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Machine learning modeling for proton exchange membrane fuel cell performance

Energy and AI 2022年第4期10卷 1-16页

作者： Adithya legala Jian Zhao Xianguo li Department of Mechanical and Mechatronics Engineering University of WaterlooWaterlooOntario N2L 3G1 Canada

Proton exchange membrane fuel cell (PEMFC) is considered essential for climate change mitigation, and a fast and accurate model is necessary for its control and operation in practical applications. In this study, various machine learning methods are used to develop data-based models for PEMFC performance attributes and internal states. Techniques such as Artificial neural network (Ann) and Support Vector Machine Regressor (SVR) are used to predict the cell voltage, membrane resistance, and membrane hydration level for various operating conditions. Varying input features such as cell current, temperature, reactant pressures, and humidity are introduced to evaluate the accuracy of the model, especially under extreme conditions. Two different sets of data are considered in this study, which are acquired from, a physics-based semiempirical model and a 1-D reduced-dimension Computational Fluid Dynamics model, respectively. The aspect of data preprocessing and hyperparameter tuning procedures are investigated that are extensively used to calibrate the artificial neural network layers and support vector regressor to predict the fuel cell attributes. Ann clearly shows an advantage in comparison with SVR, especially on a multivariable output regression. However, the SVR is advantageous to model simple regressions as it greatly reduces the level of computation without sacrificing accuracy. Data-based models for PEMFC are successfully developed on both the data sets by adapting advanced modeling techniques and calibration procedures such as Ann incorporating the dropout technique, resulting in an R2 ≥ 0.99 for all the predicted variables, demonstrating the ability to build accurate data-based models solely on data from validated physics-based models, reducing the dependency on extensive experimentation.

关键词： Fuel cell Machine learning Artificial neural network Support vector machine regressor Data-based models

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Porous perovskite films integrated with Au-Pt nanowire-based electrodes for highly flexible large-area photodetectors

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npj Flexible Electronics 2020年第1期4卷 271-278页

作者： Rohit Saraf Hua Fan Vivek Maheshwari Department of Chemistry Waterloo Institute for NanotechnologyUniversity of WaterlooWaterlooONN2L 3G1Canada

Flexible,large-area,and stable perovskite photodetectors have drawn increasing widespread research attention for next-generation wearable and portable optoelectronic ***,high mechanical durability coupled with large device area and enhanced environmental stability has not been demonstrated yet to attain practical ***,a highly bendable,stable,and large-area(3 cm^(2))flexible polystyrene incorporated perovskite photodetector is *** to the formation of a porous polystyrene-perovskite composite film in a single step it allows unprecedented mechanical stability,maintaining 85%of its original photocurrent value after 10,000 bending cycles at a bending angle of 120°.Equally crucial,the solution-processed self-assembled Pt-Au nanochains were developed to provide a simple and fast method of patterning the conductive and flexible electrodes onto the filter *** optimized polystyrene-perovskite photodetector exhibits a high responsivity up to 2.73 A W^(−1),a maximum specific detectivity of 6.2×10^(13) Jones,and a superior switching ratio of 1.0×10^(4).In addition,the polystyrene-perovskite photodetector yields excellent stability under the combined stresses of moisture,ambient air,and room light,and retains 92%of its original performance for over 30 *** these results demonstrate that this work provides a facile and cost-effective approach that paves the way to develop high-performance,stable,and highly flexible optoelectronic devices.

