Asymmetric Current Research Articles

Study on the Characteristics of Tidal Current Velocity in Estuarine and Bay Areas

Abstract In estuarine and bay regions, reciprocating tidal currents frequently constitute the predominant hydrodynamic forces. Nonetheless, there exists a paucity of research concerning the hydrodynamic characteristics under intricate tidal conditions. This study employs tidal current data collected from nine sites within the Yellow River Estuary and Hangzhou Bay to examine the periodic characteristics of tidal currents, the vertical velocity distribution, and the attributes of ebb and flood peak velocities. The study revealed that the Yellow River Estuary and Hangzhou Bay predominantly exhibit nearly symmetrical reciprocating tidal currents. Nevertheless, certain regions within Hangzhou Bay also demonstrate asymmetrical tidal currents. The vertical velocity distribution throughout various phases of a single tidal cycle generally adheres to the characteristics described by the SOULSBY distribution. The peak velocities of ebb and flood tides are correlated with the rate of change in water depth (hm/tm), and an equation for calculating these peak velocities has been derived through fitting data.

In situ hydrodynamic observations on three reef flats in the Nansha Islands, South China Sea

Waves and currents are responsible for sediment movement around and off coral reefs, affecting reef growth at both geological and modern timescales. Given the wide distribution and limited hydrodynamic information of reefs in the South China Sea, we carried out observations on tidal-cycle hydrodynamics in the Nansha Islands with tripod stationary instruments on the seafloor in order to fill the gap in our understanding of these processes. It was found that the magnitudes of near-bed orbital velocity were comparable with that of the mean tidal current, despite generally calm wave conditions. Waves dominated the combined wave-current skin-friction shear velocities acting on reef sediment, which were significantly higher than those generated by currents alone. Due to the large physical roughness of reef, drag coefficient and hydrodynamic roughness length estimated from logarithmic velocity profiles were two orders of magnitude higher than that in macro-tidal-estuary or inner shelf areas covered with siliceous muds or sands. The combined sinusoidal wave and asymmetric tidal current, along with the physical reef roughness, shaped velocity profile structures in the bottom boundary layer, which exhibited a logarithmic profile during the flood tide and a potential flow during the ebb. In absence of wave breaking, strong turbulence dissipation was observed across the rough reef, promoting strong mixing of water, which is crucial for delivering nutrients for coral growth. These findings imply the need to consider the unique characteristics of rough reef structure and combined effects of waves and currents to model the hydrodynamics in reef environment correctly. This understanding is critical for predicting energy and material transport in reef environments, which is essential for maintaining healthy coral ecosystems, and opens new paths for managing and preserving coral reefs in the face of environmental change.

Flux-pinning mediated superconducting diode effect in NbSe2/CrGeTe3 heterostructure

In ferromagnet/superconductor bilayer systems, dipolar fields from the ferromagnet can create asymmetric energy barriers for the formation and dynamics of vortices through flux pinning. Conversely, the flux emanating from vortices can pin the domain walls of the ferromagnet, thereby creating asymmetric critical currents. Here, we report the observation of a superconducting diode effect (SDE) in a NbSe2/CrGeTe3 van der Waals heterostructure in which the magnetic domains of CrGeTe3 control the Abrikosov vortex dynamics in NbSe2. In addition to extrinsic vortex pinning mechanisms at the edges of NbSe2, flux-pinning-induced bulk pinning of vortices can alter the critical current. This asymmetry can thus be explained by considering the combined effect of this bulk pinning mechanism along with the vortex tilting induced by the Lorentz force from the transport current in the NbSe2/CrGeTe3 heterostructure. We also provide evidence of critical current modulation by flux pinning depending on the history of the field setting procedure. Our results suggest a method of controlling the efficiency of the SDE in magnetically coupled van der Waals superconductors, where dipolar fields generated by the magnetic layer can be used to modulate the dynamics of the superconducting vortices in the superconductors.

Larval and Adult Traits Coevolve in Response to Asymmetric Coastal Currents to Shape Marine Dispersal Kernels.

