External Field Increases Research Articles

Dissociation characteristics of bromoethane under external electric fields

Bromoethane dissociates and generates the bromine radical under the radiation from the sun, which destroys the atmospheric ozone layer. So, it is necessary to take effective measures to degrade bromoethane. We use the density function theory (DFT) and calculate the dissociation properties and spectral characteristics of bromoethane under the external electric fields (0-0.028 5 a.u.) at the B3LYP/6-31G+(d, p) level. It is showed that the total energy of the molecule decreases as the external field increases from 0 a.u. to 0.028 5 a.u. along the Z-axis. Meanwhile, the energy gap decreases monotonically and the dipole moment increases. It is shown in the potential energy curves that the electric field of 0.030 a.u. is strong enough to break the C-Br bond. The results provide important information for the degradation of bromoethane under external electric fields.

The unique magnetic damping enhancement in epitaxial Co2Fe1−xMnxAl films**Project supported by the Natural Science Foundation of Guangdong Province, China (Grant No. 2015A030310003) and the Program for Scientific Research Start-up Funds of Guangdong Ocean University, China.

Uniform precession dynamics and its magnetic damping are investigated in epitaxial Co2Fe1−xMnxAl films by using the time-resolved magneto–optical Kerr effect under out-of-plane configuration. The decay time of uniform precession mode decreases, and thus the magnetic damping increases with the increase of external field. Moreover, the decay time decreases as x decreases, so that the enhancement of magnetic damping occurs in Fe-rich sample. Furthermore, the decay time decreases as the excitation fluence increases, which drops rapidly at low magnetic field comparing with the slow reduction at high magnetic field. This unique magnetic damping enhancement is attributed to the enhancement of homogeneous magnetization.

Magnetic properties of permalloy antidot array fabricated by interference lithography

The magnetic properties of a Permalloy antidot array in square lattice geometry, with circular-rhomboidal hole shape and fabricated by interference laser lithography and ion-beam sputtering have been reported. Magneto-optical Kerr effect magnetometry indicated that the sample exhibits four-fold anisotropic behaviour, i.e. different magnetization loops were observed when the external magnetic field was applied along either x- or y-axis, or along the array diagonal. Broadband ferromagnetic resonance measurements revealed a rich variety of different magnetization configurations in the unsaturated state that can be controlled by the orientation of the external magnetic field. Micromagnetic simulations have been performed to explain the observed results. On the contrary, in the saturated regime the system demonstrated almost isotropic magnetic behaviour that improves with external field increase. The obtained results show the potential of interference lithography for the fabrication of large area antidot arrays.

Specific features of penetration and trapping of a magnetic flux in film and bulk YBCO high-temperature superconductors

An oscillatory differential method of local diagnostics of superconductors is applied to the analysis of the trapped magnetic flux and the effective demagnetization factor in YBCO samples. Regular steps over certain intervals of the external field are observed on the magnetic-field dependence of these parameters. It is demonstrated that, as the external field increases, crystallites in a sample are decomposed into sub- and nanocrystallites with a size much less than the penetration depth [Formula: see text] of the magnetic field. The first critical thermodynamic magnetic fields of sub- and nanocrystallites are determined. These results allow one to reveal the interaction mechanism between magnetic and crystalline microstructures of superconductors and provide a deeper insight into the physical processes that occur in high-temperature superconductors (HTSCs) in a magnetic field.

