The sharp increase of the amount of Internet Chinese text data has significantly prolonged the processing time of classification on these data. In order to solve this problem, this paper proposes and implements a parallel naive Bayes algorithm (PNBA) for Chinese text classification based on Spark, a parallel memory computing platform for big data. This algorithm has implemented parallel operation throughout the entire training and prediction process of naive Bayes classifier mainly by adopting the programming model of resilient distributed datasets (RDD). For comparison, a PNBA based on Hadoop is also implemented. The test results show that in the same computing environment and for the same text sets, the Spark PNBA is obviously superior to the Hadoop PNBA in terms of key indicators such as speedup ratio and scalability. Therefore, Spark-based parallel algorithms can better meet the requirement of large-scale Chinese text data mining.
As a widely distributed geological and engineering material, the soil-rock mixture always undergoes frequentative and short-term freeze-thaw cycles in some regions. Its internal structure is destroyed seriously, but the damage mechanism is not clear. Based on the damage factor, the damage research of properties of soil-rock mixture after different times of freeze-thaw cycles is investigated. Firstly, the size-distributed subgrade gravelly soil samples are prepared and undergo different times of freeze-thaw cycles periodically (0, 3, 6, 10), and indoor large-scale triaxial tests are completed. Secondly, the degradation degree of elastic modulus is considered as a damage factor, and applied to macro damage analysis of soil-rock mixture. Finally, the mesoscopic simulation of the experiments is achieved by PFC3D, and the influence on strength between soil-rock particles caused by freeze-thaw cycles is analyzed. The results show that freeze-thaw cycles cause internal damage of samples by weakening the strength between mesoscopic soil-rock particles, and ultimately affect the macro properties. After freeze-thaw cycles, on the macro-scale, elastic modulus and shear strength of soil-rock mixture both decrease, and the decreasing degree is related to the times of cycles with the mathmatical quadratic form; on the meso-scale, freeze-thaw cycles mainly cause the degradation of the strength between soil-rock particles whose properties are different significantly.
In this study, the effect of welding parameters on the microstructure and mechanical properties of the dissimilar resistance spot welded DP1000–QP1180 joints was investigated. Heat affected zone (HAZ) width of QP1180 side was smaller than that of DP1000 side. HAZ width and indentation depth increased with increasing welding current and welding time. The nugget size increased with increasing welding current whereas it increased at lower currents and decreased at higher currents with increasing welding time. The lowest hardness was on the DP1000 side. On the QP1180 side, the center of HAZ had the peak hardness. With increasing welding current, hardness values throughout the weld zone decreased and the tensile shear load increased. At lower welding currents, the welding time did not affect the tensile shear load. Tensile elongation decreased with the increase of welding time, whereas there is no relationship between the welding current and elongation. The spot-welded joints having higher strength exhibited a more ductile fracture characteristic.
As a production quality index of hematite grinding process, particle size (PS) is hard to be measured in real time. To achieve the PS estimation, this paper proposes a novel data driven model of PS using stochastic configuration network (SCN) with robust technique, namely, robust SCN (RSCN). Firstly, this paper proves the universal approximation property of RSCN with weighted least squares technique. Secondly, three robust algorithms are presented by employing M-estimation with Huber loss function, M-estimation with interquartile range (IQR) and nonparametric kernel density estimation (NKDE) function respectively to set the penalty weight. Comparison experiments are first carried out based on the UCI standard data sets to verify the effectiveness of these methods, and then the data-driven PS model based on the robust algorithms are established and verified. Experimental results show that the RSCN has an excellent performance for the PS estimation.
The goethite iron precipitation process consists of several continuous reactors and involves a series of complex chemical reactions, such as oxidation reaction, hydrolysis reaction and neutralization reaction. It is hard to accurately establish a mathematical model of the process featured by strong nonlinearity, uncertainty and time-delay. A modeling method based on time-delay fuzzy gray cognitive network (T-FGCN) for the goethite iron precipitation process was proposed in this paper. On the basis of the process mechanism, experts’ practical experience and historical data, the T-FGCN model of the goethite iron precipitation system was established and the weights were studied by using the nonlinear hebbian learning (NHL) algorithm with terminal constraints. By analyzing the system in uncertain environment of varying degrees, in the environment of high uncertainty, the T-FGCN can accurately simulate industrial systems with large time-delay and uncertainty and the simulated system can converge to steady state with zero gray scale or a small one.
