The interface properties between hydrated cement paste (hcp) and aggregates largely determine the various performances of concrete. In this work, molecular dynamics simulations were employed to explore the atomistic interaction mechanisms between the commonly used aggregate phase calcite/silica and calcium silicate hydrates (C-S-H), as well as the effect of moisture. The results suggest that the C-S-H/calcite interface is relatively strong and stable under both dry and moist conditions, which is caused by the high-strength interfacial connections formed between calcium ions from calcite and high-polarity non-bridging oxygen atoms from the C-S-H surface. Silica can be also adsorbed on the dry C-S-H surface by the H-bonds; however, the presence of water molecules on the interface may substantially decrease the affinities. Furthermore, the dynamics interface separation tests of C-S-H/aggregates were also implemented by molecular dynamics. The shape of the calculated stress-separation distance curves obeys the quasi-static cohesive law obtained experimentally. The moisture conditions and strain rates were found to affect the separation process of C-S-H/silica. A wetter interface and smaller loading rate may lead to a lower adhesion strength. The mechanisms interpreted here may shed new lights on the understandings of hcp/aggregate interactions at a nano-length scale and creation of high performance cementitious materials.

Based on the first-principles calculations of density functional theory, co-adsorption models of C or CO with Cl₂ on rutile TiO₂ (100) surface were established. The adsorption structures and electronic properties during chlorination process were predicted. Then, the adsorption energy, charge density, electron density difference and density of state of the adsorption structures were calculated and analyzed. The stabilities of the adsorption structures and the charge distributions between atoms were studied. It was found that both C and CO could promote the adsorption reactions of Cl₂ on TiO₂ (100) surface, and C was more favorable to the adsorption process. The results show that the adsorption process of Cl₂ on TiO₂(100) surface was physisorption, and the co-adsorption processes of C or CO with Cl₂ on TiO₂(100) surface were chemisorptions.

Ab initio calculations are used to understand the fundamental mechanism of the solid solution softening/hardening of the Mo-binary system. The results reveal that the Mo-Ti, Mo-Ta, Mo-Nb, and Mo-W interactions are primarily attractive with negative heats of formation, while the interactions of Mo-Re, and Mo-Zr would be mainly repulsive with positive heats of formation. It is also shown that the addition of Re and Zr would cause the solid solution softening of Mo by the decrease of the unstable stacking fault energy and the increase of ductility. On the contrary, the elements of W, Ta, Ti, and Nb could bring about the solid-solution hardening of Mo through the impediment of the slip of the dislocation and the decrease of ductility. Electronic structures indicate that the weaker/stronger chemical bonding due to the alloying elements should fundamentally induce the solid solution softening/hardening of Mo. The results are discussed and compared with available evidence in literatures, which could deepen the fundamental understanding of the solid solution softening/hardening of the binary metallic system.

In order to produce low-cost titanium (Ti) with high productivity, fundamental studies on producing metallic Ti from titanium dioxide (TiO₂) in the cold pressed pellets were conducted by metallothermic reduction with an indirect contact method. This paper focuses on discussing the mechanism of the reduction process and the relationships of R_M (a revised reduction index) with reduction temperature, reduction time, and mole ratio of TiO₂ to CaCl2 (

) in the pellets. The results show that metallic Ti was obtained from the reduction of TiO₂ in the pellets by calcium (Ca) vapor; pellets were reduced homogenously and Ca vapor diffused into the porous pellets by Knudsen diffusion or the mixing diffusion of molecular diffusion and Knudsen diffusion at 1273 K; R_M increased with the increases of temperature and reduction time and was 96.34% when T_Redu=1273 K, t_Redu=6 h, and

n_{{\text{TiO}}_2}/n_{{\text{CaCl}}_2}=4

\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${n_{{\rm{Ti}}{{\rm{O}}_2}}}/{n_{{\rm{CaC}}{{\rm{l}}_2}}} = 4$$\end{document}

; the reasonable n_TiO2/n_CaCl2 value is 3–5 for the pellets with enough strength and high R_M.

