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The modified LCL (MLCL) is commonly applied in PV string inverters to suppress the leakage current and enhance the EMI performance of the grid current. However, the potential risk of resonance appears in the common mode (CM) loop caused by the MLCL filter. In this paper, the CM model of the inverter is firstly built considering the inductance saturation. It is found that the variable inductor brings phase margin decreasing problem and additional resonance points in the CM loop. To suppress the CM resonance (CMR), novel passive and active damping strategies are explored in this paper. The improved passive damping (IPD) strategy is realized by introducing a paralleled RC unit which greatly reduces the damping resistor losses without affecting the damping performance. Besides, a novel active damping strategy (NAD) is proposed to compensate the time delay and to raise the phase margin. Moreover, considering the gradient mutation issue brought by the discontinuous pulse width modulation (DPWM) scheme, an anti-saturation PWM (ASPWM) scheme is applied to eliminate the oscillation. Finally, experiments are conducted on an 80 kW PV string inverter. After applying the proposed CMR damping strategy with the ASPWM scheme, CMR is fully eliminated in the whole power range despite the grid condition.

The multilevel connected dc–dc converters system is considered a practical technology to increase the capacity and reduce voltage and current stresses on the power devices. In practice, mismatched parameters are inevitable, which increase the challenge of output voltage regulation and current sharing control. In order to conquer these difficulties, this article investigates the current sharing based on incremental passivity control for multilevel connected dc–dc converters. Combined with passivity-based control, a finite-time estimator is given to improve the robustness against the load variations. The proposed method results in a linear control law despite the bilinear nature of this system. Moreover, analysis exhibits that stability and current sharing are independent of inductor parameters. Furthermore, stability of the closed-loop system has been proved that the proposed approach is valid both for a linear and nonlinear load. After introducing the proposed control scheme, simulation and experiments are offered to validate its fast transit response and antidisturbance performance.

In order to deal with the challenges in establishing a high input voltage high step-down auxiliary power supply (APS) for modular converters, a flyback converter utilizing series-connected silicon carbide (SiC) MOSFETs is proposed in this article. With the aid of a novel snubber circuit structure, the used series-connected SiC MOSFETs can switch with nearly perfect dynamic voltage sharing. Besides, the snubber circuit acts as voltage clamping circuit for the flyback converter, so voltage overshoot caused by transformer leakage inductance can be effectively controlled. Furthermore, the snubber circuit helps to power the control, gate driver, and startup circuits of the APS, leading to a reduction in system complexity and improvement in efficiency. Detailed circuit analysis and design considerations of the APS are presented. Finally, hardware of a 4 kV/120 W APS is established and experimentally verified.

In this brief, a novel differential-mode (DM) interference propagation mathematical modeling method based on parasitic inductive coupling theory for SiC wirebond multichip power module (SWMPM) with adjacent decoupling capacitor is proposed. Based on the proposed model, the strong and weak inductive coupling theory of DM interference equivalent circuit is proposed. And the influence of different position of decoupling capacitors on DM equivalent current is mathematically analyzed. A custom-made 1.2kV 160A power module based on DM interference optimized layout is built. It is compared with a commercial SiC power module, which can verify the feasibility and validity of the theoretical analysis.

Series-connection of silicon carbide (SiC)-MOSFETs is an attractive method to achieve a high-voltage and fast-switching power semiconductor switch. In order to deal with the unequal voltage sharing problem in such series connection method, a novel active voltage clamping circuit topology is proposed in this letter. The maximum drain–source voltages of the series-connected SiC-MOSFETs are clamped by individual clamping capacitors; therefore, high reliable switching of the power semiconductors is guaranteed. Besides, the accumulated energy in the clamping capacitors can be actively transferred back into the power supply through a simple gate drive signal adjustment algorithm; thus, the induced clamping circuit loss can be effectively suppressed. The proposed active clamping topology has been experimentally verified in a half-bridge inverter with four SiC-MOSFETs connected in series.

The isothermal sections of the Fe-Si-Cr-Al quaternary system at 800 °C with the Fe composition being fixed at 67 at.% and 50 at.% were determined experimentally using optical microscopy, scanning electron microscopy coupled with energy dispersive x-ray spectroscopy, and x-ray diffractometry. Two three-phase regions (BCC-A2 + σ + D03, FeSi + Fe5Si3 + D03) were found in the isothermal sections at 67 at.% Fe. Phase microstructures of Fe-corner in the quaternary Fe-Si-Cr-Al system were investigated, especially the multiphase regions containing bcc disordered phase and bcc ordered phases. D03 occupies almost half of the isothermal section and could maintain equilibrium with all phases (BCC-A2, σ, Fe5Si3, FeSi) in the isothermal section. One four-phase region (BCC-A2 + σ + Cr3Si + D03) and five three-phase regions (Cr3Si + D03 + BCC-A2, Cr3Si + σ + BCC-A2, Cr3Si + D03 + σ, Cr3Si + Fe5Si3 + D03, FeSi + Fe5Si3 + D03) were found in the isothermal section at 50 at.% Fe.