关键词： perovskite stability bending

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A modeling and experimental study of capacity fade for lithium-ion batteries

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Energy and AI 2020年第2期2卷 74-82页

作者： Andrew Carnovale Xianguo li Department of Mechanical and Mechatronics Engineering University of WaterlooWaterlooOntario N2L 3G1Canada

lithium-ion batteries are extensively used in electric vehicles,however,their significant degradation over dis-charge and charge cycles results in severe capacity fade,limiting driving ranges of electric vehicles over time and useful lifetime of *** this study,capacity fade for lithium-ion battery has been investigated through modeling and experiment.A predictive model is developed based on first principles incorporating degradation *** mechanisms of degradation considered include solid-electrolyte interface(SEI)growth and ac-tive material loss at both negative and positive *** performance including capacity is measured experimentally under discharge and charge cycling with battery operation temperature *** is shown that battery capacity is reduced over battery discharge/charge cycling at a given battery operation temperature,and the model predicted battery performance,including capacity fade,agrees well with the experimental *** the number of discharge/charge cycles are increased,battery capacity is reduced significantly;battery ca-pacity fade is increased substantially when battery operation temperature is increased,indicating significantly accelerated aging of the battery at elevated operation temperatures and hence the importance of battery thermal management in the control of battery operation temperature for practical applications such as electric *** capacity fade is mainly caused by SEI film growth at the negative electrode,which is the largest contribut-ing factor to the capacity fade,and the active material isolation at the negative electrode,which is the second largest influencing aging factor.

关键词： lithium-ion batteries Capacity fade Degradation Aging Modeling Experiment

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Signaling Kinetics of DnA and Aptamer Biosensors Revealing Graphene Oxide Surface Heterogeneity

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Journal of Analysis and Testing 2022年第1期6卷 11-18页

作者： Po-Jung Jimmy Huang Juewen liu Department of Chemistry Waterloo Institute for NanotechnologyUniversity of WaterlooWaterlooON N2L 3G1Canada

Adsorption of fluorescently labeled DnA and aptamer probes to graphene oxide(GO)has been one of the most popular methods for developing *** the presence of target analytes,the quenched fluorescence would *** this work,we followed the kinetics of the reactions and found that the fluorescence would eventually drop after an initial increase,and this was attributed to the re-adsorption of the desorbed probe DnA *** a DnA probe and an aptamer for adenosine were *** re-adsorption was attributed to the surface heterogeneity of GO,and the DnA probes desorbed from relatively weaker binding sites were re-adsorbed on the stronger binding *** re-adsorption can be avoided by extensive washing the samples,and also by blocking the GO surface or by *** fundamental understanding is important for achieving a stable signal of such biosensors.

关键词： Kinetics DnA Aptamer Biosensors Graphene

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Fucoidan and topography modification improved in situ endothelialization on acellular synthetic vascular grafts

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Bioactive Materials 2023年第4期22卷 535-550页

作者： Yuan Yao Aung Moe Zaw Deirdre E.J.Anderson YeJin Jeong Joshua Kunihiro Monica T.Hinds Evelyn K.F.Yim Department of Chemical Engineering University of Waterloo200 University Avenue WestWaterlooONN2L 3G1Canada Department of Biomedical Engineering Oregon Health&Science UniversityPortlandOR97239USA Waterloo Institute for nanotechnology University of Waterloo200 University Avenue WestWaterlooONN2L 3G1Canada Center for Biotechnology and Bioengineering University of Waterloo200 University Avenue WestWaterlooONN2L 3G1Canada

Thrombogenesis remains the primary failure of synthetic vascular *** coverage is crucial to provide an antithrombogenic ***,most synthetic materials do not support cell adhesion,and transanastomotic endothelial migration is ***,a surface modification strategy using fucoidan and topography was developed to enable fast in situ endothelialization of polyvinyl alcohol,which is not endothelial *** three different immobilization approaches compared,conjugation of aminated-fucoidan promoted endothelial monolayer formation while minimizing thrombogenicity in both in vitro platelet rich plasma testing and ex vivo non-human primate shunt *** of six topographical patterns showed that 2μm gratings increased endothelial cell migration without inducing inflammation responses of endothelial *** studies demonstrated that fucoidan could attract fibronectin,enabling integrin binding and focal adhesion formation and activating focal adhesion kinase(FAK)signaling,and 2μm gratings further enhanced FAK-mediated cell *** a clinically relevant rabbit carotid artery end-to-side anastomosis model,60%in situ endothelialization was observed throughout the entire lumen of 1.7 mm inner diameter modified grafts,compared to 0%of unmodified graft,and the four-week graft patency also *** work presents a promising strategy to stimulate in situ endothelialization on synthetic materials for improving long-term performance.