This paper presents a model of fatigue crack growth in a welded joint and a two-dimensional model of anodic dissolution based on Donahue model and anodic dissolution mechanism, respectively. In addition, a model for predicting the corrosion fatigue crack growth rate in welded joints of steel marine structures is established and crack growth mechanisms are analyzed. The results show that during early stages of crack growth, corrosion fatigue crack growth rate in welded joints is mainly controlled by corrosion action, whereas cyclic loading becomes more influential during the later stage of crack propagation. Loading frequency and effective stress ratio can affect rupture period of protective film at the corrosion fatigue crack tip and the length of corrosion crack increment, respectively, which changes the influence of corrosion action on crack growth rate. However, the impact of stress amplitude on crack growth rate is only significant when crack propagation is caused by cyclic loading. Welding residual stress not only improves the effective stress ratio of cyclic loading, but also promotes crack closure and increases corrosion fatigue crack growth rate in welded joints. Compared to corrosion action, welding residual stress has a more significant influence on crack growth caused by cyclic loading.

A plumbomicrolite concentrate (PMC) was leached with the mixture of HF and H₂SO₄, HF and HNO₃ acids, respectively. Optimal conditions ensuring high recovery of tantalum and niobium (up to 99%) into solution, and radionuclides into insoluble residue were determined. Fluoride-sulfuric acid and fluoride-nitric acid schemes were proposed for PMC leaching by an extractive separation of tantalum form niobium, lead and impurities, and production of high-purity tantalum compounds. Octanol-1 was used as an extractant. Optimal conditions for production of high-purity tantalum strip solutions were defined for all stages (extraction-scrubbing-stripping). Produced tantalum compounds, such as tantalum pentoxide and potassium heptafluotanthalate, comply with the norms for high-purity substances in terms of impurities content. Final choice of the PMC processing scheme is determined by its profitability.

In this study, the effects of drying temperature, hot airflow speed and diameter of green pellet on drying rate of artificial magnetite pellet were deeply investigated to clarify the drying characteristics of artificial magnetite green pellet. The results show that the drying process of artificial magnetite green pellet has three stages, accelerated drying stage, constant drying stage and decelerated drying stage. And drying temperature and hot airflow speed both have significant reciprocal effects on moisture ratio and drying rate of green pellet during the drying process. However, the diameter of green pellet has little effect on drying process of green pellet. Then the drying fitting models of Correction Henderson and Pabis, Lewis, Correction Page (III), Wang and Singh are used to describe the drying kinetics of artificial magnetite green pellet. The fitting results indicate that the drying process of artificial magnetite pellet can be described by Correction Page (III) model accurately. Finally, the contrast experiments demonstrate that the fitting model can well describe the actual drying process.

The quality of contour blasting depends on many initial blasting parameters. The parameters including blasthole diameter, rock Protodyakonov coefficient, tunnel area and distance between cracks on the tunnel face are more important. In this study, an algorithm linking between Delphi programming language and AutoCAD was created to develop a tunnel blasting model. Using this model, tunnel contour blasting passport in AutoCAD can be obtained automatically. The effects of rock Protodyakonov coefficient and cracks’ distance on blastholes number and specific charge with the variation of blasthole diameter and the semi-circular tunnel face area were investigated to yield a set of equations with the highest correlations. The results show that specific charge increases as rock Protodyakonov coefficient, cracks’ distance and drillhole diameter increase, but decreases when tunnel face area increases. In addition, the number of drillholes increases linearly as tunnel face area increases but decreases when drillhole diameter increases.

This study aims to examine the usability of environmentally harmless vegetable oil in the minimum quantity of lubrication (MQL) system in face milling of AISI O2 steel and to optimize the cutting parameters by different statistical methods. Vegetable oil was preferred as cutting fluid, and Taguchi method was used in the preparation of the test pattern. After testing with the prepared test pattern, cutting performance in all parameters has been improved according to dry conditions thanks to the MQL system. The highest tool life was obtained by using cutting parameters of 7.5 m cutting length, 100 m/min cutting speed, 100 mL/h MQL flow rate and 0.1 mm/tooth feed rate. Optimum cutting parameters were determined according to the Taguchi analysis, and the obtained parameters were confirmed with the verification tests. In addition, the optimum test parameter was determined by applying the gray relational analysis method. After using ANOVA analysis according to the measured surface roughness and cutting force values, the most effective cutting parameter was observed to be the feed rate. In addition, the models for surface roughness and cutting force values were obtained with precisions of 99.63% and 99.68%, respectively. Effective wear mechanisms were found to be abrasion and adhesion.

The thermal elasto-hydrodynamic lubrication characteristics of the internal meshing gears in a planetary gear train under vibrations were examined considering the influence of the modification coefficient and time-varying meshing stiffness. Based on dynamic theory of the gear system, a dynamic model of the planetary gear train was established. The lubrication performances of modified gear systems under vibrations and static loads were analyzed. Compared with other transmission types, the best lubrication effect could be produced by the positive transmission. A thicker lubricating oil film could be formed, and the friction coefficient and oil film flash temperature are the smallest. Increasing modification coefficient improves the lubrication performance continuously but intensifies the engage-in and tooth-change impact. For the planetary and inner gears, the increase in the modification coefficient also leads a decrease in the oil film stiffness.