Background ABO-incompatible liver transplantation (ABO-i LT) has become a rescue therapeutic option for patients with severe hepatic failure. Although the use of rituximab greatly reduces the morbidity of antibody-mediated rejection (AMR), severe adverse effects, such as infection and biliary complications, still seriously threaten the survival of transplant recipients. The aim of this study was to evaluate the safety and feasibility of using mesenchymal stem cells (MSCs) to replace rituximab in ABO-i LT. Methods Twenty-two patients with severe hepatic failure undergoing ABO-i LT were enrolled and randomly divided into two groups: the MSC group and the rituximab group. The safety of the application of MSCs and the incidence of allograft rejection, including antibody-mediated rejection (AMR) and acute cellular rejection (ACR), were evaluated in both groups at the 2-year follow-up period as primary endpoints. Recipients and graft survival and other postoperative complications were compared as secondary endpoints. Results No severe MSC-related adverse events were observed during the trial. MSC treatment yielded comparable, if not better, results than rituximab at decreasing the incidence of acute rejection (9.1% vs 27.3%). Inspiringly, compared to those in the rituximab group, the rates of biliary complications (0% vs 45.5%) and infection (9.1% vs 81.8%) were significantly decreased in the MSC group. In addition, there were no significant differences in 2-year graft and recipient survival between the two groups (81.8% vs 72.7%). Conclusions Our data show that MSC transfusion is comparable to rituximab treatment for AMR prophylaxis following ABO-i LT. Additionally, the results indicate that MSCs are more beneficial to the prevention of infection and biliary complications and may be introduced as a novel immunosuppressive approach for ABO-i LT. Trial registration Trial registration: chictr.org.cn, ChiCTR2000037732. Registered 31 August 2020- Retrospectively registered, http://www.chictr.org.cn/showproj.aspx?proj=57074.

The concept of vehicle-to-grid has received considerable attentions over the past decade. Electric vehicle (EV), a common load of dc microgrids, can serve as distributed energy storage system to improve the reliability and stability of the dc microgrid, support integration of renewable energy source, and improve the overall system efficiency. In order to achieve bidirectional power transmission between the dc microgrid and EV, this article proposes a novel three-level CLLC resonant converter for off-board EV charger. By adding resonant CLLC components and by combining the working modes of the two three-level full bridges, the proposed converter adapts to the wide voltage range of EV, from 200 to 700 V. An equivalent circuit model with first harmonic approximation approach is established to analyze the frequency characteristics of the resonant converter. Moreover, an algorithm of working mode selection is proposed on the principle of minimum transformer RMS current. Finally, a 3.5 kW hardware prototype was built to verify the feasibility and the advantage of the three-level CLLC resonant converter. The efficiency of the proposed converter changes little over a wide output voltage range, and the flying capacitor voltages of the proposed converter are balanced well.

Underlying control circuit failure problems, especially control signal output failure problems, widely occur in high-voltage large-current modular multilevel converter (MMC) valve towers. The failure mechanism for the digital signal processor (DSP)-based control circuit is studied in this article. This study is based on the combination of low-voltage-level integrated circuit (IC) immunity model and a new perspective on the field-to-trace coupling effect. A novel copper-layer-based field-to-trace coupling model which combines the power system and digital control circuit in the MMC valve tower is proposed. Therefore, the specific electromagnetic interference (EMI) value conducted into the IC can be calculated. Then a new DSP IC electromagnetic sensitivity (EMS) evaluation method is proposed, which can be a guideline in industrial applications. To show the validity and accuracy of the field-to-trace coupling model, an indirect laboratory experiment is designed, then a situation is considered in this article, and the results are compared with PSpice circuit simulations, which show acceptable relative errors. Moreover, based on the situation considered above, one application example of the novel evaluation method is described in detail.

Energy router is an emerging device based on power electronic technology, which can realize the flexible distribution of electric energy in the power system. Therefore, the use of energy routers to improve the operating conditions of the power system not only has broad development prospects, but also brings economic benefits. In this regard, this paper proposes a steady-state model of a single energy router and considers the loss of the DC/DC transformer, establishes a power flow equation with multiple energy routers, and proposes a distribution network power flow alternate iteration that takes into account multiple energy routers Calculation method. A case study of an improved IEEE-33 system with multiple energy routers under different working conditions is carried out. The calculation results show that the alternate iterative power flow calculation method used in this paper is effective and feasible, and it reasonably reflects that the network analysis model with multiple energy routers can achieve stable operation, and it can improve the node voltage and reduce the active power loss of the grid. It makes the operation of the distribution network more flexible.

This article proposes a systematic control strategy for solid-state transformer (SST) composed of dual active bridge (DAB) and cascaded H-bridge, which increases SST efficiency over a wide operating range in PV application. In real practice, the PV panel presents a wide voltage range, which could significantly affect SST efficiency, mainly for DAB. To improve the efficiency, a universal loss model for DAB under frequency domain analysis is established. Based on this, the optimum efficiency modulation scheme is derived. Besides the efficiency improvement of DAB from the modulation scheme, this article fully explores extra control freedom, which is an intermediate voltage between DAB and H-bridge. Then, the variable intermediate voltage control scheme is proposed, which reduces the conduction loss and switching loss of DAB. Furthermore, zero-sequence modulation signal injection and the proportional-resonant controller is implemented in the proposed control strategy, which expands the range for further efficiency improvement. Finally, to verify the effectiveness of the proposed method, the experiment is carried out on the submodule and 10-kV/1-MW SST real scale prototype. Under the proposed method, the SST system achieves 0.9% efficiency improvement compared with the conventional method.

Power semiconductor switches are usually connected in series to achieve higher blocking voltage. However, the series-operation of semiconductor devices is not easy due to unequal voltage sharing. In comparison with silicon (Si) devices, series-connecting silicon carbide (SiC) devices are even more challenging due to their ultrafast switching speed. In this article, a novel snubber circuit topology with energy recovery capability is proposed to control the voltage sharing of series-connected SiC mosfet s. The snubber circuits operate with a self-balancing technique; thus, the required control and sensing circuits are simple. The proposed method maintains the snubber capacitor voltage nearly constant, so the snubber capacitors are not fully discharged during the devices on -state. Besides, excess snubber energy can be transferred back to the dc bus, so the induced snubber loss is minimal. Experimental results show the effectiveness of the proposed snubber circuit topology in a half-bridge inverter with four SiC mosfet s connected in series.

