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The p-type doping process during the growth of AlGaN nanowires directly influences the optoelectronic properties of the related devices. However, research on the p-type ionization mechanism in AlxGa1-xN nanowires remains limited. In this work, we utilize first principles calculations to investigate p-type doping in AlxGa1-xN nanowires under different structural variables (Al component, doping element, doping site, and doping concentration). Our results demonstrate that p-type doping in AlxGa1-xN nanowires is an endothermic process, and increased dopant concentration leads to a decrease in system stability. Moreover, we found that dopant atoms are easier to substitute for Ga atoms than Al atoms. Among the three doping elements (Zn, Be and Mg), Zn exhibits the most challenging doping difficulty, while Be shows the easiest doping process, with Mg falling in between. Crystal Orbital Hamilton Population (COHP) and bond population calculations reveal the mechanism for the variation in doping structure stability. Doping induces a rearrangement of energy level orbitals, resulting in changes in the band gap. Specifically, the valence band exhibits an overall upward trend crossing the Fermi level, showing the p-type conductive properties. Notably, a significant decrease in electron density near Mg and Be leads to the formation of p-type conductive properties. The changes in hole density and effective mass further confirm the formation of p-type conductivity after doping. Additionally, structures with lower Al composition exhibit higher doping ionization degrees. This study is expected to provide a theoretical basis for the growth, preparation, and application of optoelectronic devices based on p-type AlGaN nanowires.

The pipe roofing method is widely used in tunnel construction because it can realize a flexible section shape and a large section area of the tunnel, especially under good ground conditions. However, the pipe roofing method has rarely been applied in soft ground, where the prediction and control of the ground settlement play important roles. This study proposes a sliced-soil–beam (SSB) model to predict the settlement of ground due to tunnelling using the pipe roofing method in soft ground. The model comprises a sliced-soil module based on the virtual work principle and a beam module based on structural mechanics. As part of this work, the Peck formula was modified for a square-section tunnel and adopted to construct a deformation mechanism of soft ground. The pipe roofing system was simplified to a three-dimensional Winkler beam to consider the interaction between the soil and pipe roofing. The model was verified in a case study conducted in Shanghai, China, in which it provided the efficient and accurate prediction of settlement. Finally, the parameters affecting the ground settlement were analyzed. It was clarified that the stiffness of the excavated soil and the steel support are the key factors in reducing ground settlement.

The development of novel cementation materials has attracted extensive interest due to the limitation of traditional cementation materials on environment. This study proposed a biomimetic mineralized mortar (BMM) based on the biomimetic chemically induced calcium carbonate precipitation (BCICP) using polyacrylic acid (PAA) as a modifier. The unconfined compression test (UCS) and scanning electron microscopy (SEM) were conducted to verify the effectiveness in improving the mechanical properties of BCICP treated samples. Moreover, the effects of cement solution ratio, cement solution concentration, and cement solution amount were investigated and an optimal scheme for BMM were further studied. The results show that the cement solution ratio and concentration would affect the form, size, and agglomerating mode of the calcium carbonate, thereby affecting the mechanical improvement. With the increase of the cement solution amount, the cementing behavior of calcium carbonate changes, which can be mainly divided into the following stages: bridging connection, pore filling, and film coating. In addition, Pearson correlation coefficient indicates that the UCS has a general tendency to increase with the calcium carbonate content. Compared to previous researches, the biomimetic mineralized mortar with PAA modifier shows excellent mechanical performance. The UCS of the sample treated by PAA is significantly greater than that of the sample treated by L-Asp or boric acid modifier with the same calcium carbonate content.

In recent years, concrete and reinforced concrete piles have been widely used to stabilize soft ground under embankments. Previous research has shown that bending failure, particularly during rapid filling on soft ground, is the critical failure mode for pile-supported embankments. Here, we propose an efficient two-stage method that combines a test-verified soil deformation mechanism and Poulos’ solution for pile–soil interaction to investigate the bending behavior of piles supporting embankments on soft ground. The results reveal that there are three possible bending failure scenarios for such piles: at the interface between the soft and firm ground layers, at mid-depths of the fan zone, and at the boundary of the soil deformation mechanism. The location of the bending failure depends on the position and relative stiffness of the given pile. Furthermore, the effect of embedding a pile into a firm ground layer on the bending behavior was investigated. When the embedded length of a pile exceeded a critical value, the bending moment at the interface between the soft and firm ground layers reached a limiting value. In addition, floating piles that are not embedded exhibit an overturning pattern of movement in the soft ground layer, and a potential failure is located in the upper part of these piles.