Effects of sort and concentration of salts on the electrosurface properties of aqueous suspensions containing hydrophobic and hydrophilic particles: Validity of the Hofmeister series

The results of systematic study of the impact of electrolytes (in a wide range of electrolyte concentration, C=10−5–10−1M) with alkali metal ions (Li+, Na+, K+, Rb+, Cs+) containing chlorides and sulphate anions on electrosurface properties of aqueous suspensions containing hydrophobic (polystyrene latex with surface sulphate or carboxylic groups) and hydrophilic (aerosil, zirconium dioxide, bentonite, Laponite RD®) particles are presented. The behaviour of zeta potential (ζ-potential) and electrical conductivity was studied.The observed ζ(C) dependencies revealed marked maxima at C=10−4–10−3M for hydrophobic and at C=10−3–10−2M for hydrophilic particles. This phenomenon was explained accounting for two opposite trends related to the polarization of the electrical double layer (EDL) in the external electric field (increase of ζ-potential at low concentration) and the effect of the EDL compression (decrease of ζ-potential at high concentration). In concentrated solutions (C>10−3–10−2M) ζ-potentials always decreased regularly in the direct Hofmeister series from Li+ to Cs+ cations. However, in more diluted solutions, the indirect Hofmeister series for some particles were also observed. Such behaviour can reflect the impact of different properties of the surface including hydrophilic or hydrophobic nature, charge density, and partial dehydration. The sort of anions also influenced the value of ζ-potential. This phenomenon was explained by dehydration effect of sulphate ions, thinning the surface hydrate layer and shift of the shear plane toward the surface.

Domain kinetics during polarization reversal in 36° Y-cut congruent lithium niobate

We present experimental study of domain kinetics in 36° Y-cut congruent lithium niobate during polarization reversal by increasing external electric field using liquid electrodes. The motion of the domain walls has been imaged on the Zs+ and Zs-polar surfaces of the crystal simultaneously. The linear dependence of the threshold field on the field rate has been revealed. The threshold field in low field rate limit has been estimated as 32.8 ± 0.3 kV/mm, which is lower than predicted value. The switching process for polarization reversal in the constant field has dramatically accelerated with increase of external electrical field above threshold. The new approach, which accelerates significantly the in situ study of 3D domain kinetics in CLN crystals, has been demonstrated.

The studies on the physical and dissociation properties of chlorobenzene under external electric fields

Chlorobenzene is one of the Persistent Organic Pollutants (POPs) threatening human health. It is significant to study the degradation mechanism under external electric fields. Based on the density functional theory, the physical and dissociation properties including C–Cl bond length, total energy, dipole moment, frontier orbital energy, energy gap, IR spectrum, UV-vis absorption spectrum and potential energy curve are studied under external electric fields. According to these results, it is found that the C–Cl bond length becomes longer and tends to break with the increase of external electric field and the energy gap decreases with the increase of positive as well as negative external electric field. Moreover, the dissociation barrier in potential energy curve decreases and equilibrium bond length increases with increase of positive external electric field. And when external electric field reaches 0.040 atomic units ([Formula: see text], 1 atomic [Formula: see text], the dissociation barrier disappears which means that degradation of chlorobenzene occurs under strong external electric field due to the breakage of C–Cl bond. These results provide important references for studying the degradation mechanism of chlorobenzene under strong external electric fields.

Plasma Polarization and Wake Formation Behind a Dust Particle in an External Electric Field

This paper presents a self-consistent model of plasma polarization around an isolated micrometer-sized dust particle being under the action of an external electric field. It describes ion focusing and wake formation for dust particles with different radii and external electric fields. It is shown that despite the formation of wake, plasma maintains a quasi-neutral condition around a negatively charged dust particle, and the volume charge formed as a result screens the dust particle completely. It is also shown that in the external electric field, the dipole moment of the part of the ion nearest to the dust particle is proportional to the dust particle charge. As the external electric field increases and reaches some threshold value, a positive peak appears in plasma potential downstream of the dust particle. It then increases linearly and shows a broad maximum.

