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1
Zhou, Wei, Haoran Li, Shiya Wen, Lijuan Xie, Ting Wang, Yongzhong Tian et 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 (21 mars 2022) : 1521. http://dx.doi.org/10.3390/rs14061521.
Texte intégralRésumé :
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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Wu, Chien-Chang, et Tsung-Lin Chen. « Dynamic Modeling of a Parallel-Connected Solid Oxide Fuel Cell Stack System ». Energies 13, no 2 (20 janvier 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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Raju, S. M. Taslim Uddin, Amlan Sarker, Apurba Das, Md Milon Islam, Mabrook S. Al-Rakhami, Atif M. Al-Amri, Tasniah Mohiuddin et Fahad R. Albogamy. « An Approach for Demand Forecasting in Steel Industries Using Ensemble Learning ». Complexity 2022 (25 février 2022) : 1–19. http://dx.doi.org/10.1155/2022/9928836.
Texte intégralRésumé :
This paper aims to introduce a robust framework for forecasting demand, including data preprocessing, data transformation and standardization, feature selection, cross-validation, and regression ensemble framework. Bagging (random forest regression (RFR)), boosting (gradient boosting regression (GBR) and extreme gradient boosting regression (XGBR)), and stacking (STACK) are employed as ensemble models. Different machine learning (ML) approaches, including support vector regression (SVR), extreme learning machine (ELM), and multilayer perceptron neural network (MLP), are adopted as reference models. In order to maximize the determination coefficient ( R 2 ) value and reduce the root mean square error (RMSE), hyperparameters are set using the grid search method. Using a steel industry dataset, all tests are carried out under identical experimental conditions. In this context, STACK1 (ELM + GBR + XGBR-SVR) and STACK2 (ELM + GBR + XGBR-LASSO) models provided better performance than other models. The highest accuracies of R2 of 0.97 and 0.97 are obtained using STACK1 and STACK2, respectively. Moreover, the rank according to performances is STACK1, STACK2, XGBR, GBR, RFR, MLP, ELM, and SVR. As it improves the performance of models and reduces the risk of decision-making, the ensemble method can be used to forecast the demand in a steel industry one month ahead.
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Ma, Zhiwen, Ramki Venkataraman et 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 (28 juin 2004) : 49–55. http://dx.doi.org/10.1115/1.1794155.
Texte intégralRésumé :
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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Akal, D., K. Kahveci et A. Cihan. « Mathematical Modelling of Drying of Rough Rice in Stacks ». Food Science and Technology International 13, no 6 (décembre 2007) : 437–45. http://dx.doi.org/10.1177/1082013207087814.
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In this study, drying behaviour of rough rice stacks up to 30 cm is simulated with several models. The suitability of models is determined by the statistical analysis by examining the values of correlation coefficient, standard deviation and mean squared deviation. The results showed that the best model to explain the drying characteristics of rough rice stack is the Midilli et al. model and the coefficients and exponent in the Midilli et al. model could be expressed as functions of drying temperatures and stack height. Statistical analyses also showed that among the models with two coefficients, that of Page, and among the models with three coefficients, that of Verma et al. and diffusion approach were acceptable models in expressing the drying behaviour of rough rice in stacks. Among the models considered here, the geometric model appeared to be the worst fit.
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Mulyazmi, Wan Ramli Wan Daud et Edy Herianto Majlan. « Design Models of Polymer Electrolyte Membrane Fuel Cell System ». Key Engineering Materials 447-448 (septembre 2010) : 554–58. http://dx.doi.org/10.4028/www.scientific.net/kem.447-448.554.
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One important aspect to develop fuel cell design is to use the concept of computational models. Mathematical modeling can be used to help research complex, estimates the optimal performance of fuel cells stack, compare several different processes, save costs and time in the investigation. This paper focuses on several reviews of research models to develop the system design of the Proton Exchange Membrane Fuel Cell (PEMFC). Purposes of this study are to determine the factors that affect system performance include: stack of PEMFC system, water management system and Supply of reactants to the PEMFC stack.
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FIORENZA, DOMENICO, CHRISTOPHER L. ROGERS et URS SCHREIBER. « A HIGHER CHERN–WEIL DERIVATION OF AKSZ σ-MODELS ». International Journal of Geometric Methods in Modern Physics 10, no 01 (15 novembre 2012) : 1250078. http://dx.doi.org/10.1142/s0219887812500788.
Texte intégralRésumé :
Chern–Weil theory provides for each invariant polynomial on a Lie algebra 𝔤 a map from 𝔤-connections to differential cocycles whose volume holonomy is the corresponding Chern–Simons theory action functional. Kotov and Strobl have observed that this naturally generalizes from Lie algebras to dg-manifolds and to dg-bundles and that the Chern–Simons action functional associated this way to an n-symplectic manifold is the action functional of the AKSZ σ-model whose target space is the given n-symplectic manifold (examples of this are the Poisson σ-model or the Courant σ-model, including ordinary Chern–Simons theory, or higher-dimensional Abelian Chern–Simons theory). Here we show how, within the framework of the higher Chern–Weil theory in smooth ∞-groupoids, this result can be naturally recovered and enhanced to a morphism of higher stacks, the same way as ordinary Chern–Simons theory is enhanced to a morphism from the stack of principal G-bundles with connections to the 3-stack of line 3-bundles with connections.
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Ibarra, Oscar H., et Ian McQuillan. « Generalizations of Checking Stack Automata : Characterizations and Hierarchies ». International Journal of Foundations of Computer Science 32, no 05 (23 avril 2021) : 481–508. http://dx.doi.org/10.1142/s0129054121410045.
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We examine different generalizations of checking stack automata by allowing multiple input heads and multiple stacks, and characterize their computing power in terms of two-way multi-head finite automata and space-bounded Turing machines. For various models, we obtain hierarchies in terms of their computing power. Our characterizations and hierarchies expand or tighten some previously known results. We also discuss some decidability questions and the space/time complexity of the models.
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Kobayashi, M., et M. H. MacDougall. « The stack growth function : cache line reference models ». IEEE Transactions on Computers 38, no 6 (juin 1989) : 798–805. http://dx.doi.org/10.1109/12.24288.
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Li, Yang, Xing Shen, Xiping Kou et Li Yu. « Design, experiment, and verification of a heating and insulation structure for the piezoelectric stack ». Journal of Intelligent Material Systems and Structures 31, no 5 (10 janvier 2020) : 719–36. http://dx.doi.org/10.1177/1045389x19898260.
