Turn-on Process Research Articles

A fluorescent probe derived from phenanthridine for selective detection of Bi3+ ion and its real-time application

To detect Bi3+ ion, a new phenanthridine-based sensing probe 5-(4-(benzyloxy)phenyl)-7,8,13,14-tetrahydrodibenzo [a,i]phenanthridine(BBA) was synthesized and characterized using mass spectral and NMR spectral analysis. Even in the presence of other cations, the probe BBA showed notable color changes through the fluorescence turn-on process when exposed to Bi3+ ions. It was found that the Limit of Detection of Bi3+ was 280 pM, and the reaction time was as low as 10 s. Additionally, it was found that adding ethylenediaminetetraacetic acid (EDTA) to BBA + Bi3+ made BBA, a reversible sensor. Test strips and real water sample experiments demonstrated the potential of the probe BBA for sensing Bi3+ in the environment. The sensing mechanism of BBA was investigated using Gaussian 16 software by performing Density Functional Theory (DFT) calculation. DFT calculations provided a theoretical validation of the experimental results. The practical application of BBA as a Bi3+ sensor has been expanded to include quantitative analysis of bismuth ions in tablets containing Bi3+.

Calculation and Analysis of the Dynamic Turn-On Process of SiC MOSFET Based on a Piecewise Linearization Method

Calculation and Analysis of the Dynamic Turn-On Process of SiC MOSFET Based on a Piecewise Linearization Method

Failure mechanisms of the thyristor switch in pulsed arc electrohydraulic discharges

In order to study the failure mechanism of the thyristor switch in the application of electric pulse fracturing, an underwater pulse power discharge experimental platform was built, the impedance characteristics of the plasma channel were analyzed and the circuit equivalence was carried out for each discharge stage. Then, based on the Silvaco simulation software, a theoretical thyristor model was established. By observing the distribution of the internal carriers and current density, the turn-on and turn-off processes of the thyristor switch under high voltage were analyzed. The formation factors of peak voltage in the turn-off process were studied, the easy breakdown position was pointed out, and a method to suppress the reverse peak voltage by creating critical damping oscillations in the discharge circuit was proposed. Finally, a pulsed power discharge experiment was carried out to verify the theoretical analysis. The experimental results show that the discharge waveform conforms to the theoretical analysis, and the high voltage breakdown damage of the thyristor is also consistent with the theoretical simulation model. Furthermore, the proposed thyristor protection method can greatly suppress the reverse voltage spike, reduce the peak voltage by 52%, and effectively avoid the damage caused by withstand voltage breakdown in the application of pulse power discharge.

A GFP Inspired 8-Methoxyquinoline-Derived Fluorescent Molecular Sensor for the Detection of Zn2+ by Two-Photon Microscopy.

An effective, GFP-inspired fluorescent Zn2+ sensor is developed for two-photon microscopy and related biological application that features an 8-methoxyquinoline moiety. Excellent photophysical characteristics including a 37-fold fluorescence enhancement with excitation and emission maxima at 440 nm and 505 nm, respectively, as well as a high two-photon cross-section of 73 GM at 880 nm are reported. Based on the experimental data, the relationship between the structure and properties was elucidated and explained backed up by DFT calculations, particularly the observed PeT phenomenon for the turn-on process. Biological validation and detailed experimental and theoretical characterization of the free and the zinc-bound compounds are presented.

Investigation of the Impedance Characteristics During the Turn-On Process of Electrically Triggered Vacuum Surface Flashover Switches

Investigation of the Impedance Characteristics During the Turn-On Process of Electrically Triggered Vacuum Surface Flashover Switches

Calculations of static and dynamic processes in the synchronizing shaft of a medium-voltage vacuum switch during the turn-on process

