Magnetic Pulse Research Articles

Three-dimensional multicontrast blood imaging with a single acquisition: Simultaneous non-contrast-enhanced MRA and vessel wall imaging in the thoracic aorta.

To evaluate MRA and vessel wall imaging (VWI) image quality in the thoracic aorta using a novel method named BRIDGE (bright and dark blood images with multishot gradient-echo EPI). The BRIDGE method consists of 3D multishot gradient-echo EPI acquisition using pulse gating, navigator gating, and magnetization preparation with a T2 -preparation pulse and a nonselective inversion-recovery pulse. The BRIDGE and conventional methods (noncontrast MRA based on 3D turbo-field-echo [TFE] and VWI based on 3D turbo spin echo with variable refocusing flip angle [VRFA-TSE]) were performed in 10 healthy volunteers and 10 patients. The SNR, contrast-to-noise ratio (CNR), and sharpness in the thoracic aorta were compared for MRA evaluation. The values of SNRlumen , SNRwall , CNRwall-lumen , contrast ratio (CR)lumen-muscle , coefficient of variation, sharpness, lumen area, and wall area in the thoracic aorta were compared for VWI evaluation. Two radiologists independently performed qualitative image-analysis assessments. When MRA and VWI were acquired, the acquisition time was 26.6% to 27.8% shorter with BRIDGE than the conventional method. In the MRA evaluation, BRIDGE and TFE methods were comparable. In the VWI evaluation, BRIDGE was superior to the VRFA-TSE method in blood suppression and evaluation of the ascending aorta. Because the blood signal suppression of BRIDGE is based on the T1 value of blood, the blood signal can be suppressed more uniformly than with the VRFA-TSE method, regardless of age, blood flow velocity, or vascular anatomy. The BRIDGE method can provide both MRA, to assess vascular anatomy and luminal changes, and VWI, to assess the vessel wall and detect vulnerable plaques, in a single scan.

Significance of diagnostic transcranial magnetic stimulation during radiotherapy

Background. Transcranial magnetic stimulation is a non-invasive, painless method that stimulates the cerebral cortex using short magnetic pulses. The information obtained as a result of the research can be further used for an objective assessment of the therapy.
 Aim. Evaluation the reliability of transcranial magnetic stimulation technique as a neurophysiological monitoring tool in patients with malignant brain tumors.
 Material and methods. There were two groups as a study objects: patients with large-focal solitary lesions of the central nervous system (glioma) who underwent radiotherapy (n=20), median age 49.55.3 (39; 60) years, and a comparison group of neurologically healthy individuals (n=16), median age 48.56.3 (43.0; 58.8) years. There were no statistically significant age differences between the studied groups. All patients underwent diagnostic transcranial magnetic stimulation before and after therapy. The MannWhitney test was used to make comparisons between the two groups. A p value 0.05 was considered statistically significant.
 Results. During transcranial magnetic stimulation in patients with malignant brain neoplasms, signs of impaired conduction along the central motor pathways were recorded in 50% of cases, and in total, signs of impaired conduction of all degrees of severity along the central motor pathway were detected in 90% of cases. Carrying out diagnostic transcranial magnetic stimulation according to a single-pulse protocol makes it possible to predict the further course of the recovery period. The use of transcranial magnetic stimulation in dynamics revealed an improvement in conduction along the central motor pathways in patients with malignant brain neoplasms. The obtained statistically significant differences allow us to conclude that transcranial magnetic stimulation can be used for an objective assessment of the state of the motor pathways in patients with neurooncological diseases.
 Conclusion. Diagnostic transcranial magnetic stimulation is applicable in large-focal solitary lesions of the central nervous system, since it allows assessing the state of the motor pathways and the functional activity of the brain at different stages of this condition.

