Abstract:In order to address the issue of deterioration of phosphorus removal performance caused by competition between denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying phosphorus-accumulating organisms (DPAOs) for carbon source in denitrification and phosphorus removal technology, three groups of the same specification of SBR reactor were set up in the experiment. Changes in the conversion of internal carbon source, denitrification and phosphorus removal performance as well as the ratio of abundance of DGAOs to that of DGAOs were explored by comparing the operation under the different anaerobic/anaerobic sections with different HRTs. The results show that with an anaerobic/anoxic HRT of 90 min/170 min, the abundance ratio of DGAOs to DPAOs is 1.97, with the maximum internal carbon storage (182.81 mg/L) and phosphorus release (31.72 mg/L). The removal rates of COD, TP, and NO^-₂-N are 94.69%, 96.37%, and 90.40%, respectively. Conversely, with an anaerobic/anoxic HRT of 50 min/210 min, the insufficient anaerobic time results in inadequate uptake of carbon by the microorganisms, with the lowest endogenous carbon storage (141.59 mg/L). Additionally, the prolonged anoxic time causes DGAOs to utilize stored glycogen (Gly) for denitrification, adversely affecting their growth and resulting in the lowest abundance ratio of DGAOs to DPAOs (0.49). When an anaerobic/anoxic HRT of 130 min/130 min, the abundance ratio of DGAOs to DPAOs increases to 2.63. However, the excessive anaerobic time detrimental to the storage of the internal carbon source of DPAOs, resulting in effluent TP levels exceeding 0.5 mg/L. Additionally, the insufficient anoxic time negatively impacts denitrification, causing the removal rate of NO^-₂-N decrease to 81.05%. At an HRT of 50 min/210 min, a higher proportion of DPAOs is more conducive to PN secretion, promoting granulation with an average particle size of 517.6 μm. In contrast, the larger proportion of DGAOs at 130 min/130 min enhances PS secretion, which is not conducive to granulation, resulting in a smaller average particle size of 255.3 μm. At an anaerobic/anoxic HRT of 90 min/170 min, the average particle size of the sludge is 480.1 μm, establishing a balance between DGAOs and DPAOs, leading to optimal system stability and pollutant removal performance.

Abstract:This study aims to elucidate the effects of exogenous additives on the rhizospheric microenvironment of rice and their subsequent influence on Cd accumulation. Biochar (BC) and arbuscular mycorrhizal fungi (AMF) were utilized as representatives of abiotic and biotic agents, respectively, jointly added to modify the rice rhizosphere in response to soil Cd contamination. Results show that the incorporation of both biochar and AMF significantly enhanced the soil organic matter content, thereby exerting a positive impact on the levels of available phosphorus, available potassium, and soil carbon-nitrogen fixation. Furthermore, these additives mitigated the inhibitory effects of Cd stress on soil urease activity, resulting in an increase in the proportion of DTPA-extractable Cd from 58.95% to 64.42%. Cd stress significantly influenced the richness and diversity of the microbial community within the rice rhizosphere soil. The addition of biochar and AMF facilitated the recovery of the abundance of the proteobacteria phylum, increasing from 29.7% to 33.1%. At the 1 mg/kg soil Cd, the abundance of the Bacillus community in the BC+AMF treatment group increased by 88.5% compared to the CK treatment group. Under a stress condition of 5 mg/kg soil Cd, the synergistic application of biochar and AMF resulted in an increase in the proportion of Cd accumulation within the rice root system, rising from 60.4% in the CK group to 77.1% in the BC+AMF treatment group, concurrently reducing the proportion of Cd accumulation in the seeds from 4.4% to 1.6%. The addition of biochar and AMF improved the nutritional conditions and the structure and functionality of the microbial community in the rice rhizosphere soil, thereby facilitating the sequestration of Cd within the rice root system and diminishing its translocation to the aboveground seeds. These findings offer substantial theoretical support for the integrated application of biotic and abiotic factors in the remediation of heavy metal-contaminated soil environments.

