Low Frequency Nuclear Magnetic Resonance Research Articles

Artificial intelligence predictability of moisture, fats and fatty acids composition of fish using low frequency Nuclear Magnetic Resonance (LF-NMR) relaxation

Artificial intelligence predictability of moisture, fats and fatty acids composition of fish using low frequency Nuclear Magnetic Resonance (LF-NMR) relaxation

Effects of tea branch liquid smoke on oxidation and structure of myofibrillar protein derived from pork tenderloin during curing

This study focused on how different concentrations of tea branch liquid smoke (TLS) in the curing solution impacted the physicochemical properties and antioxidant properties of pork tenderloin. Five experimental (1.25 mL/kg, 2.5 mL/kg, 5 mL/kg, 10 mL/kg, 20 mL/kg) and blank groups set up over 4 days, and it was found that the physicochemical indexes, antioxidant capacity, thermal stability and protein network structure of the cured meat using 5 mL/kg of liquid smoke were excellent than the other groups used (P < 0.05). However, concentrations at 20 mL/kg accelerated protein oxidation. Low frequency nuclear magnetic resonance (LFNHR) revealed that TLS also improved the water holding capacity of the cured meat by increasing the percentage of bound water. Additionally, the correlation analysis demonstrated that the inoxidizability of myofibrillar protein was significantly related to cooking loss and water distribution, which were adjusted by changing the usage of liquid smoke.

Time-dependent propagation and interaction behavior of adjacent cracks in rock-like material under hydro-mechanical coupling

Under the long-term coupling effects of seepage pressure and geo-stress, the interaction and propagation of cracks in rock mass show typical time-dependent characteristics, and directly control the failure mode of rock mass. The laboratory tests under long-term hydro-mechanical coupling were carried out based on the cement mortar specimen containing adjacent pre-existing cracks, and the micro crack evolution in the specimen was analyzed by using low-frequency nuclear magnetic resonance technology, the corresponding numerical simulation was carried out to study the propagation and interaction behavior of adjacent cracks and the time-dependent mechanism of creep failure of rocks. The results show that: The creep failure of rock mass with adjacent cracks presents a tension-shear composite mode; The macro fracture is formed by the propagation of one crack and does not connect with the adjacent crack; Due to the interaction effect between cracks, a large number of micro cracks are formed in the specimen, and the propagation of adjacent pre-existing cracks is non-uniform, and the propagation of upper and lower wing cracks of the dominant crack is asymmetric; In the crack initiation stage, the crack propagation is controlled by the shear fracture mode, and the interaction shows the inhibition of adjacent cracks; After propagating to a certain extent, the dominant crack propagation is controlled by the tensile fracture mode, and its propagation rate increases, which accelerates the failure of rock mass.

Change in rapid salting kinetics and characteristics of hen egg yolks

A study of the dynamics of egg yolk salting clarified the diffusion of salt and the resulting changes in yolk quality and thereby provided guidance for better control of the final product. The effects of different salt contents in the salting solution (between 16 and 24%) on the mass transfer kinetics and egg yolk quality were analyzed during rapid salting. The results for the egg yolks showed that the changes in weight and water concentration decreased with increasing salt mass fraction, while the NaCl change increased. An increase in the salt content in the salting solution increased the effective diffusion coefficient ( D e ) of NaCl. Low-frequency nuclear magnetic resonance (LF-NMR) spectroscopy showed that higher salt content in the solution improved the amount of water transferred. The salted egg yolks treated in the 20–24% salting solutions had higher hardness, cohesiveness, oil yield and sandiness than those treated in other salting solutions. The samples salted in 16% solution had the highest values of the egg yolk index and CIELAB colorspace dimensions a* and b*. An analysis revealed statistically significant correlations between oil yield, sandiness, texture and color with D e . Taking oil yield and sandiness as the main indexes and comprehensively considering other sensory characteristics showed that 20% NaCl was the most suitable salt water solution for the rapid salting of hen egg yolks. ● The mass transfer and quality change of egg yolks increased with the salt content. ● The effective diffusion coefficient ( D e ) increased with salt content from 20 to 24%. ● T 23 , egg yolk index, springiness, cohesiveness, a* and b* decreased with salt content. ● T 22 , oil yield, sandiness, hardness, chewiness and L* increased with salt content. ● Oil yield, sandiness, texture and color were significantly correlated with the D e .

