Search

In order to reduce the disturbance energy loss in the process of inlet diversion and outlet jet flow of parallel fan station, taking the parallel connection of two fans as an example, a high-efficiency and low resistance parallel station structure improvement mode is proposed, and the ventilation efficiency and local resistance coefficient formulas of the fan station are deduced based on the principle of aerodynamics. The similar model and the numerical model based on FLUENT software are established to measure the resistance of the improved structure, and the variation laws of the efficiency of the machine station, the local resistance coefficient and the wind speed of the tunnel section are verified. The results show that the efficiency of the improved structure is about 1% higher than that of the general structure fan station, and the local resistance coefficient is about 12% lower.

To improve the ventilation efficiency of mine engine station, aiming at the minimum local resistance coefficient of engine station, the orthogonal numerical simulation test was carried out by selecting four influencing factors including diffusion angle of engine station, roadway length in air inlet, contraction angle and roadway length in air outlet and setting reasonable levels. The results show that the main and the secondary factors affecting the local resistance coefficient of the machine station are diffusion angle, contraction angle, tunnel length in the inlet and the tunnel length in the outlet. With the change of roadway wind speed, the optimal structural parameters of the station are different. When the roadway wind speed is 1.2 m/s to 1.5 m/s, the optimal combination of the structure is 60° diffusion angle, 30° contraction angle, 9 m of roadway length in the inlet section and 6 m of roadway length in the outlet section. When the wind speed is 1.5 m/s to 2 m/s, the local resistance coefficient of 10 m station is selected as the roadway length in the wind outlet section.

To study the mechanical properties changes and deformation of the underground coal pillar dam body in the mine goaf in the underground working environment, the Lijiatun Coal Mine is taken as the research background, and the laboratory similar simulation and FLAC3D numerical simulation method are adopted. The coal samples from 3-1 coal seam of Lijiatun Coal Mine were processed into standard samples according to ISRM. The samples were subjected to water immersion treatment for a certain period of time, and the mechanical properties analysis experiments were carried out. Subsequently, numerical simulation technology was used to simulate the actual working environment of the coal pillar dam and analyze the mechanical properties and deformation of the coal pillar dam. The study shows that water has a softening effect on coal samples. With the increase of water immersion time, the unidirectional compressive strength and unidirectional tensile strength of coal samples have decreased, but there is no regular decreasing trend; under the combined action of the overburden pressure, the coal pillar immersed surface is prone to horizontal deformation, the deformation gradually increases with time, and the deformation near the bottom plate is the largest, so that the on-site coal pillar is more vulnerable to damage.

Smoke aerosols from wildfires play a vital role in marine ecosystems and the ocean carbon cycle. This study analyzed a severe wildfires incident occurred in the Indo‐China Peninsula on 26 March 2019, and assessed its impact on ocean carbon sink. The satellite observations showed that the wildfires covered an area of about 56% of the entire peninsula, burning an area of 1.17 × 106 km2. Consequently, the wildfires discharged about 0.43 × 109 kg carbon. Moreover, a substantial amount of smoke released by severe wildfires was carried downstream by the wind and reached the western Pacific Ocean within 2 days. These smoke aerosols contribute to the ocean carbon sink through the mechanisms of the biological pump and their own carbon deposition. Model simulation results showed smoke aerosols contribute 6.44 × 104 kg black carbon to surface ocean by their own carbon deposition. Moreover, during the period of smoke aerosol's deposition, the flourishing growth of phytoplankton resulted in an increased carbon export of 0.25 ± 0.09 × 109 kg carbon (the biological pump mechanism), which represented approximately 57.97% ± 20.30% of the carbon emissions originating from the wildfire‐affected source region. Our research showed a positive impact of large wildfires on the ocean carbon sink, indicating the potential of smoke aerosols to alleviate the climate pressures resulting from carbon dioxide released by wildfires through improving the capacity of ocean carbon sink. Plain Language Summary: Wildfires emit substantial amounts of carbon dioxide into the atmosphere within a short timeframe. The ocean can mitigate the environmental impact of these wildfire events by fixing carbon. As one of the world's fire hotspot and the most significant burning area in the whole of Asia, it is necessary to understand the contribution of smoke aerosols emitted from the Indo‐China Peninsula to the Pacific Ocean carbon sink. We found that the source area of wildfires emitted 0.43 × 109 kg of carbon on 26 March 2019, and the smoke aerosols emitted by wildfires were carried by winds to the western Pacific Ocean within two days, and inputted 6.44 × 104 kg of black carbon. The increased ocean carbon export during the deposition of the smoke aerosol was 0.25 ± 0.09 × 109 kg, which is about half of the carbon emissions caused by wildfires. The results of this study suggest that smoke aerosols can contribute to the oceanic carbon sink, thereby alleviating the pressure on carbon emissions caused by wildfires. Key Points: A severe fire incident which account for 56% of the land area of the Indo‐China Peninsula has been researchedContribution of smoke aerosols to surface ocean carbon sink is primarily attributed by biological pump rather than carbon self‐depositionThe ocean assimilates around 57.97% ± 20.30% of the carbon emissions released by wildfires [ABSTRACT FROM AUTHOR]