Abstract:To investigate the mediating role of oxidative stress and inflammation in the relationship between polycyclic aromatic hydrocarbon exposure and increased blood pressure, a study was conducted involving 746 petrochemical workers. Participants were selected and divided into normal blood pressure group and hypertension group based on their blood pressure values. Ten mono-hydroxylated polycyclic aromatic hydrocarbons(OH-PAHs) and six oxidative stress biomarkers(OSBs) in urine were determined. White blood cell count(WBC) was derived from workers′ blood routine examination results. The associations between urinary OH-PAHs, urinary OSBs, peripheral WBC and blood pressure were analyzed by regression models, the roles of OSBs and WBC in the relationship between OH-PAHs and blood pressure were evaluated by mediating effect model. The results indicated that 2-hydroxynaphthalene(2-OH-Nap) and 2&3-hydroxyfluorene(2&3-OH-Flu) levels in hypertension group were significantly higher than those in normal blood pressure group(P<0.05). OH-PAHs were significantly correlated with 6 OSBs(P<0.001). For each unit increase in concentrations of 2-OH-Nap and 2&3-OH-Flu, the peripheral blood WBC increased by 17.0%(β=0.170, P=0.002) and 23.3%(β=0.233, P<0.001), respectively. Additionally, for each unit increase in urinary 8-iso-prostaglandin F_2α(8-PGF_2α) and peripheral WBC, the risk of developing hypertension increased by 6.16 times(R_O=6.16, P=0.031) and 27.8 times(R_O=27.8, P=0.018), respectively. The relationship between urinary 2-OH-Nap and diastolic blood pressure was partially mediated by 8-PGF_2α and WBC, with a mediation ratio of 21.0% and 37.0%, respectively. Only WBC partially mediated the effect of 2&3-OH-Flu on blood pressure elevation. In conclusion, polycyclic aromatic hydrocarbon exposure among petrochemical workers primarily increases the risk of hypertension through the induction of inflammatory responses.

Abstract:A model of an oxygen-rich supply system based on hollow fiber membrane is proposed to solve the problem of insufficient indoor oxygen content. A mathematical model of air separation process using hollow fiber membrane is established using the microelement method and compared with experimental data, showing an average error of less then 15%, indicating the reliability of the membrane separation model. Then, a steady-state oxygen-enriched supply system containing hollow fiber membrane components and an air compressor is designed to analyze the effects of compressor pressure ratio and room pipeline return air oxygen concentration setting values on the power consumption and volume of the air compressor. The results indicate that although reducing the inlet pressure of the membrane module can reduce the power consumption of the compressor; however, it does not reduce the volume. Therefore, it is necessary to select a membrane module inlet pressure with relatively low power consumption and volume, with the optimal pressure being 200 kPa. The increase in the target value of oxygen concentration in the room's pipeline return air will increase the power consumption and volume of the compressor. When the oxygen volume fraction of the room return air is set at 21%, the compressor exhibits the lowest power consumption and volume. Based on the research results, the optimal working parameters can be selected for hollow fiber membranes in oxygen supply systems.