Novel low-field NMR method for characterization content and SARA composition of bitumen in rocks

In the oil industry, there is a need for fast and non-invasive methods for determining the bitumen content and group composition in rock samples. Determination of bitumen saturation of reservoir or source rocks has some difficulties due to existing methods limitations. For this purpose, the novel method is based on a combination of free induction decay (FID) and modified Carr-Purcell-Meilboom-Gill (CPMG) measurements using a low-frequency nuclear magnetic resonance (NMR) relaxation technique was developed. It allows obtaining the content and group composition (SARA fractions) of bitumen directly in the porous media without extraction. FID data fitting based on a combination of Voigt and exponential functions for liquid phase, as well as Abragam and exponential functions for solid phase components respectively was proposed. The developed method was tested on 20 rock samples collected from the productive formation (horizon M) located at the depth of 601–708 m of the wellbore 3001 of the Boca de Jaruco oilfield (Republic of Cuba). The bitumen content in the samples was obtained and compared with data determined by thermogravimetric analysis (TGA) and Rock-Eval pyrolysis. A good agreement of NMR results with TGA and pyrolysis was shown (R2 = 0.99 and 0.97 respectively). The values of liquid HC components (saturates, aromatics and resins) and solid HC components (asphaltenes) were compared with TGA data (R2 = 0.97 and 0.98 respectively). Finally, the proposed NMR method was applied to determine the SARA composition of the bitumen in the samples. To assess the accuracy of determining the SARA composition by the NMR method, SARA analysis (ASTM D4124-09) of extracts from the samples 632, 638, 658, 676, 689, 708 was carried out. NMR and conventional SARA analysis showed close results. To assess the completeness of the bitumen extraction from the mineral matrix, microCT and FIB-SEM were performed before and after extraction. It was found that after extraction the part of the bitumen remains in the pores, which distorts the results of SARA analysis. The proposed NMR method can be used to calculate the bitumen saturation and SARA composition for characterization of bitumen, selecting and modeling the effectiveness of applying the optimal EOR without destroying the samples. Also, the method is promising for the operational control of technological processes of oil production.

Optimization of an in-situ polymerized and crosslinked hydrogel formulation for lost circulation control

Lost circulation is a common problem during drilling and completion, and it contributes much to the nonproductive time of the operation. The Brazilian pre-salt is composed of highly heterogeneous carbonates and is highly susceptible to circulation loss. In this work, a removable, solid-free polymer gel formulation based on in-situ polymerization and gelation was proposed and optimized using design of experiments. The proposed gel contains acrylic acid (monomer), carboxymethylcellulose (thickener), ammonium persulfate (initiator), chromium (III) salt (crosslinking agent) and 240,000 NaCl brine as a solvent. The concentrations of these components, and the solution pH, were the variables considered in this study. The plateau modulus, maximum elastic modulus, gel stability, and gelation times were obtained and analyzed. The gelation time was obtained from oscillatory rheology time curves fitted by the Hill 5 model and from low-frequency nuclear magnetic resonance. Most of the studied gels presented elastic moduli from 1000 to 7000 Pa, close to and higher than the moduli of other gels for lost circulation. The gelation times ranged from 5 to 30 min, which could be improved by changing the initiator, protecting or inhibiting it. A pH of 9 led to faster gelation times, syneresis, and lower elastic moduli; therefore, pH values from 5 to 7 are ideal. Carboxymethylcellulose and the chromium salt increased slightly the gelation time, the elastic moduli, and the stability. Acrylic acid concentration controlled the overall elastic moduli, and higher concentrations led to shorter gelation times. Ammonium persulfate was able to both initiate the polymerization and also internally break the gel, depending on the concentration. Molecular explanations for these effects were provided. This proposed system is a promising candidate for lost circulation control for operations in the Brazilian pre-salt. Future steps involve studying the plugging and removable properties of the gels with optimized composition in high pressure and temperature settings. • A promising gel formulation for lost circulation control was proposed and optimized. • The pre-gel solution has low viscosity, but very high elasticity after gelation. • The gelation mechanism involves in-situ crosslinking and polymerization. • Rheological properties and gelation time can be modeled with R 2 ≥ 0.95. • Rheological properties match or surpass those from the literature.

