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Flexible and recyclable surface-enhanced Raman scattering (SERS) substrate was fabricated based on woven cotton fabric by grafting Ag nanoparticle on the TiO2 film which was deposited on the cotton fabric. Due to the synergetic effect of heterostructure Ag/TiO2 and superior adsorption capacity of fabrics, recyclable SERS cotton fabric (RSCF) possessed excellent SERS sensitivity with a detected concentration of p-Aminothiophenol as low as 10−12 M. Furthermore, SERS performance of RSCF can be recovered after 180 min in the presence of UV light illumination, resulting from the photocatalytic property of TiO2 on the surface of RSCF. It can be further utilized to reproduce SERS performance of the RSCF through the UV-assisted cleaning. As a trial for potential application, based on the flexibility of cotton fabric, RSCF was employed to detect a pesticide (carbaryl) on the surface of a pear by simply swabbing and low concentration down to 10−4 M was reached. This work provides a potential guide towards the universal design of the flexible and recyclable SERS substrates for a promising application in the SERS rapid detection of trace-level toxic pollutants on the food. [ABSTRACT FROM AUTHOR]

This paper investigates out-of-plane dynamic instability for functionally graded porous (FGP) graphene platelets reinforced composites (GPLRC) circular shallow arches subjected to a radial periodic concentrated load in a thermal environment for the first time. Hamilton principle is employed to derive the differential equations of motion of the arches associated with out-of-plane displacements. The dynamic instability regions (DIR) with period 2 T are determined by using Bolotin's method and verified by finite element software ANSYS. The effects of uniform temperature difference,out-of-plane boundary condition, pore distribution mode, the weight fraction of graphene platelets (GPLs), GPLs dimension coefficients, and the location of the concentrated periodic load on the DIRs are comprehensively analyzed. The results show that higher temperature difference can weaken the dynamic stability of the arch. The load position has no influence on the boundary excitation frequency at the lowest point of the DIR but plays a negative impact on the area of the DIRs and a positive influence on the lowest value of the load. The parametric resonance of the arch is more likely to occur if the concentrated periodic load is located near the arch crown. [ABSTRACT FROM AUTHOR]

Nanoscale zero-valent iron (nZVI) may partially or completely transform to iron (hydr)oxides when it is used to remove arsenite [As(Ⅲ)]. It is necessary to explore the dynamic phase transformation of nZVI and concurrent arsenic valent changes since reactivity is relevant to the exiting species. In this study, X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Raman spectrum, and scanning electron microscope (SEM) were used to probe the phase transformation of nZVI under the varied simulated polluted water, including different As(Ⅲ) concentration, pH, and co-existing anions. The mainly final product of nZVI corrosion was lepidocrocite (γ-FeOOH) evaluated by XRD. Because of proton release, As(Ⅲ) made more Fe0 corroded in the initial reaction and the corrosion process was faster in the later stage. The formation of iron (hydr)oxides was the main factor affecting the removal of As(Ⅲ) between pH 2–8. And the co-existing anions promoted the corrosion of Fe0, which weakened the negative effect of competitive adsorption on As(Ⅲ) removal to some extent. This research will provide vital information on the evolution and fate of nZVI under environmental conditions, as well as As(Ⅲ) stabilization and mobilization for nZVI treatment system. [Display omitted] • Phase transformation of nZVI played a vital role in As(Ⅲ) removal. • The final corrosion product of nZVI was γ-FeOOH under As(Ⅲ)-bearing conditions. • The more concurrent As(Ⅲ) made the more Fe0 corrosion and Fe(Ⅲ) content. • Mostly the formation of iron (hydr)oxides affected As(Ⅲ) removal between pH 2–8. • The co-existing anions promoted Fe0 corrosion, which weakened competitive adsorption. [ABSTRACT FROM AUTHOR]

