Weak Field Research Articles

On the Parameters of the Spherically Symmetric Parameterized Rezzolla–Zhidenko Spacetime through Solar System Tests, the Orbit of the S2 Star about Sgr A*, and Quasiperiodic Oscillations

In this paper, we find the higher-order expansion parameters α and λ of spherically symmetric parameterized Rezzolla–Zhidenko (PRZ) spacetime by using its functions of the radial coordinate. We subject the parameters of this spacetime to classical tests, including weak gravitational field effects in the solar system, observations of the S2 star that is located in the star cluster close to the Sgr A⋆, and of the frequencies of selected microquasars. Based on this spherically symmetric spacetime, we perform the analytic calculations for solar system effects such as perihelion shift, light deflection, and gravitational time delay to determine limits on the parameters by using observational data. We restrict our attention to the limits on the two higher-order expansion parameters α and λ that survive at the horizon or near the horizon of spherically symmetric metrics. The properties of the expansion of these two small parameters in PRZ parameterization are discussed. We further apply Markov Chain Monte Carlo simulations to analyze and obtain the limits on the expansion parameters by using observations of the phenomena of the S2 star. Finally, we consider the epicyclic motions and derive analytic expressions of the epicyclic frequencies. Applying these expressions to the quasiperiodic oscillations of selected microquasars allows us to set further limits on the parameters of the PRZ spacetime. Our results demonstrate that the higher-order expansion parameters can be given in the range α, λ = (−0.09, 0.09) and of order ∼10−2 as a consequence of three different tests and observations.

Oscillation of Dzyaloshinskii–Moriya interaction driven by weak electric fields

Dzyaloshinskii–Moriya interaction (DMI) is under extensive investigation considering its crucial status in chiral magnetic orders, such as Néel-type domain wall (DW) and skyrmions. It has been reported that the interfacial DMI originating from Rashba spin–orbit coupling (SOC) can be linearly tuned with strong external electric fields. In this work, we experimentally demonstrate that the strength of DMI exhibits rapid fluctuations, ranging from 10% to 30% of its original value, as a function of applied electric fields in Pt/Co/MgO heterostructures within the small field regime (< 10−2 V/nm). Brillouin light scattering (BLS) experiments have been performed to measure DMI, and first-principles calculations show agreement with this observation, which can be explained by the variation in orbital hybridization at the Co/MgO interface in response to the weak electric fields. Our results on voltage control of DMI (VCDMI) suggest that research related to the voltage control of magnetic anisotropy for spin–orbit torque or the motion control of skyrmions might also have to consider the role of the external electric field on DMI as small voltages are generally used for the magnetoresistance detection.

Variation in properties of double-walled zigzag and armchair silicon nanotubes depending on SW defects and applied electric fields by SCC-DFTB method

The geometric structure and electrical properties of the zigzag DWSiNT (8,0)@(12,0) and armchair DWSiNT (5,5)@(7,7) perfect tubes with the same diameter are simulated by self-consistent charge density functional tight binding method (SCC-DFTB). We considered the defective tubes by introducing three types of Stone-Wales (SW) defects, and further investigated the impact of both strong and weak electric fields on these defective tubes. Calculations demonstrate that the atomic arrangement regularity, degree of buckling, stability, energy gap, and charge distribution strongly depend on the type of perfect tubes. Following the introduction of the SW defects, the symmetry of the tubes disappeared, and there is a obvious atomic aggregation occurring at the defects. The armchair tubes demonstrate a higher stability compared to zigzag tubes and all exhibit metallic properties. SWⅡ and SWⅢ defects in zigzag tubes result in a transition from semiconductor to semi-metallic properties. The number of charge transfer increases, and the degree of atomic aggregation is more dispersed. The effect of applied electric field strength on perfect zigzag tubes is more obvious. The weak field has minimally impacted on the stability, and the strong field makes the stability improved to some extent. The presence of a strong field caused the energy gap values of (8,0)@(12,0) tube decrease sharply, and all tubes are transformed into semi-metal or metal. The weak electric field has a more pronounced regulation of band gap within the range of 0 V/nm - 0.3 V/nm on the inner tube. The consequences of this investigation can certainly be helpful in future experimental studies.

