Study on pressure relief and permeability enhancement effect of cutting coal seam with diamond-bead wire saw

In order to explore the pressure relief and permeability enhancement effect around coal seam slot cut by diamond-bead wire saw, firstly, the mechanical model of a doubly clamped roof beam based on the stress of the slot roof was established to analyze the force characteristics of the roof beam and the characteristics of the sinking contact bottom of slot roof (referred to as the contact bottom). Besides, the self-designed physical similarity simulation test platform was used to carry out various similar simulation tests to analyze the stress and displacement changes of coal and rock strata above and below the slot after cutting the seam using wire saw with different process parameters. Finally, based on the FLAC3D numerical simulation and the development of a coal seam gas permeability calculation program, the distribution characteristics and periodic evolution laws of stress and permeability of coal and rock mass around the advancing slot of the coal working face were analyzed. The research shows that the wire saw cuts seams, which makes the stress around the slot redistribute, and the slot roof passes through three evolution forms of roof hanging, roof contact with the bottom, and continuous sinking with the advancement of the working face. When the roof does not touch the bottom, the upper and lower parts of the slot form a ‘U’-type pressure relief zone. The maximum deflection is at the center of the roof, which is also the first part to contact the bottom. After the roof contacts the bottom, the stress recovery occurs in the middle of the slot, which weakens the pressure relief and permeability enhancement effect of the slot. The larger the diameter of the diamond-bead wire saw is, the larger the ultimate span of the roof bottom is, the later the slot contacts the bottom, and the better the pressure relief effect is. With the same slot diameter, the second slot is added, and the pressure relief zone of the two slots is connected. The pressure relief effects promote each other, which weakens the stress recovery under the action of the two slots and increases the pressure relief range. When the slot advancing distance is long enough, due to the roof contacting the bottom, the pressure relief and permeability enhancement effect on both sides of the slot is better. The influence range of pressure relief is divided into stress concentration zone, pressure relief zone, stress recovery zone, pressure relief zone and stress concentration zone from left to right. The corresponding pressure relief zone and stress recovery zone have a better permeability enhancement effect

Why elderly in rural China didn’t wear masks during the COVID-19 pandemic? A qualitative narrative interview study

Abstract Background During the COVID-19 pandemic, ageism and stigmatization towards the elderly have been prominent issues. In addition, there have been debates on Chinese social media as to why elderly people in rural areas are not wearing masks. While some factors that affect the mask-wearing behaviour of the elderly have been analyzed, little attention has been given to the lived experiences and behavioral intentions of rural elderly people who choose not to wear masks, despite government mandates to do so. Method In this research, 50 semi-structured interviews with 30 elderly individuals in three Chinese villages were carried out using the qualitative method of semi-structured interviews. Following verbatim recording and transcription of the conversations, the subject was analyzed using the Theory of Reasoned Action. Results We identified four factors that influence the non-masking behaviour of rural elderly, including past experiences, cultural concepts, cognitive attitudes, and health and safety anxiety, and identified nine sub-themes based on the four overarching themes. Past knowledge, experience, and history have led rural elderly people to distrust the government's mandatory “mask mandate,” believing that they do not need to wear masks. Rural cultural concepts and habits make the elderly feel that masks not only fail to provide protection but also become obstacles, resulting in poor daily experiences. Cognitive attitudes and emotions determine the elderly's evaluation of masks, which in turn affects their use of masks. Finally, elderly individuals’chronic diseases directly affect the physical pain and life safety caused by their use of masks, which is a major objective factor for their non-masking. Conclusions Although numerous studies have concluded that Chinese people wore masks out of collectivism and conformity during the pandemic, marginalized groups' opposition to wearing masks also contains distinctive, individualized elements and underlying causes. By exposing these elements and reasons, we can better comprehend the peculiar behavior of particular groups while fighting the pandemic. The needs of marginalized populations should be prioritized by public health policy makers to provide more equitable services

Design and Implementation of A Circuit Board Calibration System

With the development of science and technology, the traditional artificial detection methods cannot meet the requirements of modern equipment testing and calibration. Combined with the actual demand, a kind of circuit boards calibration system are put forward. It can to realize automatic testing and calibration of the circuit boards. Many functions of the calibration system such as automatic testing, self-test and monitoring are summarized. The hardware is introduced which including the industrial computer system, calibration adapter and so on. Then, development platform, the thought of program design and the structure of the software are introduced in detail. The function of automatic calibration to specific circuit boards are realized. Because the system has good commonality and easy to extend to upgrade, the development ideas and experiences can be applied to similar circuit boards automatic testing system

