External Field Coupling Research Articles

In-situ synchrotron X-ray investigating crystallization of isotactic polypropylene with β-nucleating agent during injection molding

The coupling effects of mold temperature and packing pressure fields on structure evolution of isotactic polypropylene with β-nucleating agent (iPP/β) during injection molding were systematically investigated using high-throughput in-situ synchrotron X-ray diffraction/scattering technology for the first time. A small number of β-crystals are generated in pure iPP and iPP/β due to the shear flow introduced by the filling stage. The formation of β-crystals induced by β-nucleating agent (β-NA) in iPP/β commenced after about 1.8 s of melt filling. The two-stage growth of β-crystals in iPP/β exhibits differences in growth time and orientation. Both the decrease in the lattice spacing and the β-α transition in iPP/β occur at the packing stage and are suppressed at high mold temperatures (≥ 90 °C). The polymorphism competitive growth of iPP/β is revealed, and the effects of coupling external fields on it are well elucidated by combining finite element simulation and classical nucleation theory. Additionally, the scattering intensity and orientation of iPP/β lamellae initially increase to a maximum value and subsequently decrease until reaching the equilibrium with time. Our current work lays a solid foundation to precisely customize the crystal structure of iPP/β in practical processing and thus to produce high-performance iPP products.

Measurement of steep dispersion associated with magnetically assisted gain in Zeeman degenerate two-level system of cold atoms

We report on the measurements of magnetically assisted dispersion and gain in a Zeeman degenerate two-level system associated with the closed D 2 hyperfine transition Fg=3→Fe=2 cold cesium atoms. We use a Mach–Zehnder interferometer to measure the dispersive properties of this system in the presence of a magnetic field, transversal to the quantization direction, when the atomic system is excited by a coupling and probe beams with orthogonal polarizations. We have measured the spectrum of the refraction index for different magnitudes of the external magnetic field and different coupling beam intensities. A previously published theoretical model, using a simpler atomic transition Fg=1→Fe=0 , accounts reasonably for the experimentally observed gain and dispersive lineshapes.

Electron-Delocalization-Stabilized Photoelectrocatalytic Coupling of Methane by NiO-Polyoxometalate Sub-1 nm Heterostructures.

The oxidative coupling of methane to C2 oxygenates merits great scientific and technological potential yet remains a challenge due to its inferior selectivity. Subnanomaterials (SNMs) with "p-n-p-n"-type heteroconstructions feature enhanced external field coupling properties and tunable electronic structures, serving as promising catalysts for the selective partial oxidation of methane. Here we develop NiO-polyoxometalate (POM) subnanocoils with a thickness of 1.8 nm, showing excellent catalytic activity toward photoelectrochemical coupling of methane into a C2 product under mild conditions (1 bar, 25 °C) with a notable productivity (up to 4.48 mmol gcat-1 h-1) and a high selectivity (>99%). Under photoelectrochemical coupling, C-H bonds can be activated by NiO, and the resulted *COOH intermediates are stabilized by the delocalized electrons in POM clusters. The contiguous active sites of NiO and POM at the molecular level allow the in situ coupling of *COOH into oxalate. This work points out an economic way for the oxidation of methane under mild conditions and may enlighten the design of functional SNMs from fundamental standpoints.

Resonant-dissipative model of ultrafast spin dynamics

The paper proposes a resonant-dissipative model of ultrafast spin dynamics, which takes into account the effects of both an external magnetic field and spin-orbit coupling. It is shown that under the combined action of these factors it is possible to control the polarizability of ferromagnets, which determines the permittivity and refractive index of the systems under study.

External Field Coupling to Superconducting Microstrip Transmission Line in Nonlinear Operation

External Field Coupling to Superconducting Microstrip Transmission Line in Nonlinear Operation

Optical properties of methyl-substituted germanane monolayer in the presence of the external magnetic field, strain and spin-orbit coupling.

