonomous hand control framework had a classification accuracy of 95% with a response time comparable to that of the SVM. This outcome has the potential to move non-invasive NI research into the real world and to restore hand function in an intuitive and meaningful way. A key learning of this research is that machine learning methods for non-invasive neural interfaces are not the best way to restore hand function for amputees. Hand function is best restored through the combining of machine learning and machine vision into a single NI based control framework. Additionally, this work is based in Mātauranga Māori with a western science approach. By so doing, amputees will be empowered, have increased independence and enjoy a better quality of life.

The scope of this work is limited to the consideration of hand function restoration for upper extremity amputees. In particular trans-radial amputees. Focus is given to non-invasive methods of control, therefore, investigations are limited to the electroencephalography (EEG) signal. Mimicking the human grasping system is a complex and difficult process, therefore, the attempts in this work to restore hand function only consider mechanisms and processes related directly to the motor control of the human hand.

text: Mana Motuhake Ringa: The non-invasive neural interface based artificial hand Ten million people on the earth at any given time suffer from the loss or lack of a limb. Three million of these are upper extremity amputees. No matter the cause or reason for amputation the amputees’ life is never the same again. Independence can be lost and never regained. The loss of a limb can be an overpowering event that effects the mental, social, and physical well-being of a person. Although there has been many attempts to restore hand function through neural prosthetics there is little to no credible solutions to regain it. This thesis presents methods to restore hand function based on the human grasping system and addresses key challenges in the practical application of those methods. The contribution of this work lies in improving artificial hand function by mimicking the human grasping system. The human grasping system consists of the brain, the nervous system and the hand. The methods used investigate: biomechanical design principles for artificial hands, the limitations of machine learning in non-invasive neural interfaces (NI’s) and the development of an autonomous hand control framework for artificial hand control. 

The application of the Support Vector Machine (SVM) to a non-invasive neural interface is principally limited to binary applications in the real world. In order to overcome this limitation an autonomous approach is developed to achieve better response and accuracy from NI control frameworks. In binary applications the SVM performed well with a classification accuracy of around 80% accompanied by a response time of just under 5 seconds. When applied to multiple classifications the SVM decreased in accuracy and response dramatically. The accuracy of the autonomous hand control framework had a classification accuracy of 95% with a response time comparable to that of the SVM. This outcome has the potential to move non-invasive NI research into the real world and to restore hand function in an intuitive and meaningful way. A key learning of this research is that machine learning methods for non-invasive neural interfaces are not the best way to restore hand function for amputees. Hand function is best restored through the combining of machine learning and machine vision into a single NI based control framework. Additionally, this work is based in Mātauranga Māori with a western science approach. By so doing, amputees will be empowered, have increased independence and enjoy a better quality of life.

The scope of this work is limited to the consideration of hand function restoration for upper extremity amputees. In particular trans-radial amputees. Focus is given to non-invasive methods of control, therefore, investigations are limited to the electroencephalography (EEG) signal. Mimicking the human grasping system is a complex and difficult process, therefore, the attempts in this work to restore hand function only consider mechanisms and processes related directly to the motor control of the human hand.

year: 2019