Threshold Field Research Articles

Kinetics of the Domain Structure in Uniform Electric Field in LiNbO3 with Surface Layer Modified by Soft Proton Exchange

The creation of periodic domain structures in lithium niobate crystals makes it possible to realize highly efficient nonlinear optical interactions in optical waveguides. The influence of near‐surface H+ ion concentration gradient on the domain kinetics in uniform electric field in lithium niobate crystals modified by soft proton exchange is studied. The spatial distribution of the H+ ions concentration in the surface layer is obtained by confocal Raman microscopy. The observed anomalous evolution of the domain structure at the surface represents the formation of stripe domains and their anisotropic growth along three directions. The domain imaging in the bulk allows revealing a comb‐like domain shape. The obtained strong influence of the proton exchange duration on the threshold field is attributed to the action of the concentration gradient in the near‐surface layer, which is considered as an analog of the internal bias electric field. It is shown that the internal bias field is proportional to the increase in the concentration gradient in the surface layer. The mechanism of the comb‐like domain formation is proposed. The obtained results can be used for development of domain engineering methods in optical waveguides.

The possible effect of surface barriers on the magnetic levitation of cylindrical superconductors

Abstract Superconducting magnetic levitation force measurements on large field cooled cylindrical MgB2 bulks with different diameters and thicknesses are reported. For these experiments, a special set-up permitting one to measure forces up to 500 N was used. In contradiction to previous measurements, the obtained force hysteresis cycles could not be reproduced with the analytical mean field model proposed by Bernstein et al (2017 Supercond. Sci. Technol. 30 065007). The failure of the model has been attributed to surface barriers effects which were not taken into account in the model. This last one was accordingly modified in order that the measured force cycles could be reproduced. Contrary to most other models describing surface barriers effects, the modified model suggests that above a threshold field anti-vortices and not vortices enter the superconductor. This behaviour is related to the storage by the superconductor of the mechanical work done by the operator. In addition, it has turned out that the threshold field is a decreasing function of the critical surface current density of the samples. As a consequence, the surface barriers effects occur only if this quantity and the critical current density are large enough. Otherwise, the internal magnetic field of the superconductor could be computed and was seen to be a decreasing function of the thickness of the superconductors.

The forgotten method? Pulsed electric field thresholds from the perspective of texture analysis

Pulsed electric field (PEF) technology has found applications in various industrial food sectors, including the potato industry, winemaking, biorefinery, and juice extraction, among others. The practical implementation of PEF technology in the food industry is however still hindered by several challenges. The detection and quantification of PEF effects are complex due to the variable characteristics and properties of raw materials, including cellular composition, structural organization, textural properties, and tissue porosity. Moreover, the PEF treatment parameters (e.g., pulse amplitude, duration, shape, rate), and process parameters (e.g., temperature, pH, medium conductivity) further complicate the optimization of PEF protocols, requiring a case-by-case approach. Knowledge of treated material properties and their functional dependence on PEF is a crucial prerequisite to informed, intelligent design of treatment protocols. We present an experimental study designed to gain insights into the mechanism behind the changes in textural properties induced by PEF in both plant and animal tissues. These changes in texture are then compared with findings from our previous study on electrical impedance, to highlight how different methods of detection of PEF-induced changes in tissue can yield vastly different results based on the method of analysis used depending on tissue properties. Furthermore, texture analysis unveiled the less-explored effects of PEF treatment on electroosmosis phenomena in both plant and animal tissues. We provide a comparative analysis between plant and animal tissues to elucidate the differences in deformation resulting from PEF treatment. We thus demonstrate how important it is, be it in the development phase or for process control during industrial operation, to choose an appropriate method of characterising PEF-induced changes in tissue to avoid under- or overtreatment.

