Loading rate and confining pressure effect on dilatancy,acoustic emission,and failure characteristics of fissured rock with two pre-existing flaws

Investigating the dilatancy, acoustic emission and failure characteristics of fissured rock are significant to ensure their geotechnical stability. In this paper, the uniaxial and triaxial compression experiments with AE monitoring under different loading rates were carried out on fissured rock specimens with the same geometrical distribution of two pre-existing flaws. The dilatancy and AE activity of these specimens were discussed, and the effects of the confining pressure and loading rate on the mechanical parameters and failure characteristics were analyzed. The results show that the exponential strength criterion is more suitable than the Mohr–Coulomb strength criterion to characterize the strength characteristics of fissured rock. The crack evolution and failure characteristics of fissured rock specimens are more complicated than those of intact rock specimens. The failure characteristics of the fissured rock follow the tensile shear coalescence model, crack branching occurs with increasing the loading rate, and the multi-section coalescence model is verified with increasing the confining pressure. The phenomena of stress drop and yield platform usually occur after the dilatancy onset, the specimen does not fail instantaneously, and the propagation and coalescence of cracks cause a sharp increase in the AE signals, circumferential strain, and volumetric strain.     

茴拉西坦/介孔二氧化硅的制备及释药性能

为了提高难溶性药物的溶出速率,采用水热合成法制备了MCM-41和SBA-15两种介孔二氧化硅载体材料,利用浸渍法将模型药茴拉西坦负载于两种载体上.利用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、小角X射线衍射(XRD)、N2吸附-脱附、红外光谱(IR)、差热-热重(DTA-TG)对载药前后载体材料的表面形貌、粒径、孔径、孔容、比表面积、晶胞参数、骨架结构等进行测试,结果表明MCM-41和SBA-15具有相同的二维六方孔道结构,孔径及孔容分别为3.49 nm和6.67 nm,载药后的载药量分别为17;和22;,药物以非晶态装载于介孔孔道中没有影响介孔二氧化硅的骨架结构,但使介孔孔容及比表面积都有所降低.通过在不同pH溶出介质中负载于载体上的茴拉西坦与原料药晶体的溶出比较发现,两种载体均能够显著提高茴拉西坦的溶出速率.结合材料表征、载药量及溶出度综合比较,SBA-15载体的载药及释药性能均优于MCM-41载体.     

Small angle x—ray scattering study on the conformation of polystyrene in toluene during adding anti—solvent CO2

The conformatiopn of polystyrene in the anti-solvent process of supercritical fluids(compressed CO2 polystyrene toluene)has been studied by small angle x-ray scattering with synchrotron radiation as an x-ray source.Coilto-globule transformation of the polystyrene chain was observed with the increase of the anti-solvent CO2 pressure;i.e.polystrene coiled at a prssure lower than the cloud point pressure(Pc)and turned into a globle with a uniform density at pressures higher than Pc.Fractal behaviour was also found in the chain contraction.and the mass fractal dimension increased with increasing CO2 pressure.     

双金属/TiO2纳米管复合结构中增强的光电流

将传统半导体材料与金属微纳结构相结合,利用其表面等离激元共振效应,可有效地增强复合结构的光电转换效率,使其广泛地被用于光电化学和光电探测等领域.本文以氧化铝纳米管为模板,采用原子层沉积技术制备出高有序的TiO2纳米管,并通过电子束热蒸发技术在大孔径的纳米管薄膜中分别负载金、铝和双金属金/铝纳米颗粒,形成金属纳米颗粒/T...     

