title: Supercapacitor-based linear converter for voltage regulator modules

authors: Wickramasinghe, Thilini Chintha Prabha Kumari

subjects: DC-DC converter

abstract: This thesis investigates a linear converter technique suitable for microprocessor voltage regulator modules (VRMs). The original linear regulator is the patented supercapacitor assisted low-dropout regulator (SCALDO). A less complex, lower cost design was achieved by reducing the number of switches in the original SCALDO and adding a second low dropout regulator (LDO).
In the initial implementation of this reduced-switch SCALDO (RS-SCALDO), output regulation failed due to the presence of a parasitic body-diode in standard LDOs. The body-diode forms an unwanted discharge path to ground for the supercapacitor. In order to block this path, an application specific LDO that operates in the third quadrant of a MOSFET current-vs-voltage transfer function was investigated.
A 3.5-to-1.5 V RS-SCALDO was designed with a supercapacitor, two LDOs and two switches. Compared with the standard SCALDO approach, this new design halves the number of switches required. Discrete MOSFET-based high-current LDOs were developed and combined with a common feedback control circuit. Voltage identification (VID) capability was implemented using a digital potentiometer. Theoretically, when an LDO converts 3.5 V to 1.5 V a maximum efficiency of 1.5/3.5(~43%) can be achieved. According to the general theory of SCALDO, a single supercapacitor configuration can achieve nearly twice the linear regulator efficiency. The 3.5-to-1.5 V, 5 A RS-SCALDO achieved an approximate end-to-end efficiency of 80%, thus, agreeing with SCALDO general theory.
Large-signal analysis was used to model MOSFET non-linearities and predict the performance of LDOs, switches and the overall system. Matlab  modeling predictions for body-diode behaviour were cross-checked via SPICE simulation; the results agreed with bench measurements.
RS-SCALDO regulators cycle at very low frequencies, usually in the range of millihertz to hertz. Therefore, electromagnetic interference emitted by high-frequency switched-mode VRMs is not an issue here. Compared to typical high-frequency VRMs, RS-SCALDO topology provides similar efficiencies with the high slew-rate and low noise output of a linear regulator. In generalized SCALDO configuration with n supercapacitors, a total of 3n+1 switches required; in contrast RS-SCALDO reduces the switch count to 2n. With the elimination of the body-diode parasitics, the technique can be extended to much higher currents.

text: Supercapacitor-based linear converter for voltage regulator modules This thesis investigates a linear converter technique suitable for microprocessor voltage regulator modules (VRMs). The original linear regulator is the patented supercapacitor assisted low-dropout regulator (SCALDO). A less complex, lower cost design was achieved by reducing the number of switches in the original SCALDO and adding a second low dropout regulator (LDO).
In the initial implementation of this reduced-switch SCALDO (RS-SCALDO), output regulation failed due to the presence of a parasitic body-diode in standard LDOs. The body-diode forms an unwanted discharge path to ground for the supercapacitor. In order to block this path, an application specific LDO that operates in the third quadrant of a MOSFET current-vs-voltage transfer function was investigated.
A 3.5-to-1.5 V RS-SCALDO was designed with a supercapacitor, two LDOs and two switches. Compared with the standard SCALDO approach, this new design halves the number of switches required. Discrete MOSFET-based high-current LDOs were developed and combined with a common feedback control circuit. Voltage identification (VID) capability was implemented using a digital potentiometer. Theoretically, when an LDO converts 3.5 V to 1.5 V a maximum efficiency of 1.5/3.5(~43%) can be achieved. According to the general theory of SCALDO, a single supercapacitor configuration can achieve nearly twice the linear regulator efficiency. The 3.5-to-1.5 V, 5 A RS-SCALDO achieved an approximate end-to-end efficiency of 80%, thus, agreeing with SCALDO general theory.
Large-signal analysis was used to model MOSFET non-linearities and predict the performance of LDOs, switches and the overall system. Matlab  modeling predictions for body-diode behaviour were cross-checked via SPICE simulation; the results agreed with bench measurements.
RS-SCALDO regulators cycle at very low frequencies, usually in the range of millihertz to hertz. Therefore, electromagnetic interference emitted by high-frequency switched-mode VRMs is not an issue here. Compared to typical high-frequency VRMs, RS-SCALDO topology provides similar efficiencies with the high slew-rate and low noise output of a linear regulator. In generalized SCALDO configuration with n supercapacitors, a total of 3n+1 switches required; in contrast RS-SCALDO reduces the switch count to 2n. With the elimination of the body-diode parasitics, the technique can be extended to much higher currents.

