Abstract: Carbonitride precipitates have significant effects on the mechanical properties of steels via grain refinement and precipitation hardening. Based on the two-sublattice model (metal atom sublattice and interstitial atom sublattice) of regular solution, a t
Abstract: By using PFC2D technique, the falling and moving process of top-coal and rock, and the flowing characteristics of loose medium in the process of top-coal caving in steep thick seam were analyzed for the horizontal and inclining compound working face arrangement of a coal mine by different recovering distances. The recovery of top-coal and the force characteristics of the powered supports for the top-coal caving working face by different caving sequences were discussed. The results showed that, firstly, the recovery of top-coal was high and the force characteristic of the powered supports for top-coal caving was good by adopting the top-to-down caving sequence. Secondly, the falling and moving configuration of loose medium was deflected toward the mined direction. Thirdly, the characteristic of lost coal in the process of top-coal caving was present with a particular rhythm. At last, the optimal caving distance was 1.2 m in all the conditions.
Abstract: According to locational relations between a paleo-sinkhole and a working face or tunnel, the modes of paleo-sinkhole-caused water inrush (hereinafter referred to as water inrush from paleo-sinkholes) are divided into the mode of water inrush from roof/floor and the mode from rib as well as four sub-modes, including the thin plate sub-mode of water inrush, the shear failure sub-mode, the thick wall cylinder submode and the hydro-fracture sub-mode. The thin plate sub-mode is applicable to the circumstance where the key layer of cylinder cover is complete and has small thickness, and its criterion of water inrush is the limit bending moment. The shear failure sub-mode is applicable to the circumstance where the key layer of cylinder cover has big thickness, and its criterion of water inrush is a quadratic parabola equation. In the thick wall cylinder water inrush mode, the elastic limit pressures that may lead to failure of the thick wall cylinder are different as the different yield empirical rules, but all are in direct proportion with the strength of rock stratum. The hydro-fracture sub-mode of water inrush describes the type of water inrush that occurs due to the interconnection between underground water and other inherent structures through hydro-fracture when the paleo-sinkhole is far from the working face or tunnel. The critical hydro-fracture pressure may be calculated by reference to the formula used for calculating hydro-fracture. It is indicated by an actual example that the water inrush modes and their criteria are simple and feasible, conform to the realities and have sufficient accuracy.
Abstract: Carbonitride precipitates have significant effects on the mechanical properties of steels via grain refinement and precipitation hardening. Based on the two-sublattice model (metal atom sublattice and interstitial atom sublattice) of regular solution, a thermodynamic model for the precipitates of titanium carbonitride, aluminium nitride and manganese sulfide was established to study the starting-temperature of precipitates and the austenite composition at a given temperature in a low carbon steel and applied to compact strip production (CSP for short) process. The calculation results show that starting-temperature of the precipitation of Ti(CxN1-x), MnS and AIN are 1200℃, 1 440℃ and 1 010℃, their mole fraction are 2.315×10-5, 4.18×10-4 and 3.1×10-4, respectively. By comparison the simulation results of the model are in agreement with the calculated ones by the Thermo-Calc software and the available experimental data from some publications. The thermodynamic model can be a useful tool in studying the precipitates of low carbon steels and in analyzing the CSP process.
Abstract: The precipitation behaviors of carbonitrides in a V-Ti-N microalloyed steel for nonquenched/tempered seamless oil-well tubes were calculated by the equilibrium principle of a three-phase miscibility gap including the austenite and two carbonitrides. The thermodynamic calculations indicate that the precipitates formed first at 1 473℃ are TiN particles, subsequently some of them formed at high temperatures maintain the chemical properties down to low temperatures, the others gradually transform to complex (TixV1-x) (CyNl-y) carbonitrides. In addition, the precipitates formed at 846℃ are V-and C-rich V(CxN1-x) carbonitrides. The formation sequence is verified by experimental data. These results are more consistent with the viewpoint that, the precipitation behavior of vanadium in the austenite matrix below 800℃ in medium-carbon V-bearing microalloyed steels plays a great role in controlling the decomposition of austenite.
