Gyromagnetic Ratio Research Articles

Direct observation of the active sites in methane dehydroaromatization by NMR

Direct observation of the active sites in methane dehydroaromatization by NMR

Revisiting higher-spin gyromagnetic couplings

We analyze Bosonic, Heterotic, and Type II string theories compactified on a generic torus having constant moduli. By computing the hamiltonian giving the interaction between massive string excitations and U(1) gauge fields arising from the graviton and Kalb-Ramond field upon compactification, we derive a general formula for such couplings that turns out to be universal in all these theories. We also confirm our result by explicitly evaluating the relevant string three-point amplitudes. From this expression, we determine the gyromagnetic ratio g of massive string states coupled to both gauge-fields. For a generic mixed symmetry state, there is one gyromagnetic coupling associated with each row of the corresponding Young Tableau diagram. For all the states having zero Kaluza Klein or Winding charges, the value of g turns out to be 1. We also explicitly consider totally symmetric and mixed symmetry states (having two rows in the Young diagram) associated with the first Regge-trajectory and obtain their corresponding g value.

A 16-Channel 13C Array Coil for Magnetic Resonance Spectroscopy of the Breast at 7T.

Considering the reported elevation of ω-6/ω-3 fatty acid ratios in breast neoplasms, one particularly important application of 13C MRS could be in more fully understanding the breast lipidome's relationship to breast cancer incidence. However, the low natural abundance and gyromagnetic ratio of the 13C isotope lead to detection sensitivity challenges. Previous 13C MRS studies have relied on the use of small surface coils with limited field-of-view and shallow penetration depths to achieve adequate signal-to-noise ratio (SNR), and the use of receive array coils is still mostly unexplored. This work presents a unilateral breast 16-channel 13C array coil and interfacing hardware designed to retain the surface sensitivity of a single small loop coil while improving penetration depth and extending the field-of-view over the entire breast at 7T. The coil was characterized through bench measurements and phantom 13C spectroscopy experiments. Bench measurements showed receive coil matching better than -17 dB and average preamplifier decoupling of 16.2 dB with no evident peak splitting. Phantom MRS studies show better than a three-fold increase in average SNR over the entirety of the breast region compared to volume coil reception alone as well as an ability for individual array elements to be used for coarse metabolite localization without the use of single-voxel or spectroscopic imaging methods. Our current study has shown the benefits of the array. Future in vivo lipidomics studies can be pursued. Development of the 16-channel breast array coil opens possibilities of in vivo lipidomics studies to elucidate the link between breast cancer incidence and lipid metabolics.

G-Factor and static quadrupole moment of $$^{135}$$Pr, $$^{105}$$Pd, and $$^{187}$$Au in wobbling motion

The $g$-factor and static quadrupole moment of the nuclides $^{135}$Pr, $^{105}$Pd, and $^{187}$Au in the wobbling motion are investigated in the particle-rotor model as functions of the total spin $I$. The $g$-factor of $^{105}\mathrm{Pd}$ increases with increasing $I$, due to the negative gyromagnetic ratio of a neutron valence-neutron. This behavior is in contrast to the decreasing $g$-factor of the other two nuclides, $^{135}$Pr and $^{187}$Au, which feature a valence-proton. The static quadrupole moment $Q$ depends on all three expectation values of the total angular momentum. It is smaller in the yrast band than in the wobbling band for the transverse wobblers $^{135}$Pr and $^{105}$Pd, while larger for the longitudinal wobbler $^{187}$Au.

Atomic spin-exchange collisions in magnetic fields

Spin-exchange collisions among alkali-metal atoms affect the coherence time and gyromagnetic ratio of atoms by redistributing the ground-state population. We theoretically study the interactions between magnetic fields and atoms in the presence of spin-exchange collisions. Using the modified Bloch equations derived from the density-matrix equation in a low spin-polarization limit, we obtain explicit formulas describing the role of spin-exchange collisions in the interactions between atoms and magnetic fields, especially the nonresonant radio-frequency fields, which are widely used to manipulate atoms. The results derived from these equations agree well with density-matrix simulations and previous experimental results, and provide a simple and precise way to quantitatively analyze the effect of spin-exchange collisions on atoms. Our paper is helpful to gain physical insight into the spin-exchange collisions and optimize the performance of atom-based precision measurement instruments.

