Transition metal sulfides (TMSs)-based materials have been extensively investigated as effective non-noble catalysts for various applications. However, the exploration of TMSs-based catalysts for hydrogenation of nitro compounds is limited. Herein, CoSx/NC catalysts were prepared by solvothermal sulfurization of ZIF-67, followed by high-temperature annealing (300–600 °C) under NH3 atmosphere. It was found that the structures and compositions of the as-prepared CoSx/NC can be readily tuned by varying the annealing temperature. Particularly, CoSx/NC-500, which possesses higher degree of S defects and larger specific surface areas, can achieve high conversion, selectivity and stability for catalytic reduction of nitro compounds into amines under mild reaction conditions.
Calcium phosphate nanoparticles (CaPNPs) have good biocompatibility as gene carriers; however, CaPNPs typically exhibit a low transfection efficiency. Cell penetrate peptide (TAT) can increase the uptake of nanoparticles but is limited by its non-specificity. Grafting adhesion peptide adhesion peptide on carriers can enhance their targeting. The Plekho1 gene encodes casein kinase-2 interacting protein-1 (CKIP-1) , which can negatively regulate osteogenic differentiation. Based on the above, we produced a Mg-CaPNPs-RGD-TAT-CKIP-1 siRNA carrier system via hydrothermal synthesis, silanization and adsorption. The effects of this carrier system on cell endocytosis and biological effects were evaluated by cell culture in vitro. The results demonstrate that CaPNPs with 7% Mg (60 nm particle size, short rod shape and good dispersion) were suitable for use as gene carriers. The carrier system boosted the endocytosis of MG63 cells and was helpful for promoting the differentiation of osteoblasts, and the dual-ligand system possessed a synergistic effect. The findings of this study show the tremendous potential of the Mg-CaPNPs-RGD-TAT-CKIP-1 siRNA carrier system for efficient delivery into cells and osteogenesis inducement.
Low-cost catalysts with high activity are in immediate demand for energy storage and conversion devices. In this study, polyvinyl pyrrolidone was used as a complexing agent to synthesize La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) perovskite oxide. The obtained porous layered LSCF has a large specific surface area of 23.74 m2/g, four times higher than that prepared by the traditional sol-gel method (5.08 m2/g). The oxygen reduction reaction activity of the oxide in 0.1 mol/L KOH solution was studied using a rotating ring-disk electrode. In the tests, the initial potential of 0.88 V (vs. reversible hydrogen electrode) and the limiting diffusion current density of 5.02 mA/cm2 were obtained at 1600 r/min. Therefore, higher catalytic activity and stability were demonstrated, compared with the preparation of LSCF perovskite oxide by the traditional method.
The microstructure, anisotropy in tensile strength and tensile creep resistance of the ring rolled AZ80-Ag alloy were studied. The ring exhibited higher strength along rolling direction (RD) than transverse direction (TD). The microstructure characterization and texture analysis demonstrated that the tilted basal texture was responsible for the higher tensile performance along RD. Investigations on the creep anisotropy revealed that the samples along RD had lower creep resistance, higher creep strain and higher steady creep rate at 70–80 MPa, compared with that along TD. The nominal creep stress exponent (n) values, 1.13 for RD and 3.86 for TD, indicated that diffusional creep and dislocation climb were the two corresponding creep mechanisms. During creep of the alloy, Mg17Al12 phase discontinuous precipitations were witnessed and their volume fraction enhanced with increasing stress.
In recent years, composite pellet production with added reductant has been developed instead of traditional iron production. Composite pellets produced by the addition of appropriate proportions of reductant produce sponge iron in the reductant melting process at high temperatures. The elements created in the structure by pellet production directly affect the quality of the product obtained by determining the chemical composition and the appropriate reaction temperature. In this study, sponge iron ore concentrate (scale) and reductant (coke coal dust and sodium bentonite) were mixed at certain proportions to produce composite pellet samples; the effects of addition rate of the reductant material of sodium bentonite (1 wt%–4 wt%) and variation in reaction temperature (900–1200 °C) on the metallization and compressive strength properties of the produced composite pellet samples were investigated. The analysis results show that the highest compressive strength is obtained from pellet samples produced with 3% sodium bentonite at 1100 °C. Additionally, SEM-EDS analysis results of the samples show that the morphologic structure has much lower porosity rates compared to samples produced under the other conditions which makes the samples denser and increases the metallization properties.
