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The effect of nano-CaCO3 with different contents (i.e., 0, 1, 2, 3, 4% by mass of cement) on the mechanical properties including the compressive and tensile strength of ultra-high performance fiber reinforced concrete (UHP-FRC) was investigated experimentally. It was found that the incorporation of nano-CaCO3 enhanced the mechanical properties of UHP-FRC, and the optimal nano-CaCO3 dosage to enhance the compressive and tensile properties of UHP-FRC was 3%. More specifically, the compressive strength increased by 7.7%, while the tensile strength increased by nearly 40% up to dosage of 3%.

The development of sandstone reservoirs with ultra-low permeability has become one of the most important energy resources worldwide. Such reservoirs suffer formation damage easily, such as water sensitivity, from foreign fluid during well drilling and completion for extremely poor physical properties. In order to deeply understand the damage degree of water sensitivity of there reservoirs, water sensitivity analysis of Chang 6 reservoir rock samples was carried out, including water sensitivity of block matrix and fracture rock samples. Results show that there are none or weak water sensitivity damage for block matrix while medium water sensitivity damage for fractured samples. The study is of significance to the reservoir damage control in ultra-low permeability oil reservoirs.

The size change of the forcing cone directly affects the ballistic performance of the gun and the life of the gun barrel. In order to study the force law and wear law of the forcing cone during the continuous engraving process of the projectile, which established a refined finite element model of the projectile-barrel interaction. The model contains rifling finite element mesh grid with process chamfer. Based on the established transient coupled thermo-mechanical finite element (FE) model of the projectile-barrel interaction, the effects of the temperature and pressure of the gunpowder gas, the friction coefficient between the rotating band and the forcing cone were comprehensively considered. Combined with the Archard wear model, numerical method are used to obtain the stress law of the forcing cone and the amount of wear due to friction in the continuous engraving process of the projectile. The research content in this article can provide some guidance for predicting the life of the tube.

The electrical contact resistance behavior of the interface between the copper electrode and the graphite welding pool plays an important role in penetration brazing of Cu/Ni metal wires. Based on the fractal contact resistance model, the contact resistance between the copper electrode and the graphite welding pool is established by taking the oxide ablation of the graphite surface into account. The influences of the graphite ablation on the contact resistance for different pressure and different graphite materials are experimentally investigated. The ablation phenomenon on the surface of the graphite welding pool is observed during the welding process. It is found that the contact resistance slowly increases as the ablation degree of the graphite welding pool surface increases. The present work shows that the impact of the common graphite ablation on the interface contact resistance is more obvious than that of fine graphite.

Polycrystalline BiFeO3 films were fabricated by radio frequency magnetron sputtering using a Bi1.1FeO3 target onto the glass and Si/SiO2/Ti/Pt substrates respectively. The samples which were annealed with different annealing conditions are pure without impurities. Our results indicate that there are relatively wider growth conditions for pure polycrystalline BFO phases.

The cement-based decorative mortar is a kind of good finishing material with abundant shape and colour. But the colour aberration of surface efflorescence seriously hinders the further application of cement-based decorative mortar. In the paper, it is researched of quantitative analysis on effect of calcium hydroxide content and porosity on the efflorescence degree by the function of efflorescence degree and grey scales based on image processing technology. The results show that the efflorescence degree will heighten as the content of calcium hydroxide increases, and there is a safe value of mortar without efflorescence. The open porosity plays another decisive role in the efflorescence degree of mortar. The efflorescence degree of mortar increases with the increase of porosity, and the relationship between them is linear.

The non-destructive inspection method of scale on the inner wall of the ferritic steel and austenitic steel of high temperature boiler tube and the application effect were introduced in our work. The risk of scale exfoliation on the inner wall was also assessed. The risk of tube burst caused by scale exfoliation and accumulation, was reduced greatly, or even avoided by means of the change or treatment of high-risk tube confirmed by non-destructive inspection method.