Using oyster shell powder (OSP) to prepare magnesium phosphate cement (MPC) not only reduces the pollution caused by the wasted oyster shell disposal, but also benefits the development of more environmentally friendly cement. The effect of OSP on the hydration and strength development of MPC was studied. An axial compression experiment including 45 cuboid specimens was executed to investigate the compressive strength, failure mode, stress–strain relationship, and energy absorption of MPC mixing with different mass contents (0% to 12%) of OSP over the curing times of 7, 14, and 28 days. Scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy were utilized for measuring the variation of MPC microstructure and hydration products caused by OSP. Results indicated that a new reactant CaHPO4·2H2O was formed, which optimized matrix strength. The substitution of OSP could reduce the cost of MPC by 2–9% without decreasing the strength. Compared with MPC without OSP, the compressive strength of the specimen with 3% OSP is increased by 6%. However, with the continuous increase of OSP, the compressive strength gradually decreases. Similarly, the elastic modulus of MPC increases first and then decreases with the increase of OSP. [ABSTRACT FROM AUTHOR]

In the engineering practice, arches, such as arch bridges, are often subjected to localized loading. It is known that the nonlinear in-plane instability of shallow arches is caused by the significant in-plane bending action. The different localized loading produces very different in-plane bending distributions and so the instability of arches under localized loading would be quite different from that under a central point load or under a radial load uniformly distributed over the entire arch. However, there are no studies about the nonlinear instability and post-instability of arches under localized loading reported in the literature. This paper presents nonlinear in-plane analyses for fixed shallow circular arches under a localized uniform radial load. Novel theoretical solutions for nonlinear equilibrium, limit point instability, and bifurcation instability for arches under a localized uniform load are obtained, and new theoretical solutions of the certain modified slenderness switching the instability patterns of an arch under localized uniform loading are also obtained. It is found that the length of localized loading segment significantly influences the in-plane instability and post-instability responses of an arch. The limit point and bifurcation instability loads decrease with a decrease of the length of the localized loading segment. However, the modified slenderness switching instability patterns is found to increase with a decrease of the length of the localized loading segment. Comparisons against the finite element results show the theoretical solutions derived in this paper are accurate. These theoretical solutions provide comprehensive solutions for nonlinear instability and post-instability of fixed arches and they can reduce to those under a central point load or to extend to those under a uniform load over the entire arch. [ABSTRACT FROM AUTHOR]

When an arch is subjected to a periodic load, it may lose in-plane stability dynamically owing to parametric resonance. Previous investigations have been concentrated on in-plane dynamic buckling of pin-ended shallow arches. However, in engineering practice, fixed arches with different rise-to-span ratios are often encountered. Little research on in-plane dynamic instability of deep fixed arches has been reported in the literature. This paper is concerned with experimental and analytical investigations for in-plane dynamic instability of fixed circular arches with rise-to-span ratios 1/8–1/2 under a central periodic load owing to parametric resonance. Experiments are carried out to determine the in-plane frequency and damping ratio of arches, to investigate critical regions of frequencies and amplitudes of the periodic load for in-plane dynamic instability of arches, and to explore effects of the rise-to-span ratio and additional weights on dynamic instability. The analytical method for determining the region of excitation frequencies and amplitudes of the periodic load causing in-plane instability of the arch is established using the Hamilton’s principle by accounting for effects of additional concentrated weights. Comparisons of analytical solutions with test results show that they agree with each other quite well. These results show that the rise-to-span ratio significantly influences the bandwidth of regions of critical excitation frequencies for in-plane dynamic instability of arches. The critical frequencies of the periodic load and their bandwidth increase with a decrease of the rise–span ratio of the arch, whereas the corresponding amplitude of the periodic load decreases at the same time. It is also found that the central concentrated weight influences in-plane dynamic instability of arches significantly. As the weight increases, the critical frequencies of excitation and their bandwidth for in-plane dynamic instability of arches decreases, whereas the corresponding amplitude of excitation increases. [ABSTRACT FROM AUTHOR]

