title: An analysis of the transitions between down and up states of the cortical slow oscillation under urethane anaesthesia

authors: Wilson, Marcus T.

subjects: cortex

abstract: We study the dynamics of the transition between the low- and high-firing states of the cortical slow oscillation by using intracellular recordings of the membrane potential from cortical neurons of rats. We investigate the evidence for a bistability in assemblies of cortical neurons playing a major role in the maintenance of this oscillation. We show that the trajectory of a typical transition takes an approximately exponential form, equivalent to the response of a resistor–capacitor circuit to a step-change in input. The time constant for the transition is negatively correlated with the membrane potential of the lowfiring state, and values are broadly equivalent to neural time constants measured elsewhere. Overall, the results do not strongly support the hypothesis of a bistability in cortical neurons; rather, they suggest the cortical manifestation of the oscillation is a result of a step-change in input to the cortical neurons. Since there is evidence from previous work that a phase transition exists, we speculate that the step-change may be a result of a bistability within other brain areas, such as the thalamus, or a bistability among only a small subset of cortical neurons, or as a result of more complicated brain dynamics.

text: An analysis of the transitions between down and up states of the cortical slow oscillation under urethane anaesthesia We study the dynamics of the transition between the low- and high-firing states of the cortical slow oscillation by using intracellular recordings of the membrane potential from cortical neurons of rats. We investigate the evidence for a bistability in assemblies of cortical neurons playing a major role in the maintenance of this oscillation. We show that the trajectory of a typical transition takes an approximately exponential form, equivalent to the response of a resistor–capacitor circuit to a step-change in input. The time constant for the transition is negatively correlated with the membrane potential of the lowfiring state, and values are broadly equivalent to neural time constants measured elsewhere. Overall, the results do not strongly support the hypothesis of a bistability in cortical neurons; rather, they suggest the cortical manifestation of the oscillation is a result of a step-change in input to the cortical neurons. Since there is evidence from previous work that a phase transition exists, we speculate that the step-change may be a result of a bistability within other brain areas, such as the thalamus, or a bistability among only a small subset of cortical neurons, or as a result of more complicated brain dynamics.

year: 2010

title: Estimation of total cloud cover from solar radiation observations at Lake Rotorua, New Zealand

authors: Luo, Liancong

subjects: clear-sky solar irradiance

abstract: The DYRESM-CAEDYM model is a valuable tool for simulating water temperature for biochemical studies in aquatic ecosystem. The model requires inputs of surface short-wave radiation and long-wave radiation or total cloud cover fraction (TC). Long-wave radiation is often not measured directly so a method to determine TC from commonly measured short-wave solar irradiance (E0) and theoretical short-wave solar irradiance under a clear sky (Ec) has broad application. A more than 17-year (15 November 1991 to 20 February 2009) hourly solar irradiance data set was used to estimate the peak solar irradiance for each ordinal date over one year, which was assumed to be representative of solar irradiance in the absence of cloud. Comparison between these daily observed values and the modelled clear-sky solar radiation over one year was in close agreement (Pearson correlation coefficient, r = 0.995 and root mean squared error, RMSE = 12.54W m-²). The downloaded hourly cloudiness measurements from 15 November 1991 to 20 February 2009 was used to calculate the daily values for this period and then the calculated daily values over the 17 years were used to calculate the average values for each ordinal date over one year. A regression equation between (1 - E0/Ec) and TC produced a correlation coefficient value of 0.99 (p > 0.01, n = 71). The validation of this cloud cover estimation model was conducted with observed short-wave solar radiation and TC at two sites. Values of TC derived from the model at the Lake Rotorua site gave a reasonable prediction of the observed values (RMSE = 0.10, r = 0.86, p > 0.01, n = 61). The model was also tested at Queenstown (South Island of New Zealand) and it provided satisfactory results compared to the measurements (RMSE = 0.16, r = 0.67, p > 0.01, n = 61). Therefore the model’s good performance and broad applicability will contribute to the DYRESM-CAEDYM accuracy of water temperature simulation when long-wave radiation is not available.