Generation of travelling sine-Gordon breathers in noisy long Josephson junctions

The generation of travelling sine-Gordon breathers is achieved through the nonlinear supratransmission effect in a magnetically driven long Josephson junction, in the presence of losses, a current bias, and a thermal noise source. We demonstrate how to exclusively induce breather modes by means of controlled magnetic pulses. A nonmonotonic behavior of the breather-only generation probability is observed as a function of the noise intensity. An experimental protocol providing evidence of the Josephson breather's existence is proposed.

Coupled multiphysics modeling of the thermal-magnetic-mechanical instability behavior in bulk superconductors during pulsed field magnetization

Magnetization is of great importance for the application of bulk superconductors. Flux jumps are frequently-encountered challenges during magnetization, leading to sharp temperature rises and material failure, and eventually affecting the field trapping capability of bulk superconductors. Intrinsically, the flux jumps and mechanical failure induced by thermomagnetic instability are coupled with each other, which makes the numerical simulation of the magnetization of bulk superconductors a challenging task. In this paper, a numerical simulation framework is developed based on my previous work (Jing 2020 Supercond. Sci. Technol. 33 075009), which further couples the H-formulation and the phase-field fracture model with the heat diffusion equation to simulate the flux jump and mechanical failure behaviors of bulk superconductors during magnetization. The experimentally observed features of the flux jumps are reproduced, and the corresponding mechanical failure is evaluated. The magnetic field, temperature, stress/strain, and mechanical failure within the bulk sample are presented. It is found that the varying ramp rate of the pulsed field significantly influences the flux jump behaviors of bulk superconductors. The optimum characteristic time of the pulsed field for the final trapped field is predicted through numerical simulations.

Generating 77 T using a portable pulse magnet for single-shot quantum beam experiments

We devised a portable system that generates pulsed high magnetic fields up to 77 T with 3 μs duration. The system employs the single turn coil method, a destructive way of field generation. The system consists of a capacitor of 10.4 μF, a 30 kV charger, a mono air-gap switch, a triggering system, and a magnet clamp, which weighs less than 1.0 tons in total and is transportable. The system offers opportunities for single-shot experiments at ultrahigh magnetic fields in combinations with novel quantum beams. The single-shot x-ray diffraction experiment using a x-ray free-electron laser at 65 T is presented. We comment on the possible update of the system for the generation of 100 T.

Magnetoporation: New Method for Permeabilization of Cancerous Cells to Hydrophilic Drugs.

Background: In the present study, we investigated the application of pulsed magnetic field (MF) (3.5 T, 1 Hz, 8 square-wave/160 µs) permeabilization on murine breast adenocarcinoma cells when administering bleomycin (BLM) in vivo.Objective: This cross-over study aims to find a noninvasive method to facilitate penetration of hydrophilic anti-cancer drugs through the cancerous cells membrane into the cytosoll in order to minimize the side effects of the chemotherapy treatments of tumors.Material and Methods: In this cross-over study, a total of 50 female Balb/c mice were tumorized via homograft. After about 2 weeks, magnetic pulses (3.5 T, 1 Hz, 8 square-wave/160 µs) were applied to tumor-bearing mice 3 min after intratumoral BLM solution injection. Tumor volume was measured every 48 h during 22 days.Results: The results showed that the difference between the BLM plus 3.5 T MF group versus the sham control or sham MF groups was significant. Uptake of BLM molecules by tumoral cells in the BLM plus 3.5 T MF group versus the BLM control group was 7- folds higher that this result was statistically insignificant (P<0.05, SEM=266.8676, analysis of variance).Conclusion: Significant cell permeabilization to BLM requires greater MF strength or exposure time. Further investigation is necessary.

Higher-order fractional and memory response in nonlocal double poro-magneto-thermoelastic medium with temperature-dependent properties excited by laser pulse

The present study intends to analyze the transient phenomena in a one-dimensional half-space consisting of nonlocal double poro-magneto-thermoelastic material with voids (DPMTMWV) influenced by non-Gaussian laser pulse heating subjected to temperature-dependent material properties. The higher-order Taylor’s series expansion of Fourier’s law including fractional and memory-dependent derivatives with dual-phase-lags are employed. The analytical expressions of the field variables are derived with the help of Laplace transform and numerical inversions via Zakian’s algorithm. The impacts of magnetic field, laser pulse, nonlocality parameter, and temperature-dependent properties are graphically implemented with respect to the comparative observation between fractional and memory responses. Moreover, three different generalized thermoelastic models are compared to exhibit the nature of the field variables.