Describing angular momentum conventions in circularly polarized optically pumped NMR in GaAs and CdTe

The physical phenomena governing hyperpolarization through optical pumping of conduction electrons continue to be explored in multiple semiconductor systems. One early finding has been the asymmetry between the optically pumped nuclear magnetic resonance (OPNMR) signals when generated by different circular polarizations (i.e., light helicities). Because these resonances are asymmetric, the midpoint between the signals prepared with each of the two circular polarizations is either a positive or negative value, termed an “offset” that is representative of an optical Overhauser enhancement. Both negative offsets (in GaAs) and positive offsets (in CdTe) have been observed. The origins of these offsets in semiconductors are believed to arise from thermalized electrons; however, to the best of our knowledge, no study has systematically tested this hypothesis. To that end, we have adopted two configurations for OPNMR experiments—one in which the Poynting vector of the laser light and magnetic field are parallel, and one in which they are antiparallel, while other experimental conditions are kept the same. We find that the OPNMR signal response to a fixed helicity of light depends on the experimental configuration, and this configuration needs to be accounted for in order to properly describe the OPNMR results. Further, studying the offsets as a function of field strength shows that the optical Overhauser enhancement (the offset) increases in magnitude with field strength. Finally, by describing all angular momentum and phasing conventions unambiguously, we are able to determine that the absorptively-phased appearance of 113Cd (and 125Te) OPNMR in CdTe is a consequence of the sign of the nuclear gyromagnetic ratios for these isotopes.

Subspace controllability of multi-partite spin networks

Abstract In a network of spin 1 2 particles, controlled through an external electro-magnetic field, the gyromagnetic ratio of each spin is a parameter that characterizes the interaction of the spin with the external control field. Multipartite networks are such that the spins are divided into subsets according to their gyromagnetic ratio and spins in one set interact in the same way with all spins in another set. Due to the presence of symmetries in these types of systems, the underlying Hilbert state space splits into invariant subspaces for the dynamics. Subspace controllability is verified if every unitary evolution can be generated by the dynamics on these subspaces. We give an exact characterization, in terms of graph theoretic conditions, of subspace controllability for multipartite quantum spin networks. This extends and unifies previous results.

Image of the Electron Suggested by Nonlinear Electrodynamics Coupled to Gravity

We present a systematic review of the basic features that were adopted for different electron models and show, in a brief overview, that, for electromagnetic spinning solitons in nonlinear electrodynamics minimally coupled to gravity (NED-GR), all of these features follow directly from NED-GR dynamical equations as model-independent generic features. Regular spherically symmetric solutions of NED-GR equations that describe electrically charged objects have obligatory de Sitter center due to the algebraic structure of stress–energy tensors for electromagnetic fields. By the Gürses-Gürsey formalism, which includes the Newman–Janis algorithm, they are transformed to axially symmetric solutions that describe regular spinning objects asymptotically Kerr–Newman for a distant observer, with the gyromagnetic ratio g=2. Their masses are determined by the electromagnetic density, related to the interior de Sitter vacuum and to the breaking of spacetime symmetry from the de Sitter group. De Sitter center transforms to the de Sitter vacuum disk, which has properties of a perfect conductor and ideal diamagnetic. The ring singularity of the Kerr–Newman geometry is replaced with the superconducting current, which serves as the non-dissipative source for exterior fields and source of the intrinsic magnetic momentum for any electrically charged spinning NED-GR object. Electromagnetic spinning soliton with the electron parameters can shed some light on appearance of a minimal length scale in the annihilation reaction e+e−→γγ(γ).

Determination of Effective Magnetization and Gyromagnetic Ratio of Yttrium Iron Garnet From Multi-Mode Ferromagnetic Resonance S₂₁ Spectra

We acquire ferromagnetic resonance (FMR) spectra for an out-of-plane magnetized yttrium iron garnet sample with a vector network analyzer at microwave frequencies ranging from 4.2 to 5.2 GHz. The applied static magnetic field varies from approximately 253.6 to 260.1 kA/m. Based on an empirical model for resonant features in the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> spectrum produced by the excitation of multiple modes and instrumental effects, we predict measured values of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> -parameters. For each of many microwave frequencies, for each of multiple modes, we determine the resonant field value of the applied magnetic field, an amplitude, and an FMR linewidth. Based on the frequency-dependent resonant field values produced by excitation of the main mode, we determine the effective magnetization and the gyromagnetic ratio of the sample.

