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Additional file 1: Table S1. Prevalence of depressive symptoms of employed people by socio-demographic group, in 2011, 2013, 2015 and 2018.

Additional file 2: Figure S1. Pathway of retirement and related confounding variables on depression. Figure S2. Prevalence of depression by work status and socioeconomic levels(a), chronic disease(b), and contact with children(c), respectively.

Diffusion is an important mass transfer mode of tight sandstone gas. Since nano-pores are extensively developed in the interior of tight sandstone, a considerable body of research indicates that the type of diffusion is mainly molecular diffusion based on Fick’s law. However, accurate modeling and understanding the physics of gas transport phenomena in nano-porous media is still a challenge for researchers and traditional investigation (analytical and experimental methods) have many limitations in studying the generic behavior. In this paper, we used Nano-CT to observe the pore structures of samples of the tight sandstone of western of Sichuan. Combined with advanced image processing technology, three-dimensional distributions of the nanometer-sized pores were reconstructed and a tight sandstone digital core model was built, as well the pore structure parameters were analyzed quantitatively. Based on the digital core model, the diffusion process of methane molecules from a higher concentration area to a lower concentration area was simulated by a finite volume method. Finally, the reservoir’s concentration evolution was visualized and the intrinsic molecular diffusivity tensor which reflects the diffusion capabilities of this rock was calculated. Through comparisons, we found that our calculated result was in good agreement with other empirical results. This study provides a new research method for tight sandstone digital rock physics. It is a foundation for future tight sandstone gas percolation theory and numerical simulation research.

Batch and continuous co-treatment of two typical hazardous wastes via supercritical water oxidation technology (SCWO) was investigated, that is, oil-based drill cuttings (OBDC) from a shale gas field and high-nickel-content electroplating sludge (Ni-EPS) from an electroplating factory. OBDC, an extreme representative of hazardous waste rich in organic materials, acts as an auxiliary fuel that provides heat from exothermic reactions during SCWO. The average reaction temperature in the continuous reactor increased from 378 °C to 495 °C. Ni-EPS, an extreme representative of hazardous waste rich in metals, acts as both a diluent and a catalyst. Metals in the Ni-EPS tend to form NiFe2O4, ZnFe2O4, and NiCr2O4 after SCWO treatment, and when OBDCs are present, they are transformed into metal oxides (MOx). All the metal oxides are in the form of nanoparticles and exhibit catalytic activity. Owing to the synergistic effect of high temperature and in-situ formation of nanocatalyst materials, the total organic carbon (TOC) in the effluents was as low as 8 mg L−1, and the TOC removal efficiency (CRE) reached as high as 99.96%. This study provides an alternative process for the efficient and complete treatment of hazardous waste, and the obtained information will be helpful for commercialization of SCWO technology.

The feasibility of coordinated use of water-based drilling cuttings (WDC), fly ash, and phosphogypsum (PG) as raw materials for the preparation of WDC non-autoclaved aerated concrete (WNAAC) was evaluated by laboratory experiment. The results showed that the pozzolanic reaction of the multi-component cementitious system containing 40% (in mass) of WDC is significantly promoted. Newly formed C-S-H gel and ettringite with the uniform distribution of fibrous and flake-like shape occur, presenting a denser and interlock microstructure. In addition, after cured by steam at 80 °C for 24 h, the mechanical property and unit weight of the WNAAC prepared with 40% WDC fully meet the B06, A3.5 grade of China state standard (GB/T11968-2006). Environmental performance tests confirm that the WNAAC prepared with 40% WDC does not create any secondary contamination.

Research and development of water lock inhibiting measures is very crucial in verifying the link mechanism between the internal factors of water lock and its extent of damage. Based on conventional water-lock physics experiments, however, only the consequence of macro water lock damage can be investigated, while the microscopic mechanism cannot be studied. In this paper, 3D digital cores of low-permeability sandstones were prepared by means of high-resolution micro-CT scan, and their equivalent pore network model was built as well. Virtual “imbibition” experiments controlled by capillary force were carried out by using pore-scale flow simulation. Then the link mechanism between the microscopic internal factors (e.g. wettability, water saturation and pore–throat structure parameters) and the water-lock damage degree was discussed. It is shown that the damage degree of water lock reduces gradually as the wettability transits from water wet to gas wet. Therefore, the water lock damage can be reduced effectively and gas-well productivity can be improved so long as the capillary environment is changed from strong water wettability to weak gas wettability. The more different the initial water saturation is from the irreducible water saturation, the more serious the water lock damage is. The damage degree of water lock is in a negative correlation with the coordinate number, but a positive correlation with the pore–throat ratio. Based on the existing research results, water lock tends to form in the formations composed of medium-sized throats. It is concluded that there is a critical throat radius, at which the water lock is the most serious.

