Magnetic Resonance Apparatus Research Articles

Nonequilibrium fluctuations of a quantum heat engine

The thermodynamic properties of quantum heat engines are stochastic owing to the presence of thermal and quantum fluctuations. We here experimentally investigate the efficiency and nonequilibrium entropy production statistics of a spin-1/2 quantum Otto cycle in a nuclear magnetic resonance setup. We first study the correlations between work and heat within a cycle by extracting their joint distribution for different driving times. We show that near perfect correlation, corresponding to the tight-coupling condition between work and heat, can be achieved. In this limit, the reconstructed efficiency distribution is peaked at the deterministic thermodynamic efficiency, and fluctuations are strongly suppressed. We further successfully test the second law in the form of a joint fluctuation relation for work and heat in the quantum cycle. Our results characterize the statistical features of a small-scale thermal machine in the quantum domain, and provide means to control them.

Freezing‐Thawing Hysteretic Behavior of Soils

AbstractThe soil freezing characteristic curve (SFCC) plays a crucial role in investigating the soil freezing‐thawing process. Due to the challenges associated with measuring the SFCC, there is a shortage of high‐quality or rigorous test results with sufficient metadata to be effectively used for applications. Current researchers typically conduct freezing tests to measure the SFCC and assume a singular SFCC when studying the freezing‐thawing process of soils, although limited studies indicated that there is a hysteresis during the freezing and thawing process. In this paper, a series of freezing‐thawing tests were performed to assess the SFCC, utilizing a precise nuclear magnetic resonance apparatus. The test results reveal a hysteresis between the SFCC obtained from the freezing process and that from the thawing process. Through analyzing the test results, the hysteresis mechanism of the SFCC is attributed to supercooling. Supercooling inhibits initial pore ice formation during freezing, causing a drastic liquid water‐ice phase change once supercooling ends. Despite being considered closely related, the hysteresis of the SFCC differs from the soil water characteristic curve (SWCC), and the models used to simulate the hysteresis of SWCC cannot directly be used. To address the impact of supercooling on soil freezing‐thawing hysteresis, a novel theoretical model is proposed. Comparisons between the measured and predicted results affirm the validity of the proposed model.

Proton transverse relaxation times depending on the unsaturated fatty acids: a magnetic resonance relaxometric study on beef fat samples

ABSTRACT The unsaturated fatty acid content of beef meat is an important property that affects the health and sense of taste of the consumer and determines price. Fresh beef fat samples were measured by a bilateral low-field time-domain proton magnetic resonance (MR) apparatus. The proton transverse relaxation time (T2) for 18 fat samples were measured at 40.0°C using the Carr-Purcell-Meiboom-Gill method. The results showed that T2 increased linearly with unsaturated fatty acid content. By using the linear dependence of T2 on the unsaturated fatty acid content, we successfully estimated the contents of oleic acid, total monounsaturated fatty acid, and total unsaturated fatty acid with root-mean-square errors of 2.5, 2.8, and 3.2 wt%, respectively. The proposed T2-relaxometry-based method could be performed using a portable unilateral MR surface scanner, which would enable in-vivo nondestructive noninvasive measurements of live cattle for the optimization of the feeding and fattening timing from calf to adult and for the best choice of the shipment timing in terms of the maximization of unsaturated fatty acid content of beef meat.

Preparation of ultracold ions in strong magnetic field and application to gas-phase NMR spectroscopy II

This paper presents a gas-phase nuclear magnetic resonance (NMR) apparatus, which may enable a tandem combination with an ion cyclotron resonance mass spectrometer. The NMR technique is widely used for analyzing the physical and chemical properties of materials; however, it is mostly limited to materials in condensed phases. Here, we construct a gas-phase NMR apparatus to extend this technique to gas-phase molecular ions. We outline the principle of NMR detection based on a Stern-Gerlach-type experiment and describe the experimental procedures and results for the preparation and manipulation of ultracold ions, which are fundamental for the proposed NMR detection. The development of the gas-phase NMR probe and radio-frequency excitation system and the features of the apparatus are presented. We also discuss the feasibility of combining this apparatus with an ion cyclotron resonance cell for realizing an NMR apparatus for mass-selected molecular ions briefly.