Despite a range of initiatives to reduce global carbon emission, the mean global temperature is increasing due to climate change. Since rising temperatures pose a serious threat of food insecurity, it is important to further explore important biological molecules that can confer thermotolerance to plants. Recently, melatonin has emerged as a universal abiotic stress regulator that can enhance plant tolerance to high temperature. Nonetheless, such regulatory roles of melatonin were unraveled mainly by assessing the effect of exogenous melatonin on plant tolerance to abiotic stress. Here, we generated melatonin deficient tomato plants by silencing of a melatonin biosynthetic gene, CAFFEIC ACID O-METHYLTRANSFERASE 1 (COMT1), to unveil the role of endogenous melatonin in photosynthesis under heat stress. We examined photosynthetic pigment content, leaf gas exchange, and a range of chlorophyll fluorescence parameters. The results showed that silencing of COMT1 aggravated heat stress by inhibiting both the light reactions and the carbon fixation reactions of photosynthesis. The photosynthetic pigment content, light absorption flux, trapped energy flux, energy dissipation, density of active reaction center per photosystem II (PSII) cross-section, the photosynthetic electron transport rate, the maximum photochemical efficiency of PSII photochemistry, and the rate of CO2 assimilation all decreased in COMT1-silenced plants compared with that of non-silenced plants particularly under heat stress. However, exogenous melatonin alleviated heat-induced photosynthetic inhibition in both genotypes, indicating that melatonin is essential for maintaining photosynthetic capacity under stressful conditions. These findings provide genetic evidence on the vital role of melatonin in photosynthesis and thus may have useful implication in horticultural crop management in the face of climate change. [ABSTRACT FROM AUTHOR]

A finite element method (FEM) analysis framework is introduced for the free and forced vibration analyses of functionally graded porous (FGP) beam type structures. Within the proposed computational scheme, both Euler-Bernoulli and Timoshenko beam theories have been adopted such that the explicit stiffness and mass matrices for 2-D FGP beam element through both beam theories are explicitly expressed. Both Young’s modulus and material density of the FGP beam element are simultaneously considered as grading through the thickness of the beam. The material constitutive law of a FGP beam is governed by the typical open-cell metal foam. Furthermore, the damping effects of the FGP structures can be also incorporated within the proposed FEM analysis framework through the Rayleigh damping model. Consequently, the proposed approach establishes a more unified analysis framework which can investigate simple FGP beams as well as complex FGP structural systems involving mixture of different materials. In order to demonstrate the applicability, accuracy, as well as the efficiency of the proposed computational scheme, both FGP beams and frame structures with multiple porosities have been rigorously explored. [ABSTRACT FROM AUTHOR]

Chromium (Cr) is a toxic heavy metal for both animals and plants. The multifunctional signaling molecule melatonin can confer plant tolerance to heavy metal stress, but the mechanisms remain largely unknown. Here, we unveiled the critical role of the secondary metabolite anthocyanin in melatonin-induced Cr stress tolerance. Excess Cr caused severe phytotoxicity, which was manifested by leaf yellowing, stunted growth, reduced Fv/Fm, and increased accumulation of reactive oxygen species and malondialdehyde in a dose-dependent manner. Interestingly, leaf anthocyanin content increased under Cr stress and was the highest under 100 µM Cr (7.67-fold), while exogenous melatonin further increased anthocyanin accumulation with the highest being with 100 µM melatonin (by 90.72 %). In addition, exogenous melatonin increased endogenous melatonin content and alleviated Cr stress; however, suppression of melatonin accumulation aggravated Cr phytotoxicity and inhibited anthocyanin accumulation by downregulating the transcript levels of key structural genes. Melatonin also reduced the Cr content in roots and leaves. Crucially, suppression of anthocyanin biosynthesis by silencing an anthocyanin biosynthetic gene ANTHOCYANIDIN SYNTHASE (ANS) significantly compromised melatonin-induced anthocyanin accumulation and alleviation of Cr phytotoxicity, suggesting that anthocyanin potentially acts downstream of melatonin and its accumulation is essential for melatonin-induced Cr stress tolerance in tomato plants. [Display omitted] • Cr (VI) stress caused severe phytotoxicity and oxidative stress in tomato plants. • Exogenous melatonin increased both melatonin and anthocyanin content under Cr stress. • Suppression of endogenous melatonin accumulation reduced anthocyanin accumulation. • Melatonin alleviated phytotoxicity and reduced Cr content in tomato roots and leaves. • Silencing of ANTHOCYANIDIN SYNTHASE compromised melatonin-induced Cr stress tolerance. [ABSTRACT FROM AUTHOR]

