Search

Dalvik VM is the core part of the Android platform, its performance determines the overall performance of Android. Executing code is done by interpreter. And in order to improve its efficiency, JIT compiler is supported in Dalvik VM, a technique also know as dynamic translation which is an effective method to improve the runtime performance. After analyzing the overall framework of Dalvik JIT, we propose a optimizing strategy to eliminate redundant compilation. Then we test the performance of Dalvik JIT before and after optimization, and under its different mode, using test cases such as benchmark like Linpack and Scimark2, etc. The results of tests show that program execution efficiency is higher and its performance is improved after eliminate redundant compiled.

In order to reduce agricultural pollution caused by the excessive application of nitrogen fertilizer, a field experiment was conducted to investigate the effects of different fertilization strategies on nitrate leaching in 0-100 cm soil layer using nitrate leaching device in a winter wheat-summer maize rotation system on the piedmong plain of Taihang Mountain. The results showed that soil NO3 -- N leaching and accumulation increased with the increasing of nitrogen fertilization. The effects of nitrogen applications on nitrate leaching varied in the 0-100cm soil layer, and the accumulatation rate is OPT+N > FP > FP-S > OPT > OPT-N > CK. The nitrate mainly existed in 20-40 cm soil layer in wheat season. It appeared mainly in the surface layer and deep layer in maize season. The nitrate accumulation amount in the 0-100cm soil layer have a significant increasing after 3 rotations especially in the 60-100 cm, which indicating that the primary cause of nitrate leaching and accumulation was N fertilization. Compared with other treatments, the OPT significantly increased crop yield, nitrogen use efficiency and partial factor productivity in the 3 years wheat-maize rotations. Considering the economic and ecological benefits, the OPT fertilization strategy is worth to be recommended to farmers.

Vertical distribution of diverse available heavy metal elements in vegertable soil profile ( 0 ~ 2m ) was studied with different extractants. The results indicated that the content of available heavy metal in soil decreased with the increase the depth. This regularity adequately showed that the external factors were the important resources of available heavy metal, for example the atmospheric deposition, fertilizer application, pesticides and so on. The content of one single element in deeper layer was still high in individual region, it maybe the soil was influenced by heavy metal mineralization.

This study used a long-term experiment to research the effects of long-term fertilization on cinnamon soil fertility and crop yield of Northern China Plain. The results showed that the soil applied N alone still holded high NO3 -- N after wheat harvesting, the followed arrival of the rainy season will increase the environmental risk of pollution to groundwater. Application of phosphate fertilizer and potassium fertilizer increased the soil content of available P and K significantly. Continuously applied fertilizer without phosphorus or potassium, the soil had a serious depletion of P or K. Application of zinc fertilizer had soil available zinc content increased significantly. In order to increase yield, maintain soil fertility, and protect environment, Applied Nitrogen with phosphorous and potassium is the best choice in the northern China plain.

In order to investigate the content of groundwater NO3 -- N in Hebei Province. [Methods] In 2011,500 groundwater samples were collected from 11 cities of Hebei Province before and after the rainy season, the contents of groundwater NO3 -- N was analyzed with ultraviolet and visible spectrophotometer. [Results] The groundwater NO3 -- N contents of Hebei Province changed from 0.01mg/L to 350.86 mg/L, averaged 9.37mg/L. Single maize seeding in spring and vegetable cropping had the severe effects on groundwater NO3 -- N contents and cotton cropping had the least effect. The groundwater NO3 -- N contents of Hebei Province declined with the increasing depth from where sampled. According to the NO3 -- N contents, the water from deeper than 100m had the best quality, and from shallower than 30m had the worst quality. [Conclusion] According to the national drinking water standard, there was 11% of sample with NO3 -- N contents higher than 20 mg/L. 45.40% of the sample from Hebei Province with the NO3 -- N contents was lower or equal to 2mg/L, which means better quality for drinking water.

According to the National Standard of the People's Republic of China (GB/T18407.1-2001), environmental quality assessment of heavy metal in soil of pollution-free vegetable produced in Hebei Plain Area was carried out. The results by the single-index model indicated that the areas of the Grade I of pollution-free vegetable soil with As, Hg, Pb, Cd, Cr were all above 94%, others were Grade II and upward except Cd with 0.34% area of Grade III. The result by the multi-index models showed that the areas of the Grade I, II, III were 93.02%, 6.62% and 0.31% respectively. To sum up, environmental quality of heavy metal in soil of Hebei Plain Areas is benign, and the heal mental excessive rate in soil (GB/T18407.1-2001) is relatively low, which lays a solid foundation for the wide future developments of pollution-free vegetable and green vegetable planting bases.

With investigation in field and assay in the lab, the current situation and influencing factors of groundwater nitrate nitrogen (hereinafter referred to as NO 3 − — N) content in the regions surrounding Bohai Sea in Hebei province were studied. The results show that the contents of groundwater NO 3 − — N in the regions generally meet the level III criterion of GB/T14848–93. However, the spatial variability in the region is great. In Qinhuangdao, the situation is the severest with the average value of groundwater NO 3 − — N increasing year after year from 2005 to 2007 as 4.73 mg/L, 10.38 mg/L, and 11.26 mg/L respectively. The averages of the last two years surpass the drinking water criteria ( vegetable land > rice plus fish-raising land > orchard. The water samples with the highest content are mainly from spring corn farmland. The hill in the type of physiognomy affected greatly the content of NO 3 − — N in groundwater. The content reduces sharply with the continuous decrease of groundwater depth. Fertilization, surface run-off, and aquatic product pollution are the main causes of formation for the increase of groundwater NO 3 − — N in the regions. Therefore, the regions need specific governance and management.

In order to resolve the trust problem due to the opening, the dynamics, the anonymity and uncertainty of p2p system, this paper proposes a new p2p trust model by analyzing and improving the subjective logic , a new trust quantification formula with the negative events effect and the time effect is given, and a definition of risk is also presented, By doing this, we can evaluate the trust relationships between peers more precisely and prevent the hidden security dangers of cooperative cheat and slander more effectively, thus can resolve security problems exist in p2p environment more effectively.