► In practice, many tunnels are shallow, and are subjected to supporting pressure. ► A new failure mechanism is proposed for shallow tunnels with the consideration of supporting pressure. ► The ...critical depth for classifying shallow and deep tunnels is established. ► The width of the failure block increases as the supporting pressure increases.
Collapse shape of shallow circular tunnel is derived using a new curved failure mechanism within the framework of upper bound theorem. Nonlinear Hoek–Brown failure criterion is adopted in the present analysis. With the consideration of supporting pressure, the energy dissipations of the new failure mechanism are calculated by employing integral technique. Equating the rate of energy dissipation to the external rate of work, the objective function is formulated, and is optimized with the variational approach. Numerical results are presented, and collapse mechanisms of shallow tunnel taking into account supporting pressure are obtained. The present results are compared with the previous solutions, and the agreement shows that the present method is valid. The effects of different parameters on the failure mechanisms are discussed, and a critical depth expression is proposed for classifying shallow and deep tunnels.
Abstract
Due to the long-term operation of power grid and the interference of external uneven electric field environment, silicone rubber insulators are prone to aging and scaling, and their ...hydrophobicity and external insulation performance are easily affected. In order to solve this problem, a kind of silicone rubber insulator outer surface cleaning and repairing agent was prepared with self-made composite solvent and silicone as the main raw materials, supplemented by catalyst, surfactant and other additives. So as to achieve the dual effect of efficient cleaning and aging repair, improve its hydrophobicity and prolong its service life. Through hardness test, hydrophobicity test, SEM test, FT-IR test, EDS test, mechanical property test and aging test characterization, and comparing the cleaning effect of different cleaning methods, it is found that the cleaning effect of cleaning repair agent is the best. In addition, it is found that the hydrophobicity of insulator has been greatly improved, from HC4 to HC1, and the mechanical properties have also been improved. This is because after using the cleaning and repairing agent, the powdered layer on the insulator surface is removed, and more hydrophobic methylene (Si–(CH
3
)
2
) and methylene (Si–(CH
3
)
3
) are attached to the insulator surface, which reduces the -OH binding force between the insulator surface and water molecules. In addition, through the observation of the surface and cross-section micro morphology, it is found that the surface roughness of the insulator is greatly reduced and the micro cracks disappear after using the cleaning and repairing agent, which highlights a certain repairing effect. Finally, the aging test also shows that the cleaning repair layer has a certain durability.The results show that the cleaning and repairing agent can effectively clean and repair the aged insulator, improve its anti- pollution flashover ability and prolong the service life of silicone rubber insulator.
Articular cartilage defects are common in the clinic but difficult to treat. Exploring the chondrogenic molecular mechanisms of mesenchymal stem cells (MSCs) is of great theoretical interest and ...industrial significance. Bone morphogenetic protein 2 (BMP2) is a key factor that induces cartilage differentiation and can induce stem cell chondrogenic differentiation. However, the oxidative stress in the microenvironment during cartilage injury and degeneration inhibits cartilage regeneration and homeostasis. Silent mating type information regulator 2 homolog-1 (SIRT1) is an important histone deacetylase that regulates proliferation, differentiation, aging, and inflammation processes; moreover, it is an essential factor for chondrogenesis. The specific mechanism of SIRT1 in cartilage differentiation and homeostasis is still unclear. First, we investigated whether SIRT1 could coordinate BMP2-induced chondrogenic differentiation. Second, we investigated the protective effect of SIRT1 on BMP2-induced MSCs under oxidative stress. The results showed that SIRT1 could promote BMP2-induced chondrogenic differentiation of MSCs, and reduce the apoptosis and decomposition of extracellular matrix under oxidative stress. In summary, these results suggested that SIRT1 plays an important coordination role in BMP2-induced chondrogenic differentiation of stem cells and cartilage maintenance under oxidative stress, establishing the experimental basis for exploring the use of SIRT1 in cartilage defect repair.