关键词： Blood-contacting devices Small diameter vascular graft Endothelialization Topography Fucoidan

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Controlled Synthesis of Carbon-Supported Pt-Based Electrocatalysts for Proton Exchange Membrane Fuel Cells

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Electrochemical Energy Reviews 2022年第4期5卷 138-189页

作者： Huiyuan liu Jian Zhao Xianguo li Department of Mechanical and Mechatronics Engineering University of Waterloo200 University Avenue WestWaterlooON N2L 3G1Canada

Proton exchange membrane fuel cells are playing an increasing role in postpandemic economic recovery and climate action ***,their performance,cost,and durability are significantly related to Pt-based electrocatalysts,hampering their large-scale commercial ***,considerable efforts have been devoted to improving the activity and durability of Pt-based electrocatalysts by controlled synthesis in recent years as an effective method for decreasing Pt use,and consequently,the ***,this review article focuses on the synthesis processes of carbon-supported Pt-based electrocatalysts,which significantly affect the nanoparticle size,shape,and dispersion on supports and thus the activity and durability of the prepared *** reviewed processes include(i)the functionalization of a commercial carbon support for enhanced catalyst-support interaction and additional catalytic effects,(ii)the methods for loading Pt-based electrocatalysts onto a carbon support that impact the manufacturing costs of electrocatalysts,(iii)the preparation of spheri-cal and nonspherical Pt-based electrocatalysts(polyhedrons,nanocages,nanoframes,one-and two-dimensional nanostruc-tures),and(iv)the postsynthesis treatments of supported *** influences of the supports,key experimental parameters,and postsynthesis treatments on Pt-based electrocatalysts are scrutinized in *** research directions are outlined,including(i)the full exploitation of the potential functionalization of commercial carbon supports,(ii)scaled-up one-pot synthesis of carbon-supported Pt-based electrocatalysts,and(iii)simplification of postsynthesis ***-pot synthesis in aqueous instead of organic reaction systems and the minimal use of organic ligands are preferred to simplify the synthesis and postsynthesis treatment processes and to promote the mass production of commercial carbon-supported Pt-based electrocatalysts.

关键词： Carbon-supported Pt-based electrocatalysts Synthesis Shape Functionalization of commercial carbon support Postsynthesis treatment

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Empirical Evidence of the leverage Effect in a Stochastic Volatility Model： A Realized Volatility Approach

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Frontiers of Economics in China-Selected Publications from Chinese Universities 2012年第1期7卷 22-43页

作者： Dinghai Xu Yuying li Department of Economics University of Waterloo Waterloo ON N2L 3G1 Canada School of Computer Science University of Waterloo Waterloo ON N2L 3G1 Canada

Increasing attention has been focused on the analysis of the realized volatil- ity, which can be treated as a proxy for the true volatility. In this paper, we study the potential use of the realized volatility as a proxy in a stochastic volatility model estimation. We estimate the leveraged stochastic volatility model using the realized volatility computed from five popular methods across six sampling-frequency transaction data （from 1-min to 60- min） based on the trust region method. Availability of the realized volatility allows us to estimate the model parameters via the MlE and thus avoids computational challenge in the high dimensional integration. Six stock indices are considered in the empirical investigation. We discover some consistent findings and interesting patterns from the empirical results. In general, the significant leverage effect is consistently detected at each sampling frequency and the volatility persistence becomes weaker at the lower sampling frequency.

