Field Gradient Research Articles

Research on Typical Decay-like Fracture Defects of Composite Insulators Based on Electro-Thermal Coupling

In response to the typical decay and fracture defects of composite insulators, a three-dimensional electrically and thermally coupled simulation physical model was constructed based on the finite element method, and the local electric field distortion and temperature rise were analyzed. The study confirms that the insulator interface’s axial electric and thermal fields show a U-shaped curve; the interface field strength is the largest. There is an electric field gradient difference between the mandrel and the sheath, and the thermal field is concentrated at the mandrel and the interface. The field strength at the edge of the defect is the largest, the aberrant electric field at the defect shows a sawtooth shape, and the temperature rise is concentrated in the defect area. The degradation is fast in the air gap, the etching hole diameter direction, and the carbonation channel axial direction. The larger the defect volume, the larger the aberration in the electric field and temperature rise. Water vapor air gaps, breakdown holes, and carbonized channels have the most pronounced electric field and temperature changes. The functional relationship between electric field aberration, temperature rise, and defect volume is established. The results provide a basis for the protection of insulator decay-like fracture.

Unveiling key factors in solar eruptions leading to the solar superstorm in 2024 May

NOAA active region (AR) 13664/8 produced the most intense geomagnetic effects since the Halloween event of 2003. The resulting extreme solar storm is thought to be the consequence of multiple interacting coronal mass ejections (CMEs). Notably, this AR exhibits exceptionally rapid magnetic flux emergence. The eruptions on which we focus all occurred along collisional polarity inversion lines (PILs) through collisional shearing during a three-day period of extraordinarily high flux emergence (sim 1021 Mx hr$^ $). Our key findings reveal how photospheric magnetic configurations in eruption sources influence solar superstorm formation and geomagnetic responses, and link exceptionally strong flux emergence to sequential homologous eruptions: (1) We identified the source regions of seven halo CMEs that were distributed primarily along two distinct PILs. This distribution suggests two groups of homologous CMEs. (2) The variations in the magnetic flux emergence rates in the source regions are correlated with the CME intensities. This might explain the two contrasting cases of complex ejecta that are observed at Earth. (3) Our calculations of the magnetic field gradients around the CME source regions show strong correlations with eruptions. This provides crucial insights into solar eruption mechanisms and enhances our prediction capabilities for future events.

Broad Instantaneous Bandwidth Microwave Spectrum Analyzer with a Microfabricated Atomic Vapor Cell

We report on broad instantaneous bandwidth microwave spectrum analysis with hot Rb87 atoms in a microfabricated vapor cell in a large magnetic field gradient. The sensor is a MEMS atomic vapor cell filled with isotopically pure Rb87 and N2 buffer gas to localize the motion of the atoms. The microwave signals of interest are coupled through a coplanar waveguide to the cell, inducing spin-flip transitions between optically pumped ground states of the atoms. A static magnetic field with large gradient maps the frequency spectrum of the input microwave signals to a position-dependent spin-flip pattern on absorption images of the cell recorded with a laser beam onto a camera. In our proof-of-principle experiment, we demonstrate a microwave spectrum analyzer that has ≈1 GHz instantaneous bandwidth centered around 13 GHz, 3 MHz frequency resolution, 2 kHz refresh rate, and a −23 dBm single-tone microwave power detection limit in 1 s measurement time. A theoretical model is constructed to simulate the image signals by considering the processes of optical pumping, microwave interaction, diffusion of Rb87 atoms, and laser absorption. We expect to reach more than 25 GHz instantaneous bandwidth in an optimized setup, limited by the applied magnetic field gradient. Our demonstration offers a practical alternative to conventional microwave spectrum analyzers based on electronic heterodyne detection. Published by the American Physical Society 2024

The Optical Forces and Torques Exerted by Airy Light-Sheet on Magnetic Particles Utilized for Targeted Drug Delivery