Texte intégralRésumé :
In the low-temperature environment, temperature reduction affects the properties and actuation performance of the piezoelectric stack. To solve this problem, a practical and effective heating and insulation structure, based on the working characteristics of the piezoelectric stack, is proposed in this article. Thermal conductivity models of the piezoelectric stack under two heating modes—whole heating and local heating—are developed and validated by finite element simulation analysis. The heating and insulation structure has been built according to the theoretical model, and the experimental test is conducted to measure the temperature and property variation of the piezoelectric stack, as well as its actuation performance with ambient temperature drop. The experimental results show that the theoretical and simulation results are consistent with the experimental results, as the maximum temperature difference between them is 4.3°C, which indicates the correctness and accuracy of the theoretical and finite element models. Besides, the properties and the actuation performance are almost unchanged within the range from 10°C to −70°C, which verifies the effectiveness and feasibility of the heating and insulation structure. Consequently, this structure can be redesigned according to the principles proposed in this article, and widely used in protecting piezoelectric stacks of different sizes and low-temperature environments; the application range of the piezoelectric stack can also be extended to lower temperatures.
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Liegener, Christopher-Maria, Rung Shen Chen, Peter Otto et Janos Ladik. « Effects of hydration and stacking interactions on the electronic structure of DNA models ». Collection of Czechoslovak Chemical Communications 53, no 9 (1988) : 1946–52. http://dx.doi.org/10.1135/cccc19881946.
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The energy band structures of a cytosine, adenine, and guanine stack in the presence of water have been calculated by the ab initio crystal-orbital method. The surrounding water molecules have been simulated by arrays of point charges, using for their positions the results of previous Monte-Carlo calculations of the corresponding polynucleotides. Furthermore, the effects of internucleotide interactions have been studied on the basis of calculations on base dimer stacks in comparison to the corresponding dimers and monomers.
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Cheng, Hui, Yuan Li, Kai Fu Zhang et Bin Luo. « An Efficient Model for Trust Force Dynamic Analysis in Drilling of CFRP/AL Stack ». Applied Mechanics and Materials 249-250 (décembre 2012) : 263–69. http://dx.doi.org/10.4028/www.scientific.net/amm.249-250.263.
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CFRP/AL stacks are widely used in modern aircraft manufacturing industry. Thrust force is the most important element which will cause delamination in the drilling of stack. This paper developed a thrust force dynamic analysis model for drilling of CFRP/AL stack, by firstly, representing the drilling process into a five-stage model. Secondly, the dynamic thrust force is decomposed into two parts (sub models for CFRP and AL drilling). Thirdly, the thrust force components on both tool major cutting edge and chisel edge is developed according to the analysis on infinitesimal cutting unit in both sub models for CFRP and AL drilling. Lastly, several experiments are performed to compare the result of thrust force analysis, which proves that the purposed model can analyze the dynamic thrust force in drilling of CFRP well.
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ATIG, MOHAMED FAOUZI, K. NARAYAN KUMAR et PRAKASH SAIVASAN. « ADJACENT ORDERED MULTI-PUSHDOWN SYSTEMS ». International Journal of Foundations of Computer Science 25, no 08 (décembre 2014) : 1083–96. http://dx.doi.org/10.1142/s0129054114400255.
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Multi-pushdown systems are formal models of multi-threaded programs. As they are Turing powerful in their full generality, several decidable subclasses, constituting under-approximations of the original system, have been studied in the recent years. Ordered Multi-Pushdown Systems (OMPDSs) impose an order on the stacks and limit pop actions to the lowest non-empty stack. The control state reachability for OMPDSs is 2-ETIME-COMPLETE. We propose a restriction on OMPDSs, called Adjacent OMPDSs (AOMPDS), where values may be pushed only on the lowest non-empty stack or one of its two neighbours. We describe EXPTIME decision procedures for reachability and LTL model-checking and establish matching lower bounds. We demonstrate the utility of this model as an algorithmic tool via optimal reductions from other models.
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Wang, Rui, et Bo Liu. « Applicability Analysis of Pre-Stack Inversion in Carbonate Karst Reservoir ». Energies 15, no 15 (2 août 2022) : 5598. http://dx.doi.org/10.3390/en15155598.
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Although pre-stack inversion has been carried out on reservoir prediction, few studies have focused on the application of pre-stack for seismic inversion in fractured-cavity carbonate reservoirs. In carbonate rock, complicated combinations and fluid predictions in karst caves are remain unclear. Post-stack methods are commonly used to predict the position, size, and fillings of caves, but pre-stack inversion is seldom applied in carbonate karst reservoirs. This paper proposes a pre-stack inversion method for forward modeling data and oil survey seismic data, using both points to indicate the application of pre-stack inversion in karst caves. Considering influence of cave size, depth, and filler on prediction, three sets of models (different caves volume; different fillings velocity of caves; complicated combination of caves) are employed and inverted by pre-stack inversion. We analyze the pre-stack results to depict Ordovician oil bearing and characterize caves. Geological model parameters came from actual data of the Tahe oilfield, and seismic data were synthesized from geological models based on full-wave equation forward simulation. Moreover, a case study of pre-stack inversion from the Tahe area was employed. The study shows that, from both the forward modeling and the oil seismic data points of view, pre-stack inversion is applicable to carbonate karst reservoirs.
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Kokorelis, Christos. « Sterile neutrino from D-brane models ». Journal of Physics : Conference Series 2375, no 1 (1 novembre 2022) : 012013. http://dx.doi.org/10.1088/1742-6596/2375/1/012013.
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Abstract We discuss the appearance of sterile neutrino in D-brane models. In the simplest case, the sterile neutrino (SN) appears from a 5-stack intersecting D6-brane model with a gauged baryon number. SM is mixed with a single generation of left handed active neutrinos and a right handed neutrino.
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Takei, Kenta, Wataru Kitagawa, Takaharu Takeshita et Yoshio Fujimura. « Analysis of a Serial/Parallel Type of Electromagnetic Actuator ». Sensors 20, no 10 (12 mai 2020) : 2762. http://dx.doi.org/10.3390/s20102762.
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This paper describes the design and analysis of a small-sized and high thrust electromagnetic actuator. The proposed actuator is supposed to be used for application control of the hotmelt adhesive. The hotmelt has different characteristics for each material and the electromagnetic actuator is required variable characteristics. However, the problem seems to lie in the fact that it is necessary to remake another mold again to change the characteristics of the conventional electromagnetic actuator. Therefore, this paper presents small-sized electromagnetic actuator called a basic model that can stack it in the axial direction or in the radial direction. As the analysis comparison at the same size, the characteristics of conventional two serial model which stack two basic models in the axial direction and proposed three serial models have been compared by three-dimensional finite element method. In the proposed model, characteristics have been improved by reducing the core volume and increasing the number of stacks in the basic model from the viewpoint of magnetic flux density. In addition, various electromagnetic actuators that stack basic models in the axial direction or in the radial direction have been analyzed. The analysis results have been clearly shown as characteristics mapping and it has indicated that the proposed electromagnetic actuator can be constructed easily by stacking the basic model.
