External Field Research Articles

A spin current detecting device working in the drift-diffusion and degenerate regimes

<p>A semiconductor-based device working in the spin drift-diffusion regime and for probing the injected or generated spin current was considered. The electric field effects on spin transport were analysed. A drift-diffusion equation for spin density was derived and contributions to the spin current were examined. By referring to the techniques of the spin current injection and generation, expressions for the spin current and spin-induced transverse Hall voltage arising from the injected or generated spin-polarized current were derived. The spin current and Hall voltage in dependences of the external electric field and temperature in the degenerate regime were studied. The device operated on the basis of with no external magnetic fields gives a voltage probe of the spin-induced Hall effect. Finally, a way of enhancing the spin current was explored.</p>

Structural color control by remote electrical manipulation of chiral dopant molecules in a chiral nematic phase

Abstract 1,2-Bis((cholesteryloxy)octyloxy)-4-nitrobenzene was synthesized as a chiral dopant that exhibited electroresponsiveness in nematic liquid crystal (LC) phases. Even in a nonelectroresponsive host nematic LC, the helical pitch of the chiral nematic phase, generated by doping the chiral dopant molecules, could be altered in response to an external electric field, thus controlling the selective reflection color.

Gaining Insights into the Interplay between Optical and Magnetic Properties in Photoexcited Coordination Compounds.

We describe early and recent advances in the fascinating field of combined magnetic and optical properties of inorganic coordination compounds and in particular of 3d-4f single molecule magnets. We cover various applied techniques which allow for the correlation of results obtained in the frequency and time domain in order to highlight the specific properties of these compounds and the future challenges towards multidimensional spectroscopic tools. An important point is to understand the details of the interplay of magnetic and optical properties through performing time-resolved studies in the presence of external fields especially magnetic ones. This will enable further exploration of this fundamental interactions i.e. the two components of electromagnetic radiation influencing optical properties.

Joining of single-core ex-situ MgB2/Fe wires by termination architecture

The development of reliable jointing technique is of great importance for the future of applied superconductivity, especially for superconducting magnets working in persistent mode. Superconducting joints with termination architecture between single-core not reacted ex-situ MgB2/Fe wires were manufactured and tested. I-V characteristics of joints were measured at 4.2 K and 20 K for variable external fields and compared with I-V of joined wire. The ratio of joints critical current to that of parent conductors (Ic-joint/Ic-wire) has been evaluated and discussed. It was found that Ic-joint with termination architecture may be even larger than Ic-wire at high external field, but decreasing for lower fields. Ic-joint/Ic-wire = 0.8 was measured for the best joint at 20 K and low external field 1.5 T, which is promising for functional persistent switch.

Non-conventional resonant behavior of an unconfined magnetic domain wall in a permalloy strip

The resonant dynamic of a magnetic domain wall in a permalloy microstrip has been investigated using an innovative experimental setup that enables a simultaneous measurement of the ferromagnetic resonance and the magnetoresistance. The resonance frequency associated with the presence of the magnetic domain wall increases linearly with the external magnetic field in the range of fields where the domain wall is present in the microstrip. This linear behavior is unusual in a domain wall and not related to the standard resonant modes of a magnetic domain wall, such as breathing, twisting, or translational modes. The slope of this linear dependency is 1.38 GHz/mT, which is an incredibly large value and allows the detection of very small changes in the external magnetic field. This linear behavior opens a path for developing a highly tunable radio frequency oscillator or a magnetic sensing device where the presence of an external field is detected via small variations in the resonant frequency of the domain wall.

