Dynamic Switching Process Research Articles

Emulating Radiative Field of Electromagnetic Pulse Generator Deployed With Co-Design Capacitor Under Dynamic Switching Process

Emulating Radiative Field of Electromagnetic Pulse Generator Deployed With Co-Design Capacitor Under Dynamic Switching Process

Ion Density-Dependent Dynamic Conductance Switching in Biomimetic Graphene Nanopores.

Gating in ion transport is at the center of many vital living-substance transmission processes, and understanding how gating works at an atomic level is essential but intricate. However, our understanding and finite experimental findings of subcontinuum ion transport in subnanometer nanopores are still limited, which is out of reach of the classical continuum nanofluidics. Moreover, the influence of ion density on subcontinuum ion transport is poorly understood. Here we report the ion density-dependent dynamic conductance switching process in biomimetic graphene nanopores and explain the phenomenon by a reversible ion absorption mechanism. Our molecular dynamics simulations demonstrate that the cations near the graphene nanopore can interact with the surface charges on the nanopore, thereby realizing the switching of high- and low-conductance states. This work has deepened the understanding of gating in ion transport.

A new pilot protection scheme for modular multi‐level converter‐based HVDC system based on voltage matching factor

Concerning the incorrect operation of line protection in modular multi-level converter-based multi-terminal DC system, a pilot protection method based on voltage matching factor is proposed. First, the dynamic switching process of flexible DC converter sub-module is analyzed, and the expression of DC voltage of converter station considering the influence of alternating current (AC) system is derived. On this basis, the model of DC line voltage considering the influence of AC injection current is built, and the equivalent DC line voltage is calculated according to the voltage model. Then, by constructing the distortion factor which reflects the difference between the equivalent DC line voltage and actual DC line voltage, the protection criterion for the identification of internal and external faults is established. Finally, simulation tests on real time laboratory (RT-LAB) platform verify that the proposed scheme can correctly distinguish between internal and external faults in different fault cases, with fast operation speed and strong immunity to the fault resistance.

A pilot protection scheme for flexible HVDC transmission lines based on modulus power

Existing protection methods for Flexible HVDC transmission lines easily fail to detect the fault location fast and reliably. Concerning this problem, a modulus power based pilot protection scheme is proposed. By analyzing the dynamic switching process of sub-modules in flexible DC converter station, the expression of converter station DC voltage taking into account the influence of AC system is derived. On this basis, the modulus voltage and modulus current are calculated by phase-modulus transformation, and the modulus power calculation model containing DC components alone is built. Then, the expressions of modulus power in different fault cases are derived, and a protection criterion based on the polarity difference characteristics of modulus power is established. Finally, the RT-LAB is used to build the model of a flexible DC system for simulation verification. The results of simulation tests verify that, the proposed protection scheme can detect the fault line and fault pole fast and accurately, with easy threshold setting and low demand on communication synchronization. Besides, it is unaffected by the fault resistance and the specific boundary conditions of current-limiting reactor, etc.

Detecting Dynamic Community Structure in Functional Brain Networks Across Individuals: A Multilayer Approach.

We present a unified statistical framework for characterizing community structure of brain functional networks that captures variation across individuals and evolution over time. Existing methods for community detection focus only on single-subject analysis of dynamic networks; while recent extensions to multiple-subjects analysis are limited to static networks. To overcome these limitations, we propose a multi-subject, Markov-switching stochastic block model (MSS-SBM) to identify state-related changes in brain community organization over a group of individuals. We first formulate a multilayer extension of SBM to describe the time-dependent, multi-subject brain networks. We develop a novel procedure for fitting the multilayer SBM that builds on multislice modularity maximization which can uncover a common community partition of all layers (subjects) simultaneously. By augmenting with a dynamic Markov switching process, our proposed method is able to capture a set of distinct, recurring temporal states with respect to inter-community interactions over subjects and the change points between them. Simulation shows accurate community recovery and tracking of dynamic community regimes over multilayer networks by the MSS-SBM. Application to task fMRI reveals meaningful non-assortative brain community motifs, e.g., core-periphery structure at the group level, that are associated with language comprehension and motor functions suggesting their putative role in complex information integration. Our approach detected dynamic reconfiguration of modular connectivity elicited by varying task demands and identified unique profiles of intra and inter-community connectivity across different task conditions. The proposed multilayer network representation provides a principled way of detecting synchronous, dynamic modularity in brain networks across subjects.

Real-Time Molecular-Scale Imaging of Dynamic Network Switching between Covalent Organic Frameworks.

The in situ on-surface conversion process from boroxine-linked covalent organic frameworks (COFs) to boronate ester-linked COFs is triggered and catalyzed at room temperature by an electric field and monitored with scanning tunneling microscopy (STM). The adaptive behavior within the generated dynamic covalent libraries (DCLs) was revealed, providing in-depth understanding of the dynamic network switching process.

Control Strategy of Energy Storage Inverter Based on Virtual Synchronous Generator Technology

In the microgrid system, the power supply quality of sensitive loads is directly affected by the grid-connected and off-grid operation states of the energy storage power supply as well as the dynamic switching process between the two states. To solve this problem, this paper adopts a control method of energy storage inverter based on virtual synchronous generator, which makes the energy storage inverter equivalent to a controlled voltage source with functions of inertia simulation, frequency modulation and voltage regulation. Besides, a seamless switching control strategy of energy storage inverter is proposed, which can realize the automatic smooth switching of the grid-connected state, off-grid state and state between the two.

