Journal of Central South University of Technology

Jiang, Zhong-ming; Hoxha, Dashnor; Homand, Françoise; Chen, Yong-gui

doi: 10.1007/s11771-015-2564-0pmid: N/A

To investigate and analyze the thermo-hydro-mechanical (THM) coupling phenomena of a surrounding rock mass in an argillaceous formation, a nuclear waste disposal concept in drifts was represented physically in an in-situ test way. A transversely isotropic model was employed to reproduce the whole test process numerically. Parameters of the rock mass were determined by laboratory and in-situ experiments. Based on the numerical simulation results and in-situ test data, the variation processes of pore water pressure, temperature and deformation of surrounding rock were analyzed. Both the measured data and numerical results reveal that the thermal perturbation is the principal driving force which leads to the variation of pore water pressure and deformations in the surrounding rock. The temperature, pore pressure and deformation of rock mass change rapidly at each initial heating stage with a constant heating power. The temperature field near the heater borehole is relatively steady in the subsequent stages of the heating phase. However, the pore pressure and deformation fields decrease gradually with temperature remaining unchanged condition. It also shows that a transversely isotropic model can reproduce the THM coupling effects generating in the near-field of a nuclear waste repository in an argillaceous formation.

Niu, Hui-yong; Qiao, Chen-lu; An, Jing-yu; Deng, Jun

doi: 10.1007/s11771-015-2573-zpmid: N/A

In order to research spread law and distribution law of temperature nearby fire sources on roadway in mine, according to combustion theory and other basic, the theory model of temperature attenuation was determined under unsteady heat-exchange between wind and roadway wall. The full-size roadway fire simulation experiments were carried out in Chongqing Research Institute of China Coal Technology & Engineering Group Corporation. The development processes of mine fire and flow pattern of high temperature gas were analyzed. Experimental roadway is seen as physical model, and through using CFD software, the processes of mine fire have been simulated on computer. The results show that, after fire occurs, if the wind speed is less than the minimum speed which can prevent smoke from rolling back, then the smaller wind speed can cause smoke to roll back easily. Hot plume will lead to secondary disasters in upwind side. Because of roadway wall, hot plume released from roadway fire zone has caused the occurrence of the ceiling jet, and the hot plume has been forced down. Whereas, owing to the higher temperature, buoyancy effect is more obvious. Therefore, smoke rises gradually along the roadway in the flow process, and the hierarchical interface appears wavy. Oxygen-enriched combustion and fuel-enriched combustion are the two kinds of combustion states of fire. The oxygen content of downwind side of fire is maintained at around 15% for oxygen-enriched combustion, and the oxygen content of downwind side of fire is maintained at around 2% for fuel-enriched combustion. Furthermore, fuel-enriched combustion can lead to secondary disasters easily.

Li, Xi-bing; Wang, Shi-ming; Weng, Lei; Huang, Lin-qi; Zhou, Tao; Zhou, Jian

doi: 10.1007/s11771-015-2572-0pmid: N/A

In order to investigate the mechanical properties and stress-strain curves of concrete at different ages under impact load, the impact compression tests of concrete at age of 1, 3, 7, 14 and 28 d were conducted with a large diameter split Hopkinson pressure bar, respectively. Based on statistical damage theory and Weibull distribution, combining the analysis of the change laws of stress-strain curves and viscosity coefficient of concrete with age, a damage constitutive model that can reflect the variation in dynamic mechanical properties with age was proposed. The stress-strain curves calculated from the proposed model are in good agreement with those from experimental data directly.

Xu, Xue-mei; Zhou, Li-chao; Mo, Qin; Guo, Qiao-yun

doi: 10.1007/s11771-015-2560-4pmid: N/A

Detecting the moving vehicles in jittering traffic scenes is a very difficult problem because of the complex environment. Only by the color features of the pixel or only by the texture features of image cannot establish a suitable background model for the moving vehicles. In order to solve this problem, the Gaussian pyramid layered algorithm is proposed, combining with the advantages of the Codebook algorithm and the Local binary patterns (LBP) algorithm. Firstly, the image pyramid is established to eliminate the noises generated by the camera shake. Then, codebook model and LBP model are constructed on the low-resolution level and the high-resolution level of Gaussian pyramid, respectively. At last, the final test results are obtained through a set of operations according to the spatial relations of pixels. The experimental results show that this algorithm can not only eliminate the noises effectively, but also save the calculating time with high detection sensitivity and high detection accuracy.

Bhuiyan, Mohammad; Reaz, Mamun; Jalil, Jubayer; Rahman, Labonnah; Chang, Tae

doi: 10.1007/s11771-015-2554-2pmid: N/A

Radio frequency identification (RFID) is a ubiquitous identification technology nowadays. An on-chip high-performance transmit/receive (T/R) switch is designed and simulated in 0.13-μm CMOS technology for reader-less RFID tag. The switch utilizes only the transistor width and length (W/L) optimization, proper gate bias resistor and resistive body floating technique and therefore, exhibits 1 dB insertion loss, 31.5 dB isolation and 29.2 dBm 1-dB compression point (P1dB). Moreover, the switch dissipates only 786.7 nW power for 1.8/0 V control voltages and is capable of switching in 794 fs. Above all, as there is no inductor or capacitor used in the circuit, the size of the switch is 0.00208 mm2 only. This switch will be appropriate for reader-less RFID tag transceiver front-end as well as other wireless transceivers operated at 2.4 GHz band.

