Effect Of Longitudinal Magnetic Field Research Articles

Effect of Longitudinal Magnetic Field on CMT Welding of Al-Alloy

A longitudinally varying magnetic field (MF) was applied during cold metal transfer (CMT) welding of Al alloys. The effect of MF on the welding process, macrostructure, microstructure and properties of weld beads was studied. The results showed that the application of MF led to arc expansion and rotation, the droplet transfer frequency decreased, the droplet volume became larger, and the droplets deflected. When the coil current was between 0 and 5 A, the weld beads porosity decreased from 4.47 to 0.26%. And when the coil current was increased to 8 A, the porosity of weld beads also increased to 2.84%. MF reduced the weld depth, wetting angle and weld reinforcement, and increased weld width. With the increase of coil current, the width of primary dendrite arms decreased from 7.75 to 5.01 μm. The area occupied by the Al–Si eutectic was enlarged, and the eutectic was refined. It was also found that the MF slightly increased the hardness of the weld beads, and the hardness distribution was more uniform.

Effects of probe ellipticity and longitudinal magnetic field on the polarization rotation in a coherently prepared atomic medium

The dependencies of the polarization rotation on the probe ellipticity and the longitudinal magnetic field have been studied both experimentally and theoretically in a V-type electromagnetically induced transparency for 87Rb vapour. The angle of rotation varies periodically with the change in the probe ellipticity and non-linearly with the variation of the magnetic field. We have observed that the plane of polarization is rotated maximum for linearly polarized light and have obtained angle of rotation 0.32° ± 0.01° for B = 0.036 ± 0.001 mT while it was 0.0267° ± 0.0002° without magnetic field. Thus our measurement becomes sensitive to the low magnetic field. A four-level system is considered and the corresponding density matrix equations have been solved analytically to explain these observations theoretically with the help of degenerate and non-degenerate magnetic sub-levels.

Effects of random longitudinal magnetic field on dynamics of one-dimensional quantum Ising model