Real-Time Monitoring of Pore-Fracture Structure Evolution during Coal Creep Based on NMR

Understanding the structural change of coals at micro- and mesoscales during the creep process is essential for exploring the time-dependent properties of deep coal and the long-term safe and effective operation of deep underground engineering. The conventional triaxial compression and creep tests on coal are carried out using a nuclear magnetic resonance (NMR) apparatus with a complete mechanical loading system at different confining pressures. The variations of parameters such as peak areas of various pore distributions, pore percentage, and porosity increment are quantitatively analyzed by real-time monitoring of T2 spectra during loading. Combined with nuclear magnetic resonance imaging (NMRI), accurate characterization and visualization of microscopic pore structures in coal are realized. The experimental results show that the adsorption pore proportion in the pore structure of the deep coal sample from Pingdingshan, Henan Province, is more than 80%. The changes in seepage pores and microfractures are most obvious in the triaxial compression and creep test. The creep deformation leads to the development of pore structure, and the creep porosity growth rate M increases gradually with increasing stress levels. M can accurately describe the rapid development of the pore structure and the damage accumulation due to time effects during creep. During creep, the most obvious changes in pore structure are the first and last levels of creep. The fractal dimension shows an “inverted V” trend during creep and is more sensitive to the inhibition of pore-fracture structure evolution due to increasing confining pressure. The creep strain increment and porosity increment during graded creep appear to be a similar behavior, indicating that the change of pore structure in the creep process based on the NMR system test can reveal the creep damage mechanism and indirectly characterize the deformation behavior of coal creep.

A nuclear quadrupolar spin quantum heat engine

We give an implementable scheme which uses intrinsic quadrupolar nuclear spin interactions to harvest efficient energy from a quantum Otto cycle. We employ realistic parameter regimes for the 23Na nucleus in sodium nitrate. The processes of the cycle are accomplished by orienting the sample with respect to the static magnetic field. The effects of stroke duration on the work output and efficiency are revealed in detail. Finite-time adiabatic transformations leading to quantum friction are found to substantially reduce cycle outputs which are stimulated from the non-secular parts of the quadrupolar interaction. An estimation for the power output at maximum efficiency is also given. We show that with the precise control and manipulation of the intrinsic nuclear spin interactions, for example in an advanced nuclear magnetic resonance setup, makes our scheme implement as a powerful quantum Otto cycle.

Predictive Value of Delta-Radiomics Texture Features in 0.35 Tesla Magnetic Resonance Setup Images Acquired During Stereotactic Ablative Radiotherapy of Pancreatic Cancer.

PurposeThe purpose of this work is to explore delta-radiomics texture features for predicting response using setup images of pancreatic cancer patients treated with magnetic resonance image guided (MRI-guided) stereotactic ablative radiotherapy (SBRT).MethodsThe total biological effective dose (BED) was calculated for 30 patients treated with MRI-guided SBRT that delivered physical doses of 30–60 Gy in three to five fractions. Texture features were then binned into groups based upon BED per fraction by dividing BED by the number of fractions. Delta-radiomics texture features were calculated after delivery of 20 Gy BED (BED20 features) and 40 Gy BED (BED40 features). A random forest (RF) model was constructed using BED20 and then BED40 features to predict binary outcome. During model training, the Gini Index, a measure of a variable’s importance for accurate prediction, was calculated for all features, and the two features that ranked the highest were selected for internal validation. The two features selected from each bin were used in a bootstrapped logistic regression model to predict response and performance quantified using the area under the receiver operating characteristic curve (AUC). This process was an internal validation analysis.ResultsAfter RF model training, the Gini Index was highest for gray-level co-occurrence matrix-based (GLCM) sum average, and neighborhood gray tone difference matrix-based (NGTDM) busyness for BED20 features and gray-level size zone matrix-based (GLSZM) large zones low gray-level emphasis and gray-level run length matrix-based (GLRLM) run percentage was selected from the BED40-based features. The mean AUC obtained using the two BED20 features was AUC = 0.845 with the 2.5 percentile and 97.5 percentile values ranging from 0.794 to 0.856. Internal validation of the BED40 delta-radiomics features resulted in a mean AUC = 0.567 with a 2.5 and 97.5 percentile range of 0.502–0.675.ConclusionEarly changes in treatment quantified with the BED20 delta-radiomics texture features in low field images acquired during MRI-guided SBRT demonstrated better performance in internal validation than features calculated later in treatment. Further analysis of delta-radiomics texture analysis in low field MRI is warranted.

