Direct Switching Research Articles

Directional switching of surface plasmons in a parity-time-symmetric insulator-metal-insulator structure

In the present work, we study the generation and propagation of surface plasmon polaritons (SPPs) in a geometrically flat insulator-metal-insulator (IMI) structure with parity-time (PT) symmetric modulation on the dielectric layers. Unidirectional SPPs are generated by PT-symmetric modulation. Moreover, magnetic field switching is obtained between two metal-dielectric interfaces. It has been noticed that the metal thickness affects the oscillation frequency of excited SPPs along the direction of propagation. Also, we report that the field at the upper interface is manipulated by solely maneuvering the permittivity of the bottom dielectric. The magnetic field distribution of the present structure is studied using COMSOL Multiphysics software. To ensure the accuracy and reliability of the simulation results, comprehensive analytical investigations have also been conducted.

A portable and integrated traveling-wave electroosmosis microfluidic pumping system driven by triboelectric nanogenerator

The lab-on-a-chip system can simultaneously complete the preparation, reaction, separation, and detection of samples on a centi-scale platform by manipulating trace fluids. Traveling-wave electroosmosis (TWEO) technology, with the merit of electric signal-based flexible control over the fluid behavior, can achieve precise driving of fluids, which is an important requirement of the lab-on-a-chip system. However, the peripheral power equipment such as the function generator required for TWEO limits the application in some occasions lacking power supply facilities, due to its large size and high cost. In this paper, we have developed a brand-new portable and integrated TWEO microfluidic pumping system, wherein a front-end module of triboelectric nanogenerator (TENG) is in serial connection with the back-end microfluidic pumping chip, which greatly improves portability and reduces costs. The TENG can output stable four consecutively 90°-phase-shifted alternating current voltage signals in a continuous rotational motion originated by its novel electrode structure. And the four-phase traveling potential waves are applied to four sets of electrode strips alternately distributed in the microchannel, thereby inducing nonlinear electroosmotic slip on the electrode surface, achieving stable pumping of fluids in the microchannel. Compared with traditional fluid-driven methods, this system features high safety for the operator and chip but also realizes the almost instantaneous start, stop, and directional switching in response to a turn on, turn off, and turn in reverse of TENG, respectively. Finally, this system is integrated into a droplet microfluidic chip for the efficient generation of single emulsion droplets. This study presents a promising solution for the miniaturization, integration, and commercialization of lab-on-a-chip system.

Automated fiber switch with path verification enabled by an AI-powered multi-task mobile robot

As the capacity of optical transport networks undergoes significant growth, there is an ongoing discussion on how to effectively leverage both spectral and spatial degrees of freedom to scale future network capacity. This paper presents an artificial intelligence (AI)-powered multi-task robot comprising a collaborative robotic arm and a mobile robotic base designed for optical network automation. The robot demonstrates the capability of direct fiber switching, establishing static fiber links that consume zero power and have minimal insertion loss from fiber connectors. As a precautionary measure before physically switching fiber cables, the robot performs path verification by detecting robot-driven events using real-time coherent receivers, aiming to avoid accidental unplugging. Additionally, the robot showcases its mobility by efficiently navigating between different network racks and rooms while executing various tasks. Implementing the automation of network operations using robots has the potential to reduce both capital and operational expenditures.

Faster bi-stable visual switching in psychosis

Bi-stable stimuli evoke two distinct perceptual interpretations that alternate and compete for dominance. Bi-stable perception is thought to be driven at least in part by mutual suppression between distinct neural populations that represent each percept. Abnormal visual perception has been observed among people with psychotic psychopathology (PwPP), and there is evidence to suggest that these visual deficits may depend on impaired neural suppression in the visual cortex. However, it is not yet clear whether bi-stable visual perception is abnormal among PwPP. Here, we examined bi-stable perception in a visual structure-from-motion task using a rotating cylinder illusion in a group of 65 PwPP, 44 first-degree biological relatives, and 43 healthy controls. Data from a ‘real switch’ task, in which physical depth cues signaled real switches in rotation direction were used to exclude individuals who did not show adequate task performance. In addition, we measured concentrations of neurochemicals, including glutamate, glutamine, and γ-amino butyric acid (GABA), involved in excitatory and inhibitory neurotransmission. These neurochemicals were measured non-invasively in the visual cortex using 7 tesla MR spectroscopy. We found that PwPP and their relatives showed faster bi-stable switch rates than healthy controls. Faster switch rates also correlated with significantly higher psychiatric symptom levels, specifically disorganization, across all participants. However, we did not observe any significant relationships across individuals between neurochemical concentrations and SFM switch rates. Our results are consistent with a reduction in suppressive neural processes during structure-from-motion perception in PwPP, and suggest that genetic liability for psychosis is associated with disrupted bi-stable perception.

