We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c superconducting quantum interference devices （SQUIDs）. The measurement field is in a micro-tesla range （～10 μT-100 ...We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c superconducting quantum interference devices （SQUIDs）. The measurement field is in a micro-tesla range （～10 μT-100 μT） and the experiment is conducted in a home-made magnetically-shielded-room （MSR）. The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range （～1 kHz-10 kHz） the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.展开更多
The numerical method of a coupled finite element and indirect boundary element equation for computing both the structural vibration and the acoustic radiation was presented. The coupling matrices were discussed and ph...The numerical method of a coupled finite element and indirect boundary element equation for computing both the structural vibration and the acoustic radiation was presented. The coupling matrices were discussed and physical degrees of freedom of the structure were treated in terms of its modal basis in vacuum to decouple the computation from the entire coupled structural acoustic equations. The numerical results for the ellipsoidal shell immersed in two different fluids indicate that heavy fluid changes greatly structural and acoustic behavior. This method can be applied to analyze acoustic and vibration for arbitrary complex structures in fluids.展开更多
The coal and biomass coupling power genera-tion technology is considered as a promising technology for energy conservation and emission reduction.In this paper,a novel coal and biomass indirect coupling system is prop...The coal and biomass coupling power genera-tion technology is considered as a promising technology for energy conservation and emission reduction.In this paper,a novel coal and biomass indirect coupling system is proposed based on the technology of biomass gasification and co-combustion of coal and gasification gas.For the sake of comparison,a coal and biomass direct coupling system is also introduced based on the technology of co-combustion of coal and biomass.The process of the direct and the indirect coupling system is simulated.The thermodynamic and economic performances of two systems are analyzed and compared.The simulation indicates that the thermodynamic performance of the indirect coupling system is slightly worse,but the economic performance is better than that of the direct coupling system.When the blending ratio of biomass is 20%,the energy and exergy fficiencies of the indirect coupling system are 42.70%and 41.14%,the intemal rate of returm(IRR)and discounted payback period(DPP)of the system are 25.68%and 8.56 years.The price fluctuation of fuels and products has a great influence on the economic performance of the indirect coupling system.The environmental impact analysis indicates that the indirect coupling system can inhibit the propagation of NOx and reduce the environmental cost.展开更多
A new idea about indirect coupling photodetectors is proposed. The indirect coupling photodetectors with two different mechanisms have been found and analysed: Experimental results show that they are of a class of exc...A new idea about indirect coupling photodetectors is proposed. The indirect coupling photodetectors with two different mechanisms have been found and analysed: Experimental results show that they are of a class of excellent photodetectors. Finally, the application of such photodetectors and their research prospect are discussed.展开更多
基金Project supported by the State Key Development Program for Basic Research of China (Grant Nos. 2011CBA00106 and 2009CB929102)the National Natural Science Foundation of China (Grant Nos. 11104333, 11161130519, and 10974243)
文摘We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c superconducting quantum interference devices （SQUIDs）. The measurement field is in a micro-tesla range （～10 μT-100 μT） and the experiment is conducted in a home-made magnetically-shielded-room （MSR）. The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range （～1 kHz-10 kHz） the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.
文摘The numerical method of a coupled finite element and indirect boundary element equation for computing both the structural vibration and the acoustic radiation was presented. The coupling matrices were discussed and physical degrees of freedom of the structure were treated in terms of its modal basis in vacuum to decouple the computation from the entire coupled structural acoustic equations. The numerical results for the ellipsoidal shell immersed in two different fluids indicate that heavy fluid changes greatly structural and acoustic behavior. This method can be applied to analyze acoustic and vibration for arbitrary complex structures in fluids.
基金This work was supported by the Fundamental Research Funds for the Central Universities(Grant No.30919012104)the National Key R&D Program of China(Grant No.2016YFB0600100).
文摘The coal and biomass coupling power genera-tion technology is considered as a promising technology for energy conservation and emission reduction.In this paper,a novel coal and biomass indirect coupling system is proposed based on the technology of biomass gasification and co-combustion of coal and gasification gas.For the sake of comparison,a coal and biomass direct coupling system is also introduced based on the technology of co-combustion of coal and biomass.The process of the direct and the indirect coupling system is simulated.The thermodynamic and economic performances of two systems are analyzed and compared.The simulation indicates that the thermodynamic performance of the indirect coupling system is slightly worse,but the economic performance is better than that of the direct coupling system.When the blending ratio of biomass is 20%,the energy and exergy fficiencies of the indirect coupling system are 42.70%and 41.14%,the intemal rate of returm(IRR)and discounted payback period(DPP)of the system are 25.68%and 8.56 years.The price fluctuation of fuels and products has a great influence on the economic performance of the indirect coupling system.The environmental impact analysis indicates that the indirect coupling system can inhibit the propagation of NOx and reduce the environmental cost.
文摘A new idea about indirect coupling photodetectors is proposed. The indirect coupling photodetectors with two different mechanisms have been found and analysed: Experimental results show that they are of a class of excellent photodetectors. Finally, the application of such photodetectors and their research prospect are discussed.