Investigation of external electric field effect on C24H38O4 molecule by density functional theory

The C24H38O4 (dioctyl phthalate, DOP) is a main component of the plasticizer. In order to study the influence of external electrical field on molecular structure and spectrum of DOP, the method B3LYP of the density functional theory at B3LYP/6-311G(d,p) level is employed to calculate geometrical parameters of the ground state of DOP molecule under different external electric fields (from 0 to 0.0125 a.u.) in this article. On this basis, the ultraviolet-visible absorption spectrum of DOP is calculated by using the time-dependent density functional theory in the same fundamental group and compared with the ultraviolet absorption peak of the molecules, measured by UNICO ultraviolet and visible spectrophotometer. Finally, by using the time-dependent density functional theory in the same fundamental group, we study wavelengths and oscillator strengths of the first twenty-six excited states of DOP molecule in external electric field. The obtained results are as follows. The strongest absorption of ultraviolet-visible absorption spectrum appears in the end absorption band from n to σ* transition. The stronger absorption occurs in the E band of benzene electronic transition from π to π*. The molecular geometry parameters are strongly dependent on the external field intensity. The dipole moment of DOP molecule is proved to first decrease and then increase with the sharp increase of external field, but the total energy first increases and then decreases with the increase of the external field intensity. The ultraviolet absorption peaks of excited states of DOP are proved to have observably red shift, and the oscillator strength sharply decreases with the increasing of the field intensity.

Nonlinear Stark--Wannier Equation

In this paper we consider stationary solutions to the nonlinear one-dimensional Schrödinger equation with a periodic potential and a Stark-type perturbation. In the limit of large periodic potential the Stark--Wannier ladders of the linear equation become a dense energy spectrum because a cascade of bifurcations of stationary solutions occurs when the ratio between the effective nonlinearity strength and the tilt of the external field increases.

On nonlinear deformation correction to oscillations frequencies of a strongly charged drop in an electrostatic suspension

In fourth-order nonlinear asymptotic calculations for eccentricity (which measures the stationary deformation of a charged drop in an external electrostatic field) and first-order calculations for the dimensionless amplitude of its oscillations, the frequency of a strongly charged drop in a weaker external uniform electrostatic field is calculated. The deformation corrections to the frequency related to the change in the equilibrium shape of a drop in comparison with its spherical shape are found. As the surface area of a drop in an external field increases, the oscillation frequency of the drop decreases and the deformation correction has one sign (negative). When the drop charge tends to critical (to the limit, om the sense of stability with respect to the superposition of its own and induced charges), the value of the correction is comparable to the frequency in order of magnitude.

Electric controlled spin and valley transport of massive electrons in graphene with spin-orbit coupling

In this work, we have explored the influence of an external electric field on the spin and valley transport of massive electrons in a graphene system with spin-orbit coupling. Both the strength and width of the spin- and valley-polarization are greatly dependent on the external electric field. As the external electric field increases, the spin/valley polarization can be enhanced, even up to 100%. In addition, the presence of a gap resulting from the interplay of massive electrons and spin-orbit coupling can occur in the direction of the spin polarization being changed. Without the gap, spin-down electrons can be filtered at the low-energy Fermi level. However, with the gap, the effect is just the opposite; spin-up electrons are filtered. These findings may open an avenue for the electric control of valley and spin transport in graphene-based electronic devices.

Observation of Transient Overcritical Currents in YBCO Thin Films using High-Speed Magneto-Optical Imaging and Dynamic Current Mapping

The dynamics of transient current distributions in superconducting YBa2Cu3O7−δ thin films were investigated during and immediately following an external field ramp, using high-speed (real-time) Magneto-Optical Imaging and calculation of dynamic current profiles. A number of qualitatively unique and previously unobserved features are seen in this novel analysis of the evolution of supercurrent during penetration. As magnetic field ramps up from zero, the dynamic current profile is characterized by strong peaks, the magnitude of which exceed the conventional critical current density (as determined from static current profiles). These peaks develop close to the sample edges, initially resembling screening currents but quickly growing in intensity as the external field increases. A discontinuity in field and current behaviour is newly observed, indicating a novel transition from increasing peak current toward relaxation behaviour. After this transition, the current peaks move toward the centre of the sample while reducing in intensity as magnetic vortices penetrate inward. This motion slows exponentially with time, with the current distribution in the long-time limit reducing to the expected Kim-model profile.

