Fatigue Damage Analysis of Composite Insulator Cor Rod/sheath Interface

A self-made fatigue testing machine was used to simulate the damage process of the insulator interface under working conditions and the damage degree is evaluated by the compressive shear test. The improved interface adhesion model reflects the interface debonding process under different fatigue loads by introducing the damage coefficient χ, migration coefficient α and the debonding coefficient μ. The relationship of fatigue loads and interface damage is established by the peeling force, the unit interface separation work and the peeling time. The test demonstrates that the interface damage near the bottom of the insulator is worse than that near the middle part. The result of this analysis will be beneficial in easily finding damaged places of the insulator, and so as to reduce the power breakdown

Association of psychological symptoms with job burnout and occupational stress among coal miners in Xinjiang, China: A cross-sectional study

ObjectiveThe study aimed to investigate the influencing factors of psychological symptoms in relation to job burnout and occupational stress among coal miners in Xinjiang, so as to provide data support for enterprises in an effort to help them identify internal psychological risk factors and improve the mental health of coal miners.MethodsA cross-sectional study was carried out. A total of 12 coal mines were selected using the stratified cluster random sampling method and 4,109 coal miners were investigated by means of online electronic questionnaires. The Symptoms Check List-90 (SCL-90), Chinese Maslach Burnout Inventory (CMBI), and Job Demand-Control (JDC) model were respectively used to measure the status of psychological symptoms, job burnout, and occupational stress among coal miners. The mediation analysis was performed through structural equation modeling (SEM) by using Analysis of Moment Structure (AMOS).ResultsThe prevalence of psychological symptoms was higher in the occupational stress group than in the non-occupational stress group, and increased with job burnout (P < 0.05). The multivariate logistic regression analysis results showed that mild (OR = 1.401, 95% CL: 1.165, 1.685), moderate (OR = 2.190, 95% CL: 1.795, 2.672), or severe levels of burnout (OR = 6.102, 95% CL: 3.481, 10.694) and occupational stress (OR = 1.462, 95% CL: 1.272, 1.679) were risk factors for psychological symptoms in coal miners. The results of structural equation modeling indicated that occupational stress (β = 0.11, P = 0.002) and job burnout (β = 0.46, P = 0.002) had significant positive direct effects on psychological symptoms, and job burnout was an intermediate variable between occupational stress and psychological symptoms.ConclusionHigh levels of job burnout and occupational stress were risk factors for psychological symptoms. Both occupational stress and job burnout had direct effects on psychological symptoms, and occupational stress could also have an indirect effect on coal miners' psychological symptoms through the intermediate variable of job burnout

METTL14 regulates chromatin bivalent domains in mouse embryonic stem cells

METTL14 (methyltransferase-like 14) is an RNA-binding protein that partners with METTL3 to mediate N6-methyladenosine (m6A) methylation. Recent studies identified a function for METTL3 in heterochromatin in mouse embryonic stem cells (mESCs), but the molecular function of METTL14 on chromatin in mESCs remains unclear. Here, we show that METTL14 specifically binds and regulates bivalent domains, which are marked by trimethylation of histone H3 lysine 27 (H3K27me3) and lysine 4 (H3K4me3). Knockout of Mettl14 results in decreased H3K27me3 but increased H3K4me3 levels, leading to increased transcription. We find that bivalent domain regulation by METTL14 is independent of METTL3 or m6A modification. METTL14 enhances H3K27me3 and reduces H3K4me3 by interacting with and probably recruiting the H3K27 methyltransferase polycomb repressive complex 2 (PRC2) and H3K4 demethylase KDM5B to chromatin. Our findings identify an METTL3-independent role of METTL14 in maintaining the integrity of bivalent domains in mESCs, thus indicating a mechanism of bivalent domain regulation in mammals

Development of a Novel Restrictive Medium for Monascus Enrichment From Hongqu Based on the Synergistic Stress of Lactic Acid and Ethanol

Hongqu is a famous fermented food produced by Monascus and has been used as food coloring, wine starters and food additives for thousands of years in China. Excellent Monascus strain is an important prerequisite for producing high-quality Hongqu. However, the isolation of Monascus pure culture from Hongqu samples is time-consuming and laborious because it is easily interfered by other microorganisms (especially filamentous fungi). Therefore, the development of restrictive medium for Monascus enrichment from Hongqu is of great significance for the preparation and screening of excellent Monascus strains. Results of this study showed that Monascus has good tolerance to lactic acid and ethanol. Under the conditions of tolerance limits [7.5% lactic acid (v/v) and 12.0% ethanol (v/v)], Monascus could not grow but it still retained the vitality of spore germination, and the spore activity gradually decreased with the increasing concentrations of lactic acid and ethanol. More interestingly, the addition of lactic acid and ethanol significantly changed the microbial community structure in rice milk inoculated with Hongqu. After response surface optimization, Monascus could be successfully enriched without the interference of other microorganisms when 3.98% (v/v) lactic acid and 6.24% (v/v) ethanol were added to rice milk simultaneously. The optimal enrichment duration of Monascus by the restrictive medium based on the synergistic stress of lactic acid and ethanol is 8∼24 h. The synergistic stress of lactic acid and ethanol had no obvious effects on the accumulation of major metabolites in the progeny of Monascus, and was suitable for the enrichment of Monascus from different types of Hongqu. Finally, the possible mechanisms on the tolerance of Monascus to the synergistic stress of lactic acid and ethanol were preliminarily studied. Under the synergistic stress of lactic acid and ethanol, the cell membrane of Monascus defends against lactic acid and ethanol into cells to some extent, and the superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities of Monascus were higher than those of other fungi, which significantly reduced the degree of lipid peroxidation of cell membrane, while secreting more amylase to make reducing sugars to provide the cells with enough energy to resist environmental stress. This work has great application value for the construction of Monascus strain library and the better development of its germplasm resources