Direct and indirect switch from semiconductor to metallic behavior defined by the competition between Cation–Anion–Cation and Cation–Cation interactions leading to an important technological aspect of perovskite systems

We discuss in this work the key interactions that explain the possible electrical behaviors in different perovskite systems. Multi-behavior observation characterizes each frequency and temperature dependence of various perovskite systems. We classify such observations according to the temperature regimes. Indeed, a direct switch from semiconductor to metallic feature describes the conductivity evolution indicating the direct change from the localized (cation–anion–cation interactions) to delocalized (cation–cation interactions) state. The metallic character is reached due to the reinforcement of charge delocalization effect at high temperatures and frequencies. An indirect transformation separated by a frequency-independent regime is equally observed and discussed. Subsequently, a mixed regime is described by the conductivity temperature-independence which is explored at a specific frequency. Such investigations lead to demonstrate basic and common rules relevant for oxide-perovskites multi-behavior. Equally, important technological aspects are confirmed for systems that displays such multi-behavior character according to the temperature range.

Effectiveness and Safety of Early Versus Routine Switching from Low-Molecular-Weight Heparin to Maintenance Therapy of Rivaroxaban for Acute Iliofemoral Vein Thrombosis: A Retrospective Cohort Study

The anticoagulation strategy of switching to rivaroxaban after 1week of initial low-molecular-weight heparin (LMWH) therapy is recommended by a guideline for the treatment of acute iliofemoral deep vein thrombosis (DVT). However, the initial rivaroxaban dose in the switching strategy, as well as the effectiveness and safety of the early switching (less than 1week) to rivaroxaban, remain inadequately substantiated. We aimed to evaluate the effectiveness and safety of early switching from LMWH to maintenance therapy of rivaroxaban (20mg once daily) for acute iliofemoral DVT. A retrospective cohort study was conducted using data from patients with acute iliofemoral DVT who received initial LMWH anticoagulation followed by rivaroxaban maintenance therapy. The clinical outcomes were compared between early (LMWH course ≤7days) and routine (LMWH course >7days) switching strategies within 3months of initiating anticoagulation. 217 patients were included, 59 (27.2%) receiving early switching and 158 (72.8%) receiving routine switching. Compared with routine switching, patients with early switching had a significantly shorter hospital stay (7days vs. 14days, P<0.001). The length of hospital stay was significantly positively correlated with the duration of LMWH (r=0.762, P<0.001). The incidences of recurrent venous thromboembolism (5.1% vs. 2.5%, P=0.606), major bleeding (0% vs. 1.9%, P=0.564), clinically relevant nonmajor bleeding (1.7% vs. 2.5%, P=1.000) and all-cause mortality (6.8% vs. 2.5%, P=0.283) were not statistically different between the 2 groups. Direct early switching from LMWH to maintenance therapy of rivaroxaban is effective and safe for acute iliofemoral DVT.

Topological nano-switches in higher-order topological insulators

We consider multi-terminal transport through a flake of rectangular shape of a two-dimensional topological insulator in the presence of an in-plane magnetic field. This system has been shown to be a second-order topological insulator, thus exhibiting corner states at its boundaries. The position of the corner states and their decay length can be controlled by the direction of the magnetic field. In the leads we assume that the magnetic field is absent and therefore we have helical one-dimensional propagating states characteristic of the spin-Hall effect. Using a low-energy effective Hamiltonian we show analytically that, in a two-terminal setup, transport can be turned on and off by a rotation of the in-plane magnetic field. Similarly, in a three terminal configuration, the in-plane magnetic field can be used to turn on and off the transmission between neighbouring contacts, thus realising a directional switch. Analytical calculations are supplemented by a numerical finite-difference method. For small values of the Fermi energy and field strength, the analytical results agree exceptionally well with the numerics. The effect of disorder is also addressed in the numerical approach. We find that the switching functionality is remarkably robust to the presence of strong disorder stemming from the topological nature of the states contributing to the electron transport.

