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In this research, four surrogate models appropriate for nonlinear relationship prediction including the Least Squares Support Vector Regression (LSSVR), the Kriging model, the Artificial Neural Network (ANN) and the newly proposed Ada-Kriging model are applied to estimate the structural fatigue damage of offshore wind turbine foundations based on a few structural dynamic response samples simulated by numerical method, and their accuracy and robustness are analyzed aimed to a monopile offshore prototype wind turbine. The results reveal that the Ada-Kriging model improve the efficiency by 20 times compared to the traditional time-domain method with less than 4% error. The Kriging model has similar accuracy with the Ada-Kriging model with enough training data but is less accurate if the amount of training data reduces, and the ANN and LSSVR models perform much worse. By utilizing surrogate models, the short-term and long-term fatigue damages of monopile wind turbine foundations are efficiently analyzed, which are found to reach the maximal value near the rated wind speed and high wave period. Compared to surrogate models, the commonly used superposition methods of wind and wave effects on wind turbines underestimate the fatigue damage. • The efficient fatigue estimation method of offshore wind turbine is developed. • The performance of surrogate models on fatigue estimation is analyzed. • The fatigue characteristics of wind turbine under wind and waves are studied. [ABSTRACT FROM AUTHOR]

Hyperandrogenism is one of the major characteristics of polycystic ovary syndrome (PCOS). Abnormal miR-125b-5p expression has been documented in multiple diseases, but whether miR-125b-5p is associated with aberrant steroidogenesis in preantral follicles remains unknown. Steriod hormone concentrations and miR-125b-5p expression were measured in clinical serum samples from PCOS patients. Using a mouse preantral follicle culture model and a letrozole-induced PCOS mouse model, we investigated the mechanism underlying miR-125b-5p regulation of androgen and oestrogen secretion. The decreased miR-125b-5p expression was observed in the sera from hyperandrogenic PCOS (HA-PCOS) patients. In mouse preantral follicles, inhibiting miR-125b-5p increased the expression of androgen synthesis-related genes and stimulated the secretion of testosterone, while simultaneously downregulating oestrogen synthesis-related genes and decreasing oestradiol release. Ectopically expressed miR-125b-5p reversed the effects on steroidogenesis-related gene expression and hormone release. Mechanistic studies identified Pak3 as a direct target of miR-125b-5p. Furthermore, inhibiting miR-125b-5p facilitated the activation of ERK1/2 in mouse preantral follicles, while inhibiting Pak3 abrogated this activating effect. These results were recapitulated in letrozole-induced PCOS mouse ovaries. Of note, inhibiting PAK3 antagonised the positive effect of miR-125b-5p siRNA on the expressions of androgen synthesis-related enzymes and testosterone secretion. Luteinizing hormone (LH) inhibited miR-125b-5p expression, and stimulated Pak3 expression. High serum LH concentrations in PCOS patients repress miR-125b-5p expression, which further increases Pak3 expression, leading to activation of ERK1/2 signalling, thus stimulating the expression of androgen synthesis-related enzymes and testosterone secretion in HA-PCOS. • MiR-125b-5p is decreased in the sera of HA-PCOS patients. • MiR-125b-5p regulates the release of testosterone and oestradiol. • Pak3 is a direct target of miR-125b-5p , which inhibits the activation of ERK1/2. • LH represses miR-125b-5p expression, but increases Pak3 expression. • LH/ miR-125b-5p /PAK3/ERK1/2 regulates hormone synthesis in follicles. [ABSTRACT FROM AUTHOR]

Cracks are the most common disease in reinforced concrete structures, which seriously affects the stability of the structure. At present, the evaluation criteria for the degree of crack danger are relatively vague, and there are significant shortcomings in the quantitative evaluation of the stability of concrete structures containing cracks. This article comprehensively utilizes numerical simulation, numerical fitting, and fractal theory to establish a quantitative calculation method for structural bearing performance based on crack characteristic parameters. The main research conclusions are as follows: the influence of crack length, direction, and depth characteristic parameters on the bearing performance of reinforced concrete structures is determined through numerical simulation; A quantitative calculation method for structural bearing performance was established using a step-by-step fitting method, which comprehensively considers crack characteristic parameters. On this basis, the fractal theory was used to describe the complexity of cracks and the calculation results of the combined crack-bearing performance were corrected. Compared with numerical simulation and model experiment results, the average error in calculating the structural bearing coefficient was 5%. The research results have improved the accuracy of crack evaluation and can provide an important reference for the safety analysis of cracks in concrete structures. • Through a reinforced concrete calculation model, crack simulation and bearing capacity analysis were achieved. • Revealed the influence of crack length, direction, and depth on bearing performance. • Established a calculation method for crack characteristics and load-bearing performance. [ABSTRACT FROM AUTHOR]

