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Sun-induced chlorophyll fluorescence (SIF) has been a promising indicator of plants’ physiological status, but its response to physiological changes under the verticillium wilt (VW) stress of cotton plants is complicated by concurrent nonphysiological changes. The relative contributions of the above two components to SIF variations are unclear at different VW stress severities, hindering the accurate diagnosis of VW levels. Therefore, the objective of this study is to investigate the dynamic responses of SIF, physiological and nonphysiological factors, and to evaluate the contributions of the two factors to SIF variations under different VW stress degrees of cotton. We continuously observed the diurnal variation of the top-of-canopy reflectance and SIF on healthy and VW-infected cotton during the peak incidence period of VW disease. To accurately quantify the relative contribution of each component to SIF, we proposed a practical strategy to estimate unmeasurable parameter when using Lindeman, Merenda, and Gold method. The results demonstrated the dominant role of physiological factors in SIF with an arch diurnal change pattern at the early stages of VW development. As the VW severity increased, the contribution of physiological components declined, with the maximum contribution decreasing by 47.7%, and the diurnal pattern was disrupted, with the diurnal variation amplitude of the parameter declining by 63.4%, followed by a shift in the regulatory role toward nonphysiological factors. This study contributes to a further understanding of the roles of physiological and nonphysiological components in SIF variations of cotton under VW stress, thus advancing the accurate monitoring of VW stress severity.

In pulsed electromagnetic field tumor ablation, a bipolar nanosecond pulsed electric field has obvious therapeutic advantages. This article proposes a bipolar linear transformer drive (LTD) source circuit topology with a self-triggering H-bridge for this application. In this topology, in the absence of a magnetic core reset circuit, high-frequency bipolar pulse output is realized by introducing an H-bridge while keeping the circuit structure simple. A self-triggered H-bridge is formed by cleverly introducing a self-triggered circuit in the H-bridge, which reduces the difficulty of circuit control. There are only two main control signals, and the sources of all the main control switches share the same ground. The self-triggered switches are self-triggered through the energy-taking capacitor, which improves the stability of the switch control. Theoretical analysis and simulation results demonstrated the theoretical feasibility of the above-mentioned topology; thus, an experimental prototype was built to test the key parameters. The entire prototype adopts a modular design, and each module consists of only four self-triggering H-bridges and one nanocrystalline magnetic core. The key parameters of the final designed prototype are as follows: voltage amplitude of ±4 kV, pulse width of 60–260 ns, pulse rising edge of approximately 11 ns, continuous operation at a maximum frequency of 10 kHz, and output of 500 kHz high-frequency nanosecond pulse. [ABSTRACT FROM AUTHOR]

The epoxy resin insulation in saturable reactors in a HVDC transmission converter valve is subjected to a bipolar exponential decay pulse voltages under normal operating conditions and its aging mechanism is still unclear. In this paper, an electrothermal aging experiment of epoxy resin was carried out under bipolar exponential decay pulse voltages at high temperature. The dielectric properties of epoxy resin before and after aging were measured using frequency-domain spectroscopy. To quantitatively study the aging characteristics, the double-relaxation Cole-Cole model was used to fit the dielectric spectra. As a result, an exponential function relationship between the relaxation time constant and the aging time of epoxy resin under various aging conditions was obtained. This relationship can be used as an empirical formula to evaluate the degree of aging. Furthermore, a comparison of the aging life characteristics of epoxy resin under pulse and sinusoidal voltages with the same peak value was performed. The results show that the electrothermal aging rate of epoxy resin under a pulse voltage is lower than under a sinusoidal voltage. The effect of the measurement temperature on the insulation life evaluation of epoxy resin was also analyzed. [ABSTRACT FROM AUTHOR]

