One of the surface mining methods is open-pit mining, by which a pit is dug to extract ore or waste downwards from the earth’s surface. In the mining industry, one of the most significant difficulties is long-term production scheduling (LTPS) of the open-pit mines. Deterministic and uncertainty-based approaches are identified as the main strategies, which have been widely used to cope with this problem. Within the last few years, many researchers have highly considered a new computational type, which is less costly, i.e., meta-heuristic methods, so as to solve the mine design and production scheduling problem. Although the optimality of the final solution cannot be guaranteed, they are able to produce sufficiently good solutions with relatively less computational costs. In the present paper, two hybrid models between augmented Lagrangian relaxation (ALR) and a particle swarm optimization (PSO) and ALR and bat algorithm (BA) are suggested so that the LTPS problem is solved under the condition of grade uncertainty. It is suggested to carry out the ALR method on the LTPS problem to improve its performance and accelerate the convergence. Moreover, the Lagrangian coefficients are updated by using PSO and BA. The presented models have been compared with the outcomes of the ALR-genetic algorithm, the ALR-traditional sub-gradient method, and the conventional method without using the Lagrangian approach. The results indicated that the ALR is considered a more efficient approach which can solve a large-scale problem and make a valid solution. Hence, it is more effectual than the conventional method. Furthermore, the time and cost of computation are diminished by the proposed hybrid strategies. The CPU time using the ALR-BA method is about 7.4% higher than the ALR-PSO approach.

The effect of activation properties of the precursors of zeolite directly prepared from kaolin influenced by microwave field and conventional heating was investigated. XRD, TG-DSC, FT-IR, SEM, particle size analysis, specific surface area (BET), pore size distribution (BJH) and N₂ adsorption-desorption were discussed to determine the optimal activation temperature. It is concluded that the conversion of kaolin to metakaolin in the microwave field is at 500 °C holding for 30 min, which is 100 °C lower than that in conventional calcination and 90 min shorter, and the phase transition process of kaolin under the effect of microwave field is the same as that of conventional heating method. SEM analysis indicates that the particle size is more uniform and agglomeration appears slightly in the microwave field. The N₂ adsorption-desorption isotherm, BET and BJH of kaolin indicate that the pore properties are almost invariable regardless of calcination route during the process of calcining kaolin into metakaolin. It indicates that microwave calcination is superior to conventional calcination in the activation pathway of kaolin. It is attributed to microwave heating relying on objects to absorb microwave energy and convert it into thermal energy, which can simultaneously and uniformly heat the entire substance.

Copolymer of acrylic acid and maleic acid (PMA) was used to remove Hg²⁺ from aqueous solution by complexation-ultrafiltration (C-UF) through rotating disk membrane (RDM). The effects of P/M (mass ratio of PMA to metal ions), pH and rotation speed (N) on the interception of Hg²⁺ were investigated. The interception could reach 99.7% at pH 7.0, P/M 6 and N less than 1890 r/min. The shear stability of PMA-Hg complex was studied by RDM. The critical rotation speed, at which the interception starts to decrease, was 1890 r/min, and the critical shear rate, the smallest shear rate at which PMA-Hg complex begins to dissociate, was 2.50×10⁵ s⁻¹ at pH 7.0. Furthermore, the critical radii were obtained at different rotation speeds and pHs. The results showed that the critical radius decreased with the rotation speed and increased with pH. Shear induced dissociation coupling with ultrafiltration (SID-UF) was efficiently used to recover Hg²⁺ and PMA.

Electrochemically exfoliated graphene (EEG) is a kind of high-quality graphene with few oxygen-containing functional groups and defects on the surface, and thereby is more suitable as catalyst support than other carbon materials such as extensively used reduced graphene oxide (rGO). However, it is difficult to grow functional materials on EEG due to its inert surface. In this work, ultra-small Pt nanocrystals (∼2.6 nm) are successfully formed on EEG and show better electrocatalytic activity towards methanol oxidation than Pt catalysts on rGO. The outstanding catalytic properties of Pt catalysts on EEG can be attributed to the fast electron transfer through EEG and high quality of Pt catalysts such as small grain size, high dispersibility and low oxidation ratio. In addition, SnO₂ nanocrystals are controllably generated around Pt catalysts on EEG to raise the poison tolerance of Pt catalysts through using glycine as a linker. Owing to its outstanding properties such as high electrical conductivity and mechanical strength, EEG is expected to be widely used as a novel support for catalysts.