Magnetic seeding agglomeration (MSA), i.e., adding magnetic seeds and a low intensity pre-magnetization for fine agglomeration, was applied to the flotation of coal, pyrite and hematite ore slimes. Size analysis and flotation tests highlight that the MSA improved flotation recovery and kinetics of pyrite ore while causing some loss in selectivity, and in the presences of the polyacrylamide for coal and starch for hematite the agglomeration flotation was further strengthened due to the synergetic effect between the flocculants and magnetic seeds. Magnetism analyses and calculation confirmed the adsorption of magnetic seeds onto minerals, resulting in a decreased threshold magnetic field intensity for the MSA to happen. Then atomic force microscope (AFM) study found that there exists a long range force between magnetic seeds and minerals, which facilitates the adsorption of magnetic seeds on minerals. FTIR shows both the polyacrylamide and starch adsorbed onto minerals and magnetic seeds, thus acting as the bridging media between minerals and magnetic seeds, intensifying the agglomeration in flotation. Surface characterization of the MSA was understood by SEM imaging, and models of the MSA were proposed.
A series of wear and flame resistant polyamide 6 (PA6) composites were prepared using glass fiber (GF) and talc (T) as reinforcer, polytetrafluoroethylene (PTFE) and graphite (Gr) as solid lubricants, red phosphorus (RP) and zinc borate (ZB) as flame retardant. The tribological property, mechanical property, flame retardant property and the flame retardant mechanism were investigated. The tests show that the formula of the wear resistant PA6 composite (WRPA 6) is PA6/GF/T/PTFE/Gr in the ratio of 100/15/5/10/5 by mass. Because this composite exhibits the lowest friction coefficient (0.1429) and no wear mass loss, the introduction of RP and ZB can increase the flame resistance of WRPA6, and the synergistic effect of RP and ZB is obtained. Detailedly, the composite with 4 parts of ZB and 12 parts of RP shows the best flame retardant property, achieving the highest limiting oxygen index (LOI) (30.2 vol%) and a UL94 V-0 rating, and the flame retardant mechanisms may be gas phase along with condense phase mechanism.
The objective of this research is to realize a composite nonlinear feedback control approach for a class of linear and nonlinear systems with parallel-distributed compensation along with sliding mode control technique. The proposed composite nonlinear feedback control approach consists of two parts. In a word, the first part provides the stability of the closed-loop system and the fast convergence response, as long as the second one improves transient response. In this research, the genetic algorithm in line with the fuzzy logic is designed to calculate constant controller coefficients and optimize the control effort. The effectiveness of the proposed design is demonstrated by servo position control system and inverted pendulum system with DC motor simulation results.
Traditional hand rehabilitation gloves usually use electrical motor as actuator with disadvantages of heaviness, bulkiness and less compliance. Recently, the soft pneumatic actuator is demonstrated to be more suitable for hand rehabilitation compared to motor because of its inherent compliance, flexibility and safety. In order to design a wearable glove in request of hand rehabilitation, a soft hoop-reinforced pneumatic actuator is presented. By analyzing the influence of its section shape and geometrical parameters on bending performance, the preferred structure of actuator is achieved based on finite element method. An improved hoop-reinforced actuator is designed after the fabrication and initial measurement, and its mathematical model is built in order to quickly obtain the bending angle response when pressurized. A series of experiment about bending performance are implemented to validate the agreement between the finite element, mathematical and experimental results, and the performance improvement of hoop-reinforced actuator. In addition, the designed hand rehabilitation glove is tested by measuring its output force and actual wearing experience. The output force can reach 2.5 to 3 N when the pressure is 200 kPa. The research results indicate that the designed glove with hoop-reinforced actuator can meet the requirements of hand rehabilitation and has prospective application in hand rehabilitation.