The stability of the joint between the groundwater reservoirs in the mined-out area of the mine is one of the key factors for the safety and stability of the entire underground reservoir. To investigate the deformation and failure law of the joint under the working conditions, laboratory simulation and FLAC3D numerical simulation technology were used to analyze and monitor the force and deformation of the joint under the working conditions. The experimental and simulation results show that the inside of the boundary between the dam and the joint is the part with the most severe pore water pressure; the softening effect of water reduces the mechanical properties of the contact surface, and the moisture immersed in the pore crack makes the specimen fuller, which indirectly enhances the ability of the dam to resist external pressure, and enhances the mechanical strength of about 23%; the ultimate instability and failure of the joint is the consequence of the gradual expansion and extension of the internal damage at the junction, so we choose the joint material and pay attention to the connection. Reducing the pore cracks inside the joint is a crucial step to ensure the safety and stability of the dam.

To study the change of stability and safety degree of mine goaf reservoir under vibration environment, taking Lijiahao Coal Mine as the research background, the stability and safety of the main parts of the goaf reservoir are analyzed and studied under the continuous existence of earthquake or other earthquakes by using the method of formula derivation and similar simulation experiment in laboratory. Since the dam body is a key part of supporting the normal operation of goaf reservoir, the dynamic response formula of the dam body under the action of earthquake is analyzed to obtain the dynamic response of the dam body under the condition of earthquake. At the same time, through the research of similar simulation experiments in the laboratory, the variation of the safety degree of the whole goaf after disturbance is obtained under the condition that the vibration in the goaf continues to exist. With the increase of seismic intensity, the overall safety of the reservoir decreases. And under the condition that the source location is known, the closer the source is, the less safe it is.

Photocatalysis reactions occurring during daytime and aqueous-phase reactions during both daytime and nighttime constitute the two primary processes responsible for converting aerosol iron (Fe) from insoluble to soluble forms within the atmosphere. This study investigated the composition of total Fe (FeT) and soluble Fe (FeS) in daytime and nighttime PM2.5 in Qingdao, a coastal city in eastern China, and evaluated the distinctive roles of the two pathways in enhancing the solubility of aerosol Fe (%FeS, the ratio of FeS to FeT). In clean and humid conditions characterized by sea breezes, with relative humidity (RH) prevalently exceeding 80 %, an average daytime %FeS of 8.7 % was observed, which systematically surpassed its nighttime %FeS (6.3 %). In contrast, when the air originated from land regions and was slightly polluted, the daytime %FeS (3.7 %) was noted to be lower than the nighttime %FeS (5.8 %). This discrepancy was attributable to the variations in RH, as the nighttime RH approximated to be 77 %, facilitating the more efficient formation of acidic substances and resulting in faster FeS production than during daytime, when RH was about 62 %. Furthermore, the oxidation rates of sulfur (SOR) and nitrogen (NOR) displayed strong correlations with RH, particularly when RH was below 75 %. A 10 % increase in RH resulted in a 7.6 % increase in SOR and a 7.2 % elevation in NOR, which served as the primary reason for the differences in aerosol acidity and %FeS between daytime and nighttime. These findings highlight the RH-dependent activation of aqueous-phase reactions and the augmentation of daytime photocatalysis in the formation of FeS in the coastal moisture atmosphere. [ABSTRACT FROM AUTHOR]

