A robust radio map is essential in implementing a fingerprint-based indoor positioning system(IPS).However,the offline site survey to manually construct the radio map is time-consuming and labour-intensive.Various int...A robust radio map is essential in implementing a fingerprint-based indoor positioning system(IPS).However,the offline site survey to manually construct the radio map is time-consuming and labour-intensive.Various interpolation techniques have been proposed to infer the virtual fingerprints to reduce the time and effort required for offline site surveys.This paper presents a novel fingerprint interpolator using a multi-path loss model(MPLM)to create the virtual fingerprints from the collected sample data based on different signal paths from different access points(APs).Based on the historical signal data,the poor signal paths are identified using their standard deviations.The proposed method reduces the positioning errors by smoothing out the wireless signal fluctuations and stabilizing the signals for those poor signal paths.By consideringmultipath signal propagations from different APs,the inherent noise from these signal paths can be alleviated.Firstly,locations of the signal data with standard deviations higher than the threshold are identified.The new fingerprints are then generated at these locations based on the proposed M-PLM interpolation function to replace the old fingerprints.The proposed technique interpolates virtual fingerprints based on good signal paths with more stable signals to improve the positioning performance.Experimental results show that the proposed scheme enhances the positioning accuracy by up to 44%compared to the conventional interpolation techniques such as the Inverse DistanceWeighting,Kriging,and single Path LossModel.As a result,we can overcome the site survey problems for IPS by building an accurate radio map with more reliable signals to improve indoor positioning performance.展开更多
The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have fo...The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.展开更多
Wideband IMT-Advanced mobile communication systems tend to operate in the high frequency bandsdue to a relatively large capacity available .Thus,Measurement and modelling methods of radio propaga-tion characteristics ...Wideband IMT-Advanced mobile communication systems tend to operate in the high frequency bandsdue to a relatively large capacity available .Thus,Measurement and modelling methods of radio propaga-tion characteristics are proposed for the field test of Chinese 4th generation(4G)trial system.The mea-surement system is established for 3 .5GHz based on the sophisticated measurement instruments and thevirtual instrument technology.The characteristic parameters of radio propagation such as path loss(PL)exponent and shadow fading standard deviation are extracted from measurement data,which result in thepath loss model finally.The comparisons with other existing international models results validate our mea-surement in terms of path loss model .Based on the analysis of the existing extension model assumed forthe microwave frequency at 3 .5GHz,we find that the Stanford University Interim(SUI)model fits verywell with the measurement result in the hotspot scenario,while the COST 231 model is closer to the mea-surement result in the suburban scenario.This result provides a measurement-based channel reference forthe development of the future IMT-Advanced systems in China.展开更多
Increasing attention has been paid to the efficiency improvement of the induction traction system of high-speed trains due to the high demand for energy saving. In emergency self-propelled mode, however, the dc-link v...Increasing attention has been paid to the efficiency improvement of the induction traction system of high-speed trains due to the high demand for energy saving. In emergency self-propelled mode, however, the dc-link voltage and the traction power of the motor are significantly reduced, resulting in decreased traction efficiency due to the low load and low speed operations. Aiming to tackle this problem, a novel efficiency improved control method is introduced to the emergency mode of high-speed train traction system in this paper. In the proposed method, a total loss model of induction motor considering the behaviors of both iron and copper loss is established. An improved iterative algorithm with decreased computational burden is then introduced, resulting in a fast solving of the optimal flux reference for loss minimization at each control period. In addition, considering the parameter variation problem due to the low load and low speed operations, a parameter estimation method is integrated to improve the controller's robustness. The effectiveness of the proposed method on efficiency improvement at low voltage and low load conditions is demonstrated by simulated and experimental results.展开更多
The main compressor in a supercritical carbon dioxide(SCO2)Brayton cycle works near the critical point where the physical properties of CO_(2)are far away from the ideal gas.To investigate the effectiveness of the con...The main compressor in a supercritical carbon dioxide(SCO2)Brayton cycle works near the critical point where the physical properties of CO_(2)are far away from the ideal gas.To investigate the effectiveness of the conventional one-dimensional(1D)loss models for predicting the performance of compressors working in such nontraditional conditions,detailed comparisons of 1D predicted performance,experimental data and threedimensional CFD results are made.A 1D analysis method with enthalpy and total pressure based loss system is developed for multistage SCO2 centrifugal compressors,and it is firstly validated against the experimental results of a single stage SCO2 centrifugal compressor from the Sandia National Laboratory.A good agreement of pressure ratios with experiments can be achieved by the 1D method.But the efficiency deviations reveal the potential deficiencies of the parasitic loss models.On the basis of the validation,a two-stage SCO2 centrifugal compressor is employed to do the evaluation.Three-dimensional CFD simulations are performed.Detailed comparisons are made between the CFD and the 1D results at different stations located in the compressor.The features of the deviations are analyzed in detail,as well as the reasons that might cause these deviations.展开更多
