Different Directions Of Magnetic Field Research Articles

Tension and bending of the particle raft driven by a magnet

The particle raft is a special soft material formed by depositing hydrophobic particles onto the water surface. This paper investigates the deformation of particle rafts under non-contact magnetic field forces. Using hydrophobic iron powder for the fabrication of particle rafts, the tensile and bending deformation of ferromagnetic particle rafts in a magnetic field is quantified for the first time. By designing experiments with two different directions of magnetic field, the corresponding deformation phenomena of the particle rafts at different distances of the magnetic field are thus obtained and their functional relationships are obtained by means of dimensional analysis. By analysing the magnetic field strength and the specific magnetisation of the iron powder during the experiments, the magnetic force is introduced into PFC3D to establish a numerical model considering the effect of the magnetic field force. These findings can deepen our understandings on the mechanical behaviors of soft materials in the magnetic field, and they can provide some inspirations for the design and fabrication of micro-devices for precision manipulation.

Experimental investigation of 3D-printed polymer-based MR sandwich beam under discretized magnetic field

Smart materials are being employed in dynamic systems to tune the stiffness and damping of the structure by using external stimuli. Magnetorheological elastomers (MREs) are considered to be as one of the smart materials because of their characteristics of altering the dynamic properties under the external magnetic field. So far, MRE sandwich beams have been developed by embedding them between two parent structures. In the present work, a novel technique of embedding MR materials is presented to create complex sandwich structures. This technique will replace the conventional embedding technique which uses adhesives to bind the MR materials with the parent structure. The vibration characteristics of the developed sandwich beams are estimated by conducting harmonic analysis to a predefined band of frequency range under the different directions of magnetic field. Sinusoidal signals of desired frequency and amplitude were proffered using NI educational laboratory virtual instrumentation suite to an amplified piezoactuator for exciting the MR sandwich beam. A non-contact-type laser displacement sensor is used in this study to avoid the additional mass of the sensor on the beam. The results indicate that the smart materials can be efficiently embedded with the sandwich beam without using the adhesives. It is also found that by changing the direction of magnetic field, the range of the variation in stiffness of MR sandwich beam can be increased to enhance the isolation effect at fundamental natural frequency.

Influence of Joint EMSFN and M-EMS on Fluid Flow in the Mold During Continuous Casting

Homogenization of physical properties and the chemical composition through the control of liquid metal flow is essential during the continuous casting production of billets. This work was aimed at obtaining improved finished products via continuous casting that implements two magnetic fields. These fields were realized via two electromagnetic stirring processes implemented in a single process: one in the nozzle and one in the mold. The qualitative effects of applying double electromagnetic stirring (EMS) were verified through numerical simulation of 178 mm × 178 mm square billets exposed to double electromagnetic fields during the continuous casting process. The accuracy of the numerical calculations was verified via physical experiments. In addition, the final simulation results were compared with the intermediate results, to determine the true effects of different EMS on the metal flow in the mold. The results revealed that casting using EMS with different directions of magnetic field in the mold and the nozzle has the best effect on the distribution of the fluid flow and minimal influence on the stability of the meniscus and yields the minimum metal-jet penetration into the mold.

Investigation of Magnetic Field Arrangement on Launching Performance of Multistage Synchronous Induction Coilgun

For the multistage induction coilgun, many researchers pay great attention to improving the system efficiency. The directions of magnetic field generated by the driving coils are consistent for conventional coilgun, because it is convenient to analyze acceleration characteristic and stress status for the armature in the barrel. In this paper, the launching performance of multistage induction coilgun is investigated in terms of different directions of magnetic field in order to improve the system efficiency. A field-circuit coupled model for a 6-stage coilgun is built. The simulation for the consistent direction of magnetic field is calculated. For the same parameter setup, the directions of magnetic field generated by the last three stages current are changed. The simulation results show that the armature endures a large braking force when going through the last three stages, and the velocity drop is obvious. Meanwhile, the currents in the last three stages are very large. The distribution of the current density and the magnetic field during the transition process of magnetic field are analyzed. The reason for velocity drop when changing the direction of magnetic field is discussed. A method that the trigger position is adjusted for the armature is proposed. The simulation results show that the armature can be accelerated to a higher speed on condition of inconsistent direction of magnetic field with adjusting the trigger position. It is feasible to improve the system launching performance through changing the direction of magnetic field. A 15-stage coilgun is built to validate the method. The experimental results show that the velocity and system efficiency are increased dramatically through changing the direction of magnetic field. It provides valuable reference for multistage induction design.