Rapid demographic ageing substantially affects socioeconomic development1–4and presents considerable challenges for food security and agricultural sustainability5–8, which have so far not been well understood. Here, by using data from more than 15,000 rural households with crops but no livestock across China, we show that rural population ageing reduced farm size by 4% through transferring cropland ownership and land abandonment (approximately 4 million hectares) in 2019, taking the population age structure in 1990 as a benchmark. These changes led to a reduction of agricultural inputs, including chemical fertilizers, manure and machinery, which decreased agricultural output and labour productivity by 5% and 4%, respectively, further lowering farmers’ income by 15%. Meanwhile, fertilizer loss increased by 3%, resulting in higher pollutant emissions to the environment. In new farming models, such as cooperative farming, farms tend to be larger and operated by younger farmers, who have a higher average education level, hence improving agricultural management. By encouraging the transition to new farming models, the negative consequences of ageing can be reversed. Agricultural input, farm size and farmer’s income would grow by approximately 14%, 20% and 26%, respectively, and fertilizer loss would reduce by 4% in 2100 compared with that in 2020. This suggests that management of rural ageing will contribute to a comprehensive transformation of smallholder farming to sustainable agriculture in China.

With the utilization of underground space, backward erosion piping (BEP) has been observed in many underground structures (e.g., shield tunnels) founded on sandy aquifers. However, due to invisibility, the geometry of the eroded pipe and its spatial evolution with time during the piping process was still not clear. In this study, we developed a Hele-Shaw cell to visualize the dynamic progression of BEP. With imaging process technology, we obtained a typical process of BEP (the erosion process can be divided into a piping progression phase and a piping stabilization phase), quantitatively characterized the formation of erosion pipes, and compared the patterns of erosion (e.g., the erosion area Aand the maximum erosion radius Rmax) that spontaneously develop under different fluxes of water. The most interesting finding is that the sand grains in a thicker Hele-Shaw model are easier to dislodge, which is possibly due to the granular system in a thicker model having more degrees of freedom, reducing the stability of the sand grains.

Capsule grouting technology (CGT) is developed to control the deformation of underground structures induced by the adjacent underground construction. Meanwhile, multiple grouting is necessary for CGT to achieve the desired effect as the heterogeneity and complexity of the soil. This study proposed a retarding and low-early-strength grouting material (RLGM) to realize the multiple grouting of CGT. Response surface methodology (RSM) was applied to study the effects of formulation on the workability and mechanical strength of RLGM, then the microstructures of optimal RLGM were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Moreover, the analysis of variance (ANOVA) models were developed to predict the performance of RLGM. Results show that different formulations lead to significantly different contributions to RLGM performance, and each factor shows positive or negative synergistic effects with others. Etidronic acid retarder (EAR) plays a dominant role in the initial setting time, and the correlation between the initial setting time and compressive strength presents an obvious negative correlation. Based on the multi-objective optimization considering the multi-performance requirement of grouts for CGT, the optimized RLGM mix proportion is obtained that water-cement ratio of 1, bentonite (B) of 27.5%, polycarboxylate superplasticizer (PCE) of 0.28%, EAR of 0.75%. Accordingly, the initial setting time and 10 days compressive strength of the optimal RLGM achieve a highly desirable goal, that is, 124.1 h and 0.2 MPa, respectively. Finally, the field trial result confirms that RLGM for CGT shows good working performance during grouting construction.

