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Abstract Objective High‐power ablation has been widely used in atrial fibrillation (AF). However, there were many studies observed the outcomes of the short‐term follow‐up. This study aims to the long‐term results of high‐power ablation guided by ablation index (AI) in patients with AF. Methods Analysis of patients with AF, who first received high‐power (40–50 W) ablation, to pulmonary vein isolation (PVI) in the Second Hospital of Shanxi Medical University from May 2020 to March 2022. All patients were managed perioperatively according to the routine treatment procedures. High‐power ablation was conducted under the guidance of our conventional power AI and baseline data, first‐pass PVI rate, ablation time, operative time, and long‐term surgical success rate were analyzed. Results A total of 83 patients with atrial fibrillation were enrolled in the study, with an average age of 61.62 ± 9.04 years, 47 male patients, and 49 paroxysmal atrial fibrillation. All patients achieved PVI, and the rate of first pass was 82%. The ablation time of the left atrial was 28.54 ± 9.11 min. There were no serious complications related to ablation, and only a small amount of pericardial effusion was found in 4 patients. During the follow‐up period of 26.36 ± 6.11 months, 8 patients were lost to follow‐up and the overall success rate was 84%, including 91% for paroxysmal AF and 71% for persistent AF. Conclusion High‐power ablation long‐term results appear a high freedom atrial arrhythmia, but further expanded samples are needed for controlled studies.

A high‐power thin film lithium niobate (TFLN) erbium‐doped waveguide amplifier (EDWA) is demonstrated with a maximum on‐chip output power of 113 mW and a gain of 16 dB. The on‐chip integrated EDWA is composed of large mode area (LMA) waveguide structures with a total length of 7 cm and a footprint of 1 × 1 cm2. Segmented LMA waveguides are connected with waveguide tapers to achieve on‐chip mode conversion, which maintains single‐mode propagation all over the EDWA even at the waveguide bends. The design leads to a significant increase in the amplified signal power by orders of magnitude and will open an avenue for applications such as on‐chip high‐power lasers and amplifier systems. [ABSTRACT FROM AUTHOR]

The growing interest for power electronics devices demands suitable materials which can perform in harsh conditions. Gallium oxide (Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$) has shown tremendous potential in high voltage, high temperature, and gassensing applications due to its unique material properties. Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$ is considered to be the next‐generation material for power electronics owing to ultrawide bandgap of 4.5–4.9 eV and high electric field of 8 MV cm−1. These material properties coupled with high‐power figure of merits make Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$ a superior material compared to GaN and SiC. Herein, state‐of‐the‐art development and recent breakthroughs in Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based field‐effect‐ transistors (FETs) highlighting major ongoing research are reviewed. The review describes the material property, band structure, and Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based field‐effect transistors in detail. Some promising applications capitalizing the epitaxial growth techniques along with the characteristics and performance of Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based devices are also explained. The prime objective of this review is to provide an up‐to‐date scientific framework pertaining to this niche emerging research area followed by device processing. This survey reveals the potential of Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based FETs for high‐ voltage and high‐power applications while several critical challenges have to be still overcome. Finally, insights are represented and future perspectives of Ga2O3$\left(\text{Ga}\right)_{2} \left(\text{O}\right)_{3}$‐based transistors along with their hetero‐structures are discussed. [ABSTRACT FROM AUTHOR]

Piezoelectric materials enabling direct conversion between electrical and mechanical energies are ubiquitously implemented in high-power apparatuses, where both superior piezoelectricity and high-power performance are demanded. However, it remains a challenge to simultaneously achieve the two goals, which are hindered by their antagonistic relationship. Herein, hot-pressing is employed to address this dilemma, as exemplified in lead-free (K,Na)NbO 3 (KNN) piezoceramics. In contrast to the samples prepared using normal sintering (NS–KNN), hot-pressed KNN (HP–KNN) polycrystals show higher density, lager piezoelectricity (d 33 ∼129 pC/N), and more active domain wall movement. In particular, the normalized strain d 33 * of HP-KNN piezoceramics exhibits high thermal stability (variation of d 33 *<10 %) in a broad temperature range from ambient temperature up to 150 °C. Moreover, the HP-KNN samples show superior high-power characteristics with a maximum vibration speed of 1.1 m/s, which is almost 78 % larger than that of NS-KNN. This study not only demonstrates that the HP-KNN lead-free piezoceramics hold great potential for high-power implements, but also opens a new avenue for integrating antagonistic properties for the enhancement of the collective performance in functional materials. [ABSTRACT FROM AUTHOR]

High‐power all‐fiber thulium lasers have gained considerable interest in recent times due to their distinct characteristics and versatile applications in the medical and industrial sectors. This review article presents a comprehensive examination of the advancements and challenges in this field. It begins with an overview of thulium‐doped silica fiber, which is a critical component for high‐power lasers operating at the 2 µm (micrometer) wavelength band. The research progress of essential high‐power thulium laser sources, including continuous‐wave (CW), quasi‐continuous wave (QCW), and pulsed lasers, is then thoroughly analyzed, highlighting their respective strengths and limitations. Additionally, the diverse applications of high‐power thulium fiber lasers in medical and industrial domains are summarized. Furthermore, the article emphasizes the current challenges in the advancement of high‐power thulium‐doped fiber lasers (TDFLs) and outlines potential avenues for future development. Despite TDFLs being the predominant laser source in lithotripsy and material processing applications, optimizing their performance and expediting further progress in thulium laser technology remain crucial objectives. This review article aims to provide valuable insights for researchers, engineers, and professionals working in the field of high‐power fiber lasers operating at 2 µm. [ABSTRACT FROM AUTHOR]

