Developing high resolution finite difference scheme and enabling the use of this scheme on complex geometry are the aims of this study.High resolution has been achieved by Dissipative Compact Schemes(DCS),however,acco...Developing high resolution finite difference scheme and enabling the use of this scheme on complex geometry are the aims of this study.High resolution has been achieved by Dissipative Compact Schemes(DCS),however,according to the recent research,applications of DCS on complex geometry may have serious problem for that the Geometric Conservation Law(GCL)is not satisfied,and this may cause numerical instability.To cope with this problem,a new scheme named Hybrid cell-edge and cell-node Dissipative Compact Scheme(HDCS)has been formulated.The formulation of the HDCS contains two steps.First,a new central compact scheme is formulated for the purpose of conveniently fulfilling the GCL,and then dissipation is added on the central scheme by high-order dissipative interpolation of cell-edge variables.The solutions of Euler and Navier-Stokes equations show that the HDCS can be applied successfully on complex geometry,while the DCS may suffer numerical instabilities.Moreover,high resolution of the HDCS may be observed in the test of scattering of acoustic waves by multiple cylinders.展开更多
Reconfigurable intelligent surface(RIS)is a promising solution to deal with the blockage-sensitivity of millimeter wave band and reduce the high energy consumption caused by network densification. However, deploying l...Reconfigurable intelligent surface(RIS)is a promising solution to deal with the blockage-sensitivity of millimeter wave band and reduce the high energy consumption caused by network densification. However, deploying large scale RISs may not bring expected performance gain due to significant channel estimation overhead and non-negligible reflected interference.In this paper,we derive the analytical expressions of the coverage probability, area spectrum efficiency(ASE)and energy efficiency (EE)of a downlink RIS-aided multi-cell network.In order to optimize the network performance, we investigate the conditions for the optimal number of training symbols of each antenna-to-antenna and antenna-to-element path (referred to as the optimal unit training overhead) in channel estimation.Our study shows that:1)RIS deployment is not“the more, the better”, only when blockage objects are dense should one deploy more RISs;2) the coverage probability is maximized when the unit training overhead is designed as large as possible;3)however,the ASE-and-EE-optimal unit training overhead exists. It is a monotonically increasing function of the frame length and a monotonically decreasing function of the average signal-to-noise-ratio (in the high signal-to-noise-ratio region). Additionally,the optimal unit training overhead is smaller when communication nodes deploy particularly few or many antennas.展开更多
The open ratio of a current collector has a great impact on direct methanol fuel cell(DMFC)performance.Although a number of studies have investigated the influence of the open ratio of DMFC current collectors,far too ...The open ratio of a current collector has a great impact on direct methanol fuel cell(DMFC)performance.Although a number of studies have investigated the influence of the open ratio of DMFC current collectors,far too little attention has been given to how geometry(including the shape and feature size of the flow field)affects a current collector with an equal open ratio.In this paper,perforated and parallel current collectors with an equal open ratio of 50%and different feature sizes are designed,and the corresponding experimental results are shown to explain the geometry effects on the output power of the DMFC.The results indicate that the optimal feature sizes are between 2 and 2.5 mm for both perforated and parallel flow field in the current collectors with an equal open ratio of 50%.This means that for passive methanol fuel cells,to achieve the highest output power,the optimal feature size of the flow field in both anode and cathode current collectors is between 2 and 2.5 mm under the operating mode of this experiment.The effects of rib and channel position are also investigated,and the results indicate that the optimum pattern depends on the feature sizes of the flow field.展开更多
The neutronic properties of molten salt reactors(MSRs)differ from those of traditional solid fuel reactors owing to their nuclear fuel particularity.Based on the Monte-Carlo N particle transport code,the effects of th...The neutronic properties of molten salt reactors(MSRs)differ from those of traditional solid fuel reactors owing to their nuclear fuel particularity.Based on the Monte-Carlo N particle transport code,the effects of the size and shape of the fuel salt channel on the neutron physics of an MSR cell are investigated systematically in this study.The results show that the infinite multiplication factor(k?)first increases and then decreases with the change in the graphite cell size under certain fuel volume fraction(FVF)conditions.For the same FVF and average chord length,when the average chord length is relatively small,the k?values for different fuel salt channel shapes agree well.When the average chord length is relatively large,the k?values for different fuel salt channel shapes differ significantly.In addition,some examples of practical applications of this study are presented,including cell selection for the core and thermal expansion displacement analysis of the cell.展开更多