Biological column leaching of Ni from low-grade Ni ore was studied, and the effects of ore particle size on leaching rate were investigated. The Ni ore with an average Ni content of 0.23% was crushed into four different particle size fractions: >10 mm, 5–10 mm, 2–5 mm and <2 mm. The main strain components at the genus level were acidithiobacillus (53.11%), leptospirillum (43.52%), and acidiphilium (3.37%). The leaching tests were carried out at pH 2.0 and ∼23°C. The Ni leaching rates from ores with particle sizes >10 mm (bioleaching), 5–10 mm (acid leaching), 5–10 mm (bioleaching), and 2–5 mm (bioleaching) were 23.76%, 22.15%, 32.42% and 54.17%, respectively, after 180 d of bioleaching. The ore particle size changed after leaching, compared with the original ore size, the proportion of the same size of 2–5 mm ore decreased to 44.64%. Ore with particle size of 2–5 mm was most suitable for column bioleaching, and effective Ni extraction was achieved with appropriate control of ore granularity.
In order to control the dust pollution produced by air leg rock drill in the trolley area during the excavation of long-distance single ended tunnel, the full-scale physical model of working face was established by using FLUENT software, and the numerical simulation analysis of tunnel drilling ventilation and dust removal parameters was carried out. The results show that it is difficult to control the dust pollution of the face by conventional ventilation, and the drilling dust is distributed in the range of 10 m from the face; after the introduction of the long pressure and short suction ventilation scheme, when the ratio of compressed air volume to exhaust air volume is 0.72, the height of the pressure fan is 2.5 m, the distance between the pressure fan and the palm face is 20 m, and the exhaust fan is 12 m away from the palm, the dust concentration control efficiency of the working face is increased by about 60%. Therefore, in the similar long-distance single head tunnel construction, it is appropriate to adopt the dust removal method of long-distance short suction and exhaust fan to ensure the working environment.
The sliding-rolling mixed motion behavior degrades the ball screw’s precision at different levels. Based on the sliding-rolling mixed motion between ball and screw/nut raceway, the ball screw’s precision loss considering different given axial loading and rotational speed working conditions was investigated. Since creep and lubrication relate to sliding and rolling motion wear, the creep and lubrication characteristics are analyzed under different working conditions. Besides, the precision loss was calculated considering the sole influence of sliding behavior between ball and screw and compared with the results from other current models. Finally, research on precision loss owing to the sliding-rolling mixed motion behavior was realized under given working conditions, and suitable wear tests were carried out. The analytical results of precision loss are in good agreement with the experimental test conclusions, which is conducive to better predicting the law of precision loss in stable wear period.
The effect of the design parameter on the clutch engagement process of the hydro-mechanical continuously variable transmission (CVT) was investigated. First, the model of the power train was developed with the software of SimulationX, and the clutch shift experiment was used to validate the correctness of the model. Then, the friction coefficient function was fitted with the test data to get the friction coefficient model suitable for this paper. Finally, based on the evaluating index of the friction torque and the friction power, two groups of design parameters (oil pressure and friction coefficient) were simulated and explained the changing regulation theoretically. According to the simulation results, the high oil pressure and friction coefficient can reduce the slipping time. The large oil pressure can increase the peak torque but the effect of friction coefficient on the peak torque is not so significant. The friction power reaches the maximum value at 3.2 s, the peak value increases as the oil pressure and friction coefficient increase. The effect of the oil pressure on the clutch engagement and thermal performance is greater than the friction coefficient.
Leakage is one of the most important reasons for failure of hydraulic systems. The accurate positioning of leakage is of great significance to ensure the safe and reliable operation of hydraulic systems. For early stage of leakage, the pressure of the hydraulic circuit does not change obviously and therefore cannot be monitored by pressure sensors. Meanwhile, the pressure of the hydraulic circuit changes frequently due to the influence of load and state of the switch, which further reduces the accuracy of leakage localization. In the work, a novel Bayesian networks (BNs)-based data-driven early leakage localization approach for multi-valve systems is proposed. Wavelet transform is used for signal noise reduction and BNs-based leak localization model is used to identify the location of leakage. A normalization model is developed to improve the robustness of the leakage localization model. A hydraulic system with eight valves is used to demonstrate the application of the proposed early micro-leakage detection and localization approach.