Design and Implementation of A Circuit Board Calibration System

With the development of science and technology, the traditional artificial detection methods cannot meet the requirements of modern equipment testing and calibration. Combined with the actual demand, a kind of circuit boards calibration system are put forward. It can to realize automatic testing and calibration of the circuit boards. Many functions of the calibration system such as automatic testing, self-test and monitoring are summarized. The hardware is introduced which including the industrial computer system, calibration adapter and so on. Then, development platform, the thought of program design and the structure of the software are introduced in detail. The function of automatic calibration to specific circuit boards are realized. Because the system has good commonality and easy to extend to upgrade, the development ideas and experiences can be applied to similar circuit boards automatic testing system

Toxicity and fate of cadmium in hydroponically cultivated lettuce (Lactuca sativa L.) influenced by microplastics

Although more attention has been paid to microplastics (MPs) pollution in environment, research on the synthetic influence of microplastic and heavy metals remains limited. To help fill this information gap, we investigated the adsorption behavior of virgin polyvinyl chloride microplastics (PVCMPs) (≤450 µm white spherical powder) on cadmium (II). The effects on seed germination, seedling growth, photosynthetic system, oxidative stress indicators of lettuce, and changes in Cd bioavailability were evaluated under Cd2+ (25 μmol/L), PVCMPs (200 mg/L), and PVCMP-Cd combined (200 mg/L + 25 μmol/L) exposures in hydroponic system. The results demonstrated that the PVCMPs effectively adsorbed Cd ions, which validated by the pseudo-second-order kinetic and the Langmuir isotherm models, indicating the sorption of Cd2+ on the PVCMPs was primary chemisorption and approximates monomolecular layer sorption. Compared to MPs, Cd significantly inhibits plant seed germination and seedling growth and development. However, Surprising improvement in seed germination under PVCMPs-Cd exposure was observed. Moreover, Cd2+ and MPs alone or combined stress caused oxidative stress with reactive oxygen species (ROS) including H2O2, O2- and Malondialdehyde (MDA) accumulation in plants, and substantially damaged to photosynthesis. With the addition of PVCMPs, the content of Cd in the leaves significantly (P<0.01) decreased by 1.76-fold, and the translocation factor and Cd2+removal rate in the water substantially (P<0.01) decreased by 6.73-fold and 1.67-fold, respectively in contrast to Cd2+ stress alone. Therefore, it is concluded the PVCMP was capable of reducing Cd contents in leaves, alleviating Cd toxicity in lettuce. Notably, this study provides a scientific foundation and reference for comprehending the toxicological interactions between microplastics and heavy metals in the environment

Microstructure and Mechanical Properties of 4343/3003/6111/3003 Four-Layer Al Clad Sheets Subjected to Different Conditions

To meet the lightweight demands of automobiles, Al composite sheets require excellent mechanical properties under the condition of minimal thickness after high-temperature brazing processing. Generally, the standard used Al brazing sheets have a low strength before and after brazing. To overcome this issue, this work develops a novel 4343/3003/6111/3003 four-layer Al clad sheet, whose microstructure and mechanical properties are systematically investigated. The results show the observable fibrous microstructure with elongated grains parallel to the rolling direction in the developed four-layer Al clad sheet of the cold-rolled and annealed states. After brazing, this fibrous microstructure transforms into coarse equiaxed grains. In addition, the 4343 layer is the brazing layer. Si is mainly distributed in the 4343 layer of the cold-rolled Al clad sheets, whereas Si penetrates into the core layer along the grain boundaries after brazing. The cold-rolled samples present a certain brittleness from fracture morphology, whereas the final annealed ones show a typical ductile fracture. Meanwhile, the typical intergranular fracture is visible after brazing. The mechanical properties of the Al clad sheets are improved after brazing, with an increase of 76% in tensile strength and 62% in yield strength, compared with the final annealed ones. The elongation is increased by 29% compared with that of the cold-rolled ones. This study provides a theoretical basis for further improvement of the strength of aluminum honeycomb panels

Fluoride-free and low concentration template synthesis of hierarchical Sn-Beta zeolites: efficient catalysts for conversion of glucose to alkyl lactate