Abstract:As a common low-temperature physical phenomenon, frosting often results in negative effects in daily life and industrial production. Frosting simulation technology not only helps to deepen the understanding of the frosting process, but also provides theoretical guidance for the development of frost prevention and control technology, thereby reducing or avoiding potential hazards caused by frosting in fields such as energy, aerospace, transportation, electricity, and refrigeration. To fully understand this complex heat and mass transfer and flow coupling process, which is characterized by non-uniformity, variable density, moving boundaries, and continuous phase changes, this study systematically analyzes existing models and results of the four stages of droplet condensation, solidification tip-growth, virtual frost growth, and frost layer maturity in the low-temperature surface condensation frosting process. The results show that during the droplet condensation stage, existing models achieve a simulation accuracy of over 80% for indicators such as droplet size and nucleation rate. During the solidification tip-growth stage, the simulation accuracy of parameters such as freezing front height and freezing duration can reach 85.3%. The simulation accuracy of indicators such as frost thickness and frost density during the growth and maturity stages of frost layer can reach over 82%. Additionally, the accuracy of simulating and predicting frost climate can reach up to 88.4%. Existing frost simulation techniques can be divided into three types based on their underlying principles: mathematical models based on physical and mathematical principles, numerical simulations based on computational fluid dynamics and numerical methods, and data analysis models based on statistical and machine learning principles. Among these, the final method is mostly used in the frost growth stage, and has the greatest potential for development due to their long duration, multiple predictive parameters, and high accuracy throughout the frost formation process. During the entire condensation frosting process on low-temperature surface, the simulation of droplet nucleation in complex scenarios is difficult due to its small scale, fast changes, multiple influencing factors, and its occurrence in the early stage of dendrite growth. Similarly, the periodic reverse melting and regeneration of frost crystal in the later stage of frosting growth is also a current challenge due to the drastic changes inside the frost layer and the physical obstruction during precise measurements, which cannot be clearly observed. The conclusions of this study provide valuable references and inspiration for fundamental research and technological development related to frost and ice in complex scenarios, such as frosting, defrosting, frost prevention, and frost control, etc.

Abstract:This research addresses the theoretical limitations of conventional single-scale optimization approaches in understanding filler topology regulation mechanisms, molecular alignment coupling effects, and multi-scale cooperative interactions. Through a multi-level collaborative strategy of "filler topology design-molecular ordering-density coordination", we systematically investigate the synergistic control mechanism between filler architectural design and resin matrix modification on the thermal conductive performance of epoxy-based composite materials. Fiber, sheet, and ellipsoid models are constructed based on finite element homogenization theory, revealing the regulation rules of filler volume fraction, aspect ratio, and spatial orientation on the heat transfer network. In conjunction with the reverse non-equilibrium molecular dynamics (RNEMD) method, we propose a novel strategy to enhance the intrinsic thermal conductivity of the resin through the synergistic effects of molecular ordering and density-induced non-bonded interactions. The study shows that the flake filler with 25% volume fraction exhibits an effective thermal conductivity (ETC) of 4.2 W/(m·K). The ordered cross-linked structure and enhanced density-induced non-bond interactions (where non-bonded energy accounts for 60%) increase the intrinsic thermal conductivity of the resin from 0.3 W/(m·K) to 2.85 W/(m·K). Multi-scale synergistic analysis shows that under the coupled effects of 25% filling and density enhancement, the ETC of the doped ordered cross-linked system exceeds 6.8 W/(m·K). The density synergistic effect (ρ>1.5 g/cm³) reduces the standard deviation of heat flux density by 64%. The cross-scale simulation framework established in the study reveals the quantitative correlation between heat transfer network construction and molecular ordering, providing a new theoretical paradigm for designing high thermal conductivity composites.

Abstract:The analysis of the erosion characteristics of ceramic channel walls during the operation of Hall thruster is of great significance to evaluate the performance and lifespan of Hall thruster. Traditional erosion evaluation methods mainly rely on measuring the depth of erosion, which is time-consuming and unable to provide real-time online monitoring capabilities and multi-condition monitoring. Therefore, this paper uses non-invasive and in-situ online optical emission spectroscopy to monitor the erosion during the operation of the Hall thruster, and successfully detects the boron atom signal. Then, advanced actinometry method is used to calculate the boron atom reduced concentration under different working conditions based on the ratio of xenon atomic spectral line to boron atomic spectral line and the electron temperature calculated by xenon atomic collision radiation model. The results indicate that the reduced concentration of boron increases with the increase of mass flow rate and voltage, and the influence of magnetic field intensity on the boron atom reduced concentration is complex and requires further investigation. The use of emission spectroscopy and advanced photometry enables real-time and in-situ efficient assessment of erosion characteristics of aerospace equipment under different operating conditions, provideing guidance for the design and lifetime optimization of thrusters in key applications such as deep space exploration and gravitational wave detection.