In order to obtain a high-performance surface on TiAl alloy that can meet the requirements in hot corrosion environment, Si-Al-Y coatings were fabricated by pack cementation process at 1050 °C for 4 h. Corrosion behaviors of the TiAl alloy with and without Si-Al-Y coatings are compared to illustrate the factors and corresponding mechanism in molten salt environment of 25wt% K₂SO₄ and 75wt% Na₂SO₄ at 900 °C. The obtained Si-Al-Y coating was mainly composed of a TiSi₂ outer layer, a (Ti, X)₅Si₄ and (Ti, X)₅Si₃ (X represents Nb or Cr element) middle layer, a TiAl₂ inner layer and a Al-rich inter-diffusion zone. The inter-phase selective corrosion containing corrosion pits extending along α₂ phase from lamellar interfaces in hot corrosion tested TiAl alloy was observed. However, by being coated with Si-Al-Y coating, the hot corrosion performance of TiAl alloy was improved remarkably.

To improve the ablation resistance of carbon/carbon (C/C) composites, a SiC/ZrC-ZrB₂ double layer coating was fabricated by pack cementation and slurry-sintering method. The ablation resistance of the SiC/ZrC-ZrB₂ coating was tested under plasma flame above 2300 °C. The results indicate that the SiC/ZrC-ZrB₂ double layer coating exhibits superior ablation resistance than the ZrC-ZrB₂ single layer coating. After being ablated under the plasma flame for 20 s, the mass and linear ablation rates of the ZrC-ZrB₂ coating are 0.89 mg/s and 15.3 µm/s, while those for SiC/ZrC-ZrB₂ coating are 0.09 mg/s and 24.15 µm/s, respectively. During ablation, the SiC inner layer can generate SiO₂ glass and result in the formation of ZrO₂-SiO₂ molten film. Compared with the ZrO₂ molten film formed on the ZrC-ZrB₂ coating surface, the ZrO₂-SiO₂ molten film with lower oxygen diffusion rate and viscosity enables the SiC/ZrC-ZrB₂ coating to have better self-healing ability. Therefore, the enhanced ablation resistance of the SiC/ZrC-ZrB₂ coating can be attributed to the formation of dense ZrO₂-SiO₂ molten film under the plasma flame.

By employing sintering additives of Li₂CO₃ and Y₂O₃, porous Si₃N ceramics are prepared after experiencing the processes of sintering and post-vacuum heat treatment at 1680 and 1550 °C, respectively. The experimental results demonstrate the completed phase transformation from α to β-Si₃N₄ in Si₃N₄ ceramic samples with a amount of 1.60 wt% Li₂CO₃ (0.65 wt% Li₂O) and 0.33 wt% Y₂O₃ additives. The as-synthesized porous Si3N4 ceramics exhibit high flexural strength ((126.7±2.7) MPa) and high open porosity of 50.4% at elevated temperature (1200 °C). These results are attributed to the significant role of added Li₂CO₃ as sintering additive, where the volatilization of intergranular glassy phase occurs during sintering process. Therefore, porous Si₃N₄ ceramics with desired mechanical property prepared by altering the addition of sintering additives demonstrate their great potential as a promising candidate for high temperature applications.

Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test. SEM, EDS and XRD were performed to analyze the composites before and after erosion. The results indicate that a U shape relationship curve presents between the erosion rates and Al content, and the lowest erosion rate occurs at 40 wt% Al. Except for the important influence of compactness, the increasing soft Al mixed with reactive SiC, namely the mixture located between carbon and residual Si also, plays a key role in the erosion of the C/C-SiC composites through crack deflection, plastic deformation and bonding cracked Si.

The effects of SiCp surface modifications (Cu coating, Ni coating and Ni/Cu coating) on the microstructures and mechanical properties of Al matrix composites were investigated. Surface modification of SiC particles with Cu, Ni and Cu/Ni, respectively, was carried out by electroless plating method. SiCp/Al composites were prepared by hot pressed sintering followed by hot extrusion. The results show that the surface modification of SiC particles plays an effective role, which is relative to the type of surface coating, and the interfacial bonding become stronger in the following order: untreated SiCp<Ni(Cu)-coated SiCp<Ni/Cu-coated SiCp. The Ni/Cu-coated SiCp/Al composites exhibit the best comprehensive mechanical properties, with ultimate tensile strength (σ_UTS) and fracture strain (ε_f) of 389 MPa and 6.3%, respectively. Compared with that of untreated-SiCp/Al composites, the σ_UTS and ε_f are enhanced by 19.3% and 57.5%.

