From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly int...From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly interlinked multiple microgrids(MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.展开更多
One of the potential solutions to steel-corrosion-related problems is the usage of fiber reinforced polymer （FRP） as a replacement of steel bars. In the past few decades, researchers have conducted a large number of...One of the potential solutions to steel-corrosion-related problems is the usage of fiber reinforced polymer （FRP） as a replacement of steel bars. In the past few decades, researchers have conducted a large number of experimental and theoretical studies on the behavior of small size glass fiber reinforce polymer （GFRP） bars （diameter smaller than 20 ram）. However, the behavior of large size GFRP bar is still not well understood. Particularly, few studies were conducted on the stress relaxation of grouted entirely large diameter GFRP soil nail. This paper investigates the effect of stress levels on the relaxation behavior of GFRP soil nail under sustained deformation ranging from 30% to 60% of its ultimate strain. In order to study the behavior of stress relaxation, two B-GFRP soil nail element specimens were developed and instrumented with fiber Bragg grating （FBG） strain sensors which were used to measure strains along the B-GFRP bars. The test results reveal that the behavior of stress relaxation of B-GFRP soil nail element subjected to pre-stress is significantly related to the elapsed time and the initial stress of relaxation procedure. The newly proposed model for evaluating stress relaxation ratio can substantially reflect the influences of the nature of B-GFRP bar and the property of grip body. The strain on the nail body can be redistributed automatically. Modulus reduction is not the single reason for the stress degradation.展开更多
The complex effects of different nitrogen （N） contents and thermal routines on the microstructure and mechanical properties of 33Mn2V steels for N80-Class seamless casing tube application were investigated using Gle...The complex effects of different nitrogen （N） contents and thermal routines on the microstructure and mechanical properties of 33Mn2V steels for N80-Class seamless casing tube application were investigated using Gleeble simulation technique. The results showed that the N additions of 0. 014 %- 0. 021 % in the steels for the in-line normalization process （ILNP） increased the strength while the toughngss remained at a high level as compared with the steel with N content of 0. 005 %. It was also revealed that the N addition of 0. 021%could enhance the performance combination of strength and toughness in the steels by using 700 ℃ as the cooling interrupted temperature （CIT） for the non in-line normalizing process （NILNP）. It was further evidenced that the toughness was improved at expense of strength to some degree in all the steels by decreasing reheating temperature for the ILNP, while an increase of CIT for NILNP severely impaired the toughness and slightly improve the strength in the high-N steel with N content of 0. 021%. This can be attributed to the dissolution and precipitation behavior of V（C,N）. The optimization of V （C,N） precipitation could be achieved by enhancing N. The precipitation of V（C, N） in austenite was promoted by cooling to a certain temperature lower than the A,1 for the ILNP. The V（C,N） particles formed in austenite contrib- uted to grain refinement by the VN-induced nucleation of intragranular ferrite, but as a result the effect of precipitation on strengthening would become weaker due to a decrease of the precipitation of V in ferrite.展开更多
Purpose:To evaluate the efficacy of the Seamless Transfer of Care Model(STCM)to improve readmission occurrence of patients withstroke.Methods:The sample was comprised of fifty-nine subjects with stroke who were hospit...Purpose:To evaluate the efficacy of the Seamless Transfer of Care Model(STCM)to improve readmission occurrence of patients withstroke.Methods:The sample was comprised of fifty-nine subjects with stroke who were hospitalized in the geriatric and neurology departments of a large university hospital in China.Subjects were allocated to an STCM group(n=30)or a routine care(control)group(n=29).Results:Compared with the control group,the STCM group had a higher quality of life(p<0.05),higher compliance(p<0.05)and a lower readmission rate(p<0.05).Conclusion:Based on our results,the application of the STCM in Chinese stroke patients can improve quality of life and compliance,and reduce readmission rate.展开更多
Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 &#...Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 × 1080- LCDs and a half-transmission and half- reflection prisms was proposed in this paper.The physical principal and error model due to the splicing structure has been discussed and analyzed in detail.Based on the Tsinghua Micro star tracker,the error effect and system accuracy has been carefully tested and calibrated.The result showed that this simulator can get the accuracy of 10.4 "(3sigma) within a field of view of,which can meet the simulating requirement of modern star tracker,whose accuracy can reach 3"(3sigma) 。展开更多
With the aid of FE （finite element） code MSC.Superform 2005, 2-D coupled thermo-mechanical simulation of center-crack occurrence in round billet during 2-roll rotary rolling process was presented using Oyane ductile...With the aid of FE （finite element） code MSC.Superform 2005, 2-D coupled thermo-mechanical simulation of center-crack occurrence in round billet during 2-roll rotary rolling process was presented using Oyane ductile fracture criteria. A simple modeling is put forward based on the spiral motion of the workpiece as an essential characteristic in movement. The influence of the feed angle and the entry cone angle of the main roll on the process was taken into account in the modeling. The soundness for simplifying the 3-D rotary rolling into a 2-D problem was discussed. By adopting the parameters of Diescher piercer in 140mm mandrel mill of Bao Steel, the distribution and development of strain/stress were analyzed, and the eigen value of ductile fracture as well. The critical percentage of diameter reduction was obtained from the simulation. The result showed a good agreement with the experimental value, and therefore was of widely guiding significance to the practical process for rationally formulating the deformation parameters of steel tube piercing.展开更多
基金supported by National NaturalScience Foundation of China (No. 51507109, No. 51707128)Science and Technology Project of China Southern Power Grid (No. GZKJQQ00000417)
文摘From flexible interconnection among feeders to hybrid alternating current(AC) and direct current(DC)distribution structures of future smart distribution systems medium-voltage DC distribution centers with flexibly interlinked multiple microgrids(MGs) will have wide applications on the demand side. A generic coordinated control framework based on a distributed cooperation scheme is proposed for such DC centers, as opposed to centralized control structures. A novel unified control only using local measurements is proposed for these interlinking converters. During normal power disturbances, automatic coordinated power control and mutual support among sub-systems can be realized, thereby improving DC voltage and AC frequency stability to enable multiple MGs to be treated as a real unified cluster. Moreover, with this method, interlinking converters can realize seamless transition in power dispatching mode, common DC bus voltage control mode, and MG support mode without communication and control system switching. A simplified dynamic model has been developed to verify the proposed control strategy. This work is expected to provide a new solution for flexible interconnection and operational control of large-scale MG clusters.