Microscopic mechanism analysis of calcareous sand in electrolysis desaturation using 1H L-F NMR

Electrolysis desaturation is a novel method to improve the liquefaction resistance of liquefiable foundations. The microscopic mechanism of the horizontal-layered electrolysis desaturation of calcareous sand specimens was revealed using a low-field nuclear magnetic resonance (1H L-F NMR) apparatus. The expansion and recovery of sand pores was detected, and variation pattern of saturation distribution was explored, as well as the generation and migration of gas bubbles. The test results show that the electrolysis mainly discharged free water from the specimen, and the content of bound water or mechanical bound water kept basically unchanged. The rapid generation of the bubbles could lead to the expansion of the sand pores. Within 3 h after stopping electrolysis, the macropores in the calcareous sand essentially returned to the initial state, and the expansion of micropores and mesopores also remained basically stable. The construction method of prolonged low-current electrolysis or short-time multiple electrolysis could be applied for on-site desaturated foundation treatment. The shape and size of the bubbles produced by electrolysis were related to the calcareous sand pores. The migration of gas after stopping electrolysis was mainly in the vertically upward direction, resulting in the fusion of bubbles and the formation of larger bubbles.

Portable single-sided NMR measurements at variable temperatures: Implementation of a thermo-controlled device and application to the heating of bread dough.

A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample.

Experimental Validation of Fully Quantum Fluctuation Theorems Using Dynamic Bayesian Networks.

Fluctuation theorems are fundamental extensions of the second law of thermodynamics for small systems. Their general validity arbitrarily far from equilibrium makes them invaluable in nonequilibrium physics. So far, experimental studies of quantum fluctuation relations do not account for quantum correlations and quantum coherence, two essential quantum properties. We here apply a novel dynamic Bayesian network approach to experimentally test detailed and integral fully quantum fluctuation theorems for heat exchange between two quantum-correlated thermal spins-1/2 in a nuclear magnetic resonance setup. We concretely verify individual integral fluctuation relations for quantum correlations and quantum coherence, as well as for the sum of all quantum contributions. We further investigate the thermodynamic cost of creating correlations and coherence.

Quantification and division of unfrozen water content during the freezing process and the influence of soil properties by low-field nuclear magnetic resonance

In this study, a low-field nuclear magnetic resonance (NMR) apparatus with the ability to adjust sample temperatures was used to measure the unfrozen water content of frozen soils sampled from the Qinghai-Tibet Plateau. Based on low-field NMR theory, two cutoff values were proposed to quantitatively identify three types of unfrozen water (bulk, capillary, and bound water) in the frozen soils. The influences of soil properties (the clay content, particle size distribution, and clay mineral content) on these three different types of unfrozen water during the soil freezing process were analyzed. The results showed that the soil-freezing characteristic curve of unfrozen water could be divided into three stages, namely, the unfrozen, the rapid-drop, and the residual stages. In the rapid-drop stage, the unfrozen bound water content increases gradually with the increasing clay or clay mineral content, and at a certain temperature, the unfrozen capillary water content increases as the sand and silt content increases. A published power function model is then used to fit the measured data in this study. We found that the single parameter related to soil properties in this model could not sufficiently reflect the influence of clay mineral content or clay content on unfrozen water content.

Easy Access to Energy Fluctuations in Nonequilibrium Quantum Many-Body Systems.

We combine theoretical and experimental efforts to propose a method for studying energy fluctuations, in particular, to obtain the related bistochastic matrix of transition probabilities by means of simple measurements at the end of a protocol that drives a many-body quantum system out of equilibrium. This scheme is integrated with numerical optimizations in order to ensure a proper analysis of the experimental data, leading to physical probabilities. The method is experimentally evaluated employing a two interacting spin-1/2 system in a nuclear magnetic resonance setup. We show how to recover the transition probabilities using only local measures, which enables an experimental verification of the detailed fluctuation theorem in a many-body system driven out of equilibrium.

Quantum Irreversibility in a Misaligned Spin System

A single spin that is misaligned with respect to the static external magnetic field is investigated as a toy model to clarify the nature of irreversibility in terms of inner friction and irreversible work. The coherence generation and the effects of unwanted transitions are analyzed in detail. The behavior of inner friction and irreversible work as a function of protocol time are analyzed for a finite-time unitary transformation. The coherence generation is shown to be the common sign for the inner friction and irreversible work. The excess energy sourced by the unwanted transitions for a quasistatic transformation is found to be the only sign for irreversible work. The angle The angle dependencies of the inner friction and irreversible work are also analyzed explicitly. The selected model and the considered realistic parameters are available to be implemented for the finite-time operations on the nuclear magnetic resonance setups.

