title: Efficiency of cycled batteries analyzed through voltage-current phase differences

authors: Wilson, Marcus T.

abstract: Ageing of rechargeable batteries is routinely characterized in the frequency domain by electrochemical impedance spectroscopy, but the technique requires laboratory measurements to be made on a time scale of days. However, the normal cycling of a battery as it is used in situ provides equivalent information in the time domain, though extracting robust frequency information from a time series is challenging. In this work, we explore, in the time domain, the relationship between instantaneous voltage-current phase difference and cycle efficiency. Moreover, we demonstrate that phase measures can be used to identify battery ageing. We have cycled a 250 mA h Nickel-Cobalt cell several hundred times and used Hilbert Transforms to identify phase difference between voltage and current. This phase difference becomes closer to zero as the battery ages, commensurate with a drop in energy cycle efficiency. In another experiment, we applied a synthetic current profile mimicking behaviour of an electric car cell, to a 3.2 A h LiNiMnCoO2 cell, for 100 days. For this more complicated profile with a wide range of frequency content, we used wavelet analysis to identify changes in phase difference and impedance as the battery aged. For this cell, drop in cycle efficiency was associated with a rise in internal resistance. The results imply that time-series analysis of in situ measurements of voltage and current, when applied with equivalent circuit models and underlying theory, can identify markers of battery ageing.

text: Efficiency of cycled batteries analyzed through voltage-current phase differences Ageing of rechargeable batteries is routinely characterized in the frequency domain by electrochemical impedance spectroscopy, but the technique requires laboratory measurements to be made on a time scale of days. However, the normal cycling of a battery as it is used in situ provides equivalent information in the time domain, though extracting robust frequency information from a time series is challenging. In this work, we explore, in the time domain, the relationship between instantaneous voltage-current phase difference and cycle efficiency. Moreover, we demonstrate that phase measures can be used to identify battery ageing. We have cycled a 250 mA h Nickel-Cobalt cell several hundred times and used Hilbert Transforms to identify phase difference between voltage and current. This phase difference becomes closer to zero as the battery ages, commensurate with a drop in energy cycle efficiency. In another experiment, we applied a synthetic current profile mimicking behaviour of an electric car cell, to a 3.2 A h LiNiMnCoO2 cell, for 100 days. For this more complicated profile with a wide range of frequency content, we used wavelet analysis to identify changes in phase difference and impedance as the battery aged. For this cell, drop in cycle efficiency was associated with a rise in internal resistance. The results imply that time-series analysis of in situ measurements of voltage and current, when applied with equivalent circuit models and underlying theory, can identify markers of battery ageing.

year: 2024-03-07

title: The evolution of productivity performance on China's dairy farms in the new millennium

authors: Ma, Hengyun

subjects: China

abstract: China's dairy farm structure has experienced fundamental changes across farm types. As the number of backyard farms has dramatically declined, the share of dairy cows from backyard farms has decreased by 22.4% from 2003 to 2008. However, the herd numbers of larger dairy farms have increased. In particular, the share of dairy cows has risen by 18.8% on small farms, by 22.2% on medium farms, and by 80.8% on large farms over the same period. Total factor productivity was decomposed into technical efficiency and technological change on China's dairy farms using the stochastic production frontier framework. The estimated results indicate that patterns of productivity growth appear to have shifted in the 2000s compared with the 1990s, from generally driven by technological change to exclusively driven by technological change on backyard and small farms and uniquely driven by the improvement of technical efficiency on large farms. Tests of the econometric assumption indicate that the variations in total factor productivity growth patterns across farm types and regions are likely caused by the feed input biases and cropping production practice.

text: The evolution of productivity performance on China's dairy farms in the new millennium China's dairy farm structure has experienced fundamental changes across farm types. As the number of backyard farms has dramatically declined, the share of dairy cows from backyard farms has decreased by 22.4% from 2003 to 2008. However, the herd numbers of larger dairy farms have increased. In particular, the share of dairy cows has risen by 18.8% on small farms, by 22.2% on medium farms, and by 80.8% on large farms over the same period. Total factor productivity was decomposed into technical efficiency and technological change on China's dairy farms using the stochastic production frontier framework. The estimated results indicate that patterns of productivity growth appear to have shifted in the 2000s compared with the 1990s, from generally driven by technological change to exclusively driven by technological change on backyard and small farms and uniquely driven by the improvement of technical efficiency on large farms. Tests of the econometric assumption indicate that the variations in total factor productivity growth patterns across farm types and regions are likely caused by the feed input biases and cropping production practice.

year: 2012

title: He huringa āhuarangi, he huringa ao: A changing climate, a changing world

authors: Awatere, S

subjects: climate change adaptation

abstract: Iwi/hapū (tribe/subtribe) governance institutions are increasingly asserting their rangatiratanga (autonomy) to manage climate change risks and meet the well-being of whānau (family)/ hapū/iwi. Howevere, there is a shortange of specific guidance for whānau/hapū/iwi with respect to climate change adaptation and mitigation. We provide a commentary about risk and uncertainty, knowledge gaps, and options for climate change mitigation and adaptation for whānau/hapū/iwi.

text: He huringa āhuarangi, he huringa ao: A changing climate, a changing world Iwi/hapū (tribe/subtribe) governance institutions are increasingly asserting their rangatiratanga (autonomy) to manage climate change risks and meet the well-being of whānau (family)/ hapū/iwi. Howevere, there is a shortange of specific guidance for whānau/hapū/iwi with respect to climate change adaptation and mitigation. We provide a commentary about risk and uncertainty, knowledge gaps, and options for climate change mitigation and adaptation for whānau/hapū/iwi.

year: 2021-10