An important direction of theoretical research of modern electrical devices, medium voltage switches and contactors is the study of mechanical processes that occur during their operation. First of all, this is due to sufficiently large forces and accelerations acting on the structural elements and the synchronizing shaft of such devices in the process of switching on. In the article, on the basis of developed mathematical models, calculations of mechanical processes in the synchronizing shaft of a vacuum switch in static and dynamic mode for an absolutely rigid and real shaft are performed and their comparative analysis is carried out. The results of computer modeling are obtained in tabular and graphical forms, which include data on static and dynamic deformations of the shaft, as well as mechanical forces in its supports. It is shown that the mechanical deformation of the shaft causes a decrease in contact drop and contact pressure forces, but with a correctly selected cross-section of the synchronizing shaft, these values slightly affect the operation of the switch itself (the decrease is about 20% and 7%, respectively). It is also shown that as a result of the bending of the shaft, additional axial forces appear in the supports compared to the simplified calculation, which significantly affect the choice of bearings according to the equivalent static load. The calculated dynamic forces, taking into account the masses of contacts and contact rods, exceed similar static forces by 1.3 times, which must also be taken into account when choosing bearings in which the synchronizing shaft is held.

A novel coumarin-derived fluorescent probe for real-time detection of pH in living zebrafish and actual food samples

A coumarin-based fluorescent probe DIC (3-(2-(5-(4-(diphenylamino)phenyl)isoxazol-3-yl)-1-hydroxyvinyl)-7-hydroxy-2H-chromen-2-one) with high performance was exploited for detecting pH changes in biological system and food samples. The probe DIC could sensitively sense alkaline pH fluctuations in the range of 6.50‒9.98 with the pKa value of 8.12 through a remarkable fluorescence turn-on process. The probe DIC exhibited excellent photostability and reversibility in monitoring the pH fluctuations. The detection mechanism of DIC for pH was confirmed by 1H NMR titration experiment and theoretical calculation. This probe owned a low cytotoxicity and was successfully employed for in-suit tracking of pH fluctuations in living zebrafish. In addition, the probe DIC could be applied in the visualization of meat and prawn freshness.

Decoherence and Turbulence Sources in a Long Laser.

We investigate the turn-on process in a laser cavity where the round-trip time is several orders of magnitude greater than the active medium timescales. In this long delay limit, we show that the universal evolution of the photon statistics from thermal to Poissonian distribution involves the emergence of power dropouts. While the largest number of these dropouts vanish after a few round-trips, some of them persist and seed coherent structures similar to dark solitons or Nozaki-Bekki holes described by the complex Ginzburg-Landau equation. These coherent structures connect stationary laser emission domains having different optical frequencies. Moreover, they emit intensity bursts which travel at a different speed, and, depending on the cavity dispersion sign, they may collide with other coherent structures, thus leading to an overall turbulent dynamics. The dynamics is well-modeled by delay differential equations from which we compute the laser coherence time evolution at each round-trip and quantify the decoherence induced by the collisions between coherent structures.

Variable Amplitude Gate Voltage Synchronous Drive Technique for Improving Dynamic Current Balancing in Paralleled IGBTs

The problem of current sharing imbalance in the parallel connection of IGBT multi-modules affects the wide-scale application of parallel IGBT. The current imbalance problem in the dynamic process is mainly caused by the difference in control loop parameters. In parallel IGBT applications, current sharing is a critical concern. Objective differences in IGBT module and driver circuit parameters, as well as incomplete symmetry in the power circuit, lead to inconsistent parasitic parameters, resulting in both static and dynamic current-sharing issues. Static current sharing refers to the uneven distribution of load current under static operating conditions, while dynamic current sharing refers to the imbalance in current distribution among parallel IGBT modules during turn-on and turn-off processes. This is mainly influenced by the synchronization of turn-on and turn-off timings and the consistency of collector current change rates during these processes. The difference in characteristic parameters of IGBT modules is an important factor leading to the difference in control loop parameters, which has a profound impact on the dynamic current-sharing characteristics of IGBT parallel applications. In the case where the device parameters cannot be changed, some drive compensation controls can compensate for the influence of device differences on dynamic current sharing. Accurate identification of the characteristic parameters of the IGBT module is the key to this method. This paper mainly studies a synchronous variable-amplitude drive scheme and studies the influence of parameters such as synthetic gate resistance, gate-emitter capacitance, and on-off gate threshold voltage on the dynamic current-sharing characteristics. The correlation characteristics of the characteristic parameters of the IGBT device body are studied, and the characteristic model of each parameter and the influencing variable is constructed. The parallel working model of PSpice devices is established, and the influence of different characteristic parameters on the current-sharing characteristics is evaluated, and its sensitivity is summarized through simulation analysis. Through the 1700 V/300 A IGBT parallel switch characteristic experiment, the current sharing effectiveness of the synchronous variable amplitude driving method is verified. Finally, the effects of different gate control voltages and different action times on the dynamic current-sharing characteristics are summarized.