基金financially supported by the Government of Guangdong Province and the Ministry of Education of China (Grant No. 2009B09060011)
文摘One of the potential solutions to steel-corrosion-related problems is the usage of fiber reinforced polymer （FRP） as a replacement of steel bars. In the past few decades, researchers have conducted a large number of experimental and theoretical studies on the behavior of small size glass fiber reinforce polymer （GFRP） bars （diameter smaller than 20 ram）. However, the behavior of large size GFRP bar is still not well understood. Particularly, few studies were conducted on the stress relaxation of grouted entirely large diameter GFRP soil nail. This paper investigates the effect of stress levels on the relaxation behavior of GFRP soil nail under sustained deformation ranging from 30% to 60% of its ultimate strain. In order to study the behavior of stress relaxation, two B-GFRP soil nail element specimens were developed and instrumented with fiber Bragg grating （FBG） strain sensors which were used to measure strains along the B-GFRP bars. The test results reveal that the behavior of stress relaxation of B-GFRP soil nail element subjected to pre-stress is significantly related to the elapsed time and the initial stress of relaxation procedure. The newly proposed model for evaluating stress relaxation ratio can substantially reflect the influences of the nature of B-GFRP bar and the property of grip body. The strain on the nail body can be redistributed automatically. Modulus reduction is not the single reason for the stress degradation.
基金Item Sponsored by High-Tech Research and Development Program of China (863 Program) (2007AA03Z506)
文摘The complex effects of different nitrogen （N） contents and thermal routines on the microstructure and mechanical properties of 33Mn2V steels for N80-Class seamless casing tube application were investigated using Gleeble simulation technique. The results showed that the N additions of 0. 014 %- 0. 021 % in the steels for the in-line normalization process （ILNP） increased the strength while the toughngss remained at a high level as compared with the steel with N content of 0. 005 %. It was also revealed that the N addition of 0. 021%could enhance the performance combination of strength and toughness in the steels by using 700 ℃ as the cooling interrupted temperature （CIT） for the non in-line normalizing process （NILNP）. It was further evidenced that the toughness was improved at expense of strength to some degree in all the steels by decreasing reheating temperature for the ILNP, while an increase of CIT for NILNP severely impaired the toughness and slightly improve the strength in the high-N steel with N content of 0. 021%. This can be attributed to the dissolution and precipitation behavior of V（C,N）. The optimization of V （C,N） precipitation could be achieved by enhancing N. The precipitation of V（C, N） in austenite was promoted by cooling to a certain temperature lower than the A,1 for the ILNP. The V（C,N） particles formed in austenite contrib- uted to grain refinement by the VN-induced nucleation of intragranular ferrite, but as a result the effect of precipitation on strengthening would become weaker due to a decrease of the precipitation of V in ferrite.
基金This study was supported by the Research Foundation of Fudan University(FNF201208)Health And Family Planning Commission Of Shanghai(201440090)and Minhang(2012MHZ028).
文摘Purpose:To evaluate the efficacy of the Seamless Transfer of Care Model(STCM)to improve readmission occurrence of patients withstroke.Methods:The sample was comprised of fifty-nine subjects with stroke who were hospitalized in the geriatric and neurology departments of a large university hospital in China.Subjects were allocated to an STCM group(n=30)or a routine care(control)group(n=29).Results:Compared with the control group,the STCM group had a higher quality of life(p<0.05),higher compliance(p<0.05)and a lower readmission rate(p<0.05).Conclusion:Based on our results,the application of the STCM in Chinese stroke patients can improve quality of life and compliance,and reduce readmission rate.
文摘Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 × 1080- LCDs and a half-transmission and half- reflection prisms was proposed in this paper.The physical principal and error model due to the splicing structure has been discussed and analyzed in detail.Based on the Tsinghua Micro star tracker,the error effect and system accuracy has been carefully tested and calibrated.The result showed that this simulator can get the accuracy of 10.4 "(3sigma) within a field of view of,which can meet the simulating requirement of modern star tracker,whose accuracy can reach 3"(3sigma) 。
文摘With the aid of FE （finite element） code MSC.Superform 2005, 2-D coupled thermo-mechanical simulation of center-crack occurrence in round billet during 2-roll rotary rolling process was presented using Oyane ductile fracture criteria. A simple modeling is put forward based on the spiral motion of the workpiece as an essential characteristic in movement. The influence of the feed angle and the entry cone angle of the main roll on the process was taken into account in the modeling. The soundness for simplifying the 3-D rotary rolling into a 2-D problem was discussed. By adopting the parameters of Diescher piercer in 140mm mandrel mill of Bao Steel, the distribution and development of strain/stress were analyzed, and the eigen value of ductile fracture as well. The critical percentage of diameter reduction was obtained from the simulation. The result showed a good agreement with the experimental value, and therefore was of widely guiding significance to the practical process for rationally formulating the deformation parameters of steel tube piercing.