Molecular dynamics simulations are carried out to examine the heterogeneous solidification of aluminum solution seeded by foreign boron-nitride nanotubes (BNNTs). The final structure indicates noticeably that Al atoms are concentrated to form incredible hierarchical nanostructures composed of coaxial and equidistant cylindrical shells with the BNNTs as the heterogeneous core. The structures of so-formed Al cylinders show strict structural matching and strong structural relevance with BNNTs. Heterogeneous solidification occurred on BNNTs follows a spiral nucleating mechanism. Heredity effect of these hollow cylinders can be clearly observed during the heterogeneous nucleation. The uniform internal potential field around BNNTs is found to be responsible for the formation of the coaxial cylindrical Al shells.

The refinement of primary silicon particles in hypereutectic aluminium–silicon alloys with exceptionally high Si contents (Al–high Si alloys) has been studied using optical microscopy, scanning electron microscopy and electron probe microanalysis. A new Si–20P master alloy has been developed which was used to study the optimal melt treating technology for achieving a satisfactory refinement of primary silicon. The experimental results show that the optimal superheating temperature and the amount of phosphorus addition increase abruptly when silicon content reaches about 50 wt-%. A few of experiential formulae are presented for the optimal superheating temperature and the amount of phosphorus addition. The refinement mechanism of the primary silicon is also discussed.

In this paper, 3 mm diameter (Cu 47 Ti 34 Zr 11 Ni 8 ) 100− x Nb x ( x = 0,1,2) glass forming alloys were fabricated by water-cooled copper mould cast. Microstructural characterization reveals that the monolithic Cu 47 Ti 34 Zr 11 Ni 8 bulk metallic glass exhibits homogenous amorphous structure. While the alloys with Nb addition exhibit a composite structure. For alloys with x = 1, micro-scaled crystalline particles were found to distribute in the glassy matrix. For alloys with x = 2, the microstructure is dominated by a high density of dendritic phase embedded in the glassy matrix. Bonded interface technique was adopted to study the deformation behavior of the alloys underneath the Vickers indentation. It reveals that the subsurface shear patterns are significantly affected by the precipitated phases. The different deformation mechanism of the alloys resulted from the minor Nb addition was put forward and discussed.

To improve the permeability of porous concrete, the factors that affect permeability have been analyzed and compared by a theoretical and experimental method, and then the improved treatment to ensure water cross section performance on the basis of predetermined strength has been chosen. Experimental results show that the cross section pore structure of porous concrete is mainly determined by the aggregate size. An aggregate-cement ratio of 3.5 is more suitable. The mixing of fly ash reduces the permeability of porous concrete.

We report growth of self-organized In0.4Ga0.6As quantum dots on Si substrates by molecular-beam epitaxy. Low-temperature (17 K) photoluminescence spectra show that the optical properties of In0.4Ga0.6As quantum dots grown on Si are comparable to quantum dots grown on GaAs substrates. We also present preliminary characteristics of In0.4Ga0.6As quantum-dot lasers grown on Si substrates. Light versus current measurements at 80 K under pulsed bias conditions show that Ith=3.85 kA/cm2. The lasing spectral output has a peak emission wavelength of 1.013 μm and a linewidth (full width at half maximum) of ∼4 A at the threshold.

Strain relaxation in the As ion implanted Si0.57Ge0.43 epilayers was studied by double-crystal x-ray diffractometry and transmission electron microscopy, and was compared to that in the nonimplanted Si0.57Ge0.43 epilayers. Experimental results show that after rapid thermal annealing (RTA) the x-ray linewidth of the As+-implanted Si0.57Ge0.43 epilayers is narrower than that of the nonimplanted epilayers, and than that of the partially relaxed as-grown samples, which is due primarily to low density of misfit dislocations in the As+-implanted SiGe epilayers. RTA at higher than 950 degrees C results in the formation of misfit dislocations for the nonimplanted structures, and of combinations of dislocations and precipitates (tentatively identified as GeAs) for the As+-implanted epilayers. The results mean that the strain relaxation mechanism of the As+-implanted Si1-xGex epilayers may be different from that of the nonimplanted Si1-xGex epilayers. (C) 1998 American Institute of Physics.