Numerical Investigation of Liquid Metal Magneto-Convection in a Squared Enclosure Based on OpenFOAM

In liquid metal blankets for fusion power plant, magneto-convection phenomenon cannot be neglected when liquid metal flows slowly. The buoyant convective flow can be comparable to the forced flow in this case. In order to understand the basic knowledge of MHD buoyant flow, a numerical code was developed and validated based on OpenFOAM platform, which is an open source CFD library toolkit. Laminar flow, Boussinesq hypotheses and constant physical properties were assumed to simplify the magneto-convection problem. Liquid metal magneto-convection flow in a long vertical enclosure under different boundary conditions and different directions of magnetic field have been chosen as the benchmark cases. A qualitative and quantitative comparison between the numerical results and analytical solution shows quite good agreement, which indicates the correctness of the magneto-convection code. Furthermore, a 3D case at high Grashof number within the experimental setup was simulated. The numerical results showed that with the decrease of Ha number the flow turns unstable, which agrees with the experimental phenomena. What’s more, the implementation procedure of the algorithm into OpenFOAM platform shows the flexibility and extensibility, which indicates that OpenFOAM can be used to develop more complex algorithm and the developer can pay more attention on the numerical algorithm of magneto-convection and analysis of physical phenomenon.

Low-temperature heat transport in the geometrically frustrated antiferromagnetsR2Ti2O7(R = Gd and Er)

We report a systematic study on the low-temperature thermal conductivity ($\ensuremath{\kappa}$) of ${R}_{2}$Ti${}_{2}$O${}_{7}$ ($R$ = Gd and Er) single crystals with different directions of magnetic field and heat current. It is found that the magnetic excitations mainly act as phonon scatterers rather than heat carriers, although these two materials have long-range magnetic orders at low temperatures. The low-$T$ $\ensuremath{\kappa}(H)$ isotherms of both compounds show rather complicated behaviors and have good correspondences with the magnetic transitions, where the $\ensuremath{\kappa}(H)$ curves show drastic dip- or steplike changes. In comparison, the field dependencies of $\ensuremath{\kappa}$ are more complicated in Gd${}_{2}$Ti${}_{2}$O${}_{7}$, due to the complexity of its low-$T$ phase diagram and field-induced magnetic transitions. These results demonstrate the significant coupling between spins and phonons in these materials and the ability of heat-transport properties probing the magnetic transitions.

NMR Studies of Yb-Based Heavy Fermion Compound YbCo2Zn20

We have carried out 59 Co-nuclear magnetic resonance (NMR) measurements on the heavy Fermion compound YbCo 2 Zn 20 , which shows an extremely large specific heat. After examining site symmetry at the Co position by studying a single crystal sample at different directions of magnetic field, we have analyzed powder patterns obtained over a wide range of field from 0.8 to 7.2 T. The temperature dependent component of the Knight shift, which arises from 4 f moments, is largely suppressed with increasing field, resulting in weak temperature dependence at low temperatures. This is a sign of field-induced Fermi liquid states, consistent with previous transport measurements on this compound.

Influence of Neutral Beam Injection Direction and Magnetic Axis Position on Fast Ion Distribution Function in Large Helical Device

Effective ion heating and good fast ion confinement are essential for ignition. Therefore the influence of various types of plasma heating on the fast ion distribution function in various magnetic field comfigurations should be studied. To study the distribution of fast ions in LHD plasma, a new Angular Resolved Multi-Sightline Neutral Particle Analyzer (ARMS-NPA) has been developed. It scans plasma by 20 sightlines and can provide detailed information about angular and radial distribution of fast particles. In this paper, the influence of co- and counter- neutral beam injection (NBI) on angular distribution of the suprathermal particle tail is shown. Measurements were made for different directions of magnetic field in inward- (Rax = 3.6 m) and outward-shifted (Rax = 3.9 m) magnetic axis position. The suprathermal ion tail angular distribution during co- and counter-NBI was measured for different magnetic field strengths in the current work. The simulation results of fast particle orbits are shown as well to explain the experimental results.

Magnetic observation of deformation substructure in cyclically deformed Fe3Al single crystals

abstractFe–28.0 at% Al single crystals with the D03 structure were cyclically deformed in tension-compression mode at constant total-strain amplitudes (εt). At and less than εt ¼ 0:25%; the maximum stress increased rapidly with increasing number of cycles to 20, then remained constant during further cycling. In contrast, small cyclic softening appeared at and more than εt ¼ 0:30% between the initial and the final stages of cyclic hardening. The deformation substructure in cyclically deformed Fe3Al single crystals was observed by both transmission electron microscopy (TEM) and magnetic technique. From TEM observation, pairs of superpartial dislocations with Burgers vector (b) of 1/4[111] moved dragging a next-nearest-neighbour antiphase boundary (NNN-APB) in the cyclic softening stage, though four superpartials generally moved in a group in the initial hardening stage. The change in dislocation configuration from four- to two-coupled superpartials may ease the cross-slip event resulting in the dislocation rearrangement and the cyclic softening. The magnetic properties of cyclically deformed Fe3Al single crystals were examined by a vibrating sample magnetometer. In particular, magnetic anisotropy in the primary slip plane was evaluated by measuring high-field susceptibility in the approach to magnetic saturation at different directions of magnetic field. The cyclically deformed crystals exhibited strong magnetic anisotropy due to atomic rearrangement near NNN-APB and internal strain around screw dislocations. Two types of magnetic anisotropy were separated from each other by the Fourier transformation. In the cyclic softening stage, the amplitude of NNN-APB-dependent anisotropy rose abruptly between 102 and 103 cycles while that due to screw dislocations remained constant during fatigue. This suggested that a disordering of D03 phase due to fatigue did not occur in the softening stage. The maximum stress of Fe3Al single crystals exceeded the required for superpartial pairs to drag NNN-APB, resulting in the cyclic softening.

