基于LF-NMR技术对不同鸡汤制品的营养品质分析及区分

以原味鸡汤、浓缩鸡汤(吴太婆牌和史云生牌)和勾兑鸡汤(家乐牌浓汤宝和太太乐牌浓缩鸡汁)为研究对象,对不同鸡汤制品普通营养成分(粗脂肪、粗蛋白和固形物)含量、色差和感官评分等进行分析比较;并利用低场核磁共振(LF-NMR)技术结合主成分分析法对上述鸡汤进行检测区分。结果表明:原味鸡汤营养成分含量和感官评分最高;LF-NMR数据结合主成分分析的结果,可使不同种类鸡汤得到明显的区分;且LF-NMR弛豫特性数据与食品感官评分、鸡汤的理化营养成分参数3者之间具有较好的相关性。该研究结果说明低场核磁共振技术应用于食品品质的区分识别具有可行性。

Advances in low-field nuclear magnetic resonance(NMR) technologies applied for characterization of pore space inside rocks:a critical review

NMR serves as an important technique for probing rock pore space,such as pore structure characterization,fluid identification,and petrophysical property testing,due to the reusability of cores,convenience in sample processing,and time efficiency in laboratory tests.In practice,NMR signal collection is normally achieved through polarized nuclei relaxation which releases crucial relaxation messages for result interpretation.The impetus of this work is to help engineers and researchers with petroleum background obtain new insights into NMR principals and extend existing methodologies for characterization of unconventional formations.This article first gives a brief description of the development history of relaxation theories and models for porous media.Then,the widely used NMR techniques for characterizing petrophysical properties and pore structures are presented.Meanwhile,limitations and deficiencies of them are summarized.Finally,future work on improving these insufficiencies and approaches of enhancement applicability for NMR technologies are discussed.

A machine learning framework for low-field NMR data processing

Low-field(nuclear magnetic resonance)NMR has been widely used in petroleum industry,such as well logging and laboratory rock core analysis.However,the signal-to-noise ratio is low due to the low magnetic field strength of NMR tools and the complex petrophysical properties of detected samples.Suppressing the noise and highlighting the available NMR signals is very important for subsequent data processing.Most denoising methods are normally based on fixed mathematical transformation or handdesign feature selectors to suppress noise characteristics,which may not perform well because of their non-adaptive performance to different noisy signals.In this paper,we proposed a“data processing framework”to improve the quality of low field NMR echo data based on dictionary learning.Dictionary learning is a machine learning method based on redundancy and sparse representation theory.Available information in noisy NMR echo data can be adaptively extracted and reconstructed by dictionary learning.The advantages and application effectiveness of the proposed method were verified with a number of numerical simulations,NMR core data analyses,and NMR logging data processing.The results show that dictionary learning can significantly improve the quality of NMR echo data with high noise level and effectively improve the accuracy and reliability of inversion results.

Low-field NMR inversion based on low-rank and sparsity restraint of relaxation spectra

In this paper,we proposed a novel method for low-field nuclear magnetic resonance(NMR)inversion based on low-rank and sparsity restraint(LRSR)of relaxation spectra,with which high quality construction is made possible for one-and two-dimensional low-field and low signal to noise ratio NMR data.In this method,the low-rank and sparsity restraints are introduced into the objective function instead of the smoothing term.The low-rank features in relaxation spectra are extracted to ensure the local characteristics and morphology of spectra.The sparsity and residual term are contributed to the resolution and precision of spectra,with the elimination of the redundant relaxation components.Optimization process of the objective function is designed with alternating direction method of multiples,in which the objective function is decomposed into three subproblems to be independently solved.The optimum solution can be obtained by alternating iteration and updating process.At first,numerical simulations are conducted on synthetic echo data with different signal-to-noise ratios,to optimize the desirable regularization parameters and verify the feasibility and effectiveness of proposed method.Then,NMR experiments on solutions and artificial sandstone samples are conducted and analyzed,which validates the robustness and reliability of the proposed method.The results from simulations and experiments have demonstrated that the suggested method has unique advantages for improving the resolution of relaxation spectra and enhancing the ability of fluid quantitative identification.