Hydraulic Conductivity from Nuclear Magnetic Resonance Logs in Sediments with Elevated Magnetic Susceptibilities.

This study examined the application of slim-hole nuclear magnetic resonance (NMR) tools to estimate hydraulic conductivity (KNMR ) in an unconsolidated aquifer that contains a range of grain sizes (silt to gravel) and high and variable magnetic susceptibilities (MS) (10-4 to 10-2 SI). A K calibration dataset was acquired at 1-m intervals in three fully screened wells, and compared to KNMR estimates using the Schlumberger-Doll research (SDR) equation with published empirical constants developed from previous studies in unconsolidated sediments. While KNMR using published constants was within an order of magnitude of K, the agreement, overprediction, or underprediction of KNMR varied with the MS distribution in each well. An examination of the effects of MS on NMR data and site-specific empirical constants indicated that the exponent on T2ML (n-value in the SDR equation, representing the diffusion regime) was found to have the greatest influence on KNMR estimation accuracy, while NMR porosity did not improve the prediction of K. KNMR was further improved by integrating an MS log into the NMR analyses. A first approach detrended T2ML for the effects of MS prior to calculating KNMR , and a second approach introduced an MS term into the SDR equation. Both were found to produce similar refinements of KNMR in intervals of elevated MS. This study found that low frequency NMR logging with short echo times shows promise for sites with moderate to elevated MS levels, and recommends a workflow that examines parameter relationships and integrates MS logs into the estimation of KNMR .

Automated Low-Cost In Situ IR and NMR Spectroscopy Characterization of Clinical-Scale 129Xe Spin-Exchange Optical Pumping.

We present on the utility of in situ nuclear magnetic resonance (NMR) and near-infrared (NIR) spectroscopic techniques for automated advanced analysis of the 129Xe hyperpolarization process during spin-exchange optical pumping (SEOP). The developed software protocol, written in the MATLAB programming language, facilitates detailed characterization of hyperpolarized contrast agent production efficiency based on determination of key performance indicators, including the maximum achievable 129Xe polarization, steady-state Rb-129Xe spin-exchange and 129Xe polarization build-up rates, 129Xe spin-relaxation rates, and estimates of steady-state Rb electron polarization. Mapping the dynamics of 129Xe polarization and relaxation as a function of SEOP temperature enables systematic optimization of the batch-mode SEOP process. The automated analysis of a typical experimental data set, encompassing ∼300 raw NMR and NIR spectra combined across six different SEOP temperatures, can be performed in under 5 min on a laptop computer. The protocol is designed to be robust in operation on any batch-mode SEOP hyperpolarizer device. In particular, we demonstrate the implementation of a combination of low-cost NIR and low-frequency NMR spectrometers (∼$1,100 and ∼$300 respectively, ca. 2020) for use in the described protocols. The demonstrated methodology will aid in the characterization of NMR hyperpolarization hardware in the context of SEOP and other hyperpolarization techniques for more robust and less expensive clinical production of HP 129Xe and other contrast agents.

Characterization of syneresis phenomena in stirred acid milk gel using low frequency nuclear magnetic resonance on hydrogen and image analyses

Water retention is an important quality attribute for yogurt. Classically, stirred yogurt water retention is investigated using induced syneresis measurement (centrifugation), which does not characterize spontaneous syneresis. Low-frequency nuclear magnetic resonance (1H-LF-NMR) is a non-destructive technique to detect spontaneous syneresis. Experimental yogurt from pasteurized skim milk, and commercial stirred yogurts were analyzed with 1H-LF-NMR. After Laplace's transformation of the signal, hydrogen atoms pools were differentiated according to their mobility. Each hydrogen pool stood for a type of water mobility in the matrices characterized by a relaxation time (T2(i)), and a signal intensity (I2(i)). Yogurt water retention was assessed by induced syneresis and their structure was characterized using microscopy. Low frequency 1H-NMR detected four different water mobility groups in the matrices. Among these, there was a signal from bulk water, and another attributed to the separated serum (spontaneous syneresis). In experimental yogurts, spontaneous syneresis was visible, resulting in induced syneresis higher than 50%. Moreover, induced syneresis and spontaneous syneresis detected by 1H-LF-NMR were similar. In commercial yogurts, bulk water mobility reduced with increasing protein content and protein network density. Induced syneresis and bulk-water mobility correlated only in yogurts without gelatin. In the presence of gelatin, the network was more open, probably favoring bulk water mobility. This study shows that 1H-LF-NMR associated with microscopy image analysis efficiently assesses and describes yogurts water retention and spontaneous syneresis.