The remarkable properties of magnetic nanostructures have sparked considerable interest within the biomedical domain, owing to their potential for diverse applications. In targeted drug delivery systems, therapeutic molecules can be loaded onto magnetic nanocarriers and precisely guided and released within the body with the assistance of an externally applied magnetic field. However, conventional external magnetic fields generated by permanent magnets or electromagnets are limited by finite magnetic field gradients, shallow penetration depths, and low precision. The novel structured light field known as the Airy light-sheet possesses unique characteristics such as non-diffraction, self-healing, and self-acceleration, which can potentially overcome the limitations of traditional magnetic fields to some extent. While existing studies have primarily focused on the manipulation of dielectric particles by Airy light-sheet, comprehensive analyses exploring the intricate interplay between Airy light-sheet and magnetic nanostructures are currently lacking in the literature, with only preliminary theoretical discussions available. This study systematically explores the mechanical response of magnetic spherical particles under the influence of Airy light-sheet, including radiation forces and spin torques. Furthermore, we provide an in-depth analysis of the effects of particle size, permittivity, permeability, and incident light-sheet parameters on the mechanical effects. Our research findings not only offer new theoretical guidance and practical references for the application of magnetic nanoparticles in biomedicine but also provide valuable insights for the manipulation of other types of micro/nanoparticles using structured light fields.

Sandstone wettability in supercritical CO2-brine-rock interactions evaluated with 13C and 1H magnetic resonance

During the first decades of geologic CO2 storage in saline formations and depleted reservoirs, structural trapping is the most important storage mechanism. The effectiveness of CO2 containment hinges on the assumption that the sealing formation remains water wet in the presence of dense CO2. In this work, multiple 13C and 1H magnetic resonance (MR) methodologies were employed for the first time to evaluate the interactions between supercritical CO2, brine, and the pore surface of a Berea sandstone core plug under reservoir conditions. These studies employed a novel variable field superconducting MR and magnetic resonance imaging (MRI) instrument which permitted sequential 1H and 13C measurements of core plugs at high-pressure and high-temperature. To systematically study the wettability of rock core exposed to supercritical CO2, four experiments were designed including bulk CO2 in a high-pressure vessel, bulk CO2-brine, 13CO2 in dried rock core, and a 13CO2-brine-rock experiment.The measured 13C and 1H MR relaxation times in this work indicate that the Berea sandstone remained strongly water-wet when the brine saturated core plug was exposed to supercritical CO2 under reservoir conditions. For both 13C and 1H, T1 relaxation times provide more reliable wettability evaluation as compared to T2 due to the impact of molecular diffusion through internal magnetic field gradients. One-dimensional (1D) MRI was employed to spatially resolve 13CO2 and brine in the core plug. Two-dimensional (2D) MRI was able to image 13CO2 and brine in a PEEK vessel. The quantities of CO2 and brine in the core plug were determined from the MR signal intensities of 13CO2 and brine.

O2/N2 separation via delocalization of the magnetic moment in the TM-CNT nano-magnets array under external magnetic field gradient: A molecular dynamic simulation study

This work presents the design of a new membrane including an array of nano-magnets (magnetic CNTs) as an alternative candidate for efficient O2/N2 separation by using the molecular dynamics (MD) technique. The behavior of the magnetic CNTs is based on the delocalized magnetic moments of transition metal elements which embedded within the CNTs. Hence, the magnetic membrane technology is employed together with the magnetic separation technology for O2/N2 separation; Different responses of paramagnetic oxygen and diamagnetic nitrogen molecules under an applied magnetic field gradient are the basis of the performance of this system. Permeability and selectivity of the membrane are investigated through the involvement of magnetic dipole–dipole and pare-particle Lennard-Jones (L-J) interactions in a constant gas pressure difference on the sides of the membrane. The effects of the multilayering and other design parameters (interlayer distance d, interablock spacing ℓ, slit size s) on the separation performance of MCNTM are investigated. It was found that the separation performance is sensitive to variations in d, ℓ, and s. Furthermore, the influence of the strong or weak magnetic gradient rate and also the temperature are evaluated numerically. Finally, this work provides computational evidence that the magnetic multilayer MCNTM can be used as a high-performance O2/N2 separator, as well as, an oxygen buffer or a temporary storage system at room temperature and 77 K.