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Milewski, Andrzej, Piotr Kluk, Witold Kardyś et Paweł Kogut. « Modelling and Designing of Ultrasonic Welding Systems ». Archives of Acoustics 40, no 1 (1 mars 2015) : 93–99. http://dx.doi.org/10.1515/aoa-2015-0011.
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Abstract This article presents the main stages and challenges in modelling and designing of modern ultrasonic welding and cutting systems. First, the key components of such a system, such as an ultrasonic stack (con- sisting of a high power ultrasonic transducer and a sonotrode) and a digitally controlled ultrasonic power supply with precise control of the output power, have been considered. Next, a concept of measurement system for verification and validation of mathematical models of ultrasonic stacks and its components has been presented. Finally, a method of ultrasonic stack e-diagnosis based on ultrasonic transducer electrical impedance measurement during welding and cutting process has been described
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Gharehgozli, Amir, Orkideh Gharehgozli et Kunpeng Li. « Mixed Integer Programming Models on Scheduling Automated Stacking Cranes ». International Journal of Business Analytics 8, no 4 (octobre 2021) : 11–33. http://dx.doi.org/10.4018/ijban.2021100102.
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Automated deep-sea container terminals are the main hubs to move millions of containers in today's global supply chains. Terminal operators often decouple the landside and waterside operations by stacking containers in stacks perpendicular to the quay. Traditionally, a single automated stacking cranes (ASC) is deployed at each stack to handle containers. A recent trend is to use new configurations with more than one crane to improve efficiency. A variety of new configurations have been implemented, such as twin, double, and triple ASCs. In this paper, the authors explore and review the mixed integer programming models that have been developed for the stacking operations of these new configurations. They further discuss how these models can be extended to contemplate diverse operational constraints including precedence constraints, interference constraints, and other objective functions.
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Rizzo, Riccardo, Seetharaman Parashuraman, Peppino Mirabelli, Claudia Puri, John Lucocq et Alberto Luini. « The dynamics of engineered resident proteins in the mammalian Golgi complex relies on cisternal maturation ». Journal of Cell Biology 201, no 7 (17 juin 2013) : 1027–36. http://dx.doi.org/10.1083/jcb.201211147.
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After leaving the endoplasmic reticulum, secretory proteins traverse several membranous transport compartments before reaching their destinations. How they move through the Golgi complex, a major secretory station composed of stacks of membranous cisternae, is a central yet unsettled issue in membrane biology. Two classes of mechanisms have been proposed. One is based on cargo-laden carriers hopping across stable cisternae and the other on “maturing” cisternae that carry cargo forward while progressing through the stack. A key difference between the two concerns the behavior of Golgi-resident proteins. Under stable cisternae models, Golgi residents remain in the same cisterna, whereas, according to cisternal maturation, Golgi residents recycle from distal to proximal cisternae via retrograde carriers in synchrony with cisternal progression. Here, we have engineered Golgi-resident constructs that can be polymerized at will to prevent their recycling via Golgi carriers. Maturation models predict the progress of such polymerized residents through the stack along with cargo, but stable cisternae models do not. The results support the cisternal maturation mechanism.
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Wiens, Kyle, et Peter Corcoran. « Repairability Smackdown : How Do the Latest Tablet Models Stack Up ? » IEEE Consumer Electronics Magazine 2, no 1 (janvier 2013) : 42–50. http://dx.doi.org/10.1109/mce.2012.2223155.
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Patil, Dr Ritesh, Vaishali Gentyal, Vaishnavi Mudaliar, Gauri Kanpurne et Devyani Ambi. « College Website Using MERN Stack ». International Journal for Research in Applied Science and Engineering Technology 10, no 4 (30 avril 2022) : 1096–98. http://dx.doi.org/10.22214/ijraset.2022.41450.
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Abstract: College Website is that the Growing significance of internet sites for various organizations is well known. Today, a well-planned digital strategy plays a significant role in an institution’s marketing strategies — especially considering younger generations’ growing dependence on technology. Put simply, a well-designed website will facilitate you’re engaging, current students, connect with prospective ones, and inform parents all without delay. It encompasses promoting school events, displaying course offerings, and showcasing campus life, etc. during this paper, we discuss the models submitted by our team, login, Admin panel, Instructor, Fees payment, and About us page. For these modules, we’ve used technical stacks React.js, Bootstrap (Front-end), Node.js, Express.js, and MongoDB for Database. Keywords: Full-Stack Development, College Website, Web Design, Web Development, Reactjs, Nodejs, Express, MongoDB.
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Faddeev, Nikita, Evgeny Anisimov, Maxim Belichenko, Alexandra Kuriganova et Nina Smirnova. « Investigation of the Ambient Temperature Influence on the PEMFC Characteristics : Modeling from a Single Cell to a Stack ». Processes 9, no 12 (24 novembre 2021) : 2117. http://dx.doi.org/10.3390/pr9122117.
Texte intégralRésumé :
Power supply systems based on air-cooled proton exchange membrane fuel cell (PEMFC) stacks are becoming more popular as power sources for mobile applications. We try to create a PEMFC model that allows for predicting the PEMFC operation in various climatic conditions. A total of two models were developed and used: the membrane electrode assemble (MEA) model and the PEMFC stack model. The developed MEA model allows to determine the influence of external factors (temperature) on the PEMFC power density. The data obtained using the developed model correlate with experimental data at low ambient temperatures (10–30 °C). The difference between the simulation and experimental data is less than 10%. However, the accuracy of the model during PEMFC operation at high (>30 °C) and negative ambient temperatures remains in doubt and requires improvement. The obtained data were integrated into the air-cooled PEMFC stack model. Data of the temperature fields distribution will help to manage the processes in the PEMFC stack. The maximum temperature is slightly above 60 °C, which corresponds to the optimal conditions for the operation of the stack. The temperature gradient across the longitudinal section is very low (<20 °C), which is a positive factor for the chemical reaction. However, the temperature gradient observed across the cross section of the PEMFC stack is 30 °C. The data obtained will help to optimize the mass-dimensional characteristics of air-cooled proton exchange membrane fuel cell and increase their performance. The synergetic effect between the MEA model and the PEMFC stack model can be successfully used in the selection of materials and the development of a thermoregulation system in the PEMFC stack.
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Vasyukov, Ivan. « Computer Models of Pem Fuel Cells for the Study of Transient Modes in Electrical Power Supply Complexes ». Известия высших учебных заведений. Электромеханика 64, no 3 (2021) : 60–67. http://dx.doi.org/10.17213/0136-3360-2021-3-60-67.
