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As an emerging pollutant, microplastics (MPs) cause widespread concern around the world owing to the serious threat they pose to ecosystems. In particular, sediments are thought to be the long-term sink for the continual accumulation of MPs in freshwater ecosystems. Polyethylene (PE) and polyethylene terephthalate (PET) have been frequently detected with large concentration variations in freshwater sediments from the lower reaches of the Yangtze River, one of the most economically developed regions in China, characterized by accelerated urbanization and industrialization, high population density and high plastics consumption. However, the impact of PE and PET on the sedimental bacterial community composition and its function has not been well reported for this specific region. Herein, PE and PET particles were added to freshwater sediments to assess the effects of different MP types on the bacterial community and its function, using three concentrations (500, 1500 and 2500 items/kg) per MP and incubations of 35, 105 and 175 days, respectively. This study identified a total of 68 phyla, 211 classes, 518 orders, 853 families and 1745 genera. Specifically, Proteobacteria, Chloroflexi, Acidobacteriota, Actinobacteriota and Firmicutes were the top five phyla. A higher bacterial diversity was obtained in control sediments than in the MP-treated sediments. The presence of MPs, whether PET or PE, had significant impact on the bacterial diversity, community structure and community composition. PICRUSt2 and FAPOTAX predictions demonstrated that MPs could potentially affect the metabolic pathways and ecologically functional groups of bacteria in the sediment. Besides the MP-related factors, such as the type, concentration and incubation time, the physicochemical parameters had an effect on the structure and function of the bacterial community in the freshwater sediment. Taken together, this study provides useful information for further understanding how MPs affect bacterial communities in the freshwater sediment of the lower reaches of the Yangtze River, China. [Display omitted] • Impact of microplastics in freshwater sediments in the lower reaches of Yangtze River, China was explored. • MP presence reduces the richness and diversity of bacterial communities, alters bacterial community composition. • The type, exposure time and concentration of MP had a significant impact on sedimental bacterial communities. • MP presence shifted a part of the bacterial function in freshwater sediment. [ABSTRACT FROM AUTHOR]

• A model was proposed to analyze the feature guided wave (FGW) propagating in a L-shaped bend. • Dispersive characteristics of different families of FGWs modes and the interaction between these FGW modes and defects were obtained. • Feasibility of combining the FGWs and time-reversal (TR) method for defect detection in topographic structure is validated. The utilization of L-shaped bends has become widespread due to their versatility and ease of application in various industrial fields. Nevertheless, the geometric configuration of these bends makes them susceptible to stress concentration in the bending zone, which can lead to wall thinning caused by accelerated corrosion. This poses a profound challenge to the bearing capacity and reliability of L -shaped bends and highlights the urgent necessity for an effective technique to assess corrosion-induced wall thinning in the bending zone. In this study, we propose a nondestructive testing (NDT) method based on ultrasonic feature guided waves (FGWs) for the evaluation of local corrosion-induced wall thinning in L -shaped bends. Propagation characteristics of FGWs in L -shaped bends were analyzed using the semi-analytical finite element (SAFE) method and perfectly matched layer (PML) technique. Time-reversal (TR) method was employed to address the dispersion and multi-modes phenomenon of the selected guided wave modes and improve the signal-to-noise ratio (SNR) of measured FGW signals. Enhanced SNR of two types of FGW modes signals at different frequencies were verified by experimental and numerical results. Obtained results reveal that FGWs can effectively detect corrosion-induced wall thinning inside L -shaped bends, with improving the signal reflection coefficient by TR method. [ABSTRACT FROM AUTHOR]