Positive and negative electrocaloric effect inBaTiO3in the presence of defect dipoles

The influence of defect dipoles on the electrocaloric effect (ECE) in acceptor doped ${\mathrm{BaTiO}}_{3}$ is studied by means of lattice-based Monte-Carlo simulations using a Ginzburg-Landau type effective Hamiltonian. Oxygen vacancy-acceptor associates are described by fixed local dipoles with orientation parallel or antiparallel to the external field. By a combination of canonical and microcanonical simulations the ECE is directly evaluated. Our results reveal that in the case of antiparallel defect dipoles the ECE can be positive or negative depending on the dipole density. Moreover, a transition from a negative to positive ECE can be observed when the external field increases. These transitions are due to the delicate interplay of internal and external fields and are explained by the domain structure evolution and related field-induced entropy changes. The results are in good qualitative agreement to those obtained by molecular dynamics simulations employing an ab initio based effective Hamiltonian. Finally, a modified electrocaloric cycle, which makes use of the negative ECE in the presence of defect dipoles, is proposed to enhance the cooling effect.

Field-induced dielectric response saturation in o-TaS3

We investigated dependence of the dielectric properties on temperature and electric field below 50 K along the chain direction of o-TaS3. With external electric field increase, two threshold features could be identified. For electric fields somewhat larger than the lower threshold , the dielectric constant starts to decrease whereas the conductivity increases due to the tunnelling of solitons. For higher external electric field we observe a saturation of dielectric response and analyze that the possible reasons may be related to the polarization behavior of charged solitons. With a decrease in temperature, the effect of external field on the dielectric response of the system weakens gradually and at 13 K it diminishes due to soliton freezing.

Microstructure and electrical properties of 0-3 connectivity barium titanate−Portland cement composite with 40% barium titanate content

ABSTRACTIn this paper, a study is presented on the microstructure, dielectric and piezoelectric properties of 0–3 connectivity barium titanate-Portland cement composite with 40% barium titanate content at this composition has an acoustic impedance that match with concrete structure. The results show that both of dielectric constant (ϵr) and dielectric loss (tanδ) of composite were found to decrease with increasing frequency. The ϵr value of composite was 239 at a frequency of 1 kHz. In addition, the ferroelectric hysteresis loops of composite indicate that the “apparent” remnant polarization increases as an applied external electrical field increases. Furthermore, the piezoelectric coefficient was 7 pC/N under a low poling field of 1 kV/mm.

Polarised black holes in AdS

We consider solutions in Einstein–Maxwell theory with a negative cosmological constant that asymptote to global AdS4 with conformal boundary . At the sphere at infinity we turn on a space-dependent electrostatic potential, which does not destroy the asymptotic AdS behaviour. For simplicity we focus on the case of a dipolar electrostatic potential. We find two new geometries: (i) an AdS soliton that includes the full backreaction of the electric field on the AdS geometry; (ii) a polarised neutral black hole that is deformed by the electric field, accumulating opposite charges in each hemisphere. For both geometries we study boundary data such as the charge density and the stress tensor. For the black hole we also study the horizon charge density and area, and further verify a Smarr formula. Then we consider this system at finite temperature and compute the Gibbs free energy for both AdS soliton and black hole phases. The corresponding phase diagram generalizes the Hawking–Page phase transition. The AdS soliton dominates the low temperature phase and the black hole the high temperature phase, with a critical temperature that decreases as the external electric field increases. Finally, we consider the simple case of a free charged scalar field on with conformal coupling. For a field in the SU(N ) adjoint representation we compare the phase diagram with the above gravitational system.

