Sunflower(Helianthus annuus L.)is one of the four major oil crops in the world and has high economic value.However,the lack of discrete element method(DEM)models and parameters for sunflower seeds hinders the applicat...Sunflower(Helianthus annuus L.)is one of the four major oil crops in the world and has high economic value.However,the lack of discrete element method(DEM)models and parameters for sunflower seeds hinders the application of DEM for computer simulation in the key working processes of sunflower seed sowing and harvesting.The present study was conducted on two varieties of sunflower,and the DEM model of sunflower seeds was established by using 3D scanning technology based on the distribution of triaxial dimensions and volumes of the geometric model of sunflower seeds.Similarly,the physical characteristics parameters of sunflower seeds were determined by physical tests and the simulation parameters were screened for significance based on the Plackett-Burman test.Our results show that the coefficient of static friction between sunflower seeds and the coefficient of rolling friction have significant effects on the repose angle of the simulation test.Furthermore,the optimal range of the significance parameters was further determined by the steepest climb test,and the second-order regression model of the significance parameters and the repose angle was obtained according to the Box-Behnken design test and Response Surface Methodology(RSM),with the repose angle measured by the physical test as the optimized target value to obtain the optimal parameter combination.Finally,a two-sample t-test for the repose angle of the physical test and the repose angle of the simulation test yielded P>0.05.Our results confirms that the repose angle obtained from simulation is not significantly different from the physical test value,and the relative errors between the repose angle of the simulation test and the physical test are 1.43%and 0.40%,respectively,for the optimal combination of parameters.Based on these results it can be concluded that the optimal parameters obtained from the calibration can be used for DEM simulation experiments related to the sunflower seed sowing and harvesting process.展开更多
Objective ：To evaluate the effect of osteogenic potential on human marrow mesenchymal stem cells （hMSCs） transferred with human vascular endothelial growth factor（VEGF） gene by adenovirus, methods：hMSCs were iso...Objective ：To evaluate the effect of osteogenic potential on human marrow mesenchymal stem cells （hMSCs） transferred with human vascular endothelial growth factor（VEGF） gene by adenovirus, methods：hMSCs were isolated from human marrow, cultured in vitro and randomly divided into 3 groups ：Ad-VEGF165 group： adding 1×10^10 OPU/ml Ad-VEGF in hMSCs culture fluid after incubating 24 hours, changing into ordinary complete culture and continuing culturing; Positive control group： Cultured hMSCs with 1 nmol/L dexamethasone, 10 mmol/L glycerophosphate and 50 mg/L vitamin C ,exchanging this conditioned medium twice a week; blank control group：no special treatment but culturing hMSCs in DMEM.To evaluate osteogenesis competence, Von Kossa＇s staining and a quantitative alkaline phosphates （ALP） activity analysis were performed after 2 weeks treatment. Results：The calcified nodes formed after 2 weeks treatment in Ad-VEGF165 group and Positive control group but not in blank control group. ALP activities in Ad-VEGF165 group ,Positive control group and blank control group were （7.91 ± 0.90）u/L, （8.18 ± 0.76 u/L） and （3.46 ± 0.49）u/L respectively. The differences were no statistical significance between Ad-VEGF165 group and positive control group （P 〉 0.05）, but Ad-VEGF165 group and Positive control group were significantly different with blank control group （P 〈 0.05）. Conclusion：Adenovirus mediated VEGF165 gene can transfect hMSCs and promote osteogenesis of hMSCs.展开更多
Using the data of China's OFDI in more than 150 host countries or regions for the period of 1991-2009, in this paper we examine the underlying motivations and locational determinants of China's OFDI, with a fo...Using the data of China's OFDI in more than 150 host countries or regions for the period of 1991-2009, in this paper we examine the underlying motivations and locational determinants of China's OFDI, with a focus on the role of natural resources and technology. Our findings indicate that the host country's natural resource abundance, interacted with its institutional quality, is a crucial determinant of China's OFDI. There is strong evidence that in the recent period of 2003-2009, the host country's overall natural resource abundance, oil abundance and metal abundance had a sizable positive effect on China's OFDI. In particular, China's OFDI was driven to resource-abundant countries with poor institutional quality and governance, and this pattern was strongest for oil but not metal resources. However, we find little evidence supporting the resourceseeking motivation in the pre-2003 period. Furthermore, we find strong evidence for the technology-exploiting motivation but not for the technology-seeking hypothesis. We show that, when the host is a lowincome country, China's OFDI increases if the host country's technology is more backward, indicating that Chinese investors might be taking advantage of their technology gap relative to the local firms.展开更多
During power grid cascading failure,the operating point changes frequently,resulting in a mismatch or inaccuracy of online pre-decision making emergency control strategy.To solve this problem,an online power system st...During power grid cascading failure,the operating point changes frequently,resulting in a mismatch or inaccuracy of online pre-decision making emergency control strategy.To solve this problem,an online power system stability decisionmaking and control method based on super-real-time simulation is presented in this paper.A decision-making and control system is developed in which the three main operation modes,offline pre-decision-making,online pre-decision-making,and real-time control,are all coordinated.To verify the method,ADPSS(advanced digital power system simulator)is used to simulate a digital power grid with about 20,000 buses.The closed-loop operation of the digital power grid and the online decisionmaking and control system are implemented.Test results show that when online pre-decision making control strategies are mismatched,aided real-time control works well and can prevent power grid stability loss.展开更多
基金funding for this study from Nature Science Foundation of China,Grant No.(51865047).
