Magnetic Field Parallel Research Articles

Body-loop related MRI radiofrequency-induced heating hazards: Observations, characterizations, and recommendations.

To assess RF-induced heating hazards in 1.5T MR systems caused by body-loop postures. Twelve advanced high-resolution anatomically correct human body models with different body-loop postures are created based on poseable human adult male models. Numerical simulations are performed to assess the radiofrequency (RF)-induced heating of these 12 models at 11 landmarks. A customized phantom is developed to validate the numerical simulations and quantitatively analyze factors affecting the RF-induced heating, eg, the contact area, the loop size, and the loading position. The RF-induced heating inside three differently posed phantoms is measured. The RF-induced heating from the body-loop postures can be up to 11 times higher than that from the original posture. The RF-induced heating increases with increasing body-loop size and decreasing contact area. The magnetic flux increases when the body-loop center and the RF coil isocenter are close to each other, leading to increased RF-induced heating. An air gap created in the body loop or generating a polarized magnetic field parallel to the body loop can reduce the heating by a factor of three at least. Experimental measurements are provided, validating the correctness of the numerical results. Safe patient posture during MR examinations is recommended with the use of insulation materials to prevent loop formation and consequently avoiding high RF-induced heating. If body loops cannot be avoided, the body loop should be placed outside the RF transmitting coil. In addition, linear polarization with magnetic fields parallel to the body loop can be used to circumvent high RF-induced heating.

Magneto-Endosomalytic Therapy for Cancer.

A remarkably simple yet effective mode of cancer treatment is reported by repurposing clinically approved magnetic nanoparticles (MNPs). Intracellular nanoparticle self-assembly directed by static parallel magnetic fields leads to cell death in targeted tissues while leaving other cells and organs intact. This simple concept opens a new avenue to treat cancer, capitalizing on nanosciences and the nanoparticle (NP) design principles accumulated in the past decades.

Balmer-series spectral lines for hydrogen atoms in parallel magnetic and electric fields of white dwarfs

ABSTRACT We extended the two-dimensional B-spline approach recently developed to investigate the influence of a strong electric field on atomic structures and spectra for hydrogen atoms in magnetic fields of white dwarfs. Spectral lines for hydrogen in parallel magnetic and electric fields have been calculated. Wavelengths and oscillator strengths are presented for 14 Balmer α transitions as a function of magnetic and electric fields. The magnetic and electric field strengths involved span a scope, respectively, from around 23.5 to 2350 MG, and from 0 to 108 V/m. Our calculations show that the shift of Balmer-series spectral lines induced by a strong electric field reduces as the magnetic field strength increases. The obtained energy levels, wavelengths, and oscillator strengths are compared to available results in the literature, and excellent agreement was discovered. The spectral data reported in this paper can be applied to interpret the shifts of spectral lines of hydrogen in magnetic white dwarfs due to the presence of electric fields, and to predict additional spectral lines dipole-forbidden in a pure magnetic field.

Full parity phase diagram of a proximitized nanowire island

We measure the charge periodicity of Coulomb blockade conductance oscillations of a hybrid InSb-Al island as a function of gate voltage and parallel magnetic field. The periodicity changes from $2e$ to $1e$ at a gate-dependent value of the magnetic field, $B^*$, decreasing from a high to a low limit upon increasing the gate voltage. In the gate voltage region between the two limits, which our numerical simulations indicate to be the most promising for locating Majorana zero modes, we observe correlated oscillations of peak spacings and heights. For positive gate voltages, the $2e$-$1e$ transition with low $B^*$ is due to the presence of non-topological states whose energy quickly disperses below the charging energy due to the orbital effect of the magnetic field. Our measurements demonstrate the importance of a careful exploration of the entire available phase space of a proximitized nanowire as a prerequisite to define future topological qubits.

Electromagnetic turbulence in increased β plasmas in the Large Plasma Device

The variation of pressure-gradient-driven turbulence with plasma $\beta$ (up to $\beta \approx 15\,\%$ ) is investigated in linear, magnetized plasma. The magnitude of magnetic fluctuations is observed to increase substantially with increasing $\beta$ . More importantly, parallel magnetic fluctuations are observed to dominate at higher $\beta$ values, with $\delta B_\parallel / \delta B_\perp \approx 2$ and $\delta B / B_0 \approx 1\,\%$ . Parallel magnetic fluctuations are strongly correlated with density fluctuations and the two are observed to be out of phase. The relative magnitude of and cross-phase between density and parallel magnetic field fluctuations are consistent with the dynamic pressure balance ( $P+{B_{0}^2}/{2\mu _0} = \textrm {constant}$ ). A local slab model theory for electromagnetic, modified drift Alfvén waves, including parallel magnetic fluctuations, shows partial agreement with experimental observations.