In this work, we have fabricated a single layer graphene spin transistor on SiO2/Si with a semiconducting tri-layer MoS2 as the tunneling barrier between the ferromagnetic electrodes and the graphene channel. The spin transport in this parallel heterostructure were investigated in detail. The spin switch signal was controlled by tuning the conductivity of MoS2 with different gate voltages. When MoS2 was turned off under negative back gate voltage, the spin switch signal was clearly obtained, whereas it disappeared when MoS2 was conductive under positive back gate bias. This spin transistor showed on, subthreshold and off states when back gate voltage changed from negative to positive. This work exploited a new possibility of semiconducting 2D materials as the tunneling barrier of spin valves.

Higher integration, smaller size and better performance are the trends of device development. Metasurfaces exhibit the versatile manipulation capabilities on electromagnetic fields and have provide...

A multi-cell hybrid 21-Level multilevel inverter is proposed in this paper. The proposed topology includes two-unit; an H-bridge is cascaded with a modified K-type unit to generate an output voltage waveform with 21 levels based only on two unequal DC suppliers. The proposed topology's advantage lies in the fine and clear output voltage waveforms with high output efficiency. Meanwhile, the high number of output voltage waveform levels generates a low level of distortion and reduces the level of an electromagnetic interface (EMI). Moreover, it reduces the voltage stress on the switching devices and gives it a long lifetime. Also, the reduction in the number of components has a noticeable role in saving size and cost. Regarding the capacitors charging, the proposed topology presents an online method for charging and balancing the capacitor's voltage without any auxiliary circuits. The proposed topology can upgrade to a high number of output steps through the cascading connection. Undoubtedly this cascading will increase the power level to medium and high levels and reduce the harmonics content to a neglectable rate. The proposed system has been tested through the simulation results, and an experimental prototype based on the controller dSPACE (DS-1103) hardware unit used to support the simulation results.

This paper proposes a new topology of the switched-capacitor multilevel inverter (SCMLI) for photovoltaics system, which can eliminate the leakage current. In the proposed topology, the capacitors are employed as a virtual DC power supply to boost the input voltage. Here, all capacitors are charging equal to DC source, thus, just one DC source is needed to achieve the staircase waveform. In this structure in order to make the negative levels, the capacitors are connected to the output in reverse polarity. Thus, the H-bridge circuit which is used in traditional SCMLI to build zero and negative voltage levels and leads a variable common mode voltage is removed. Due to the direct connection of the neutral terminal of the grid to the negative polarity of the PV; then this topology can eliminate the leakage current. In addition, the topology has an excellent ability to path the reverse current as well as an acceptable output waveform spectrum. The operating states of all components and loss calculations are analyzed and formulated accurately as well as simulated by using MATLAB-SIMULINK software. To confirm the performance of the proposed topology; a 500 W prototype is built and experimental results are presented.

The efficient near-infrared light detection of the MoTe2/germanium (Ge) heterojunction has been demonstrated. The fabricated MoTe2/Ge van der Waals heterojunction shows excellent photoresponse performances under the illumination of a 915 nm laser. The photoresponsivity and specific detectivity can reach to 12,460 A/W and 3.3 × 1012 Jones, respectively. And the photoresponse time is 5 ms. However, the MoTe2/Ge heterojunction suffers from a large reverse current at dark due to the low barrier between MoTe2 and Ge. Therefore, to reduce the reverse current, an ultrathin GeO2 layer deposited by ozone oxidation has been introduced to the MoTe2/Ge heterojunction. The reverse current of the MoTe2/GeO2/Ge heterojunction at dark was suppressed from 0.44 µA/µm2 to 0.03 nA/µm2, being reduced by more than four orders of magnitude. The MoTe2/Ge heterojunction with the GeO2 layer also exhibits good photoresponse performances, with a high responsivity of 15.6 A/W, short response time of 5 ms, and good specific detectivity of 4.86 × 1011 Jones. These properties suggest that MoTe2/Ge heterostructure is one of the promising structures for the development of high performance near-infrared photodetectors.

In recent years, dc microgrids have been widely concerned for natural interface with renewable energy sources, dc loads, and energy storage systems (ESS). A novel neutral point clamped (NPC) dual-active-bridge (DAB) converter with a blocking capacitor is proposed for ESS in dc microgrids. By inserting a blocking capacitor in primary loop of the traditional NPC DAB converter, the voltage amplitudes across the primary and the secondary windings of the transformer can be matched when the voltage ratio is equal to 0.25, 0.5, 0.75, and 1. Therefore, the proposed topology can adapt to a wide range of energy storage battery voltage variations. Asymmetric pulsewidth modulation plus phase shift modulation are applied to improve the dynamic performance of the proposed converter. The phase-shift ratio between the two bridges and the asymmetric duty ratio are regulated to control the power flow of the proposed NPC DAB converter. Compared with the traditional NPC DAB converter, the proposed topology has lower transformer rms current and wider soft-switching region. Finally, experimental results from a 500-W hardware prototype are presented to verify the feasibility and the advantage of the proposed converter. Compared with the traditional NPC DAB converter, the maximum promotion of efficiency is up to 3.8%.

