This study aims to quantify the shear surface morphology of jointed rock and its evolution under shearing, cyclic freezing, and thawing using the Gaussian filtering method. Gaussian filtering method enables the construction of the (large-scale) waviness surface and the (small-scale) unevenness surface of a digitized surface (created by laser scanning). Both waviness and unevenness surfaces are then quantified by roughness coefficient ratio (S) and degradation degrees of the waviness surface (D_w) and unevenness surface (D_r). These (microscopic) morphological parameters (S, D_w and D_r) are subsequently used to explain the development of the (macroscopic) shear strength of the jointed rocks on direct shear tests. The results indicate that compared with fresh jointed rocks, the freezing and thawing causes the potential shear surface asperities to be easier to damage and fail under shear load. Such damage is well represented by the significant decrease in D_w and D_r. On the other hand, with the increase of the freeze-thaw cycle (N), D_w increases while D_r reaches the maximum at an early stage of the cycle, where D_r > D_w. This difference reveals the underlying shear mechanism microscopically; that is, in the initial stage, the shear surface morphology is mainly dominated by the unevenness surface D_r, and then it is controlled by the waviness surface D_w during the freeze-thaw cycle.

The primary aim of this study was to investigate the boron leaching process from alkali-activated ludwigite ore. Initially, the ore underwent activation through roasting at 1050 °C for 60 min with 20% sodium carbonate. Subsequently, the study examined the influence of leaching parameters, including temperature, time, liquid-to-solid ratio, and particle size, using the activated ore as the raw material. Additionally, water leaching characteristics of the residues and boron kinetics were analyzed. The results demonstrated that boron leaching efficiency reached 93.71% from the reduced ludwigite ore under specific conditions: leaching temperature of 180 °C, leaching time of 6 h, liquid-to-solid ratio of 8:1, and feed particle size of 52.31 μm (average particle size). Leach residue characteristics indicated the dissolution of minerals during the process. The boron behavior during water leaching followed the Avrami Equation, and the kinetics equation was derived by fitting the leaching data. Moreover, the activation energy (E_a) value for boron leaching was determined to be 8.812 kJ·mol⁻¹ using the Arrhenius Equation, indicating that the leaching process is controlled by diffusion.

Introduction: Rapid urbanization and industrialization in Xi’an have precipitated a sharp conflict between spatial expansion and environmental conservation, necessitating a rigorous spatiotemporal assessment of regional ecological quality. Methods: This study evaluates the eco-environmental quality of Xi’an’s main urban area from 2021 to 2024 by synergizing the Remote Sensing Ecological Index (RSEI) with advanced spatial statistical models, including Geodetector and spatial autocorrelation algorithms. Specifically, the Coefficient of Variation (CV) is introduced to quantify the temporal stability and volatility intensity of ecological quality under top-down policy interventions. Results: Empirical results indicate that: (1) The region exhibited a generally stable trajectory, with approximately 65% of the study area maintaining a steady state. Notably, the proportion of areas showing slight improvement consistently surpassed those exhibiting degradation, signaling a cessation of historical decline; (2) Spatiotemporal stability analysis identifies a distinct “Matrix-Spot” configuration via the CV metric, characterized by a dominant low-volatility background punctuated by discrete, spatially confined high-volatility anomalies. This structure confirms that anthropogenic perturbations remained localized, preventing the propagation of systemic instability; (3) Pronounced spatial heterogeneity was corroborated by Global Moran’s I indices consistently exceeding 0.79. This distribution is predominantly characterized by high-high (H-H) clusters in ecological barriers and low-low (L-L) agglomerations in central districts, with minimal transitional patterns; (4) Factor detection identified Land Use/Land Cover change as the primary determinant of ecological differentiation. Furthermore, interaction analysis elucidated a significant “Enhancement Effect” between Land Use/Land Cover and temperature, highlighting the amplification of climatic sensitivity by urbanization. Discussion: These findings provide empirical evidence for the “immediate efficacy” of strategic interventions such as the “14th Five-Year Plan” and Ecological Red Lines. The observed “policy-driven resilience“ demonstrates that state-led governance has effectively buffered the negative externalities of rapid urban development within a constrained temporal window.

The instability and collapse of surrounding rock in mine goaf areas often lead to the destabilization of geological structures, surface subsidence, and mining safety accidents. To investigate the evolutionary mechanisms and precursor characteristics of rock instability and failure processes, uniaxial loading and cyclic loading–unloading tests were conducted on red sandstone using a rock mechanics loading system. These experiments aimed to explore the mechanical behavior of the rock and the development process of internal fractures. The characteristics of infrasonic signals generated during red sandstone fracturing and the laws governing damage evolution were analyzed with an infrasonic acquisition system. The research results indicate that the infrasonic signal activity generated by rock under loading conditions can be characterized by three distinct stages, namely the relative stability period, the active period, and the pre-failure precursor period. Prior to peak strength, a substantial number of infrasonic signals are generated in rocks with significant activity; this characteristic is independent of the loading path but dependent on the stress magnitude. The variation in cumulative infrasonic energy reflects the accumulation of damage in rock specimens during the loading process, and as damage accumulates, the stress–strain curve exhibits hysteresis effects and nonlinear increases, accompanied by a rapid rise in infrasonic energy. By analyzing the characteristics of infrasonic parameters and characterizing the damage and its evolutionary features in red sandstone based on infrasonic energy, the internal crack damage evolution process in rocks can be effectively characterized. This approach provides theoretical foundations and technical support for early warning and monitoring prior to rock failure.