A novel pyrimidine-based two-photon fluorogenic probe for rapidly visualizing nitroreductase activity in hypoxic cancer cells and in vivo

Nitroreductase (NTR) is an overexpressed enzyme in hypoxic tumor microenvironment that can be a specific recognition site for tumor diagnosis in clinical trials. Therefore, the development of probs for NTR activity with precision and instantaneity is significant. In this work, a NTR probe (ZJ) was constructed on the structure of pyrimidine derivatives with 4-animobenzyl carbamate groups. ZJ exhibited a responsive “turn-on” two-photon excited fluorescence by NTR recognition in cells and in vivo. The 4-nitrobenzyl carbamate groups in ZJ could be reduced by NTR to 4-animobenzyl carbamate groups in the presence of reduced nicotinamide adenine dinucleotide (NADH). Attributed to its self-immolation property, 4-animobenzyl carbamate would release to generate primary amine on pyrimidine, accompanied by fluorescence signal recovery of ZJ. Such responsive fluorescence turn-on process accomplished as fast as within 20 mins. The favorable stability and specificity of ZJ on NTR activity sensing was further illustrated according to the negligible interference by biological factors and the distinguishing on different NTR types. ZJ successfully visualized the distribution of over-expressed NTR in hypoxic cancer cells and in zebrafish using two-photon fluorescence microscopy, which demonstrated the potential application in studying the relationship between tumor hypoxic microenvironment and cancer.

Variable Gate Resistance Drive Circuit Based on di/dt Feedback for IGBT

To overcome the rigid control of the classical drive method which used fixed resistance to drive IGBT, a variable gate resistance drive method was proposed. This method detected the change rate of collector current through the parasitic inductor of the IGBT module, and the closed-loop feedback was used to control this rate of change. All the expressions between voltage overshoot , overcurrent and di/dt were derived. Based on these expressions, the di/dt feedback control was designed. The feedback circuit selected gate resistances with different resistance values to drive IGBT in various stages of the turn-on and off process. According to the simulation analysis, both switching time and loss were reduced ultimately. The current peak and overvoltage were controlled effectively, and the switching performance was improved.

A novel red-emitting aggregation-induced emission probe for determination of β-glucosidase activity

β-Glucosidase (β-Glu) is a ubiquitous enzyme which has multiple roles in medical diagnosis, food production, agriculture, etc. Existing β-Glu assays have limitations such as complex operation, long running time, and high background noise. Here we report a red-emissive probe TBPG for measuring the activity of β-Glu. The probe was synthesized through conjugating a β-Glu targeting glucoside to an aggregation-induced emission (AIE) fluorophore. In the presence of β-Glu, TBPG was hydrolyzed and exhibited a fluorescence turn-on process. The detection conditions including time, temperature, pH value, buffer, and probe concentration were optimized systematically. Afterwards, fluorescence titration was conducted showing an excellent linearity (R2 = 0.998), a wide linear dynamic range (0–5.0 U/mL), and a limit of detection as low as 0.6 U/L. The detection specificity and ion interference were evaluated by adding various biological species and ions to probe without or with β-Glu. Next, we demonstrate the applicability of probe TBPG in determining the β-Glu activity in living cells using confocal microscopy and flow cytometry. Finally, this newly established assay was applied to real soil samples. Comparable results were obtained as the commercial assay, manifesting its great potential in soil enzyme analysis.