Cement-soil mortar is a composite material that provides an efficient and cost-effective solution for a wide range of construction applications. This study analyzes the mechanical properties of cement-soil mortar through experimental investigation and explores the application and parameter calibration of the Concrete Damage Plasticity (CDP) model in the finite element simulation of cement-soil mortar. Additionally, an innovative Initial Defect Generation (IDG) method is proposed to enhance the accuracy in simulation of failure mode. The research findings provide a simulation framework that balances simplicity and accuracy for cement-soil mortar. Uniaxial compressive tests are first conducted on cement-soil mortar specimens with water contents ranging from 40 % to 70 %, and cement-to-soil proportions from 30 % to 300 %. Based on the experimental results, the regression relationships correlating unconfined compressive strength (UCS) with elastic modulus, peak strain and stress-strain curves are established. Then, the simplified equations for calculating CDP model parameters from the UCS of cement-soil mortar are further proposed following damage mechanics. A parameter table summarizing the calculation methods for all relevant CDP parameters is provided to streamline the model calibration process. Simulations incorporating the simplified calibration method and IDG method successfully replicated the stress-strain responses and failure modes observed in uniaxial compressive strength tests of cement-soil specimens with varied strength. The results demonstrate the reliability and broad applicability of this simulation framework in predicting the mechanical performance of cement-soil mortar.

The sustainable and efficient treatment of massive granite waste powder (GWP) has received increasing attention. This study proposes a novel method for recycling GWP cemented by inorganic binder-stabilized materials (IBSM) for sustainable pavement subgrade filler, i.e., IBSM-stabilized GWP (ISG). IBSM consists of Portland cement (PC), quicklime (QL), ground granulated blast furnace slag (GGBS), and sodium dodecyl benzene sulfonate (SDBS). Response surface methodology (RSM) and microstructure analysis were employed to analyze the effects of IBSM components on ISG mechanical properties and durability. The 56d compressive strength of ISG is above 2.62 MPa, meeting the minimum criterion of 1 MPa. The residual strength coefficient after 5 freezing-drawing cycles is generally greater than 65 %, except for the groups with high QL content. Both PC and GGBS are positively correlated with the performance of ISG. Moreover, multi-objective optimization identifies the optimal mix ratio: 3.03 % PC, 0.83 % QL, 3.47 % GGBS, and 0.18 % SDBS. The optimal ISG presents excellent strength and durability performance, with S7dof 1.61 MPa, S56dof 3.88 MPa, Swof 3.35 MPa, Rftcof 90 %, Rwdcof 92.01 %. These findings provide insight into the stabilization strategies of GWP using in highway subgrade filler, which can alleviate the environmental pollution induced by GWP waste.

AbstractIn this article, a novel artificial intelligence method, i.e. random forest (RF), was adopted as a computer-aided tool to predict the vertical displacement of several pile-supported bridge piers above two overlapped earth-pressure-balanced machine (EPBM) tunnels. Naive Bayes theory was introduced for the statistical analysis of the results predicted by the RF method to address the operational variables of the EPBMs required to safely pass beneath the bridge piers. The in situobservations indicated that the EPBM variables were reasonably determined based on the fact that the vertical displacements of the concerned piers were successfully controlled within the allowable range.

Metastable austenitic stainless steels (ASSs) have excellent ductility but low strength, so that their usage as load-bearing components is significantly limited. Rolling is an effective method of increasing strength, whereas the effect of rolling temperature on microstructural evolution, the hydrogen embrittlement (HE) sensitivity and fracture mechanisms is still unclear. In present study, the effect of cold/warm rolling on detailed microstructural characteristics of 304 ASS was quantitatively investigated, and the corresponding HE sensitivity was evaluated via slow strain rate test (SSRT). The results suggest that cold-rolling led to high strength but poor plasticity and deteriorated HE sensitivity, while warm-rolled samples provided combination of high strength and ductility and also superior HE resistance. Compared with 18% α′-martensite in cold -rolled steel, warm-rolled specimens consisted of complete austenite, less twins and lower dislocation density，moreover, the favorable {112} ND and {110} ND textures replaced the harmful {001} ND texture. Based on in-situEBSD observation during SSRT, the HE sensitivity was governed by the combined effect of pre-deformation microstructures and the dynamic microstructural evolution. Advanced method of time-of-flight secondary ion mass spectrometry was used to observe the distribution of hydrogen, and the hydrogen content of specimens was determined by the gas chromatograph thermal desorption analysis method. An exceedingly small amount of hydrogen entered the warm-rolled samples, while a large amount of hydrogen was trapped at grain boundaries of cold-rolled sample, leading to complete intergranular fracture. Therefore, warm rolling is an effective pathway for obtaining high combination of strength and ductility together with excellent HE sensitivity.