Probing Development of Mierostrueture of Early Cement Paste using1H Low-field NMR

Development of microstructure of early cement paste （0-6 h） was investigated with 1H low- field NMR. It was found that T2 （transverse relaxation time） distributions of fresh cement paste were bimodal and two peaks were ＇long component＇ and ＇short component＇. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree： the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T2 distribution gradually moved to the left and T2 of long component and initial fluidity were linearly correlated.

Monitoring Cr(Ⅵ)photoreduction at different depths by operando low-field NMR relaxometry

Chromium(VI)(Cr(VI)),a toxic metal ion,is widely present in industrial wastewater.To reduce the contamination of Cr(VI),many technologies for the photocatalytic reduction of Cr(VI)to Cr(III)have been developed in the past decades.However,the practical application of photocatalysts for the reduction of Cr(VI)inwastewater treatment is often hindered by the complicated photoreduction processes due to the sedimentation and stratification of catalyst particles that present during the treatment of the wastewater.Probing and understanding the influences of the sedimentation and stratification of the catalyst particles on the photoreduction processes are long-term challenges in the field.Herein,we demonstrate that this issue can be solved by using layer location integrated low-field time-domain nuclear magnetic resonance(LF-NMR)relaxometry.With paramagnetic Cr(III)cation as the molecular probe,we successfully monitored the Cr(VI)photoreduction processes by operando probing the 1 H T2 relaxation time of the photoreduction systems.The influences of catalyst sedimentation and the light wavelength on photocatalysis were studied and discussed.The results showed the great potential of LF-NMR relaxometry in the study of Cr(VI)photoreduction processes during industrial wastewater treatments.

Probing Development of Microstructure of Early Cement Paste using ~1H Low-field NMR

Development of microstructure of early cement paste (0–6 h) was investigated with 1H low-field NMR. It was found that T 2 (transverse relaxation time) distributions of fresh cement paste were bimodal and two peaks were ‘long component’ and ‘short component’. Separation degree of two peaks was a sign of exchange of water within flocculation and outside flocculation. Factors such as water cement ratio, specific surface area and dosage of superplasticizer had influences on the separation degree: the separation degree increased with the water cement ratio; the separation degree of cement paste prepared with cement with a high specific surface area was zero; dosage of superplasticizer will decrease separation degree. Results also suggested that T 2 distribution gradually moved to the left and T 2 of long component and initial fluidity were linearly correlated.

低场固体NMR研究纳米复合凝胶结构与动力学

纳米复合水凝胶复杂的微观结构和动力学决定了其宏观性能,阐明其结构和动力学的非均匀性对揭示凝胶相变机理、认识其宏观物理和化学性质和设计新型高分子凝胶都具有重要意义.通过合成不同粘土含量的系列聚异丙基丙烯酰胺(PNIPAm)/锂藻土纳米复合水凝胶,运用多种先进的低场固体NMR技术详细研究了凝胶微观结构和动力学的非均匀性.首先建立了分析多组分凝胶体系中刚性和柔性高分子组分相对含量的计算方法,然后在不同粘土含量下,通过测量凝胶FID信号和质子T1定量研究了凝胶中刚性和柔性高分子组分的相对含量;通过偶极滤波双量子NMR实验,研究了体系中与交联密度关联的残余偶极作用参数随黏土含量的变化.结果表明:在纳米复合水凝胶中,随着粘土含量的增加,凝胶中聚合物的刚性相增加,而柔性相下降,当粘土含量达到12%(Wclay/Wwater)时体系中的刚性相含量趋于平衡.多量子实验结果表明,随着粘土含量的增加,纳米复合水凝胶中高分子链的残余偶极作用参数逐渐增大,反映了体系中高分子链的受限运动和二维无机纳米片层形成的物理交联密度增大的趋势.