文摘Sunflower(Helianthus annuus L.)is one of the four major oil crops in the world and has high economic value.However,the lack of discrete element method(DEM)models and parameters for sunflower seeds hinders the application of DEM for computer simulation in the key working processes of sunflower seed sowing and harvesting.The present study was conducted on two varieties of sunflower,and the DEM model of sunflower seeds was established by using 3D scanning technology based on the distribution of triaxial dimensions and volumes of the geometric model of sunflower seeds.Similarly,the physical characteristics parameters of sunflower seeds were determined by physical tests and the simulation parameters were screened for significance based on the Plackett-Burman test.Our results show that the coefficient of static friction between sunflower seeds and the coefficient of rolling friction have significant effects on the repose angle of the simulation test.Furthermore,the optimal range of the significance parameters was further determined by the steepest climb test,and the second-order regression model of the significance parameters and the repose angle was obtained according to the Box-Behnken design test and Response Surface Methodology(RSM),with the repose angle measured by the physical test as the optimized target value to obtain the optimal parameter combination.Finally,a two-sample t-test for the repose angle of the physical test and the repose angle of the simulation test yielded P>0.05.Our results confirms that the repose angle obtained from simulation is not significantly different from the physical test value,and the relative errors between the repose angle of the simulation test and the physical test are 1.43%and 0.40%,respectively,for the optimal combination of parameters.Based on these results it can be concluded that the optimal parameters obtained from the calibration can be used for DEM simulation experiments related to the sunflower seed sowing and harvesting process.
基金This work was supported by Science Fund of Department of Edu-cation of Hubei Province( No.D200524007)
文摘Objective ：To evaluate the effect of osteogenic potential on human marrow mesenchymal stem cells （hMSCs） transferred with human vascular endothelial growth factor（VEGF） gene by adenovirus, methods：hMSCs were isolated from human marrow, cultured in vitro and randomly divided into 3 groups ：Ad-VEGF165 group： adding 1×10^10 OPU/ml Ad-VEGF in hMSCs culture fluid after incubating 24 hours, changing into ordinary complete culture and continuing culturing; Positive control group： Cultured hMSCs with 1 nmol/L dexamethasone, 10 mmol/L glycerophosphate and 50 mg/L vitamin C ,exchanging this conditioned medium twice a week; blank control group：no special treatment but culturing hMSCs in DMEM.To evaluate osteogenesis competence, Von Kossa＇s staining and a quantitative alkaline phosphates （ALP） activity analysis were performed after 2 weeks treatment. Results：The calcified nodes formed after 2 weeks treatment in Ad-VEGF165 group and Positive control group but not in blank control group. ALP activities in Ad-VEGF165 group ,Positive control group and blank control group were （7.91 ± 0.90）u/L, （8.18 ± 0.76 u/L） and （3.46 ± 0.49）u/L respectively. The differences were no statistical significance between Ad-VEGF165 group and positive control group （P 〉 0.05）, but Ad-VEGF165 group and Positive control group were significantly different with blank control group （P 〈 0.05）. Conclusion：Adenovirus mediated VEGF165 gene can transfect hMSCs and promote osteogenesis of hMSCs.
文摘Using the data of China's OFDI in more than 150 host countries or regions for the period of 1991-2009, in this paper we examine the underlying motivations and locational determinants of China's OFDI, with a focus on the role of natural resources and technology. Our findings indicate that the host country's natural resource abundance, interacted with its institutional quality, is a crucial determinant of China's OFDI. There is strong evidence that in the recent period of 2003-2009, the host country's overall natural resource abundance, oil abundance and metal abundance had a sizable positive effect on China's OFDI. In particular, China's OFDI was driven to resource-abundant countries with poor institutional quality and governance, and this pattern was strongest for oil but not metal resources. However, we find little evidence supporting the resourceseeking motivation in the pre-2003 period. Furthermore, we find strong evidence for the technology-exploiting motivation but not for the technology-seeking hypothesis. We show that, when the host is a lowincome country, China's OFDI increases if the host country's technology is more backward, indicating that Chinese investors might be taking advantage of their technology gap relative to the local firms.
基金supported in part by State Grid Corporation of China(SGCC)under Grant EPRIXFKJ(2010)2897.
文摘During power grid cascading failure,the operating point changes frequently,resulting in a mismatch or inaccuracy of online pre-decision making emergency control strategy.To solve this problem,an online power system stability decisionmaking and control method based on super-real-time simulation is presented in this paper.A decision-making and control system is developed in which the three main operation modes,offline pre-decision-making,online pre-decision-making,and real-time control,are all coordinated.To verify the method,ADPSS(advanced digital power system simulator)is used to simulate a digital power grid with about 20,000 buses.The closed-loop operation of the digital power grid and the online decisionmaking and control system are implemented.Test results show that when online pre-decision making control strategies are mismatched,aided real-time control works well and can prevent power grid stability loss.
