Search

Search Results

• 11. [Article] Determining the Power and Energy Capacities of a Battery Energy Storage System to Accommodate High Photovoltaic Penetration on a Distribution Feeder

  The integration of distributed energy generation systems has begun to impact the operation of distribution feeders within the balancing areas of numerous electrical utilities. Battery energy storage systems ...

  Citation × Citation Citation Abstract Copy Title: Determining the Power and Energy Capacities of a Battery Energy Storage System to Accommodate High Photovoltaic Penetration on a Distribution Feeder Author: Bass, Robert B., Carr, Jennifer, Aguilar, José, Whitener, Kevin Year: 2016 The integration of distributed energy generation systems has begun to impact the operation of distribution feeders within the balancing areas of numerous electrical utilities. Battery energy storage systems may be used to facilitate greater integration of renewable energy generation. This paper describes a method for determining the power and energy capacities a battery energy storage system would need in order to accommodate a particular photovoltaic penetration level within a distribution feeder, or conversely, the amount of photovoltaic that could be installed on a feeder with a minimal investment in power and energy battery energy storage system (BESS) capacities. This method determines the BESS capacities required to compensate both intra-hour and inter-hour load and photovoltaic fluctuations to achieve a flat feeder power profile. By managing the feeder power, the voltage drop along the length of feeder may be managed, thereby mitigating the voltage fluctuation induced by the stochastic nature of both renewables generation and load. Doing so facilitates system benefits, such as conservation voltage reduction, fewer operations of load tap changers, and voltage regulators, and allows for deferment of capital expenditures. Title: Determining the Power and Energy Capacities of a Battery Energy Storage System to Accommodate High Photovoltaic Penetration on a Distribution Feeder Author: Bass, Robert B., Carr, Jennifer, Aguilar, José, Whitener, Kevin Year: 2016 The integration of distributed energy generation systems has begun to impact the operation of distribution feeders within the balancing areas of numerous electrical utilities. Battery energy storage systems may be used to facilitate greater integration of renewable energy generation. This paper describes a method for determining the power and energy capacities a battery energy storage system would need in order to accommodate a particular photovoltaic penetration level within a distribution feeder, or conversely, the amount of photovoltaic that could be installed on a feeder with a minimal investment in power and energy battery energy storage system (BESS) capacities. This method determines the BESS capacities required to compensate both intra-hour and inter-hour load and photovoltaic fluctuations to achieve a flat feeder power profile. By managing the feeder power, the voltage drop along the length of feeder may be managed, thereby mitigating the voltage fluctuation induced by the stochastic nature of both renewables generation and load. Doing so facilitates system benefits, such as conservation voltage reduction, fewer operations of load tap changers, and voltage regulators, and allows for deferment of capital expenditures. Close

• 12. [Article] Prussian Green: A High Rate Capacity Cathode for Potassium Ion Batteries

  The influence of the precursors, namely potassium ferrocyanide and potassium ferricyanide on the particles sizes of Prussian Blue (PB) and Prussian Green (PG), under identical reaction conditions have ...

  Citation × Citation Citation Abstract Copy Title: Prussian Green: A High Rate Capacity Cathode for Potassium Ion Batteries Author: Pradigi, Prasanna, Thiebes, Joseph, Swan, Mitchell, Goncher, Gary, Evans, David, Solanki, Raj Year: 2015 The influence of the precursors, namely potassium ferrocyanide and potassium ferricyanide on the particles sizes of Prussian Blue (PB) and Prussian Green (PG), under identical reaction conditions have been investigated. It was found that the particle sizes influence the gravimetric capacity utilization of these materials as cathodes for aqueous potassium (K+ ) ion batteries. The PG particle sizes were on the order of 50-75 nm, whereas PB particles size were on the order of 2-10 microns. The PG cathodes demonstrated a reversible capacity of 121.4 mAhr/g, with a coulombic efficiency of 98.7% compared to PB cathodes which demonstrated 53.8 mAhr/g, with a coulombic efficiency of 100%. We interpret the increased capacity of PG batteries relative to PB batteries as being a result of the smaller particle size of PG, which results in greater accessibility of the cathode to K+ ions. Title: Prussian Green: A High Rate Capacity Cathode for Potassium Ion Batteries Author: Pradigi, Prasanna, Thiebes, Joseph, Swan, Mitchell, Goncher, Gary, Evans, David, Solanki, Raj Year: 2015 The influence of the precursors, namely potassium ferrocyanide and potassium ferricyanide on the particles sizes of Prussian Blue (PB) and Prussian Green (PG), under identical reaction conditions have been investigated. It was found that the particle sizes influence the gravimetric capacity utilization of these materials as cathodes for aqueous potassium (K+ ) ion batteries. The PG particle sizes were on the order of 50-75 nm, whereas PB particles size were on the order of 2-10 microns. The PG cathodes demonstrated a reversible capacity of 121.4 mAhr/g, with a coulombic efficiency of 98.7% compared to PB cathodes which demonstrated 53.8 mAhr/g, with a coulombic efficiency of 100%. We interpret the increased capacity of PG batteries relative to PB batteries as being a result of the smaller particle size of PG, which results in greater accessibility of the cathode to K+ ions. Close