Investigation of lethal thresholds of nanosecond pulsed electric field in rabbit VX2 hepatic tumors through finite element analysis and verification with a single-needle bipolar electrode: A prospective strategy employing three-dimensional comparisons

Pulsed electric field has emerged as a promising modality for the solid tumor ablation with the advantage in treatment planning, however, the accurate prediction of the lesion margin requires the determination of the lethal electric field (E) thresholds. Herein we employ the highly repetitive nanosecond pulsed electric field (RnsPEF) to ablate the normal and VX2 tumor-bearing livers of rabbits. The ultrasound-guided surgery is operated using the conventional double- and newly devised single-needle bipolar electrodes. Finite element analysis is also introduced to simulate the E distribution in the practical treatments. Two- and three-dimensional investigations are performed on the image measurements and reconstructed calcification models on micro-CT, respectively. Specially, an algorithm considering the model surface, volume and shape is employed to compare the similarities between the simulative and experimental models. Blood vessel injury, temperature and synergistic efficacy with doxorubicin (DOX) are also investigated. According to the three-dimensional calculation, the overall E threshold is 4536.4 ± 618.2 V/cm and the single-needle bipolar electrode is verified to be effective in tissue ablation. Vessels are well preserved and the increment of temperature is limited. Synergy of RnsPEF and DOX shows increased apoptosis and improved long-term tumor survival. Our study presents a prospective strategy for the evaluation of the lethal E threshold, which can be considered to guide the future clinical treatment planning for RnsPEF.

Modeling “Wrong Side” Failures Caused by Geomagnetically Induced Currents in Electrified Railway Signaling Systems in the UK

AbstractThe majority of studies into space weather impacts on ground‐based systems focus on power supply networks and oil and gas pipelines. The effects on railway signaling infrastructure remain a sparsely covered aspect even though these systems are known to have experienced adverse effects in the past as a result of geomagnetic activity. This study extends recent modeling of geomagnetic effects on DC signaling for AC‐electrified railways in the UK that analyzed “right side” failures in which green signals are turned to red. The extended model reported here allows the study of “wrong side” failures where red signals are turned green: a failure mode that is potentially more dangerous. Railway lines using track circuit signaling, like those modeled in this study, are separated into a number of individual blocks. This study shows that a relay is most susceptible to “wrong side” failure when a train is at the end of a track circuit block. Assuming that each train is positioned at the end of the block it is occupying, the results show that the geoelectric field threshold at which “wrong side” failures can occur is lower than for “right side” failures. This misoperation field level occurs on a timescale of once every 10 or 20 years. We also show that the estimated electric field caused by a 1‐in‐100 years event could cause a significant number of “wrong side” failures at multiple points along the railway lines studied, although this depends on the number of trains on the line at that time.

Liver-tumor mimics as a potential translational framework for planning and testing irreversible electroporation with multiple electrodes.

Irreversible electroporation (IRE) has emerged as an appealing non-ionizing, non-thermal ablation therapy, independent of antineoplastic drugs. Limited but successful outcomes in IRE conducted in vivo, in small focal hepatocellular carcinomas (HCC), have been reported. Nonetheless, the electric parameters of IRE are usually delivered in an unplanned manner. This work investigates the integration of computational modeling to hydrogels mimicking the HCC microenvironment, as a powerful framework to: circumvent ethical concerns of in vivo experimentation; safely tune the electric parameters reaching the IRE electric field threshold; and propel the translation of IRE as a routine clinical alternative to the treatment of HCC. Therefore, a parametric study served to evaluate the effects of the pulse amplitude, the number of pulses and electrodes, the treatment time, the hydrogel-tumor size, and the cell type. The ablation extent was surveyed by confocal microscopy and magnetic resonance imaging (MRI) in cylindrical and realistic tumor-shaped hydrogels, respectively. A large ablation (70%-100%) was verified in all constructs.

Machine Learning Driven Channel Thickness Optimization in Dual-Layer Oxide Thin-Film Transistors for Advanced Electrical Performance.