Fan, Xiang; Kulatilake, P.; Chen, Xin; Cao, Ping

doi: 10.1007/s11771-015-2565-zpmid: N/A

The ratio of crack initiation stress to the uniaxial compressive strength (S CI,B/S UC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength $$\left( {S_{A,S_{CI,B} } /S_{A,S_{UC,B} } } \right)$$ were studied by performing numerical stress analysis on blocks having multi flaws at close spacing’s under uniaxial loading using PFC3D. The following findings are obtained: S CI,B/S UC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°, $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found between $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ and β; however, the average $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ seems to slightly decrease with increasing k. The variability of $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ is found to increase with k. Based on the cases studied in this work, $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ ranges between 0.3 and 0.5. This range is quite close to the range of 0.4 to 0.6 obtained for S CI,B/S UC,B. The highest variability of ± 0.12 for $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ is obtained for k=0.8. For the remaining k values the variability of $$S_{A,S_{CI,B} } /S_{A,S_{UC,B} }$$ can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of S CI,B/S UC,B.

Song, Zu-wei; Zhong, Zhao-ping; Zhong, Dao-xu; Wu, Long-hua; Luo, Yong-ming

doi: 10.1007/s11771-015-2547-1pmid: N/A

Sequential and single extraction procedures were applied to both fresh and dried Sedum Plumbizincicola leaves and stems. The extractants, different from those of soil, sediment or sewage sludge metal fractions, were water, 80% (v/v) ethanol, 1 mol/L NaCl, 2% HAc and 0.6 mol/L HCl. Zn, Cd and Cu in the extracts and samples were measured by flame atomic adsorption spectrometry. In sequential extraction procedures, water soluble form and ethanol soluble form are the main fractions for Zn, while water soluble form and NaCl soluble form for Cd, and comparatively uniform distribution for Cu with the residue form most and HCl soluble form second. Single extraction procedures are used to compare the extraction efficiencies of the five reagents to screen appropriate extractants and operating conditions for liquid extraction to deal with large amount of harvested metal-contained biomass, which will pose a threat to the environment if treated improperly. The sequences of extraction efficiencies are HCl>NaCl≈HAc>Water≈Ethanol for Zn and HCl≈NaCl≈HAc>Water>Ethanol for Cd. As for Cu, all the five extractants cannot effectively extract Cu, but HCl achieves a higher efficiency (>70% in fresh samples, and 45%–60% in dried samples). Besides, extraction efficiencies for most extractants in fresh samples are higher than those in dried samples, and extraction efficiencies of stems and leaves for the five extractants are close. The two extraction procedures can obtain high degree of accuracy with the relative standard deviation (RSD) lower than 10%, and metal recoveries are controlled between 80%–120% with most of 90%–110%.

Tian, Hong-qi; Huang, Sha; Yang, Ming-zhi

doi: 10.1007/s11771-015-2578-7pmid: N/A

According to the analysis of the turbulent intensity level around the high-speed train, the maximum turbulent intensity ranges from 0.2 to 0.5 which belongs to high turbulent flow. The flow field distribution law was studied and eight types of flow regions were proposed. They are high pressure with air stagnant region, pressure decreasing with air accelerating region, low pressure with high air flow velocity region I, turbulent region, steady flow region, low pressure with high air flow velocity region II, pressure increasing with air decelerating region and wake region. The analysis of the vortex structure around the train shows that the vortex is mainly induced by structures with complex mutation and large curvature change. The head and rear of train, the underbody structure, the carriage connection section and the wake region are the main vortex generating sources while the train body with even cross-section has rare vortexes. The wake structure development law studied lays foundation for the train drag reduction.

Singh, Subhashree; Sahoo, H.; Rath, S.; Palei, B.; Das, B.

doi: 10.1007/s11771-015-2540-8pmid: N/A

The separation of iron oxide from banded hematite jasper (BHJ) assaying 47.8% Fe, 25.6% SiO2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite, jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of 56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.

Chen, Xing-hua; Hu, Yue-hua; Peng, Hong; Cao, Xue-feng

doi: 10.1007/s11771-015-2548-0pmid: N/A

The degradation behavior of ethyl xanthate (EX) salt was the most widely used collector in sulfide mineral flotation and emission of flotation tailings with residual EX was harmful to environment. In this work, hydrogen peroxide (H2O2) was investigated by UV-visible spectroscopy (UV/Vis) at different pH values from 3 to 12. For pH value from 5 to 12, EX was oxidized into ethyl per xanthate (EPX) by H2O2. Then EPX was further oxidized into thiosulfate (TS) salt rather than ethyl thiocarbonate (ETC) and this step was the reaction-limited step. Then depending on pH values, TS was degraded into sulphate and carbonate salts (pH>7) or elemental sulfur (pH<7). The kinetics data show that the degradation rate of EX increases with increasing the H2O2 concentration and is independent on the pH values. Without H2O2, EX is hydrolyzed to carbon disulfide fast at pH value <3.0, but the reaction of hydrolysis is undetectable at pH value >3.0 during test time.