Lithium Anode Stability Enhanced by Micro-Potentials from Spontaneous Polarization in BaTiO3 Films

Lithium metal is widely recognized as an ideal anode material due to its high specific capacity and low redox potential. However, challenges such as severe lithium dendrite growth have significantly impeded its practical applications. Herein, we introduce a BaTiO3 (BTO) ferroelectric thin film into the lithium anode. During the charge/discharge cycles, the BTO film generates a micro-potential in the direction opposite to the applied electric field, owing to its spontaneous polarization. The micro-potential effectively reduces the electric field gradient, thereby suppressing inhomogeneous nucleation and the growth of lithium dendrites. Consequently, the incorporation of the BTO ferroelectric thin film significantly enhances the cycling performance of the batteries. The half cells demonstrate stable operation after more than 100 cycles at high capacity of 4 mAh·cm−2. Furthermore, the LiFePO4 (LFP) full cell delivers a specific capacity of 146.6 mAh·g−1 after 300 cycles. This work demonstrates a promising strategy for the development of lithium batteries with improved longevity and enhanced capacity.

Vertical Gradient of the Geomagnetic Field by Multiple Altitude Aeromagnetic Survey

Vertical Gradient of the Geomagnetic Field by Multiple Altitude Aeromagnetic Survey

Advances in Design and Fabrication of Micro-Structured Solid Targets for High-Power Laser-Matter Interaction

Accelerated particles have multiple applications in materials research, medicine, and the space industry. In contrast to classical particle accelerators, laser-driven acceleration at intensities greater than 1018 W/cm2, currently achieved at TW and PW laser facilities, allow for much larger electric field gradients at the laser focus point, several orders of magnitude higher than those found in conventional kilometer-sized accelerators. It has been demonstrated that target design becomes an important factor to consider in ultra-intense laser experiments. The energetic and spatial distribution of the accelerated particles strongly depends on the target configuration. Therefore, target engineering is one of the key approaches to optimizing energy transfer from the laser to the accelerated particles. This paper provides an overview of recent progress in 2D and 3D micro-structured solid targets, with an emphasis on fabrication procedures based on laser material processing. Recently, 3D laser lithography, which involves Two-Photon Absorption (TPA) effects in photopolymers, has been proposed as a technique for the high-resolution fabrication of 3D micro-structured targets. Additionally, laser surface nano-patterning followed by the replication of the patterns through molding, has been proposed and could become a cost-effective and reliable solution for intense laser experiments at high repetition rates. Recent works on numerical simulations have also been presented. Using particle-in-cell (PIC) simulation software, the importance of structured micro-target design in the energy absorption process of intense laser pulses—producing localized extreme temperatures and pressures—was demonstrated. Besides PIC simulations, the Finite-Difference Time-Domain (FDTD) numerical method offers the possibility to generate the specific data necessary for defining solid target material properties and designing their optical geometries with high accuracy. The prospects for the design and technological fabrication of 3D targets for ultra-intense laser facilities are also highlighted.

Stern-Gerlach centennial: Parity, gradient effect, and an analogy with the Higgs field

In this article, which celebrates 100 years of the Stern-Gerlach experiment, we identify and discuss some limitations of the mathematical field we intend to represent as the Stern-Gerlach magnetic field. We extend some recent theoretical results concerning Stern-Gerlach eigenenergies, where what we call “the gradient effect” manifests itself: the contribution of the magnetic field gradient to the self-energies. Finally, based on an analogy with the Stern-Gerlach effect, we visualized that the Higgs field must be homogeneous in its minimum energy configuration within the context of the Higgs mass generation mechanism.

Water compression induced ionic negative differential resistance in nanopores.

