核磁共振(Nuclear Magnetic Resonance,NMR)射频脉冲发生器对成像质量至关重要.传统的直接数字频率合成技术(Direct Digital Synthesizer,DDS)要想实现较高精度则需要依赖大容量查找表,因此会占用较多的片上随机块存储器(Block Random A...核磁共振(Nuclear Magnetic Resonance,NMR)射频脉冲发生器对成像质量至关重要.传统的直接数字频率合成技术(Direct Digital Synthesizer,DDS)要想实现较高精度则需要依赖大容量查找表,因此会占用较多的片上随机块存储器(Block Random Access Memory,BRAM)资源且灵活度受限.本文提出一种基于坐标旋转数字计算机(Coordinate Rotation Digital Computer,CORDIC)算法的磁共振射频脉冲发生器设计,通过在现场可编程门阵列(Field-Programmable Gate Array,FPGA)中构建自定义CORDIC核实现射频信号的频率、相位和幅度的数字化调制,结合Zynq-7000全可编程片上系统(System on Chip,SoC)实现高集成度、低功耗的硬件架构.实验结果表明,所设计脉冲发生器可输出频率分辨率为0.046 Hz、相位分辨率为0.0055˚的射频脉冲信号,且四通道所占用的BRAM资源较传统DDS方案降低约21.4%.该设计为NMR设备的射频前端小型化与高性能化提供了可行方案.展开更多
Cubic-shaped magnetic particles subjected to a dimensionless uniaxial anisotropy(Q=0.1)aligned with one of the crystallographic axes provide an ideal system for investigating magnetic equilibrium states.In this system...Cubic-shaped magnetic particles subjected to a dimensionless uniaxial anisotropy(Q=0.1)aligned with one of the crystallographic axes provide an ideal system for investigating magnetic equilibrium states.In this system,three fundamental magnetization configurations are identified:(i)the flower state,(ii)the twisted flower state,and(iii)the vortex state.This problem corresponds to standard problem No.3 proposed by the NIST Micromagnetics Modeling Group,widely adopted as a benchmark for validating computational micromagnetics methods.In this work,we approach the problem using a computational method based on direct dipolar interactions,in contrast to conventional techniques that typically compute the demagnetizing field via finite difference-based fast Fourier transform(FFT)methods,tensor grid approaches,or finite element formulations.Our results are compared with established literature data,focusing on the dimensionless parameterλ=L/l_(ex),where L is the cube edge length and l_(ex)is the exchange length of the material.To analyze equilibrium state transitions,we systematically varied the size L as a function of the simulation cell number N and intercellular spacing a,determining the criticalλvalue associated with configuration changes.Our simulations reveal that the transition between the twisted flower and vortex states occurs atλ≈8.45,consistent with values reported in the literature,validating our code(Grupo de Física da Matéeria Condensada-UFJF),and shows that this standard problem can be resolved using only interaction dipolar of a direct way without the need for sophisticated additional calculations.展开更多
为了调查与抗逆转录病毒治疗(antiretroviral therapy,ART)相关的静息状态功能连接的动态特性,从45名接受治疗的HIV感染者(people with HIV,PWH)、56名未接受治疗的PWH与68名健康对照者采集得到功能磁共振成像数据.使用组独立成分分析...为了调查与抗逆转录病毒治疗(antiretroviral therapy,ART)相关的静息状态功能连接的动态特性,从45名接受治疗的HIV感染者(people with HIV,PWH)、56名未接受治疗的PWH与68名健康对照者采集得到功能磁共振成像数据.使用组独立成分分析、滑动窗分析提取窗功能连接矩阵及量化其动态特性.结果表明,基线状态、弱激活状态体现了HIV相关异常动态及ART相关恢复,弱激活状态体现小脑相关连接恢复、壳核相关功能代偿,基线状态体现除视觉网络外的广泛网络连接恢复.视觉相关连接在两种状态中均体现为ART相关的不良反应.这些发现表明小脑、壳核可能是ART相关恢复的敏感生物标志物,视觉网络可作为辅助治疗的目标.展开更多
Nuclear magnetic resonance(NMR)spectroscopy is a powerful tool for analyzing molecular structure and composition.However,traditional NMR experiments suffer from long acquisition times,especially in multidimensional NM...Nuclear magnetic resonance(NMR)spectroscopy is a powerful tool for analyzing molecular structure and composition.However,traditional NMR experiments suffer from long acquisition times,especially in multidimensional NMR spectroscopy.This problem,to some extent,limits broader applications of NMR techniques.Various methods have been proposed to accelerate sampling,including non-uniform sampling(NUS),multi-FID acquisition(MFA),Hadamard encoding,Fourier encoding,spatial encoding Ultrafast 2D NMR(UF2DNMR),and so on.The review focuses on rapid sampling methods developed in contemporary China,introducing their fundamental principles and applications while discussing their respective advantages and disadvantages.展开更多
高场固体核磁共振(NMR)技术具有高灵敏度和多核检测能力,但在研究锂离子电池之类的顺磁材料时,过渡金属离子(如Mn^(3+)、Fe^(3+)等)的强顺磁效应会导致高场下磁场不均匀、谱线展宽、信号衰减、无法魔角旋转(MAS)等问题.低场条件下,顺磁...高场固体核磁共振(NMR)技术具有高灵敏度和多核检测能力,但在研究锂离子电池之类的顺磁材料时,过渡金属离子(如Mn^(3+)、Fe^(3+)等)的强顺磁效应会导致高场下磁场不均匀、谱线展宽、信号衰减、无法魔角旋转(MAS)等问题.低场条件下,顺磁效应引起的磁场畸变显著减弱,为解决这些问题提供了可能.本文通过理论分析低场环境对顺磁物质研究的优势,研制了用于0.5 T Halbach磁体的低场固体MAS探头,并构建了一套完整的低场固体MAS谱仪.实验在12 kHz转速下采集到多种顺磁样品的7Li NMR信号,验证了自主研制的低场固体MAS技术在顺磁样品体系中的可行性.该方案解决了高场条件下自旋边带叠加和MAS失效的问题,为顺磁材料的NMR研究提供了新途径.展开更多
文摘核磁共振(Nuclear Magnetic Resonance,NMR)射频脉冲发生器对成像质量至关重要.传统的直接数字频率合成技术(Direct Digital Synthesizer,DDS)要想实现较高精度则需要依赖大容量查找表,因此会占用较多的片上随机块存储器(Block Random Access Memory,BRAM)资源且灵活度受限.本文提出一种基于坐标旋转数字计算机(Coordinate Rotation Digital Computer,CORDIC)算法的磁共振射频脉冲发生器设计,通过在现场可编程门阵列(Field-Programmable Gate Array,FPGA)中构建自定义CORDIC核实现射频信号的频率、相位和幅度的数字化调制,结合Zynq-7000全可编程片上系统(System on Chip,SoC)实现高集成度、低功耗的硬件架构.实验结果表明,所设计脉冲发生器可输出频率分辨率为0.046 Hz、相位分辨率为0.0055˚的射频脉冲信号,且四通道所占用的BRAM资源较传统DDS方案降低约21.4%.该设计为NMR设备的射频前端小型化与高性能化提供了可行方案.
