Field Configuration Research Articles

Controlled Capture of Magnetic Nanoparticles from Microfluidic Flows by Ferromagnetic Antidot and Dot Nanostructures.

The capture of magnetic nanoparticles (MNPs) is essential in the separation and detection of MNPs for applications such as magnetic biosensing. The sensitivity of magnetic biosensors inherently depends upon the distribution of captured MNPs within the sensing area. We previously demonstrated that the distribution of MNPs captured from evaporating droplets by ferromagnetic antidot nanostructures can be controlled via an external magnetic field. In this paper, we demonstrate the capture of magnetic nanoparticles from a microfluidic flow by four variants of antidot array nanostructures etched into 30 nm thick Permalloy films. The nanostructures were exposed to 130 nm MNP clusters passing through microfluidic channels with square cross-sections of 400 μm × 400 μm. In the presence of a parallel magnetic field, up to 83.1% of nanoparticles were captured inside the antidot holes. Significantly higher proportions of nanoparticles were captured within the antidots from the flow than when applying the nanoparticles via droplets. In the parallel field configuration, MNPs can be focused into the regularly spaced antidot indents in the nanostructure, which may be useful when detecting or observing MNPs and their conjugates. Conversely, up to 84% of MNPs were caught outside of antidots under a perpendicular magnetic field. Antidot nanostructures under this perpendicular configuration show potential for MNP filtration applications.

Modeling Femtosecond Beam Propagation in Dielectric Hollow-Core Waveguides

The propagation of femtosecond pulses in guided structures is a matter of both fundamental and practical interest in nonlinear optics. In particular, hollow-core waveguides (HCWs) filled with a gas medium are fabricated and used as devices for the generation of attosecond pulses from high-order harmonics. In this process, the configuration of the laser field (intensity and phase) inside the waveguide is of crucial importance for enhancing the (well-known, low) efficiency of high-order harmonic generation (HHG). Here, we present numerical calculations which demonstrate the main features of the propagation process in fabricated HCWs. We consider a variety of experimental parameters like gas pressure, waveguide size, laser wavelength, and pulse energy and duration. In particular, the beam profile at the fiber input is found to be a sensitive parameter which influences the whole evolution of the laser field along the propagation. Our model is based on a split-step method modified to account for propagation in ionized media and is validated against experimental and theoretical data from the literature. Our results contribute to the description of the main features of beam propagation in HCWs and provide guiding directions for designing efficient configurations for HHG.

M5-brane prongs, string soliton bound states and wall-crossing

We study Abelian M5-brane field configurations representing BPS bound states of self-dual string solitons whose locations correspond to the endlines of M2-branes ending on the M5-branes. The BPS equations are obtained from appropriate Bogomolny completion of the effective Abelian low energy functional with two transverse scalars, using two vectors representing the directions along which these endline strings extend. Then we impose boundary conditions on the scalars near the string soliton cores. This leads to a molecule-like equilibrium structure of two non-parallel string solitons at fixed transverse separations, with the M5-brane “prong” deformations comprising two “spikes”, each shaped like a ridge. The resulting picture becomes increasingly accurate as one approaches the wall of marginal stability, on which these states decay. There are various parallels with wall-crossing phenomena for string web configurations obtained from D3-brane deformations.

Observations of Small‐Scale Magnetic Flux Ropes Associated With Significant Values of Partial Variance Increment Indices

