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
Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic ...Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic resonance （NMR） studies on the effects of water on the adsorption and diffusion of methane in nanopores. Silica materials with one-dimensional pores of ZSM-22, MCM-41, and SBA-15, with pore sizes ranging from 0.5 to 6 nm, were chosen as models. Hyperpolarized （HP） 129Xe NMR results show that water adsorption does not affect the pore sizes of ZSM-22 and MCM-41 but reduces that of SBA-15. The presence of water suppresses methane adsorption; this suppression effect is stronger in smaller pores. The self-diffusion coefficients of methane within ZSM-22 and MCM-41 are not significantly influenced by the presence of water, as measured by ~H pulsed field gradient （PFG） NMR. However, within SBA-15, which has a pore size of 6 nm, the diffusion coefficient of methane increases as the amount of water adsorption increases, peaks, and then decreases to a constant value with further water adsorption. These experiments reveal the effects of the pore size and the presence of water on methane adsorption and diffusion in constrained spaces, which could have important implications for flow simulations of methane in shales.展开更多
The ongoing pandemic of coronavirus disease 2019(COVID-19)has been a great burden for the healthcare system in many countries because of its high transmissibility,severity,and fatality.Chest radiography and computed t...The ongoing pandemic of coronavirus disease 2019(COVID-19)has been a great burden for the healthcare system in many countries because of its high transmissibility,severity,and fatality.Chest radiography and computed tomography(CT)play a vital role in the diagnosis,detection of complications,and prognostication of COVID-19.Additionally,magnetic resonance imaging(MRI),especially multi-nuclei MRI,is another important imaging technique for disease diagnosis because of its good soft tissue contrast and the ability to conduct structural and functional imaging,which has also been used to evaluate COVID-19-related organ injuries in previous studies.Herein,we briefly reviewed the recent research on multi-nuclei MRI for evaluating injuries caused by COVID-19 and the clinical 1 H MRI techniques and their applications for assessing injuries in lungs,brain,and heart.Moreover,the emerging hyperpolarized 129Xe gas MRI and its applications in the evaluation of pulmonary structures and functional abnormalities caused by COVID-19 were also reviewed.展开更多
Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃...Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.展开更多
采用固体多核13C,27Al及29Si MAS NMR结合吸附气体Xe后的129Xe NMR,详细研究了乙烯和2-丁烯歧化生成丙烯反应过程中6%Mo/Hβ-Al2O3催化剂上积炭的类型和落位.结果表明,积炭以饱和烷烃为主,并随着反应的进行生成更多的支链烷烃,积炭主要...采用固体多核13C,27Al及29Si MAS NMR结合吸附气体Xe后的129Xe NMR,详细研究了乙烯和2-丁烯歧化生成丙烯反应过程中6%Mo/Hβ-Al2O3催化剂上积炭的类型和落位.结果表明,积炭以饱和烷烃为主,并随着反应的进行生成更多的支链烷烃,积炭主要分布在Hβ分子筛上,并主要落位在分子筛的交叉孔道处.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.
文摘Understanding the properties and behavior of water molecules in restricted geometries, such as the nanopores of rocks, is of interest for shale gas exploitation. We present herein ex situ and in situ nuclear magnetic resonance （NMR） studies on the effects of water on the adsorption and diffusion of methane in nanopores. Silica materials with one-dimensional pores of ZSM-22, MCM-41, and SBA-15, with pore sizes ranging from 0.5 to 6 nm, were chosen as models. Hyperpolarized （HP） 129Xe NMR results show that water adsorption does not affect the pore sizes of ZSM-22 and MCM-41 but reduces that of SBA-15. The presence of water suppresses methane adsorption; this suppression effect is stronger in smaller pores. The self-diffusion coefficients of methane within ZSM-22 and MCM-41 are not significantly influenced by the presence of water, as measured by ~H pulsed field gradient （PFG） NMR. However, within SBA-15, which has a pore size of 6 nm, the diffusion coefficient of methane increases as the amount of water adsorption increases, peaks, and then decreases to a constant value with further water adsorption. These experiments reveal the effects of the pore size and the presence of water on methane adsorption and diffusion in constrained spaces, which could have important implications for flow simulations of methane in shales.
基金This work is supported by National key Research and Development Project of China(grant no.2018YFA0704000)National Natural Science Foundation of China(grant no.91859206,81625011,21921004)+3 种基金Scientific Instrument Developing Project of the Chinese Academy of Sciences(grant no.GJJSTD20200002,YJKYYQ20200067)Key Research Program of Frontier Sciences,CAS(grant no.ZDBS-LY-JSC004)Haidong Li acknowledges the support from Youth Innovation Promotion Association,CAS(grant no.2020330)Xin Zhou acknowledges the support from the Tencent Foundation through the XPLORER PRIZE.
文摘The ongoing pandemic of coronavirus disease 2019(COVID-19)has been a great burden for the healthcare system in many countries because of its high transmissibility,severity,and fatality.Chest radiography and computed tomography(CT)play a vital role in the diagnosis,detection of complications,and prognostication of COVID-19.Additionally,magnetic resonance imaging(MRI),especially multi-nuclei MRI,is another important imaging technique for disease diagnosis because of its good soft tissue contrast and the ability to conduct structural and functional imaging,which has also been used to evaluate COVID-19-related organ injuries in previous studies.Herein,we briefly reviewed the recent research on multi-nuclei MRI for evaluating injuries caused by COVID-19 and the clinical 1 H MRI techniques and their applications for assessing injuries in lungs,brain,and heart.Moreover,the emerging hyperpolarized 129Xe gas MRI and its applications in the evaluation of pulmonary structures and functional abnormalities caused by COVID-19 were also reviewed.
基金supported by the Key Program of the National Natural Science Foundation of China(Grant Nos.61227902,61273067,and 6137210)SAST Foundation of China
文摘Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.
文摘采用固体多核13C,27Al及29Si MAS NMR结合吸附气体Xe后的129Xe NMR,详细研究了乙烯和2-丁烯歧化生成丙烯反应过程中6%Mo/Hβ-Al2O3催化剂上积炭的类型和落位.结果表明,积炭以饱和烷烃为主,并随着反应的进行生成更多的支链烷烃,积炭主要分布在Hβ分子筛上,并主要落位在分子筛的交叉孔道处.