Role of Ce concentration on the structural and magnetic properties of functional magnetic oxide particles.

Functional magnetic oxide particles offer exceptional GHz frequency capabilities, which can significantly enhance the utility of communication and signal processing devices. In the present work, we have investigated the structural and magnetic properties of rational multifunctional oxide Y2.9−xCexBi0.1Fe5O12 particles – a full series with x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1 via a conventional solid-state route. The X-ray diffraction pattern validated the Ia3̄d cubic garnet phase in all samples. From Rietveld refinement, it is observed that the ceric oxide (CeO2) impurity increases with an increase of Ce concentration, evincing a partial substitution of cerium (Ce) element into the garnet structure. The magnetic oxide particles with Ce concentration x = 0.4 showed a better crystallite size, dodecahedral site occupancy and solubility of cerium in the garnet phase. The morphological visualization of random shaped grains in the micrometer range was performed using the scanning electron microscopy (SEM) technique. The static magnetic properties showed that the saturation magnetization (Ms) decreases up to 43% and coercivity increases up to 59% with the increase of Ce concentration. The dynamic investigation on these oxide particles exhibits various intriguing and novel properties. Various intrinsic material parameters such as saturation magnetization (Ms), gyromagnetic ratio (γ), Gilbert damping constant (α) and extrinsic contribution (ΔHo) to linewidth were determined from the fitting of resonance field (Hr) and field linewidth (ΔHr) data. We ascertained that the damping constant increases with the increase of Ce concentration, which can be explained in terms of two magnon scattering and local defects caused by CeO2 inhomogeneity. The proposed doped garnets can be a potential candidate for high frequency microwave applications and spin-transfer-torque devices.

High-frequency magnetotransport in La1-xSrxMnO3 (x = 0.12-0.20)

We report the magnetization, magnetic field dependence of direct current magnetoresistance (dc MR) and alternating current magnetoresistance (ac MR) in La1-xSrxMnO3 (x = 0.12, 0.18, and 0.20) in the frequency range f= 30 MHz to 3000 MHz, at room temperature. The ac MR is negative in all three compositions and shows a dramatic increase in magnitude compared to the dc MR when f = 30 MHz and in a magnetic field H = ±3 kOe. With increasing frequency of current, the sign of ac MR at 3 kOe progressively changes from negative to positive in all these samples which is initiated by appearance of two peaks at H = ±Hr. Line shape analysis of the data indicate that Hr increases linearly with f in x = 0.12 and 0.18. We attribute the two peak behavior at high frequencies to electron paramagnetic resonance in x = 0.12 and 0.18 samples. From the analysis, we obtain the gyromagnetic ratio γ/2π = 2.428 MHz/Oe and 2.690 MHz/Oe for x = 0.18 and 0.12 respectively. The smaller value of γ/2π in x = 0.18 possibly reflects short-range correlations among Mn-spins in the paramagnetic state.

Research progress of &lt;sup&gt;10&lt;/sup&gt;B concentration and distribution measurement in boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a dual tumor radiotherapy method combining boron-10 containing drugs and heavy ion therapy, which can kill cancer cells with almost no damage to normal cells, and achieve precise cell-scale treatment. However, the BNCT does not really enter into clinical application stage though it has been developed for nearly 70 years. The methods of measuring the concentration distribution of boron-10 containing drugs in vivo cannot meet the clinical needs, which is one of the core problems affecting the effect and safety of clinical application of BNCT. This article reviews the current methods of measuring the concentration distribution of boron-10 drugs, including the invasive estimation methods that have been used in clinical practice, the researching single photon emission tomography (SPECT) method, positron emission tomography (PET) method, nuclear magnetic resonance (NMR) method, etc., and analyzes the advantages and limitations of current methods. Based on the characteristics of the low gyromagnetic ratio of the boron-10 element and the extremely short magnetic resonance transverse relaxation time, the research ideas of ultra-short echo time magnetic resonance boron-10 quantitative imaging are proposed. The feasibility of quantitative measurement of boron-10 distribution in vivo based on ultrashort echo time magnetic resonance imaging is analyzed theoretically.

Fluorine (19F) MRI to Measure Renal Oxygen Tension and Blood Volume: Experimental Protocol.