<sec>The dynamical properties of quantum spin systems are a hot topic of research in statistical and condensed matter physics. In this paper, the dynamics of one-dimensional quantum Ising model with both transverse and longitudinal magnetic field (LMF) is investigated by the recursion method. The time-dependent spin autocorrelation function <inline-formula><tex-math id="M1">\begin{document}$C\left( t \right) = \overline {\left\langle {\sigma _j^x\left( t \right)\sigma _j^x\left( 0 \right)} \right\rangle } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M1.png"/></alternatives></inline-formula> and corresponding spectral density <inline-formula><tex-math id="M2">\begin{document}$\varPhi \left( \omega \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M2.png"/></alternatives></inline-formula> are calculated. The Hamiltonian of the model system can be written as </sec><sec> <inline-formula><tex-math id="M3">\begin{document}$H = - \dfrac{1}{2}J\displaystyle\sum\limits_i^N {\sigma _i^x\sigma _{i + 1}^x - \dfrac{1}{2}\displaystyle\sum\limits_i^N {B_i^x\sigma _i^x} } - \dfrac{1}{2}\displaystyle\sum\limits_i^N {B_i^z\sigma _i^z}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M3.png"/></alternatives></inline-formula>. </sec><sec>This work focuses mainly on the effects of LMF (<inline-formula><tex-math id="M4">\begin{document}$ B_i^x $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M4.png"/></alternatives></inline-formula>) on spin dynamics of the Ising system, and both uniform LMF and random LMF are considered respectively. Without loss of generality, the transverse magnetic field <inline-formula><tex-math id="M5">\begin{document}$ B_i^z = 1 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M5.png"/></alternatives></inline-formula> is set in the numerical calculation, which fixes the energy scale. </sec><sec>The results show that the uniform LMF can induce crossovers between different dynamical behaviors (e.g. independent spins precessing, collective-mode behavior or central-peak behavior) and drive multiple vibrational modes (multiple-peaked behavior) when spin interaction (<inline-formula><tex-math id="M6">\begin{document}$ J $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M6.png"/></alternatives></inline-formula>) is weak. However, the effect of uniform LMF is not obvious when spin interaction is strong. For the case of random LMF, the effects of bimodal-type and Gaussian-type random LMF are investigated, respectively. The dynamical results under the two types of random LMFs are quite different and highly dependent on many factors, such as the mean values (<inline-formula><tex-math id="M7">\begin{document}$ {B_1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M7.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M8">\begin{document}$ {B_2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M8.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M9">\begin{document}$ {B_x} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M9.png"/></alternatives></inline-formula>) or the standard deviation (<inline-formula><tex-math id="M10">\begin{document}$ \sigma $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M10.png"/></alternatives></inline-formula>) of random distributions. The nonsymmetric bimodal-type random LMF (<inline-formula><tex-math id="M11">\begin{document}$ {B_1} \ne {B_2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M11.png"/></alternatives></inline-formula>) may induce new vibrational modes easily. The dynamical behaviors under the Gaussian-type random LMF are more abundant than under the bimodal-type random LMF. When <inline-formula><tex-math id="M12">\begin{document}$ \sigma $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M12.png"/></alternatives></inline-formula> is small, the system undergoes two crossovers: from a collective-mode behavior to a double-peaked behavior, and then to a central-peak behavior as the mean value <inline-formula><tex-math id="M13">\begin{document}$ {B_x} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M13.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M13.png"/></alternatives></inline-formula> increases. However, when <inline-formula><tex-math id="M14">\begin{document}$ \sigma $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M14.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M14.png"/></alternatives></inline-formula> is large, the system presents only a central-peak behavior. </sec><sec>For both cases of uniform LMF and random LMF, it is found that the central-peak behavior of the system is maintained when the proportion of LMF is large. This conclusion can be generalized that the emergence of noncommutative terms (noncommutative with the transverse-field term <inline-formula><tex-math id="M15">\begin{document}$\displaystyle\sum\nolimits_i^N {B_i^z\sigma _i^z}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M15.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20210631_M15.png"/></alternatives></inline-formula>) in Hamiltonian will enhance the central peak behavior. Therefore, noncommutative terms, such as next-nearest-neighbor spin interactions, Dzyaloshinskii-Moryia interactions, impurities, four-spin interactions, etc., can be added to the system Hamiltonian to modulate the dynamical properties. This provides a new direction for the future study of spin dynamics.</sec>

纵向磁场对316L不锈钢窄间隙激光-MIG多层焊接接头微观组织与疲劳裂纹扩展的影响

纵向磁场对316L不锈钢窄间隙激光-MIG多层焊接接头微观组织与疲劳裂纹扩展的影响

Magnetic field effect on the free induction decay of hydroxyl radicals (OH) in the terahertz region.

The effect of an external longitudinal magnetic field on the optical free induction decay from a free radical is observed for the first time. The experiments were performed on a rotational transition of the hydroxyl radical, OH (2Π3/2(J = 1) ← 2Π3/2(J = 0) at 83.8 cm-1), using a terahertz free electron laser. In contrast to the results of the experiments with a stable paramagnetic molecule, NO, the observed effect of an external magnetic field on the free induction decay from hydroxyl radicals is more complicated. A longitudinal magnetic field leads to the rotation of the polarization plane of the FID radiation and to an additional modulation of the signal intensity. The angle of the rotation of the plane of polarization is large, in agreement with the theoretical predictions. The observed FID kinetics in the time domain are in semi-quantitative agreement with the modeling. This observation opens an opportunity for the selective detection of weak signals of short-lived reactive paramagnetic free radicals from overwhelming signals that originate from stable non-paramagnetic species by polarization discrimination.