AbstractWe report recent findings for the magnetic field configurations of small‐scale magnetic flux ropes (SFRs) broadly defined and identified by using the Grad‐Shafranov‐based techniques for in situ measurements via the Parker Solar Probe (PSP), Solar Orbiter (SolO), and two Helios spacecraft. Since the current sheets were found to occur at boundaries of SFRs and/or inside SFRs at 1 AU via the partial variance increment (PVI) and the Grad‐Shafranov (GS) reconstruction technique by Pecora et al. (2019), https://doi.org/10.3847/2041‐8213/ab32d9, we further examine such a co‐existence in this study by assessing the maximum PVI indices within SFR intervals using the above four spacecraft observations throughout the inner heliosphere (1 AU). Less than 15% of SFRs have maximum PVI indices exceeding a threshold value of 6 that is used to indicate a current sheet structure. Three representative events are selected to explain the most common situations. (a) Current sheets occur at SFR boundaries and near the center. Each could be a weak switchback feature in the time‐series profile of the gradually bipolar magnetic field rotations. (b) An SFR configuration is confirmed by both the measurement of counterstreaming electrons and the GS reconstruction result, despite that a large PVI value occurs near the SFR center which is due to an arbitrary kink instead of a current sheet. (c) A current sheet is falsely identified as an SFR where a significant PVI value ( 7) occurs near the center. In the end, we discuss the necessity of using multi‐point spacecraft measurements to discern the structures associated with SFRs.

Constraints on axion-like particles from the gamma-ray observation of the Galactic Center

High energy photons originating from the Galactic Center (GC) region have the potential to undergo significant photon-axion-like particle (ALP) oscillation effects, primarily induced by the presence of intense magnetic fields in this region. Observations conducted by imaging atmospheric Cherenkov telescopes have detected very high energy gamma-rays originating from a point source known as HESS J1745-290, situated in close proximity to the GC. This source is conjectured to be associated with the supermassive black hole Sagittarius A*. The GC region contains diverse structures, including molecular clouds and non-thermal filaments, which collectively contribute to the intricate magnetic field configurations in this region. By utilizing a magnetic field model specific in the GC region, we explore the phenomenon of photon-ALP oscillations in the gamma-ray spectrum of HESS J1745-290. Our analysis does not reveal any discernible signature of photon-ALP oscillations, yielding significant constraints that serve as a complement to gamma-ray observations of extragalactic sources across a broad parameter region. The uncertainties arising from the outer Galactic magnetic field models have minor impacts on our results, except for ALP masses around 10-7 eV, as the dominant influence originates from the intense magnetic field strength in the inner GC region.

INFLUENCE OF APPLYING MAGNETIC FIELD ON THERMAL AND HYDRAULIC CHARACTERISTICS OF FE3O4/WATER MAGNETIC NANOFLUID MOVING IN A TWISTED DUCT

This study introduces an investigation of the effect of combining passive and active techniques on enhancing heat transfer by using a ferrofluid passing through a twisted duct subjected to an external magnetic field. The effect of changing the number of magnets, magnetic flux density, nanoparticle volume fraction, and twist ratio on the heat transfer enhancement is studied. The optimum magnetic field configuration was achieved by adjusting the rate of increase of magnetic flux density to 80% between each two successive magnets. Results show that the proposed hybrid technique is promising in providing significant heat transfer enhancement compared to the traditional techniques, but the pressure drop values become relatively higher due to the increased friction levels. The twist ratio value that achieves the optimum thermo-hydraulic performance is found to be 3.7. The limit of magnetic flux density, which, if exceeded, causes the thermo-hydraulic performance to decline, is 800 Gauss. It is found that applying a magnetic field with 1,000 Gauss flux density with a nanoparticle volume concentration of 5% and a twist ratio of 3.7 at Reynolds number of 8,400, enhances the Nusselt number by 25.78% compared to the case using water without twisting in the absence of a magnetic field.

Robustness of inflation to kinetic inhomogeneities

We investigate the effects of large inhomogeneities in both the inflaton field and its momentum. We find that in general, large kinetic perturbations reduce the number of e-folds of inflation. In particular, we observe that inflationary models with sub-Planckian characteristic scales are not robust even to kinetic energy densities that are sub-dominant to the potential energy density, unless the initial field configuration is sufficiently far from the minimum. This strengthens the results of our previous work. In inflationary models with super-Planckian characteristic scales, despite a reduction in the number of e-folds, inflation is robust even when the potential energy density is initially sub-dominant. For the cases we study, the robustness of inflation strongly depends on whether the inflaton field is driven into the reheating phase by the inhomogeneous scalar dynamics.