• 13. [Article] Determining the Power and Energy Capacity of a Battery Energy Storage System Utilizing a Smoothing Feeder Profile to Accommodate High Photovoltaic Penetration on a Distribution Feeder

  Electricity is a perishable commodity; once it is generated it needs to be consumed or stored. Electric energy storage provides both power and energy capacity. Power capacity applications reduce the need ...

  Citation × Citation Citation Abstract Copy Title: Determining the Power and Energy Capacity of a Battery Energy Storage System Utilizing a Smoothing Feeder Profile to Accommodate High Photovoltaic Penetration on a Distribution Feeder Author: Mansour, Osama Mohammed Abbas Aly Year: 2016 Electricity is a perishable commodity; once it is generated it needs to be consumed or stored. Electric energy storage provides both power and energy capacity. Power capacity applications reduce the need for generation, while energy capacity allows for energy consumption to be decoupled from generation. Previous research was done to develop an algorithm for determining the power (MW) and energy (MWh) capacities of a battery energy storage system (BESS) to mitigate the adverse impacts of high levels of photovoltaic (PV) generation. The algorithm used a flat feeder profile, and its performance was demonstrated on the equinoxes and solstices. Managing feeder power leads to fewer voltage fluctuations along the length of the feeder, potentially mitigating load management issues caused by variability of renewable generation and load profile. These issues include lighting flicker, compressor seizing, equipment shut-off, loss of motor torque, frequent transformer tap changes and even voltage collapse due to loss of reactive power support. The research described in this thesis builds on this algorithm by incorporating a smoothed feeder profile and testing it over an entire year. Incorporating a smoothing function reduces the requisite BESS energy capacity necessary to provide firming and shaping to accommodate the stochastic nature of PV. Specifically, this method is used to conduct a year-long study on a per second basis, as well as a one-minute basis, for a distribution feeder. Statistical analytical methods were performed to develop recommendations for appropriately sizing the BESS. This method may be used to determine the amount of PV generation that could be installed on a distribution feeder with a minimal investment in the BESS power and energy capacities that would be required to manage the distribution feeder power. Results are presented for PV penetration levels of 10%-50% of the distribution feeder capacity and show that the use of a smooth feeder profile reduces the required energy capacity by a minimum factor of 10 when compared to a flat feeder profile. Results indicated that it is sufficient to have a one-minute sampling rate, as it provides the necessary granularity to model cloud-induced fluctuations. This method can be applied to any distribution feeder where a load profile and a PV profile are available. Title: Determining the Power and Energy Capacity of a Battery Energy Storage System Utilizing a Smoothing Feeder Profile to Accommodate High Photovoltaic Penetration on a Distribution Feeder Author: Mansour, Osama Mohammed Abbas Aly Year: 2016 Electricity is a perishable commodity; once it is generated it needs to be consumed or stored. Electric energy storage provides both power and energy capacity. Power capacity applications reduce the need for generation, while energy capacity allows for energy consumption to be decoupled from generation. Previous research was done to develop an algorithm for determining the power (MW) and energy (MWh) capacities of a battery energy storage system (BESS) to mitigate the adverse impacts of high levels of photovoltaic (PV) generation. The algorithm used a flat feeder profile, and its performance was demonstrated on the equinoxes and solstices. Managing feeder power leads to fewer voltage fluctuations along the length of the feeder, potentially mitigating load management issues caused by variability of renewable generation and load profile. These issues include lighting flicker, compressor seizing, equipment shut-off, loss of motor torque, frequent transformer tap changes and even voltage collapse due to loss of reactive power support. The research described in this thesis builds on this algorithm by incorporating a smoothed feeder profile and testing it over an entire year. Incorporating a smoothing function reduces the requisite BESS energy capacity necessary to provide firming and shaping to accommodate the stochastic nature of PV. Specifically, this method is used to conduct a year-long study on a per second basis, as well as a one-minute basis, for a distribution feeder. Statistical analytical methods were performed to develop recommendations for appropriately sizing the BESS. This method may be used to determine the amount of PV generation that could be installed on a distribution feeder with a minimal investment in the BESS power and energy capacities that would be required to manage the distribution feeder power. Results are presented for PV penetration levels of 10%-50% of the distribution feeder capacity and show that the use of a smooth feeder profile reduces the required energy capacity by a minimum factor of 10 when compared to a flat feeder profile. Results indicated that it is sufficient to have a one-minute sampling rate, as it provides the necessary granularity to model cloud-induced fluctuations. This method can be applied to any distribution feeder where a load profile and a PV profile are available. Close

