Abstract:In order to culture nitrite DPAOs to achieve aerobic granular sludge (AGS) short-range nitrification and endogenous denitrification and phosphorus removal, three groups of SBR with the same specifications were operate in anaerobic/aerobic/anoxic followed by short aeration (AO₁A-O₂) mode. The aeration intensity and duration of aerobic/post aerobic (O₁/O₂) varied among the reactor. By comparing the operational performance and functional microbial activity of the three reactor groups over a period of 60 days, the pollutant removal efficiency and activity of functional bacteria in each system were investigated. The results showed that R2 with short time hypoxia aeration for 10 min and the DO concentrations of O₁ and O₂ at 5 and 2.5 L/(h·L) had the best nitrogen and phosphorus removal effect, and the removal rates of COD, TP, NH+₄-N and TN reached 95.49%, 95.57%, 100% and 95.52%, respectively. The optimal environment for short-range nitrification and endogenous denitrification and phosphorus removal was created by short-term aerobic starvation and low dissolved oxygen. Approximately 60% of the phosphorus removal bacteria in R2 were DPAOs, with the highst proporton being nitrite phosphate-polyphosphate bacteria, accouting for 38.76%. The R_NA of the aerobic phase of the reactor was 74.19%, which achieved high NO-₂-N accumulation. The concentration of FNA was 1.03 μg/L, which inhibited PAOs and NOB while enriching more AOB and DPAOs.

Abstract:Nanofiltration is one of the core technologies to address water crises and ensure water quality safety and security. However, the performance of nanofiltration membranes has long been limited by the permeance/selectivity trade-off. Thus, developing high-performance nanofiltration membranes is an urgent need. Nanofiltration membrane fabrication involves factors such as aqueous phase monomer concentration, aqueous phase additive concentration, oil phase monomer concentration, polymerization time, etc. Traditional trial-and-error experimental method consumes substantial manpower, material and financial resources. In this study, based on the fabrication parameters of nanofiltration membranes, we constructed a machine learning-based predictive screening model for nanofiltration membranes. The results show that the XGBoost machine learning model effectively predict the permeance and rejection performance of nanofiltration membranes, with R² evaluation scores of 0.84 and 0.90, respectively, for the permeance and rejection performance. The quantitative analysis of the input parameters in the XGBoost machine learning model using the SHAP value method reveals that the aqueous-phase monomer concentration and the substrate type had high average SHAP values of 2.77 and 2.59 for permeance. The average SHAP values of the key parameters oriented towards the rejection performance were relatively close. The results of the monomer substructure characterization show that the hydrophilic and branched substructure features contribute to the permeance, while the amine group promote the rejection performance. The nanofiltration membrane prediction and screening model can identify and optimize the key parameters, providing theoretical and technical support for developing nanofiltration membranes.

Abstract:Gravity-driven membrane bioreactor (GDMBR) confers the process characteristics of low energy consumption, low maintenance and stable effluent. However, there is limited research on the direct treatment of rural domestic wastewater. This study investigates the pattern of flux variation and removal efficiency of pollutants using GDMBR process to treat domestic wastewater, as well as the influence of different membrane pore sizes on the treatment of domestic wastewater using GDMBR. The results indicate that the membrane flux of GDMBR process can be maintained at a steady state without any cleaning procedures during the long-term filtration in treating the domestic wastewater, with a steady flux of 1.3-1.5 L/(m²·h). This is attributed to the formation of loose and porous structure within the bio-cake layer attached on the membrane surface, resulting in extremely low concentration of pollutants deposited within the membrane pores. With relatively low sludge concentration, the GDMBR process achieves high removal efficiency of COD and UV₂₅₄. The removal rates of 78% and 85%, respectively, while effectively retaining the nitrogen and phosphorus sources in the wastewater. Furthermore, different membrane pore sizes exhibits minimal effects on the removal efficiency of GDMBR process. However, the steady fluxes of the GDMBR system configured with microfiltration membranes are slightly higher than the GDMBR system integrated with ultrafiltration membranes.

Abstract:To achieve timely and accurate identification of contamination source in water distribution networks, a sequential Bayesian method was proposed specifically for water distribution systems equipped with online water quality monitoring devices. The method utilized temporal information from water quality sensors to identify the contamination source in water distribution network with stochastic fluctuation in water demand. Monte Carlo simulations were conducted to generate contamination events and establish the observation probability distribution function for each node. Then this information was used to compute the posterior probability of each possible source for the observed alarm pattern in real time by using Bayesian inference. Finally, the contamination source was identified by ranking the posterior probabilities. Furthermore, the influence of different utilizations of sensor information on the identification results was also compared. The results show that the proposed method enables continuous updating of the posterior probabilities of suspicious nodes when sensor information is gathered, resulting in fewer candidate nodes and lower information entropy. The method can effectively identify the contamination source, and the accuracy of contamination source identification improves with deeper utilization of sensor information. Introduction of initial alarm time as auxiliary information can reduce the number of candidate nodes and reduce the uncertainty in probability distribution of suspicious contamination nodes, thus improving the accuracy of identification.