Casimir-Polder shift of ground-state hyperfine Zeeman sublevels of hydrogen isotopes in a micron-sized metallic cavity at finite temperature

The frequencies of transitions between hyperfine levels of ground-state atoms can be measured with exquisite precision using magnetic-resonance techniques. This makes hyperfine transitions ideal probes of QED effects originating from the interaction of atoms with the quantized electromagnetic field. One of the most remarkable effects predicted by QED is the Casimir-Polder shift experienced by the energy levels of atoms placed near one or more dielectric objects. Here we compute the Casimir-Polder shift and the width of hyperfine transitions between ground-state Zeeman sub-levels of an hydrogen atom placed in a micron-sized metallic cavity, over a range of temperatures extending from cryogenic temperatures to room temperature. Results are presented also for deuterium and tritium. We predict shifts of the hyperfine transitions frequencies of a few tens of Hz that might be measurable with present-day magnetic resonance apparatus.

Monitoring of Motor Nerve Function Rehabilitation in Patients with Upper Extremity Hemiplegia Based on Functional Magnetic Resonance Imaging

Through functional magnetic resonance imaging (fMRI) technology, it is planned to use complex brain network technology to track brain functional imaging tracking treatment of stroke hemiplegia with scalp acupuncture. Functional magnetic resonance imaging (fMRI) can continuously monitor the rehabilitation process of motor nerve function in patients with stroke and upper limb hemiplegia, and explore the mechanism of brain plasticity changes at different levels of neural function cortex, motor function neural circuit, and behavior level. First, the fMRI test uses a block design, and the subjects complete the movement of the thumb and index finger. After completing the dysfunction assessment, fMRI data collection was performed on the patient before the CIMT treatment using a magnetic resonance apparatus, and a second fMRI data collection was performed 2 weeks after the CIMT treatment; only one fMRI data collection was performed on the volunteers. The functional magnetic resonance data was processed using the AFNI software package, and the functional scores of subjects were calculated using SPSS software. Second, studying the remodeling of residual brain tissue and functional compensation pathways can help to further clarify the recovery mechanism of motor function after stroke hemiplegia. Finally, compulsory exercise therapy can effectively improve upper limb motor dysfunction in stroke patients. The forced use of upper extremities during treatment induces the reorganization and compensation of cerebral cortical functional areas. This change in brain functional areas is consistent with the increase of upper extremity movement and improvement of motor function, fMRI can provide neuronal reorganization after exercise therapy evidence with compensation.

Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla.

The overall goal of this article is to demonstrate a state-of-the-art ultrahigh field (UHF) magnetic resonance (MR) protocol of the brain at 7.0 Tesla in multiple sclerosis (MS) patients. MS is a chronic inflammatory, demyelinating, neurodegenerative disease that is characterized by white and gray matter lesions. Detection of spatially and temporally disseminated T2-hyperintense lesions by the use of MRI at 1.5 T and 3 T represents a crucial diagnostic tool in clinical practice to establish accurate diagnosis of MS based on the current version of the 2017 McDonald criteria. However, the differentiation of MS lesions from brain white matter lesions of other origins can sometimes be challenging due to their resembling morphology at lower magnetic field strengths (typically 3 T). Ultrahigh field MR (UHF-MR) benefits from increased signal-to-noise ratio and enhanced spatial resolution, both key to superior imaging for more accurate and definitive diagnoses of subtle lesions. Hence, MRI at 7.0 T has shown encouraging results to overcome the challenges of MS differential diagnosis by providing MS-specific neuroimaging markers (e.g., central vein sign, hypointense rim structures and differentiation of MS grey matter lesions). These markers and others can be identified by other MR contrasts other than T1 and T2 (T2*, phase, diffusion) and substantially improve the differentiation of MS lesions from those occurring in other neuroinflammatory conditions such as neuromyelitis optica and Susac syndrome. In this article, we describe our current technical approach to study cerebral white and grey matter lesions in MS patients at 7.0 T using different MR acquisition methods. The up-to-date protocol includes the preparation of the MR setup including the radio-frequency coils customized for UHF-MR, standardized screening, safety and interview procedures with MS patients, patient positioning in the MR scanner and acquisition of dedicated brain scans tailored for examining MS.

