Soil aggregation varies according to climatic and manage- ment factors, and is difficult to measure because of irregular shapes and sizes of soil aggregates. We applied fractal theory to assess soil aggrega- tion as a...Soil aggregation varies according to climatic and manage- ment factors, and is difficult to measure because of irregular shapes and sizes of soil aggregates. We applied fractal theory to assess soil aggrega- tion as affected by （1） land use change from forest to savanna, （2） nutri- ent additions in forest, ecotone, and savanna ecosystems, and （3） tillage practice and residue treatments in an agro-ecosystem. We used fractal dimensions nonlinear （D,o,-lin） and linear （Dlin） based on number of ag- gregates （N） and mass of aggregates （M） （the range of values were 2.6-2.89 and 2.694.41, respectively） to capture the variations in the sizes of soil aggregates due to land use and treatments/management in these ecosystems. The variation in the values of non-linear fractal dimension based on mass （DMnon-lin） was smaller in forest and savanna ecosystems with and without nutrient additions, while the variation was wider in agro-ecosystems with different management practices. Linear fractal dimensions based on number （Dr^i,） and mass （DMlin） of aggregates var- ied marginally in these ecosystems and did not capture the variations in soil aggregates well. The variations in non-linear fractal dimension indi- cate that continued nitrogen loading in forest accelerates the formation of macro-aggregates, whereas in savanna the situation was reversed. The values of non-linear fractal dimensions did not show significant change after 6 years of nutrient additions in the ecotone; reflecting a buffering mechanism of this system in soil aggregate formation. On the basis of non-linear fractal dimension values, we conclude that residue retention and minimum tillage are appropriate for proper maintenance of soil ag- gregate stability for sustained crop production in the Indian dry land agro-ecosystems展开更多
Thin films of CdSe and silver(Ag)-doped CdSe have been prepared on glass substrates by thermal evaporation in argon gas atmosphere. X-ray diffraction pattern indicates the presence of hexagonal structure with preferre...Thin films of CdSe and silver(Ag)-doped CdSe have been prepared on glass substrates by thermal evaporation in argon gas atmosphere. X-ray diffraction pattern indicates the presence of hexagonal structure with preferred orientation along (100) plane. Elemental composition of the thin films has been analyzed using energy dispersive X-ray analysis. Scanning electron microscopy has been used to investigate the morphology of the thin films. Transmission electron microscope reveals spherical nature of nanoparticles. A decrease in the band gap due to the formation of band tails in the band gap with increase in Ag doping in CdSe lattice has been observed. Photoluminescence spectra indicate redshift in band edge emission peak with increase in Ag doping in CdSe. Electrical conductivity measurements are also studied, and two types of conduction mechanisms taking part in the transport phenomena are observed. Hall measurements indicate n-type behavior of undoped and Ag-doped CdSe thin films.展开更多
Thin films of Ag-doped CdSe are deposited on the glass substrates by thermal evaporation technique using inert gas condensation method. The elemental composition of the prepared thin film is confirmed by EDX spectra. ...Thin films of Ag-doped CdSe are deposited on the glass substrates by thermal evaporation technique using inert gas condensation method. The elemental composition of the prepared thin film is confirmed by EDX spectra. SEM analysis reveals the uniform distribution of the grains over the substrate. TEM analysis reveals the spherical nature of nanoparticles having size in the range of 25-30 nm. X-ray diffraction study indicates an increase in the grain size after thermal annealing and the decrease in the grain size after light soaking treatment. Transmittance spectra are found to decrease with corre- sponding red shift after annealing and light soaking of as-deposited thin films. The value of the band gap is found to decreases and refractive index increases, after annealing and light soaking treatment. The dispersion of refractive index is described using the Wemple-DiDomenico single oscillator model and the effects of the annealing and the light soaking on the dispersion parameters are studied. The dark conductivity is found to change from 2.24 × 10^-8 to 1.54 × 10^-7 and 1.45 ×10^-9 Ω-1 cm-1 after annealing and light soaking of thin films, respectively. Hall effect measurement reveals n-type behavior of as-deposited, annealed and light-soaked thin films.展开更多