Geant4 Monte Carlo investigation of the magnetic field effect on dose distributions in low-density regions in magnetic resonance image-guided radiation therapy

It is necessary to evaluate the effect of the presence of a magnetic field when treating lung tumors with MRIgRT. In this study, the effect of transverse and longitudinal magnetic fields on dose distributions in low-density regions was quantitatively investigated. The dose distributions in a virtual lung phantom under the influence of magnetic fields were calculated using the Geant4 Monte Carlo code. The phantom size was 30 × 20 × 30 cm3, and it was composed of three layers: water (3 cm thickness), lung (12 cm thickness), and water (5 cm thickness). The density of the lung layer was set to 0.1, 0.3 and 0.6 g/cm3. The uniform magnetic flux densities of 0.35 T and 1.5 T were used for 2 × 2, 5 × 5, and 10 × 10 cm2 fields at a source-to-surface distance of 100 cm, using a 6 MV photon spectrum. The dose at the water–lung interface in a lung phantom increased by 58%, 51%, and 22% for the lung densities of 0.1, 0.3, and 0.6 g/cm3, respectively. In the 1.5 T longitudinal magnetic field, the penumbra at the lung center (at the depth of 9 cm) decreased by 5.14, 1.50 and 0.35 mm for a 5 × 5 cm2 field, respectively. The dose distributions in lowdensity regions are more affected by the magnetic field. In conclusion, the doses at the water–lung interface increased in the transverse magnetic field. The depth dose increased, and the penumbra decreased in the longitudinal magnetic field.

Dyson-Maleev theory of ferrimagnetic spin chain with bond alternation in longitudinal magnetic field

By using the method of Dyson–Maleev mean-field theory, we study the effect of bond alternation and longitudinal magnetic field in the model of ferrimagnetic spin chain. Based on the numerical results of self-consistent equations, properties of the excited spectrums, magnon internal energy, static susceptibility, magnetization plateau and specific heat are obtained with different bond alternation parameters δ and external magnetic field B. This method provides qualitative consistent results to describe the phase from ferrimagnetic state to bond altered state.

Evaluation of Layer Thickness Dependence of Critical Current Density using Longitudinal Magnetic Field Effect in Superconducting Coated Conductors

When the critical current density Jc for a superconductor is constant, the critical current Ic increases in proportion to the superconducting cross-sectional area. However, in the case of a superconducting coated conductor, when the thickness of the superconducting layer exceeds about 2 μm, there is no further increase in Ic. This is because Jc decreases due to the structural degradation of the superconducting layer. In this study, Jc for samples with superconducting layers of different thicknesses was measured using the longitudinal magnetic field effect in order to investigate the optimum layer thickness for maximizing Ic. Differences in the Jc characteristics due to the layer thickness appeared more clearly under a longitudinal magnetic field than a transverse magnetic field. This was particularly true at low temperatures, and the optimum layer thickness was found to be approximately 1 μm.

Longitudinal Magnetic Field Effects on (Y,Gd)Ba2Cu3O7−δ Coated Conductor With BaHfO3 Nanoparticles Fabricated by UTOC-MOD Method

To clarify the effects of longitudinal magnetic field (LMF) on Y0.77Gd0.23Ba2Cu3O7- δ coated conductors fabricated by the trifluoroacetic-acid based metal organic decomposition method with the ultra-thin-once-coating process (UTOC-MOD (Y,Gd)BCO-CCs), and to understand the contributions of BaHfO3 nanoparticles (BHO-NPs) to this, we investigated the critical current density J c under a wide range of temperature and magnetic field conditions. We found that J c in the LMF configuration increased compared to those in the in-plane transverse magnetic field configuration under whole conditions in samples both with (w/) and without (w/o) BHO-NPs. J c enhancement due to the LMF configuration was remarkable in the w/ BHO-NPs sample at higher temperatures, indicating that introduction of BHO-NPs to UTOC-MOD (Y,Gd)BCO-CC would be useful for LMF DC cable applications.

Chiral mixed phase in disordered 3d Heisenberg models under magnetic fields

Using Monte Carlo simulations, we studied the effect of uniform external longitudinal magnetic field on the 3d isotropic Heisenberg disordered model. Simulations are performed for a variety of fields. Our results confirm that the mixed chiral phase must belong to the same class of universality with those of zero fields and with same group of critical exponent.

