title: Fractional modelling of rechargeable batteries

authors: Hasan, Rahat

subjects: Modelling

abstract: To develop a compact battery model, many authors begin by measuring the impedance of a battery over a frequency range of interest. Most of the models in the literature are either Thevenin-style or Randles’ model consisting of one or two RC networks and sometimes a Warburg element. These models are usually based on frequency range that stretches to only 1 mHz. This explains why they require several parameters to accurately reproduce the measured impedance data. In most applications, a battery goes through a charge/discharge cycle daily or even longer. Therefore, it seems logical to measure the impedance of the cell at frequencies reciprocal of period of charge. This corresponds to approximately 11.6 µHZ or lower. The impedance data at lower frequencies shows that any rechargeable battery can be simply modelled with a constant phase element in series with a resistor. Based on this observation, an equivalent circuit model and a mathematical model were proposed in this study. Similar to Randles’ model presented in 1947, the proposed models do not contain a source or any purely reactive element. The models were then fitted to the measured impedance data of both lithium-ion and nickel-metal hydride cells, the linear region of the charge-voltage curve, and the transient recovery tail that results from a step-change in load current.

text: Fractional modelling of rechargeable batteries To develop a compact battery model, many authors begin by measuring the impedance of a battery over a frequency range of interest. Most of the models in the literature are either Thevenin-style or Randles’ model consisting of one or two RC networks and sometimes a Warburg element. These models are usually based on frequency range that stretches to only 1 mHz. This explains why they require several parameters to accurately reproduce the measured impedance data. In most applications, a battery goes through a charge/discharge cycle daily or even longer. Therefore, it seems logical to measure the impedance of the cell at frequencies reciprocal of period of charge. This corresponds to approximately 11.6 µHZ or lower. The impedance data at lower frequencies shows that any rechargeable battery can be simply modelled with a constant phase element in series with a resistor. Based on this observation, an equivalent circuit model and a mathematical model were proposed in this study. Similar to Randles’ model presented in 1947, the proposed models do not contain a source or any purely reactive element. The models were then fitted to the measured impedance data of both lithium-ion and nickel-metal hydride cells, the linear region of the charge-voltage curve, and the transient recovery tail that results from a step-change in load current.

year: 2021

title: The use of chronosequences in studies of ecological succession and soil development

authors: Walker, Lawrence R.

subjects: chronosequences

abstract: 1. Chronosequences and associated space-for-time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time-scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development.
2. Chronosequences are appropriate to study plant succession at decadal to millennial time-scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time-scales of centuries to millennia, sometimes independently of their application to shorter-term plant and soil biological communities.
3. Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach.
4. Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species-rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages.
5. Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences.

text: The use of chronosequences in studies of ecological succession and soil development 1. Chronosequences and associated space-for-time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time-scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development.
2. Chronosequences are appropriate to study plant succession at decadal to millennial time-scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time-scales of centuries to millennia, sometimes independently of their application to shorter-term plant and soil biological communities.
3. Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach.
4. Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species-rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages.
5. Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences.

year: 2010

title: Māori women’s perspectives of leadership and wellbeing

authors: Ruru, Stacey Mariu

subjects: Māori leadership

abstract: Within Aotearoa, New Zealand, Māori women are engaged in leadership roles in community and professional workplace settings, however little is known about how they maintain their wellbeing. This research sought to unravel how Māori women leaders maintain their wellbeing, while occupied in complex leadership roles. We report on the findings from semi-structured interviews, acknowledging kaupapa Māori theory and principles, with five Māori women leaders. Thematic analysis was used, and these themes related to five whakataukī (proverb) that provided overarching themes and directions relating to Māori women’s leadership and wellbeing. Each whakataukī describe unique aspects of leadership and wellbeing from a Māori worldview. Themes include humility, collectiveness, courage, future orientations and positivity. While the themes are housed in whakataukī, central to the success of these Māori women leaders was being connected to whānau (family) and friends, and being influenced by tamariki (children), tauira (students) and employees. These social connections made Māori women leaders strong and resilient to change and challenges.

text: Māori women’s perspectives of leadership and wellbeing Within Aotearoa, New Zealand, Māori women are engaged in leadership roles in community and professional workplace settings, however little is known about how they maintain their wellbeing. This research sought to unravel how Māori women leaders maintain their wellbeing, while occupied in complex leadership roles. We report on the findings from semi-structured interviews, acknowledging kaupapa Māori theory and principles, with five Māori women leaders. Thematic analysis was used, and these themes related to five whakataukī (proverb) that provided overarching themes and directions relating to Māori women’s leadership and wellbeing. Each whakataukī describe unique aspects of leadership and wellbeing from a Māori worldview. Themes include humility, collectiveness, courage, future orientations and positivity. While the themes are housed in whakataukī, central to the success of these Māori women leaders was being connected to whānau (family) and friends, and being influenced by tamariki (children), tauira (students) and employees. These social connections made Māori women leaders strong and resilient to change and challenges.

year: 2017