中南大学学报·社会科学版杂志 CSSCI南大期刊 北大期刊

中南大学学报·社会科学版 2016年第11期杂志 文档列表

中南大学学报·社会科学版杂志Materials,Metallurgy,Chemical and Environmental Engineering

Enhanced dielectric permittivity of graphite oxide/polyimide composite films2747-2753

摘要：Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 10~2 Hz and was 26 times that of the pure PI.

Effect of melt spinning on gaseous hydrogen storage characteristics of nanocrystalline and amorphous Nd-added Mg2Ni-type alloys2754-2762

摘要：Nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg24Ni10Cu2)100-xNdx（x=0, 5, 10, 15, 20） were prepared by melt spinning technology and their structures as well as gaseous hydrogen storage characteristics were investigated. The XRD, TEM and SEM linked with EDS detections reveal that the as-spun Nd-free alloy holds an entire nanocrystalline structure but a nanocrystalline and amorphous structure for the as-spun Nd-added alloy, implying that the addition of Nd facilitates the glass forming in the Mg2Ni-type alloy. Furthermore, the degree of amorphization of the as-spun Nd-added alloy and thermal stability of the amorphous structure clearly increase with the spinning rate rising. The melt spinning ameliorates the hydriding and dehydriding kinetics of the alloys dramatically. Specially, the rising of the spinning rate from 0（the as-cast was defined as the spinning rate of 0 m/s） to 40 m/s brings on the hydrogen absorption saturation ratio（R5a）（a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity） increasing from 36.9% to 91.5% and the hydrogen desorption ratio(R1 0d)（a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity） rising from 16.4% to 47.7% for the（x=10） alloy, respectively.

Microstructure and properties of low-temperature aged Dy-doped Nd-Fe-B magnet2763-2770

摘要：In this work, a low temperature ageing process for the high coercivity Dy-doped Nd-Fe-B magnets was developed by the optimizing ageing process. The experimental results show that there is no difference in microstructures, crystal orientation, magnetic and mechanical properties between the low-temperature aged and the two-stage aged sintered Dy-doped Nd-Fe-B magnets. Because of the uneven stress distribution in the sintered Dy-doped Nd-Fe-B magnet and the high activation of Dy element, Dy atoms could diffuse into the main crystal phase and the grain boundary phases of the magnets during low-temperature ageing process, which results in the reasonable distribution of Dy element and formation of the thin and uniform grain boundary phases, which are the main reasons to improve intrinsic coercivity of the Dy-doped Nd-Fe-B magnets by the low-temperature ageing.

Wear resistance of TC4 by deformation accelerated plasma nitriding at 400 °C2771-2776

摘要：An integrated low temperature nitriding process for TC4（Ti6Al4V） has been developed and the effect on wear resistance has been investigated. Through the process of solid solution strengthening—cold deformation—nitriding at 400 °C, the TC4 alloy is nitrided on surface and dispersion strengthened in bulk at the same time. The white nitriding layer is formed after some time of nitriding. The nitriding speed increases with the deformation degree. The construction was investigated by XRD and the nitride is Ti3N2-X. The wear test was carried out and results exhibit that the nitrided samples have better wear resistance.

Comparison of up ladder type and terraced type normalizing heat treatments of heavy cylinder2777-2783

摘要：Because of the mixed grain and coarse grain structure, the long heat treatment cycle and large energy conservation in the heavy cylinder heat treatment process, the up ladder type and terraced type normalizing heat treatment of heavy cylinder after rolling were put forward. The microstructure and mechanical properties of 2.25Cr1Mo0.25 V steel after the up ladder type normalizing, terraced type normalizing and isothermal type normalizing were studied. Experimental results show that: 1) For the grain refinement, the twice terraced type normalizing is better than the up ladder type and isothermal type normalizing, and the average grain size is 18 μm; 2) The yield strength, tensile strength and-30 °C charpy impact energy after twice terraced type normalizing are 681 MPa, 768 MPa and 181 J, respectively, and the mechanical properties are better than those of the up ladder type and isothermal type normalizing; 3) Compared with the isothermal type normalizing, the holding time of terraced type normalizing can be shortened by 30%, which greatly reduces the energy consumption.