text: Estimation of total cloud cover from solar radiation observations at Lake Rotorua, New Zealand The DYRESM-CAEDYM model is a valuable tool for simulating water temperature for biochemical studies in aquatic ecosystem. The model requires inputs of surface short-wave radiation and long-wave radiation or total cloud cover fraction (TC). Long-wave radiation is often not measured directly so a method to determine TC from commonly measured short-wave solar irradiance (E0) and theoretical short-wave solar irradiance under a clear sky (Ec) has broad application. A more than 17-year (15 November 1991 to 20 February 2009) hourly solar irradiance data set was used to estimate the peak solar irradiance for each ordinal date over one year, which was assumed to be representative of solar irradiance in the absence of cloud. Comparison between these daily observed values and the modelled clear-sky solar radiation over one year was in close agreement (Pearson correlation coefficient, r = 0.995 and root mean squared error, RMSE = 12.54W m-²). The downloaded hourly cloudiness measurements from 15 November 1991 to 20 February 2009 was used to calculate the daily values for this period and then the calculated daily values over the 17 years were used to calculate the average values for each ordinal date over one year. A regression equation between (1 - E0/Ec) and TC produced a correlation coefficient value of 0.99 (p > 0.01, n = 71). The validation of this cloud cover estimation model was conducted with observed short-wave solar radiation and TC at two sites. Values of TC derived from the model at the Lake Rotorua site gave a reasonable prediction of the observed values (RMSE = 0.10, r = 0.86, p > 0.01, n = 61). The model was also tested at Queenstown (South Island of New Zealand) and it provided satisfactory results compared to the measurements (RMSE = 0.16, r = 0.67, p > 0.01, n = 61). Therefore the model’s good performance and broad applicability will contribute to the DYRESM-CAEDYM accuracy of water temperature simulation when long-wave radiation is not available.

year: 2010

title: ‘Let’s Get Wild’: Sensuous Geographies of Kāwhia Kai and Hokitika Wildfoods Festivals in Aōtearoa New Zealand

authors: Modlik, Melanie

subjects: Food Festivals

abstract: Food Festivals allow communities to celebrate local food and drink. This original thesis examines the mutual relationship between food festival organisers, festival attendees and festival spaces. Two unique New Zealand regional food festivals – Kāwhia Kai on the West Coast of the North Island and Wildfoods Hokitika on the West Coast of the South Island - are critically examined. The research addresses three questions. First, how do these food festivals construct their locations and vice versa? Second, in what ways do food festivals contribute to place identity? And, third, how do food festival attendees sensually experience the festivals?
The concept of embodiment provides the overarching framework for this research. With academic interests in both tourism and geography, I weave understandings of culinary tourism, festivals, tourist embodied experiences, sensuality, visercality and abjection to address my research questions. I use this theoretical ‘toolbox’ alongside qualitative methodological approaches which enable research participants to express their embodied experiences and emotions. Ten semi-structured interviews were conducted with festival organisers and food stall holders. Participant ‘sensing’ was carried out in both Kāwhia and Hokitika. In thinking about the social, cultural and ‘felt’ aspects of food, I also use my own body as an instrument of research. Promotional texts were collected and all data analysed using critical discourse analysis.
The empirical material is divided into two themes. The first theme focuses on location and place identity. Concepts of ‘place attachment’ and ‘sense of belonging’ construct food festival regions. The formation of ‘new colonial’ and ‘new Māori’ traditions is another way in which these food festivals created unique place identities. The second theme highlights the embodied experiences and spaces of both food festivals. Bodily senses, place and spaces are created through visceral and abject reactions to food experiences.
Food festivals have the potential to enhance the economic, social and cultural wellbeing of regional communities. The success of food festivals, however, is dependent on multi-sensual embodied experiences.

text: ‘Let’s Get Wild’: Sensuous Geographies of Kāwhia Kai and Hokitika Wildfoods Festivals in Aōtearoa New Zealand Food Festivals allow communities to celebrate local food and drink. This original thesis examines the mutual relationship between food festival organisers, festival attendees and festival spaces. Two unique New Zealand regional food festivals – Kāwhia Kai on the West Coast of the North Island and Wildfoods Hokitika on the West Coast of the South Island - are critically examined. The research addresses three questions. First, how do these food festivals construct their locations and vice versa? Second, in what ways do food festivals contribute to place identity? And, third, how do food festival attendees sensually experience the festivals?
The concept of embodiment provides the overarching framework for this research. With academic interests in both tourism and geography, I weave understandings of culinary tourism, festivals, tourist embodied experiences, sensuality, visercality and abjection to address my research questions. I use this theoretical ‘toolbox’ alongside qualitative methodological approaches which enable research participants to express their embodied experiences and emotions. Ten semi-structured interviews were conducted with festival organisers and food stall holders. Participant ‘sensing’ was carried out in both Kāwhia and Hokitika. In thinking about the social, cultural and ‘felt’ aspects of food, I also use my own body as an instrument of research. Promotional texts were collected and all data analysed using critical discourse analysis.
The empirical material is divided into two themes. The first theme focuses on location and place identity. Concepts of ‘place attachment’ and ‘sense of belonging’ construct food festival regions. The formation of ‘new colonial’ and ‘new Māori’ traditions is another way in which these food festivals created unique place identities. The second theme highlights the embodied experiences and spaces of both food festivals. Bodily senses, place and spaces are created through visceral and abject reactions to food experiences.
Food festivals have the potential to enhance the economic, social and cultural wellbeing of regional communities. The success of food festivals, however, is dependent on multi-sensual embodied experiences.

year: 2015