Abstract: Based on the particle flow theory and PFC3D code, a draw model with the meso-mechanical properties of ore granular media was constructed to study influencing factors on the flow characteristics of an isolated extraction zone in caving mining. Major factors that have significant influence on the flow characteristics of the isolated extraction zone and their sensibility and relationships with the flow characteristics were determined by statistical knowledge. Simultaneously, the suitability and reliability of the draw model based on PFC3D code and used in influencing factor research of the isolated extraction zone were validated by contrastive analysis between existing research conclusions and simulated results. The research results show that particle shape, friction coefficient, and drawpoint size are important parameters significantly influencing the flow characteristics of the caved ore and rock. In the initial stage of drawing, drawpoint size has the greatest influence on the form of the isolated extraction zone followed by friction coefficient and particle shape;in the following stage of drawing, particle shape has the greatest influence on the form of the isolated extraction zone followed by drawpoint size and friction coefficient. The drawing will be more difficult if the particle shape is more irregular, the inter-nal friction angle of particles is larger and the drawpoint size is smaller.
Abstract: Using model experiment, in the condition that the sliding force unchanged, the internal cohesive force and friction force of the slope were analyzed by the natural vibration frequency. The stabilization of landslides was decided by comparing the friction force with the maximum static friction force in the weak stable phase. Experimental results show that the friction force can effectively analyze the safety of landslides in the weak stable phase and that the natural vibration frequency is more sensitive than the displacement. By monitoring the natural vibration frequency, a quantitative assessment about the damage of landslides can be made, which provide the static friction force index, and the safety assessment of landslides after disturbances is achieved.
Abstract: The effects of vacuum processing time, nitrogen pressure and gas types on the total oxygen and micro non-metallic inclusions in molten steel were investigated to further improve the technology of micro non-metallic inclusion removal from molten steel with gas bubbles generated by the nitrogen absorbing and releasing method. It is found that in the vacuum treatment process, non-metallic inclusions can act as heterogeneous nucleation sites for the evolution of supersaturated nitrogen from molten steel to form bubbles on their surface, the total oxygen decreases, and these micro non-metallic inclusions are effectively removed by the nitrogen absorbing and releasing technology. The longer the vacuum processing time, the lower the content of total oxygen and amount of micro non-metallic inclusions in steel will be, and the removal rate of total oxygen reaches to 81.6% after the steel is vacuum treated 30 min, with the lowest total oxygen content about 7 ×10-6 in steel.
Abstract: Solidification of micro-alloyed steels under different cooling processes was simulated by confocal laser scanning micros-copy (CLSM), and the change of the sample surface was in-situ observed. The correlation between the change of the sample surface and the precipitation of secondary phases was discussed. It is found that some small reliefs appear on the sample surface during liquid steel solidification. The appearing temperature and the distribution of reliefs are consistent with the results of the theoretical calculation of secondary phase precipitation and the characterization of transmission electron microscopy (TEM). The precipitation of secondary phases can be indirectly characterized by in-situ observations of surface reliefs, which will be helpful to analyze the effect of secondary phases on the evolution of the matrix.
Abstract: A method combining microwave sulphation low-temperature roasting-water immersion and goethite processes was used to gain clean and valuable metals, such as Zn and Cu enriching to the leach liquor and Pb and Ag enriching to the leach residue. The process conditions to remove iron by using water immersion were optimized, and the iron removal effect was investigated when the pH value, the added amount of the leach liquor every time and the iron concentration in the leach liquor changed. X-ray diffraction and scanning electron microscopy were used to characterize the iron precipitates. It is found that with 200 mL of 0.01 mol·L-1 ZnSO4 solu-tion as a base solution, the iron removal rate can be reach to 99.3% and the residual iron concentration in the solution is about 0.065 g·L-1 under the optimum conditions that the dosage of the goethite crystal seed is 20 g·L-1, the pH value is 3, the temperature is 90℃ and 3 mL leach solution is added per 5 min (to keep the iron concentration in the solution 〈1 g·L-1). In the iron removal process, the loss rate of Zn is only 4.1%.