Manufacturing thin‐film components is crucial for achieving high‐efficiency and high‐power thermal batteries (TBs). However, developing binders with low‐gas production at the operating temperature range of TBs (400–550 °C) has proven to be a significant challenge. Here, we report the use of acrylic acid derivative terpolymer (LA136D) as a low‐volatile binder for thin‐film cathode fabrication and studied the chain scission and chemical bond‐breaking mechanisms in pyrolysis. It is shown LA136D defers to random‐chain scission and cross‐linking chain scission mechanisms, which gifts it with a low proportion of volatile products (ψ, ψ = 39.2 wt%) at even up to 550 °C, well below those of the conventional PVDF (77.6 wt%) and SBR (99.2 wt%) binders. Surprisingly, LA136D contributes to constructing a thermal shock‐resistant cathode due to the step‐by‐step bond‐breaking process. This is beneficial for the overall performance of TBs. In discharging test, the thin‐film cathodes exhibited a remarkable 440% reduction in polarization and 300% enhancement in the utilization efficiency of cathode materials, while with just a slight increase of 0.05 MPa in gas pressure compared with traditional "thick‐film" cathode. Our work highlights the potential of LA136D as a low‐volatile binder for thin‐film cathodes and shows the feasibility of manufacturing high‐efficiency and high‐power TBs through polymer molecule engineering. [ABSTRACT FROM AUTHOR]

In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as the seed. Both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects have been effectively suppressed by using a long passive fiber between the seed and the amplifier. Based on the fiber amplifier, we have ultimately boosted the narrow linewidth laser from ~40 W to 3.2 kW with a slope efficiency of 85.1% and a 3-dB linewidth of ~0.1 nm. The SRS suppression ratio of the laser is ~29.7 dB at maximum power. Due to our fiber mode control strategies, the beam quality always stays near-diffraction-limited while amplifying, and the measured M2 factor is ~1.4 at the maximum power. Further increase in output power is limited by the SBS effect. [ABSTRACT FROM AUTHOR]

Modular multilevel converters with non-sinusoidal ac voltage output can reduce cost and volume in medium-voltage-connected electric vehicle battery charging applications. The use of full-bridge submodules in such converters enables single-stage ac/ac voltage conversion, allowing a medium-voltage grid to be directly connected to a medium-frequency isolation transformer. The application of a square wave voltage at the medium-frequency transformer's single-phase port enhances the converter's efficiency and power density in comparison to a sinusoidal voltage. This paper presents the analysis and modelling of a modular multilevel converter, comparing its operation with sinusoidal and square wave output voltages. A single control scheme for both output voltage waveforms is proposed for the three-phase and single-phase ac currents, circulating currents, and the energy stored in the submodule capacitors. The control strategy of the three-phase and single-phase port currents is verified through simulation and experiments using a scaled-down prototype, thereby validating its suitability for high-power bidirectional battery chargers. [ABSTRACT FROM AUTHOR]

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For a phased‐array antenna system, position mismatches in spacing distances between source's output and antenna arrays' input ports are common. At present, flexible radiofrequency cables are always utilized to electrically connect those two parts, which will result in the reduced integration. To tackle this problem, a low‐profile aperture converter array (ACA) is first proposed, which is applied between a microwave source and antenna arrays. Each stripline‐structured channel of the ACA is composed of the signal lines with different routing shapes to achieve nearly the same phase shift. In this study, a high‐power and high‐efficiency 16‐channel ACA is designed, fabricated and measured at X‐band. Experimental results show that it meets the requirement of 5‐kW pulse wave input, and the power transfer efficiency of each channel is more than 93.8%. Furthermore, its profile is only 0.42 λ0 ${\lambda }_{0}$ at 9 GHz, which is favorable to transforming the integration of the whole system. [ABSTRACT FROM AUTHOR]

This paper presents a promising winding technique which enables higher power-densities in partially superconducting electrical machines with a slotless stator, e.g., self-supporting windings. Firstly, the formulation for defining the skewing factor of the helical winding is given. Afterwards, the skew angle and how diverse winding configurations can be characterised as a function of this angle is explained, along with different parameters such as the skewing factor, the harmonic content of the magnetomotive force wave in the airgap or the resistance per phase of the winding. The sine-shaped winding, a particular case of helical winding, is shown, with which, thanks to the benefits of the additive manufacturing, a better electromagnetic performance is achieved. Finally, the implementation of the helical winding configuration in a slotless partially superconducting 2 MW high-power and high-voltage electric machine for electric aircraft propulsion is assessed, comparing the machine active part weight and their power density.

In this work we investigate patterned large-active area AlGaAs vertical-cavity surface-emitting lasers (VCSELs) targeting high-power single-transverse-mode emission. As a first step, our in-house 3D electromagnetic vectorial mode solver VELMS is validated against preliminary experimental data. Then, VELMS is applied to implement single-mode operation on VCSELs featuring large-area rectangular oxide apertures. A comparative appraisal of different mode selection strategies based on patterning the outcoupling facet of the device is presented, providing a number of alternatives for a broad audience of technologists.