In order to overcome the phenomenon of image blur and edge loss in the process of collecting and transmitting medical image, a denoising method of medical image based on discrete wavelet transform (DWT) and modified median filter for medical image coupling denoising is proposed. The method is composed of four modules: image acquisition, image storage, image processing and image reconstruction. Image acquisition gets the medical image that contains Gaussian noise and impulse noise. Image storage includes the preservation of data and parameters of the original image and processed image. In the third module, the medical image is decomposed as four sub bands (LL, HL, LH, HH) by wavelet decomposition, where LL is low frequency, LH, HL, HH are respective for horizontal, vertical and in the diagonal line high frequency component. Using improved wavelet threshold to process high frequency coefficients and retain low frequency coefficients, the modified median filtering is performed on three high frequency sub bands after wavelet threshold processing. The last module is image reconstruction,which means getting the image after denoising by wavelet reconstruction. The advantage of this method is combining the advantages of median filter and wavelet to make the denoising effect better, not a simple combination of the two previous methods. With DWT and improved median filter coefficients coupling denoising, it is highly practical for high-precision medical images containing complex noises. The experimental results of proposed algorithm are compared with the results of median filter, wavelet transform, contourlet and DT-CWT, etc. According to visual evaluation index PSNR and SNR and Canny edge detection, in low noise images, PSNR and SNR increase by 10%–15%; in high noise images, PSNR and SNR increase by 2%–6%. The experimental results of the proposed algorithm achieved better acceptable results compared with other methods, which provides an important method for the diagnosis of medical condition.
The effects of basicity and temperature on the reduction process of Hongge high-chromium vanadium-titanium magnetite (HCVTM) sinter were investigated in this work. The main characterization methods of X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and metallographic microscope were employed in this study. In this work, the reduction of HCVTM sinter with different temperature and basicity were experimented. The Fe, FeO, and TiO in reductive samples increase with increasing basicity and temperatures. The increase of basicity and temperature is favorable to the reduction of HCVTM sinter. The Fe phase has out-migration tendency to the surface of sinter while the perovskite and silicate phases have in-migration tendency to the inside of sinter. The reduction degradation index (RDI) decreases while the reduction index (RI) increases with increasing basicity. The RI increases from 67.14% to 82.09% with increasing temperature from 1073 K to 1373 K.
Pesticide contamination causes precarious implications on human health and environment. Thus the investigation of its sorption phenomenon is highly imperative. Endosulfan insecticide was examined for its adsorption behavior on ten assorted soils through batch equilibrium method. Adsorption coefficient values (Kd) ranged from 1.4 μg/mL to 18 μg/mL. The highest Kd value was obtained for Peshawar soil owing to the presence of highest amount of organic matter (1.4%). Negative values of Gibbs free energy displayed a low interaction between soil and pesticide, exhibiting that the reaction was physiosorption and exothermic in nature. Statistical analysis showed a negative correlation of soil pH and Kd (R2=–0.77 and p=0.03) and a positive correlation with organic matter (R2=0.96). Activated carbon prepared from Saccharum officinarum bagasse removed significant amount pesticide. The maximum removal observed was 93% and 97% in 5×10–6 and 7.5×10–6, respectively. Activated carbon prepared from biomass for removal purposes was proved to be highly efficient and cost effective.
As semiconductor technologies have been shrinking, the speed of circuits, integration density, and the number of I/O interfaces have been significantly increasing. As a consequence, electromagnetic emanation (EME) becomes a critical issue in digital system designs. Electronic devices must meet electromagnetic compatibility (EMC) requirements to ensure that they operate properly, and safely without interference. I/O buffers consume high currents when they operate. The bonding wires, and lead frames are long enough to play as efficient antennas to radiate electromagnetic interference (EMI). Therefore, I/O switching activities significantly contribute to the EMI. In this paper, we evaluate and analyze the impact of I/O switching activities on the EME. We will change the circuit configurations such as the supply voltage for I/O banks, their switching frequency, driving current, and slew rate. Additionally, a trade-off between the switching frequencies and the number of simultaneous switching outputs (SSOs) is also considered in terms of EME. Moreover, we evaluate the electromagnetic emissions that are associated with the different I/O switching patterns. The results show that the electromagnetic emissions associated I/O switching activities depend strongly on their operating parameters and configurations. All the circuit implementations and measurements are carried out on a Xilinx Spartan-3 FPGA.
