Search

Under the Internet+ information era background, the barriers between traditional and modern education are melting away. This paper takes the OMO teaching mode as the entry point and constructs the design of professional practical training teaching of landscape engineering technology based on virtual simulation technology analysis of the OMO teaching mode. While drawing on the OMO teaching mode, it combines the system posture detection and binocular vision position-solving technology in virtual simulation to build a cyclic development system of OMO mode and professional practical teaching of landscape engineering technology and promote the deep integration of the two. The experimental results show that through 18 weeks of comparison between the OMO teaching mode based on virtual simulation technology and the traditional teaching mode of practical teaching, it is found that the average scores of students are 84.31 and 77.41, respectively, with an effective increase of 10% in performance. Regarding student participation, the OMO teaching mode based on virtual simulation technology mainly focuses on the 68-82 range, effectively stimulating students’ enthusiasm. The OMO teaching mode based on virtual simulation technology proposed in this paper can effectively improve the current problems of traditional teachings, such as resources without rules and regulations, poor correlation, and one-sided evaluation methods, to more effectively cultivate students’ independent learning ability and improve their vocational skills.

In the present research work, the 2.25Cr1Mo0.25V steel plates with a thickness of 112 mm were welded using the multi-pass submerged automatic arc welding process. The creep specimens were prepared from the base metal (BM) and weld metal (WM) in the welded joint after heat treatment process. The uniaxial creep tests were performed to investigate the creep deformation and rupture behaviors at 550°C under different applied stress levels. The microstructure and fracture surface morphology of crept BM and WM samples were also characterized using the scanning electron microscope with energy-dispersive X-ray spectroscopy. The results showed that typical three-stage creep deformation curves are observed in both BM and WM specimens, and the BM exhibits a faster deformation rate than the WM. Both the creep rupture time and uniaxial creep ductility are found to be increased with a decrease in applied stress. Furthermore, the relationship between the minimum creep rate and time to rupture of both BM and WM samples was obtained, and it can be described using a unified Monkman–Grant equation. In addition, it is found that the creep fractures of the BM and WM are a transgranular ductile failure. The creep damages of both materials are mainly associated with the microstructural degradations, that is, the initiation and coalescence of creep cavities at second phase particles such as carbide and inclusion particles along the loading direction.

High-dimensional nonlinear relationships between the irradiated yield strength and its influencing factors, including doses, temperatures, and crystal structures, are difficult to explicitly characterize in the absence of a comprehensive database. In this study, we developed a machine learning method with the Fourier-transform-based feature extension, successfully constructing the prediction model of irradiated yield strength by a relatively small and sparse database of irradiated material properties. The analysis suggests that the proposed feature extension method improves the training performances of machine learning with small dataset. And the present model is accurate and feasible for predicting the irradiated yielding behaviors. Furthermore, we attempt the inverse machine learning model to determine material properties and irradiation conditions according to the desired yield strength. Since the parameter combinations commensurate with a fixed strength are diverse, the optimal model is helpful in reversely calculating and optimizing material performances. The data-driven machine learning method, which can detect the implicit correlations among numerous data, exhibits great prospects in investigating irradiated mechanical properties and exploring multiscale links in the nuclear material field. This work holds the promise for optimizing the design of in-pile structural components and can be further extended to other machine learning problems with the small dataset. [ABSTRACT FROM AUTHOR]

In this paper, graphite and Fe2O3 are introduced into MgH2 powder by the method of hydrogenation after magnetic grinding. Hydrogen storage materials which composite of MgH2–5 wt.% C and MgH2–5 wt.% C–5 wt.% Fe2O3 are successfully prepared. The physical structure of these materials was analyzed and characterized by XRD, SEM, etc. Furthermore, the influence of graphite and Fe2O3 on the hydrolysis of MgH2 was systematically investigated. The results show that MgH2–C–Fe2O3 composite powder has the fastest hydrogen release rate in municipal drinking water and the highest conversion rate. Graphite and Fe2O3 can effectively reduce the activation energy of the hydrolysis reaction of MgH2 and improve the hydrolysis kinetics of MgH2. The synergistic effect of the coaddition of graphite and Fe2O3 can significantly increase the hydrolysis conversion rate of MgH2 and improve the hydrolysis kinetics. [ABSTRACT FROM AUTHOR]