Abstract: To study the impact of austenitizing temperature and cooling rate on the spheroidizing annealing process of 40Cr steel, the spheroidizing annealing behavior and the mechanical properties of 40Cr steel were investigated by conventional intercritical annea-ling. It is found that with the austenitizing temperature between 760℃ and 800℃, the hardness varies as a "V" shape but the ce-mentite spheroidization rate changes as an inverted "V" shape with increasing cooling rate from 10℃·h-1 to 30℃·h-1. Higher sphe-roidization level and finer carbides, which are obtained at an austenitizing temperature of 760℃ and a cooling rate of 20℃·h-1, make the steel having a better cold formability. A divorced eutectoid transformation (DET) reaction mechanism of the spheroidizing annea-ling process was proposed, and the occurrence of the divorced eutectoid transformation reaction depends strongly on austenitizing tem-perature, cooling rate and holding time.
Abstract: Cup-drawing test was performed to study the effect of transverse pre-stretching, namely 3%, 6%, 9% and 12% deformation, on the surface ridging resistance during deep drawing of a 17% Cr ultra-purified ferritic stainless steel cold-rolled annealed sheet. The evolution of textures and grain clusters in the tested sheet after transverse pre-stretching was analyzed by electron back-scatter diffraction and X-ray diffraction. It is found that the ridging resistance apparently improves after the 9% transverse pre-stretching. Because the content of {001} 〈uvw〉 orientation grains is not enough to meet the requirement of the Chao ridging model, this model is not suitable for ridging of the tested sheet. However, the Takechi model, which is called an out-of-plane shearing strain model, is considered to be suitable for ridging of the tested sheet. It is concluded that the narrow of the width of γ-fiber texture clusters and the deflection of grain clusters to the rolling direction are the major causes of improving the ridging resistance.
Abstract: The effect of four alloying elements, N, Cr, Mo and Ni, on the grain size, mechanical properties and pitting corrosion resistance of 316LN austenitic stainless steel for primary coolant pipes in nuclear power plants were investigated. When the nitrogen concentration increases in the stainless steel, the grain size and growth trend dramatically decrease. Increasing the nitrogen concentra-tion can improve the mechanical properties and particularly, the pitting corrosion resistance goes up before the nitrogen concentration reaches 0.20%. Grain refinement achieved by the addition of nitrogen is propitious to the mechanical properties of the stainless steel, but this is not the main mechanism for the increase in mechanical properties. Cr and Ni elements have no obvious impact on the grain size and mechanical properties, but Cr can improve the pitting corrosion resistance slightly while the passive film loses its stability as the Ni concentration increases. When the Mo concentration increases, the strength and pitting corrosion resistance increase, but the grain size and elongation decrease.
Abstract: The pitting corrosion of 304 L austenitic stainless steel joints with 308 L austenitic stainless steel as welding sticks was investigated in simulated concrete pore solutions with different chloride ion concentrations by potentiodynamic polarization curves, electrochemical impedance spectroscopy and Mott-Schottky curves. It is found that chloride ions play an important role in the corrosion behavior of the joints. When the chloride ion concentration increases, the corrosion potential, breakdown potential and charge transfer resistance of the joints at three different weld zones, i. e., base metal (BM), weld metal (WM) and heat affected zone (HAZ), in the simulated solutions decrease, but the charge carrier density and the number of pitting sites in the joints increase. In the same simu-lated solution, the weld metal shows a better corrosion resistance, followed by the heat affected zone, and the base metal has the lowest corrosion resistance due to its much lower charge transfer resistance and higher doping content.
Abstract: Four accelerated weathering tests were carried out on polyurethane coated steels. The apparent properties and electro-chemical characteristics of the coatings were studied to compare the effects of different accelerated weathering tests on the coating fail-ure behavior. It is found that UV exerts the greatest influence on the glossiness of the coatings and the gloss loss reaches up to 85.7% after 32 d aging. The linear polarization resistance decreases rapidly in the early period of the salt spray test and stabilizes in the later period due to the formation of a salt film. In the mixed aging (xenon light aging+salt spray) test, the variation tendency of both gloss loss and linear polarization resistance are similar to those presented in the early period of xenon light aging and similar to those presen-ted in the later period of salt spray test. Moreover, the equivalent circuit of the mixed aging test shows two time constants in the early period, which is consistent with the single xenon light aging test. In the later period, the failure process of the coatings can be mani-fested with three time constants, in which the formation of a salt film is the typical feature.
