The revitalization of vitality in historic cultural districts can enhance a city’s cultural attractiveness and promote the upgrading of the urban cultural industry and sustainable development. Revealing the threshold and synergistic effects of different districts’ scene elements on district vitality helps to identify the distribution patterns of district vitality and provides a basis for managerial decision-making. This study first uses a geographic information system (ArcGIS) to overlay Baidu heatmaps with the street-network distribution in order to depict the spatiotemporal heterogeneity of district vitality and to compute vitality values by partitions at the district scale. Subsequently, based on an explanatory framework that integrates the physical space and subjective cognition, multi-source data such as street-view panoramas and points of interest (POIs) are quantified to obtain scene-element values for each unit area. Then, the scene-element values and vitality values are integrated into a consolidated database. Additionally, the LightGBM model and the SHAP method are employed to evaluate each element’s marginal contribution and relative importance to district vitality, thereby screening out the key scene elements. Finally, by means of SHAP dependence plots and interaction-effect analysis, the threshold intervals of the key elements and their synergistic relationships are identified, revealing the nonlinear threshold effects and synergies by which scene elements influence spatial vitality. The results show that during rest days, district vitality exhibits stronger diffusion, and the synergistic effect between Leisure-Facility Attractiveness and Street-Network Accessibility is the most prominent in enhancing vitality. High Exhibition-Facility Attractiveness is difficult to sustain crowds on its own; only when Leisure-Facility Attractiveness is likewise high does its effectiveness increase significantly. When Transport Accessibility is within the 0.20–0.40 interval, the positive effect of Leisure-Facility Attractiveness is significantly amplified. An excessive Traditional–Modern Facility Mix readily leads to homogenization of districts; therefore, when introducing modern business formats, local cultural characteristics must be retained. Overall, the generation of district vitality relies more on the synergy between material factors and subjective cognition than on improvements to any single element. The findings of this study provide suggestions for the planning of scene elements and the enhancement of vitality in historic cultural districts.

Aluminum nitride (AlN) ceramics are widely used in high-power electronic packaging and thermal management applications owing to their excellent thermal conductivity and electrical insulation properties. However, their high hardness and intrinsic brittleness make them susceptible to severe surface and subsurface damage during precision grinding, which can significantly degrade component reliability. In this study, the effects of abrasive grit size on the surface integrity of AlN ceramics were systematically investigated using diamond grinding wheels with grit sizes of 325#, 600#, 1500#, and 5000#. The results demonstrate that both surface roughness and subsurface damage depth decrease monotonically with increasing abrasive grit size. A clear transition in material removal mechanism is observed, from crack-dominated brittle fracture at coarse grit sizes to plastic deformation dominated by dislocation activity at ultra-fine grit sizes. These findings provide a comprehensive understanding of grinding-induced damage evolution in AlN ceramics and offer practical guidance for optimizing grinding processes to achieve low damage and high reliability.