913 research outputs found

    Reactive force field molecular dynamics simulation of pyridine combustion assisted by an electric field

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    The reduction of nitrogen oxides (NOx) is a perennial challenge for fuel combustion. Electric field enhanced combustion is a promising technology to decrease NOx emissions during the combustion process. This study aims to investigate the effects of electric field on fuel-NOx formation during pyridine (the main nitrogen-containing compounds in fossil fuels) combustion. The yields of main products (NO, NO2, N2, CO and CO2) are investigated during pyridine oxidation with external electric field imposed. Results indicate that electric field can reduce emissions (CO and NO) during pyridine combustion. Moreover, the reaction mechanisms of pyridine oxidation under different electric fields are explored at atomic scales, which provides an explanation for the changes of main products at varying electric field characteristics. This study fills the current knowledge gaps concerning the electric field influence on fuel-NOx emissions, which has the potential to form control strategies for NOx emissions during fossil fuel combustion

    Understanding mechanisms of pyridine oxidation with ozone addition via reactive force field molecular dynamics simulations

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    Ozone assisted combustion is a promising method to control combustion, ignition and pollutant formation. In this study, we investigated the ozone behaviours in fuel-NOx control through reactive force field (ReaxFF) molecular dynamics (MD) simulations of pyridine (a main nitrogen-containing compound in coal) oxidation under different ozone concentrations. The results show that ozone enhances the pyridine combustion process and facilitates the conversion of CO to CO2 and NO to NO2. Ozone participates in the reactions with intermediates and promotes the generation of active particles like OH, HO2, HO3 and H2O2. This research reveals mechanisms, at the atomic level, for the effects of main products formation during pyridine oxidation under different levels of ozone addition. The present study provides the scientific base for the control of NOx emissions through ozone assisted combustion technology

    Understanding the Role of Endothelial Glycocalyx in Mechanotransduction via Computational Simulation: A Mini Review

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    Endothelial glycocalyx (EG) is a forest-like structure, covering the lumen side of blood vessel walls. EG is exposed to the mechanical forces of blood flow, mainly shear, and closely associated with vascular regulation, health, diseases, and therapies. One hallmark function of the EG is mechanotransduction, which means the EG senses the mechanical signals from the blood flow and then transmits the signals into the cells. Using numerical modelling methods or in silico experiments to investigate EG-related topics has gained increasing momentum in recent years, thanks to tremendous progress in supercomputing. Numerical modelling and simulation allows certain very specific or even extreme conditions to be fulfilled, which provides new insights and complements experimental observations. This mini review examines the application of numerical methods in EG-related studies, focusing on how computer simulation contributes to the understanding of EG as a mechanotransducer. The numerical methods covered in this review include macroscopic (i.e., continuum-based), mesoscopic [e.g., lattice Boltzmann method (LBM) and dissipative particle dynamics (DPD)] and microscopic [e.g., molecular dynamics (MD) and Monte Carlo (MC) methods]. Accounting for the emerging trends in artificial intelligence and the advent of exascale computing, the future of numerical simulation for EG-related problems is also contemplated

    Effects of water on pyridine pyrolysis: A reactive force field molecular dynamics study

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    The emission of nitrogen oxides (NOx) from coal combustion causes serious environmental problems. Fuel splitting and staging is a promising method for NOx control by combustion modification. In this process, nitrogen-containing compounds generated from pyrolysis gas play an important role in regulating NOx generation. Water from coal could potentially change reactions during the coal pyrolysis process. Adjusting the content of water in coal may be an effective way to control coal pyrolysis reactions. This work aims to investigate the effects of water on pyridine (a main nitrogen-containing compound in coal) pyrolysis via reactive force field (ReaxFF) molecular dynamics (MD) simulations. Results indicate that the addition of water during the pyridine pyrolysis process increases the number of OH radicals in the system and accelerates the consumption of pyridine at the initial stage. However, at a later stage, water inhibits the consumption of pyridine as it impedes the condensation reaction of pyridine molecules. Common and unique intermediates are identified and quantified under various water-content conditions. Results suggest that water also reduces the proportion of nitrogen atoms in the polycondensation product. Furthermore, ring opening processes of pyridine molecules are reproduced at the atomic level. The changes in reaction pathways due to the presence of water are also revealed. The new insights into the mechanisms of pyridine pyrolysis under water and water-free conditions provide a possibility to control nitrogen migration during the pyrolysis process, which is of great significance to emission reduction from coal combustion