Workers in the iron casting industries are exposed to various chemicals, especially graphite in furnace process. This study aims to investigate the toxic effects of graphite particles on human lung ...cells. Particle characteristics were confirmed by electron microscope and light scattering. Cell viability and oxidative stress markers were measured. The expression of oxidative repair genes, namely OGG1, MTH1, and ITPA, was evaluated. The average particle size was determined to be 172.1 ± 11.96 nm. The median inhibition concentration (IC
50
) of graphite particles was 46.75 µg/mL. Notably, 25 and 50 µg/mL concentrations resulted in significant GSH depletion and MDA production. The high concentration of graphite particles (200 µg/mL) led to OGG1 suppression and increased MTH1 expression. Based on these findings, graphite exposure may induce toxicity in human lung cells by increasing oxidative stress. Further research is necessary to fully understand the mechanisms underlying graphite toxicity.
The significance of implementing long-term structural health monitoring systems for large-scale bridges, in order to secure structural and operational safety and issue early warnings on damage or ...deterioration prior to costly repair or even catastrophic collapse, has been recognized by bridge administrative authorities. Developing a long-term monitoring system for a large-scale bridge—one that is really able to provide information for evaluating structural integrity, durability and reliability throughout the bridge life cycle and ensuring optimal maintenance planning and safe bridge operation—poses technological challenges at different levels, from the selection of proper sensors to the design of a structural health evaluation system. This paper explores recent technology developments in the field of structural health monitoring and their application to large-scale bridge projects. The need for technological fusion from different disciplines, and for a structural health evaluation paradigm that is really able to help prioritize bridge rehabilitation, maintenance and emergency repair, is highlighted.
One of the main objectives of the APPLET project was to quantify the variability of concrete properties to allow for a probabilistic performance-based approach regarding the service lifetime ...prediction of concrete structures. The characterization of concrete variability was the subject of an experimental program which included a significant number of tests allowing the characterization of durability indicators or performance tests. Two construction sites were selected from which concrete specimens were periodically taken and tested by the different project partners. The obtained results (mechanical behavior, chloride migration, accelerated carbonation, gas permeability, desorption isotherms, porosity) are discussed and a statistical analysis was performed to characterize these results through appropriate probability density functions.
The detection of cracks is the most important step during the inspection of bridge substructures. However, traditional crack detection methods are subjective and expensive. Therefore, crack detection ...techniques based on image processing have been proposed. In this paper, a long-distance image acquisition device and an integrated image processing method are proposed for precisely extracting cracks. The proposed method consists of three parts. Firstly, general steps for crack extraction are realized which include image clipping, enhancement, smoothing, segmentation, crack marking and rotation. Secondly, the electronic distance measurement algorithm is approved to calculate the crack width in millimeters. Finally, an improved image segmentation algorithm based on C–V model is provided for crack extraction. We evaluate the proposed method on a collection of 1000 bridge images which have been gathered under different conditions. Experimental results show that the modified algorithm could effectively improve the detection precision rate and reduce the running time.
•We provide a long-distance image acquisition device for detecting cracks.•We provide an integrated image processing method for extracting cracks.•An improved image segmentation algorithm based on C–V model is provided.•We develop dedicated software for the crack detection system.•We realize the image mosaic for producing a crack panorama.
Checking for mistakes: By conjugating a catalytic domain with a guide RNA, deamination activity can be harnessed to repair a specific codon on mRNA. This method can be used for the highly selective ...repair of point mutations in mRNA by site‐selective editing.
Superhydrophobic surfaces show promise in a wide variety of potential applications that require self‐cleaning, antifogging, anti‐icing, anticorrosion, and antifouling properties. However, these ...surfaces often exhibit poor durability against physical or chemical damage, such as deep cut, ultraviolet irradiation, and oxygen plasma treatment. Superhydrophobic surfaces with self‐repairing properties have been recently developed to overcome these durability issues. The recent progress in the fabrication and characteristics of self‐repairing superhydrophobic surfaces, including chemical component, physical structure, and combined repair is summarized. The application of these superhydrophobic surfaces is also described. The critical limitations regarding self‐repairing surfaces are highlighted and perspectives on future development are discussed.
An overview of the recent progress in the fabrication and characteristics of self‐repairing superhydrophobic surfaces is provided, including chemical component, physical structure, and combined repair. The application of superhydrophobic coatings is briefly described and the advantages and disadvantages of self‐repairing superhydrophobic coatings are highlighted. Further, outlook on future research and development are provided.
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