东北林业大学

Anthropogenic activities have concurrently increased atmospheric nitrogen (N) deposition and altered forest litterfall dynamics, both of which can profoundly influence soil microbial communities. The individual influence of these two factors on soil microorganisms is extensively investigated, whereas their interactive effect remains poorly understood. To address this gap, a 10-year full-factorial experiment with N addition (control and 10 g N m–2 yr–1) and litter manipulation (removal, ambient, and addition) was conducted in a Pinus sylvestris var. mongolica plantation. We measured 10 variables related to soil acid-base status and N availability, and assessed soil microbial biomass and community composition using phospholipid fatty acid analyses. Results revealed that chronic N addition reduced soil bacterial and fungal biomass, as well as reshaped microbial communities. These changes in soil microorganisms were associated with N addition-induced soil acidification and increases in soil N availability. Litter manipulation alone had minor effects, but its interaction with N addition markedly influenced soil microbial biomass. Specifically, litter addition mitigated N addition-induced declines in soil bacterial and total microbial biomass. This significant interactive effect was attributed to the role of litter addition in mitigating soil acidification caused by N addition. Overall, these results suggest that litter addition could alleviate N enrichment effects on soil acid-base status and consequently on soil microbial biomass likely owing to the rapid N immobilization and followed by slow N mineralization during litter decomposition, and underscore that litterfall conservation is critical for enhancing soil microbial resistance to N deposition.

Abstract This study focuses on the preparation of high-strength and high-ductility engineered geopolymer composites (EGCs) using ground granulated blast-furnace slag (GGBS) and coal gangue (CG). The effect of alkali equivalent (AE; 6% to 12%) on the multiscale mechanical properties and reaction products was systematically investigated through mechanical testing and multiscale characterization. The results indicate that an AE of 10% yields optimal performance, with a compressive strength of 84.56 MPa and an ultimate tensile strain of 11.48%, achieving a synergistic enhancement of strength and ductility in high-calcium EGCs. Microstructural analysis reveals that the primary hydration products are calcium sodium aluminosilicate hydrate [C-(N)-A-S-H] gel and gismondine crystals. Gismondine originated from Al 3 + supersaturation ( Al / Si ≥ 0.5 )–induced phase separation. Increasing AE enhanced gel polymerization and introduced a crystal nanofiller effect, raising the micro-elastic modulus of the matrix by up to 34.4%. Matrix densification also improved fiber/matrix bonding, increasing fiber bridging stress by 2.89 times. This led to multiple cracking and efficient stress transmission, resulting in a strain energy density of 329.01 kJ / m 3 . The findings advance the understanding of alkali activation in composite precursors and demonstrate a promising route for high-value CG usage.

Abstract This study conceptualizes the track slab and self-compacting concrete filling layer as a composite system designed for equal service life, grounded in the mechanical characteristics of track slab structures. Using theoretical models, a comparative analysis was performed on reinforcement configurations and crack widths under three design methodologies: the limit state method, the equivalent stiffness method, and the performance-based design approach. Track composite slabs reinforced with steel, basalt fiber-reinforced polymer (BFRP) bars, and hybrid fiber-reinforced polymer (HFRP) bars were then fabricated and tested to evaluate their flexural performance. Drawing on the results of HFRP–concrete pull-out tests, an interface bond–slip constitutive model was subsequently developed. Based on this model, numerical simulations of the track composite slab were conducted. The findings indicate that performance-based design can effectively reduce the reinforcement ratio of HFRP while ensuring adequate crack control, thereby balancing structural performance with cost efficiency. Compared with BFRP reinforcement, replacing steel with HFRP bars enhanced the load-bearing capacity of the track composite slab by 100.57% and improved the ductility index by 8.89%. Moreover, the developed bond–slip model accurately captured the mechanical response of HFRP-reinforced track composite slabs, highlighting the value of service-life design principles and performance-oriented methods in advancing new-type ballastless track structures.

Single-crystal silicon is a critical substrate material in silicon-based semiconductor manufacturing, and its nanoscale surface integrity directly affects subsequent device fabrication accuracy and reliability. In this study, a molecular dynamics (MD) model was developed to clarify the atomistic interaction mechanism between an Al2O3 abrasive and single-crystal silicon during nanoscale polishing. Polishing depths from 1 to 3 nm at intervals of 0.5 nm were used to represent different abrasive-workpiece contact states, and their effects on surface formation, material flow, thermo-mechanical response, microstructural evolution, subsurface damage, and residual stress were analyzed. The results show that the average normal force, average temperature in the chip zone, subsurface damage layer thickness, and maximum von Mises residual stress do not increase proportionally with polishing depth. With increasing depth, they increase by 132.4%, 95.6%, 94.7%, and 15.6%, respectively. Meanwhile, the maximum chip width increases by 68.5%, while the maximum chip height increases by 358.0%, and the relative increase in normal force also exhibits different growth rates. In summary, as the polishing depth increases, the material response is mainly characterized by intensified material pile-up in front of and above the abrasive, as well as the expansion of subsurface lattice distortion and structural disorder; in contrast, the lateral affected range and peak residual stress do not increase synchronously. The findings provide atomistic guidance for understanding Al2O3-Si interfacial interactions and balancing material removal with damage control in nanoscale polishing of single-crystal silicon.