Influence of external electric field on piezotronic effect in ZnO nanowires

In this work, the piezotronic effect is investigated for the first time in external electric fields ranging from 0 V·cm–1 to 2,000 V·cm–1 by using n-type ZnO nanowires supported by a flexible substrate. In the presence of an external electric field, the Schottky barrier height (SBH) is lowered by the image force, allowing more free carriers to pass through the metal-semiconductor junction and enhancing the screening effect on positive piezoelectric polarization charges. As the strength of the external electric field increases, the piezotronic effect is significantly suppressed and the metal-semiconductor contact finally exhibits Ohmic behavior. The experimental results show that devices can be classified into three groups, corresponding to low, moderate, and high carrier densities of the nanowires used. This work not only helps us to explicate the basic physical mechanism of the piezotronic effect in a harsh environment in an electric field but also provides guidelines for future design and fabrication of piezotronic devices.

Conformations, hydrodynamic interactions, and instabilities of sedimenting semiflexible filaments.

The conformations and dynamics of semiflexible filaments subject to a homogeneous external (gravitational) field, e.g., in a centrifuge, are studied numerically and analytically. The competition between hydrodynamic drag and bending elasticity generates new shapes and dynamical features. We show that the shape of a semiflexible filament undergoes instabilities as the external field increases. We identify two transitions that correspond to the excitation of higher bending modes. In particular, for strong fields the filament stabilizes in a non-planar shape, resulting in a sideways drift or in helical trajectories. For two interacting filaments, we find the same transitions, with the important consequence that the new non-planar shapes have an effective hydrodynamic repulsion, in contrast to the planar shapes which attract themselves even when their osculating planes are rotated with respect to each other. For the case of planar filaments, we show analytically and numerically that the relative velocity is not necessarily due to a different drag of the individual filaments, but to the hydrodynamic interactions induced by their shape asymmetry.

Electron transport through a two-terminal Aharonov-Bohm interferometer coupled with linear di-quantum dot molecules

A two-terminal Aharonov-Bohm (A-B) interferometer coupled with linear di-quantum dot molecules is presented. By employing Keldysh non-equilibrium Green's function technique, the conductance without introducing time-dependent external field and the average current with applying time-dependent external field are theoretically studied. In the absence of time-dependent external field, two identical linear diquantum dot molecules embedded respectively in the two arms of A-B interferometer lead to degeneracy energy levels. The central resonance peak at εd = 0 in the conductance spectrum splits into two resonance peaks as the inter-coupling strength of di-quamtum dot increases over a threshold. In the case that the two linear di-quantum dot molecules are different, three or four resonance peaks appear in the conductance spectrum. When tuning magnetic flux ψ= π, the destructive quantum interference of electron waves in the A-B interferometer takes place. The conversion between 0 and 1 for conductance is performed by switching on/off the magnetic flux, which suggests a new physical scheme of quantum switches. The effect of Rashba spin-orbit interaction on the conductance is discussed. The functionality of spin filter is suggested through adjusting the Rashba spin-orbit coupling strength and the external magnetic flux. When time-dependent external field is applied, the notable side-band effect appears in the average current curve. A series of resonance peaks is produced, with the peak-peak separation of ħω. Two main peaks become reduced as the amplitude of time-dependent external field increases, however, the sideband peaks grow gradually. This indicates that both the magnitude and the position of average current resonance peak are controllable by adjusting the amplitude of time-dependent external field. The sideband effect remains always in the average current curve no matter how much the frequency of time-dependent external field changes. But the increase in the frequency of external field leads to the growth of two main peaks at the bonding and anti-bonding energy respectively, and the decay of the corresponding sideband peaks as well. The conversion between the current peak and valley can be realized by tuning the frequency of time-dependent field. Moreover, the dependence of A-B effect of the average current on the magnetic flux is found. As the magnetic flux is ψ≠nπ, each peak in average current curves splits into two peaks. But under the condition of ψ=2nπ, the splitting phenomenon disappears. The spin-dependent average current shows effective controllability by tuning the magnetic flux and Rashba spin-orbit coupling. The results would be useful for gaining a physical insight into electron transport in the multi-quantum-dot molecules coupled A-B interferometer and for designing the quantum devices.