Synthesis of size-controllable Fe3O4 magnetic submicroparticles and its biocompatible evaluation in vitro2784-2791

摘要：Large scaled uniform and size-controllable magnetic submicroparticles（MSPs） were synthesized via solvothermal method with ferric chloride as iron source and sodium acetate as trapping agent. The influence of Fe3+ and Na Ac contents on the size distribution of MSPs was investigated. The structural and morphological properties of the synthesized particles were studied by scanning electron microscopy（SEM）, X-ray power diffraction（XRD） and vibrating sample magnetometer（VSM）. The well-dispersed MSPs with size of 100-1000 nm were obtained by simply adjusting the contents of Fe3+ and NaA c. In addition, the hemolysis and cytotoxicity of Fe3O4 MSPs, and their ability to case arrest in cell life-cycles were studied. The results indicate that larger size could lead to lower hemolysis. From MTT（3-（4,5-dimethylthuazol-2-yl）-2,5-diphenyltetrazolium bromide） assay, the interactions between MSPs and adhesive mouse fibroblast cell line（L929） were probed. Larger size of Fe3O4 MSPs demonstrates lower cell viability following an exposure to the cells.

Swelling behavior of hot preheated pellets in reduction roasting process2792-2799

摘要：One kind of facile coal-based direct reduction process is using hot preheated pellets for reduction in grate kiln. In this work, effects of reduction parameters on swelling index of hot preheated pellets were investigated by photographic technique under isothermal conditions. Experimental results show that swelling index of pellets is firstly increased then gradually decreased with increasing reduction time, while that is found to be an obvious decrease from 175 % to 30% with the variation of temperature from 900 °C to 1100 °C. Results of XRD combined with SEM reveal that swelling behavior of pellets is decided by structure of newly formed metal iron grains. The formation and growth of fibers iron grains promote the increase in volume. Low temperature and low CO content are favored to the formation and orientated growth of metal iron grains in the one step process.

Scalable preparation of functionalized graphite nanoplatelets via magnetic grinding as lubricity-enhanced additive2800-2808

摘要：Graphite nanoplatelets were prepared by a novel magnetic-grinding method using self-made equipments. Under a variant magnetic field, magnetic needles collided at a high rotating speed and exfoliated pristine graphite into graphite nanoplatelets with high efficiency. The obtained graphite nanoplatelets are highly crystalline, and the thickness is less than 10 nm. Moreover, the surface area could reached 738.1 m~2/g with a grinding time of 4 h. Silanized graphite nanoplatelets can disperse well in SG 15W-40 engine oil and serve as lubricant additive. Tribological results indicate that the friction coefficient and wear-scar of the friction pairs are lower than 76% and 41%, respectively, by adding 1.5‰(mass fraction) of silanized graphite nanoplatelets. Notably, the functionalized graphite nanoplatelets can realize large-scale production and commercial application.

Removal of Pb(Ⅱ) from aqueous solution by magnetic humic acid/chitosan composites2809-2817

摘要：A novel adsorbent named magnetic humic acid/chitosan composite（M-HA/Cs） was synthesized by decorating humic acid/chitosan composites with Fe3O4 nanoparticles. The adsorption capacity of M-HA/Cs was 1.5 times that of MCs. The effects of solution p H, initial concentration of Pb（Ⅱ） ions and adsorption temperature on Pb（Ⅱ） removal were examined in a batch system and further optimized using Box-Behnken analysis. The recommended optimum conditions are initial Pb（Ⅱ） concentration of 139.90 mg/L, initial pH of 4.98, and temperature of 43.97 oC. The adsorption processes could be well described by pseudo-second-order and Elovich models. Isotherm studies reveal that the adsorption process follows Sips and Temkin models. The thermodynamic study indicats that the adsorption process is spontaneous and exothermic. The potential mechanism of Pb（Ⅱ） on M-HA/Cs at pH 5 may be surface electrostatic attraction, coordination and hydrogen bonding.

Analysis on differentially expressed genes in watermelon rind color based on RNA–Seq2818-2826

摘要：In order to screen the genes controlling watermelon rind color and luster, the experiment was carried out with yellow watermelon skin mutants as tester and green wild type watermelon as control, and transcriptome sequencing and bioinformatics analysis were done. The results show that 34.27 Gb clean data were got by transcriptome sequencing. There are 261 differentially expressed genes among Y1vsG1, Y2vsG2 and Y3vsG3. The pathways contenting most differentially expressed genes are plant hormone signal transduction pathway, phenylpropanoid biosynthesis pathway, photosynthesis pathway, starch and sucrose metabolism pathway. 9-cis-epoxycarotenoid dioxygenase（Cla002942）, alcohol dehydrogenase（Cla004992）, photosystem Ⅰ reaction center subunit Ⅲ, chloroplastic（precursor）（Cla009181）, long-chain acyl coenzyme A synthetase（Cla017341）, threonine dehydratase biosynthetic（Cla018352） candidates genes were screened out.

