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Zhou, Wei, Haoran Li, Shiya Wen, Lijuan Xie, Ting Wang, Yongzhong Tian, and Wenping Yu. "Simulation of Soil Organic Carbon Content Based on Laboratory Spectrum in the Three-Rivers Source Region of China." Remote Sensing 14, no. 6 (March 21, 2022): 1521. http://dx.doi.org/10.3390/rs14061521.
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Soil organic carbon (SOC) changes affect the land carbon cycle and are also closely related to climate change. Visible-near infrared spectroscopy (Vis-NIRS) has proven to be an effective tool in predicting soil properties. Spectral transformations are necessary to reduce noise and ensemble learning methods can improve the estimation accuracy of SOC. Yet, it is still unclear which is the optimal ensemble learning method exploiting the results of spectral transformations to accurately simulate SOC content changes in the Three-Rivers Source Region of China. In this study, 272 soil samples were collected and used to build the Vis-NIRS simulation models for SOC content. The ensemble learning was conducted by the building of stack models. Sixteen combinations were produced by eight spectral transformations (S-G, LR, MSC, CR, FD, LRFD, MSCFD and CRFD) and two machine learning models of RF and XGBoost. Then, the prediction results of these 16 combinations were used to build the first-step stack models (Stack1, Stack2, Stack3). The next-step stack models (Stack4, Stack5, Stack6) were then made after the input variables were optimized based on the threshold of the feature importance of the first-step stack models (importance > 0.05). The results in this study showed that the stack models method obtained higher accuracy than the single model and transformations method. Among the six stack models, Stack 6 (5 selected combinations + XGBoost) showed the best simulation performance (RMSE = 7.3511, R2 = 0.8963, and RPD = 3.0139, RPIQ = 3.339), and obtained higher accuracy than Stack3 (16 combinations + XGBoost). Overall, our results suggested that the ensemble learning of spectral transformations and simulation models can improve the estimation accuracy of the SOC content. This study can provide useful suggestions for the high-precision estimation of SOC in the alpine ecosystem.
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Xu, Yine, Qi Yu, Yan Zhang, and Weichun Ma. "Numerical Study on the Plume Behavior of Multiple Stacks of Container Ships." Atmosphere 12, no. 5 (May 5, 2021): 600. http://dx.doi.org/10.3390/atmos12050600.
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This paper showed different plume behaviors of exhausts from different number of stacks of the container ship, using CFD code PHOENICS version 6.0. The plume behavior was quantitatively analyzed by mass fraction of the pollutant in the exhaust and plume heights. Three simplified typical configurations were constructed by CFD according to the investigation of container ships. The configurations included a single main stack (BL1), one main stack and multiple auxiliary stacks (BL2), and two main stacks and multiple auxiliary stacks (BL3). All the main stacks had the same emission characteristics, and all the auxiliary stacks had the same emission characteristics. The results show that the transmission and diffusion characteristics of the exhaust from multiple stacks are different from those of the exhaust from a single stack. In BL2 and BL3 simulations, the maximum mass fraction of SO2 in the exhaust (C1max) of multiple stack emissions was approximately 329% and 269% higher than that of single stack emissions over the main stack, respectively, and the plume height of multiple stack emissions is higher than that of single stack emissions. In BL2 and BL3 simulations, the plume height of multiple stack emissions was 41% and 75% higher than that of single stack emissions, respectively. The increase of C1max, due to multiple stack emissions, is weakened as the distance of the stacks increase. The difference in plume behavior between multiple stack emissions and single stack emissions is of great significance for air quality management and pollution control in port areas.
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Muthusundari, S., V. Devi, S. Sharath Kumar, D. Sudhish Reddy, Kannedari Uday Kiran, Pulimi Hanith Sai Kumar Reddy, Gosani Bhanu Sai Priya, and Katragunta Yagna Priya. "Stack sort – a new approach with sorting network and a buffer." Salud, Ciencia y Tecnología - Serie de Conferencias 3 (June 14, 2024): 898. http://dx.doi.org/10.56294/sctconf2024898.
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Knuth introduced the problem of stack sorting. Stack sorting was implemented by t stacks in series. In this paper, we propose a new dimension to stack sorting problem by introducing a stack with sorting network and a petty buffer. Instead of using t stacks in series, it helps to improve the performance by avoiding shuffles the stack. The basic idea behind in this paper is to perform a stack sorting with a single stack, and to achieve greater performance. In this novel approach, 2 bit buffer is compared to stack and insert the element into stack in order to avoid multiple stack. The result shows the time complexity of the proposed algorithm is O (n).
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Bursztyn, Henrique, Francesco Noseda, and Chenchang Zhu. "Principal Actions of Stacky Lie Groupoids." International Mathematics Research Notices 2020, no. 16 (July 5, 2018): 5055–125. http://dx.doi.org/10.1093/imrn/rny142.
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Abstract Stacky Lie groupoids are generalizations of Lie groupoids in which the “space of arrows” of the groupoid is a differentiable stack. In this paper, we consider actions of stacky Lie groupoids on differentiable stacks and their associated quotients. We provide a characterization of principal actions of stacky Lie groupoids, that is, actions whose quotients are again differentiable stacks in such a way that the projection onto the quotient is a principal bundle. As an application, we extend the notion of Morita equivalence of Lie groupoids to the realm of stacky Lie groupoids, providing examples that naturally arise from non-integrable Lie algebroids.
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Kim, Hanki, Jiyeon Choi, Namjo Jeong, Yeon-Gil Jung, Haeun Kim, Donghyun Kim, and SeungCheol Yang. "Correlations between Properties of Pore-Filling Ion Exchange Membranes and Performance of a Reverse Electrodialysis Stack for High Power Density." Membranes 11, no. 8 (August 10, 2021): 609. http://dx.doi.org/10.3390/membranes11080609.
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The reverse electrodialysis (RED) stack-harnessing salinity gradient power mainly consists of ion exchange membranes (IEMs). Among the various types of IEMs used in RED stacks, pore-filling ion exchange membranes (PIEMs) have been considered promising IEMs to improve the power density of RED stacks. The compositions of PIEMs affect the electrical resistance and permselectivity of PIEMs; however, their effect on the performance of large RED stacks have not yet been considered. In this study, PIEMs of various compositions with respect to the RED stack were adopted to evaluate the performance of the RED stack according to stack size (electrode area: 5 × 5 cm2 vs. 15 × 15 cm2). By increasing the stack size, the gross power per membrane area decreased despite the increase in gross power on a single RED stack. The electrical resistance of the PIEMs was the most important factor for enhancing the power production of the RED stack. Moreover, power production was less sensitive to permselectivities over 90%. By increasing the RED stack size, the contributions of non-ohmic resistances were significantly increased. Thus, we determined that reducing the salinity gradients across PIEMs by ion transport increased the non-ohmic resistance of large RED stacks. These results will aid in designing pilot-scale RED stacks.
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Halpern-Leistner, Daniel, and Anatoly Preygel. "Mapping stacks and categorical notions of properness." Compositio Mathematica 159, no. 3 (March 2023): 530–89. http://dx.doi.org/10.1112/s0010437x22007667.
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One fundamental consequence of a scheme $X$ being proper is that the functor classifying maps from $X$ to any other suitably nice scheme or algebraic stack is representable by an algebraic stack. This result has been generalized by replacing $X$ with a proper algebraic stack. We show, however, that it also holds when $X$ is replaced by many examples of algebraic stacks which are not proper, including many global quotient stacks. This leads us to revisit the definition of properness for stacks. We introduce the notion of a formally proper morphism of stacks and study its properties. We develop methods for establishing formal properness in a large class of examples. Along the way, we prove strong $h$ -descent results which hold in the setting of derived algebraic geometry but not in classical algebraic geometry. Our main applications are algebraicity results for mapping stacks and the stack of coherent sheaves on a flat and formally proper stack.
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Toën, Bertrand. "Descente fidèlement plate pour les n-champs d’Artin." Compositio Mathematica 147, no. 5 (July 25, 2011): 1382–412. http://dx.doi.org/10.1112/s0010437x10005245.
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AbstractWe prove two flat descent results in the setting of Artin n-stacks. First of all, a stack for the etale topology which is an Artin n-stack (in the sense of Simpson and Toën–Vezzosi) is also a stack for the flat (fppf) topology. Moreover, an n-stack, for the fppf topology, which admits a flat (fppf) n-atlas is an Artin n-stack (i.e. possesses a smooth n-atlas). We deduce from these two results a comparison between etale and fppf cohomologies (with coefficients in non-smooth group schemes and also non-abelian). This work is written in the setting of the derived stacks of Toën and Vezzosi, and all of these results are therefore also valid for derived Artin n-stacks.
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Dombrovskis, Johanna, Victor Shokhen, Lisa Kylhammar, and Andreas Bodén. "(Invited) Optimized Conditioning and Performance of PEM Fuel Cell Stacks." ECS Meeting Abstracts MA2024-02, no. 46 (November 22, 2024): 3264. https://doi.org/10.1149/ma2024-02463264mtgabs.