• The seismic response characteristics of a composite bridge consisting of an inclined arch and a curved beam (BIACB) were studied. • A 1:40 scaled test model of BIACB was designed and fabricated to achieve a shaking table test by using simulated earthquake. • A method of applying the compensation mass of inclined arch was proposed. • The influences of seismic wave characteristics, input directions and multi-dimensional excitations on the seismic responses of the BIACB were studied. In this work, a shaking table test was conducted on a new special-shaped arch bridge consisting of an inclined arch and a curved beam called BIACB. In order to meet a landscape requirement, the design of BIACB is unique and complex. Therefore, different from conventional bridges, it exhibits a prominent space effect and unpredictable complex seismic responses. To check the seismic performance of the BIACB, a 1:40 scaled test model was designed and fabricated to achieve a shaking table test by using simulated earthquake. The seismic responses of the tested BIACB model under three typical seismic excitations (El-Centro wave, Taft wave and Artificial wave) were explored. It is found that: (1) The scaled test bridge model can well reflect the seismic response characteristics of the prototype bridge verified by the corresponding finite element analysis. (2) Obvious dynamic amplification phenomena in the transverse and vertical directions of the bridge were observed, showing that the vertical response of the curved beam is greater than the transverse one, while the transverse response of the leaning arch is much more apparent than the vertical one. Generally, the seismic responses of BIACB under transverse seismic excitation are more obvious than those under longitudinal seismic excitation. (3) Higher-order vibration mode of the BIACB has a substantial participation under the longitudinal seismic excitation. (4) The inclined arch significantly amplifies the impact of vertical seismic excitation on the BIACB. (5) The relative variation amplitudes of suspender force of short suspenders on the BIACB are greater than that of long suspenders under longitudinal seismic excitation. The research findings are of great potential to critically guide the seismic design of relevant bridges. [ABSTRACT FROM AUTHOR]

Chromium (Cr) is one of the toxic elements that harms all forms of life, including plants. Industrial discharges and mining largely contribute to Cr release into the soil environment. Excessive Cr pollution in arable land significantly reduces the yield and quality of important agricultural crops. Therefore, remediation of polluted soil is imperative not only for agricultural sustainability but also for food safety. Arbuscular mycorrhizal fungi (AMF) are widespread soil-borne endophytic fungi that form mutualistic relationships with the vast majority of land plants. In mycorrhizal symbiosis, AMF are largely dependent on the host plant-supplied carbohydrates and lipids, in return, AMF aid the host plants in acquiring water and mineral nutrients, especially phosphorus, nitrogen and sulfur from distant soils, and this distinguishing feature of the two-way exchange of resources is a functional requirement for such mutualism and ecosystem services. In addition to supplying nutrients and water to plants, the AMF symbiosis enhances plant resilience to biotic and abiotic stresses including Cr stress. Studies have revealed vital physiological and molecular mechanisms by which AMF alleviate Cr phytotoxicity and aid plants in nutrient acquisition under Cr stress. Notably, plant Cr tolerance is enhanced by both the direct effects of AMF on Cr stabilization and transformation, and the indirect effects of AMF symbiosis on plant nutrient uptake and physiological regulation. In this article, we summarized the research progress on AMF and associated mechanisms of Cr tolerance in plants. In addition, we reviewed the present understanding of AMF-assisted Cr remediation. Since AMF symbiosis can enhance plant resilience to Cr pollution, AMF may have promising prospects in agricultural production, bioremediation, and ecological restoration in Cr-polluted soils. [ABSTRACT FROM AUTHOR]