Objective: Unipolar pulses have been used in cell electrofusion over the last decades. However, the problem of high mortality with unipolar pulses has not been solved effectively. The cell fusion rate is restricted by cell mortality. By using the advantages of bipolar pulses which cause less cell damage, this paper attempts to use bipolar pulses to increase the cell fusion rate. Methods: the transmembrane voltage and pore density of cells subjected to unipolar/bipolar pulses were simulated in COMSOL software. In an experiment, two 40 μs unipolar and two 20–20 μs bipolar pulses with electric fields of 2, 2.5, and 3 kV/cm were applied to SP2/0 murine myeloma cells. To determine the cell fusion rate and cell mortality, cells were stained with Hoechst 33342 and propidium iodide. Results: the simulation in this paper showed that a high transmembrane voltage and a high pores density were concentrated only at the contact area of cells when bipolar pulses were used. The results of the cell staining experiment verified the simulation analysis. When bipolar pulses were applied, the cell mortality was significantly reduced. In addition, the cell fusion rate with bipolar pulses was almost two times higher than that with unipolar pulses. Conclusion: for cell electrofusion, compared with unipolar pulses, bipolar pulses can not only reduce the cell mortality remarkably but also improve the cell fusion rate obviously. Significance: this paper introduces a novel way to increase the fusion rate of cells. [ABSTRACT FROM AUTHOR]

This paper considers the electroporation characteristics of a cell under high-frequency nanosecond pulse bursts. A typical two-dimensional cell system, including an organelle membrane, was discretized into nodes using MATLAB, and the mesh transport network method model was established after the bidirectional coupling properties of electrical transport and pore transport were assigned to the nodes within this model. The dynamic process in single-cell electroporation under the application of 10 unipolar high-frequency nanosecond pulse bursts at 1 Hz to the target system was simulated and analyzed. The electroporation characteristics of a single pulse burst and multiple pulse bursts were evaluated. Particularly, the effect of intra-burst frequency on the average pore radius was examined. For the plasma membrane, when multiple pulses were applied, the pore number remained unchanged while the pore radius at the transition region exhibited a more obvious cumulative effect at higher intra-burst frequencies. For the organelle membrane, the number of pores significantly increased when the intra-burst frequency was high (1 MHz). Repetitive pulse bursts expanded the pore radius but do not change the pore number. The results of the present study further enrich our understanding of the electroporation mechanism of a pulsed electric field acting on biological cells. [ABSTRACT FROM AUTHOR]

The rise/fall time of a high-voltage nanosecond pulse affects the application effect of the pulse; therefore, it is of great significance to study the adjustment of the rise/fall time. In this paper, a new type of generator topology based on a half-bridge modular multilevel converter (HB-MMC) is proposed that uses MOSFETs as solid-state switches to produce a unipolar/bipolar high-voltage nanosecond pulse with an adjustable rise/fall time. The proposed topology consists of 2 arms, each of which contains several HB-MMC submodules. The capacitors of each arm are charged with a positive voltage and negative voltage in parallel. By controlling the discharging sequence of the two arms, a unipolar or bipolar pulse can be generated. For each arm, by setting the switching sequence of the MOSFETs, the number of capacitors inserted into the discharging circuit can be controlled to allow a multilevel pulse to be generated. The rise/fall time of the output pulse can be adjusted by changing the number of levels and the duration of each level. Detailed illustrations of the proposed configuration and its operational concept are presented. Experimental results for a scaled-down prototype are presented to validate the concept. [ABSTRACT FROM AUTHOR]

This paper introduces unipolar high-frequency nanosecond pulse bursts, which combine the advantages of microsecond pulsed electric fields and nanosecond pulsed electric fields, for the treatment of tumors. To take full advantage of this nonthermal pulsed electric field treatment, it is necessary to study the thermal effects of the high-electric-field nanosecond pulse bursts inside tumor tissue. A multiparametric analysis is performed based on a finite-element model of skin with a melanoma tumor that is nipped using the Tweezertrodes. The electric field ranges from 1 to 10 kV/cm, the pulsewidth ranges from 50 to 500 ns, and the frequency in the pulse bursts ranges between 100 kHz and 1 MHz. The total pulselength is $100~\mu \text{s}$ , and the frequency of the pulse bursts is 1 Hz. The Pennes bioheat transfer equation and the Arrhenius equation are used to calculate the temperature and the thermal damage. For pulse parameters of 5 kV/cm, 500 ns, and 1 MHz, the simulated temperature of the skin tumor is only 37.48 °C after 1 s, and the thermal damage is negligible. The temperature and thermal damage to the melanoma tumor in the skin are simulated and calculated for various electric fields, pulse widths, and frequencies. The relationship between the thermal effects on the tumor and the pulse parameters is researched, and pulse parameters for a tumor without thermal damage are ascertained. Temperature measurements of melanoma tumors in nude mice in vivo show that the change in experimental temperature in the tumors is consistent with the simulated average tumor temperature. [ABSTRACT FROM AUTHOR]