Dye-sensitized solar cells(DSCs)are promising photochemical solar cells owing to their high efficiency and low cost.In this study,the influence of cell geometry,electrolyte composition,and counter electrode(CE)charact...Dye-sensitized solar cells(DSCs)are promising photochemical solar cells owing to their high efficiency and low cost.In this study,the influence of cell geometry,electrolyte composition,and counter electrode(CE)characteristics on the performance of DSCs was investigated to aim at improving the cell efficiency.Using an U-type cell geometry proposed decreased the internal resistance of DSCs and therefore increased the fill factor and energy conversion efficiency.The addition of DMPII to the I-/I3-based electrolyte increased the open-circuit voltage by decreasing the dark current.Compared to the DSCs with the Pt CE prepared by the thermal decomposition of H2PtCl6,the DSCs with the sputtered Pt CE showed a higher fill factor and short-circuit current density,owing to the high electrical conductivity and enhanced light-reflecting ability of the mirror-like sputtered Pt CE.Based on these results,the energy conversion efficiency of the DSC with the TiO2 porous films fabricated by a room temperature cold spray method was increased from 3.93%to 5.11%.The relatively high efficiency shows that the room temperature cold spray is a prospective method in fabricating nanocrystalline TiO2 films for flexible DSCs.展开更多
Fuel cell vehicles(FCVs)are facing severe heat dissipation challenges because fuel cell stacks are required to operate at a narrower temperature range and higher heat dissipation than those in the internal combustion ...Fuel cell vehicles(FCVs)are facing severe heat dissipation challenges because fuel cell stacks are required to operate at a narrower temperature range and higher heat dissipation than those in the internal combustion engine.This study conducts a numerical analysis of a tube-strip heat exchanger applied in a high-performance FCV.The typical unit cell of the tube-strip heat exchanger is selected to numerically optimize the cell-level thermal performance of the heat exchanger.Effects of structural parameters and operational conditions are investigated.The optimal structure is obtained by focusing on the heat transfer rate and fan power at the air side,where the overall heat transfer rate of heat exchanger is determined by the effectiveness number of transfer unit method and the theoretical framework of volume averaging.The results show that the heat exchanger with rectangular fins exhibits a greater heat transfer rate than those with trapezoidal and triangular fins at an inlet air velocity of 4 m/s.Compared with the fin without a louver,the heat exchangers equipped with louvers parallel and vertical with the air flow achieve heat transfer rates of 33.1 and 42.8 kW,respectively,which increase by 2.0 kW(6.4%)and 11.7 kW(37.5%)in heat transfer rate.For high-power heat dissipation,the louvered heat exchanger with a fin pitch of 2 mm shows the best thermal performance given the same fan power.展开更多
This paper investigates the uplink throughput of Cognitive Radio Cellular Networks(CRCNs).As oppose to traditional performance evaluation schemes which mainly adopt complex system level simulations,we use the theoreti...This paper investigates the uplink throughput of Cognitive Radio Cellular Networks(CRCNs).As oppose to traditional performance evaluation schemes which mainly adopt complex system level simulations,we use the theoretical framework of stochastic geometry to provide a tractable and accurate analysis of the uplink throughput in the CRCN.By modelling the positions of User Equipments(UEs)and Base Stations(BSs)as Poisson Point Processes(PPPs),we analyse and derive expressions for the link rate and the cell throughput in the Primary(PR)and Secondary(SR)networks.The expressions show that the throughput of the CRCN is mainly affected by the density ratios between the UEs and the BSs in both the PR and SR networks.Besides,a comparative analysis of the link rate between random and regular BS deployments is concluded,and the results confirm the accuracy of our analysis.Furthermore,we define the cognitive throughput gain and derive an expression which is dominated by the traffic load in the PR network.展开更多
