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When partial discharge occurs within transformers， the pulse current signal propagates along the winding. Detecting this pulse current signal at both ends of the winding enables the identification of partial discharge within the transformer. To this end， a wideband equivalent circuit model for the transformer is established. In high-voltage windings where partial discharges are likely to occur， partial discharge pulses are applied between different wound disks and the ground to simulate the discharge to the ground at different locations of the high-voltage winding. Pulse current signals are then collected at the end screen of the high-voltage casing and at the neutral point to study the propagation rules of the partial discharge pulse current signal at different locations within the transformer windings. Through calculations， it is observed that the energy ratios of pulse current signals in two distinct frequency bands are linearly correlated with the distance ratio of pulse current propagation， and the maximum error observed in this context is 9.80 wound disks. This method facilitates localization of partial discharge within the transformer， and the results of field experiment subsequently validate the effectiveness of this localization technique.

The construction of the teaching resources sharing platform provides high-quality teaching resource retrieval and browsing channels for teachers and students in schools and the majority of off-campus users. This paper combines the functional objectives of the sharing platform design, analyzes the functional requirements of the sharing platform, and designs the overall functional framework of the platform with the advantage of cloud platform technology architecture. Gagne's classification theory of learning results is used to categorize vocal music teaching resources. Blockchain copyright protection technology has been selected to manage the digital resources of vocal music and optimize the privacy protection of users and resource copyright information. Design a user-friendly interface, update the learning interest model using the user interest model, form a personalized recommendation model based on students’ learning interests, and design a sharing scheme for vocal music teaching resources. Test the response performance of blockchain copyright protection and analyze the service impact of a college vocal music teaching resource-sharing platform from the perspective of learning support service. Most of the students have learning communities in the learning process, and the learning communities give the learners a “common identity” and emotional support services so as to achieve the purpose of the construction of a college vocal music teaching resources sharing platform.

The two-phase operation mode of a flexible low-frequency transmission system is based on the M3C （modular multilevel matrix converter）. This paper establishes a complex sequence network for the low-frequency system to analyze the steady-state operation characteristics of low-frequency transmission lines and M3C under the conventional control strategy. The analysis shows that： 1） There appears zero-sequence current that shares equal amplitude and opposite phase of the positive-sequence current in transmission lines； 2） The zero-sequence voltage and negative-sequence voltage can also appear in the transmission lines； 3） There is an unbalanced capacitor voltage between M3C sub-converters with fixed power control on the low-frequency side and negative sequence current suppression strategy； 4） There is a double frequency oscillation component in the M3C average capacitor voltage. A simulation model of the dual-terminal flexible low-frequency transmission system is built in PSCAD/EMTDC， and the correctness of the obtained conclusions is verified.

Propulsion performance produced by laser ablation of polymer made of acrylonitrile butadiene styrene is experimentally investigated using the first, second, and third harmonics of a Nd: YAG laser. A ballistic pendulum is employed to assess the impulse and coupling coefficient for laser propulsion application. Fast photography, target ablation, and optical emission spectroscopy are proposed to analyze the energy coupling characteristic. The impulse and coupling coefficient under different pressures are demonstrated to depend on the target ablation and plasma properties which are relevant to laser wavelength. As the laser wavelength decreases, the crater depth and ablation mass are enhanced. Meanwhile, the plasma plume separates at atmospheric pressure and its length extends continuously in the low-pressure range. As a result, plasma including more ejected particles with higher velocity contributes to obtaining excellent impulse and coupling coefficient. In addition, the decreased electron density and temperature indicate higher collision frequency and photoionization dominate rather than inverse bremsstrahlung absorption at shorter laser wavelengths. This work provides a better understanding of the energy conversion mechanism and a reference for improving propulsion performance. [ABSTRACT FROM AUTHOR]

Ferrohydrodynamic pumps, with their compact design, offer a practical and efficient alternative to traditional pneumatic or mechanical pumps for driving microfluidic channels and fluidic devices, eliminating mechanical vibrations. A novel self‐circulating ferrohydrodynamic system has been developed to remotely control fluid flow within a linear acoustic cavity using a laser‐induced photothermal temperature gradient. This system enables the modulation of fluid flow rates in compact channels through adjustments in a D.C. magnetic field or laser‐induced surface temperature changes. Notably, laser intensity can accelerate, decelerate, or reverse flow rates within the channel, influencing ultrasonic waves propagating through fluidic cavities designed to resonate between 500 kHz and 700 kHz. The dynamic nature of the magnetoactive fluid cavity enhances wave‐matter interactions, particularly in acoustic domains. Laser‐induced flow control allows for precise manipulation of ultrasonic wave characteristics such as frequency, amplitude, mode splitting, phase shifting, and unidirectional transmission. This capability also supports the optical regulation of acoustic energy flow rates by halting or reversing fluid motion within the cavity. These advancements hold significant potential for applications in cavity acoustodynamics and underwater signal processing, promising innovations in remote fluidic control and acoustic modulation technologies. [ABSTRACT FROM AUTHOR]

The principle of the conventional ultrasound test states that the detectable voids cannot be smaller than the acoustic wavelength. However, by using effective medium approximation, the fraction of small voids can be estimated by the variation of the effective density. In this study, a non-contacting ultrasound-based porosity fraction mapping methodology is developed for estimated small voids in coal with long operating wavelength in air. This novel ultrasonic technique based on the mechanical properties of coal offers a rapid scan of the effective density mapping and distribution of void fraction over a large sample area, which overcame the limitation of small voids detection in the conventional ultrasound testing. [ABSTRACT FROM AUTHOR]