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How to effectively withstand the dc magnetic bias is one of the key aspects of transformer design. General approaches either require additional active power electronics devices or apply complicated control strategies, causing the increased cost or reduced reliability. In this article, a passive negative magnetic reluctance structure (NMRS) is proposed and installed in the air gap of the open-core transformer, which could achieve improved dc magnetic bias withstanding capability without extra active devices. The key criterion of the proposed design is to employ the NMRS with a frequency-variation magnetic reluctance property as a magnetic bandpass filter, which shows a negative equivalent magnetic reluctance for the fundamental component of flux. Nevertheless, it presents a high magnetic reluctance for the dc component. With the proposed design, the transformer provides a strong withstanding dc bias capability and a low magnetizing current as well as high efficiency. Accordingly, both the advantages of open-core and closed-core transformers could be obtained with the proposed design. For verification, a 500-W EE55-based core prototype is constructed and verified with sinusoidal and square wave excitation. Electromagnetic analysis and experimental results are provided to demonstrate the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

The conventional diagnosis examination for cancerous tissue relies on the cumbersome and time-consuming pathologic section technology. In this article, we propose a 1-T portable magnetic resonance (MR) sensor equipped with a 3-mm probe, which enabled the rapid discrimination of ex vivo breast cancerous tissue in mice based on the MR longitudinal relaxation time (${T}_{{1}}$) measurement approach. First, the excellent distinction ability between ex vivo breast cancerous tissue and normal tissue using the proposed 1-T portable MR sensor is demonstrated. The ${T}_{{1}}$ contrast (i.e., ${T}_{\text {1cancerous}}/{T}_{\text {1normal}})$ is also compared with the other magnetic field strength MR systems, i.e., 0.23, 0.51, and 1.41 T. The results show that the average values of ${T}_{{1}}$ contrast at different MR measurement systems are all about 1.41. Then, the potential of the proposed 1-T MR sensor is validated in terms of sensitivity and portability. Finally, the limitations and future work of this preliminary study are discussed. Taken together, the proposed 1-T portable MR sensor with the ${T}_{{1}}$ value measurement approach has the promise to provide a low-cost, rapid, and accurate means for clinical assessment of the properties of tissue specimens, especially the trace tissue specimen taken from biopsy techniques. [ABSTRACT FROM AUTHOR]

Cysteine is a significant biothiol and plays a crucial role in physiological and clinical diagnosis. In the current research, we report a novel near-infrared (NIR) fluorescence sensor derived from triphenylamine-isophorone conjugate for the detection of cysteine. In the sensing pathway, an NIR fluorescence emitting moiety is released after a fast addition-cyclization of cysteine to the methacrylate group, which acts as an emission quencher. The detection platform demonstrates an excellent linear response to cysteine. It has been determined that the probe displays a fast response time (about 4 min), a low detection limit (12.4 nM), and a high signal-to-noise ratio. Easy and quick practical applications such as visual thin layer chromatography (TLC) plate and cotton swab have been established. Also, the current promising approach is effectively applied for the bio-imaging of cysteine in yeast cells and for drug analysis. Thus, this strategy allows the current probe to sense selectively cysteine over other biothiols in “turn-on” mode. [ABSTRACT FROM AUTHOR]

High temperature superconducting generators (HTSGs) have great potential of high power density for future large direct-drive wind turbines. As synchronous machines, HTSGs have rapid rise of field currents during a sudden short circuit fault which cause AC losses in the HTS tapes. This paper applies H-A formulation of Maxwell equations for finite element simulation of electromagnetic behavior of a 10 MW, 9.6 rpm HTSGs. The model is integrated to a short circuit model to calculate the characteristics of the HTS field winding, such as field currents and AC losses during a three-phase no-load short circuit fault at the armature winding terminal. Two HTSG designs are compared. The $n$ value characterizing the sharpness of the superconducting-resistive state transition of the HTS tape and the number of armature winding segments are analyzed as key variables. The result indicates high AC losses are produced but more armature winding segments can effectively reduce the AC loss and the field current. A lower $n$ value can also lower the AC loss level but only for the non-magnetic rotor design. The field current is not affected by the $n$ value for both HTSG designs. [ABSTRACT FROM AUTHOR]

SpinQ Triangulum is the second generation of the desktop quantum computers designed and manufactured by SpinQ Technology. SpinQ’s desktop quantum computer series, based on a room-temperature nuclear magnetic resonance (NMR) spectrometer, provides lightweight, cost-effective, and maintenance-free quantum computing platforms that aim to provide real-device experience for quantum computing education for kindergarten through 12th grade (K–12) and the college level. These platforms also feature quantum control design capabilities for studying quantum control and quantum noise. [ABSTRACT FROM AUTHOR]

Naphthalenediimide derivatives have shown applications in the area of chemical sensors for anions due to their special optical and electrical properties. In the current work, NDI derivative having phenyl amine end group (PPD-NDI) has been synthesized and tested for sensitivity towards trifluoroacetic acid (TFA), hydrochloric acid (HCl), nitric acid (HNO3) and sulfuric acid (H2SO4) for 1-65 mM concentrations. PPD-NDI displays reversible optical and visible sensitivity for detection of acids, specially, for HCl and TFA. PPD-NDI shows charge transfer band in the range of 500-600 nm in absorption spectra along with color change in presence of acid. To understand the mechanism of sensitivity, an exclusion method has been applied by analyzing other reference NDI molecules with different end groups and linkers. PPD-NDI shows selective sensitivity for TFA present in low concentration (1 mM) and HCl at all other concentrations. Binding constants for the association between PPD-NDI and acids are obtained from the Benesi Hildebrand plot and highest value is observed in case of TFA. The sensitivity of NDI derivatives can be very helpful in detection of acids in various industrial effluents from cloth, paper, refineries and in smelting industries. We have demonstrated the reversible lab-on paper strip testing experiment for detection of HCl acid by naked eye in low and high concentrations without need of any excitation light source. [ABSTRACT FROM AUTHOR]