Abstract:To explore the toxicological mechanism of benz[a]opyrene (B[a]P) in gall bladder for aquatic animals, common carp (Cyprinus carpio) was used as the experimental material in this study. A 15-day chronic toxicity test was conducted with different concentrations of B[a]P (0,0.025 and 0.25 mg/L) exposure to examine the toxicological mechanisms of B[a]P on carp gall bladder by measuring the content of B[a]P, antioxidant parameters, transcriptional response and immune gene expressions in common carp gall bladder. Results show that the accumulation of B[a]P in gall bladder tissues increased significantly with the concentration of B[a]P stress, which indicates that gall bladder plays an important role in detoxification. The activities of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) and the concentration of malondialdehyde increased after B[a]P exposure, indicating that the gall bladder can respond to oxidative stress by activating the antioxidant oxidase system. In addition, exposure to low concentrations of B[a]P can induce immune responses in common carp gall bladder tissues, activating the Notch receptor signaling pathway, thereby causing apoptosis and eliminating excessive or abnormal cells in their own tissues. However, high-concentration exposure to B[a]P can inhibit the RIG-I and Notch receptor signaling pathways, causing an imbalance in gall bladder immune homeostasis. This inhibition of cell apoptosis prolongs the survival time of abnormal cells, and further activates immune cells, leading to self-tissue damage. This study provides preliminary insights into the potention self-protective mechanisms of common carp gall bladder cells in response to B[a]P exposure, laying the fundation for early warning and ecological risk assessment of polycyclic aromatic hydrocarbon pollution in water environment.

Abstract:In order to improve the impact resistance of large steel tanks, this paper conducts numerical simulation and theoretical analysis research on the impact response of polyurea coated large steel storage tanks. The finite element model of polyurea-coated steel tank is established based on the model developed and validated in previous studies. Numerical results show that external polyurea layers can effectively reduce the local plastic deformation and avoid the perforation damage induced by impact loadings with the angle of 45°. The main mechanism of polyurea coatings are speed reduction and cushion effect. The maximum energy absorption and energy absorption efficiency of the tanks increase with the polyurea layers′ thickness. When the coating thickness is 15 mm, the tank does not be damaged with penetration, meeting the requirements of the British tank design code. According to the tank′s impact response characteristics and the polyurea coating′s mechanism, a theoretical formula for predicting the critical impact velocity is established, which can predict the maximum energy absorption value of the coating tank with a small error, and can be used as a basis for the impact protection design of polyurea coated steel tanks.

Abstract:The reinforced concrete shear walls of nuclear power plants have a low shear span ratio and high reinforcement ratio. Multiple openings are required to allow for the introduction of doors and pipelines into the building. However, research on the seismic performance of low-rise shear walls with openings is relatively limited. Therefore, three 1∶2.7 squat reinforced concrete shear walls were experimentally investigated through quasi-static testing to analyze the impact of shear span ratio on seismic performance. The study included analysis and discussion of the failure mode, hysteresis curves, ductility coefficients, stiffness degradation, energy dissipation capacity, and deformation capacity of the specimens. The results indicated that the failure in low-rise shear walls was primarily caused by the significant increase in the width of diagonal principal cracks in the wall legs, leading to a rapid decrease in bearing capacity. Furthermore, reducing the shear span ratio increased the bearing capacity, stiffness, and energy dissipation of low-rise shear walls, but significantly reduced their deformation capacity and ultimate displacement, resulting in lower cumulative energy dissipation. Specimens with smaller shear span ratios were prone to develop plastic hinges above the openings, and subsequent beam rotation caused concrete crushing near the openings, with significant shear effects. Moreover, the presence of small openings resulted in severe asymmetry, affecting the seismic performance of the shear walls.