基金CAPES,CNPq,and FAPEMIG(Brazilian Agencies)for their financial support。
文摘Cubic-shaped magnetic particles subjected to a dimensionless uniaxial anisotropy(Q=0.1)aligned with one of the crystallographic axes provide an ideal system for investigating magnetic equilibrium states.In this system,three fundamental magnetization configurations are identified:(i)the flower state,(ii)the twisted flower state,and(iii)the vortex state.This problem corresponds to standard problem No.3 proposed by the NIST Micromagnetics Modeling Group,widely adopted as a benchmark for validating computational micromagnetics methods.In this work,we approach the problem using a computational method based on direct dipolar interactions,in contrast to conventional techniques that typically compute the demagnetizing field via finite difference-based fast Fourier transform(FFT)methods,tensor grid approaches,or finite element formulations.Our results are compared with established literature data,focusing on the dimensionless parameterλ=L/l_(ex),where L is the cube edge length and l_(ex)is the exchange length of the material.To analyze equilibrium state transitions,we systematically varied the size L as a function of the simulation cell number N and intercellular spacing a,determining the criticalλvalue associated with configuration changes.Our simulations reveal that the transition between the twisted flower and vortex states occurs atλ≈8.45,consistent with values reported in the literature,validating our code(Grupo de Física da Matéeria Condensada-UFJF),and shows that this standard problem can be resolved using only interaction dipolar of a direct way without the need for sophisticated additional calculations.
文摘为了调查与抗逆转录病毒治疗(antiretroviral therapy,ART)相关的静息状态功能连接的动态特性,从45名接受治疗的HIV感染者(people with HIV,PWH)、56名未接受治疗的PWH与68名健康对照者采集得到功能磁共振成像数据.使用组独立成分分析、滑动窗分析提取窗功能连接矩阵及量化其动态特性.结果表明,基线状态、弱激活状态体现了HIV相关异常动态及ART相关恢复,弱激活状态体现小脑相关连接恢复、壳核相关功能代偿,基线状态体现除视觉网络外的广泛网络连接恢复.视觉相关连接在两种状态中均体现为ART相关的不良反应.这些发现表明小脑、壳核可能是ART相关恢复的敏感生物标志物,视觉网络可作为辅助治疗的目标.
基金financially supported by the National Natural Science Foundation of China(grant numbers 22174118,12411530077,and 22374124).
文摘Nuclear magnetic resonance(NMR)spectroscopy is a powerful tool for analyzing molecular structure and composition.However,traditional NMR experiments suffer from long acquisition times,especially in multidimensional NMR spectroscopy.This problem,to some extent,limits broader applications of NMR techniques.Various methods have been proposed to accelerate sampling,including non-uniform sampling(NUS),multi-FID acquisition(MFA),Hadamard encoding,Fourier encoding,spatial encoding Ultrafast 2D NMR(UF2DNMR),and so on.The review focuses on rapid sampling methods developed in contemporary China,introducing their fundamental principles and applications while discussing their respective advantages and disadvantages.
文摘高场固体核磁共振(NMR)技术具有高灵敏度和多核检测能力,但在研究锂离子电池之类的顺磁材料时,过渡金属离子(如Mn^(3+)、Fe^(3+)等)的强顺磁效应会导致高场下磁场不均匀、谱线展宽、信号衰减、无法魔角旋转(MAS)等问题.低场条件下,顺磁效应引起的磁场畸变显著减弱,为解决这些问题提供了可能.本文通过理论分析低场环境对顺磁物质研究的优势,研制了用于0.5 T Halbach磁体的低场固体MAS探头,并构建了一套完整的低场固体MAS谱仪.实验在12 kHz转速下采集到多种顺磁样品的7Li NMR信号,验证了自主研制的低场固体MAS技术在顺磁样品体系中的可行性.该方案解决了高场条件下自旋边带叠加和MAS失效的问题,为顺磁材料的NMR研究提供了新途径.