A Robust Switching Control Strategy for Three-Phase Voltage Source Converters with Uncertain Circuit Parameters

This study proposes a novel double closed-loop robust control strategy based on a power switching affine model of three-phase voltage source converters (VSCs). The aim is to overcome the challenges posed by inaccurate mathematical models, complex controller configurations, indirect switching control, and performance degradation under circuit parameters uncertainty or load variation in conventional methods. These conventional methods rely on linearization models, duty ratio regulation, and pulse width modulation (PWM) technologies. The contributions of work are the following: (1) A two-dimensional (2D) power switching affine model is constructed without any approximation or averaging. (2) The proposed approach achieves direct switching control of three-phase VSCs, eliminating the need for complex rotation coordinate transformation, PWM, and phase locking loop (PLL), which are utilized in traditional control methods. (3) The rigor of the system stability analysis is enhanced based on the 2D power switching model compared to the existing three-dimensional (3D) current switching model. (4) A simple control structure with only two control parameters is employed to address circuit parameter uncertainties. The effectiveness and superiority of the proposed method is validated through simulation and experimental comparison results.

Learning-assisted optimization for transmission switching

The design of new strategies that exploit methods from machine learning to facilitate the resolution of challenging and large-scale mathematical optimization problems has recently become an avenue of prolific and promising research. In this paper, we propose a novel learning procedure to assist in the solution of a well-known computationally difficult optimization problem in power systems: The Direct Current Optimal Transmission Switching (DC-OTS) problem. The DC-OTS problem consists in finding the configuration of the power network that results in the cheapest dispatch of the power generating units. With the increasing variability in the operating conditions of power grids, the DC-OTS problem has lately sparked renewed interest, because operational strategies that include topological network changes have proved to be effective and efficient in helping maintain the balance between generation and demand. The DC-OTS problem includes a set of binaries that determine the on/off status of the switchable transmission lines. Therefore, it takes the form of a mixed-integer program, which is NP-hard in general. In this paper, we propose an approach to tackle the DC-OTS problem that leverages known solutions to past instances of the problem to speed up the mixed-integer optimization of a new unseen model. Although our approach does not offer optimality guarantees, a series of numerical experiments run on a real-life power system dataset show that it features a very high success rate in identifying the optimal grid topology (especially when compared to alternative competing heuristics), while rendering remarkable speed-up factors.

Measurement Performance Evaluation of a Non-Contact Narrow Shape Measurement with Direction Switching

Measurement Performance Evaluation of a Non-Contact Narrow Shape Measurement with Direction Switching

From instable directional switching to controlled unidirectional operation in a nonlinear fiber ring laser

We investigate a new phenomenon, where a reciprocal fiber ring laser switches from bidirectional to unidirectional operation above a certain pump power threshold. Significant simplifications regarding earlier experiments are presented, which for the first time allow the identification of individual nonlinear effects. We highlight the unique role of stimulated Raman scattering in triggering unidirectional operation, and that additional conditions apply. The threshold is reduced from 30 to 3.8 W, which eases potential applications.

Structural basis of directional switching by the bacterial flagellum.

The bacterial flagellum is a macromolecular protein complex that harvests energy from uni-directional ion flow across the inner membrane to power bacterial swimming via rotation of the flagellar filament. Rotation is bi-directional, with binding of a cytoplasmic chemotactic response regulator controlling reversal, though the structural and mechanistic bases for rotational switching are not well understood. Here we present cryoelectron microscopy structures of intact Salmonella flagellar basal bodies (3.2-5.5 Å), including the cytoplasmic C-ring complexes required for power transmission, in both counter-clockwise and clockwise rotational conformations. These reveal 180° movements of both the N- and C-terminal domains of the FliG protein, which, when combined with a high-resolution cryoelectron microscopy structure of the MotA5B2 stator, show that the stator shifts from the outside to the inside of the C-ring. This enables rotational switching and reveals how uni-directional ion flow across the inner membrane is used to accomplish bi-directional rotation of the flagellum.

Research on force/position switching control of servo actuator for hydraulically driven joint robot

According to the robot’s walking motion characteristics, the position/force switching control is studied to realize the segmental control of the robot stroke. This stroke is controlled by position when the foot end of the robot descends from the suspension to the ground. To avoid excessive contact force when the robot touches the ground, force control is carried out when the foot touches the ground. Due to the force and position control methods and control parameters of the hydraulic quadruped robots are different, the precise mathematical model for the joint position control and joint force control of the leg joints of the hydraulic quadruped robot is established using the system identification method. A fuzzy multi-model switching algorithm is proposed to solve the problem of jumping and jitter of system parameters in the process of force/position switching. Through simulation and prototype experiments, fuzzy multi-model switching is compared with direct switching and multi-model switching, and the switching effect of the algorithm is verified.

Conversion to Brivaracetam Monotherapy in Clinical Practice: A Retrospective Study.