With the development of underground space, underground construction inevitably affects the safety of surrounding structures. Capsule grouting technology (CGT) is proposed to protect adjacent structures from the impact of underground construction. This study developed a high-performance cement grout (HPCG) for CGT using chemical additives. The orthogonal test was performed to optimize the material composition and study the synergistic effect of cement additives of HPCG. Then, the microstructure of HPCG was further analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. The results show that the water-cement ratio shows a significant influence on flowability, bleeding, and compressive strength of HPCG. Then, the retarder presents a dramatic effect on prolonging the setting time (more than 70 h) by hindering the hydration reaction process. As the polycarboxylate superplasticizer content increases from 0 to 0.2%, the flowability of HPCG increases by 81.7%, while the bleeding increases 115.4%. However, the influence of each factor on the performance is not a single target but a synergistic influence, so a comprehensive analysis should be considered to determine the optimal dosage of additives. Accordingly, the optimal design of HPCG can be recommended that 1.0 for water-cement ratio, 0.45% for retarder, 0.2% for polycarboxylate superplasticizer, and 3% for fluid loss additive, which shows high performance for CGT, with the flowability of 28.3 cm, bleeding rate of 1.61%, initial setting time of 71.1 h, 7 days compressive strength of 2.3 MPa.

AbstractThis article reports the application of the Eulerian FE method in face stability analysis of shield tunnels in undrained clay. Numerical simulation was first conducted under the total stress framework to verify the accuracy of the approach. Then it was extended to effective stress analysis combined with a critical state model, taking complex behaviours (small strain non-linearity) of soil into consideration. The predictions under the two analysis frameworks were compared in detail, which indicated the small strain formulation of the effective stress constitutive model does not influence the solution for the collapse load but may enhance the predictions of deformation.

An increasing number of engineering accidents have shown that the failure of a tunnel can propagate to a neighbouring tunnel. However, due to the complex interaction between the failed tunnel structure and the soil medium, the mechanism by which the failure is propagated between two closely spaced tunnels remains unclear. In this study, the coupled Eulerian-Lagrangian (CEL) modelling technique was adopted to investigate the influence of a failed tunnel (FT) on an adjacent tunnel, which was termed an “influenced tunnel” (IT). The safety of the IT was analysed in detail under different circumstances, such as different failure positions of the FT, different failure degrees of the FT, and different spatial relationships between the two tunnels. The simulation results indicated that the most adverse case may occur when the two tunnels are arranged as offsets and the IT is the upper tunnel. Under this circumstance, significant shear deformation may occur in IT because IT is located at the shear band of the FT.

The Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.25Fe-0.2Si (wt%) alloy is a novel two-phase high temperature alloy for short-term application. The effects of different heat treatments on the microstructure and mechanical properties were investigated through electron probe microanalysis (EPMA), optical microcopy (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and tensile tests at room temperature and 650°C. Subjected to the annealing treatment at α+β region (1010 °C/2 h, FC to 990 °C+990 °C/2 h, AC), the microstructure was composed of bimodal structure, which consists of equiaxed primary α (αp) phase and lamellar transformed β (βt) structure. As a strong β stabilizer, the content of Fe in α phase is much less than that in β phase. Annealing at β region (1040 °C/2 h, AC) resulted in the formation of widmannstatten structure, consisting of coarse raw β grain and secondary α phase precipitated on the β grain. With respect to the tensile property, different heat-treated alloys obtained similar strength. However, widmannstatten structure was characterized by lower plasticity, with the elongation only half that of bimodal structure. The fracture characteristics at room temperature for the alloy with bimodal structure and widmannstatten structure are dominated by ductile fracture and cleavage fracture, respectively.