Machine learning (ML) provides temporal advantage and performance improvement in practical electronic device design by adaptive learning. Herein, Bayesian optimization (BO) is successfully applied to the design of optimal dual-layer oxide semiconductor thin film transistors (OS TFTs). This approach effectively manages the complex correlation and interdependency between two oxide semiconductor layers, resulting in the efficient design of experiment (DoE) and reducing the trial-and-error. Considering field effect mobility (𝜇) and threshold voltage (Vth ) simultaneously, the dual-layer structure designed by the BO model allows to produce OS TFTs with remarkable electrical performance while significantly saving an amount of experimental trial (only 15 data sets are required). The optimized dual-layer OS TFTs achieve the enhanced field effect mobility of 36.1cm2 V-1 s-1 and show good stability under bias stress with negligible difference in its threshold voltage compared to conventional IGZO TFTs. Moreover, the BO algorithm is successfully customized to the individual preferences by applying the weight factors assigned to both field effect mobility (𝜇) and threshold voltage (Vth ).

Densification effect on field emission characteristics of CNT film emitters for electron emission devices

Field electron emission characteristics of the carbon nanotube (CNT) film emitters were investigated according to densification conditions such as nitric acid, acetic acid, and salicylic acid. The emission performance of the CNT film emitters was strongly affected by the densification conditions. Salicylic acid exhibits the best field electron emission properties of the CNT film emitters, followed by nitric acid and acetic acid. The efficient densification of the CNT film emitter by salicylic acid is caused by the role of polarity and p orbitals, nitric acid by hydrogen ions, and acetic acid by weak polarity. After the densification with salicylic acid, the turn-on field of the CNT film emitter decreases from 1.94 V μm−1 to 1.86 V μm−1, the threshold field decreases from 3.41 V μm−1 to 2.95 V μm−1, the emission current significantly increases from 20.92 mA to 43.98 mA, and the degradation rate from the long-term emission stability decreases from 49.9% to 21%. The improved emission characteristics are attributed to the increased emission sites at the CNT film and the increased electrical conductivity of the CNT film. The densification is a useful way to enhance the field electron emission properties of CNT film emitters.

High frequency amplification of acoustic phonons in fluorine-doped single-walled carbon nanotubes

Herein, we report on a strong high-frequency induced amplification of coherent acoustic phonons in a non-degenerate fluorine-doped single-walled carbon nanotubes (FSWCNTs) by utilising a tractable analytical approach in the hypersound regime, ql≫1 (where q is the acoustic wavenumber and l is the carrier mean free path). The acoustoelectric gain obtained is highly nonlinear and is due to stimulated Cerenkov phonon emission by electrically driven carriers undergoing intraminiband transport and capable of performing Bloch oscillations. The transport process causes the carriers to undergo population inversion leading to intraminiband phonon-assisted processes. The generation rate (phonon emission) is expansive and surpasses phonon losses. The threshold field (Eo), at which attenuation switches over to amplification (gain) depends on the FSWCNT parameters (Δs&Δz), carrier drift velocity (vd=μEo), sound velocity (vs) and the ratio ζs,z. This result has potential for intense sources of reasonable acoustic phonons in the sub-THz regime and is vital for the generation of SASER (sound amplification by stimulated emission of acoustic radiation). The amplified phonons also have THz frequencies with wavelengths in the nanometer range, and depends on high spatial parameters which has potential applications for phonon filters and spectrometers.

Development of a 3 MV coaxial peaking capacitor for large-scale electromagnetic pulse simulator.

Coaxial peaking capacitor is a key component in high-altitude electromagnetic pulse (EMP) simulators with fast front pulse output. It poses significant technical and engineering challenges in limiting radiation field amplitude and test space. This paper presents the design and testing of a 180 pF, 3 MV coaxial peaking capacitor with improved insulation performance. In the insulation design, the length of the dielectric film is extended to reduce the background electric field on the flashover path. The electric field threshold obtained from image diagnosis is used as a reference. During capacitor testing, the insulation characteristics are diagnosed using both direct and indirect methods. The voltage measured by a D-dot probe, the output waveform of the Marx generator in the primary source, and the radiation field waveform are analyzed to understand the flashover characteristics of the capacitor and to improve the reliability of the test results. The experimental results demonstrate that the peaking capacitor can operate stably at 3.0 MV. If flashover occurring on the dropping edge of the pulse is permitted, the operating voltage can be greater than 3.7 MV without significantly affecting the radiation field waveform. The analysis on the surface flashover morphology of the peaking capacitor reveals that the flashover mainly occurs at the dropping edge of the capacitor's waveform, indicating that the damage to the film is not serious. This research significantly increases the working voltage of coaxial peaking capacitors and contributes to the development of high-altitude EMP simulation technology.