year: 2016

title: Neo-structuralist analysis of green-marketing discourse: interpreting hybrid car manufacturers and consumers

authors: Kadirov, Djavlonbek

subjects: culture

abstract: To explain inconsistent behaviour that is well documented in green-marketing and consumption, the authors develop the (neo)structuralist model of meaning co-creation that is based on the signifying practices of hybrid car manufacturers and consumers. The model reveals that market agents are recruited into a symbolic order that requires the perpetual reinforcement of self-opposing meanings as a condition for signification. The main problem of green practice is not the issue of market agents' authenticity/hypocrisy. Rather it represents a more interactive phenomenon – the common structure of meaning-creation – which silences important transformative action choices and thus defeats its own purpose.

text: Neo-structuralist analysis of green-marketing discourse: interpreting hybrid car manufacturers and consumers To explain inconsistent behaviour that is well documented in green-marketing and consumption, the authors develop the (neo)structuralist model of meaning co-creation that is based on the signifying practices of hybrid car manufacturers and consumers. The model reveals that market agents are recruited into a symbolic order that requires the perpetual reinforcement of self-opposing meanings as a condition for signification. The main problem of green practice is not the issue of market agents' authenticity/hypocrisy. Rather it represents a more interactive phenomenon – the common structure of meaning-creation – which silences important transformative action choices and thus defeats its own purpose.

year: 2013

title: Ahumoana tawhito (ancient aquaculture): The translocation of  toheroa (Paphies ventricosa) and other marine species by Māori

authors: Taikato, Vanessa Rona

subjects: Mātauranga

abstract: Throughout time, humans have cultivated and translocated plants and animals. Ancient mariculture (the cultivation of marine species) often leaves little trace of human agency. Consequently, the extent to which mariculture was used in the distant past largely remains a mystery. In Aotearoa (New Zealand), Māori have a long history of translocating and cultivating terrestrial and freshwater species. Increasingly, it is becoming apparent that the translocation of marine species is a resource management tool that has been utilized by Māori for hundreds of years. Research into the population genetic structure of a large surf clam endemic to Aotearoa, the toheroa (Paphies ventricosa), has led to the hypothesis that Māori have undertaken long-distance transport and translocation of this shellfish during the earlier phases of Māori occupation within Aotearoa. Specifically, this “translocation hypothesis” suggests that Māori successfully transported toheroa from the West Coast of Te ika-a-Māui (the North Island) to the South Coast of Te Waipounamu (the South Island) thereby explaining the unique and disjunct distribution pattern of this taonga (treasured) species. This thesis weaves together knowledge from multiple disciplines to test the toheroa translocation hypothesis, explore technologies used by Māori and reclaim traditional knowledge regarding resource management. 

An examination of archaeological databases revealed a record that was not consistent with toheroa being endemic to Murihiku (southern South Island). On the west coast of Te Ika-a-Māui, 968 midden records were identified of which 40% either contained or consisted entirely of toheroa. In contrast, along the South Coast of Murihiku (Southland, Te Waipounamu), 122 midden records were examined, of which only 6.5% contained toheroa. Toheroa were not a major component of any of these middens. Toheroa were also absent from a natural shell deposit within Murihiku that pre-dates human arrival to Aotearoa. The general absences of toheroa in all but a few southern middens lends itself to the notion that toheroa did not occur there naturally, but were introduced by Māori at a later date. 

An examination of anthropological, historical and traditional knowledge was conducted to explore the human elements of toheroa translocation. Specifically, I wanted to better understand the reasons why early-Māori might have wanted to translocate toheroa, as well as the capacity and opportunities they would have had to undertake such long-distance transport of live bivalves. The movement of iwi from the north to the south is a concept steeped in kōrero tuku iho (oral history) and is referred to many times in ethnohistorical and contemporary literature. This included the very first movements of Polynesian explorers north to south, as well as multiple accounts of expeditions and southward migrations by Māori originating from the north. Toheroa were an important resource for the earliest occupants of northern regions in Aotearoa and this is evident in the prominence of toheroa in northern Māori culture. Interestingly, while they are a taonga of southern Māori today, toheroa are conspicuously absent in the narratives, whakataukī (proverbs) and whakapapa (genealogy) of Murihiku (Southland). This could be explained by a later introduction of toheroa to the area, leading to less time and opportunity of the resource to shape southern Māori identity. While toheroa may not have been endemic to the south, there was ample opportunity for them to be relocated, either through trade, or as part of a southward migration. Archaeological records of industrial stone, such as obsidian, provide evidence for trade between northern and southern Māori as early as the 14th century. It is clear that people who had come from or were closely connected to northern Māori have occupied the southern most areas of Aotearoa, in the earliest phases of the prehistoric sequence. 
While it is apparent that the opportunity for shellfish translocation existed, the suitability of toheroa for relocation was unknown. This would depend on their ability to cope with and combat stressors (such as hypoxia, bacterial proliferation, starvation and desiccation) associated with such a journey. Respiration rates, morphometric indices, behavioural responses and physiological responses to these stressors were measured in a series of in situ experiments. Toheroa displayed an overall physiological robustness to lack of oxygen and food and, when held in seawater and treated with antibiotics, toheroa were able to switch to anaerobiosis and survive for extended periods of time (more than two weeks). The primary causes of health deterioration were found to be bacterial proliferation (of particular prevalence when held in anoxic water) and desiccation. These are risks that could easily have been mitigated during a translocation journey.

