Homogeneous Static Magnetic Field Research Articles

Advances in high-resolution nuclear magnetic resonance methods in inhomogeneous magnetic fields using intermolecular multiple quantum coherences

Strong and extremely homogeneous static magnetic field is usually required for high-resolution nuclear magnetic resonance (NMR). However, in the cases of in vivo and so on, the magnetic field inhomogeneity owing to magnetic susceptibility variation in samples is unavoidable and hard to eliminate by conventional methods such as shimming. Recently, intermolecular multiple quantum coherences (iMQCs) have been employed to eliminate inhomogeneous broadening and obtain high-resolution NMR spectra, especially for in vivo samples. Compared to other high-resolution NMR methods, iMQC method exhibits its unique feature and advantage. It simultaneously holds information of chemical shifts, multiplet structures, coupling constants, and relative peak areas. All the information is often used to analyze and characterize molecular structures in conventional one-dimensional NMR spectroscopy. In this work, recent technical developments including our results in this field are summarized; the high-resolution mechanism is analyzed and comparison with other methods based on interactions between spins is made; comments on the current situation and outlook on the research directions are also made.

Explicit time-reversible orbit integration in Particle In Cell codes with static homogeneous magnetic field

A new explicit time-reversible orbit integrator for the equations of motion in a static homogeneous magnetic field – called Cyclotronic integrator – is presented. Like Spreiter and Walter’s Taylor expansion algorithm, for sufficiently weak electric field gradients this second order method does not require a fine resolution of the Larmor motion; it has however the essential advantage of being symplectic, hence time-reversible. The Cyclotronic integrator is only subject to a linear stability constraint ( ΩΔ t < π, Ω being the Larmor angular frequency), and is therefore particularly suitable to electrostatic Particle In Cell codes with uniform magnetic field where Ω is larger than any other characteristic frequency, yet a resolution of the particles’ gyromotion is required. Application examples and a detailed comparison with the well-known (time-reversible) Boris algorithm are presented; it is in particular shown that implementation of the Cyclotronic integrator in the kinetic codes SCEPTIC and Democritus can reduce the cost of orbit integration by up to a factor of ten.

Most Typical1∶2Resonant Perturbation of the Hydrogen Atom by Weak Electric and Magnetic Fields

We study a perturbation of the hydrogen atom by small homogeneous static electric and magnetic fields in a specific mutual alignment with angle approximately pi/3 which results in the 1 ratio 2 resonance of the linearized Keplerian n-shell approximation. The bifurcation diagram of the classical integrable approximation has for most such field configurations the same typical structure that we describe. The structure of the corresponding quantum energy spectrum, which we describe in detail, is in certain ways an analogue of the well-known degeneracy found by Herrick [Phys. Rev. A 26, 323 (1982)] for the quadratic Zeeman effect.

Directed transport in classical and quantum chaotic billiards

We construct an autonomous chaotic Hamiltonian ratchet as a channel billiard subdivided by equidistant walls attached perpendicularly to one side of the channel, leaving an opening on the opposite side. A static homogeneous magnetic field penetrating the billiard breaks time-reversal invariance and renders the classical motion partially chaotic. We show that the classical dynamics exhibits directed transport, owing to the asymmetric distribution of regular regions in phase space. The billiard is quantized by a numerical method based on a finite-element algorithm combined with the Landau gauge and the Bloch formalism for periodic potentials. We discuss features of the billiard eigenstates such as node lines and vortices in the probability flow. Evidence for directed quantum transport, inherited from the corresponding features of the classical dynamics, is presented in terms of level-velocity statistics.

3 T homogeneous static magnetic field of a clinical MR significantly inhibits pain in mice

Aims In recent years nuclear magnetic resonance (MR) systems have proliferated worldwide. This imaging/spectroscopy technique utilizes a strong homogeneous static magnetic field, much smaller time-varying gradient magnetic fields, and radiofrequency radiation. Many studies addressed the question of potential adverse side effects induced by MR, but less attention has been paid to its potential beneficial, therapeutical effects. The present study shows that whole body exposure of mice to the 3 T homogeneous static magnetic field of a clinical MR resulted in a statistically significant antinociceptive activity. Main methods Antinociceptive activity was studied in the writhing test, where pain was elicited by the intraperitoneal injection of 0.6% acetic acid in the mouse. No imaging sequence of the MR was used during the experiments. Mice could freely move in their cage without any restraint. Key findings An antinociceptive activity of 68 ± 2% ( p < 0.001, n = 18) was found. Subcutaneous injection of naloxone (0.2 mg/kg) in the mice reversed the magnetic field-induced antinociceptive activity. The effect of noise, vibration and lighting stimuli could be neglected. Although motion-induced effects generated in the body of the mice could not be completely excluded, their influence on pain perception was estimated to be below threshold. Significance MR's static magnetic field should be regarded as a potential therapeutical tool.