Abstract: The dynamic continuous cooling transformation (CCT) diagrams of a kind of V-alloyed high strength hull steel were determined by the use of a thermo-simulating machine after multi-pass deformation designed to simulate the industrial controlled rolling procedures for the production of plates at different temperatures. The effects of finish rolling temperature and cooling rate on the microstructure, γ/α transformation and CCT diagrams of the hull steel were investigated. The results show that the dynamic CCT diagrams shift to left and upper, and the region of cooling rate to obtain ferrite and pearlite is widened with decreasing finish rolling temperature. With the increase of cooling rate, the onset of γ transformation (Ar3) is lowered gradually, and the bainite start temperature Bs changes in a parabolic way. As the finish rolling temperature decreases or the cooling rate increases, the grains of ferrite are refined.
Abstract: The structure of sandwich panels bonded by brazing and transient liquid diffusion welding was analyzed from mechanical properties and vibration damping. Structure optimization of the sandwich panels was performed with the thicknesses of plate and honeycomb, and the length and thickness of honeycomb sides as the designed variables, and with shearing strength, bending strength, bending rigidity, critical bucking load, inherent frequency and mass as the objective functions. The optimized data were studied by test. Experimental results showed that the mechanical properties and vibration damping of the optimized sandwich panel were better than those of the compared sandwich panels, and the tested values were basic coincident with the calculated ones. This structure design can be used for vibration damping sandwich panels and commercial production.
Abstract: The self-passivating behavior of 316L stainless steel in acetic acid solution was studied. The constant current polarization curve and the corrosion potential-to-time curve were measured. The results showed that passivation film was formed by three layers:oxides of Fe and small amount Cr in the first layer; oxides of Cr and small amount Fe, Mo, Ni in the second layer; and oxides of Mo, Ni and small amount Fe in the third layer. The structure model of passivation film can explain the electrochemical results well.
Abstract: A nanocrystalline Al-Zn-Mg-Cu alloy was synthesized by mechanically milling at cryogenic temperature (cryomilling). The effect of cryomilling process on the microsturcture, phase transformation in solid, grain size and microstrain of this alloy was investigated by X-ray diffraction (XRD), optical microscopy (OM) and transmission electron microscopy (TEM). During the cryomilling, the second phase MgZn2 was gradually disappeared and ultimately super-saturated to α-A1. With increasing milling time, the grain size of the alloy decreased sharply. Howerver there were still a few coase grains in the core of powders after low-speed (200 r·min-1) cryomilling for 10 h. Contrastively, high speed (400 r·min-1) cryomilling could result in more uniform nanometer grains. According to the XRD results, the average grain size was 45 nm after low speed cryomilling for 6 h and kept stable until 10 h, but the average grain size reduced to 34 nm after farther high speed cryomilling for 5 h. The microstrain increased gradually to a maximum, and then fell off along the milling processing.
Abstract: A high performance sintered NdFeB magnet with N52 was prepared by strip casting, hydrogen decrepitation, jet milling, rubber isostatic pressing with impulse magnetic field and vibrating. The structure of the magnet was investigated by XRD, optical microscope, TEM and SEM, and its demagnetization curve was tested by magnetograph. The results show that the room-temperature magnetic properties of the Nd29.0Pr0.5Ga0.2Fe69.1Nb0.2B1.0 magnet can reach up to Br=1.457T,Hci=1097kÅm-1,(BH)max=409kJ·m-3, with a better homogeneity and consistency.
Abstract: The effects of sodium azide used as solid nitrogen source and ammonium halide used as active diluent on the combustion synthesis of Si3N4 powder were investigated through analyzing the combustion temperature profiles and the phase composition of the combustion products, The research results show that the endothermic decomposition of these two kinds of additives can increase the porosity of the reactants and thus improve the nitrogen permeability. The additives can also provide interior nitrogen source and act as catalysts of Si-N reaction that facilitates the combustion reaction of silicon in nitrogen atmosphere, The addition of sodium azide and ammonium halide can effectively lower the combustion temperature and maintain the combustion reaction at a relatively low temperature which is in favor of the formation of α-Si3N4. Appropriate addition of sodium azide and ammonium halide can promote the nitridation of silicon and increase the α-content in the combustion products.
Abstract: The distributed rules of some rolling factors such as tension and friction stress in the strip transect along the rolling direction as well as the relationships between these factors and strip thickness were discussed by discretization of the rolling deformation zone. The metal deformation resistance was calculated by a mathematic model with the ANN technique. An online calculation model of rolling force was setup for a tandem cold rolling mill. Experimental data of a huge industrial rolling mill showed that the errors of the predict model were less then 6.1%. It is concluded that this proposed model can meet the requirements of online control and improve the online calculated precision of rolling force.