Maintaining eco-health of urban waterscapes with imbedded integrating ecological entity: Experimental approach2827-2837

摘要：An imbedded integrating ecological entity(IIEE) was designed to combine landscaping, replenishing-water purifying and ecosystem maintaining simultaneously. With this IIEE, within 15 d experiment, simulated replenish water(SRW) with high(SRW-Ⅰ) or low(SRW-Ⅱ) nutrients concentration was well purified. Relative removal rates of CODCr, TP, TN, Chl-a and turbidity reached 84.87%, 84.05%, 94.76%, 188.17%, 110.93% when dealing SRW-Ⅰ, and 52.62%, 90.05%, 82.44%, 166.15%, 202.99%, respectively, when dealing SRW-Ⅱ. The well grew flora and fauna of IIEE benefit eco-maintaining and landscaping. Separately, the maximal root and stem length-increments of Cyperus alternifolius Linn. were 26.1 mm and 28.4 mm, while for Potamogeton crispus Linn. 18.3 mm and 25.7 mm. Mortality for both Bellamya aeruginosa and Misgurnus anguillicaudatus was both under 2.96%. The analysis of variance(ANOVA) indicated that most experimental indexes in each group performed more significantly better than those in their control. All results indicated that the IIEE is a promising technology for future urban waterscapes construction.

Fragmentation mechanism of low-grade hematite ore in a high pressure grinding roll2838-2844

摘要：The fragmentation mechanism of low-grade hematite ore in a high pressure grinding roll(HPGR) was studied based on the characteristics of comminuted products at different specific pressure levels. The major properties included the reduction ratio, liberation, specific surface energy, and specific surface area. The results showed that the fracture of low-grade hematite ore in HPGR was an interactive dynamic process in which the interaction between coarse particles of gangue minerals and fine particles of valuable minerals was alternately continuous with increased compactness and compacting strength of materials. Within a range of 2.8–4.4 N/mm~2, valuable minerals were crushed after preferentially absorbing energy, whereas gangue minerals were not completely crushed and only acted as an energy transfer medium. Within a range of 4.4–5.2 N/mm~2, gangue minerals were adequately crushed after absorbing the remaining energy, whereas preferentially crushed valuable minerals acted as an energy transfer medium. Within a range of 5.2–6.0 N/mm~2 range, the low-grade hematite ore was not further comminuted because of the 'size effect' on the strength of materials, and the comminution effect of materials became stable.

中南大学学报·社会科学版杂志Mechanical Engineering,Control Science and Information Engineering

Stress-strain analysis on AA7075 cylindrical parts during hot granule medium pressure forming2845-2857

摘要：Hot granule medium pressure forming(HGMF) is a technology in which heat-resistant granules are used to replace liquids or gases in existing flexible-die forming technology as pressure-transfer medium. Considering the characteristic of granule medium that seals and loads easily, the technology provides a new method to realize the hot deep-drawing forming on high strength aluminum alloy sheet. Based on the pressure-transfer performance test of granule medium and the material performance test of AA7075-T6 sheet, plastic mechanics analysis is conducted for the areas, such as the flange area, force-transfer area and free deforming area, of cylindrical parts deep-drawn by HGMF technology, and the function relation of forming pressure is obtained under the condition of nonuniform distribution of internal pressure. The comparison between theoretical result and experimental data shows that larger deviation occurs in the middle and later period of forming process, and the maximum theoretical forming force is less than the experimental value by 24.6%. The variation tendency of the theoretical thickness curve is close to the practical situation, and the theoretical value basically agrees well with experimental value in the flange area and the top area of spherical cap which is in the free deforming area.

Bayesian zero-failure reliability modeling and assessment method for multiple numerical control(NC) machine tools2858-2866

摘要：A new problem that classical statistical methods are incapable of solving is reliability modeling and assessment when multiple numerical control machine tools(NCMTs) reveal zero failures after a reliability test. Thus, the zero-failure data form and corresponding Bayesian model are developed to solve the zero-failure problem of NCMTs, for which no previous suitable statistical model has been developed. An expert-judgment process that incorporates prior information is presented to solve the difficulty in obtaining reliable prior distributions of Weibull parameters. The equations for the posterior distribution of the parameter vector and the Markov chain Monte Carlo(MCMC) algorithm are derived to solve the difficulty of calculating high-dimensional integration and to obtain parameter estimators. The proposed method is applied to a real case; a corresponding programming code and trick are developed to implement an MCMC simulation in Win BUGS, and a mean time between failures(MTBF) of 1057.9 h is obtained. Given its ability to combine expert judgment, prior information, and data, the proposed reliability modeling and assessment method under the zero failure of NCMTs is validated.