NMR永磁体精密温度控制器的设计与实现

低场核磁共振(low-field NMR)谱仪常采用钕铁硼(NdFeB)永磁体提供静磁场.NdFeB对温度非常敏感,磁体温度变化会引起磁场漂移,影响NMR实验的可靠性.为提高低场磁共振谱仪的稳定性,本文提出了一种基于双回路控制算法的磁共振永磁体精密温度控制方案,并在0.06 T磁共振谱仪上进行验证.结果表明:24 h内控温精度达到±0.005℃;相比无温控时,质子共振频率0.5 h内漂移量由255 Hz减小至15 Hz,24 h内漂移量由4 950 Hz减小至145 Hz,有效提高了低场磁共振谱仪永磁体的稳定性.

Porosity of gas shale:Is the NMR-based measurement reliable?

Aiming at obtaining an accurate porosity of gas shale,various approaches are attempted.Therein,nuclear magnetic resonance(NMR),being treated as a kind of new-developed technique,possesses the representative significance.However,as a booming technique,the reliability of NMR-based porosity of shale is not exactly defined.Depending on NMR device,this work measured the porosity of shale experiencing different water soaking time,accordingly,judging the reliability of NMR-based porosity.Results indicate the NMR outcomes vary with the water soaking time,making a doubt about the objectivity of NMRbased porosity in reflecting the real shale porosity.Furthermore,some supplementary means were adopted to verify the water soaking-induced variation in the pore system of shale sample,which intensities the suspicion if the NMR-based porosity is reliable or not.To sum up,this work considers that the NMR-based porosity of shale is not reliable enough when water is used as the probe.Besides,this work also offers some suggestions on how to enhance the reliability of NMR-based porosity of shale sample.Basically,this work selects a fresh perspective to analyze the NMR approach in determining shale porosity,which is hopefully helpful in promoting the development of NMR technique in the shale-related field.

Further discussion of CO_(2) huff-n-puff mechanisms in tight oil reservoirs based on NMR monitored fluids spatial distributions

Due to the poor physical properties of tight reservoirs,CO_(2) huff-n-puff(HNP)is considered a potential enhanced oil recovery(EOR)method after primary depletion.Optimization plays a critical role in the effective implementation of CO_(2) huff-n-puff.But the optimization requires a good understanding of the EOR mechanisms.In this work,the spatial distribution of oil saturation under different experimental conditions was analyzed by the NMR method to further discuss the HNP mechanisms.According to the variation of 1D frequency signal amplitude,we divided the core into the hardly movable area and movable area,the region with the obvious signal decline was defined as the movable area,and the hardly movable area was the region with limited signal decline.Based on that the recovery characteristics of different scenarios were evaluated.Firstly,the necessity of the soaking stage was studied,where three scenarios with different soaking times were carried out.Secondly,the injection pressure was adjusted to investigate the effect of the pressure gradient.The T_(2) spectra show that soaking has significantly improved the production of crude oil in small pores,and higher oil recovery in a single cycle is observed,but it is lower when the elapsed time(total operation time)is the same.31.03% of oil can be recovered after 3 cycles HNP,which increases to 33.8% and 37.06% for the 4 cycles and 6 cycles cases.As the pressure gradient increases,more oil is removed out of the matrix,and the oil in the deep part of the reservoir can be effectively recovered.During the CO_(2) huff-n-puff process,the oil distributions are similar to the solution gas drive,the residual oil is distributed at the close end of the core and the range that the oil can be efficiently recovered is limited.

