Strong Ac Research Articles

Generation of patterns and higher harmonics in 1D quantum droplets in tilted and driven quasi-periodic confinements

The generation of patterns by breaking the spatial symmetry in external confinement is a captivating area of physics. The emergence of patterns is a fundamental inquiry spanning various disciplines such as nonlinear optics, condensed matter physics, and fluid dynamics. The article investigates the generation of a variety of patterns in a one-dimensional binary mixture of Bose–Einstein condensate forming quantum droplets. By solving the extended Gross–Pitaevskii equation in the presence of tilted and driven engineered bi-chromatic optical lattices (BOL), the out-of-equilibrium dynamics of droplets under strong dc and ac fields are illustrated. Under the influence of a dc field, a stripe-like pattern emerges in the temporal domain, while the scenario with ac fields demonstrates temporal periodic and bi-periodic oscillations of density waves. The width and period of formed patterns are directly correlated with the strength of ac and dc fields. Moreover, temporal modulation of the BOL potential depth yields various harmonics in the oscillations of the condensate density pattern. Through Fast Fourier Transform (FFT) analysis, it is confirmed that these harmonics encompass multiple and combinational frequencies, suggesting potential applications in generating desired frequency combs within quantum droplets. We have also carried out a thorough numerical stability check of the obtained solutions and found them sufficiently stable.

Advanced Anti-icing and Deicing Strategies for Overhead Power Transmission Lines Based on Giant Magnetocaloric Effect of La0.7Ca0.254Sr0.046MnO3.

Perovskite manganates (AMnO3) exhibit diverse structural, thermal, electrical, and magnetic properties. Their strong magnetocaloric effect (MCE) near the Curie temperature (TC) makes them ideal for magnetic-thermal anti-icing and deicing in power transmission lines. Below TC, ferromagnetic AMnO3 produces heat through multiple mechanisms, with the changing magnetic field induced by the strong AC current, causing heat through magnetic hysteresis and eddy currents, alongside the direct MCE. Above TC, no heating is generated, as MCE is unfavorable, thus preventing additional energy loss at elevated temperatures. In this work, La0.7Ca0.254Sr0.046MnO3 with TC close to 0 °C were synthesized by solid-state reaction. It is found that particle size >10 μm is beneficial for a large MCE, based on the results of particle size dependence of MCE. The resulting maximum magnetic entropy change at 277 K is 7.69 J·kg-1·K-1, and an adiabatic temperature change of 3.87 K at 277 K is achieved under 5 T. The prototype cable is fabricated using a well-established wire drawing process. A climate-simulation chamber is employed for the anti-icing and deicing experiments. The prototype cables demonstrated a strong capability for deicing and anti-icing. This simple and cost-effective prototype cable shows significant potential for mitigating the icing problem of overhead high-voltage power transmission lines.

An incremental permeability detection method for yield strength of ferromagnetic materials based on permanent magnet excitation

ABSTRACT In this paper, in order to meet the engineering requirements of mechanical properties detection of materials with low power consumption, a novel incremental permeability detection system based on permanent magnet excitation is proposed to reduce system power consumption. Initially, a new incremental permeability sensor was designed to extract magnetic incremental permeability (MIP) signal. Through finite element simulation, experimental parameters were optimised, and a rational arrangement of double permanent magnets was devised to furnish an optimally strong AC bias field intensity. Subsequently, a practical detection platform was assembled to extract electromagnetic signal features. From the perspective of domain wall displacement, a characteristic value θ was proposed to predict the yield strength, with experimental results yielding a relative error of less than ±10%. These experiments have validated the capability of permanent magnet-type MIP to enable quantitative detection of the yield strength in ferromagnetic materials.

Complete mitogenome and intra-family comparative mitogenomics showed distinct position of Pama Croaker Otolithoides pama

The Pama Croaker, Otolithoides pama, is an economically important fish species in Bangladesh. Intra-family similarities in morphology and typical barcode sequences of cox1 create ambiguities in its identification. Therefore, morphology and the complete mitochondrial genome of O. pama, and comparative mitogenomics within the family Sciaenidae have been studied. Extracted genomic DNA was subjected to Illumina-based short read sequencing for De-Novo mitogenome assembly. The complete mitogenome of O. pama (Accession: OQ784575.1) was 16,513 bp, with strong AC biasness and strand asymmetry. Relative synonymous codon usage (RSCU) among 13 protein-coding genes (PCGs) of O. pama was also analyzed. The studied mitogenomes including O. pama exhibited consistent sizes and gene orders, except for the genus Johnius which possessed notably longer mitogenomes with unique gene rearrangements. Different genetic distance metrics across 30 species of Sciaenidae family demonstrated 12S rRNA and the control region (CR) as the most conserved and variable regions, respectively, while most of the PCGs undergone a purifying selection. Different phylogenetic trees were congruent with one another, where O. pama was distinctly placed. This study would contribute to distinguishing closely related fish species of Sciaenidae family and can be instrumental in conserving the genetic diversity of O. pama.