Fluorinated compounds feature favorable toxicity profile and can be used as a contrast agent for magnetic resonance imaging and spectroscopy. Fluorine nucleus from fluorinated compounds exhibit well-known advantages of being a high signal nucleus with a natural abundance of its stable isotope, a convenient gyromagnetic ratio close to that of protons, and a unique spectral signature with no detectable background at clinical field strengths. Perfluorocarbon core nanoparticles (PFC NP) are a class of clinically approved emulsion agents recently applied in vivo for ligand-targeted molecular imaging. The objective of this chapter is to outline a multinuclear 1H/19F MRI protocol for functional kidney imaging in rodents for mapping of renal blood volume and oxygenation (pO2) in renal disease models.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This experimental protocol chapter is complemented by a separate chapter describing the basic concept of functional imaging using fluorine (19F) MR methods.

Selective observation of spin and charge dynamics in an organic superconductor λ−(BETS)2GaCl4 using Ga69,71 NMR measurements

For the unconventional organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ [BETS = bis(ethylenedithio) tetraselenafulvalene], the importance of both spin and charge degrees of freedom has been discussed based on the broadening of the NMR linewidth due to charge disproportionation and the occurrence of a spin-density-wave phase near the superconducting phase. NMR with the nuclear spin of $1/2$, previously used for studying organic conductors, is an effective method for revealing electronic states microscopically; however, it cannot distinguish between charge and spin anomalies. To resolve this problem, in this paper, we performed $^{69,71}\mathrm{Ga}$-NMR measurements, which enabled us to study both charge and spin dynamics using different gyromagnetic ratios and quadrupole moments between two isotopes. The spin-lattice relaxation rate is dominated by electric-field gradient fluctuations originating from molecular dynamics above 150 K and, below this temperature, it is dominated by spin fluctuations derived from the $\ensuremath{\pi}$ electrons of BETS layers. This change in the relaxation mechanism is considered to be due to the development of interactions between ${\mathrm{GaCl}}_{4}$ ions and BETS layers upon freezing of the molecular motion by cooling. Below 150 K, the contribution of spin fluctuations monotonically increases, and no increase in the charge fluctuation was observed, suggesting that the spin degree of freedom plays a major role in low-temperature physical properties. Our findings will aid theoretical studies on superconducting properties.

Characterization and correction of center-frequency effects in X-nuclear eddy current compensations on a clinical MR system.

PurposeThe aim of the study was to investigate whether incorrectly compensated eddy currents are the source of persistent X‐nuclear spectroscopy and imaging artifacts, as well as methods to correct this.MethodsPulse‐acquire spectra were collected for 1H and X‐nuclei (23Na or 31P) using the minimum TR permitted on a 3T clinical MRI system. Data were collected in 3 orientations (axial, sagittal, and coronal) with the spoiler gradient at the end of the TR applied along the slice direction for each. Modifications to system calibration files to tailor eddy current compensation for each X‐nucleus were developed and applied, and data were compared with and without these corrections for: slice‐selective MRS (for 23Na and 31P), 2D spiral trajectories (for 13C), and 3D cones trajectories (for 23Na).ResultsLine‐shape distortions characteristic of eddy currents were demonstrated for X‐nuclei, which were not seen for 1H. The severity of these correlated with the amplitude of the eddy current frequency compensation term applied by the system along the axis of the applied spoiler gradient. A proposed correction to eddy current compensation, taking account of the gyromagnetic ratio, was shown to dramatically reduce these distortions. The same correction was also shown to improve data quality of non‐Cartesian imaging (2D spiral and 3D cones trajectories).ConclusionA simple adaptation of the default compensation for eddy currents was shown to eliminate a range of artifacts detected on X‐nuclear spectroscopy and imaging.

Collective Spin Glass State in Nanoscale Particles of Ferrihydrite

Ferromagnetic resonance was used to study three types of ferrihydrite nanoparticles: nanoparticles formed as a result of the cultivation of microorganisms Klebsiella oxytoca; chemically prepared ferrihydrite nanoparticles; chemically prepared ferrihydrite nanoparticles doped with Cu. It is established from the ferromagnetic resonance data that the frequency-field dependence (in the temperature range ТP < T < T*) is described by the expression: 2πν/γ = НR + HA(T = 0)(1 – T/Т*), where γ is the gyromagnetic ratio, HR is the resonance field. The induced anisotropy HA is due to the spin-glass state of the near-surface regions. TP temperature characterizes the energy of the interparticle interaction of nanoparticles.