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Static and dynamic computer models of fuel cells are considered. A static model is determined that most ac-curately reproduces the current-voltage characteristic of a real fuel cell. A method for tuning it according to the experimental I - V characteristic by the least squares method is proposed. A method for its adjustment ac-cording to the experimental I - V characteristic by the method of gradient descent is proposed. A modified elec-trical equivalent circuit of a fuel cell has been developed, which simulates its dynamic response, taking into ac-count the damping effect of eddy currents during operation of a stack of fuel cells on a pulse voltage converter. A method is proposed for determining the parameters of the model from the experimental oscillograms of the current and voltage of the stack. A universal model of a stack of fuel cells in LTspice has been developed, which makes it possible to simulate a dynamic response and, if necessary, simulate a real static I – V characteristic of the stack.
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Hasegawa, Shigeki, Yoshihiro Ikogi, Sanghong Kim, Miho Kageyama et Motoaki Kawase. « Modeling of the dynamic behavior of an integrated fuel cell system including fuel cell stack, air system, hydrogen system, and cooling system ». ECS Transactions 109, no 9 (30 septembre 2022) : 15–70. http://dx.doi.org/10.1149/10909.0015ecst.
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1-dimentional (1-D) physical modeling methods of the dynamic behavior of an integrated fuel cell (FC) system are investigated, which consist of the models of the FC stack and subsystems of the air, hydrogen (H2), and cooling systems. To ensure numerical simulation of the entire FC system in life-long system operation (> 10 years) in acceptable calculation time, a proper model resolution is selected. The subsystem models are integrated with the FC stack model and controllers developed in our previous research to build a closed-loop simulator of an integrated FC system. It demonstrated that the impacts of the FC stack material properties on the overall FC system performance can be investigated by numerical simulation.
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Liang, Jingming, et Zefeng Wu. « Simulation and Optimization of Air-Cooled PEMFC Stack for Lightweight Hybrid Vehicle Application ». Mathematical Problems in Engineering 2015 (2015) : 1–11. http://dx.doi.org/10.1155/2015/738207.
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A model of 2 kW air-cooled proton exchange membrane fuel cell (PEMFC) stack has been built based upon the application of lightweight hybrid vehicle after analyzing the characteristics of heat transfer of the air-cooled stack. Different dissipating models of the air-cooled stack have been simulated and an optimal simulation model for air-cooled stack called convection heat transfer (CHT) model has been figured out by applying the computational fluid dynamics (CFD) software, based on which, the structure of the air-cooled stack has been optimized by adding irregular cooling fins at the end of the stack. According to the simulation result, the temperature of the stack has been equally distributed, reducing the cooling density and saving energy. Finally, the 2 kW hydrogen-air air-cooled PEMFC stack is manufactured and tested by comparing the simulation data which is to find out its operating regulations in order to further optimize its structure.
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Shen, Wei, Lei Fan, Zhirong Pan, Chunguang Chen, Ning Wang et Su Zhou. « Comparison of Different Topologies of Thermal Management Subsystems in Multi-Stack Fuel Cell Systems ». Energies 15, no 14 (10 juillet 2022) : 5030. http://dx.doi.org/10.3390/en15145030.
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The performance of a fuel cell stack is affected by the operating temperature of the stack. The thermal management subsystem of a multi-stack fuel cell system (MFCS) is particularly significant for the operating temperature control of each stack in the MFCS. To study the influence of different topologies of a MFCS thermal management subsystem, this paper proposes and establishes two different topologies. Firstly, the integrated topology is proposed. Secondly, seven component models, namely the mixer, thermostat, radiator, tank, pump, bypass value, and proton exchange membrane fuel cell stack temperature models, are described in detail. Finally, the performance of the two topologies of the MFCS thermal management subsystem under two working conditions, steady (200 A) and variable (China heavy-duty commercial test cycle, C-WTVC), is compared. Furthermore, there are two evaluating indicators, including the stability duration and deviation of the operating temperatures of the single stack in the MFCS. Results show that when the MFCS operates under steady working conditions, the integrated topology is superior in operating temperature control accuracy (ΔT<0.5 K), while the distributed topology is superior in the adjustment process (t ≤ 100 s). Moreover, when the MFCS operates under variable working conditions, the distributed topology is superior in operating temperature control accuracy.
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Guo, Hongrui, Wenli Zhang, Zishu Yu et Mingyu Chen. « Queueing-Theoretic Performance Analysis of a Low-Entropy Labeled Network Stack ». Intelligent Computing 2022 (5 septembre 2022) : 1–16. http://dx.doi.org/10.34133/2022/9863054.
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Theoretical modeling is a popular method for quantitative analysis and performance prediction of computer systems, including cloud systems. Low entropy cloud (i.e., low interference among workloads and low system jitter) is becoming a new trend, where the Labeled Network Stack (LNS) based server is a good case to gain orders of magnitude performance improvement compared to servers based on traditional network stacks. However, it is desirable to figure out 1) where the low tail latency and the low entropy of LNS mainly come from, compared with mTCP, a typical user-space network stack in academia, and Linux network stack, the mainstream network stack in industry, and 2) how much LNS can be further optimized. Therefore, we propose a queueing theory-based analytical method defining a bottleneck stage to simplify the quantitative analysis of tail latency. Facilitated by the analytical method, we establish models characterizing the change of processing speed in different stages for an LNS-based server, an mTCP-based server, and a Linux-based server, with bursty traffic as an example. Under such traffic, each network service stage's processing speed is obtained by non-intrusive basic tests to identify the slowest stage as the bottleneck according to traffic and system characteristics. Our models reveal that the full-datapath prioritized processing and the full-path zero-copy are primary sources of the low tail latency and the low entropy of the LNS-based server, with 0.8%-24.4% error for the 99th percentile latency. In addition, the model of the LNS-based server can give the best number of worker threads querying a database, improving 2.1×-3.5× in concurrency.
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Amirfazli, Amir, Saeed Asghari et Mehrdad Bazazzadeh. « An Analytical and Experimental Study on Coolant Flow and Temperature Distribution within Pem Fuel Cell Stack ». Applied Mechanics and Materials 390 (août 2013) : 301–5. http://dx.doi.org/10.4028/www.scientific.net/amm.390.301.
Texte intégralRésumé :
In the present study, a mathematical model is developed for investigation of coolant flow and temperature distribution within PEMFC stack. The model consists of two main sub models: (1) a coolant flow distribution model, which is used to determine the coolant mass flow distribution between different cooling flow fields of the fuel cell stack; and (2) a thermal model, which computes the coolant temperature increase along the flow field and also the temperature distribution within each cell of the stack. By using this model, optimized amount of effective parameters on stack coolant flow and temperature distribution could be obtained with respect to lower pressure drop along the manifolds and flow fields and more stack temperature uniformity. Test results of a 65-cells stack are presented to verify the simulation results.