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The fuel cell market is maturing, and the production volumes are increasing. In parallel, expectations on performance, lifetime and operational range for fuel cell stacks are growing. As fuel cell technology matures, more fuel cell stacks are used in real life applications instead of laboratory environment. These positive developments bring with them new challenges and opportunities to learn. Several of these challenges and their impact on stack design and validation will be discussed. The focus will be on optimization of useful stack power density, fuel cell stack conditioning, enlarging the LT-PEM fuel cell operation range and on durability testing. This talk addresses why conditioning and durability testing are closely connected and illustrates how this can impact stack platform and fuel cell development. In addition, the interactions between power density, stack integration and stack operational window are illustrated showing how each of these parameters could be optimized utilizing a current distribution plate and what trade-offs are relevant for optimized fuel cell stack and system performance. Powercell is active in various market segments and has developed stacks and stack components for ~20 years. The optimizations and trade-offs described hinge heavily on key PEM stack requirements which can be widely different in different PEM fuel cell market sectors, as illustrated by the emerging usage of fuel cells in aviation.
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Baid, Jayant, and Sapna Gupta. "COMPARATIVE ANALYSIS OF MERN, MEAN AND MEVN STACKS IN WEB DEVELOPMENT." INTERANTIONAL JOURNAL OF SCIENTIFIC RESEARCH IN ENGINEERING AND MANAGEMENT 08, no. 02 (February 8, 2024): 1–10. http://dx.doi.org/10.55041/ijsrem28539.
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Choosing a technology stack is a critical decision that affects how software projects progress in the ever- changing field of web development. Regarding web development, a technology stack is a set of tools, frameworks, and programming languages that are utilized in the construction of an application's front end and back end. In addition to making the development process easier, these stacks provide the groundwork for the finished product's performance, scalability, and maintainability. JavaScript-based stacks are becoming serious contenders as businesses and developers search for frameworks that provide efficiency, scalability, and flexibility. Starting with a thorough examination and comparison of three popular JavaScript stacks, this research paper examines MEAN (MongoDB, Express, Angular and Node.js), MERN (MongoDB, Express, React and Node.js) and MEVN (MongoDB, Express, Vue.js and Node.js). Keywords: Web Development, MERN Stack, MEAN Stack, MEVN Stack, ReactJS, AngularJS, VueJS
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Wu, Chien-Chang, and Tsung-Lin Chen. "Dynamic Modeling of a Parallel-Connected Solid Oxide Fuel Cell Stack System." Energies 13, no. 2 (January 20, 2020): 501. http://dx.doi.org/10.3390/en13020501.
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This study proposes novel simulation methods to model the power delivery function of a parallel-connected solid-oxide-fuel-cell stack system. The proposed methods are then used to investigate the possible thermal runaway induced by the performance mismatch between the employed stacks. A challenge in this modeling study is to achieve the same output voltage but different output current for each employed stack. Conventional fuel-cell models cannot be used, because they employ fuel flow rates and stack currents as the input variables. These two variables are unknown in the parallel-connected stack systems. The proposed method solves the aforementioned problems by integrating the fuel supply dynamics with the conventional stack models and then arranging them in a multiple-feedback-loop configuration for conducting simulations. The simulation results indicate that the proposed methods can model the transient response of the parallel-connected stack system. Moreover, for the dynamics of the power distribution, there exists an unstable positive feedback loop between employed stacks when the stack temperatures are low, and a stable negative feedback loop when the stack temperatures are high. A thermal runaway could be initiated when the dynamics of the stack temperature is slower than that of the current distribution.
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Shi, Jixin, Yue Yao, Ruiyu Zhang, Yuqing Wang, Junhua Fan, Yixiang Shi, Bo Liang, and Ningsheng Cai. "Experimental Study on High-Efficiency Microtubular Solid Oxide Fuel Cell Stacks Using Various Fuels." ECS Transactions 111, no. 6 (May 19, 2023): 839–49. http://dx.doi.org/10.1149/11106.0839ecst.
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Microtubular solid oxide fuel cell (mTSOFC) is a clean and low carbon emission power generation technology that has great prospects in the field of portable power generation. Improving the efficiency and broadening the variety of available fuels can significantly improve the performance of portable power generation devices based on mTSOFC. In this study, mTSOFC stack assembled by mounting modular sub-stacks in an array on a designed fuel/air distribution base were tested. By changing the connection of the current collection nodes, the influence of circuit connection modes on the overall output performance of the stack was studied. At a temperature of 700℃ and a fuel feed of hydrogen, the mTSOFC stack composed of 6 sub-stacks can achieve a maximum power of 353W. Fuel cascade utilization was realized by transferring the spent fuel gas from the upstream sub-stacks to the downstream sub-stacks. A maximum power generation efficiency of 45.67% was achieved in the two-cascade stack. The feasibility of using hydrogen, ammonia, propane and diesel as fuel for the mTSOFC stack has also been experimentally verified. A total continuous discharge time of 21h was achieved at an average power ≥ 190W under ammonia feeding conditions.
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Hou, Shuo, Xing Tan, Jincheng He, Xi Deng, Chen Xi, Guangyao Lu, and Huan He. "Dynamic similarity analysis for a piezo-electromechanical system." International Journal of Applied Electromagnetics and Mechanics 64, no. 1-4 (December 10, 2020): 103–10. http://dx.doi.org/10.3233/jae-209312.
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Most research about using piezoelectric stacks to suppress vibration of mechanical structures didn’t involve the similarity problem for the piezoelectric stacks. The goal of this paper is to investigate the dynamic similarity between a prototype piezo stack and a scaled up or down piezo stack, whilst discussing the feasibility of predicting the vibration of prototype structure which use the piezoelectric stacks for vibration control. To illustrate this problem concisely, a single-DOF system consists of a proof mass and a piezo stack shunted with a series RL circuit is considered. Firstly, the governing equation of such piezo-electromechanical system in frequency domain is derived. Next the dynamic similarity of prototype and model stack is analyzed by similitude theory. After that the scaling laws are derived. Finally, a numerical simulation and relative error analysis are given to demonstrate the scaling laws.
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Atig, Mohamed Faouzi, Benedikt Bollig, and Peter Habermehl. "Emptiness of Ordered Multi-Pushdown Automata is 2ETIME-Complete." International Journal of Foundations of Computer Science 28, no. 08 (December 2017): 945–75. http://dx.doi.org/10.1142/s0129054117500332.
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We consider ordered multi-pushdown automata, a multi-stack extension of pushdown automata that comes with a constraint on stack operations: a pop can only be performed on the first non-empty stack (which implies that we assume a linear ordering on the collection of stacks). We show that the emptiness problem for multi-pushdown automata is 2ETIME-complete. Containment in 2ETIME is shown by translating an automaton into a grammar for which we can check if the generated language is empty. The lower bound is established by simulating the behavior of an alternating Turing machine working in exponential space. We also compare ordered multi-pushdown automata with the model of bounded-phase (visibly) multi-stack pushdown automata, which do not impose an ordering on stacks, but restrict the number of alternations of pop operations on different stacks.
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Dronen, Blake, Aric Shorey, B. K. Wang, and Leon Tsai. "Production Proven, High Precision Temporary Bond/De-bond Process." International Symposium on Microelectronics 2013, no. 1 (January 1, 2013): 000861–65. http://dx.doi.org/10.4071/isom-2013-thp35.
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Wafer thinning represents a critical step in 2.5D and 3D-IC integration. Achieving low total thickness variation (TTV) of a bonded stack is essential since it directly impacts the TTV of the thinned device wafer. It is essential to understand and utilize appropriate processes and materials that provide precision bonded stacks prior to thinning operations in order to achieve high process yields. The 3M™ Wafer Support System and Corning's precision glass carrier wafers were used to produce bonded stacks. Leveraging metrology tools like the Flatmaster MSP-300 and low coherence interferometric probes allow for characterization of the TTV of each layer of a bonded stack and better understanding of the stack-up as well as how to minimize stack TTV. The ability to deliver stack TTV of < 2 um in a repeatable manner has been demonstrated.
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Ajay, Adithya, Aditya Yadav, and Akshoy Ranjan Paul. "Dispersion of Particulate Matters from Separated Plume Stacks using Discrete Phase Modelling." IOP Conference Series: Earth and Environmental Science 1279, no. 1 (December 1, 2023): 012024. http://dx.doi.org/10.1088/1755-1315/1279/1/012024.
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Abstract Dispersion of particulate matter from plume stacks of industries is crucial in analysing the extent of air pollution. Particulate matter is highly influenced by gravity causing it settle quickly. Dispersion of pollutants from dual plume stack separated by a certain distance is analysed here. Dual stack is effective in shielding the downstream plume causing it to spread vertically higher than single stack. PM10 particles are emitted along with gaseous pollutants from the stack in to the atmosphere having a temperature gradient of -0.2K/100 m. Particles from the stack disperse to higher distance from the ground when there is pollutant gas along with it. Furthermore, presence of discreet plumes causes splitting of the upstream one in horizontal direction causing the particles to spread more. Present study helps to monitor the spreading of particulate matter from plume stacks.
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Ma, Zhiwen, Ramki Venkataraman, and Mohammad Farooque. "Study of the Gas Flow Distribution and Heat Transfer for Externally Manifolded Fuel Cell Stack Module Using Computational Fluid Dynamics Method." Journal of Fuel Cell Science and Technology 1, no. 1 (June 28, 2004): 49–55. http://dx.doi.org/10.1115/1.1794155.