A new scheme of all-optical 2:1 multiplexer (MUX) and MUX-based combinational circuits using nonlinear kerr-type materials

Optoelectronics, often known as photon-based electronics, is well recognised for being more effective than conventional electronics for communication. To create a superfast computer, several devices have previously been developed in the field of all optical computing systems. Here, we have put forth an all-optical 2:1 multiplexer with the usage of nonlinear material exhibiting a strong ac Kerr effect and 2:1 Multiplexer (MUX) based all optical -photonic switches - NOT, OR, AND, NAND, NOR etc The sole method for building combinational logic circuits is to utilise MUX. This work is made simpler by the Shannon decomposition theorem than by other approaches. In this study, input and output are expressed as the presence of a light signal with a prefixed intensity as binary 1 and the absence of a light signal as binary 0 using an intensity-based all-optical device and positive logic. Since the system is entirely optical, our current design enables very-high speed (terahertz) computation, which is not possible with typical semiconductor electronic switches. Validation through mathematical computations-based PYTHON simulations establishes the efficacy of the proposed approach. This research holds promise for applications in industrial and commercial contexts, offering enhanced performance and versatility.

Dual-anion chemistry synchronously regulating the solvation structure and electric double layer for durable Zn metal anodes

Dual-anion chemistry is engineered by adding strong polarity Ac− into Zn(OTf)2 electrolyte, which enables synchronous regulation of solvation structure and electric double layer, thereby countering rapid Zn2+ consumption and prompting favorable interphase formation for durable Zn metal anodes.

Accurate Distinction of Weak and Strong AC Grids for Emerging Hierarchical-Infeed LCC-UHVDC Systems

Accurate Distinction of Weak and Strong AC Grids for Emerging Hierarchical-Infeed LCC-UHVDC Systems

Creep and Superplasticity of Gadolinium‐Doped Ceria Ceramics under AC Electric Current

Shaping of dense ceramics is difficult due to their inherent brittleness. Nanograined ceramics like tetragonal zirconia (TZP) can be superplastically deformed and shaped at high temperatures owing to grain boundary sliding (GBS). Herein, the enhanced plasticity of gadolinium‐doped ceria (GDC) ceramics under mild and strong AC electric current in terms of steady state creep rate under both compressive and tensile loading is demonstrated. A current density of 25 and 200 mA mm−2 is used for the creep deformation. The creep rate increases by up to two orders of magnitude under electric current. The stress exponent remains unchanged for creep experiments at 1200 °C with and without electric current, suggesting a GBS mechanism of plastic deformation in both cases. The field‐enhanced creep rate is attributed to the interaction of space–charge layer and the electric field resulting in enhanced GBS. A higher current density results in enhanced ductility of GDC even when the Joule heating effect is compensated by reducing the furnace temperature.

Control Strategy of Suppressing Short-circuit Current VSCs Feeding into the AC Grid in a Hybrid Cascaded UHVDC System

Hybrid cascaded ultra-high voltage dc is a new dc technique with a line commutated converter cascaded with one or several voltage source converters. It is an effective solution for large capability transmission as well as improving the stability of the ac grid with multiple dc transmission systems feeding in. Baihetan-jiangsu dc project in China is the first cascaded ultra-high voltage dc project in the world. For a receiving end with a strong ac system, the short circuit current is always large and close to the maximum ac breaker breaking capability, which is a threat to the ac system fault clearance. In this paper, the issue of excessive short circuit current in a hybrid cascaded ultra-high voltage dc system is discussed and revealed. The process of the short circuit current developing is divided into 2 stages. Characteristics and the calculation method of the short circuit are proposed, and based on this, a control method is proposed, which can suppress the short circuit current during the fault clearance effectively. The parameter setting method is proposed. Finally, based on the scenario of the Baihetan-jiangsu dc project, the strategy and the parameters setting method are validated under PSCAD/EMTDC.

Adaptive fault ride through control of VSM Grid-forming converters

Recently, many high voltage direct current (HVdc) transmission lines are being constructed with the intention of becoming “backbones” of future power grids. Grid-forming (GFM) controlled Voltage Source Converters (VSCs) are anticipated to provide significant stability advantages compared with Grid-following (GFL) VSCs in HVdc converters connected to weak ac grids or to grids with high penetration of renewable inverter-based resources (IBRs). This paper proposes an adaptive fault ride through controller for Virtual Synchronous Machine (VSM) GFM control, which has significantly improved fault ride through capability over the more conventional GFM control with cascaded or switchable current limiting. The performance of the proposed adaptive control is investigated using Electromagnetic Transient (EMT) simulation. The results show that the proposed adaptive control has superior post disturbance recovery from ac faults as well as phase angle shifts, and overcomes the instability reported in GFM converters connected to strong ac networks.