In this paper, the springback of TC4 titanium alloy under hot stamping condition was studied by means of experiment and numerical analysis. Firstly, an analytical model was established to predict the V-shaped springback angle Δα under the stretch-bending conditions. The model took into account of blank holder force, friction, property of the material, thickness of the sheet and the neutral layer shift. Then, the influence of several process parameters on springback was studied by experiment and finite element simulation using a V-shaped stamping tool. In the hot stamping tests, the titanium alloy sheet fractured seriously at room temperature. The titanium alloy has good formability when the initial temperature of the sheet is 750–900 °C. However, the springback angle of formed parts is large and decreases with increasing temperature. The springback angle Aa decreased by 50% from 0.5° to 0.25°, and the angle Δβ decreased by 46.7% from 1.5° to 0.8° when the initial temperature of sheet increased from 750 °C to 900°C. The springback angle of titanium alloy sheet increases gradually with the increase of the punch radius, because of the increase of elastic recovery, the complex distribution of stress, the length of forming region and the decreasing degree of stress. Compared with the simulation results, the analytical model can better predict the springback angle Δα.

We have established an elastoplastic analysis model to explore the effect of loading path in an incompressible thin-walled tube under the combined action of axial force and torque based on Mises yield condition and isotropic linear hardening assumption. Further, four stress areas (σ_x, τ_x) are divided according to the characteristics of the final stress, and the plastic stress-strain relationship of twelve stress paths in different stress areas is derived. The “primary effect” of the stress path on plastic strain is demonstrated, namely, the plastic strain caused by the pre-loaded stress in path A (tensile stress is initially applied, followed by shear stress) is always greater than that caused by the post-loaded stress in path C (shear stress is initially applied, followed by tensile stress) irrespective of the value of final stress. The “recency effect” of the strain path on the stress is also established, which indicates that the stress caused by the post-loaded strain in path A is always greater than that caused by the pre-loaded strain in path C irrespective of the value of final strain. From the perspective of deformation, the “primary effect” of the stress path on the plastic strain and the “recency effect” of the strain path on the stress are unified. These effects are succinct and universal, and they provide useful insights on the plastic stress-strain relationship under different loading paths. Furthermore, they can serve as a useful reference for optimizing the processing technologies and construction procedures.

With the rise of the electric vehicle industry, as the power source of electric vehicles, lithium battery has become a research hotspot. The state of charge (SOC) estimation and modelling of lithium battery are studied in this paper. The ampere-hour (Ah) integration method based on external characteristics is analyzed, and the open-circuit voltage (OCV) method is studied. The two methods are combined to estimate SOC. Considering the accuracy and complexity of the model, the second-order RC equivalent circuit model of lithium battery is selected. Pulse discharge and exponential fitting of lithium battery are used to obtain corresponding parameters. The simulation is carried out by using fixed resistance capacitance and variable resistance capacitor respectively. The accuracy of variable resistance and capacitance model is 2.9%, which verifies the validity of the proposed model.

In this paper, we consider a multi-UAV surveillance scenario where a team of unmanned aerial vehicles (UAVs) synchronously covers an area for monitoring the ground conditions. In this scenario, we adopt the leader-follower control mode and propose a modified Lyapunov guidance vector field (LGVF) approach for improving the precision of surveillance trajectory tracking. Then, in order to adopt to poor communication conditions, we propose a prediction-based synchronization method for keeping the formation consistently. Moreover, in order to adapt the multi-UAV system to dynamic and uncertain environment, this paper proposes a hierarchical dynamic task scheduling architecture. In this architecture, we firstly classify all the algorithms that perform tasks according to their functions, and then modularize the algorithms based on plugin technology. Afterwards, integrating the behavior model and plugin technique, this paper designs a three-layer control flow, which can efficiently achieve dynamic task scheduling. In order to verify the effectiveness of our architecture, we consider a multi-UAV traffic monitoring scenario and design several cases to demonstrate the online adjustment from three levels, respectively.

Due to the advantages of low cost, fast response and pollution resistance, digital hydraulic pump/motor can replace conventional variable hydraulic pump/motor in many application fields. However, digital hydraulic components produce large hydraulic impact at variable moments, which will shorten the service life of mechanical components. Through the simulation analysis of the variable process of digital pump/motor, it is found that the discontinuous flow caused by displacement step changes is the fundamental cause of hydraulic impact. The data analysis results of experimental tests are in good agreement with the simulation analysis results. In view of hydraulic secondary components, a variable control method based on dual-mode operating characteristics is proposed. The TOPSIS algorithm is used to give comprehensive evaluation of the displacement control results after this method. The results show that the control quality of digital pump/motor after adopting the control method has been effectively improved, with an average improvement of about 40%.