Tuning phase structure for enhanced electrostrain in Nb5+-doped Bi0.5(Na0.81K0.19)0.5TiO3 lead-free piezoelectric ceramics

The synthesis of Bi0.5(Na0.81K0.19)0.5Ti1−xNbxO3 (BNKT-xNb) lead-free piezoelectric ceramics via the traditional solid-state method, with varying x from 0.5 % to 4.0 %, is reported. Investigating the influence of Nb5+ ions on dielectric, ferroelectric, and electrostrain properties, alongside assessing the temperature stability of electrical properties, unveiled a notable electrostrain of 0.46 % at room temperature under 80 kV/cm for the 2.0 mol.% Nb5+ doped composition. The incorporation of Nb5+ prompted a transition from the ferroelectric to the relaxor phase, facilitating reversible induction into the ferroelectric phase under an external electric field, leading to the observed large electrostrain. Leveraging the first-order reversal curve (FORC) approach, a detailed analysis of the dynamic response process of different phase structures under the influence of the external electric field was conducted. This analysis elucidated that the continuous polarization response near the boundary of ferroelectric and relaxor phases, induced by the external electric field, primarily drives strain enhancement. These findings underscore the effective modulation of phase structure through Nb5+ doping, offering significant advancements in strain properties. This study opens avenues for the utilization of the material in micro actuators and provides valuable insights for the development of high-performance lead-free piezoelectric ceramics.

The Fermi-LAT view of the changing-look blazar OQ 334

Context. Unusually, there are still certain characteristics of the changing-look (CL) active galactic nuclei (AGNs) that remain undetected. Consequently, the trigger mechanism behind the CL phenomenon observed in partial AGNs remains unknown. Aims. We explore the light curve and spectral energy distribution (SED) of the CL blazar OQ 334 as obtained by Fermi-LAT. Methods. By examining the variability of the equivalent width (EW), we categorise the Fermi-LAT light curves of OQ 334 during the epoch of MJD 54628−58677 into seven distinct epochs, including the flat spectrum radio quasar (FSRQ) state, the transition state, and the BL Lac state. We obtained both a Fermi-LAT SED and a multi-wavelength SED for each of these distinct epochs. Results. The source exhibits a transformation from a quiescent state to a highly active state, as evidenced by the variability of the EW. The multi-wavelength SEDs display a prominent external Compton characteristic, even though the Fermi-LAT SED reveals both a FSRQ and a BL Lac state across the seven different epochs. To gain further insights, we employed a leptonic model that takes into account the soft photon fields originating from both synchrotron radiation and the external environment. By simulating the multi-wavelength SEDs for each epoch, we uncover the following results. Firstly, the energy density of the external photon fields evolves in an oscillatory manner over the seven different epochs. Also, the energy density of the external photon fields in the BL Lac state is lower than that in the FSRQ state. Conclusions. These findings suggest that the CL blazar represents a unique phase in the blazar sequence. Considering that the energy density of the external photon fields is proportional to the accretion rate, we propose that evidence for the interconversion of advection-dominated accretion flow (ADAF) discs and standard Shakura–Sunyaev discs (SSDs), – as variations in accretion modes in the CL blazar – can be obtained through observations by Fermi-LAT.

Laser-induced electro-response of oil shale: Principles and applications

This study introduces a laser-induced electro-response (LIER) method to address the challenges arising from the harsh detection environment and energy consumption in the conversion engineering of oil shale. LIER system with pulsed laser and continuous-wave laser was used to investigate the feasibility of oil yield detection and real-time pyrolysis characterization, respectively. The equivalent circuit model for oil shale measurement under the pulse laser irradiation was established, considering the laser-induced plasma and photoelectric effect. While the laser-induced thermal effect is the main cause of the LIER response of oil shale under continuous-wave laser irradiation. Due to the complex interactions between laser and oil shale, the LIER of oil shale is affected by many factors, such as external electric field, laser source type, laser wavelength, and laser energy or power. The external electric field can improve the responsivity of LIER. The LIER signal of oil shale strongly positively correlates with oil yield. Hence, the LIER evaluated oil yield more quickly without pyrolysis than traditional methods, which is helpful for the exploration for oil shale. In addition, the multi-stage LIER responses were monitored in real time during the combustion and pyrolysis processes of oil shale samples in air and N2 atmosphere, respectively, realizing an evaluation of the organic and mineral decomposition, which provides a supplementary approach to conventional chemical techniques. These results show that LIER has great significance for the precise evaluation and effective development of oil shale reservoirs, which will drive the advances in the exploration for oil shale.