Using a polarized maser to detect high-frequency relic gravitational waves

A GHz maser beam with Gaussian-type distribution passing through a homogenous static magnetic field can be used to detect gravitational waves (GWs) with the same frequency. The presence of GWs will perturb the electromagnetic fields, giving rise to perturbed photon fluxes. After being reflected by a fractal membrane, the perturbed photons suffer little decay and can be measured by a microwave receiver. This idea has been explored to a certain extent as a method for very high-frequency gravitational waves. In this paper, we examine and develop this method more extensively, and confront the possible detection with the predicted signal of relic gravitational waves (RGWs). A maser beam with high linear polarization is used to reduce the background photon fluxes in the detecting direction as the main noise. As a key factor of applicability of this method, we give a preliminary estimation of the sensitivity of a sample detector limited by thermal noise using currently common technology. The minimal detectable amplitude of GWs is found to be h{sub min}{approx}10{sup -30}. Comparing with the known spectrum of the RGWs in the accelerating universe for {beta}=-1.9, there is still roughly a gap of 4{approx}5 orders. However, possible improvements on the detector can furthermore » narrow down the gap and make it a feasible method to detect high-frequency RGWs.« less

The theory of the oscillating cup viscometer filled with two immiscible conductive liquids and placed in the magnetic field

In connection with the experiments investigating the phenomenon of exfoliation in metal melts, a decision of the problem of a torsion viscometer filled with two immiscible conductive liquids and placed in the homogeneous static axial magnetic field is found. The cases when the melt's surface is free and when it touches upon a solid cover are considered.

Computing Lorentz forces generated by gradient coils in an open MRI system

Magnetic Resonance Imaging requires the use of gradient coils to perturb the main homogeneous static magnetic field. Sequential perturbations in each of the orthogonal cartesian directions results in the magnetic field becoming spatially encoded. The fast switching of the gradient coils produces large Lorentz forces which act on the coils. These unwanted forces dissipate as acoustic noise at sound pressure levels upward of 130dB. We present a method for designing open magnetic resonance imaging coils that produce reduced Lorentz forces whilst still producing highly accurate gradient fields. We show that when gradient fields of approximately 1% are considered, a linearised regularisation solves for the Fourier series coefficients. References R. Turner. A target field approach to optimal coil design. J. Phys. D: Appl. Phys., 19, 1986, pages L147--L151. doi:10.1088/0022-3727/19/8/001 M. A. Brideson, L. K. Forbes and S. Crozier. Determining complicated winding patterns for shim coils using stream functions and the target-field method. Concepts in Magnetic Resonance, 14(1), 2002, pages 9--18. doi:10.1002/cmr.10000 P. Mansfield, P. M. Glover and J. Beaumont. Sound generation in gradient coil structures for mri. Magnetic Resonance in Medicine, 39(4), 1998, 539--550. doi:10.1002/mrm.1910390406 P. Mansfield, B. Haywood and R. Coxon. Active Acoustic Control in Gradient Coils for mri. Magnetic Resonance in Medicine, 46(4), 2001, 807--818. doi:10.1002/mrm.1261 M. A. Brideson, L. K. Forbes and S. Crozier. Winding patterns for actively shielded shim coils with asymmetric target-fields. Measurement Science and Technlogy, 14, 2003, pages 484--493. doi:10.1088/0957-0233/14/4/312 L. K. Forbes, M. A. Brideson, S. Crozier and P. T. While, An analytical approach to the design of quiet cylindrical asymmetric gradient coils in mri. Concepts in Magnetic Resonance Part B. 31B(4), 2007, 218--236. doi:10.1002/cmr.b.20095.

Classification of perturbations of the hydrogen atom by small static electric and magnetic fields

We consider perturbations of the hydrogen atom by sufficiently small homogeneous static electric and magnetic fields of all possible mutual orientations. Normalizing with regard to the Keplerian symmetry, we uncover resonances and conjecture that the parameter space of this family of dynamical systems is stratified into zones centred on the resonances. The 1 : 1 resonance corresponds to the orthogonal field limit, studied earlier by Cushman &amp; Sadovskií (Cushman &amp; Sadovskií 2000 Physica 142 , 166–196). We describe the structure of the 1 : 1 zone, where the system may have monodromy of different kinds, and consider briefly the 1 : 2 zone.