Existence of electron–hole charge puddles and the observation of strong universal conductance fluctuations in a 3D topological insulator

Phase-coherent transport manifests itself in various quantum phenomena. Universal conductance fluctuations (UCF) are one of them. Here, we report the detailed study of dephasing of electronic wavefunction by analyzing UCF and weak antilocalization in a device, made by exfoliation from a bulk insulating topological insulator single crystal (Bi1Sb1Te1.5Se1.5). From the parallel magnetic field measurement, we proved that the quantum phenomena in our sample are caused by surface Dirac electrons. Our sample showed very slow dephasing of electronic wavefunction, which has rarely been observed in topological insulator materials. This kind of dephasing indicates the presence of electron–hole charge puddles in our system. The RMS amplitude of the UCF is also surprisingly higher (13 e2h) than the universal value of the conductance fluctuation (e2h) and the fluctuations persist in our sample until the temperature as high as 20 K and above. We also show that the shape of the flake has a significant impact on the prefactor, α, of the Hikami–Larkin–Nagaoka equation. Moreover, the formation of Aharonov–Bohm loops of different areas is responsible for UCF. By analyzing the fast Fourier transform of the UCF data, we have obtained these Aharonov–Bohm loops which are contributing to the UCF.

Many-Electron System on Helium and Color Center Spectroscopy.

Electrons on the helium surface display sharp resonant absorption lines related to the transitions between the subbands of quantized motion transverse to the surface. A magnetic field parallel to the surface strongly affects the absorption spectrum. We show that the effect results from admixing the intersubband transitions to the in-plane quantum dynamics of the strongly correlated electron liquid or a Wigner crystal. This is similar to the admixing of electron transitions in color centers to phonons. The spectrum permits a direct characterization of the many-electron dynamics and also enables testing the theory of color centers in a system with controllable coupling.

Tuning superconductivity in Ge:Ga using Ga+ implantation energy

High-fluence gallium $({\mathrm{Ga}}^{+})$ implantation at medium energies is proven to be an effective tool in forming superconducting (SC) thin films in germanium (Ge). By changing the post-implantation annealing conditions nanocrystalline to single-crystalline Ge matrices have been produced. Irrespective of crystallinity, such processes have mostly led to supersaturated Ge:Ga films where superconductivity is controlled by the extent of coherent coupling between Ga precipitates. Here we use ${\mathrm{Ga}}^{+}$ implantation energy as a means to tailor the spatial distribution and the coupling energy of the Ga precipitates. By systematic structural and magneto-transport studies, we unravel the complex connection between the internal structure of Ge:Ga films and their global SC parameters. At the shallowest implantation depth, we observe the strongest coupling leading to a robust superconductivity that sustains parallel magnetic fields as high as 9.95 T, above the conventional Pauli paramagnetic limit and consistent with a quasi-2D geometry. Further measurements at mK temperatures revealed an anomalous upturn in perpendicular critical field ${\mathrm{B}}_{\ensuremath{\perp}}$ vs temperature whose curvature and thus origin may be tuned between weakly coupled SC arrays and vortex glass states with quenched disorder. This warrants future investigations into Ge:Ga films for applications where tunable disorder is favorable, including test-beds for quantum phase transitions and superinductors in quantum circuits.

Chiral symmetry restoration and deconfinement in the contact interaction model of quarks with parallel electric and magnetic fields

We study the impact of steady, homogeneous, and external parallel electric and magnetic field strengths ( ) on the chiral symmetry breaking-restoration and confinement-deconfinement phase transition. We also sketch the phase diagram of quantum chromodynamics (QCD) at a finite temperature T and in the presence of background fields. The unified formalism for this study is based on the Schwinger-Dyson equations, symmetry preserving vector-vector contact interaction model of quarks, and an optimal time regularization scheme. At , in the purely magnetic case (i.e., ), we observe the well-known magnetic catalysis effect. However, in a pure electric field background ( ), the electric field tends to restore the chiral symmetry and deconfinement above the pseudo-critical electric field . In the presence of both and , we determine the magnetic catalysis effect in the particular region where dominates over , whereas we observe the chiral inhibition (or electric chiral rotation) effect when overshadows eB. At finite T, in the pure electric field case, the phenomenon of inverse electric catalysis appears to exist in the proposed model. Conversely, for a pure magnetic field background, we observe the magnetic catalysis effect in the mean-field approximation and inverse magnetic catalysis with -dependent coupling. The combined effects of and on the pseudo-critical yields an inverse electromagnetic catalysis, with and without an -dependent effective coupling of the model. The findings of this study agree well with the already predicted results obtained via lattice simulations and other reliable effective models of QCD.