High-repetition-rate nanosecond pulses are used widely in many fields, and pulses of different polarities have different effects. A new pulse-generator structure is proposed based on an improved Blumlein pulse-forming line (BPFL) and a transmission-line transformer (TLT). The proposed structure generates pulses with polarity that can be adjusted among positive, negative, and bipolar. A modular design is used for the generator. In each module, three groups of solid-state switches are used to control the BPFL. By adjusting the timing of the control signal, the BPFL can generate high-repetition-rate nanosecond primary pulses with adjustable polarity. These primary pulses are then transmitted to the load through the TLT with amplification and superposition. The pulse-forming process is analyzed theoretically for matched impedance. The strategy for controlling the switches is also illustrated. In addition, the feasibility of the proposed generator is verified by simulations and experiments. Finally, a four-stage prototype is developed that can produce pulses with amplitudes of 0–10 kV, a width of 30 ns, repetition rates up to 200 kHz and adjustable polarity. [ABSTRACT FROM AUTHOR]

The Marx circuit structure based on fast high-power semiconductor devices is the classical way of generating picosecond pulses. However, most reported studies suggest that as the number of stages in the Marx circuit increases, the output pulse amplitude tends to saturate. This has of late made high-voltage picosecond-pulse generation a challenge. In this paper, as the number of stages increases, the internal resistance of the avalanche transistor tends to decrease with increasing current flowing through the avalanche transistor. A step-by-step wiring and debugging of the avalanche transistor-based Marx circuit demonstrates this experimentally. That is, for a certain range in the number of stages, saturation of the output pulse amplitude for the Marx circuit of avalanche transistors is not apparent. Introducing a parallel structure for the transistors not only increases the current level of the entire circuit but also further reduces the equivalent resistance of the avalanche transistors, thereby improving the output efficiency. Drawing on microstrip transmission theory, and combining the Marx circuit and avalanche transistor parallel structure, component parameters and circuit topology of the picosecond-pulse generator were redesigned, and a 30-level Marx circuit with a parallel structure of two avalanche transistors was developed. The picosecond-pulse generator outputs a pulse with adjustable voltage amplitude of 0.9–3.1 kV, a 350-ps full-width at half-maximum, a 150-ps rise time, and an adjustable high-stability repetition rate of up to 10 kHz. The number of pulses is precisely controlled. The generator is an all-solid-state compact device with high frequency suitable for research needs. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of low-field high-frequency nanosecond pulsed electric fields (nsPEFs) on multiple biological behaviors of human A375 melanoma cells and to optimize suitable parameters for further study and clinical use. Methods: An nsPEF generator was developed to generate appropriate pulses. Cell apoptosis and the cell cycle were evaluated by flow cytometry. The CCK-8 assay was performed to explore the effect of nsPEFs on the viability of A375 melanoma cells. Cell migration was assessed using a Transwell Boyden Chamber. The proliferation of A375 melanoma cells was determined by the cloning efficacy test. Furthermore, the nude mouse tumorigenicity assay was used to detect the effectiveness of nsPEFs in vivo. Results: The nsPEFs with our tested parameters failed to induce apoptosis of A375 melanoma cells, though nsPEFs with high pulse duration (500 ns) induced necrosis. However, the viability and migration of A375 melanoma cells were significantly inhibited by nsPEFs. nsPEFs also suppressed the proliferation of A375 melanoma cells by restricting cells in G0/G1 phase. Moreover, animal experiments demonstrated that nsPEFs inhibited the growth of melanoma in vivo. Conclusion: Low-field high-frequency nsPEFs failed to induce apoptosis but effectively inhibited the growth of melanoma via affecting other biological behaviors of melanoma cells, such as cell viability, proliferation, and migration. Significance: This study investigated the influence of low-field high-frequency nsPEFs on melanoma through evaluating their effects on multiple biological behaviors and is helpful in the treatment of melanoma and other tumors. [ABSTRACT FROM AUTHOR]