The study aimed to evaluate the effectiveness and safety of brivaracetam (BRV) as conversion monotherapy in adults with focal epilepsy treated in the context of real-world clinical practice. This was a retrospective, observational, non-interventional study in adults with focal epilepsy who converted to BRV monotherapy following the withdrawal of background antiseizure medications (ASMs). Primary effectiveness outcome was the retention rate of BRV as single ASM at 6 and 12months. Secondary outcomes included the 6- and 12-month rates of seizure freedom. Safety and tolerability outcomes included the frequency and type of adverse events (AEs) and the occurrence of treatment discontinuation due to AEs. A total of 44 participants with a median age of 63.5 (interquartile range 44-73.5) years were included; 17 subjects were seizure free at baseline, and 9 of them switched from levetiracetam because of lack of tolerability. The retention rate of BRV monotherapy was 88.6% (39/44) at 6months and 83.9% (26/31) at 12months. The rates of seizure freedom were 72.7% (32/44) in subjects with 6-month follow-up and 58.1% (18/31) in subjects with 12-month follow-up. The median maintenance dosage of BRV monotherapy was 150 (100-200) mg/day at 6months and 125 (100-200) mg/day in subjects with 12-month follow-up. Adverse events were recorded in 6/44 (13.6%) participants and led to BRV discontinuation in 2/44 (4.5%) cases. The reported AEs were somnolence (n = 3), fatigue (n = 2), and irritability (n = 1); no serious AEs were experienced. In 21/44 (47.7%) participants, BRV monotherapy resulted from the direct switch from levetiracetam. The rates of treatment retention and seizure freedom at 6 and 12months were higher among people who switched from levetiracetam to BRV monotherapy. Brivaracetam may be a valuable treatment of focal seizures in people who converted to monotherapy in a real-life setting.

Ultrafast diffusion tensor imaging based on deep learning and multi-slice information sharing

Objective. Diffusion tensor imaging (DTI) is excellent for non-invasively quantifying tissue microstructure. Theoretically DTI can be achieved with six different diffusion weighted images and one reference image, but the tensor estimation accuracy is poor in this case. Increasing the number of diffusion directions has benefits for the tensor estimation accuracy, which results in long scan time and makes DTI sensitive to motion. It would be beneficial to decrease the scan time of DTI by using fewer diffusion-weighted images without compromising reconstruction quality. Approach. A novel DTI scan scheme was proposed to achieve fast DTI, where only three diffusion directions per slice was required under a specific direction switching manner, and a deep-learning based reconstruction method was utilized using multi-slice information sharing and corresponding T 1-weighted image for high-quality DTI reconstruction. A network with two encoders developed from U-Net was implemented for better utilizing the diffusion data redundancy between neighboring slices. The method performed direct nonlinear mapping from diffusion-weighted images to diffusion tensor. Main results. The performance of the proposed method was verified on the Human Connectome Project public data and clinical patient data. High-quality mean diffusivity, fractional anisotropy, and directionally encoded colormap can be achieved with only three diffusion directions per slice. Significance. High-quality DTI-derived maps can be achieved in less than one minute of scan time. The great reduction of scan time will help push the wider application of DTI in clinical practice.

Transfer of magnetic anisotropy in epitaxial Co/NiO/Fe trilayers

The magnetic properties of Co(10 Å)/NiO(40 Å)/Fe trilayer epitaxially grown on W(110) substrate were investigated with use of x-ray magnetic linear dichroism (XMLD) and x-ray magnetic circular dichroism (XMCD). We showed that magnetic anisotropy of Fe film that can be controlled by a thickness-driven spin reorientation transition is transferred via interfacial exchange coupling not only to NiO layer but further to ferromagnetic Co overlayer as well. Similarly, a temperature driven spin reorientation of Fe sublayer induces a reorientation of NiO spin orientation and simultaneous switching of the Co magnetization direction. Finally, by element specific XMCD and XMLD magnetic hysteresis loop measurements we proved that external magnetic field driven reorientation of Fe and Co magnetizations as well as NiO Néel vector are strictly correlated and magnetic anisotropy fields of Fe and Co sublayers are identical despite the different crystal structures.

Nonreciprocal Goos-Hänchen shift in a Dirac semimetal based asymmetric photonic crystal structure.