Magneto-transport properties of thin flakes of Weyl semiconductor tellurium* *Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDC07010000), the National Natural Science Foundation of China (Grant Nos. 11974324, U1832151, 11804326, and 11904001), the National Key Research and Development Program of China (Grant No. 2017YFA0403600), the Anhui Initiative Fund in Quantum Information Technologies

As an elemental semiconductor, tellurium has recently attracted intense interest due to its non-trivial band topology, and the resulted intriguing topological transport phenomena. In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process. The sample is self-hole-doped, and exhibits typical weak localization behavior at low temperatures. Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region, which is considered to share the same origin with that in tellurium bulk crystals, i.e., the Weyl points near the top of valence band. However, with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency, differing distinctly from the bulk counterparts. Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures. Our results further extend Weyl physics into a low-dimensional semiconductor system, which may find its potential application in designing topological semiconductor devices.

Quasi-isotropic orbital magnetoresistance in lightly doped SrTiO3

A magnetic field parallel to an electrical current does not produce a Lorentz force on the charge carriers. Therefore, orbital longitudinal magnetoresistance is unexpected. Here we report on the observation of a large and non saturating magnetoresistance in lightly doped SrTiO$_{3-x}$ independent of the relative orientation of current and magnetic field. We show that this quasi-isotropic magnetoresistance can be explained if the carrier mobility along all orientations smoothly decreases with magnetic field. This anomalous regime is restricted to low concentrations when the dipolar correlation length is longer than the distance between carriers. We identify cyclotron motion of electrons in a potential landscape tailored by polar domains as the cradle of quasi-isotropic orbital magnetoresistance. The result emerges as a challenge to theory and may be a generic feature of lightly-doped quantum paralectric materials.

Gap-Opening Transition in Dirac Semimetal ZrTe_{5}.

We apply ^{125}Te nuclear magnetic resonance (NMR) spectroscopy to investigate the Dirac semimetal ZrTe_{5}. With the NMR magnetic field parallel to the b axis, we observe significant quantum magnetic effects. These include an abrupt drop at 150K in spin-lattice relaxation rate. This corresponds to a gap-opening transition in the Dirac carriers, likely indicating the onset of excitonic pairing. Below 50K, we see a more negative shift for the Te_{z} bridging site, indicating the repopulation of Dirac levels with spin polarized carriers at these temperatures. This is the previously reported 3D quantum Hall regime; however, we see no sign of a charge density wave as has been proposed.

Thermal chiral anomaly in the magnetic-field-induced ideal Weyl phase of Bi1-xSbx.

The chiral anomaly is the predicted breakdown of chiral symmetry in a Weyl semimetal with monopoles of opposite chirality when an electric field is applied parallel to a magnetic field. It occurs because of charge pumping between monopoles of opposite chirality. Experimental observation of this fundamental effect is plagued by concerns about the current pathways. Here we demonstrate the thermal chiral anomaly, energy pumping between monopoles, in topological insulator bismuth-antimony alloys driven into an ideal Weyl semimetal state by a Zeeman field, with the chemical potential pinned at the Weyl points and in the absence of any trivial Fermi surface pockets. The experimental signature is a large enhancement of the thermal conductivity in an applied magnetic field parallel to the thermal gradient. This work demonstrates both pumping of energy and charge between the two Weyl points of opposite chirality and that they are related by the Wiedemann-Franz law.

C-Term Faraday Rotation in Metallocene Containing Thin Films.

The Faraday effect is a magneto-optical (MO) phenomenon that causes the plane of linearly polarized light to rotate when passing through a medium subjected to a parallel magnetic field. Informed by the established quantum mechanical model developed by Buckingham and Stephens, we sought to identify molecules that would exhibit large MO responses. Magnetic circular dichroism studies of ferrocenium in the 1970s revealed its potential as an MO material; however, it has not been evaluated in the context of Faraday rotation and thin-film optical applications. Herein, we report near-infrared (NIR) Faraday rotation in thin films of decamethylferrocenium/poly(methyl methacrylate) composites with maximum Verdet constants of -3.45 × 104 deg T-1 m-1 at 810 nm (absorbance = 0.09) and -1.44 × 104 deg T-1 m-1 at 870 nm (absorbance = 0.01). These polymer-metallocene thin films deliver larger Verdet constants than commercially used NIR inorganic Faraday rotators and are facile and inexpensive to produce. The temperature dependence and distinct lineshape of the MO responses observed in decamethylferrocenium radical cations, decamethylmanganocene, and chromocene are in accordance with the quantum mechanical model. The observation of a strong C-term Faraday rotation in solid-state organometallic materials provides the groundwork for the development of high-performance metallocene-based Faraday rotators.