FINITE ELEMENT ANALYSIS OF CONTACT CHARACTERISTIC OF OVERHEAD CONDUCTOR IN AEOLIAN VIBRATION

Overhead transmission line is mainly aluminum conductor steel reinforced（ ACSR）,which is prone to occur fatigue fracture and fretting wear because of the action of the long-time aeolian vibration. A finite element model of the contact between conductor strands was built to carry on the simulation on the stress distribution of the conductor in different static pretension and the dynamic mechanics in aeolian vibration. The results show that the contact stress of strands increase with the pretension,and the stress increment is maximal when the pretension increases from 20% T to 25% T. The contact point stress distribution in axis of the strand is uniform while the pretension is less than 20% T and is uneven while the pretension is more than 20% T. In the condition of arolian vibration,the stress in constrained position and the middle of the test conductor which is imposed vibration is the maximum. Meanwhile,the contact points stress distribution of the same layer is uniform and the contact stress of adjacent layers in axis is cyclical. The frequency has less impact on the amplitude and the fretting displacement

Analytical Solution for Forced Vibration Characteristics of Rotating Functionally Graded Blades under Rub-Impact and Base Excitation

This paper presents an analytical investigation on the forced vibration characteristics of a rotating functionally graded material (FGM) blade subjected to rub-impact and base excitation. Based on the Kirchhoff plate theory, the rotating blade is modelled theoretically. The material properties of the FGM blade are considered to vary continuously and smoothly along the thickness direction according to a volume fraction power-law distribution. By employing Hamilton’s principle, the equations of motion are derived. Then, the Galerkin method and the small parameter perturbation method are utilized to obtain the analytical solution for the composite blade under a combined action of radial force, tangential force and displacement load. Finally, special attention is given to the effects of power-law index, rub-impact location, friction coefficient, base excitation amplitude and blade aspect ratio on the vibration characteristics of the FGM structure. The obtained results can play a role in the design of rotating FGM blades to achieve significantly improved structural performance

ANALYSIS ON THE FATIGUE FRACTURE CHARACTERISTICS OF COMPOSITE INSULATOR CORE ROD

In order to analyze the fatigue fracture surface characteristics of composite insulator core rod, the fatigue damage process of insulators under different amplitude/torsion angle conditions was simulated by dynamic load fatigue test. The surface morphology of insulator fracture was observed by using an super deep scene 3 D microscope, and combined with fatigue loads and the number of stress cycles, the formation mechanism of the fracture surface was analyzed. The fractal geometry theory was used to describe the complexity of the fracture morphology in quantitatively and discussed the relationship between the fractal dimension and the fatigue loads. The results show that the fatigue fracture process of core rod is actually a stress corrosion process, which means that under the action of stress, the crack of the fiber gradually deepens until it breaks. The deformation and abrasion caused by the cyclic stress all determined the fracture surface morphology. The fractal dimension of the fracture surface is between 2 and 3, and the linear regression correlation coefficient is above 0.99, the strong correlation shows that the fracture surface of the insulator has obvious fractal characteristics. The formation of the fracture surface is not only related to the deformation, but also related to the number of stress cycles. The fractal dimension of the fracture surface is positively correlated with the loads and negatively correlated with the number of load cycles

Exploring the relationship between different types of reference group influence and young consumers' health tourism intention

Despite the many achievements in health tourism, relatively few studies conducted on the health tourism consumption decisions of young consumers. This study primarily investigates how different types of reference group influence affect young consumers' health tourism intentions. Based on the theoretical framework of Stimuli-Organism-Response (SOR), a mediation model including perceived value was constructed and structural equation modeling was used to analyze the relationship between the types of reference group influence, perceived value, and health tourism intention. The results showed that both informational influence and utilitarian influence in the reference group influence have a positive impact on health tourism intention. Of these, informational influence is greater. Secondly, perceived value also has a positive effect on consumers' health tourism intention and plays a mediating role between the reference group influence and the health tourism intention. The findings contribute to our understanding of the impact of different types of reference group influence on health tourism intentions and enrich the application of SOR theory. The findings have implications for promoting healthy tourism consumption among young consumers

Effect of Graphite Filling Pore Structure Size on the Tribology Behaviors of Tin Bronze/45 Steel Pairs With Grease Under Low-Speed and Heavy Load Conditions

Copper-based solid lubrication inlay technology is widely used in industrial production, especially in low-speed and heavy load conditions, and the structure and distribution of the filling pore have a significant influence on the friction performance due to the distribution of contact stress. In this paper, based on the operating conditions of the bottom pivot of the Three Gorges gate, graphite is used as a solid filled lubricant. The effects of filling pore diameter, filling pore depth, and area distribution rate on the friction and wear properties were studied by orthogonal equivalent test on MMW-1A tester with grease. Combining the three-dimensional morphology test and ferrography analysis, the results show that: 1) the influence of three parameters on the test results are: filling pore diameter > area distribution rate > filling pore depth; 2) when the filling pore diameter is 3 mm, the area distribution rate is 12%, and the filling pore depth is 0.5 mm, which is the equivalent the optimal structure of the filling pore size under working conditions. According to this conclusion, the actual filling structure can be obtained based on the similarity theory. As Coulomb friction is material and contact stress related, the calculation of the stress distribution during dynamic operation is difficult and therefore the analysis is carried out experimentally