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.

Abstract:

A fault tolerant control scheme based on integral sliding mode surface is developed for spacecraft attitude stabilization in the presence of actuator faults, misalignments, magnitude saturation and external disturbances simultaneously. This approach is based on a novel integral-type sliding mode control strategy to compensate for these un-desired issues without controller reconfiguration. Especially, it guarantees the reachability of the system states by involving adaptive control technique to relax the boundary information in advance. A sufficient condition for the controller to accommodate magnitude saturation is also presented and then the fault tolerant attitude control system can be guaranteed theoretically to be asymptotically stable by using Lyapunov method. Numerical simulation results shows that the proposed control law can quarantee the stability of the spacecraft attitude control system in the presence of actuators' failures, and it has good robust performance.

Abstract:

The self-centering buckling-restrained brace (SBRB) was formed by making a self-centering system consisting of stacked disc springs (DS) and a buckling-restrained brace (BRB) work in parallel to control the residual deformation of BRB. Quasi-static tests were done to examine the effects of stiffness of stacked springs, end connections, self-centering ratios, etc. on the hysteretic behavior of SBRBs. The tests revealed that, compared with BRBs, the residual deformations of SBRBs were reduced greatly. SBRBs exhibited flag-shaped hysteretic curves, and in the later stage of tests, the steel plate brace underwent tensile failure while other components remained intact. The bearing capacity and energy dissipation capacity of SBRBs are mainly from the DS parts and BRB parts, respectively. Approximately 23%-36% energy dissipation in SBRBs is from the DS parts due to the friction between stacked springs. When the other constructional details remained the same, the DS parts with a higher stiffness of springs had a greater increase in bearing capacity after starting, and the DS parts with a higher starting force also had a higher self-centering ratio and smaller residual deformations. On the whole, the end connections had little effect on the residual deformations. The tension fracture of steel plate brace occurred earlier in the SBRB with rigid end connections due to bearing additional bending moments, while the SBRBs with pin end connections exhibited better energy dissipation. With the increase of self-centering ratios, the residual deformations of SBRBs reduced gradually and the appropriate ratios of SBRBs should be kept within 0.7-0.9 to efficiently control residual deformations and to avoid excessive demand of DS parts.

Abstract:

It is well known that unmanned aerial vehicle (UAV) is more and more widely applied in military and civil areas. In order to play the better role of UAV, it is needed to utilize multi UAVs cooperative formation to accomplish cooperative reconnaissance, combat, defense and spraying pesticides and other tasks. The multi UAVs cooperative formation control technology mainly contains the following key techniques: data fusion technology, sensing technology, task allocation technology, path planning technology, formation control technology, communication network technology and virtual/physical verification platform technology. Firstly, summarize the research and development of key technologies worldwide. Then, the classification for multi UAVs formation control methods is mainly investigated, and the problems about formation design and adjustment, formation reconfiguration are summarized. Finally, the challenges and future development for multi UAV cooperative formation are prospected. Research shows: at present, the theory of multi UAV formation flight has acquired fruitful results, while the real cooperative formation flight test can only be implemented in the simple communication environment. The real time performance for task allocation and path planning is not high. The robustness of control methods to cope with the unexpected situation is low. The cooperative sensing ability for multi UAV with multi sensor is insufficient. The simulation of the entity is lacked. Breaking through the above key technologies, carrying out the cooperative formation flight of multi UAV in complex sensing constraints and complex communication environment, putting forward more effective control method and carrying out the UAV physical formation flying test so that the UAV can finish the task better may be the future research directions.

Abstract:

To explore the effects of lightweight sand on the strain hardening properties of ultra high performance concrete (UHPC) with different specimen sizes, the lightweight sand was used to replace the yellow sand by equal volume. Nine groups of uniaxial tensile tests were carried out with different lightweight sand volume rate ranging from 0 to 35% and different specimen thicknesses from 30 mm to 100 mm. Meanwhile, simultaneous acoustic emission real-time flaw detection tests were conducted. Results show that the volume rate of lightweight sand demonstrates little effect on the stress and strain at the elastic limit point of UHPC, but when the volume rate of lightweight sand increases from 0 to 35%, the ultimate tensile strength and ultimate tensile strain of UHPC grow from 10.6 MPa and 2.35×10^-3 to 19.4 MPa and 4.3×10^-3 respectively. When the volume rate of lightweight sand is greater than 15%, the strain hardening degree of UHPC significantly increase with more damage points generated and more uniformly distributed inside the specimen, showing remarkable crack control capability. With the same lightweight sand volume rate, the strain hardening degree of UHPC decreases with the increase of specimen thickness, and the damage points inside the specimen tend to be concentrated, exhibiting an obvious size effect.

Abstract:

In the ultra-dense network environment, each access point is deployed in the hotspot area, which forms a complex heterogeneous network. Users need to choose the appropriate network to access, so as to achieve the best performance. Network selection problem is to choose the optimal network for the user, so that the user or network performance reaches the best. In order to solve the access selection problem of users in ultra-dense networks, we proposed an ultra-dense network access selection algorithm based on the improved deep Q network (DQN), considering network states, user preferences, and service types, and combining with load balancing strategies. First, by analyzing the influence of network attributes and user preferences on network selection, the appropriate network parameters were selected as the parameters of the access selection algorithm. Then, the problem of network access selection was modeled by Markov decision-making process, and the states, actions, and reward functions of the model were designed. Finally, the optimal network strategy was obtained by using DQN to solve the network selection model. In addition, the target function of traditional DQN was optimized to avoid overestimation of Q value by DQN, and a priority experience replay mechanism was introduced to improve learning efficiency. Simulation results show that the method could well solve the problem of overestimation of traditional DQN, accelerate the convergence of neural network, effectively reduce user congestion, and improve network throughput performance.

Abstract:

In order to accurately predict the rotational stiffness of embedded steel column bases, shallowly embedded, in particular, this paper proposes a stiffness model that collectively allows for the effects of the embedded depth, shear deformation of the embedded column, axial force applied to the column and restraint from the base plate. For developing the model, the embedded segment of the column is simplified as a beam on the Winkler foundation, and its deformation is computed using the Timoshenko beam theory on Winkler foundation, considering the influence of axial force applied to the column and solved by initial parameter method. To investigate the influence of the above-mentioned factors and verify the proposed model, finite element (FE) models are developed and validated against existing experimental results. Comparisons between the FE results and model predictions show that the proposed model exhibits higher accuracy than the theoretical models reported, especially for shallowly embedded column bases. The model prediction and FE results indicate that the rotational stiffness of the column base depends on the embedded depth in a nonlinear fashion-the stiffness increases rapidly for small embedded depth but remains almost constant when embedded depth is larger than a certain value; the axial compression load applied to the steel column is a beneficial factor to the stiffness; the restraint from the base plate shows a significant effect on the rotational stiffness of embedded column bases with the embedded depth ratio less than 1.5, being negligible when the embedded depth ratio increases up to 2.5.

Abstract:

To reduce the cost of Pt electrode for hydrogen production by PEM electrolysis, the Pt-Ni composite electrode was prepared by electrochemical deposition method using nickel foam as substrate. The prepared Pt-Ni composite electrode was characterized by scanning electron microscope, X-ray diffractometer, and X-ray spectrometer. The hydrogen evolution property of five composite electrodes with different Pt/Ni mass ratios of 1∶7,1∶1,1∶2,1∶14 and 1∶23 were carried out by electrochemical workstation and PEM electrolytic cell. The experimental results show that the Pt-Ni composite electrode prepared by the electrochemical deposition method with nickel foam as the substrate has stable properties, and the amount of deposited Pt has a great influence on the hydrogen evolution property of the Pt-Ni composite electrode. There is an optimal Pt/Ni mass ratio and the best Pt/Ni mass ratio under experimental conditions is m(Pt)∶m(Ni)=1∶12. With either too much or too little Pt deposition, the hydrogen evolution property will be reduced, and the impact of too much Pt deposition stacking on the hydrogen evolution property will be more obvious. In the preparation of Pt-Ni composite electrodes with trace Pt deposition, the principle that the best Pt/Ni mass ratio should be used as a benchmark and the amount of Pt deposited should be "less rather than more" should be kept, while the misconception of "the more Pt deposited the better the electrode property" should be avoided in practical engineering applications.

Abstract:

Seismic action tends to result in the liquefication failure of offshore fan foundation in the sand deposit. Monopile-bucket hybrid foundation is a novel type of offshore fan foundation, combining the advantages of monopile and suction bucket foundations. To investigate the seismic response of this hybrid foundation in sand, a series of centrifugal shaking table model tests of monopile and the hybrid foundations in dry and saturated sand were conducted. White noise and seismic waves with different frequency spectrum components were used to stimulate the vibration for obtaining the natural vibration frequency, excess pore pressure accumulation of foundation soil, acceleration response of the offshore wind system and foundation bending moment distribution of the two foundation forms in sandy soil. The results show that the excess pore pressure of soil in saturated soil decreases in shallow depth under the bucket component of the hybrid foundation,while the acceleration amplitude is enlarged correspondingly. The shallow bending moment response of the monopile in saturated site is relatively larger with the turbine exhibiting obvious residual displacement. Compared with the monopile, the hybrid foundation shows greater acceleration response and smaller horizontal displacement in tests. The study provides a fresh reference for the seismic design of offshore wind structures with monopile and monopile-bucket hybrid foundations.

Abstract:

In order to accurately simulate the hysteretic response of exterior beam-column joints under seismic conditions element model of exterior beam-column joints that took the bond degradation mechanism into account is established. Based on the ANSYS finite element platform, the Voce-Chaboche combined hardening model is used to define the cyclic constitutive relationship of reinforcement, and the composite spring elements are developed to simulate the bond degradation mechanism between steel bar and concrete under reciprocating loading. A prediction model for the bond-slip constitutive relationship under reciprocating loading is proposed based on damage theory. The hysteresis curves, skeleton curves, stiffness degradation curves and stress nephogram obtained from the finite element calculation are compared with the experimental results. The comparison shows that the combined hardening constitutive model can better describe the hysteretic response of steel bars under reciprocating loads. Composite spring elements successfully invert the bond degradation characteristics between steel bars and concrete under reciprocating loads. The development of plastic hinges in the joint beam under reciprocating loads leads to plastic elongation of the beam, which will adversely affect the exterior column. The numerical simulation results are in good agreement with the experimental results, providing an important theoretical basis and technical platform for accurately simulating the hysteretic performance of exterior beam-column joints.

