The ecogeomorphic processes occurring on semiarid rangelands are reviewed, with emphasis on the source-sink relations and positive feedback loops that existed between shrub patches and intershrub areas, and the way li...The ecogeomorphic processes occurring on semiarid rangelands are reviewed, with emphasis on the source-sink relations and positive feedback loops that existed between shrub patches and intershrub areas, and the way livestock presence affected these interactions. Compared with intershrub areas, the shrub patches had a higher soil porosity, infiltration capacity, water-holding capacity, hydraulic conductivity, structural stability, and organic matter content, and lower bulk density. These differences derived from a host of processes whose intensity was less in the shrub patches, including raindrop impact, mechanical crust formation, overland water flow, soil erosion, evaporative moisture loss, and flock trampling. There was also greater shading of the soil surface; soil and litter deposition; water accumulation; microbial, fungal, and mesofaunal activities in the shrub patches. The overland flow of water carried soil and litter from the intershrub areas to the shrub patches and resulted in microtopographic modifications that tended to strengthen these source-sink relations. Grazing had an impact on these processes, not only at the shrub-intershrub scale but also within the intershrub areas, through the creation of highly compacted trampling routes. The combined role of the above ecogeomorphic processes was to maintain the rangeland＇s functionality. Without these inter-relationships, water loss, soil erosion, and nutrient depletion would occur at the hillside scale, causing degradation of the landscape.展开更多
Polycrystalline SrBi_(4)Ti_(3.975)Zr_(0.025)O_(15)(SBTZ)was prepared using solid-state reaction technique.SBTZ was characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).XRD analysis indicated th...Polycrystalline SrBi_(4)Ti_(3.975)Zr_(0.025)O_(15)(SBTZ)was prepared using solid-state reaction technique.SBTZ was characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).XRD analysis indicated the formation of a single-phase orthorhombic structure.Particle size was found using SEM.The dielectric,ferroelectric,piezoelectric,modulus and impedance spectroscopy studies on SBTZ were investigated in the frequency range 1Hz-1MHz from room temperature(RT)to 600℃.Piezoelectric charge and electromechanical coupling coefficients were calculated from resonance and anti-resonance frequencies.Impedance and modulus plots were used as tools to analyze the sample behavior as a function of frequency.Cole-Cole plots showed a non-Debye relaxation.Conductivity measurements were performed on SBTZ.展开更多
文摘The ecogeomorphic processes occurring on semiarid rangelands are reviewed, with emphasis on the source-sink relations and positive feedback loops that existed between shrub patches and intershrub areas, and the way livestock presence affected these interactions. Compared with intershrub areas, the shrub patches had a higher soil porosity, infiltration capacity, water-holding capacity, hydraulic conductivity, structural stability, and organic matter content, and lower bulk density. These differences derived from a host of processes whose intensity was less in the shrub patches, including raindrop impact, mechanical crust formation, overland water flow, soil erosion, evaporative moisture loss, and flock trampling. There was also greater shading of the soil surface; soil and litter deposition; water accumulation; microbial, fungal, and mesofaunal activities in the shrub patches. The overland flow of water carried soil and litter from the intershrub areas to the shrub patches and resulted in microtopographic modifications that tended to strengthen these source-sink relations. Grazing had an impact on these processes, not only at the shrub-intershrub scale but also within the intershrub areas, through the creation of highly compacted trampling routes. The combined role of the above ecogeomorphic processes was to maintain the rangeland＇s functionality. Without these inter-relationships, water loss, soil erosion, and nutrient depletion would occur at the hillside scale, causing degradation of the landscape.
文摘Polycrystalline SrBi_(4)Ti_(3.975)Zr_(0.025)O_(15)(SBTZ)was prepared using solid-state reaction technique.SBTZ was characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM).XRD analysis indicated the formation of a single-phase orthorhombic structure.Particle size was found using SEM.The dielectric,ferroelectric,piezoelectric,modulus and impedance spectroscopy studies on SBTZ were investigated in the frequency range 1Hz-1MHz from room temperature(RT)to 600℃.Piezoelectric charge and electromechanical coupling coefficients were calculated from resonance and anti-resonance frequencies.Impedance and modulus plots were used as tools to analyze the sample behavior as a function of frequency.Cole-Cole plots showed a non-Debye relaxation.Conductivity measurements were performed on SBTZ.