In the early stage of aircraft engine design, the through-flow method is an important tool for designers. The accuracy of the through-flow method depends heavily on the accuracy of the loss model. However, most existi...In the early stage of aircraft engine design, the through-flow method is an important tool for designers. The accuracy of the through-flow method depends heavily on the accuracy of the loss model. However, most existing models cannot(or cannot well) provide the spanwise loss distribution. To construct an effective spanwise loss model, both turbomachinery knowledge and machine learning skills were used in this paper. A large number of numerical simulations were carried out to build a database containing more than 1000 compressor cascade numerical samples. Secondary flow intensity was introduced as the independent variable to carry out feature engineering. A model containing a selector based on support vector machine regression and estimators based on K-nearest neighbor regression was constructed. Numerical test set and design data of two former highpressure core compressors were used for validation. Results suggest that the spanwise loss model show good consistency with both numerical test set and data of two former compressors. It can reflect the influence of secondary flow and can also predict both value and trend of total pressure loss coefficient well, with mean absolute error general around or less than 1% and R^(2)(coefficient of determination) more than 0.8 on the test set. Especially when dealing with loss coefficient at midspan position, the model shows even better performance, with R^(2)over 0.97 on the test set. And the selector of the model can well classify the samples, predict the intensity of secondary flow and help estimators to capture the phenomenon that end-wall secondary flow extends to the mid-span.展开更多
Hybrid Si/SiC switches constituting a parallel connection of a lower current rated SiC MOSFET and a higher current rated Si IGBT are becoming very attractive solution for designing high frequency and high-power densit...Hybrid Si/SiC switches constituting a parallel connection of a lower current rated SiC MOSFET and a higher current rated Si IGBT are becoming very attractive solution for designing high frequency and high-power density power electronic converters.Due to the complementary nature of Si IGBT devices(smaller inverter cost and smaller conduction loss)and SiC devices(smaller switching loss and higher junction temperature capability),these novel switch device configurations enable a good tradeoff between cost and efficiency for high power converter applications.One such recent application of hybrid Si/SiC switches for efficiency-cost optimization is an Si/SiC hybrid switch based ANPC inverter proposed in Ref.[30].In Ref.[30]the topology structure,modulation strategy and the efficiency-cost benefits of the proposed ANPC inverter is presented.In this paper a precise electro-thermal power loss model for this ANPC inverter topology will be presented based on the modulation strategy of the inverter and the operating characteristics of the Si/SiC hybrid switches.The power loss model development takes into account how the current sharing between the two internal devices of the Si/SiC hybrid switches and their corresponding gate control method affects their power loss.A brief introduction to the topology structure and operation principle of the Si/SiC based ANPC inverter is first highlighted to provide context for readers and then a detailed description of the proposed electro-thermal power loss model is presented.The precision of the electro-thermal power loss model introduced in this paper is then validated using experimentally measured energy loss,device temperature and inverter efficiency data.展开更多
The modeling of switching loss in semiconductor power devices is important in practice for the prediction and evaluation of thermal safety and system reliability.Both simulation-based behavioral models and data proces...The modeling of switching loss in semiconductor power devices is important in practice for the prediction and evaluation of thermal safety and system reliability.Both simulation-based behavioral models and data processing-based empirical models are difficult and have limited applications.Although the artificial neural network(ANN) algorithm has often been used for modeling, it has never been used for modeling insulated gate bipolar transistor(IGBT) transient loss.In this paper, we attempt to use the ANN method for this purpose, using a customized switching loss test bench.We compare its performance with two conventional curve-fitting models and verify the results by experiment.Our model is generally superior in calculation speed, accuracy, and data requirement, and is also able to be extended to loss modeling for all kinds of semiconductor power devices.展开更多
Age-related hearing loss (AHL), or presbycusis, is the most common neurodegenerative disorder and top communication deficit of the aged population. Genetic predisposition is one of the major factors in the development...Age-related hearing loss (AHL), or presbycusis, is the most common neurodegenerative disorder and top communication deficit of the aged population. Genetic predisposition is one of the major factors in the development of AHL. Generally, AHL is associated with an age-dependent loss of sensory hair cells, spiral ganglion neurons and stria vascularis cells in the inner ear. Although the mechanisms leading to genetic hearing loss are not completely understood, caspase-family proteases function as important signals in the inner ear pathology. It is now accepted that mouse models are the best tools to study the mechanism of genetic hearing loss or AHL. Here, we provide a brief review of recent studies on hearing improvement in mouse models of AHL by anti-apoptotic treatment.展开更多