Abstract:

Reinforced concrete slabs during the service period may suffer repeated impacts from falling objects with different impact angle. The capability of reinforced concrete slabs to resist multiple impacts, the performance evolution of reinforced concrete slabs under multiple impacts and the residual performance evaluation are vital to people's livelihood and safety. Notably, the multiple impact loading system is the key to investigate the impact resistance of reinforced concrete slabs. To study the impact resistance of reinforced concrete slabs under multiple impacts, drop hammer and pendulum impact test was carried out, and the impact performance of reinforced concrete (RC) slabs under amplitude impacts was scrutinized with the cumulative damage characteristics of the RC slabs analyzed, the impact force-time history curves of each impact and the global and the local deformations of the RC slabs after each impact examined. The energy-absorbed capacity and the residual performance of the impacted slab were explored. The experimental results show that the deformation of the RC slabs is affected by the impact angle with the oblique impact producing a greater influence on the safety performance of reinforced concrete slabs. Moreover, the energy-absorbed capacity of the RC slabs is reduced due to the amplitude impact force which causes more damage of the slab. The impact response of the slab under amplitude impacts proves to be more stable than that of the repeated-impact with a constant weight.

Abstract:

Premise plumbing have special working conditions such as long-term detention of hydraulic regimes and intermittent water use. In this study, based on the hourly water consumption data of 1 100 households in a residential area of HZ City, an indoor non-circulating pipeline simulation platform was built, and five hydraulic regimes were set up: high varied flow (HIG), medium varied flow (MED), low varied flow (LOW), steady state (SS) and 168 h retention (RET), to explore the influence of special hydraulic conditions of premise plumbing on the microbial communities and opportunistic pathogens. After three months of operation, 33 sets of biofilm and water samples were collected, and real time qPCR and 16S rRNA gene sequencing analysis were performed. In addition, the absolute abundance of Pseudomonas aeruginosain the samples was quantified. The microbial community and diversity were analyzed. The results showed that the total number of RET water-like bacteria was the largest, and the proportion of viable bacteria in the biofilm was the highest. Conditionally pathogenic bacteria in the water samples has higher number and abundance under intermittent hydro-working conditions. The total number of bacteria in HIG biofilms and the highest relative abundance of conditionally pathogenic bacteria was 78.38%. The quantitative results of Pseudomonas aeruginosawere 4 798.81/cm², which was 7.59 times that of RET biofilms. The RDA results showed that turbidity and pH were the main environmental factors for Pseudomonas and Pseudomonas aeruginosa respectively.

Abstract:

In order to explore the reinforcement effect and working mechanism of spliced wood columns strengthened by fiber reinforced polymer, the axial compression tests of 10 reinforced wood columns were carried out considering the influence of different fiber sheets and splicing methods. The failure modes and axial compressive properties of reinforced columns under three kinds of FRP sheets (AFRP, BFRP, CFRP) and four kinds of splicing methods (tenon joint, keban tenon joint, mortise joint, straight tenon joint) weree compared and analyzed. The results indicated that the traditional pier jointed columns without FRP reinforcement show the cracking of jointed timber and local buckling fracture after cracking. However, after FRP reinforcement, the integrity of the pier joint area is good, while the failure mainly occurred at the interface between the upper and lower piers, which was manifested as wood crushing and fiber cloth folding. The bearing capacity and stiffness of unconstrained pier joints were only recovered to 42%-69% and 43%-65% respectively. After the FRP reinforced pier was connected to the wooden column, the axial compression capacity can be restored to 75%-100% of the intact wooden column, the stiffness can be restored to 66%-107%, the ductility can be improved by 24%-96%, and the axial compression bearing capacity and deformation capacity of the wooden column can be effectively restored or improved. In addition, the stiffness degradation was not obvious. The load displacement curves and mechanical properties obtained by simulation were in good agreement with the experimental results. In conclusion, the spliced timber columns reinforced by FRP sheets had good mechanical properties, which can provide reference for the repair of traditional timber structures and the splicing of wooden columns.

Abstract:

To investigate the ground motion intensity measures suitable for evaluating high-rise structures under near-fault ground motions with pulse-like effect, this paper proposes a new ground motion intensity measure considering period elongation effect and higher mode effect based on acceleration spectrum. Taking two high-rise reinforced chimney structures (120 m and 240 m) as research objects, the correlation between damage indices (ParkAng damage index, maximum inter-story drift ratio, maximum structural curvature, maximum floor acceleration, and maximum roof displacement) of high-rise structures and 37 ground motion intensity measures was studied under near-fault ground motions using OpenSEES. Results show that the proposed intensity measure was the optimal index in predicting the ParkAng damage of high-rise concrete structures under near-fault ground motions. High correlation between velocity-related intensity measures and structural damage index was observed. As the structural period increased, the correlation between damage indices and displacement-related intensity measures was improved. Besides, peak ground acceleration had limitations in characterizing the deformation and failure of high-rise structures, but it could be used to analyze the seismic performance of non-structural components. The research results can provide reference for selecting proper measures and structural damage indices to evaluate the seismic performance of high-rise structures under near-fault ground motions.

Abstract:

To make the directional demolition of the cooling tower safer and more controllable, the axial force calculation method of the retained columns of the cooling tower is proposed. Firstly, in the light of the similarity relationship of the force, the relationship between the axial and Z-direction force of the column was investigated. Based on the plane section assumption, the calculation formula of the Z-direction force of the retained columns was deduced. Then, the effects of 5 parameters, specifically the elastic modulus of the ring beam and the column, the height of the column, the number of retained columns and the central angle corresponding to the top of the adjacent column on the Z-direction force of the retained column were explored by FEM. The calculation formula of the Z-direction force of the retained column was modified according to the results of FEM, and the applicability of the modified formula was studied. The results show that the blasted cooling towers do not satisfy the assumption of plane section on all retained columns. In practical engineering, the above 5 parameters do not affect the distribution characteristics of the Z-direction force of the retained columns: the distribution of the Z-direction force along the y-axis direction is always ′compression at both ends and tension in the middle′, the maximum compression in the retained columns always appears on the n row, with the maximum tension always on the (n-4) row. When the blasting center angle is in 200°-240°, the relative error of the modified formula is within 21%, and the modified formula exhibits good applicability in different cooling towers. The calculation formulas of axial force of retained column provide theoretical supports for the demolition of cooling tower from the perspective of mechanics, improving the safety of directional demolition of cooling tower.

Abstract:

The secondary effluent of the chemical industry park contains a variety of toxic pollutants, which still poses a great risk to the ecological environment. In this study, the microbubble O₃/H₂O₂ process was established for advanced treatment of secondary effluent from a chemical industry park, and the operation parameters, pollutant degradation mechanism and toxicity evaluation were studied. The best operating parameters were pH 7.3, ozone dosage 60 mg/L, H₂O₂ initial dosage 114 mg/L, reaction time 15 min. Under this condition, the removal rates of COD and TOC were 47.41% and 46.61% respectively in microbubble O₃/H₂O₂ process. The microbubble O₃ can significantly improve the ozone utilization efficiency and shorten the reaction time. Compared with ordinary O₃ aeration, the ozone utilization rate increased by 10% and the reaction time shortened by two thirds. The removal process of organics by microbubble O₃/H₂O₂ process followed the apparent second-order reaction kinetics; the electron paramagnetic resonance (EPR) technology proved that hydroxyl radical (·OH) played a role in the degradation of organic substances, H₂O₂ promoted the formation of ·OH and microbubbles aeration promoted the production of more ·OH by O₃/H₂O₂ through the process. Dissolved organic matter had the tendency of transforming macromolecular substances into small molecular substances in the process of advanced treatment. H₂O₂ can enhance the removal ability of ozone to hydrophobic neutral components and change the degradation path of ozone to pollutants. Compared with 100% luminescence inhibition rate of microbubble O₃, the luminescence inhibition rate of microbubble O₃/H₂O₂ was less than 20%, suggesting that the addition of H₂O₂ can effectively inhibit the increase of acute toxicity.

Abstract:

To investigate the mechanism of the effect of calcium oxide and sodium carbonate activated slag on the autogenous shrinkage of alkali-activated cement, an alkali-activated slag martar (AM) was prepared using calcium oxide and sodium carbonate (molar ratio of 1∶1) as the combined activator. The effect of combined activator Na₂O equivalent (i.e. the by weight ratio of Na₂O produced by the reaction of the combined activators to slag, i.e. 2.5%, 4.5%, 6.5% and 8.5%) on the autogenous shrinkage of AM was investigated. The hydration products and microstructure were characterized by X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and nuclear magnetic resonance. The results indicate that with the increase of Na₂O equivalent, the increase of water consumption due to the reaction of activators and pore structure refinement leads to the increase of pore pressure, and the amount of absorbed Na+ increases due to the increase of amount of Si⁴⁺ in C-(A)-S-H replaced by Al³⁺, resulting in the increase of C-(A)-S-H slippage. The increase of hydration degree induces the increase of the amount of hydration products, resulting in the increase of the autogenous shrinkage. AM with Na₂O equivalent of 6.5% is the best group with its mechanical properties higher than those of ordinary Portland cement mortar (OM), but its autogenous shrinkage greater than that of OM due to its lower crystal content and denser pore structure.

Abstract:

To study the mechanical properties of perforated steel plate (PSP) shear connectors in prefabricated double-channel steel-concrete composite beams, seven groups of standard specimens were designed and push-out tests were conducted to compare and analyze the shear capacity and failure modes of PSP shear connectors with different parameters. The ABAQUS nonlinear finite element model was developed to numerically simulate the failure mode and force mechanism of PSP shear connectors, and the reliability of the finite element results was verified by comparing with the experimental results. On this basis, further analysis is conducted on the effects of the thickness of the perforated steel plate, the diameter of the hole, the strength of the concrete, the perforated reinforcement and the spacing between the connectors on the mechanical properties of PSP shear connectors. The results showed that, except for the 10 mm thick PSP shear connectors, all PSP shear connectors with the thicknesses of 4 mm and 6 mm underwent obvious bending deformation, and oblique cracks appeared in the concrete around the connectors when all specimens were failed.The diameter of the hole and the perforated reinforcement had little effect on the shear capacity and shear stiffness, while increasing the thickness of the perforated steel plate and concrete strength could improve the shear capacity and shear stiffness of PSP shear connectors. For double-row PSP shear connectors, increasing the spacing between the connectors could significantly improve the average bearing capacity of single-row PSP shear connectors, and when the spacing was 250 mm, the average shear capacity of single-row PSP shear connectors reached 91.2% of that of a single PSP connector. Finally, an equation for the calculation of the load-slip curve of a single PSP shear connector in prefabricated double-channel steel-concrete composite beams was proposed based on the experiment and finite element load-slip curve providing a reference for the design of prefabricated double-channel steel-concrete composite beams.