Improved Sobel algorithm for defect detection of rail surfaces with enhanced efficiency and accuracy2867-2875

摘要：A more effective and accurate improved Sobel algorithm has been developed to detect surface defects on heavy rails. The proposed method can make up for the mere sensitivity to X and Y directions of the Sobel algorithm by adding six templates at different directions. Meanwhile, an experimental platform for detecting surface defects consisting of the bed-jig, image-forming system with CCD cameras and light sources, parallel computer system and cable system has been constructed. The detection results of the backfin defects show that the improved Sobel algorithm can achieve an accurate and efficient positioning with decreasing interference noises to the defect edge. It can also extract more precise features and characteristic parameters of the backfin defect. Furthermore, the BP neural network adopted for defects classification with the inputting characteristic parameters of improved Sobel algorithm can obtain the optimal training precision of 0.0095827 with 106 iterative steps and time of 3 s less than Sobel algorithm with 146 steps and 5 s. Finally, an enhanced identification rate of 10% for the defects is also confirmed after the Sobel algorithm is improved.

Adaptive trajectory linearization control for hypersonic reentry vehicle2876-2882

摘要：This paper presents an improved design for the hypersonic reentry vehicle(HRV) by the trajectory linearization control(TLC) technology for the design of HRV. The physics-based model fails to take into account the external disturbance in the flight envelope in which the stability and control derivatives prove to be nonlinear and time-varying, which is likely in turn to increase the difficulty in keeping the stability of the attitude control system. Therefore, it is of great significance to modulate the unsteady and nonlinear characteristic features of the system parameters so as to overcome the disadvantages of the conventional TLC technology that can only be valid and efficient in the cases when there may exist any minor uncertainties. It is just for this kind of necessity that we have developed a fuzzy-neural disturbance observer(FNDO) based on the B-spline to estimate such uncertainties and disturbances concerned by establishing a new dynamic system. The simulation results gained by using the aforementioned technology and the observer show that it is just due to the innovation of the adaptive trajectory linearization control(ATLC) system. Significant improvement has been realized in the performance and the robustness of the system in addition to its fault tolerance.

Weak thruster fault detection for AUV based on stochastic resonance and wavelet reconstruction2883-2895

摘要：When the bi-stable stochastic resonance method was applied to enhance weak thruster fault for autonomous underwater vehicle(AUV), the enhancement performance could not satisfy the detection requirement of weak thruster fault. As for this problem, a fault feature enhancement method based on mono-stable stochastic resonance was proposed. In the method, in order to improve the enhancement performance of weak thruster fault feature, the conventional bi-stable potential function was changed to mono-stable potential function which was more suitable for aperiodic signals. Furthermore, when particle swarm optimization was adopted to adjust the parameters of mono-stable stochastic resonance system, the global convergent time would be long. An improved particle swarm optimization method was developed by changing the linear inertial weighted function as nonlinear function with cosine function, so as to reduce the global convergent time. In addition, when the conventional wavelet reconstruction method was adopted to detect the weak thruster fault, undetected fault or false alarm may occur. In order to successfully detect the weak thruster fault, a weak thruster detection method was proposed based on the integration of stochastic resonance and wavelet reconstruction. In the method, the optimal reconstruction scale was determined by comparing wavelet entropies corresponding to each decomposition scale. Finally, pool-experiments were performed on AUV with thruster fault. The effectiveness of the proposed mono-stable stochastic resonance method in enhancing fault feature and reducing the global convergent time was demonstrated in comparison with particle swarm optimization based bi-stochastic resonance method. Furthermore, the effectiveness of the proposed fault detection method was illustrated in comparison with the conventional wavelet reconstruction.

Multi-mode process monitoring based on a novel weighted local standardization strategy and support vector data description2896-2905

摘要：There are multiple operating modes in the real industrial process, and the collected data follow the complex multimodal distribution, so most traditional process monitoring methods are no longer applicable because their presumptions are that sampled-data should obey the single Gaussian distribution or non-Gaussian distribution. In order to solve these problems, a novel weighted local standardization(WLS) strategy is proposed to standardize the multimodal data, which can eliminate the multi-mode characteristics of the collected data, and normalize them into unimodal data distribution. After detailed analysis of the raised data preprocessing strategy, a new algorithm using WLS strategy with support vector data description(SVDD) is put forward to apply for multi-mode monitoring process. Unlike the strategy of building multiple local models, the developed method only contains a model without the prior knowledge of multi-mode process. To demonstrate the proposed method’s validity, it is applied to a numerical example and a Tennessee Eastman(TE) process. Finally, the simulation results show that the WLS strategy is very effective to standardize multimodal data, and the WLS-SVDD monitoring method has great advantages over the traditional SVDD and PCA combined with a local standardization strategy(LNS-PCA) in multi-mode process monitoring.