Frequency Of External Magnetic Field Research Articles

Триплеттриплетная аннигиляция молекулярных электронных возбуждений вблизи диамагнитной металлической микрочастицы в переменном магнитном поле

A mathematical model of the spinselective reaction of triplettriplet annihilation of molecules on the surface of a spherical microparticle or a cylindrical rod of micrometer radius in an alternating magnetic field transformed by conducting microparticles is presented. Based on these models, the calculations of the integral and local rates of magnetically sensitive molecular processes were performed. It has been shown that in the local nearsurface regions of the conducting microparticles in an alternating magnetic field, the rate of spinselective bimolecular reactions changes. The comparison of the nanoand microsphere showed that with the external magnetic field induction value B0 = 1 T, the maximum resulting field at the equator of the particle was equal to 12 mT and 100 mT, respectively. It was also revealed that for nanoand microcylinders with a similar value of the external magnetic field induction B0 = 1 T, the maximum resulting field at the point (R,0) of the 2d magnetic pole was equal to 12 mT and 1.5 T, respectively. The amplitude of the magnetic effect for different times and particle sizes was equal to +1 % and 2 %. For a silver microcylinder with a radius R = 25 μm, there was switching from a purely negative magnetic effect at the time t = 0 ns to an effect with positive and negative parts. For the case of a silver cylinder of radius R = 30 μm and external magnetic field frequency ω = 5∙108 s1, an increase in the amplitude of the positive part of the magnetic effect curve from 0.25 % to 1 % was observed when the time instant changed from t = 0 ns, which corresponds to the maximum of the external magnetic field, up to t = 3.68 ns when the resulting field of the microwire reaches its maximum. This work may be of interest to physicists and chemists involved in science in the field of chemical physics, physics of magnetic phenomena, spinselective reactions and spintronics.

The effect of external force and magnetic field on atomic behavior and pool boiling heat transfer of Fe3O4 /ammonia nanofluid: A molecular dynamics simulation

BackgroundIn this study, the pool boiling heat transfer of Fe3O4 /ammonia nanofluid in a copper (Cu) nanochannel is done using the molecular dynamics (MD) simulation. MethodsTo increase and improve the performance of heat transfer, the effect of external force, and external magnetic field frequency on the atomic and thermal performance of the simulated nanostructure was checked. The results show that the density increased with a positive slope when the external force was imposed on the nanostructure with a growing trend. The amount of velocity and temperature similarly increased. So, by increasing the external force from 0.001 to 0.005 eV/Å, the maximum values ​​of density, velocity, and temperature converge to the values ​​of 0.1441 atom/Å3, 13.939 Å/fs, and 794.61 K. Moreover, increasing the applied external force caused an increase in the heat flux and thermal conductivity in the nanostructure. Finally, studying the effect of external magnetic field on the nanofluid's atomic behavior shows that with the change in the frequency of external magnetic field, Poiseuille behavior was remained. The results of the increase in the frequency of external magnetic field show the increasing trend of velocity and temperature. Numerically, the maximum values of velocity and temperature increase from 7.133 to 11.476 Å/fs, and from 210.23 to 410.07 K, respectively. Furthermore, HF increases by increasing the frequency of external magnetic field. Significant findingsAs particles' movement increased, the structure's thermal resistance decreased. So, by increasing external force, the thermal resistance in the structure decreased.

Investigation on thermal effect of bulk high-temperature superconductors under varying external magnetic field

Superconducting bulks applied to high-temperature superconducting (HTS) maglev vehicles are susceptible to magnetic field, resulting in alternating current (AC) losses and heat generation, which affect the stability of the suspension system. Therefore, the thermal effect of superconducting bulk under external magnetic field is worth studying. The paper uses finite element software to establish a 2D electromagnetic-thermal coupling model. The distribution and variation of HTS bulks’ temperature under varying external magnetic field are simulated and analyzed, and the loss and temperature rise of rectangular bulks with different thicknesses are studied. Finally, the effect of increasing the critical current density on the thermal effect of the superconducting bulk is discussed. The results show that the temperature rise of bulk has a positive correlation with the amplitude and frequency of external magnetic field. The maximum temperature is affected by the angle of magnetic field. Under the same external magnetic field, the bulk with smaller thickness produces smaller loss and temperature rise. The research results can provide important references for the operation and furniture design of HTS maglev vehicles.