AbstractDispersal emerges as an outcome of organismal traits and external forcings. However, it remains unclear how the emergent dispersal kernel evolves as a by-product of selection on the underlying traits. This question is particularly compelling in coastal marine systems, where dispersal is tied to development and reproduction and where directional currents bias larval dispersal downstream, causing selection for retention. We modeled the dynamics of a metapopulation along a finite coastline using an integral projection model and adaptive dynamics to understand how asymmetric coastal currents influence the evolution of larval (pelagic larval duration) and adult (spawning frequency) life history traits, which indirectly shape the evolution of marine dispersal kernels. Selection induced by alongshore currents favors the release of larvae over multiple time periods, allowing long pelagic larval durations and long-distance dispersal to be maintained in marine life cycles in situations where they were previously predicted to be selected against. Two evolutionarily stable strategies emerged: one with a long pelagic larval duration and many spawning events, resulting in a dispersal kernel with a larger mean and variance, and another with a short pelagic larval duration and few spawning events, resulting in a dispersal kernel with a smaller mean and variance. Our theory shows how coastal ocean flows are important agents of selection that can generate multiple, often co-occurring evolutionary outcomes for marine life history traits that affect dispersal.

Analysis of three-phase asymmetrical currents in the secondary voltage of signal change sensors in the power supply system using graph models

This article presents the principles of modeling three-phase asymmetrical currents in the form of secondary voltages of signal change sensors in the power supply system. The classical methods of signal transformation modeling do not provide the necessary accuracy due to the complexity in representing the interdependence between input and output quantities and parameters, as well as the difficulty in capturing the interchain dependencies and associated physical-technical effects. The analysis in this work focuses on the principles of signal transformation based on graph models, including the physical and technical effects of the three-phase primary current electromagnetic sensor that creates the interacting magnetic fields. The modifications to elements with nonlinear parameters and the values of the electric network currents in the power supply system during estimation have been considered as an object with concentrated parameters. In contrast to traditional single-phase current transformers, the complex transducing components, weight, and volume of the items are laborintensive when used in combined power measurement and control systems. They also do not provide the universality of the output value when interfacing with microprocessors and electronic technologies in intelligent systems.

Asymmetric Ionospheric Jets in Jupiter's Aurora

AbstractSimultaneous infrared observations of and H2 emissions from Jupiter's northern aurora using the Near Infrared Spectrograph at Keck Observatory were used to measure the ionospheric and thermospheric wind velocities. ions supercorotate near the dawn auroral oval and subcorotate across the dusk sector and in the dawn polar region relative to the planetary rotation rate, broadly in agreement with past observations and models. An anticyclonic vortex is discovered in H2 flows, closely matching the mean magnetospheric subcorotation when the observed magnetospheric flows are averaged azimuthally. In comparing ion and neutral winds, we measure the line‐of‐sight effective ion drift in the neutral reference frame for the first time, revealing two blue‐shifted sunward flows of ∼2 km/s. Observed and H2 emissions overlap with predictions of the Pedersen conductivity layer, suggesting two different regions of the ionosphere: (a) a deep layer, where neutral forces dominate the thermosphere and symmetric breakdown‐in‐corotation currents can close, and (b) a higher layer, where the observed effective ion drift allows dawn‐to‐dusk Pedersen currents within the upper atmosphere, in turn closing asymmetric currents within the magnetosphere. This ionospheric structure aligns well with recent Juno observations of Jupiter's aurora. The detected thermospheric vortex implies the driving of neutral flows by the momentum from the magnetosphere within the thermosphere and deeper in the atmosphere to potentially 20 mbar. Jovian neutral thermosphere might bridge the gap between current observations and modelings and perhaps be significant to the dynamics of aurora on Earth and other outer planets.

ELECTROCHEMICAL SYNTHESIS OF HYBRID MATERIALS BASED ON POLYELECTROLYTE CHITOSAN COMPLEXES AND INVESTIGATION OF THEIR PHYSICAL AND CHEMICAL PROPERTIES

A study of the morphology, structure and elemental composition of hybrid materials on the surface of stainless steel based on polyelectrolyte complexes of chitosan with cobalt and nickel oxides, obtained using an alternating asymmetric current, was carried out. It was established by X-ray phase analysis that the main phase of the obtained hybrid materials is cobalt hydroxyisocyanate. The prospects of using the obtained hybrid materials as electrodes for supercapacitors with alkaline electrolyte are shown, while its specific capacitance at a current density of 1 A∙g-1 reaches 479 F∙g-1. The antibacterial activity of hybrid materials against gram-positive (S.aureus) and gram-negative (E.coli) microorganisms was determined. A study of corrosion-protective properties of the developed hybrid materials in a solution of 3.5 wt. % NaCl was carried out, it is shown that for the hybrid material the corrosion potential is shifted to the region of positive values compared to pure steel.