In this work,we propose incorporating the finite cell method(FCM)into the absolute nodal coordinate formulation(ANCF)to improve the efficiency and robustness of ANCF elements in simulating structures with complex loca...In this work,we propose incorporating the finite cell method(FCM)into the absolute nodal coordinate formulation(ANCF)to improve the efficiency and robustness of ANCF elements in simulating structures with complex local features.In addition,an adaptive subdomain integration method based on a triangulation technique is devised to avoid excessive subdivisions,largely reducing the computational cost.Numerical examples demonstrate the effectiveness of the proposed method in large deformation,large rotation and dynamics simulation.展开更多
Hanging-drop method has been widely used to fabricate three-dimensional (3D) in vitro tissue models due to its advantages such as being easy to perform, inexpensive, and permitting precise control of cell spheroid for...Hanging-drop method has been widely used to fabricate three-dimensional (3D) in vitro tissue models due to its advantages such as being easy to perform, inexpensive, and permitting precise control of cell spheroid formation. The geometry of hanging drop may play a critical role on the formation of cell spheroids, which, however, has not been explored. In this study, we developed a modified hanging-drop platform that enables the production of cell spheroids in a high-throughput manner by controlling hanging drop geometry with defined spreading ring. The surface tension force is proportional to the spreading ring and gravitational force is determined by the droplet volume, and the geometry can be determined by the balance between surface tension and gravity.β-TC-6 cell spheroids with optimized diameters were fabricated as 3D in vitro islet models. The models show morphology similar to primary islets and have functionality that more closely resembles primary islets than two-dimensional cell culture. The developed platform holds great potential for engineering well-controlled in vitro tissue models for various applications such as physiological and pathological studies, drug screening, as well as transplantation for treatment purpose.展开更多
基金supported by the National Basic Research Program of China(Grant no.2009CB723800)National Natural Science Foundation of China(Grand Nos.11072259 and 11202226)the Foundation of State Key Laboratory of Aerodynamics(Grand Nos.JBKY11030902 and JBKY11010100)
文摘Developing high resolution finite difference scheme and enabling the use of this scheme on complex geometry are the aims of this study.High resolution has been achieved by Dissipative Compact Schemes(DCS),however,according to the recent research,applications of DCS on complex geometry may have serious problem for that the Geometric Conservation Law(GCL)is not satisfied,and this may cause numerical instability.To cope with this problem,a new scheme named Hybrid cell-edge and cell-node Dissipative Compact Scheme(HDCS)has been formulated.The formulation of the HDCS contains two steps.First,a new central compact scheme is formulated for the purpose of conveniently fulfilling the GCL,and then dissipation is added on the central scheme by high-order dissipative interpolation of cell-edge variables.The solutions of Euler and Navier-Stokes equations show that the HDCS can be applied successfully on complex geometry,while the DCS may suffer numerical instabilities.Moreover,high resolution of the HDCS may be observed in the test of scattering of acoustic waves by multiple cylinders.
基金supported in part by the National Natural Science Foundation of China under Grants 62341108,62022049,and 62111530197.
文摘Reconfigurable intelligent surface(RIS)is a promising solution to deal with the blockage-sensitivity of millimeter wave band and reduce the high energy consumption caused by network densification. However, deploying large scale RISs may not bring expected performance gain due to significant channel estimation overhead and non-negligible reflected interference.In this paper,we derive the analytical expressions of the coverage probability, area spectrum efficiency(ASE)and energy efficiency (EE)of a downlink RIS-aided multi-cell network.In order to optimize the network performance, we investigate the conditions for the optimal number of training symbols of each antenna-to-antenna and antenna-to-element path (referred to as the optimal unit training overhead) in channel estimation.Our study shows that:1)RIS deployment is not“the more, the better”, only when blockage objects are dense should one deploy more RISs;2) the coverage probability is maximized when the unit training overhead is designed as large as possible;3)however,the ASE-and-EE-optimal unit training overhead exists. It is a monotonically increasing function of the frame length and a monotonically decreasing function of the average signal-to-noise-ratio (in the high signal-to-noise-ratio region). Additionally,the optimal unit training overhead is smaller when communication nodes deploy particularly few or many antennas.