Traditional microwave absorbers can hide target objects from the detection of radar waves without tackling optical waves. However, in actual scenarios, the objects might still be observed by a hyperspectral remote sensor or an imaging system from comparison with environmental optical features, in particular for variable backgrounds. For this aspect, a comprehensive stealthing technique able to deal with microwaves and optical features simultaneously adapting to the variable environment is highly desired. In this work, an ultrathin flexible metamaterial that can simultaneously realize wideband microwave absorption and controllable visible and near-infrared luminescence spectra is proposed. The designed artificial coat can absorb more than 80% of the incident energy in the X-band (8-12 GHz) within a large incidence angle range up to 54° at low polarization sensitivity, while its real-time visible and near-infrared luminescence spectrum can be electrically adjusted through an integrated emission system. The method proposed here can be extended to broader wave bands and find important applications in multifunctional stealthing technologies.

Silicon carbide MOSFET is gradually replacing silicon devices as the preferred power devices with its advanced performance. However, in practical application, the interaction in a SiC MOSFET phase-leg configuration may lead one switch turn on by error, which is called the crosstalk effect and will cause catastrophic damage to the circuit. This paper proposed a mathematical model for analyzing the crosstalk effect of SiC MOSFET. The model considered the parasitic inductance in the loop and the possible added capacitor between gate and source and systematically investigated the influence of multi parameters on the crosstalk effect. The circuit parameters dependence of the crosstalk effect provides theoretical implications and practical guidelines for the gate drive design of SiC MOSFET. The crucial to utilize the active clamp function in the commercial driver chip to suppress crosstalk is to reduce the parasitic inductance. Experiment results validate the driving resistance and the added capacitor dependence of the crosstalk effect.

Flexible and bendable inductors have attracted increasing attention because of their broad application prospects in power supplies for wearable devices. This paper proposes a coaxial flexible inductor that consists of a cable-embedded bendable magnetic core and a copper conductor. The inductor’s design, modeling, and optimization procedure are presented in detail. This flexible inductor can eliminate the rigid block of a discrete inductor from the wearable device, making it more comfortable to wear. Also, because its heat distribution is more uniform, the surface temperature of the inductor can be greatly reduced. The inductor’s inductance, losses, and flexibility have been modeled using geometric parameters, the current waveform, and material characteristics of ferrite sheets. These derived models can be used to optimize the inductor. A case study of a 1- $\mu \text {H}$ inductor used in a 3.3–5-V 5-W boost converter has been performed to exemplify this procedure. Finally, based on the optimization results, a prototype has been fabricated and experimentally tested. The results verify the good performance of the cable-embedded inductor and the effectiveness of the optimization method.

Here, we propose a metasurface based on the phase change material vanadium dioxide (VO2), which can switch between the meta-lens and the absorber by controlling temperature. Before phase change, VO2 is in the insulating phase and the metasurface proposed here works as a focusing lens near the wavelength of $10.6~\boldsymbol {\mu }\text{m}$ . When the temperature rises above the phase change point (341 K), VO2 becomes metallic and the metasurface will change into a good absorber, which absorbs more than 90% of the incident light energy. Moreover, in this case, the metasurface still has a meta-lens feature that will operate on the residual light. The special application of our metasurface as a light-dose sensitive smart meta-lens for bio-imaging is discussed.

Bionic devices, such as potentiated synaptic devices, have obtained a lot of attention over the past years. However, depressed synaptic devices, which are equally significant in brain-inspired computation devices, have attracted less attention due to the lack of a proper electrolyte. In this work, an indium-gallium-zinc-oxide (IGZO) and aluminum oxide (Al2O3) film based synaptic transistor was fabricated for depressed neuromorphic applications. An Al2O3 film desposited by the atomic layer deposition (ALD) at 100 °C was used as the insulator. The low temperature introduced a lot of electron trappings at the IGZO-Al2O3 interface, which contributed to the depression feature of the synaptic transistor. The energy consumption of the fabricated transistor was estimated to be as low as ∼3.8 pJ/spike. The recovery time of a pulse was as short as ∼150 ms. Paired-pulse depression (PPD) and low-frequency filter behaviors were also mimicked in the transistor.

Commercially available normally -off GaN power high-electron-mobility transistor (HEMT) devices have typically adopted a p-GaN gate structure. In the gate region, there exist a Schottky junction (between gate electrode and the p-GaN layer) and a p-GaN/AlGaN/GaN heterojunction. As the p-GaN layer is not directly shorted to the gate electrode and conducting channel, it can be considered as electrically “floating.” With drain voltage changing during a switching process, the variation of net charge in the floating p-GaN layer would cause instability in threshold voltage. Besides, because of the distinctive features of the p-GaN gate HEMT structure under certain gate/drain bias, gate-related junction capacitances would exhibit behavior different from those of a Si mosfet . Consequently, the switching transient performance of a GaN transistor with a p-GaN gate could be significantly influenced by the aforementioned factors. In this work, the threshold voltage instability associated with the drain-to-gate voltage stress is first analyzed. Despite the difficulty in directly performing capacitance measurements inside the device structure, a hybrid physical-behavior modeling method is proposed. The model is capable of extracting the capacitance bias relationships with regard to the gate region from static terminal measurements. In previous works, the advanced analytical model would make modest change on a Si mosfet 's model. As a result, without fully considering the specific features of a GaN transistor with the p-GaN gate, the simulated waveforms would exhibit 20–50% discrepancy from the experiment. In contrast, the proposed switching transient analytical approach would exhibit improved accuracy (