Ni2+-doped MgTa2O6 phosphors capable of near-infrared II and III emission under blue-light excitation

Presently, Ni2+-activated near-infrared (NIR) phosphors still have disadvantages such as relatively short emission wavelength and narrow half-peak width, mismatched excitation wavelength to that of commercially available high-efficiency blue chips. Here, Ni2+-doped tetragonal MgTa2O6 NIR phosphor was successfully prepared by high-temperature solid phase method. The matrix material provided an octahedral lattice for Ni2+ to replace Ta5+ in the [TaO6] octahedron of the crystal lattice. Under the excitation of 470 nm blue light, Ni2+ was excited through 3T2(F)→3A2(F) spin-allowed transition and emitted an ultra-broadband NIR light that was 1300–2000 nm in wavelength, peaked ∼ 1620 nm, covered the NIR-II and NIR-III regions, had a full width at half maximum reached 297 nm, and a PLQY of 25.62 %. The unique ultra-broadband and long wavelength NIR emission by this phosphor was derived from Ni2+ which is situated in a weak crystal field environment due to space asymmetric distortion caused by a high charge polarization surrounding the center of the [TaO6] octahedron in a MgTa2O6 matrix. A NIR pc-LED was constructed using Ni2+-doped near-infrared phosphors packaged with a commercial high-efficiency blue LED chip (@ 470 nm), and its application prospect was demonstrated by NIR night vision monitoring and nondestructive imaging of venous in human fingers.

Reactive molecular dynamics simulations of plastics pyrolysis with additives: Comparison of ReaxFF branches and experimental results

In this work, the efficiency of the combustion and aqueous branches of the reactive potential ReaxFF are compared through pyrolysis investigations from reactive molecular simulations of three polymers: polyethylene (PE), polystyrene (PS) and polypropylene (PP) with additive compounds. Thermogravimetric analyses were implemented, computing the weight loss percentage along with analyzes of the pyrolysis products. Three force fields were considered: the CHON-2019 and the CHOSFClN potentials coming from the combustion branch and the CHONCl-2022_weak potential coming from the aqueous branch. The results show that both CHON-2019 and CHONCl-2022_weak force fields give similar results in adequacy with the experimental results and are better than the CHOSFClN force field from the combustion branch. They can correctly predict the kinetic order of polymer degradation and identify the species formed and their quantities. As a result, the latest versions of the ReaxFF potential, belonging to the aqueous branch, are well suited to study the pyrolysis processes and may give equal or better results than force fields from the combustion branch. Furthermore, force fields from the aqueous branch seem to be more reliable for the investigation of the effect of the additives’ role on plastic pyrolysis. Finally, an important aspect presented in this article is the use of statistical simulations for the different investigations. An uncertainty estimation of 30 K was computed from ten thermogravimetric analyses simulated with ReaxFF on the PP pyrolysis.

Review of: "Nanowires ( SiNWs) have high mobility and surface-to-volume ratio, which makes them easy to control using a weak electric field."

Review of: "Nanowires ( SiNWs) have high mobility and surface-to-volume ratio, which makes them easy to control using a weak electric field."

Mg content regulating built-in electric field for self-powered ZnO/MgxZn1-xO Schottky UV photodetector

In recent years, self-powered Schottky ultraviolet (UV) photodetectors (PDs) have attracted great attention due to their low manufacturing cost and zero-bias response. However, the development of high-performance self-powered Schottky devices is limited by the weak light response due to the internal weak electric field. Here, we introduce a MgxZn1-xO capping layer on ZnO and fabricate a ZnO/MgxZn1-xO heterojunction Schottky UV PD by using the sol-gel method. The improved device exhibits excellent self-powered characteristics and stability, specifically, an increase of 909% in photocurrent, an improvement of more than one order of magnitude in responsivity, and an improved linear dynamic region (LDR: 33.7 dB). The introduction of the MgxZn1-xO capping layer is responsible for the improved device performance, resulting in enhanced built-in electric field and depletion region width due to the increase of the Schottky barrier, thereby facilitating the separation and transport of photogenerated carriers. This work provides an effective way to fabricate high-performance self-powered ZnO Schottky UV PDs.

A phenomenological wobbling model for isolated pulsars and the braking index

ABSTRACT An isolated pulsar is a rotating neutron star possessing a very high magnetic dipole moment, thus providing a powerful radiating mechanism. These stars loose rotational energy E through various processes, including a plasma wind originating from a highly magnetized magnetosphere and the emission of magnetic dipole radiation (MDR). Such phenomena produce a time decreasing angular velocity Ω(t) of the pulsar that is usually quantified in terms of its braking index. Although these mechanisms are widely acknowledged as the primary drivers of the spin evolution of isolated pulsars, it is plausible that other contributing factors influencing this effect have yet to be comprehensively investigated. Most of young isolated pulsars present a braking index different from that given by the MDR and plasma wind processes. Working in the weak field (Newtonian) limit, we take in this work a step forward in describing the evolution of such a system by allowing the star’s shape to wobble around an ellipsoidal configuration as a backreaction effect produced by its rotational deceleration. It is assumed that an internal damping of the oscillations occurs, thus introducing another form of energy loss in the system, and this phenomenon may be related to the deviation of the braking index from the models based on $\dot{E} \sim -\Omega ^4$ predictions. Numerical calculations suggest that the average braking index for typical isolated pulsars can be thus explained by a simple phenomenological model.

