UHMWPE fibers exhibit impressive modulus and strength,but they have not reached their theoretical limits.Researchers focus on molecular weight,orientation,and crystallinity of UHMWPE,yet their contributions to mechani...UHMWPE fibers exhibit impressive modulus and strength,but they have not reached their theoretical limits.Researchers focus on molecular weight,orientation,and crystallinity of UHMWPE,yet their contributions to mechanical properties are unclear.Molecular dynamics simulations are valuable but often limited by computational constraints.Our aim is to simulate higher molecular weights to better represent real UHMWPE fibers.We used Packmol and Polyply methodologies to construct PE systems,with Polyply reproducing more reasonable properties of UHMWPE fibers.Additionally,tensile simulations showed that orientation and crystallinity greatly impact Young's modulus more than molecular weight.Energy decomposition indicated that higher molecular weights lead to covalent bonds that can withstand more energy during stretching,thus increasing breaking strength.Combining simulations with machine learning,we found that orientation has the most significant impact on Young's modulus,contributing 60%,and molecular weight plays the most crucial role in determining the breaking strength,accounting for 65%.This study provides a theoretical basis and guidelines for enhancing UHMWPE's modulus and strength.展开更多
In nature,cavitation bubbles typically appear in clusters,engaging in interactions that create a variety of dynamicmotion patterns.To better understand the behavior ofmultiple bubble collapses and the mechanisms of in...In nature,cavitation bubbles typically appear in clusters,engaging in interactions that create a variety of dynamicmotion patterns.To better understand the behavior ofmultiple bubble collapses and the mechanisms of interbubble interaction,this study employs molecular dynamics simulation combined with a coarse-grained force field.By focusing on collapsemorphology,local density,and pressure,it elucidates how the number and arrangement of bubbles influence the collapse process.The mechanisms behind inter-bubble interactions are also considered.The findings indicate that the collapse speed of unbounded bubbles located in lateral regions is greater than that of the bubbles in the center.Moreover,it is shown that asymmetrical bubble distributions lead to a shorter collapse time overall.展开更多
This research focuses on the seismic responses of the historic masonry minarets,conducted through the creation of a digital twin model using finite element methods.The study initiated the development of a comprehensiv...This research focuses on the seismic responses of the historic masonry minarets,conducted through the creation of a digital twin model using finite element methods.The study initiated the development of a comprehensive model in the ANSYS Workbench,supplemented by operational modal analysis(OMA),to ascertain the dynamic characteristics of the minaret.The alignment of numerical and experimental frequency data was achieved using the response surface method(RSM)within ANSYS Workbench DesignXplorer.This process resulted in the establishment of a digital twin,accurately representing the physical minaret in a virtual environment.Blender^(■)software was then used to simulate the effects of two consecutive earthquakes in Türkiye that occurred on February 6,2023.The simulations highlighted the heightened susceptibility of the minaret,especially in its upper sections,to consecutive seismic activities,culminating in significant damage and collapse.This innovative approach,merging traditional engineering methods with a cutting-edge digital simulation,provides a profound insight into the seismic behavior of historical structures.The research underscores the importance of advanced seismic modeling for the effective preservation and resilience of architectural heritage sites against earthquake risks.展开更多
Combining the phase-field method and the moving boundary method,a three-dimensional phase-field simulation was conducted for the growth and grain evolution of Ti films deposited by physical vapor deposition under diff...Combining the phase-field method and the moving boundary method,a three-dimensional phase-field simulation was conducted for the growth and grain evolution of Ti films deposited by physical vapor deposition under different deposition rates and grain orientations.The evolution of grain morphology and grain orientation was also taken into consideration.Simulation results show that at lower deposition rates,the surface of the formed Ti film exhibits a distinct oriented texture structure.The surface roughness of the Ti film is positively correlated with the grain misorientation.Moreover,the surface roughness obtained from the simulation is in good agreement with the experiment results.展开更多