基金supported by the National Natural Science Foundation of China (No.51405342)Natural Science Foundation of Tianjin (No.20JCYBJC00050)Jiangsu Key Laboratory of Precision and Micro-Manufacturing Technology.
文摘The open ratio of a current collector has a great impact on direct methanol fuel cell(DMFC)performance.Although a number of studies have investigated the influence of the open ratio of DMFC current collectors,far too little attention has been given to how geometry(including the shape and feature size of the flow field)affects a current collector with an equal open ratio.In this paper,perforated and parallel current collectors with an equal open ratio of 50%and different feature sizes are designed,and the corresponding experimental results are shown to explain the geometry effects on the output power of the DMFC.The results indicate that the optimal feature sizes are between 2 and 2.5 mm for both perforated and parallel flow field in the current collectors with an equal open ratio of 50%.This means that for passive methanol fuel cells,to achieve the highest output power,the optimal feature size of the flow field in both anode and cathode current collectors is between 2 and 2.5 mm under the operating mode of this experiment.The effects of rib and channel position are also investigated,and the results indicate that the optimum pattern depends on the feature sizes of the flow field.
基金This work was supported by the Chinese TMSR Strategic Pioneer Science and Technology Project(No.XDA02010000)the Frontier Science Key Program of Chinese Academy of Sciences(No.QYZDYSSW-JSC016)the Shanghai Sailing Program(No.Y931021031).
文摘The neutronic properties of molten salt reactors(MSRs)differ from those of traditional solid fuel reactors owing to their nuclear fuel particularity.Based on the Monte-Carlo N particle transport code,the effects of the size and shape of the fuel salt channel on the neutron physics of an MSR cell are investigated systematically in this study.The results show that the infinite multiplication factor(k?)first increases and then decreases with the change in the graphite cell size under certain fuel volume fraction(FVF)conditions.For the same FVF and average chord length,when the average chord length is relatively small,the k?values for different fuel salt channel shapes agree well.When the average chord length is relatively large,the k?values for different fuel salt channel shapes differ significantly.In addition,some examples of practical applications of this study are presented,including cell selection for the core and thermal expansion displacement analysis of the cell.
文摘Dye-sensitized solar cells(DSCs)are promising photochemical solar cells owing to their high efficiency and low cost.In this study,the influence of cell geometry,electrolyte composition,and counter electrode(CE)characteristics on the performance of DSCs was investigated to aim at improving the cell efficiency.Using an U-type cell geometry proposed decreased the internal resistance of DSCs and therefore increased the fill factor and energy conversion efficiency.The addition of DMPII to the I-/I3-based electrolyte increased the open-circuit voltage by decreasing the dark current.Compared to the DSCs with the Pt CE prepared by the thermal decomposition of H2PtCl6,the DSCs with the sputtered Pt CE showed a higher fill factor and short-circuit current density,owing to the high electrical conductivity and enhanced light-reflecting ability of the mirror-like sputtered Pt CE.Based on these results,the energy conversion efficiency of the DSC with the TiO2 porous films fabricated by a room temperature cold spray method was increased from 3.93%to 5.11%.The relatively high efficiency shows that the room temperature cold spray is a prospective method in fabricating nanocrystalline TiO2 films for flexible DSCs.
基金Natural Science Foundation of China(51876113)project is acknowledged.