Objective: The feasibility of conducting in vivo non-localized 31P Magnetic Resonance Spectroscopy (MRS) with a 1.0T extremity scanner and the potential to increase accessibility of this important diagnostic tool for low cost applications is revisited. Methods: This work presents a custom transmit-only quadrature birdcage, four-element receive coil array, and spectrometer interfaced to a commercial ONI 1.0T magnet for enabling multi-channel, non-1H frequency capabilities. A custom, magnetic resonance compatible plantar flexion-extension exercise device was also developed to enable exercise protocols. The coils were assessed with bench measurements and 31P phantom studies before an in vivo demonstration. Results: In pulse and acquire spectroscopy of a phantom, the array was found to improve the signal-to-noise ratio (SNR) by a factor of 1.31 and reduce the linewidth by 13.9% when compared to a large loop coil of the same overall size. In vivo testing results show that two averages and a four second repetition time for a temporal resolution of eight seconds was sufficient to obtain phosphocreatine recovery values and baseline pH levels aligned with expected literature values. Conclusion: Initial in vivo human skeletal muscle 31P MRS allowed successful monitoring of metabolic changes during an 18-minute exercise protocol. Significance: Adding an array coil and multinuclear capability to a commercial low-cost 1.0T extremity scanner enabled the observation of characteristic 31P metabolic information, such as the phosphocreatinerecovery rate and underlying baseline pH. [ABSTRACT FROM AUTHOR]

The aim of this study is 1) to demonstrate the interactions resulting from mixing ethylenediaminetetraacetic acid (EDTA) withsodium hypochlorite (NaOCl) and 2) to monitor the experimental interaction after cold plasma energy transferring mimicking physicochemical activation of solutions. Freshly opened pharmaceutical lavage solutions of 5.25% hypochlorite and 17% EDTA were used in experiments. A mixture of 40 ml was prepared using 5.25% hypochlorite/17% EDTA at a 1:1 ratio. The experimental cold atmospheric-pressure plasma jet (APPJ) treatment was performed using a dielectric barrier discharge (DBD) device for mimicking the activation of lavage solutions. pH measurements of the samples were performed. Spectral changes were analyzed with nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and UV-visible spectrophotometry. N-CH2-COOR and N-CH2-CH2-N were observed in EDTA at 4.65 and 2.90 p/min, respectively. The emergence of new signals at 3.70, 3.07, and 2.91 p/min was observed in the mixture of the EDTA and NaOCl. Decreased peak intensities of EDTA were observed in the APPJ treatment groups at 4.65 and 2.90 p/min with no spectral shift. The main findings are that carbon and nitrogen bonds formed on the EDTA molecule at 2357.08 and 2309.10 cm $^{\mathrm {-1 {}}}$ after oxidation with hypochlorite as middle-narrow and mid-wide, respectively. The molecular structure of EDTA is observed to change after the oxidization by hypochlorite. The newly formed peaks attributed to carbon and nitrogen on the oxidized EDTA molecule disappeared after the experimental APPJ application. The obtained absorbance maxima in the APPJ treatment are in the characteristic region for the $\pi $ - $\pi ^\ast $ transitions. Within the limitations of an in vitro study, the findings of the study demonstrated that the subsequent molecule occurred by the oxidization by hypochlorite or activated hypochlorite is different from each other and also is different from the characteristic structure of EDTA. Experimentally activated hypochlorite by APPJ might have caused the molecular electronic transitions of EDTA. [ABSTRACT FROM AUTHOR]

The motivation of this work is to analyze the in-band intermodulation distortion (IMD) occurring in surface acoustic wave (SAW) devices, using a recently developed fast method based on the input–output equivalent sources (IOES). The method calculates the equivalent current sources of a given harmonic (H) or IMD, which when applied at the boundaries of any uniform nonlinear region produce the same nonlinearities as the full distributed circuit. The accuracy of the method is validated with a very simplified SAW resonator with ten digits, which is modeled by a discretized Mason-based circuit. The IOES method provides equal results to the ones obtained through harmonic balance (HB) simulations, performed by means of commercial software, being the first 1000 times faster. Once the accuracy of the method is guaranteed, it is used to analyze the measured in-band IMD3 of several lithium tantalite 42° cut leaky SAW (LSAW) resonators with different pitches and duty factors at the B66 long term evolution (LTE) frequency band. Those resonators are comprised of 100 and 20 electrode pairs for the active region and each of the reflectors, respectively, which implies the analysis of a very large distributed nonlinear problem with thousands of nonlinear local sources. The IOES method takes 35.4 s in simulating 51 frequency points, whereas this simulation is not possible using a commercial HB simulator on a general-purpose computer. [ABSTRACT FROM AUTHOR]

Time-Domain Nuclear Magnetic Resonance (TD-NMR) is a powerful method used for general characterization of a variety of materials as well as to online or in-situ monitoring of process. Because of that industries increasingly benefit from its use in process analytical technology (PAT) for production control and quality assurance. However, there is an increasing number of applications that requires automated signal acquisition as a function of temperatures, a resource that is not always available in many of the commercial equipments. We describe an automation procedure using the Bruker Minispec mq20 spectrometer with the BVT3000 temperature control, building software and hardware to execute TD-NMR experiments as a function of the temperature as well as the temperature calibration in an automatic form. Despite being developed for this specific equipment, the general idea can be used in other TD-NMR equipments that could benefit from this type of automation. As a demonstration, the system was used to monitor the temperature dependence of molecular mobility in polymers. All developed codes are shared in an open repository on GitHub. [ABSTRACT FROM AUTHOR]

Regression analysis based methods have shown strong robustness and achieved great success in face recognition. In these methods, convex $l_1$ l 1 -norm and nuclear norm are usually utilized to approximate the $l_0$ l 0 -norm and rank function. However, such convex relaxations may introduce a bias and lead to a suboptimal solution. In this paper, we propose a novel Enhanced Group Sparse regularized Nonconvex Regression (EGSNR) method for robust face recognition. An upper bounded nonconvex function is introduced to replace $l_1$ l 1 -norm for sparsity, which alleviates the bias problem and adverse effects caused by outliers. To capture the characteristics of complex errors, we propose a mixed model by combining $\gamma$ γ -norm and matrix $\gamma$ γ -norm induced from the nonconvex function. Furthermore, an $l_{2,\gamma }$ l 2 , γ -norm based regularizer is designed to directly seek the interclass sparsity or group sparsity instead of traditional $l_{2,1}$ l 2 , 1 -norm. The locality of data, i.e., the distance between the query sample and multi-subspaces, is also taken into consideration. This enhanced group sparse regularizer enables EGSNR to learn more discriminative representation coefficients. Comprehensive experiments on several popular face datasets demonstrate that the proposed EGSNR outperforms the state-of-the-art regression based methods for robust face recognition. [ABSTRACT FROM AUTHOR]