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Zhang, Shidong, Steven B. Beale, Uwe Reimer, Robert T. Nishida, Martin Andersson, Jon G. Pharoah et Werner Lehnert. « Simple and Complex Polymer Electrolyte Fuel Cell Stack Models : A Comparison ». ECS Transactions 86, no 13 (23 juillet 2018) : 287–300. http://dx.doi.org/10.1149/08613.0287ecst.
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Napoli, G., M. Ferraro, F. Sergi, G. Brunaccini et V. Antonucci. « Data driven models for a PEM fuel cell stack performance prediction ». International Journal of Hydrogen Energy 38, no 26 (août 2013) : 11628–38. http://dx.doi.org/10.1016/j.ijhydene.2013.04.135.
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Yanbin, Huang, Yin Zhiqiang et Shi Yueyan. « Optical properties of multilayer stack models for solar selective absorbing surfaces ». Renewable Energy 8, no 1-4 (mai 1996) : 559–61. http://dx.doi.org/10.1016/0960-1481(96)88918-x.
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Ballesteros, Miguel, Chris Dyer, Yoav Goldberg et Noah A. Smith. « Greedy Transition-Based Dependency Parsing with Stack LSTMs ». Computational Linguistics 43, no 2 (juin 2017) : 311–47. http://dx.doi.org/10.1162/coli_a_00285.
Texte intégralRésumé :
We introduce a greedy transition-based parser that learns to represent parser states using recurrent neural networks. Our primary innovation that enables us to do this efficiently is a new control structure for sequential neural networks—the stack long short-term memory unit (LSTM). Like the conventional stack data structures used in transition-based parsers, elements can be pushed to or popped from the top of the stack in constant time, but, in addition, an LSTM maintains a continuous space embedding of the stack contents. Our model captures three facets of the parser's state: (i) unbounded look-ahead into the buffer of incoming words, (ii) the complete history of transition actions taken by the parser, and (iii) the complete contents of the stack of partially built tree fragments, including their internal structures. In addition, we compare two different word representations: (i) standard word vectors based on look-up tables and (ii) character-based models of words. Although standard word embedding models work well in all languages, the character-based models improve the handling of out-of-vocabulary words, particularly in morphologically rich languages. Finally, we discuss the use of dynamic oracles in training the parser. During training, dynamic oracles alternate between sampling parser states from the training data and from the model as it is being learned, making the model more robust to the kinds of errors that will be made at test time. Training our model with dynamic oracles yields a linear-time greedy parser with very competitive performance.
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Ryoo, Won Sun, et Jinsu Yoo. « Study on Key Parameters of Reverse Electrodialysis (RED) Cell-Stack Performance Based on Equivalent Circuit Model ». ECS Meeting Abstracts MA2022-02, no 50 (9 octobre 2022) : 2550. http://dx.doi.org/10.1149/ma2022-02502550mtgabs.
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Reverse electrodialysis (RED) is a direct process to convert salinity-gradient energy to electricity utilizing ion exchange membranes. The current density of a unit cell based on normal area of ion exchange membrane is well related to the membrane resistances, channel structure, flowrates and salinities of dilute and concentrate water feed. Alternate stacking of cation and anion exchange membranes enables directional control of ion migration relaxing the concentration gradient, and it increases the voltage in proportion to stack number. High salinity of concentrate water often causes parasitic currents between adjacent cells, and this complicates the power charateristics of a RED cell stack. In order to evaluate the effects of key parameters and to optimize the efficiency of energy harvesting, various equivalent circuit models are developed for typical structures of RED cell stacks. Input parameters are resistances of membranes and electrodes, structure of flow channels, stack number, and salt concentrations. The electrical potential across a membrane is calculated from Nernest equation and used as electromotive force for each unit cell. Output such as power density, short-circuit current, open-circuit voltage, and the distribution of parasitic currents can be estimated by the model. The internal resistance of a cell stack, which is most affected by dilute water concentration, is the critical parameter influencing the power efficiency. Parasitic currents that degrade the overall power characteristics were also considered. Those effects evaluated by the model agree with experimental measurements with varying concentrations, the thickness of water channels, and stack number. Figure 1
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Dabre, Raj, et Atsushi Fujita. « Recurrent Stacking of Layers for Compact Neural Machine Translation Models ». Proceedings of the AAAI Conference on Artificial Intelligence 33 (17 juillet 2019) : 6292–99. http://dx.doi.org/10.1609/aaai.v33i01.33016292.
Texte intégralRésumé :
In encoder-decoder based sequence-to-sequence modeling, the most common practice is to stack a number of recurrent, convolutional, or feed-forward layers in the encoder and decoder. While the addition of each new layer improves the sequence generation quality, this also leads to a significant increase in the number of parameters. In this paper, we propose to share parameters across all layers thereby leading to a recurrently stacked sequence-to-sequence model. We report on an extensive case study on neural machine translation (NMT) using our proposed method, experimenting with a variety of datasets. We empirically show that the translation quality of a model that recurrently stacks a single-layer 6 times, despite its significantly fewer parameters, approaches that of a model that stacks 6 different layers. We also show how our method can benefit from a prevalent way for improving NMT, i.e., extending training data with pseudo-parallel corpora generated by back-translation. We then analyze the effects of recurrently stacked layers by visualizing the attentions of models that use recurrently stacked layers and models that do not. Finally, we explore the limits of parameter sharing where we share even the parameters between the encoder and decoder in addition to recurrent stacking of layers.
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Hmad, Ali A., et Nihad Dukhan. « Cooling Design for PEM Fuel-Cell Stacks Employing Air and Metal Foam : Simulation and Experiment ». Energies 14, no 9 (7 mai 2021) : 2687. http://dx.doi.org/10.3390/en14092687.
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A new study investigating the cooling efficacy of air flow inside open-cell metal foam embedded in aluminum models of fuel-cell stacks is described. A model based on a commercial stack was simulated and tested experimentally. This stack has three proton exchange membrane (PEM) fuel cells, each having an active area of 100 cm2, with a total output power of 500 W. The state-of-the-art cooling of this stack employs water in serpentine flow channels. The new design of the current investigation replaces these channels with metal foam and replaces the actual fuel cells with aluminum plates. The constant heat flux on these plates is equivalent to the maximum heat dissipation of the stack. Forced air is employed as the coolant. The aluminum foam used had an open-pore size of 0.65 mm and an after-compression porosity of 60%. Local temperatures in the stack and pumping power were calculated for various air-flow velocities in the range of 0.2–1.5 m/s by numerical simulation and were determined by experiments. This range of air speed corresponds to the Reynolds number based on the hydraulic diameter in the range of 87.6–700.4. Internal and external cells of the stack were investigated. In the simulations, and the thermal energy equations were solved invoking the local thermal non-equilibrium model—a more realistic treatment for airflow in a metal foam. Good agreement between the simulation and experiment was obtained for the local temperatures. As for the pumping power predicted by simulation and obtained experimentally, there was an average difference of about 18.3%. This difference has been attributed to the poor correlation used by the CFD package (ANSYS) for pressure drop in a metal foam. This study points to the viability of employing metal foam for cooling of fuel-cell systems.