This paper addresses a unified approach of the PID controller design for low as well as high order unstable processes with time delay. The design method is based on the direct synthesis (DS) approach to achieve the enhanced load disturbance rejection. To improve the servo response, a two-degree of freedom control scheme has been considered. A suitable guideline has been provided to select the desired reference model in the DS scheme. The direct synthesis controller has been approximated to the PID controller using the frequency response matching method. A consistently better performance has been obtained in comparison with the recently reported methods.

The annealing time is an important affecting factor in the performance of many furnaces. The present work deals with the transient simulation of annealing process in a cubic furnace in which a solid element is placed in its center. As the working gas can have some radiating features, a set of governing equations including the energy balance with the radiative transfer equation (RTE) for the gray radiating medium and the conduction equation inside the solid product are numerically solved with progressing in time. Numerical results which are validated against both analytical and theoretical findings in the literature demonstrate that during the starting period, a high rate of radiant energy transfers into the solid body even at small optical thickness. This behavior which hastens the rate of heat transfer at low values of the radiation conduction parameter, causes a fast annealing process in which the solid body warms up to its maximum temperature. Moreover, it is revealed that the rate of heat transfer is an increasing function of radiation-conduction parameter.

In order to improve the force tracking performance of hydraulic quadruped robots in uncertain and unstructured environments, an impedance-based adaptive reference trajectory generation scheme is used. Secondly, in order to improve the robustness to environmental changes and reduce the contact force errors caused by trajectory tracking errors, the backstepping sliding mode controller is combined with the adaptive reference trajectory generator. Finally, a virtual damping control based on velocity and pressure feedback is proposed to solve the problem of contact force disappearance and stall caused by sudden environmental change. The simulation results show that the proposed scheme has higher contact force tracking accuracy when the environment is unchanged; the contact force error can always be guaranteed within an acceptable range when the environment is reasonably changed; when the environment suddenly changes, the drive unit can move slowly until the robot re-contacts the environment.

To ensure the control of the precision of air-fuel ratio (AFR) of port fuel injection (PFI) spark ignition (SI) engines, a chaos radial basis function (RBF) neural network is used to predict the air intake flow of the engine. The data of air intake flow is proved to be multidimensionally nonlinear and chaotic. The RBF neural network is used to train the reconstructed phase space of the data. The chaos algorithm is employed to optimize the weights of output layer connection and the radial basis center of Gaussian function in hidden layer. The simulation results obtained from Matlab/Simulink illustrate that the model has higher accuracy compared to the conventional RBF model. The mean absolute error and the mean relative error of the chaos RBF model can reach 0.0017 and 0.48, respectively.

Conventional feature description methods have large errors in froth features due to the fact that the image during the zinc flotation process of froth flotation is dynamic, and the existing image features rarely have time series information. Based on the conventional froth size distribution characteristics, this paper proposes a size trend core feature (STCF) considering the froth size distribution, i.e., a feature centered on the time series of the froth size distribution. The core features of the trend are extracted, the inter-frame change factor and the inter-frame stability factor are given and two calculation methods of the feature factors are proposed. Meanwhile, the STCF feature algorithm was established based on the core features by adding the inter-frame change factor and the inter-frame stability factor. Finally, a flotation condition recognition model based on BP neural network was established. The experiments show that the recognition model has achieved excellent results, proving that the method proposed effectively overcomes the limitation of the lack of dynamic information in the existing traditional size distribution features and the introduction of the two factors can improve the classification accuracy to varying degrees.

We have developed a type of L-shaped single-component geophone array as a single station (L-array station) for surface microseismic monitoring. The L-array station consists of two orthogonal sensor arrays, each being a linear array of single-component sensors. L-array stations can be used to accurately estimate the polarization of first arrivals without amplitude picking. In a synthetic example, we first use segmentally iterative ray tracing (SIRT) method and forward model to calculate the travel time and polarization of first arrivals at a set of L-array stations. Then, for each L-array station, the relative delay times of first arrivals along sensor arrays are used to estimate the polarization vector. The small errors in estimated polarization vectors show the reliability and robustness of polarization estimation based on L-array stations. We then use reverse-time ray-tracing (RTRT) method to locate the source position based on estimated polarizations at a set of L-array stations. Very small errors in inverted source location and origin time indicate the great potential of L-array stations for source localization applications in surface microseismic monitoring.