With the emergence of high-performance materials and the demand for light-weight long-span structures, high-strength concrete-filled-steel-tubular(HS-CFST)structures become increasingly popular. However, relevant research on HS-CFST arch remains scarce, and there is no systematic understanding on its mechanical characteristics. In this study, the in-plane ultimate bearing capacity of parabolic HS-CFST arch with fixed ends under vertical five-point-symmetrical-concentrated-loads along the span was studied experimentally. In total, 15 parabolic arch specimens consisting of different strength of steel tubes and core concretes were designed and tested. The mechanical responses of the arch specimens, including ultimate bearing capacity, failure modes, ductility coefficients, and confinement effects were analyzed. It is found that the ultimate bearing capacity, confinement effect and ductility of a HS-CFST arch are closely related to the strength of steel and core concrete. In addition, finite element models were established to predict the bearing capacity of the HS-CFST arch specimens, where the good agreements showcase the practical usefulness of the proposed HS-CFST arch. • The in-plane ultimate bearing capacity of parabolic high strength concrete-filled-steel-tubular arch was investigated. • 15 parabolic arch specimens consisting of different strength of steel tubes and core concretes were designed and tested. • The ultimate bearing capacity, failure modes, ductility coefficients, and confinement effects were analyzed. • The experiment results were compared with the finite element analysis results. [ABSTRACT FROM AUTHOR]

• The mode shape functions for out-of-plane displacement of arches with different elastic rotational restraints are analytically determined. • Analytical solution for instability regions with elastic rotational restraints under a localized uniform radial periodic load is presented. • The analytical solution of dynamic instability regions are verified by frequency sweep transient finite element analyses (FEA). • Affected parameters on dynamic instability regions are comprehensively analyzed. Out-of-plane dynamic instability of a circular arch with elastic rotational constraints under localized uniform radial periodic load is studied in this paper which has not been yet reported in the literature. In the out-of-plane dynamic instability analysis, the coupled equation of motion associated with lateral displacement and twist angle is derived by using an energy method and Hamiltonian principle. Then the mode shape functions of arches with different elastic rotational restraints are deduced and analytical solution for unstable regions with a period of 2 T are obtained by using Bolotin's method. Finite element numerical analysis is employed to justify the dynamic unstable regions by frequency sweeping simulation and the results show a desirable agreement. It is found that when the flexibility of out-of-plane elastic rotational restraints decreases, the unstable region moves towards the direction of higher frequencies owing to the increase in rigidity of the arch, with the out-of-plane dynamic stability of the arch being improved. The load localized parameter significantly impacts the dynamic stability for the arches with various flexibility of out-of-plane restraints. These results give us a deep understanding of the instability mechanism of engineering structures with arches and provide insight into the effective design of arch structures. [ABSTRACT FROM AUTHOR]

For the first time, analytical solutions for the in-plane dynamic instability of laminated composite circular arches under a vertical base excitation are developed and experimentally verified in this paper. Hamilton principle is used to derive the governing equation of motion of the laminated arch from which the principal instability region corresponding to parameter resonance can be determined. An experimental system is designed and set up to verify the developed solutions and investigate the dynamic performance of laminated arches. Comprehensive analytical and experimental results are presented, with a particular focus on the effects of rise-to-span ratio and stacking sequence on the dynamic instability region of the laminated arch. It is found that dynamic instability region mainly occurs when the excitation frequency is nearly twice the fundamental frequency. For an arch with a lower rise-to-span ratio, both the critical excitation frequency and the width of its dynamic instability region increase significantly. Under the same excitation amplitude, the dynamic instability region of an angle-ply laminated arch becomes wider as the ply-angle increases. Results also show that the critical excitation frequency is highly sensitive to the stacking sequence and quickly grows as the zero-degree ply is placed further away from the midplane. [ABSTRACT FROM AUTHOR]