Gravitational lensing effects of black hole with conformally coupled scalar hair

In this paper, we investigate the gravitational lensing effects in the weak and strong field limits of a static black hole with conformally coupled scalar field. In the weak field limit, with the use of Gauss–Bonnet theorem we calculate the deflection angle of the light. It is found that comparing to Schwarzschild and Reissner–Nordstro¨\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ddot{\ ext {o}}$$\\end{document}m (RN) black holes in general relativity, the weak deflection angle can be enhanced/suppressed by the scalar hair. In the strong field limit, we first compute the light deflection angle via calculating the lensing coefficients, all of which increase as the values of electric and scalar charges increase. Then we evaluate the lensing observables in strong field regime by supposing the hairy black hole as the candidate of M87* and SgrA* supermassive black holes, respectively. We find that the scalar hair has significant influences on various observables. In particular, the lensing observables of the charged black hole with positive scalar hair and RN black hole have degeneracy, which will be broken by the case with negative scalar hair. Our theoretical findings imply that it is feasible to employ the gravitational lensing effects as a probe of Einstein–Maxwell theory with negative scalar field differentiating from general relativity, once the future astrophysical observation is precise enough.

Passive electroreception in bottlenose dolphins (Tursiops truncatus): implication for micro- and large-scale orientation.

For the two dolphin species Sotalia guianensis (Guiana dolphin) and Tursiops truncatus (bottlenose dolphin), previous research has shown that the vibrissal crypts located on the rostrum represent highly innervated, ampullary electroreceptors and that both species are correspondingly sensitive to weak electric fields. In the present study, for a comparative assessment of the sensitivity of the bottlenose dolphin's electroreceptive system, we determined detection thresholds for DC and AC electric fields with two bottlenose dolphins. In a psychophysical experiment, the animals were trained to respond to electric field stimuli using the go/no-go paradigm. We show that the two bottlenose dolphins are able to detect DC electric fields as low as 2.4 and 5.5 µVcm-1, respectively, a detection threshold in the same order of magnitude as those in the platypus and the Guiana dolphin. Detection thresholds for AC fields (1, 5 and 25 Hz) were generally higher than those for DC fields, and the sensitivity for AC fields decreased with increasing frequency. Although the electroreceptive sensitivity of dolphins is lower than that of elasmobranchs, it is suggested that it allows for both micro- and macro-scale orientation. In dolphins pursuing benthic foraging strategies, electroreception may facilitate short-range prey detection and target-oriented snapping of their prey. Furthermore, the ability to detect weak electric fields may enable dolphins to perceive the Earth's magnetic field through induction-based magnetoreception, thus allowing large-scale orientation.

Optical bistability modulation based on graphene sandwich structure with topological interface modes.

In this paper, we have investigated optical bistability modulation of transmitted beam that can be achieved by graphene sandwich structure with topological interface modes at terahertz frequency. Graphene with strong nonlinear optical effect was combined with sandwich photonic crystal to form a new sandwich structure with topological interface modes. The light-limiting properties of the topological interface modes, as well as its high unidirectionality and high transmission efficiency, all contribute positively to the reduction of the optical bistability threshold. In addition, the topological interface modes can effectively ensure the stability of the two steady state switching in the case of external interference. Moreover, optical bistability is closely related to the incident angle, the Fermi energy, the relaxation time, and the number of layers of graphene. Through parameter optimization, optical bistability with threshold of 105 V/m can be obtained, which has reached or is close to the range of the weak field.

For description of the wave (quantum) component of all living beings: A nonlinear Schrodinger equation is offered analog of the Kardar-Parisi-Zhang nonlinear mathematical model

Everything material is material body and nonlinear electromagnetic field (NEMF1), which is the basis of the duality wave-particle. All living beings have one more NEMF (NEMF2) - a weak informational field that rules and regulates everything in the body not with its strength, but with the information it carries, which makes it essential for the health of all living beings. The article first explains why the Kardar-Parisi-Zhang nonlinear mathematical model is universally applicable to all states in dynamic nonequilibrium. At the roots of this success is the fact that all dynamic events are successfully described only with nonlinear equations and Kardar-Parisi-Zhang mathematical model is a nonlinear differential equation. The model proved to be successfully applicable to a wide range of events: growing bacterial colonies, growing crystals, aggregating colloidal clusters, the dynamic of burning regions of forest or grassland, even the dynamic of eroded by acid rain statues, etc. Since everything material is a material body and a wave component - nonlinear electromagnetic field (NEMF1) and every living being is NEMF1 + NEMF2, by analogy with the Kardar-Parisi-Zhang nonlinear mathematical model, this article offers a nonlinear Schrödinger equation to describe the wave component (NEMF1) of everything material and NEMF1 + NEMF2 of every living being.