In this research, we use the tight-binding model, which includes spin-orbit coupling and an external magnetic field, to describe the optical properties of the methyl-substituted germanane (GeCH3) monolayer. We have applied the Kubo formula, linear response theory, and Green's function approach to calculate the optical absorption coefficient of the GeCH3monolayer. Here, the effects of an external magnetic field, strain, spin-orbit coupling, temperature, and electron/hole doping on the frequency dependence behavior of the optical conductivity have been investigated in detail. Our numerical results show that with increasing the external magnetic field, strain, and electron doping, the weight of the Drude increases. The optical absorption peak decreases and shifts to higher frequencies by applying an external magnetic field, strain, and electron doping. Controlling the optical and electronic properties of GeCH3is leading to use this structure it in the electronic and optoelectronic industries.

Mechanical tailoring of dislocations in ceramics at room temperature: A perspective

AbstractThe potential of dislocations (line defects) in ceramics may have been greatly underrated until most recently. Promising proofs‐of‐concept have been demonstrated for dislocation‐tuned functional and mechanical properties, revealing a new research front for dislocations in ceramics for a wide range of potential applications. However, it is commonly known that ceramics are hard (difficult to deform) and brittle (easy to fracture), particularly at room temperature. It remains a great challenge to mechanically tailor dislocations in ceramics. To address this pressing bottleneck, this article discusses the mechanics‐based dislocation engineering in ceramics by examining the three fundamental factors of dislocation nucleation, multiplication, and motion. Successful experimental approaches to tune dislocation density and plastic zone size on single‐crystal strontium titanate are demonstrated. The dislocation‐based competition between plastic deformation and crack formation is discussed. The aspects of coupling external fields to manipulate dislocations are highlighted, which may hold the key to modulating the charged dislocation cores in ceramics and opening new routes for mechanical tailoring of dislocations at room temperature. Some open questions and challenges for engineering dislocations in ceramics are discussed.

Recent Advances in External Fields‐Enhanced Electrocatalysis

AbstractElectrocatalytic technology provides a promising approach for energy storage, conversion, and utilization. The design and modification of electrocatalysts have been widely applied to improve the performance of electrocatalytic reactions, but bottlenecks can be entered that make it hard to make dramatic progress. The achievement of high‐performance electrocatalysis requires a continuous effort in advancing the new techniques. The introduction of external fields is an attractive approach to improve the mass transfer and change the reaction kinetics, which can remarkably enhance the electrocatalytic performance. This review describes the recent developments in the application of various external fields, including light, magnetic fields, elastic strain, external pressure, and gravity, to boost electrocatalytic reactions (e.g., water splitting, alcohols oxidation, CO2 reduction, and N2 reduction). The relevant mechanisms of external fields to boost charge transport, mass transfer, and the adsorption of reactants are highlighted. Finally, the remaining challenges and future opportunities for coupling external fields with electrocatalysis are discussed.

Plants transpiration-inspired antibacterial evaporator with multiscale structure and low vaporization enthalpy for solar steam generation

Solar-driven vapor generation by localized solar heating of a photothermal material is an environmentally friendly approach for seawater desalination and wastewater purification. In this work we designed a novel bionic evaporator, inspired by plant transpiration in nature, to realize highly efficient solar vapor generation. The plant transpiration inspired three-dimensional structure has a hydrophilic cellulose skeleton with high porosity and low thermal conductivity, and decorated with photothermal polypyrrole (PPy) that self-organize as nano branches and leaves exhibiting excellent photothermal conversion capacity. The cellulose skeleton has microchannels that facilitates water transport and reduces the water evaporation enthalpy. PPy nano branches and leaves can not only efficiently absorb and convert sunlight, but the thermal gradient distribution in this microstructure induces Marangoni convection which guarantees efficient water transportation in evaporative regions. Moreover, the coupling of external wind fields further enhances the rate of vapor escape. The as-fabricated vapor generator based on the bionic structure achieved an impressive high evaporation rate of 2.05 kg m−2 h−1 under one sun (1 kW m−2) irradiation, with the solar thermal conversion efficiency up to 97.7%. A significantly higher water vapor generation rate of 2.9 kg m−2 h−1 is obtained under one sun irradiation at a wind speed of 2 m s−1. In addition, the evaporator has excellent photothermal antibacterial activity against both E. coli and S. aureus. This bionic evaporator offers a potential low-cost and highly efficient water purification technology that could help mitigate the global water crisis.