In light‐emitting diode (LED) illumination (e.g., LED maritime lighting for ships), creating a uniform light environment for optical systems is an important challenge. In this study, we present a high‐power collimating system based on Fresnel lenses, which allows high‐brightness LED illumination in the earlier‐mentioned remote distance. The work presented in this article focuses on improving the power, compacting the optical structure, and promoting the brightness of the spot. To prove the claims, the system with a total power of 1 kW is designed. The system consists of a 27 W LED array, a freeform surface lens array, and a confocal Fresnel lens array. In comparison with the traditional optical system, the optical structure shortens from 390 to 120 mm, and the divergent angle decreases from 3° to 2°$$ {}^{{}^{\circ}} $$. Meanwhile, the illuminance of the system is obtained as high as 230 lx at the near field of 200 m and 3.0 lx at the far field of 1.5 nautical miles. This new method provides a practical and effective way to solve the problem of low power, insufficient illuminance, and long optical structure for LED array illumination, which is suitable for remote illumination and guidance of ships. [ABSTRACT FROM AUTHOR]

Unlike operating PEMFC systems with internal humidification from hydrogen recirculation, fuel cell stack test stations mainly rely on external humidification. Response time in the order of 10s and power over 100 kW are crucial requirements for test stations for vehicle fuel cell stacks. In the present study, a 3D computational fluid dynamics (CFD) model of a swirl spray humidifier is developed to simulate the conjugated heat and mass transfer in such a humidifier. In the model, hot, dry air enters from the bottom portion of the humidifier tangentially and mixes with liquid droplets from a nozzle placed near the middle. A discrete phase model (DPM) is employed to model the atomized droplets. Time variations of the flow structure and humidity distribution are studied. A parametric study with the nozzle parameters on humidifier performance is carried out, showing that optimal humidifier performance can be obtained with a single nozzle and spray temperature at 300 K. The humidity response at the humidifier exit subject to a load change is investigated. The simulation results show that the humidifier's dynamic response time for the baseline case is about 32s, with a steady relative humidity of 95.25% and an evaporation rate of 98.4% at the exit. The present model can guide the future design of fast-response, high-power humidifiers for fuel cell stack test stations. [Display omitted] • A CFD model of a fast-response humidifier for PEMFC test stations is developed. • The flow structure and capabilities of the humidifier are studied. • A parametric study and an investigation of the humidifier's dynamic response are carried out. [ABSTRACT FROM AUTHOR]

Myocardium baseline impedance (BI) is an important factor in ablation effectiveness. This study examined the performance of low-power and long-duration (LPLD), high-power and short-duration (HPSD) ablation at different BIs by computer simulation. A 3D model of the ablation region was constructed for simulation, and in vitro experiments were performed to validate the simulation. Three ablation power and duration configurations of 30 W/30 s, 50 W/10 s, and 90 W/5 s were used for simulation with BI values of 90, 100, 110, 120, 130, and 140 Ω. Roll-off time and ablation volume were measured to evaluate ablation results. The simulation is consistent with the in vitro experiments. When BI is changed from 90 Ω to 140 Ω , the lesion volume over 50 °C with BI of 140 Ω was reduced by 6.3%, 6.7%, and 7.3% for 30 W/30 s, 50 W/10 s, and 90 W/5 s configurations, respectively, and the lesion volume over 100 °C was reduced by 62.8%, 49.7%, and 22.5% under 30 W/30 s, 50 W/10 s, and 90 W/5 s, respectively. Simulation results revealed that HPSD (vHPSD) and LPLD ablation were more affected by changes in BI in the lesion volumes over 50 °C and 100 °C, respectively, and demonstrated that resistive and conductive heating were the main heating effects in HPSD (vHPSD) and LPLD, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Rolling Stock (1002-7602) is the property of Rolling Stock Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To meet the increasing heating needs of the China Fusion Experimental Tokamak Reactor (CFETR), the output power in each Lower Hybrid Current Drive (LHCD) transmission line should be increased from 250 kW to 500 kW. Therefore, a new high-power water load must be developed for the 4.6 GHz 500 kW LHCD system. This paper aims to report the most recent research progress of the water load: aluminum nitride (AlN) ceramic is used as the media material to isolate the water and vacuum, and the radio frequency (RF) simulation results show that the return loss of the water load is less than −25dB at 4.6 GHz over a wide temperature range. Under 500 kW continuous wave (CW) operation, the maximum temperatures of the ceramic and water are separately 67 °C and 62 °C, resulting in thermal deformation of the ceramic of approximately 0.003 mm. Moreover, the AlN water load was tested on the 4.6 GHz 250 kW high-power test bench and found to work well with low reflected power.

In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as the seed. Both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects have been effectively suppressed by using a long passive fiber between the seed and the amplifier. Based on the fiber amplifier, we have ultimately boosted the narrow linewidth laser from ~40 W to 3.2 kW with a slope efficiency of 85.1% and a 3-dB linewidth of ~0.1 nm. The SRS suppression ratio of the laser is ~29.7 dB at maximum power. Due to our fiber mode control strategies, the beam quality always stays near-diffraction-limited while amplifying, and the measured M2 factor is ~1.4 at the maximum power. Further increase in output power is limited by the SBS effect.

Diamond crystals have garnered significant attention for applications in photonics, owing to their characteristics of ultra-high thermal conductivity, extremely broad spectral transmission range, and high Raman gain coefficient. These characteristics are particularly advantageous for the development of high-power, multi-wavelength lasers. In this work, we utilize single crystal diamond as a Raman gain medium, for intracavity wavelength-conversion of emission from a side-pumped, electro-optically Q-switched Nd:YAG module. Cascaded Raman conversion is demonstrated and dual-wavelength, pulsed laser emission at wavelengths of 1.2 μm (first-Stokes wavelength) and 1.5 μm (second-Stokes wavelength) is achieved (with a maximum combined pulse energy of 6.19 mJ). The relative ratio of output energy at the two Stokes orders could be varied by tuning the characteristics of the output coupling mirror and the length of the laser resonator. When operating at maximum pump power, the pulse width of the second-Stokes field was approximately half that of the first-Stokes field (second-Stokes ∼10 ns, first-Stokes ∼18 ns), resulting in maximum peak powers of 174 kW (at 1.2 μm) and 220 kW (at 1.5 μm). To the best of our knowledge, this is the highest reported peak power generated from a dual-wavelength, intracavity diamond Raman laser. This work highlights the diversity and utility of diamond as an effective wavelength-conversion component in high-power lasers, and stands as the current state-of-the-art in high pulse-energy, high peak-power, multi-wavelength intracavity Raman lasers.