H/D isotope effect observed in the isotropic Fermi contact interaction of formyl radical: Experimental and theoretical analysis of the inter- and intra-molecular dynamics

An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions.

Sensitivity enhancement by sequential data acquisition for 13C-direct detection NMR

13C-direct detection NMR has several advantages compared to proton detection, including a tendency to relax slower and wider chemical shift range. However, the sensitivity of 13C-direct detection is much lower than that of proton detection because of its lower gyromagnetic ratio. In addition, a virtual decoupling procedure is often performed to remove peak splitting in the 13C-direct detection axis, which further reduces the sensitivity to 1/√2. In this study, to enhance the sensitivity of 13C-direct detection experiments, we developed a HCACO-type new pulse sequence in which anti-phase (AP) and in-phase (IP) signals are acquired sequentially in a single scan. The developed experiment was tested on an amino acid (valine) and two proteins (streptococcal protein G B1 domain (GB1) and α-synuclein). The AP and IP spectra were successfully obtained in all cases. Using these spectra, IPAP virtual decoupling was performed, and peak splitting was successfully removed. The sensitivity of the experiment was increased by 1.43, 1.26 and 1.26 times for valine, GB1 and α-synuclein, respectively, compared to the conventional HCACO experiment. In addition, we developed another HCACO-type pulse sequence, where AP and IP signals are simultaneously acquired in a single FID. The sensitivity of the experiment was increased by 1.40 and 1.35 times for valine and GB1, respectively. These methods are potentially applicable to other 13C-direct detection experiments that measure one-bond correlations and will further extend the utility of the 13C-direct detection method, especially for structural analyses of intrinsically disordered proteins.

Nuclear magnetic resonance spin-lattice relaxation of lithium ions in aqueous solution by NMR and molecular dynamics.

We study the aqueous solvation dynamics of lithium ions using nuclear magnetic resonance spectroscopy, molecular dynamics, and viscosity measurements. Several relaxation mechanisms are examined to explain the strong increases of spin-lattice relaxation toward high concentrations. The use of both 6Li and 7Li isotopes is helpful to identify the quadrupolar contribution to the relaxation rate. In particular, it is found that the quadrupolar interaction constitutes the strongest contribution above a concentration of ∼10 molal. The next-strongest contribution arises from interactions that scale with the square of the gyromagnetic ratio (mostly the dipolar interaction), and the experimental relaxation rates appear to be fully accounted for when these mechanisms are combined over the concentration range up to the saturation concentration. The study of solvation dynamics, particularly at high concentrations, could be of relevance for electrolyte dynamics in aqueous Li-ion rechargeable batteries.

Magnetism and ion diffusion in honeycomb layered oxide {hbox {K}_2hbox {Ni}_2hbox {TeO}_6}

In the quest for developing novel and efficient batteries, a great interest has been raised for sustainable K-based honeycomb layer oxide materials, both for their application in energy devices as well as for their fundamental material properties. A key issue in the realization of efficient batteries based on such compounds, is to understand the K-ion diffusion mechanism. However, investigation of potassium-ion (K^+) dynamics in materials using e.g. NMR and related techniques has so far been very challenging, due to its inherently weak nuclear magnetic moment, in contrast to other alkali ions such as lithium and sodium. Spin-polarised muons, having a high gyromagnetic ratio, make the muon spin rotation and relaxation (mu ^+SR) technique ideal for probing ions dynamics in these types of energy materials. Here we present a study of the low-temperature magnetic properties as well as K^+ dynamics in honeycomb layered oxide material {hbox {K}_2hbox {Ni}_2hbox {TeO}_6} using mainly the mu ^+SR technique. Our low-temperature mu ^+SR results together with complementary magnetic susceptibility measurements find an antiferromagnetic transition at T_{mathrm{N}}approx 27 K. Further {mu}^{+}SR studies performed at higher temperatures reveal that potassium ions (K^+) become mobile above 200 K and the activation energy for the diffusion process is obtained as E_{mathrm{a}}=121 (13) meV. This is the first time that K^+ dynamics in potassium-based battery materials has been measured using mu ^+SR. Assisted by high-resolution neutron diffraction, the temperature dependence of the K-ion self diffusion constant is also extracted. Finally our results also reveal that K-ion diffusion occurs predominantly at the surface of the powder particles. This opens future possibilities for potentially improving ion diffusion as well as K-ion battery device performance using nano-structuring and surface coatings of the particles.