Corresponding Factors Influencing Crude Oils Assay Using Low-field Nuclear Magnetic Resonance

In this study, the main factors influencing the measurements by means of the off-line low-field 1H NMR in the lab were discussed base on a robust calibration model established by the PLS algorithm using 255 crude oil samples. The preheating temperature had a great influence on the viscosity of oil samples and the resolution of spectral analysis. The repeatability of spectral measurements was impacted by the metal and wax content of the oil samples. For the case of high wax content oils, the wax species began to crystallize in the course of determination that could affect the repeatability of spectral measurements. These factors have evidenced why the preheating devices and filter unit are necessary when low field NMR system is used in the online analysis process. The investigation is very important for the on-line application of the low field NMR.

Functional group resolved NMR relaxation of 3-carbon adsorbates in mesoporous alumina

NMR relaxation analysis provides a unique and non-invasive probe of fluid dynamics within porous materials,and may be applied to the interpretation of a wide variety of material and interfacial characteristics.Here,we report two-dimensional^(1)H T_(1)-T_(2)relaxation correlation measurements of a range of three-carbon adsorbates(1-propanol,2-propanol and propanoic acid)imbibed within the mesoporous metal oxide gamma-alumina.Our data,acquired across field strengths of 2 MHz,12.7 MHz and 43 MHz,clearly reveal two populations in each measurement,identified as the alkyl and hydroxyl moieties of each adsorbate.These results expand the range of materials in which such functional group resolved relaxation is known to occur,and demonstrate the clear persistence of such phenomena using a range of typical benchtop NMR systems employed to study fluid-saturated porous media.

Evaluation of Cinnamon by Solid-State NMR Employing Relaxometry

To evaluate the molecular dynamics and the molecular regions presented in the cinnamon types it was chosen to evaluate them without any treatment, and for that it was used low-field nuclear magnetic resonance (NMR) through the pulse sequence such as MSE-FID, an NMR sequence in the time domain, and from the longitudinal relaxation time (with a time constant T1), employing the inversion-recovery pulse sequence. The low-field NMR results indicate that the techniques chosen were a very good alternative to evaluate these types of samples food and their structural organization according to their constituents. The molecular mobility is different.

低场核磁共振分析乳酸菌细胞中水分分布及其变化

该文选取乳酸菌发酵剂为研究对象,利用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)分析方法研究乳酸菌细胞水分分布及其变化。横向弛豫时间(T_(2))可以提供样品组织结构中的水分状态及水分分布的信息。根据弛豫时间T_(2)可以将乳酸菌细胞的水分依次划分为结合水(T_(21))、半结合水(T_(22))以及自由水(T_(23)),并分别对应不同的细胞结构中,包括T_(21)<10 ms对应与细胞壁结合的水质子;10 ms<T_(22)<100 ms对应细胞质中与蛋白质等大分子结合的水质子;T_(23)>100 ms具有较高的自由度,代表细胞壁水。渗透压冲击会改变乳酸菌细胞内水分分布情况,使得水分的自由度增大;而反复冻融会使得细胞内的水分结成冰晶,损伤细胞结构,造成解冻后细胞内水流失,导致细胞塌陷破裂。研究结果表明,LF-NMR分析方法可以准确地提供乳酸菌细胞内部水分分布信息,并且细胞内部水分分布情况的变化与细胞损伤情况密切相关。

水热处理对污泥水分分布的影响

采用低场核磁共振(LF-NMR)技术研究水热处理对污泥水分分布的影响.通过研究水热温度、反应时间、CaCl2与非离子型聚丙烯酰胺(PAM)添加量对污泥离心水的质量分数的影响,确定最佳处理工况.结合泥饼水的质量分数、氨氮(NH3-N)及溶解性化学需氧量(SCOD)分析,评价经水热处理后污泥样品的脱水性能.研究水热单一变量对污泥水分分布变化的影响.结果表明:反应温度的提高使得污泥中结合水和机械结合水均显著降低;反应时间的延长降低了污泥中的结合水比例;投放氯化钙主要降低机械结合水的比例;PAM的添加量对水分分布影响较小.水热正交实验结果表明:在水热温度为230℃、处理时间为45min时,同时添加140mg/g干污泥(DS)CaCl2,在水热处理后添加10-6 g/g DS PAM试剂的工况下,泥饼经离心脱水后水的质量分数由88.67%降至70.68%.与污泥原样相比,悬浮液中的SCOD、NH3-N值大幅上升,说明污泥絮体中不溶的有机组分发生了水解,并改变了污泥的水分分布.