The core-shell structure in bulk TiNb binary alloy was designed and studied by phase-field simulations,where various core-shell structures were obtained by precise control of the initial and boundary conditions of the...The core-shell structure in bulk TiNb binary alloy was designed and studied by phase-field simulations,where various core-shell structures were obtained by precise control of the initial and boundary conditions of the TiNb binary alloy system during spinodal decomposition,and then the formation mechanism of core-shell structure was revealed.In addition,the influences of initial temperature gradient,average temperature,and initial concentration distribution of the system on the core-shell structure were investigated.Results show that the initial concentration gradient is the key factor for forming the core-shell structure.Besides,larger initial temperature gradient and higher average temperature can promote the formation of core-shell structure,which can be stabilized by adjusting the initial concentration distribution of the Nb-rich region in TiNb binary alloy.As a theoretical basis,this research provides a novel and simple strategy for the preparation of TiNb-based alloys and other materials with peculiar core-shell structures and desirable mechanical and physical properties.展开更多
Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing addit...Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.展开更多
Polyethersulfone(PES)can be widely used in extreme environments due to its exceptional strength and stability.In this study,molecular dynamics(MD)simulations were used to construct tribological models of PES under var...Polyethersulfone(PES)can be widely used in extreme environments due to its exceptional strength and stability.In this study,molecular dynamics(MD)simulations were used to construct tribological models of PES under varying pressures.The variations of PES molecular chains and frictional interface properties were explored for understanding microscopic tribological mechanism.The simulation results show that high pressure and high vacuum conditions reduce the coefficient of friction and wear rate.The variations in radial distribution function(RDF),relative concentration of atoms,friction interface temperature,and atomic motion velocity were analyzed.It was found that high pressure and high vacuum promote PES molecular chains moving away from the surface of the iron atomic layer,decreasing interaction energy,RDF,temperature,and velocity at the friction interface.This work offers novel methodologies and theoretical insights for studying the friction and wear of polymer composites in complex environments.展开更多
The F_(1)-ATPase and V_(1)-ATPase are rotary biomotors.Alignment of their amino acid sequences,which originate from bovine heart mitochondria(1BMF)and Enterococcus hirae(3VR6),respectively,demonstrates that the segmen...The F_(1)-ATPase and V_(1)-ATPase are rotary biomotors.Alignment of their amino acid sequences,which originate from bovine heart mitochondria(1BMF)and Enterococcus hirae(3VR6),respectively,demonstrates that the segment forming the ATP catalytic pocket is highly conserved.Single-molecule experiments,however,have revealed subtle differences in efficiency between the F_(1) and V_(1) motors.Here,we perform both atomistic and coarse-grained molecular dynamics simulations to investigate the mechanochemical coupling and coordination in F_(1) and V_(1) ATPase.Our results show that the correlation between conformational changes in F_(1) is stronger than that in V_(1),indicating that the mechanochemical coupling in F_(1) is tighter than in V_(1).Moreover,the unidirectional rotation of F_(1) is more processive than that of V_(1),which accounts for the higher efficiency observed in F_(1) and explains the occasional backward steps detected in single-molecule experiments on V_(1).展开更多
The rapid advancement of machine learning based tight-binding Hamiltonian(MLTB)methods has opened new avenues for efficient and accurate electronic structure simulations,particularly in large-scale systems and long-ti...The rapid advancement of machine learning based tight-binding Hamiltonian(MLTB)methods has opened new avenues for efficient and accurate electronic structure simulations,particularly in large-scale systems and long-time scenarios.This review begins with a concise overview of traditional tight-binding(TB)models,including both(semi-)empirical and first-principles approaches,establishing the foundation for understanding MLTB developments.We then present a systematic classification of existing MLTB methodologies,grouped into two major categories:direct prediction of TB Hamiltonian elements and inference of empirical parameters.A comparative analysis with other ML-based electronic structure models is also provided,highlighting the advancement of MLTB approaches.Finally,we explore the emerging MLTB application ecosystem,highlighting how the integration of MLTB models with a diverse suite of post-processing tools from linear-scaling solvers to quantum transport frameworks and molecular dynamics interfaces is essential for tackling complex scientific problems across different domains.The continued advancement of this integrated paradigm promises to accelerate materials discovery and open new frontiers in the predictive simulation of complex quantum phenomena.展开更多