Proton relaxation in freeze-dried broccoli as measured by low-frequency nuclear magnetic resonance (LF-NMR) and its relationship with the thermal glass transition

Low-frequency nuclear magnetic resonance (LF-NMR) was used to identify different proton pools and their mobility in freeze-dried broccoli (moisture 0.01 to 0.25 g g sample−1 and temperature 193 to 443 K) containing un-freezable water. Three pools of protons were determined from transversal T2 (i.e., spin–spin) relaxation times. These were T2b (i.e., tightly bound pools of protons associated with macromolecules), T21 (i.e., protons in the strongly bound water with the solids) and T22 (i.e., protons in the weakly bound or capillary water). Two critical temperatures and one peak temperature from the plot of T2b, T21 and T22 versus temperature were identified and related to the moisture content. The critical temperatures determined from T2b and T21 increased with the increase in moisture up to BET-monolayer followed by an exponential decrease. However, the first critical temperature from T22 increased and reached to a plateau, while the second and third critical temperatures increased linearly with the increase in moisture. The critical temperature from T2b was determined from the intersection of the first and second segments and compared with the onset glass as measured earlier by differential scanning calorimetry (DSC). At moisture 0.01 g g sample−1, this critical temperature showed lower than the thermal glass transition temperature. The opposite trend was observed at or above moisture 0.05 g g sample−1, and the difference between critical temperature and glass transition temperature increased with the increase in moisture content. It was also observed that peak temperatures were close to the solids-melting temperature as measured by thermal analysis. The peak indicated the disruption of the macromolecules and creating interlinked melted or compacted solid mass and caused to decrease the proton mobility.

Litz wire RF coils for low frequency NMR applications

Radiofrequency (RF) coils are key components in Nuclear Magnetic Resonance (NMR) systems since the use of dedicated coils is necessary for obtaining high-quality images. As a first approximation, an RF coil is essentially a tuned electrical circuit comprising an inductor and a capacitor. Conductors cross-geometry choice affects the coil overall performance, since the RF current doesn’t flow uniformly in all the conductor volume. The use of Litz wire conductor for the RF coil design can help to maximize the surface where the current flows and to minimize the conductor resistance.This paper briefly reports the literature on Litz wires employed for MR coil design and their influence on coil performance. Successively four circular coils, tuned at frequencies in kHz and MHz ranges, were built by using wire and Litz wire conductors. Realized coils were tested and characterized by laboratory workbench in order to measure quality factors and to compare the performance of the different conductors typology. Our results are applicable in several situations as MR imaging in low field scanners, imaging of nuclear species at low fields, Overhauser systems and prepolarized NMR. Moreover, we believe Litz wire could be successfully employed in MRI/magnetic particle hyperthermia (MPH) systems.

Investigating the influence of ultrasound pre-treatment on drying kinetics and moisture migration measurement in Lactobacillus sakei cultured and uncultured beef jerky

Low Frequency-Nuclear Magnetic Resonance (LF-NMR) was employed to elucidate changes in water distribution in cultured (Lactobacillus sakei) and uncultured beef jerky samples subjected to ultrasound pre-treatment. Ultrasound pre-treatment at frequencies of 25, 33 and 45 kHz for 30 min, followed by marination (18 h) was carried out for both cultured and uncultured jerky samples. Among the various kinetic models assessed, the Wang and Singh model provided the closest fit to the drying experimental data, with high R2 (≥0.994), low RMSE (≤0.023) and low AICc (<−74.535) values for both cultured and uncultured samples. Distributed exponential analysis of T2 transversal relaxation times measured by LF-NMR curves revealed the presence of three distinct peaks attributed to; bound water, water present within the dense myofibrillar protein matrix and free-water at a relaxation time range of 0–10 ms (T2b), 10–100 ms (T21) and >100 ms (T22), respectively. Results presented in this study demonstrates that the ultrasound effect on drying behaviour was frequency dependent and that LF-NMR can be employed to evaluate moisture mobility and drying degree of beef jerky.

