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The face stability analysis of a longitudinally inclined shield tunnel using an analytical approach in water‐rich areas is still a research gap. To solve this face stability problem, a numerical simulation based on the FLAC3D is first conducted to calculate the seepage field behind the inclined tunnel face. An improved rotational failure mechanism is developed to make it possible to investigate the face stability of inclined tunnels using analytical approaches. In the framework of the kinematic approach of limit analysis, the limit support pressures and corresponding failure surfaces of the inclined tunnel face are determined to analyze the face stability issue. The interpolation tool (griddata) in MATLAB is adopted to involve the obtained numerical values of pore water pressures into the analysis of the stability issue. The analytical solutions obtained from the proposed method are validated by comparisons with existing results from published literatures and numerical results. For a quick estimation of the inclined tunnel face stability in water‐rich areas, a series of design charts are then presented for various soil strength parameters, water tables, and inclined angles. Finally, an application of the proposed method to a practical tunneling case is provided, which further illustrates the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Comprehensive assessment of the active/passive seismic stability of shallow tunnel faces is an urgent and complex task. This work establishes a promising three-dimensional (3D) approach using upper-bound limit analysis to evaluate the active and passive seismic stability of shallow shield tunnel faces. The outcrop failure model and inside failure model are provided for active failure analysis. To capture the spatiotemporal variations of seismic loading, the pseudodynamic approach is employed to assess the limit active and passive support pressures. Comparisons with published studies and numerical simulations demonstrate that the proposed 3D approach greatly improves existing 2D results for limit active and passive support pressures. A detailed investigation is then conducted to analyze the effects of pseudodynamic parameters, surface surcharge, and buried depth on face stability of shallow tunnels. Finally, the proposed approach is further tested by conducting the seismic face stability analysis of Changsha Metro 2 tunnel based on actual seismic response. The results indicate that the surface surcharge has a greater influence on limit passive support pressure than limit active support pressure, and increasing of buried depth leads to a larger safety range of limit support pressure. Practical Applications: Active and passive face failure of shallow tunnels under earthquakes can endanger the safety of tunnels and ground surfaces, leading to severe casualties and property losses. Determination of limit support pressures under seismic forces is a critical task in shield tunnel construction. This work establishes an approach to assess 3D active and passive seismic stability of shallow shield tunnel faces. Time–space variations of seismic loading are incorporated to accurately determine limit active and passive support pressures using pseudodynamic approach. Effects of seismic parameters, surface surcharge, and buried depth on face stability of shallow tunnels are then presented and discussed. Finally, the proposed approach is tested by conducting the seismic face stability analysis of Changsha Metro 2 tunnel based on actual seismic response. The results indicate that surface surcharge has a greater influence on limit passive support pressure compared with limit active support pressure, and increasing buried depth leads to a larger safety range of limit support pressure. The proposed approach determines a safety range of limit support pressures more accurately for shallow shield tunnels during earthquakes. [ABSTRACT FROM AUTHOR]

This study aims to propose an effective approach to evaluate the seismic stability of heterogeneous slopes reinforced by inclined soil nails. The modified pseudo dynamic approach is applied to properly describe the characteristics of seismic loads with time and space. The discretization-based failure mechanism generated from the slope crest is divided horizontally into many blocks to incorporate the heterogeneous soil properties and depth-dependent seismic accelerations into the analysis of the stability issue. The critical seismic acceleration coefficient is then determined to assess the slope stability using the kinematic approach of limit analysis. The proposed method is validated by comparisons with existing solutions and numerical results for some available cases. A systematic parametric analysis is conducted to discuss the effects of model parameters on the slope stability. Results show that there exist optimal relative nail lengths and optimal incline angles of soil nails to obtain the maximum critical seismic acceleration coefficient for reinforced slopes. Finally, an application of the proposed model to spatially variable soil strength properties is performed to illustrate that the proposed method has the potential to serve as a benchmark for the slope stability under complex geological conditions. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: In this study, we successfully synthesized two titanium‐oxo clusters, namely Ti19(μ3‐O)19(μ2‐O)10(1,10‐phn)2(OiPr)18] (PTC‐178) and (EMIm)3[Ti17(μ4‐O)4(μ3‐O)16(μ2‐O)4(SO4)3(μ2‐OiPr)4(OiPr)13] (PTC‐179). These clusters were synthesized using an ionothermal reaction and possess similar nuclearity (Ti19 vs. Ti17) moieties. Additionally, we observed that these complexes exhibit varying activities for photocatalytic degradation of Methylene Blue (MB) dye and distinct photocurrent responses for photoelectrochemical studies due to their different surface‐decorated ligands. This study provides valuable insights into the design of Ti‐oxo molecular clusters with similar nuclearity but different surface environments, allowing for the establishment of critical structure‐property relationships. Furthermore, our research contributes to the exploration of sustainable synthetic methods for high nuclearity TOCs using ionic liquids. [ABSTRACT FROM AUTHOR]

