A new fully digital and home-built NMR (Nuclear Magnetic Resonance) spectrometer working at very-low magnetic field (4.5 mT) is presented. This spectrometer was initially dedicated for the in situ measurement of the a...A new fully digital and home-built NMR (Nuclear Magnetic Resonance) spectrometer working at very-low magnetic field (4.5 mT) is presented. This spectrometer was initially dedicated for the in situ measurement of the absolute polarization of hyperpolarized 129Xe. It allows detection and acquisition of NMR signals of proton (1H) at 190 kHz and of hyperpolarized xenon-129 (HP 129Xe) at 50 kHz. In this new NMR instrument, we replaced as much analog electronics as possible by digital electronic and software. Except for the power amplifier and the preamplifier, the whole system is digital. The transmitter is based on the use of a Direct Digital Synthesizer (DDS) board. The receiving board allows direct digitalization of the NMR signals thanks to an 8-bits analog-to-digital converter (ADC) clocked at 100 MHz. Decimation is preformed to dramatically improve the ADC resolution so as the final achieved effective resolution could be as high as 14-bits at 5 MHz sampling frequency. NMR signals are then digitally downconverted (DDC). Low-pass decimation filtering is applied on the base-band signals (I/Q) to enhance much more the dynamic range. The system requires little hardware. The transmitter and the receiver are controlled using Labview environment. It is a versatile, flexible and easy-to-replicate system. This was actually one of underlying ideas behind this development. Both 1H and hyperpolarized 129Xe NMR signals were successfully acquired. The system is used for the measurement of the absolute polarization of hyperpolarized 129Xe in hyperpolarizing experiments for the brain perfusion measurements. The high degree of flexibility of this new design allows its use for a large palette of other potential applications.展开更多
Secondary pores are formed during hydrothermal treatment of NH<sub>4</sub>NaY accompanyingdealumination and production of extraframework aluminum. There exist different views onthe formation of secondary p...Secondary pores are formed during hydrothermal treatment of NH<sub>4</sub>NaY accompanyingdealumination and production of extraframework aluminum. There exist different views onthe formation of secondary pores. Lohse suggested that the formation of secondarypores was due to partial structural breakdown resulting from dealumination of sodalite. ButYoshida reported that secondary pores would be formed after the Si（3Al） was展开更多
Adsorption of xenon in zeolite MCM-22, a zeolite containing two separate pore systems, has been investigated in detail by variable temperature (VT) 129Xe NMR spectroscopy. NMR results suggest that Xe atoms are prefere...Adsorption of xenon in zeolite MCM-22, a zeolite containing two separate pore systems, has been investigated in detail by variable temperature (VT) 129Xe NMR spectroscopy. NMR results suggest that Xe atoms are preferentially adsorbed in the supercages of the zeolite at low Xe pressure (less than a few atmosphere), while Xe atoms can penetrate into the two-dimensional sinusoidal channels at high Xe pressure. Exchange of xenon at the different adsorption sites in the same supercage, i.e. xenon atoms in the two pockets and those in the central part of the supercage, was confirmed at 145 K by two-dimensional (2D) 129Xe NMR exchange spectroscopy. The time scale for the exchange is about several milliseconds.展开更多
文摘A new fully digital and home-built NMR (Nuclear Magnetic Resonance) spectrometer working at very-low magnetic field (4.5 mT) is presented. This spectrometer was initially dedicated for the in situ measurement of the absolute polarization of hyperpolarized 129Xe. It allows detection and acquisition of NMR signals of proton (1H) at 190 kHz and of hyperpolarized xenon-129 (HP 129Xe) at 50 kHz. In this new NMR instrument, we replaced as much analog electronics as possible by digital electronic and software. Except for the power amplifier and the preamplifier, the whole system is digital. The transmitter is based on the use of a Direct Digital Synthesizer (DDS) board. The receiving board allows direct digitalization of the NMR signals thanks to an 8-bits analog-to-digital converter (ADC) clocked at 100 MHz. Decimation is preformed to dramatically improve the ADC resolution so as the final achieved effective resolution could be as high as 14-bits at 5 MHz sampling frequency. NMR signals are then digitally downconverted (DDC). Low-pass decimation filtering is applied on the base-band signals (I/Q) to enhance much more the dynamic range. The system requires little hardware. The transmitter and the receiver are controlled using Labview environment. It is a versatile, flexible and easy-to-replicate system. This was actually one of underlying ideas behind this development. Both 1H and hyperpolarized 129Xe NMR signals were successfully acquired. The system is used for the measurement of the absolute polarization of hyperpolarized 129Xe in hyperpolarizing experiments for the brain perfusion measurements. The high degree of flexibility of this new design allows its use for a large palette of other potential applications.
基金Project supported by the National Natural Science Foundation of China.
文摘Secondary pores are formed during hydrothermal treatment of NH<sub>4</sub>NaY accompanyingdealumination and production of extraframework aluminum. There exist different views onthe formation of secondary pores. Lohse suggested that the formation of secondarypores was due to partial structural breakdown resulting from dealumination of sodalite. ButYoshida reported that secondary pores would be formed after the Si（3Al） was
基金This work was supported by the National Natural Science Foundation of China (Grant No. 29873065).
文摘Adsorption of xenon in zeolite MCM-22, a zeolite containing two separate pore systems, has been investigated in detail by variable temperature (VT) 129Xe NMR spectroscopy. NMR results suggest that Xe atoms are preferentially adsorbed in the supercages of the zeolite at low Xe pressure (less than a few atmosphere), while Xe atoms can penetrate into the two-dimensional sinusoidal channels at high Xe pressure. Exchange of xenon at the different adsorption sites in the same supercage, i.e. xenon atoms in the two pockets and those in the central part of the supercage, was confirmed at 145 K by two-dimensional (2D) 129Xe NMR exchange spectroscopy. The time scale for the exchange is about several milliseconds.