Aims The optimal interlesion distance (ILD) for 90 and 50 W radiofrequency applications with low ablation index (AI) values in the atria has not been established. Excessive ILDs can predispose to interlesion gaps, whereas restrictive ILDs can predispose to procedural complications. The present study sought, therefore, to experimentally determine the optimal ILD for 90 W–4 s and 50 W applications with low AI values to optimize catheter ablation outcomes in humans. Methods and results Posterior intercaval lines were created in eight adult sheep using CARTO and the QDOT-MICRO catheter in a temperature-controlled mode. In four animals, the lines were created with 50 W applications, a target AI value ≥350, and ILDs of 6, 5, 4, and 3 mm, respectively. In the other four animals, the lines were created with 90 W–4 s applications and ILDs of 6, 5, 4, and 3 mm, respectively. Activation maps were created immediately after ablation and at 21 days to assess linear block prior to gross and histological analyses. All eight lines appeared transmural and continuous on histology. However, for 50 W-only applications with an ILD of 3 mm resulted in durable linear electrical block, whereas for 90 W applications, only the lines with ILDs of 4 and 3 mm were blocked. No complications were detected during ablation procedures, but all power and ILD combinations except 50 W–6 mm resulted in asymptomatic shallow lung lesions. Conclusion In the intercaval region in sheep, for 50 W applications with an AI value of ∼370, the optimal ILD is 3 mm, whereas for 90 W–4 s applications, the optimal ILD is 3–4 mm. [ABSTRACT FROM AUTHOR]

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The field of ultrafast science has experienced significant growth over the last decade, largely attributed to advancements in optical and laser technologies such as chirped-pulse amplification and high-harmonic generation. The distinctive characteristics of intense ultrafast free-electron lasers (FELs) have introduced novel prospects for investigating molecular dynamics, as well as providing an opportunity to gain deeper insights into nonlinear processes in materials. Therefore, high-power ultrafast FELs can be widely used for both fundamental research and practical applications. This study presents a novel approach for producing high-power femtosecond FEL pulses, utilizing chirped-pulse amplification in echo-enabled harmonic generation. Chirped seed pulses are employed to induce frequency-chirped energy modulation in the electron beam. The generated FEL pulse, which inherits the chirped frequency, can be compressed through the gratings in the off-plane mount geometry to provide ultraintense ultrafast pulses. The numerical modeling results indicate that peak power exceeding 20 GW and a pulse duration in the order of several femtoseconds can be achieved. [ABSTRACT FROM AUTHOR]

The developed spatiotemporal mode‐locked (STML) laser has emerged as an effective platform for investigating high‐dimensional nonlinear spatiotemporal dynamics. Additionally, it offers a novel avenue for the design of fiber oscillators capable of operating at high power levels. At present, the focus of STML laser research primarily revolves around this aspect. However, considering practical applications, there is a strong desire to conceive a simple all‐fiber STML oscillator with both high beam quality and high power. In this study, an all‐fiber, high‐power STML oscillator based on multimode fibers is constructed and investigated. By manipulating the pump power and the polarization state, the laser could operate in a dissipative soliton or noise‐like pulse regime, both with average output powers of two operation states reaching the Watt level. Simultaneously, high‐quality output beam profiles are observed in both operation states. To the best of knowledge, this is the first demonstration of high‐power spatiotemporal mode‐locking with high beam quality. The study holds great benefits for advancing the investigations of compact all‐fiber STML lasers which deliver high‐power outputs with superior beam quality and ultimately propels the application of STML lasers. Furthermore, this study contributes to the understanding of the behavior of STML lasers with high power. [ABSTRACT FROM AUTHOR]

Dielectric capacitors, serving as the indispensable components in advanced high-power energy storage devices, have attracted ever-increasing attention with the rapid development of science and technology. Among various dielectric capacitors, ceramic capacitors with perovskite structures show unique advantages in actual application, e.g., excellent adaptability in high-temperature environments. And the optimization of their energy storage performance has become a hot research topic recently. This review presents the basic principles of energy storage in dielectric ceramics and introduces multi-scale synergic optimization strategies according to the key factors for superior energy storage performance. By summarizing the common points in numerous works, several universal modification strategies are reviewed, and future research on fatigue fracture of ceramic capacitors under multi-field including but not limited to force, electric, and thermal coupling conditions is also anticipated.

This paper presents a high‐power and sharp‐skirt‐selectivity bandpass filter with flexible transmission zero (TZ) and bandwidth. The proposed filter consists of three cascaded dual‐mode resonant cavities and a bandstop resonant structure. The dual‐mode resonant cavity is composed of a substrate‐integrated waveguide structure and a mushroom metal structure, which can implement a controllable bandwidth and generate a TZ for sharp skirt selectivity. Meanwhile, the middle dual‐mode resonant cavity is an oversized waveguide structure to improve power capacity. Moreover, the integrated bandstop resonant structure is used to generate another flexible TZ. The effect of different dimensional mushroom metal structures and bandstop resonant structures are also analyzed in detail. Finally, the proposed structure is fabricated and tested. Simulation results show that the proposed filter has an insertion loss of −1 dB at the passband 8.9–10.7 GHz with two TZs on both sides of the passband. Additionally, the proposed filter can obtain an 11 MW power capacity. Compared with the traditional filters, the proposed filter possesses high‐power and sharp skirt selectivity characteristics, and its position of TZ and bandwidth can be properly adjusted. [ABSTRACT FROM AUTHOR]