A unified method of evaluating the dispersed microdefects' equivalent damage area/volume is innovatively proposed by using the M-integral. The corresponding damage evolution rate and fatigue driving force is preliminarily studied for the dispersed microdefects. First, the analytical expression of M-integral is deduced by using the Lagrangian energy density function (Λ), and the corresponding physical meaning of the M-integral is elucidated as the change of the total potential energy due to the damage evolution. Second, the actual damage area/volume induced by underlying dispersed microdefects are assumed equivalent to the area/volume of an individual circular/spherical void while the corresponding values of the M-integral for both cases are equal. As examples, the equivalent damage area associated with the M-integral for a series of representative defect(s) configurations is calculated, including the singular defect (void, crack, and ellipse) and the interactive defects (two voids, two cracks, one void, and one crack). The influences of the defects interaction effect and distribution on the damage level are analyzed quantitatively. Finally, the present method of damage evaluation is proposed to predict fatigue problems of the dispersed defects. A unified fatigue damage evolution law for the dispersed microdefects is preliminarily defined, and a protocol to experimentally measure the damage evolution rate is proposed. The present research will be beneficial to the damage tolerance design and lifetime prediction of engineering structures with dispersed microdefects. [ABSTRACT FROM AUTHOR]

The fundamental concepts of material configurational mechanics are formulated in piezoelectric materials. A consistent thermodynamic framework is outlined to develop the corresponding theory of material configurational stresses and forces associated with the $$J_{k}$$ -, M- and L-integrals by the gradient, divergence and curl operation of the electric enthalpy density, respectively. The physical interpretation of material configurational stresses is explored, and they can be explained as the energy release rates due to the translation of material point along $$x_{k}$$ -direction, the self-similar expansion, the rotation of material element, respectively. The path independence or path dependence of variant integrals such as the $$J_{k}$$ -, M- and L-integrals is examined in piezoelectric material. As an application of material configurational mechanics in piezoelectric materials, an explicit method is derived to calculate the change of the J-integral as a dominant fracture parameter for a crack interaction with domain switching near the crack tip. It is concluded that domain switching has an obvious shielding effect on the fracture toughness in piezoelectrics by the present explicit forms. The present framework of material configurational mechanics is expected to provide an effective and convenient tool to deal with various crack or damage problems in piezoelectric materials. [ABSTRACT FROM AUTHOR]

In order to improve some characteristics of a β-1,3-1,4-glucanase from Bacillus subtilis MA139, directed evolution was conducted in this study. After error-prone PCR, the β-1,3-1,4-glucanase gene, glu-opt, was cloned into the vector pBGP1 and transformed into Pichia pastoris X-33 to construct a mutant library. Three variants named as 7-32, 7-87, and 7-115 were screened from 8000 colonies. Amino-acid sequence analysis showed that these mutants had one or two amino-acid substitutions (7-32: T113S, 7-87: M44V/N53H, and 7-115: N157D). The variants were over-expressed in P. pastoris by methanol induction. After purification of the enzyme proteins, the characteristics of the variants were analyzed in detail. It indicated that these mutant enzymes had broader ranges of pH value and better pH stability than the wild-type enzyme. The mutant enzyme 7-87 had the best ability to tolerate an acid environment (pH 2.0), while the wild-type enzyme had no activity under this condition. Moreover, all these mutants demonstrated improved thermal stability. In particular, the mutant enzyme 7-32 had residual enzymatic activity of 60% and 40% after being incubated at 80 °C and 90 °C for 10 min. While, the wild-type enzyme had no residual enzymatic activity after being incubated at 80 °C for 4 min. In addition, the mutant enzymes had better tolerance to some chemicals than the wild-type enzyme. The improved stability could enhance the prospects for this enzyme to have use in the feed industry to reduce the effects of the anti-nutritional factor β-glucan. [ABSTRACT FROM AUTHOR]