Abstract:To investigate the mechanism of flexural overstrength of cast-in-situ reinforced concrete floor beams incorporating structural spatial restraints, this article takes the spatial position and longitudinal reinforcement ratio of the floor beams in the structure as variables, designs 12 floor beam specimens with upper erection bar not extending into the support, and conducts static tests on the mid-span flexural performance. Based on the experimental method of establishing classical concrete theory, a comparative test of 4 simply supported beams is conducted. The failure mode, bearing capacity, deformation capacity and axial elongation of beam specimens are studied in this article. The results show that the ratio of the bearing capacity of the floor beam specimen to the calculated bearing capacity based on flexural components is 1.57-2.77, which is significantly improved compared to the corresponding rectangular and T-shaped simply supported beam specimens. The degree of overstrength is inversely proportional to the longitudinal reinforcement ratio. Compared with the simply supported beam, the failure mode of the mid-span section of the floor beams do not change significantly due to the axial compression, but the ductility of the floor beam decrease. The axial elongation increases with the increase of the deflection. Regarding the floor beams as compression-flexure components, a method is proposed to determine the corresponding axial force and flexural moment according to the test peak load of the floor beam. The calculation results show that the ratio of the moment of the mid-span section of the floor beams subjected to compression and flexure to the moment subjected to flexure is 1.28 to 2.19. The finite element numerical simulation of the floor beam is carried out in this article. The results show that with the increase of the included floor range of the floor beam section, the axial force tends to be uniform along the beam span.

Abstract:Effective seismic measures for pipeline joints are the key to optimizing the seismic performance and post-earthquake functional recovery capability of urban water supply pipeline networks. In this paper, a new type of self-anchored anti-seismic joint for ductile iron pipes is proposed based on the thoughts of mechanical self-anchoring design and self-deformation compensation. This article conducted axial tensile quasi-static tests and refined three-dimensional finite element numerical simulations of anti-seismic joint, and studied the mechanical characteristics of the anti-seismic joint, including tensile bearing capacity, initial tensile stiffness, deformation resistance, and ultimate damage state. The research results show that the water pressure variation within 0.2 MPa has little effect on the axial mechanical properties and damage mode of the common push-on joint, and the transition deformation from the initial leakage to the functional failure state of the joint is about 2.5 mm; the new self-anchored anti-seismic joint has good tensile bearing capacity and resistance to large deformation, and its tension resistance curve is divided into three stages: the gasket bearing stage, the snap ring bearing stage and failure damage. When the deformation of the snap ring is about 9 mm, it reaches a peak bearing capacity of about 330 kN.

Abstract:To explore the impact of low-cost sensors on the earthquake early warning (EEW) magnitude estimation of convolutional neural network (CNN) model, taking five destructive earthquakes (MS≥5.8) that occurred in China in 2022 as examples, seismic data was applied to the CNN model, and the magnitude estimation results after incorporating the data recorded by low-cost sensors were analyzed. The results show that within 3 s after the P-wave arrival, based on single station, the magnitude estimation error of the low-cost sensors and the strong-motion instruments is mainly distributed in the range of ±1 magnitude unit. For the seismic records with epicentral distance less than 100 km, within 10 s after the P wave arrival, the mean value of magnitude estimation error of the low-cost sensor is closer to 0 than that of the strong-motion instrument. For the seismic records with signal noise ratio less than 20, the mean value of magnitude estimation error of strong-motion instrument is closer to 0 than that of low-cost sensor, and the low-cost sensor has greater uncertainty of magnitude estimation error. Additionally, for these 5 earthquakes, compared with the strong-motion instrument, the low-cost sensor has a larger quantity and denser distribution. the CNN model obtains robust magnitude estimation faster when considering the data recorded by low-cost sensors. The results provide a basis for the applicability of low-cost sensors in CNN magnitude estimation models, and serve as a reference for magnitude estimation in EEW systems.

Abstract:To investigate the effect of ambient temperature on the mechanical properties of rubber bearings, high-speed compression shear apparatus is used to conduct a series of compression-shear tests at varying temperatures (-0,0, 23 °C), frequencies (0.2,0.5,0.3 Hz), and shear strains (50%, 100%, 250%) on rubber bearings (LRB700 and LNR700). Given that the significant inertial and frictional forces generated by the high-speed and high-pressure (15 MPa vertial compressive stress) , this paper firstly proposes correction methodologies for accurately determining the performance indexes of bearings under conditions of high-speed and high-pressure loading. Test results indicate that with an increasing number of loading circles, the temperature variation within the internal lead core of LRB700 is more pronounced and exhibits symmetry with respect to the height of the lead core, whereas the temperature variation on the inner wall of LNR700 is minimal. In addition, the primary mechanical indexes of LRB700 and LNR700 (such as characteristic strength, post-yield horizontal stiffness, and horizontal equivalent stiffness) exhibit varying degrees of an upward trend as ambient temperature decreases. Specifically, the characteristic strength of LRB700 increases by 15% to 32%, the post-yield stiffness of LRB700 increases by 7% to 16%, and the horizontal equivalent stiffness of LRB700 and LNR700 increases by 12% to 23% and 5% to 16%, respectively. Finally, this research concludes by proposing mechanical performance adjustment coefficients for LRB700 and LNR700 that account for the effect of ambient temperature based on the aforementioned results and in accordance with relevant standards.