Magnetic field effects on the thermomechanical vibration behavior of functionally graded biocompatible material sandwich nanobeams

This study focuses on modeling and analyzing the thermomechanical vibration behavior of sandwich nanobeams made from biocompatible zirconia and Ti-6Al-4V materials. The sandwich nanobeam is composed of the materials mentioned earlier, featuring a porous structure in the core layer. The sandwich nanobeam experiences significant thermal load and is subjected to a horizontal external electromagnetic field. The equations of motion for the sandwich nanobeam were derived through the application of the sinusoidal high-order shear stress theorem and the constitutive equation based on nonlocal strain gradient elasticity. The equations were converted into equations of motion using Hamilton’s principle, incorporating the thermal load and the Lorentz force generated in the electromagnetic field, and solved using the Navier method. Analyses were conducted on the thermomechanical vibration behavior of the sandwich nanoplate, taking into consideration the properties of the sandwich layers, the impact of temperature, and the intensity of the applied horizontal magnetic field. The impact of the porous core layer in the sandwich nanoplate on the porosity volume ratio and porosity distribution function in thermomechanical behavior has been established. Research has demonstrated that the application of an external magnetic field can effectively mitigate the adverse impacts of thermal loads caused by high temperatures.

Relationship between vorticity near the surface and a long-lived vortex raised above it

The ability to predict the behavior of vortices is valuable for solving various scientific problems. One such problem is the evolution of tornado-like vortices near the surface and their connection with the original vortex located at a certain height above the surface. This article considers a two-dimensional axisymmetric hydrodynamic model in which the initial vorticity is maintained by an external force. Using the model, the influence of external force and temperature field on the evolution of vorticity near the surface is studied. It is shown that at relatively short times, the behavior of the resulting tornado-like vortices near the surface is universal and weakly depends on the external force and temperature field. However, over time, this influence becomes significant. It is shown that, depending on the presence of an anomaly in the temperature distribution, the vortex formed at the surface can exist for a long time.

The TDHF code Sky3D version 1.2

The Sky3D code has been widely used to describe nuclear ground states, collective vibrational excitations, and heavy-ion collisions. The approach is based on Skyrme forces or related energy density functionals. The static and dynamic equations are solved on a three-dimensional grid, and pairing is been implemented in the BCS approximation. This updated version of the code aims to facilitate the calculation of nuclear strength functions in the regime of linear response theory, while retaining all existing functionality and use cases. The strength functions are benchmarked against available RPA codes, and the user has the freedom of choice when selecting the nature of external excitation (from monopole to hexadecapole and more). Some utility programs are also provided that calculate the strength function from the time-dependent output of the dynamic calculations of the Sky3D code. New version program summaryProgram Title: Sky3DCPC Library link to program files:https://doi.org/10.17632/vzbrzvyrn4.2Developer's repository link:https://github.com/manybody/sky3dLicensing provisions: GPLv3Programming language: Fortran, with one post-processing utility in Python.Journal reference of previous version:: Schuetrumpf, B., Reinhard, P.G., Stevenson, P.D., Umar, A.S., and Maruhn, J.A. (2018). The TDHF code Sky3D version 1.1. Comput. Phys. Commun. 229 (2018) 211–213.Does the new version supersede the previous version?: Yes.Reasons for the new version: The capability of reproducing the nuclear strength function for a variety of newly-coded external boosts has been added.Nature of problem: Calculating nuclear multipole strength functions is a crucial probe that can help model the nuclear system and its structure properties. A variety of models exist for this task, such as QRPA (Quasiparticle Random Phase Approximation) and its variants, but such approaches are often limited due to symmetry constraints. Time-dependent Hartree Fock (TDHF) has been used to simulate nuclear vibrations and collisions between nuclei for low energies without assuming any symmetry in the system. This code extends the TDHF to calculate the multi-pole strength functions of atomic nuclei. We showcase its reliability by comparing it with the established RPA codes for the calculation of such strength functions.Solution method: We extended previous versions of the Sky3D code [1,2] to include an external boost of multipole type where the user can provide custom input that decides the nature of the multipole (monopole, quadrupole, octupole, and so on) boost. The principal aim is to calculate the multipole strength function, which is the Fourier transform of the time-dependent expectation value of the multipole operator, which has the same form as the external boost. The proper unit conversion is done so that one can extract the exact unit of the thus calculated strength function, which is comparable to the available literature in the field. The boundary conditions are chosen such that a Woods-Saxon-like function cuts off the external field, driving it to zero at the boundary.Summary of revisions: The ability to give a more general external field for excitation has been implemented, which can be of a chosen multipolarity and isospin nature. Then, as a function of time, moments for both isospins and for multipolarities up to L=5 are followed. A new analysis program is included to calculate strength functions and energy weighted sum rules. The ability to specify a mixing parameter in the pairing force is included. This allows a mixed surface-volume pairing to be selected in a way more compatable with QRPA codes for comparison. An updated Makefile is included which makes compilation on Apple silicon computers easier.