Co:ZnS nanostructures have been synthesized via the solvothermal method by modifying the stoichiometry of Zn and S sources in the solvothermal process. The structure and morphology analysis demonstrates that the increase of the Zn/S molar ratio leads to changes in the morphology and structure, from Co:ZnS nanorods and hexagonal nanocrystals to core–shell Co:ZnS/ZnO nanocrystals. The photoluminescence spectrum for Co:ZnS/ZnO exhibits strong visible light emissions due to the presence of a large amount of structural defects, whereas the emissions for Co:ZnS nanorods almost disappear because of the high crystallinity. All the samples display obvious room-temperature ferromagnetism. The saturated magnetic moment of the samples strongly depends on the concentration of structural defects in the nanostructures and can be effectively enhanced by the introduction of abundant defects.

Epitaxial Fe3O4/BiFeO3 heterostructures with different BiFeO3 thicknesses were deposited on (001) SrTiO3 substrates by magnetron sputtering. An unexpected enhancement in the magnetization measured with a high sensitivity of ∼10−7 emu magnetometer was observed, especially for the Fe3O4/BiFeO3 heterostructures with 22-nm-thick BiFeO3 layers. The magnetization of the heterostructures can be up to 133% of the sum of both single Fe3O4 and BiFeO3 layers deposited directly on the SrTiO3 substrate under the same conditions. The enhanced magnetization is considered to originate from the magnetic spin moments which interact and arrange ferromagnetically at the interface due to the strong interfacial coupling.

We present a scheme to measure the thermal conductivity of individual nanowires using temperature-dependent and microphotoluminescence spectroscopy. The CdS nanowires suspended over trenches in silicon substrate were excited with a focused laser beam in confocal configuration. The photoluminescence at the laser spot gave a measure of the local temperature rise determined by the excitation laser intensity and the thermal conductance of the nanowires. By obtaining the temperature gradient across the nanowire and the length of the suspended segment, the thermal conductivity of CdS nanowires with diameters in the range of 200–400 nm was extracted to be in the range of 4.9–6.2 W/m K.

A series of films deposited under different oxygen partial pressures and annealed under different atmospheres were prepared to investigate the role of oxygen vacancies in tuning magnetic properties of Co-doped SnO2 films. The inclusive Co in SnO2 is in the 2+ state and substitutes for the Sn4+ site. Intrinsic room temperature ferromagnetism is observed in all films, which is not carrier mediated, but coexists with the dielectric behavior. A maximum magnetic moment of 2.37 μB∕Co is achieved by vacuum annealing due to the increase and diffusion of oxygen vacancies rather than the improvement of crystallinity of the film, and the magnetic moment decreases considerably after air annealing or increasing the oxygen partial pressure during deposition. The changes of oxygen vacancy concentration and distribution are indirectly demonstrated by the relative shifts of Co 2p3∕2 peaks in XPS spectra. The band gap of Co-doped SnO2 film is larger than that of pure SnO2 film, suggesting the influence of inclusive Co on t...

Our report describes the growth and characterization of self-organized In0.4Ga0.6As/GaAs quantum dots on Si substrates. The size, shape, and density of the dots grown on Si are quite different than dots grown on GaAs substrates under similar conditions. From structural characterization, it is apparent that the dots, themselves, may be defect free. We present electroluminescent characteristics of edge-emitting In0.4Ga0.6As quantum dot lasers grown on Si. The laser spectra indicates the emission wavelength is 1.01 μm at threshold with a linewidth full width at half maximum ∼4 A. We observe a blueshift towards smaller wavelengths with increasing current, suggesting the filling of smaller dots.