Abstract:

To reveal the bond-slip relationship between the rebar and the grout material in the grouted-sleeve connection, the rib-scale refined finite element (FE) models of the joint specimens are established using the FE software DIANA 10.3. The local bond-slip relationships of joint specimens are investigated based on the results of FE analyses. The results show that, the distribution of the rebar bond stress is roughly saddle-shaped along the anchorage length, and the peak near the loaded end transfers inwards with the increment of the load. The relative slippage between the bar and the grout increases from the rebar free end to the loaded end. As the yielding load is beyond, the relative slippage shoots up at the loaded end and develops inwards gradually. The local bond-slip curve is divided into five stages. The curves at different anchorage positions develop similarly, but their developing paths are different at the developing extent and characteristic value. The position function of the joint specimen is a binary function of the anchorage position and the relative slippage, whose function image is roughly shaped as “M”. It is suggested to fit it with the elliptic curve and the quadratic curve. The rib-scale refined FE models are capable of investigating the bond-slip constitutive models of the grouted-sleeve connections.

Abstract:

To evaluate the durability of reinforced concrete structures in marine, salt lakes, etc., this paper explored the characteristics of corrosion-induced cover cracking under combined chloride and sulfate attack by experimental and theoretical analysis. The reinforced concrete specimens were exposed to 5%NaCl, 5%NaCl+5%Na₂SO₄ solutions with electric field for degradation acceleration. The visual appearance of concrete and corrosion of reinforcement under different conditions were compared. Moreover, an accompanied experiment for concrete deterioration was designed in analogy to the cover deterioration, and the mechanical properties of concrete were analyzed. The results showed that in presence of sulfate, the concrete cover appearance altered before cracking; the "white whiskers" under the single chloride solution disappeared while efflorescence existed on the surface of the concrete with sulfate crystallization. Furthermore, the presence of sulfate also extented the time before corrosion-induced cracking. The corrosion level of the reinforcement under the combined attack was lower than that under the single chloride attack, and both were much lower than the predicted value by Faraday′s law. The crack width was linearly correlated with the corrosion level, and the presence of sulfates increased the development of crack width with the corrosion level. Under the electric field, the compressive strength of concrete increased at first and then decreased, while the tensile splitting strength reduced with exposure time. An empirical formula for the tensile strength of deteriorated concrete was proposed. The effect of filling rust products in the cracks was taken into account based on the classic model for corrosion-induced cover cracking. In addition, the effect of sulfate was considered in the tensile strength of concrete and corrosion current density. On these bases, a time prediction model for the corrosion-induced cracking of reinforced concrete under combined attack was established, and the validity of the model was verified.

Abstract:

To explore the differences between the heat transfer processes of the envelope of the manned lunar research station caused by the special solar-thermal environment on the lunar surface and those of the buildings on the earth. a heat transfer model of lunar building envelope was established based on the finite difference method and the model of the solar radiation on the lunar surface. Various factors affecting the temperature on the inner surface, such as the surface parameters and the orientation of the envelope, were analyzed by simulation. The results showed that when the thermal protection layer, thermal insulation layer, and gas barrier layer were respectively made of 20 mm Nextel BF-0,0 mm Pyrogel 6650, and 20 mm Kapton,the surface temperature of inner horizontal roof fluctuated between 16.8 ℃ to 22.4 ℃. In addition, the thickness and thermal conductivity were found to be the most important factors affecting the heat transfer performance of the building envelope. To balance construction costs and thermal insulation performance, the thickness and thermal conductivity of the building envelope should be reduced as much as possible by using low-density, high-specific-heat materials. It was also concluded that the convective heat transfer coefficient of the inner surface and the emissivity of the outer surface directly affected the boundary heat transfer of the envelope. Therefore, materials with differential thermal inertia and emissivity of the outer surface can be customized based on the radiation characteristics of different orientations and thermal comfort requirements.

Abstract:

A research approach of "dismantling and building" is proposed for high-precision ocean scene infrared simulation of sea surface with state level above 3. In this approach, the large-scale sea surface is described as a combination of rough sea surface, foam and breaking waves; then three kinds of featured multi-scale voxels, namely "rough sea surface", "rough sea surface covering foam", and "rough sea surface covering breaking waves", are abstracted from the complex sea surface. Finally, by means of sea surface gridding, featured voxels matching, rendering based on directional-spectral characteristics reconstruction and other methods, the large-scale sea surface radiation/scattering characteristics are reconstructed with the three kinds of featured multi-scale voxels and the calculation of large-scale sea surface "air-surface-body" coupling radiation/scattering characteristics is completed. This article conducted modeling research on multi-scale coupled radiation and scattering characteristics of three kinds of featured multi-scale voxels. A calculation model for the radiation/scattering directional-spectral characteristics of three kinds of featured multi-scale voxels was constructed and the factors influencing the radiation scattering direction spectral characteristics of the structures were analyzed. The calculation results indicate that with the increase of the sea surface wind speed, the thickness of foam and the concentration of bubbles in the typical structure on the sea surface gradually increase, which makes the scattering ability of the structure increase, thus increasing the bidirectional reflectance distribution function of the structure. With the increase of the detection wavelength, the absorption of seawater is significantly enhanced, which leads to a significant increase in the difference between the bidirectional reflectance distribution function of structures under different wind speeds. For different incident angles, the zenith angle corresponding to the maximum value of bidirectional reflectance distribution function of any structure gradually changes along with the incident zenith angle.

Abstract:

Microbial co-metabolism can effectively degrade the polycyclic aromatic hydrocarbons (PAHs) in polluted sediment of river. The salinity of overlying water in tide river section at the junction of inland and outland water in coastal cities fluctuates greatly due to tidal influence, but the effect of salinity fluctuation on the co-metabolism degradation of PAHs in the sediment and the response of microbial community are still unclear. In this study, sodium acetate and phthalic acid were used as co-metabolic carbon sources to investigate the effect of fluctuation with a range of 0-50‰ salinity of overlying water on the degradation of PAHs in the sediment, monitor the changes of the physicochemical properties and sulfide content of the sediment, and analyze the changes of the microbial community in the sediment under the condition of salinity fluctuation. The results showed that a low-salt environment (0-20‰) was more conducive to co-metabolism and degradation of PAHs, and the degradation rate of PAHs was 1.5-3.3 times higher than that of a high-salt environment (>20‰-50‰). Moreover, the high osmotic pressure produced by the high-salt environment would affect the microbial activity and inhibit the co-metabolism reaction, resulting in a slow decline in pH and oxidation-reduction potential (ORP) of the sediment and a decrease in the reduction rate of SO^2-₄. High-throughput sequencing showed that salinity fluctuation could significantly change the microbial community structure of the sediment. Proteobacteria, Firmicutes, and Bacteroides were dominant in the low-salt environment while Marinobacterium and Marinobacter were the dominant genera involved in the co-metabolism and degradation of PAHs. In addition, the stress effect of the high-salt environment inhibited the activity of most microorganisms, while the abundance of Desulfobacter and Chloroflexi continued to increase, and SBR1031 and Sulfurovum became the dominant bacteria.

Abstract:

In view of the weaknesses of poor computing and storage capabilities of edge devices, lightweight processing was carried out on the backbone network CSPDarkNet53 for feature extraction in the traditional YOLOv5 model, and a lightweight gesture recognition algorithm MPE-YOLOv5 was proposed to realize the deployment of the model in low-power edge devices. Considering the problem that it is difficult to identify large-scale transformation targets and tiny targets due to less feature extraction in lightweight model, efficient channel attention (ECA) mechanism was added to alleviate the loss of information after high-level feature mapping due to the reduction of feature channel. A detection layer for tiny targets was added to improve the sensitivity to tiny target gestures. EIoU was selected as the loss function of the detection frame to improve the positioning accuracy. The effectiveness of the MPE-YOLOv5 algorithm was verified on the self-made dataset and NUS-Ⅱ public dataset, and the MPE-YOLOv5 algorithm was compared with lightweight M-YOLOv5 algorithm and original YOLOv5 algorithm on the self-made dataset. Experimental results show that the model parameters, model size, and computational complexity of the improved algorithm were 21.16%, 25.33%, and 27.33% of the original algorithm, and the average accuracy was 97.2%. Compared with the lightweight model M-YOLOv5, MPE-YOLOv5 improved the average accuracy by 8.72% while maintaining the original efficiency. The proposed MPE-YOLOv5 algorithm can better balance between the detection accuracy and real-time reasoning speed of the model, and can be deployed on edge terminals with limited hardware.

Abstract:

Considering the failure mechanism and weaknesses of traditional fabricated shear wall structures under strong earthquakes, a new type of fabricated shear wall with functions of energy dissipation and shock absorption was proposed. On the basis of model test and numerical simulation, seismic performance tests were carried out on four specimens with scale ratio of 1∶1.54 and shear span ratio of 1.52. Further analysis was conducted to investigate the effects of bolt number, axial compression ratio, and reinforcement ratio of edge members on the seismic performance of the new fabricated shear wall, including failure modes, hysteretic performance, bearing capacity, displacement ductility, stiffness degradation, and energy dissipation capacity. Test results show that the four specimens experienced shear compression failure, which was the same as the cast-in-place shear wall with the same shear span ratio. However, the proposed shear wall had better hysteretic performance and energy dissipation capacity, and the energy dissipation capacity was higher than that of the cast-in-place shear wall at the failure point. When the number of bolts decreased, the hysteretic performance of the new fabricated shear wall decreased, the wall deformation increased, while the bearing capacity remained almost unchanged. When the axial compression ratio or reinforcement ratio of edge members decreased, the bearing capacity decreased, and the ultimate displacement increased. Finally, the finite element model of the specimens was established by ABAQUS program. Comparisons of numerical results and test results showed a good agreement, verifying the correctness of the model, which can be applied to the analysis of the new fabricated shear wall.

Abstract:

Autonomous navigation based on sequential images (ANBSI) is the key technology of pinpoint landing missions for future deep space exploration and also is one of the major development directions for deep space exploration technology. The necessity of developing ANBSI for planetary pinpoint landing is elaborated in this paper. Firstly, state-of-art developments of ANBSI are reviewed in terms of active sensing and passive sensing. Then, the key techniques applied in ANBSI for planetary landing are summarized and analyzed. Finally, according to the analysis of the key techniques, the main issues of ANBSI are raised and their future developments are overviewed.