The central solenoid(CS) is an important component of China Fusion Engineering Test Reactor, for producing, forming and stabilizing plasma in the superconducting tokamak. It is a complicated work to design and manufac...The central solenoid(CS) is an important component of China Fusion Engineering Test Reactor, for producing, forming and stabilizing plasma in the superconducting tokamak. It is a complicated work to design and manufacture the large superconducting CS magnet, so it is meaningful to design a central solenoid model coil(CSMC) and analyze its electromagnetic properties in advance. In this paper, the structure, design parameters and magnetic field distribution of the CS model coil are discussed. The peak power of radial and axial turn conductors and time bucket loss are analyzed by using piecewise-linear method. The CSMC AC loss with different Nb3 Sn CICCs and AC loss of ITER CS coil are compared. The special electrometric method to measure AC loss of the CS model coil for future reference is presented.展开更多
This paper discusses the model-based predictive controller design of networked nonlinear systems with communica- tion delay and data loss. Based on the analysis of the closed-loop networked predictive control systems,...This paper discusses the model-based predictive controller design of networked nonlinear systems with communica- tion delay and data loss. Based on the analysis of the closed-loop networked predictive control systems, the model-based networked predictive control strategy can compensate for communication delay and data loss in an active way. The designed model-based predictive controller can also guarantee the stability of the closed-loop networked system. The simulation re- suits demonstrate the feasibility and efficacy of the proposed model-based predictive controller design scheme.展开更多
For multivariate linear model Y=XΘ+ε, ~N(0, σ 2ΣV), this paper is concerned with the admissibility of linear estimators of estimable function SXΘ in the class of all estimators. All admissible linear estimators ...For multivariate linear model Y=XΘ+ε, ~N(0, σ 2ΣV), this paper is concerned with the admissibility of linear estimators of estimable function SXΘ in the class of all estimators. All admissible linear estimators of SXΘ are given under each of four definitions of admissibility.展开更多
This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass particles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly prem...This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass particles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly premixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions: gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity(i.e.u≥1). The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the determining factors on the flame temperature and burning velocity of biomass particles are declared in this research.展开更多
Objective To establish an animal model of sudden onset sensorineural hearing loss (SSNHL) to study its mechanisms. Materials and methods The inner ear was exposed to 3-nitropropionic acid at 0.5 mol/L (3-NP (H)) and 0...Objective To establish an animal model of sudden onset sensorineural hearing loss (SSNHL) to study its mechanisms. Materials and methods The inner ear was exposed to 3-nitropropionic acid at 0.5 mol/L (3-NP (H)) and 0.3 mol/L (3-NP (L)) through the round window membrane for 30 minutes in 50 male guinea pigs. Thresholds of auditory brainstem responses(ABR) were established before the treatment and retested at 4 hours, 1 day, 3 days and 6 days following 3-NP exposure. Control animals were treated with phosphate buffered saline (PBS) and their ABRs were retested at 4 hours and 1 day after the treatment. Animals were monitored for nystagmus and postural signs of vestibular dysfunction, using a digital video camera, following the treatment procedure. Specimens were taken at 12 hours, 1 day, 3 days and 7 days following 3-NP(H) exposure and embedded in JB4 for light microscopy observation. Results ABRs were lost in all animals tested at 4 hours following 3-NP (H) exposure. The rate of complete ABR loss decreased as post-treatment test time increased. ABRs were lost in 80% (4/5) of the animals at 1 day after exposure to 3-NP (L). Spontaneous horizontal nystagmus with a fast phase away from the treated ear developed in all 3-NP (H)-treated animals and in 20 % ( 1/5) of the animals exposed to 3-NP (L), except for the one treated bilaterally. Various degree of postural disturbances consistent with unilateral vestibular dysfunction, such as spontaneous barrel rolling towards the exposure side while walking, were seen in all animals exposed to 3-NP(H) and 40% (2/5) of animals exposed to 3-NP(L), except for the one animal treated bilaterally, which showed no signs of imbalance. Both nystagmus and postural disturbances resolved in 2 days following 3-NP exposure. Histological study showed temporary edema tin the organ or Corti, Claudius cells and the inner sulcus cells 3 days after 3-NP (H) treatment. Enlargement of intercellular space in the spiral prominence was first noticed at 12 hours post-3-NP (H) exposure, progressed at day 3 and recovered at day 7. Vacuoles in the cellular plasm and nucleus was seen as early as at 12 hours post-3-NP exposure in the spiral ganglion cells, and signs of degeneration were visible at day 7. Conclusion Inner ear exposure to 3-NP through the round window membrane appears to reproduce clinic manifestations and may serve as a legitimate animal model of SSNHL展开更多
Podocyte loss was well known in type 2 diabetic nephropathy patients. The objective of the present study was to determine the number of podocytes and the degree of albuminuria in diabetic KK-Ay/Ta (KK-Ay) mice which h...Podocyte loss was well known in type 2 diabetic nephropathy patients. The objective of the present study was to determine the number of podocytes and the degree of albuminuria in diabetic KK-Ay/Ta (KK-Ay) mice which had been reported as diabetic nephropathy model. Diabetic KK-Ay mice, diabetic KK/Ta mice and non-diabetic BALB/cA Jcl (BALB/cA) mice were studied. We analyzed glomerular lesions in all mice by morphometric analysis and immunofluorescence to determine the number of podocytes. Level of urinary albumin was also measured. Glomerular enlargement and mesangial expansion were observed in KK-Ay mice. Mean number of podocytes per glomerulus (NG pod) in diabetic KK-Ay mice was significantly lower than that in non-diabetic BALB/cA mice. Mean NG pod/glomerular area (GA) per glomerulus was also significantly decreased in diabetic KK-Ay mice. The level of urinary albumin/creatinine ratio (ACR) in diabetic KK-Ay mice was significantly higher than that in non-diabetic BALB/cA mice. These data suggest that podocyte loss might induce albuminuria in KK-Ay mice. This finding confirmed our previous report that KK-Ay mice, especially in terms of histological findings, are a suitable animal model for glomerular injury in type 2 diabetic nephropathy.展开更多