Refinement of metal structure in arc surfacing under the effect of longitudinal magnetic field

Refinement of metal structure in arc surfacing under the effect of longitudinal magnetic field

Измельчение структуры металла при дуговой наплавке под воздействием продольного магнитного поля

Измельчение структуры металла при дуговой наплавке под воздействием продольного магнитного поля

Investigation of the longitudinal magnetic field effect in SmBa2Cu3Oy films with various shaped artificial pinning centers

The longitudinal magnetic field (LMF) state, in which the magnetic field is applied parallel to the applied current direction and ab-plane of SmBa2Cu3Oy (Sm123) films with shaped artificial pinning centers (APCs) of various shapes is investigated. The in-field critical current density (Jc) of pure Sm123 films in the LMF state and films with Y2O3, Sm2BaCuO5, BaHfO3, and a multilayered structure with short BaHfO3 nanorods were measured in the configuration. The measurement revealed that there was significant Jc enhancement only in the multilayered film. From the viewpoint of flux pinning, 3D flux pinning is key to improving in-field Jc in the LMF state. However, the Sm123 films with APCs, such as Y2O3 and Sm2BaCuO5, did not have a larger Jc than the pure Sm123 films in the LMF state. This indicates that the APCs prevent the current flowing along the external magnetic field. Both of the 3D flux pinning and the pure layer in which current can flow without disturbance are important for the Jc enhancement in the LMF state.

Longitudinal magnetization and specific heat of the anisotropic heisenberg antiferromagnet on honeycomb lattice

We study the effects of longitudinal magnetic field and temperature on the thermodynamic properties of two dimensional Heisenberg antiferromagnet on the honeycomb lattice in the presence of anisotropic Dzyaloshinskii-Moriya interaction and next nearest neighbor coupling exchange constant. In particular, the temperature dependence of specific heat have been investigated for various physical parameters in the model Hamiltonian. Using a hard core bosonic representation, the behavior of thermodynamic properties has been studied by means of excitation spectrum of mapped bosonic gas. The effect of Dzyaloshinskii-Moriya interaction term on thermodynamic properties has also been studied via the bosonic model by Green's function approach. Furthermore we have studied the magnetic field dependence of specific heat and magnetization for various anisotropy parameters. At low temperatures, the specific heat is found to be monotonically increasing with temperature for magnetic fields in the gapped field induced phase region. We have found the magnetic field dependence of specific heat shows a monotonic decreasing behavior for various magnetic fields due to increase of energy gap in the excitation spectrum. Also we have studied the dependence of magnetization on Dzyaloshinskii-Moriya interaction strength for different next nearest neighbor coupling constant.

Longitudinal magnetic field effect on torsional vibration of carbon nanotubes

Torsional dynamic analysis of carbon nanotubes under the effect of longitudinal magnetic field is carried out in the present study. Torque effect of an axial magnetic field on a carbon nanotube has been defined using Maxwell’s relation. Nonlocal governing equation and boundary conditions for carbon nanotubes are obtained by using Hamilton’s minimum energy principle. Eringen’s nonlocal stress gradient elasticity theory is used in the formulation. Fourth order nonlocal equation of motion is solved by utilizing differential quadrature method. Clamped-clamped and clamped-free nonlocal boundary conditions are considered. Nonlocal and axial magnetic field effects on torsional vibration of carbon nanotubes are investigated. The magnetic field has significant effects on the dynamics of carbon nanotubes and may lead to torsional buckling. Critical torsional buckling load reduces with nonlocal effects. Nonlocality shows softening effect on carbon nanotube’s lattice structure. Present results can be used in the design and analysis of nanoelectromechanical products like nano-motors.

Improvement of soft magnetic properties for distinctly high Fe content amorphous alloys via longitudinal magnetic field annealing

The effects of longitudinal magnetic field annealing on soft-magnetic properties (SMPs) and magnetic domain structure of Fe(82.6-85.7)Si(2-4.9)B(9.2-11.2)P(1.5-2.7)C0.8 amorphous alloys with a distinctly high Fe content of 93.5–95.5 wt% for high Bs were investigated. It was found that longitudinal magnetic field annealing could improve soft-magnetic properties (SMPs) of amorphous alloys effectively, except the one with poor thermal stability. Superb magnetic properties containing a minimum coercivity of 0.8 A/m, a maximum effective permeability of 11 × 103 at 1 kHz and minimum core loss of 0.052 W/kg (at Bm = 0.9 T and f = 50 Hz) were successfully obtained. Domain structures were characterized with a Magneto-optical Kerr Microscope to unveil the mechanism of SMPs improvement. Stripe domains were observed in the annealed high Fe content amorphous alloy ribbons with optimal soft magnetic properties.