Entanglement of a cavity with a three-level atom and a graphene membrane in the presence of a laser field

This paper examines the entanglement and coherence of a hybrid quantum system in the presence of an external laser field. The hybrid system is composed of a single-mode cavity field containing a vibrating graphene membrane and a superconducting qutrit in a cascade configuration. Specifically, we investigate how the coupling of qutrit-graphene, detuning parameters, and external field coupling affects different measures, such as negativity tangle, algebraic tangle, geometric tangle, and the l1 norm of coherence. Our results demonstrate that the upper bounds of tangle measures and coherence decrease with increasing the detuning parameters. The external field amplifies the detrimental impact caused by detuning. Furthermore, heightened qutrit-graphene coupling elevates the maximum bounds of tangle and coherence quantifiers, while also increasing the frequency of oscillations.

Higher-order magnetic skyrmions in nonuniform magnetic fields

For a two-dimensional Hubbard model with spin-orbit Rashba coupling in external magnetic field the structure of effective spin interactions is studied in the regime of strong electron correlations and at half-filling. It is shown that in the third order of perturbation theory, the scalar and vector chiral spin-spin interactions of the same order arise. The emergence of the latter is due to orbital effects of magnetic field. It is shown that for nonuniform fields, scalar chiral interaction can lead to stabilization of axially symmetric skyrmion states with arbitrary topological charges. Taking into account the hierarchy of effective spin interactions, an analytical theory on the optimal sizes of such states, the higher-order magnetic skyrmions, is developed for axially symmetric magnetic fields of the form $h(r)\ensuremath{\sim}{r}^{\ensuremath{\beta}}$ with $\ensuremath{\beta}\ensuremath{\in}\mathbb{R}$.

Phase transition of three-dimensional finite-sized charged dust clusters in a plasma environment.

The dynamics of a harmonically trapped three-dimensional Yukawa ball of charged dust particles immersed in plasma is investigated as function of external magnetic field and Coulomb coupling parameter using molecular dynamics simulation. It is shown that the harmonically trapped dust particles organize themselves into nested spherical shells. The particles start rotating in a coherent order as the magnetic field reaches a critical value corresponding to the coupling parameter of the system of dust particles. The magnetically controlled charged dust cluster of finite size undergoes a first-order phase transition from disordered to ordered phase. At sufficiently high coupling and strong magnetic field, the vibrational mode of this finite-sized charged dust cluster freezes, and the system retains only rotational motion.

The effects of spin-orbit coupling on optical properties of monolayer text {MoS}_{2} due to mechanical strains

We have studied the optical conductivity of a quasi two-dimensional text {MoS}_{2} in the presence of external magnetic field and spin-orbit coupling. Specially, we address the frequency dependence of optical conductivity due to spin-orbit interaction. Using linear response theory the behavior of optical conductivity has been obtained within Green’s function method. We have also considered the effects of uniaxial and biaxial in-plane strain on the optical absorption of text {MoS}_{2} layer. In the absence of external magnetic field with negative uniaxial strain parameter, optical conductivity includes Drude weight at zero frequency limit while Drude weight vanishes for text {MoS}_{2} layer under positive uniaxial strain. Our results show that the increase of uniaxial positive strain parameter causes to move the position peak to the higher frequencies. In contrast to uniaxial strain case, the Drude weight in optical conductivity appears at positive biaxial strain value 0.15. Also we have studied the effects of magnetic field, electron doping, hole doping in the presence of spin-orbit coupling on frequency dependence of optical conductivity of text {MoS}_{2} in details. The magnetic field dependence of optical absorption shows a monotonic decreasing behavior for each value of temperature in the absence of strain parameter.