The shielding of electromagnetic noise is critical in obtaining magnetic resonance imaging measurements in the ultra-low magnetic field regime where the intrinsic signal-to-noise ratio is very small. The traditional approach of using an enclosure for electromagnetic shielding is expensive and hinders system portability. We describe here the use of a CNN-based software gradiometer to suppress the effect of electromagnetic ambient background noise sources that inductively couple into the signal detection coils. The system involves three ambient noise monitoring coils placed at a distance from the magnetic resonance signal detector. The three coils were used to synthesize the ambient noise captured by the signal detector; a convolutional neural network approach was used. Mathematical foundations are provided to justify the noise suppression framework. The results show that as much as 20-fold noise suppression can be achieved using an optimized convolutional neural network and simultaneous ambient noise measurements. The proposed approach has the potential to replace the requirement for magnetically shielded enclosures and make ultra-low field magnetic resonance imaging truly portable. [ABSTRACT FROM AUTHOR]

Biological functions of a cell are typically carried out through protein complexes. The detection of protein complexes is therefore of great significance for understanding the cellular organizations and protein functions. In the past decades, many computational methods have been proposed to detect protein complexes. However, most of the existing methods just search the local topological information to mine dense subgraphs as protein complexes, ignoring the global topological information. To tackle this issue, we propose the DPCMNE method to detect protein complexes via multi-level network embedding. It can preserve both the local and global topological information of biological networks. First, DPCMNE employs a hierarchical compressing strategy to recursively compress the input protein-protein interaction (PPI) network into multi-level smaller PPI networks. Then, a network embedding method is applied on these smaller PPI networks to learn protein embeddings of different levels of granularity. The embeddings learned from all the compressed PPI networks are concatenated to represent the final protein embeddings of the original input PPI network. Finally, a core-attachment based strategy is adopted to detect protein complexes in the weighted PPI network constructed by the pairwise similarity of protein embeddings. To assess the efficiency of our proposed method, DPCMNE is compared with other eight clustering algorithms on two yeast datasets. The experimental results show that the performance of DPCMNE outperforms those state-of-the-art complex detection methods in terms of F1 and F1+Acc. Furthermore, the results of functional enrichment analysis indicate that protein complexes detected by DPCMNE are more biologically significant in terms of P-score. [ABSTRACT FROM AUTHOR]

In this article, a silicone rubber-based composite material is selected as the test sample, and a 100-h corona aging test is conducted under different environments using multiple pin-plate electrodes to study the corona discharge characteristics of pin-plate under different humidity, salt fog, and haze environments. The corona aging characteristics of silicone rubber material are analyzed by the static contact angle, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The results show that, with the increase in the relative humidity (RH), the frequency and energy of corona discharge increase. The discharge frequency under a haze environment is small, but the number and amplitude of the positive half-cycle pulse are larger. With the increase in RH and the deterioration of the environment, the oxidation degree and hydrophobicity loss rate of the material surface are accelerated, and the material surface damage is also aggravated. The aging characteristics of silicone rubber have a positive correlation with the content of water molecules in the air, some hydrophilic -OH, and acidic -COOH appear on the material surface, leading to the insulation performance decrease. As the aging of silicone rubber deepens, its equivalent transverse relaxation time drop increases, the number of H atoms that become low bond energy state inside increases, and the resistance to corona aging decreases. The results of this article can provide some reference for the evaluation, diagnosis, and production of composite insulators in different regions. [ABSTRACT FROM AUTHOR]

Significant sensitivity improvements have been achieved by utilizing high temperature superconducting (HTS) resonators in nuclear magnetic resonance (NMR) probes. Many nuclei such as 13C benefit from strong excitation fields which cannot be produced by traditional HTS resonator designs. We investigate the use of double-sided, counter-wound multi-arm spiral HTS resonators with the aim of increasing the excitation field at the required nuclear Larmor frequency for 13C. When compared to double-sided, counter-wound spiral resonators with similar geometry, simulations indicate that the multi-arm spiral version develops a more uniform current distribution. Preliminary tests of a two-arm resonator indicate that it may produce a stronger excitation field. [ABSTRACT FROM AUTHOR]

Electromagnetic geophysical methods are widely applied in urban shallow exploration, considering their convenience and noninvasiveness. As one of the emerging techniques, polarizing surface nuclear magnetic resonance (SNMR) shows significant potential for water-based target detections. However, problems involving weak signal response and strong noise interference are challenging to avoid. Therefore, numerous studies focused on suppressing the electromagnetic interference and improving the effective electromagnetic control accuracy to achieve high-precision shallow imaging. On this basis, we proposed a new magnetic-field enhancement technology that explored double-polarization coils, instead of the single loop, to improve the applications of polarizing SNMR. By controlling the current for double-polarization coils, the magnetic field, which is twice as strong as the single coil, could be provided. As a result, the sensitivities and signal responses for subsurface detection sensitive areas with the same power consumption were further enhanced. Considering the SNMR research, we also identified that this new configuration with double-polarization coil can effectively improve the resolution of the shallow depth because it compensates for the magnitude of the static magnetic field in the center. Based on the theoretical analysis, we developed the instrument and, for the first time, realized the accurate interpretation of the real ground soil in an urban environment, verifying the effectiveness of the proposed configuration and the reliability of the system. [ABSTRACT FROM AUTHOR]

The utility of wideband high field nuclear magnetic resonance (NMR) spectrometers is significant in many applications. Wideband radio frequency (RF) front-ends are critical for the realization of multi-nuclei spectrometers. To realize such systems, wideband Transmit-Receive (TR) switches and low noise amplifiers (LNA) should be implemented at the RF front-end (FE) of the system. Most of the common designs used nowadays on NMR spectrometers are either inherently narrowband and/or of relatively high noise-figure which limit the overall system performance to a large extent. To improve upon the conventional FE performance, a new design of wideband high-power TR switch which could be devised for multi-nuclei NMR spectrometers is introduced in this brief. The developed wideband TR switch employs PIN diode switching technique and a dual-driver circuit. A prototype was constructed and experimentally characterized. The small-signal measurement results show that the switch has a bandwidth from 30 – 200MHz where the return loss is maintained below 18 dB with insertion loss of 0.09 - 0.2dB in the transmit mode and 0.11 – 0.37dB in the receive mode. It also exhibits a very high isolation of 63 - 80dB over the entire bandwidth. It is demonstrated that the switch can withstand continuous-wave RF input with power levels as high as 125 W while maintaining low insertion loss and high isolation. [ABSTRACT FROM AUTHOR]