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Uniform gas flow distribution in a fuel cell system is desired to attain maximum power operation potential. Two types of manifold systems are often used in fuel cell stacks; they are internal manifold system and external manifold system. This paper presents the modeling approach using the Computational Fluid Dynamics (CFD) method in analyzing fluid flow and heat transfer for the external manifold fuel cell stacks and stack module design. Computational models based on a Megawatt carbonate fuel cell stack module have been developed for investigating the fuel and oxidant flow distributions through the external manifold systems. This paper presents the modeling approaches and flow and temperature distribution results for externally manifolded fuel cell stack and stack module.
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Calderón, Antonio José, Francisco José Vivas, Francisca Segura, and José Manuel Andújar. "Integration of a Multi-Stack Fuel Cell System in Microgrids: A Solution Based on Model Predictive Control." Energies 13, no. 18 (September 19, 2020): 4924. http://dx.doi.org/10.3390/en13184924.
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This paper proposes a multi-objective model predictive control (MPC) designed for the power management of a multi-stack fuel cell (FC) system integrated into a renewable sources-based microgrid. The main advantage of MPC is the fact that it allows the current timeslot to be optimized while taking future timeslots into account. The multi-objective function solves the problem related to the power dispatch at time that includes criteria to reduce the multi-stack FC degradation, operating and maintenance costs, as well as hydrogen consumption. Regarding the scientific literature, the novelty of this paper lies in the proposal of a generalized MPC controller for a multi-stack FC that can be used independently of the number of stacks that make it up. Although all the stacks that make up the modular FC system are identical, their levels of degradation, in general, will not be. Thus, over time, each stack can present a different behavior. Therefore, the power control strategy cannot be based on an equal distribution according to the nominal power of each stack. On the contrary, the control algorithm should take advantage of the characteristics of the multi-stack FC concept, distributing operation across all the stacks regarding their capacity to produce power/energy, and optimizing the overall performance.
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Miller, FC, ER Harper, and BJ Macauley. "Field examination of temperature and oxygen relationships in mushroom composting stacks dash consideration of stack oxygenation based on utilisation and supply." Australian Journal of Experimental Agriculture 29, no. 5 (1989): 741. http://dx.doi.org/10.1071/ea9890741.
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Temperature and oxygen concentration in Phase I composting stacks were investigated in the field. that both determine and are consequences of biological Investigations focused on various physical factors activity. Data indicate that oxygen concentrations in Phase I stacks are affected by convection, gaseous diffusion and utilisation rates, but that these rates vary significantly spatially and temporally. When stack temperatures exceed 60�C, biological rates of activity, and therefore oxygen uptake, decrease, allowing oxygen to penetrate well into the centres of stacks. While natural convection is commonly used to explain stack oxygenation, this is an over simplification that does not adequately describe stack oxygen concentrations.
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Zhao, Xiaobo, and Seunghun Jung. "Shunt Current Analysis of Vanadium Redox Flow Battery System with Multi-Stack Connections." ECS Meeting Abstracts MA2023-02, no. 65 (December 22, 2023): 3111. http://dx.doi.org/10.1149/ma2023-02653111mtgabs.
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Vanadium redox flow battery (VRFB) systems with multiple stacks due to long lifetime, low self-discharge, and flexible design, are commonly used in large-scale electrical energy storage applications In a VRFB system, pumps deliver positive and negative electrolytes to each stack through a piping system including channels and manifolds. However, the electrolyte flowing between cells through channels and manifolds and the electrolyte flowing between stacks through pipes are electrically conductive. Shunt currents are generated due to the voltage difference between the cells and between the stacks, which reduce the energy efficiency of the battery system. In particular, under different load connections, the shunt currents of a multi-stack VRFB system have different distributions and cause different impairments to the system efficiency. Therefore, it is important to predict the shunt currents of the multi-stack system under different load connections before the actual construction of the system. In this paper, a multi-stack VRFB system with 120 cells was explored by circuit-based modeling to evaluate the shunt currents according to the stack configuration such as serial, parallel, and mixed connections.Then, the Coulomb efficiencies (CEs) were investigated with operating currents at 36 and 54A. The results show that shunt currents are generally more significant at the center cell of a stack than at other cells under these stack configurations and exhibit a positive correlation with the battery state of charge (SOC), i.e., larger shunt currents increase with SOC. In addition, the CEs of the system are higher at 54A compared to those at 36A due to smaller shunt current losses regardless of the stack configurations. Furthermore, regardless of the operating current levels, the multi-stack system connected by parallel loads achieves the highest CEs compared to the series and mixed connected systems due to the absence of shunt current losses in the piping system. Figure 1
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Suo, Chun Guang, Wen Bin Zhang, and Shi Su. "Fabrication of Micro DMFC Stack Using MEMS Technology." Advanced Materials Research 690-693 (May 2013): 985–88. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.985.
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This paper presents two kinds of direct methanol fuel cell (μDMFC) stack in planar array. The silicon-based DMFC stack is designed in a flip-flop configuration using MEMS technology, and the stainless steel stack is fabricated using stamping technology. Compared to stainless steel stack, the flip-flop silicon-based stack may reduce the connection space and lower the contact resistance between the membrane electrode assembly and the plates. The electrical characterization of this μDMFC stack was carried out by tests. The experimental results showed the prototype was able to generate an open-circuit voltage of 2.7V and a maximum power density of 2.2mW/cm2 at room temperature, demonstrating the feasibility of this new configuration. Application of μDMFC stacks as portable power sources were demonstrated using small electric devices powered by this stack.
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Lang, Michael, Young-sang Lee, In-sung Lee, Patric Szabo, Jongsup Hong, Joonhoon Cho, and Rémi Costa. "Analysis of Degradation Phenomena of SOC Stacks Operated in Reversible SOFC / SOEC Cycling Mode." ECS Transactions 111, no. 6 (May 19, 2023): 181–93. http://dx.doi.org/10.1149/11106.0181ecst.
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The present paper focusses on the detailed analysis and discussion of degradation phenomena of two SOC stacks during galvanostatic steady-state SOFC and reversible SOFC/SOEC cycling operation. The stacks with ASCs of Elcogen (Estonia) were fabricated by the industrial project partner E&KOA (Daejeon, Korea) within the Korean-German project “Solid Oxide Reversible Fuel Cell / Electrolysis Stack” (SORFES). The first 10-cell stack was tested at DLR during 1400 h and the results were used to improve the second 6-cell stack, which was operated during 2800 h at E&KOA. For electrochemical characterization jV-curves and electrochemical impedance spectroscopy were measured. The results between galvanostatic steady-state operation and reversible SOFC/SOEC cycling are presented and compared. The degradation of the OCV, the power and the different resistances of the individual repeat units are presented and discussed. Moreover, the improvement of the stack components and of the operating conditions between the two SOC stacks are outlined.
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Degefa, Tolera G., Andrzej Wróbel, and Marek Płaczek. "Modelling and Study of the Effect of Geometrical Parameters of Piezoelectric Plate and Stack." Applied Sciences 11, no. 24 (December 14, 2021): 11872. http://dx.doi.org/10.3390/app112411872.
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The piezoelectric stack is employed as an actuator and a sensor in a variety of technical applications. The dynamic modelling of piezoelectric plates and stack is used to investigate and search for new applications in mechatronics systems that are based on various loading frequencies. Stacks are composed of series of the same size and whose plates feature the same material properties and are layered by dielectric sheets. This enables increased displacements to be achieved while freeing up more space. The major aim of this study was to investigate the feasibility of using differently modulated piezoelectric plates in a single stack. Mathematical modelling and the study of the characteristics of piezoelectric plates, as well as the stack, with respect to various geometrical parameters, enhances the utilization of the plate in mechatronics systems. The work focuses on the ability of piezoelectric stacks to generate complex vibration spectra comprising numerous frequencies. This is accomplished by utilizing different piezoelectric plates in the stack or by stimulating each plate with a distinct carrier frequency. The plate responses at a wide frequency of piezoelectric plates were investigated using several modeling environments and, finally, experimental findings were obtained. In addition to generating the hypothesis of triggering the plate in a single stack with a varied frequency spectrum, the experiment performed was employed for parameter identification. The experiment demonstrated that it is possible to increase the flexibility of systems by employing piezoelectric stacks as a mode of actuation and that piezo stacks can be used in systems that require precise actuation over a wide frequency range.
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Bhatti, Umar Nawaz, Salem Bashmal, Sikandar Khan, and Rached Ben-Mansour. "Numerical Modeling and Performance Evaluation of Standing Wave Thermoacoustic Refrigerators with a Multi-Layered Stack." Energies 13, no. 17 (August 24, 2020): 4360. http://dx.doi.org/10.3390/en13174360.