Dielectric Properties of Ovalene-Like Nanostructure with RKKY Interactions: Monte Carlo Study

In this study, we investigated the dielectric properties of ovalene-like nanostructure with RKKY (Ruderman–Kittel–Kasuya–Yoshida) interactions, using Monte Carlo simulations. Nanosystem consists of an ovalene-like nanostructure with mixed spins [Formula: see text]-7/2 and S-1, separated by non-electric layers (NEL). We investigated the effect of the non-electric layers, external longitudinal electric field and ferrielectric exchange coupling on polarization and dielectric susceptibility of the nanostructure. We find that the transition temperature is affected by an increase in the number of non-electrical layers. These results can enrich the dielectric properties of ovalene-like nanostructure for future nanotechnology applications.

Fluid-Thermal Interaction Simulation of a Hypersonic Aircraft Optical Dome

Hypersonic aircraft design is an enabling technology. However, many problems are encountered, including the design of the hood. The aircraft optical dome can become heated due to aerodynamic effects. Since the optical dome of a hypersonic aircraft should satisfy optical imaging requirements, a conventional ablative coating cannot be adopted. The aerodynamic heating characteristics during the whole flight must be studied. In this study, a numerical simulation method for the aerodynamic heat of hypersonic aircraft under long-term variable working conditions is proposed. In addition, the numerical simulation of the external flow field and structure coupling of the aerodynamic heat problem is performed. The dynamic parameters of temperature and pressure are obtained, and the thermal protection basis of the internal equipment is obtained. Numerical results indicate that the average temperature and maximum temperature of the optical dome for inner and outer walls exhibit an “M” shape with time, with two high-temperature cusps and one low-temperature cusp. The time of average temperature coincides with that of maximum wall temperature. During the flight, the wall pressure changes with time, exhibiting the characteristics of higher temperature at both ends of the flight and lower temperature in the middle. The structural temperature of the hypersonic aircraft is higher than that of the external flow behind the shock wave after 310 s. Therefore, this study provides a reliable reference for the preliminary design and parameter research of optical domes of hypersonic aircraft.

Transient response of nonparallel frequency-dependent transmission lines due to nearby lightning strikes in the presence of finitely-conducting ground

Overvoltage transients due to lightning strikes is a common occurrence in power transmission lines which can ultimately lead to line outages. Simulation of transmission line networks under the influence of lighting plays a vital and essential role in predicting their transient behaviour . The transient behaviour of uniform transmission lines due to lightning has been studied extensively. However, in modern transmission line networks, nonuniformities and discontinuities such as nonparallel wire, line crossings or bends are becoming increasingly common. Therefore, in such cases, inaccuracies might be present in analysis performed using conventional uniform transmission line approaches. A recent publication by the authors analysed the transient behaviour of nonparallel and crossing transmission lines above perfect electric conductor (PEC) ground. However, the PEC assumption can only be used in a limited scope. In this paper a nonuniform transmission line model with external field coupling is presented to analyse the transient behaviour of a nonuniform wire structure due to the field coupling from a nearby lightning strike in the presence of lossy ground. Simulation results generated by the proposed model is compared with full-wave simulations and results published by other researchers. A case study to compare the results from the proposed model with a conventional uniform transmission line model under various ground-conductivity values and terminating conditions is also performed. The study indicates that the presence of nearby nonparallel lines can cause the transient behaviour of the structure to deviate from the behaviour predicted using uniform approaches. • The transient behaviour of a nonuniform wire structure a nearby lightning strike in the presence of lossy ground is studied. • Simulation results generated by the proposed model is compared with full-wave simulations and results published by other researchers. • Results from the proposed model have been compared with a conventional uniform transmission line model. • The study indicates that the presence of nearby nonparallel lines intensify the transient behaviour.

The spin-[formula omitted] particle on a rotating curved surface in time-varying fields

To quantitatively characterize the behaviors of a spin-12 particle moving on a rotating curved surface and in a time-varying field, we derived the Schrödinger equation of the particle on the surface with the induced Pauli matrices based on the local curvilinear coordinate. To consider the relativistic effects, Minkowski space M is employed. Based on the solution of the Schrödinger equation, we found that the evolution of phase is influenced by the coupling of external fields and the geometry of surfaces as well as the relativistic effect originating from rotation. As examples, the solutions on a rotating cylinder/sphere in a damping magnetic field are calculated. The spin-flip behavior of the particle and the effects of external field and rotation are demonstrated. The results may help stimulate the ideas of modulating and controlling the spin on nano-surfaces.

