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The heterocharge accumulated in the oil‐paper insulation system of the converter transformer will enhance the local electric field and cause insulation deterioration. Numerical simulation is an effective method to analyze heterocharge. Currently, the numerical simulation of heterocharge is mainly based on the bipolar charge transport (BCT) model and the impurity ion transport (IIT) model. However, the effects of temperature, conductivity, and thickness of oil‐impregnated paper on charge transport have not been considered in these models. In view of this, a modified charge transport (MCT) model by introducing the Maxwell–Wagner model and heat conduction equation is proposed in this paper based on the BCT model and IIT model. Then, the influence of multi‐factors (temperature gradient, moisture content, and oil‐impregnated paper thickness) on heterocharge accumulation is investigated by using the MCT model. The simulation results obtained by the MCT model are more consistent with the experimental results than the BCT model, which proves the accuracy and superiority of the MCT model. Moreover, the increase in temperature gradient, moisture content, and oil‐impregnated paper thickness will enlarge the ion dissociation rate, conductivity, and trap density, and thus promote the generation of heterocharge. In that respect, the MCT model is expected to optimize the insulation design and provide a reference for space charge dynamic simulation. [ABSTRACT FROM AUTHOR]

The accuracy and feasibility of the traditional XY model of transformer oil–paper insulation system are disputable since it ignored the effect of non‐uniform aging and conductance on dielectric response property. Given this issue, this work attempted to report a modified XY model to overcome these defects. The novelty of this work is in the exploration of the modified XY model as a potential tool for establishing the quantitative correlation among the complex relative permittivity of the liquid insulation, solid insulation, and liquid–solid composite insulation. In that respect, the presented verification experiments proved the feasibility and accuracy of the reported model. The contributions are expected to provide a theoretical basis for the condition evaluation of transformer solid insulation under non‐uniform aging conditions. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) materials have unique structural and optoelectronic properties and have very important applications in energy, environment, and high‐performance optoelectronic sensing. Among them, the nonlinear optical properties and related applications are hot research fields. Herein, a novel 2D Bi2Te3–FeTe2 heterostructure is successfully prepared by Fe3+ induction and site‐selective overgrowth using a seed‐mediated growth method. This heterostructure has a plate−satellite geometry with an open spatially separated surface. The Z‐scan measurement characterizes the nonlinear transmittance of the heterostructure and proves the broadband saturation absorption behavior experimentally, which are superior to those of some mainstream 2D materials. In addition, the femtosecond‐transient absorption spectra reveal an ultrashort recovery time of 1.7 ps at pump wavelength of 780 nm. By integrating the Bi2Te3–FeTe2 saturable absorber into fiber laser, a 164.7‐ps pulse and a 481‐fs pulse are produced at center wavelengths of 1064 and 1550 nm, respectively, which are better than that of the Bi2Te3 nanoplate‐based mode‐locking. A new approach for the synthesis of 2D composites with spatially separated structures is provided. It is demonstrated that the synthesized Bi2Te3–FeTe2 heterojunction can be a promising broadband nonlinear optical material in ultrafast optical applications. [ABSTRACT FROM AUTHOR]

In this paper, we introduce the notion of a left-symmetric algebroid, which is a generalization of a left-symmetric algebra from a vector space to a vector bundle. The left multiplication gives rise to a representation of the corresponding sub-adjacent Lie algebroid. We construct left-symmetric algebroids from [ABSTRACT FROM AUTHOR]

The ageing rate of cellulose insulation materials (paper/pressboard) in oil‐impregnated transformers is largely determined by moisture. In this paper, several experiments were conducted under controlled laboratory conditions to quantitatively diagnose the amount of moisture in cellulose insulation using frequency domain spectroscopy (FDS) technique, which has been proven to be an effective tool to predict the insulation condition in oil‐impregnated power equipment. The frequency dielectric response in oil‐impregnated pressboards, moisture content as well as test temperature, was monitored carefully, and a new dielectric characteristic parameter for the diagnosis of moisture content was proposed. In addition, the master curve technique was introduced to calibrate the temperature effect on FDS measurement results. These experiments revealed that a strong correlation exists between frequency dielectric parameter and moisture content in cellulose insulation. Such correlation can be utilised for better prediction of moisture content in paper–oil insulation. A modified assessment method for the diagnosis of moisture content in paper–oil insulation was investigated and its effectiveness was also demonstrated using a case. [ABSTRACT FROM AUTHOR]