In this work, synchronous cutting of concave and convex surfaces was achieved using the duplex helical method for the hypoid gear, and the problem of tooth surface error correction was studied. First, the mathematical model of the hypoid gears machined by the duplex helical method was established. Second, the coordinates of discrete points on the tooth surface were obtained by measurement center, and the normal errors of the discrete points were calculated. Third, a tooth surface error correction model is established, and the tooth surface error was corrected using the Levenberg-Marquard algorithm with trust region strategy and least square method. Finally, grinding experiments were carried out on the machining parameters obtained by Levenberg-Marquard algorithm with trust region strategy, which had a better effect on tooth surface error correction than the least square method. After the tooth surface error is corrected, the maximum absolute error is reduced from 30.9 µm before correction to 6.8 µm, the root mean square of the concave error is reduced from 15.1 to 2.1 µm, the root mean square of the convex error is reduced from 10.8 to 1.8 µm, and the sum of squared errors of the concave and convex surfaces was reduced from 15471 to 358 µm2. It is verified that the Levenberg-Marquard algorithm with trust region strategy has a good accuracy for the tooth surface error correction of hypoid gear machined by duplex helical method.
Water alternating gas (WAG) injection is a widely used strategy for enhancing oil recovery (EOR) during gas flooding, and the mechanisms, operating parameters, and influencing factors of which have been extensively studied. However, with respect to its capacity in expanding macroscopic sweep volume under varying heterogeneities, the related results appear inadequate. In this research, three cores with different heterogeneities were used and flooded by the joint water and CO2 WAG, then the effects of heterogeneity on oil recovery were determined. More importantly, the cores after CO2 WAG injection were investigated using the nuclear magnetic resonance (NMR) technique for remaining oil distribution research, which could help us to understand the capacity of CO2 WAG in enlarging sweep volume at different heterogeneities. The results show that the presence of heterogeneity may largely weaken the effectiveness of water flooding, the more severe the heterogeneity, the worse the water flooding. The WAG injection of CO2 performs well in EOR after water flooding for all the cores with different heterogeneities; however, it could barely form a complete or full sweep throughout the low-permeability region, and un-swept bypassed regions remain. The homogeneous core is better developed by the injection of the joint water and CO2 WAG than the heterogeneous and fractured cases.
Based on the complex correlation between the geochemical element distribution patterns at the surface and the types of bedrock and the powerful capabilities in capturing subtle of machine learning algorithms, four machine learning algorithms, namely, decision tree (DT), random forest (RF), XGBoost (XGB), and LightGBM (LGBM), were implemented for the lithostratigraphic classification and lithostratigraphic prediction of a quaternary coverage area based on stream sediment geochemical sampling data in the Chahanwusu River of Dulan County, Qinghai Province, China. The local Moran’s I to represent the features of spatial autocorrelations, and terrain factors to represent the features of surface geological processes, were calculated as additional features. The accuracy, precision, recall, and F1 scores were chosen as the evaluation indices and Voronoi diagrams were applied for visualization. The results indicate that XGB and LGBM models both performed well. They not only obtained relatively satisfactory classification performance but also predicted lithostratigraphic types of the Quaternary coverage area that are essentially consistent with their neighborhoods which have the known types. It is feasible to classify the lithostratigraphic types through the concentrations of geochemical elements in the sediments, and the XGB and LGBM algorithms are recommended for lithostratigraphic classification.
The failure criterion of rocks is a critical factor involved in reliability design and stability analysis of geotechnical engineering. In order to accurately evaluate the triaxial compressive strength of rocks under different confining pressures, a nonlinear empirical strength criterion based on Mohr-Coulomb criterion was proposed in this paper. Through the analysis of triaxial test strength of 11 types of rock materials, the feasibility and validity of proposed criterion was discussed. For a further verification, six typical strength criteria were selected, and the prediction results of each criterion and test results were statistically analyzed. The comparative comparison results show that the prediction results obtained by applying this new criterion to 97 conventional triaxial compression tests of 11 different rock materials are highly consistent with the experimental data. Statistical analysis was executed to assess the application of the new criterion and other classical criteria in predicting the failure behavior of rock. This proposed empirical criterion provides a new reference and method for the determination of triaxial compressive strength of rock materials.