The elastic network models (ENMs)are known as representative coarse-grained models to capture essential dynamics of proteins. Due to simple designs of the force constants as a decay with spatial distances of residue pairs in many previous studies, there is still much room for the improvement of ENMs. In this article, we directly computed the force constants with the inverse covariance estimation using a ridge-type operater for the precision matrix estimation (ROPE)on a large-scale set of NMR ensembles. Distance-dependent statistical analyses on the force constants were further comprehensively performed in terms of several paired types of sequence and structural information, including secondary structure, relative solvent accessibility, sequence distance and terminal. Various distinguished distributions of the mean force constants highlight the structural and sequential characteristics coupled with the inter-residue cooperativity beyond the spatial distances. We finally integrated these structural and sequential characteristics to build novel ENM variations using the particle swarm optimization for the parameter estimation. The considerable improvements on the correlation coefficient of the mean-square fluctuation and the mode overlap were achieved by the proposed variations when compared with traditional ENMs. This study opens a novel way to develop more accurate elastic network models for protein dynamics. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) relaxometry techniques have been widely used for evaluating hydrated cement paste as non-destructive and quantitative measurements. The important crystalline solid phases, such as Portlandite and Ettringite, are formed in the hydration of cement paste. However, it is challenging to quantify these crystalline solid phases by conventional NMR relaxation methods, due to their short-lived NMR signal lifetimes. A novel method for 2-D NMR $T_{1}$ – $T_{\mathrm {2S}}$ measurement of hydrated cement paste is proposed in this article. Combining a homebuilt NMR probe with short deadtime and high sensitivity, the $T_{1}$ – $T_{\mathrm {2S}}$ method can provide a more complete assessment of hydrogen-bearing crystalline solid phases (i.e., Portlandite and Ettringite) in hydrated cement paste. Experimental results demonstrated that the proposed method produced two additional distinct peaks in the $T_{1}$ – $T_{2}$ correlation map, compared with conventional methodologies. The attribution of the two peaks to Portlandite and Ettringite in hydrated cement paste was confirmed by heating experiments and partial least-square regression (PLSR) method. This technique has enabled detection and quantification of Portlandite and Ettringite in hydrated cement paste. [ABSTRACT FROM AUTHOR]

A series of ten $\alpha $ , $\beta $ -unsaturated benzotriazolyl-1,3,4-oxadiazole derivatives was synthesized and all compounds were evaluated in vitro against three breast cancer cell lines (MCF-7, MDA-MB-231 and 4T1) at different concentrations (0.1, 0.5, 1, 2, 3, 4 and 5 mg/mL). The results showed that compounds 6a, 6c, 6d, 6f, 6g, and 6i displayed acceptable anticancer activity, where compound 6f was the most active on the three cell lines (IC50 = 0.80, 0.07, and 0.30 mg/mL, respectively). Regarding the cytotoxicity assay, the compounds exhibited modest toxicity on murine splenocytes and peripheral human blood cells at the highest concentration tested (5 mg/mL). Compound 6f was further evaluated at different concentrations showing moderate cytotoxicity at the 5 mg/mL concentration and negligible cytotoxicity at the minimum concentration evaluated (0.05 mg/mL). Finally, the compounds 6a, 6c, 6d, 6f, 6g, 6i, and 6j were evaluated as fluorescence markers due to their ability to be internalized into MCF-7 cells. [ABSTRACT FROM AUTHOR]

Objective: In biomanufacturing there is a need for quantitative methods to map cell viability and density inside 3D bioreactors to assess health and proliferation over time. Recently, noninvasive MRI readouts of cell density have been achieved. However, the ratio of live to dead cells was not varied. Herein we present an approach for measuring the viability of cells embedded in a hydrogel independently from cell density to map cell number and health. Methods: Independent quantification of cell viability and density was achieved by calibrating the $\boldsymbol{^1}$ H magnetization transfer- (MT) and diffusion-weighted NMR signals to samples of known cell density and viability using a multivariate approach. Maps of cell viability and density were generated by weighting NMR images by these parameters post-calibration. Results: Using this method, the limits of detection (LODs) of total cell density and viable cell density were found to be $\boldsymbol{3.88 \times 10^{8}}$ cells $\boldsymbol{\cdot }$ mL $\boldsymbol{^{-1}\cdot }$ Hz $\boldsymbol{^{-1/2}}$ and $\boldsymbol{2.36 \times 10^{9}}$ viable cells $\boldsymbol{\cdot }$ mL $\boldsymbol{^{-1}\cdot }$ Hz $\boldsymbol{^{-1/2}}$ respectively. Conclusion: This mapping technique provides a noninvasive means of visualizing cell viability and number density within optically opaque bioreactors. Significance: We anticipate that such nondestructive readouts will provide valuable feedback for monitoring and controlling cell populations in bioreactors. [ABSTRACT FROM AUTHOR]

Transverse relaxation T2 spectrum obtained by nuclear magnetic resonance (NMR) logging tools is an intuitive reflection of the pore size distribution for subsurface formation, which is valuable for petroleum reservoir characterization. However, the deployment of NMR logging tools is constrained by financial and operational factors, while NMR data are only available in very limited wells. This seriously limits its application in practices. Therefore, researchers try to synthesize NMR T2 spectra from more widely measured conventional logging data with the help of machine learning technologies. In the article, we propose the spectrum regression forest (SRF) algorithm for the prediction of NMR T2 spectra from conventional logging responses. Based on the experiment on the real-world well data of carbonate reservoir, the proposed algorithm is proved to provide effective NMR T2 spectrum predictions with accuracy amplitudes and consist morphology, which is believed to enhance the understanding of formation pore structures for future reservoir characterization practices. [ABSTRACT FROM AUTHOR]

The transverse relaxation time of the spin-exchange optical pumped noble gas nuclei is a fundamental parameter to evaluate the performance of a nuclear magnetic resonance (NMR) rotation sensor. In practical tests and applications, measuring the transverse relaxation time in real-time is challenging. Due to the conflict with feedback loops, the traditional methods are unsuitable for real-time measurement. To address this limitation, this paper proposes a real-time method based on parameter identification to measure the transverse relaxation time. In the proposed method, a step signal is added to the oscillation magnetic field to excite nuclear spins, and the phase response generated is collected for identification. An NMR rotation sensor prototype is developed for the proof of concept. The experimental results verify the effectiveness and the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Low-field NMR technology has been widely used in many fields, among which the most representative method is the use of CPMG sequence for T2 measurement. Important parameters such as permeability, saturation and fluid type of porous media can be obtained by T2 spectrum inversion calculation of NMR echo sequence signal. However, T2 spectrum inversion calculation is easily affected by noise signals. Improving the signal-to-noise ratio (SNR) of echo signal is one of the key problems with the application of low-field NMR technology. Therefore, in order to obtain more accurate analysis results, it is necessary to develop corresponding noise reduction methods. The past researches on NMR signal noise reduction mainly focus on echo string. In this paper, a complete NMR signal model is constructed, and the problem of the echo and echo string de-noising is discussed. FIR filter and orthogonal modulation filter (OMF) are studied for noise reduction of echo. To solve the problem of echo string de-noising, an improved complementary ensemble empirical mode decomposition (CEEMD) threshold de-noising method is proposed and compared with the heuristic threshold de-noising method based on sym4 wavelet and the previous empirical mode decomposition (EMD) threshold de-noising method. Based on the construction model and practical verification, it is proved that the proposed method can invert the more accurate T2 spectrum while improving the signal-to-noise ratio. The research results of this paper provide a strong support for the application of low-field NMR technology in the environment of strong noise.