Role of grain boundary and nanoholes in geometrical deformation and bonding energies of graphene/hexagonal boron nitride

The geometric deformation, bonding energies and mechanical properties of graphene-h-BN heterostructures (Gr-h-BN) under the coupling of external field (strain rate and temperature) and internal field (grain boundary (GBs) and nanoholes) were studied by using molecular dynamics and nonlinear mechanics. The results show that GBs and nanoholes will cause the Gr-BN-GBs configuration to deviate from the plane configuration, and produce a saddle shape with positive curvature and negative curvature, and its displacement field diverges with distance. In addition, the presence of GBs and nanoholes leads to a reduction in failure stress, Young's modulus and Von-mises stress. However, the presence of GBs and nanoholes also improves the bending rigidities of two dimensional (2D) materials. The adverse and strengthening effects induced by GBs and nanoholes are strongly dependent on temperature and strain rate. A full study of the built-in distorted stress field generated by the interaction of defects in 2D materials will help us to understand the physical mechanism of the relationship between structure and properties in low dimensions, and even design new applications.

ESTUDIO ANALÍTICO Y POR SIMULACIÓN MONTE CARLO DE LA INFLUENCIA DECAMPOS MAGNÉTICOS INTENSOS EN LA TRAYECTORIA DE ELECTRONES CONENERGÍAS TÍPICAS DE RADIOTERAPIA MRI-LINAC

Both analytical and numerical methods have proven to be suitable for describing radiation transport and interactions. The standard Boltzmann formalism derived from statistical mechanics requires to be specifically re-formulated to account for the interactions with external electromagnetic fields. Verifying the proper implementation of the external electromagnetic field coupling in Monte Carlo simulation codes is a key issue to confirm the feasibility of using such a tool to describe complex applications like image-guided radiotherapy based on integrating magnetic resonance scanner to the radiant field of ionizing radiation along with the subsequent dosimetric effects. The present work reports on the feasibility and reliability of the Monte Carlo FLUKA and PENELOPE main codes to assess electron trajectory in presence of strong magnetic fields. The obtained results confirm the ability of FLUKA and Penelope to model the alterations in the electron trajectories due to external magnetic field effects, also demonstrating an excellent agreement between both codes and with the theoretical-analytical model.

Study of band alignment type in Janus HfSe2/Ga2SeS and HfSeS/GaSe heterostructures

Motivated by the successful preparations and excellent properties of Janus monolayers, we construct the van der Waals (vdW) heterostructures HfSe2/Ga2SeS, and HfSeS/GaSe. Their electronic features and the type of band alignment are investigated. We find that the HfSe2/Ga2SeS exhibits the similar electronic properties to HfSe2/GaSe. Both heterostructures own type-I band alignment, in which both valence band maximum (VBM) and conduction band minimum (CBM) are provided by HfSe2 layer. However, the HfSeS/GaSe heterostructure owns type-II band alignment, in which the electrons and holes are located within the HfSeS layer and the layer of GaSe, respectively. This means that the HfSeS/GaSe heterostructure can facilitate the effective separation of the photo-generated hole and electron pairs. The band offsets of valence bands are 0.09 eV, 0.26 eV and 0.17 eV for HfSe2/GaSe, HfSe2/Ga2SeS, and HfSeS/GaSe heterostructures. The small band offsets indicate the band alignment can easily be modulated by some external means. Thus, the external electric field and interlayer coupling effect are considered to modulate the electronic properties of those heterostructures. They can simultaneously tune the band gap and induce the band alignment transition between type-I and type-II. These results indicate that HfSe2/GaSe and Janus HfSe2/GaSe heterostructures have great applications in nanoelectronic device.