Abstract:

This paper proposes a low-latency intelligent network data transmission scheduling algorithm for real-time network transmission demand scenarios of low latency, stable transmission, and high quality of experience (QoE). The algorithm consists of two parts: data block queuing control strategy and congestion control strategy. The data block queuing control strategy presents a cost-effective model that integrates the creation time and effective time of data blocks, effectively solving the problem of uneven information transmission under transmission time constraint. The congestion control strategy proposes a deep deterministic policy gradient (DDPG) method based on the Gumbel distribution sampling reparameterization with mixed experience prioritization model, which solves the problem that DDPG is not applicable to the congestion control of discrete network action space and significantly improves the quality of network congestion control by adaptively adjusting the sending parameters through learning. Results show that the proposed queuing algorithm could effectively improve QoE in real-time transmission scenarios, and the improved DDPG for congestion control could significantly reduce transmission delay. In the same scenario, compared with traditional network data transmission scheduling algorithms, by integrating the proposed queuing and congestion control strategies, the improved intelligent network data transmission scheduling algorithm could maintain a good balance between low latency and stable transmission and provide higher data transmission quality.

Abstract:

In view of the problems of low brightness and obvious color distortion of the sky in restored images in most existing algorithms for image dehazing, a haze removal method for UAV aerial images based on atmospheric light value and graph estimation was proposed. First, the depth-of-field image was obtained according to the color attenuation prior theory, and the mean value of the region with the minimum deviation in the depth-of-field image was taken as the atmospheric light value. Then, a random walk clustering method was designed to estimate the atmospheric light map. The random walk algorithm was used to cluster the image into N sub-regions, and the mean value of the first 0.1% pixels of the sub-regions was taken as the regional atmospheric light value, which was then combined and refined by guided filtering to obtain the atmospheric light map. Next, the two atmospheric light estimators were fused into a new atmospheric light map with atmospheric light valuegraph estimation, which is a more accurate atmospheric light estimator. The transmittance was obtained by haze-lines prior method, and a dark compensation method was proposed to improve the transmission accuracy. Finally, according to the atmospheric scattering model, a clear restored image was obtained based on the fused atmospheric light map and optimized transmittance. Experimental results show that compared with other algorithms, the proposed algorithm improved the information entropy, mean gradient, blur coefficient, and contrast by 1.1%, 6.3%, 8.5%, and 6.4%, respectively, with better subjective visual effect and more abundant information.

Abstract:

Image segmentation is to divide the region with special meanings into several disjoint sub-regions according to certain rules, which is the key link between image processing and image analysis. The traditional watershed image segmentation method is widely used, which has the advantages of fast and simple. However, it is easily interfered by noise, and the segmentation results are prone to lose important edge information, resulting in over-segmentation. In view of the problem of the traditional watershed image segmentation method, an improved watershed image segmentation method based on adaptive structural elements was proposed. First, the adaptive structural elements with variable shapes were constructed by using local density, symmetry, and boundary features of adjacent pixels of image targets, so as to ensure a good consistency between the proposed structural elements and the shape of image targets. Then, the adaptive structural elements were used to obtain the morphological gradient of the image, which could improve the positioning accuracy of the target edge. The L₀ norm gradient minimization and morphological open-close hybrid reconstruction were used to modify the gradient image, so as to reduce the local invalid minimum points in the gradient image and suppress the occurrence of over-segmentation. Finally, watershed segmentation was performed on the modified gradient image to realize accurate segmentation of the target region of the image. Experimental results show that the method could effectively restrain over-segmentation of traditional watershed algorithm and improve the accuracy of the target edge positioning, with high precision of image segmentation.

Abstract:

In view of the problem that general pre-trained models are not suitable for named entity recognition tasks in the medical domain, a neural network architecture that integrates knowledge graph in the medical domain was proposed. The elastic position and masking matrix were used to avoid semantic confusion and semantic interference in self-attention calculation of pre-trained model. The idea of multi-task learning in fine-tuning was adopted, and the optimization algorithm of recall learning was employed for pre-trained model to balance between general semantic expression and learning of the target task. Finally, a more efficient vector representation was obtained and label prediction was conducted. Experimental results showed that the proposed architecture achieved better results than the mainstream pre-trained models in the medical domain, and had relatively good results in the general domain. The architecture avoided retraining pre-trained models in particular domain and additional coding structures, which greatly reduced computational cost and model size. In addition, according to the ablation experiments, the medical domain was more dependent on the knowledge graph than the general domain, indicating the effectiveness of integrating the knowledge graph method in the medical domain. Parameter analysis proved that the optimization algorithm which used recall learning could effectively control the update of model parameters, so that the model retained more general semantic information and obtained more semantic vector representation. Besides, the experimental analysis showed that the proposed method had better performance in the category with a small number of entities.

Abstract:

The advent of Industry 4.0 has spawned the widespread application of digital twin technology, providing digital solutions for intelligent manufacturing and product life-cycle management. In the field of civil engineering, the enhancement of digital disaster prevention and civil structure management is a critical component in the development of future smart cities. On one hand, the establishment of precise and reliable digital twins of real-life civil structures can facilitate disaster prevention from extreme hazards, as well as identify and warn against potential risks. On the other hand, digital twins lay the foundation for technological advancements in the digital construction and management of future cities. This study first categorizes the fundamental concepts and developmental stages of digital twin technology. Then, the acquisition of twining data and construction of digital twins for civil structures are systematically summarized. Building on this foundation, a comprehensive review and outlook is presented on the application of digital twin technology in civil engineering, encompassing the operation and maintenance of structures, disaster simulation and digital twin cities.

Abstract:

The development of advanced nano-integrated circuit processes has led to a decreasing threshold charge in microelectronic devices, resulting in an increased rate of soft errors caused by single-event effects in digital circuits. To enhance the radiation resistance of standard cells in integrated circuits, this paper proposes a NAND gate structure that is resistant to single-event transients (SETs). In the triple well process, by shorting the substrate and source of each NMOS transistor in the pull-down network, the radiation resistance of the NAND gate was effectively improved, and the hardening of the proposed NAND gate became more effective as the number of inputs increased. Particle incidence simulation experiments were performed by Sentaurus TCAD software in hybrid simulation mode. For the NMOS transistor connected to the output node, the three-dimensional physical model that has been calibrated by the process was used, and the Spice model provided by the manufacturer was adopted for other MOS transistors. Simulation results show that the proposed two-input NAND in 40 nm process could reduce the output voltage fluctuation amplitude in three-input cases at the linear energy transfer (LET) value of incidence particle of 10 MeV·cm²/mg. Besides, the effect of immunity to single particle incidence was achieved in the input mode with N₂ transistor closed. For the hardened three-input NAND gate, the output voltage disturbance could be reduced by up to 85.4% even in the “worst case”. Therefore, the proposed hardening method for NAND gate has a significant effect against SET.

Abstract:

To study the mechanical performance of concrete-filled double-skin steel tubular long columns under compressive and torsional loads, two ordinary circular steel tube reinforced concrete columns and two double-layered steel tube reinforced concrete columns were subjected to low-cycle reciprocating tests under pure torsion and torsion-compression loading using a developed Stewart six-degree-of-freedom loading platform. Based on the tests, the bearing capacity, torsional deformation, energy dissipation, and hysteresis performance of each specimen were compared and analyzed, and finite element parameter analysis was conducted. The study shows that both ordinary circular steel tube reinforced concrete columns and double-layered circular steel tube reinforced concrete columns have good torsional resistance. Compared with ordinary circular steel tube reinforced concrete columns, the initial stiffness and bearing capacity of double-layered steel tube reinforced concrete columns are slightly improved, the hysteresis curve is more full, and the energy dissipation capacity and ductility are greatly improved. Parameter analysis shows that when the steel content is constant, the larger the thickness ratio of the inner steel tube, the more beneficial it is for torsional resistance; and within a certain range of axial loads, the torsional resistance of steel tube reinforced concrete columns can be improved.

Abstract:

Due to the complex background of ship targets and much irrelevant interference in visual images, it is difficult to conduct ship detection. In addition, there are few datasets for multi-category ship detection and the samples are often unbalanced, which makes the ship target detection performance degraded. Considering the ship detection background interference, an improved YOLOv3 model was proposed by introducing SimAM attention mechanism, which was used to enhance the weight of the ship target in the extracted features and suppress the weight of background interference, thus improving the model detection performance. Meanwhile, strong real-time data augmentation was applied to improve the unbalanced distribution of sample scales, and transfer learning was combined to improve the ship detection accuracy in the condition of a restricted number of samples. The visualization results of extracted features show that the improved model could suppress irrelevant background features, and the abilities of feature extraction and target localization were enhanced. Without introducing additional learnable parameters, the proposed model achieved 96.93% and 71.49% for mAP.5 and mAP.75 on the SeaShips dataset, and detection speed reached 66 frames per second, indicating a good balance between detection accuracy and efficiency. The improved model optimized the target features more effectively compared with the Saliency-aware CNN and eYOLOv3 models, resulting in an improvement of mAP.5 by 9.53% and 9.19%. The mAP.5 for ship type target detection on Singapore Maritime Dataset reached 81.81%, indicating that the proposed model has good generalization performance.

Abstract:

To study the influence of the alkaline activator on the performance of steel slag cement, the effects of alkaline activators (water glass、Na₂CO₃/NaOH、NaOH) on the macroscopic mechanical properties of steel slag cement are studied in this article. Further, the microscopic characteristic is investigated by hydration heat release, X-ray diffraction (XRD), thermogravimetric analysis (DSC-TG), scanning electron microscope (SEM) and mercury intrusion porosimetry test (MIP). The results show that the alkaline activators increased the basicity in the early hydration liquid phase of steel slag cement, accelerating depolymerization of steel slag vitreous to produce H₃SiO-₄ and H₃AlO^2-₄, improving the reaction rate, facilitating the formation of C-S-H gel and zeolite products, which is manifested by the shortening of setting time and induction period, the increase of reaction heat, cumulative heat release and early mechanical strength; the influence of alkaline activators on the properties of steel slag cement is related to its molecular structure of activators, and the order of influence was water glass, Na₂CO₃/NaOH, NaOH in descending order; Water glass could increase the alkalinity of liquid phase in steel slag cement, and the SiO^2-₃ could react with Ca(OH)₂ to produce C-S-H gel. The addition of alkaline activators can promote the hydration reaction of steel slag cement, which is helpful to the improvement of the mechanical properties and the compactness of the microstructure of steel slag cement.