The mass transport behavior through nanoscale channels, greatly influenced by the structures and dynamics of nanoconfined water, plays an essential role in many biophysical processes. However, the dynamics of nanoconfined water under an external field and its effects are still not fully understood. Here, on the basis of molecular dynamics simulations, we theoretically show that the ionic current of [Bmim][PF6] through narrow pores in graphene membrane exhibits an ionic negative differential resistance effect-the ionic current decreases as the voltage increases over a certain threshold. This effect arises from the violation of traditional fluid dynamics as the assumption of continuity and homogeneity of fluids is no longer effective in ultrathin nanopores. The gradient of electric field around the atomic-thin layer produces a strong gradient force on the polarized water inside the nanopore. This dielectrophoretically compressed water leads to a hydrostatic force that repels ions from entering the nanopore. Our findings may advance the understanding of hydrostatic mechanism, which governs ion transport through nanopores.

Fission Dynamics of a Ferrofluid Droplet on a Smooth Plate under a Nonuniform Magnetic Field.

A ferrofluid droplet on a plate undergoes interesting fission under a magnetic field. In this article, a recently developed simplified multiphase lattice Boltzmann method coupled with a self-correction solution for the magnetic potential equation is employed to explore this complex flow phenomenon. It is found that the droplet fission follows a four-pattern process under a nonuniform magnetic field. The mechanisms behind this behavior are influenced by the strength and gradient of the magnetic field, surface tension, droplet size, and the wetting boundary condition. These findings provide valuable insights into the application of ferrofluids in droplet microfluidics and contribute to advancements in this field.

Estimate of in-band eddy current effect in space gravitational wave detection

Abstract In space detection of gravitational waves (GWs), the presence of a low-frequency varying magnetic field will generate eddy currents in the test mass, resulting in a varying magnetic moment. This magnetic moment will couple with a constant magnetic field gradient, producing residual acceleration within the frequency band of GW detection, causing the test mass to deviate from the free-falling mode. However, this effect has not yet been studied clearly in the noise budget for TianQin and LISA Pathfinder since the constant DC magnetic susceptibility was applied to quantify the varying magnetic moment. This paper utilizes the parameter of alternating current (AC) magnetic susceptibility to define this process, and further analyzes and evaluates the effect. In a general magnetic field environment, the contribution of this effect to TianQin acceleration noise reaches 20\% from 0.1 mHz to 3 mHz. The contribution to LISA noise is less than 10\% from $10^{-4}$ to 0.1 Hz, and less than 10\% below $10^{-4}$ Hz. This effect does not have a potential limit on LISA low-frequency science down to 20 $\mu$Hz [Phys. Rev. Lett. 120, 061101 (2018)].

Experimental Assessment of Magnetic Resonance Imaging Distortion for Radiation Therapy Planning

MRI is widely used in radiation therapy planning, particularly in stereotactic radiosurgery for brain metastases. The article addresses the geometric distortion of MRI images, which can lead to errors in radiation therapy planning. A series of experiments with a simple phantom were conducted on two MRI scanners with 0.5 T and 1.5 T magnetic fields. Deviations in the positions of the phantom objects from their actual locations were observed. The detected deviations can reach up to 5 mm. A theoretical dependence of the magnetic field gradient on the distance to the center of homogeneity was calculated, which agrees well with the approximation of experimental data. An assessment was made of the dependence of the image area distortion of objects located at the center of the field homogeneity on their actual sizes. It was found that the area deviation can reach up to 20%.

τSPECT: a spin-flip loaded magnetic ultracold neutron trap for a determination of the neutron lifetime

The confinement of ultracold neutrons (UCNs) in three-dimensional magnetic field gradient or magneto-gravitational traps allows for a measurement of the free neutron lifetime τ n with superior control over loss channels related to UCNs interacting with material surfaces. The most precise measurement τ n has been achieved using a magneto-gravitational trap, in which UCN are prevented from escaping at the top of their trap by gravity. More compact horizontal confinement geometries with variable energy acceptance ranges can be obtained by using steep magnetic field gradients in all spatial directions, generated by combinations of either permanent or (variable) superconducting magnets. In this paper, we present the first successful implementation of a pulsed spin-flip based loading scheme to fill a three-dimensional magnetic trap with externally produced UCN. The measurements with the τSPECT experiment were performed at the pulsed UCN source of the research reactor TRIGA Mainz. The extracted neutron storage time constant of τ = 859(16) s is compatible with the most precise determinations of τ n . We report on detailed, but statistically limited, investigations of major systematic effects influencing the neutron storage time. The statistical limitations are mitigated by the relocation of the experiment to a stronger UCN source.

