Dynamic characteristic analysis of TBM tunnelling in mixed-face conditions

In this paper, by taking into account the periodically varying mesh stiffness in multiple pinions transmission and the speed–torque characteristics of variable frequency motor drives, the dynamic model for the revolving system of tunnel boring machine (TBM) has been established. Based on the soft ground/hard rock assumption of mixed-face conditions and the analysis of cutting force on each disc cutter and each drag bit, the time-varying excavation torque on the TBM cutterhead in mixed-face tunnelling is obtained. The dynamic excavation torque and cutterhead rotation speed are discussed and compared for TBM tunnelling in several typical mixed-face conditions, which are characterized by the area percentage of soft ground on the excavation face and the uniaxial compressive strength (UCS) of rock. The results show that the excavation torque may run up to a critical value and fluctuate greatly in extremely adverse excavation environments, which may lead to an unexpected TBM stoppage and even a catastrophic failure of the drive motor. To decrease the penetration per revolution in time through applying a lower advance velocity and a higher cutterhead revolution will significantly reduce the excavation torque and effectively avoid such situations.     

基于偏相干分析的轮胎六分力信号识别

由于轮胎多边形的磨损与胎面自激振动有很大的关系,故对问题轿车进行了实车车轮六分力试验,以找出其振动规律.因为测得的六分力信号成分非常复杂,所以将其信号中的侧向力信号作了重点分析,利用偏相干分析法,排除该信号中的其他干扰频率成分,并将其自激振动的频率与计算仿真中所得到的频率作了对比,验证了理论模型的正确性.     

Surface Activity and Cleavability of Gemini Surfactants Featuring Hydrophilic Spacer Groups

In this study we prepared and characterized a series of novel ester-linked gemini surfactants, featuring ester bonds in their structures, through the reactions of polyethylene glycol (PEG400) with various fatty acids (C8?CC18). These gemini surfactants exhibit excellent surface activities, as evidenced by their surface tension, wetting power, and low-foaming and buffer abilities. We examine the influence of the concentrations of the ester-linked gemini surfactants on the surface tension, from which we obtain the critical micelle concentrations. Under basic conditions, each of these cleavable surfactants decomposes into a water-insoluble fatty acid and two water-soluble products; in contrast, they are stable under neutral and acidic conditions.     

Adsorption of phenol and 1-naphthol onto XC-72 carbon

XC-72 carbon (XC-72) was characterized by SEM, XPS, N₂ adsorption-desorption, particle size distribution analysis and potentiometric acid-base titration. The adsorption of phenol and 1-naphthol on XC-72 was studied as a function of contact time, pH, adsorbent content and temperature. The kinetic adsorption data were described well by the pseudo-second-order model. The adsorption isotherms of phenol were described well by Freundlich model, while the adsorption isotherms of 1-naphthol were fitted well by Langmuir model. The results demonstrated that XC-72 had much higher adsorption capacity for 1-naphthol than for phenol. The adsorption thermodynamic data were calculated from the temperature-dependent adsorption isotherms at T=293, 313 and 333 K, and the results indicated that the adsorption of phenol was an exothermic process, whereas the adsorption of 1-naphthol was an endothermic process. XC-72 is a suitable material for the preconcentration of phenol and 1-naphthol from large volumes of aqueous solutions.     

Influences of graphene oxide support on the electrochemical performances of graphene oxide-MnO2 nanocomposites

MnO₂ supported on graphene oxide (GO) made from different graphite materials has been synthesized and further investigated as electrode materials for supercapacitors. The structure and morphology of MnO₂-GO nanocomposites are characterized by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Nitrogen adsorption-desorption. As demonstrated, the GO fabricated from commercial expanded graphite (denoted as GO(1)) possesses more functional groups and larger interplane gap compared to the GO from commercial graphite powder (denoted as GO(2)). The surface area and functionalities of GO have significant effects on the morphology and electrochemical activity of MnO₂, which lead to the fact that the loading amount of MnO₂ on GO(1) is much higher than that on GO(2). Elemental analysis performed via inductively coupled plasma optical emission spectroscopy confirmed higher amounts of MnO₂ loading on GO(1). As the electrode of supercapacitor, MnO₂-GO(1) nanocomposites show larger capacitance (307.7 F g^-1) and better electrochemical activity than MnO₂-GO(2) possibly due to the high loading, good uniformity, and homogeneous distribution of MnO₂ on GO(1) support.     

