Theoretical analysis on ground vibration attenuation using sub-track asphalt layer in high-speed rails

Using a finite element method （FEM） program, a Portland cement concrete slab trackbed （So）, and a sub- track asphalt roadbed （RAC-S） were modeled under high- speed train loads to analyze their responses to ground vibration attenuation, by considering 10, 15, 20, 25, and 30 thick sub-track asphalt layer replaced on the top of the upper subgrade. FEM results show that the vibration amplitude of RAC-S is at least three times lower than the vibration for So. The maximum vibration amplitude of RAC-S is linearly increased with train speed. The vertical acceleration is found to be reduced by more than 10 % when the asphalt layer thickness is increased from 10 to 20 cm. However, the reduction in vertical acceleration is only about 1% when the thickness of the asphalt layer changes from 20 to 30 cm. The vibration level is slightly lower if the asphalt layer has higher resilient modulus in the seasons of autumn or winter. This theoretical analysis indicates that a railway substructure that consists of a 10-20 cm thick high modulus asphalt layer located at the top of trackbed shows a good performance in ground vibration control for high-speed rails.

Research on Properties of Metasilicate Bonded Carbon-free Basic Dry Vibration Mix

Carbon-free basic dry vibration mix was prepared using middle grade magnesia and fused magnesia as main starting materials,metasilicate replacing phenolic resin as binder,adding a certain amount of medium and low temperature intensifiers. Effects of binder,grain composition,and additives on basic dry vibration mix for tundish were studied,and the bonding mechanism was also analyzed. The results show that：（1） when using metasilicate as binder,the higher strength can be acquired; （2） the suitable grain composition is q=0.48,the critical granularity is 5 or 3 mm,the fines addition is 10%-20% （mass percent）; （3） the strength and corrosion resistance of the basic dry vibration mix can be improved by the melting compound of metasilicate and additives; （4） with temperature rising,the bonding type in dry vibration mix changes from cohere bonding to reaction bonding,and then to ceramic bonding at last.

Formation of Uniform Oil-Soluble Fe_3O_4 Nanoparticles via Oil-Water Interface System

Nowadays,the novel oil water interface method has attracted a considerable attention owing to the advantages of mild reaction conditions,simple operation,low cost,and high efficiency.In this paper,uniform oil-soluble Fe_3O_4 nanoparticles(NPs) were synthesized by oil-water interface method from mixing iron tristearate of 0.067mol/L in cyclohexane with ferrous sulfate in water.The as-prepared products were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),vibrating sample magnetometer(VSM),Fourier transform infrared spectroscopy(FT-IR) and thermogravimetric analyzer(TGA).TEM images and XRD profiles showed that the size of the oil-soluble products ranged in 1.7-6.9 nm.VSM indicated that the Fe_3O_4 NPs were superparamagetic.FT-IR and TGA proved that oleic acid was combined to the surface of Fe_3O_4 NPs closely.TEM images and XRD profiles revealed that the most suitable reaction concentration of NH_3·H_2O,oleic acid/water in volume,reaction temperature and reaction time were 4.5 mol/L,50:1 000,80℃ and 6 h,respectively.The formation mechanism of the nearly monodispersed Fe_3O_4 NPs was that the preformed Fe_3O_4 nuclei were capped by oleic acid as early as the nucleation occurred in oil-water interface and subsequently entered into oil phase to stop growing.