High-power optical parametric oscillators (OPOs), as mature radiation sources in mid-infrared (MIR), degenerate gradually with wavelength increase, mainly above 3700 nm. Using a periodically poled magnesium-oxide-doped lithium niobate (MgO:PPLN) as the nonlinear crystal, we build a high-power signal-resonant OPO pumped by ytterbium-doped fiber laser (YDFL). To improve the OPO's output power at ~3.8 μm, the parameters, such as the pump beam's waist diameter and location, the curvature radius of the output coupler and the length of MgO:PPLN, are discussed in detail. When pump power is 79 ± 4 W with a repetition rate of 200 kHz, the OPO provides up to 8 ± 0.4 W average power in beam quality with M2 factors of ~1.84 and ~1.69 in the two axes. Under the highest output power, the center wavelength of the idler beam is 3768.4 nm with a full-width at half-maximum (FWHM) bandwidth of ~18.6 nm. When the output power reaches ~6.3 W, its power stability is 1.6% root mean square (RMS) over 7 h. Further analysis of the factors affecting OPO's performance and simple structure are critically essential for compact OPO prototypes with a capacity of high output power. [ABSTRACT FROM AUTHOR]

This paper presents the design of a 2 MW superconducting electric machine capable of replacing a conventional regional aircraft turbine. The main objective of this work is to advance in the path towards the more-electric aircraft, by incorporating and assessing in the same design technologies such as a superconducting rotor and its cooling by means of helium at cryogenic temperatures, the skewed armature winding or the oil-flooded cooling of the stator, to obtain high specific power density and efficiency values. Although the use of these technologies is well known in the literature, no work is found to implement all of them simultaneously, which poses great challenges both for their subsequent manufacture and later performance. After showing and justifying each element of the design of the electric machine, the electromagnetic performance of the motor and of the superconducting coils is assessed, it is thermally evaluated so that it does not exceed the strict temperature limits and a mechanical analysis of the elements of the motor is also carried out. The main finding of this work is the validation of the proposed model, and that, even though the designed engine is feasible at the proposed power level, the specific power density and efficiency values would improve in the case of upscaling the engine for implementation in larger aircraft.

This paper presents a frequency reconfigurable evanescent-mode cavity-backed slot antenna (ECBSA) with a wide tuning range, high-power handling capability, and simplified manufacturing. The tuning mechanism consists of external long-range linear actuators and a contactless tuner disc to vary the capacitive loading of an evanescent-mode cavity. The antenna’s operating frequency is tuned by changing the cavity’s critical gap size. Radiation occurs through an annular slot aperture on the cavity’s ground plane. The design is realized on a printed circuit board (PCB) using substrate-integrated waveguide (SIW) technology to facilitate easier system integration with other planar circuits. The fabricated prototype of the antenna shows 40% tuning from 1.71-2.58 GHz when the contactless tuner is displaced vertically across a distance of $508~\mu \text{m}$ . Measurement results for the peak realized gain of ECBSA is as high as 5.48 dB at the maximum operating frequency of 2.58 GHz. Due to a larger range of the cavity’s critical gap sizes, achieved using external linear actuators, the power handling capability is higher than the typically used piezoelectric disk tuners in ECBSA design. The proposed antenna also exhibits the largest tuning range among the high-power mechanically-tuned cavity-backed slot antennas presented in the literature.

Background: High-power, short-duration (HPSD) radiofrequency ablation (RFA) may reduce ablation time. Concerns that catheter-mounted thermocouples (TCs) can underestimate tissue temperature, resulting in elevated risk of steam pop formation, potentially limit widespread adoption of HPSD ablation. Objective: The purpose of this study was to compare the safety and efficacy of HPSD and low-power, long-duration (LPLD) RFA in the context of pulmonary vein isolation (PVI). Methods: An open-irrigated ablation catheter with a contact force sensor and a flexible-tip electrode containing a TC at its distal end (TactiFlexTM Ablation Catheter, Sensor EnabledTM, Abbott) was used to isolate the left pulmonary veins (PVs) in 12 canines with HPSD RFA (50 W for 10 seconds) and LPLD RFA (30 W for a maximum of 60 seconds). PVI was assessed at 30 minutes and 28 ± 3 days postablation. Computed tomographic scans were performed to assess PV stenosis after RFA. Lesions were evaluated with histopathology. Results: A total of 545 ablations were delivered: 252 with LPLD (0 steam pops) and 293 with HPSD RFA (2 steam pops) (P = .501). Ablation time required to achieve PVI was >3-fold shorter for HPSD than for LPLD RFA (P = .001). All 24 PVs were isolated 30 minutes after ablation, with 12/12 LPLD-ablated and 11/12 HPSD-ablated PVs still isolated at follow-up. Histopathology revealed transmural ablations for HPSD and LPLD RFA. No major adverse events occurred. Conclusion: An investigational ablation catheter effectively delivered RFA lesions. Ablation time required to achieve PVI with HPSD with this catheter was >3-fold shorter than with LPLD RFA.