This paper designs a joint controller/observer framework using a state dependent Riccati equation (SDRE) approach for an active transfemoral prosthesis system. An integral state control technique is utilized to design a tracking controller for a robot/prosthesis system. This framework promises a systematic flexible design using which multiple design specifications such as robustness, state estimation, and control optimality are achieved without the need for model linearization. Performance of the proposed approach is demonstrated through simulation studies, which show improvements versus a robust adaptive impedance controller and an extended Kalman filter-based state estimation method. Numerical results confirm the benefits of our method over the above-mentioned approaches with regard to control optimality and state estimation.

With the huge rise of energy demand, the power system in the current era is moving to a new standard with increased access to renewable energy sources (RESs) integrated with distribution generation (DG) network. The RESs necessitate interfaces for controlling the power generation. The multilevel inverter (MLI) can be exploited for RESs in two diverse modes, namely, the power generation mode (stand-alone mode), and compensator mode (statcom). Few works have been carried out in optimization of controller gains with the load variations of the single type such as reactive load variation in different cases. Nevertheless, this load type may be unbalanced hence, to overcome such issues. So, a sophisticated optimization algorithm is important. This paper aims to introduce a control design via an optimization assisted PI controller for a 7-level inverter. In the present technique, the gains of the PI controller are adjusted dynamically by the adopted hybrid scheme, grey optimizer with dragon levy update (GD-LU), based on the operating conditions of the system. Here, the gains are adjusted such that the error between the reference signal and fault signal should be minimal. Thus, better dynamic performance could be attained by the present optimized PI controller. The proposed algorithm is the combined version of grey wolf optimization (GWO) and dragonfly algorithm (DA). Finally, the performance of the proposed work is compared and validated over other state-of-the-art models concerning error measures.

Luffing mechanism is a key component of the construction machinery. This paper proposes a two degree of freedom (2-DOF) luffing mechanism, which has one more pair of driving cylinders than the single DOF luffing mechanism, to improve the performance of the machinery. To establish the dynamic model of the 2-DOF luffing mechanism, firstly, we develop a hierarchical method to deduce the Jacobian matrix and Hessian matrix for obtaining the kinematics equations. Subsequently, we divide the luffing mechanism into six bodies considering actuators, and deduce the kinetic equations of each body by the Newton-Euler method. Based on the dynamic model, we simulate the luffing process. Finally, a prototype is built on a pile driver to validate the model. Simulations and experiments show that the dynamic model can reflect the dynamic properties of the proposed luffing mechanism. And the control strategy that the front cylinders retract first shows better mechanical behavior than the other two control strategies. This research provides a reference for the design and application of 2-DOF luffing mechanism on construction machinery. The modeling approach can also be applied to similar mechanism with serial closed kinematic chains, which allows to calculate the dynamic parameters easily and exactly.

Recognition of substrates in cobalt crust mining areas can improve mining efficiency. Aiming at the problem of unsatisfactory performance of using single feature to recognize the seabed material of the cobalt crust mining area, a method based on multiple-feature sets is proposed. Features of the target echoes are extracted by linear prediction method and wavelet analysis methods, and the linear prediction coefficient and linear prediction cepstrum coefficient are also extracted. Meanwhile, the characteristic matrices of modulus maxima, sub-band energy and multi-resolution singular spectrum entropy are obtained, respectively. The resulting features are subsequently compressed by kernel Fisher discriminant analysis (KFDA), the output features are selected using genetic algorithm (GA) to obtain optimal feature subsets, and recognition results of classifier are chosen as genetic fitness function. The advantages of this method are that it can describe the signal features more comprehensively and select the favorable features and remove the redundant features to the greatest extent. The experimental results show the better performance of the proposed method in comparison with only using KFDA or GA.