Investigation into the thermo-hydrodynamics of ferrofluid flow under the influence of constant and alternating magnetic field by InfraRed Thermography

Convective flow of single-phase ferrofluids under the influence of constant and alternating magnetic field has attracted attention as an effective strategy for enhanced heat transfer in mini/micro thermal systems. In the present study, an attempt has been made to gain deep insight of the heat transfer characteristics of single-phase ferrofluid flow in a heated stainless steel tube under the influence of constant and time-varying magnetic field. The governing parameters are mainly the magnetic flux density (B) and perturbation frequency (f) of the applied magnetic field. Three magnetic flux density value of B = 0 G, 700 G and 1080 G have been used for constant magnetic field. Constant value of B = 1080 G was used for alternating magnetic field while, frequencies of applied magnetic field has been varied from 0.1 Hz to 5 Hz. Flow Reynolds number was kept constant to Re = 66. Some 2-D numerical simulations have also been performed to qualitatively support the experimental data. The study is focused to delineate the mechanism of augmentation of heat transfer through the interaction of available force fields, i.e., interplay of magnetic force and inertia of the flow, and also the effect of various time scales on the flow and thermal behavior. Major inferences of the study are (a) on the application of external magnetic (constant and alternating), heat transfer augments (b) existence of a threshold frequency of external magnetic field for maximum augmentation as outcome of advective time-scale and magnetic perturbation time-scale. InfraRed Thermography (IRT) has been used to measure the wall temperature, while, some bright field visualizations have also been done to qualitatively support the explanations of experimental data.

Numerical Investigation of Bone Tumor Hyperthermia Treatment Using Magnetic Scaffolds

This works claims to define, via numerical simulations, magnetic field parameters to perform an effective in situ bone tumor hyperthermia treatment using magnetic scaffolds. A Cole-Cole model to describe the frequency response of the magnetic susceptibility of nanoparticles embedded in novel magnetic biomaterials is explored. The heating phenomenon is investigated, considering both the ischemic and inflamed state of the fracture gap at the bone/implants interface. Both Osteosarcoma and Fibrosarcoma tumors are analyzed. Magnetic hydroxyapatite and poly-ϵ-caprolactone scaffolds are investigated. From the thermal analysis, it is found that the fracture behaves as a resistance to heat conduction, and therefore, strength and frequency of external magnetic field has to be tuned to perform the treatment taking the fracture status into account. Moreover, numerical experiments indicate that low perfused Fibrosarcoma can be treated using moderate-strength field, whereas more intense external fields are required to treat strongly vascularized Osteosarcoma without damaging healthy bone tissue. Magnetic hydroxyapatite stands out to be the best performing and versatile material to treat both tumors. These simulations can be regarded as a starting point to analyze possible clinical use of magnetic scaffolds for in situ bone hyperthermia.

A novel frequency tuned wireless actuator with snake-like motion

In this work, we propose a novel wireless actuator which is composed of magnetostrictive material/copper bi-layer film. The actuator can be controlled to move like a snake bi-directionally along a pipe by tuning the frequency of external magnetic field near its first order resonant frequency. The governing equation for the actuator is established and the vibration mode shape function is derived. Theoretical analysis shows that motion of the actuator is achieved by asymmetric vibration mode shape, specific vibration bending deformation, and effective net total impacting force. The simulation and experimental results well confirm the theoretical analysis. This work provides contribution to the development of wireless micro robots and autonomous magnetostrictive sensors.

Rashba coupling induced spin susceptibility and magnetic phase transition of conduction electrons in monolayer graphene

Isolated graphene cannot be obtained by the known synthesis processes and it should be placed on a substrate. This substrate introduces a new type of spin–orbit interaction known as Rashba coupling. Using the Kubo formalism, the magnetic properties of the system in the linear regime have been investigated. Mainly the effect of non-magnetic substrate on the spin susceptibility is calculated. Results show that the Rashba coupling has a central role in the magnetic response function of the system and it is really remarkable since this type of spin orbit coupling can be effectively controlled by an external gate voltage. Most importantly, it was shown that, in the presence of the Rashba interaction a magnetic phase transition could be observed. This magnetic phase corresponds to a magnetic order of conduction electrons that takes place at some special frequencies of external magnetic field.

Thermal properties of a particle confined to a parabolic quantum well in two-dimensional space with conical disclination

The thermal properties of a system, comprising of a spinless noninteracting charged particle in the presence of a constant external magnetic field and confined in a parabolic quantum well are studied. The focus has been on the effects of a topological defect, of the form of conical disclination, with regard to the thermodynamic properties of the system. We have obtained the modifications to the traditional Landau-Fock-Darwin spectrum in the presence of conical disclination. The effect of the conical kink on the degeneracy structure of the energy levels is investigated. The canonical formalism is used to compute various thermodynamic variables. The study shows an interplay between magnetic field, temperature, and the degree of conicity by setting two scales for temperature corresponding to the frequency of the confining potential and the cyclotron frequency of external magnetic field. The kink parameter is found to affect the quantitative behavior of the thermodynamic quantities. It plays a crucial role in the competition between the external magnetic field and temperature in fixing the values of the thermal response functions. This study provides an important motivation for studying similar systems, however with nontrivial interactions in the presence of topological defects.