Low melting point metals (LMPMs) have greater potential to address the cooling difficulties of high-power airborne equipment than conventional phase change materials (PCMs). However, the heating power in existing LMPM-based heat sinks is generally low. Here, a bismuth-based alloy, Bi44.7Pb22.6In19.1Sn8.3Cd5.3, is adopted. Experiments were conducted in a pin fin heat sink (PFHS) and an empty heat sink (EHS) under 50–1500 W. Experimental results on the effect of PCMs indicate that heat sinks filled with LMPMs outperform n-dodecane. The heating wall temperature is decreased, and the holding time is prolonged significantly. The EHS and PFHS remain below 50 °C from 847 and 1268 s to 2209 and 2302 s at 50 W, respectively. Experimental data illustrate that for LMPM-based heat sinks, the heating wall temperature and holding time are improved by applying pin fins. The EHS and PFHS remain below 50 °C for 143 and 183 s at 500 W, respectively. However, the difference between the holding time below 70 °C for EHS and PFHS is reduced to ±3%. Experimental results reveal that increasing the heating power results in rising heating wall temperature and falling holding time. The holding time of the LMPM-based PFHS decreases from 2302 s at 50 W to 61 s at 1500 W, and the heating power effect weakens from approximately 50% at 100–200 W to approximately 10% at 900–1500 W. Moreover, the Nusselt number (Nu) decreases with increasing dimensionless time, but the decrease is increasingly smaller. A higher Rayleigh number correlated with a larger heating power leads to a higher Nu due to the intensive effect of natural convection. New dimensionless correlations of Nu are developed, yielding mean absolute deviations of 3.5% and 2.7% for the LMPM-based PFHS and EHS, respectively.

High-power ultrasonic transducers need piezoelectric ceramics with a high piezoelectric coefficient, d33, high quality factor, Qm, large coercivity field, EC, high Curie temperature TC , etc, so that they can work in a high electric field for a long time. Here, 0.04Pb (Mn1/3Nb2/3) O3–0.96Pb (Zr0.515Ti0.485) O3-xmol%Nb2O5 (PMN–PZT-x%Nb2O5, x = 0.0–1.0) ceramics with high piezoelectric performance and cost-effective merits were prepared using low-cost industry-grade raw materials. The PMN–PZT-0.6%Nb2O5 ceramic shows the optimal comprehensive electrical properties, such as a high d33 of 411 pC/N, a Qm of 653, a dielectric loss tanδ of 0.30%, a relative permittivity εr of 1457, an electromechanical coupling factor kp of 0.58, a high TC of 355°C, and a large EC of 1.3 kV/mm. Under the electric field of 100 V/mm, the PMN–PZT-0.4%Nb2O5 ceramic shows a large vibration velocity of 0.9 m/s. Since PMN–PZT-x%Nb2O5 ceramics have the merits of high quality, high-cost performance ratio, and easy mass production, they are promising for applications of high-power devices. [ABSTRACT FROM AUTHOR]

The gallium-nitride (GaN) high electron-mobility transistor (HEMT) technology has emerged as an attractive candidate for high-frequency, high-power, and high-temperature applications due to the unique physical characteristics of the GaN material. Over the years, much effort has been spent on measurement-based modeling since accurate models are essential for allowing the use of this advanced transistor technology at its best. The present analysis is focused on the modeling of the scattering (S-) parameter measurements for a 0.25 μm GaN HEMT on silicon carbide (SiC) substrate at extreme operating conditions: a large gate width (i.e., the transistor is based on an interdigitated layout consisting of ten fingers, each with a length of 150 μm, resulting in a total gate periphery of 1.5 mm), a high ambient temperature (i.e., from 35 °C up to 200 °C with a step of 55 °C), a high dissipated power (i.e., 5.1 W at 35 °C), and a high frequency in the millimeter-wave range (i.e., from 200 MHz up to 65 GHz with a step of 200 MHz). Three different modeling approaches are investigated: the equivalent-circuit model, artificial neural networks (ANNs), and gated recurrent units (GRUs). As is shown, each modeling approach has its pros and cons that need to be considered, depending on the target performance and their specifications. This implies that an appropriate selection of the transistor modeling approach should be based on discerning and prioritizing the key features that are indeed the most important for a given application. [ABSTRACT FROM AUTHOR]

A high-power, narrow-linewidth, continuous-wave, thulium-doped fiber laser (TDFL) based on a master-oscillator power-amplifier (MOPA) was experimentally demonstrated. The main oscillator (seed source) yielded 0.64 W of narrow-linewidth laser output at a central wavelength of 1940.32 nm and a 3 dB spectral bandwidth of 0.05 nm. The output narrow-linewidth laser from the main oscillator was amplified by two-stage, cladding-pumped, thulium-doped, all-fiber amplifiers. The main amplifier yielded 26 W of narrow-linewidth laser at a central wavelength of 1940.33 nm. The slope efficiency of the main amplifier was approximately 55.6%. Significant residual pumping light component in the output laser was not observed. During the amplification process, no stimulated Brillouin scattering (SBS) effect, strong amplified spontaneous emission (ASE) effect, and parasitic lasers were observed at the reverse monitoring end. Moreover, the output power was only limited by the incident pump power and the output power had a good stability in a 50 min monitoring period. [ABSTRACT FROM AUTHOR]

This article presents a wideband bias circuit with low parasitic inductance for high-power pulsed amplifiers. The proposed bias circuit works similarly to the traditional bias circuit in that it can ensure the transmission of microwaves from the power amplifier to the load while preventing the transmission of microwaves from the power amplifier to the power supply. By making the bias line shorter and the transmission line wider than the traditional bias circuit, the proposed bias circuit reduces its parasitic inductance. The reduction of parasitic parameters is critical for reducing the drain voltage overshoot of the high-power pulse power amplifier and ensuring its safety. The simulation results demonstrate that the proposed bias circuit has a lower parasitic inductance and a wider bandwidth. To validate the theory and simulation results, the traditional and the proposed bias circuits are fabricated using microstrip circuits. Both the simulation and experimental results indicate that the proposed bias circuit has a one-third lower parasitic inductance than the traditional bias circuit. Furthermore, the proposed bias circuit has a wider bandwidth. [ABSTRACT FROM AUTHOR]