Abstract:

To improve the ductility of steelultra-high performance concrete (UHPC) composite structures, we proposed a type of demountable steelUHPC composite slab based on demountable shear connectors. The flexural tests for demountable steelUHPC composite slabs with different shear connection degrees were designed and completed. The failure mode, ultimate capacity, stiffness, cracking behavior, and relative slip of demountable steelUHPC composite slabs were analyzed and compared with those of steelUHPC composite slabs with welded shear connectors. The demountability of demountable steelUHPC composite slabs was discussed. The ultimate flexural capacity and flexural stiffness of demountable steelUHPC composite slabs were theoretically analyzed, and related calculation formulas were deduced. Results showed that the failure mode of demountable steelUHPC composite slabs was longitudinal horizontal shear bonding failure. Reducing the stud spacing could enhance the cooperative deformation capacity of demountable steelUHPC composite slabs, resulting in the improvement of their ultimate flexural capacity, stiffness at the elastic-plastic stage, and crack control ability. Different from the steelUHPC composite slabs with welded shear connectors, the steel slab and UHPC slab of the demountable steelUHPC composite slabs could be easily disassembled even in the condition of large deformation. The formulas for the ultimate flexural capacity and flexural stiffness of demountable steelUHPC composite slabs were derived. It was proposed that the height of UHPC slab should be reduced when calculating the flexural stiffness, and the reduction coefficient (β_U) was suggested to be 0.85 in serviceability state. The theoretical calculation results were in good agreement with the test results. The research results can provide theoretical basis for the design and application of steelUHPC composite slabs with demountable shear connectors.

Abstract:

To improve the construction efficiency of building envelope and solve the long-term problems of falling off and ignition of traditional external insulation systems, a kind of rock wool composite insulation external formwork (RWCIEF) system integrating insulation and building formwork was proposed. The RWCIEF structure from inside to outside was designed as follows: inner reinforcing layer, rock wool insulation core material, adhesive layer, insulation transition layer, and outer reinforcing layer. Taking Harbin as an example, the optimal thickness of rock wool insulation core material was determined based on the life cycle cost (C_lc). The feasibility of RWCIEF in engineering was explored by combining finite element analysis with theoretical calculation. The bending properties, construction bearing capacity, and stress and deformation under temperature effect of RWCIEF were calculated and analyzed. The influences of groove form, groove width, groove depth, and groove spacing on the bending properties of RWCIEF were discussed. Results showed that the theoretical calculation results of bending properties of RWCIEF were in good agreement with the finite element analysis results. The grooving treatment effectively improved the bending properties of RWCIEF. Considering the bending properties, thermal characteristics, and processing angle, groove forms of symmetrical cross grooves or symmetrical longitudinal grooves were suggested, with the groove depth and width of 10 mm and the groove spacing of 150 mm. The designed RWCIEF met the construction bearing capacity and could fully guarantee the construction quality of the thermal insulation works of the outer enclosure structure. The maximum tensile stress and compressive stress caused by temperature effect did not exceed the bearing capacity of the outer reinforcing layer of RWCIEF, which indicates that RWCIEF is unlikely to hollow in summer or crack in winter. The proposed RWCIEF system can provide a new idea and method for the future research directions of exterior envelope insulation and building formwork engineering.

Abstract:

In order to compare the mechanical performance differences between grouted sleeve lapping connectors and butt connectors, uniaxial tensile and high stress repeated tension-compression tests were conducted on 41 lap connectors and 20 butt connectors. Results showed that under uniaxial tension and high stress repeated tension-compression loading, the total elongation ratio with maximum force of two kinds of connectors was greater than 6% and the ductility coefficient was greater than 4. The strength basically met the requirements of the codes. Under uniaxial tension after high stress repeated tension-compression, the bearing capacity of both connectors increased, while the initial stiffness and ductility of the specimens decreased. Moreover, the residual deformation of the lap connector was reduced by the anti-deflection measures, but the measured value of the residual deformation of the lap connector was slightly larger than that of the butt connector due to the limited constraint stiffness of the anti-deflection measures. However, the residual deformation of the lap connector and the butt connector of anti-deflection generally met the requirements of the specification. After high stress repeated tension-compression, during uniaxial tension testing, the middle section of the sleeve of the lap connector was longitudinally compressed and circumferentially stretched in the early stage of loading. In the later stage of loading, it experienced longitudinal stretch and circumferential compression, while the sleeve of the butt connector was longitudinally stretched and circumferentially stretched throughout the loading process. In the case of uniaxial tension after high stress repeated tension-compression, the maximum longitudinal tensile strain of the middle section of the sleeve near the bar side of the anti-deflection and non-deflection lap connector was 0.10 to 0.39 times and 0.13 to 0.18 times of the butt connector, respectively. Furthermore, the maximum circumferential compressive strain was 0.09 to 0.49 times and 0.02 to 0.32 times of the butt connector, respectively, which indicated that the lap connector had relatively low requirements on the material of the sleeve. When the diameter of rebar was the same, the material cost of the lap connector was about 35% lower than that of the butt connector.

Abstract:

With the gradual deepening of the study of seepage erosion in soil, the research methods of soil particle loss and deformation and failure mechanism show the characteristics of multi-scale. The computational fluid dynamics-discrete element coupling method (CFD-DEM) provides an effective method to study the macroscopic mechanical characteristics of soil on the microscale, considering the influence of fluid-solid interaction. Regarding the current application status of CFD-DEM coupling method in geotechnical engineering, this paper systematically summarizes the advantages and disadvantages of existing fluid-solid coupling calculation methods, focusing on the modeling strategies of CFD-DEM coupling method. These strategies include solid particle shape modeling and inter-particle contact models, control equations and parameter calculation methods for the fluid phase, as well as CFD-DEM coupling calculation. Furthermore, the paper conducts an in-depth exploration of related issues and concludes by proposing future development directions for the CFD-DEM coupling method.

Abstract:

To reasonably select a suitable set of ground motion parameters and effectively reduce the uncertainty of structural damage prediction, various ground motion parameters were preferentially selected based on the elastic network regression technique. First, the elastic network regression model was established based on various ground motion parameters and the seismic capacity of a generic set of single-degree of freedom (SDOF) systems obtained from the results of incremental dynamical analysis. Second, the values of regression coefficients in the elastic network regression model and the number of times that the regression coefficients have non-zero values were used to define the sensitivity and frequency of ground motion parameters, respectively. Third, the ranking of ground motion parameters used for seismic capacity prediction was established in terms of sensitivity and frequency of ground motion parameters obtained from the results of elastic network regression on a generic set of SDOF systems. Results were statistically organized to evaluate the influence of various ground motions, structural types and structural limit-states. The analysis result obtained from an 8-story steel frame verified that the use of ground motion parameters selected based on elastic network regression can effectively reduce the uncertainty of structural damage prediction. In addition, results showed that the standard deviation of the residuals in the regression analysis for different structural limit-states was significantly reduced when the representative ground motion parameters were employed in the least squares regression model. Moreover, representative ground motion parameters that are less affected by various ground motions, structural types and structural limit-states were selected based on the ranking results obtained from a generic set of SDOF systems. Findings of this study can provide a theoretical basis for the comparison of ground motion parameters used for the prediction of structural seismic capacity.

Abstract:

In order to investigate the flexural behavior of ultra-high performance concrete (UHPC) lightweight composite decks under local wheel load, four demountable steelUHPC composite slabs connected by high-strength bolts were designed and four-point bending test was conducted. The influence of steel plate type and spacing of shear connector on the flexural characteristics of demountable steelUHPC composite slabs was analyzed, including failure mode, load-deflection curve, interface relative slip, crack width, and sectional strain distribution. Results showed that under positive bending moment, the failure mode of composite slabs adopting Q355 steel plate was that the high-strength bolt was cut off. While the failure mode of composite slabs using steel plate with negative Poisson’s ratio (NPR) was as follows: part of high-strength bolts was cut off, part of pre-embedded elongated nuts with cushion was pulled out, and UHPC collapsed due to instantaneous instability. Besides, under the same spacing of high-strength bolts, the relative slip of plate end of composite slabs employing NPR steel plate was relatively small, indicating that NPR steel plate can effectively delay and restrain the relative slip between steel plate and UHPC plate, thus improving the synergistic deformation capacity, flexural stiffness, and flexural bearing capacity for composite slabs. According to the sectional strain distribution analysis, due to the negative Poisson’s ratio effect, high stiffness, and high yield strength of NPR steel plate, the tensile strain between NPR steel plate and the bottom UHPC layer maintained strain compatibility during the whole loading process, and the upward displacement for sectional plastic neutral axis could be ignored with increasing load. Therefore, under the premise that NPR steel plate is employed to improve the flexural performance of steelUHPC composite slab system, the thickness of UHPC should be reasonably matched with the performance of NPR steel plate, so as to give full play to their material properties, and avoid the buckling failure prior to the material strength failure of UHPC.

Abstract:

To investigate the seismic behavior of reinforced concrete (RC) columns with stay-in-place ultra-high performance concrete (UHPC) formworks, named URC columns for short, we selected different assembly methods and surface treatment methods of UHPC formworks as design parameters and carried out pseudo-static tests on nine URC columns and one RC column. The assembly methods of UHPC formworks were boltangle steel connection, bolt connection, and epoxy resin mortar. The surface treatment methods of UHPC formworks were natural surface, bubble film printing, and adding ribs. The pseudo-static tests were conducted to study the influence of different assembly methods and surface treatment methods on the seismic behaviors of the URC columns. Additionally, on the basis of the assumption of plane section, a formula was proposed to predict the eccentric compressive bearing capacity of the URC columns. Results show that the bonding surface between UHPC formwork and concrete core had no apparent damage before the peak load, indicating that the URC columns have good integrity. In particular, the URC columns connected by boltangle steel had no interface bonding failure even under the failure load. Compared with the traditional RC column, the ultimate bearing capacity, ductility, and energy consumption of the URC columns were increased by 6.4%43.3%, 11.4%48.7%, and 27.7%85.3%, respectively. Among the three assembly methods, the URC columns connected by bolt and angle steel had the highest bearing capacity and the most reliable connection. Finally, the results calculated by the proposed formula were in good agreement with the test results, which can provide reference for practical application.

Abstract:

In order to improve the separability of powdered activated carbon, a new type of magnetic activated carbon was prepared using chemical co-precipitation.Using methylene blue as target pollutants, performance of the powdered magnetic activated carbon was studied under varied conditions of pH, contact time and initial methylene blue concentrations, via the comparison with powdered activated carbon. The results showed that the adsorption capacity of synthetic magnetic powdered activated carbon was higher than that of the powdered activated carbon, and an alkaline pH value and adequate contact time were favorable for the pollutants removal. Under the condition of 100 mg/L methylene blue concentration, 0.4 g/L magnetic activated carbon dosage of, pH 9 and a reaction time of 300 minutes, the removal rate of methylene blue reached 98.9%. The adsorption behavior of methylene blue on magnetic activated carbon fitted the Langmuir isotherm and Elovich dynamics model. Thermodynamic analysis indicated that the adsorption was spontaneous endothermic reaction of single molecule layer, and the chemical adsorption played an important role during the adsorption process. The magnetic activated carbon had a good recyclable performance, it could complete precipitation in 10 minutes under natural condition, and could be quickly separated in 30 seconds under the action of outside magnetic field.