To advance the utilization of dune sand, a sustainable albeit flawed resource, for structural engineering, the incorporation of graphene oxide (GO) is suggested as a potential means for improving durability of dune sand cementitious composites (DSCC). In this study, DSCC samples with varying GO concentrations were prepared. The effect of GO on the freeze–thaw resistance of DSCC was then studied by freeze–thaw cyclic test and mechanical test. In addition, to elucidate the mechanism underlying the observed enhancement in freeze–thaw resistance due to GO incorporation, thermogravimetric, mercury injection, adsorption, and morphological analyses were performed. The experimental results showed that incorporating GO into DSCC can enhance its freeze–thaw resistance without compromising its mechanical properties. The weight loss and relative dynamic modulus of elasticity of the specimen with 0.06 wt% GO decreased by 92.83% and 64.96%, respectively, as well as the compressive strength increased by 22.76% after 150 freeze–thaw cycles compared with the control specimen. The enhancing effect of adding GO on the freeze–thaw resistance of DSCC was found to be attributed to the promotion of hydration and the control of internal structure. Notably, the modification of GO on the smooth dune and the reinforcement of GO on the interface between dune sand particles and cement matrix was identified, which may be the new evidence for testifying the GO enhancement on the freeze–thaw resistance of dune sand cementitious composites. [ABSTRACT FROM AUTHOR]

In recent years, MXene has become a hotspot because of its good conductivity, strong broadband absorption, and tunable band gap. In this contribution, 0D MXene Ti3C2Tx quantum dots are synthesized by a liquid exfoliation method and a wideband nonlinear optical response from 800 to 1550 nm is studied, which have a larger nonlinear absorption coefficient β of –(11.24 ± 0.14) × 10–2 cm GW–1. The carrier dynamic processes of 0D MXene are explored with ultrahigh time resolution nondegenerate transient absorption (TA) spectroscopy, which indicates that the TA signal reaches its maximum in 1.28 ps. Furthermore, 0D MXene is used to generate ultrashort pulses in erbium or ytterbium‐doped fiber laser cavity. High signal‐to‐noise (72 dB) femtosecond lasers with pulse durations as short as 170 fs with spectrum bandwidth of 14.8 nm are obtained. Finally, an ultranarrow fiber laser based on 0D MXene is also investigated and has a full width at half maximum of only 5 kHz, and the power fluctuation is less than 0.75% of the average power. The experimental works prove that 0D MXene is an excellent SA and has a promising application in ultrafast and ultranarrow photonics. [ABSTRACT FROM AUTHOR]

A new member of the IV–V compounds, germanium–phosphorus (Ge–P) compounds, has been shown in experiment and theory to have a tunable bandgap (Eg), excellent chemical stability, strong in‐plane anisotropy, and wide‐range optical absorption, all indicating a promising future in electronic and optoelectronic applications. In this work, the application potential of Ge–P compounds as nonlinear optical (NLO) materials in ultrafast photonics is studied for the first time. The strong light–matter interaction, broad and tunable Ep, and broadband and strong optical response make GeP a likely NLO material for photonics, especially in infrared photonic devices. In addition, 2D GeP nanosheets are mixed with poly(vinylidene fluoride) (PVDF) to obtain a GeP@PVDF composite film, which further improves the stability of the GeP and, for the development of organic photonic devices, helps to slow its degradation. From Z‐scan data and fitting results, it is found that GeP has an excellent broadband NLO response. Moreover, using the GeP@PVDF composite film as a saturable absorber, a high‐stability femtosecond laser with a 722 fs pulse width is obtained in the telecommunications band. Preliminarily, Ge–P compounds display excellent optical properties suggesting that they may be used as NLO materials in advanced photonic devices. [ABSTRACT FROM AUTHOR]

All‐optical modulators, where one light modulates the parameters of another light (intensity, phase, frequency, etc.) without external electronic control, have drawn extraordinary attention in all‐optical information processing. In this contribution, by taking advantage of the two‐pass structure of Michelson interferometer and the strong photothermal conversion efficiency of MXene nanomaterials, an all‐optical modulator is demonstrated with a modulation depth of >27 dB, a free spectrum range of 16.8 nm and a pump‐induced phase shift slope of 0.043 π mW−1. Moreover, the all‐optical modulator is successfully employed to switch on/off the intensity of the signal light and load information from one channel to another with comparable response time and baudrate. It is believed that the MXene‐based all‐optical modulator will open a door to practical applications of 2D materials‐based all‐optical devices in all‐optical signal processing. [ABSTRACT FROM AUTHOR]