A common noise source in surface nuclear magnetic resonance (NMR) is narrowband noise sources that occur at frequencies close to the Larmor frequency, such as power-line harmonics or other sinusoidal signals of unknown origin. These noise sources can lead to significant perturbation on the estimated NMR signal and degrade the accuracy of subsurface characterizations. We demonstrate that the spectral analysis envelope detection scheme, where the envelope is estimated using the discrete Fourier transform for a suite of sliding windows, can be modified to mitigate the effect of narrowband noise sources. Selection of an appropriate length rectangular window is shown to allow one to effectively place a stopband at frequencies very close to the Larmor frequency, where the stopband may be selected to coincide with narrowband noise sources. The result is a significant reduction in the influence of the narrowband noise source on the estimated envelope, without introduction of distorting transients on the signal. Synthetic and field results are presented to illustrate the effectiveness of the proposed approach, as well as identify limits on the required resolution of the narrowband noise source’s frequency. [ABSTRACT FROM AUTHOR]

We optimized the magnetic field homogeneity of two canonical designs for mobile microfluidic nuclear magnetic resonance (NMR) applications: two parallel magnets with an air gap and a modified Halbach array. Along with the influence of the sample length, general design guidelines will be presented. For a fair comparison, the sensitive length of the sample has been chosen to be the same as the gap size between the magnets to ensure enough space for the transmitting and receiving unit, as well as basic electric shimming components. Keeping the compactness of the final device in mind, a box with an edge length 5 times the gap size has been defined, in which the complete magnet configuration should fit. With the chosen boundary conditions, the simple parallel cuboid configuration reaches the best homogeneity without active shimming (0.5 Bs, 41 ppm), while the pseudo-Halbach configuration has the highest field strength (0.9 Bs, 994 ppm), assuming perfect magnets. However, permanent magnet configurations suffer from imperfections, such as magnetization, fabrication, and positioning errors, which results in worse magnetic field homogeneities than expected from simulations using a fixed optimized parameter set. We present a sensitivity analysis for a magnetic cube and the results of studies of the variations in the magnetization and angle of magnetization of magnets purchased from different suppliers, composed of different materials and coatings, and of different sizes. We performed a detailed Monte Carlo simulation on the effect of the measured distribution of magnetic properties on the mentioned configurations. The cuboid design shows a mean homogeneity of 430 ppm (std. dev. 350 ppm), the Pseudo-Halbach has a mean homogeneity of 1086 ppm (std dev. 8 ppm). [ABSTRACT FROM AUTHOR]

Obtaining the information of shallow surface hydrogeological parameters is of great significance to the study of the groundwater cycle, the development and utilization of groundwater, and the protection of groundwater. Nuclear magnetic resonance (NMR) technology is the only method among all geophysical methods that can directly qualitatively and quantitatively measure groundwater content and evaluate aquifer reservoirs. The emergence of small-diameter NMR logging tools provides a powerful tool for the evaluation of shallow surface hydrogeological parameters. However, the low signal-to-noise ratio (SNR) of the NMR signal is still an important factor restricting the development of such instruments. In this article, we propose a design scheme for the receiving system of a small-diameter NMR logging tool. Its main design purpose is to improve the SNR of the receiving signal. The receiving system mainly includes an integrated differential coil, MOSFET-based duplexer, series LCR signal processing circuit, and ultralow noise lithium battery power. To verify the effect of the receiving system we designed, a sand sample moisture content test experiment has been conducted. The experimental results show that the NMR logging system can measure the water content accurately and reflect the distribution of porosity of the sample. The comparison with other small-diameter NMR logging systems shows that the receiving system we designed has a good receiving effect and is close to the level of commercial equipment. Finally, we expect such instruments to play an important role in the evaluation of pollution on the shallow surface. [ABSTRACT FROM AUTHOR]

Surface nuclear magnetic resonance (SNMR) technology based on a prepolarization field is a new geophysical method that offers a higher resolution for detecting shallow groundwater than traditional SNMR. However, when a prepolarization SNMR system works in noisy environments (such as cities), it is difficult to obtain high-quality data because of the low signal-to-noise ratio (SNR). Moreover, a traditional air-core coil sensor system has a relatively large dead time, which can cause early signal loss and further reduce the SNR. To solve these problems, we proposed an innovative air-core coil sensor design method to improve the detection capability of prepolarization SNMR in complex noise space. To suppress environmental noise and increase the signal amplitude, a passive matching network based on a differential structure was designed, which has a gain of 9.69 dB and a bandwidth of 700 Hz. In addition, a fast switch based on back-to-back technology was also used to replace the mechanical high-voltage relay, and the switching time was reduced to less than $10~\mu \text{s}$. The effectiveness of the new sensor was tested via experiments in the laboratory and field. The test results showed that the switching speed between transmitting and receiving is thousands of times faster than that of the traditional sensor, and the new sensor can still detect effective free induction decay (FID) signals in a noisy environment where the traditional sensor completely fails. Therefore, this research can effectively improve the SNR and provide strong support for the application of prepolarization field magnetic resonance technology in areas with complex noise environments. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) spectroscopy, whose time domain data is modeled as the sum of damped exponential signals, has become an indispensable tool in various scenarios, such as biomedicine, biology, and chemistry. NMR spectroscopy signals, however, are usually corrupted by Gaussian noise in practice, raising difficulties in sequential analysis and quantification. The low-rank Hankel property of exponential signals plays an important role in the denoising issue, but selecting an appropriate parameter still remains a problem. In this work, we explore the effect of the regularization parameter of a convex optimization denoising method based on low-rank Hankel matrices for exponential signals corrupted by Gaussian noise. An accurate estimate on the spectral norm of weighted Hankel matrices is provided as a guidance to set the regularization parameter. The bound can be efficiently calculated since it only depends on the standard deviation of the noise and a constant. Aided by the bound, one can easily obtain an auto-setting regularization parameter to produce promising denoised results. Our results on synthetic and realistic NMR spectroscopy data demonstrate a superior denoising performance of the proposed approach over typical Cadzow and the state-of-the-art QR decomposition methods, especially in the low signal-to-noise ratio regime. [ABSTRACT FROM AUTHOR]