• 14. [Article] Organizational Change and Racial Equity: Implications for Capacity-Building Practice for Organizations and Networks

  The changing environment both locally and nationally has heightened the need of nonprofit leadership and organizations to address issues of racial and ethnic disparities with more equitable systems and ...

  Citation × Citation Citation Abstract Copy Title: Organizational Change and Racial Equity: Implications for Capacity-Building Practice for Organizations and Networks Author: Hill, Curdina, Curry-Stevens, Ann Year: 2016 The changing environment both locally and nationally has heightened the need of nonprofit leadership and organizations to address issues of racial and ethnic disparities with more equitable systems and practice. This article examines the research on nonprofit organizational change through a racial equity lens and looks at implications for nonprofit capacity builders in using this research to create more effective long-term change. Title: Organizational Change and Racial Equity: Implications for Capacity-Building Practice for Organizations and Networks Author: Hill, Curdina, Curry-Stevens, Ann Year: 2016 The changing environment both locally and nationally has heightened the need of nonprofit leadership and organizations to address issues of racial and ethnic disparities with more equitable systems and practice. This article examines the research on nonprofit organizational change through a racial equity lens and looks at implications for nonprofit capacity builders in using this research to create more effective long-term change. Close

• 15. [Article] Impact Analysis of Increased Dispatchable Resources on a Utility Feeder in OpenDSS

  Oregon utilities are replacing their portfolios of traditional fossil fuel generation with renewable generating sources. Stepping away from carbon-producing energy will leave a deficit of on-demand power, ...

  Citation × Citation Citation Abstract Copy Title: Impact Analysis of Increased Dispatchable Resources on a Utility Feeder in OpenDSS Author: Eppinger, Crystal Year: 2017 Oregon utilities are replacing their portfolios of traditional fossil fuel generation with renewable generating sources. Stepping away from carbon-producing energy will leave a deficit of on-demand power, resulting in decreased reliability. To overcome these technical challenges, utilities must maximize the use of their present dispatchable resources. One such resource is the Portland General Electric (PGE) Dispatchable Standby Generation Program (DSG), which is an aggregated 105 MWs of distributed generation (DG). These resources are brought on-line when there is a critical need for power. Resources are added to the program if a transfer trip scheme is in place or a modeling study reveals that the feeder load is at least three times the generator capacity. If the load-to-capacity ratio were lower, more assets could be added to the DSG program. To investigate the impacts of lowering the DG load-to-capacity ratio on existing distribution feeders, we use Open-Source Distribution System Simulator (OpenDSS). We modeled the Oxford Rural feeder by converting a utility CYME database to instantiation files using several MATLAB programs. A MATLAB control program varies the load-to-capacity ratio of the OpenDSS feeder model and monitors the generator behavior immediately following a fault. We analyzed the results to determine the ideal load-to-capacity ratio that prevents unintentional islanding. The results show that the instantaneous (50) relay element settings dictate both the minimum load-to-capacity ratio and the maximum DG capacity. The present three-to-one ratio is very conservative and can be reduced. Additional dispatchable resources include a five MW battery-inverter system currently used as grid-back up. The battery is grid-tied to a 12.4 kV feeder making it an ideal candidate for conservation voltage reduction (CVR). Using the same feeder model, we investigated the effects of lowering the system voltage to the allowable minimum using injections of reactive power. A lower system voltage reduces the load at peak times. Conversely, increasing the voltage prevents generation conflicts. To determine the benefit of CVR by VAr-injection on the Oxford Rural feeder, we created a MATLAB optimization program to output the optimal feeder voltage for reduced system power. We use a Simulink feedback model to determine the appropriate reactive power needed to achieve the voltage change. We analyze the system model to reveal that the feeder is ideal for CVR but the system capacity must be increased to achieve the maximum power reduction. Title: Impact Analysis of Increased Dispatchable Resources on a Utility Feeder in OpenDSS Author: Eppinger, Crystal Year: 2017 Oregon utilities are replacing their portfolios of traditional fossil fuel generation with renewable generating sources. Stepping away from carbon-producing energy will leave a deficit of on-demand power, resulting in decreased reliability. To overcome these technical challenges, utilities must maximize the use of their present dispatchable resources. One such resource is the Portland General Electric (PGE) Dispatchable Standby Generation Program (DSG), which is an aggregated 105 MWs of distributed generation (DG). These resources are brought on-line when there is a critical need for power. Resources are added to the program if a transfer trip scheme is in place or a modeling study reveals that the feeder load is at least three times the generator capacity. If the load-to-capacity ratio were lower, more assets could be added to the DSG program. To investigate the impacts of lowering the DG load-to-capacity ratio on existing distribution feeders, we use Open-Source Distribution System Simulator (OpenDSS). We modeled the Oxford Rural feeder by converting a utility CYME database to instantiation files using several MATLAB programs. A MATLAB control program varies the load-to-capacity ratio of the OpenDSS feeder model and monitors the generator behavior immediately following a fault. We analyzed the results to determine the ideal load-to-capacity ratio that prevents unintentional islanding. The results show that the instantaneous (50) relay element settings dictate both the minimum load-to-capacity ratio and the maximum DG capacity. The present three-to-one ratio is very conservative and can be reduced. Additional dispatchable resources include a five MW battery-inverter system currently used as grid-back up. The battery is grid-tied to a 12.4 kV feeder making it an ideal candidate for conservation voltage reduction (CVR). Using the same feeder model, we investigated the effects of lowering the system voltage to the allowable minimum using injections of reactive power. A lower system voltage reduces the load at peak times. Conversely, increasing the voltage prevents generation conflicts. To determine the benefit of CVR by VAr-injection on the Oxford Rural feeder, we created a MATLAB optimization program to output the optimal feeder voltage for reduced system power. We use a Simulink feedback model to determine the appropriate reactive power needed to achieve the voltage change. We analyze the system model to reveal that the feeder is ideal for CVR but the system capacity must be increased to achieve the maximum power reduction. Close