Abstract:

In order to give full play to the advantages of the high degree of industrialization of assembly and the excellent mechanical properties of steel-concrete composite structures, a kind of assembled double-slotted channel steel-concrete composite floor slab was proposed. Three groups of simply supported composite floor slab specimens were tested under four-point loading, and the mechanical properties of the composite floor slab under vertical static load were studied. The development law of floor cracks, deflection and strain (steel bar, steel beam, concrete slab) with load was analyzed. Based on the limit equilibrium method, the bearing capacity calculation formula considering the tensile membrane effect and stiffness strengthening coefficient was proposed. The results showed that the deformation of the composite slab is characterized by two-way slab. When the specimens are destroyed, the corner cracks and arc cracks appear on the top of the slab, the central area of the concrete slab bottom shows mesh cracks and oblique cracks extending to the corner, and the plastic bending of the double main girder occurs. When the center deflection of the floor reaches l₀/40, the load of the specimens is 327.63 kN, 436.92 kN and 406.12 kN respectively, and the bearing capacity of the composite floor is higher. The strain development of the steel bar is larger in the direction perpendicular to the steel beam and yields along the plastic hinge line. The calculation formula considering the tensile membrane effect and the stiffness strengthening coefficient is in good agreement with the test results, and the load-deflection curve of the floor is accurately predicted.

Abstract:

To study the impact of corrosion of both longitudinal bar and stirrup on the bonding performance of steel bar and concrete, we fabricated 25 corroded reinforced concrete (RC) specimens by the accelerated corrosion method of electroosmosis-constant current-dry wet cycles. Pullout tests were carried out on the specimens, and the influences of parameters such as longitudinal bar corrosion, stirrup corrosion, cover thickness, and stirrup spacing on bonding properties were studied. The effect of corrosion on the bonding force between concrete and steel bar was analyzed, and the degradation of the bonding performance was attributed to the reduction of the material behavior and the degradation of the constraint effect. On the basis of the test results, a modified bondslip constitutive model was established and verified considering design parameters and both corrosion of longitudinal bar and stirrup. A stressslip model of corroded longitudinal bar was obtained by combining the proposed constitutive model and infinitesimal algorithm. In the OpenSees platform, the stressslip model was applied to the zero-length section element, and the numerical model of corroded RC components considering bondslip behavior was established by adopting fiber-based beam-column element and zero-length section element. The accuracy of the model was verified according to the quasi-static test data of the corroded RC column, and the fiber model considering only corrosion damage was used for auxiliary verification. Results show that the bonding force between concrete and steel bar increased first and then decreased with the increase in the corrosion degree. Increasing the cover thickness could slightly improve the bonding force, while the increase in stirrup density could significantly improve the bonding force. Compared with the fiber model, the bearing capacity, cumulative energy dissipation, and ultimate displacement errors were reduced by 12.8%, 23.5%, and 14.2% in the constructed fiber model, indicating that the constructed model can reasonably calculate the contribution of steel bar slip and accurately predict the overall seismic response of the corroded RC columns.

Abstract:

To accurately evaluate the safety and comfortability of structures after a long period of service under dynamic loads such as earthquakes and wind, it is critical to establish a structural dynamic model that can accurately reflect the dynamic responses of actual buildings under seismic, wind and other dynamic loads utilizing the monitoring/inspection data. In this paper, for popular frame building structures, an equivalent simplified dynamic modeling method is proposed by using a few numbers of wireless mobile sensors. First, the principle of equivalent interstory shear force for a simplified model of buildings is proposed, which proves that the simplified model constructed based on this principle has the ability to accurately simulate the dynamic response of actual buildings. Second, the form of simplified model of frame structure was derived, and the characteristics of the simplified model parameters were studied. Then, an iterative identification method for the parameters of the simplified model was proposed, which can identify all parameters of the simplified model by solely using a small number of wireless mobile sensors. Finally, a numerical simulation example of a 12-story 3-span steel frame structure was conducted, which investigates the predictive capability of the equivalent simplified model constructed by the method proposed herein to predict the dynamic responses of the actual frame structure subjected to different types of horizontal excitations, under the condition of without knowing the specific format of structural stiffness degradation and using only a small number of moving acceleration sensors. Simulation results show that the equivalent simplified model can very accurately predict the dynamic responses of the actual frame structure subjected to different types of horizontal excitations. Therefore, the model updating method for the equivalent simplified model of frame structures proposed herein will have important application potential in evaluating the structural safety and comfort of existing frame building structures under dynamic loads, such as wind and earthquake.

Abstract:

With the increasing scale of network, the accurate and real-time prediction of network flow is essential for traffic scheduling and routing design. However, due to the nonlinearity and uncertainty of network flow data, some traditional methods fail to achieve good prediction accuracy. Considering the complex spatialtemporal features of network flow, a novel network flow prediction method based on spatialtemporal features fusion (ST-Fusion) was proposed, combined with encoderdecoder architecture. First, the encoder was designed with two parallel feature channels: temporal and spatial channels. The temporal features were extracted by integrating gated recurrent unit (GRU) and self-attention mechanism, and the graph convolutional network (GCN) was used to extract the spatial features. Then, the temporal and spatial features extracted by the encoder were fused by using the bilateral gated mechanism. Finally, the fused features were input into the GRU-based decoder to generate prediction results. Experiments were conducted on three public datasets (GEANT, ABILENE, and CERNET) using evaluation metrics including MAE, RMSE, ACCURACY, and VAR. Experimental results showed that the ST-Fusion method achieved better performance in network flow prediction.

Abstract:

To investigate widely applicable shear capacity calculation methods of reinforced concrete column-steel beam (RCS) hybrid connection, this study analyzed the shear failure experimental data of RCS connections in recent years. The experimental results were compared with the calculation results of Chinese specification, Nishiyama method, Parra method, and ASCE guideline, and the parametric applicability of each method was discussed. The comparison results showed that all the four methods had engineering value. The minimum discreteness of the results of Parra method was obtained, and the calculation process of Chinese specification was the simplest. The results of parametric study showed that all the four methods were suitable for connections with different stirrup ratios and positions. However, conservative estimates were obtained for specimens with small axial load ratios (from 0 to 0.2) and column-through connections. For the Chinese specification, the predicted strength of connections with concrete strength higher than 60 MPa was unsafe, while the predicted strength of connections with transverse beams was conservative. Therefore, it is suggested to introduce concrete strength coefficient and confined coefficient of transverse beam into the equation considering the influence of these two factors.

Abstract:

To study the bending performance of prestressed steelbamboo composite I-shaped beams, 12 prestressed composite I-shaped beams were designed and manufactured for bending tests, considering prestress loads, prestressing schemes, and loading schemes as basic parameters. The experimental phenomenon was observed, and failure characteristics were analyzed during the test. The influences of different parameters on the load-bearing capacity, strain distribution, and deformation performance were explored, and an approximate formula for the bearing capacity of the prestress composite beam was proposed. The results indicated that the prestressed composite beams have relatively good performances from the perspectives of combination effect, deformation characteristic, and bearing capacity. Failure modes of tested specimens were mainly owing to the bamboo flanges damage and the local buckling of steel plates. With the technique of prestress and the increase of prestress level, the deformation performances can be improved effectively, as well as the load-bearing capacity considering the same deflection situation. Moreover, the improvements can be more significant with the two-point prestressing scheme. The mid-span strain distribution of prestressed composite beams conforms to the plane section assumption, and the neutral axis moves down with the increase of the prestressing level. Finally, the bearing capacities based on the theoretical calculation matched well with the experimental results, which showed the applicability of the proposed methods.

Abstract:

The existing graph-construction methods for graph optimization-based SLAM are summarized. The SLAM methods can be divided into three main classes, Kalman filter-based, partical filter-based and graph optimization-based, and the advantages and disadvantages of each class are overviewed. Moreover, there are mainly three graph modeling methods for the graph optimization-based SLAM problem, namely dynamic Bayesian network (DBN)-based model, factor graph-based model and Markov random field-based model. The key techniques of the front-end stage in graph optimization-based SLAM method, which mainly include data association between consecutive frame and loop closure detection, are discussed. Some newest research achievements on feature extraction, matching method, motion estimation, loop closure detection are introduced.

Abstract:

To explore the improvement mechanism of welding round steel at soffit on the flexural performance of eccentric concrete-filled steel tube (CFST) members, we established a numerical model of CFST beams reinforced with round steel by using ABAQUS software and verified the model by test results. By analyzing the bending momentdeflection curve, bending momentaxial strain curve, hoop strain curve, restraint index, and neutral axis offset of eccentric CFST members reinforced with round steel, the improvement mechanism of the flexural performance of the eccentric CFST members was revealed. Besides, the influence of the diameter of the round steel and the slenderness ratio of the beams on the flexural performance of eccentric CFST members reinforced with round steel was analyzed. Results show that welding round steel could lower the position of the neutral axis of the section and increase the hoop strain of the steel tube on the compression side. Therefore, the concrete area in compression was increased, and the restraint effect of the steel tube on the compression side on the concrete was enhanced. Furthermore, the flexural bearing capacity and flexural stiffness of the eccentric CFST members were improved, and the larger the diameter of the round steel, the greater the improvement. The ultimate bending moment of the eccentric CFST members decreased with the increase in the axial compression ratio, and the larger the diameter of round steel and the slenderness ratio of beams, the greater the reduction. Welding round steel had a better effect on improving the bending performance of the eccentric member with a large slenderness ratio, and the larger the axial compression ratio, the better the improvement effect.

Abstract:

It is well known that unmanned aerial vehicle (UAV) is more and more widely applied in military and civil areas. In order to play the better role of UAV, it is needed to utilize multi UAVs cooperative formation to accomplish cooperative reconnaissance, combat, defense and spraying pesticides and other tasks. The multi UAVs cooperative formation control technology mainly contains the following key techniques: data fusion technology, sensing technology, task allocation technology, path planning technology, formation control technology, communication network technology and virtual/physical verification platform technology. Firstly, summarize the research and development of key technologies worldwide. Then, the classification for multi UAVs formation control methods is mainly investigated, and the problems about formation design and adjustment, formation reconfiguration are summarized. Finally, the challenges and future development for multi UAV cooperative formation are prospected. Research shows: at present, the theory of multi UAV formation flight has acquired fruitful results, while the real cooperative formation flight test can only be implemented in the simple communication environment. The real time performance for task allocation and path planning is not high. The robustness of control methods to cope with the unexpected situation is low. The cooperative sensing ability for multi UAV with multi sensor is insufficient. The simulation of the entity is lacked. Breaking through the above key technologies, carrying out the cooperative formation flight of multi UAV in complex sensing constraints and complex communication environment, putting forward more effective control method and carrying out the UAV physical formation flying test so that the UAV can finish the task better may be the future research directions.

