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In order to distinguish the influences of moisture and aging on the frequency domain dielectric response of oil-paper insulation and better apply frequency domain spectroscopy (FDS) to assess the insulation condition of power transformers, the oil-paper insulation samples with different moisture contents and different aging states were prepared in the laboratory. The FDS of the samples were tested and a group of characteristic parameters were extracted from dissipation factor (tanδ) curves which could be used to assess the moisture content and aging states of oil-paper insulation respectively. The quantitative relationship among characteristic parameters, degree of polymerization (DP) and moisture contents (K m.c ) was accurately established. The observations show that the proposed characteristic parameters are sensitive to the moisture in 10 -3 -10 2 Hz, while the aging states influence the characteristic parameters in 10 -3 -10 -1 Hz. Meanwhile, an exponential relationship equation which could be used to assess the oil-paper insulation condition was established among the characteristic parameters, DP and the moisture content. Finally, the evaluation technique proposed in this paper was used to diagnose the insulation condition of several field transformers in this way, and its validity was preliminary and reasonably verified.Index Terms -Frequency domain spectroscopy, oil-paper insulation, moisture content, aging state, dissipation factor, quantitative analysis.

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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 Ti 3 C 2 T x 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 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.

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.

In this paper, a set of dissolved gas analysis (DGA) new feature combinations is selected as input from the mixed DGA feature quantity, and an improved krill herd (IKH) algorithm optimized support vector machine (SVM) transformer fault diagnosis model is established to solve the problem that the single characteristic gas or characteristic gas ratio, which are utilized as the DGA feature quantity cannot fully reflect the transformer fault classification. The following work has been done in this paper: 1) IEC TC 10 fault data and other 117 sets of fault data in China are preprocessed in order to reduce the influence on the diagnosis results causing by the edge data in the fuzzy area; 2) the SVM parameters and 11 features are encoded by a binary code technique; 3) a preferred DGA feature set for fault diagnosis of power transformers is selected by genetic algorithm (GA) and SVM, and; 4) IKH is utilized to optimize the parameters of SVM. Combining with cross-validation principle, a transformer fault diagnosis model based on IKH algorithm to optimize SVM is established. The fault diagnosis results based on the new fault sample show that the proposed DGA feature set to increase the accuracy by 26.78% and 10.83% over the DGA full data and IEC ratios. Moreover, the accuracy of IKHSVM is better than the GASVM, back-propagation neural network (BPNN), and particle swarm optimization optimized support vector machine (PSOSVM), the accuracy rates are 85.71%, 75%, 64.29%, and 71.43%, which proves the validity of the proposed fault diagnosis model. INDEX TERMS Power transformers, fault diagnosis, support vector machine, improved krill herd algorithm, DGA feature.

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In this paper, we introduce a 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 O-operators on Lie algebroids. We study phase spaces of Lie algebroids in terms of left-symmetric algebroids. Representations of left-symmetric algebroids are studied in detail. At last, we study deformations of left-symmetric algebroids, which could be controlled by the second cohomology class in the deformation cohomology.