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Thermoacoustic refrigerators have huge potential to replace conventional refrigeration systems as an alternative clean refrigeration technology. These devices utilize conversion of acoustic power and heat energy to generate the desired cooling. The stack plays a pivotal role in the performance of Standing Wave Thermoacoustic Refrigerators (SWTARs), as the heat transfer takes place across it. Performance of stacks can be significantly improved by making an arrangement of different materials inside the stack, resulting in anisotropic thermal properties along the length. In the present numerical study, the effect of multi-layered stack on the refrigeration performance of a SWTAR has been evaluated in terms of temperature drop across the stack, acoustic power consumed and device Coefficient of Performance (COP). Two different aspects of multi-layered stack, namely, different material combinations and different lengths of stacked layers, have been investigated. The combinations of four stack materials and length ratios have been investigated. The numerical results showed that multi-layered stacks produce lower refrigeration temperatures, consume less energy and have higher COP value than their homogeneous counterparts. Among all the material combinations of multi-layered stack investigated, stacks composed of a material layer with low thermal conductivity at the ends, i.e., RVC, produced the best performance with an increase of 26.14% in temperature drop value, reduction in the acoustic power consumption by 4.55% and COP enhancement of 5.12%. The results also showed that, for a constant overall length, an increase in length of side stacked material layer results in an increase in values of both temperature drop and COP.
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Zou, Changwei, Xudong Wang, Yaoqing Gao, and Jingling Xue. "Buddy Stacks: Protecting Return Addresses with Efficient Thread-Local Storage and Runtime Re-Randomization." ACM Transactions on Software Engineering and Methodology 31, no. 2 (April 30, 2022): 1–37. http://dx.doi.org/10.1145/3494516.
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Shadow stacks play an important role in protecting return addresses to mitigate ROP attacks. Parallel shadow stacks, which shadow the call stack of each thread at the same constant offset for all threads, are known not to support multi-threading well. On the other hand, compact shadow stacks must maintain a separate shadow stack pointer in thread-local storage (TLS) , which can be implemented in terms of a register or the per-thread Thread-Control-Block (TCB) , suffering from poor compatibility in the former or high performance overhead in the latter. In addition, shadow stacks are vulnerable to information disclosure attacks. In this paper, we propose to mitigate ROP attacks for single- and multi-threaded server programs running on general-purpose computing systems by using a novel stack layout, called a buddy stack (referred to as Bustk ), that is highly performant, compatible with existing code, and provides meaningful security. These goals are met due to three novel design aspects in Bustk . First, Bustk places a parallel shadow stack just below a thread’s call stack (as each other’s buddies allocated together), avoiding the need to maintain a separate shadow stack pointer and making it now well-suited for multi-threading. Second, Bustk uses an efficient stack-based thread-local storage mechanism, denoted STK-TLS , to store thread-specific metadata in two TLS sections just below the shadow stack in dual redundancy (as each other’s buddies), so that both can be accessed and updated in a lightweight manner from the call stack pointer rsp alone. Finally, Bustk re-randomizes continuously (on the order of milliseconds) the return addresses on the shadow stack by using a new microsecond-level runtime re-randomization technique, denoted STK-MSR . This mechanism aims to obsolete leaked information, making it extremely unlikely for the attacker to hijack return addresses, particularly against a server program that sits often tens of milliseconds away from the attacker. Our evaluation using web servers, Nginx and Apache Httpd , shows that Bustk works well in terms of performance, compatibility, and security provided, with its parallel shadow stacks incurring acceptable memory overhead for real-world applications and its STK-TLS mechanism costing only two pages per thread. In particular, Bustk can protect the Nginx and Apache servers with an adaptive 1-ms re-randomization policy (without observable overheads when IO is intensive, with about 17,000 requests per second). In addition, we have also evaluated Bustk using other non-server applications, Firefox , Python , LLVM , JDK and SPEC CPU2006 , to demonstrate further the same degree of performance and compatibility provided, but the protection provided for, say, browsers, is weaker (since network-access delays can no longer be assumed).
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Lang, Michael, Young-sang Lee, In-sung Lee, Patric Szabo, Jongsup Hong, Joonhoon Cho, and Rémi Costa. "Analysis of Degradation Phenomena of SOC Stacks Operated in Reversible SOFC / SOEC Cycling Mode." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 29. http://dx.doi.org/10.1149/ma2023-015429mtgabs.
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The reversible SOFC/SOEC operation of solid oxide cell (SOC) stacks promise high overall electricity-to-electricity round-trip efficiencies and low storage costs. Although in recent years the degradation rates of SOFC and SOEC stacks in single mode long-term operation have been steadily decreased, the understanding of degradation mechanisms during reversible SOFC/SOEC operation remains an important and challenging issue. Therefore, the Korean-German project “Solid Oxide Reversible Fuel Cell / Electrolysis Stack” (SORFES) focuses on the development of the core component technology for a 1 kW reversible SOC stack in order to enhance the hydrogen productivity and its utilization. The primary goals are the improvement of the performance and the durability of SOC stacks during reversible SOFC/SOEC operation and the quantification and the qualification of the relevant degradation effects. The paper presents and compares the performance and degradation results of two SOC stacks which were operated mainly in galvanostatic steady-state SOFC mode and in reversible SOFC/SOEC cycling mode. The stacks with ASC cells of Elcogen (Estonia) were fabricated by the industrial project partner E&KOA (Daejeon, Korea). The reversible cycles consist of day/night switches between SOEC and SOFC, thus covering intermittent renewable electricity supply (e.g. of photovoltaics). The stacks were electrochemically characterized by jV-curves and electrochemical impedance spectroscopy (EIS). The first SOC stack with 10 cells was operated during 500 h in SOFC at constant current density followed by 500 h of operation under reversible SOFC/SOEC cycling conditions. The initial performance and homogeneity along the repeat units (RUs) of the stack in SOFC and SOEC at the beginning of operation are presented. In order to better understand the stack degradation, the results between reversible SOFC/SOEC cycling and galvanostatic steady-state SOFC operation are compared. The degradation, especially of the OCV, the power density and the area specific resistance (ASR) of the different RUs are analyzed and discussed. Moreover, the progression of the individual resistances, specifically of the ohmic-, the electrode polarization- and the gas concentration resistances of the RUs are evaluated and presented. The influence of temperature gradients and thermo-mechanical stresses during reversible exothermic (SOFC) and endothermic (SOEC) cycling are outlined and discussed. The results of the first stack test were used to improve the stack components and setup, e.g. the contacting and sealing of the cells in the stack and the protective coating on the interconnects. Moreover, the operating conditions during reversible SOFC/SOEC cycling were optimized. The second improved stack with 6 RUs was operated for 2800 h in galvanostatic steady-state SOFC mode and reversible SOFC/SOEC cycling mode with low degradation rate. The results of the present paper help to understand and improve the long-term stability of SOC stacks during reversible SOFC/SOEC cycling, thus promoting the SOC technology for renewable energy storage applications.
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Kajurek, Jakub, and Artur Rusowicz. "Experimental Investigation on the Thermoacoustic Effect in Easily Accessible Porous Materials." Energies 14, no. 1 (December 25, 2020): 83. http://dx.doi.org/10.3390/en14010083.
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Thermoacoustic devices are the systems which use acoustic power to transport heat through a stack in a resonance tube. The stack is one of the most important parts of the thermoacoustic systems. It can have different geometries, like parallel plates, circular pores, or pin arrays. However, the fabrication of stacks with regular geometries is sometimes impractical due to material and assembly costs. These problems can be solved by using stack fabricated with random and easily accessible porous materials. In this paper an experimental investigation on the thermoacoustic effect in easily accessible porous materials is presented. The measurements with the stacks were made in a standing wave device filled with air at atmospheric pressure. The reported results confirm that some of the materials with high porosity can be an alternative to a traditional stack geometries and materials.
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Babaie Rizvandi, Omid, and Robert Braun. "Utilizing Neural Networks for Optimizing the Performance of Solid Oxide Cell Stacks." ECS Meeting Abstracts MA2024-02, no. 48 (November 22, 2024): 3342. https://doi.org/10.1149/ma2024-02483342mtgabs.
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Solid oxide cells (SOCs) are one of the promising energy conversion devices due to their high efficiency and relevance to many commercial and industrial applications. Much development progress has been made in the last 10-years improving the scale-up, degradation, and commercialization outlook globally. Further commercialization of the SOCs necessitates a deeper understanding of their complex internal processes. Experimental methods, albeit valuable, are constrained by cost and time and often cannot capture intricate details like distributions of species, current density, and temperature. Therefore, numerical analyses are essential as they offer a deeper understanding of the complex phenomena within SOCs. Yet, high-fidelity modeling SOCs is computationally expensive as it includes a multitude of physical and chemical phenomena spanning various layers and length scales. Even at the single-cell and repeating unit levels, 3D simulations are computationally costly due to the intricate interplay of mass, momentum, species transport, charges, and heat. Cell-level models, while useful, cannot capture all of the thermophysical behavior of SOC stacks accurately, particularly along the height of the stack. Full-stack models, while more comprehensive, come with significant computational costs. A breakthrough in addressing this challenge comes through a multi-scale modeling approach, leveraging homogenization techniques to transform the layered complexity of SOC stacks into computationally tractable representations [1,2]. By replacing the layered domains of the stacks with equivalent mediums and calculating effective modeling variables, this approach makes the stack-scale simulations feasible on standard computational computers/workstations. Even with homogenized models, the optimization at the stack scale is not feasible due to prolonged run times and high computational demands. To address this challenge, this study employs parametric studies on stack-scale models to train a neural network. The trained neural network correlates stack outputs such as voltage, outflow temperatures, and fuel utilization with operational parameters like load current, inlet temperatures, flow rates, and inlet fuel compositions. The neural network is utilized to optimize the stack performance under various conditions while ensuring adherence to manufacturer-defined limits. For instance, the neural network can be used to optimize stack output power under fuel cell mode while avoiding overheating or exceeding maximum current densities. In essence, this work combines the detailed physics of multi-scale stack models with the efficiency of neural networks, paving the way for faster and more comprehensive optimization of SOC stacks. References [1] Navasa, M., Miao, X. Y., & Frandsen, H. L. (2019). A fully-homogenized multiphysics model for a reversible solid oxide cell stack. International Journal of Hydrogen Energy, 44(41), 23330-23347. [2] Rizvandi, O. B., Miao, X. Y., & Frandsen, H. L. (2021). Multi-scale modeling of degradation of full solid oxide fuel cell stacks. International Journal of Hydrogen Energy, 46, 27709-27730.