The pōhā, a natural kelp bag fashioned from the large brown alga Durvillaea spp., is a southern Māori technology said to have been used in the translocation and re-seeding of toheroa and other shellfish species, prehistorically. An important first step in understanding this technology was to review the traditional knowledge associated with pōhā and of rimurapa (southern Bull Kelp) from which pōhā are constructed. The literature contained a variety of information covering prehistoric practices to contemporary management of this natural resource as well as details of its wide and varied uses. Interestingly, contemporary use of pōhā and rimurapa has included translocation and restoration of seagrass in Te Waipounamu. 

While there are many historical references to pōhā being used for translocating shellfish, the details of exactly how they were used are missing, both in the literature and in the memories of traditional practitioners of pōhā with whom I have been lucky enough to speak with. Consequently, the final component of this thesis explored the biochemical and bacterial implications of holding live toheroa in pōhā. I found that the photosynthetic blades of the algae were able to replenish dissolved oxygen consumed by the toheroa during respiration. Furthermore, it was clear that the microbiome associated with pōhā, or the secondary metabolites released by pōhā, influenced the bacterial community to which toheroa were exposed when held within the algal bags. From these experiments, it appears unlikely that pōhā were used in the manner employed in this experiment (filled with seawater and left to stagnate) as this resulted in the rapid deterioration of the pōhā bags. However, the biochemical and bacterial results that were found, have direct implications for the functionality of pōhā and the toheroa held within. While possibly not the main vessel in which toheroa were translocated, kōrero tuku iho about the use of pōhā in shellfish re-seeding, suggest that raw pōhā may have been the last link in the chain of shellfish translocation by providing protection while acclimating to a new area. 

The research I have undertaken for this thesis is novel and it contributes to our growing understanding of indigenous resource management in Aotearoa. While I have not been able to determine definitively whether toheroa in the south are solely a consequence of Māori translocation, the evidence presented here is consistent with that hypothesis. The experiments undertaken here are the first of their kind for toheroa, and they highlight how the complex nature of surf clam physiology and behaviour would play into their cultivation, either in ancient or contemporary contexts. This thesis reclaims traditional knowledge regarding the management of two taonga species (toheroa and rimurapa) and highlights several possible avenues for future research. Furthermore, this research demonstrates how academic knowledge and indigenous knowledge can be interwoven, to attempt to unravel the mysteries of the past and to pave the way for the future.

text: Ahumoana tawhito (ancient aquaculture): The translocation of  toheroa (Paphies ventricosa) and other marine species by Māori Throughout time, humans have cultivated and translocated plants and animals. Ancient mariculture (the cultivation of marine species) often leaves little trace of human agency. Consequently, the extent to which mariculture was used in the distant past largely remains a mystery. In Aotearoa (New Zealand), Māori have a long history of translocating and cultivating terrestrial and freshwater species. Increasingly, it is becoming apparent that the translocation of marine species is a resource management tool that has been utilized by Māori for hundreds of years. Research into the population genetic structure of a large surf clam endemic to Aotearoa, the toheroa (Paphies ventricosa), has led to the hypothesis that Māori have undertaken long-distance transport and translocation of this shellfish during the earlier phases of Māori occupation within Aotearoa. Specifically, this “translocation hypothesis” suggests that Māori successfully transported toheroa from the West Coast of Te ika-a-Māui (the North Island) to the South Coast of Te Waipounamu (the South Island) thereby explaining the unique and disjunct distribution pattern of this taonga (treasured) species. This thesis weaves together knowledge from multiple disciplines to test the toheroa translocation hypothesis, explore technologies used by Māori and reclaim traditional knowledge regarding resource management. 

An examination of archaeological databases revealed a record that was not consistent with toheroa being endemic to Murihiku (southern South Island). On the west coast of Te Ika-a-Māui, 968 midden records were identified of which 40% either contained or consisted entirely of toheroa. In contrast, along the South Coast of Murihiku (Southland, Te Waipounamu), 122 midden records were examined, of which only 6.5% contained toheroa. Toheroa were not a major component of any of these middens. Toheroa were also absent from a natural shell deposit within Murihiku that pre-dates human arrival to Aotearoa. The general absences of toheroa in all but a few southern middens lends itself to the notion that toheroa did not occur there naturally, but were introduced by Māori at a later date. 