Aiming at determining the thermal contact resistance of ball screws, a new analytical method combining the minimum excess principle with the MB fractal theory is proposed to estimate thermal contact resistance of ball screws considering microscopic fractal characteristics of contact surfaces. The minimum excess principle is employed for normal stress analysis. Moreover, the MB fractal theory is adopted for thermal contact resistance. The effectiveness of the proposed method is validated by self-designed experiment. The comparison between theoretical and experimental results demonstrates that thermal contact resistance of ball screws can be obtained by the proposed method. On this basis, effects of fractal parameters on thermal contact resistance of ball screws are discussed. Moreover, effects of the axial load on thermal contact resistance of ball screws are also analyzed. The conclusion can be drawn that the thermal contact resistance decreases along with the fractal dimension D increase and it increases along with the scale parameter G increase, and thermal contact resistance of ball screws is retained almost constant along with axial load increase before the preload of the right nut turns into zero in value. The application of the proposed method is also conducted and validated by the temperature measurement on a self-designed test bed.
High-level expression of β-mannanase has been reported in Pichia pastoris under control of the GAP promoter. Two factors that strongly influence protein production and fermentation process development in Pichia pastoris protein expression system are gene dosage and cultivation temperature. The aim of this research was to improve the expression level of β-mannanase in Pichia pastoris by proper increasing the gene dosage and decreasing the culture temperature. To this end, a panel of strains harboring different copy numbers of β-mannanase gene were obtained by multiple zeocin concentration gradients screening, the influence of gene copy number on the expression of β-mannanase in Pichia pastoris X33 was investigated. With the constitutive GAP promoter, the four copies strain exhibited a 4.04-fold higher β-mannanase yield and a 1.83-fold higher total secretion proteins than the one copy strain, but an increase of the copy number above four resulted in a decrease of expression. Furthermore, the effects of culture temperature were studied in flask. The decreased culture temperature of four copies strain resulted in a 1.8-fold (26 °C) and 3.5-fold (22 °C) higher β-mannanase activity compared to that at 30 °C. A fed-batch strategy was successfully used for high cell-density fermentation and β-mannanase activity reached 2124 U/mL after cultivation for 72 h in a 5 L fermenter.
Textile reinforced concrete (TRC) has good bearing capacity, crack resistance and corrosion resistance and it is suitable for repairing and reinforcing concrete structures in harsh marine environments. The four-point bending method was used to analyze the influence of the salt concentration, the damage degree and the coupled effect of the environment and load on the bending performance of TRC-strengthened beams with a secondary load. The results showed that as the salt concentration increased, the crack width and mid-span deflection of the beam quickly increased, and its bearing capacity decreased. As the damage degree increased, the early-stage crack development and mid-span deflection of the beam were less affected and the ultimate bearing capacity significantly decreased. In addition, the coupled effect of the environment and load on the beams with a secondary load was significant. As the sustained load increased, the ultimate bearing capacity of the strengthened beam decreased, and cracks developed faster in the later stage. In addition, the mid-span deflection of the beam decreased at the same load level because of the influence of the initial deflection due to the sustained load corrosion.
We report herein a highly selective method for directly determining the trace Co2+ in highly concentrated zinc electrolyte. This novel method is based on a second derivative wave of catalytic adsorptive polarography generated by complexing Co2+ with dimethylglyoxime and nitrite onto a dropping mercury electrode. By employing a medium with NH3-NH4Cl buffer, DMG and NaNO2 during determining the trace Co2+, any interferences of highly concentrated Zn2+ and other coexisting metal ions in the electrolyte are completely eliminated due to the selective masking effect of EDTA. When the concentration of Co2+ is within 1.0×10–10–3.2×10–7 mol/L range, it shows a good linear relationship with the current peak. Detection limit is 1.0×10–11 mol/L, and RSD ≤2.7% for six successive assays. We have compared the efficiency of the current method to that obtained by cobalt nitroso-R-salt spectrophotometry, and the absolute values of relative deviations are ≤4.2%. The method developed and described herein has been successfully employed in determining the trace Co2+ in actual zinc electrolyte.