Wireless sensor network has the advantages of low cost, low energy consumption, high flexibility and convenient deployment. It has a wide application market in environment, military, medical and other fields. In the wireless sensor network, LEACH algorithm could cause the waste of node energy due to the cluster nodes are far away from the cluster head and close to the base station. To solve this problem, a partition sensor network scope K-LEACH algorithm was proposed based on the LEACH algorithm. It introduced the distance parameter K. Nodes within the scope of base station as the center and k as the range of radius did not participate in cluster head election rotation, and communicate with the base station directly. The optimal value of k was selected from the experimental results. Through simulation, the analysis compares of the performance between LEACH and K-LEACH algorithm were provided mainly focus on the network stabilization and life cycle.

The compressive strength of shale is a comprehensive index for evaluating the shale strength, which is linked to shale well borehole stability. Based on correlation analysis between factors (confining stress, height/diameter ratio, bedding angle, and porosity) and shale compressive strength (Longmaxi Shale in Sichuan Basin, China), we develop a dimension analysis-based model for prediction of shale compressive strength. A nonlinear-regression model is used for comparison. A multitraining method is used to achieve reliability of model prediction. The results show that, compared to a multi-nonlinear-regression model (average prediction error = 19.5%), the average prediction error of the dimension analysis-based model is 19.2%. More importantly, our dimension analysis-based model needs to determine only one parameter, whereas the multi-nonlinear-regression model needs to determine five. In addition, sensitivity analysis shows that height/diameter ratio has greater sensitivity to compressive strength than other factors.

Rainfall-induced soil erosion of a mountain area plays a significant role in supplying sediment and shaping the landscape. The related area of soil erosion, as an index of the changed landscape, is easier to calculate visually using some popular imaging tools. By image analysis, our work shows that the changing of the soil erosion area admits the structure of an S-growth curve. Therefore, we propose to establish an S-curve model, based on incremental learning, to predict the soil erosion area. In the process of incremental learning, we dynamically update the accumulative rainfall and rainfall intensity to train the parameters of our S-curve model. In order to verify our prediction model, the index of area is utilized to express the output of eroded soil in a series of experiments. The results show that the proposed S-growth curve model can be used to estimate the growth of the soil erosion area (average relative error 3%–9.7%) according to variable soil material and rainfall intensity. The original S-growth curve model can calculate the erosion areas of just one soil material and one rainfall condition whose average relative error is 7.5%–12.2%, compared to the simple time series analysis-moving average method (average relative error 5.7%–12.1%), our proposed S-growth curve model can reveal the physical mechanism and evolution of the research object.

Shale gas reservoirs have risen in importance in China’s new power source exploration and development program. The investigation of the propagation of ultrasonic waves in shale forms the basis for the full waveform application of acoustic logging data to the exploration of shale gas. Using acoustic wave theory, initial conditions, vibration source conditions, and stability conditions are developed in combination with experimental background of ultrasonic wave transmission. With improved boundary conditions, we performed numerical simulations of the ultrasound transmission experiments in shale using the high-order staggered-grid finite difference method (second-order in the time domain and fourth-order in the space domain). With programs developed within MatLab, the results obtained from numerical simulations agree well with experimental results based on physical models. In addition, using snapshots of the wave field that give a microscopic perspective, the propagation laws for ultrasonic waves can be analyzed. Using this method, human error is avoided, transmission experiments costs can be reduced and efficiency improved. This method extends the scope of experimental investigations regarding the transmission of ultrasonic waves in a shale gas reservoir with increasing stratification, and thus has great theoretical value and practical significance.

The averaging in optimal switching control problems is considered under the following two cases: the switching cost does not depend on ∈ and the switching cost vanishes as ∈ tends to zero. The value function of the original fast problem converges locally uniformly to the value function of the averaged problem under both cases. The ways of averaging turn out to be different between both cases.

Field experiments, designed to evaluate the effect of direct application of phosphate rock, were carried out on red soil (Ultisol) uplands at three different places. The results indicated: (1) for the first year's crop, the rapeseed yields with phosphate rock treatment and triple superphosphate treatment were almost identical when their rate of phosphorus application was the same; (2) when the same level of phosphorus fertilizer was applied, the residual effect of phosphate rock was better than that of triple superphosphate, and the residual effect of all phosphorus fertilizers on winter crop yields increased with the increase of the amount of Phosphorus applied; (3) with the application of phosphate rock, the pH value, the amount of available phosphorus and exchangeable Ca and Mg of soils went up, whereas the content of active Al in soils decreased. Therefore, the direct application of phosphate rock to red soil also has an important role in improving soil properties.