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Smolana, Mateusz, and Krzysztof Gromysz. "Effect of Eccentricity of Applied Force and Geometrical Imperfections on Stiffness of Stack of Cuboidal Steel Elements." Materials 13, no. 14 (July 16, 2020): 3174. http://dx.doi.org/10.3390/ma13143174.
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Experimental tests were performed on a stack of cuboidal steel elements and its mathematical model was developed. Each cuboidal element was made of rolled profiles. Such stacks are the part of temporary supports that can be used to eliminate deflections of buildings. Stacks were loaded eccentrically through the inaccurate position of a jack. Moreover, two types of geometrical imperfections could be noticed. They included inaccurate contact between the stack elements and initial relative displacements of profiles that formed cuboidal elements. A mathematical model was developed to describe deformations of the stack and its parameters were determined by analysing test results. The eccentricity of the applied force had a slight impact on the stack stiffness, which was considerably reduced by geometrical imperfections. The imperfection covering initial relative displacements of rolled profiles inside cuboidal elements had the greatest impact on the stiffness. It could cause even a 10-fold drop in the stack stiffness when compared with the theoretical stiffness resulting from the stiffness of the stack section, and the stiffness dropped by ca. 3.5 times when the imperfection included the inaccurate contact between the cuboidal elements. Finally, the occurrence of both types of geometrical imperfections generated the real stiffness more than ten times lower than the theoretical stiffness that did not take into account imperfections.
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Floerchinger, Gus, Chris Cadigan, Neal P. Sullivan, and Rob J. Braun. "Characterizing the Performance of kW-Scale Multi-Stack Solid Oxide Fuel Cell Modules through Modeling." ECS Meeting Abstracts MA2023-01, no. 54 (August 28, 2023): 125. http://dx.doi.org/10.1149/ma2023-0154125mtgabs.
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Commercial-scale SOFC systems are comprised of power modules that contain multiple SOFC stacks. In the last decade, there has been much work on individual SOFC stack development and SOFC systems at the commercial scale (100-1000 kWe). Development of these commercial systems often utilizes models of a single representative SOFC stack to simulate the system’s prime mover. In practice, however, these representative single-stack SOFC models fail to consider the effects that arise due to the reality of multi-stack power modules used to construct commercial scale systems. Effects such as flow maldistribution, inter-stack heat transfer, and area-specific resistance (ASR) variation between stack units within a single module will create deviations in performance from a single stack-based system simulation. In this presentation, we consider these thermofluidic effects and the associated performance deviations of a novel 30kWe SOFC multi-stack module using models in the gPROMS ModelBuilder environment and experimental test data. The model-predicted thermal and electrochemical performance of the multi-stack module is established from calibration and validation efforts that utilize full-scale test data from a unique pressurized test facility at Mines. In this presentation, we consider the effect of reactant gas flow maldistribution on stack and module performance characteristics. A model for fluid flow in branching manifolds is presented. The parameters in the fluid flow model are calibrated from high-fidelity computational fluid dynamic simulation results for both inlet and outlet reactant gas manifolds. Anode and cathode inlet gases affect the fuel utilization, operating voltage, and temperature for an individual stack. Deviations in these operating parameters among stacks are investigated for a range of flow maldistributions (±10% of stack design flow) to quantify their effect on performance. Additionally, we simulate module performance over the expected load operating envelope for given supply fuel and air manifold geometries. Simulated performance deviations are presented and discussed over the module’s envelope to quantify changes in module performance that arise from changes in maldistribution at various flowrates. The manifold under study in this case shows a maximum anode gas fluid maldistribution of 1.5% at the design flowrate. Stack performance characteristics such as voltage, ASR, power output, and degree of internal reforming, are highly dependent on operating temperature. Individual stack and module heat loss can affect performance. An inter-stack heat transfer model is presented and calibrated using single-stack experimental test results. The model is extended to multiple stack module configurations described above and is then exercised to evaluate the effect of insulation materials and inter-stack heat transfer on multi-stack module performance. This presentation will discuss modeling results and characterization of insulation properties. Simulation results indicate that deviations of up to 10°C in stack operating temperature can be reached which strongly affects the effective operating ASR of a given stack. The presentation concludes with a discussion of performance impacts due to combined thermofluidic deviations can have on module operation vs a single-stack modeling framework.
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Golani, Sadhana, Holger Bausinger, Andreas Mai, and Andre Weber. "Towards an Impedance-Based Analysis of SOFC-Stacks." ECS Transactions 111, no. 6 (May 19, 2023): 1689–97. http://dx.doi.org/10.1149/11106.1689ecst.
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This proceeding aims to understand the performance of SOFC stacks using impedance spectroscopy. For the stack analysis, gradients over the active cell area are averaged out, preventing access to local phenomena. Hence, to get better insight into the spatial distribution of losses, single cells with an active electrode area of 1 cm² are characterized at 850 °C based on EIS and DRT-analysis. To ensure an appropriate deconvolution of processes, symmetrical anode and cathode cells are also tested. Next to the ideally contacted cells, metallic interconnecting repeat units are analyzed to study the impact of contacting and gas supply in the stack. The effect of fuel utilization was also investigated by mimicking different locations in the stack. In this contribution, the complex impedance behavior of the stack based on polarization losses will be discussed. The paper also provides disentangled information often lost or averaged out in stacks.
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Linderoth, Søren, Peter Halvor Larsen, M. Mogensen, Peter V. Hendriksen, N. Christiansen, and H. Holm-Larsen. "Solid Oxide Fuel Cell (SOFC) Development in Denmark." Materials Science Forum 539-543 (March 2007): 1309–14. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1309.
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The SOFC technology under development at Risø National Laboratory (RISØ) and Topsoe Fuel Cell A/S (TOFC) is based on an integrated approach ranging from basic materials research on single component level over development of cell and stack manufacturing technology to system studies and modelling. The effort also comprises an extensive cell and stack testing program. Systems design, development and test is pursued by TOFC in collaboration with various partners. The standard cells are thin and robust with dimensions of 12 x 12 cm2 and cell stacks are based on internal manifolding. Production of cells is being up-scaled continuously. The durability of the standard stack design with standard cells has been tested for more than 13000 hours including nine full thermal cycles with an overall voltage degradation rate of about 1% per 1000 hours. Recently, the degradation rate has been significantly reduced by introduction of improved stack component materials. 75-cell stacks in the 1+ kW power range have been tested successfully. Stacks have been delivered in a pre-reduced state to partners and tested successfully in test systems with natural gas as fuel. The consortium of TOFC and RISØ has an extended program to develop the SOFC technology all the way to a marketable product. Stack and system modelling including cost optimisation analysis is used to develop multi kW stack modules for operation in the temperature range 700-850oC. To ensure the emergence of cost-competitive solutions, a special effort is focused on larger anode-supported cells as well as a new generation of SOFCs based on porous metal supports and new electrode and electrolyte materials. The SOFC program comprises development of next generation of cells and multi stack modules for operation at lower temperature with increased durability and mechanical robustness in order to ensure long-term competitiveness.
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Simon Araya, Samuel, Sobi Thomas, Andrej Lotrič, Simon Lennart Sahlin, Vincenzo Liso, and Søren Juhl Andreasen. "Effects of Impurities on Pre-Doped and Post-Doped Membranes for High Temperature PEM Fuel Cell Stacks." Energies 14, no. 11 (May 21, 2021): 2994. http://dx.doi.org/10.3390/en14112994.
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In this paper, we experimentally investigated two high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) stacks for their response to the presence of reformate impurities in an anode gas stream. The investigation was aimed at characterizing the effects of reformate impurities at the stack level, including in humidified conditions and identifying fault features for diagnosis purposes. Two HT-PEMFC stacks of 37 cells each with active areas of 165 cm2 were used with one stack containing a pre-doped membrane with a woven gas diffusion layer (GDL) and the other containing a post-doped membrane with non-woven GDL. Polarization curves and galvanostatic electrochemical impedance spectroscopy (EIS) were used for characterization. We found that both N2 dilution and impurities in the anode feed affected mainly the charge transfer losses, especially on the anode side. We also found that humidification alleviated the poisoning effects of the impurities in the stack with pre-doped membrane electrode assemblies (MEA) and woven GDL but had detrimental effects on the stack with post-doped MEAs and non-woven GDL. We demonstrated that pure and dry hydrogen operation at the end of the tests resulted in significant recovery of the performance losses due to impurities for both stacks even after the humidified reformate operation. This implies that there was only limited acid loss during the test period of around 150 h for each stack.