Search for baryon junctions in e+A collisions at the electron ion collider

Constituent quarks in a nucleon are the essential elements in the standard “quark model” associated with the electric charge, spin, mass, and baryon number of a nucleon. Quantum chromodynamics (QCD) describes nucleon as a composite object containing current quarks (valence quarks and sea (anti-)quarks) and gluons. These subatomic elements and their interactions are known to contribute in complex ways to the overall nucleon spin and mass. In the early development of QCD theory in the 1970s, an alternative hypothesis postulated that the baryon number might manifest itself through a non-perturbative configuration of gluon fields forming a Y-shaped topology known as the gluon junction. In this work, we propose to test such hypothesis by measuring (i) the Regge intercept of the net-baryon distributions for e+(p)Au collisions, (ii) baryon and charge transport in the isobaric ratio between e+Ru and e+Zr collisions, and (iii) target flavor dependence of proton and antiproton yields at large rapidity, transported from the hydrogen and deuterium targets in e+p(d) collisions. Our study indicates that these measurements at the EIC can help determine what carries the baryon number.

Functional information geometry of Euclidean quantum fields

Information geometry provides differential geometric concepts like a Riemannian metric, connections and covariant derivatives on spaces of probability distributions. We discuss here how these concepts extend in a functional sense to quantum field theories in the Euclidean domain which can also be seen as statistical field theories. The geometry has a dual affine structure corresponding to source fields or expectation value fields seen as coordinates. In the latter version the coordinates label the macrostates of the classical field theory. A key concept is a new generating functional, which is a functional generalization of the Kullback-Leibler divergence. From its functional derivatives one can obtain connected as well as one-particle irreducible correlation functions. It also encodes directly the geometric structure, i.e. the functional Fisher information metric and the two dual connections, and it determines asymptotic probabilities for field configurations through Sanov’s theorem. Based on the two dual connections one can construct covariant functional derivatives which allow one to calculate connected and one-particle irreducible correlation functions in general functional coordinate systems. Published by the American Physical Society 2024

ANALYTICAL DESCRIPTION OF THE POTENTIAL OF ELECTROSTATIC MULTIPOLE SYSTEMS BASED ON A CONDUCTING CIRCULAR CYLINDER

An urgent task of corpuscular optics and scientific instrumentation is the creation of new methods for calculating the physical and instrumental parameters of mass spectrometers. Leveraging the increased capabilities of computational technology, these methods provide a solid basis for the design and calculation of instruments with improved analytical capabilities. In this work, a method was developed for calculating the electrostatic field of multipole systems based on a conducting circular cylinder. This method uses the broad analytical capabilities of the theory of functions of a complex variable (TFCV). Analytical expressions are found for the electrostatic field potential of a quadrupole system for the case of infinitely narrow gaps between the electrodes. Analytical expressions for the derivatives of the potential are also obtained. A study was carried out of the influence of the finite size of the gaps between the electrodes on the field configuration. For this purpose, numerical simulations of planar electric fields satisfying the Laplace equation were carried out. The calculation of the electrostatic field potential was carried out using the boundary element method in two stages. First, the distribution of electric charge at the boundary was calculated according to the known boundary potential distribution, that is, the “inverse” problem was solved. Then, using the found values of the charge distribution and the found potential values, the “direct” problem was solved. To solve this problem, a method was developed for solving integral equations with singular and quasi-singular kernels, which provides high accuracy in field calculations for electron-optical systems (EOS) with rectilinear boundaries. The inaccuracies in the calculations resulted solely from rounding mistakes. In the case of an Equation of State (EOS) characterized by curved boundaries, the precision is dependent exclusively on how accurately the boundaries are represented using linear segments. For the purpose of segmenting the curved borders of the second-order EOS, these boundaries were broken down into arcs with an angular measurement not exceeding one degree.