Mechanical behavior of multi-layer CORC cable in high external field with 3D numerical model

The degradation of critical current due to mechanical deformation in a high field has a profound impact on the performance of high-temperature superconducting (HTS) structures. The multi-layer conductor on round core (CORC) cable is a widely-applied HTS structure in engineering. Due to the complexity of the multi-layer CORC cable, the contact between the tapes should be considered when simulating the mechanical behavior in high field. In this paper, 3D electromagnetic and mechanical models were developed to investigate the mechanical behavior of the multi-layer CORC cable. Under the same electromagnetic force, the comparisons of mechanical models of a 5-layer CORC cable with different contact methods are presented. Subsequently, the effects of the loading path of the external magnetic field and transport current, the bending geometry of the CORC cable, the winding direction of the HTS tape in the CORC cable, and the shielding current on the mechanical behavior are discussed, respectively. The numerical results are useful for the design and operation of CORC cable in high field.

A kinetic theory approach to modeling prey–predator ecosystems with expertise levels: analysis, simulations and stability considerations

In this paper a kinetic modeling approach for an ecological system is proposed, based on the prey–predator structure in terms of individuals experience. Specifically, a system of nonlinear kinetic equations is formulated using standard tools. Both conservative and nonconservative events are considered since proliferative/destructive rates and an external force field occur. These results are compared to the ones of the classical theory of dynamical system to show their consistency. In addition to a first local analytical result, some numerical simulations are performed. The results thus obtained ensure that the kinetic model behaves in a way consistent with other similar ecological models formulated by dynamical systems, involving ordinary differential equations with lumped dependent variables. For each simulation, stationary solutions are shown. Moreover, oscillations appear for some values of the parameters of the ecological system, and this suggests that bifurcations may appear.

Advanced fuel fusion, phase space engineering, and structure-preserving geometric algorithms

Non-thermal advanced fuel fusion trades the requirement of a large amount of recirculating tritium in the system for that of large recirculating power. Phase space engineering technologies utilizing externally injected electromagnetic fields can be applied to meet the challenge of maintaining non-thermal particle distributions at a reasonable cost. The physical processes of the phase space engineering are studied from a theoretical and algorithmic perspective. It is emphasized that the operational space of phase space engineering is limited by the underpinning symplectic dynamics of charged particles. The phase space incompressibility according to the Liouville theorem is just one of many constraints, and Gromov's non-squeezing theorem determines the minimum footprint of the charged particles on every conjugate phase space plane. In this sense and level of sophistication, the mathematical abstraction of phase space engineering is symplectic topology. To simulate the processes of phase space engineering, such as the Maxwell demon and electromagnetic energy extraction, and to accurately calculate the minimum footprints of charged particles, recently developed structure-preserving geometric algorithms can be used. The family of algorithms conserves exactly, on discretized spacetime, symplecticity and thus incompressibility, non-squeezability, and symplectic capacities. The algorithms apply to the dynamics of charged particles under the influence of external electromagnetic fields as well as the charged particle–electromagnetic field system governed by the Vlasov–Maxwell equations.