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Zhang, Xueping, Mingtao Wu, Liusheng Xiao, Hao Wang, Yingqi Liu, Dingrong Ou, and Jinliang Yuan. "Thermal Stress in Full-Size Solid Oxide Fuel Cell Stacks by Multi-Physics Modeling." Energies 17, no. 9 (April 25, 2024): 2025. http://dx.doi.org/10.3390/en17092025.
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Mechanical failures in the operating stacks of solid oxide fuel cells (SOFCs) are frequently related to thermal stresses generated by a temperature gradient and its variation. In this study, a computational fluid dynamics (CFD) model is developed and further applied in full-size SOFC stacks, which are fully coupled and implemented for analysis of heat flow electrochemical phenomena, aiming to predict thermal stress distribution. The primary object of the present investigation is to explore features and characteristics of the thermal stress influenced by electrochemical reactions and various transport processes within the stacks. It is revealed that the volume ratio of the higher thermal stress region differs nearly 30% for different stack flow configurations; the highest probability of potential failure appears in the cell cathodes; the more cells applied in the stack, the greater the difference in the predicted temperature/thermal stress between the cells; the counter-flow stack performs the best in terms of output power, but the predicted thermal stress is also higher; the cross-flow stack exhibits the lowest thermal stress and a lower output power; and although the temperature and thermal stress distributions are similar, the differences between the unit cells are bigger in the longer stacks than those predicted for shorter stacks. The findings from this study may provide a useful guide for assessing the thermal behavior and impact on SOFC performance.
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Tsviatkou, V. Yu. "LIFO-STACK SIZE DETERMINATION FOR GROWING OF THE IMAGE REGIONS." Doklady BGUIR 18, no. 2 (March 31, 2020): 45–52. http://dx.doi.org/10.35596/1729-7648-2020-18-2-45-52.
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This paper considers the problem of memory allocation for the organization of the LIFO-stack in the algorithm for image segmentation based on growing regions is considered. Segmentation divides the image into regions with identical or similar properties and is the most demanding process for the capacity of RAM. The cultivation of areas begins with the neighborhoods of pre-selected initial growth pixels and uses stacks to store the coordinates of adjacent pixels attached to the cultivated region. Stack loading is maximized when the segment size matches the size of the YX image. In the absence of an expression for the exact determination of the size of the stack, it is possible to guarantee the stable operation of the algorithm for growing regions, eliminating the overflow of the memory allocated for processing if the stack size is assumed equal to YX. However, this approach does not take into account the fact that filling the coordinate stacks is also accompanied by a selection of them, which makesthe stack size always smaller than YX. The article proposes an expression that allows one to increase the accuracy of determining the required size of the LIFO-stack for storing the coordinates of adjacent pixels depending on the image size. The expression takes into account the conditions of the maximum load of the LIFO-stack when: a) the segmentation of the square region with the initial growth pixel in the corner of this region is carried out; b) in the scan window, adjacent pixels are always selected in order with the first selectable pixel located in the corner of the scan window. Using the proposed expression to calculate the required capacity of the LIFO-stack under conditions of its maximum load in the image segmentation algorithm based on growing regions provides a 2-fold reduction in the number of LIFO-stack memory cells.
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Yasukata, Kenichi. "iip: An Integratable TCP/IP Stack." ACM SIGCOMM Computer Communication Review 54, no. 1 (January 30, 2024): 21–28. http://dx.doi.org/10.1145/3687230.3687233.
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This paper presents iip, an integratable TCP/IP stack, which aims to become a handy option for developers and researchers who wish to have a high-performance TCP/IP stack implementation for their projects. The problem that motivated us to newly develop iip is that existing performance-optimized TCP/IP stacks often incur tremendous integration complexity and existing portability-aware TCP/IP stacks have significant performance limitations. In this paper, we overhaul the responsibility boundary between a TCP/IP stack implementation and the code provided by developers, and introduce an API that enables iip to allow for easy integration and good performance simultaneously, then report performance numbers of iip along with insights on performance-critical factors.
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Smara, Anis, Thomas Reis, Vicente Climente-Alarcon, and Bartek A. Glowacki. "Magnetization reduction by varying normal field in stacks of composite superconductors in an electrical motor." European Physical Journal Applied Physics 92, no. 2 (November 2020): 20902. http://dx.doi.org/10.1051/epjap/2020200034.
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Trapped field magnets of superconducting stacks could be an alternative to conventional magnets in electrical machine applications. A conceptual design of an electrical motor using these stacks was proposed in [1,2]. Superconducting stacks offer many advantages; however, they can be demagnetized when exposed to the varying field present in electrical motors during operation. This varying field can be generated by salient magnetic circuit or generated from the armature winding as harmonics. To study this demagnetization effect, we carried out an experiment on a superconducting stack in an electrical machine, exposing it to different levels of varying cross and normal fields. The experimental measurements recorded a demagnetization of the stack. In this work, the analyses of the reduction of magnetization of the superconducting stack by an alternating normal field and the comparison of the results with experimental measurements in the electrical motor are presented.
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Shen, Wei, Hongtao Su, Jianhua Gao, Lei Fan, Gang Zhang, and Su Zhou. "A Multi-Objective Temperature Control Method for a Multi-Stack Fuel Cell System with Different Stacks Based on Model Predictive Control." Energies 18, no. 10 (May 9, 2025): 2443. https://doi.org/10.3390/en18102443.
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The multi-stack fuel cell system (MFCS) has advantages such as a wide range, long life, and high efficiency; however, its multiple heat sources impose higher requirements on the thermal management system, especially for different stacks. In order to control each stack temperature in an MFCS, the model predictive control (MPC) algorithm based on the backpropagation (BP) neural network is proposed. Firstly, dynamic characteristics have been obtained experimentally for selected PEMFC stacks of different powers. Based on experimental data, a parallel multi-stack fuel cell thermal management subsystem with different stack powers model is established and a system prediction model of the BP neural network is trained by applying the MFCS thermal management subsystem model simulation data. Then, the step response matrix of the system prediction model is obtained at typical operating conditions, and a dynamic matrix controller (DMC) is designed. Finally, a test operating condition is designed for simulation analysis. The results show that the DMC based on BP neural network can quickly and accurately control each stack temperature of the MFCS, while having the characteristics of small overshoot and short regulation time.
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Cubizolles, Geraud, Simon Alamome, Félix Bosio, Brigitte Gonzalez, Christian Tantolin, Lucas Champelovier, Sebastien Fantin, and Jerome Aicart. "Development of a Versatile and Reversible Multi-Stack Solid Oxide Cell System Towards Operation Strategies Optimization." ECS Transactions 111, no. 6 (May 19, 2023): 1677–88. http://dx.doi.org/10.1149/11106.1677ecst.
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Solid oxide cell technology is currently experiencing a rapid industrialization phase. To investigate operational strategy, CEA/LITEN has designed and constructed its first multi-stack reversible solid oxide cell (rSOC) module. While it is able to host four of CEA’s standard 25-cell stacks, the present work reports on preliminary validation results obtained in a 2-stack configuration. Thermal losses have been quantified and identified. While the hotbox is showing high performances, the overall losses increased twofold when taking into account pass-through piping and current connections. Module fluid distribution was verified to be homogeneous, and does not affect nominal stack operation. A durability test of more than 2 kh is presented. Over the first 1.1 kh, the stacks behavior was compared to that of a stack previously operated on a test bench. The remarkable similarities indicate adequate control of the module. Finally, a detailed analysis of the recorded efficiency was conducted.
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Bellasio, Roberto, and Roberto Bianconi. "Analysis of the Odor Levels at the Closest Receptors Depending on the Stack Terminal Types." Atmosphere 16, no. 2 (February 2, 2025): 169. https://doi.org/10.3390/atmos16020169.
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This paper presents the results of a numerical analysis for evaluating the effects of different stack terminal configurations on the odor levels estimated at the receptors located close to the plant. Stack terminals may be of different types, for example vertical unobstructed, vertical with rain cap, horizontal, gooseneck or with any slope with respect to the vertical. The comparison between CALPUFF and LAPMOD with vertical unobstructed stacks, rain capped stacks and different emission temperatures shows that the results are comparable, even though there is a tendency of LAPMOD to underpredict when vertical unobstructed stacks are used. A detailed numerical analysis has then been performed with the LAPMOD dispersion model, which adopts a numerical plume rise scheme capable to simulate releases with any orientation. Two different sites have been considered, both located in northern Italy: one with almost flat orography, and one with relatively complex orography. The results show that the choice of the stack terminal has important effects on the odor levels predicted at the closest receptors. The vertical unobstructed stack always has a smaller impact than all the other terminal types, particularly for low emission temperatures.
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Kim, Donghyuk, and Joon-Young Choi. "Development of a Common API for Multiple Ethernet Fieldbus Protocols in Embedded Slave Devices." Electronics 14, no. 3 (February 5, 2025): 613. https://doi.org/10.3390/electronics14030613.