Abstract: For the case of constant stress wave input in analyzing a hydraulic rock drill, the value of stress waves which arrived the damping piston was calculated after many transmissions and reflections. Based on the transfer principle of stress waves in different media, a variable input model was deduced by the Fourier transform. The stress wave forms were tested by using a strain gauge and the variable input model was revised according to the test results. An equivalent rigid-flexible model of the accumulator and a structure model of the double damping system were established based on Newton's theory. The damping piston movement laws and the pressure change laws of order 1 and order 2 damping chambers were analyzed. The performance parameters of the double damping system were summarized and optimized by a multi-objective optimization method. The optimized results show that the flow of the damping system is 8.5 L·min-1, the annular clearance is 0.017 mm, the inflation pressure of the accumulator is 2.3 MPa and the working pressure is 7.6 MPa.
Abstract: To obtain characteristic pressure signals in the cavity of a self-resonating water jet nozzle, a detection system was built by using micro high-responsive pressure sensors. The characteristics of self-resonating water jet were studied and the nozzle's structure was designed. The sensors' layout was determined based on computational fluid dynamics (CFD) simulation results, and the respon-sive frequency of the sensors was determined according to theoretical calculations of the nozzle's self-excited oscillation frequency. The Hilbert-Huang transform was used due to the nonstationarity of pressure signals in the cavity. It is found that the pressure oscillation signals are focused on the frequency band of 40-60 Hz, 110-150 Hz and 200-310 Hz, and each frequency has different fluctuation am-plitudes. Pressure signals near the water outlet reach larger amplitudes with narrow bandwidth.
Abstract: A 2D axisymmetric mathematical model was developed for an O2 generator and the protective performance of the O2 generator was simulated. The model's rationality was verified by experiments under typical operational conditions. Then, the influ-ences of labor intensity, inlet CO2 volume faction, equivalent diameter of oxygen-generating particles, and pipe diameter at the entrance on the protective performance of the O2 generator were studied by the model. The simulated results show that both labor inten-sity and inlet CO2 volume faction have significant effect on the protective performance of the O2 generator. A higher labor intensity and a higher inlet CO2 volume faction share the same trend, which means a much shorter protective time and a much higher outlet peak temperature. The protective time decreases with increasing equivalent diameter of oxygen-generating particles, exhibiting an approxi-mately negative liner relationship. The protective time for 12 mm particles is 32.15 min shorter than that for 6 mm particles. However, larger particles will lead to a lower outlet peak temperature. Different from the front three factors, pipe diameter at the entrance has limited effect on both the protective time and outlet temperature.
Abstract: Catalytic cracking experiments were carried out on biomass tar in a fixed-bed reactor to study the influence of reaction temperature and catalyst type on the cracking reaction product, secondary tar. The experimental results show that there is an aromatic trend in the secondary tar components, and the types and content of polycyclic aromatic hydrocarbons (PAHs) both increase with the increase of reaction temperature when using the high-alumina brick as an acid catalyst. The rise of reaction temperature can not only improve the deep conversion of biomass tar and reduce the production rate of secondary tar, but also increase the aromatization degree of secondary tar, which is more likely to cause the catalyst deactivation with carbon deposition. When the reaction temperature is 900℃, the secondary tar components are similar with alkaline catalysts (dolomite or limestone), and their types reduce to about 10, which mainly include complex macromolecular hydrocarbon. However, the secondary tar components are still very complex with the high-alumina brick as an acid catalyst, and their types are nearly 30, including not only macromolecular hydrocarbon but also paraffin hydrocarbon and polycyclic aromatic hydrocarbons, in 2-ring, 3-ring and 4-ring.
Abstract: Convolutional neural networks (CNNs), which show success in achieving translation invariance for many image processing tasks, were investigated for continuous speech recognition. Compared to deep neural networks (DNNs), which are proven to be successful in many speech recognition tasks nowadays, CNNs can reduce the neural network model sizes significantly, and at the same time achieve even a better recognition accuracy. Experiments on standard speech corpus TIMIT and conversational speech corpus show that CNNs outperform DNNs in terms of the accuracy and the generalization ability.