A picosecond-pulse electric field, matching ultra-wideband antenna, can be applied to biomedical noninvasive therapy. Its effect depends largely on the electric field intensity on the target. Because the amplitude enhancement of a picosecond-pulse source is restricted by many factors, ultra-wideband time-domain antenna research has become important. Here, the intensity of the electromagnetic radiation propagated by the antenna was greatly improved by arraying the antenna feed structure. For targeted focusing, an ellipsoidal reflective surface is commonly utilized, but this structure limits the formation feasibility of the feed structure. Here, the feed structure and the reflector were arrayed at the same time, while satisfying the time and spatial consistency of the electromagnetic waves at the target, the intensity of the electric field at the target was greatly improved, and the size of the focal spot was reduced simultaneously. A Gaussian pulse with a 1-V amplitude and a 200-ps width was used as the excitation source. Using this antenna array, a focal spot less than $1\times 1\times 1$ cm was formed at the target. Also, with the increased number of elements in the antenna array, the electric field intensity of the target increased. The relationship between the field intensity at the target and the number of combined antennas is discussed. The increased field strength eventually levels off, which is also consistent with the theory. [ABSTRACT FROM AUTHOR]

Magnetic pulse compression (MPC) systems are suitable for generating dielectric barrier discharges (DBDs) owing to their capability of producing high-amplitude, short pulse voltage waves. This paper proposes a high-frequency, bipolar magnetic compression system to study DBD plasma characteristics. First, the principle of bipolar MPC is explained [a bipolar MPC system comprises a full bridge inverter circuit, pulse transformer (PT), and magnetic switch (MS)]. Additionally, the design of the PT and MS is described. Then, the waveform of the resistive load is tested and compared with PSpice simulation results. It was found that the nanosecond pulse generator produces a pulse on a resistor with an amplitude of 0–13 kV, a rise time of approximately 100 ns, and a repetition frequency of 0 to several kHz. Finally, this paper studies the plasma characteristics under the application of a high-frequency bipolar pulse, and the charge–voltage Lissajous figure of the discharge waveform is analyzed. Combining discharge photographs and theoretical calculation results yields the relationship between the discharge characteristics and the frequency, which enriches the theoretical study of high-frequency bipolar discharges. [ABSTRACT FROM AUTHOR]

Nanosecond pulsed electric fields (nsPEFs) with higher repetition frequency presents potential better clinic applicability for tumor treatment. However, the biophysical mechanisms of high-frequency multi-pulse protocols are currently unclear. In this study, a multicellular model with scale of 131 × 121 μm was used to evaluate the accumulation of pore number and pore radius with increasing numbers of pulses. This multicellular system was established based on the transport lattice model combined with the Smoluchowski equation (SE) electroporation model and solved using Pspice and Matlab. The transient and spatial responses of the system under 10 unipolar high-frequency 500 ns pulses with different field intensities (3 kV/cm, 5 kV/cm and 10 kV/cm) and different frequencies (100 kHz, 500 kHz and 1 MHz) were then analyzed. The results show that with increasing numbers of pulses, the pore number remained basically the same but its value was larger when a higher intensity field was applied. The pore evolutions were similar at different field intensities. However, pulse frequency had a significant influence on the changes of pore radius. Pore radius growth effects were more obvious with higher frequency because of its shorter pulse intervals. The results presented here provide theoretical support for mechanism of tumor treatment with high-frequency nanosecond pulses. [ABSTRACT FROM AUTHOR]

Given its nonthermal property and other advantages, irreversible electroporation (IRE) has quickly translated into clinical applications. An increasing number of clinical cases using IRE have also revealed crucial issues. The uneven distribution of the electric field caused by the heterogeneity of biological tissues has not been completely and effectively addressed to date. The use of high-frequency monopolar pulse bursts (HFMPBs) is expected to solve this problem. The high-frequency content of the HFMPB is used to ensure the uniform distribution of the electric field in the tissue. A temperature increase similar to that of the conventional pulse method does not cause thermal damage and results in a killing effect similar to that of the conventional technique. Meanwhile, the subpulse has a pulse duration of 1– 100~\mu \texts , which remains unexplored and may induce new cell responses. This paper analyzes the HFMPB based on the frequency domain and infers that the cell death pathways under this pulse induce necrosis and other processes, such as apoptosis. The phosphatidylserine externalization rate had a peak value at a different inner frequency of HFMPB when the electric field was 1 kV/cm for melanoma cells. This new type of pulse is expected to solve the problem of the uneven distribution of the electric field without altering the cell killing effect. If this effect is also verified in tissue ablation, these new types of pulses will promote the clinical application of IRE. [ABSTRACT FROM AUTHOR]