Development of neutron resonance spin flipper for high resolution NRSE spectrometer

Neutron spin echo (NSE) is one of the techniques with the highest energy resolution for measurement of quasi-elastic scattering. In neutron resonance spin echo (NRSE), two separated neutron resonance spin flippers (RSFs) replace a homogeneous static magnetic field for spin precession in a conventional NSE. We have made a new type of RSF with pure aluminum wires in order to reduce the scattering from the surface. Test experiments have been performed at cold neutron beam line MINE1 at JRR-3M reactor in JAERI and the beam line CN3 at KUR The spin-flip probability was higher than 0.95 at a neutron wavelength of 0.81 nm and a RSF frequency of 100 kHz.

Molecular dynamics simulation of reorientation of polyethylene chains under a high magnetic field

The purpose of this investigation is to clarify the dynamical process of reorientation of a polyethylene chains under high magnetic fields. Molecular dynamics (MD) simulations at constant temperature and pressure are carried out to study the reorientation of two polyethylene chains with different configurations. We utilized static homogeneous external magnetic fields of 25 T into the velocity Verlet integration algorithm through a suitable Taylor expansion. Simulations reveal that the gained potential energy through magnetic annealing facilitated the reorganization of the polyethylene chains closer to the direction of the applied magnetic field. The current study offer an alternative explanation for the orientation that was not available through the hydrodynamics continuum approach based on the diamagnetic susceptibilities as the driving force for reorientation.

Time-of-Flight Secondary Mass Spectrometry Analysis of Isotope Composition for Measurement of Self-Diffusion Coefficient

The analysis of isotope ratio in a material consisting of a single element was developed as a fundamental technique to determine a self-diffusion coefficient in a melt based on time-of-flight secondary mass spectrometry (TOF-SIMS). The self-diffusion coefficient for a pure Ge melt was measured using the stable isotope 73Ge as a tracer under a homogeneous static magnetic field in order to evaluate the influence of thermal convection upon isotope distribution. The results obtained showed that the magnetohydrodynamic effect in the melt obviously damped the convection, but it was not strong enough for the self-diffusion measurement.

Yoke-free magnetic system for low field studies in magnetically affected reaction yield spectroscopy

The article reports the development of a specialized magnetic system for application in low field studies of chemical reactions involving paramagnetic intermediates. We have designed and built a yoke-free magnetic system optimized for creating rather low static homogeneous magnetic fields that can be cleanly swept through zero value. The actually built system creates magnetic field in the range from “−500” to “+500” G in a cylindrical working region with a length of 8 cm and a diameter of 1 cm with a relative field homogeneity of about 10−4 without using ferromagnetic elements or employing a field-sensing feedback loop. At a distance of greater than or equal to 15 cm from the center of the system along the sweeping axis, the magnetic field does not exceed 100 G due to active shielding, which allows putting magnetic field-sensitive elements of the installation that close to the sample. We have tried to provide a detailed account of the design choices we faced and the compromises we had reached for each key aspect of the system, being rather specific about the reasoning behind each decision. The system actually built was thoroughly tested to verify the assumptions made at the design and the calculation stages and to check their practical realizability. The system will serve as the basis of a magnetically affected reaction yield spectrometer that is currently being developed in our laboratory, but hopefully can also be used in a wider array of applications centered around studies in low magnetic fields.

NMR detection of thermal damage in carbon fiber reinforced epoxy resins

Composite materials of epoxy resins reinforced by carbon fibers are increasingly being used in the construction of aircraft. In these applications, the material may be thermally damaged and weakened by jet blast and accidental fires. The feasibility of using proton NMR relaxation times T 1, T 1 ρ , and T 2 to detect and quantify the thermal damage is investigated. In conventional spectrometers with homogeneous static magnetic fields, T 1 ρ is readily measured and is found to be well correlated with thermal damage. This suggests that NMR measurements of proton T 1 ρ may be used for non-destructive evaluation of carbon fiber-epoxy composites. Results from T 1 ρ measurements in the inhomogeneous static and RF magnetic fields of an NMR-MOUSE are also discussed.