Nearly complete regression of tumors via collective behavior of magnetic nanoparticles inhyperthermia

One potential cancer treatment selectively deposits heat to the tumor through activation ofmagnetic nanoparticles inside the tumor. This can damage or kill the cancer cells withoutharming the surrounding healthy tissue. The properties assumed to be most important forthis heat generation (saturation magnetization, amplitude and frequency of externalmagnetic field) originate from theoretical models that assume non-interactingnanoparticles. Although these factors certainly contribute, the fundamental assumption of‘no interaction’ is flawed and consequently fails to anticipate their interactions withbiological systems and the resulting heat deposition. Experimental evidence demonstratesthat for interacting magnetite nanoparticles, determined by their spacing and anisotropy,the resulting collective behavior in the kilohertz frequency regime generates significantheat, leading to nearly complete regression of aggressive mammary tumors in mice.

Shielding of AC Magnetic Fields by Coils and Sheets of Superconducting Tapes

Magnetic field shielding properties of coils and sheets of silver sheathed (Bi,Pb)2Sr2Ca2Cu3O10+x tapes (1G superconductor tapes) and YBa2Cu3O7 coated conductors (2G superconductor tapes) are reported. Shielding properties were measured at 77 K, with varying field amplitude and frequency of external magnetic field, using Hall probes and a phase sensitive technique. Shielding factor data on several coils and sheets are presented as a function of external field amplitude and frequency. Magnetic field shielding of up to 50% was observed at field amplitudes of < 10 mT. Differences in frequency dependence of shielding properties of test shields fabricated from 1G and 2G conductors are discussed.

Dynamic hysteresis of magnetic aggregates with non-integer dimension

We investigate the dynamic hysteresis of nanoscale magnetic aggregates by employing Monte Carlo simulation, based on Ising model in non-integer dimensional space. The diffusion-limited aggregation (DLA) model with adjustable sticking probability is used to generate magnetic aggregates with different fractal dimension D. It is revealed that the exponential scaling law A( H 0, ω)∼ H 0 α ·ω β , where A is the hysteresis area, H 0 and ω the amplitude and frequency of external magnetic field, applies to both the low- ω and high- ω regimes, while exponents α and β decrease with increasing D in the low- ω regime and keep invariant in the high- ω regime. A mean-field approach is developed to explain the simulated results.

813 磁場の正弦的時間変動を受ける導体長方形柱の電磁熱弾性問題 : 非定常熱弾性挙動に及ぼす外部磁場の変動周波数の効果(GS-3 熱応力・熱弾性(1))

813 磁場の正弦的時間変動を受ける導体長方形柱の電磁熱弾性問題 : 非定常熱弾性挙動に及ぼす外部磁場の変動周波数の効果(GS-3 熱応力・熱弾性(1))

Visualization of coupling current paths in striated YBCO-coated conductors at frequenciesup to 400 Hz

The magnetic flux density component perpendicular to the broad tape face was mapped byminiature Hall probes in the vicinity of a striated YBCO-coated tape at frequencies ofexternal magnetic field from 21 to 400 Hz, applied perpendicularly to the tapesurface. For reasons of modelling the coupling current behaviour in tapes with aconductive substrate, we amplified the coupling current–amplitude by soldering25 µm thick copper foil on the top of the filaments. The aim of this procedure was to decrease thetransverse resistivity of the tape. The longitudinal components of the total currents flowingin the tape were calculated by an inverse method from the field map corresponding to thezero phase of the applied field. The diffusion lengths, characterizing the flux penetrationinto the tape, were determined for the respective frequencies. The experimentallydetermined diffusion length is in good accordance with theoretical models. While at 21 Hzboth weak coupling currents and distinctive hysteretic currents of individual filaments areobserved, at 400 Hz the coupling currents are predominant in this YBCO tape.

Magnetic Fluid Devices for Driving Micro Machines

This paper is concerned with the development of micro magnetic fluid devices for driving micro machines. Two kinds of new magnetic fluid devices are proposed. One is the magnetic fluid motor, and another one is reciprocating actuator. These micro devices are composed of a permanent NdFeB magnet and kerosene-based magnetic fluid HC-50. They are characterized by wireless operation with alternating magnetic field. The driving characteristics of micro magnetic fluid devices are examined by using a digital high speed video camera system. The rotary motion of the micro magnetic fluid motor shows the existence of rotational regions and irrotational regions in frequencies of external magnetic field. The amplitude of reciprocating actuator depends on the frequency of magnetic field. The effect of the volume of magnetic fluid adsorbed to the permanent magnet is also revealed experimentally.

Generation of large Barkhausen jump in bilayered thin film

A pulse voltage of half-amplitude width of approximately 20 /spl mu/s was induced in a detecting coil wound around a wire by large Barkhausen effect, when torsional stress and AC external magnetic field were applied to Fe-Co-V fine wires. Effective characteristics of the pulse voltage, the pulse amplitude and the pulse width were found not depend on frequency of external magnetic field. Based on this phenomenon, a unique magnetic sensor was developed for a flow meter. In this study, the bilayered thin films with several different coercive forces and residual stresses were fabricated in order to simulate the Barkhausen effect in the thin film. As a result we observed a large Barkhausen jump in the bilayered film having the upper layer in tension and the lower layer in compression. The induced pulse voltages are not dependent on the external magnetic field frequency.