Spatial variation of reference crop evapotranspiration on Tibetan Plateau

This study is based on meteorological observation data collected at 38 weather stations on the Tibetan Plateau over several decades. Daily reference crop evapotranspiration （ETo） was calculated with the FAO-56 standard Penman-Monteith formula. A test of normality was performed with Statistica 6.0 software, isotropic and anisotropic semi-variogram analysis was conducted with the GS＋ （geostatistics for the environmental sciences） system for Windows 7.0, and the characteristics of spatial variation of daily ETo were obtained. The following results can be obtained Daily ETo for different periods on the Tibetan Plateau are distributed normally; Except for daily ETo in the E-W （east-west） direction in the summer, which showed a slight negative correlation with distance change, the Moran＇s indexes of daily ETo for different periods in all directions on the Tibetan Plateau within a 100-km distance were positive, demonstrating a positive correlation with distance change; Variograms of daily ETo in June, the dry season, the wet season, as well as annual average daily ETo fit well with the Gaussian model; A variogram of daily ETo in December fit well with the exponential model; Variograms of daily ETo for the four seasons fit well with the linear With sill model.

Experimental study and simulations of infiltration in evapotranspiration landfill covers

Various cover systems have been designed for landfill sites in order to minimize infiltration （percolation） into the underlying waste. This study evaluated the soil water balance performance of evapotranspiration covers （ET covers） and simulated percolation in the systems using the active region model （ARM）. Experiments were conducted to measure water flow processes and water balance components in a bare soil cover and different ET covers. Results showed that vegetation played a critical role in controlling the water balance of the ET covers. In soil profiles of 60-cm depth with and without vegetation cover, the maximum soil water storage capacities were 97.2 mm and 62.8 mm, respectively. The percolation amount in the bare soil was 2.1 times that in the vegetation-covered soil. The ARM simulated percolation more accurately than the continuum model because it considered preferential flow. Numerical simulation results also indicated that using the ET cover system was an effective way of removing water through evanotransoiration, thus reducing nercolation.

Effect of La addition on semi-solid microstructure evolution of Mg-7Zn magnesium alloy

Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment.The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated.Meanwhile,the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied.Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure.During the semi-solid thermal transformation,the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time.The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605℃ for 30 min is the optimal.The average size of solid particles,shape factor,and solid fraction are 42μm,1.45 and 61.8%,respectively.At the same time,a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.