• Generation of quasistatic component (QSC) in hollow cylindrical structures is studied. • Mode conversion, cumulative effect, and generation efficiency of QSC are investigated. • A microdamage localization method is proposed using QSC generation. • Experiment in aluminum pipes with different early corrosions validates the method. Quasistatic component (QSC) of guided wave (GW) has relatively low attenuation due to low frequency and high sensitivity to microdamage. The group velocity matching between primary GW and its QSC or higher harmonics usually facilitates the measurement of nonlinear signals due to cumulative effect of amplitude, but it restricts the determination of microdamage location. While group velocity mismatch is general for most of the wave mode pairs in nonlinear GW testing, this study presents a novel method for identifying the location of early stage microdamage using QSC generation of ultrasonic GW propagation in tubular structures under group velocity mismatching condition. A three-dimensional finite element (FE) model is developed to provide insights into the generation and propagation characteristics of the QSC induced by both global material weak nonlinearity and simulated local microdamage in metallic pipes. The FE analysis verifies the L(0,1) mode of the QSC generated from propagations of different fundamental wave modes. The generation efficiency and cumulation feature of the QSC pulse are obtained and discussed. By exploiting the group velocity mismatching condition, a microdamage localization method is proposed based on the L(0,1)-QSC mode pair, which requires one-way excitation of only one primary wave. Experiments are conducted using early corrosion aluminum specimens to investigate the QSC pulse signals and verify the proposed method. The FE and experimental results demonstrate the fundamental properties of QSC generation by GWs in isotropic metallic hollow cylindrical structures. The feasibility of the proposed microdamage localization method is validated experimentally for promising industrial applications. [ABSTRACT FROM AUTHOR]

• Theoretical model for SHG of guided waves developed in topographic structure. • Verification of energy trapping effect for guided waves in topographical structure. • Cumulative SHG of feature guided waves observed in a welded joint. Cumulative second harmonic generation (SHG), where the amplitude of the generated second harmonic increases with propagation distance, is commonly utilized to enhance the measurability of nonlinear guided waves by providing a sufficient signal-to-noise ratio. Investigating and confirming the cumulative SHG of feature guided waves (FGWs) in topographical waveguides is crucial for accurately assessing material nonlinearity in such structures. This study examines the cumulative SHG of FGWs propagating in a typical topographic structure of a welded joint through both numerical simulations and experimental investigations. A theoretical model is developed using the semi-analytical finite-element (SAFE) method and perfectly matched layer (PML) to analyze the propagation characteristics of FGWs in a welded joint. The numerical and experimental results provide verification of the "trapping effect" of FGWs within the welded joint. Furthermore, the "cumulative effect" of SHG of FGWs is observed. Remarkably, both the experimental and numerical findings demonstrate that cumulative SHG of FGWs can be achieved by employing suitable mode selection and frequency tuning in the topographic structure, which aligns well with the theoretical predictions. This investigation contributes to advancing our understanding of cumulative SHG in FGWs propagated within topographical structures. These findings have practical implications for accurately characterizing material nonlinearity in topographic waveguides. [ABSTRACT FROM AUTHOR]

Abstract One of the effective ways to quantitatively inspect or monitor an industrial structure is to obtain images via either scanning or tomography. A combination of ultrasonic guided wave approach and tomographic technique by employing a reconstruction algorithm for the probabilistic inspection of damage (RAPID) can be used to inspect effectively the damage area via visual images. In this paper, surface cracks in polymer bonded explosives (PBXs) were quantitatively evaluated by a Rayleigh surface wave tomographic approach. Considering the relative low wave velocity in the material tested, special surface wave transducers with silicone wedge were designed and produced. The measured signals of Rayleigh surface wave propagation in the specimen with and without cracks were used in a tomographic algorithm to reconstruct images of defects. Results indicate that the setup of the array of transducers has significant influence on the appearance of images. Optimal transducer array setups were also proposed to measure the ultrasonic wave signals for irregular shaped defects to quantitatively image irregular surface cracks in PBXs. It was shown that the image generated by the proposed approach with the optimal transducer array and shape factor calculation method has good agreement with the real defect shape. The present approach provides an alternative tool that can be applied to detecting, locating and imaging the surface defects in PBXs. Highlights • Specific transducers for generation and detection of surface waves in PBXs are designed and manufactured. • The effect of transducer setup on reconstructed image is investigated to optimize setup to get the defects images. • The quantifications via imaging of surface crack with irregular shape in PBXs is achieved by specific transducers designed. [ABSTRACT FROM AUTHOR]