Balanced issues of neutral-point (NP) voltage in the neutral-point-clamped (NPC) three-level photovoltaic converter have been studied in depth. Numerous algorithms for NP voltage control have been proposed and proven to be effective in normal operations. However, most of the previous studies fail to consider the effect of imbalanced loads on NP voltage, especially under low-voltage-ride-through (LVRT) condition, which faces problems of imbalanced grid voltages and low power factor. In this paper, through derivation of NP current model for different loading conditions, the behavior of NP voltage under LVRT condition is comprehensively analyzed for the first time. Then, theoretical limitations of NP voltage control based on two common space-vector-pulsewidth modulations (SVPWMs) that three-nearest-vectors and symmetric SVPWM are investigated, and additional low-frequency oscillation in NP voltage is analyzed. This oscillation is dominated by fundamental frequency and has different generation mechanisms under different imbalanced grid faults. Then, a novel method of selective hybrid SVPWM, as selective combinations of SVPWM and virtual SVPWM according to different imbalanced grid faults, is proposed to effectively suppress NP voltage oscillations in LVRT operation without any complex improvements and increase of dc-link capacitor values. Finally, the analytical result and performance of the proposed method are confirmed in an existing 300 kW NPC converter.

In order to solve the considerable issues of air pollution, climate warming and fossil energy shortage, many governments around the world have formulated policies to encourage the development of electric vehicles over the past decade. This paper proposes a three-level dual-active-bridge (DAB) converter with blocking capacitors for bidirectional electric vehicle charger. In the proposed three-level DAB converter, two blocking capacitors are placed in series with the two windings of the transformer, respectively. Both of the two three-level bridges can operate in four modes, and generate square waves with four kinds of amplitude. Therefore, the proposed three-level DAB converter can adapt to the wide voltage range of electric vehicle. A working mode selection algorithm is developed to minimize the transformer RMS current of the three-level DAB converter. The optimal working mode can be selected in real time according to the voltage ratio and the active power. Finally, experimental results are presented to verify the feasibility and the advantage of the proposed three-level DAB converter.

Taking a third generation nuclear power plant as the research background, a refined model of a prestressed concrete containment which consisted of 270 complex spatial prestressed tendons was accurately established, using FE software ABAQUS. The cooling method was adopted to simulate the tensioning process of tendons. The simulation method of the tensioning of tendons during the prestressing construction of containment was verified by comparing with the measured data on site of the practical project. The mechanical behavior of the containment during the prestressing construction according to the prestressing construction scheme on site was studied in detail. Then the influence of steel liner and reinforcement on mechanical behavior of the containment during the prestressing construction of prestressed tendons was discussed. Finally, four prestressing construction schemes were analyzed and a reasonable optimization scheme was obtained.

Information on coronavirus disease 2019 (COVID-19) has been a significant focus for the global public since the outbreak of the disease. In response, data visualization has become the main form of media used to inform the public about the global pandemic’s progress. This paper studies the example of China, the main country affected by the virus in the early stage of the pandemic, to explain the problems regarding the differences in time, knowledge, and technology for information transmission. This paper also tries to explain the causes behind the dissemination of rumors, misjudgment of the public, and the difficulties of perception regarding pandemic information based on the three aspects of information collection, processing, and presentation. We argue that comprehensive information transmission with direct and clear visual presentation could help the public better understand the development of the pandemic, relieve social panic, and help authorities promptly adjust public health policies to absorb the social and economic impacts of the pandemic. Based on a case study, we propose that hierarchical presentation, comprehensive descriptions, and accurate visualizations of pandemic data can effectively improve information transmission, thus providing helpful references for authorities and organizations to improve the effectiveness of pandemic information transmission.

A coherent phase-sensitive optical time domain reflectometer (COTDR) based on digital orthogonal pulses is proposed. The digital orthogonal pulses provide phase diversity demodulation with a single detector and system sampling frequency will not reduce.

The accuracy of the estimate of the calculation of power dissipation of the circuit in the technical evaluation and the application of the appropriate equipment and thus the final cost has a significant impact. In switched-capacitor multilevel inverters (SCMLIs), to build higher levels, the capacitors are series connected to the output and pump the stored energy to the load, which reduces the voltage of the capacitors and creates a spike current when the capacitor is paralleled with the source. Charging and discharging modes by the switching frequency makes small spikes. In the intervals, which the capacitor is continuously connected to the output as the series, thus causes more voltage drop and massive spikes. In this paper, small and massive spikes due to the voltage drop of the capacitor and the energy dissipation caused by that are calculated and formulated individually and accurately. MATLAB-SIMULINK is used to the modelling and simulation.

This paper proposes a novel single-phase transformerless 5-level inverter for grid-connected photovoltaic (PV) system. The main advantages of the proposed inverter are 1) By direct connecting the neutral point of the grid to the negative terminal of the PV, this inverter can eliminate the leakage current; 2) It can boost the input voltage; 3) It does not suffer from the current spike. 4) This inverter has an excellent capacity to conduct the reverse current as well as an acceptable output waveform spectrum. The first stage of the proposed circuit consists of two inductance, which makes a boost or buck-boost converter in each half-cycle. Therefore, the capacitor of the converter circuit can be used as the virtual dc source in the inverter stage, which decreases the size and cost of the proposed inverter. Some simulation results by using MATLAB/SIMULINK software are shown to demonstrate the efficacy of the proposed circuit.