Study on Transient Turn-On Characteristics of Pulse Power Thyristor-Type Devices Under Ultrahigh di/dt Condition

Specially optimized thyristor-type devices for fast turn-on and high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{d}{i}/\text{d}{t}$ </tex-math></inline-formula> capability are promising in pulse power applications. In this work, the transient turn-on characteristics of MOS-gate triggered and current-gate triggered thyristor-type devices operating at ultrahigh <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{d}{i}/\text{d}{t}$ </tex-math></inline-formula> conditions are first studied. The injected charge transport process is theoretically analyzed and modeled by considering the effect of the transient electric field, during short pulse duration, which then clearly reveals the difference between the MOS-gate triggered and current-gate triggered thyristor-type devices on the transient turn-on characteristics. TCAD simulations and experimental measurements are carried out to verify the transient turn-on process. The theoretical, simulated, and experimental results show that the MOS-gate triggered thyristor has better turn-on characteristics than the current-gate triggered thyristor, which attributes to the reduced turn-on step and consequently stronger conductivity modulation. This work helps further optimization of thyristor-type devices achieving fast turn-on and high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{d}{i}/\text{d}{t}$ </tex-math></inline-formula> capability.

Interface regulation toward low driving voltage perovskite light-emitting diodes

Electroluminescence (EL) at sub-bandgap voltages has been observed in perovskite light-emitting diodes (PeLEDs), which, however, does not appear as a universal phenomenon in current reports, and the mechanism remains in debate. Herein, we verify that the turn-on voltage of PeLEDs depends neither on the carrier injection nor on the energy levels of charge-transport layers, ruling out the Auger-assisted upconversion charge injection effect. The recombination of diffused and thermally generated charge carriers, rather than the high-order effect, is believed to be responsible for the sub-bandgap EL behavior. Moreover, we demonstrate that a critical prerequisite for the sub-bandgap EL is the strong confinement of charge carriers in the emissive layer, which can be achieved by inserting a CdSe/ZnS quantum-dot monolayer at the interface of the perovskite/electron-transport layer. The accumulated holes induced by the CdSe/ZnS monolayer can reduce the electron-injection barrier, thus leading to an observable EL at a sub-bandgap voltage. Our work provides a substantial evidence for the sub-bandgap EL turn-on processes and addresses the debate in PeLEDs.

Effects of Short Pulse on Lateral Current Spreading in Turn-on Process of Pulsed Thyristors Under Inductive Load

Pulsed thyristors widely used in pulsed power generators are more easily confronted with damage problems in the turn-on process due to insufficient lateral current spreading under short pulses. This study aims to explore the spatial and temporal characteristics of the lateral current spreading under short pulses and reveal the relationship between the lateral current spreading and the external circuit with inductive load. Based on turn-on characteristics experiments of a thyristor with an amplifying gate and emitter shorts, mixed semiconductor device, and circuit simulations were carried out to compute the variation of current density in the thyristor under a ten-microsecond pulse. The results show that the current spreads incompletely under 17 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> pulse due to the external circuit and the emitter short. For comparison, the current can continue spreading at the back of the first emitter short as the pulsewidth is 150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> . The relationship between the current lateral spreading and the external circuit with inductive load under short pulses is established, and a necessary condition for the current to spread at the back of the first emitter short is proposed.

A Novel Isolated Resonant Gate Driver With Adjustable Duty Ratio for SiC MOSFET

Resonant gate driver is a promising technique to save gate driver loss at high switching frequencies to further promote the integration level of gate driver with power modules. State-of-the-art isolated resonant gate drivers (RGDs) have to keep duty ratio fixed at 0.5 to avoid transformer saturation, which significantly limits the practical applications. A new isolated RGD (IRGD) with adjustable duty ratio to drive silicon carbide (SiC) MOSFET is proposed in this article by employing switching period expansion technique with a dual-secondary transformer. Transformer secondary windings are involved in the turn-on and turn-off processes alternatively and are switched at the falling edge of each input driving cycle. The effective switching frequency at gate driver transformer is reduced to 1/2 to further save power losses at high switching frequencies. This article further discusses the optimal damping approach to suppress <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$v_{\mathrm {gs}}$ </tex-math></inline-formula> overshoot and oscillation due to an adjacent second driving stage brought by parasitic gate resistor for IRGDs. The proposed IRGD is built with printed circuit board (PCB) integrated planar transformers, designed at leakage inductance of 303 nH with primary-side silicon (Si) devices and secondary bidirectional gallium nitride (GaN) devices. The duty ratio is proven to be adjusted from 0.15 to 0.9. The power consumption of the prototype is 0.883 W at 500 kHz and 1.473 W at 1 MHz driving a 900-V SiC device with 87-nC gate charge, which is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6\times $ </tex-math></inline-formula> less power consumed than a conventional gate driver (CGD). The adopted SiC power device achieves dv/dt on of 18 V/ns and dv/dt off of 35 V/ns with the proposed IRGD.