Abstract:In order to address the complex numerical calculations of the heat and mass transfer processes in the wet coating of electrode plates during convective drying, this study comprehensively considers the combined effects of hot air and the aluminum substrate on the thermal and mass transfer characteristics of the wet coating. Based on the multi-field coupling theory in porous media, a three-dimensional mathematical model of heat and mass transfer in the hot air-electrode plate wet coating is established using a meshless parallel method. Meanwhile, a difference calculation method for the heat and mass transfer process in the wet coating is proposed. Due to the high requirements for computational accuracy in mathematical model, a scale simulation method based on similarity theory is proposed to improve computational efficiency. The reliability of this method is validated through the comparison of temperature and humidity variations of wet coatings at different scaling ratios. The results show that the determination coefficient R² of humidity assessment of the wet coating at different scaling ratios is greater than 0.99. The simulation time for the original-scale model is 5 hours, while the simulation time for the scaled model with a scaling factor of 800 is 2.77 hours, representing a 44.6% reduction compared to the original model, thus effectively improving the numerical computation efficiency. Finally, the reliability of mathematical model is validated based on scale simulation method. The results show that the simulation temperature and humidity values from the hot air-electrode plate wet coating heat and mass transfer model have errors within ±15% of the experimental data, with only a few data points exhibiting slightly larger discrepancies, indicating that the model is reliable.

Abstract:To investigate the punching failure of slab-column connections in cases where the longitudinal tensile reinforcement of the slab yields, a novel experimental approach is proposed. This experimental setup facilitates the application of bending moments at the free end of the slab and vertical loads around the perimeter of the slab. Following this experimental design, three slab-column connection punching tests were conducted, each with varying punching span ratios and relative compression zone heights. The findings from the tests reveal that, when the specimens reached peak loads, the longitudinal tensile reinforcement in the slab had yielded near the column edge. Additionally, an increase in the ratio of longitudinal tensile reinforcement from 1.04% to 1.25% corresponded to a decrease in the secant inclination angle of the punching failure surface from 46.3° to 39.4°. Building upon the data from this study and compiled punching tests, a calculation formula was developed to determine the secant inclination angle of the punching failure surface, considering the punching span ratio, concrete compressive strength, longitudinal tensile reinforcement ratio, and slab effective depth. Furthermore, a calculation formula for the punching capacity of the slab was established, taking into consideration the punching span ratio, relative height of the compression zone, and secant inclination angle of the punching failure surface.

Abstract:To study the seismic performance of T-shaped fully precast shear walls with vertical reinforcement connected by sleeve grouted lapping connectors (referred to as APC connectors), quasi-static tests were conducted on one cast-in-place wall and two pieces of precast wall based on type I and type II sleeve grouted lapping connectors. The results showed that the initial horizontal cracks of the cast-in-place wall appeared at the top surface of the foundation, and the initial horizontal cracks of the precast wall appeared above the sleeve due to the restraint of the concrete by the sleeve. In the limit state, the specimens were all flexural-shear damage. In the cast-in-place wall, concrete crushed and rebar flexed at the edge of the footing, along with buckling of the rebars. For the precast wall, failure was characterized by buckling of the rebars above the sleeve, concrete crushing, and spalling of the concrete outside the sleeve. In terms of cracking load, yield load, peak load, stiffness, ductility and energy dissipation capacity, precast walls with type I sleeves were comparable to cast-in-place walls, while precast walls with type II sleeves were greater than cast-in-place walls. Both types of sleeves remained elastic during the loading process of precast shear walls, and both were effective in transmitting reinforcement stresses. The out-of-plane displacements of the precast specimens accumulated in the negative direction during loading, but the absolute values of out-of-plane displacements of the prefabricated walls were comparable to those of the cast-in-place walls at the same load level.