Highlights • Forest thinning did not significantly change soil carbon stocks in general. • Forest thinning increased soil respiration in general. • Soil respiration was increased initially but decreased to original level gradually after thinning. • The effects of forest thinning on soil respiration vary by tree species. Abstract Forest thinning is widely used in forest management activities and has complex effects on underground carbon processes. Although many case studies have been done, how forest thinning affects soil carbon stocks and dynamics remains unclear, especially at different recovery stage. Here, we synthesized the results from 53 peer-reviewed publications and conducted a meta-analysis to evaluate the general responses of 10 variables related to forest soil carbon stocks and dynamics to forest thinning management. Overall, we did not find remarkable effects of thinning on soil moisture, fine root biomass and soil carbon stocks (including soil total carbon, soil organic carbon and microbial biomass carbon). However, thinning resulted in a significant reduction in litterfall production (−23.7%), while significantly increasing soil temperature (+8.7%) and soil respiration (+29.4%) in general. In particular, the effect of forest thinning on soil respiration was significant in light (thinning intensity <33%) to moderate (33–67% of thinning intensity) thinning. In the early stage of recovery (≤2 yr after thinning), this effect was also significant. Thinning significantly increased soil respiration in both broadleaved (+35.6%) and mixed forests (+9.3%) but not in coniferous forest due to the difference of litterfall quality. These results provide a synthetic review of the effects of forest thinning on soil carbon stocks and dynamics and may help to improve forest management strategies. [ABSTRACT FROM AUTHOR]

Deoxynivalenol (DON) and zearalenone (ZEN) pose a serious threat to human health, and have been frequently detected in the aqueous environment. To protect consumers from the harm of mycotoxins, a nanozyme-mediated multiplexed lateral flow immunoassay (LFIA) integrated with a smartphone was developed for rapid, highly sensitive and simultaneous quantitative detection of DON and ZEN in the aqueous environment. Highly efficient peroxidase mimicking core-shell Au@Pt nanozymes were synthesized by one-pot method, and then used as signal amplification to highly improve sensitivity of the detection, while a smartphone-based quantitative detection device could rapidly quantify results to improve the detection efficiency of the LIFA for on-site detection. After optimization, the detection time of the assay was 10 min, and the detection limits of the LIFA for DON/ZEN were 0.24/0.04 ng/mL, which were improved 416 and 150 folds compared to the conventional gold nanoparticles (GNPs)-based LFIA. Moreover, there was no obvious cross-reaction with other related mycotoxins, indicating that LFIA had a high specificity. The average recoveries of DON and ZEN from corn, wheat and three water samples were obtained from 94.3 % to 107.9 % with relative standard deviations of 0.2–7.6 %. Furthermore, the accuracy and reliability of the LIFA were evaluated with three spiked water samples, and the results presented good correlations with analytic results from the enzyme-linked immunosorbent assay (R2 =0.988 for DON, and 0.983 for ZEN). The results indicate the proposed LIFA was potentially a rapid, on-site simultaneous and highly sensitive method for DON and ZEN detection in the aqueous environment. [Display omitted] • An efficient detection method was established for deoxynivalenol and zearalenone in the aqueous environment. • The self-developed quantitative detection equipment can realize the on-site quantitative detection of mycotoxins. • The Au@Pt/AEC-based LFIA can significantly improve detection sensitivity compared to the conventional GNPs-based LFIA. [ABSTRACT FROM AUTHOR]

We show a superplastic diffusion bonding method to join metallic glasses (MGs) via high-speed heating at 2000 K/min taking a timescale of the order of microseconds to milliseconds at ambient pressure because the minimum viscosity of supercooled liquid drastically decreases as the heating rate increases. The results show strong metallic bonds are formed but the amorphous structure is still maintained. Finally, we establish a general equation containing the involved parameters for high-speed heating bonding. This method provides a new path to join MGs rapidly and benefits for improving the critical size of MGs. [ABSTRACT FROM AUTHOR]