Introduction: The long‐term efficacy of high‐power (50 W) ablation guided by lesion size index (LSI‐guided HP) for pulmonary vein isolation (PVI) in patients with atrial fibrillation (AF) remains undetermined. Our study sought to assess the clinical efficacy of LSI‐guided HP ablation for PVI in patients with AF and explore the potential predictors associated with clinical outcomes. Methods: We consecutively included 186 patients with AF who underwent LSI‐guided HP (50 W) ablation at Fuwai Hospital from June 2019 to October 2021. The target LSI values of 4.5–5.5 and 4.0–4.5 at the anterior and posterior walls, respectively, were used in our study. The baseline clinical characteristics, procedural and ablation data, and clinical outcomes were evaluated. The independent potential predictors associated with AF recurrence were further evaluated. Results: The incidence rate of first‐pass PVI was 83.9% (156/186). A total of 11 883 lesions were analyzed, and compared with posterior walls of pulmonary veins, anterior walls had significantly lower mean contact force (8.2 ± 3.0 vs. 8.3 ± 2.3 g, p =.015), longer mean radiofrequency duration (16.9 ± 7.2 vs. 12.9 ± 4.5 s, p <.001) and higher mean LSI (4.8 ± 0.2 vs. 4.4 ± 0.2, p <.001). The overall incidence of periprocedural complications was 3.7%, and steam pops without pericardial effusion occurred in three patients (1.6%). During a mean follow‐up of 24.0 ± 8.4 months, the overall AF recurrence‐free survival was 87.1% after a single procedure. Patients with paroxysmal AF had a higher incidence of freedom from AF recurrence than those with persistent AF (91.2% vs. 80.8%, log‐rank p =.034). Higher LSI (HR 0.50, p <.001) and paroxysmal AF (HR 0.39, p =.029) were significantly associated with decreased AF recurrence. By receiver operating characteristic analysis, the LSI of 4.7 and 4.3 for the anterior and posterior walls of the PVs had the highest predictive value for AF recurrence, respectively. Conclusion: LSI‐guided HP (50 W) ablation for PVI was an efficient and safe strategy and led to favorable single‐procedure 2‐year AF recurrence‐free survival in patients with AF. Higher LSI and paroxysmal AF were independent predictors of decreased 2‐year AF recurrence. The LSI of 4.7 for the anterior wall and 4.3 for the posterior wall of the PVs were the best cutoff values for predicting AF recurrence after LSI‐guided HP ablation. [ABSTRACT FROM AUTHOR]

Background: Ablation index (AI)-guided ablation for posterior wall isolation (PWI) using high-power, short-duration remains untested. We sought to evaluate the acute outcomes of AI-guided 50 W ablation vs. conventional ablation, and investigate the differences in relationship between contact force (CF), time and AI in both groups. Methods: Consecutive patients undergoing first-time AI-guided ablation with PWI using either 50 W or 35–40 W ablation were enrolled. Acute procedural metrics and individual lesion level ablation data were compared between groups. Results: 40 patients (50 W: n = 20, 35–40 W: n = 20) with atrial fibrillation were included. Total procedure time was significantly reduced with 50 W (120 vs. 143 mins, p = 0.004) and there was a trend toward decreased ablation time (22 vs. 28 mins, p = 0.052). First pass and acute success of PWI were comparable between the 50 W and 35–40 W groups (10 vs. 8 patients, p = 0.525 and 20 vs. 19 patients, p = 1.000, respectively). Individual lesion analysis of all 959 RF applications (50 W: n = 458, 35–40 W: n = 501) demonstrated that 50 W ablation led to lower ablation time per lesion (10.4 vs. 13.0s, p 600 for roof line; AI>500 elsewhere) were more frequently observed in the 50 W group (9.0% vs. 4.6%, p = 0.007). CF had very good discriminative capability for excessive ablation in both groups. At 50 W, limiting the CF to

ABSTRACT: With the development of fuel cells, multi-stack fuel cell system (MFCS) for high power application has shown tremendous development potential owing to their obvious advantages including high efficiency, durability, reliability, and pollution-free. Accordingly, the state-of-the-art of MFCS is summarized and analyzed to advance its research. Firstly, the MFCS applications are presented in high-power scenarios, especially in transportation applications. Then, to further investigate the MFCS, MFCS including hydrogen and air subsystem, thermal and water subsystem, multi-stack architecture, and prognostics and health monitoring are reviewed. It is noted that prognostics and health monitoring are investigated rarely in MFCS compared with previous research. In addition, the efficiency and durability of MFCS are not only related to the application field and design principle but also the energy management strategy (EMS). The reason is that the EMS is crucial for lifespan, cost, and efficiency in the multi-stack fuel cell system. Finally, the challenge and development potential of MFCS is proposed to provide insights and guidelines for future research.