Interaction of two magnetic resonance modes in the polar phase of superfluid 3He

We report results of low frequency nuclear magnetic resonance (NMR) experiments in the superfluid polar phase of 3He which is stabilized by a new type of "nematic" aerogel - nafen. We have found that an interaction between transverse and longitudinal NMR modes may essentially influence the spin dynamics. Theoretical formulas for NMR resonant frequencies are derived and applied for interpretation of the experimental results.

Translational dynamics of ionic liquid imidazolium cations at solid/liquid interface in gel polymer electrolyte

Gel polymer electrolyte (GPE) based on ethoxylated bisphenol A dimethacrylate and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) ionic liquid (IL) at the mass ratio of 20:80 was prepared by in situ photopolymerization. The obtained material showed an exceptional behavior: its ionic conductivity was approximately twice higher than that of pure IL (as measured by impedance method). To explain the observed effect the translational diffusion of cations was studied indirectly by means of fast field-cycling (FFC) proton (1H) nuclear magnetic resonance (NMR) relaxometry method. The spin–lattice relaxation times of proton in cations were measured for neat IL and the IL involved in the polymer matrix in the temperature range from 248 to 343K. The relaxation data obtained for bulk IL were analyzed in terms of both translational self-diffusion (Torrey’s model) and local molecular reorientations around a long and a short molecular axis of the IL cation (Woessner’s model). The relaxation of IL confined to polymer matrix revealed a low-frequency dispersion (not observed for bulk liquid) which is the fingerprint of the ionic liquid cations/polymer matrix interactions. Therefore, the low-frequency NMR relaxation data in GPE were analyzed assuming the reorientation mediated by translational displacements (RMTD) mechanism. This dynamic process allows to explain a very long correlation time of the order of 10−5s calculated for the cations at the polymer/IL interface and determine their diffusion coefficient. It was found that the latter is unexpectedly higher than that of the self-diffusion constant of cations in pure IL and/or inside pools of IL in the polymer matrix. This finding indicates that in the presence of the GPE matrix new cation-conducting pathways may be created which play an important role in ionic conduction at the microscopic and/or quasi-macroscopic scale.

Effects of Ultrasound and Microwave Pretreatments of Apple Before Spouted Bed Drying on Rate of Dehydration and Physical Properties

Pretreatments of fruits before drying have been proposed as alternative way to improve the quality of dried fruits and reduce drying time. In the present study, the effects of different pretreatments (ultrasound and microwave) on apple cubes prior to spouted bed drying were investigated. Ultrasound pretreatment resulted in a great loss of sugars (25.7% for 15 min) compared to microwave pretreatment, where little rise in sugar content was observed (1.6% at 300 W). Ultrasound pretreatment improved the drying rate more than microwave pretreatment. Nevertheless, microwave-pretreated dried apples were harder and had lower water activity than ultrasound-pretreated ones. Low-frequency nuclear magnetic resonance (LF-NMR) analysis was used to study the water state and revealed that all pretreatments promoted redistribution of water among apple cell compartments and showed that most of the water lost was from the vacuoles. If dried low-calorie fruits are required then ultrasound pretreatment would be preferred.

The Instrument Set for Generating Fast Adiabatic Passage

The design and construction of a high-performance, low-cost, and easy to assemble adiabatic extension set for homebuilt and commercial spectrometers is described. Described apparatus set was designed for the fast adiabatic passage generation and is based on direct digital synthesizer DDS. This solution gives generator high signal to noise ratio, phase stability even during frequency change which is only possible in expansive commercial high-end hardware. Critical synchronization and timing issues are considered and solutions are discussed. Different experimental conditions and techniques for the measurements are briefly discussed. The proposed system is very flexible and might be used for the measurement of low-frequency nuclear magnetic resonance.

