Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement

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.

Thermodynamic and economic analyses of a coal and biomass indirect coupling power generation system

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.

Multipartite entanglement generation with dipole induced transparency effect in indirectly coupled dipole-microcavity systems

We propose a feasible scheme of generating multipartite entanglement with the dipole induced transparency （D/T） effect in indirectly coupled dipole-microcavity systems. It is shown that the transmission spectrum is closely related with the interference of dipole-microcavity systems, and we can generate different classes of multi- partite entanglement, e.g., the Greenberger-Horne-Zeilinger state, the W state, and the Dicke state, of the di- pole emitters just by choosing an appropriate frequency of the incident photon. Benefiting from the DIT effect, the schemes may work in the bad or low-Q cavity regime only if the large Purcell factor of the dipole-microcavity system is fulfilled, and they are also insensitive to experimental noise, which may be feasible with present acces- sible technology.