Modulation of electronic and optical properties of Bi2Se3/MoTe2 heterostructure by vertical strain and external electric field

Based on the first-principles, the electronic and optical properties of Bi2Se3/MoTe2 van der Waals heterostructure (vdWH) under vertical strain and electric field are studied. The calculated results show that the Bi2Se3/MoTe2 is a type-II band alignment with an indirect band gap of 4.6meV. Compressive strain can increase interfacial charge transfer, the refractive index, reflectivity and absorption coefficient in the infrared region. The electric field can regulate the energy band gap but has little effect on the optical properties. Importantly, the combined action of positive electric field of 0.11 VÅ−1 and vertical strain with the interlayer distance of 2.90Å, leads to the reflectivity reaching 88%. The absorption coefficient is up to 0.7×106 cm-1 in the visible region. The fundamental reason is that the contribution coming from Bi-pz, Te-pz and Mo-dz2 orbital increase near the Fermi level. These research results provide a theoretical basis for material design and device optimization.

Controllable and reversible electric field tuning of photoluminescence response in lanthanide ions doped ferroelectric films

The rare-earth doped ferroelectric photoluminescence (PL) phosphors are attracting considerable interest because of their flexible structure, wide band gap and high-quality fluorescence signal emission. Although the change of PL performance in different samples have been solved to a certain extent, how to achieve the tuning of PL intensity in one sample sensitively and reversibly is still an issue. In this work, we present an "electric-elastic-optical" coupled structure of 0.94Bi0.5Na0.5TiO3–0.06BaTiO3:1 mol%Eu3+ (BNTBT:Eu)/ 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) heterostructures, which transfers strain from the PMN-PT to the BNTBT:Eu film via the converse piezoelectric effect and dynamically modulates the PL response of the epitaxial thin film. Our findings demonstrate that the PL response of the thin film can be effectively and linearly tuned under the influence of an external electric field. The relative change in the PL intensity (ΔI/I) of the BNTBT:Eu film was found to be linearly correlated with the lateral strain of the substrate. We also propose a novel design strategy for detecting strain, with significant implications for using BNTBT:Eu/PMN-PT heterostructures as sensors for integrating piezophotonic devices. This work provides valuable insights into the feasibility of electric field tuning of PL performance, which could inspire future research endeavors in the fields of nanophotonics, optical storage technology and photovoltaics.

Designing of highly-efficient OER and ORR transition metal-nitrogen active centers with the aid of the revised d electron density

It is quite important to suggest a suitable modification method for the design of highly-efficient catalysts with the aid of the local atomic structures of active center. In this work, the d electron density (D’d) of transition metal (TM) ions was revised to correlate the local atomic structures and catalytic activity of TM1N4 active centers by introducing the dynamic radius of TM and N ions. Meanwhile, the “volcano” relationship between the OER/ORR potentials and D’d values was acquired to suggest the modification methods. The pressure (tensile) stress would be applied to increase (weaken) the d-p orbital hybrid strength of Fe1-N (Co1-N and Ni1-N) bonds and increase (reduce) the D’d values of Fe1N4 (Co1N4 and Ni1N4) active centers. Based on the theoretical prediction, the Fe1-pyrrolee N4 (0 %) and Fe1-pyrrolee N4 (−2%) active centers respectively exhibited the lowest overpotentials of 213 mV for OER and 189 mV for ORR in this work. Hence, the revised d electron density could be applied for the method of external stress field, and this strategy would be adopted to design more highly-efficient catalysts.