The exponential-doping GaN nanowire arrays (GaN NWAs) photocathode has a "light-trapping effect", and the built-in electric field can promote the concentration of the photogenerated carrier center to the top surface of the nanowire. However, in the preparation of actual NWAs photocathodes, the problem that photons emitted from the sides of the nanowires cannot be effectively collected has been encountered. Our proposed field-assisted exponential-doping GaN NWAs can bend the motion trajectory of the emitted electrons toward the collecting side. In this study, the quantum efficiency (QE) and collection efficiency (CE) of the external field-assisted exponential-doping GaN NWAs photocathode are derived based on the two-dimensional carrier diffusion equation and the initial energy and angular distribution, respectively. For a field-assisted exponential-doping GaN NWAs with a width d = 200 nm and a height H = 400 nm, the optimal structural parameters are obtained: the incident angle θ = 50° and the nanowire spacing is L = 335.6 nm. On this basis, the field intensity of 0.5 V/μm can maximize the CE of the NWAs. All the results show that the field-assisted approach does contribute to the collection of emitted electrons, which can provide theoretical guidance for high-performance electron sources based on exponential-doping GaN NWAs photocathodes. And field-assisted exponential-doping GaN NWAs cathode is expected to be verified by the experimental results in the future. [ABSTRACT FROM AUTHOR]

Coal dust prevention is crucial for the environment and the safety of coal miners. This study proposed a biomimetic mineralized dust suppressant (BMDS) with polyacrylic acid (PAA) modifier, based on calcium carbonate precipitation technology. The consolidation effect of BMDS on coal dust was evaluated through wind erosion resistance tests, unconfined compressive strength tests, and microscopic characterizations. The results show that the consolidation effect of the BMDS on coal dust heavily depends on the PAA concentration. When the PAA concentration is 4 g/L and the concentration of calcium chloride and sodium carbonate is 0.5 mol/L, the BMDS presents the best dust suppression effect and could realize the practical application requirements. The generated calcium carbonate is mainly calcite type, and the efficiency of cementing coal dust particles is the highest. Moreover, similar to bacteria in biological dust suppressants, it confirms that PAA could effectively modify the nucleation and growth of calcium carbonate, promote the adhesion of calcium carbonate to the surface of coal dust particles, and enable the generated calcium carbonate to effectively bond coal dust particles. Accordingly, the BMDS with PAA modifier can be effectively used in the prevention of secondary coal dust pollution.

Ti-6.5Al-2Zr-1Mo-1V (TA15) and Ti-6.5Al-3Sn-3Zr-3Mo-3Nb-1W-0.2Si (BTi-6431S) dissimilar titanium alloy plates were welded through electron beam welding (EBW) method and different ultrasonic impact treatment (UIT) technologies were performed on the weldment. The effects of UIT on the microstructure and residual stress distribution and mechanical properties for the welding joint were investigated. A significant microstructural change occurs after welding. The structure of welding joint is composed of fusion zone (FZ), heat-affected zone (HAZ) and base metal. The microstructure of FZ is composed of martensite structure and a clear interface is observed because of the fusion of dissimilar alloys. HAZ near fusion zone is comprised of martensite structure, while the grain size is much smaller than that in FZ. The HAZ microstructure near TA15 alloy is composed of coarse equiaxed α phases and HAZ microstructure near BTi-6431S alloy is lamellar α phases. Through ultrasonic impact treatment for three times, the residual stress near the welding joint shows a uniform distribution and the maximum tensile stress changes to compressive stress. A characteristic asymmetrical microhardness profile is observed in TA15/BTi-6431S dissimilar alloy welded joint. The HAZ in BTi-6431S alloy side possesses higher hardness compared with that in TA15 alloy side. The microhardness and tensile properties change slightly after ultrasonic impact treatment.