Abstract:The construction of urban seismic resilience has become an important topic of international concern. As one of the most critical infrastructure systems in cities, the road traffic systems have suffered severe damage and even lost their functionality in previous major earthquakes, which greatly hindered the post-earthquake emergency rescue and recovery work, resulting in huge indirect losses and profound social impacts. Therefore, it is of great theoretical significance and practical value for building resilient cities and sustainable development of human civilization to evaluate the seismic resilience of road traffic system under potential earthquake threat and provide scientific and reasonable improvement suggestions. In this paper, the development history of urban resilience is introduced firstly, and the definition and connotation of seismic resilience are expounded, taking road traffic system as the main object. Then, the main methods and achievements of the existing research are systematically summarized in the fields of post-earthquake functionality assessment method, seismic resilience indicator, post-earthquake recovery strategy and pre-earthquake retrofit strategy of road traffic system, and the limitations of current researches are pointed. Finally, the future research trend is discussed.

Abstract:The essence of subgrade mud pumping under train load is the migration of fine particles in subgrade soil. The migration of fine particles will change the pore structure of overlying gravel, thus affect the mechanical and hydraulic properties of gravel layer. To study the influence of fine particle migration from subgrade soil on the microscopic pore structure of gravel layer under cyclic loading, a series of tests are carried out by a self-developed subgrade mud pumping test model, combined with X-ray computed tomography (CT) scanning technology. It has been shown that under cyclic loading, compression of the gravel pores and clogging of migrated fine particles not only change the distribution characteristics of gravel plane porosity, but also decrease the porosity and porosity connectivity. Moreover, the characteristics of the pore size distribution are not affected by loading. The pores of the gravel layer show features of more small pores and fewer large pores, and the characteristic curves of the pore distribution satisfy log-normal distribution before and after loading. However, with the application of cyclic load, the total number of pores decreases. The distribution of pore shape parameters (slenderness ratio and flatness) shows a normal distribution characteristic. The slenderness ratio has not changed significantly with the number of cycles, while the distribution of flatness is more uniform after loading. The pores of the gravel layer have a distinct fractal character. In addition, the three-dimensional fractal dimension of the pores is distributed between 2.40 and 2.50 before loading. With the application of cyclic loading, the three-dimensional fractal dimension gradually decreases.

Abstract:Following the background of "dual carbon" energy with peak carbon and carbon neutrality, conventional heat storage capsule with phase change materials (PCM) and latent heat thermal storage system (LHTES) with packed bed cannot meet the current heat storage demand. The application of bionics in the field of heat storage offers a new approach to improve the heat storage efficiency of the capsule and LHTES. This paper introduces a novel bionic-calabash-shaped capsule for thermal energy storage units to increase heat transfer surface area and improve the thermal performance of LHTES systems. Firstly, the influence of optimized dimensional parameters of the biomimetic gourd unit on its melting characteristics is analyzed to determine the optimal dimensions for achieving desirable melting characteristics. Secondly, the analysis of temperature distribution, liquid fraction, heat storage capacity, and other performance indicators is conducted for LHTES of conventional sphere and biomimetic calabash. The results reveal that the bionic-calabash capsule can increase the heat transfer area by 14.5%. Compared to the traditional model, the liquid phase fraction and heat storage completion rate of biomimetic model increase by 12.67% and 6.2%, respectively. On this basis, the influence of inlet temperature and flow rate on system performance is analyzed, and the results show that the inlet temperature significantly impacts the system′s thermal storage performance. A 15 K increase in the import temperature leads to a 59.6% reduction in the thermal storage time for the stacked bed system. This study provides valuable insights for optimizing stacked bed LHTES systems and enhancing their thermal performance under real-world conditions.