This paper presents a new switched-capacitor multi-level inverter (SCMLI) for photovoltaic systems which can eliminate the leakage current. The traditional SCMLI suffer from the H-Bridge to obtain negative levels, which create variable common mode voltage (CMV) and so generates the leakage current. Here, by direct connection the negative polarity of the DC source to the neutral point of the grid, it can guaranty giving constant CMV and then eliminating the leakage current. In this topology, without applying any extra circuit, all capacitors can be charged in binary asymmetrical structure, then, by reducing the number of components, it has aimed to increase the output levels with acceptable total harmonic distortion (THD). The other advantages of propose topology are that; it has the capability to boost the voltage as well as conduct the reverse current to the PV. To confirm the validity of the proposed topology, some simulation results for 15-level inverter by using MATLAB/SIMULINK software are given.

DC microgrids get a lot of attention because of its good characteristics. DC-DC converter is necessary in DC microgrids to interface energy. The dual active bridge (DAB) converter is one of most promising DC-DC converters. But when the normalized voltage gain is far from 1, the DAB converter is difficult to realize soft switching. In this paper, the neutral point clamped (NPC) dual-active-bridge (DAB) converter with a blocking capacitor is adopted. This converter is able to work in different modes to achieve wide zero voltage switching (ZVS) range. A ZVS range optimization strategy is proposed based on ZVS range analysis in different modes. This strategy makes the NPC DAB converter work in the optimal mode. The simulation results show this strategy is effective.

An optical fiber refractive index (RI) sensor based on open microcavity Mach-Zehnder interferometer (OMZI) and fiber ring laser (FRL) is proposed and demonstrated experimentally. The OMZI is manufactured by splicing a tiny single mode fiber (SMF) segment with multi-mode fiber (MMF) joints laterally. The large offset structure forms an open microcavity which can be filled with the liquid under test. Through inserting the OMZI into an erbium-doped FRL, the RI measurement can be achieved by discriminating the lasing wavelength, and the detection limit (DL) can be effectively improved owing to the laser sensing spectrum with narrower 3-dB bandwidth and higher optical signal-to-noise ratio (OSNR). Experimental results show that the output laser wavelength has a linear response to the RI change with a sensitivity of −2947.818 nm/RIU during the range of 1.33302~1.33402, and the DL is as low as 5.89×10−6 RIU. Compared with other optical fiber RI sensors, the proposed fiber laser RI sensor with an open microcavity has the advantages of small size, high sensitivity and low DL, making itself a competitive candidate for the microfluidic RI measurement in biochemistry.

This paper presents a novel two-degree-of-freedom (two-DOF) passive damping system dedicated to the vibration suppression of a dual-axis precision force sensor. The damping system consists of two identical eddy current dampers (ECDs), each of which utilizes a double-layer Halbach-array permanent magnet (PM) structure and a middle-layer copper plate to generate a large damping force. Analytical models are established to predict the damping characteristic of the ECD. The finite element simulations are conducted to verify the effectiveness of the analytical models. The simulation results indicate the large damping coefficient of the developed ECD.

Molybdenum ditelluride (MoTe2) has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taking advantage of high-κ screening effect, we have fabricated back-gated MoTe2 transistors on an Al2O3 high-κ dielectric and systematically investigated the electronic and optoelectronic properties. A high current on/off ratio exceeding 106 is achieved in the Al2O3-based MoTe2 transistors, and the hole mobility is demonstrated to be 150 cm2 V−1 s−1, compared to 0.2–20 cm2 V−1 s−1 ever obtained from back-gated MoTe2 transistors in the literatures. Moreover, a considerable hole concentration of 1.2 × 1013 cm−2 is attained in our Al2O3-based MoTe2 transistors owing to the strong gate control capability, leading to a high on-state hole current of 6.1 μA μm−1. After optimization, our Al2O3-based MoTe2 phototransistor exhibits outstanding photodetective performance, with a high responsivity of 543 A W−1 and a high photogain of 1,662 at 405 nm light illumination, which are boosted around 419 times compared to the referential SiO2-based control devices. The mechanisms of photoconductivity in the Al2O3-based MoTe2 phototransistors have been analyzed in detail, and the photogating effect is considered to play an important role. This work may provide useful insight to improve carrier mobility in two-dimensional layered semiconductors and open opportunities to facilitate the development of high-performance photodetectors in the future.

Arc welding inverter supply with switch and digital control is widely used, due to the advantages of high controllability, small size, and high efficiency. With the constant increasing of switching frequency and decreasing of arc welding machine size, the conducted electromagnetic interference (EMI) becomes serious, especially for common mode (CM)-conducted EMI. Meanwhile, as the development of digital processing technique, digital active EMI filter (DAEF) technology, which uses digital control and embedded mode, has become a hot research topic. However, the conventional DAEF fails to consider time delay effect. Its model cannot accurately describe DAEF filtering behavior. Moreover, decoupling circuit lacks scientific design method. To cope with these, this paper proposes a precise DAEF model which considers both the time delay of digital processing portion and the parasitic parameters of passive components. Moreover, based on impedance matching principle, a detailed and scientific design method of decoupling circuit is put forward. Meanwhile, the arc welding inverter system with embedded DAEF is designed, modeled, and compensated. Finally, experiment results show that the proposed precise model can predict the system filtering performance accurately. And the proposed design method of decoupling circuit is very effective to suppress the CM-conducted EMI. The embedded DAEF can improve system stability and dynamic performance.

In this paper, the failure mechanism of DSP-based control circuits in high-voltage large-current modular multilevel converter (MMC) valve towers is studied. This study combines a low-voltage integrated circuit (IC) immunity model with a new perspective on electromagnetic interference (EMI) coupling effects. A new copper layer based coupling model of MMC valve tower combined with power system and digital control IC was established. By using the new model, the EMI introduced into the IC can be quantified. This advantage translates into a new DSP electromagnetic sensitivity (EMS) evaluation method that can be used as a guide for industrial applications.