During the past several decades, inexpensive compact nuclear magnetic resonance (NMR) instruments have been widely used for on-site detections of chemical identity and sample analyses in industrial applications. In general, via shim coils and control strategies, automatic search shimming methods are capable of improving the magnetic field uniformity so that optimized signals can be acquired and particularly suited for rapid detections in compact NMR instruments. However, because these methods inherently endure the inefficiency in multidimensional shims and the sensitivity of starting points, it is time-consuming to obtain acceptable results in a field infected with distortions and strays. Here, two remedies that improve the shimming speed for the search shimming method are proposed. First, analyzing and compensating for magnetic susceptibility effects, we relocate starting points closely to optima and reduce the complexity of global exploration. Second, modifying the simplex movement with adaptive scale factors and gradient-like centroid, we have improved the convergence of the simplex shimming algorithm in a multidimensional search space. Via theoretical analyses and lab experiments, we find that the proposed shimming method outperforms regular shimming methods in terms of handling complex magnetic fields and reducing shimming times and hope that our study can help further improve NMR shimming methods in the future. [ABSTRACT FROM AUTHOR]

Despite the powerfulness for revealing molecular structures and compositions, conventional 2D ${J}$ -resolved nuclear magnetic resonance (NMR) experiments are generally exposed to crowded NMR resonances, distorted peak lineshapes, strong coupling artifacts, and inhomogeneous broadening effects, thus rendering its potential applications restricted. Herein, we propose a general NMR method to circumvent these complications and record absorption-mode 2D ${J}$ -resolved spectra, in which pure chemical shifts and ${J}$ couplings are presented in two orthogonal dimensions. Thereby, this method facilitates peak assignments at congested spectral regions and implements high-resolution measurements on the desired structural information of ${J}$ couplings and chemical shifts, even under nonideal magnetic field conditions. Experimental results on samples of a biomolecule and clinical antibiotics demonstrate its suitability and effectiveness for analyzing complex samples exhibiting crowded resonances or strong coupling responses under adverse magnetic field conditions. More importantly, it is available for directly probing heterogeneous biological samples containing intrinsic susceptibility variations and abundant metabolites. In addition, a multiband version is further developed to enhance the spectral sensitivity by collecting signals from multiple spatial slices. This proposed technique is applicable to common commercial liquid NMR spectrometers without special requirements on instrument hardwares and sample pretreatments. Consequently, this study permits composition measurements and multiplet structure analyses on complex samples even in inhomogeneous magnetic fields, thus showing interesting prospects for future chemical and biological applications. [ABSTRACT FROM AUTHOR]

In this article, a static-sample magnetometer is presented to measure the relative permeability of weakly magnetic materials. The method consists of scanning the magnetic field inside a dipole magnet by using an NMR teslameter to measure the perturbation of a test specimen on the externally applied field. Then, an inverse problem is used to compute the specimen’s relative permeability. As a case study, the measurement of three different materials with different shapes and dimensions is carried out. The method was validated by measuring the same material by vibrating sample magnetometry as proposed by the standard ASTM A342/A342M-14. The expanded measurement uncertainty of the relative permeability, evaluated by Monte Carlo simulations, is about 10−4 for all the cases, with a level of confidence of 95%. [ABSTRACT FROM AUTHOR]

Double resonance experiments in field-cycling nuclear magnetic resonance (NMR) are powerful tools for the indirect detection of quadrupolar and electron resonances, dynamic nuclear polarization-induced signal amplification, within other possibilities. In the context of magnetic resonance imaging, double irradiation at high and low magnetic fields in field-cycling experiments can be conveniently used for instrumental calibration purposes and contrast manipulation. The basic goal of this article is to present a practical method for the measurement and calibration of the magnetic field in field-cycling magnetic resonance imaging instruments using proton resonances at high and low fields. We discuss an experimental protocol to adjust the optimal position of the gradient unit respect to the sample and the magnet system, and to measure the effective magnetic field gradient across the sample. A new modality of slice selection by irradiating the sample in the presence of a gradient field at low magnet-field conditions is also discussed. As a practical matter, we show how the sample irradiation at low fields can be used for contrast-enhancement, while handling the NMR signal intensity with spatial selectivity. To the best of our knowledge, this is the first calibration and adjustment package for a field-cycled magnetic resonance imaging instrument and the first example of double irradiation direct manipulation of contrasts in a proton image. [ABSTRACT FROM AUTHOR]

Silicone rubber insulators (SRIs) play an important role in high-voltage power transmission lines. Given that SRIs critically threaten the safe operation of the power grid, quantitatively assessing the aging status of SRIs in situ is crucial. In this article, a portable unilateral magnetic resonance (UMR) sensor with a U-shaped magnet structure and its measuring circuit were designed for the nondestructive detection of the aging status of SRIs in situ. First, the optimization efficiency of the magnet structure was improved through a uniform design method. Then, the planar radio frequency (RF) coil was designed by the finite-element method. Furthermore, the demagnetization effect of eddy currents induced in metal materials on the RF magnetic field was analyzed. We measured the SRI sheds at different service times and obtained the corresponding $^{1}\text{H}$ transverse relaxation decay curves by importing the Carr–Purcell–Meiboom–Gill (CPMG) sequence. Finally, the transverse relaxation decay curves were postprocessed using inverse Laplace transformation, and the 1-D spectrum distributions of transverse relaxation time ($T_{2}$) were obtained. The results reveal that $T_{2}$ of the surface of the SRI shed decreases as the service time of the SRI increases. In addition, the difference in $T_{2}$ between the surface and interior of the SRI shed increases. The comparison experiments demonstrate that the U-shaped sensor designed in this article is superior to the curved sensor previously designed by our team. The effect of temperature variation on SRIs aging assessment was considered at last. [ABSTRACT FROM AUTHOR]