Vitrimers belong to a class of polymeric materials capable of bond exchange reactions,showing great promise for environmental protection and sustainable development.However,studies on the coupling mechanism between th...Vitrimers belong to a class of polymeric materials capable of bond exchange reactions,showing great promise for environmental protection and sustainable development.However,studies on the coupling mechanism between the bond exchange kinetics and segmental dynamics near the glass transition temperature(T_(g))remain scarce.Herein,we employed molecular dynamics simulations to investigate the dynamic heterogeneity of the segment motion and bond exchange in vitrimers.The simulation results revealed that the bond exchange energy barrier exerts a much stronger influence on the bond exchange kinetics than on the segmental dynamics.At lower temperatures,slower segmental relaxation further constraind the bond exchange rate.Additionally,increasing the bond exchange energy barrier markedly enhanced the dynamic heterogeneity of segment motion.A close correlation was observed between heterogeneity and bond exchange.This study elucidated the coupling mechanism between bond exchange and segmental dynamics at the molecular scale,thereby providing a theoretical basis for designing vitrimer materials with tunable dynamic properties.展开更多
In federated learning,backdoor attacks have become an important research topic with their wide application in processing sensitive datasets.Since federated learning detects or modifies local models through defense mec...In federated learning,backdoor attacks have become an important research topic with their wide application in processing sensitive datasets.Since federated learning detects or modifies local models through defense mechanisms during aggregation,it is difficult to conduct effective backdoor attacks.In addition,existing backdoor attack methods are faced with challenges,such as low backdoor accuracy,poor ability to evade anomaly detection,and unstable model training.To address these challenges,a method called adaptive simulation backdoor attack(ASBA)is proposed.Specifically,ASBA improves the stability of model training by manipulating the local training process and using an adaptive mechanism,the ability of the malicious model to evade anomaly detection by combing large simulation training and clipping,and the backdoor accuracy by introducing a stimulus model to amplify the impact of the backdoor in the global model.Extensive comparative experiments under five advanced defense scenarios show that ASBA can effectively evade anomaly detection and achieve high backdoor accuracy in the global model.Furthermore,it exhibits excellent stability and effectiveness after multiple rounds of attacks,outperforming state-of-the-art backdoor attack methods.展开更多
With the rapid proliferation of electric vehicles,their charging loads pose new challenges to power grid stability and operational efficiency.To address this,this study employs a Monte Carlo simulation model to analyz...With the rapid proliferation of electric vehicles,their charging loads pose new challenges to power grid stability and operational efficiency.To address this,this study employs a Monte Carlo simulation model to analyze the charging load characteristics of six battery electric vehicle categories in Hebei Province,leveraging multi-source probabilistic distribution data under typical operational scenarios.The findings reveal that electric vehicle charging loads are primarily concentrated during midday and nighttime periods,with significant load fluctuations exerting substantial pressure on the grid.In response,this paper proposes strategic interventions including optimized charging infrastructure planning,time-of-use electricity pricing mechanisms,and smart charging technologies to balance grid loads.The results provide a theoretical foundation for electric vehicle load forecasting,smart grid dispatching,and vehicle-grid integration,thereby enhancing grid operational efficiency and sustainability.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52303298 and 52233002)。
文摘UHMWPE fibers exhibit impressive modulus and strength,but they have not reached their theoretical limits.Researchers focus on molecular weight,orientation,and crystallinity of UHMWPE,yet their contributions to mechanical properties are unclear.Molecular dynamics simulations are valuable but often limited by computational constraints.Our aim is to simulate higher molecular weights to better represent real UHMWPE fibers.We used Packmol and Polyply methodologies to construct PE systems,with Polyply reproducing more reasonable properties of UHMWPE fibers.Additionally,tensile simulations showed that orientation and crystallinity greatly impact Young's modulus more than molecular weight.Energy decomposition indicated that higher molecular weights lead to covalent bonds that can withstand more energy during stretching,thus increasing breaking strength.Combining simulations with machine learning,we found that orientation has the most significant impact on Young's modulus,contributing 60%,and molecular weight plays the most crucial role in determining the breaking strength,accounting for 65%.This study provides a theoretical basis and guidelines for enhancing UHMWPE's modulus and strength.