In the present study, the mechanical properties of polyvinyl alcohol (PVA)-basalt hybrid fiber reinforced engineered cementitious composites (ECC) after exposure to elevated temperatures were experimentally investigated. Five temperatures of 20, 50, 100, 200 and 400 °C were set to evaluate the residual compressive, tensile and flexural behaviors of hybrid and mono fiber ECC. It was shown that partial replacement of PVA fibers with basalt fibers endowed ECC with improved residual compressive toughness, compared to brittle failure of mono fiber ECC heated to 400 °C. The tension tests indicated that the presence of basalt fibers benefited the tensile strength up to 200 °C, and delayed the sharp reduction of strength to 400 °C. Under flexural load, the peak deflections corresponding to flexural strengths of hybrid fiber ECC were found to be less vulnerable ranging from 20 to 100 °C. Further, the scanning electron microscopy (SEM) results uncovered that the rupture of basalt fiber at moderate temperature and its pullout mechanism at high temperature was responsible for the mechanical evolution of hybrid fiber ECC. This work develops a better understanding of elevated temperature and basalt fiber impact on the residual mechanical properties and further provides guideline for tailoring ECC for improved fire resistance.
The aim of this research was to explain the effects of relative density, mean effective stress, grading characteristics, consolidation stress ratio and initial fabric anisotropy produced during specimen preparation on shear wave velocity (Vs). It is shown that the Vs of the consolidated specimens under anisotropic compression stress is greater than that of the consolidated specimens under isotropic or anisotropic extension stress states at a given relative density and effective confining stress. It is also shown that the depositional technique that was used to create reconstituted specimens has important effect on the Vs. A parallel comparison of measured values from the resonant column and bender element tests is also presented. These results of the tests have been employed to develop a generalized relationship for predicting Vs of granular soils. The Vs model is validated using data collected from literatures. Based on the results, it can be conducted that the proposed model has a good performance and is capable of evaluating the Vs of granular soil.
The use of electro-osmotic chemical is an effective method to improve the clayey soil foundation. Various boundary conditions can be adopted in this method. In this work, two electrode-clay contacts, three solution conditioners, and four anode solution supply times were used for clayey soil improvement. Based on the experimental data, electro-osmotic consolidation theory, and transport of ion theory, it is found that the electro-osmotic chemical effect of the separation of electrode-clay (E_S) is more beneficial for the transport of Ca2+, production of cementing material, and reduction of water content than that of electrode-clay (E_C) joining; through electrode-clay contact separation, the anode solution conditioner (NaPO3)6 (E_SHMP) delayed the cementing reaction and then increased the transport of Ca2+ near the cathode, which increased the amount of cementing material and the electro-osmotic chemical effect; and when the anode conditioner (NaPO3)6 was used, two days of anode solution supply followed by three days cut off from the anode solution led to the highest undrained shear strength increase after the application of electro-osmotic chemical, which resolved the uneven electro-osmotic chemical effect in the E_SHMP.
Rock bolts have been widely used in slopes as a reinforcement measure. Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts. Rock bolts under shear action exhibit the guide rail effect; that is, the rock mass slides along the rock bolt as if the rock bolt is a rail. The normal stress can inhibit the guide rail effect and reduce the axial force on bolts. However, this factor is not considered by the existing analysis models. Shear tests of bolted joints under different normal stresses were carried out in the laboratory. During the test, the axial force on each point monitored on the bolt was recorded by a strain gauge, and the attenuation trend of the strain was studied. An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints. The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage, and the estimated values agree well with the results of the direct shear tests in the laboratory. The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.
Seepage is one of the main causes for the deformation and instability of canal slopes in Xinjiang, China. In this study, centrifugal model tests under wetting-drying (WD) and wetting-drying-freezing-thawing (WDFT) cycles were performed to investigate the water infiltration characteristics below a canal. The results show that the shallow soil of the canal models was fully saturated in the wetting process. Compared with the canal model under the WD cycles, the canal model under the WDFT cycles had larger saturated areas and a higher degree of saturation below the canal top after each cycle, indicating that the freezing-thawing (FT) process in the WDFT cycles promoted the water infiltration behavior below the canal slope. The cracks on the surface of the canal model under the cyclic action of WDFT developed further and had a higher connectivity, which provided the conditions for slope instability from a transverse tensile crack running through the canal top. On this basis, a field test was conducted to understand the water infiltration distribution below a typical canal in Xinjiang, China, which also verified the accuracy of the centrifugal results. This study provides a preliminary basis for the maintenance and seepage treatment of canals in Xinjiang, China.