Objective To evaluate the efficacy and safety of radiofrequency ablation(RFA) for patients with lung cancers using meta-analysis. Methods and materials A literature search (PubMed, Embase, Web of science and China National Knowledge Infrastructure) was undertaken until August 2017 to identify sufficient studies evaluating the efficacy and safety of RFA. Pooled proportions of estimates were calculated by performing the random effect model, including technical success rate, recurrence rate, local tumor progression rate and complications. Results A total of 25 eligible studies were collected, giving a sample size of 1989 patients with 3025 lung tumors. In the present series, the pooled technical success rate was 96%(95%CIs: 93%–100%). Further, we observed pooled recurrence rate of 35%(95%CIs: 12%–59%) following RFA. Additionally, the pooled rate of local tumor progression was 26%(95%CIs: 20%–32%). One hundred and ninety major complications of RFA were reported in 20 studies, giving a pooled proportion of 6% (95%CIs: 3%–8%) for major RFA complications. Pooled rate of minor complications was 27% (95%CIs:14%–41%). Conclusion In this meta-analysis, RFA was found to be a safe and efficient treatment for the patients with lung cancers. The efficacy and safety of RFA for lung cancer deserve future investigation in further well-designed randomized controlled trials.

This paper presents a novel compact circuit combining function of gate control and voltage balancing for series-connected silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET). Two series-connected SiC MOSFETs with the proposed circuit only require a single standard gate driver to achieve the gate control and voltage balancing during both steady-state and switching transition. Moreover, the proposed circuit is only composed of ten passive components. Therefore, the proposed circuit provides a low-cost and highly reliable method to increase the blocking voltage of the SiC MOSFET. The operation principles of the proposed circuit are theoretically analyzed. In addition, the high-blocking-voltage device is not only required in switching-mode power supply (SMPS) but also in dc-breaker applications. The proposed circuit is then modified to make it suitable to the dc-breaker applications. The simulation and experimental results validate the effectiveness and superiority of the proposed circuit in both SMPS and dc-breaker applications.

The silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) has a more serious voltage overshoot than the silicon insulated gate bipolar transistor (IGBT) due to the fundamental differences of the devices’ parasitic parameters. In this paper, a novel low-inductance packaging structure for a wire-bond-based multichip phase-leg SiC MOSFET module to suppress the voltage overshoot is proposed. This packaging structure is based on the adjacent decoupling concept achieved by several decoupling capacitors to reduce the size of the commutation loop. The improvement in the packaging parasitics has been verified through an Ansys Q3D extractor. Furthermore, the influence of adjacent decoupling capacitors is analyzed in detail by frequency-domain analysis and verified with LTspice simulation analysis. Thereafter, the selection and thermal reliability of adjacent decoupling capacitors are expounded. The experimental results demonstrate the effectiveness and superiority of the proposed packaging structure.

Gallium nitride high electron mobility transistors (GaN HEMTs) are promising switching devices in high-efficiency and high-density dc–dc converters due to their fast switching speed and small conduction resistance. However, GaN HEMTs are very sensitive to parasitic inductance because of their high switching speed, low-threshold voltage, and small driving safety margin. Parasitic inductance can cause severe voltage overshoot and ringing, which may result in electromagnetic interference issues, false turn-on, or even device breakdown. This paper aims at reducing the parasitic inductance (including power loop inductance and driver loop inductance) by optimizing the layout. First, a multiloop method is proposed to reduce the parasitic inductance. Optimization of both the conventional single-loop structure and the proposed multiloop structure are presented. Second, three kinds of power loop layouts based on the proposed multiloop structure are realized on PCB substrate and one of them is realized on aluminum nitride (AlN) substrate, which has higher thermal conductivity but less copper layers. The power loop inductance on PCB substrate is reduced to 0.1 nH, which is only 25% of the state-of-art layout. The power loop inductance on AlN substrate is reduced to 0.22 nH. Third, the driver loop layout is optimized and achieves 50% reduction of driver loop inductance compared with the conventional single-layer layout. Finally, integrated modules using the proposed layouts are built to validate the analyses and designs.

In order to construct a low impedance loop for common mode electromagnetic interference (EMI) signals, traditional method is to use Y-capacitors as filtering components. However, in the commonly used isolated AC-DC switching mode power supplies (SMPS), the Y-capacitors branch also behaves as a terrible leakage current loop. For the safety of human beings, this leakage current is not allowed in commercial used equipment such as chargers, medical instruments and so on. Therefore, certain works should be done to both acquire good EMI performance and satisfy the strict leakage current limitation. The goal of this paper is try to meet these two demands at the same time. In this paper, a novel non-Y-capacitor EMI design concept for SMPS is proposed for the first time. By getting rid of traditional EMI filtering component---the Y-capacitors, the leakage current can be eliminated entirely. Meanwhile, to face with EMI design challenge, optimized transformer architecture is presented. Analysis of the transformer architecture as well as the auxiliary winding has been carried out. Then a novel topology suitable for non-Y-capacitors converter is proposed and the design procedure of the proposed topology is discussed in detail. The proposed concept is applied to several popular converter topologies. The experiment results demonstrated the effectiveness and feasibility of the proposed non-Y-capacitor design schemes.

A magnetic field sensor based on the magnetic-field-induced nanoparticle assembly effect in microcapillary whispering gallery mode (WGM) ring resonator is proposed and experimentally demonstrated. The chemical characteristics of nanoparticles and the silica microcapillary are used to link up the surface density of the resonator and the magnetic field intensity. The magnetic field variation changes the surface density of nanoparticles adsorbed on the sensor surface and respond to the WGM transmission spectra shift. Because of the powerful surface sensing capability of WGM, the maximum sensing sensitivity reaches 57.59 nm/mT and the detection limit reaches 1.39 × 10 –4, respectively. The magnetic field response characteristic of the sensor is studied as well. This provides the potential to fiber-based magnetic field sensing applications.