Implementation of the adaptive phase-field method with variable-node elements for cohesive fracture

In this paper, an adaptive phase-field model based on variable-node elements and error-indicator is presented to predict cohesive fracture evolution. The phase-field cohesive-zone model is characterized by the parameterized energetic degradation and crack geometric functions. A staggered iteration scheme is used to solve the coupled non-linear system of displacement field and phase field. The adaptive local refinement algorithm facilitated with error-indicator and variable-node elements is developed to improve computational efficiency. To determine the adaptive local refinement regions, we apply the phase-field threshold to characterize the crack regions and a novel history field threshold to denote crack tips. The variable-node elements are acted as transition elements to flexibly yet simply link the fine and coarse meshes. In addition, a fast method to generate the variable-node elements is given. Several representative numerical examples are studied to demonstrate the performance and accuracy of the proposed adaptive phase-field model, consisting of a mixed-model fracture of L-shape panel, the wedge-splitting test, the classic three point bending experiment and a plate with a hole and multi-cracks under tensile/shear loadings. The computer codes can be accessed at: https://github.com/hhuztc/Adaptive-PFM.git.

Improved field emission properties of reduced graphene oxide decorated with indium nanoparticles

Low work function metals decoration of graphene is a effective method for the improvement of electron field emission properties. Indium, a relatively lower work function metal, is used to decorate reduced graphene oxide (RGO) films for the first time by simple and efficient solution process combined with magnetron sputtering method and the field emission properties are investigated. At continue voltage mode, the indium decorated RGO films display lower turn-on and threshold field as well as better emission stability than those of pristine RGO films. Moreover, the field emission performance of indium decorated RGO films is affected by the spacing between the cathode and anode. At pulse voltage mode, the indium decorated RGO films show approximately 10 times higher maximum emission current density compared to that at continue voltage mode. The calculation results by density functional theory indicate that the indium decoration of RGO significantly increases the density of states (DOS) near Fermi level and reduces the work function.

Relativistic Runaway Electron Avalanche Development Near the Electric Field Threshold in Inhomogeneous Air

AbstractRelativistic Runaway Electrons Avalanches (RREAs) development depends on the applied electric field and the environment's air density. This dependency controls the RREA exponential growth length scale. The RREA development affects the bremsstrahlung excess occurring due to the passage of charged particles through the thundercloud's electric fields, the gamma‐ray glow. We used Monte Carlo simulations to develop an empirical model showing the RREA behavior in a realistic atmospheric density profile. The new formulation shows how the density variation modulates the electron population under electric field strengths near the RREA electric field threshold. The model limits the initial RREA altitude range as a function of the electric field strength. The new model is valid between ∼0.6 and ∼18 km, covering the relevant heights to investigate the generation of ground‐detected gamma‐ray glows.

Decision making in bone conduction and active middle ear implants – hearing outcomes and experiences over a 10-year period

Objectives To review the decision-making paradigm in the recommendations of BCI and aMEI overlapping candidacy for patients with conductive or mixed HL, and to determine if there are differences in hearing and quality of life outcomes between these implantable hearing devices. Methods Retrospective data from patients receiving BCI or aMEI in the past decade were analysed. Patients were grouped into: 1. BCI candidates, 2. BCI or aMEI candidates, and 3. aMEI candidates. We compared outcomes and examined the impact of BC threshold, age at implantation, and duration of hearing loss on candidacy. Results 89 participants were included: 30 BCI, 37 aMEI, and 22 BCI or aMEI candidates. All groups performed similarly in aided sound field threshold testing. BCI group had lower speech scores in quiet compared to 'BCI or aMEI.' No significant differences were found in APHAB global scores. BC threshold, duration of hearing loss, and age at implantation had no significant effects. Discussion Outcomes were generally similar across groups, except for higher effective gain in the aMEI group. Conclusion Our proposed patient pathway and decision-making approach facilitate candidate selection for aMEI and BCI, aiming to optimise outcomes.

