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Multiwindow discrete Gabor transform (M-DGT) is applied to present the Gabor time–frequency representation for transient signals (exponentially damped sinusoidal signals) with high time–frequency resolution. Due to the limitation of the constrained time–frequency localization governed by the Heisenberg uncertainty principle, using a wider analysis window in time domain will lead to the Gabor time–frequency spectrum (or representation) with higher frequency resolution but poor time resolution for the transient signals, and using a narrower analysis window in time domain will result in the Gabor time–frequency spectrum (or representation) with higher time resolution but poor frequency resolution for the transient signals. To obtain the Gabor time–frequency representation with both higher frequency resolution and higher time resolution, the above two spectra can be combined by geometric average. The experimental results show that the combined Gabor time–frequency representation for the transient signals has higher time–frequency resolution than that obtained when only the single analysis window is used in the traditional discrete Gabor transform.

Self-assembly of lead halide perovskite nanocrystals (NCs) into close-packed, long-range-ordered nanostructures can effectively modulate their photoelectronic properties, yet significantly challenging. Herein, an efficient approach is reported to induce the hierarchical self-assembly of perovskite CsPbBr 3 NCs by phase transition using chiral cysteine ligands, yielding asymmetric Cs 4 PbBr 6 nanorods (NRs) with the circularly polarized luminescent response. An interfacial phase transition process is found during the conversion of CsPbBr 3 nanocubes to Cs 4 PbBr 6 NCs initiated by cysteine molecules. Then the Cs 4 PbBr 6 NCs aggregate sequentially to form nanoclusters, which further self-assemble into the chiral Cs 4 PbBr 6 NRs. Molecular dynamics simulations reveal that the Cs 4 PbBr 6 nanochains gradually approach each other to achieve an asymmetric structure, and the simulated circular dichroism spectrum further supports the formation of a chiral structure. This work offers a facile method for the hierarchical chiral self-assembly of lead halide perovskite nanostructures, which brings new insights to explore chiral nanostructures by modulating the surface chemistry and post self-assembly.

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Vegetable freshness evaluation is of great significance to ensure the quality of vegetables and realize fine production. Existing vegetable freshness evaluation methods have difficulty realizing rapid online evaluation and industrial applications due to such disadvantages as being susceptible to subjective factors, complicated operation, large computation, and high hardware cost. To solve the above problems, a rapid online vegetable freshness evaluation method was developed based on the single turnover chlorophyll fluorescence parameters F o ′ , F v ′ / F m ′ and σ P S I I ′ . A freshness evaluation model for spinach and swamp cabbage was established based on a classification and regression tree algorithm, using F o ′ , F v ′ / F m ′ and σ P S I I ′ as sample features. The model divided the freshness of spinach and swamp cabbage into three grades: good, medium, and poor, and the leave-one-out cross validation results showed that the freshness evaluation accuracies of spinach and swamp cabbage reached 98.1% and 94.3%, respectively.