Depolarization by Jet Precession in Early Optical Afterglows of Gamma-Ray Bursts

Abstract Polarization observations provide a unique way to probe the nature of jet magnetic fields in gamma-ray bursts (GRBs). Recently, some GRBs have been detected to be polarized in their early optical afterglows. However, the measured polarization degrees (PDs) of these GRBs are much lower than those predicted by theoretical models. In this work, we investigate the depolarization induced by jet precession in combination with the measured PDs of the GRB early optical afterglows in the reverse shock (RS) dominated phase (∼102–103 s). We calculate the PDs of RS emissions with and without jet precession in both magnetic field configurations, i.e., aligned and toroidal magnetic fields, and meanwhile explore the effects of different parameters on the PDs. We find that the PDs are slightly affected by the configurations of the ordered magnetic fields and are positively related to the precession period. Moreover, the PDs are sensitive to the observed angle, and the measured low PDs favor a small one. Thus, as one of the plausible origins of the structured jets, jet precession could be considered as an alternative mechanism for the low PDs observed in GRB early optical afterglows.

Combined Fit of Spectrum and Composition for FR0 Radio-galaxy-emitted Ultra–high energy Cosmic Rays with Resulting Secondary Photons and Neutrinos

This study comprehensively investigates the gamma-ray dim population of Fanaroff–Riley Type 0 (FR0) radio galaxies as potentially significant sources of ultra–high energy cosmic rays (UHECRs, E > 1018 eV) detected on Earth. While individual FR0 luminosities are relatively low compared to the more powerful Fanaroff–Riley Type 1 and Type 2 galaxies, FR0s are substantially more prevalent in the local universe, outnumbering the more energetic galaxies by a factor of ∼5 within a redshift of z ≤ 0.05. Employing CRPropa3 simulations, we estimate the mass composition and energy spectra of UHECRs originating from FR0 galaxies for energies above 1018.6 eV. This estimation fits data from the Pierre Auger Observatory (Auger) using three extensive air shower models; both constant and energy-dependent observed elemental fractions are considered. The simulation integrates an approximately isotropic distribution of FR0 galaxies, extrapolated from observed characteristics, with UHECR propagation in the intergalactic medium, incorporating various plausible configurations of extragalactic magnetic fields, both random and structured. We then compare the resulting emission spectral indices, rigidity cutoffs, and elemental fractions with recent Auger results. In total, 25 combined energy-spectrum and mass-composition fits are considered. Beyond the cosmic-ray fluxes emitted by FR0 galaxies, this study predicts the secondary photon and neutrino fluxes from UHECR interactions with intergalactic cosmic photon backgrounds. The multimessenger approach, encompassing observational data and theoretical models, helps elucidate the contribution of low-luminosity FR0 radio galaxies to the total cosmic-ray energy density.

Engineering skyrmion from spin spiral in transition metal multilayers.

Skyrmions having topologically protected field configurations with particle-like properties play an important role in various fields of science. Our present study focus on the generation of skyrmion from spin spiral in the magnetic multilayers of 4d/Fe/Ir(111) with 4d = Y, Zr, Nb, Mo, Ru, Rh. Here we investigate the impact of 4d transition metals on the isotropic Heisenberg exchanges and anti-symmetric Dzyaloshinskii-Moriya interactions originating from the broken inversion symmetry at the interface of 4d/Fe/Ir(111) multilayers. We find a strong exchange frustration due to the hybridization of the Fe-3d layer with both 4d and Ir-5d layers which modifies due to band filling effects of the 4d transition metals. We strengthen the analysis of exchange frustration by shedding light on the orbital decomposition of isotropic exchange interactions of Fe-3d orbitals. Our spin dynamics and Monte Carlo simulations indicate that the magnetic ground state of 4d/Fe/Ir(111) transition multilayers is a spin spiral in theab-plane with a period of 1 to 2.5 nm generated by magnetic moments of Fe atoms and propagating along thea-direction. The spiral wavelengths in Y/Fe/Ir(111) are much larger compared to Rh/Fe/Ir(111). In order to manipulate the skyrmion phase in 4d/Fe/Ir(111), we investigate the magnetic ground state of 4d/Fe/Ir(111) transition multilayers with different external magnetic field. An increasing external magnetic field of ∼12 T is responsible for deforming the spin spiral into a isolated skyrmion which flips into skyrmion lattice phase around ∼18 T in Rh/Fe/Ir(111). Our study predict that the stability of magnetic skyrmion phase in Rh/Fe/Ir(111) against thermal fluctuations is upto temperatureT⩽90 K.