Polarization-dependent intensity ratios in double resonance spectroscopy.

Double Resonance is a powerful spectroscopic method that unambiguously assigns the rigorous quantum numbers of one state of a transition. However, there is often ambiguity as to the branch (ΔJ) of that transition. Spectroscopists have resolved this ambiguity by using the dependence of the double resonance intensity on the relative polarization directions of pump and probe radiation. However, published theoretical predictions for this ratio are based upon a weak (i.e., non-saturating) field approximation. This paper presents theoretical predictions for these intensity ratios for cases where the pump field is strongly saturating in the two limits of transitions dominated by homogeneous or of inhomogeneous broadening. Saturation reduces but does not eliminate the magnitude of the polarization effect (driving the intensity ratio closer to unity) even with strong pump saturation. For the case of an inhomogeneously broadened line, such as when Doppler broadened linewidth dominates over the power-broadened homogeneous line width, a large fraction of the low pump power polarization anisotropy remains. This paper reports predicted polarization ratios for both linear and circular pump and probe field polarizations. The present predictions are compared with experimental measurements on CH4 ground state → ν3 → 3ν3 transitions recently reported by de Oliveira et al.63 and these are in better agreement than with the weak field predictions.

Synergistic effects of periodic weak spark and spatial electric field for one-step dispersion of carbon-based micro/nanomaterial agglomerates

Agglomeration and entanglement pose significant challenges in carbon-based micro/nanomaterials application, hindering the complete expression and fine-tuning of individual properties. A universal spatiotemporal electrified (STE) approach is proposed, which enables the efficient separation of individual constituents from agglomerates, achieving one-step dispersion in the gas phase. This process operates through two features: (1) periodic weak spark loosening and (2) spatial electric field attraction. The periodic weak spark, self-induced and automatically triggered by the material, generates induced electromagnetic fields and shock waves that facilitate repulsion, propulsion, and loosening of the agglomerate structure, endowing the material with capability to overcome the high frictional barriers. Simultaneously, the constructed spatial electric field continuously attracts, selectively separating and outputting individual micro/nanomaterials in real-time. This results in a one-step, concise dispersion process with additional benefits like alignment and blending. Overall, the STE approach has broad applicability and potential to unlock the full capabilities of micro/nanomaterials in various applications.

Research on Rotor Loss and Rotor Structure Optimization of Rare Earth Permanent Magnet Synchronous Motors in the Weak Field Area

The rotor loss of rare earth permanent magnet synchronous motor (PMSM) affects the efficiency and reliability of the motor and is an important research direction of rare earth permanent magnet synchronous motors. In this paper, the influence of rotational speed on the loss of the rotor core and the permanent magnet is analyzed through the analysis of the motor magnetic field and rotor loss calculation. Specifically, with the increase in rotational speed, the weak magnetic current increases, the amplitude of flux density change in the rotor core decreases, and the loss of the rotor core also decreases. The greater the influence of the harmonic current magnetic field on the outside of the rotor, the greater the loss. The core loss on the rotor is mainly distributed on the outside of the rotor. For further engineering applications, this paper analyzes the loss composition of three kinds of motors with different rotor structures and judges the optimal scheme based on the minimum loss. Finally, the correctness of this research is verified by comparing the experimental and simulation results of two kinds of motors with different rotor structures. The research content of this paper can provide a reference for the loss analysis and optimization and rotor structure selection of rare earth permanent magnet synchronous motor rotor design.