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Oyarza´bal, Borja, Michael W. Ellis et Michael R. von Spakovsky. « Development of Thermodynamic, Geometric, and Economic Models for Use in the Optimal Synthesis/Design of a PEM Fuel Cell Cogeneration System for Multi-Unit Residential Applications ». Journal of Energy Resources Technology 126, no 1 (1 mars 2004) : 21–29. http://dx.doi.org/10.1115/1.1647130.
Texte intégralRésumé :
Thermodynamic, geometric, and economic models are developed for a proton exchange membrane (PEM) fuel cell system for use in cogeneration applications in multi-unit residential buildings. The models describe the operation and cost of the fuel processing sub-system and the fuel cell stack sub-system. The thermodynamic model reflects the operation of the chemical reactors, heat exchangers, mixers, compressors, expanders, and stack that comprise the PEMFC system. Geometric models describe the performance of a system component based on its size (e.g., heat exchanger surface area), and, thus, relate the performance at off-design conditions to the component sizes chosen at the design condition. Economic models are based on data from the literature and address the cost of system components including the fuel processor, the fuel cell materials, the stack assembly cost, the fuel cost, etc. As demonstrated in a forthcoming paper, these models can be used in conjunction with optimization techniques based on decomposition to determine the optimal synthesis and design of a fuel cell system. Results obtained using the models show that a PEMFC cogeneration system is most economical for a relatively large cluster of residences (i.e. 50) and for manufacturing volumes in excess of 1500 units per year. The analysis also determines the various system performance parameters including an electrical efficiency of 39% and a cogeneration efficiency of 72% at the synthesis/design point.
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Mogelsvang, Soren, Natalia Gomez-Ospina, Jon Soderholm, Benjamin S. Glick et L. Andrew Staehelin. « Tomographic Evidence for Continuous Turnover of Golgi Cisternae in Pichia pastoris ». Molecular Biology of the Cell 14, no 6 (juin 2003) : 2277–91. http://dx.doi.org/10.1091/mbc.e02-10-0697.
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The budding yeast Pichia pastoris contains ordered Golgi stacks next to discrete transitional endoplasmic reticulum (tER) sites, making this organism ideal for structure–function studies of the secretory pathway. Here, we have used P. pastoris to test various models for Golgi trafficking. The experimental approach was to analyze P. pastoris tER-Golgi units by using cryofixed and freeze-substituted cells for electron microscope tomography, immunoelectron microscopy, and serial thin section analysis of entire cells. We find that tER sites and the adjacent Golgi stacks are enclosed in a ribosome-excluding “matrix.” Each stack contains three to four cisternae, which can be classified as cis, medial, trans, or trans-Golgi network (TGN). No membrane continuities between compartments were detected. This work provides three major new insights. First, two types of transport vesicles accumulate at the tER-Golgi interface. Morphological analysis indicates that the center of the tER-Golgi interface contains COPII vesicles, whereas the periphery contains COPI vesicles. Second, fenestrae are absent from cis cisternae, but are present in medial through TGN cisternae. The number and distribution of the fenestrae suggest that they form at the edges of the medial cisternae and then migrate inward. Third, intact TGN cisternae apparently peel off from the Golgi stacks and persist for some time in the cytosol, and these “free-floating” TGN cisternae produce clathrin-coated vesicles. These observations are most readily explained by assuming that Golgi cisternae form at the cis face of the stack, progressively mature, and ultimately dissociate from the trans face of the stack.
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Wilberforce, Tabbi, Mohammad Biswas et Abdelnasir Omran. « Power and Voltage Modelling of a Proton-Exchange Membrane Fuel Cell Using Artificial Neural Networks ». Energies 15, no 15 (1 août 2022) : 5587. http://dx.doi.org/10.3390/en15155587.
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A proton exchange membrane fuel cell (PEMFC) is a more environmentally friendly alternative to deliver electric power in various applications, including in the transportation industry. As PEMFC performance characteristics are inherently nonlinear and involved, the prediction of the performance in a given application for different operating conditions is important in order to optimize the efficiency of the system. Thus, modelling using artificial neural networks (ANNs) to predict its performance can significantly improve the capabilities of handling the multi-variable nonlinear performance of the PEMFC. However, further investigation is needed to develop a dynamic model using ANNs to predict the transient behavior of a PEMFC. This paper predicts the dynamic electrical and thermal performance of a PEMFC stack under various operating conditions. The input variables of the PEMFC stack for the analysis consist of the cathode inlet temperature, anode inlet pressure, anode and cathode inlet flow rates, and stack current. The performances of the ANN models using three different learning algorithms are determined based on the stack voltage and temperature, which have been shown to be consistently predicted by most of these models. Almost all models with varying hidden neurons have coefficients of determination of 0.9 or higher and mean squared errors of less than 5. Thus, the results show promise for dynamic modelling approaches using ANNs for the development of optimal operation of a PEMFC in various system applications.
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Allwood, J. M., et G. F. Bryant. « Fast modelling of roll stack behaviour for control applications ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 211, no 5 (1 mai 1997) : 373–86. http://dx.doi.org/10.1243/0954406971522123.
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A fast model of roll stack deformation is presented. Appropriate simplified structural models are chosen by careful consideration of the application of general theories. Discretization of continuous variables allows the use of matrix-based weighting functions in describing component deformation and leads to a vectorized solution. All model non-linearities are considered, with particular attention given to the variable region of contact between adjacent rolls in the stack. A novel and efficient ‘binary choice matrix’ method is developed to describe the uncertainty in defining this region. This leads to a more efficient solution than previously published related models. Opportunities for future extensions are discussed.
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Schreiber, Owen, Krishna Shah, Mohammad Parhizi et Suryanarayana Kolluri. « A General Three-Dimensional Electrochemical-Thermal Modeling Framework to Study Large-Format Batteries ». ECS Meeting Abstracts MA2022-01, no 25 (7 juillet 2022) : 1214. http://dx.doi.org/10.1149/ma2022-01251214mtgabs.