• 16. [Article] Lab Failure Analysis Capacity Optimization

  Purpose – The purpose of this paper is to showcase a case study of how five separate optimization models were used to establish true capacity capabilities for a lab facing a situation in which upper management ...

  Citation × Citation Citation Abstract Copy Title: Lab Failure Analysis Capacity Optimization Author: Lamb, Ann-Marie, Myers, Patricia, Peterman, Wendy Year: 2010 Purpose – The purpose of this paper is to showcase a case study of how five separate optimization models were used to establish true capacity capabilities for a lab facing a situation in which upper management set a goal, then left the lab to attempt to meet the goal. This paper highlights the first step for this failure analysis laboratory: determining current baseline capacity. It also delves into showing how the lab might demonstrate its ability to successfully increase its capacity from 200 to 400 units of lab evaluations (metrology units or MUs) per week in future. Design/methodology/approach – An important note in approach is that the researchers developed five separate models in order to more definitely establish baseline capacity. Given the lab problem characteristics, it was determined that integer linear programming (ILP) would form the basis of four of the separate models. One of the models deviated more from this approach by encompassing goal programming for target values of MUs in each metrology. The overall design/approach for each model was to follow as closely as possible the model building approach of 1) Identifying Problem, 2) Formulate and Implement Model, 3) Analyze Model, 4) Test Results/Re-formulate, and 5) Implement Solution. A literature review was used to establish current state of knowledge and fit within capacity optimization research. Findings – While the topic fits into a general category of capacity optimization, more specifically after examining multiple problems facing the laboratory under study, it was found to be one of a subset of optimizing product-mix production. The models showed that the 400MU goal could not be reached. Instead, the maximum appears to be on the order of 200MUs and is in line with historically assumed throughput. Goal programming to meet targets of MUs in each metrology type was unsatisfactory in that it gave fewer MUs per week. The final model suggested that a second shift, or doubling the equipment and technicians available, could reach the 400MU goal. Research limitations/implications – Research implications include an example of product-mix problem analysis and associated ILP and GP model for a type of business which is not often under study, laboratory testing. Future work could include aspects of throughput-time (TPT) and/or flow optimization through bottleneck reduction. Cost was not a primary criterion for the lab under study, but future work could include cost as a constraint and/or decision variable – this would align well with a myriad of previous literature on similar problems. If cost becomes more important to the lab, then looking at economic lot quantity (EOQ) could also prove relevant. Originality/value – This case study provides value with a model which appears somewhat unique in that cost is not of primary importance to the business; so this example could prove invaluable for researchers sifting through a large quantity of product-mix learnings, but finding it difficult to find examples without cost as a primary constraint or decision variable to be minimized. Additionally, this study illustrates the added importance of rigorous understanding of the business problem from the onset. The researchers also provide indication that goal-programming may not be an appropriate approach for similar capacity problems. Title: Lab Failure Analysis Capacity Optimization Author: Lamb, Ann-Marie, Myers, Patricia, Peterman, Wendy Year: 2010 Purpose – The purpose of this paper is to showcase a case study of how five separate optimization models were used to establish true capacity capabilities for a lab facing a situation in which upper management set a goal, then left the lab to attempt to meet the goal. This paper highlights the first step for this failure analysis laboratory: determining current baseline capacity. It also delves into showing how the lab might demonstrate its ability to successfully increase its capacity from 200 to 400 units of lab evaluations (metrology units or MUs) per week in future. Design/methodology/approach – An important note in approach is that the researchers developed five separate models in order to more definitely establish baseline capacity. Given the lab problem characteristics, it was determined that integer linear programming (ILP) would form the basis of four of the separate models. One of the models deviated more from this approach by encompassing goal programming for target values of MUs in each metrology. The overall design/approach for each model was to follow as closely as possible the model building approach of 1) Identifying Problem, 2) Formulate and Implement Model, 3) Analyze Model, 4) Test Results/Re-formulate, and 5) Implement Solution. A literature review was used to establish current state of knowledge and fit within capacity optimization research. Findings – While the topic fits into a general category of capacity optimization, more specifically after examining multiple problems facing the laboratory under study, it was found to be one of a subset of optimizing product-mix production. The models showed that the 400MU goal could not be reached. Instead, the maximum appears to be on the order of 200MUs and is in line with historically assumed throughput. Goal programming to meet targets of MUs in each metrology type was unsatisfactory in that it gave fewer MUs per week. The final model suggested