An improved design method of pervious concrete was proposed to lower the deviation between the designed and actual porosity and maintain both mechanical property and permeability of pervious concrete. The improved design method is mainly based on the optimal volume ratio of paste to aggregate (VRPA), which was determined by testing the average thickness of cement paste coating aggregate. The performances of pervious concrete designed by the traditional method and the improved one were compared. The results show that with the increase of designed porosity, the reduction of compressive strength and flexural strength of pervious concrete designed by the improved method is significantly smaller than those designed by the traditional one. The maximum deviation between the designed and actual porosity of the pervious concrete by the improved method is only 1.54%, which is far less than 8.7% obtained by the traditional one. Micro-structural analysis shows that the porous distribution of pervious concrete designed by improved method exhibits better uniformity.
Many analytical methods have been adopted to estimate the slope stability by providing various stability numbers, e.g. static safety of factor (static FoS) or the critical seismic acceleration coefficient, while little attention has been given to the relationship between the slope stability numbers and the critical seismic acceleration coefficient. This study aims to investigate the relationship between the static FoS and the critical seismic acceleration coefficient of soil slopes in the framework of the upper-bound limit analysis. Based on the 3D rotational failure mechanism, the critical seismic acceleration coefficient using the pseudo-static method and the static FoS using the strength reduction technique are first determined. Then, the relationship between the static FoS and the critical seismic acceleration coefficient is presented under considering the slope angle β, the fractional angle φ, and the dimensionless coefficients B/H and c/γH. Finally, a fitting formula between the static FoS and the critical seismic acceleration coefficient is proposed and validated by analytical and numerical results.
In this paper, the content and density of adsorbed water in fine-grained soil are determined. According to the test results, the calculation method of compaction degree of the solid-phase and void ration of soil is improved. Four kinds of fine-grained soils from different regions in China were selected, and the adsorbed water content and density of four kinds of fine-grained soils were determined by thermogravimetry and volumetric flask method. Furthermore, SEM and XRD experiments were used to analyze the differences in the ability of each soil sample to absorb water. In order to study the compression characteristics of adsorbed water, four saturated soil samples were tested by consolidation method. The results show that the desorption temperature range of the adsorbed water and its density were equal to 100–115 °C and 1.30 g/cm3, respectively. Adsorbed water plays a positive role in keeping the compressibility of fine-grained soil at a low rate when it has high water content. Besides, adsorbed water can be a stable parameter and is difficult to discharge during the operation period of subgrade. The settlement of fine-grained soil embankment is predicted by engineering example, and compared with the result of conventional calculation method. The results show that it is more close to the field monitoring results by using the improved void ratio of soil as the parameter.
Wear and scuffing failures often occur in marine transmission gears due to high friction and flash temperature at the interface between the meshing-teeth. In this paper, a numerical solution procedure was developed for the predictions of transient friction and flash temperature in the marine timing gears during one meshing circle based on the 3D line contact mixed lubrication simulation, which had been verified by comparing the flash temperature with those from Blok’s theory. The effect of machined surface roughness on the mixed lubrication characteristics is studied. The obtained results for several typical gear pairs indicate that gear pair 4–6 exhibits the largest friction and the highest interfacial temperature increase due to severe rough surface asperity contacts, while the polished gear surfaces yield the smallest friction and the lowest interfacial temperature. In addition, the influences of the operating conditions and the gear design parameters on the friction-temperature behaviors are discussed. It is observed that the conditions of heavy load and low rotational velocity usually lead to significantly increased friction and temperature. In the meantime, by optimizing the gear design parameters, such as the modulus and the pressure angle, the performance of interfacial friction and temperature can be significantly improved.
Traffic assignment has been recognized as one of the key technologies in supporting transportation planning and operations. To better address the perfectly rational issue of the expected utility theory (EUT) and the overlapping path issue of the multinomial logit (MNL) model that are involved in the traffic assignment process, this paper proposes a cumulative prospect value (CPV)-based generalized nested logit (GNL) stochastic user equilibrium (SUE) model. The proposed model uses CPV to replace the utility value as the path performance within the GNL model framework. An equivalent mathematical model is provided for the proposed CPV-based GNL SUE model, which is solved by the method of successive averages (MSA). The existence and equivalence of the solution are also proved for the equivalent model. To demonstrate the performance of the proposed CPV-based GNL SUE model, three road networks are selected in the empirical test. The results show that the proposed model can jointly deal with the perfectly rational issue and the overlapping path issue, and additionally, the proposed model is shown to be applicable for large road networks.