Many certificateless signature schemes using bilinear pairings have been proposed. But the relative computation cost of the pairing is approximately twenty times higher than that of the scalar multiplication over elliptic curve group. In order to improve the performance we propose a certificateless signature scheme without bilinear pairings. With the running time being saved greatly, our scheme is more practical than the previous related schemes for practical application.
A geographic information system (GIS) was utilized to apply a modified DRASTIC method to the assessment of ground water contamination sensitivity in Goshen County, Wyoming. Several basic environmental characteristics, identified as influencing contaminant transport through the vadose zone to groundwater systems, were mapped, automated, and analyzed. These characteristics include: depth to groundwater, net recharge, hydrogeologic setting, vadose zone soil properties, land surface slope, and saturated hydraulic conductivity. Sensitivity ratings were developed for each parameter based on a combination of mathematical functions and the inherent capacity of each characteristic to influence transport of contaminants. A raster‐based overlay analysis was performed to derive a map that portrays cumulative aquifer sensitivity ratings across the county, providing a relative indication of groundwater vulnerability to contamination. A process‐based numerical model was used to simulate water flow and solute transport in the vadose zone and groundwater systems. The model incorporated soil and hydraulic properties produced with the GIS into the simulations. Numerical simulations described the time and spatial distributions of contaminants. Chemical mass stored in the soil and leaching out from the vadose zone were computed to characterize groundwater contamination. Groundwater sensitivity indexes, which were developed based on the numerical modeling results, were compared with the GIS sensitivity map and used to verify the reliability of the map.
temporal distributions of RLD using experimental measurements and simulations. The root length density (RLD) is an important parameter to modelExperimental measurement approaches of RLD diswater and nutrient movement in the vadose zone and to study soiltributions include the root sampling method (Kumar root-shoot-atmosphere interactions. However, it is difficult and time- et al., 1993) and rhizotron (or minirhizotron) method consuming to measure and determine RLD distributions accurately. Especially RLD distributions change with different soil environment, (Ephrath et al., 1999). The root sampling method is plant species, growing seasons, and climatic conditions. In this study, direct and reliable, however, time-consuming and demeasured data sets of wheat RLD distributions were collected from structive. The rhizotron method can be used to monitor the literature and transformed into normalized root length density root development under almost undisturbed conditions (NRLD) distributions. A total of 610 values of wheat NRLD distribuby comparing a series of root photographs taken during tions were pooled together. These data showed a general trend, indesuccessive time periods. Nevertheless, reliability of the pendent of soil environment, wheat species, growing seasons, and rhizotron technique has yet to be fully assessed. Many climates. A generalized function was established to characterize the factors, such as insertion angles of observation tubes NRLD distributions versus normalized root depths. To verify the for photographs and the calibration curve between root generalized function, we measured RLD distributions of winter wheat count and RLD can affect the accuracy of the RLD (Triticum aestivum L.) using laboratory and field experiments for distribution. Therefore, the accurate and effective meadifferent soils, growing stages of wheat, atmospheric conditions, and surement of transient RLD distributions is still a chalwater supplies. Using the generalized function, we predicted winter wheat RLD and compared the predicted results with the experimental lenging task. data and with results using other NRLD functions. The comparison Simulation approaches of RLD distributions include showed that the generalized function predicted RLD distributions root architecture models (Diggle, 1988; Grabarnik et more accurately than the other functions. Although simulated results al., 1998; Thaler and Pagè s, 1998; Bidel et al., 2000), of soil water dynamics in soil-wheat systems were similar for the plant growth models (e.g., AFRCWHEAT2, CERESdifferent NRLD functions, the generalized function should be advan-Wheat, Jamieson et al., 1998; Jamieson and Ewert, tageous for applications that require accurate information of root 1999), and shoot and root models (Thornley, 1995, development and distribution. use a single L nrd function for each crop. Nonetheless, 430072, China; and Dep. of Renewable Resources, University of Wyothe results need additional examinations because of the ming, Laramie, WY 82071-3354, USA
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