    Regimes of Flow over Complex Structures of Endothelial Glycocalyx: A Molecular Dynamics Simulation Study

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    Flow patterns on surfaces grafted with complex structures play a pivotal role in many engineering and biomedical applications. In this research, large-scale molecular dynamics (MD) simulations are conducted to study the flow over complex surface structures of an endothelial glycocalyx layer. A detailed structure of glycocalyx has been adopted and the flow/glycocalyx system comprises about 5,800,000 atoms. Four cases involving varying external forces and modified glycocalyx configurations are constructed to reveal intricate fluid behaviour. Flow profiles including temporal evolutions and spatial distributions of velocity are illustrated. Moreover, streamline length and vorticity distributions under the four scenarios are compared and discussed to elucidate the effects of external forces and glycocalyx configurations on flow patterns. Results show that sugar chain configurations affect streamline length distributions but their impact on vorticity distributions is statistically insignificant, whilst the influence of the external forces on both streamline length and vorticity distributions are trivial. Finally, a regime diagram for flow over complex surface structures is proposed to categorise flow patterns

    Large-scale molecular dynamics simulation of coupled dynamics of flow and glycocalyx: towards understanding atomic events on an endothelial cell surface

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    The glycocalyx has a prominent role in orchestrating multiple biological processes occurring at the plasma membrane. In this paper, an all-atom flow/glycocalyx system is constructed with the bulk flow velocity in the physiologically relevant ranges for the first time. The system is simulated by molecular dynamics using 5.8 million atoms. Flow dynamics and statistics in the presence of the glycocalyx are presented and discussed. Complex dynamic behaviours of the glycocalyx, particularly the sugar chains, are observed in response to blood flow. In turn, the motion of the glycocalyx, including swing and swirling, disturbs the flow by altering the velocity profiles and modifying the vorticity distributions. As a result, the initially one-dimensional forcing is spread to all directions in the region near the endothelial cell surface. Furthermore, the coupled dynamics exist not only between the flow and the glycocalyx but also within the glycocalyx molecular constituents. Shear stress distributions between one-dimer and three-dimer cases are also conducted. Finally, potential force transmission pathways are discussed based on the dynamics of the glycocalyx constituents, which provides new insight into the mechanism of mechanotransduction of the glycocalyx. These findings have relevance in the pathologies of glycocalyx-related diseases, for example in renal or cardiovascular conditions

    Electromechanical modeling and experimental analysis of a compression-based piezoelectric vibration energy harvester

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    Over the past few decades, wireless sensor networks have been widely used in the field of structure health monitoring of civil, mechanical, and aerospace systems. Currently, most wireless sensor networks are battery-powered and it is costly and unsustainable for maintenance because of the requirement for frequent battery replacements. As an attempt to address such issue, this article theoretically and experimentally studies a compression-based piezoelectric energy harvester using a multilayer stack configuration, which is suitable for civil infrastructure system applications where large compressive loads occur, such as heavily vehicular loading acting on pavements. In this article, we firstly present analytical and numerical modeling of the piezoelectric multilayer stack under axial compressive loading, which is based on the linear theory of piezoelectricity. A two-degree-of-freedom electromechanical model, considering both the mechanical and electrical aspects of the proposed harvester, was developed to characterize the harvested electrical power under the external electrical load. Exact closed-form expressions of the electromechanical models have been derived to analyze the mechanical and electrical properties of the proposed harvester. The theoretical analyses are validated through several experiments for a test prototype under harmonic excitations. The test results exhibit very good agreement with the analytical analyses and numerical simulations for a range of resistive loads and input excitation levels. © 2014 The Author(s)

