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To investigate the response mechanism of mechanical properties for compacted loess to dry-wet cycles, multi-scale tests including direct shear, consolidation compression, crack quantification, SEM, NMR and XRD were designed and performed on samples from 0 to 9 cycles. The results indicate that both the shear strength and overall compressibility deteriorate substantially after the first dry-wet cycle and stabilize after five cycles. Meanwhile, mesoscopic cracks appear on the loess surface during the initiation, propagation and equilibrium phases, accompanied by a growth in the crack ratio, as well as a more chaotic crack distribution with cycles. The penetration of the pore space during repeated dry-wet leads to a decrease in the volume of micropores and small pores and an increase in that of mesopores and macropores. Additionally, particle rounding and orientation are slightly enhanced and the soil microstructure becomes more fragmented. Furthermore, the relative content of the primary minerals has grown insignificantly after performing the dry-wet cycles, while the clay minerals and soluble salts content has decreased inconsiderably. The deterioration of the macroscopic mechanical properties of compacted loess can be considered as the comprehensive manifestation of irreversible fatigue damage to its microscopic and mesoscopic structures induced by dry-wet cycles. [ABSTRACT FROM AUTHOR]

Here, we present an experimental investigation on the nonlinear optical (NLO) and optical limiting properties of metalloporphyrin compounds (Cu-1-OH, Zn-1-OH, Cu-1-E and Zn-1-E) using spatial self-phase modulation (SSPM) method in the visible range. It is found that all of the samples show a large self-defocusing effect at 532 nm, which is attributed to the thermal nonlinear optical effects with negative nonlinear refractive index coefficient n2 due to the relatively high absorption at 532 nm. In contrast, at 780 nm where absorption is weak for both Zn- and Cu-porphyrins, Zn-porphyrins still exhibit visible self-defocusing while Cu-porphyrins do not show any nonlinear diffraction pattern. Such a phenomenon can be explained by the Kerr effect of Cu-porphyrins at 780 nm. As the thermal nonlinear optical effects (of negative n2) at 780 nm are reduced due to the low absorption, the Kerr effect with positive n2 becomes comparable and the overall nonlinearity is reduced. The Kerr effect of Cu-porphyrins is stronger than that of Zn-porphyrins because of the enhanced π-electron delocalization effect as Cu(II) has a variable number of valence electrons and incompletely filled d atomic orbitals. Finally, the optical limiting performance of Zn-porphyrins is demonstrated as a representative and its dependence on sample position is examined. This work not only enriches the understanding of the physical mechanism of optical limiting in porphyrin materials, but also provides a significant reference to improve the third-order NLO coefficient by adjusting the structure of compounds. [ABSTRACT FROM AUTHOR]