低场核磁共振短死时间射频线圈与射频开关的设计

本文以核磁共振(NMR)射频线圈振铃信号产生原理为对象进行分析研究,提出了一种适用于低场环境下由环状间隙腔线圈与螺线管线圈构成的收发分离式短死时间射频线圈设计方案,采用优化调谐匹配网络提高发射效率;根据射频线圈方案需求设计了快速切换的射频开关及驱动.在此基础上依据仿真结果制作了短死时间射频线圈,并应用于自主研制的低场9.51 MHz便携式NMR谱仪系统,进行NMR实验,结果显示可将收发切换时间缩短至10μs以内,验证了该设计方案的可行性.

基于小波变换的低场核磁共振信号去噪方法的研究进展

低场核磁共振(low-field Nuclear Magnetic Resonance,low-field NMR)技术因其自身具有的独特优越性常被应用于极端条件下的测量,而且由于其采用的是永磁体,因而采集到的信号信噪比常常较低,在很大程度上影响了测量值的准确性.因此,如何去除混杂在信号中的加性高斯白噪声增加测量值的可靠性显得尤为重要.针对这一问题,国内外学者相继提出了众多优秀的去噪方法,其核心都是在不损失含噪信号中有效信息的基础上滤除掉夹杂在其中的噪声信号.本文在基于对小波变换理论分析的基础上,介绍了3种目前较为流行的用于低场核磁共振信号去噪的方法,分别是小波阈值去噪、模极大值去噪和小波系数相关性去噪,并给出了用于评价去噪效果的四个参数及其计算方法.

低场核磁共振仪器振铃抑制新方法及其电路实现

加快天线残余能量释放以减弱天线振铃信号有利于缩短低场核磁共振仪器的回波间隔(TE),从而提高快弛豫组分的测量分辨率和信噪比(SNR).而天线Q值对能量的发射效率和泄放速度起着相反的作用.为此,我们首先设计了一种新型Q转换电路,在保证发射效率的同时,可以大大缩短能量泄放时间.在此基础上,应用了一种优化的脉冲序列以弥补传统相位交替对脉冲序列(PAPs)不能消除90脉冲振铃的缺陷,通过相位循环的方法进一步提高了信噪比.最后,在2 MHz岩心分析仪上测试了新型Q转换电路,当天线Q值降为发射期间的约1/5时,天线恢复时间由280.0μs降为18.2μs;而且,使用新型Q转换电路和优化的脉冲序列后,TE=60μs时,可以有效获得快弛豫组分的T2信号.

低场核磁共振技术在鱼用冻干疫苗保护剂筛选中的应用

为筛选适合鱼类冻干疫苗中使用的保护剂,采用低场核磁共振技术(LF-NMR)对冻干后不同保护剂中的水分分布和迁移规律进行了分析。根据水中氢质子的弛豫时间,可将保护剂中的残留水分为结合水、不易移动水和自由水3种形态。结果显示:冷冻干燥过程中二次干燥温度对甘露醇和蔗糖中残留水的分布有较大影响,随着温度从4℃升高到37℃,大部分自由水解吸而小部分转化为结合水。当冻干后的样品暴露在相对湿度43%和温度25℃的环境中时,大部分保护剂吸收水分,并将其固定为结合水,而甘露醇中的部分结合水则转变为自由水,并解吸到环境中。不同冻干保护剂中的水分分布和迁移并不相同,代表其具有不同的水分结合能力。该研究结果有助于鱼用冻干疫苗中保护剂的筛选和冻干工艺的优化,以便获得更加稳定的疫苗产品。