    Large-scale molecular dynamics simulation of flow under complex structure of endothelial glycocalyx

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    In this research, large-scale molecular dynamics (MD) simulations were conducted to study the fluid dynamics inside the endothelial glycocalyx layer. A work flowchart regarding constructing the flow/glycocalyx system, undertaking production simulation using the MD method and post-processing was proposed. Following the flowchart, physiological and accelerating flow cases were simulated to reveal velocity and shear stress distributions over the dendritic (tree-like) structure of the glycocalyx, thereby contributing to understanding of the influence of biomolecular complex structures on flow profiles. Besides, the selection of thermostat algorithm was discussed. Results have shown that when the forcing is below a critical value, the velocity fluctuates around a zero mean along the height in the presence of the dendritic glycocalyx. When the forcing is larger than a critical value, the bulk flow was accelerated excessively, departing from the typical physiological flow. Furthermore, distributions of shear stress magnitude among three sub-regions in the ectodomain indicate that shear stress is enhanced near the membrane surface but is impaired in the sugar-chain-rich region due to the flow regulation by sugar chains. Finally, comparisons of velocity evolutions under two widely used thermostats (Lowe-Andersen and Berendsen thermostats) imply that the Lowe-Andersen algorithm is a suitable thermostat for flow problems

    Membrane Deformation of Endothelial Surface Layer Interspersed with Syndecan-4: A Molecular Dynamics Study

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    The lipid membrane of endothelial cells plays a pivotal role in maintaining normal circulatory system functions. To investigate the response of the endothelial cell membrane to changes in vascular conditions, an atomistic model of the lipid membrane interspersed with Syndecan-4 core protein was established based on experimental observations and a series of molecular dynamics simulations were undertaken. The results show that flow results in continuous deformation of the lipid membrane, and the degree of membrane deformation is not in monotonic relationship with the environmental changes (either the changes in blood velocity or the alteration of the core protein configuration). An explanation for such non-monotonic relationship is provided, which agrees with previous experimental results. The elevation of the lipid membrane surface around the core protein of the endothelial glycocalyx was also observed, which can be mainly attributed to the Coulombic interactions between the biomolecules therein. The present study demonstrates that the blood flow can deform the lipid membrane directly via the interactions between water molecules and lipid membrane atoms thereby affecting mechanosensing; it also presents an additional force transmission pathway from the flow to the lipid membrane via the glycocalyx core protein, which complements previous mechanotransduction hypothesis

    Estimation of land production and its response to cultivated land conversion in North China Plain

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    Major State Basic Research Development Program of China 2010CB950904;National Natural Science Foundation of China 70503025 40801231;Chinese Academy of Sciences KZCX2-YW-305-2Food safety and its related influencing factors in China are the hot research topics currently, and cultivated land conversion is one of the significant factors influencing food safety in China. Taking the North China Plain as the study area, this paper examines the changes of cultivated land area using satellite images, estimates land productivity from 1985 to 2005 using the model of Estimation System for Land Productivity (ESLP), and analyzes the impact of cultivated land conversion on the land production. Compared with the grain yield data from statistical yearbooks, the results indicate that ESLP model is an effective tool for estimating land productivity. Land productivity in the North China Plain showed a slight decreasing trend from 1985 to 2005, spatially, increased from the north to the south gradually, and the net changes varied in different areas. Cultivated land area recorded a marginal decrease of 8.0 x 10(5) ha, mainly converted to other land uses. Cultivated land conversion had more significant negative impacts on land production than land productivity did. Land production decreased by about 6.48 x 10(6) t caused by cultivated land conversion between 1985 and 2005, accounting for 91.9% of the total land production reduction. Although the land productivity increased in Anhui and Jiangsu provinces, it can not offset the overall adverse effects caused by cultivated land conversion. Therefore, there are significant meanings to control the cultivated land conversion and improve the land productivity for ensuring the land production in the North China Plain