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Slave devices in Ethernet-based fieldbus networks often require extensive reprogramming of applications and replacement of protocol stacks and Ethernet drivers whenever the fieldbus protocol needs to be changed. To address this challenge, we develop a common application programming interface (API) and stack interfaces that enable seamless protocol switching among EtherCAT, PROFINET, and EtherNet/IP without requiring protocol-specific code modifications. The real-time data exchange between the API and each protocol stack is realized in the stack interface by using the synchronization mechanism provided by FreeRTOS. The developed common API and stack interfaces facilitate the development of slave device applications that are universally compatible with multiple protocols, EtherCAT, PROFINET, and EtherNet/IP. Moreover, once a required protocol is selected in the integrated development environment (IDE) software before building the slave device firmware, the corresponding protocol stack and Ethernet drivers are automatically specified and the need to replace protocol stacks or Ethernet drivers is even eliminated when switching protocols. To validate the developed common API and stack interfaces, they were implemented on a slave device using TI’s TMDS243EVM board, and a fieldbus network was built by connecting the slave device to a master device executed by Beckhoff’s TwinCAT on a Windows PC. Experimental results confirmed the API’s functionality, reliability, and practical applicability in streamlining protocol management for Ethernet-based fieldbus networks.
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Kumar, M. Arul, Sivasambu Mahesh, and P. Venkitanarayanan. "A Rate-Independent 'Stack' Model of a Polycrystalline Aggregate." Materials Science Forum 702-703 (December 2011): 192–95. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.192.
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The 'stack' model of a rate-independent rigid-plastic polycrystalline material is developed. In the 'stack' model, stacks of N neighboring sub-grain domains collectively accommodate the imposed macroscopic deformation while enforcing the velocity and traction continuity condition with its neighbors. The developed 'stack' model is applied to simulate the two-dimensional polycrystalline aggregate under macroscopically imposed plane-strain tension. The effect of inter- and intra-grain interactions on qualitative and quantitative variations in the predicted macroscopic stress-strain response and texture evolution are presented. The diminishing trend of constraint on individual sub-grain domains and texturing rate with stack size N, and saturation for large N also given.
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Xu, Yu, Anton Kukolin, Daifen Chen, and Wei Yang. "Multiphysics Field Distribution Characteristics within the One-Cell Solid Oxide Fuel Cell Stack with Typical Interdigitated Flow Channels." Applied Sciences 9, no. 6 (March 20, 2019): 1190. http://dx.doi.org/10.3390/app9061190.
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Generally, the manufacturing technology of fuel cell units is considered to satisfy the current commercialization requirements. However, achieving a high-performance and durable stack design is still an obstacle in its commercialization. The solid oxide fuel cell (SOFC) stack is considered to have performance characteristics that are distinct from the proton exchange membrane fuel cell (PEMFC) stacks. Within the SOFC stack, vapor is produced on the anode side instead of the cathode side and high flow resistance within the fuel flow path is recommended. In this paper, a 3D multiphysics model for a one-cell SOFC stack with the interdigitated channels for fuel flow path and conventional paralleled line-type rib channels for air flow path is firstly developed to predict the multiphysics distribution details. The model consists of all the stack components and couples well the momentum, species, and energy conservation and the quasi-electrochemical equations. Through the developed model, we can get the working details within those SOFC stacks with the above interdigitated flow channel features, such as the fuel and air flow feeding qualities over the electrode surface, hydrogen and oxygen concentration distributions within the porous electrodes, temperature gradient distribution characteristics, and so on. The simulated result shows that the multiphysics field distribution characteristics within the SOFC and PEMFC stacks with interdigitated flow channels feature could be very different. The SOFC stack using the paralleled line-type rib channels for air flow path and adopting the interdigitated flow channels for the fuel flow path can be expected to have good collaborative performances in the multiphysics field. This design would have good potential application after being experimentally confirmed.
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Kraft, Juergen, Michael T. Y. Paul, and Michael Goetz. "(Invited) Automated Production of High Performance PEMFC Stacks and Components According to Automotive Requirements." ECS Meeting Abstracts MA2022-02, no. 45 (October 9, 2022): 1693. http://dx.doi.org/10.1149/ma2022-02451693mtgabs.
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EKPO Fuel Cell GmbH was founded in 2021 by two parent companies, ElringKlinger and Plastic Omnium, whom both are strong and established automotive suppliers with mass manufacturing capabilities and strategic approaches to hydrogen and the fuel cell businesses. The aim of EKPO is the development and production of proton exchange membrane fuel cell stack components and stack modules. Drawing from the experiences of the pilot automated production line since 2016, a fully optimized automated production, with improved production technologies and products, was developed by EKPO in 2021 to achieve an output capability of 10,000 stacks per year. The line was designed with a modular and scalable approach that allows flexibility as well as increased capacity by parallelization. The implementation is successful of producing EKPO’s various stack platforms while maintaining a high level of quality and production standard for the automotive industry. Since EKPO offers a wide range of products, the automated line can cover stack power ranges from 10 kW up to > 200 kW. As a prerequisite for excellent technical performance, in addition to function quality measures were set as key targets from the start of the development. EKPO has thus established consistent and stringent quality process flows and processes for all production steps. These measures include the early involvement of measurability and manufacturability assessment on all process and analysis steps on the different levels (i.e., components and stack). The feedback from each workflow can then continuously improve products, processes, and documentation regarding product specific codes standards and regulations (CSR). The accumulative knowledge from two decades of activity of fuel cell component and stack development enabled EKPO to establish a production range starting from cell and stack components (i.e., bipolar plates, sealings, and plastic end plate modules) to fuel cell stacks and modules produced by fully automated MEA and stack assembly and end-of-line testing. The automated production covers all processes from bipolar plate manufacturing and assembly, CCM and GDL roll good cutting, MEA-assembly, stacking, and the final compression and characterization of the fuel cell stack. The quality matrixes include inspecting performance key figures as well as quality and geometries of the stack and its components. The incoming materials are typically supplied as roll goods, (i.e., GDL, CCM, and metal coil) or as raw material (i.e., plastic granules). As the incoming materials and finished components are very sensitive to environmental conditions and particle contamination, the entire MEA processing and stack assembly process takes place in a cleanroom with controlled climate for maximum process stability and reliability. With a key approach of “design to manufacture” and deep understanding of stack technology and component requirements, EKPO is able to deliver two best in class stacks, namely the NM5 evo and NM12 single and twin platforms.
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Scheu, Max, Karlo Komorowski, Chen Shen, and Tim Salditt. "A stalk fluid forming above the transition from the lamellar to the rhombohedral phase of lipid membranes." European Biophysics Journal 50, no. 2 (February 15, 2021): 265–78. http://dx.doi.org/10.1007/s00249-020-01493-2.
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AbstractIn this work, we present evidence for the formation of transient stalks in aligned multilamellar stacks of lipid membranes. Just above the phase transition from the fluid ($$L_\alpha$$ L α ) lamellar phase to the rhombohedral phase (R), where lipid stalks crystallize on a super-lattice within the lipid bilayer stack, we observe a characteristic scattering pattern, which can be attributed to a correlated fluid of transient stalks. Excess (off-axis) diffuse scattering with a broad modulation around the position which later transforms to a sharp peak of the rhombohedral lattice, gives evidence for the stalk fluid forming as a pre-critical effect, reminiscent of critical phenomena in the vicinity of second-order phase transitions. Using high-resolution off-specular X-ray scattering and lineshape analysis we show that this pre-critical regime is accompanied by an anomalous elasticity behavior of the membrane stack, in particular an increase in inter-bilayer compressibility, i.e., a decrease in the compression modulus.
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Brysk, Henry, and Douglas W. McCowan. "A slant‐stack procedure for point‐source data." GEOPHYSICS 51, no. 7 (July 1986): 1370–86. http://dx.doi.org/10.1190/1.1442187.
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The proper implementation of the τ-p method for surface data excited by a point source requires a cylindrical slant stack. Usually the common (Cartesian) slant stack is computed instead as an approximation to the geometrically correct procedure. Here we describe a formulation of the cylindrical slant stack as a weighted sum of Cartesian slant stacks; our cylindrical slant stack is computationally efficient to perform. We show how, although the usefulness of the slant stack is most easily seen with Cartesian coordinates, it can also be used with Fourier‐Bessel transforms. An example of the method shows results computed from data recorded on the West Florida Shelf. Severe edge‐effect noise which overwhelms the Cartesian slant stack is attenuated by the cylindrical slant‐stacking. Applications of the cylindrical slant stack to other seismological calculations, such as Lamb’s problem, are also discussed. In particular, we prove that the plane‐wave reflection coefficients apply exactly in the τ-p domain; hence an amplitude‐versus‐offset analysis is unambiguous in that domain.
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Sharma, Harshit, Vaibhav Garg, Sakshi ., Pankhuri Kalra, and Dr Manjot Kaur Bhatia. "Why MERN Stack?" International Journal for Research in Applied Science and Engineering Technology 10, no. 12 (December 31, 2022): 521–27. http://dx.doi.org/10.22214/ijraset.2022.47927.