We present a design overview of the MIT 1.3-GHz LTS/HTS NMR magnet (1.3G) with a newly designed 835-MHz REBCO insert (H835) as a replacement for the 800-MHz REBCO insert (H800) that was damaged when it quenched during operation in 2018. The new H835 is designed to contribute 19.6 T in a background field of 10.93 T by an LTS NMR magnet that normally rated at 11.74 T (500 MHz): combined, 1.3G generates a total field of 30.53 T corresponding to a proton resonance frequency of 1.3 GHz. H835 is designed to operate stably while meeting 1.3G design constraints. We have also designed H835 to protect it from permanent damage in an improbable event like a quench. Key design features are: 1) a single-coil formation, composed of 38 stacked metal-co-wound no-insulation and 2 stacked no-insulation double-pancake coils, all with mechanically improved cross-over sections; 2) enhanced thermal stability; and 3) reduced current margin with a detect-and-heat method. This paper includes: 1) electromagnetic and mechanical design of H835; 2) cryogenics overview; 3) quench protection strategy; and 3) discussion on the next steps to successfully complete 1.3G. [ABSTRACT FROM AUTHOR]

A 20 T/ϕ32 mm all REBa2Cu3O7−δ (REBCO, RE = rare earth) REBCO superconducting magnet for 850 MHz nuclear magnetic resonance spectroscopy is being designed. The high-temperature superconductors, REBCO-coated conductors with both high tensile stress and high critical current density under high magnetic field would allow superconducting magnets to be compact and lighter than their low-temperature superconductor counterparts. The 20-T REBCO superconducting magnet consists of a stack of 28 double-pancake coils with the so-called no-insulation methods. Considering the perpendicular magnetic field to the c-axis, five different width tapes, i.e., 4.1, 5.1, 6.1, 7.1, and 8.1 mm were placed on the midplane to both end positions in an axial direction. To improve the magnetic field homogeneity, the inside notch on the 4.1-mm tapes was adopted. The peak-to-peak magnetic field homogeneity over a 5-mm diameter spherical volume is better than 0.8 ppm. In this article, the design of the REBCO coils, electromagnetic field analysis, and stress analysis of the superconducting coils were presented. [ABSTRACT FROM AUTHOR]

A multisection slightly tapered RF cavity for millimeter-wave gyrotron is designed and investigated to enhance the tunable bandwidth for dynamic nuclear polarization (DNP)/nuclear magnetic resonance (NMR) application. The present cavity is operated in TE7.2,q mode at ~260 GHz, in which q is varied from 1 to 9 to achieve the desired tuning range. The effect of the multisection gyrotron cavity on the diffractive quality factor and effective cavity length are analyzed. The proposed multisection RF cavity enhances the tunable bandwidth of gyrotron to ~1.85 GHz through a magnetic tuning scheme. Besides, the effect of temperature and the corresponding deformation in the RF cavity is also studied. The tunable bandwidth of the gyrotron is further enhanced from ~1.85 to ~2.32 GHz by varying the coolant temperature, i.e., the tuneable bandwidth is increased by ~25% using a thermal tuning scheme. [ABSTRACT FROM AUTHOR]

Gyrotron, as a most likely practical high-power terahertz (THz) radiation source, has been widely applied to THz dynamic nuclear polarization-enhanced nuclear magnetic resonance (DNP-NMR) spectroscopy. In this article, an iris cavity with high-quality factor is theoretically designed for a frequency-tunable THz gyrotron, which could be tuned at three frequency regimes: 140, 250, and 263 GHz, respectively. Based on the self-developed nonlinear code, the beam wave interactions in the designed cavity are studied in detail when the corresponding high-order axial modes (HOAMs) are TE−6.1.q, TE0.4.q', and TE8.2.q. By tuning the applied magnetic field under the condition that the beam voltage U0 is 20 kV and beam current I0 is 0.10 A, the output power and frequency tuning ranges could achieve 0.75 kW and 1.15 GHz, 0.63 kW and 3.10 GHz, and 0.59 kW and 2.54 GHz. Meanwhile the calculation results are compared with the 3-D particle software CST, which have confirmed that the frequency and power tuning ranges of TE−6.1.q, TE0.4.q', and TE8.2.q'' could reach 0.46 kW and 1.07 GHz, 0.37 kW and 2.24 GHz, and 0.34 kW and 1.96 GHz. These results could be beneficial for the development of frequency-tunable gyrotron toward some up-and-coming novel THz applications. [ABSTRACT FROM AUTHOR]

In this paper, the evolution process of microstructures of fine-grained marble and coarse-grained marble under cyclic dynamic impact is studied. The split Hopkins pressure bars (SHPB) are used to apply multiple impacts on rock samples with a constant dynamic stress. And the microstructural changes caused by each impact were detected by a nuclear magnetic resonance (NMR) system. Porosity, transverse relaxation time (T2) spectral distribution, pore size distribution and magnetic resonance imaging under different dynamic impact cycles were obtained, and the evolution of the T2 cutoff value (T2c) of the rock was obtained by combining the centrifugal technique to calculate the permeability. The pores were classified into two categories according to the pore size and the fluidity of the fluid in the pores to study the effect of impact on the pore connectivity. According to the results of X-ray fluorescence (XRF) and X-ray diffractometry (XRD), it is found that the two marbles are the same in mineral composition but different in composition ratios. Due to the difference in particle size of marble and the difference in the number of pores, the magnitudes of microstructure changes of the two marbles are different, but they have a consistent trend: under the cyclic dynamic impact, the porosity of the two marbles gradually decreases, the pore size continues to decrease, the marble framework is compacted, the pore structure is gradually closed, and the permeability is weakened. The weakening of rock permeability is mainly caused by the overall decrease in pore size and loss of pore connectivity.

The pore structure of rock has a great influence on its physical and mechanical properties. Factors such as chemical corrosion and temperature changes affect the pore structure evolution. In this paper, the pore structure of sandstone was investigated under rapid freeze-thaw (F-T) cycles and chemical corrosion. A nuclear magnetic resonance (NMR) testing system is used to study the pore structure of tight sandstone samples immersed in different chemical solutions after 10, 20, and 30 F-T cycles. Permeability is determined by using empirical method. Results found that permeability is strongly affected by the erosion of NaOH and NaCl solutions. The pores in the rock were divided into three categories based on the pore size, i.e., minipores, mesopores, and macropores. The results showed that the amount of mini-pores and mesopores both decreased with an increase in the number of F-T cycles while the amount of macropores increased for groups of NaOH, NaCl, and pure water. No conclusive trend can be found in the H2SO4 group. Fractal analysis of the pore structure revealed that no conclusive trend was observed for fractal dimension of mini-pores D1. Fractal dimension of mesopores D2 ranged from 2.79 to 2.93, indicating a medium complexity pore structure of the mesopores. Fractal dimension of macropores D3 was over 2.9, implying that the pore structure of the macropores is the most complex. The fractal dimension of the T2 spectrum DNMR ranged from 2.55 to 2.77. Correlations between the fractal dimensions and porosity are also presented. Results showed that D2 and D3 can be good indicators for the pore size volume of sandstone samples immersed in H2SO4, NaOH and NaCl solutions, while DNMR is a good indicator for the pore size volume of sandstone samples immersed in NaOH solution and pure water.