Long range self-transport of liquid droplets driven by electric field and roughness gradient

It is well known that roughness and charge gradients could be used for droplet self-transport. The key issue is how to synergize the two effects. The uniform density charge can form linearly increasing charge gradient on a roughness gradient surface. Under this condition, the influence on the droplet self-transport under the synergy of these two effects was obtained by statics analysis, and the driving function was presented. An energy equation was constructed to study the conditions for crossing periodic boundaries, and the problem of distance limitation on periodic surfaces due to energy dissipation was solved by converting electric potential into droplet kinetic energy. A periodic roughness gradient surface with K = 0.07 was designed and prepared via 3D printing. Water droplets can be transported over long distances and the maximum velocity increases with charge density up to 46 mm/s. Finally, the effect of different structures on the maximum charge density in the Cassie state was investigated by simulation. The biomimetic structures exhibit great compressive stability, which can increase the surface charge density of droplets in the Cassie state by 3.6 times compared to pillar structures. It can be widely used in the fields of materials science and interface chemistry, etc.

Ferrimagnetic Tb/Co multilayers patterned by ion bombardment as substrates for magnetophoresis

Ion bombardment with 30 keV Ga+ ions can locally change the magnetic properties of perpendicular magnetic anisotropy ferrimagnetic Tb/Co based multilayers. The induced changes in the effective magnetization create high gradients of magnetic fields in the proximity of the perimeters of the bombarded areas. Superparamagnetic, micrometer-sized beads floating in an aqueous suspension over such a patterned structure respond to the ensuing magnetostatic energy landscape. This landscape, and its associated forces on the beads, can be controlled with a time varying, external, homogeneous magnetic field. It is shown that with a 3.37 kA/m (approx. 4.2 mT) field and switching the direction at 10 Hz frequencies the beads can be driven with average forward velocities reaching 40 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu$$\\end{document}m/s. This has the potential for use in lab-on-a-chip type assays.

Assessing tumor microstructure with time-dependent diffusion imaging: Considerations and feasibility on clinical MRI and MRI-Linac.

Quantitative imaging biomarkers (QIBs) can characterize tumor heterogeneity and provide information for biological guidance in radiotherapy (RT). Time-dependent diffusion MRI (TDD-MRI) derived parameters are promising QIBs, as they describe tissue microstructure with more specificity than traditional diffusion-weighted MRI (DW-MRI). Specifically, TDD-MRI can provide information about both restricted diffusion and diffusional exchange, which are the two time-dependent effects affecting diffusion in tissue, and relevant in tumors. However, exhaustive modeling of both effects can require long acquisitions and complex model fitting. Furthermore, several introduced TDD-MRI measurements can require high gradient strengths and/or complex gradient waveforms that are possibly not available in RT settings. In this study, we investigated the feasibility of a simple analysis framework for the detection of restricted diffusion and diffusional exchange effects in the TDD-MRI signal. To promote the clinical applicability, we use standard gradient waveforms on a conventional 1.5 T MRI system with moderate gradient strength (Gmax=45 mT/m), and on a hybrid 1.5 T MRI-Linac system with low gradient strength (Gmax=15 mT/m). Restricted diffusion and diffusional exchange were simulated in geometries mimicking tumor microstructure to investigate the DW-MRI signal behavior and to determine optimal experimental parameters. TDD-MRI was implemented using pulsed field gradient spin echo with the optimized parameters on a conventional MRI system and a MRI-Linac. Experiments in green asparagus and 10 patients with brain lesions were performed to evaluate the time-dependent diffusion (TDD) contrast in the source DW-images. Simulations demonstrated how the TDD contrast was able to differentiate only dominating diffusional exchange in smaller cells from dominating restricted diffusion in larger cells. The maximal TDD contrast in simulations with typical cancer cell sizes and in asparagus measurements exceeded 5% on the conventional MRI but remained below 5% on the MRI-Linac. In particular, the simulated TDD contrast in typical cancer cell sizes (r=5-10µm) remained below or around 2% with the MRI-Linac gradient strength. In patients measured with the conventional MRI, we found sub-regions reflecting either dominating restricted diffusion or dominating diffusional exchange in and around brain lesions compared to the noisy appearing white matter. On the conventional MRI system, the TDD contrast maps showed consistent tumor sub-regions indicating different dominating TDD effects, potentially providing information on the spatial tumor heterogeneity. On the MRI-Linac, the available TDD contrast measured in asparagus showed the same trends as with the conventional MRI but remained close to typical measurement noise levels when simulated in common cancer cell sizes. On conventional MRI systems with moderate gradient strengths, the TDD contrast could potentially be used as a tool to identify which time-dependent effects to include when choosing a biophysical model for more specific tumor characterization.