Thermodynamic variational relation.

In systems far from equilibrium, the statistics of observables are connected to entropy production, leading to the thermodynamic uncertainty relation (TUR). However, the derivation of TURs often involves constraining the parity of observables, such as considering asymmetric currents, making it unsuitable for the general case. We propose a thermodynamic variational relation (TVR) between the statistics of general observables and entropy production, based on the variational representation of f divergences. From this result, we derive a universal TUR and other relations for higher-order statistics of observables.

STUDY OF THE PROPERTIES OF COATINGS BASED ON COBALT-MANGANESE SPINEL OBTAINED BY THE METHOD OF NON-STATIONARY ELECTROLYSIS

Coatings based on cobalt-manganese spinel (Mn, Co)·(Mn, Co)2O4 were obtained on the surface of stainless steel by polarization with alternating asymmetric current. The study of the mechanical properties showed that the coatings are characterized by a sufficiently high adhesion to the substrate, their thickness is about 30 μm, and the microhardness value is 40 HV, which is comparable to similar oxide materials. The study of thermal stability in air shows their stability at temperatures up to 1000 °C, and the study of corrosion-protective properties - about the stability of the resulting coatings in a solution of 3.5% (wt.) NaCl.

The interaction of gravity currents in a porous layer with a finite edge

The interactions of upper (lighter) and lower (heavier) gravity currents are closely related to fluid-phase resource recovery in porous layers and cleaning of confined spaces. The addition of a second current increases the sweep efficiency of fluid displacement. In this paper, we first derive two ordinary differential equations to describe the interaction of gravity currents in the quasi-steady regime. Two asymptotic regimes are identified, characterised by whether or not the two currents attach to each other, depending on whether the source fluxes are large enough. In the attached regime, a symmetry condition is also identified that describes whether or not the pumping and buoyancy forces balance each other. The model also leads to analytical solutions for the interface shape of the interacting currents in both the detached and attached regimes and for both symmetric and asymmetric currents. For symmetric currents, analytical solutions can also be obtained for the pressure distribution along cap rocks and the sweep efficiency of flooding processes. A particularly interesting aspect is that the displaced fluid remains quiescent at any steady state, regardless of whether the currents attach to each other. Correspondingly, the interface shape of the currents can be described by relatively simple equations and solutions, as if the currents propagate independently in unconfined porous layers. Time transition towards quasi-steady solutions is provided, employing time-dependent numerical solutions of two coupled partial differential equations for dynamic current interaction.

Thrust Ripple Suppression Based on Negative Current Control for Short-Primary Low-Speed Large LIM Under Transient Operation

End effect of linear induction motor (LIM) leads to magnetic asymmetry and thrust ripple, which seriously restricts the performance and application of LIM. Existing methods for thrust ripple modeling and compensating have mostly focused on the steady state, which suffer from poor transient performance. Moreover, the influence of asymmetric currents on output thrust is not considered. In this paper, the thrust ripple characteristics and impact factors of a low-speed large LIM with negligible dynamic longitudinal end effect are analyzed in details, firstly. Then, a data-driven extracting and modeling method for transient thrust ripple is proposed. The non-stationary time-varying thrust ripple signal is extracted through wavelet decomposition and reconstruction, the polynomial parameters of thrust ripple model are trained off-line by particle swarm optimization algorithm. Finally, an improved suppressing scheme for transient thrust ripple is proposed, considering the decoupling and feedback control of positive and negative currents, based on the dynamic model of six-phase LIM. Full-scale experimental results have fully demonstrated the accuracy of proposed data-driven transient thrust ripple model is more than 90%. During the high-thrust operating stage, the axial vibration acceleration level of LIM within 100Hz is reduced by more than 12dB, with the adoption of improved control scheme.

