title: Achieving reliable and repeatable electrochemical impedance spectroscopy of rechargeable batteries at extra-low frequencies

authors: Dunn, Christopher

abstract: There is a need for techniques for efficient and accurate measurement of the impedance of rechargeable batteries at extra-low frequencies (ELFs, of the order of microhertz), as these reflect real usage and cycling patterns, and their importance in fractional battery circuit modeling is becoming increasingly apparent. Major impediments include the time required to perform such measurements and “drift” in impedance values when measurements are taken from the same battery at different times. Moreover, commercial impedance analyzers are generally unable to measure at these frequencies. We describe here our use of programmable two-quadrant power supplies to deliver multiple small-signal measurement tones in the presence of large-signal “working” currents, and our use of these data to generate impedance measurements with good precision and in reasonable time. The improvement in the quality of electrochemical impedance spectroscopy (EIS) data is verified through root-mean-square error (RMSE) when fitting equivalent-circuit models (ECMs).

text: Achieving reliable and repeatable electrochemical impedance spectroscopy of rechargeable batteries at extra-low frequencies There is a need for techniques for efficient and accurate measurement of the impedance of rechargeable batteries at extra-low frequencies (ELFs, of the order of microhertz), as these reflect real usage and cycling patterns, and their importance in fractional battery circuit modeling is becoming increasingly apparent. Major impediments include the time required to perform such measurements and “drift” in impedance values when measurements are taken from the same battery at different times. Moreover, commercial impedance analyzers are generally unable to measure at these frequencies. We describe here our use of programmable two-quadrant power supplies to deliver multiple small-signal measurement tones in the presence of large-signal “working” currents, and our use of these data to generate impedance measurements with good precision and in reasonable time. The improvement in the quality of electrochemical impedance spectroscopy (EIS) data is verified through root-mean-square error (RMSE) when fitting equivalent-circuit models (ECMs).

year: 2022

title: Bioconversion of Glycerol to Dihydroxyacetone by immobilized Gluconacetobacter xylinus cells

authors: Black, Cathryn Sesengel

subjects: Glycerol

abstract: Dihydroxyacetone, (DHA) is one of the primary ingredients used in tanning products by the cosmetic industry. DHA reacts with the free amino acids on the epidermis to form a tan-like appearance. DHA is also a building block for lactic acid; that is, a common ingredient in the food industry. In the pharmaceutical industry, DHA is used as a precursor for 1, 2-propylene glycerol and methotrexate. 
Due to the Food and Drug Administration’s strict regulations, DHA is produced via microbial synthesis. This is because the chemical synthesis involves toxic chemical reactions with epichlorohydrin. This poses problems with a chemical widely used for human application. Currently, the industrial process of DHA is carried out under microbial synthesis of glycerol. The strain, Gluconobacter oxydans produces high DHA yields although its productivity is low. As a result, its high cost of production is reflected in its price.
Glycerol is the only organic compound that can be converted into DHA. The conversion requires oxidation of the secondary hydroxyl group by glycerol dehydrogenase (GlyDH). In this study, DHA was converted from glycerol using Gluconacetobacter xylinus (G.xylinus) in a large-scale reactor. Previously the strain, G.xylinus, has been shown to produce high DHA yields under immobilization. 
In this study, G.xylinus was immobilized inside two carrier materials- calcium alginate and chitosan-coated alginate beads. A series of investigations were carried out to determine the DHA conversion efficiency using the mentioned carriers. The conversion efficiency of alginate immobilized cells was investigated under varying initial glycerol concentrations of: 1%, 2%, 4% and 7% (w/v) and aeration rates of: 0.3, 0.6 and 1.0 vvm. This study found that the optimal glycerol concentration was at 2% (w/v) and the optimal aeration rate was at 0.3 vvm. The DHA conversion efficiency of chitosan-alginate immobilized cells was also tested under the same aeration rate previously mentioned. The investigation found that chitosan coating provided greater stability to the alginate matrix with increased aeration rate. The optimal aeration rate was found at 1.0 vvm.