Magnetic Moments of Short-Lived Nuclei with Part-per-Million Accuracy: Toward Novel Applications of β -Detected NMR in Physics, Chemistry, and Biology

We determine for the first time the magnetic dipole moment of a short-lived nucleus with part-per-million (ppm) accuracy. To achieve this two orders of magnitude improvement over previous studies, we implement a number of innovations into our $\beta$-detected Nuclear Magnetic Resonance ($\beta$-NMR) setup at ISOLDE/CERN. Using liquid samples as hosts we obtain narrow, sub-kHz linewidth, resonances, while a simultaneous in-situ $^1$H NMR measurement allows us to calibrate and stabilize the magnetic field to ppm precision, thus eliminating the need for additional $\beta$-NMR reference measurements. Furthermore, we use ab initio calculations of NMR shielding constants to improve the accuracy of the reference magnetic moment, thus removing a large systematic error. We demonstrate the potential of this combined approach with the 1.1 s half-life radioactive nucleus $^{26}$Na, which is relevant for biochemical studies. Our technique can be readily extended to other isotopic chains, providing accurate magnetic moments for many short-lived nuclei. Furthermore, we discuss how our approach can open the path towards a wide range of applications of the ultra-sensitive $\beta$-NMR in physics, chemistry, and biology.

Molecular beam magnetic resonance coupled with a cryogenically cooled, pulsed laser vaporization source and time-of-flight mass spectrometry

A molecular beam magnetic resonance apparatus designed for the study of polyatomic molecules and small metal clusters is described. In contrast to atoms, vibrational and rotational excitation in clusters and molecules invoke spin relaxation upon a change of magnetic flux density. To prevent this, a pulsed laser vaporization source with a cryogenically cooled nozzle is utilized to minimize thermal excitation and a magnet setup has been designed to diminish magnetic field fluctuations. The apparatus is evaluated by Stern–Gerlach and resonance experiments on an atomic europium beam with the identical pulsed laser vaporization source.

Cl- and Na+ ions binding in slag and fly ash cement paste during early hydration as studied by 1H, 35Cl and 23Na NMR

Lacking effective and in particular direct methods, the study on Cl- and Na+ ion binding during hydration has rarely been reported. In this study, a specially developed Nuclear Magnetic Resonance setup was employed to study the Cl- and Na+ ion binding of cement pastes during hydration. Influence factors, such as slag and fly ash replacement, on the 1H, 35Cl and 23Na relaxation of the cement paste made with 1 mol/L NaCl solutions were investigated. It was found that the increase of slag in the cement gives rise to bigger pores during hydration, and the fly ash resulted in less water being consumed. The Cl- signals would first be stable then gradually decrease as a function of time. The slag in cement has minor impacts on the Cl- ions binding, and the fly ash replacement in the cement would result in less Cl- ions binding during the hydration. Results also suggest that the slag could result in later Na+ binding, and the fly ash in the cement will significantly reduce the Na+ binding. Besides, the Cl- ions will bind earlier compared to the Na+ ions, which is probably related to the characteristics of the hydrates. The normalized 35Cl and 23Na signal intensity, in general, decrease with water consumption reflecting the hydration. Furthermore, the early formed hydrates would consume relatively less water but bind more Cl- and Na- ions.

Quantum Carnot cycle with inner friction

A single driven spin is investigated as the working substance of a six-stroke irreversible quantum Carnot cycle. The role of inner friction associated with the finite-time adiabatic transformations on the cycle efficiency and the harvested work are investigated in detail. The inner friction is found to significantly reduce the work output and the cycle efficiency which can make the engine incapable to produce positive work for the too fast adiabatic transformations. The ideal Carnot efficiency is found to be reached only for the quasistatic transformations. A deviation of the cycle efficiency from the classical Carnot efficiency has been given by an efficiency lag which is directly related to the total entropy production due to the inner friction. The released heat in the relaxation processes of the cycle is associated with the entropy production and the inner friction. The extension of the results for a scale-invariant quantum working substance and the possible experimental implementation of the irreversible quantum Carnot cycle in a liquid-state nuclear magnetic resonance setup are also discussed.