Weed management in summer season foxtall millet field was studied by evaluating weed damage and exploring competition between weeds and foxtail millet, and a few fitting models were simulated and compared by employing...Weed management in summer season foxtall millet field was studied by evaluating weed damage and exploring competition between weeds and foxtail millet, and a few fitting models were simulated and compared by employing field plot experiment and nonlinear regression analysis. The results showed that the millet yield losses and weed density were extremely significantly correlated. Among the tested models, the determination coefficient ( R2 ) of hyperbolic model was 0.997 12, and minimum residual sum of squares was 16.174, which was considered the optimal model to simulate the competition relation between weeds and millet. The predicted equation was Y = d/( 1. 733 + 0. 018d) ; the interspecific competitiveness of weeds was 0. 577 0 and the intraspecific competitiveness was 0.010 3 ; the maximum loss rate of millet yield was 55.56%. This study had established an analysis model with high gcodness-of-fit and practical prediction which could help weed management in summer season millet field.展开更多
Droughts and soil erosion are among the most prominent climatic driven hazards in drylands,leading to detrimental environmental impacts,such as degraded lands,deteriorated ecosystem services and biodiversity,and incre...Droughts and soil erosion are among the most prominent climatic driven hazards in drylands,leading to detrimental environmental impacts,such as degraded lands,deteriorated ecosystem services and biodiversity,and increased greenhouse gas emissions.In response to the current lack of studies combining drought conditions and soil erosion processes,in this study,we developed a comprehensive Geographic Information System(GIS)-based approach to assess soil erosion and droughts,thereby revealing the relationship between soil erosion and droughts under an arid climate.The vegetation condition index(VCI)and temperature condition index(TCI)derived respectively from the enhanced vegetation index(EVI)MOD13A2 and land surface temperature(LST)MOD11A2 products were combined to generate the vegetation health index(VHI).The VHI has been conceived as an efficient tool to monitor droughts in the Negueb watershed,southeastern Tunisia.The revised universal soil loss equation(RUSLE)model was applied to quantitatively estimate soil erosion.The relationship between soil erosion and droughts was investigated through Pearson correlation.Results exhibited that the Negueb watershed experienced recurrent mild to extreme drought during 2000–2016.The average soil erosion rate was determined to be 1.8 t/(hm2•a).The mountainous western part of the watershed was the most vulnerable not only to soil erosion but also to droughts.The slope length and steepness factor was shown to be the most significant controlling parameter driving soil erosion.The relationship between droughts and soil erosion had a positive correlation(r=0.3);however,the correlation was highly varied spatially across the watershed.Drought was linked to soil erosion in the Negueb watershed.The current study provides insight for natural disaster risk assessment,land managers,and stake-holders to apply appropriate management measures to promote sustainable development goals in fragile environments.展开更多
Due to the influence of magnetic hysteresis and energy loss inherent in giant magnetostrictive materials (GMM), output displacement accuracy of giant magnetostrictive actuator (GMA) can not meet the precision and ...Due to the influence of magnetic hysteresis and energy loss inherent in giant magnetostrictive materials (GMM), output displacement accuracy of giant magnetostrictive actuator (GMA) can not meet the precision and ultra precision machining. Using a GMM rod as the core driving element, a GMA which may be used in the field of precision and ultra precision drive engineering is designed through modular design method. Based on the Armstrong theory and elastic Gibbs free energy theory, a nonlinear magnetostriction model which considers magnetic hysteresis and energy loss characteristics is established. Moreover, the mechanical system differential equation model for GMA is established by utilizing D'Alembert's principle. Experimental results show that the model can preferably predict magnetization property, magnetic potential orientation, energy loss for GMM. It is also able to describe magnetostrictive elongation and output displacement of GMA. Research results will provide a theoretical basis for solving the dynamic magnetic hysteresis, energy loss and working precision for GMA fundamentally.展开更多
On the basis of Artificial Neural Network theory, a back propagation neural network with one middle layer is building in this paper, and its algorithms is also given, Using this BP network model, study the case of Mal...On the basis of Artificial Neural Network theory, a back propagation neural network with one middle layer is building in this paper, and its algorithms is also given, Using this BP network model, study the case of Malian-River basin. The results by calculating show that the solution based on BP algorithms are consis- tent with those based multiple - variables linear regression model. They also indicate that BP model in this paper is reasonable and BP algorithms are feasible.展开更多
基金funded by the Ministry of Higher EducationMalaysia under the Fundamental Research Grant Scheme(FRGS)with grant number FRGS/1/2019/ICT02/MMU/02/1.