A neurostimulator system for real, sham, and multi-target transcranial magnetic stimulation

Objective. Transcranial magnetic stimulation (TMS) is a clinically effective therapeutic instrument used to modulate neural activity. Despite three decades of research, two challenging issues remain, the possibility of changing the (a) stimulated spot and (b) stimulation type (real or sham) without physically moving the coil. In this study, a second-generation programmable TMS device with advanced stimulus shaping is introduced that uses a five-level cascaded H-bridge inverter and phase-shifted pulse-width modulation. The principal idea of this research is to obtain real, sham, and multi-locus stimulation using the same TMS system. Approach. We propose a two-channel modulation-based magnetic pulse generator and a novel coil arrangement, consisting of two circular coils with a physical distance of 20 mm between the coils and a control method for modifying the effective stimulus intensity, which leads to the live steerability of the target and type of stimulation. Main results. Based on the measured system performance, the stimulation profile can be steered ±20 mm along a line from the centroid of the coil locations by modifying the modulation index. Significance. The proposed system supports electronic control of the stimulation spot without physical coil movement, resulting in tunable modulation of targets, which is a crucial step towards automated TMS machines.

Initial Response of Nightside Auroral Currents to a Sudden Commencement: Observations of Electrojet and Substorm Onset

AbstractStorm sudden commencements (SSC) often precede geomagnetic storms. Commonly, it takes some hours from the step‐like change that marks the SSC to the start of the magnetic storm activity. In a subset of cases, however, auroral activity starts almost instantaneously after the SSC. To the authors knowledge, the conditions that enable this rapid activation have not been investigated in detail before. Here we consider all the sudden commencements (SC) during the years 2000–2020. Our focus is on the initial response of the auroral currents on the nightside. For that purpose, we make use of the IMAGE Magnetometer Network in Fennoscandia. In about 30% of SC events an initial activation of the westward electrojet is observed. Magnetic deflections of the northward component, surpassing frequently 1,000 nT, are observed only 4 min after the SC. These intense westward currents, flowing typically in narrow channels of 1°–2° latitudinal width, last some 10 min. The electrojets are conjugate to regions in the magnetosphere near geostationary orbits. In several cases geomagnetic substorm onsets are observed about 30 min after the SC. These start typically at fairly high latitude, around 71° magnetic latitude. This is an indication for rather quiet conditions preceding the onset. The magnetic pulse of the SC seems to play an important role in initiating the strong electrojets and the substorms. These initial activities are of relevance for space weather effects because of their strong and rapid variations. This paper provides detailed observations of the initial auroral activity following some SCs.

Current Research Developments of Electromagnetic Joining Technology in China-A Review

: With the increasing applications of multi-material structures in lightweight vehicle, traditional joining techniques are highly challenged in joining dissimilar materials. To meet the multimaterial structures requirements of lightweight design, electromagnetic joining (EMJ) technology, including electromagnetic riveting (EMR) and magnetic pulse welding (MPW), developed rapidly in recent years, which can achieve good connection performance for complex-shaped structures and dissimilar materials. This paper presents a comprehensive review of the research progress of the EMJ technology in China. Moreover, this review aims at providing a guideline for researchers engaged in electromagnetic joining technology and other connecting processes to further improve the level of lightweight vehicle design and manufacture. Firstly, the development history and status of EMJ were presented. Then the basic joining principles and characteristics of EMR and MPW were analyzed in detail. Subsequently, the investigation of joints formation mechanism, mechanical properties of joints and equipment development of EMR and MPW techniques were reviewed and analyzed. Specially, the operating principle is described along with various factors affecting the mechanical and microcosmic properties of joints. Finally, the future development trend of the EMJ technology based on the current research progress is highlighted.