Effect of osmotic dehydration on Actinidia deliciosa kiwifruit: A combined NMR and ultrastructural study

The effects of individual osmotic dehydration processes (OD) on kiwifruit outer pericarp tissue were studied as reliant on treatment temperature (25, 35 and 45°C) and extent (0–300min). Macro (Low Frequency Nuclear Magnetic Resonance, LF-NMR), micro (Light Microscopy, LM) and ultrastructural (Transmission Electron Microscopy, TEM) measurements were performed to evaluate modifications of three cellular compartments, namely vacuole, cytoplasm – extracellular space and cell wall.Both LF-NMR relaxometry and LM observations highlighted shrinkage of the vacuole compartment along the OD. Intercellular space formations, observed at TEM, were in agreement with LF-NMR results. Cell walls of outer pericarp showed considerable changes in size, structure and stain uptake during OD, at both LM and TEM. Furthermore cell walls showed extensive swelling, which intensity varied from cell to cell and even within the same cell.The proposed multianalytical approach should enable both better designs of combined processing technologies and estimations of their effects on tissue response.

Application of low field NMR T2 measurements to clathrate hydrates

Low field (2 MHz) Nuclear Magnetic Resonance (NMR) proton spin–spin relaxation time ( T 2) distribution measurements were employed to investigate tetrahydrofuran (THF)—deuterium oxide (D 2O) clathrate hydrate formation and dissociation processes. In particular, T 2 distributions were obtained at the point of hydrate phase transition as a function of the co-existing solid/liquid ratios. Because T 2 of the target molecules reflect the structural arrangements of the molecules surrounding them, T 2 changes of THF in D 2O during hydrate formation and dissociation should yield insights into the hydrate mechanisms on a molecular level. This work demonstrated that such T 2 measurements could easily distinguish THF in the solid hydrate phase from THF in the coexisting liquid phase. To our knowledge, this is the first time that T 2 of guest molecules in hydrate cages has been measured using this low frequency NMR T 2 distribution technique. At this low frequency, results also proved that the technique can accurately capture the percentages of THF molecules residing in the solid and liquid phases and quantify the hydrate conversion progress. Therefore, an extension of this technique can be applied to measure hydrate kinetics. It was found that T 2 of THF in the liquid phase changed as hydrate formation/dissociation progressed, implying that the presence of solid hydrate influenced the coexisting fluid structure. The rotational activation measured from the proton response of THF in the hydrate phase was 31 KJ/mole, which agreed with values reported in the literature.

Screening system for detection of contraband swallowed narcotics

Swallowing small, water-tight packages filled with heroin and cocaine has become an increasingly popular method of transporting modest quantities of these narcotics across international borders. The most common carriers are airline passengers who enter a country after an airline flight. In many cases, these flights are of long duration. Quantum Magnetics (QM) has developed a system to screen selected airline passengers for the presence of swallowed narcotics. This system utilizes nonimaging, low-frequency nuclear magnetic resonance (NMR) to detect the presence of narcotics against the background response from the body. Scanning takes place quickly with nonionizing radiation, thus avoiding the operational difficulties associated with the use of ionizing radiation. Since the NMR system is nonimaging, it provides a “red light/green light” output, thus eliminating the need for trained medical personnel for image interpretation. The system has been tested on volunteers and on a phantom designed to mimic the NMR response of the human body Responses of the NMR screening system to both the presence and the absence of swallowed narcotics have been recorded, and these are presented and interpreted.

The relationship between crystal structure and methyl and t-butyl group dynamics in van der Waals organic solids.

We report x-ray diffractometry in a single crystal of 2-t-butyl-4-methylphenol (TMP) and low-frequency solid state nuclear magnetic resonance (NMR) proton relaxometry in a polycrystalline sample of TMP. The x-ray data show TMP to have a monoclinic, P2(1)/c, structure with eight molecules per unit cell and two crystallographically inequivalent t-butyl group (C(CH(3))(3)) sites. The proton spin-lattice relaxation rates were measured between 90 and 310 K at NMR frequencies of 8.50, 22.5, and 53.0 MHz. The relaxometry data is fitted with two models characterizing the dynamics of the t-butyl groups and their constituent methyl groups, both of which are consistent with the determined x-ray structure. In addition to presenting results for TMP, we review previously reported x-ray diffractometry and low-frequency NMR relaxometry in two other van der Waals solids which have a simpler structure. In both cases, a unique model for the reorientational dynamics was found. Finally, we review a similar previously reported analysis in a van der Waals solid with a very complex structure in which case fitting the NMR relaxometry requires very many parameters and serves mainly as a flag for a careful x-ray diffraction study.