文摘A robust radio map is essential in implementing a fingerprint-based indoor positioning system(IPS).However,the offline site survey to manually construct the radio map is time-consuming and labour-intensive.Various interpolation techniques have been proposed to infer the virtual fingerprints to reduce the time and effort required for offline site surveys.This paper presents a novel fingerprint interpolator using a multi-path loss model(MPLM)to create the virtual fingerprints from the collected sample data based on different signal paths from different access points(APs).Based on the historical signal data,the poor signal paths are identified using their standard deviations.The proposed method reduces the positioning errors by smoothing out the wireless signal fluctuations and stabilizing the signals for those poor signal paths.By consideringmultipath signal propagations from different APs,the inherent noise from these signal paths can be alleviated.Firstly,locations of the signal data with standard deviations higher than the threshold are identified.The new fingerprints are then generated at these locations based on the proposed M-PLM interpolation function to replace the old fingerprints.The proposed technique interpolates virtual fingerprints based on good signal paths with more stable signals to improve the positioning performance.Experimental results show that the proposed scheme enhances the positioning accuracy by up to 44%compared to the conventional interpolation techniques such as the Inverse DistanceWeighting,Kriging,and single Path LossModel.As a result,we can overcome the site survey problems for IPS by building an accurate radio map with more reliable signals to improve indoor positioning performance.
文摘The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.
基金supported by the High Technology Research and Development Programme of China(2007AA01Z278)
文摘Wideband IMT-Advanced mobile communication systems tend to operate in the high frequency bandsdue to a relatively large capacity available .Thus,Measurement and modelling methods of radio propaga-tion characteristics are proposed for the field test of Chinese 4th generation(4G)trial system.The mea-surement system is established for 3 .5GHz based on the sophisticated measurement instruments and thevirtual instrument technology.The characteristic parameters of radio propagation such as path loss(PL)exponent and shadow fading standard deviation are extracted from measurement data,which result in thepath loss model finally.The comparisons with other existing international models results validate our mea-surement in terms of path loss model .Based on the analysis of the existing extension model assumed forthe microwave frequency at 3 .5GHz,we find that the Stanford University Interim(SUI)model fits verywell with the measurement result in the hotspot scenario,while the COST 231 model is closer to the mea-surement result in the suburban scenario.This result provides a measurement-based channel reference forthe development of the future IMT-Advanced systems in China.
基金supported in part by the Science Foundation of the Chinese Academy of Railway Sciences under Grant Number:2023QT001。
文摘Increasing attention has been paid to the efficiency improvement of the induction traction system of high-speed trains due to the high demand for energy saving. In emergency self-propelled mode, however, the dc-link voltage and the traction power of the motor are significantly reduced, resulting in decreased traction efficiency due to the low load and low speed operations. Aiming to tackle this problem, a novel efficiency improved control method is introduced to the emergency mode of high-speed train traction system in this paper. In the proposed method, a total loss model of induction motor considering the behaviors of both iron and copper loss is established. An improved iterative algorithm with decreased computational burden is then introduced, resulting in a fast solving of the optimal flux reference for loss minimization at each control period. In addition, considering the parameter variation problem due to the low load and low speed operations, a parameter estimation method is integrated to improve the controller's robustness. The effectiveness of the proposed method on efficiency improvement at low voltage and low load conditions is demonstrated by simulated and experimental results.
基金supported by the National Key Research and Development Program of China(No.2016YFB0600100)National Natural Science Foundation of China(No.51506195)the Collaborative Innovation Center of Major Machine Manufacturing in Liaoning。
文摘The main compressor in a supercritical carbon dioxide(SCO2)Brayton cycle works near the critical point where the physical properties of CO_(2)are far away from the ideal gas.To investigate the effectiveness of the conventional one-dimensional(1D)loss models for predicting the performance of compressors working in such nontraditional conditions,detailed comparisons of 1D predicted performance,experimental data and threedimensional CFD results are made.A 1D analysis method with enthalpy and total pressure based loss system is developed for multistage SCO2 centrifugal compressors,and it is firstly validated against the experimental results of a single stage SCO2 centrifugal compressor from the Sandia National Laboratory.A good agreement of pressure ratios with experiments can be achieved by the 1D method.But the efficiency deviations reveal the potential deficiencies of the parasitic loss models.On the basis of the validation,a two-stage SCO2 centrifugal compressor is employed to do the evaluation.Three-dimensional CFD simulations are performed.Detailed comparisons are made between the CFD and the 1D results at different stations located in the compressor.The features of the deviations are analyzed in detail,as well as the reasons that might cause these deviations.