Simultaneous NMR microimaging of multiple single‐cell samples

AbstractNuclear magnetic resonance (NMR) microimaging experiments performed on small samples such as single cells typically require long data acquisition times and are usually carried out on high‐field systems with limited access time. When using small probe coils on millimetre (or smaller) size scale to study single cells, it is desirable to take advantage of the comparatively large volume of homogeneous static magnetic field within the magnet to increase the efficiency of NMR data acquisition. Here we describe the development of a four‐channel probehead that consists of four individual solenoid coils (length 2.8 mm, outer diameter 2 mm) stacked along the z axis. The probehead was designed for a 17.6 Tesla (750 MHz) wide‐bore magnet, and operates within a 40 mm inner diameter gradient set with maximum strength 1 Tesla per metre. We performed simulations to estimate the impact of shielding between the coils on the B1 field distribution. Results showed that for coil‐shield separations on the order of a coil radius, no significant change in B1 homogeneity is expected, and therefore coils were spaced accordingly. Coil isolation of greater than 35 dB was achieved for all coils, and the Q values were ∼160 unloaded and ∼60 loaded with 100 mM NaCl solution. Practical use of the probehead was demonstrated by obtaining simultaneously four three‐dimensional T1 maps of chemically fixed Xenopus laevis oocytes at a spatial resolution of 30 × 60 × 60 μm. The T1 values for the nucleus were ∼2.7 seconds, and the animal pole ∼1.2 seconds. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 22B: 7–14, 2004.

Magnetic Field Effects on Electrochemical Processes: A Theoretical Hydrodynamic Model

The effect of a static homogeneous magnetic field that is directed parallel to the planar electrode surface is analyzed in terms of a hydrodynamic boundary layer formation and equivalent mass transfer model for a semi-infinite electrode. The model predicts the decrease of the boundary layer thickness upon increasing either the magnetic field strength, B, or reagent bulk concentration, C*, with the power dependence corresponding to C*4/3B1/3. This permits the interpretation of the enhanced mass transfer at electrode surfaces via hydrodynamic principles.

Myosin Light Chain Modification Depending on Magnetic Fields: II. Experimental

Recent experiments have revealed that Ca2+ -calmodulin dependent myosin light chain phosphorylation in a cell-free preparation exhibits unexpectedly high sensitivity to weak magnetic fields. This enzyme system is a well-studied biochemical system, which appears to depend upon ion binding. A previous article in this journal discussed the theoretical background of myosin phosphorylation and the ion-dependent interactions of EMF with soft tissues. Because of the electromagnetic field (EMF) sensitivity of this cell-free system, experiments were designed to test the effect of a pulsed radio frequency (PRF) field, pulsating magnetic fields (TEMF), gradient magnetic fields (Magnabloc), and homogeneous static magnetic fields (in Helmholtz arrangement) designed for clinical application. It is concluded that these various magnetic fields affect this cell-free enzyme system by modulating ion–protein interactions.

Myosin Light Chain Modification Depending on Magnetic Fields: II. Experimental

Recent experiments have revealed that Ca2+ -calmodulin dependent myosin light chain phosphorylation in a cell-free preparation exhibits unexpectedly high sensitivity to weak magnetic fields. This enzyme system is a well-studied biochemical system, which appears to depend upon ion binding. A previous article in this journal discussed the theoretical background of myosin phosphorylation and the ion-dependent interactions of EMF with soft tissues. Because of the electromagnetic field (EMF) sensitivity of this cell-free system, experiments were designed to test the effect of a pulsed radio frequency (PRF) field, pulsating magnetic fields (TEMF), gradient magnetic fields (Magnabloc), and homogeneous static magnetic fields (in Helmholtz arrangement) designed for clinical application. It is concluded that these various magnetic fields affect this cell-free enzyme system by modulating ion–protein interactions.

Effects of transverse magnetic field during directional solidification of monotectic Al-6.5wt%Bi alloy

Monotectic Al-6.5wt%Bi alloy was directionally solidified in the presence of a transverse static homogeneous magnetic field up to 2.0 kG to determine if gravity-induced convection effects could be reduced or eliminated. Growth rate Vwas varied over the range 1 to 100 μm/s, while temperature gradient at the liquid-solid interface was 120 K/cm. The microstructures of Al-6.5wt%Bi alloy is characterized by regular, aligned Bi fibres or Bi droplets under given growth conditions. Morphological, thermal and magnetic analyses were carried out on sample grown with and without an applied magnetic field. Results indicated that spacing and diameter of Bi fibres decreased in a transverse magnetic field, and the microstructure became more homogeneous, which means that transverse static homogeneous magnetic field can effectively reduce or eliminate gravity-driven and thermal convection during directional solidification of Al-Bi monotectic alloy.

High-order harmonic generation in relativistic ionization of magnetically dressed atoms

We study the generation of high-order harmonics during the ionization process for atoms described by relativistic classical mechanics with a special focus on retardation and Doppler shifts. We will then extend the discussion to a regime for which the atom-laser interaction takes place in a static homogeneous magnetic field. We demonstrate theoretically the possibility to tune the strength of the magnetic field to relativistic resonances to enhance the frequency components in the scattered light harmonic signal. @S1050-2947~99!00810-0#