MHD in a Cylindrical Shearing Box. II. Intermittent Bursts and Substructures in MRI Turbulence

By performing ideal magnetohydrodynamical (MHD) simulations with weak vertical magnetic fields in unstratified cylindrical shearing boxes with modified boundary treatment, we investigate MHD turbulence excited by magnetorotational instability. The cylindrical simulation exhibits extremely large temporal variation in the magnetic activity compared with the simulation in a normal Cartesian shearing box, although the time-averaged field strengths are comparable in the cylindrical and Cartesian setups. Detailed analysis of the terms describing magnetic energy evolution with “triangle diagrams” surprisingly reveals that in the cylindrical simulation the compression of toroidal magnetic field is unexpectedly as important as the winding due to differential rotation in amplifying magnetic fields and triggering intermittent magnetic bursts, which are not seen in the Cartesian simulation. The importance of the compressible amplification is also true for a cylindrical simulation with tiny curvature; the evolution of magnetic fields in the nearly Cartesian shearing box simulation is fundamentally different from that in the exact Cartesian counterpart. The radial gradient of epicyclic frequency, κ, which cannot be considered in the normal Cartesian shearing box model, is the cause of this fundamental difference. An additional consequence of the spatial variation of κ is continuous and ubiquitous formation of narrow high-density (low-density) and weak-field (strong-field) localized structures; seeds of these ring gap structures are created by the compressible effect and subsequently amplified and maintained under the marginally unstable condition regarding “viscous-type” instability.

Correlated random walk and noise suppression in detecting electric fields

Detecting a weak electric field in a strong noisy background is always an interesting but hard task. We investigate the collective effects of charged Brownian particles in the presence of a weak electric field together with a strong noisy background field by numerical simulation. We show that the pattern formed by snapshots touched by the Brownian particles on one boundary surface can manifest the direction of an applied weak electric field but will be spoiled if there exists a strong noisy background. Moreover, we find that the influence of noise can be suppressed effectively if the correlations caused by the inter-particle electric interaction are taken into account. This work is expected to provide a new angle of view: correlated random walk plays a constructive role in noise suppression.

Data-constrained Magnetohydrodynamic Simulation of an Intermediate Solar Filament Eruption

Solar eruptive activities could occur in weak magnetic field environments and over large spatial scales, which are especially relevant to eruptions involving intermediate or quiescent solar filaments. To handle the large scales, we implement and apply a flux rope embedding method using regularized Biot–Savart laws in the spherical coordinate system. Combined with a potential field source surface model and a magneto-frictional method, a nonlinear force-free field comprising a flux rope embedded in a potential field is constructed. Using the combined nonlinear force-free field as the initial condition, we then perform a zero-β data-constrained magnetohydrodynamic (MHD) simulation for an M8.7 flare at 03:38 UT on 2012 January 23. The MHD model reproduces the eruption process, flare ribbon evolution (represented by the quasi-separatrix layer evolution), and kinematics of the flux rope. This approach could potentially model global-scale eruptions from weak field regions.

Grain-size effect on Cr3+ and F-centres photoluminescence in nanophase MgAl2O4 ceramics

Photoluminescence (PL) spectroscopy of transparent MgAl2O4 spinel ceramics with grain size between 100 and 300 nm was studied at 7 K temperature in the near-IR-VUV range of spectrum with synchrotron radiation excitation. The PL spectra were composed of optical transitions from spatially different regions of the ceramics, which analysis evidenced grain size effect on the emission line-shapes and intensities. In particular, emission of impurity Cr3+ ions, being structured in the crystalline bulk, became broad-band in the grain boundary regions, which was associated with respectively strong and weak local crystalline fields. It was observed that (i) excitons and F centres transfer energy to Cr3+ and (ii) Cr(2Eg)/Cr(4T2g) and F-centres/Cr3+ PL intensity ratios underwent a linear dependence on the grain size.

Influence of Crustal Magnetic Fields on Horizontal Plasma Transport and Ion Escape on Mars

Owing to its unevenly distributed crustal fields, Mars acts as a unique obstacle to the solar wind. In the presence of the crustal fields, the transport of the planetary ions on the dayside ionosphere exhibits north–south asymmetry. Additionally, the heavy-ion loss in the magnetotail is affected by the crustal fields. In this paper, a three-dimensional multispecies magnetohydrodynamic model is employed to simulate Mars–solar wind interactions. Numerical results indicate that the meridional transport is dominant in most areas on the dayside ionosphere. In the presence of the crustal fields, the meridional transport on the southern hemisphere (southward transport) is reduced by more than 70% above the strong crustal sources, and the zonal velocity shows local changes inside strong and weak crustal field regions. These effects result in an increase or decrease in the number density of the heavy ions reaching the terminator, thereby influencing the thickness of the ionosphere. Decreased southward velocity leads to a reduction in the heavy-ion loss on the southern magnetotail. The radial outward flux is reduced by more than 30% for O2 + and CO2 + and by 10% for O+. This study shows that in addition to the zonal transport, the meridional transport is important for the day-to-night transport on the dayside of Mars. Collectively, the horizontal plasma transport, controlled by crustal fields, is associated with the altered ionosphere structure and reduced heavy-ion loss in the magnetotail.