Thermally enhanced Majorana-mediated spin transport in the Kitaev model

We study how stable the Majorana-mediated spin transport in a quantum spin Kitaev model is against thermal fluctuations. Using the time-dependent thermal pure quantum state method, we examine finite-temperature spin dynamics in the Kitaev model. The model exhibits two characteristic temperatures $T_L$ and $T_H$, which correspond to energy scales of the local flux and the itinerant Majorana fermion, respectively. At low temperatures $(T\ll T_L)$, an almost flux-free state is realized and the spin excitation propagates in a similar way to that for the ground state. Namely, after the magnetic pulse is introduced at one of the edges, the itinerant Majorana fermions propagate the spin excitations even through the quantum spin liquid state region, and oscillations in the spin moment appear in the other edge with a tiny magnetic field. When $T\sim T_L$, larger oscillations in the spin moments are induced in the other edge, compared to the results at the ground state. At higher temperatures, excited $Z_2$ fluxes disturb the coherent motion of the itinerant Majorana fermions, which suppresses the spin propagation. Our results demonstrate a crucial role of thermal fluctuations in the Majorana-mediated spin transport.

Crack problem in a functionally graded superconductor cylinder under pulsed field magnetization

In the paper, the fracture of functionally graded superconductor under pulsed magnetic field is numerically analyzed, and the effect of electromagnetic stress and thermal stress on crack problem under pulsed magnetic field is studied. A FEM model based on H formula and heat transfer equation is proposed for the electromagnetic thermal behavior of inhomogeneous superconductors with central cracks. The influence of the gradient parameter η of critical current density on the stress intensity factor was investigated. The numerical results show that the gradient parameter η has a great influence on the change of stress intensity factor caused by electromagnetic force and thermal strain with time, which makes the crack easy to expand. In addition, the results show that the electromagnetic stress decreases gradually with the increase of crack length, and the thermal stress has a significant effect on the stress intensity factor.

LOFAR Observations of Lightning Initial Breakdown Pulses

AbstractThis paper reports an observational study of lightning initial breakdown pulses (IBPs) using the low‐frequency array radio telescope and a broadband magnetic field sensor. The data show that the overall spatiotemporal evolution of the electrical breakdown causing an IBP is rather complex. During an IBP, spatially and temporally separated bursts of very high frequency (VHF) electromagnetic radiation occur in a volume on the order of 1003 m3, and they are coincident with brief magnetic field pulses, indicating that the location of the active breakdown region can change suddenly. Furthermore, recurrent breakdown activity is observed, especially at the location of the VHF burst. Interpreting each VHF burst as being generated by a corona burst, an IBP pulse appears to start off from an initial corona burst and subsequent corona bursts enhance it. We further suggest that the generation of IBPs likely involves multiple space stems/leaders and connections between them.

Monophasic-Quadripulse Theta Burst Magnetic Stimulation for Motor Palsy Functional Evaluation After Intracerebral Hemorrhage.

Transcranial magnetic stimulation (TMS) is commonly employed for diagnostic and therapeutic purposes to enhance recovery following brain injury, such as stroke or intracerebral hemorrhage (ICH). Single-pulse TMS, most commonly used for diagnostic purposes and with motor evoked potential (MEP) recordings, is not suitable for clinical use in patients with severe motor paresis. To overcome this problem, we developed a quadripulse theta burst transcranial magnetic stimulation (QTS) device that combines the output from 16 stimulators to deliver a train of 16 monophasic magnetic pulses through a single coil. High-frequency theta rhythm magnetic bursts (bursts of four monophasic pulses, at 500 Hz, i.e., with a 2-ms interpulse interval, repeated at 5 Hz) were generated via a set of 16 separate magnetic stimulators connected to a specially designed combination module. No adverse effects or electroencephalogram (EEGs) abnormalities were identified during or after the recordings. MEP amplification in the QTS during four-burst theta rhythm stimulations produced four independent MEPs 20 ms after each burst onset maximizing the final third or fourth burst, which exhibited significantly greater amplitude than those resulting from a single burst or pulse. Motor functional palsy grades after ICH and QTS-MEP parameters and resting motor threshold (RMT) and amplitudes were significantly correlated (r = −0.83/−0.81 and 0.89/0.87; R2 = 0.69/0.66 and 0.79/0.76, p < 0.001; anterior/posterior-stimulus polarity, respectively). In conclusion, QTS-MEPs enabled a linear functional evaluation in patients with various degrees of motor paresis. However, the benefits, safety, and limitations of this device should be further explored in future studies.