Longitudinal magnetic field effect in critical current characteristics of Bi-2223 superconducting tape

In this study, we focused on the longitudinal magnetic field effect in critical current densities and investigated the enhancement of the electrical conduction properties in a commercial Bi-2223 superconducting tape. Since the samples used in this study were polycrystalline and tape-shaped, the longitudinal magnetic field effect was expected to differ from that in single crystals or conventional superconducting alloys. Therefore, the critical current characteristics at magnetic fields of up to 5 T as well as at various angles between the magnetic field and current were measured in detail.

Simulation and analysis of heat transfer and fluid flow characteristics of arc plasma in longitudinal magnetic field-tungsten inert gas hybrid welding

In the present work, an axisymmetrical model based on the magnetohydrodynamics (MHD) is established to investigate the effect of external longitudinal magnetic field (LMF) on arc characteristics during the gas tungsten arc welding (GTAW) process. The profiles of temperature and voltage drop, distributions of axial velocity, shear stress, and arc pressure, etc., in the cases of different applied LMF strengths ranging from 0 to 0.06 T are simulated by utilizing the fluid dynamic theory coupled with Maxwell equations. In order to achieve more accurate values of heat transfer and fluid flow of arc plasma, we take the boundary layer of electrodes into consideration. The results show that the applied LMF could drive particles to rotate and expand the arc, and a negative pressure area appears at the center and induces an upward streaming of gas (i.e., anti-gravity flow) through the arc core with the effects of centrifugal force, concentrating the anodic energy to the cathode. When the magnetic induction strength is 0.06 T, vortexes are dramatically formed around the arc axis by the interaction between the anti-gravity flow from the arc center and outside downward flow from the arc fringes. Thus, the distribution of current density, anodic heat flux, and arc pressure shifts from the arc center to the periphery and forms a bimodal pattern. The various thermal fluxes and subsequent thermal efficiency are also quantitatively investigated for a better understanding of the effects of LMF on arc behaviors and the theoretical predictions show good agreement with the experimental results.

Effect of Longitudinal Magnetic Field on Vibration Response of Double-Walled Carbon Nanotubes Embedded in Viscoelastic Medium

This paper aims to study the effect of externally applied longitudinal magnetic field on the transverse vibration of viscoelastic double-walled carbon nanotubes (visco-DWCNTs) embedded in a viscoelastic medium. The analyses are carried out based on the nonlocal viscoelastic model and Euler–Bernoulli beam theory. Governing equations are derived for the vibration of the embedded visco-DWCNT subjected to a magnetic field, where the Lorentz magnetic force, the surrounding viscoelastic medium, the intertube van der Waals forces and viscoelasticity of the DWCNT are taken into consideration. In this study, the transfer function method is employed to solve the governing equations, which enables one to obtain the natural frequencies and the corresponding mode shapes in closed form for the DWCNTs with arbitrary boundary conditions. Here the developed mechanics model is first compared with the existing techniques available in the literature in a few particular cases, where excellent agreement is achieved. The validation of the model is followed by a detailed parametric study of the effects of longitudinal magnetic field, nonlocal parameter, boundary conditions, structural damping coefficient and aspect ratio of the DWCNTs on their vibration. The study demonstrates the efficiency of the present technique designed for vibration analysis of a complicated multi-physics system comprising DWCNTs, the viscoelastic medium and a magnetic field in longitudinal direction.

Effect of Longitudinal Static Magnetic Field on the Columnar to Equiaxed Transition in Directionally Solidified GCr15 Bearing Steel

Effect of Longitudinal Static Magnetic Field on the Columnar to Equiaxed Transition in Directionally Solidified GCr15 Bearing Steel