Face anti-spoofing is a relatively important part of the face recognition system, which has great significance for financial payment and access control systems. Aiming at the problems of unstable face alignment, complex lighting, and complex structure of face anti-spoofing detection network, a novel method is presented using a combination of convolutional neural network and brightness equalization. Firstly, multi-task convolutional neural network (MTCNN) based on the cascade of three convolutional neural networks (CNNs), P-net, R-net, and O-net are used to achieve accurate positioning of the face, and the detected face bounding box is cropped by a specified multiple, then brightness equalization is adopted to perform brightness compensation on different brightness areas of the face image. Finally, data features are extracted and classification is given by utilizing a 12-layer convolution neural network. Experiments of the proposed algorithm were carried out on CASIA-FASD. The results show that the classification accuracy is relatively high, and the half total error rate (HTER) reaches 1.02%.

Human-object interaction (HOIs) detection is a new branch of visual relationship detection, which plays an important role in the field of image understanding. Because of the complexity and diversity of image content, the detection of HOIs is still an onerous challenge. Unlike most of the current works for HOIs detection which only rely on the pairwise information of a human and an object, we propose a graph-based HOIs detection method that models context and global structure information. Firstly, to better utilize the relations between humans and objects, the detected humans and objects are regarded as nodes to construct a fully connected undirected graph, and the graph is pruned to obtain an HOI graph that only preserving the edges connecting human and object nodes. Then, in order to obtain more robust features of human and object nodes, two different attention-based feature extraction networks are proposed, which model global and local contexts respectively. Finally, the graph attention network is introduced to pass messages between different nodes in the HOI graph iteratively, and detect the potential HOIs. Experiments on V-COCO and HICO-DET datasets verify the effectiveness of the proposed method, and show that it is superior to many existing methods.

The cohesion weakening and friction strengthening (CWFS) model for rock reveals the strength components mobilization process during progressive brittle failure process of rock, which is very helpful in understanding mechanical properties of rock. However, the used incremental cyclic loading-unloading compression test for the determination of strength components is very complicated, which limits the application of CWFS model. In this paper, incremental cyclic loading-unloading compression test was firstly carried out to study the evolution of deformation and the strength properties of Beishan granite after various temperatures treated under different confining pressures. We found the axial and lateral unloading modulus are closely related to the applied stress and damage state of rock. Based on these findings, we can accurately determine the plastic strain during the entire failure process using conventional tri-axial compression test data. Furthermore, a strength component (cohesive and frictional strength) determination method was developed using conventional triaxial compression test. Using this method, we analyzed the variation of strength mobilization and deformation properties of Beishan granite after various temperatures treated. At last, a non-simultaneous strength mobilization model for thermally treated granite was obtained and verified by numerical simulation, which demonstrated the effectiveness of the proposed strength determination method.

In the finite element method, the numerical simulation of three-dimensional crack propagation is relatively rare, and it is often realized by commercial programs. In addition to the geometric complexity, the determination of the cracking direction constitutes a great challenge. In most cases, the local stress state provides the fundamental criterion to judge the presence of cracks and the direction of crack propagation. However, in the case of three-dimensional analysis, the coordination relationship between grid elements due to occurrence of cracks becomes a difficult problem for this method. In this paper, based on the extended finite element method, the stress-related function field is introduced into the calculation domain, and then the boundary value problem of the function is solved. Subsequently, the envelope surface of all propagation directions can be obtained at one time. At last, the possible surface can be selected as the direction of crack development. Based on the aforementioned procedure, such method greatly reduces the programming complexity of tracking the crack propagation. As a suitable method for simulating tension-induced failure, it can simulate multiple cracks simultaneously.

Estimation of support pressure is extremely important to the support system design and the construction safety of tunnels. At present, there are many methods for the estimation of support pressure based on different rock mass classification systems, such as Q system, GSI system and RMR system. However, various rock mass classification systems are based on different tunnel geologic conditions in various regions. Therefore, each rock mass classification system has a certain regionality. In China, the BQ-Inex (BQ system) has been widely used in the field of rock engineering ever since its development. Unfortunately, there is still no estimation method of support pressure with BQ-index as parameters. Based on the field test data from 54 tunnels in China, a new empirical method considering BQ-Inex, tunnel span and rock weight is proposed to estimate the support pressure using multiple nonlinear regression analysis methods. And then the significance and necessity of support pressure estimation method for the safety of tunnel construction in China is explained through the comparison and analysis with the existing internationally widely used support pressure estimation methods of RMR system, Q system and GSI system. Finally, the empirical method of estimating the support pressure based on BQ-index was applied to designing the support system in the China’s high-speed railway tunnel—Zhengwan high-speed railway and the rationality of this method has been verified through the data of field test.