Boosting the hypnotic experience. Inhibition of the dorsolateral prefrontal cortex alters hypnotizability and sense of agency. A randomized, double-blind and sham-controlled tDCS study

Hypnotizability refers to the individual responsiveness to hypnosis, and literature shows that the greater the hypnotizability, the more effective the hypnotic suggestions. So far, few studies attempted to enhance hypnotizability, and only two adopted brain stimulation with magnetic pulses. In the present study, we aimed to boost hypnotizability through transcranial direct current stimulation (tDCS). To this aim, bilateral tDCS was applied over the dorsolateral prefrontal cortex (DLPFC) with the target electrode providing negative current (cathodal stimulation) over the left hemisphere. Twenty-nine subjects participated in the study and they were randomly assigned to the sham or the active group in a double-blind design. The hypnotic experience was assessed before and after the stimulation through a phenomenological measure of consciousness (the PCI-HAP). The main findings revealed that a single tDCS session enhanced the hypnotic depth by 11% and reduced the volitional control by 30%, while no differences emerged in the sham group. This is the first study adopting the electrical neurostimulation to produce an alteration of hypnotizability and sense of agency, and confirmed the key-role of the DLPFC and executive control in the hypnotic phenomena. If confirmed, these findings could have relevant implications as enhanced hypnotizability could be translated into better outcomes for many hypnotic interventions.

Possibility of mechanical fracture of superconducting ring bulks due to thermal stress induced by local heat generation during pulsed-field magnetization

During quasi-static magnetization of bulk superconductors using field-cooled magnetization (FCM) from high fields at low temperatures, such bulks are sometimes broken, which is believed to be mainly due to an electromagnetic force—and subsequent stress—larger than the fracture strength. However, a ring bulk can break, even during pulsed field magnetization (PFM), from relatively lower pulsed fields and at relatively higher temperatures. Previous simulation results suggest that the ring bulk should not break due to the electromagnetic force during PFM. In this paper, taking experimental and numerical results into consideration, we propose the possibility of mechanical fracture of a ring bulk during PFM due to thermal stress induced by local heat generation, which has not been considered and investigated to date. Two numerical models with different sizes of heat-generating region were constructed for the ring bulk with a relatively large inner diameter (60 mm outer diameter, 36 mm inner diameter, 17 mm height). For Model-1, with a large heat region, the bulk fracture due to the thermal stress results from the tensile stress along the radial direction in the neighboring heat region. The risk of bulk fracture is enhanced at the inner or outer edges of the bulk surface, compared with that inside the bulk. For Model-2, with a small heat region inside the bulk, the bulk fracture due to the thermal stress results from the compressive stress along the radial direction in the neighboring heat region. These results strongly suggest the possibility of mechanical fracture of an actual ring bulk due to thermal stress induced by local heat generation. This idea is also applicable more generally to the fracture mechanism during FCM of superconducting bulks.

Экспериментальное исследование и численное моделирование метания алюминиевого образца для магнитно-импульсной сварки

The induction acceleration method is quite widely used in impact experiments with conductive disks. The paper presents an experimental study and numerical simulation concerning magnetic pulse acceleration of thin flat discs made of D16AM aluminium alloy. We used a flat copper coil and a capacitor power source to investigate magnetic pulse welding possibilities. The high-energy pulse method is efficient, safe, capable of precisely setting pulse discharge power by varying the capacitor (energy storage) capacitance and voltage, while heating the work piece with induced current can lead to an increase in its plasticity. We used the LS-DYNA finite element analysis software package to run our numerical simulation. The results obtained show that there is a significant disadvantage to using this acceleration setup: it is difficult to ensure that the sample accelerated remains planar.