Abstract: A new two-step noise variance estimation algorithm was proposed based on image segmentation. In the first step, a noisy image was smoothed and was segmented by the statistical region merge (SRM) algorithm, then the variance of each region was computed, and some regions were selected based on the statistical rule to estimate the noise variance. In the second step, the parame-ters of filtering, segmentation and estimation were revised according to the estimated noise variance, and a new cycle of image filte-ring, segmentation and estimation was performed to obtain more accurate estimation. Experimental results on large numbers of images and various noises show that the proposed algorithm can estimate the noise variance quickly and accurately.
Abstract: Due to biological characteristic similarity in image acquisition and physiological complementarity of the face and the ear, a face and ear multimodal fusion template protection method was proposed, in which the face and the ear were combined in the feature level and then a fuzzy vault was utilized to protect the fusion feature template. The basic flow of the scheme was divided into 5 parts:image preprocessing, Gabor-PCA feature extraction, feature fusion, fusion template encryption, and fusion template decryp-tion. On the multimodal image dataset consisted of the ORL face dataset and the USTB ear dataset 3, authentication experimental re-sults show the effectiveness of the proposed fusion template protection method. Also the fusion template protection method outperforms the unimodal template protection method on both genuine accept rate and false accept rate.
Abstract: A finite element model was built for a curve bridge with an unseating-prevention device. The collision effect of the curved bridge under rare earthquake was studied and the dynamic response mechanism was discussed based on this finite element mod-el. The influence of expansion joint setting on the dynamic characteristics of the curved bridge was analyzed. It is found that the spec-tral characteristics of seismic waves have significant effect on the collision effect, and the collision frequency between the adjacent frames increases under far field earthquake, while the collision force decreases. When the expansion joint increases, the effect on the axial force of the unseating-prevention device weakens, the collision force increases, but the collision times are basically unchanged. The expansion joint significantly affects the plastic development of the pier bottom. The curvature ductility demand reduces with decreasing expansion joint, and more than 62.5% drops compared that without the expansion joint.
Abstract: The effects of desulfurization ash and ferric chloride as conditioners on the sludge dewatering performance were investi-gated with the capillary suction time and the water content of the sludge cake as evaluating indicators. Extracellular polymeric substance measurements and Fourier transform infrared spectroscopy were used to analyze the sludge dewatering mechanism. The results show that a significantly better treatment effect can be obtained with desulfurization ash and ferric chloride together than just one conditioner. In the treatment process, a large amount of the tightly bound extracellular polymeric substance is spalled by desulfuriza-tion ash and ferric chloride, in which a part turns into a loosely bound extracellular polymeric substance and a slime extracellular polymeric substance, and the other part is removed by ferric hydroxide, which effectively decreases the water content of the sludge cake and the capillary suction time. Pearson correlation analysis results indicate that the tightly bound extracellular polymeric substance has significant correlation with the capillary suction time and the water content of the sludge cake, so it is an important factor affecting the sludge dewatering performance. Infrared spectrum analysis of the sludge filtrate reveals that hydrolysis happens when the extracellular polymeric substance enters into the sludge supernatant, and the contents of amino acid, aliphatic acid and other small molecule organic matter increase. When the dosages of desulfurization ash and ferric chloride are 300 mg·g-1 and 60 mg·g-1, respec-tively, the capillary sop time and the water content of the sludge cake decrease to the lowest. Their minimum values are 14.3 s and 70.22%, falling by 98.48% and 16.10%, respectively.
Abstract: Taking a commercial vehicle as the study example, the preference price of reversal threshold, the preference reversal threshold as well as the mean value and standard deviation of the preference reversal Weber number were measured through question-naire survey. The price preference reversal phenomenon was analyzed during the rising and falling process of this commercial vehicle's price. The asymmetry of price preference reversal was also studied. It is found that the adjustment of product price should be controlled within the preference reversal threshold. Differences are made between price rising and falling during the process of price adjustment. The adjustment strategy is taken into careful consideration.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