Field induced ferroelectric phase transition and dielectric spectrum behavior in PMN ceramics

The problem of field induced phase transition into the ferroelectric phase in relaxor ceramics and in particular in PMN ceramics was studied for many years, but the results are still controversial. The temperature and field dependences of PMN polycrystalline ceramics dielectric spectra have been studied. The transitions from the glass-like into the ferroelectric phase were found both in field cooling and zero field heating after field cooling regimes under the fields above 3 kV/cm. Electric field scans near the diffuse maximum of the dielectric permittivity demonstrated the shift of the loss maximum to the high frequency at increasing of applied electric field. The experimentally observed frequency-dependent sign of the C–V effect (the decrease (negative effect) or the increase (positive effect) of dielectric permittivity at increasing field) is due to spectra hardening. In contrast to single crystal, where the application of the electric field higher than 1.6 kV/cm in <111> direction induces phase transition into ferroelectric state, in polycrystalline ceramics no clear evidence of the phase transition from the paraelectric into the ferroelectric state up to 6 kV/cm neither at 242 K nor at 246 K was found. This difference between the single crystal and polycrystalline ceramics can be explained by very strong dependence of the threshold field from the field orientation at this transition. The influence of external field on low frequency relaxation process parameters for PMN single crystal and ceramics is compared.

Current fluctuations and domain depinning in quasi-two-dimensional charge-density-wave 1T-TaS2 thin films

We investigated the temperature dependence of the current fluctuations in thin films of the quasi-two-dimensional 1T-TaS2 van der Waals material. The current fluctuations, determined from the derivative current–voltage characteristics of two-terminal 1T-TaS2 devices, appear prominently at the electric fields that correspond to the transitions between various charge-density-wave macroscopic quantum condensate phases and at the onset of the depinning of the charge density wave domains. The depinning threshold field, ED, monotonically increases with decreasing temperature within the nearly commensurate charge-density-wave phase. The ED value increases with the decreasing 1T-TaS2 film thickness, revealing the surface pinning of the charge density waves. Our analysis suggests that the domain depinning is pronounced in the nearly commensurate phase. It is induced by the electric field but facilitated by local heating. The measured trends for ED of the domain depinning are important for understanding the physics of charge density waves in quasi-two-dimensional crystals and for developing electronic devices based on this type of quantum materials.

Study on particle size and field effect with sp2/sp3 ratio of hydrogenated diamond-like carbon

Hydrogenated diamond-like carbon (HDLC) films were synthesized through a reactive gas-plasma process employing methane (CH4) and hydrogen (H2) as precursor gases on a silicon (100) wafer substrate, conducted at room temperature. The deposition process utilized a biased enhanced nucleation technique, varying the flow rate ratio of hydrogen and methane. The investigations revealed that increasing the methane flow rate led to a reduction in grain size and an augmented nucleation density of HDLC, as evidenced by contact-mode atomic force microscopy (AFM) images. This study demonstrated the effective control of diamond grain growth by introducing high-methane-concentration pulses during deposition. The field emission characteristics of HDLC samples were analyzed, revealing threshold fields of 12.2 V/μm for nanocrystalline films, 8.5 V/μm for subcrystalline films and 4.1 V/μm for microcrystalline films, corroborated by Raman spectra. Surface energy measurements indicated hydrophobic behavior in the samples. Notably, a decrease in the hydrogen/methane ratio was found to increase the sp2 character, which correlated with the emission field. AFM analysis of HDLC samples yielded surface roughness values ranging from 0.2 nm to approximately 0.01 nm, confirming the continuous, non-porous and smooth nature of the surfaces.