Insights into enhanced antiferroelectricity in doped-niobate perovskites for high energy-storage density applications

Lead-free antiferroelectric (AFE) ceramics have attracted increasing attention in recent years for application in high-power capacitors due to their environmental friendliness and high energy density. Among these ceramics, NaNbO3 is noteworthy as one of the few lead-free perovskites displaying an AFE structure. However, despite the nature of AFE symmetry in NaNbO3 with Nb antipolar state, in most cases, it behaves like a ferroelectric (FE) material with an external electric field and exhibits a single polarization-electric field (P-E) hysteresis loop. In order to enhance the antiferroelectricity, a composition modification strategy based on the tolerance factor (t) has been used to stabilize the AFE phase effectively. Yet, in the context of NaNbO3 ceramics, the impact of doping on the evolution of antiferroelectricity has remained unexplored. Through first-principles calculations, we unveil how the chemical modification of NaNbO3 enhances antiferroelectricity by investigating local distortions that favor the AFE state over the FE state in solid solutions. This adjustment in the relative stability between the FE state and AFE state results in a significant modification in the switching barrier in NaNbO3-based antiferroelectrics, ultimately leading to well-defined double polarization loops. This work offers a rationalized atomic-scale perspective on the AFE-FE phase transition in NaNbO3-based ceramics, aiming to contribute to the development of novel lead-free antiferroelectric oxides for energy storage applications.

Numerical simulation of fluid-thermal-structural coupling characteristics of stratospheric non-rigid airship

The voluminous stratospheric non-rigid airship is very sensitive to the external thermal environment. The temperature change of internal gas caused by the variation in the external thermal environment and wind speed will lead to a change in the shape and buoyancy of the airship, thereby affecting its flight control. The traditional static analysis method is difficult to accurately reflect this fluid-thermal-structural coupling process. In this paper, the iterative analysis method was established for the fluid-thermal-structural coupling effect of stratospheric non-rigid airship based on the models of fluid, thermal, and structural deformation. Considering the load such as the internal thermal effect and external flow field of the airship, the simulation of the thermo-induced structural deformation effect was conducted using Fluent and Abaqus software. The influence of local time and external wind speed on the structural deformation, volume, and equilibrium altitude of the airship was analyzed. The results demonstrate that, at low wind speed, the influence of aerodynamic pressure on the deformation of the airship is negligible. However, a great amount of heat is carried away by the wind, then the structural deformation caused by internal and external pressure difference is alleviated and the equilibrium altitude of the airship change obviously. This can serve as a guideline for the design and flight test of the long-endurance stratospheric non-rigid airship.

Data-driven surrogate modelling of multistage Taylor cone–jet dynamics

The Taylor cone jet is an electrohydrodynamic flow typically induced by applying an external electric field to a liquid within a capillary, commonly utilized in colloidal thrusters. This flow generation involves a complex multiphase and multiphysics process, with stability contingent upon specific operational parameters. The operational window is intrinsically linked to flow rate and applied electric voltage magnitude. High voltages can induce atomization instabilities, resulting in the production of an electrospray. Our study presents initially a numerical investigation into the atomization process of a Taylor cone jet using computational fluid dynamics. Implemented within OpenFOAM, our numerical model utilizes a volume-of-fluid approach coupled with Maxwell's equations to incorporate electric body forces into the incompressible Navier–Stokes equations. We employ the leaky-dielectric model, subjecting the interface between phases to hydrodynamic surface tension and electric stress (Maxwell stress). With this model, we studied the droplet breakup of a heptane liquid jet, for a range of operation of 1.53–7.0 nL s−1 and 2.4–4.5 kV of extraction. First, the developed high-fidelity numerical solution is studied for the jet breakup and acceleration of the droplets. Second, we integrate a machine learning model capable of extending the parametric windows of operation. Additionally, we explore the influence of extractor and acceleration plates on colloidal propulsion systems. This work offers a numerical exploration of the Taylor cone–jet transition and droplet acceleration using novel, numerically accurate approaches. Subsequently, we integrate machine learning models, specifically an artificial neural network and a one-dimensional convolutional neural network, to predict the jet's performance under conditions not previously evaluated by computationally heavy numerical models. Notably, we demonstrate that the convolutional neural network outperforms the artificial neural network for this type of application data, achieving a 2% droplet size prediction accuracy.