A Sensor for the Ultraweak DC Current Covered by Strong AC Currents

In the field of insulation monitoring of high-voltage power equipment, the dc leakage current is an important indicator to evaluate the insulation state. However, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{A}$ </tex-math></inline-formula> -level dc leakage currents are usually mixed with mA-level power-frequency ac currents, bringing obstacles to the accuracy of the dc measurement. In this regard, a new magnetic modulator with a suppressing structure is proposed. Based on the fact that Lenz law only keeps valid for a changing magnetic flux, the ac suppressing structure is developed to enclose the original magnetic modulator. Then, the factors of the suppression structure’s performance, including weakening the ac magnetic flux and reducing the dc measurement sensitivity, have been analyzed. And the performance is found to be closely related to the magnet dimensions, the magnetic permeability, and the suppressing winding turns. Finally, the improved prototype current sensor for the converter transformer valve side bushing has been developed, and experiments are conducted to verify its dc accuracy and ac suppressing performance.

Research on the Voltage Supporting Capability of Multi-VSC-HVDC Subsystems Operation Strategy to Receiving-end LCC-HVDC Network in Weak AC Grid

For the hybrid multi-infeed HVDC system in which the receiving-end grid is a strong AC grid including LCC-HVDC subsystems and multiple VSC-HVDC subsystems, it has higher voltage support capability. However, for weak AC grid, the voltage support capability of the multi-VSC-HVDC subsystems to the LCC-HVDC subsystem (voltage support capability-mVSCs-LCC) can resist the risk of commutation failure. Based on this consideration, this paper proposes an evaluation index called Dynamic Voltage Support Strength Factor (DVSF) for the hybrid multi-infeed system, and uses this index to qualitatively judge the voltage support capability-mVSCs-LCC in weak AC grid. In addition, the proposed evaluation index can also indirectly judge the ability of the LCC-HVDC subsystem to suppress commutation failure. Firstly, the mathematical model of the power flow of the LCC and VSC networks in the steady-state is analyzed, and the concept of DVSF applied to hybrid multi-infeed system is proposed. Furthermore, the DVSF index is also used to qualitatively judge the voltage support capability-mVSCs-LCC. Secondly, the influence of multiple VSC-HVDC subsystems with different operation strategies on the DVSF is analyzed with reference to the concept of DVSF. Finally, the indicators proposed in this paper are compared with other evaluation indicators through MATLAB simulation software to verify its effectiveness. More importantly, the effects of multi- VSC-HVDC subsystems using different coordinated control strategies on the voltage support capability of the receiving-end LCC-HVDC subsystem are also verified.

Fast High-Fidelity Gates for Galvanically-Coupled Fluxonium Qubits Using Strong Flux Modulation

Long coherence times, large anharmonicity, and robust charge-noise insensitivity render fluxonium qubits an interesting alternative to transmons. Recent experiments have demonstrated record coherence times for low-frequency fluxonium qubits. Here, we propose a galvanic coupling scheme with flux-tunable XX coupling. To implement a high-fidelity entangling iSWAP gate, we modulate the strength of this coupling and devise variable-time identity gates to synchronize required single-qubit operations. Both types of gates are implemented using strong ac flux drives, lasting for only a few drive periods. We employ a theoretical framework capable of capturing qubit dynamics beyond the rotating-wave approximation as required for such strong drives. We predict an open-system fidelity of F>0.999 for the iSWAP gate under realistic conditions.3 MoreReceived 14 July 2022Accepted 18 November 2022DOI:https://doi.org/10.1103/PRXQuantum.3.040336Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum controlQuantum gatesQuantum information with solid state qubitsPhysical SystemsSuperconducting qubitsQuantum InformationCondensed Matter, Materials & Applied Physics

Ultrasonic Waveguides for Quench Detection in HTS Magnets

High-temperature superconductors (HTS) are expected to have a major impact on the development of future particle accelerators and fusion energy systems. One of key challenges associated with HTS is a slow propagation of the normal zone that complicates early detection of thermal runaway (quench) in an HTS magnet using voltage-based techniques. Furthermore, fusion systems require field ramping rates up to several T/s under strong time-varying ac magnetic fields imposed on the conductor which makes voltage-based quench detection difficult or impractical. We propose an alternative non-voltage quench detection solution based upon monitoring ultrasonic wave propagation in a solid fiber-like flexible waveguide. The latter can be co-wound with the superconducting cable and carry acoustic waves over long distances. Acoustic waveguides allow for measuring local variation of strain or temperature in a way similar to optical fibers. However, unlike fiber-optic sensors, mechanical waveguides are constructed of robust materials and eliminate the need for expensive and complex signal receivers and data processing equipment. We will present our early developments in cryogenic ultrasonic waveguide technology, and discuss preliminary experiments conducted towards validating it for future use in practical HTS magnets.