Objective: To study the safety and efficacy of high-power ablation for atrial fibrillation (AF) guided by lesion size index (LSI) and impedance cutoff. Method: A total of 223 patients who underwent radiofrequency catheter ablation of atrial fibrillation (including paroxyparal atrial fibrillation and persistent atrial fibrillation) in the Department of Cardiology of Anhui Provincial Hospital from February 2019 to July 2020 were enrolled, and were divided into 123 patients in the high-power ablation group (HPAI) and 100 patients in the conventional power ablation group (CPAI). The HPAI group adopted high-power (40–50 W) ablation by impedance cutoff, and the CPAI group adopted conventional-power (30–35 W) ablation. Patients in both groups were ablated guided by the same LSI. For both groups, we analyzed the pulmonary vein single-circle isolation rate, ablation time, X-ray exposure, impedance drop value, incidence of complications, and recurrence rate within one year after operation. Results: There was no significant difference in the success rate of pulmonary vein single-circle isolation, X-ray perspective time, and X-ray exposure quantity between the HPAI group and the CPAI group (88.60% vs 82.00%, P = 0.161; 8.7 ± 3.74 min vs 7.82 ± 3.86 min, P = 0.067; 54.74 ± 28 min vs 52.78 ± 39.58 min, P = 0.139); the annular pulmonary vein ablation time and total ablation time were less in the HPAI group (35.74 ± 7.25 min vs 65.49 ± 7.34 min, P

Objective: The purpose of this study was to evaluate the difference in effectiveness and safety of high-power, short-duration (HPSD) radiofrequency catheter ablation (RFA) guided by relatively low ablation index (AI) values and conventional RFA in paroxysmal atrial fibrillation (PAF) patients. Methods: The HPSD RFA strategy (40–50 W, AI 350–400 for anterior, 320–350 for posterior wall; n = 547) was compared with the conventional RFA strategy (25–40 W, without AI; n = 396) in PAF patients who underwent their first ablation. Propensity-score matching analyses were used to compare the outcomes of the two groups while controlling for confounders. Results: After using propensity-score matching analysis, the HPSD group showed a higher early recurrence rate (22.727% vs. 13.636%, p = 0.003), similar late recurrence rate, and comparable safety (p = 0.604) compared with the conventional group. For late recurrent atrial arrhythmia types, the rate of regular atrial tachycardia was significantly higher in the HPSD group (p = 0.013). Additionally, the rate of chronic pulmonary vein reconnection and non-pulmonary vein triggers during repeat procedures was similar in both groups. Conclusions: For PAF patients, compared with the conventional RFA strategy, the HPSD RFA strategy at relatively low AI settings had a higher early recurrence rate, similar long-term success rate, and comparable safety. [ABSTRACT FROM AUTHOR]

Background: For patients with persistent atrial fibrillation (AF), whether linear ablation should be performed remains controversial, and the efficacy and safety for ablation index (AI)-guided high-energy linear ablation of mitral isthmus (MI) and left atrial (LA) posterior box isolation is still unclear. The aims of this study were to assess the feasibility and clinical success rate of pulmonary veins isolation (PVI) combined with linear ablation of LA roof and posterior inferior (posterior wall isolation) and MI compare with the PVI-alone method in patients of persistent AF. Methods and results: 362 consecutive persistent AF patients were enrolled from two electrophysiology centers. A total of 200 cases were in PVI-plus group and 162 cases were in PVI-alone group. The PVI-alone group received wide circumferential isolation of both ipsilateral pulmonary veins. PVI combined with linear ablation of left atrial posterior wall isolation (LAPWI)and MI were performed in the PVI-plus group. The primary study end point was the first recurrence of an atrial arrhythmia. After 24 months, freedom from the primary endpoint was achieved in 73.5% of the patients in the PVI-plus group and 62.5% in the PVI-alone group (hazard ratio = 0.62, 95% confidence interval: 0.43–0.91, log rank p = 0.012). The procedure-related complication rates were 2.5% in PVI-plus group and 1.9% in PVI-alone group (p = 0.808). Conclusion: In this study, the ablation strategy of ablation (PVI plus linear ablation of mitral isthmus and posterior box isolation) was feasible and safe for persistent AF patients. Compared with the PVI-alone method, it improved outcomes in patients with persistent AF. [ABSTRACT FROM AUTHOR]

The past two decades have seen an increasing interest in Hall thrusters in space propulsion, thanks to their favorable performance characteristics with respect to a wide variety of missions of current and future interest and to the significant extension in operational life potential achievable with magnetic shielding. Nevertheless, the physics underlying their behavior is complex and not yet fully understood, limiting the practical applications of models based on first principles due to their inability to self-consistently predict the device performance. Fortunately, modern Hall thrusters were developed through a lengthy process of gradual refinement, and thus they represent convenient reference devices to design new thrusters using appropriately defined scaling criteria. The objective of this work is to propose a new scaling methodology, especially intended for magnetically shielded high-power Hall thrusters. To this purpose, a novel phenomenological model for shielded thrusters is presented and discussed. This model includes free coefficients, whose values are chosen based on the agreement with the empirical data collected in a specially created high-power Hall thruster database. The proposed methodology features a new reference thruster and aims at keeping unchanged its main plasma intensive parameters in a scaling transformation. The possibility of creating performance maps at constant discharge power, which show how the scaling results vary with the channel dimensions, is also proposed as a preliminary design tool. [ABSTRACT FROM AUTHOR]

The field of ultrafast science has experienced significant growth over the last decade, largely attributed to advancements in optical and laser technologies such as chirped-pulse amplification and high-harmonic generation. The distinctive characteristics of intense ultrafast free-electron lasers (FELs) have introduced novel prospects for investigating molecular dynamics, as well as providing an opportunity to gain deeper insights into nonlinear processes in materials. Therefore, high-power ultrafast FELs can be widely used for both fundamental research and practical applications. This study presents a novel approach for producing high-power femtosecond FEL pulses, utilizing chirped-pulse amplification in echo-enabled harmonic generation. Chirped seed pulses are employed to induce frequency-chirped energy modulation in the electron beam. The generated FEL pulse, which inherits the chirped frequency, can be compressed through the gratings in the off-plane mount geometry to provide ultraintense ultrafast pulses. The numerical modeling results indicate that peak power exceeding 20 GW and a pulse duration in the order of several femtoseconds can be achieved.