Effect of transverse and parallel magnetic fields on thermal and thermo-hydraulic performances of ferro-nanofluid flow in trapezoidal microchannel heat sink

Purpose This paper aims to study the thermal and thermo-hydraulic performances of ferro-nanofluid flow in a three-dimensional trapezoidal microchannel heat sink (TMCHS) under uniform heat flux and magnetic fields. Design/methodology/approach To investigate the effect of direction of Lorentz force the magnetic field has been applied: transversely in the x direction (Case I);transversely in the y direction (Case II); and parallel in the z direction (Case III). The three-dimensional governing equations with the associated boundary conditions for ferro-nanofluid flow and heat transfer have been solved by using an element-based finite volume method. The coupled algorithm has been used to solve the velocity and pressure fields. The convergence is reached when the accuracy of solutions attains 10–6 for the continuity and momentum equations and 10–9 for the energy equation. Findings According to thermal indicators the Case III has the best performance, but according to performance evaluation criterion (PEC) the Case II is the best. The simulation results show by increasing the Hartmann number from 0 to 12, there is an increase for PEC between 845.01% and 2997.39%, for thermal resistance between 155.91% and 262.35% and ratio of the maximum electronic chip temperature difference to heat flux between 155.16% and 289.59%. Also, the best thermo-hydraulic performance occurs at Hartmann number of 12, pressure drop of 10 kPa and volume fraction of 2%. Research limitations/implications The embedded electronic chip on the base plate generates heat flux of 60 kW/m2. Simulations have been performed for ferro-nanofluid with volume fractions of 1%, 2% and 3%, pressure drops of 10, 20 and 30 kPa and Hartmann numbers of 0, 3, 6, 9 and 12. Practical implications The authors obtained interesting results, which can be used as a design tool for magnetohydrodynamics micro pumps, microelectronic devices, micro heat exchanger and micro scale cooling systems. Originality/value Review of the literature indicated that there has been no study on the effects of magnetic field on thermal and thermo-hydraulic performances of ferro-nanofluid flow in a TMCHS, so far. In this three dimensional study, flow of ferro-nanofluid through a trapezoidal heat sink with five trapezoidal microchannels has been considered. In all of previous studies, in which the effect of magnetic field has been investigated, the magnetic field has been applied only in one direction. So as another innovation of the present research, the effect of applying magnetic field direction (transverse and parallel) on thermo-hydraulic behavior of TMCHS is investigated.

Comparison of 3-D and 2-D models of a soft magnetic composite material

In this article, we compare 3-D finite element models of a soft magnetic composite (SMC) material to 2-D models, obtained by slicing some 2-D intersections of the 3-D geometries, in terms of magnetization curves and losses. A 3-D nonlinear static model, providing computational B-H curves, is compared to two 2-D models, one with the magnetic field parallel to the 2-D plane, and the other with the magnetic field perpendicular to the 2-D plane. We find that the 2-D models provide largely inconsistent results with the 3-D model. A 3-D time-harmonic model, providing computational effective permeabilities and losses, is compared to two 2-D models, one with the magnetic field parallel to the 2-D plane, and the other with the magnetic field perpendicular to the 2-D plane. We find that the 2-D models provide largely inconsistent results with the 3-D model, with an exception of the computational losses of the 2-D model, with the magnetic field perpendicular to the plane, almost agreeing with the computational losses provided by the 3-D model. However, the computational permeabilities do not match in these two models. This article proposes to be very critical before publishing 2-D models of SMC materials without a proper justification by symmetry.