基金funded by the Natural Science Foundation of China[U20A20292]Shandong Province Science andTechnology SMES InnovationAbility Improvement Project[2023TSGC0005]China Postdoctoral Science Foundation[2024M752697].
文摘In nature,cavitation bubbles typically appear in clusters,engaging in interactions that create a variety of dynamicmotion patterns.To better understand the behavior ofmultiple bubble collapses and the mechanisms of interbubble interaction,this study employs molecular dynamics simulation combined with a coarse-grained force field.By focusing on collapsemorphology,local density,and pressure,it elucidates how the number and arrangement of bubbles influence the collapse process.The mechanisms behind inter-bubble interactions are also considered.The findings indicate that the collapse speed of unbounded bubbles located in lateral regions is greater than that of the bubbles in the center.Moreover,it is shown that asymmetrical bubble distributions lead to a shorter collapse time overall.
基金product of the research project titled,Video Camera Based Structural Health Monitoring of Historic Masonry Minarets and Development of a Long-Term Decision-Making Model Based on Deep Learning Method(Project No.222M140)supported by TÜBİTAK 1001-Scientific and the Technological Research Projects Support Program.
文摘This research focuses on the seismic responses of the historic masonry minarets,conducted through the creation of a digital twin model using finite element methods.The study initiated the development of a comprehensive model in the ANSYS Workbench,supplemented by operational modal analysis(OMA),to ascertain the dynamic characteristics of the minaret.The alignment of numerical and experimental frequency data was achieved using the response surface method(RSM)within ANSYS Workbench DesignXplorer.This process resulted in the establishment of a digital twin,accurately representing the physical minaret in a virtual environment.Blender^(■)software was then used to simulate the effects of two consecutive earthquakes in Türkiye that occurred on February 6,2023.The simulations highlighted the heightened susceptibility of the minaret,especially in its upper sections,to consecutive seismic activities,culminating in significant damage and collapse.This innovative approach,merging traditional engineering methods with a cutting-edge digital simulation,provides a profound insight into the seismic behavior of historical structures.The research underscores the importance of advanced seismic modeling for the effective preservation and resilience of architectural heritage sites against earthquake risks.
基金National MCF Energy R&D Program of China(2018YFE0306100)Natural Science Foundation of Hunan Province for Distinguished Young Scholars(2021JJ10062)+1 种基金National Natural Science Foundation of China(52101028)China Postdoctoral Science Foundation(2021M703628)。
文摘Combining the phase-field method and the moving boundary method,a three-dimensional phase-field simulation was conducted for the growth and grain evolution of Ti films deposited by physical vapor deposition under different deposition rates and grain orientations.The evolution of grain morphology and grain orientation was also taken into consideration.Simulation results show that at lower deposition rates,the surface of the formed Ti film exhibits a distinct oriented texture structure.The surface roughness of the Ti film is positively correlated with the grain misorientation.Moreover,the surface roughness obtained from the simulation is in good agreement with the experiment results.
基金National Natural Science Foundation of China(12372152)Guangdong Basic and Applied Basic Research Foundation(2023A1515011819,2024A1515012469)Shandong Provincial Natural Science Foundation(ZR2023MA058)。
文摘The core-shell structure in bulk TiNb binary alloy was designed and studied by phase-field simulations,where various core-shell structures were obtained by precise control of the initial and boundary conditions of the TiNb binary alloy system during spinodal decomposition,and then the formation mechanism of core-shell structure was revealed.In addition,the influences of initial temperature gradient,average temperature,and initial concentration distribution of the system on the core-shell structure were investigated.Results show that the initial concentration gradient is the key factor for forming the core-shell structure.Besides,larger initial temperature gradient and higher average temperature can promote the formation of core-shell structure,which can be stabilized by adjusting the initial concentration distribution of the Nb-rich region in TiNb binary alloy.As a theoretical basis,this research provides a novel and simple strategy for the preparation of TiNb-based alloys and other materials with peculiar core-shell structures and desirable mechanical and physical properties.