Application of square-wave inverter in excitation system for magnetic nanoparticle tomography

To collect the signals of magnetic nanoparticles (MNPs) at a distance from a magnetic nanoparticle tomography, a strong ac magnetic field should be generated by applying a high current to the excitation coil. To this end, sinusoidal excitation using a linear amplifier-type ac power source has been applied to the tomography. Although this source can provide a high-quality sinusoidal voltage, its low power efficiency is not suitable for generating the required high current. To overcome this limitation, we use an H-bridge voltage source inverter to achieve high efficiency by generating a square-wave voltage. However, the third harmonic component in the square wave, undermines the acquisition of MNP signals. Thus, we suppress the third harmonic by shifting the switching phase of the inverter transistors. As a result, the third harmonic in the excitation current is reduced to less than one-tenth of that obtained after conventional suppression. We verify the distribution of MNP signals at depths up to 50 mm using the proposed excitation approach. The results demonstrate the effectiveness of the proposed approach based on square-wave inverter excitation for magnetic nanoparticle tomography.

Step response of Rectifier DC Current Controller and Inverter DC Current-Voltage-Extinction Angle Controllers in a Current Source Converter Based HVDC Transmission Link Connected to a Strong Inverter Side AC system

Abstract: Transmission of electrical energy with High Voltage Direct Current (HVDC) has provided the electric power industry with a dominant means to transmit huge quantity of electricity over very long distances. To investigate the performance, a welldeveloped current source converter based HVDC transmission system model is projected, in which the AC system represented as damped LLR equivalent and is equipped with double tuned harmonic filter to mitigate the AC-DC harmonics and the DC system is secured with rectifier current control, inverter current control, voltage control and inverter extinction angle control. The MATLAB/Simulink based simulation results validate the step response of HVDC transmission system with various controllers. Keywords: HVDC transmission systems, double tuned filter, Rectifier DC Current Control, Inverter DC Current-Voltage - Extinction Angle Control, Step response.

Analysis and Simulation Research of Cascading Faults in AC/DC Hybrid Grid

In the development of power systems, the traditional AC power grids are gradually evolving into AC/DC hybrid grids. However, the safety of hybrid grids is threatened by cascading faults, which is a set of chain events caused by a single fault and will eventually lead to a blackout. Based on the blackout accident that happened in Brazil on March 21st, 2018, this paper analyzes the cause, mechanism, and development of cascading faults in AC/DC hybrid grids. Simulations based on PSCAD/EMTDC software have been carried out to illustrate the typical cascading fault scenario including HVDC commutation failure, DC blocking, power flow transferring, incorrect relay protection and the outage of the network. Both analysis and simulation results shows that the “strong DC weak AC” structure and unreasonable cooperation of relay protections and stability control devices are important factors of cascading faults. Finally, this paper prospects a series of protection and control technologies that are expected to solve the problem.

Comprehensive small-signal stability analysis for master hybrid MMC connected with strong and weak AC systems

The small-signal stability problem of power electronic converters has always been a critical concern for safe operation. This paper conducts a comprehensive analysis of the small-signal stability for the hybrid modular multilevel converter (MMC), which is promising in the application of future over-head-line high-voltage-direct-current transmission. The impacts of the strong and weak AC system connection are comparatively researched through eigenvalue-based analysis. The newly emerging factors that hamper the stability are identified for the weak AC system integration. The work in this paper provides valuable guidance for robust control parameter configuration of the hybrid MMC.

Nonlinear magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics driven by a strong ac magnetic field

The nonlinear magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics subjected to a strong alternating current (ac) magnetic field is studied according to the reaction–diffusion equation. The general nonlinear response is evaluated via the perturbation theory. An analytic equation of nonlinear magnetization is derived based on Legendre function. Numerical calculations are carried out, and the results show that both the magnetization and the probability distribution decrease with the reaction process due to the consumption of the reactants. Both the probability distribution and the magnetization are affected by the anisotropy, the reaction rate and the field energy.

Nonperturbative quasiclassical theory of graphene photoconductivity

We present a nonperturbative quasi-classical theory of graphene photoconductivity. We consider the influence of low-frequency (microwave, terahertz, mid-infrared) radiation on the static conductivity of a uniform graphene layer and calculate its photoconductivity as a function of frequency, polarization and strength of the external ac electric field, as well as on the material properties (electron density, scattering time) and temperature. The theory is valid at frequencies $\hbar\omega\lesssim 2E_F$ and at arbitrarily strong ac electric fields. We compare our results with those of the third-order perturbation theory and determine the applicability range of the perturbative solutions.