Abstract:In order to study the splitting tensile properties of early-age concrete, a 3D meso-concrete model with a 35% coarse aggregate volume content was established using Python scripting language for secondary development based on ABAQUS software platform. 3D zero-thickness cohesive elements were embedded in the mortar elements interface and the mortar-aggregate interface transition zone (ITZ). The splitting tensile strength of concrete cylinders with three mesh sizes of 4,5 and 6 mm and different ages were simulated. The results show that the combination of 3D random polyhedral aggregates meso-concrete model and cohesive elements is suitable for the fracture simulation of early-age concrete cylinders, which can not only accurately show the geometric shape and spatial distribution of actual aggregates, but also predict the mechanical properties and failure state of concrete with a high degree of visualization. The three different mesh sizes have minimal influence on the splitting tensile strength, but they do have some influence on the descending section of load-displacement curves. The maximum error between the calculated value of the formula, the simulated average value and the test value is 17.65% and 16.18% at the first day, and the errors are less than 5% in other ages, which validates the applicability and reliability of the model. The failure processes and final failure states of models at different ages are similar. Microcracks initiate and propagate in the ITZ, and localized areas of concrete experience crushing, ultimately resulting in vertical main cracks that traverse the cross-section of the concrete cylinder.

Abstract:In order to improve the accuracy of elastic-plastic analysis for SRC (steel reinforced concrete) beam-column members, the prediction model for fiber element parameters of SRC members (PMFEP-SRC) based on random forest algorithm is proposed to optimize the hysteresis curve fitting of SRC beam-column fiber elements. Based on 153 collected SRC beam-column specimens, with the peak load capacity ratio R_F and energy dissipation capacity ratio R_E are taken as target parameters, and the load capacity adjustment factor C_F and stiffness adjustment factor C_S are taken as adjustment parameters, the hill climbing algorithm is employed to determine the optimal parameters of the fiber element. PMFEP-SRC was trained and established by the random forest algorithm with the test control parameters of SRC beam-column specimens as the characteristic parameters and the optimal adjustment parameters of the fiber element (the solved load capacity adjustment factor C_F and stiffness adjustment factor C_S) as the labels. Finally, a batch of SRC columns with different shear-to-span ratios were designed and completed for low-cyclic loading tests, and the accuracy and reliability of PMFEP-SRC was further validated using the test data. The results show that PMFEP-SRC can effectively fit the hysteresis curves of SRC beam-column specimens with different failure modes, and the fitting accuracy of peak load capacity and energy dissipation of SRC specimens is significantly higher than that of the fiber elements without parameter optimization.

Abstract:Assembled buckling-restrained braces have advantages of easy disassembly, precise manufacturability, and light weight. However, conventional buckling-restrained braces often face challenges in conducting rapid post-earthquake damage assessment and typically require integral disassembly to replace localized damaged components. A segmental assembled buckling-restrained brace (SA-BRB) is proposed to address this issue, which facilitates post-earthquake visual inspection and localized replacement of damaged components after an earthquake. By establishing a simplified equivalent beam model of SA-BRB bolted connection, the relationships among the steel core contact force, bolt prying force, and bolt axial force are determined. Additionally, a bolted connection method for SA-BRBs is proposed, and the axial force calculation formula for the SA-BRB bolts is fitted and determined based on finite element simulation results. The results indicate that key parameters such as channel steel flange height, thicknesses of channel steel flange and web, the widths of cover plates, shim plate and inner core, and bolt spacing significantly influence the bolt prying force coefficient. These parameters, compared to the midspan bolted connections, exhibit a greater amplifying effect on the prying force in end bolt-connections. It is recommended to consider a bolt axial force amplification factor of 1.1 in the design, with a longitudinal bolt spacing of 100-200 mm. The proposed design method effectively predicts the failure modes of SA-BRB bolted connections and provides theoretical references for research and design methodologies related to buckling-resistant braces.