Abstract:Standard platinum cobalt resistance thermometers (SPCRTs) are important temperature sensors used in lowtemperature region especially from 0.65 K to 24.556 1 K (triple point of neon), and highstability ones have the potential to be used as the data carrier for temperature calibration and international comparison. Based on our previous research, this article establishes a lowtemperature assessment system with temperature control stabilities of 13 μK at 5 K and 27 μK at 24.556 1 K. It is currently the most stable lowtemperature assessment systems reported in the world. Based on the system, stability of the developed SPCRTs is investigated under hundred lowtemperature cycling from 5 K to 24.556 1 K, and five highstability SPCRTs are obtained. Among them, the stability of four 50 Ω SPCRTs is better than 0.2 mK and the stability of one 100 Ω SPCRT is better than 0.5 mK at 24.556 1 K, which is the best international result for low temperature stability of SPCRTs. In the future, the high stability SPCRTs selected in this article will be used in the relevant applications and research of temperature calibration and international comparison at low temperatures.

Abstract:The thermal efficiency of the Maisotsenko gas turbine cycle (MGTC) needs to be further improved, and its economic feasibility has not been properly evaluated. Unlike the two-stage MGTC with aftercooling and regenerative processes, a three-stage MGTC system (IMGTC) layout with coupling of intercooling process was constructed by fully considering the reuse of cooling water and energy recovery. The effects of pressure ratio (R_c), air saturator degree of humidification (H_ASD) and combustor outlet temperature (T_CO) on thermal efficiency, saturation amount of water in saturator, equivalent carbon dioxide emissions (E_EC), and levelized cost of electricity (C_LOE) were studied. Finally, a multi-objective optimization of the system was carried out on the ISIGHT platform to select the best parameter combination. The results indicate that the intercooler and its energy efficiency improvement in IMGTC can adjust and effectively reduce the saturation amount of water in the saturator. The minimum saturation amount of water in the IMGTC system is only 57.55% of that in the no-intercooling mode. The multi-objective optimization shows that when using the optimal parameter combination, the thermal efficiency of IMGTC reaches 49.89%, while E_EC and C_LOE are only 5.496 kg/s and 0.059 5 USD/kWh, respectively. This research confirms the significant advantages of IMGTC over MGTC in terms of thermodynamic performance and economic feasibility.

Abstract:Icing is a nonlinear, variable density liquid-solid phase change process coupled with thermal and mass transfer and flow, which occurs widely in nature and industry, often with negative consequences. Trace amounts of air dissolved in water converge and nucleate into larger bubbles during icing due to the extrusion of ice crystals. These bubbles then remain at the freezing front due to adhesion, ultimately forming microscale trapped air bubbles of varying sizes and distributions in ice. The formation of micro-scale trapped air bubbles in the icing process not only affects the later dynamic icing process by changing the internal structure, density distribution, thermal conductivity and freezing rate of ice, but also affects the overall thermal conductivity, thermal resistance distribution, compressive strength, stress distribution and other macroscopic thermal and mechanical properties of the ice body after the icing process concludes. To accurately predict and control the icing process, as well as to develop and optimize various types of anti-icing technologies, the study of the growth and distribution characteristics of microscale trapped air bubbles and the macro-thermal effects has attracted much attention in both academia and industry. Firstly, this paper takes micro-scale trapped air bubbles in ice as the research object, and reviews their nucleation mechanism, growth process, distribution characteristics and static stability from the micro and macro scales. The results show that the bubble shape is directly related to the freezing rate, and when the freezing rate exceeds 25 μm/s, egg-shaped trapped air bubbles with a length-to-width ratio smaller than 5 appear in ice. When the freezing rate is between 5 and 25 μm/s, needle-shaped trapped air bubbles with a length-to-width ratio larger than 5 appear in ice. No bubbles can be found in ice when the ice freezing rate is below 3 μm/s. Secondly, by reviewing and analyzing existing literature, the influencing factors of the whole life cycle of trapped air bubbles and their different influencing mechanisms on the thermal and mechanical characteristics during icing and after ice formation are summarized and explained. Trapped air bubbles in ice significantly reduce the effective thermal conductivity of the ice by lowering its the density and changing the internal ice crystal structure. In ice melting experiments, ice with a bubble volume fraction of 57% exhibits a delay of approximately 50% in the starting time of melting compared to clear ice without bubbles. Additionally, the ice with bubbles has a 36.81% lower meting height within the same time frame. With the increase of bubble volume fraction, both the horizontal and vertical compressive strength of the ice decrease gradually. When the bubble volume fraction increases from 4% to 34%, the horizontal and vertical compressive strengths decrease to 8.38% and 8.10% of the original values, respectively. Finally, based on existing research on trapped air bubbles, the current research gaps and development trends are predicted and elaborated. This review is helpful for clarifying the complex characteristics of trapped air bubbles and enriching the mass transfer theory of icing process. It can also provide references and insights for the optimal design of existing anti-deicing technologies.