Abstract:

The self-centering buckling-restrained brace (SBRB) was formed by making a self-centering system consisting of stacked disc springs (DS) and a buckling-restrained brace (BRB) work in parallel to control the residual deformation of BRB. Quasi-static tests were done to examine the effects of stiffness of stacked springs, end connections, self-centering ratios, etc. on the hysteretic behavior of SBRBs. The tests revealed that, compared with BRBs, the residual deformations of SBRBs were reduced greatly. SBRBs exhibited flag-shaped hysteretic curves, and in the later stage of tests, the steel plate brace underwent tensile failure while other components remained intact. The bearing capacity and energy dissipation capacity of SBRBs are mainly from the DS parts and BRB parts, respectively. Approximately 23%-36% energy dissipation in SBRBs is from the DS parts due to the friction between stacked springs. When the other constructional details remained the same, the DS parts with a higher stiffness of springs had a greater increase in bearing capacity after starting, and the DS parts with a higher starting force also had a higher self-centering ratio and smaller residual deformations. On the whole, the end connections had little effect on the residual deformations. The tension fracture of steel plate brace occurred earlier in the SBRB with rigid end connections due to bearing additional bending moments, while the SBRBs with pin end connections exhibited better energy dissipation. With the increase of self-centering ratios, the residual deformations of SBRBs reduced gradually and the appropriate ratios of SBRBs should be kept within 0.7-0.9 to efficiently control residual deformations and to avoid excessive demand of DS parts.

Abstract:

A fault tolerant control scheme based on integral sliding mode surface is developed for spacecraft attitude stabilization in the presence of actuator faults, misalignments, magnitude saturation and external disturbances simultaneously. This approach is based on a novel integral-type sliding mode control strategy to compensate for these un-desired issues without controller reconfiguration. Especially, it guarantees the reachability of the system states by involving adaptive control technique to relax the boundary information in advance. A sufficient condition for the controller to accommodate magnitude saturation is also presented and then the fault tolerant attitude control system can be guaranteed theoretically to be asymptotically stable by using Lyapunov method. Numerical simulation results shows that the proposed control law can quarantee the stability of the spacecraft attitude control system in the presence of actuators' failures, and it has good robust performance.

Abstract:

To study the development status of wearable soft upper limb exoskeleton and its key technical challenges, the current literature in this field was analyzed and summarized. Exoskeletons can effectively provide functions such as protection and support to address limb fatigue and physical function decline resulting from high-intensity and repetitive work, as well as limb movement disorders caused by stroke or occupational diseases. Additionally, they have the capability to restore or enhance human movement ability through additional power and functionality. Wearable soft exoskeletons, as a new development direction of exoskeletons, have obvious advantages over traditional rigid exoskeletons, such as structural flexibility, human-machine interaction, and wearable comfort. Firstly, this paper provides a detailed analysis of three main driving methods of soft upper limb exoskeleton (rope drive, pneumatic, shape memory alloy). The relevant research results and corresponding structural characteristics of different driving methods are throughly examined. Then, the key technical challenges of soft upper limb exoskeleton are analyzed and expounded from four aspects: structure, material, control and auxiliary technology. Finally, considering the needs of exoskeleton applications in different fields, future trends in soft upper limb exoskeleton technology are speculated to focus on flexibility, comfort, compliance and intelligence. This study shows that the technology for wearable soft upper limb exoskeletons is still in its early stages, with many technical challenges to be solved. Futhurmore, breakthroughs in key technological challenges can be facilitated by novel soft actuators, soft sensors and other related advancements.

Abstract:

In the ultra-dense network environment, each access point is deployed in the hotspot area, which forms a complex heterogeneous network. Users need to choose the appropriate network to access, so as to achieve the best performance. Network selection problem is to choose the optimal network for the user, so that the user or network performance reaches the best. In order to solve the access selection problem of users in ultra-dense networks, we proposed an ultra-dense network access selection algorithm based on the improved deep Q network (DQN), considering network states, user preferences, and service types, and combining with load balancing strategies. First, by analyzing the influence of network attributes and user preferences on network selection, the appropriate network parameters were selected as the parameters of the access selection algorithm. Then, the problem of network access selection was modeled by Markov decision-making process, and the states, actions, and reward functions of the model were designed. Finally, the optimal network strategy was obtained by using DQN to solve the network selection model. In addition, the target function of traditional DQN was optimized to avoid overestimation of Q value by DQN, and a priority experience replay mechanism was introduced to improve learning efficiency. Simulation results show that the method could well solve the problem of overestimation of traditional DQN, accelerate the convergence of neural network, effectively reduce user congestion, and improve network throughput performance.

Abstract:

Autonomous navigation based on sequential images (ANBSI) is the key technology of pinpoint landing missions for future deep space exploration and also is one of the major development directions for deep space exploration technology. The necessity of developing ANBSI for planetary pinpoint landing is elaborated in this paper. Firstly, state-of-art developments of ANBSI are reviewed in terms of active sensing and passive sensing. Then, the key techniques applied in ANBSI for planetary landing are summarized and analyzed. Finally, according to the analysis of the key techniques, the main issues of ANBSI are raised and their future developments are overviewed.

Abstract:

In view of the weaknesses of poor computing and storage capabilities of edge devices, lightweight processing was carried out on the backbone network CSPDarkNet53 for feature extraction in the traditional YOLOv5 model, and a lightweight gesture recognition algorithm MPE-YOLOv5 was proposed to realize the deployment of the model in low-power edge devices. Considering the problem that it is difficult to identify large-scale transformation targets and tiny targets due to less feature extraction in lightweight model, efficient channel attention (ECA) mechanism was added to alleviate the loss of information after high-level feature mapping due to the reduction of feature channel. A detection layer for tiny targets was added to improve the sensitivity to tiny target gestures. EIoU was selected as the loss function of the detection frame to improve the positioning accuracy. The effectiveness of the MPE-YOLOv5 algorithm was verified on the self-made dataset and NUS-Ⅱ public dataset, and the MPE-YOLOv5 algorithm was compared with lightweight M-YOLOv5 algorithm and original YOLOv5 algorithm on the self-made dataset. Experimental results show that the model parameters, model size, and computational complexity of the improved algorithm were 21.16%, 25.33%, and 27.33% of the original algorithm, and the average accuracy was 97.2%. Compared with the lightweight model M-YOLOv5, MPE-YOLOv5 improved the average accuracy by 8.72% while maintaining the original efficiency. The proposed MPE-YOLOv5 algorithm can better balance between the detection accuracy and real-time reasoning speed of the model, and can be deployed on edge terminals with limited hardware.

Abstract:

The existing graph-construction methods for graph optimization-based SLAM are summarized. The SLAM methods can be divided into three main classes, Kalman filter-based, partical filter-based and graph optimization-based, and the advantages and disadvantages of each class are overviewed. Moreover, there are mainly three graph modeling methods for the graph optimization-based SLAM problem, namely dynamic Bayesian network (DBN)-based model, factor graph-based model and Markov random field-based model. The key techniques of the front-end stage in graph optimization-based SLAM method, which mainly include data association between consecutive frame and loop closure detection, are discussed. Some newest research achievements on feature extraction, matching method, motion estimation, loop closure detection are introduced.

Abstract:

In order to improve the separability of powdered activated carbon, a new type of magnetic activated carbon was prepared using chemical co-precipitation.Using methylene blue as target pollutants, performance of the powdered magnetic activated carbon was studied under varied conditions of pH, contact time and initial methylene blue concentrations, via the comparison with powdered activated carbon. The results showed that the adsorption capacity of synthetic magnetic powdered activated carbon was higher than that of the powdered activated carbon, and an alkaline pH value and adequate contact time were favorable for the pollutants removal. Under the condition of 100 mg/L methylene blue concentration, 0.4 g/L magnetic activated carbon dosage of, pH 9 and a reaction time of 300 minutes, the removal rate of methylene blue reached 98.9%. The adsorption behavior of methylene blue on magnetic activated carbon fitted the Langmuir isotherm and Elovich dynamics model. Thermodynamic analysis indicated that the adsorption was spontaneous endothermic reaction of single molecule layer, and the chemical adsorption played an important role during the adsorption process. The magnetic activated carbon had a good recyclable performance, it could complete precipitation in 10 minutes under natural condition, and could be quickly separated in 30 seconds under the action of outside magnetic field.

Abstract:

Starting from the tactile sensing performance of human skin, the progress and key technologies of tactile sensors for e-skin (electronic skin) akin to human skin by multidisciplinary fields are comprehensively reviewed. The sensing principle, new materials and structures, advanced design and making methods, sensing characteristics and performance of tactile sensors are analyzed. The recent domestic and foreign research advances of electronic skin tactile sensor array in flexibility, elasticity, spatial resolution, sensitivity, fast response, transparency, lightweight, multifunction and other aspects are summarized. It is difficult to achieve the tactile sensors for e-skin with high stretchable and flexible, less complex production process for high sensitivity e-skin, strong extensibility and low cost. The tactile sensors for e-skin can be widely used in robotics, medical health, aeronautics and space military, intelligent manufacturing, automotive security and other fields. The development of tactile sensors for e-skin toward the direction of high stretchable and flexible, high sensitivity in wide range, multifunction, self-healing and self-cleaning, self-powered and transparent, has been pointed out.

Abstract:

Considering the failure mechanism and weaknesses of traditional fabricated shear wall structures under strong earthquakes, a new type of fabricated shear wall with functions of energy dissipation and shock absorption was proposed. On the basis of model test and numerical simulation, seismic performance tests were carried out on four specimens with scale ratio of 1∶1.54 and shear span ratio of 1.52. Further analysis was conducted to investigate the effects of bolt number, axial compression ratio, and reinforcement ratio of edge members on the seismic performance of the new fabricated shear wall, including failure modes, hysteretic performance, bearing capacity, displacement ductility, stiffness degradation, and energy dissipation capacity. Test results show that the four specimens experienced shear compression failure, which was the same as the cast-in-place shear wall with the same shear span ratio. However, the proposed shear wall had better hysteretic performance and energy dissipation capacity, and the energy dissipation capacity was higher than that of the cast-in-place shear wall at the failure point. When the number of bolts decreased, the hysteretic performance of the new fabricated shear wall decreased, the wall deformation increased, while the bearing capacity remained almost unchanged. When the axial compression ratio or reinforcement ratio of edge members decreased, the bearing capacity decreased, and the ultimate displacement increased. Finally, the finite element model of the specimens was established by ABAQUS program. Comparisons of numerical results and test results showed a good agreement, verifying the correctness of the model, which can be applied to the analysis of the new fabricated shear wall.