Hierarchical Sn-Beta zeolite was prepared through a hydrothermal postsynthesis method, which employed no fluoride and only a small amount of tetraethyl ammonium hydroxide (TEAOH). The dual roles of TEAOH as a base and as a structure directing agent were discussed in detail, which were significantly affected by its concentration. At a TEAOH concentration of 0.2-0.4 mol L-1, hierarchical Sn-Beta zeolites with the most probable mesopore diameter of 7.8 nm were achieved. Other physicochemical properties of the hierarchical Sn-Beta including the content and state of Sn and the acidity were also characterized. The hierarchical Sn-Beta zeolite gave a higher yield of methyl lactate (58%) than the microporous Sn-Beta zeolite synthesized in fluoride medium (47%) due to the promoting effect of the hierarchical porosity on the conversion of glucose in methanol, which is an important and challenging process of a bio-refinery. The hierarchical Sn-Beta zeolite is stable and can be recycled and reused five times without significant loss of activity and selectivity

Photosynthetic Responses of <i>Racomitrium japonicum</i> L. to Strontium Stress Evaluated through Chlorophyll a Fluorescence OJIP Transient Analysis

Nuclides pollution and its biological effects are of great concern, especially for bryophytes during their terrestrial adaptation. Understanding PSII activity and electron transport response is vital for comprehending moss abiotic stress reactions. However, little is known about the photosynthetic performance of moss under nuclide treatment. Therefore, this study aimed to evaluate the chlorophyll fluorescence of Racomitrium japonicum L. The moss was subjected to Sr2+ solutions at concentrations of 5, 50, and 500 mg/L to evaluate chlorophyll a fluorescence using the OJIP test. Moderate and high Sr2+ stress led to inner cell membrane dissolution and reduced chlorophyll content, indicating impaired light energy absorption. At 5 mg/L Sr2+, fluorescence kinetics showed increased light energy capture, energy dissipation, and total photosynthetic driving force, thus stimulating transient photosynthetic activity of PSII and improving PSI reduction. Linear electron transfer and PSII stability significantly decreased under moderate and high Sr2+ stress, indicating potential photosynthetic center damage. Cyclic electron transfer (CEF) alleviated photosynthetic stress at 5 mg/L Sr2+. Thus, low Sr2+ levels stimulated CEF, adjusting energy flux and partitioning to protect the photosynthetic apparatus. Nevertheless, significant damage occurred due to inefficient protection under high Sr2+ stress

Serum angiopoietin-2 and β-hCG as predictors of prolonged uterine bleeding after medical abortion in the first trimester.

OBJECTIVE: The combination of mifepristone and misoprostol is an established method for induction of early first trimester abortion, but there is no consensus about the best evaluation of treatment outcome. We evaluate serum Angiopoietin-2 (Ang-2) and β human chorionic gonadotropin (β-hCG) in women who had undergone a medical abortion as markers of prolonged uterine bleeding (PUB). METHODS: Prospective trial involving 2843 women attending an gynecology outpatient clinic who following a medical abortion with mifepristone and misoprostol, the study cohort was divided into women with duration of uterine bleeding >14 days (PUB) and women with duration of uterine bleeding ≤14 days (normal uterine bleeding, NUB). Serum determinations of Ang-2 levels by ELISA and β-hCG levels by electrochemiluminiscence immunoassay. Receiver Operating Characteristics (ROC) analyses were calculated and plotted for the diagnostic accuracy of serum β-hCG and Ang-2 concentration to discriminate PUB and NUB. RESULTS: Baseline characteristics for both groups were similar, Only duration of bleeding showed a significant difference between the PUB group and NUB group. Ang-2 serum levels moderately correlated with serum β-hCG levels with statistically significant correlation coefficients of 0.536. Serum β-hCG and Ang-2 levels on day 7 and on day 14 after medical abortion were signifcantly higher in PUB group than in NUB group. Plotted as ROC curves, β-hCG area under curve (AUC) was 0.65 (95% CI, 0.53-0.76) on day 7, rising to AUC = 0.83 (95% CI, 0.75-0.92) on day 14. Using Ang-2 on day 7 and day 14 as predictive parameter resulted in an analogous AUC (AUC = 0.61 on day 7, AUC = 0.78 on day 14). CONCLUSIONS: Both parameters are clinically useful as a diagnostic test in predicting PUB after medical abortion, and can be helpful in uncertain clinical situations, but should be considered as supplementary to a general clinical evaluation