Numerical study on light triggering characteristics of NiO/SiC heterojunction thyristor

In this paper, the performance of silicon carbide (SiC) light-triggered thyristor (LTT) with a p-type NiO emitter region is analyzed through numerical simulation. The conductivity modulation in SiC LTT is significantly enhanced with the help of high injection efficiency of holes in NiO/SiC heterojunction. The injected hole density at the surface of the p− long base is increased by ∼21.2 times and the corresponding specific on-state resistance (Ron,sp) is only 36.7 mΩ cm2, which is reduced by about 29%. Moreover, hole-injection enhancement by NiO/SiC heterojunction also exhibits excellent potential in improving the dynamic characteristics of SiC LTTs. The simulation results indicate that the turn-on time of SiC LTT can be reduced by ∼57.76% when triggered by 1.0 W/cm2 ultraviolet light. Furthermore, energy dissipations of SiC LTT during the turn-on and turn-off processes can be reduced by 91.4% and 21.9%, respectively.

Dual Optical Nanosensor Based on Ormosil Nanoparticles for Monitoring O2 and pH.

Monitoring O2 and pH has excellent potential in different sensing applications, especially in biological and clinical applications. This report presents a protocol for synthesizing an optical dual nanosensor for those two parameters. The organically modified silica (ormosil) nanoparticles were prepared based on phenytrimethoxysilane in an aqueous solution using an acid-base one-pot strategy. Ormosil was selected as a lipophilic matrix for loading fluorescent O2-sensitive dye platinum(II)-tetrakis-(pentafluorophenyl) porphyrin (Pt-TPFPP), which was quenched in the presence of O2 gas and exhibited a considerable detection proficiency within a percentage range of (0-100%) O2. Commercially available drug ingredient salicylamide was labeled on the surface of the nanoparticles using a coupling agent (3-glycidoxypropyl) trimethoxysilane (GPTMS). For measuring pH, salicylamide acted for the first time as a pH-sensitive probe based on a turn-on process with increasing pH. The nanosensor displayed a significant pH detection efficiency in the range of (pH = 6-10). Salicylamide turn-on fluorescence was attributed to the excited state intramolecular transfer (ESIPT) process followed by the inter charge transfer (ICT). The presented dual nanosensor opens new opportunities as a promising candidate material for industrial systems and medical applications.

A dC/dV Measurement for Quantum-Dot Light-Emitting Diodes

We present dC/dV analysis based on the capacitance-voltage (C–V) measurement of quantum-dot light-emitting diodes (QLEDs), and find that some key device operating parameters (electrical and optical turn-on voltage, peak capacitance, maximum efficiency) can be directly related to the turning points and maximum/minimum of the dC/dV (versus voltage) curve. By the dC/dV study, the behaviors such as low turn-on voltage, simultaneous electrical and optical turn-on process, and carrier accumulation during the device aging can be well explained. Moreover, we perform the C–V and dC/dV measurement of aged devices, and confirm that our dC/dV analysis is correct for them. Thus, our dC/dV analysis method can be applied universally for QLED devices. It provides an in-depth understanding of carrier dynamics in QLEDs through simple C–V measurement.

DYNAMIC PROPERTIES OF THYRISTORS

In this work the dynamic properties of thyristors are considered. The property of the p-n barrier is briefl y reviewed and the principle of thyristor turn-on by means of a two-transistor model explained, along with an illustrative graphic interpretation of the basic equation. Described next are the dynamic properties of thyristors with a more detailed analysis of the du/dt and di/dt effects and the dynamic turn-on process.