关键词： realized volatility stochastic volatility model leverage effect high frequency data MlE trust-region method

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RISK REDUCTIOn In A PROJECT PORTFOlIO

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Journal of Systems Science and Systems Engineering 2017年第1期26卷 3-22页

作者： Dujuan Guan Peng Guo Keith W. Hipel liping Fang School of Management Northwestern Polytechnical University Xi 'an 710072 China Department of Management Hefei University Hefei 230601 China Department of Systems Design Engineering University of Waterloo Waterloo Ontario Canada N2L 3G1 Centre for International Governance Innovation Waterloo Ontario Canada N2L 6C2 Department of Mechanical and Industrial Engineering Ryerson University Toronto Ontario Canada M5B 2K3

The positive impacts of managing projects as a portfolio are quantified by comparing the value of the integrated risk of a project portfolio and the aggregation of single project risks implemented separately. Firstly, the integrated risk is defined by proposing risky events based on set theory. Secondly, as projects interact with each other in a project portfolio, the integrated risk is evaluated by using a Bayesian network structure learning algorithm to construct an interdependent network of risks. Finally, the integrated risk of a practical case is assessed using this method, and the results show that the proposed method is an effective tool for calculating the extent of risk reduction of implementing a project portfolio and identifying the most risky project, so as to assist companies in making comprehensive decisions in the phase of portfolio selection and portfolio controlling.

关键词： Project portfolio integrated risk set theory Bayesian network risk assessment

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Robust D-Stability Test of lTI General Fractional Order Control Systems

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IEEE/CAA Journal of Automatica Sinica 2020年第3期7卷 853-864页

作者： Reza Mohsenipour Xinzhi liu Department of Aerospace Engineering Sharif University of TechnologyTehran ***Iran Department of Applied Mathematics University of WaterlooOntario N2L 3G1Canada

This work deals with the robust D-stability test of linear time-invariant(lTI) general fractional order control systems in a closed loop where the system and/or the controller may be of fractional order. The concept of general implies that the characteristic equation of the lTI closed loop control system may be of both commensurate and non-commensurate orders, both the coefficients and the orders of the characteristic equation may be nonlinear functions of uncertain parameters, and the coefficients may be complex numbers. Some new specific areas for the roots of the characteristic equation are found so that they reduce the computational burden of testing the robust D-stability. Based on the value set of the characteristic equation, a necessary and sufficient condition for testing the robust D-stability of these systems is derived. Moreover, in the case that the coefficients are linear functions of the uncertain parameters and the orders do not have any uncertainties, the condition is adjusted for further computational burden reduction. Various numerical examples are given to illustrate the merits of the achieved theorems.

关键词： Fractional order control system lTI system robust D-stability value set

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CFD-DEM analysis of particle polydispersity on the performance of fluidised bed reactor during silane pyrolysis Author links open overlay panel

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Particuology 2024年第8期91卷 72-87页

作者： Akshayveer Vijay M.Shinde MS2Discovery Interdisciplinary Research Institute Wilfrid Laurier UniversityWaterlooOntarioN2L3C5Canada Department of Chemical Engineering Indian Institute of Technology(BHU)Varanasi221005India

A CFD-DEM model is developed for chemical vapour deposition of silane in a fluidized bed reactor to investigate the effect of polydispersity on local phase dynamics,mass and heat transport,as well as the rate of Si *** gas-phase fines formation and heterogeneous deposition on the seed particle,as well as the scavenging effect for Si particle growth,are *** method is first validated against the experimentally measured Si deposition rate,percentage of fine production and minimum fluidisation ***,the properties,primarily particle intermixing,fluidisation behaviour and bubble dynamics along with the deposition process,are analyzed for several polydisperse beds under various operating *** effect of polydispersity of the bed on a fraction of the bubble size,dense phase expansion and interchange coefficient between various phases is thoroughly investigated to establish a correlation with reactor *** results show that broad-Gaussian particle size distribution(PSD)exhibits excellent improvement in fluidisation behaviour,resulting in a high deposition rate,and minimum formation of Si fines.

关键词： CFD-DEM method Chemical vapour deposition(CVD) Particle size distribution Silicon Gas-solid fluidized bed

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