Advanced Materials Research Vols. 415-417

Abstract: La _0.7 Sr _0.3 MnO ₃ powders have been synthesized at different temperatures by the traditional solid state method. The crystal structures have been characterized by X-ray diffraction (XRD). The electromagnetic parameters were measured by vector network analyzer (VNA) within the frequency range of 5.85-18GHz. It’s found that the pure perovskite structure has been obtained at the temperature of 1000°C. The bandwidth for R<-6dB became thinner with the sintering temperature’s increase from 1000°C to 1150°C, and the absorbing peak moves to the higher frequency first and low frequency then, the absorbing peak is enhanced first and weakened then.

Abstract: An exponential doping NEA InGaAs photocathode is theoretically proposed to apply in the near infrared streak camera. The photocathode time response is calculated and analyzed by using a photoelectron non-steady method. The numerical results show that the excited electrons in the InGaAs active layer is accelerated due to the built-in electric field induced by the exponential doping structure, which shortens the transport time of minority carriers in the photocathode and thus, the time response is greatly improved. In addition, the exponential doping InGaAs photocathode possesses time response of less than 10 picoseconds and near-infrared quantum efficiency of 10%.

Abstract: By using the first-principles calculations within the density functional theory (DFT), we investigate the electronic structure, magnetism and half-metallic stability of half-Heusler compound NiMn_1-xNb_xSb. The results showed that the lattice constants and magnetic moments per unit respectively follow the Vegard law and the Slater-Pauling rule well. The most stable half-metallicity occurs at doping concentration x=0.25 due to the Fermi level is situated the middle of the spin-down gap. Our studies also indicate that the competition of hybridization of d-electrons and RKKY-type magnetic coupling plays a dominating role in determining the magnetism.

Abstract: The aim of this study is to study the protection performance of fluorocarbon resin coatings on galvanized sheets with electrochemical impedance spectra(EIS) and scanning electron microscopy (SEM) for UV ageing to simulate nature environment. The results indicated that impedance of the coatings acted as a capacitive character at the early UV ageing stage. the diffusion impedance was shown in low-frequency range, which was attributed to the self-healing effect of the chromate layer to the metal interface. After 2000 hours of ageing in the UV chamber, there is a low impedance values in the impedance spectra. Taking into account defects were found on the film surface on SEM picture, it is easy that the outside corrosive substances meet metal substrate through the coating at the defects.

Abstract: This paper builds the formulations of thermomechanical damage modeling approach with generalized non-linear strength theory. The bulk and the likely damage behavior can be described. The independent kinematic internal variables are introduced to describe the damage behavior and structural rearrangement of the Geo-granules for bulk deformation. The accordingly generalized stress can be deduced by combining the given thermodynamical energy functions. A systematic constitutive presentation is presented through the thermodynamical damage framework with generalized non-linear strength theory. The theory is based on previous work by Houlsby et al., and extends to the multi-mechanisms (Guo&Zhao et al.) description for geomaterial.

Abstract: The improvement effect of the external concrete to stability of the core steel-tube was demonstrated by the steel-tube replacement ratio through experimental study. The test results show that, with the steel-tube replacement ratio increasing, the ultimate bearing capacity of composite columns increased correspondingly, and the ductility of composite columns was improved obviously also. Therefore, the steel-tube replacement ratio should be involved in the formula for calculating the ultimate bearing capacity of composite columns. By finite element method and regression analysis, the slenderness ratio is amended by the steel-tube replacement ratio and the calculation results of the eccentric compression bearing capacity agreed well with the test results．

Abstract: This paper analyzed the actual heat transfer coefficient of exterior wall external insulation, which was detected by temperature controlled hot box-heat flow meter method in Nanjing from March to December, 2010 .Research showed that: impacted by one-dimensional stability heat transfer assumption ,78.27% of test values of the heat transfer coefficient for exterior wall external insulation , are less than the calculated values; under certain circumstance, that the external thermal insulation material(Expandable polystyrene shutter, EPS board for short, and Extruded polystyrene shutter, XPS board for short)are the same, the more stable the wall substrate density and material , the greater the heat storage coefficient is and the smaller the relative detection error will be. When using the same stable wall substrate material, the calculation error of XPS board was significantly better than EPS board’s. The analysis, which is about error influence factors of test value of the heat transfer coefficient of exterior wall external insulation, shows that current temperature controlled hot box-heat flow meter heat transfer coefficient method needs further improved and perfect in order to improve the reliability of its conclusion.

Abstract: Characterization of geotechnical digging and control the dynamical settlement is very necessary to mitigate construction risk. The metro tunnels of being constructed access to each other or near to the ground is high risk and physically difficult and costly. The control method becomes imperative. Some cases of digging prediction of ground movements and assessment of risk of damage to above or adjacent constructions have become an important issue especially in urban projec. Ground adaptability characterization is the key of control the tunneling in complex geotechnical conditions both in rock and soft stratum. High and changed water-soil pressure also is risk factors to effect tunneling process. Beside discussion of risk mitigation associate to tunnel construction, the developing settlement control and simulations are given to describe the methods of control risk.

Abstract: In order to investigate conductive mechanism of carbon fiber filled cement-based composites, the conductive properties of cement paste, carbon fiber filled cement-based composites containing different contents of carbon fibers or aggregates were studied. Experimental results indicate that the electrical resistance of the plain cement paste obviously increases with hydration time, which results from the ionic conduction in strong electrolyte solution. The electrical resistivity of the carbon fiber filled cement-based composites decreases with the increase of fiber content. Both contacting conduction and ionic conduction are in charge of the electrical conduction in these composites. The electrical resistivity of the carbon fiber filled cement-based composites decreases under compression, which is due to the improvement of interface contact between matrix and fibers and the increase of fiber bridging probability. The fiber pull-out and breaking under tension lead to an increase in electrical resistivity of these composites. Aggregates block fiber dispersion and contact. This causes an increase in electrical resistivity of the composites.

Abstract: This paper builds the formulations of damage model for dissipative materials with generalized non-linear strength theory. The proposed model reflects the internal structural configuration and damage behavioure. The structural evolution parameters are introduced to account for the progressive loss of the internal structure. The proposed damage model is proposed by generalized non-linear strength theory, the capability of the models in predicting behavior of clay has been examined.