that a second shift, or doubling the equipment and technicians available, could reach the 400MU goal. Research limitations/implications – Research implications include an example of product-mix problem analysis and associated ILP and GP model for a type of business which is not often under study, laboratory testing. Future work could include aspects of throughput-time (TPT) and/or flow optimization through bottleneck reduction. Cost was not a primary criterion for the lab under study, but future work could include cost as a constraint and/or decision variable – this would align well with a myriad of previous literature on similar problems. If cost becomes more important to the lab, then looking at economic lot quantity (EOQ) could also prove relevant. Originality/value – This case study provides value with a model which appears somewhat unique in that cost is not of primary importance to the business; so this example could prove invaluable for researchers sifting through a large quantity of product-mix learnings, but finding it difficult to find examples without cost as a primary constraint or decision variable to be minimized. Additionally, this study illustrates the added importance of rigorous understanding of the business problem from the onset. The researchers also provide indication that goal-programming may not be an appropriate approach for similar capacity problems. Close

• 17. [Article] Building Community Research Capacity: Process Evaluation of Community Training and Education in a Community-Based Participatory Research Program Serving a Predominately Puerto Rican Community

  Background: Education and training build community research capacity and have impact on improvements of health outcomes. Objectives: This manuscript describes the training and educational approaches to ...

  Citation × Citation Citation Abstract Copy Title: Building Community Research Capacity: Process Evaluation of Community Training and Education in a Community-Based Participatory Research Program Serving a Predominately Puerto Rican Community Author: Tumiel-Berhalter, Laurene M., Mclaughlin-Diaz, Victoria, Vena, John, Crespo, Carlos J. Year: 2007 Background: Education and training build community research capacity and have impact on improvements of health outcomes. Objectives: This manuscript describes the training and educational approaches to building research capacity that were utilized in a community-based participatory research program serving a Puerto Rican population and identifies barriers and strategies for overcoming them. Methods: A process evaluation identified a multitiered approach to training and education that was critical to reaching the broad community. Results: This approach included four major categories providing a continuum of education and training opportunities: networking, methods training, on-the-job experience, and community education. Participation in these opportunities supported the development of a registry, the implementation of a survey, and two published manuscripts. Barriers included the lack of a formal evaluation of the education and training components, language challenges that limited involvement of ethnic groups other than Puerto Ricans, and potential biases associated with the familiarity of the data collector and the participant. The CBPR process facilitated relationship development between the university and the community and incorporated the richness of the community experience into research design. Strategies for improvement include incorporating evaluation into every training and educational opportunity and developing measures to quantify research capacity at the individual and community levels. Conclusions: Evaluating training and education in the community allows researchers to quantify the impact of CBPR on building community research capacity. Title: Building Community Research Capacity: Process Evaluation of Community Training and Education in a Community-Based Participatory Research Program Serving a Predominately Puerto Rican Community Author: Tumiel-Berhalter, Laurene M., Mclaughlin-Diaz, Victoria, Vena, John, Crespo, Carlos J. Year: 2007 Background: Education and training build community research capacity and have impact on improvements of health outcomes. Objectives: This manuscript describes the training and educational approaches to building research capacity that were utilized in a community-based participatory research program serving a Puerto Rican population and identifies barriers and strategies for overcoming them. Methods: A process evaluation identified a multitiered approach to training and education that was critical to reaching the broad community. Results: This approach included four major categories providing a continuum of education and training opportunities: networking, methods training, on-the-job experience, and community education. Participation in these opportunities supported the development of a registry, the implementation of a survey, and two published manuscripts. Barriers included the lack of a formal evaluation of the education and training components, language challenges that limited involvement of ethnic groups other than Puerto Ricans, and potential biases associated with the familiarity of the data collector and the participant. The CBPR process facilitated relationship development between the university and the community and incorporated the richness of the community experience into research design. Strategies for improvement include incorporating evaluation into every training and educational opportunity and developing measures to quantify research capacity at the individual and community levels. Conclusions: Evaluating training and education in the community allows researchers to quantify the impact of CBPR on building community research capacity. Close