基金the support of National Science and Technology Major Project of China(No.2017-I-0005-0006)。
文摘In the early stage of aircraft engine design, the through-flow method is an important tool for designers. The accuracy of the through-flow method depends heavily on the accuracy of the loss model. However, most existing models cannot(or cannot well) provide the spanwise loss distribution. To construct an effective spanwise loss model, both turbomachinery knowledge and machine learning skills were used in this paper. A large number of numerical simulations were carried out to build a database containing more than 1000 compressor cascade numerical samples. Secondary flow intensity was introduced as the independent variable to carry out feature engineering. A model containing a selector based on support vector machine regression and estimators based on K-nearest neighbor regression was constructed. Numerical test set and design data of two former highpressure core compressors were used for validation. Results suggest that the spanwise loss model show good consistency with both numerical test set and data of two former compressors. It can reflect the influence of secondary flow and can also predict both value and trend of total pressure loss coefficient well, with mean absolute error general around or less than 1% and R^(2)(coefficient of determination) more than 0.8 on the test set. Especially when dealing with loss coefficient at midspan position, the model shows even better performance, with R^(2)over 0.97 on the test set. And the selector of the model can well classify the samples, predict the intensity of secondary flow and help estimators to capture the phenomenon that end-wall secondary flow extends to the mid-span.
文摘Hybrid Si/SiC switches constituting a parallel connection of a lower current rated SiC MOSFET and a higher current rated Si IGBT are becoming very attractive solution for designing high frequency and high-power density power electronic converters.Due to the complementary nature of Si IGBT devices(smaller inverter cost and smaller conduction loss)and SiC devices(smaller switching loss and higher junction temperature capability),these novel switch device configurations enable a good tradeoff between cost and efficiency for high power converter applications.One such recent application of hybrid Si/SiC switches for efficiency-cost optimization is an Si/SiC hybrid switch based ANPC inverter proposed in Ref.[30].In Ref.[30]the topology structure,modulation strategy and the efficiency-cost benefits of the proposed ANPC inverter is presented.In this paper a precise electro-thermal power loss model for this ANPC inverter topology will be presented based on the modulation strategy of the inverter and the operating characteristics of the Si/SiC hybrid switches.The power loss model development takes into account how the current sharing between the two internal devices of the Si/SiC hybrid switches and their corresponding gate control method affects their power loss.A brief introduction to the topology structure and operation principle of the Si/SiC based ANPC inverter is first highlighted to provide context for readers and then a detailed description of the proposed electro-thermal power loss model is presented.The precision of the electro-thermal power loss model introduced in this paper is then validated using experimentally measured energy loss,device temperature and inverter efficiency data.
基金Project supported by the Power Electronics Science and Education Development Program of Delta Environmental & Educational Foundation (No. DREO2006022)the National Natural Science Foundation of China (No. 50737002)
文摘The modeling of switching loss in semiconductor power devices is important in practice for the prediction and evaluation of thermal safety and system reliability.Both simulation-based behavioral models and data processing-based empirical models are difficult and have limited applications.Although the artificial neural network(ANN) algorithm has often been used for modeling, it has never been used for modeling insulated gate bipolar transistor(IGBT) transient loss.In this paper, we attempt to use the ANN method for this purpose, using a customized switching loss test bench.We compare its performance with two conventional curve-fitting models and verify the results by experiment.Our model is generally superior in calculation speed, accuracy, and data requirement, and is also able to be extended to loss modeling for all kinds of semiconductor power devices.
基金supported by National Natural Science Foundation of China (No. 81271092, 81570927)Scientific and Technological Developing Grant in Shandong Province (2014GSF118083)+1 种基金Scientific and Technological Developing Grant for Medicine and Health in Shandong Province (2015WS0507)Research Initiation Grant of Binzhou Medical University (BY2012KYQD01, BY2013KYQD15)
文摘Age-related hearing loss (AHL), or presbycusis, is the most common neurodegenerative disorder and top communication deficit of the aged population. Genetic predisposition is one of the major factors in the development of AHL. Generally, AHL is associated with an age-dependent loss of sensory hair cells, spiral ganglion neurons and stria vascularis cells in the inner ear. Although the mechanisms leading to genetic hearing loss are not completely understood, caspase-family proteases function as important signals in the inner ear pathology. It is now accepted that mouse models are the best tools to study the mechanism of genetic hearing loss or AHL. Here, we provide a brief review of recent studies on hearing improvement in mouse models of AHL by anti-apoptotic treatment.