Semianalytical solutions for circular tunnels under biaxial in situ stress fields are developed in this study. The surrounding rock is assumed to behave as an elastic–brittle–plastic model and is characterized by the unified strength criterion. For the stress analysis, the perturbation solutions for arbitrary-orders plastic radius for deep-buried tunnels are presented with a newly developed numerical iterative method. Furthermore, a stress renewal algorithm is provided for determining the stress function in elastic zones more accurately. In accordance with the small deformation assumption and nonassociated flow rule, the analytical expressions for radial and circumference displacement in a plastic zone are presented for the first time. Subsequently, the undetermined coefficients in plastic displacement can be solved numerically with the least square method. Based on the proposed semianalytical solutions for circular tunnels, an improved equivalent circular method is developed for estimating the plastic radius and convergence of tunnels with arbitrary shaped cross sections approximately. The reliabilities of the proposed semianalytical solutions and the improved equivalent circular method are verified by comparing with numerical simulation and field data. Meanwhile, the whole calculating process is illustrated in a flow chart for the convenience of programming. From the perspective of practicality, the provided solutions can be employed for predicting plastic radius and ground response curves in tunnel excavation, which can supply important references for the tunnel stability assessment and support design. [ABSTRACT FROM AUTHOR]

Heterometallic oxo clusters have been attracting intensive interest due to their unique properties originating from the synergistic interactions between different components. Herein, we report the construction and catalytic applications of a family of copper-doped polyoxo-titanium clusters (Cu-PTCs) coordinated with different acetate derivative ligands. The solvothermal reactions of metal salts and trimethylacetic acid or 1,2-phenylenediacetic acid in ethanol produced Ti6Cu3(μ3-O)4(μ2-O)(OEt)16(L1)4 (L1 = trimethyl acetate, PTC-367) and H2Ti8Cu2Br2(μ4-O)2(μ2-O)4(OEt)20(L2)2 (L2 = 1,2-phenylenediacetate, PTC-368), respectively. When smaller acetic acid was introduced as a stabilizing ligand, higher nuclei H2Ti16Cu3(μ4-O)5(μ3-O)15(μ2-O)3(OiPr)18(Ac)8 (Ac = acetate, PTC-369) and H3Ti29Cu3(μ4-O)6(μ3-O)30(μ2-O)8(OiPr)17(Ac)20 (PTC-370) were prepared. The number of metal ions exposed on the surface of the four clusters changes due to variations in the steric hindrance of functionalizing ligands, and theoretically, so does their catalytic activity as Lewis acids. In light of this, we conducted a carbon dioxide cycloaddition reaction in an atmospheric environment and the four obtained compounds displayed increasing catalytic activities from PTC-367 to PTC-370. These results provide a feasible synthetic method for modulating the structures of Cu-doped titanium oxide materials and improving their catalytic activities. [ABSTRACT FROM AUTHOR]

A chiral metal–organic cage (MOC) was extended and fixed into a porous framework using a post‐assembly modification strategy, which made it easier to study the host–guest chemistry of the solid‐state MOC using a single‐crystal diffraction technique. Anionic Ti4L6 (L=embonate) cage can be used as a 4‐connecting crystal engineering tecton, and its optical resolution was achieved, thus homochiral ΔΔΔΔ‐ and ΛΛΛΛ‐[Ti4L6] cages were obtained. Accordingly, a pair of homochiral cage‐based microporous frameworks (PTC‐236(Δ) and PTC‐236(Λ)) were easily prepared by a post‐assembly reaction. PTC‐236 has rich recognition sites provided by the Ti4L6 moieties, chiral channels and high framework stability, affording a single‐crystal‐to‐single‐crystal transformation for guest structure analyses. Thus it was successfully utilized for the recognition and separation of isomeric molecules. This study provides a new approach for the orderly combination of well‐defined MOCs into functional porous frameworks. [ABSTRACT FROM AUTHOR]

Herein, the combination of anionic Zr4L6 (L = embonate) cages and N, N-chelated transition-metal cations leads to a series of new cage-based architectures, including ion pair structures (PTC-355 and PTC-356), dimer (PTC-357), and 3D frameworks (PTC-358 and PTC-359). Structural analyses show that PTC-358 exhibits a 2-fold interpenetrating framework with a 3,4-connected topology, and PTC-359 shows a 2-fold interpenetrating framework with a 4-connected dia network. Both PTC-358 and PTC-359 can be stable in air and other common solvents at room temperature. The investigations of third-order nonlinear optical (NLO) properties indicate that these materials show different degrees of optical limiting effects. It is surprising that increasing coordination interactions between anion and cation moieties can effectively enhance their third-order NLO properties, which can be attributed to the formation of coordination bonds that facilitate charge transfer. In addition, the phase purity, UV-vis spectra, and photocurrent properties of these materials were also studied. This work provides new ideas for the construction of third-order NLO materials. [ABSTRACT FROM AUTHOR]