Low frequency surface waves in the magnetized dusty plasma

The dispersion relation for low-frequency surface waves in the multicomponent magnetized dusty plasma is derived for both, plane and plasma cylinder geometries. The dispersion relation is analyzed for different directions of magnetic field. The surface wave spectrum is obtained.

The critical current in a NbTi tape measured in different directions of magnetic field and the current reduction due to the self field

With reference to the application of NbTi tape in a superconducting thermal switch, the critical current of a 20- mu m-thick NbTi tape was measured in several directions of the magnetic field. The critical current was found to behave strongly anisotropically, due to the deformation of the NbTi. The tape is extrasensitive to the component of the magnetic field perpendicular to the surface. Without an external field this component of the self-field reduces the critical current far below its intrinsic value. A one-dimensional model can describe the reduction of critical current due to the self-field in a thin tape. >

Current contacts and the breakdown of the quantum Hall effect.

The nonlinearities in the I-V characteristics have been studied of high-mobility Si metal oxide semiconductor field-effect transistors in the quantum Hall regime. The breakdown curves were measured with different sets of voltage contacts and for different directions of magnetic field and current. Comparison of these curves shows that the breakdown of the quantum Hall effect (QHE) in these samples is an intrinsic effect that starts at the current contact where the electrons are injected into the two-dimensional electron gas (2DEG). This fundamental asymmetry and the crucial role of the current contact are explained using the B\"uttiker-Landauer approach to the QHE and its recent extension to the nonlinear regime. The electron-injection process contains two mechanisms that lead to breakdown voltages in the 2DEG. We have identified both experimentally by comparing the critical currents of different configurations of current and voltage contacts. In one of the mechanisms, the nonequilibrium distribution of electrons that is injected into the 2DEG extends to the voltage contacts. This means that the equilibration length of the 2D electrons is at least of the order of 100 \ensuremath{\mu}m. For currents far beyond breakdown and for voltage contacts that are further from the electron-injection contact, the breakdown characteristics are harder to understand. The variation of the electron density of the 2DEG due to the large Hall voltage has to be taken into account as well as the equilibration induced by additional voltage contacts.

Gamma8-bands anisotropy and selection rules for far-infrared magneto-optical transitions in HgTe

Far-infrared (FIR) magnetotransmission spectra of n-type HgTe in Voigt configuration (polarised light; E perpendicular to B and E//B) for different directions of magnetic field in the (110) plane have been measured. The experiment was done in a magnetic field up to 5T at liquid helium temperature. Intraband and interband ( Gamma 8v to Gamma 8c) transitions were observed. The experimental data were analysed in the Luttinger (quasigermanium) approximation. Observed strong anisotropy effects in interband transitions are very well described by means of the 'interaction' between the hole Landau levels induced by the D1 and D2 terms in Luttinger notation. From the fitting of the theoretical model to the experimental data the Luttinger band structure parameters were evaluated: gamma 1=-16.8+or-0.2, gamma 2=-10.6+or-0.1, gamma 3=-8.8+or-0.1, kappa =-10.1+or-0.2, q=-0.5+or-0.1. A small disagreement in the absolute value of calculated and observed transition energies as well as the negative sign of the q parameter may be connected with the non-local electron-electron interaction near the Gamma point.

Decomposition of spin susceptibility of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) and analogous compounds

The method of separating the spin susceptibility, $\ensuremath{\chi}$, of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) and analogous quasi-one-dimensional compounds into the contributions of the individual chains by means of EPR data is reexamined in the light of more recent information on the compounds. For TTF-TCNQ it is concluded that, if proper consideration is given to the experimental uncertainties, the method can be used to obtain reliable qualitative results. For hexamethylene-tetrathiafulvalenium tetracyanoquinodimethanide (HMTTF-TCNQ), however, it is shown that the decomposition is unreliable since analysis of the data for different directions of magnetic field yields quite different results for the individual stack susceptibilities. It is suggested that the reason the decomposition does not work in this case, among others, is that the interstack interaction is too large. Recognizing these difficulties with the decomposition removes a number of apparent paradoxes or anomalies, such as: (1) the sign for thermoelectric power being opposite to the sign of charge of the carrier responsible for conduction; (2) $\ensuremath{\chi}$ for TTF being 5 or more times $\ensuremath{\chi}$ for tetraselenafulvalenium; (3) $\ensuremath{\chi}$ for the HMTTF chain being independent of temperature over the range where for all other chains investigated in this family it is not.