Metasurfaces have been widely investigated for various applications enabled by their strong light manipulation capabilities. Their monolithic designs offer the convenience to incorporate novel natural materials in order to realize advanced electromagnetic (EM) functionalities. Here, based on the usage of the phase change material vanadium dioxide (VO2), a switchable metasurface that could work at two different working states is proposed. With insulating VO2, we show that helicity-dependent metasurface could be rigorously designed by adopting two phase variables, i.e., initial phase and Pancharatnam-Berry (P-B) phase, which is verified by showing an asymmetric photonic spin Hall effect (APSHE). When VO2 goes into the metallic phase (e.g., by raising the operating temperature above ~341K), the loss factor of the unit cell will be enhanced, and in this case with the assistance of multi-mode resonances, the metasurface will turn into a perfect broadband circular-polarization-insensitive EM absorber. Based on these, switchable beam splitters and focus-lenses have been designed and discussed in the paper. The method proposed here may pave a new way to pursue active and multifunctional optical devices.

Gate-all-around nanowire junctionless transistor with an auxiliary gate (AG-GAAJLT) is proposed to restrain the band-to-band tunneling (BTBT) resulted in off-state leakage current in junctionless transistor. The device is investigated through three-dimensional (3D) numerical simulations. Results show that the AG-GAAJLT has seven orders of magnitude lower off-state current compared with the conventional gate-all-around junctionless transistor (CGAAJLT). The effects of auxiliary gate voltage (V AG ) and distance between control gate and auxiliary gate (d G-AG ) are studied, and the optimizations of V AG and d G-AG are presented. This work provides a new method to solve the BTBT in GAAJLT.

We have fabricated high performance p-and n-type molybdenum ditelluride (MoTe 2 ) transistors and demonstrated their temperature dependent characteristics. The carrier mobility increases and the absolute value of threshold voltage decreases with the rise of temperature for both p-and n-type MoTe 2 transistors. Furthermore, the slopes of threshold voltage shift with temperature are estimated to be 171 mV/K and 71 mV/K for p-and n-type MoTe 2 transistors, respectively. The large difference results from their different carrier transport mechanisms. These results open opportunities to facilitate the development of high-performance functional devices based on two-dimensional layered semiconductors in the future.

The aim of the present study was to explore the indications for and safety of orthotopic liver transplantation for polycystic liver disease (PLD). Orthotopic liver transplantation in 11 patients with PLD between May 2004 and September 2013 was retrospectively analyzed. Patient epidemiological, clinical and follow-up data were collected. The survival rate was calculated using the Kaplan-Meier method. Over the 10-year period, 11 patients received orthotopic liver transplantation (n=9) and combined liver-kidney transplantation (n=2) for PLD. The recipients' median age was 56 years [(interquartile range (IQR), 52-57 years], and 7 of the patients (63.6%) were classified as having Gigot type II PLD and 4 (36.4%) as having Gigot type III. A total of 8 (72.7%) patients had a severely decreased quality of life (Eastern Cooperative Oncology Group performance status score, ≥3). Only 3 cases (27.3%) were of Class C stage. The mean hospitalization duration was 45.4±15.3 days and the mean length of stay at the intensive care unit was 4.1±1.9 days. The peri-operative mortality was 18.2% and the morbidity was 54.5%. The median follow-up period was 111 months (IQR, 33-132 months). A total of 2 patients died of severe complications after combined liver-kidney transplantation. Furthermore, 1 patient died of ischemia cholangitis during the follow-up period. The actuarial 1-, 5- and 10-year survival rate during the follow-up period was 81.8, 81.8 and 65.5%, respectively. The mean physical component summary score was 87.1±6.9 and the mean mental component summary score was 81.5±6.4. In conclusion, liver transplantation is the only curative procedure for PLD, and the present study indicated that it is relatively and safe and leads to good long-term prognosis and high quality of life. Based on our experience and results, liver transplantation is a primary option for cases of PLD with progressive or advanced symptomatic disease where previous other forms of therapy to palliate symptoms have been insufficient.

Parity-time (PT) symmetry, a concept ranging from quantum field theories and mathematical physics to classical optics, is generalized to a wireless power transfer (WPT) system in [7]. However, the already introduced system is based on an operational amplifier, limiting the power transfer efficiency of the whole system. In this paper, the concept of PT symmetry is generalized to a switch-mode WPT system. PT symmetry is achieved with a nonlinear gain element which is a single-phase bridge inverter, achieving robust wireless power transfer scheme. It is shown in simulation that the system could adjust the frequency within tens of switching period, providing attractive way of dynamic charging. The analysis of the whole system is based on coupled mode theory (CMT).

This paper focuses on the problem of conducted electromagnetic interference (EMI) in multi-load magnetic resonant wireless power transfer (WPT) system. A high frequency equivalent model is established to analyze the common mode (CM) and the differential mode (DM) conducted EMI by simulations in Saber. The comparison of CM interference has been made when the number of loads changing and the load impedances becoming unbalanced at the primary side. The circulation of the CM interference at the load side between two loads by coupling capacitors of resonant coils have been discussed. Filtering methods are put forward for multi-load magnetic resonant WPT system to reduce the CM interference. Both simulations and experimental results verify the complexity of EMI conditions and the significant effect of the filter.