基金the University Grants Commission and the Department of Science and Technology,New Delhi for financial support for the establishment of plots, collection and analysis of soil aggregate dataISRO (SAC), Ahmedabad, India for the funding support through a research project
文摘Soil aggregation varies according to climatic and manage- ment factors, and is difficult to measure because of irregular shapes and sizes of soil aggregates. We applied fractal theory to assess soil aggrega- tion as affected by （1） land use change from forest to savanna, （2） nutri- ent additions in forest, ecotone, and savanna ecosystems, and （3） tillage practice and residue treatments in an agro-ecosystem. We used fractal dimensions nonlinear （D,o,-lin） and linear （Dlin） based on number of ag- gregates （N） and mass of aggregates （M） （the range of values were 2.6-2.89 and 2.694.41, respectively） to capture the variations in the sizes of soil aggregates due to land use and treatments/management in these ecosystems. The variation in the values of non-linear fractal dimension based on mass （DMnon-lin） was smaller in forest and savanna ecosystems with and without nutrient additions, while the variation was wider in agro-ecosystems with different management practices. Linear fractal dimensions based on number （Dr^i,） and mass （DMlin） of aggregates var- ied marginally in these ecosystems and did not capture the variations in soil aggregates well. The variations in non-linear fractal dimension indi- cate that continued nitrogen loading in forest accelerates the formation of macro-aggregates, whereas in savanna the situation was reversed. The values of non-linear fractal dimensions did not show significant change after 6 years of nutrient additions in the ecotone; reflecting a buffering mechanism of this system in soil aggregate formation. On the basis of non-linear fractal dimension values, we conclude that residue retention and minimum tillage are appropriate for proper maintenance of soil ag- gregate stability for sustained crop production in the Indian dry land agro-ecosystems
基金supported financially by the Major Research Project of University Grant Commission (UGC), N. Delhi, India (No. 42-781/2013 (SR))
文摘Thin films of CdSe and silver(Ag)-doped CdSe have been prepared on glass substrates by thermal evaporation in argon gas atmosphere. X-ray diffraction pattern indicates the presence of hexagonal structure with preferred orientation along (100) plane. Elemental composition of the thin films has been analyzed using energy dispersive X-ray analysis. Scanning electron microscopy has been used to investigate the morphology of the thin films. Transmission electron microscope reveals spherical nature of nanoparticles. A decrease in the band gap due to the formation of band tails in the band gap with increase in Ag doping in CdSe lattice has been observed. Photoluminescence spectra indicate redshift in band edge emission peak with increase in Ag doping in CdSe. Electrical conductivity measurements are also studied, and two types of conduction mechanisms taking part in the transport phenomena are observed. Hall measurements indicate n-type behavior of undoped and Ag-doped CdSe thin films.
基金financially supported by University Grant Commission (UGC) [F.No. 42-781/2013(SR)]
文摘Thin films of Ag-doped CdSe are deposited on the glass substrates by thermal evaporation technique using inert gas condensation method. The elemental composition of the prepared thin film is confirmed by EDX spectra. SEM analysis reveals the uniform distribution of the grains over the substrate. TEM analysis reveals the spherical nature of nanoparticles having size in the range of 25-30 nm. X-ray diffraction study indicates an increase in the grain size after thermal annealing and the decrease in the grain size after light soaking treatment. Transmittance spectra are found to decrease with corre- sponding red shift after annealing and light soaking of as-deposited thin films. The value of the band gap is found to decreases and refractive index increases, after annealing and light soaking treatment. The dispersion of refractive index is described using the Wemple-DiDomenico single oscillator model and the effects of the annealing and the light soaking on the dispersion parameters are studied. The dark conductivity is found to change from 2.24 × 10^-8 to 1.54 × 10^-7 and 1.45 ×10^-9 Ω-1 cm-1 after annealing and light soaking of thin films, respectively. Hall effect measurement reveals n-type behavior of as-deposited, annealed and light-soaked thin films.