• Bond behaviors between UHPC and deformed rebar were studied by a pullout test. • The effects of cover, embedded length and steel fiber on bond strength were analyzed. • A model for predicting the bond strength between pre- and post-yield rebar and UHPC was proposed. • The distribution of bond stress along the embedded length was analyzed. The ductility of reinforced concrete structures is often determined by the ductility of post-yield deformed rebar. However, to date, few studies have been conducted on the bond behavior of post-yield deformed rebars embedded in ultra-high performance concrete (UHPC). Therefore, a pull-out test was conducted to investigate the effects of the cover, embedded length, and steel fiber on the bond behaviors between UHPC, and pre- and post-yield deformed rebars. The test results showed that a 50% increase in the bond strength could be obtained when the cover was increased from 1 d to 2 d, where d is the diameter of the deformed rebar. As the anchorage length was increased from 2.5 d to 5 d , the bond strength decreased by approximately 50%. Meanwhile, the bond strength increased by 126% with an increase in steel fiber content from 0 to 2%. To predict the bond strength of the pre- and post-yield deformed rebar embedded in UHPC, a modified thick-walled cylinder model was proposed. Subsequently, the distribution of the bond stress along the embedded length was revealed, and the position function was provided. Finally, the bond stress–slip model including the anchorage position function provides an insight into the bond stress between UHPC and deformed rebars. [ABSTRACT FROM AUTHOR]

The analysis of dynamic characteristics is crucial in the design of wind tower structures. The dynamic behavior of wind towers is primarily influenced by structural stiffness and mass distribution. In particular, the segment thickness of prefabricated concrete towers should be selected and optimized based on computed results of stress distribution in order to achieve the desired dynamic performance. The main objective of this research is to investigate the effects of design factors, such as segmental thickness and top mass of wind blades, hub, and nacelle, on the natural frequencies and vibration modes of the precast concrete towers. For the finite element analysis, a high-rise wind turbine tower with a hub height of 120 m (HH120 tower) is utilized. Finally, the theoretical model for the reduced degrees of freedom system is validated using the results from the finite element analysis. • Analysis of dynamic characteristics of high-rise wind turbine tower structures. • The effects of segment thickness of the prefabricated concrete tower on the dynamic properties. • The effects of lumped mass at the tower top on the dynamic properties of the tower. • Comparison between the Finite-element and theoretical models for tower structures. [ABSTRACT FROM AUTHOR]

A porous silicon material (PSM) was successfully prepared by using a CO 2 -storage material (CO 2 SM) as raw material, in which Na 2 SiO 3 was used as a silicon source and the CO 2 SM was used as an acid source. The effects of CO 2 SM dosage, particle size, post-treatment temperature, and post-treatment time on CO 2 adsorption capability was systemically evaluated, and the optimum condition was confirmed by response surface experiments as follows: 10 g CO 2 SM dosage, 50 mL 0.5 M Na 2 SiO 3 , 40–160 mesh, the post-treatment temperature of 80 °C, and the post-treatment time of 36 h with the maximum adsorption capacity of 9.74 mg CO 2 /g adsorbent for 8% CO 2 /N 2 at 25 °C. Based the optimum condition, SiO 3 2− extraction from coal gangue was used as the silicon source to prepare the PSM with the maximum adsorption capacity of 9.02 mg CO 2 /g adsorbent for 8% CO 2 /N 2 at 25 °C. Next, PSM was impregnated with ethanediamine (EDA), after that the CO 2 adsorption capacity increased to 17.14 mg CO 2 /g adsorbent. In addition, the optimum PSM was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and N 2 adsorption-desorption isotherms. Although the resulting materials showed a low adsorption capacity, its silicon source was inexpensive, which was of significance in the rational utilization of coal gangue. [ABSTRACT FROM AUTHOR]