Abstract:Recycled aggregate concrete (RAC) composite slabs with closed-profiled steel decking not only take full advantages of composite slabs, but also realize the reuse of waste concrete. In this work, flexural tests on this novel composite slabs with different coarse recycled aggregate (CRA) replacement rates were carried out. The failure modes, load-displacement curves and strain development at the mid-span were investigated. Afterwards, a finite element model of the composite slabs was established, and the effects of CRA replacement rate, clear span and thickness of steel decking on the flexural capacity were analyzed. Finally, based on the experimental results and finite element parameter analysis, a calculation formula for the flexural capacity of the new composite slab under positive flexural conditions was proposed. Results indicated that the degree of upward shift of the neutral axis decreases with increasing CRA replacement rate during the whole bending process. The composite slabs with different CRA replacement rates mainly exhibits bending failure. The flexural capacity of recycled concrete composite slabs is 6.6% to 8.9% lower than that of normal concrete slabs. A simplified calculation formula that considers partial plastic development of the steel section and the influence of recycled aggregate replacement rate can effectively predict the bending capacity of the composite slabs.

Abstract:To promote the application of isolation technology in low-rise village buildings, a low-cost and easy-to-produce layer-bonded scrap tire rubber pads (LBSTP) is developed. Three types of high-toughness bonding agents were selected to reinforce the scrap tire rubber pads (STP) through interlayer bonding. Bonding failure tests and mechanical performance tests were conducted to observe the failure pehomena of bonding delamination and shear. Based on the bonding failure mehcanisms, the mechcanical properties of LBSTP were analyzed. Results show that the V-SC2000 adhesive has the highest strength but the lowest ductility, while the Yuzhu adhesive has the lowest strength but the best ductility, corresponding to the tensile bonding failure phenomena observed at the corners of LBSTP during the shear test. The LBSTP-2 bonded with Weili-801 adhesive shows a significantly higher vertical ultimate bearing capacity compared to other supports. The ultimate shear strain of LBSTP-2 is 150%, which is a 50% increase over the STP, indicating improved energy dissipation and repositioning capabilities. The LBSTP exhibits excellent mechanical properties, and the research findings provide theoretical references for the application of waste tire shock absorbers in isolation technology for village buildings.

Abstract:To improve the maturity of the containment leakage rate measurement technology, this study evaluates the applicability and reliability of the theoretical model of constant pressure method for containment leakage rate. Two theoretical analysis models, namely the standard condition mean method and the operating condition mean method were proposed. The validation of the theoretical models requires the acquisition of gas parameters within the containment under a constant internal pressure environment, followed by the calculation of the leakage rate. Firstly, sensors were arranged in the simulation body of steel containment with a free volume of 1 000 m³ to monitor the gas status, and a flow regulation device was designed in the inflation pipe to maintain constant pressure. Experiments were carried out in the environment of positive pressure and negative pressure. The stability and consistency of the containment leakage rate calculated by means of standard conditions and working conditions were explored. Secondly, the data from engineering test of pressure drop method in a nuclear power plant were analyzed by using the theoretical model of constant pressure method. The applicability of the theoretical model of constant pressure method to engineering scale containment and its compatibility with pressure drop methods were explored. The study indicates that the two theoretical analysis models have good consistency in calculating the containment leakage rate, with a relative deviation of less than ± 0.2%. The leakage rate calculated by the theoretical model of constant pressure method can achieve the accuracy of the traditional pressure drop method, with a relative deviation of less than 5% between the two methods. Therefore, the theoretical model of constant pressure method can be used to analyze the test data of pressure drop method. The findings of this research can provide support for the theoretical research and engineering application of the constant pressure method for containment leakage rate technology.