The generation and control of the Goos-Hänchen (GH) shift is a vital step toward its realistic applications, but investigations have mainly been limited to the directional-dependent ones; i.e., the GH shift is reciprocal for two opposite propagating directions. Here, by designing the asymmetrical multilayered structure with three-dimensional bulky Dirac semimetal (BDS) films, we theoretically confirm the footprint of the pronounced directional-dependent GH shift, and that it can be switched by the Fermi energy of the BDS. In addition to this electric field induced switching, the period numbers of the unit cells in the asymmetrical structure can also modulate the directional-dependent GH shift. The asymmetrical feature of the multilayered structure dominantly causes the emergence of the directional-dependent GH shift. Our discovery related to the directional-dependent GH shift constitutes an important ingredient for directional-dependent optophotonic devices such as directional sensors, optical switches, and detectors.

Emergent ultrasmall multiferroics in paraelectric perovskite oxide by hole polarons.

Ultimately small multiferroics with coupled ferroelectric and ferromagnetic order parameters have drawn considerable attention for their tremendous technological potential. Nevertheless, these ferroic orders inevitably disappear below the critical size of several nanometers in conventional ferroelectrics or multiferroics. Here, based on first-principles calculations, we propose a new strategy to overcome this limitation and create ultrasmall multiferroic elements in otherwise nonferroelectric CaTiO3 by engineering the interplay of oxygen octahedral rotations and hole polarons, though both of them are generally believed to be detrimental to ferroelectricity. It is found that the hole doped in CaTiO3 spontaneously forms a localized polaronic state. The lattice distortions associated with a hole polaron interacting with the intrinsic oxygen octahedral rotations in CaTiO3 effectively break the inversion symmetry and create atomic-scale ferroelectricity beyond the critical size limitation. The hole polaron also causes highly localized magnetism attributed to the associated spin-polarized electric state and thus manifests as a multiferroic polaron. Moreover, the hole polaron exhibits high hopping mobility accompanied by rich switching of polarization and magnetic directions, indicating strong magnetoelectric coupling with a mechanism dissimilar from that of conventional multiferroics. The present work provides a new mechanism to engineer inversion symmetry and opens avenues for designing unusual multifunctional materials.

Theoretical design of rhombohedral-stacked MoS2-based ferroelectric tunneling junctions with ultra-high tunneling electroresistances.

The sliding ferroelectrics formed by rhombohedral-stacked transition metal dichalcogenides (R-TMDs) greatly broaden the ferroelectric candidate materials. However, the weak ferroelectricity and many failure behaviors (such as irreversible lattice strains or defects) regulated by applied stimuli hinder their application. Here we systematically explore the interface electronic and transport properties of R-MoS2-based van der Waals heterojunctions (vdWHJs) by first-principles calculations. We find that the polarization and the band non-degeneracy of 2R-MoS2 increase with decreasing interlayer distance (d1). Moreover, the polarization direction of graphene (Gra)/2R-MoS2 P↑ state can be switched with a small increase in d1 (about 0.124 Å) due to the weakening of the polarization field (Ep) by a built-in electric field (Ei). The equilibrium state of superposition (|Ep + Ei|) or weakening (|Ep - Ei|) can be modulated by interface distances, which prompts vertical strain-regulated polarization or Schottky barriers. Furthermore, Gra/2R-MoS2 and Gra/R-MoS2/WS2 vdW ferroelectric tunneling junctions (FTJs) demonstrate ultra-high tunneling electroresistance (TER) ratios of 1.55 × 105 and 2.61 × 106, respectively, as the polarization direction switches. Our results provide an avenue for the design of future R-TMD vdW FTJs.

Improved Model Predictive Control With Reduced DC-Link Capacitor RMS Current for Back-to-Back Converter-Fed PMSM Drives

A low root mean square (RMS) current flowing through the intermediate DC-link capacitor is always desired in the back-to-back (BTB) voltage source converters (VSCs)-fed motor drive, such that the designed capacitor lifespan can be extended or a lower DC-link size could be the alternative with improved power density. The conventional modulator-based control involves the inherent carrier-based switching operation, and hence the dominant harmonics at carrier frequency multiplier and carrier sideband are introduced into the capacitor current. Therefore, the finite-control-set model predictive control (FCS-MPC) is proposed to optimize the capacitor RMS current. The direct switching pulse generation without using the carrier can give a distinctive capacitor current spectrum and more possible current pulse cancellation between the BTB VSCs can be conveniently achieved through the cost function. Besides, the acceptable grid-current quality and the motor performance are maintained by using a tunable weighting factor. The simulated and experimental results highlight the effectiveness and benefits of the proposed method in terms of 20%-35% capacitor RMS current reduction compared to the synchronous carrier-based space vector pulse-width modulation (SVPWM) scheme and also significant improvements over the distributed predictive manner.