• 18. [Article] Computational Capacity and Energy Consumption of Complex Resistive Switch Networks

  Resistive switches are a class of emerging nanoelectronics devices that exhibit a wide variety of switching characteristics closely resembling behaviors of biological synapses. Assembled into random networks, ...

  Citation × Citation Citation Abstract Copy Title: Computational Capacity and Energy Consumption of Complex Resistive Switch Networks Author: Bürger, Jens, Goudarzi, Alireza, Stefanovic, Darko, Teuscher, Christof Year: 2015 Resistive switches are a class of emerging nanoelectronics devices that exhibit a wide variety of switching characteristics closely resembling behaviors of biological synapses. Assembled into random networks, such resistive switches produce emerging behaviors far more complex than that of individual devices. This was previously demonstrated in simulations that exploit information processing within these random networks to solve tasks that require nonlinear computation as well as memory. Physical assemblies of such networks manifest complex spatial structures and basic processing capabilities often related to biologically-inspired computing. We model and simulate random resistive switch networks and analyze their computational capacities. We provide a detailed discussion of the relevant design parameters and establish the link to the physical assemblies by relating the modeling parameters to physical parameters. More globally connected networks and an increased network switching activity are means to increase the computational capacity linearly at the expense of exponentially growing energy consumption. We discuss a new modular approach that exhibits higher computational capacities and energy consumption growing linearly with the number of networks used. The results show how to optimize the trade-off between computational capacity and energy efficiency and are relevant for the design and fabrication of novel computing architectures that harness random assemblies of emerging nanodevices. Title: Computational Capacity and Energy Consumption of Complex Resistive Switch Networks Author: Bürger, Jens, Goudarzi, Alireza, Stefanovic, Darko, Teuscher, Christof Year: 2015 Resistive switches are a class of emerging nanoelectronics devices that exhibit a wide variety of switching characteristics closely resembling behaviors of biological synapses. Assembled into random networks, such resistive switches produce emerging behaviors far more complex than that of individual devices. This was previously demonstrated in simulations that exploit information processing within these random networks to solve tasks that require nonlinear computation as well as memory. Physical assemblies of such networks manifest complex spatial structures and basic processing capabilities often related to biologically-inspired computing. We model and simulate random resistive switch networks and analyze their computational capacities. We provide a detailed discussion of the relevant design parameters and establish the link to the physical assemblies by relating the modeling parameters to physical parameters. More globally connected networks and an increased network switching activity are means to increase the computational capacity linearly at the expense of exponentially growing energy consumption. We discuss a new modular approach that exhibits higher computational capacities and energy consumption growing linearly with the number of networks used. The results show how to optimize the trade-off between computational capacity and energy efficiency and are relevant for the design and fabrication of novel computing architectures that harness random assemblies of emerging nanodevices. Close

• 19. [Article] Temporal Variation in Nutrient Uptake Capacity by Intact Roots of Mature Loblolly Pine

  Nutrient uptake is generally thought to exhibit a simple seasonal pattern, but few studies have measured temporal variation of nutrient uptake capacity in mature trees. We measured net uptake capacity ...

