Using a pump with a multi-line spectrum to broaden the Brillouin gain bandwidth is an effective way to achieve lowdistortion amplification with high gain. Here, we theoretically and experimentally investigate the gene...Using a pump with a multi-line spectrum to broaden the Brillouin gain bandwidth is an effective way to achieve lowdistortion amplification with high gain. Here, we theoretically and experimentally investigate the generation of a broadband Brillouin gain spectrum based on multi-frequency intensity modulation in an optical fiber. The arbitrary bandwidth of the Brillouin gain spectrum of stimulated Brillouin scattering(SBS) can be obtained as expected. In our experiment, a broadband Brillouin gain spectrum with a bandwidth of about 200 MHz is demonstrated. We also achieve a low-distortion amplification of a weak signal, whose maximum magnification is 65 d B for a-68-dBm input power signal.展开更多
A new moving or dynamic thermal tensioning technique-welding with trailing intense cooling was numerically simulated by finite element method(FEM)and experimentally investigated.The simulation results indicate that tr...A new moving or dynamic thermal tensioning technique-welding with trailing intense cooling was numerically simulated by finite element method(FEM)and experimentally investigated.The simulation results indicate that trailing intense cooling can increase significantly the longitudinal tensile plastic strain within the weld and its adjacent zone during cooling stage,which can partially or completely counterbalance the longitudinal compressive plastic strain formed in the heating stage and the solidification shrinkage formed in the cooling stage.Therefore the longitudinal shrinkage remaining in the weld and the adjacent zone is greatly reduced,which means that the residual stresses in the weldments are kept in a lower value and the residual distortion can be mitigated effectively.Meanwhile a series of parametric studies were conducted to demonstrate the influences of several key parameters such as cooling distance, cooling power and cooling width on the effectiveness of distortion control.Experimental results also verify the effectiveness of this distortion control technique and the reliability of the numerical simulation.展开更多
The paper measures the industrial structure distortion(ISD)index by region in China from 1978 to 2016 using data on employment and output shares of the three industries.It also analyzes the impact of ISDs by region on...The paper measures the industrial structure distortion(ISD)index by region in China from 1978 to 2016 using data on employment and output shares of the three industries.It also analyzes the impact of ISDs by region on energy intensity using a spatial panel model.The results show that since the reform and opening up,the ISD index by region has declined significantly,with the lowest index in the eastern region,the medium one in the central region and the highest in the western region.The estimated results of the spatial econometric model indicate that there is a significant inter-regional dependence of energy intensity in China;there is a significant indirect effect of ISD,despite no significant direct effect on energy intensity;in terms of total effect,ISD is an important factor inhibiting the decline of energy intensity.The results also unveil that higher energy prices and foreign trade are positive factors declining energy intensity,while FDI worsens energy intensity and R&D spending has no significant positive impact on curbing energy intensity.In order to reduce energy intensity,China should work to eliminate the micro cause of ISDs,promote the transfer of agricultural labor,establish a market-oriented mechanism for energy price formation,and enhance the efficiency of R&D spending.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.61605034)
文摘Using a pump with a multi-line spectrum to broaden the Brillouin gain bandwidth is an effective way to achieve lowdistortion amplification with high gain. Here, we theoretically and experimentally investigate the generation of a broadband Brillouin gain spectrum based on multi-frequency intensity modulation in an optical fiber. The arbitrary bandwidth of the Brillouin gain spectrum of stimulated Brillouin scattering(SBS) can be obtained as expected. In our experiment, a broadband Brillouin gain spectrum with a bandwidth of about 200 MHz is demonstrated. We also achieve a low-distortion amplification of a weak signal, whose maximum magnification is 65 d B for a-68-dBm input power signal.
文摘A new moving or dynamic thermal tensioning technique-welding with trailing intense cooling was numerically simulated by finite element method(FEM)and experimentally investigated.The simulation results indicate that trailing intense cooling can increase significantly the longitudinal tensile plastic strain within the weld and its adjacent zone during cooling stage,which can partially or completely counterbalance the longitudinal compressive plastic strain formed in the heating stage and the solidification shrinkage formed in the cooling stage.Therefore the longitudinal shrinkage remaining in the weld and the adjacent zone is greatly reduced,which means that the residual stresses in the weldments are kept in a lower value and the residual distortion can be mitigated effectively.Meanwhile a series of parametric studies were conducted to demonstrate the influences of several key parameters such as cooling distance, cooling power and cooling width on the effectiveness of distortion control.Experimental results also verify the effectiveness of this distortion control technique and the reliability of the numerical simulation.
基金funded by the China National Social Science Foundation project(18BJL057)。
文摘The paper measures the industrial structure distortion(ISD)index by region in China from 1978 to 2016 using data on employment and output shares of the three industries.It also analyzes the impact of ISDs by region on energy intensity using a spatial panel model.The results show that since the reform and opening up,the ISD index by region has declined significantly,with the lowest index in the eastern region,the medium one in the central region and the highest in the western region.The estimated results of the spatial econometric model indicate that there is a significant inter-regional dependence of energy intensity in China;there is a significant indirect effect of ISD,despite no significant direct effect on energy intensity;in terms of total effect,ISD is an important factor inhibiting the decline of energy intensity.The results also unveil that higher energy prices and foreign trade are positive factors declining energy intensity,while FDI worsens energy intensity and R&D spending has no significant positive impact on curbing energy intensity.In order to reduce energy intensity,China should work to eliminate the micro cause of ISDs,promote the transfer of agricultural labor,establish a market-oriented mechanism for energy price formation,and enhance the efficiency of R&D spending.