文摘Fuel cell vehicles(FCVs)are facing severe heat dissipation challenges because fuel cell stacks are required to operate at a narrower temperature range and higher heat dissipation than those in the internal combustion engine.This study conducts a numerical analysis of a tube-strip heat exchanger applied in a high-performance FCV.The typical unit cell of the tube-strip heat exchanger is selected to numerically optimize the cell-level thermal performance of the heat exchanger.Effects of structural parameters and operational conditions are investigated.The optimal structure is obtained by focusing on the heat transfer rate and fan power at the air side,where the overall heat transfer rate of heat exchanger is determined by the effectiveness number of transfer unit method and the theoretical framework of volume averaging.The results show that the heat exchanger with rectangular fins exhibits a greater heat transfer rate than those with trapezoidal and triangular fins at an inlet air velocity of 4 m/s.Compared with the fin without a louver,the heat exchangers equipped with louvers parallel and vertical with the air flow achieve heat transfer rates of 33.1 and 42.8 kW,respectively,which increase by 2.0 kW(6.4%)and 11.7 kW(37.5%)in heat transfer rate.For high-power heat dissipation,the louvered heat exchanger with a fin pitch of 2 mm shows the best thermal performance given the same fan power.
基金supported by the National Key Basic Research Program of China (973 Program)under Grant No. 2009CB320401the National Natural Science Foundation of China under Grants No. 61171099, No. 61101117+1 种基金the National Key Scientific and Technological Project of China under Grants No. 2012ZX03004005-002, No. 2012ZX03003-007the Fundamental Research Funds for the Central Universities under Grant No. BUPT2012RC0112
文摘This paper investigates the uplink throughput of Cognitive Radio Cellular Networks(CRCNs).As oppose to traditional performance evaluation schemes which mainly adopt complex system level simulations,we use the theoretical framework of stochastic geometry to provide a tractable and accurate analysis of the uplink throughput in the CRCN.By modelling the positions of User Equipments(UEs)and Base Stations(BSs)as Poisson Point Processes(PPPs),we analyse and derive expressions for the link rate and the cell throughput in the Primary(PR)and Secondary(SR)networks.The expressions show that the throughput of the CRCN is mainly affected by the density ratios between the UEs and the BSs in both the PR and SR networks.Besides,a comparative analysis of the link rate between random and regular BS deployments is concluded,and the results confirm the accuracy of our analysis.Furthermore,we define the cognitive throughput gain and derive an expression which is dominated by the traffic load in the PR network.
基金supported by the National Natural Science Foundation of China(Grant Nos.52175223,and 11802072)the Fundamental Research Funds for the Central Universities(Grant No.B210201038).
文摘In this work,we propose incorporating the finite cell method(FCM)into the absolute nodal coordinate formulation(ANCF)to improve the efficiency and robustness of ANCF elements in simulating structures with complex local features.In addition,an adaptive subdomain integration method based on a triangulation technique is devised to avoid excessive subdivisions,largely reducing the computational cost.Numerical examples demonstrate the effectiveness of the proposed method in large deformation,large rotation and dynamics simulation.
基金the National Natural Science Foundation of China (Grants 51605377 and 81300696)the Natural Science Foundation of Shaanxi Province (Grant 2017JQ5004).
文摘Hanging-drop method has been widely used to fabricate three-dimensional (3D) in vitro tissue models due to its advantages such as being easy to perform, inexpensive, and permitting precise control of cell spheroid formation. The geometry of hanging drop may play a critical role on the formation of cell spheroids, which, however, has not been explored. In this study, we developed a modified hanging-drop platform that enables the production of cell spheroids in a high-throughput manner by controlling hanging drop geometry with defined spreading ring. The surface tension force is proportional to the spreading ring and gravitational force is determined by the droplet volume, and the geometry can be determined by the balance between surface tension and gravity.β-TC-6 cell spheroids with optimized diameters were fabricated as 3D in vitro islet models. The models show morphology similar to primary islets and have functionality that more closely resembles primary islets than two-dimensional cell culture. The developed platform holds great potential for engineering well-controlled in vitro tissue models for various applications such as physiological and pathological studies, drug screening, as well as transplantation for treatment purpose.