文摘The central solenoid(CS) is an important component of China Fusion Engineering Test Reactor, for producing, forming and stabilizing plasma in the superconducting tokamak. It is a complicated work to design and manufacture the large superconducting CS magnet, so it is meaningful to design a central solenoid model coil(CSMC) and analyze its electromagnetic properties in advance. In this paper, the structure, design parameters and magnetic field distribution of the CS model coil are discussed. The peak power of radial and axial turn conductors and time bucket loss are analyzed by using piecewise-linear method. The CSMC AC loss with different Nb3 Sn CICCs and AC loss of ITER CS coil are compared. The special electrometric method to measure AC loss of the CS model coil for future reference is presented.
基金Project supported by the Key Program for the National Natural Science Foundation of China(Grant No.61333003)the General Program for the National Natural Science Foundation of China(Grant No.61273104)
文摘This paper discusses the model-based predictive controller design of networked nonlinear systems with communica- tion delay and data loss. Based on the analysis of the closed-loop networked predictive control systems, the model-based networked predictive control strategy can compensate for communication delay and data loss in an active way. The designed model-based predictive controller can also guarantee the stability of the closed-loop networked system. The simulation re- suits demonstrate the feasibility and efficacy of the proposed model-based predictive controller design scheme.
文摘For multivariate linear model Y=XΘ+ε, ~N(0, σ 2ΣV), this paper is concerned with the admissibility of linear estimators of estimable function SXΘ in the class of all estimators. All admissible linear estimators of SXΘ are given under each of four definitions of admissibility.
文摘This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass particles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly premixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions: gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity(i.e.u≥1). The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the determining factors on the flame temperature and burning velocity of biomass particles are declared in this research.
基金Supported by grants from National Natural Science Foundation of China: 30572019Xinhua Hospital Foundation, Shanghai Jiaotong University School of Medicine.
文摘Objective To establish an animal model of sudden onset sensorineural hearing loss (SSNHL) to study its mechanisms. Materials and methods The inner ear was exposed to 3-nitropropionic acid at 0.5 mol/L (3-NP (H)) and 0.3 mol/L (3-NP (L)) through the round window membrane for 30 minutes in 50 male guinea pigs. Thresholds of auditory brainstem responses(ABR) were established before the treatment and retested at 4 hours, 1 day, 3 days and 6 days following 3-NP exposure. Control animals were treated with phosphate buffered saline (PBS) and their ABRs were retested at 4 hours and 1 day after the treatment. Animals were monitored for nystagmus and postural signs of vestibular dysfunction, using a digital video camera, following the treatment procedure. Specimens were taken at 12 hours, 1 day, 3 days and 7 days following 3-NP(H) exposure and embedded in JB4 for light microscopy observation. Results ABRs were lost in all animals tested at 4 hours following 3-NP (H) exposure. The rate of complete ABR loss decreased as post-treatment test time increased. ABRs were lost in 80% (4/5) of the animals at 1 day after exposure to 3-NP (L). Spontaneous horizontal nystagmus with a fast phase away from the treated ear developed in all 3-NP (H)-treated animals and in 20 % ( 1/5) of the animals exposed to 3-NP (L), except for the one treated bilaterally. Various degree of postural disturbances consistent with unilateral vestibular dysfunction, such as spontaneous barrel rolling towards the exposure side while walking, were seen in all animals exposed to 3-NP(H) and 40% (2/5) of animals exposed to 3-NP(L), except for the one animal treated bilaterally, which showed no signs of imbalance. Both nystagmus and postural disturbances resolved in 2 days following 3-NP exposure. Histological study showed temporary edema tin the organ or Corti, Claudius cells and the inner sulcus cells 3 days after 3-NP (H) treatment. Enlargement of intercellular space in the spiral prominence was first noticed at 12 hours post-3-NP (H) exposure, progressed at day 3 and recovered at day 7. Vacuoles in the cellular plasm and nucleus was seen as early as at 12 hours post-3-NP exposure in the spiral ganglion cells, and signs of degeneration were visible at day 7. Conclusion Inner ear exposure to 3-NP through the round window membrane appears to reproduce clinic manifestations and may serve as a legitimate animal model of SSNHL
文摘Podocyte loss was well known in type 2 diabetic nephropathy patients. The objective of the present study was to determine the number of podocytes and the degree of albuminuria in diabetic KK-Ay/Ta (KK-Ay) mice which had been reported as diabetic nephropathy model. Diabetic KK-Ay mice, diabetic KK/Ta mice and non-diabetic BALB/cA Jcl (BALB/cA) mice were studied. We analyzed glomerular lesions in all mice by morphometric analysis and immunofluorescence to determine the number of podocytes. Level of urinary albumin was also measured. Glomerular enlargement and mesangial expansion were observed in KK-Ay mice. Mean number of podocytes per glomerulus (NG pod) in diabetic KK-Ay mice was significantly lower than that in non-diabetic BALB/cA mice. Mean NG pod/glomerular area (GA) per glomerulus was also significantly decreased in diabetic KK-Ay mice. The level of urinary albumin/creatinine ratio (ACR) in diabetic KK-Ay mice was significantly higher than that in non-diabetic BALB/cA mice. These data suggest that podocyte loss might induce albuminuria in KK-Ay mice. This finding confirmed our previous report that KK-Ay mice, especially in terms of histological findings, are a suitable animal model for glomerular injury in type 2 diabetic nephropathy.
