tang 1,2 ✉ to evaluate tooth behaviours under various maxillary incisor retraction protocols for clear aligner therapy. A three-dimensional finite element model of maxillary dentition was constructed for first premolar extraction. A loading method was developed to mimic the mode of action of clear aligners for incisor en masse retraction. Three protocols with different amounts of retraction and intrusion on incisors were designed. Initial tooth displacements and stresses on periodontal ligaments were analysed with ANSYS software. The central (U 1) and lateral (U 2) incisors exhibited uncontrolled lingual tipping and extrusion upon 0.25 mm retraction. U1 exhibited translation movement, while U 2 underwent less tipping during 0.2 mm retraction and 0.15 mm intrusion. Labial tipping and intrusion of U 1 and bodily intrusion of U 2 were observed during 0.1 mm of retraction and 0.23 mm of intrusion. With the additional intrusion on incisors, canine showed extrusion movement, and higher stresses on periodontal ligaments were shifted from U 2 to canines. Incisors also exhibited different mesial-distal angulation in the three simulations, while posterior teeth all suffered mesial inclination. Incorporating intrusion displacement in clear aligners led to a tendency of lingual root movement during incisor retraction. the complexity of tooth movement should be recognized regarding clear aligner therapy.
In recent years, the development of computer network technology, especially the hot Internet of things, has brought great convenience and comfort to people's life. Steel structure is also more and more widely used in the field of construction in China. The purpose of this study is to explore the application of Internet of things health monitoring system in steel structure construction management. In this study, through the use of example analysis, comprehensive data analysis and other methods, combined with steel structure health monitoring system and construction process management analysis. The results show that the relative deviation of the data within 1-33 is mostly less than 10%, but the relative deviation of 34-40 suddenly increases to 60%, and the actual data suddenly decreases, resulting in the deviation of about 50%. It is concluded that the time series model established in this study can objectively reflect the change trend and law of strain data, has certain prediction accuracy, and has certain value significance for monitoring data analysis and construction management of steel building structures.
Per- and polyfluoroalkyl substances (PFAS) is the emerging contaminants of critical concern. Comprehensive understanding of the transport and fate of PFAS in the vadose-zone, a type of water-unsaturated porous media, is key to determination of the risks of the PFAS contamination in the subsurface and to the development of the effective remediation strategies. PFAS transport in the unsaturated porous media is a complex process. In order to disclose the main factors controlling the PFAS transport in unsaturated porous media, we develop the theoretical model based on the dimensionless governing equations for the transient water flow and PFAS transport. The effects of the dimensionless parameters and numbers on the PFAS transport in 2D unsaturated porous media are uncovered based on the second order accurate finite volume method. We find that the retardation numbers and the dimensionless parameters relevant to the properties of porous media as well as the relation between the surface tension and the PFAS concentration play an important role in the PFAS transport in the unsaturated porous media. The effects of the Péclet numbe, Damköhler numbers, and fraction of instantaneous sorption are not significant, however. These findings provide a better understanding of the PFAS transport in vadose zone.
Per- and polyfluoroalkyl substances (PFASs) have become emerging contaminants of critical concern. Comprehensive understanding of the transport and fate of PFAS in the vadose-zone, a type of water-unsaturated porous media, is key to determination of the risks of the PFAS contamination in the subsurface and to the development of the effective remediation strategies. Accurate modeling of the PFAS transport in the unsaturated porous media is still a challenge due to the variable surface tension induced by the adsorption of PFAS to the air-water interfaces. In an effort to address this challenge, we propose a multidimensional modeling framework for the transient PFAS transport in the unsaturated porous media based on the second order accuracy finite volume method. In the modeling, the adsorption of PFAS to the solid surfaces and to the air-water interfaces is described by the two-domain sorption kinetics model, i.e., both the instantaneous and the rate limited PFAS adsorptions are taken into account. The diffusive and convective terms in the governing equations for the PFAS transport and the water flow are discretized by the central difference and the quadratic upstream interpolation for convective kinetics schemes, respectively. Both of these two schemes have the second order accuracy. We investigate the effects of the convergent criteria, coupling method, and variation of the surface tension on the average and the local PFAS concentration and water content in the computational domain. We find that the convergent criteria should be chosen carefully so as to get the accurate results. The differences between the different coupling methods are affected by the boundary conditions. The variation in the surface tension due to the variation of the PFAS concentration cannot be neglected. These studies not only guide the numerical schemes used in the modeling but also provide the insights into the transport of PFAS in unsaturated porous media. The multidimensional modeling framework presented in this work can be further extended to explore in detail the transport of PFAS in the vadose-zone.
The rapid development of wind power generator, the service life and efficiency but various fault often will not only shorten the wind generator, also brought the loss of life and property to the people. For fault diagnosis is an effective method of fault diagnosis using the motor vibration signals, This paper adopts the HHT analysis method, the vibration signal of the wind machine for processing fault characteristics are obtained, and the fault diagnosis,improve the efficiency of fault diagnosis, the conclusion shows that it is an effective method of fault diagnosis for fan, troubleshooting and repair of fans have important practical significance.
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