Experimental signatures of the chiral anomaly in Dirac–Weyl semimetals

We provide a review of recent experimental results on the chiral anomaly in Dirac/Weyl semimetals. After a brief introduction, we trace the steps leading to the prediction of materials that feature protected 3D bulk Dirac nodes. The chiral anomaly is presented in terms of charge pumping between the chiral Landau levels of Weyl fermions in parallel electric and magnetic fields. The related chiral magnetic effect and chiral zero sound are described. Current jetting effects, which present major complications in experiments on the longitudinal magnetoresistance, are carefully analyzed. We describe a recent test that is capable of distinguishing these semiclassical artifacts from intrinsic quantum effects. Turning to experiments, we review critically the longitudinal magnetoresistance experiments in the Dirac/Weyl semimetals Na3Bi, GdPtBi, ZrTe5 and TaAs. Alternate approaches to the chiral anomaly, including experiments on non-local transport, thermopower, thermal conductivity and optical pump-probe response are reviewed. In the Supplement, we provide a brief discussion of the chiral anomaly in the broader context of high energy physics and relativistic quantum field theory, as well the anomaly's starring role at the nexus of quantum physics and differential geometry.

Effects of loading a magnetic field longitudinal to the linear particle-beam track on yields of reactive oxygen species in water

The effects of a magnetic field longitudinal to the ion beam track on the generation of hydroxyl radicals (•OH) and hydrogen peroxide (H2O2) in water were investigated. A longitudinal magnetic field was reported to enhance the biological effects of the ion beam. However, the mechanism of the increased cell death by a longitudinal magnetic field has not been clarified. The local density of •OH generation was estimated by a method based on the EPR spin-trapping. A series of reaction mixtures containing varying concentrations (0.76‒2278 mM) of DMPO was irradiated by 16 Gy of carbon- or iron-ion beams at the Heavy-Ion Medical Accelerator in Chiba (HIMAC, NIRS/QST, Chiba, Japan) with or without a longitudinal magnetic field (0.0, 0.3, or 0.6 T). The DMPO-OH yield in the sample solutions was measured by X-band EPR and plotted versus DMPO density. O2-dependent and O2-independent H2O2 yields were measured. An aliquot of ultra-pure water was irradiated by carbon-ion beams with or without a longitudinal magnetic field. Irradiation experiments were performed under air or hypoxic conditions. H2O2 generation in irradiated water samples was quantified by an EPR spin-trapping, which measures •OH synthesized from H2O2 by UVB irradiation. Relatively sparse •OH generation caused by particle beams in water were not affected by loading a magnetic field on the beam track. O2-dependent H2O2 generation decreased and oxygen-independent H2O2 generation increased after loading a magnetic field parallel to the beam track. Loading a magnetic field to the beam track made •OH generation denser or made dense •OH more reactive.

Coalescence of Andreev Bound States on the Surface of a Chiral Topological Semimetal

We experimentally investigate the magnetic field dependence of Andreev transport through a region of proximity-induced superconductivity in the CoSi topological chiral semimetal. With increasing magnetic field parallel to the CoSi surface, the sharp subgap peaks, associated with Andreev bound states, move together to nearly-zero bias position, while there is only monotonic peaks suppression for normal to the surface fields. The zero-bias $$dV{\text{/}}dI$$ resistance value is perfectly stable with changing the in-plane magnetic field. As the effects are qualitatively similar for In and Nb superconducting leads, they reflect the properties of a proximized CoSi surface. The Andreev states coalescence and stability of the zero-bias $$dV{\text{/}}dI$$ value with increasing in-plane magnetic field are interpreted as the joined effect of the strong spin–orbit coupling and the Zeeman interaction, known for proximized semiconductor nanowires. We associate the observed magnetic field anisotropy with the recently predicted in-plane polarized spin texture of the Fermi arcs surface states.

The effect of magnetic field on the dynamics of gas bubbles in water electrolysis

This study determines the effect of the configuration of the magnetic field on the movement of gas bubbles that evolve from platinum electrodes. Oxygen and hydrogen bubbles respectively evolve from the surface of the anode and cathode and behave differently in the presence of a magnetic field due to their paramagnetic and diamagnetic characteristics. A magnetic field perpendicular to the surface of the horizontal electrode causes the bubbles to revolve. Oxygen and hydrogen bubbles revolve in opposite directions to create a swirling flow and spread the bubbles between the electrodes, which increases conductivity and the effectiveness of electrolysis. For vertical electrodes under the influence of a parallel magnetic field, a horizontal Lorentz force effectively detaches the bubbles and increases the conductivity and the effectiveness of electrolysis. However, if the layout of the electrodes and magnetic field results in upward or downward Lorentz forces that counter the buoyancy force, a sluggish flow in the duct inhibits the movement of the bubbles and decreases the conductivity and the charging performance. The results in this study determine the optimal layout for an electrode and a magnetic field to increase the conductivity and the effectiveness of water electrolysis, which is applicable to various fields including energy conversion, biotechnology, and magnetohydrodynamic thruster used in seawater.