基金National Key Research and Development Program of China(2022YFB4600902)Shandong Provincial Science Foundation for Outstanding Young Scholars(ZR2024YQ020)。
文摘Wire arc additive manufacturing(WAAM)has emerged as a promising approach for fabricating large-scale components.However,conventional WAAM still faces challenges in optimizing microstructural evolution,minimizing additive-induced defects,and alleviating residual stress and deformation,all of which are critical for enhancing the mechanical performance of the manufactured parts.Integrating interlayer friction stir processing(FSP)into WAAM significantly enhances the quality of deposited materials.However,numerical simulation research focusing on elucidating the associated thermomechanical coupling mechanisms remains insufficient.A comprehensive numerical model was developed to simulate the thermomechanical coupling behavior in friction stir-assisted WAAM.The influence of post-deposition FSP on the coupled thermomechanical response of the WAAM process was analyzed quantitatively.Moreover,the residual stress distribution and deformation behavior under both single-layer and multilayer deposition conditions were investigated.Thermal analysis of different deposition layers in WAAM and friction stir-assisted WAAM was conducted.Results show that subsequent layer deposition induces partial remelting of the previously solidified layer,whereas FSP does not cause such remelting.Furthermore,thermal stress and deformation analysis confirm that interlayer FSP effectively mitigates residual stresses and distortion in WAAM components,thereby improving their structural integrity and mechanical properties.
基金supported by the National Natural Science Foundation of China(Grant No.52275460)the Key Research and Development Program Academician Cooperation Project of Tianjin(Grant No.24YFYSHZ00270)the Tianjin University of Technology Graduate Research(Grant No.YJ2303).
文摘Polyethersulfone(PES)can be widely used in extreme environments due to its exceptional strength and stability.In this study,molecular dynamics(MD)simulations were used to construct tribological models of PES under varying pressures.The variations of PES molecular chains and frictional interface properties were explored for understanding microscopic tribological mechanism.The simulation results show that high pressure and high vacuum conditions reduce the coefficient of friction and wear rate.The variations in radial distribution function(RDF),relative concentration of atoms,friction interface temperature,and atomic motion velocity were analyzed.It was found that high pressure and high vacuum promote PES molecular chains moving away from the surface of the iron atomic layer,decreasing interaction energy,RDF,temperature,and velocity at the friction interface.This work offers novel methodologies and theoretical insights for studying the friction and wear of polymer composites in complex environments.
基金supported by the National Natural Science Foundation of China(Grant Nos.22193032 and 32401033)the Research Fund of Wenzhou Institute,Chinese Academy of Sciences(Grant Nos.WIUCASQD2020009,WIUCASQD2023005,XSZD2024004,2021HZSY0061,and WIUCASICTP2022)。
文摘The F_(1)-ATPase and V_(1)-ATPase are rotary biomotors.Alignment of their amino acid sequences,which originate from bovine heart mitochondria(1BMF)and Enterococcus hirae(3VR6),respectively,demonstrates that the segment forming the ATP catalytic pocket is highly conserved.Single-molecule experiments,however,have revealed subtle differences in efficiency between the F_(1) and V_(1) motors.Here,we perform both atomistic and coarse-grained molecular dynamics simulations to investigate the mechanochemical coupling and coordination in F_(1) and V_(1) ATPase.Our results show that the correlation between conformational changes in F_(1) is stronger than that in V_(1),indicating that the mechanochemical coupling in F_(1) is tighter than in V_(1).Moreover,the unidirectional rotation of F_(1) is more processive than that of V_(1),which accounts for the higher efficiency observed in F_(1) and explains the occasional backward steps detected in single-molecule experiments on V_(1).