Texte intégralRésumé :
Lithium-ion batteries’ performance, degradation, and safety are highly sensitive to their operating temperature [1-3]. Depending upon the form-factor, construction, and thermal boundary conditions, large temperature variations may be present within a battery in more than one direction. Physics-based battery models, such as single-particle model (SPM), enhanced single-particle model (ESPM), tank-in-series model, and the widely used pseudo-two-dimensional (p2D) model, ignore the effect of temperature variations in one or more directions [4]. Specifically, p2D model can resolve temperature variation within anode, cathode, and separator of a single stack but this is often not useful as the temperature variation within a single stack will be negligible due to the small length scale. Also, a commercial-scale Li-ion battery is a multi-stack system with possibly significant temperature variation across the stacks as compared to within a single stack. The recently developed thermal tank-in-series battery model accounts for temperature variation across a multi-stack battery system but does not account for temperature variation in the direction parallel to the current collector [5]. In the case of large-format batteries, significant temperature variations are also expected along the directions corresponding to the longer dimensions. This would typically involve temperature variations in the directions parallel to the current collector. Multi-scale multi-domain (MSMD) models have been developed in the past to extend the single-stack level physics-based models to account for temperature nonuniformity in these directions [6-8]. However, temperature variation in the direction corresponding to the shortest dimension may also be appreciable due to the anisotropic/orthotropic nature of heat transfer in the battery system at the macroscale [9,10]. This is because the heat transfer in this direction may be severely impeded by the multi-stack construct leading to poor thermal conductivity in that direction. This in turn may lead to a large temperature gradient even along the direction corresponding to the shortest dimension of the large-format battery system. This suggests the need for careful formulation of MSMD battery models considering the construction, design parameters, and external thermal conditions of a particular battery system. In the present work, we propose a general three-dimensional modeling framework that accounts for the effect of the three-dimensional temperature field on the local variations in thermodynamics, transport processes, and reaction kinetics in the battery system. This type of battery modeling framework can be used to study nonuniform temperature distribution driven spatially uneven degradation, particularly in large-format batteries. Additionally, this modeling framework can help design physics-aware battery-specific thermal management systems to improve performance and reduce degradation. This will be a drastic departure from the present approach of designing battery thermal management system which treats the battery in a rather simplistic manner. References [1] J. Shim, et al, J. Power Sour. 112, 222-230, 2002. [2] S.S. Zhang, et al, J. Power Sour. 115, 137-140, 2003. [3] X. Feng, et al, Energy Storage Mater. 10, 246-267, 2018. [4] V. Ramadesigan, et al, J. Electrochem. Soc. 159, 31-45, 2012. [5] A. Subramaniam, et al, J. Electrochem. Soc. 167, 113506, 2020. [6] G. Fan, et al, J. Electrochem. Soc. 164, A252, 2017. [7] A. Schmidt, et al, Electrochim. Acta. 393, p.139046, 2021. [8] A. Awarke, et al, J. Electrochem. Soc. 160, A172, 2013. [9] K. Shah, et al, J. Power Sour. 271, 262-268, 2014. [10] S.J. Drake, et al, J. Power Sour. 252, 298-304, 2014.
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Georges, Aïna Linn, Alix Trieu et Lars Birkedal. « Le temps des cerises : efficient temporal stack safety on capability machines using directed capabilities ». Proceedings of the ACM on Programming Languages 6, OOPSLA1 (8 décembre 2022) : 1–30. http://dx.doi.org/10.1145/3527318.
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Capability machines are a type of CPUs that support fine-grained privilege separation using capabilities , machine words that include forms of authority. Formal models of capability machines and associated calling conventions have so far focused on establishing two forms of stack safety properties, namely local state encapsulation and well-bracketed control flow. We introduce a novel kind of directed capabilities and show how to use them to make an earlier suggested calling convention more efficient. In contrast to earlier work on capability machine models we do not only consider integrity properties but also confidentiality properties; we provide a unary logical relation to reason about the former and a binary logical relation to reason about the latter, each expressive enough to reason about temporal stack safety. While the logical relations are useful for reasoning about concrete examples, they do not on their own demonstrate that stack safety holds for a large class of programs. Therefore, we also show full abstraction of a compiler from an overlay semantics that internalizes the calling convention as a single call step and explicitly keeps track of the call stack and frame lifetimes to a base capability machine. All results have been mechanized in Coq.
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Shi, Hui, Sicun Gao, Yuandong Tian, Xinyun Chen et Jishen Zhao. « Learning Bounded Context-Free-Grammar via LSTM and the Transformer : Difference and the Explanations ». Proceedings of the AAAI Conference on Artificial Intelligence 36, no 8 (28 juin 2022) : 8267–76. http://dx.doi.org/10.1609/aaai.v36i8.20801.
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Long Short-Term Memory (LSTM) and Transformers are two popular neural architectures used for natural language processing tasks. Theoretical results show that both are Turing-complete and can represent any context-free language (CFL).In practice, it is often observed that Transformer models have better representation power than LSTM. But the reason is barely understood. We study such practical differences between LSTM and Transformer and propose an explanation based on their latent space decomposition patterns. To achieve this goal, we introduce an oracle training paradigm, which forces the decomposition of the latent representation of LSTMand the Transformer and supervises with the transitions of the Pushdown Automaton (PDA) of the corresponding CFL. With the forced decomposition, we show that the performance upper bounds of LSTM and Transformer in learning CFL are close: both of them can simulate a stack and perform stack operation along with state transitions. However, the absence of forced decomposition leads to the failure of LSTM models to capture the stack and stack operations, while having a marginal impact on the Transformer model. Lastly, we connect the experiment on the prototypical PDA to a real-world parsing task to re-verify the conclusions
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Tung, Lun Hao, Fei Chong Ng, Aizat Abas, M. Z. Abdullah, Zambri Samsudin et Mohd Yusuf Tura Ali. « Effect of different temperature distribution on multi-stack BGA package ». Microelectronics International 38, no 2 (26 février 2021) : 33–45. http://dx.doi.org/10.1108/mi-10-2020-0066.
Texte intégralRésumé :
Purpose This paper aims to determine the optimum set of temperatures through correlation study to attain the most effective capillary flow of underfill in a multi-stack ball grid array (BGA) chip device. Design/methodology/approach Finite volume method is implemented in the simulation. A three-layer multi-stack BGA is modeled to simulate the underfill flow. The simulated models were well validated with the previous experimental work on underfill process. Findings The completion filling time shows high regression R-squared value of up to 0.9918, which indicates a substantial acceleration on the underfill process because of incorporation of thermal delta. An introduction of 11 °C thermal delta to the multi-stacks BGA managed to reduce the filling time by up to 16.4%. Practical implications Temperature-induced capillary flow is a relatively new type of driven underfill designed specifically for package on package BGA components. Its simple implementation can further improve the productivity of existing underfill process in the industry that is desirable in reducing the process lead time. Originality/value The effect of temperature-induced capillary flow in underfill encapsulation on multi-stacks BGA by means of statistical correlation study is a relatively new topic, which has never been reported in any other research according to the authors’ knowledge.
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Wang, Jianjun, Weijie Li, Lei Qin, Jing Zhang et Peijun Wei. « Effects of electrodes and protective layers on the electromechanical characteristics of piezoelectric stack actuators ». Advanced Composites Letters 28 (1 janvier 2019) : 096369351987741. http://dx.doi.org/10.1177/0963693519877419.