Protoporphyrin IX iron(II) revisited. An overview of the Mössbauer spectroscopic parameters of low-spin porphyrin iron(II) complexes.

Mössbauer parameters of low-spin six-coordinate [Fe(II)(Por)L2] complexes (where Por is a synthetic porphyrin; L is a nitrogenous aliphatic, an aromatic base or a heterocyclic ligand, a P-bonding ligand, CO or CN) and low-spin [Fe(Por)LX] complexes (where L and X are different ligands) are reported. A known point charge calculation approach was extended to investigate how the axial ligands and the four porphyrinato-N atoms generate the observed quadrupole splittings (ΔEQ) for the complexes. Partial quadrupole splitting (p.q.s.) and partial chemical shifts (p.c.s.) values were derived for all the axial ligands, and porphyrins reported in the literature. The values for each porphyrin are different emphasising the importance/uniqueness of the [Fe(PPIX)] moiety, (which is ubiquitous in nature). This new analysis enabled the construction of figures relating p.c.s and p.q.s values. The relationships presented in the figures indicates that strong field ligands such as CO can, and do change the sign of the electric field gradient in the [Fe(II)(Por)L2] complexes. The limiting p.q.s. value a ligand can have and still form a six-coordinate low-spin [Fe(II)(Por)L2] complex is established. It is shown that the control the porphyrin ligands exert on the low-spin Fe(II) atom limits its bonding to a defined range of axial ligands; outside this range the spin state of the iron is unstable and five-coordinate high-spin complexes are favoured. Amongst many conclusions, it was found that oxygen cannot form a stable low-spin [Fe(II)(Por)L(O2)] complex and that oxy-haemoglobin is best described as an [Fe(III)(Por)L(O2-)] complex, the iron is ferric bound to the superoxide molecule.

Ionic selectivity of nanopores: Comparison among cases under the hydrostatic pressure, electric field, and concentration gradient

The ionic selectivity of nanopores is crucial for the energy conversion based on nanoporous membranes. It can be significantly affected by various parameters of nanopores and the applied fields driving ions through porous membranes. Here, with finite element simulations, the selective transport of ions through nanopores is systematically investigated under three common fields, i.e. the electric field (V), hydrostatic pressure (p), and concentration gradient (c). For negatively charged nanopores, through the quantitative comparison of the cation selectivity (t+) under the three fields, the cation selectivity of nanopores follows the order of t+V > t+c > t+p. This is due to the transport characteristics of cations and anions through the nanopores. Because of the strong transport of counterions in electric double layers under electric fields and concentration gradients, the nanopore exhibits a relatively higher selectivity to counterions. We also explored the modulation of t+ on the properties of nanopores and solutions. Under all three fields, t+ is directly proportional to the pore length and surface charge density, and inversely correlated to the pore diameter and salt concentration. Under both the electric field and hydrostatic pressure, t+ has almost no dependence on the applied field strength or ion species, which can affect t+ in the case of the concentration gradient. Our results provide detailed insights into the comparison and regulation of ionic selectivity of nanopores under three fields which can be useful for the design of high-performance devices for energy conversion based on nanoporous membranes.