To characterize and recognize the debris flow-related deposits, the physico-mechanical performance of four deposits from the Dongyuege (DYG), Shawa (SW), Jiangjia Gully (JJG), and Gengdi (GD) debris flows in southwest China is investigated through laboratory analyses and tests. The four debris-flow materials can all be remolded into coherent, homogeneous cylinders with high densification and strength–porosity of 25%–36%, mean pore-throat radius of 0.46–5.89 µm, median pore-throat radius of 0.43–4.28 µm, P-wave velocity of 800–1200 m/s, modulus of elasticity of 28–103 MPa, unconfined compressive strength (UCS) of 220–760 kPa, and cohesion of 65–281 kPa. Based on the comparison in slurryability and formability among debris-flow deposits, granular flow deposits, fluvial deposits, residual lateritic clay and loess, whether a sediment can be cast into competent cylinders for physico-mechanical tests can be regarded as a diagnostic evidence of old debris-flow deposits. The discrepancy in physico-mechanical properties among the four debris-flow deposits suggests that the combination of foregoing physico-mechanical parameters can characterize assembling characteristics of debris flow-related sediments including grain size distribution, mineralogy, and accidental detritus. Four deposited sediments above can be surprisingly classified as hard soil-soft rocks according to UCS, and the hard soil-soft rock behaviors can advance the further understanding of debris flows.

A prevalent kind of failure of rock slopes is toppling instability. In secondary toppling failures, these instabilities are stimulated through some external factors. A type of secondary toppling failure is “slide-toe-toppling failure”. In this instability, the upper and toe parts of the slope have the potential of sliding and toppling failures, respectively. This failure has been investigated by an analytical method and experimental tests. In the present study, at first, the literature review of toppling failure is presented. Then a simple theoretical solution is suggested for evaluating this failure. The recommended method is compared with the approach of AMINI et al through a typical example and three physical models. The results indicate that the proposed method is in good agreement with the results of AMINI et al’s approach and experimental models. Therefore, this suggested methodology can be applied to examining the stability of slide-toe-toppling failure.

A model of quantum thermoacoustic refrigeration micro-cycle (QTARMC) is established in which heat leakage is considered. A single particle contained in a one-dimensional harmonic potential well is studied, and the system consists of countless replicas. Each particle is confined in its own potential well, whose occupation probabilities can be expressed by the thermal equilibrium Gibbs distributions. Based on the Schrodinger equation, the expressions of coefficient of performance (COP) and cooling rate for the refrigerator are obtained. Effects of heat leakage on the optimal performance are discussed. The optimal performance region of the refrigeration cycle is obtained by the using of Q objective function. The results obtained can enrich the thermoacoustic theory and expand the application of quantum thermodynamics.

This paper proposes a novel collision post structure designed to improve the crashworthiness of subway cab cars. The structure provides two innovative features: 1) a simpler connection between the post and the car roof, which gives a more reasonable load transfer path to reduce the stress concentration at the joint; and 2) a stiffness induction design that provides an ideal deformation model to protect the safe space of the cab cars. The novel collision post structure was evaluated with finite element analysis, and a prototype cab car was mechanically tested. The results demonstrate that the deformation response was stable and agreed well with the expected ideal mode. The maximum load was 874.17 kN and the responses remained well above the elastic design load of 334 kN as required by the design specification. In addition, there was no significant tearing failure during the whole test process. Therefore, the novel collision post structure proposed has met the requirements specified in new standard to improve the crashworthiness of subway cab cars. Finally, the energy absorption efficiency and light weight design highlights were also summarized and discussed.

To research the influence of asymmetric brake shoe forces(ABSF) induced by braking failure on the dynamic performance of six-axle locomotive, the static equilibrium model of three-axle bogie and dynamic model for locomotive are established. The coupling vibration equations of axle hung motor and wheelset are derived. For the air braking, the influence mechanism of ABSF on the wheel-rail asymmetric motion and force characteristics are discussed. It can be found that if the ABSF is applied in the front wheelset, all the wheelsets move laterally in the same direction. Once the ABSF occurs in the middle or rear one, other wheelsets may move laterally towards the opposite direction. The motion amplitude and direction of all wheelsets strictly depend on the resultant moment of suspension yawing moment and brake shoe asymmetric moment. For the asymmetric braking, the free lateral gap of axle-box could increase the wheelset motion amplitude, but could not change the moving direction. In both the straight line and curve, the ABSF may lead to wheelset misaligning motion, intensify the wheel-rail lateral dynamic interaction and deteriorate wheel-rail contact state. Especially for the steering wheelsets, the asymmetric braking increases the wheelset attack angle significantly, which forms the worst braking condition.

This article has been retracted. Please see the retraction notice for more detail: https://doi.org/10.1007/s11771-018-3937-y