Phase field simulation of de-aging process in acceptor-doped ferroelectrics

A phenomenological de-aging model with uniformly distributed defect dipoles for acceptor-doped ferroelectrics is proposed with the dynamic switching process of defect dipoles being simulated by the kinetic Monte Carlo method. The shifted P-E loops at different frequencies and temperatures were theoretically investigated. The results showed that the internal bias field increases with frequency and decreases with temperature. The scaling relation of the internal bias field with frequency was calculated at 298 K, 318 K and 338 K. The number of defect dipoles along different directions was calculated during the de-aging process, which is a key factor affecting the shape of P-E hysteresis loop. At 0.1 Hz, the defect dipoles can align with the polarization direction, but when the frequency is more than 10 Hz, they could not follow the field change and the internal bias field will saturate to a fixed value as the field frequency is beyond 100 Hz.

IGBT Junction Temperature Measurements: Inclusive of Dynamic Thermal Parameters

Insulated gate bipolar transistors (IGBTs) are widely used in new energy fields, such as wind power converters and electric vehicles. The junction temperature characteristics and junction temperature measurements greatly influence the reliability of the IGBT. During switching, the electrical parameters of the IGBT undergo considerable change. The thermo sensitive electrical parameter (TSEP) method has been commonly used to extract junction temperature. The TSEP method has the inherent advantages of being able to take measurements quickly and accurately, in a non-intrusive manner. The junction temperature estimate under the on-state condition cannot reflect the reliability of the IGBT during the dynamic switching process. The solution to this dilemma is to measure the junction temperature using the dynamic TSEP method during the IGBT turn-off process. The junction temperature is measured by the reverse voltage peak between the auxiliary emitter and power emitter, which forms during the IGBT turn-off process. The feasibility of the proposed method has been experimentally verified.

The switching of rotaxane-based motors

Linear molecular motors have recently attracted considerable interest. In this paper weuse molecular dynamics simulations to investigate the structural and energeticproperties of neutral and oxidized [2]rotaxane motors. We first consider a neutralstructure to identify the stable configuration of a bistable [2]rotaxane whose ringcomponent is on the tetrathiafulvalene (TTF) recognition site, followed by a study ofthe dynamic switching process of an oxidized [2]rotaxane. The study shows thatfor a neutral structure the ring component stays at the TTF station in bothfree and constrained situations. When the station is oxidized, the ring is pushedto the other station and the dynamic switching process finishes in about 10 ns.By comparing the results for the cases of free and fixed ends, the simulationsshow that structural deformation plays an important role during the switchingprocess and can significantly affect the displacement output of molecular motors.

Solid triphenylmethanol: A molecular material that undergoes multiple internal reorientational processes on different timescales

In solid triphenylmethanol, the molecules are arranged in hydrogen-bonded tetramers, and it is already well established that the hydrogen bonding in this material undergoes a dynamic switching process between different hydrogen bonding arrangements. In addition to this motion, we show here, from solid-state 2H NMR studies of the deuterated material (C 6D 5) 3COH, that each phenyl ring in this material undergoes a 180°-jump reorientation about the C 6D 5–C(OH) bond, with an activation energy of ca. 50 kJ mol −1. The timescale for the phenyl ring dynamics is several orders of magnitude longer than the timescale for the hydrogen bond dynamics in this material, and is uncorrelated with the dynamics of the hydrogen bonding arrangement.

High speed characteristics of thin film write heads at deep submicron track width

This article presents a micromagnetic study of the dynamic magnetic switching process in the pole tip region of stitched-pole thin film write heads. The impacts of track width reduction and pole material saturation moment on the high frequency performance of the heads have been investigated. It is found that the magnetic switching process of the pole tip region at low recording frequencies can be characterized by three stages: the nucleation of a vortex (or vortices), followed by the motion of the vortex (or vortices), and finally the annihilation of the vortex (or vortices). At high frequencies, however, a residual vortex (or vortices) will always remain in the pole tips, resulting in lower head field amplitude. Frequency roll-off characteristics of the head field response have been calculated. The roll off is the result of residual vortex (or vortices), and the vortex moving speed limits the operational frequency range of the head. Reducing the track width lowers the head field 3 dB roll-off frequency. The simulation also finds that the use of 45/55 NiFe, which has significantly higher moment than permalloy, results in higher roll-off frequency as compared to permalloy.

Dynamic switching process of sandwich-structured MR elements

The dynamic behavior of sandwich-structured magnetoresistive (MR) memory elements is studied analytically by solving Gilbert's equation together with the one-dimensional micromagnetic torque equation. The typical element is 2 mu m*20 mu m and consists of two 150-AA thick magnetic layers separated by a 50-AA thick nonmagnetic layer. The easy axis is along the short dimension of the element. The theoretical study shows that wall nucleation is present when the switching is driven by a field applied in the easy-axis direction, whereas switching by a field in the hard-axis direction is accomplished by coherent rotation. The switching speed predicted by this one-dimensional model is in the nanosecond range and increases linearly with the external fields. >