  Citation × Citation Citation Abstract Copy Title: Temporal Variation in Nutrient Uptake Capacity by Intact Roots of Mature Loblolly Pine Author: Lucash, Melissa S., Joslin, J. Devereux, Yanai, Ruth D. Year: 2005 Nutrient uptake is generally thought to exhibit a simple seasonal pattern, but few studies have measured temporal variation of nutrient uptake capacity in mature trees. We measured net uptake capacity of K, NH+ 4, NO 3 −, Mg and Ca across a range of solution concentrations by roots of mature loblolly pine at Calhoun Experimental Forest in October 2001, July 2001, and April 2002. Uptake capacity was generally lowest in July; rates in October were similar to those in April. Across a range of concentrations, antecedent nutrient solution concentrations affected the temporal patterns in uptake in July but not in October or April. In July, uptake of NH+ 4, Mg and Ca was positively correlated with concentration when roots were exposed to successively lower concentrations, but negatively correlated with concentration when exposed to successively higher concentrations. In contrast, uptake in October was constant across the range of concentrations, while uptake increased with concentration in April. As in studies of other species, we found greater uptake of NH+ 4 than NO 3 −. Temporal patterns of uptake capacity are difficult to predict, and our results indicate that experimental conditions, such as experiment duration, antecedent root conditions and nutrient solution concentration, affect measured rates of nutrient uptake. Title: Temporal Variation in Nutrient Uptake Capacity by Intact Roots of Mature Loblolly Pine Author: Lucash, Melissa S., Joslin, J. Devereux, Yanai, Ruth D. Year: 2005 Nutrient uptake is generally thought to exhibit a simple seasonal pattern, but few studies have measured temporal variation of nutrient uptake capacity in mature trees. We measured net uptake capacity of K, NH+ 4, NO 3 −, Mg and Ca across a range of solution concentrations by roots of mature loblolly pine at Calhoun Experimental Forest in October 2001, July 2001, and April 2002. Uptake capacity was generally lowest in July; rates in October were similar to those in April. Across a range of concentrations, antecedent nutrient solution concentrations affected the temporal patterns in uptake in July but not in October or April. In July, uptake of NH+ 4, Mg and Ca was positively correlated with concentration when roots were exposed to successively lower concentrations, but negatively correlated with concentration when exposed to successively higher concentrations. In contrast, uptake in October was constant across the range of concentrations, while uptake increased with concentration in April. As in studies of other species, we found greater uptake of NH+ 4 than NO 3 −. Temporal patterns of uptake capacity are difficult to predict, and our results indicate that experimental conditions, such as experiment duration, antecedent root conditions and nutrient solution concentration, affect measured rates of nutrient uptake. Close

• 20. [Article] Multivalent Rechargeable Batteries

  Li+ ion batteries have been the mainstay of high energy storage devices that have revolutionized the operating life time of consumer electronic devices for the past two decades. However, there is a steady ...