Orientational Transitions in Magnetically Compensated Liquid-Crystal Suspensions of Ferromagnetic Carbon Nanotubes

Purpose of research is to study the influence of ferromagnetic carbon nanotubes on orientational transitions in magnetically compensated liquid-crystal suspensions.Methods. The problem was solved in the framework of the continuum theory. By minimizing the Helmholtz free energy functional, a system of Lagrange-Euler equations is obtained that determines the equilibrium dependences of the orientation angles of liquid crystal and impurity ferromagnetic carbon nanotubes directors, as well as the concentration distributions of the dispersed phase of the suspension as a function of the transverse coordinate, material parameters, and magnetic field strength.Results. It is shown that in the presence of an external magnetic field, a liquid-crystal suspension of ferromagnetic carbon nanotubes can be in a non-uniform phase (angular phase) and two uniform phases (planar and homeotropic phases). Expressions for the threshold fields of transitions between coexisting orientational phases are obtained analytically as functions of the material parameters of the composite. Diagrams of the orientational phases of the suspension are plotted.Conclusion. As a result of the research, it was shown that the addition of low concentrations of ferromagnetic carbon nanotubes can significantly reduce the threshold of the magnetic Fréedericksz transition compared to a pure liquid crystal, which is important for various technical applications. The obtained analytical formulas for the threshold fields of transitions between different orientational phases can be used to determine the anchoring energy and material parameters of suspensions of ferromagnetic carbon nanotubes in a liquid crystal.

Magnetic field assisted stabilization of circular double wall domain lattice in oxidized Fe3GeTe2 flakes

The family of 2D ferromagnets is in the center of research for novel spintronics applications. Among the various 2D ferromagnets, Fe3GeTe2 has drawn significant attention since it combines a high Curie temperature with a van der Waals structure, which allows easy exfoliation, and a high spin polarization/large spin–orbit coupling. The presence of interfacial DMI in 2D ferromagnets have a significant impact on the behavior of magnetic domain walls, which are fundamental in magnetic memory and logic devices. By controlling the interfacial DMI, it is possible to manipulate the motion of domain walls and the magnetic domain configuration, which is essential for the development of efficient and reliable magnetic devices. In this study, we investigate the effect of an, inversion symmetry breaking, oxidized layer on the magnetic domain structure of Fe3GeTe2 flakes due to the emergence of interfacial DMI. By combining magneto-optical Kerr effect microscopy images and micromagnetic simulations, we study the formation of a circular double wall (CDW) domain lattice in oxidized flakes under specific field cooling and magnetic field sweeping protocols. Their formation is attributed to a competition between the exchange interaction both symmetric and antisymmetric (associated to interfacial DMI), magnetocrystalline anisotropy and the external magnetic field. The CDW domains have a diameter of several microns, a magnetic structure resembling that of a skyrmionium and are arranged in regular lattice that survives thermal fluctuations close to T c. Our results suggest that these CDW domains transition to Néel type skyrmions after a magnetic field threshold. These findings could have important implications for the design and optimization of 2D ferromagnetic materials for spintronic applications.

Dendritic flux avalanches in superconducting hybrid structures

Magneto-optical imaging was employed to study dendritic flux avalanches in metal/superconductor and superconductor/superconductor hybrid structures over an extended range of magnetic field ramping rates. Our results in Cu/NbN show that the previously reported suppression of dendritic flux avalanches in metal coated superconducting films is limited to low ramping rates; as the ramping rate increases, the metal coating becomes less and less effective. A more complex behavior is exhibited in superconductor/superconductor hybrid structures. Our measurement in NbN partially coated with Nb, reveal three distinctive types of dendritic avalanches: those propagating in only one layer, either as regular dendrites in the uncoated NbN or as surface dendrites in the Nb layer, and hybrid dendrites that propagate in both the Nb and NbN layers simultaneously. These three types of dendrites are distinguished by their morphology, temperature dependence and instability threshold field. The overall stability of the hybrid structure significantly exceeds that of its weak component.