A biomimetic-chemically induced carbonate precipitation method (BCICP) using boric acid as a crystal modifier is proposed to develop new cementing material. This study further explored the potential application of biomimetic mineralized composites using the BCICP method in different environments, including particle size, alkaline conditions, and sand mineralogy. The results show that as the particle size increases, the UCS value decreases by 1.52 MPa, and the compressive strength of biomimetic mineralized composites with multi-graded (0.1–1.0 mm) is significantly better than that with single-graded (0.1–0.2 mm). Moreover, the effect of alkaline sand depends on the alkali content, and the low alkali level is beneficial for cementation with a maximum UCS of 1.68 MPa. However, high alkali content would consume boric acid, resulting in poor pore filling and significantly reducing strengthening efficiency. In addition, BCICP also has a higher strengthening cementing efficiency for sand with copper oxide and calcium carbonate as the main minerals, and the UCS increases by 16.2% and 57.3% compared to Toyoura sand, respectively. The findings of this study provide insights into future design and applications of biomimetic mineralized composites.

This paper adopted the biomimetic mineralized method (BMM) with L-Aspartate (L-Asp) as the crystal modifier to develop the biomimetic mineralized cement material. The structural integrity and mechanical property of cemented samples treated by BMM were studied through the direct shear test and unconfined compressive strength (UCS) test. Meanwhile, the micro-morphology and mechanism of calcium carbonate crystals generated from biomimetic mineralization in water solution and sand environment were investigated by XRD, FTIR, XPS, and SEM. The results reveal that the biomimetic mineralized cement with L-Asp modifier is feasible to cement the loose sand into a high-strength integrated structure. With the gradually increasing spraying cycles, the ultimate shear strength of the cemented samples was significantly improved. Moreover, the hydrogen–bond interaction inducing calcium carbonate crystals and sand particles, as well as the particle agglomerated growth are the fundamental reasons for the cementation of loose sand. The feasibility of biomimetic mineralized cement using an L-Asp modifier is verified.

Tunnel collapse presents a serious threat to the safety of urban construction. The traditional approach adopted to assess this risk is to evaluate the factor of safety against failure. However, this analysis only determines on whether the tunnel will collapse or not, and does not provide information on the magnitude of the post-failure behavior (for example, catastrophic or progressive) if the tunnel collapse occurs. In this study, a meshless method based on the material point method (MPM) was used to investigate the post-failure behavior of tunnel heading collapse in two-dimensional plane-strain conditions. The capability and accuracy of MPM were verified by comparing the elicited results to centrifuge test data and to analytical solutions obtained from limit state methods. MPM simulations were conducted at different soil conditions (clay or sand) and profiles (homogenous or linear increasing strength) as well as at different tunnel geometries (i.e. tunnel depth and unlined length). The differences in the post-failure behavior and mechanisms are examined and reported.

Eye-specific segregation in the dorsal lateral geniculate nucleus (dLGN) and superior colliculus (SC) starts from the embryonic stage and continues to develop postnatally until eye-opening in mice. However, there have been few systematic studies on the details of this developmental process. Here, we carried out time-dependent studies of eye-specific segregation in the dLGN and SC. Our results demonstrated that the development of eye-specific segregation in the SC is completed before postnatal day 12 (P12), which is earlier than in the dLGN (P20). During the whole period, ipsilateral and overlapping axonal projections decreased continuously in both the dLGN and SC. On the other hand, contralateral axonal projections showed little change, except for a slight decrease between P8 and P20 in the dLGN.

The adsorption of 4,4‘-bipyridine (BiPy) on Cu(111) has been investigated in 0.1 M HClO4 by cyclic voltammetry, electrochemical scanning tunneling microscopy (STM), and surface-enhanced infrared adsorption spectroscopy (SEIRAS). Cyclic voltammetry showed the double layer region extending from −0.2 to 0.26 V and a pair of redox waves superposing on hydrogen evolution wave at more negative potentials. Diprotonated BiPy, BiPyH22+, is adsorbed flat on the Cu(111) (1 × 1) surface and forms a well-ordered monolayer with a (3 × 4) symmetry in the double-layer potential region. At more negative potential, BiPyH22+ is reduced to its monocation radical, BiPyH2•+, and forms another well-ordered structure in which the radicals are stacked in molecular rows with a face-to-face self-dimer as the building unit. The SEIRA spectra of both BiPyH22+ and BiPyH2•+ are dominated by gerade modes which should be IR-inactive for the centrosymmetric species. The breakdown of the selection rule of IR absorption is ascribed to the vibronic coupling associated with charge transfer between BiPyH22+ and the surface and between the radicals.