Получение покрытий на основе шпинели Co-Mn-O с использованием переменного асимметричного тока

Получение покрытий на основе шпинели Co-Mn-O с использованием переменного асимметричного тока

Increasing linear flux range of SQUID amplifier using self-feedback effect

Superconducting quantum interference devices (SQUIDs) are low-noise amplifiers that are essential for the readouts of translation edge sensors (TESs). The linear flux range is an important parameter for SQUID amplifiers, especially those controlled by high-bandwidth digital flux-locked-loop circuits. A large linear flux range conduces to accurately measuring the input signal and also increasing the multiplexing factor in the time-division multiplexed (TDM) readout scheme of the TES array. In this work, we report that the linear flux range of an SQUID can be improved by using self-feedback effect. When the SQUID loop is designed to be asymmetric, a voltage-biased SQUID shows an asymmetric current–flux (I–Φ) response curve. The linear flux range is improved along the I–Φ curve with a shallow slope. The experimental results accord well with the numerical simulations. The asymmetric SQUID will be able to serve as a building block in the development of the TDM readout systems for large TES arrays.

A Novel Error-Injected Solution for Compensation of Current Measurement Errors in PMSM Drive

Current measurement errors including offset error and scaling error can generate asymmetric phase currents and 1st- and 2nd-order harmonics in motor steady-state torque/speed. In this paper, a novel method using artificial error injection is proposed to calculate and compensate for the offset error and scaling error in permanent magnet synchronous motor (PMSM) drive. The artificial errors are injected to introduce additional equations for the calculation of current measurement errors because of the problem of rank deficiency existing in the equation about the offset/scaling error and the 1st/2nd-order harmonic magnitude. In order to guarantee the calculation accuracy of the offset error and scaling error, the cascade multiple second-order generalized integrators (Cascade-Multi-SOGIs) are employed to extract the magnitudes of the 1st- and 2nd-order harmonics in steady-state speed error under different error injections. The method does not require the values of motor parameters, and it can be used either as part of an initial debugging or start-up program, or periodically during the regular operation of the motor. The experiments can verify its validity and practicability.

Disruption halo current rotation scaling on Alcator C-Mod and HBT-EP

Asymmetric halo currents (HCs) can exert large net forces on the vacuum vessel and other components during disruptions on tokamaks. The displacements caused by these forces can then be amplified if these asymmetric forces rotate at frequencies resonant with the vessel. This paper reports on the investigation of a recently proposed scaling law for the disruption HC rotation frequency [Saperstein et al., “Halo current rotation scaling in post-disruption plasmas,” Nucl. Fusion 62, 026044 (2022)] that combines measurements on Alcator C-Mod with those on HBT-EP. We find that a new non-circular version of the scaling law [ ⟨ f rot ⟩ m / ⟨ m ⟩ ∝ 1 B T ( S / π )] takes into consideration the dependence of frot on the poloidal structure of the MHD instability (m) driving the asymmetry and describes the disruption-averaged rotation frequency on C-Mod. Disruption rotation is also found to be insensitive to the vertical position and impurity content of the plasma at the onset of the disruption. However, a stagnation in the time evolution of frot is occasionally observed. Observations are consistent with the dominance of poloidal rotation during the disruption, which is motivated by the poloidal drift nature of the scaling law.

Study on determination of an asynchronous motor’s reactive power by the current-to-voltage converter

This article presents a method for determining the primary currents, non-sinusoidal and asymmetrical currents flowing through the stator windings of an asynchronous motor based on the signal in the form of the output voltage from the current converter loops placed in each phase between the poles of the asynchronous motor stator and in the arrangement of the stator windings. Differences and characteristics of output signals are researched based on independent, series and opposite (bifilar) connection schemes of asynchronous motor current converter loops of measuring coil. In order to determine the value of the currents generated in each phase of the asynchronous motor stator windings, the output signals of the current converter with independent loop and loops connected in series were mutually analyzed. Measuring non-sinusoidal and asymmetrical currents, according to the opposite (bifilar) connection scheme, the loops of measuring coils are placed in the inter-pole grooves of each phase of the stator in the order corresponding to the three-phase stator windings, the current converter measuring coils each consists of two loops, bifilarly connected to each other. The end of loops of the measuring coils has two exits. Diodes and phase meter-regulators are placed on the first outputs of the loops, and they are oppositely connected to the microprocessor unit for measuring and controlling the asymmetry. The second outputs of the loops are connected directly opposite to the microprocessor unit for measuring and controlling non-sinusoidal currents. This type of current converter is important for determining the non-sinusoidal and asymmetrical currents generated in asynchronous motors, it increases the functional capabilities and accuracy of the current converter, and based on the determined results, it simplifies theoretical calculations, and at the same time, the dynamic and it will be possible to determine the static characteristics through theoretical differential equations. As a result of the research, practical and theoretical results were compared.