The conveying distance during the backfill operation has become extensively large with the advancement of mining work. It requires the immediate attention of academic and industrial communities. Adding air entraining agent (AEA) can improve the rheological properties of the filling slurry and facilitat the filling slurry transfer to the long-distance underground stope. The AEA can generate a large number of tiny bubbles, which acted as floating balls and reduced the friction between the particles. In addition, AEA acted as a dispersing and wetting agent. Herein, we have obtained filling material from the Sanning mine (Hubei, China) and utilized sodium abietate (SA) and triterpenoid saponins (SJ), as air entraining agents, to improve the fluidity of filling slurry. The influence of AEA content on mechanical properties, structure and morphology has been analyzed by uniaxial compressive strength (UCS) testing, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results reveal that the addition of AEA increased the fluidity of filling slurry. Moreover, UCS of the AEA-free cemented paste backfill (CPB) sample, cured for 28 days, was found to be 2.23 MPa. However, the addition of 0.2% AEA (SA and SJ) increased the UCS to 2.31 MPa and 2.35 MPa, respectively. However, when SA and SJ amount was increased to 0.6%, UCS decreased to 2.19 MPa and 2.13 MPa, respectively. Hence, UCS of the CPB initially increased with the addition of AEA, followed by a gradual decrease, which can be ascribed to the pore structure inside CPB. One should note that the presence of AEA increased the number of small pores inside the CPB. The SEM results shows that pore structure of CPB can be optimized by adding an optimal proper amount of AEA.

Surface and underground nuclear magnetic resonance (UNMR) method has the advantage of direct and quantitative detection of groundwater and has been widely used in water resource survey and advance detection of water sources causing disaster in underground space. However, the UNMR signal is extremely weak in tunnels or mines. The signal-to-noise ratio (SNR) of received data at one single record is even less than -20 dB because of the strong environmental noise. A nearby reference noise cancellation (NRNC) method is proposed in this study to improve SNR. The method calculates the transfer function between the reference coil and the detection coil by using the second half of the received data to determine the noise estimation in the first half of the detection coil. The non-linear fitting method is used to estimate and remove the UNMR signal in the noise estimation and avoid the loss of the UNMR signal in the detection coil. We compare the nearby reference coil layouts of coaxial, non-separation tri-axial, and separation tri-axial types, as well as the NRNC results of the number and distance of different reference coils, through a large number of experiments. The non-separation tri-axial reference coil is optimal. The experimental results show that the SNR can be increased significantly by 18.1 dB, and the uncertainty in UNMR signal parameter estimation is evidently decreased. We prove that the NRNC algorithm is superior to the existing remote reference noise cancellation and power frequency modeling algorithms, and discuss that the improvement in SNR will be beneficial to improve the accuracy of inversion results.

Consider a spectrally sparse signal x that consists of r complex sinusoids with or without damping. We study the robust recovery problem for the spectrally sparse signal under the fully observed setting, which is about recovering x and a sparse corruption vector s from their sum z = x + s. In this paper, we exploit the low-rank property of the Hankel matrix formed by x , and formulate the problem as the robust recovery of a corrupted low-rank Hankel matrix. We develop a highly efficient nonconvex algorithm, coined accelerated structured alternating projections (ASAP). The high computational efficiency and low space complexity of ASAP are achieved by fast computations involving structured matrices, and a subspace projection method for accelerated low-rank approximation. Theoretical recovery guarantee with a linear convergence rate has been established for ASAP, under some mild assumptions on x and s. Empirical performance comparisons on both synthetic and real-world data confirm the advantages of ASAP, in terms of computational efficiency and robustness aspects. [ABSTRACT FROM AUTHOR]

Pure shift techniques, as one of the rapidly developing frontiers in nuclear magnetic resonance (NMR) fields, can significantly enhance the resolution of NMR spectrum with a removal of splittings induced by scalar couplings. However, periodic artifacts due to residual scalar couplings during acquisition arise on all direct pure shift spectra, causing severe problems in analysis of complicated samples. Herein, we construct a signal model for the pure shift data and discuss the mechanism of periodic artifacts. Then, based on constraints on the low-rank property of pure shift NMR data, a subsequent artifact-suppression method is proposed to reconstruct a clean pure shift spectrum. With the proposed method, clean $^{\mathbf {1}}\text{H}$ pure shift spectrum can be obtained from only one experiment, greatly accelerating the experiment time while remaining the accuracy of the quantitative measurement. Experiments on a synthesis NMR signal, a complex sample of quinine with pseudo 2-D acquisition, and a medicine sample of azithromycin with 1-D acquisition are carried out to evaluate the feasibility and universality of the proposed method for different experimental techniques. Both the theoretical analysis and experimental results demonstrate the effectiveness of the proposed method for periodic artifacts suppression on complex samples and its potential for practical applications. [ABSTRACT FROM AUTHOR]

In tunnel construction, to prevent the occurrence of water inrush, the geological conditions of faults and underground rivers must be determined in advance. As a direct detection method of groundwater, magnetic resonance sounding (MRS) has been applied for the advanced detection of water-related hazards in tunnels and mines recently. However, the results of conventional 1-D MRS cannot correctly reflect the spatial distribution characteristics of complicated water-bearing structures. In this article, we propose a measurement scheme using a rotating coil with separated transmitter and receiver loop configuration (SEP) for the 2-D imaging of water-bearing structures, such as faults and conduits. In this scheme, the receiver coil rotates several times, while the transmitter coil, which is separated from the receiver coil by a certain distance, remains stationary. Moreover, all the observed data participate in the inversion to achieve the 2-D magnetic resonance tomography (MRT). Numerical simulations of water-bearing faults are performed, and we compare and analyze the 2-D sensitivity and inversion results of two measurement schemes for a rotating coil, i.e., an overlapping transmitter and receiver loop configuration (OVE) and SEP. The results showed that the imaging results of the SEP are better than those of the OVE because the OVE imaging has a symmetric artifact. Finally, we discuss the influence of the transceiver distance, the resistivity, and the environmental noise on the imaging results. Moreover, the imaging results of the water-bearing conduit at different locations were obtained to validate the effectiveness of the SEP rotating coil measurement scheme. [ABSTRACT FROM AUTHOR]