Generation of shear flows induced by AE / EPM in LHD plasma

Abstract The generation of shear flows (SFs) by Alfven Eigenmodes (AEs) and energetic particle modes (EPMs) have important effects on the operation of future nuclear fusion reactors, because SFs regulate the saturation of the AEs/EPMs, the transport of EPs and thermal plasma, as well as the formation of transport barriers among other consequences. The aim of this study is the analysis of SFs generation during the saturation phase of AEs and EPMs in LHD plasma. Experiments performed in the 23rd and 24th LHD experimental campaigns are dedicated to explore the destabilization of AEs/EPMs in discharges with different heating patterns, thermal plasma and magnetic field configurations. In particular, the shots 176490 and 179697 show the destabilization of MHD bursts and energetic-ion-driven resistive interchange modes (EIC), respectively. Charge exchange spectroscopy measurements in both discharges indicate that the generation of SFs by AE/EPM is uncorrelated with the perturbation induced by the neutral beam injector (NBI). Nonlinear simulations performed using the gyro-fluid code FAR3d show the generation of zonal structures, especially SFs, induced during the saturation phase of Toroidal Alfven Eigenmodes (TAEs) triggered in the MHD burst as well as by the 1 / 1 EIC in the bursting phase. The simulations indicate that SFs are caused by the radial electric fields powered by energy transfers from the unstable AE/EPM towards the thermal plasma. The strongest SFs are measured during the EIC bursting phase once the 1 / 1 EPM overlaps with nearby resonances at the plasma periphery. Likewise, the largest SFs during the MHD burst are observed once TAEs radially overlap in the inner-middle plasma region.

On the Geometry of the Near-core Magnetic Field in Massive Stars

Abstract It is well-known that the cores of massive stars sustain a stellar dynamo with a complex magnetic field configuration. However, the same cannot be said for the field's strength and geometry at the convective–radiative boundary, which are crucial when performing asteroseismic inference. In this Letter, we present 3D magnetohydrodynamic (MHD) simulations of a 7 M ⊙ mid-main-sequence star, with particular attention given to the convective–radiative boundary in the near-core region. Our simulations reveal that the toroidal magnetic field is significantly stronger than the poloidal field in this region, contrary to recent assumptions. Moreover, the rotational shear layer, also important for asteroseismic inference, is specifically confined within the extent of the Brunt–Väisälä frequency peak. These results, which are based on the inferred properties of HD 43317, have widespread implications for asteroseismic studies of rotation, mixing, and magnetism in stars. While we expect our results to be broadly applicable across stars with similar Brunt–Väisälä frequency profiles and stellar masses, we also expect the MHD parameters (e.g., Rem) and the initial stellar rotation rate to impact the geometry of the field and differential rotation at the convective–radiative interface.

Effect of supersaturation distribution on particle heterogeneous condensation in growth tube

AbstractSupersaturation is a critical factor influencing the growth of fine particles in heterogeneous nucleation processes. To further investigate its effects on particle growth behavior, this study employs numerical simulations, coupling the particle growth rate equation with a population balance model to systematically analyze the impact of various supersaturation distributions on particle growth. The results indicate that, in the axial direction, the closer the supersaturation peak is to the outlet of the growth tube, the more effective the particle growth, with a maximum increase of 10.20%. In the radial direction, higher supersaturation near the tube wall results in better particle growth at the outlet, with a maximum increase of 28.70%. A more uniform supersaturation field is found to promote particle growth. Conversely, when the supersaturation near the wall is relatively low, particles are less likely to be effectively activated, leading to restricted growth. Additionally, this paper explores the growth of fine particles under different supersaturation field configurations, demonstrating the generality of the observed patterns.