• Innovative T-shaped embedded nut bolted shear connectors (T-ENBCs) with superior mechanical performance and demountability are proposed and investigated. • Push-out tests and finite element analysis were employed to evaluate the shear behavior of T-ENBCs in a steel–concrete composite beam. • Specific design formulae were proposed for predicting the ultimate shear strength and the load-slip relationship for members with T-ENBCs. • T-ENBCs have a larger shear resistance and higher shear stiffness than high-strength friction-grip bolt connectors. Steel–concrete composite beams joined by shear connectors are extensively used in building and bridge engineering owing to their favourable structural performance, ease of construction, and low cost. Recently, owing to the demand for prefabricated structures, research on demountable shear connectors for prefabricated steel–concrete composite beams has become widespread. In this study, innovative T-shaped embedded nut bolted shear connectors (T-ENBCs) with superior mechanical performance and demountability are proposed and investigated. Push-out tests were conducted to evaluate the shear behavior of T-ENBCs in a steel–concrete composite beam, including twenty-one T-ENBC steel–concrete (EN) specimens and three high-strength friction-grip bolt connector (HF) specimens. For the EN specimens, various types of T-ENBCs were examined to ascertain the effect of variables, such as the diameter of the bolt, length of the embedded nut, and embedded nut type. Accordingly, the failure modes, load–slip curves, ultimate shear resistance, and shear stiffness of the specimens were obtained. Finite element (FE) models for T-ENBCs, validated with test data, were employed to analyse the influence of a number of parameters. Using the experimental and FE results, the properties of the connector, such as its shear resistance, stiffness, ductility, and failure modes, are discussed. The study shows that T-ENBCs have larger shear resistance and higher shear stiffness than high-strength friction-grip bolt connectors. Finally, specific design formulae are proposed for predicting the ultimate shear resistance and load–slip relationship for members with T-ENBCs. [ABSTRACT FROM AUTHOR]

• An improved YOLOv4 network adopting the pruning technique and the EvoNorm-S0 structure was presented. • The pruning technique is used to light-weight the network structure, and the EvoNorm-S0 could improve the detection accuracy. • Compared with the original network, the mAP50 of the improved network is increased from 91.69% to 92.54% (after 100 epochs of training for both the original and the improved YOLOv4), and the weight of the proposed network is just 54.9% of the original ones. • Compared with three other leading algorithms in this field, the proposed network can identify the largest number of target species in the image, and has the highest mAP50. oncrete is a widely used material in the infrastructure system. However, this material is susceptible to several factors that eventually create concrete cracks. Thus, accurately identifying the cracks' size and location in concrete structures is crucial for structural safety evaluation. In this research, an improved YOLOv4 network adopting the pruning technique and the EvoNorm-S0 structure was put forward to better identify concrete cracks from many misleading targets. The pruning technique is used to light-weight the network structure, and the EvoNorm-S0 could improve the detection accuracy. The results indicate that compared with the original YOLOv4, the mAP50 of the improved network is increased from 91.69% to 92.54% when both models are trained for 100 epochs, and the 1-Batch inference time is reduced by 15.9%. Moreover, the weight of the proposed network is just 54.9% of the original ones. The proposed network was also compared with three other leading algorithms in this field (i.e., SSD300, YOLOv3, and YOLO X-L) using the same dataset. The results show that the proposed network can not only correctly classify the largest number of objects with a fast calculation speed, but also has the highest mAP50. Thus, this proposed network exhibits several advantages for detecting concrete cracks and is a desirable tool for practical engineering. [ABSTRACT FROM AUTHOR]