A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using 137Cs technique in the Rolling Loess Plateau, China

By comparison of volumes and ¹³⁷Cs contents of the deposited sediments before and after 1993, changes of specific sediment yields and relative sediment contributions from the gully area and from the inter gully area after closing cultivation on the later area on a small catchment of Zhaojia Gully, in the Rolling Loess Plateau, are analyzed in this paper. Closing cultivation in a large scale has not resulted in decrease but increase of specific sediment yield of the catchment, in sharp decrease of the sediment yield and the relative sediment contribution of the inter-gully area, and in increase of the sediment yield and the contribution of the gully area, for a short term. The mean specific sediment yield of 29650 t km⁻² a⁻¹ of 1994–1996 in the catchment was 2.2 times the average value of 13413 t km⁻² a⁻¹ for a long term. The specific sediment yield of the inter-gully area decreased from the 14335 t km⁻² a⁻¹ in 1994 to 7034 t km⁻² a⁻¹ in 1995 and 3517 t km⁻² a⁻¹ in 1996, while the yield of the gully area varied between 44944 and 62136 t km⁻² a⁻¹ during the period of 1994–1996 which was much greater than the value of 21118 t km⁻² a⁻¹ before 1993. The relative sediment contribution from the inter-gully area decreased from 23% in 1994 to 15% in 1995 and 6% in 1996, while the contribution from the gully area increased from 77% in 1994 to 85% in 1995 and 94% in 1996. It is suggested that compacting of ploughed soils resulted in increasing of the erosion resistance but in decreasing of the precipitation infiltration, therefore, the soil erosion reduced but the runoff amount increased on the inter-gully area. Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements, consequently, in increase of the total sediment yield from the catchment.     

On bounding Hecke-Siegel eigenvalues

We use the action of the Hecke operators (1≤j≤n) on the Fourier coefficients of Siegel modular forms to bound the eigenvalues of these Hecke operators. This extends work of Duke-Howe-Li and of Kohnen, who provided bounds on the eigenvalues of the operator T(p).     

Computer simulation of cage processes and some difficulties with present models

A simple model involving random displacements of particles in a cubic lattice is used to evaluate the importance of primary and secondary recombination in cage processes and leads to estimates of the lifetime of cage pehnomena. However, it is pointed out that all such models, and treatments which attempt to relate processes at the molecular level with bulk viscosity or diffusion constants, are inherently qualitative since they ignore the important correlation between motions of neighboring molecules.     

Oxygen evolution as a critical test of mechanism in the ferric-ion catalyzed decomposition of hydrogen peroxide

The stoichiometry of O₂ evolution in the Fe³ catalyzed decomposition of H₂O₂ in dilute HClO₄ at high [Fe³⁺]/[H₂O₂] ratios is 2H₂O₂ → 2H₂O + O₂ with no deficiency indicating accumulation of an intermediate complex. This and the observed kinetics are shown to be consistent with a “redox chain” but not a “complex” mechanism for the reaction.     

Elastic-plastic aluminium ring response to pulsed electron beam impulse

Aluminum alloy 6061-T6 and 7075-T73 rings with lead and tin blowoff overlays were exposed to the Hermes II pulsed electron beam. The resultant energy deposition and subsequent expansion of the overlay produced an impulse load on the ring. High speed framing camera photographs permitted determination of the peak impulse and the variation of the impulse with angular location. The framing camera photographs also yielded the time dependent ring deformation profiles. Favorable comparisons were obtained between the UNIVALVE calculated response and the observed ring response.     

The decomposition of substituted benzoyl peroxides in the presence of dimethoxybenzenes

Benzoyl peroxides, particularly those containing electron withdrawing substituents, undergo rapid decomposition in the presence of m-dimethoxybenzene, p-dimethoxybenzene, 2,5-di-t-butyl-1,4-dimethoxybenzene, and 2,5-dimethyl-1,4-dimethoxybenzene. Reactions are first order in peroxide and dimethoxy benzene, increasing in the order given. Identified products are the acids corresponding to the peroxide and esters involving ring substitution, ring-substitution with elimination of a t-Bu group, and benzylic substitution. It is proposed that reaction involves a rate-determining charge transfer transition state leading to radical ion pairs which collapse to products. No free radicals have been detected.     

A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using ^137Cs technique in the Rolling Loess Plateau, China

By comparison of volumes and ^137Cs Contents of the deposited sediments before and after 1993,changes of specific sediment yields and relative sediment contributions from the gully area and from the inter gully area after closing cultivation on the later area on a small catchment of Zhaojia Gully,in the Rolling Loess Plateau,are analyzed in this paper.Closing cultivation in a large scale has not resulted in decrease but increase of specific sediment yield and the relative sediment contribution of the inter-gully area,and in increase of the sediment yield and the contribution of the gully area,for a short term.The mean specific sediment yield of 29650 t km^-2a^-1 of 1994-1996 in the catchment was 2.2 times the average value of 13413 t km^-2 a^-1 for a long term.The specific sediment yield of the inter-gully area decreased from the 14335t km^-2a^-1 in 1994 to 7034 t km^-2 a^-1 in 1995 and 3517 t km^-1a^-1 in 1996 which was much greater than the value of 21118 t km^-2 a^-1 before 1993.The relative sediment contribution from the inter-gully area decreased form 23% in 1994 to 15% in 1995 and 6% in 1996,while the contribution from the gully area increased form 77% in 1994 to 85% in 1995 and 94% in 1996.It is suggested that compacting of ploughed soils resulted in increasing of the erosion resistance but in decreasing of the precipitation infiltration,therefore,the soil erosion reduced but the runoff amount increased on the inter-gully area.Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements,consequently,in increase of the total sediment yield from the catchment.