A high pulse repetition frequency (PRF) nanosecond pulse generator based on Blumlein pulse forming line (BPFL) and transmission line transformer (TLT) is proposed in this paper. The generator combines the BPFL characteristic, which is used to generate a narrow, high PRF pulse, with the excellent performance at high frequency of a transmission line transformer. A modular structure was adopted for this design. The primary pulse produced by the BPFL in each module will output to the load through the TLT amplifier; further, the output of multiple modules can be cascaded to improve the load voltage and output power. Moreover, this reduces the ratio of the output impedance and the input impedance of the TLT, making the generator more suitable for light loads. A microstrip line was used for the transmission line, which makes it possible to match random loads. Additionally, the size of generator was greatly reduced to realize a compact design. MOSFETs were used in the generator to facilitate the control of both the amplitude and PRF of the output. A two-stage laboratory prototype was fabricated to verify the performance of the proposed topology. As a result, the generator produced pulses for matched loads with amplitudes of 0?2.5 kV, pulse width of 20 ns, and repetition frequencies of 0?10 kHz. The generator can be used as a hardware foundation for research on the biomedical effects of exposure to high PRF nanosecond pulse electric fields. [ABSTRACT FROM AUTHOR]

For non-invasive treatments in the biomedical field, sub-nanosecond pulse electric field matching ultra-wideband antennas have aroused great interest for their excellent directivity and targeted treatment. Sub-nanosecond pulse generators have proved difficult to control in pulsed power technologies despite many studies of pulse generators based on avalanche transistor theory and the Marx circuit. However, no solution exists to the problems of non-ideal waveform of the output sub-nanosecond pulse and the relatively low effectiveness of the Marx circuit. To resolve these problems, the paper describes a sub-nanosecond pulse generator simulation model based on gradient transmission line theory in PSPICE simulation software and the development of a compact solid-state sub-nanosecond pulse generator (18 cm?18 cm?4 cm). From experimental tests, trigger signals of 5-V amplitude, 5-ns rise and fall times (pulse-width 10 ns-50 ns) were generated by Field-Programmable Gate Array (FPGA). A pulse with 1600-V voltage amplitude, 300-ps full width at half maximum, 150-ps rise time, and 10-kHz high-stability repetition rate was generated in an attenuator load with high-bandwidth (8 GHz, 50 ?). The effectiveness (Output pulse voltage amplitude / Charge voltage ? Stages) of this Marx circuit reached to 41.7%, improving considerably on previous efforts. [ABSTRACT FROM AUTHOR]

Pulsed electric fields have recently been the focus of considerable attention because of their potential application in biomedicine. However, their practical clinical applications are limited by poor understanding of the interaction mechanism between pulsed electric fields and cells, particularly in the process of electroporation and its effect on parameter selection. This paper established a multishelled dielectric model based on finite elements to simulate and analyze the processes involved in electroporation. In particular, the processes include the dynamic development of the pore radius and electroporation region: the distribution of recoverable, nonrecoverable, and nonelectroporation areas on the cell; and the influence of pulse parameters on varying degrees of electroporation. Results showed that membrane conductivity, pore density, transmembrane potential, and distribution of pore radii are functions of time and position on the cell. The electroporation areas were divided into recoverable, nonrecoverable, and no-electroporation pores. For 10~\mu \texts , 1.5-kV/cm pulse was observed in the regions exposed to sufficiently high transmembrane voltage (1 V), electroporation occurred, membrane conductivity and pore density (up to 10^\mathrm 16/\textm^\mathrm 2) rapidly increased with time, and electroporation areas increased gradually and were mainly distributed in the range 0°–70° (recoverable pore [0°, 35°], nonrecoverable pore [35°, 70°], and no-electroporation pore [70°, 90°]). Electric field strength was the major factor that induced electroporation, particularly in the recoverable pore, but it had minimal effect on pore expansion. However, pulse duration affects the nonrecoverable pore, such that the high-intensity wide pulse is more useful in the field of irreversible electroporation. The high-intensity short pulse can increase permeability and maintain cell viability. [ABSTRACT FROM AUTHOR]