Asymmetric Electrode Influence upon Ferroelectric Switching Dynamics in Ag/PVDF‐HFP/ITO Capacitor Structures

Asymmetric electrode (Ag and indium tin oxide (ITO)) influence upon ferroelectric switching dynamics in polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) thin films across Ag/PVDF-HFP/ITO capacitor structures is systematically investigated. Grazing incidence X-Ray diffraction (GI–XRD), atomic force microscopy (AFM), and UV–visible spectroscopy are utilized to comprehend the structural and microstructural characteristics of PVDF–HFP thin films upon ITO interface. Low voltage rectified and asymmetric current–voltage (I–V) curves reveal the varied barrier potential due to the asymmetric electrodes. Typical squared hysteresis loops along with uniform domain growth model are verified from quasi-static and dynamic ferroelectric loop measurements. Further, from low-frequency (10 and 15 mHz) quasi-static and dynamic (100–1000 Hz) triangular pulses, the switching time, domain dimension with respect to frequency, and amplitude of the electric field are separately evaluated and noted that smaller switching times when electron traverses from Ag to ITO electrode.

Theory of asymmetric and piezotronically modified double Schottky barriers

We present a theoretical model for double Schottky barriers at zinc oxide grain boundaries that accounts for piezotronically modified barrier heights resulting in generally asymmetric current–voltage (I–V) characteristics with respect to the applied electrical field direction. The model is based on charge distributions in the vicinity of the barrier and its related electrical potential distributions and can be considered as a generalization of the famous model of Blatter and Greuter. The natural asymmetry of current with respect to forward and reverse bias can be explained by different grain orientations and donor densities. The previously experimentally found change of I–V curves due to the application of mechanical loads can be reproduced via the piezotronic effect, leading to changes in the barrier potential profile due to piezoelectrically induced surface charges. Also, the I–V characteristics of degraded grain boundaries can be interpreted in terms of asymmetric changes in the donor densities. In addition, a second approach is presented that is able to explain experimental data of asymmetric I–V curves of wide grain boundaries with different surface terminations (O and Zn-polar).

Modeling and Analysis of Asymmetrical Faults for Relay Settings in Electric Power Protection System Learning

This study examines the analysis of Asymmetrical fault, namely single-phase ground faults for e-jobsheet products based on Information and Communication Technology (ICT) or utilizing computer programs for study. A study of short-circuit faults in the electric power system, is used to solve problems in the field of reliability and protection. the electric power system, namely the handling of single-phase short-circuit faults to ground which, if not neutralized, cause equipment damage to the electric power system. Parameters from modeling and analysis of asymmetrical faults are used for setting the Ground Fault Relay or often known as the Ground Fault Relay (GFR). The research study begins with modeling the interconnection system in the form of a reactance diagram, then modeling it with the bus impedance matrix equation, to determine the magnitude of the short circuit impedance value on the diagonal matrix. Then calculate the fault current of a single-phase short circuit to ground. From these results it is determined to determine the amount of the relay setting. The results showed that the asymmetrical fault current was 3.0 Pu with a setting time value of 2,45 seconds. The results of the study are used for learning relay settings. The simulation program was validated by experts, with a very good category with an Aikensv index of 0.872.

A High-Efficiency and High-Power-Density Interleaved Integrated Buck-Boost-LLC Converter and Its Comprehensive Optimal Design Method

Integrated buck-boost- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> (IBBL) dcconverter is a good solution for high efficiency and high power density applications. However, the bridge leg integration causes asymmetrical zero-voltage-switching process and asymmetrical secondary current. The method of high quality factor or symmetric phase shift modulation proposed in the existing research can improve the asymmetrical current issue under heavy load, but is ineffective for light load conditions. This article proposes a novel Interleaved IBBL converter to improve the asymmetry issue for whole load range. Interleaving makes the secondary current be symmetric naturally. In addition, a comprehensive optimal design method for phase-shift angle and choke inductor is proposed to minimize the total power loss of all primary elements. A 600 W/1 MHz prototype verifies that the proposed IIBBL converter achieves symmetric secondary current in whole load range, and it achieves 95.7% efficiency and 180 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> under the proposed comprehensive optimal design method.