Mechanical properties and joining mechanisms of Al-Fe magnetic pulse welding by spot form for automotive application

Magnetic pulse welding (MPW) has the unique advantages in realizing the connection of dissimilar materials, such as waveform interface, reliable joint and high strength. However, the air gap must be ensured by placing the gasket. Magnetic pulse spot welding (MPSW) has great potential in industrial applications for not requiring additional equipment to ensure the air gap between the two plates during the welding process. In this paper, a comparative study of flat-head type welding joint and convex-head type welding joint with dissimilar materials jointed by MPSW was carried out. Mechanical properties, joining mechanism, and interfacial morphology of the two joints were studied by tensile tests, numerical simulations, and microscopic observations. The results showed that different forms of flyer plate had a significant influence on the performance of the joint as it led to different weld lengths. The tensile strength of the convex-head type was higher than that of the flat-head type. In contrast, the flat-head type had better shear strength than the convex-head type because additional torsional force was formed. In general, these two different joints of MPSW had their characteristics. Therefore, the type of welding joint could be selected according to the actual needs. This research broadens the idea of the MPSW of Al-Fe for vehicle bodies applications.

Magnetization switching in the inertial regime

We have numerically solved the Landau-Lifshitz-Gilbert (LLG) equation in its standard and inertial forms to study the magnetization switching dynamics in a $3d$ thin film ferromagnet. The dynamics is triggered by ultrashort magnetic field pulses of varying width and amplitude in the picosecond and Tesla range. We have compared the solutions of the two equations in terms of switching characteristic, speed and energy analysis. Both equations return qualitatively similar switching dynamics, characterized by regions of slower precessional behavior and faster ballistic motion. In case of inertial dynamics, ballistic switching is found in a 25 % wider region in the parameter space given by the magnetic field amplitude and width. The energy analysis of the dynamics is qualitatively different for the standard and inertial LLG equations. In the latter case, an extra energy channel, interpreted as the kinetic energy of the system, is available. Such extra channel is responsible for a resonant energy absorption at THz frequencies, consistent with the occurence of spin nutation.

Dynamic properties of spin-orbital correlation effects in the spinel MnV2O4

The spin-orbital-lattice coupling in spinel ${\mathrm{MnV}}_{2}{\mathrm{O}}_{4}$ single crystal has been investigated by static field magnetization (field sweep rate of 50 Oe/s), pulsed field magnetization (field sweep rate $\ensuremath{\sim}{10}^{5}$ kOe/s), dielectric permittivity, and magnetostriction. Experimental results show that the magnetization and magnetostriction are related to the field sweep rate. The analysis of the magnetization, dielectric permittivity and magnetostriction in static magnetic field shows that the collinear (CL) and non-CL (NCL) spin configurations coexist between ${T}_{N}\ensuremath{\sim}56$ K and ${T}^{*}\ensuremath{\sim}52$ K, and the NCL spin configuration can be induced by applied magnetic field. In particular, the magnetization and magnetostriction steps associated with CL and NCL transitions observed in the static magnetic field becomes smooth in the pulsed magnetic field, indicating the slow relaxation characteristic of these phase transitions. Based on the orbital state of ${\mathrm{MnV}}_{2}{\mathrm{O}}_{4}$ and the Kugel-Khomskii model, we propose an quasiadiabatic spin-orbital correlation mechanism in which the interaction between the spin and the ${t}_{2g}$ orbital of ${\mathrm{V}}^{3+}$ ions is rather weak; this weak interaction results in the magnetic properties of ${\mathrm{MnV}}_{2}{\mathrm{O}}_{4}$ is related to the field sweep rate.