基金Supported by Science and Technology Support Program of Hebei Province(09250307D)Special Fund for Agro-scientific Research in the Public Interest (20120304201)
文摘Weed management in summer season foxtall millet field was studied by evaluating weed damage and exploring competition between weeds and foxtail millet, and a few fitting models were simulated and compared by employing field plot experiment and nonlinear regression analysis. The results showed that the millet yield losses and weed density were extremely significantly correlated. Among the tested models, the determination coefficient ( R2 ) of hyperbolic model was 0.997 12, and minimum residual sum of squares was 16.174, which was considered the optimal model to simulate the competition relation between weeds and millet. The predicted equation was Y = d/( 1. 733 + 0. 018d) ; the interspecific competitiveness of weeds was 0. 577 0 and the intraspecific competitiveness was 0.010 3 ; the maximum loss rate of millet yield was 55.56%. This study had established an analysis model with high gcodness-of-fit and practical prediction which could help weed management in summer season millet field.
基金Chinese Academy of Sciences (CAS)The World Academy of Science (TWAS) for providing financial support
文摘Droughts and soil erosion are among the most prominent climatic driven hazards in drylands,leading to detrimental environmental impacts,such as degraded lands,deteriorated ecosystem services and biodiversity,and increased greenhouse gas emissions.In response to the current lack of studies combining drought conditions and soil erosion processes,in this study,we developed a comprehensive Geographic Information System(GIS)-based approach to assess soil erosion and droughts,thereby revealing the relationship between soil erosion and droughts under an arid climate.The vegetation condition index(VCI)and temperature condition index(TCI)derived respectively from the enhanced vegetation index(EVI)MOD13A2 and land surface temperature(LST)MOD11A2 products were combined to generate the vegetation health index(VHI).The VHI has been conceived as an efficient tool to monitor droughts in the Negueb watershed,southeastern Tunisia.The revised universal soil loss equation(RUSLE)model was applied to quantitatively estimate soil erosion.The relationship between soil erosion and droughts was investigated through Pearson correlation.Results exhibited that the Negueb watershed experienced recurrent mild to extreme drought during 2000–2016.The average soil erosion rate was determined to be 1.8 t/(hm2•a).The mountainous western part of the watershed was the most vulnerable not only to soil erosion but also to droughts.The slope length and steepness factor was shown to be the most significant controlling parameter driving soil erosion.The relationship between droughts and soil erosion had a positive correlation(r=0.3);however,the correlation was highly varied spatially across the watershed.Drought was linked to soil erosion in the Negueb watershed.The current study provides insight for natural disaster risk assessment,land managers,and stake-holders to apply appropriate management measures to promote sustainable development goals in fragile environments.
基金Supported by National Natural Science Foundation of China(Grant No.51305277)Doctoral Program of Higher Education China(Grant No.20132102120007)+1 种基金Shenyang Science and Technology Plan Project(Grant No.F15-199-1-14)China Postdoctoral Science Foundation(Grant No.2014T70261)
文摘Due to the influence of magnetic hysteresis and energy loss inherent in giant magnetostrictive materials (GMM), output displacement accuracy of giant magnetostrictive actuator (GMA) can not meet the precision and ultra precision machining. Using a GMM rod as the core driving element, a GMA which may be used in the field of precision and ultra precision drive engineering is designed through modular design method. Based on the Armstrong theory and elastic Gibbs free energy theory, a nonlinear magnetostriction model which considers magnetic hysteresis and energy loss characteristics is established. Moreover, the mechanical system differential equation model for GMA is established by utilizing D'Alembert's principle. Experimental results show that the model can preferably predict magnetization property, magnetic potential orientation, energy loss for GMM. It is also able to describe magnetostrictive elongation and output displacement of GMA. Research results will provide a theoretical basis for solving the dynamic magnetic hysteresis, energy loss and working precision for GMA fundamentally.
基金Supported by Brilliant Youth Fund in Hebei Province
文摘On the basis of Artificial Neural Network theory, a back propagation neural network with one middle layer is building in this paper, and its algorithms is also given, Using this BP network model, study the case of Malian-River basin. The results by calculating show that the solution based on BP algorithms are consis- tent with those based multiple - variables linear regression model. They also indicate that BP model in this paper is reasonable and BP algorithms are feasible.