表面波在表面活性剂流变学研究中的应用

论述了表面波的原理及其发展,文中进一步讨论了毛细波和纵向波的特点,较为详细地介绍了纵向波的实验方法和装置以及在表面活性剂流学变性质研究中的应用。     

Influences of hyperbranched polyethylenimine on the reactive compatibilization of polycarbonate/polyamide blends

The influences of hyperbranched polyethylenimine(h PEI), which possesses many reactive amino end-groups, on the blending properties of bisphenol-A polycarbonate(PC) and amorphous polyamide(a PA) were systematically investigated. Scanning electron microscopy(SEM) and differential scanning calorimetry(DSC) were used to observe the effect of h PEI on morphologies of PC and a PA phases in bulk blends. While the interfacial fracture toughness between planar PC and a PA layers with and without h PEI was studied by using augmented double cantilever beam(ADCB) method. Results show that the compatibility in PC/a PA blends can be significantly improved by adding a small amount of h PEI, mainly due to the interchange reactions between the polymers leading to the formation of block copolymers, cross-linked polymers and molecules with other constitutions. The augmented double cantilever beam experiments showed that the reactive process drastically reinforced the interfacial adhesion between planar layers of PC and a PA. However, degradation takes place during annealing at 180 °C, which was responsible for the production of small molar mass species of PC.     

Effects of non-smooth characteristics on bionic bulldozer blades in resistance reduction against soil

The phenomenon of soil adhesion occurs widely when terrain machines and construction machines work; this adhesion increases their working resistance. Bionics is one of the most effective methods to reduce resistance against soil. Several non-smooth convex form bulldozer blades were tested to study the effects of non-smooth characteristics on resistance reduction against soil. Under the same soil and test conditions, the draft forces of different non-smooth samples were obtained, and were lower than those of smooth samples. The sample with largest convex base diameter had the lowest draft force. The experiments with smooth and non-smooth samples were repeated to observe soil adhesion and test resistance. A minimum amount of soil adhered to the surface of the non-smooth sample, and the draft force varied smoothly. The smooth sample was different in soil adhesion and draft force.     

Hydrodynamic diffusivity of spherical particles in polymer solution

In this research experiments were performed to examine the hydrodynamic diffusion of spherical particles in a highly filled suspension. The suspension consisted of nearly monodisperse polymethylmethacrylate spheres in a density matched polymer solution. The polymer solution was prepared by dissolving 0–700 ppm of polyacrylamide in a mixture of ethyleneglycol and glycerine. The polymer solution did not show appreciable shear thinning. The particle loading was varied from 30 to 55%. The hydrodynamic diffusivity was estimated by measuring the time-dependent viscosity when the suspension was subjected to a circular Couette flow with an air bubble trapped under the rotor of the Couette apparatus. The results show that the dimensionless diffusivity (D/γ˙a ²) of particles in polymer solution is not proportional to shear rate (γ˙), as in the case of a Newtonian fluid, but that it decreases with increasing shear rate. The diffusivity also decreases with increasing polymer concentration. It is suggested that the elongational thickening behaviour and the increased lubrication force due to the first normal stress difference may be responsible for the reduction of diffusivity in the polymer solution. Received: 18 January 2000 Accepted: 6 April 2000     

Rh-Catalyzed Kinetic Resolution-Based Enantioselective [4+2]-Cycloaddition-Isomerization of Allene-1,3-dienes

The first example of Rh-catalyzed kinetic resolution of 1,3-disubstituted allene-1,3-dienes involving intramolecular[4+2]-cycloaddition has been developed.Follo...     

Limit cycle bifurcations near a double homoclinic loop with a nilpotent saddle of order m

In this paper, we study the explicit expansion of the first order Melnikov function near a double homoclinic loop passing through a nilpotent saddle of order m in a near-Hamiltonian system. For any positive integer $m(m\ge 1)$, we derive the formulas of the coefficients in the expansion, which can be used to study the limit cycle bifurcations for near-Hamiltonian systems. In particular, for $m=2$, we use the coefficients to consider the limit cycle bifurcations of general near-Hamiltonian systems and give the existence conditions for 10, 11, 13, 15 and 16 (11, 13 and 16, respectively) limit cycles in the case that the homoclinic loop is of cuspidal type (smooth type, respectively) and their distributions. As an application, we consider a near-Hamiltonian system with a nilpotent saddle of order 2 and obtain the lower bounds of the maximal number of limit cycles.