  Citation × Citation Citation Abstract Copy Title: Multivalent Rechargeable Batteries Author: Padigi, Sudhaprasanna Kumar Year: 2015 Li+ ion batteries have been the mainstay of high energy storage devices that have revolutionized the operating life time of consumer electronic devices for the past two decades. However, there is a steady increase in demand for energy storage devices with the ability to store more energy and deliver them at high power at low cost, without comprising safety and lifetime. Li-ion batteries have had significant challenges in increasing the amount of stored energy without affecting the overall lifetime and the ability to deliver stored energy. In order to store and deliver more energy, more lithium ions need to be inserted and extracted from a given electrode (cathode or anode). Upon inserting a large number of Li ions, the crystal lattice of the materials undergo severe mechanical distortions, leading to un-desirable structural changes. This results in underutilization of theoretical energy storage capacities of the electrodes and early failure of the batteries owing to instabilities in the electrode materials. Unlike monovalent Li+ ions, multivalent rechargeable batteries offer a potential solution to the above problems. Multivalent cations, such as Ca2+, are doubly-ionized as opposed to Li+ which is a monovalent cation. The advantages of using Ca2+ ions instead of Li+ ions are multifold. Due to the doubly-ionized nature, only half the number of Ca2+ ions need to be inserted and extracted from a given electrode to store and deliver energy from a high capacity cathode as compared to Li+ ions. This reduces the probability of lattice distortion and un-desirable structural changes, further leading to increased utilization of high theoretical energy storage capacities of the electrodes (cathode and anode). The use of Ca2+ ions also helps in delivering twice the amount of current density as compared to Li+ ions due to its doubly ionized nature. In this work, a set of eight metal hexacyanoferrate compounds were synthesized using the following metal ions: Ba2+, Mn2+, Zn2+, Co2+, Fe3+, Al3+, Sn4+, Mo5+. The resulting metal hexacyanoferrate compounds were subjected to physical characterization using scanning electron microscope (SEM) and powder x-ray diffraction (XRD), to determine physical properties such as size, morphology, unit cell symmetry and unit cell parameters. This was followed by electrochemical characterization utilizing cyclic voltammetry and galvanic cycling, to determine the specific capacity and kinetics involved in the transport of Ca2+ ions to store charge. Optical characterization of the metal hexacyanoferrates using Fourier transform infrared (FTIR) spectroscopy, allowed for the identification of metal-nitrogen stretching frequency, which was used as a measure of the strength of the metal-nitrogen bond to understand the role of the above mentioned metal ions in electron density distribution across the unit cell of the metal hexacyanoferrates. The specific capacity utilization of the metal hexacyanoferrates, when compared to the electronegativity values (Xi) of the above mentioned metal ions, the σ- parameter, and the metal-nitrogen stretching frequency (v), revealed an empirical trend suggesting that the materials (FeHCF, CaCoHCF and CaZnHCF) that possessed intermediates values for the above mentioned parameters demonstrated high capacity utilization (≥50%). Based on these empirical trends, it is hypothesized that a uniform distribution of electron density around a unit cell, as reflected by intermediate values of the electronegativity (Xi) of the above mentioned metal ions, the σ-parameter and the metal-nitrogen stretching frequency (v), results in minimal electrostatic interactions between the intercalating cation and the host unit cell lattice. This results in relatively easy diffusion of the cations, leading to high specific capacity utilization for metal hexacyanoferrate cathodes. These parameters may be used to select high efficiency cathode materials for multivalent batteries. Title: Multivalent Rechargeable Batteries Author: Padigi, Sudhaprasanna Kumar Year: 2015 Li+ ion batteries have been the mainstay of high energy storage devices that have revolutionized the operating life time of consumer electronic devices for the past two decades. However, there is a steady increase in demand for energy storage devices with the ability to store more energy and deliver them at high power at low cost, without comprising safety and lifetime. Li-ion batteries have had significant challenges in increasing the amount of stored energy without affecting the overall lifetime and the ability to deliver stored energy. In order to store and deliver more energy, more lithium ions need to be inserted and extracted from a given electrode (cathode or anode). Upon inserting a large number of Li ions, the crystal lattice of the materials undergo severe mechanical distortions, leading to un-desirable structural changes. This results in underutilization of theoretical energy storage capacities of the electrodes and early failure of the batteries owing to instabilities in the electrode materials. Unlike monovalent Li+ ions, multivalent rechargeable batteries offer a potential solution to the above problems. Multivalent cations, such as Ca2+, are doubly-ionized as opposed to Li+ which is a monovalent cation. The advantages of using Ca2+ ions instead of Li+ ions are multifold. Due to the doubly-ionized nature, only half the number of Ca2+ ions need to be inserted and extracted from a given electrode to store and deliver energy from a high capacity cathode as compared to Li+ ions. This reduces the probability of lattice distortion and un-desirable structural changes, further leading to increased utilization of high theoretical energy storage capacities of the electrodes (cathode and anode). The use of Ca2+ ions also helps in delivering twice the amount of current density as compared to Li+ ions due to its doubly ionized nature. In this work, a set of eight metal hexacyanoferrate compounds were synthesized using the following metal ions: Ba2+, Mn2+, Zn2+, Co2+, Fe3+, Al3+, Sn4+, Mo5+. The resulting metal hexacyanoferrate compounds were subjected to physical characterization using scanning electron microscope (SEM) and powder x-ray diffraction (XRD), to determine physical properties such as size, morphology, unit cell symmetry and unit cell parameters. This was followed by electrochemical characterization utilizing cyclic voltammetry and galvanic cycling, to determine the specific capacity and kinetics involved in the transport of Ca2+ ions to store charge. Optical characterization of the metal hexacyanoferrates using Fourier transform infrared (FTIR) spectroscopy, allowed for the identification of metal-nitrogen stretching frequency, which was used as a measure of the strength of the metal-nitrogen bond to understand the role of the above mentioned metal ions in electron density distribution across the unit cell of the metal hexacyanoferrates. The specific capacity utilization of the metal hexacyanoferrates, when compared to the electronegativity values (Xi) of the above mentioned metal ions, the σ- parameter, and the metal-nitrogen stretching frequency (v), revealed an empirical trend suggesting that the materials (FeHCF, CaCoHCF and CaZnHCF) that possessed intermediates values for the above mentioned parameters demonstrated high capacity utilization (≥50%). Based on these empirical trends, it is hypothesized that a uniform distribution of electron density around a unit cell, as reflected by intermediate values of the electronegativity (Xi) of the above mentioned metal ions, the σ-parameter and the metal-nitrogen stretching frequency (v), results in minimal electrostatic interactions between the intercalating cation and the host unit cell lattice. This results in relatively easy diffusion of the cations, leading to high specific capacity utilization for metal hexacyanoferrate cathodes. These parameters may be used to select high efficiency cathode materials for multivalent batteries. Close