地电位升高对通信设备的影响及其防护

针对电力通信系统运行特点，着重对电力系统接地故障引起的地电位升高及其对通信设备的影响进行了分析，提出了相应的保护措施，并介绍了两种保护装置。     

Use of native species and biodegradable chelating agents in the phytoremediation of abandoned mining areas

BACKGROUND: The application of phytostabilization and assisted phytoextraction to the remediation of abandoned mining areas can be a valuable method to reclaim these areas without modifying soil and landscape characteristics. An in situ application of a continuous phytoextraction technique was carried out in the area of Campo Pisano (Sardinia, Italy), followed by a laboratory assisted phytoextraction test using the biodegradable chelating agents methylglycine diacetic acid (MGDA) and iminodissuccinic acid (IDSA). The plants used were Scrophularia canina subsp. bicolor, Cistus salviifolius and Teucrium flavum subsp. glaucum. RESULTS: The plant that accumulated more Pb was T. glaucum (353 mg kg^?1) while C. salviifolius demonstrated better ability to accumulate Zn (1560 mg kg^?1). S. bicolor showed a better tolerance to metals but accumulated 119 mg kg^?1 of Pb. Accumulation of metals immediately after chelant application was up to 300 mg kg^?1 of Pb and 3000 mg kg^?1 of Zn which did not further increase during the assisted phytoextraction experiment. CONCLUSION: The plant that demonstrated to be most suitable for phytoremediation application was S. bicolor due to its higher biomass production and tolerance to metals. The low cation exchange capacity and the high concentration of Ca and Mg in soil determined a low chelant effectiveness. Copyright © 2009 Society of Chemical Industry     

Characteristics of Ventricular Electrophysiological Substrates in Metabolic Mice Treated with Empagliflozin

Empagliflozin (EMPA) is a sodium–glucose transporter 2 (SGLT2) inhibitor that functions as a new-generation glucose-lowering agent and has been proven to be beneficial for patients with cardiovascular diseases. However, the possible benefits and mechanisms of its antiarrhythmic effects in cardiac tissue have not yet been reported. In this study, we elucidated the possible antiarrhythmic effects and mechanisms of EMPA treatment in cardiac tissues of metabolic syndrome (MS) mice. A total of 20 C57BL/6J mice (age: 8 weeks) were divided into four groups: (1) control group, mice fed a standard chow for 16 weeks; (2) MS group, mice fed a high-fat diet for 16 weeks; (3) EMPA group, mice fed a high-fat diet for 12 weeks and administered EMPA at 10 mg/kg daily for the following 4 weeks; and (4) glibenclamide (GLI) group, mice fed a high-fat diet for 12 weeks and administered GLI at 0.6 mg/kg daily for the following 4 weeks. All mice were sacrificed after 16 weeks of feeding. The parameters of electrocardiography (ECG), echocardiography, and the effective refractory period (ERP) of the left ventricle were recorded. The histological characteristics of cardiac tissue, including connexin (Cx) expression and fibrotic areas, were also evaluated. Compared with the MS group, the ECG QT interval in the EMPA group was significantly shorter (57.06 ± 3.43 ms vs. 50.00 ± 2.62 ms, p = 0.011). The ERP of the left ventricle was also significantly shorter in the EMPA group than that in the GLI group (20.00 ± 10.00 ms vs. 60.00 ± 10.00 ms, p = 0.001). The expression of Cx40 and Cx43 in ventricular tissue was significantly lower in the MS group than in the control group. However, the downregulation of Cx40 and Cx43 was significantly attenuated in the EMPA group compared with the MS and GLI groups. The fibrotic areas of ventricular tissue were also fewer in the EMPA group than that in the MS group. In this study, the ECG QT interval in the EMPA group was shorter than that in the MS group. Compared with the MS group, the EMPA group exhibited significant attenuation of downregulated connexin expression and significantly fewer fibrotic areas in ventricles. These results may provide evidence of possible antiarrhythmic effects of EMPA.     

Stability analysis and bang-bang sliding control of a class of single-input bilinear systems

Introduces a bang-bang sliding control of a class of single-input bilinear systems. The sliding function is chosen via the well-known pole-assignment method for linear time-invariant systems. Importantly, the bang-bang sliding control generates a reaching-and-sliding region and a stable-sliding region, each expressed by a set of linear inequalities. Both regions comprise the equilibrium point, shown to be asymptotically stable. However, the stability analysis is processed under the limitation that the system state should be initially located in the reaching-and-sliding region. Two numeric examples are used for demonstration.