SPATIAL DISTRIBUTION OF ELECTRIC FIELD IN A TWO STAGE HALL TYPE PLASMA SOURCE

The two-stage plasma source of Hall type having common anode and two cathodes residing at locations with essentially different magnetic field configuration is experimentally studied. Considered are peculiarities of spatial distribution of floating potential measured by moved Langmuir probes. In particular, it was established that in the middle plane of the anode on the axis of the device, the value of the floating potential of the plasma is up to 95% of the anode voltage.

Kinks and double-kinks in generalized ϕ4- and ϕ8-models

Examining the ϕ4 and ϕ8 models within a two-dimensional framework in the flat spacetime and embracing a theory with unconventional kinetic terms, one investigates the emergence of kinks/antikinks and double-kinks/antikinks. We devote our study to obtaining the field configurations with minimal energy, i.e., solutions possessing a Bogomol’nyi–Prasad–Sommerfield’s bound. Next, to accomplish our goal, we adopt non-polynomial generalizing functions, namely, hyperbolic sine and cosine functions: the first produce BPS potentials exhibiting a minimum at ϕ=0, facilitating the emergence of genuine double-kink-type configurations. Conversely, the second promotes the rise of kink-type solutions.

The impact of resistivity on the variability of black hole accretion flows

The accretion of magnetized plasma onto black holes is a complex and dynamic process in which the magnetic field plays a crucial role. The amount of magnetic flux that is accumulated near the event horizon significantly impacts the accretion flow behavior. Resistivity, which is a measure of how easily magnetic fields can dissipate, is thought to be a key factor influencing this process. This work explores the influence of resistivity on the accretion flow variability. We investigated simulations that reached the limit of the magnetically arrested disk (MAD) and simulations with an initial multi-loop magnetic field configuration. We employed 3D resistive general relativistic magnetohydrodynamic (MHD) simulations to model the accretion process under various regimes, where resistivity is globally constant (uniform resistivity). Our findings reveal distinct flow behaviors depending on resistivity. High-resistivity simulations never achieved the MAD state, which indicates a disturbed magnetic-flux accumulation process. Conversely, low-resistivity simulations converged toward the ideal MHD limit. The key results are that i) for the standard MAD model, resistivity plays a minimum role in flow variability, suggesting that flux eruption events dominate the dynamics. ii) High-resistivity simulations exhibit strong magnetic field diffusion into the disk that rearranges the efficient magnetic flux accumulation from the accretion flow. iii) In multi-loop simulations, resistivity significantly reduces the flow variability, which was not expected. However, magnetic flux accumulation becomes more variable as a result of frequent reconnection events at very low resistivity values. This study shows that resistivity affects how much the flow is distorted as a result of the magnetic field dissipation. Our findings provide new insights into the interplay between magnetic field accumulation, resistivity, variability, and the dynamics of black hole accretion.

The Minkowski vacuum of stochastic composite gravity

We present a first analysis of a nonperturbative approach to quantum gravity based on a representation of quantum field theory in terms of stochastic processes. The stochastic description accommodates a physical Lorentz-invariant ultraviolet regulator that provides a novel description of physics at ultra-short distances. In a scalar toy model, we demonstrate the evolution of a generic initial field configuration toward an equilibrium in which the composite spacetime metric fluctuates about a flat spacetime. As a diffeomorphism-invariant theory with locally Lorentz-invariant regulator, fluctuations about the vacuum are expected to give rise to an emergent gravitational interaction consistent with Einstein gravity at long distances. We uncover a formal similarity between regularization by stochastic discreteness and point-splitting regularization in the corresponding quantum field theory. We comment on the signature of the emergent spacetime, possible consequences for the early universe, and the potential for observational and experimental tests of the stochastic origin of quantum field theory and gravitation.