Embankment stability is the primary problem for the expressway construction in permafrost regions. The proposed Qinghai-Tibet Expressway (QTE) is planned to construct along the Qinghai-Tibet Project Corridor. Confronted with harsh environmental condition and intense heat exchange between earth and atmosphere, it is necessary to predict and evaluate the stability of the proposed QTE. In this study, the factors affecting the embankment stability are analyzed firstly. And then, a scheme for the stability evaluation of the embankment is established. Finally, the evaluation scheme is used for the pre-evaluation of the stability for the proposed QTE with different geothermal regulation measures (GRMs). The results indicate that the influencing factors include climatic environment, permafrost property, engineering condition and geological condition, and among them, engineering condition and permafrost property are the main influence factors for embankment stability. The stability of the proposed QTE varies greatly in the different geomorphological regions. The application effect and contribution to embankment stability of the existing GRMs are different, and using GRMs cannot completely overcome the influence of various factors on expressway stability. In the construction process, different GRMs should be adopted depending on the geomorphological environment where the embankment is located to ensure the embankment stability.

To further investigate the one-dimensional (1D) rheological consolidation mechanism of double-layered soil, the fractional derivative Merchant model (FDMM) and the non-Darcian flow model with the non-Newtonian index are respectively introduced to describe the deformation of viscoelastic soil and the flow of pore water in the process of consolidation. Accordingly, an 1D rheological consolidation equation of double-layered soil is obtained, and its numerical analysis is performed by the implicit finite difference method. In order to verify its validity, the numerical solutions by the present method for some simplified cases are compared with the results in the related literature. Then, the influence of the revelent parameters on the rheological consolidation of double-layered soil are investigated. Numerical results indicate that the parameters of non-Darcian flow and FDMM of the first soil layer greatly influence the consolidation rate of double-layered soil. As the decrease of relative compressibility or the increase of relative permeability between the lower soil and the upper soil, the dissipation rate of excess pore water pressure and the settlement rate of the ground will be accelerated. Increasing the relative thickness of soil layer with high permeability or low compressibility will also accelerate the consolidation rate of double-layered soil.

Geotechnical stability analyses based on classical continuum may lead to remarkable underestimations on geotechnical safety. To attain better estimations on geotechnical stability, the micro-polar continuum is employed so that its internal characteristic length (4) can be utilized to model the shear band width. Based on two soil slope examples, the role of internal characteristic length in modeling the shear band width of geomaterial is investigated by the second-order cone programming optimized micro-polar continuum finite element method. It is recognized that the underestimation on factor of safety (FOS) calculated from the classical continuum tends to be more pronounced with the increase of 4. When the micro-polar continuum is applied, the shear band dominated by 4 is almost kept unaffected as long as the adopted meshes are fine enough, but it does not generally present a slip surface like in the cases from the classical continuum, indicating that the micro-polar continuum is capable of capturing the non-local geotechnical failure characteristic. Due to the coupling effects of 4 and strain softening, softening behavior of geomaterial tends to be postponed. Additionally, the bearing capacity of a geotechnical system may be significantly underestimated, if the effects of 4 are not modeled or considered in numerical analyses.

Plasma jet has been widely used in supersonic combustor as an effective ignition and combustion assisted method, but currently it is mostly combined with the traditional wall fuel injection method, while the application combined with the central fuel injection method is less. In order to expand the combustion range, the plasma jet was introduced into a strut-cavity combustor with an alternating-wedge. The effects of total pressure of strut fuel injection, total pressure of cavity fuel injection, total pressure of plasma jet injection and plasma jet media on the combustion characteristics were analyzed in supersonic flow by numerical calculations in a three-dimensional domain. The combustion field structure, wall pressure distribution, combustion efficiency and distribution of H2O at the exit of the combustor with different injection conditions were analyzed. The results show that the combustion efficiency decreases with the increase of the strut fuel injection total pressure. However, the combustion area downstream increases when the total pressure of the strut fuel injection increases within the proper range. The combustion range is expanded and the combustion efficiency is improved when the cavity fuel injection total pressure is increased within the range of 0.5–2.0 MPa, but a sharp drop in combustion efficiency can be found due to limited fuel mixing when the total injection pressure of the cavity fuel is excessively increased. With the increased total injection pressure of the plasma jet, the height of the cavity shear layer is raised and the equivalence ratio of the gas mixture in the cavity is improved. When the total pressure of the plasma jet is 1.25 MPa, the combustion efficiency reaches a maximum of 82.1%. The combustion-assisted effect of different plasma jet media is significantly different. When the medium of the plasma jet is O2, the combustion-assisted effect on the combustor is most significant.