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Abstract: In the past, web development was primarily based on the LAMP stack (Linux, Apache, MySQL, PHP, or Perl) and Java-based applications (Java EE, Spring). However, these stacks are made up of different programming languages and can be difficult for a single developer to understand. Advances in web technology over the last few years have allowed developers to participate in both the front-end and back-end processes of web applications. The main goal of this thesis was to explore the basic components of the very popular MREN stack. The MERN stack, which stands for MongoDB, Express.js, React.js, and Node.js, allows developers to easily integrate web development in a single programming language called JavaScript.
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Pike, Jenna, Dennis Larsen, Tyler Hafen, Jeffrey Lingen, Becca Izatt, Michele Hollist, Abel Gomez, et al. "Reversible SOFC/SOEC System Development and Demonstration." ECS Transactions 111, no. 6 (May 19, 2023): 1629–38. http://dx.doi.org/10.1149/11106.1629ecst.
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The OxEon Energy team continues its 30+ year solid oxide fuel cell (SOFC) development history with the design, fabrication, and installation of two reversible solid oxide electrolysis (SOEC)/SOFC demonstration modules scheduled for installation and commissioning in 2023. The high temperature electrolysis (HTE) systems produce hydrogen through electrolysis using solid oxide cell (SOC) technology derived from OxEon’s heritage stack technology and advancements made during stack development for NASA’s Mars2020 mission. The demonstration units integrate reversible SOC stacks with an effective and reliable balance of plant (BOP) system. A 4-stack quad assembly forms the basis for a modular, scalable system. Thermal management includes pre-heaters within the hot section unit (HSU) enclosure and a feed path that takes advantage of the exotherm generated in SOFC mode. The system design applies mechanical compression to the stacks outside the HSU enclosure to minimize insulation envelope size and produce greater force on the stacks.
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ALDROVANDI, ETTORE, and A. EMIN TATAR. "Notes on weak units of group-like 1- and 2-stacks." Mathematical Proceedings of the Cambridge Philosophical Society 164, no. 2 (November 9, 2016): 205–20. http://dx.doi.org/10.1017/s0305004116000931.
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AbstractThe weak units of strict monoidal 1- and 2-categories are defined respectively in [15] and [14]. In this paper, we define them for group-like 1- and 2-stacks. We show that they form a contractible Picard 1- and 2-stack, respectively. We give their cohomological description which provides for these stacks a representation by complexes of sheaves of groups. Later, we extend the discussion to the monoidal case. We consider the (2-)substack of cancelable objects of a monoidal 1-(2-)stack. We observe that this (2-)substack is trivially group-like, its weak units are the same as the weak units of the monoidal 1-(2-)stack, and therefore we can recover the contractibility results in [15] and [14] by analysing it.
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de Haart, Ute, Felix Kunz, and Rüdiger-A. Eichel. "Investigation of the Stability of SOC Stacks By Thermo Cycles." ECS Meeting Abstracts MA2022-02, no. 50 (October 9, 2022): 2552. http://dx.doi.org/10.1149/ma2022-02502552mtgabs.
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In recent years different research institutes and companies have developed anode supported cells (ASCs) with an LSC ((La,Sr)CoO3δ) oxygen electrode for solid oxide cells (SOCs), which showed an improved performance in comparison to ASCs with an LSCF electrode. Until now, the SOC-stacks by Forschungszentrum Jülich GmbH (FZJ) used ASCs with LSCF on the oxygen side. To minimize undesired effects which might occur due to the inter-diffusion of the constituting cations between adjacent layers, the contact layer on the oxygen side was made of the same LSCF composition. One mayor concern accompanying the use of LSC layers in ASCs and stacks is the thermal expansion coefficient (TEC) of the LSC material, which is almost a factor two higher than the TECs of the other materials of the cells and in the stacks (La0.6Sr0.4CoO3: 20.5·10-6 K-1 [1], La0.6Sr0.4Co0.2Fe0.8O3: 17.5·10-6 K1 [1], 8mol% Y2O3 stabilized ZrO2 (8YSZ): 9.3·10-6 K-1 [2], 30vol% Ni – YSZ cermet: 11.6·10-6 K-1 [3], CroFer 22 APU: 11.6·10-6 K-1 [4]). This large difference may lead to cracking in the layers or in the worst case to delamination between the layers. To meet this concern and demonstrate the stability and robustness of ASCs with LSC on the oxygen side of SOC-stacks performance tests were done with three F-10 stacks by FZJ, each consisting of four repetitive units (RU). The first stack (stack#1) used ASCs with LSCF as electrode and contact layer on the oxygen side and was taken as reference. Then, replacing LSCF by LSC was performed step wise. First only the cells with LSCF were replaced by cells with LSC, leaving all other components of the stack the same, including the LSCF contact layer on the oxygen side (stack#2). In the second step also the contact layer on the oxygen side was manufactured from the same LSC composition (stack#3). Thereby, commercially available cells were used resulting in additional differences between stack#1 (30 µm oxygen electrode, 5 µm oxygen barrier, 10 µm electrolyte, 7 µm fuel electrode and 300 µm fuel electrode support layer) and stack#2 as well as stack#3 (30 µm oxygen electrode, 2 µm oxygen barrier, 3 µm electrolyte, 10 µm fuel electrode and 400 µm fuel electrode support layer). Each stack was characterized in fuel cell mode and investigated by thermo cycles. The performance enhancement of stack#2 due to the introduction of LSC electrodes can be reported. At an operating temperature of 700 °C with 20% humidified hydrogen as fuel, current densities well over 1.2 A/cm² could be obtained at a cell voltage of 700 mV. This is a substantial increase in performance compared to the reference stack, stack#1, with LSCF electrodes on the oxygen side for which only 0.7 A/cm² at 700 mV could be reached. An initial analysis of impedance spectra recorded showed that this improvement could be attributed a lower ohmic resistance, mainly due to the thinner electrolyte layer, and a lower polarization contribution of the ASCs with LSC electrode. After this initial characterization all three stacks were subjected to thermo cycles from the operating temperature of 700 °C down to 200 °C and backwards. After 21 initial thermo cycles both, stack#2 and stack#3 were subjected to even more severe thermo cycles down to below 100 °C and back to 700 °C. From OCV, IV and EIS measurements during each cycle the stability of all three stacks could be shown for up to 50 thermo cycles with voltage losses from 0.2 to 0.5 mV/cycle despite the introduction of LSC layers in two of these stacks. Compared to ASCs with LSCF electrodes on the oxygen side an enhancement in performance was achieved by using ASCs with LSC electrodes and LSC contact layers on the oxygen side in the FZJ F10-design. Also, the stability of performance was demonstrated for up to 50 thermo cycles despite the higher TEC of LSC compared to the other stack materials. References [1] H. Ullmann, N. Trofimenko, F. Tietz, D. Stöver, A. Ahmad-Khanlou, Correlation between thermal expansion and oxide ion transport in mixed conducting perovskite-type oxides for SOFC cathodes, Solid State Ionics 138(1) (2000) 79 – 90 [2] H. Hayashi, T. Saitou, N. Maruyama, H. Inaba, K. Kawamura, M. Mori, Thermal expansion coefficient of yttria stabilized zirconia for various yttria contents, Solid State Ionics 176(5 – 6) (2005) 613 – 619 [3] S. T. Aruna, M. Muthuraman, K. C. Patil, Synthesis and properties of Ni-YSZ cermet: anode material for solid oxide fuel cells, Solid State Ionics 111(1 – 2) (1998) 45 – 51 [4] VDM® Crofer 22 APU Datasheet: https://www.vdm-metals.com/fileadmin/user_upload/Downloads/ Data_Sheets/Data_Sheet_VDM_Crofer_22_APU.pdf Figure 1
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Harazin, J., and A. Wróbel. "Empirical analysis of piezoelectric stacks composed of plates with different parameters and excited with different frequencies." IOP Conference Series: Materials Science and Engineering 1239, no. 1 (June 1, 2022): 012008. http://dx.doi.org/10.1088/1757-899x/1239/1/012008.
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Abstract Piezoelectric materials offer an ability to exchange energy between electrical and mechanical systems with fair ease, by using the simple and inverse piezoelectric effect. Piezoelectric transceivers, sensors, microphones, actuators, or active acoustic noise cancellation devices are some of many applications for piezoelectric materials. Due to the natural ability of the material to convert electricity and mechanical strain, solutions based on piezoelectric materials are often compact and allow applications on micro scales. One of the forms of piezoelectric actuation involves the use of piezoelectric stacks. The stack is composed of multiple piezoelectric plates layered by thin dielectric sheets, with electrodes attached along the sides. The main aim of piezoelectric stacks is the increase in maximum displacement by multiplying the number of piezoelectric plates that make up the stack. Stacks are composed of plates with the same material properties and the same dimensions. This study aims to investigate the idea of composing piezoelectric stacks of plates that have separate control circuits inducing different carrier frequencies or plates with differing properties and dimensions, in search for new applications for piezoelectric stacks. The main point of interest is the investigation of the ability to use piezoelectric stacks to generate complex vibration spectrums composed of multiple frequencies, resulting from the use of different piezoelectric plates in the stack or different carrier frequencies that stimulate each plate. To achieve this, a stack composed of two piezoelectric plates, each controlled by its own circuit, will be measured by a laser vibrometer, to check the complexity of the output vibration pattern.