Abstract: A high temperature superconducting quantum interference device (SQUID) was fabricated for magnetocardiogram (MCG) measurement, and a single-channel dc SQUID magnetocardiograph was developed, According to clinical diagnosis standard, by sequentially adjusting the non-magnetic patient table with 5 cm pitch in x and y directions the magnetic field signals perpendicular to the human chest on a rectangle grid of 5×5 over the chest area were recorded in a magnetically shielded room. The significant difference of magnetocardiogram between a healthy heart and the heart with right bundle branch block was observed. A large quantity of magnetocardiogram data for clinical diagnosis analysis were recorded with the system.
Abstract: A sintering predictive model of chemical composition based on many periods was developed by the BP neural network algorithm with appending momentum and adaptive variable step size linear reinforcement. Using knowledge base that was based on database technology and illation with forward inference, an expert system was designed for controlling sinter chemistry. Since the system was plunged into application, the hit ratio of the predictive model is over 90% steadily, and the acceptance of operation suggestion is 92%. The goal of controlling chemical composition steadily is actualized.
Abstract: Aiming at the coupling problem between dynamic and static magnetic torque and magnetic filed during normal vector control, this paper investigated the influence of the directional deviation of magnetic field on the performance of a normal vector control system. Adaptive inverse control was firstly used to solve this problem, and a novel control scheme was presented. The result of simulation and the theory analysis indicate that the proposed scheme can solve the influence of coupling between magnetic torque and magnetic filed in the system with normal vector control, and can effectively improve the dynamic and static performance.
Abstract: Based on the quadratic stability theory, the problem of robust H∞control for time-delay systems with time-varying uncertainties was dealt with by using the linear matrix inequality approach. A sufficient condition for the systems to be quadratically stable with an H∞-norm bound γ was presented for all admissible uncertainties. By solving a linear matrix inequality, the H∞ state feedback controller was obtained.
Abstract: Based on the method of statistics, this paper derived the output mean value and variance of conventional parallel interference cancellation (PIC), partial parallel interference cancellation (P-PIC) and minimum mean-squared error (MV-PIC) detectors for CDMA. The results indicated that the deviations of mean value and variance of the linear decision parameters were reduced by P-PIC compared with PIC. The output mean value was increased and the variance was decreased by choosing suitable partial interference cancellation coefficient for MV-PIC, and its performance of code error is superior to PIC.
Abstract: This paper designed an high-speed image sampling and processing system based on FPGA, whose image-sampling frequency was 13.5 MHz. In the system the video A/D chip SAA7111A was employed to convert video data into digital signal, and the digital signal was storied in RAM by FPGA for next processing to obtain the useful data. In addition, the EZUSB2131Q chip was used to transmit the processed data between PC and FPGA.
Abstract: Some key issues in ear recognition were investigated. Two ear extraction and normalization methods, the mark line (long axis of the outer ear contour) based method and the mark points (the start and end points of the outer ear contour) based method, were proposed for recognizing ear images in the USTB ear database. Based on the analysis of the recent advances in ear recognition methods, the kernel principal component analysis (KPCA) was applied for ear feature extraction, and the support vector machine (SVM) model was applied for ear recognition. The ear recognition rate on USTB ear database with pose variation and lighting variation was 98.7%. The experimental result indicates the effectiveness of this method and proves the feasibility of ear recognition to be used in the field of personal authentication.
Abstract: A distributed Web log mining system model (DWLMS) is presented. Based on the analysis on the procedure and algorithm of Web frequent access pattern mining, the more general incremental updating algorithms of local frequent paths (LFP) and global frequent paths (GFP) in a distributed database system based on DWLMS are proposed for discovering the frequent access paths. Some troubles produced by real time incremental distributed Web access information and more communication data are solved better by the algorithms. The method was realized simply and tested with real world Web log information in laboratory, and the results show that the algorithms are valid.
Abstract: This paper studied the problems of filling up incomplete data, reducing redundant attributes and discretizing continuous attributes in preprocessing the incomplete information table with continuous attributes in a rough set. According to the concept of interval value and the consistency of condition attributes and decision attributes, a plus rule for interval values was defined to filling up the incomplete data. Depending on the conception of classification, the discernible vector was defined and the discernible vector addition rule was used to delete redundant attributes. By use of the super-club data and entropy of the information table, the discretization of continuous attributes was implemented. The illustration and experimental results indicate that the method is effective.
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