基金supported by the Advanced Materials-National Science and Technology Major Project(Grant No.2025ZD0618401)the National Natural Science Foundation of China(Grant No.12504285)+1 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20250472)NFSG grant from BITS-Pilani,Dubai campus。
文摘The rapid advancement of machine learning based tight-binding Hamiltonian(MLTB)methods has opened new avenues for efficient and accurate electronic structure simulations,particularly in large-scale systems and long-time scenarios.This review begins with a concise overview of traditional tight-binding(TB)models,including both(semi-)empirical and first-principles approaches,establishing the foundation for understanding MLTB developments.We then present a systematic classification of existing MLTB methodologies,grouped into two major categories:direct prediction of TB Hamiltonian elements and inference of empirical parameters.A comparative analysis with other ML-based electronic structure models is also provided,highlighting the advancement of MLTB approaches.Finally,we explore the emerging MLTB application ecosystem,highlighting how the integration of MLTB models with a diverse suite of post-processing tools from linear-scaling solvers to quantum transport frameworks and molecular dynamics interfaces is essential for tackling complex scientific problems across different domains.The continued advancement of this integrated paradigm promises to accelerate materials discovery and open new frontiers in the predictive simulation of complex quantum phenomena.
基金financially supported by the National Natural Science Foundation of China(Nos.52173020 and 52573023)。
文摘Vitrimers belong to a class of polymeric materials capable of bond exchange reactions,showing great promise for environmental protection and sustainable development.However,studies on the coupling mechanism between the bond exchange kinetics and segmental dynamics near the glass transition temperature(T_(g))remain scarce.Herein,we employed molecular dynamics simulations to investigate the dynamic heterogeneity of the segment motion and bond exchange in vitrimers.The simulation results revealed that the bond exchange energy barrier exerts a much stronger influence on the bond exchange kinetics than on the segmental dynamics.At lower temperatures,slower segmental relaxation further constraind the bond exchange rate.Additionally,increasing the bond exchange energy barrier markedly enhanced the dynamic heterogeneity of segment motion.A close correlation was observed between heterogeneity and bond exchange.This study elucidated the coupling mechanism between bond exchange and segmental dynamics at the molecular scale,thereby providing a theoretical basis for designing vitrimer materials with tunable dynamic properties.
文摘In federated learning,backdoor attacks have become an important research topic with their wide application in processing sensitive datasets.Since federated learning detects or modifies local models through defense mechanisms during aggregation,it is difficult to conduct effective backdoor attacks.In addition,existing backdoor attack methods are faced with challenges,such as low backdoor accuracy,poor ability to evade anomaly detection,and unstable model training.To address these challenges,a method called adaptive simulation backdoor attack(ASBA)is proposed.Specifically,ASBA improves the stability of model training by manipulating the local training process and using an adaptive mechanism,the ability of the malicious model to evade anomaly detection by combing large simulation training and clipping,and the backdoor accuracy by introducing a stimulus model to amplify the impact of the backdoor in the global model.Extensive comparative experiments under five advanced defense scenarios show that ASBA can effectively evade anomaly detection and achieve high backdoor accuracy in the global model.Furthermore,it exhibits excellent stability and effectiveness after multiple rounds of attacks,outperforming state-of-the-art backdoor attack methods.
基金funded by Humanities and Social Sciences of Ministry of Education Planning Fund of China,grant number 21YJA790009National Natural Science Foundation of China,grant number 72140001.
文摘With the rapid proliferation of electric vehicles,their charging loads pose new challenges to power grid stability and operational efficiency.To address this,this study employs a Monte Carlo simulation model to analyze the charging load characteristics of six battery electric vehicle categories in Hebei Province,leveraging multi-source probabilistic distribution data under typical operational scenarios.The findings reveal that electric vehicle charging loads are primarily concentrated during midday and nighttime periods,with significant load fluctuations exerting substantial pressure on the grid.In response,this paper proposes strategic interventions including optimized charging infrastructure planning,time-of-use electricity pricing mechanisms,and smart charging technologies to balance grid loads.The results provide a theoretical foundation for electric vehicle load forecasting,smart grid dispatching,and vehicle-grid integration,thereby enhancing grid operational efficiency and sustainability.