Bimetallic core-shell nanoparticles (CSNPs) often exhibit excellent and tunable properties, depending on their composition, sizes, morphology, atomic arrangement, thickness, and sequence of both core and shell. In this study, the geometrical structure, thermodynamic stability, chemical activity, electronic and magnetic properties, and catalytic activity in the hydrogen evolution reaction (HER) of 13- and 55-atom Pd, Au NPs, and Pd–Au CSNPs were systematically investigated using density functional theory calculations. The results showed that Au atoms prefer to segregate to the surface-shell, while Pd atoms were inclined to aggregate in the core region for bimetallic Pd–Au CSNPs; therefore, Pd@Au CSNPs with an Au surface-shell were thermodynamically more favorable than both the monometallic Pd/Au NPs and the Au@Pd CSNPs with a Pd surface-shell. The Pd surface-shell of the Au@Pd CSNPs displayed a positive charge, while the Au surface-shell of the Au@Pd CSNPs exhibited a negative charge due to the charge transfer in the Pd–Au CSNPs, resulting in that the d-band center of Au@Pd with the Pd surface-shell showed larger shift toward the Fermi level and higher chemical activity. The Pd@Au CSNPs with the Au surface-shell showed similar d-band curves and d-band centers with monometallic Au NPs. All 13-atom Pd, Au NPs, and Pd–Au CSNPs were magnetic, while the 55-atom NPs were non-magnetic with symmetry partial density of states' curves except for Pd55. Changing the location of Pd and Au atoms in the Pd–Au CSNPs influenced their total magnetic moments. In addition, an opposite trend was found: small 13-atom NPs with a Pd surface-shell showed superior HER activity to the ones with an Au surface-shell, while large 55-atom NPs with an Au surface-shell possessed higher HER activity than the ones with a Pd surface-shell. [ABSTRACT FROM AUTHOR]

Herein, we report a twisted cubic Cu(I)4Ti(IV)4-oxo cluster stabilized by in situ – formed 2,2′-biphenolate ligands from the oxidative coupling of phenols. The 2,2′-biphenolate-functionalized Cu(I)4Ti(IV)4O4 cluster shows short Cu⋯C contacts and exhibits smaller HOMO–LUMO gaps than those of reported Ti(IV)4O4. [ABSTRACT FROM AUTHOR]

The development of stable, Earth-abundant, and high-activity molecular water oxidation catalysts under acidic and neutral conditions remains a great challenge. Here, the use of N-heterocyclic carbene (NHC)-based iron(III) complex 1 {[phenyl(tris(3-methylimidazol-1-ylidene))borate]2Fe(III)}+ as a catalyst for water oxidation under acidic and neutral conditions was investigated. Two iron(II) carbene complexes, 2 {[2,6-bis(3-methylimidazolium-1-yl)pyridine]2Fe}2+ and 3 {[2,6-bis(3-methylimidazolium-1-yl)pyridine-4-carboxylic acid]2Fe}2+, were also used for comparison. A series of experiments demonstrate that complex 1 has excellent performance in terms of both catalytic activity and stability. In addition, the faradaic efficiency and turnover frequency (TOF) reach 95.0% and 2.8 s−1, respectively. An overpotential of ca. 490 mV is obtained at pH 1.5. Density functional theory (DFT) calculations indicate that dehydrogenation is the potential-determining step (PDS) in water oxidation. Complex 1 has a lower free energy barrier in this process than 2 and 3. High-valent Fe species are further proven in 1 by spectroelectrochemical measurements, which are crucial in promoting water oxidation. This study is expected to contribute to the development of homogeneous water oxidation catalysis under acidic and neutral conditions. [ABSTRACT FROM AUTHOR]

This study proposed an effective approach to accurately evaluate the three-dimensional (3D) seismic bearing capacity of heterogeneous and anisotropic slopes in the framework of the upper-bound limit analysis theorem. An improved discretized horn mechanism was first developed so that the properties of heterogeneous and anisotropic soils could be involved in the slope stability analysis. To incorporate the impact of seismic forces, the modified pseudo dynamic approach was adopted, which ensured that the complete time-history of the seismic-induced ground movement, the soil-damping properties, and the amplification effect could be considered in this study. The seismic bearing capacity of slopes was then calculated by using a method that integrated the upper-bound limit analysis theorem and the modified pseudo dynamic approach. The proposed method was validated by comparisons with previous analytical solutions for some available cases, showing that the proposed method is an effective approach to determine the 3D seismic bearing capacity of heterogeneous and anisotropic slopes. The effects of model parameters on the ultimate bearing capacity and the critical failure surface are then presented. Finally, the influence of pore–water pressure on the seismic slope stability is discussed. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Herein, we demonstrate a very useful strategy to construct cage‐based metal‐organic frameworks (MOFs) with third‐order nonlinear‐optical properties. More specifically, by employing the Zr4L6 (L = embonate) cages to assembly with N‐contained ligands and Mn2+/Zn2+ ions, four Zr4L6‐cage‐based MOFs have been synthesized and structurally characterized. Among them, a 3D framework with strong aromatic π − π stacking force exhibits a good optical limiting effect. [ABSTRACT FROM AUTHOR]