text: Bioconversion of Glycerol to Dihydroxyacetone by immobilized Gluconacetobacter xylinus cells Dihydroxyacetone, (DHA) is one of the primary ingredients used in tanning products by the cosmetic industry. DHA reacts with the free amino acids on the epidermis to form a tan-like appearance. DHA is also a building block for lactic acid; that is, a common ingredient in the food industry. In the pharmaceutical industry, DHA is used as a precursor for 1, 2-propylene glycerol and methotrexate. 
Due to the Food and Drug Administration’s strict regulations, DHA is produced via microbial synthesis. This is because the chemical synthesis involves toxic chemical reactions with epichlorohydrin. This poses problems with a chemical widely used for human application. Currently, the industrial process of DHA is carried out under microbial synthesis of glycerol. The strain, Gluconobacter oxydans produces high DHA yields although its productivity is low. As a result, its high cost of production is reflected in its price.
Glycerol is the only organic compound that can be converted into DHA. The conversion requires oxidation of the secondary hydroxyl group by glycerol dehydrogenase (GlyDH). In this study, DHA was converted from glycerol using Gluconacetobacter xylinus (G.xylinus) in a large-scale reactor. Previously the strain, G.xylinus, has been shown to produce high DHA yields under immobilization. 
In this study, G.xylinus was immobilized inside two carrier materials- calcium alginate and chitosan-coated alginate beads. A series of investigations were carried out to determine the DHA conversion efficiency using the mentioned carriers. The conversion efficiency of alginate immobilized cells was investigated under varying initial glycerol concentrations of: 1%, 2%, 4% and 7% (w/v) and aeration rates of: 0.3, 0.6 and 1.0 vvm. This study found that the optimal glycerol concentration was at 2% (w/v) and the optimal aeration rate was at 0.3 vvm. The DHA conversion efficiency of chitosan-alginate immobilized cells was also tested under the same aeration rate previously mentioned. The investigation found that chitosan coating provided greater stability to the alginate matrix with increased aeration rate. The optimal aeration rate was found at 1.0 vvm.

year: 2013

title: “This is not us”: But actually, it is. Talking about when to raise the issue of colonisation.

authors: Waitoki, Waikaremoana

abstract: This paper is a commentary on some of the responses to the public narrative of the events after the March 15th Christchurch attack. Several colleagues had publicly and privately, offered their views on the Government’s and media outlets use of terms such as ‘unprecedented’, ‘our loss of innocence’ and ‘our darkest day’. A fiery and empassioned exchange of words emerged on social media about the statement: ‘This is not us’. By exposing the counternarrative to these emotion laden terms, a shady past, and invisible present was revealed. However, the timing of the talk about colonisation also seemed out of step with the need for sensitivity. This paper also explores the role of White supremacy and causal racism in New Zealand. A personal I/we/us narrative style is used throughout the paper to describe how Muslim and Maori lives intersected prior to, and after the attack. The timeline of events is primarily 1 week, and up to 6 weeks post the attack.

text: “This is not us”: But actually, it is. Talking about when to raise the issue of colonisation. This paper is a commentary on some of the responses to the public narrative of the events after the March 15th Christchurch attack. Several colleagues had publicly and privately, offered their views on the Government’s and media outlets use of terms such as ‘unprecedented’, ‘our loss of innocence’ and ‘our darkest day’. A fiery and empassioned exchange of words emerged on social media about the statement: ‘This is not us’. By exposing the counternarrative to these emotion laden terms, a shady past, and invisible present was revealed. However, the timing of the talk about colonisation also seemed out of step with the need for sensitivity. This paper also explores the role of White supremacy and causal racism in New Zealand. A personal I/we/us narrative style is used throughout the paper to describe how Muslim and Maori lives intersected prior to, and after the attack. The timeline of events is primarily 1 week, and up to 6 weeks post the attack.

year: 2019