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Piezoelectric stack actuators are a type of excellent smart devices that can activate large power and displacement outputs due to their unique stack configuration and have been widely used in linear vibrators for various engineering applications. For the fabricated piezoelectric stack actuator, it usually consists of multiple thin piezoelectric wafers, multiple electrodes, and two protective layers. All the piezoelectric wafers are connected electrically in parallel through the electrodes and are protected by two protective layers at the two ends. However, in most of the theoretical models, the active piezoelectric portion is mainly considered, while the electrodes and protective layers are usually neglected to simplify the complicated problem, which results in an inaccurate prediction of the electromechanical characteristics. In our previously published work, the exact theoretical models of the piezoelectric stack energy harvester and sensor with the electrodes and the protective layers included have been established successfully to evaluate the electromechanical performance of these two types of devices, and their validity has verified by the experimental results. However, the exact theoretical model of the piezoelectric stack actuators has not been established, and the effects of the electrodes and the protective layers on the electromechanical characteristics of the actuator are not fully understood. In this article, the exact theoretical model of piezoelectric stack actuator was derived based on our previous work, and the effects of these two factors on the electromechanical characteristics were investigated. Comparisons with the results in the earlier literatures and the experimental results were presented to validate the model. Furthermore, two kinds of typical working states, including clamped–free (C-F) and free–free (F-F), were discussed. The results showed that neglecting the electrodes and the protective layers will greatly affect the accuracy of the prediction model, thus providing some valuable guidelines in designing the piezoelectric stack actuators.
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El-Raheb, Michael. « Simplified analytical models for transient uniaxial waves in a layered periodic stack ». International Journal of Solids and Structures 34, no 23 (août 1997) : 2969–90. http://dx.doi.org/10.1016/s0020-7683(96)00220-x.
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Bradean, Radu, Herwig Haas, Kjell Eggen, Chris Richards et Tomas Vrba. « Stack Models and Designs for Improving Fuel Cell Startup From Freezing Temperatures ». ECS Transactions 3, no 1 (21 décembre 2019) : 1159–68. http://dx.doi.org/10.1149/1.2356235.
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Walker, I. S., et D. J. Wilson. « Evaluating models for superposition of wind and stack effect in air infiltration ». Building and Environment 28, no 2 (avril 1993) : 201–10. http://dx.doi.org/10.1016/0360-1323(93)90053-6.
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Flecha, I., R. Carbonell, R. W. Hobbs et H. Zeyen. « Some improvements in subbasalt imaging using pre-stack depth migration ». Solid Earth Discussions 2, no 1 (8 février 2010) : 1–17. http://dx.doi.org/10.5194/sed-2-1-2010.
Texte intégralRésumé :
Abstract. Subbasalt imaging can be improved by carefully applying pre-stack depth migration. Pre-stack depth migration requires a detailed velocity model and an accurate traveltime calculation. Ray tracing methods are fast but, often fail in calculating traveltimes in complex models, specially, when they feature high velocity contrasts. Finitte difference solutions of the eikonal are more stable and can produce a traveltime field for the whole model avoiding shadow zones. A synthetic test was carried out to check the performance of a new pre-stack depth migration algorithm in a model that features a high velocity layer surrounded by lower velocities. The results reasonably reproduce the original model. The same scheme was used to process long-offset reflection data from the Faroe Shelf where conventional techniques (stack) were insufficient to assess the structure under a basalt layer. Pre-stack depth migration produced an improved image which recovered the main features in the stacked section and allowed to identify some subbasalt coherent events.
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Flecha, I., R. Carbonell, R. W. Hobbs et H. Zeyen. « Some improvements in subbasalt imaging using pre-stack depth migration ». Solid Earth 2, no 1 (3 janvier 2011) : 1–7. http://dx.doi.org/10.5194/se-2-1-2011.
Texte intégralRésumé :
Abstract. Subbasalt imaging can be improved by carefully applying pre-stack depth migration. Pre-stack depth migration requires a detailed velocity model and an accurate traveltime calculation. Ray tracing methods are fast but, often fail in calculating traveltimes in complex models, specially, when they feature high velocity contrasts. Finitte difference solutions of the eikonal are more stable and can produce a traveltime field for the whole model avoiding shadow zones. A synthetic test was carried out to check the performance of a new pre-stack depth migration algorithm in a model that features a high velocity layer surrounded by lower velocities. The results reasonably reproduce the original model. The same scheme was used to process long-offset reflection data from the Faroe Shelf where conventional techniques (stack) were insufficient to assess the structure under a basalt layer. Pre-stack depth migration produced an improved image which recovered the main features in the stacked section and allowed to identify some subbasalt coherent events.
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Joy Mathavan, Jebaratnam, Muhammad Hafiz Hassan, Jinyang Xu et Gérald Franz. « Hole Quality Observation in Single-Shot Drilling of CFRP/Al7075-T6 Composite Metal Stacks Using Customized Twist Drill Design ». Journal of Composites Science 6, no 12 (8 décembre 2022) : 378. http://dx.doi.org/10.3390/jcs6120378.
Texte intégralRésumé :
In the modern aircraft manufacturing industry, the use of fiber metal stack-up material plays an important role. During assembly, these stack-up materials need to be drilled, and single-shot drilling is the best option to avoid misalignments. This paper discusses hole quality in terms of hole edge defects and hole integrity with respect to tool geometry. In this study, tungsten carbide (WC) twist-type drills with various geometric features were fabricated, tested, and evaluated. Twenty custom twist drill bits with primary clearance angles ranging from 6° to 8°, chisel edge angles from 30° to 45°, and point angles from 130° to 140° were fabricated. The CFRP and Al 7075-T6 were stacked up, and a feed rate of 0.05 mm/rev and spindle speed of 2600 rev/min were used for all drilling experiments. The experimental array was constructed using response surface methodology (RSM) to design the experiments. The impact of factors and their importance on hole quality were investigated using analysis of variance (ANOVA). The study demonstrates that the primary clearance angle, followed by the chisel edge angle, is the most important factor determining hole quality. As a function of tool geometry, correlation models between exit delamination and burr height were developed. The findings suggested that, within the range of parameters examined, the proposed correlation models might be utilized to predict performance measures. For drilling CFRP/AL7075-T6 stack material in a single shot, the ideal twist drill geometry was determined to be a 45° chisel edge angle, 8° primary clearance angle, and 130° point angle. For optimum drill geometry, the discrepancy between the expected and actual experiment values was 0.11% for exit delamination and 9.72% for burr height. The findings of this research elucidate the relationship between tool geometry and hole quality in single-shot drilling of composite-metal stacks, and more specifically, they may serve as a useful, practical guide for single-shot drilling of CFRP/Al7075-T6 stack for the manufacture of aircraft.