The bottleneck of strontium compounds preparing from celestite is the promotion of Sr/S isolation efficiency. Low energy consumption and zero release method for isolating Sr/S in preparing Sr(OH)2 process from celestite in mild condition was described. Sr element remained in precipitation with formation of Sr(OH)2, while S element entered into leachate with formation of Na2SO4. The effects of initial concentration of NaOH, conversion temperature, liquid-to-solid (L/S) ratio and conversion time on Sr/S ratio of samples for celestite conversion were systematically investigated by experiments. The results demonstrated that the efficiency of Sr/S isolation increased with the initial concentration of NaOH, L/S ratio and conversion time, and decreased with conversion temperature. The maximum conversion ratio of Sr(OH)2 was 93.88% under the optimum condition, whose Sr/S ratio of sample could reach to 41.16. It illustrated that better isolation efficiency of celestite could be achieved in alkaline treatment. The results of SEM-EDS analyses demonstrated that the conversion reaction was a dissolution-precipitation process.
To improve the safety of trains running in an undesirable wind environment, a novel louver-type wind barrier is proposed and further studied in this research using a scaled wind tunnel simulation with 1:40 scale models. Based on the aerodynamic performance of the train-bridge system, the parameters of the louver-type wind barrier are optimized. Compared to the case without a wind barrier, it is apparent that the wind barrier improves the running safety of trains, since the maximum reduction of the moment coefficient of the train reaches 58% using the louver-type wind barrier, larger than that achieved with conventional wind barriers (fence-type and grid-type). A louver-type wind barrier has more blade layers, and the rotation angle of the adjustable blade of the louver-type wind barrier is 90–180° (which induces the flow towards the deck surface), which is more favorable for the aerodynamic performance of the train. Comparing the 60°, 90° and 120° wind fairings of the louver-type wind barrier blade, the blunt fairing is disadvantageous to the operational safety of the train.
Given the extensive utilization of cantilever retaining walls in construction and development projects, their optimal design and analysis with proper attention to seismic loads is a typical engineering problem. This research presents a new algorithm for pseudo-static analysis of retaining walls employing upper bound method. The algorithm can be utilized to design and check the external and internal stability of the wall based on the proposed mechanism. One of the main features of this algorithm is its ability to determine the critical condition of failure wedges, the minimum safety factor and maximum force acting on the wall, as well as the minimum weight of the wall, simultaneously, by effectively using the multi-objective optimization. The results obtained by the proposed failure mechanisms show that, while using the upper bound limit analysis approach, the active force should be maximized concurrent with optimizing the direction of the plane passing through the back of the heel. The present study also applies the proposed algorithm to determine the critical direction of the earthquake acceleration coefficient. The critical direction of earthquake acceleration coefficient is defined as the direction that maximizes the active force exerted on the wall and minimizes the safety factor for wall stability. The results obtained in this study are in good agreement with those of similar studies carried out based on the limit equilibrium method and finite element analysis. The critical failure mechanisms were determined via optimization with genetic algorithm.
Hydroplaning speed can be affected by pavement texture depth, thickness of water film, tire pressure and tread depth. In this study, to understand the influence of pavement texture on the hydroplaning speed, a new lab-scale apparatus has been designed and manufactured. The lack of proportion between linear movement of vehicle shaft and the wheel rotation was found to be a good index to determine hydroplaning threshold. A 5% drop in the ratio of wheel-to-axle rotation has been assumed as an index to determine hydroplaning threshold. Based on the measures, a simplified model was developed that is able to predict the hydroplaning speed depending on pavement’s texture characteristics. The results indicated that a 77% increase in mean texture depth cause 9% increase in hydroplaning threshold speed.