An examination of anthropological, historical and traditional knowledge was conducted to explore the human elements of toheroa translocation. Specifically, I wanted to better understand the reasons why early-Māori might have wanted to translocate toheroa, as well as the capacity and opportunities they would have had to undertake such long-distance transport of live bivalves. The movement of iwi from the north to the south is a concept steeped in kōrero tuku iho (oral history) and is referred to many times in ethnohistorical and contemporary literature. This included the very first movements of Polynesian explorers north to south, as well as multiple accounts of expeditions and southward migrations by Māori originating from the north. Toheroa were an important resource for the earliest occupants of northern regions in Aotearoa and this is evident in the prominence of toheroa in northern Māori culture. Interestingly, while they are a taonga of southern Māori today, toheroa are conspicuously absent in the narratives, whakataukī (proverbs) and whakapapa (genealogy) of Murihiku (Southland). This could be explained by a later introduction of toheroa to the area, leading to less time and opportunity of the resource to shape southern Māori identity. While toheroa may not have been endemic to the south, there was ample opportunity for them to be relocated, either through trade, or as part of a southward migration. Archaeological records of industrial stone, such as obsidian, provide evidence for trade between northern and southern Māori as early as the 14th century. It is clear that people who had come from or were closely connected to northern Māori have occupied the southern most areas of Aotearoa, in the earliest phases of the prehistoric sequence. 
While it is apparent that the opportunity for shellfish translocation existed, the suitability of toheroa for relocation was unknown. This would depend on their ability to cope with and combat stressors (such as hypoxia, bacterial proliferation, starvation and desiccation) associated with such a journey. Respiration rates, morphometric indices, behavioural responses and physiological responses to these stressors were measured in a series of in situ experiments. Toheroa displayed an overall physiological robustness to lack of oxygen and food and, when held in seawater and treated with antibiotics, toheroa were able to switch to anaerobiosis and survive for extended periods of time (more than two weeks). The primary causes of health deterioration were found to be bacterial proliferation (of particular prevalence when held in anoxic water) and desiccation. These are risks that could easily have been mitigated during a translocation journey.

The pōhā, a natural kelp bag fashioned from the large brown alga Durvillaea spp., is a southern Māori technology said to have been used in the translocation and re-seeding of toheroa and other shellfish species, prehistorically. An important first step in understanding this technology was to review the traditional knowledge associated with pōhā and of rimurapa (southern Bull Kelp) from which pōhā are constructed. The literature contained a variety of information covering prehistoric practices to contemporary management of this natural resource as well as details of its wide and varied uses. Interestingly, contemporary use of pōhā and rimurapa has included translocation and restoration of seagrass in Te Waipounamu. 

While there are many historical references to pōhā being used for translocating shellfish, the details of exactly how they were used are missing, both in the literature and in the memories of traditional practitioners of pōhā with whom I have been lucky enough to speak with. Consequently, the final component of this thesis explored the biochemical and bacterial implications of holding live toheroa in pōhā. I found that the photosynthetic blades of the algae were able to replenish dissolved oxygen consumed by the toheroa during respiration. Furthermore, it was clear that the microbiome associated with pōhā, or the secondary metabolites released by pōhā, influenced the bacterial community to which toheroa were exposed when held within the algal bags. From these experiments, it appears unlikely that pōhā were used in the manner employed in this experiment (filled with seawater and left to stagnate) as this resulted in the rapid deterioration of the pōhā bags. However, the biochemical and bacterial results that were found, have direct implications for the functionality of pōhā and the toheroa held within. While possibly not the main vessel in which toheroa were translocated, kōrero tuku iho about the use of pōhā in shellfish re-seeding, suggest that raw pōhā may have been the last link in the chain of shellfish translocation by providing protection while acclimating to a new area. 

The research I have undertaken for this thesis is novel and it contributes to our growing understanding of indigenous resource management in Aotearoa. While I have not been able to determine definitively whether toheroa in the south are solely a consequence of Māori translocation, the evidence presented here is consistent with that hypothesis. The experiments undertaken here are the first of their kind for toheroa, and they highlight how the complex nature of surf clam physiology and behaviour would play into their cultivation, either in ancient or contemporary contexts. This thesis reclaims traditional knowledge regarding the management of two taonga species (toheroa and rimurapa) and highlights several possible avenues for future research. Furthermore, this research demonstrates how academic knowledge and indigenous knowledge can be interwoven, to attempt to unravel the mysteries of the past and to pave the way for the future.

year: 2021