To determine the effect of water contents on the oxidation spontaneous combustion of coal gangue, the properties and combustion characteristics of coal gangue were studied using industrial and elemental analyses and Thermo Gravimetry-Differential Scanning Calorimetry (TG-DSC). The molecular dynamics simulation (MDS) and giant regular Monte Carlo simulation (GCMC)were used to investigate the adsorption isotherms of oxygen and coal gangue (kaolinite) under different water molecules (400, 500, 600, 700). The results of thermogravimetric showed that with increasing moisture content, the characteristic temperature points T3-T5 of CG4 were much lower than those of the other samples, the combustion conversion rate is the highest and the spontaneous combustion effect is the best at the same temperature. The molecular simulation results show that under 700 water-oxygen system, the adsorption of oxygen molecules and kaolinite (001) surface is the strongest. The interface has the fewest water molecules and the largest diffusion coefficient. [ABSTRACT FROM AUTHOR]

Seismic underground fluids play an important role in earthquake prediction studies and tracking. Nearly 30 years of radon concentration monitoring data at 42 observation sites in the North–South seismic belt (22°-35° N, 100°-110° E) were collected from the National Earthquake Data Center of China Earthquake Networks Center. The possible precursor anomalies of observed radon concentration in the belt before several strong earthquakes were investigated and their spatial distribution, evolution, and variation characteristics were analyzed. The results showed that radon concentration precursor anomalies before several strong earthquakes were high, and the morphological characteristics are relatively complex. The anomaly mainly shows the turning point or accelerating change of trend background change; longer anomaly durations tend to be concentrated around epicenters. The number of observation points with anomalies was positively correlated with the proximity to the epicenter; the measurement points closest to the epicenter exhibited earlier trend anomalies. The research has important practical significance and scientific value for understanding the relationship between radon concentration anomaly and strong earthquake.

Transition metal nitrides (TMNs) are promising electrode materials for high-performance energy storage devices owing to their excellent conductivity, thermal stability, high theoretical capacity and excellent electrochemical activity. However, the structural instability present in the electrochemical reaction process significantly limits their widespread application. Herein, we present a V–Ni-based nitride heterojunction on carbon cloth (VN/Ni3N–Ni/CC) as an active electrode material for flexible supercapacitors. The VN/Ni3N–Ni/CC composite electrode was successfully fabricated through controllable nitridation of the corresponding vanadium–nickel oxide grown on carbon cloth (V–Ni–O/CC) precursors. The electrochemical results reveal that the areal capacitance of the VN/Ni3N–Ni/CC based supercapacitor with a nitriding temperature of 400 °C and a nitriding time of two hours can achieve a maximum areal capacitance of 845.63 mF cm−2 at a current density of 0.5 mA cm−2, and the electrode in the three-electrode system retains 86.1% of its initial capacitance value after 1500 cycles at a current density of 10 mA cm−2. In addition, the assembled flexible all-solid-state symmetric supercapacitor using the VN/Ni3N–Ni/CC electrode exhibits an areal capacitance ratio of 19.1 mF cm−2 at a current density of 0.4 mA cm−2 and excellent cycling stability. Moreover, it displays exceptional flexibility under different bending angles highlighting its potential for integration into flexible electronic devices. [ABSTRACT FROM AUTHOR]

As the adhesive for composites, the resin matrix directly impacts the molding process and product performance of thermoplastic composites (TPCs). Carbon fiber-reinforced polyetherimide (CF/PEI) and polyaryletherketone (CF/PAEK) composites were prepared by a compression molding process. The interface, interlaminar, and low-speed impact properties of TPCs were studied. The results show that the interfacial shear strength of the CF/PEI composite is ~116 MPa, while the CF/PAEK composite is ~78 MPa. However, the interlaminar and low-speed impact performance of CF/PAEK is better than CF/PEI. Type I fracture toughness ( G IC ) and type II fracture toughness ( G IIC ) of CF/PEI are ~1051 MPa and ~1060 MPa. But those of CF/PAEK are ~1786 MPa and ~2584 MPa, respectively. The compressive strength after the impact of CF/PAEK (~321 MPa) is 40% higher than CF/PEI (~230 MPa). [ABSTRACT FROM AUTHOR]