Abstract:

To investigate the ground motion intensity measures suitable for evaluating high-rise structures under near-fault ground motions with pulse-like effect, this paper proposes a new ground motion intensity measure considering period elongation effect and higher mode effect based on acceleration spectrum. Taking two high-rise reinforced chimney structures (120 m and 240 m) as research objects, the correlation between damage indices (ParkAng damage index, maximum inter-story drift ratio, maximum structural curvature, maximum floor acceleration, and maximum roof displacement) of high-rise structures and 37 ground motion intensity measures was studied under near-fault ground motions using OpenSEES. Results show that the proposed intensity measure was the optimal index in predicting the ParkAng damage of high-rise concrete structures under near-fault ground motions. High correlation between velocity-related intensity measures and structural damage index was observed. As the structural period increased, the correlation between damage indices and displacement-related intensity measures was improved. Besides, peak ground acceleration had limitations in characterizing the deformation and failure of high-rise structures, but it could be used to analyze the seismic performance of non-structural components. The research results can provide reference for selecting proper measures and structural damage indices to evaluate the seismic performance of high-rise structures under near-fault ground motions.

Abstract:

In view of the problems of low brightness and obvious color distortion of the sky in restored images in most existing algorithms for image dehazing, a haze removal method for UAV aerial images based on atmospheric light value and graph estimation was proposed. First, the depth-of-field image was obtained according to the color attenuation prior theory, and the mean value of the region with the minimum deviation in the depth-of-field image was taken as the atmospheric light value. Then, a random walk clustering method was designed to estimate the atmospheric light map. The random walk algorithm was used to cluster the image into N sub-regions, and the mean value of the first 0.1% pixels of the sub-regions was taken as the regional atmospheric light value, which was then combined and refined by guided filtering to obtain the atmospheric light map. Next, the two atmospheric light estimators were fused into a new atmospheric light map with atmospheric light valuegraph estimation, which is a more accurate atmospheric light estimator. The transmittance was obtained by haze-lines prior method, and a dark compensation method was proposed to improve the transmission accuracy. Finally, according to the atmospheric scattering model, a clear restored image was obtained based on the fused atmospheric light map and optimized transmittance. Experimental results show that compared with other algorithms, the proposed algorithm improved the information entropy, mean gradient, blur coefficient, and contrast by 1.1%, 6.3%, 8.5%, and 6.4%, respectively, with better subjective visual effect and more abundant information.

Abstract:

In view of the problem that general pre-trained models are not suitable for named entity recognition tasks in the medical domain, a neural network architecture that integrates knowledge graph in the medical domain was proposed. The elastic position and masking matrix were used to avoid semantic confusion and semantic interference in self-attention calculation of pre-trained model. The idea of multi-task learning in fine-tuning was adopted, and the optimization algorithm of recall learning was employed for pre-trained model to balance between general semantic expression and learning of the target task. Finally, a more efficient vector representation was obtained and label prediction was conducted. Experimental results showed that the proposed architecture achieved better results than the mainstream pre-trained models in the medical domain, and had relatively good results in the general domain. The architecture avoided retraining pre-trained models in particular domain and additional coding structures, which greatly reduced computational cost and model size. In addition, according to the ablation experiments, the medical domain was more dependent on the knowledge graph than the general domain, indicating the effectiveness of integrating the knowledge graph method in the medical domain. Parameter analysis proved that the optimization algorithm which used recall learning could effectively control the update of model parameters, so that the model retained more general semantic information and obtained more semantic vector representation. Besides, the experimental analysis showed that the proposed method had better performance in the category with a small number of entities.

Abstract:

This paper proposes a low-latency intelligent network data transmission scheduling algorithm for real-time network transmission demand scenarios of low latency, stable transmission, and high quality of experience (QoE). The algorithm consists of two parts: data block queuing control strategy and congestion control strategy. The data block queuing control strategy presents a cost-effective model that integrates the creation time and effective time of data blocks, effectively solving the problem of uneven information transmission under transmission time constraint. The congestion control strategy proposes a deep deterministic policy gradient (DDPG) method based on the Gumbel distribution sampling reparameterization with mixed experience prioritization model, which solves the problem that DDPG is not applicable to the congestion control of discrete network action space and significantly improves the quality of network congestion control by adaptively adjusting the sending parameters through learning. Results show that the proposed queuing algorithm could effectively improve QoE in real-time transmission scenarios, and the improved DDPG for congestion control could significantly reduce transmission delay. In the same scenario, compared with traditional network data transmission scheduling algorithms, by integrating the proposed queuing and congestion control strategies, the improved intelligent network data transmission scheduling algorithm could maintain a good balance between low latency and stable transmission and provide higher data transmission quality.

Abstract:

Image segmentation is to divide the region with special meanings into several disjoint sub-regions according to certain rules, which is the key link between image processing and image analysis. The traditional watershed image segmentation method is widely used, which has the advantages of fast and simple. However, it is easily interfered by noise, and the segmentation results are prone to lose important edge information, resulting in over-segmentation. In view of the problem of the traditional watershed image segmentation method, an improved watershed image segmentation method based on adaptive structural elements was proposed. First, the adaptive structural elements with variable shapes were constructed by using local density, symmetry, and boundary features of adjacent pixels of image targets, so as to ensure a good consistency between the proposed structural elements and the shape of image targets. Then, the adaptive structural elements were used to obtain the morphological gradient of the image, which could improve the positioning accuracy of the target edge. The L₀ norm gradient minimization and morphological open-close hybrid reconstruction were used to modify the gradient image, so as to reduce the local invalid minimum points in the gradient image and suppress the occurrence of over-segmentation. Finally, watershed segmentation was performed on the modified gradient image to realize accurate segmentation of the target region of the image. Experimental results show that the method could effectively restrain over-segmentation of traditional watershed algorithm and improve the accuracy of the target edge positioning, with high precision of image segmentation.

Abstract:

To explore the effects of lightweight sand on the strain hardening properties of ultra high performance concrete (UHPC) with different specimen sizes, the lightweight sand was used to replace the yellow sand by equal volume. Nine groups of uniaxial tensile tests were carried out with different lightweight sand volume rate ranging from 0 to 35% and different specimen thicknesses from 30 mm to 100 mm. Meanwhile, simultaneous acoustic emission real-time flaw detection tests were conducted. Results show that the volume rate of lightweight sand demonstrates little effect on the stress and strain at the elastic limit point of UHPC, but when the volume rate of lightweight sand increases from 0 to 35%, the ultimate tensile strength and ultimate tensile strain of UHPC grow from 10.6 MPa and 2.35×10^-3 to 19.4 MPa and 4.3×10^-3 respectively. When the volume rate of lightweight sand is greater than 15%, the strain hardening degree of UHPC significantly increase with more damage points generated and more uniformly distributed inside the specimen, showing remarkable crack control capability. With the same lightweight sand volume rate, the strain hardening degree of UHPC decreases with the increase of specimen thickness, and the damage points inside the specimen tend to be concentrated, exhibiting an obvious size effect.

Abstract:

In order to accurately predict the rotational stiffness of embedded steel column bases, shallowly embedded, in particular, this paper proposes a stiffness model that collectively allows for the effects of the embedded depth, shear deformation of the embedded column, axial force applied to the column and restraint from the base plate. For developing the model, the embedded segment of the column is simplified as a beam on the Winkler foundation, and its deformation is computed using the Timoshenko beam theory on Winkler foundation, considering the influence of axial force applied to the column and solved by initial parameter method. To investigate the influence of the above-mentioned factors and verify the proposed model, finite element (FE) models are developed and validated against existing experimental results. Comparisons between the FE results and model predictions show that the proposed model exhibits higher accuracy than the theoretical models reported, especially for shallowly embedded column bases. The model prediction and FE results indicate that the rotational stiffness of the column base depends on the embedded depth in a nonlinear fashion-the stiffness increases rapidly for small embedded depth but remains almost constant when embedded depth is larger than a certain value; the axial compression load applied to the steel column is a beneficial factor to the stiffness; the restraint from the base plate shows a significant effect on the rotational stiffness of embedded column bases with the embedded depth ratio less than 1.5, being negligible when the embedded depth ratio increases up to 2.5.

Abstract:

The development of advanced nano-integrated circuit processes has led to a decreasing threshold charge in microelectronic devices, resulting in an increased rate of soft errors caused by single-event effects in digital circuits. To enhance the radiation resistance of standard cells in integrated circuits, this paper proposes a NAND gate structure that is resistant to single-event transients (SETs). In the triple well process, by shorting the substrate and source of each NMOS transistor in the pull-down network, the radiation resistance of the NAND gate was effectively improved, and the hardening of the proposed NAND gate became more effective as the number of inputs increased. Particle incidence simulation experiments were performed by Sentaurus TCAD software in hybrid simulation mode. For the NMOS transistor connected to the output node, the three-dimensional physical model that has been calibrated by the process was used, and the Spice model provided by the manufacturer was adopted for other MOS transistors. Simulation results show that the proposed two-input NAND in 40 nm process could reduce the output voltage fluctuation amplitude in three-input cases at the linear energy transfer (LET) value of incidence particle of 10 MeV·cm²/mg. Besides, the effect of immunity to single particle incidence was achieved in the input mode with N₂ transistor closed. For the hardened three-input NAND gate, the output voltage disturbance could be reduced by up to 85.4% even in the “worst case”. Therefore, the proposed hardening method for NAND gate has a significant effect against SET.

Abstract:

Due to the complex background of ship targets and much irrelevant interference in visual images, it is difficult to conduct ship detection. In addition, there are few datasets for multi-category ship detection and the samples are often unbalanced, which makes the ship target detection performance degraded. Considering the ship detection background interference, an improved YOLOv3 model was proposed by introducing SimAM attention mechanism, which was used to enhance the weight of the ship target in the extracted features and suppress the weight of background interference, thus improving the model detection performance. Meanwhile, strong real-time data augmentation was applied to improve the unbalanced distribution of sample scales, and transfer learning was combined to improve the ship detection accuracy in the condition of a restricted number of samples. The visualization results of extracted features show that the improved model could suppress irrelevant background features, and the abilities of feature extraction and target localization were enhanced. Without introducing additional learnable parameters, the proposed model achieved 96.93% and 71.49% for mAP.5 and mAP.75 on the SeaShips dataset, and detection speed reached 66 frames per second, indicating a good balance between detection accuracy and efficiency. The improved model optimized the target features more effectively compared with the Saliency-aware CNN and eYOLOv3 models, resulting in an improvement of mAP.5 by 9.53% and 9.19%. The mAP.5 for ship type target detection on Singapore Maritime Dataset reached 81.81%, indicating that the proposed model has good generalization performance.