采样位置与时间选择对土壤重金属风险评估工作的影响

目的建立一种具有代表性且能够综合、准确反映多种重金属元素在土壤中污染状况的样品采集方法,为土壤重金属风险评估工作的顺利展开提供有力的保障。方法模拟铜、铅2种元素在土壤中的迁移条件,结合试验田铜元素、铅元素的背景值,分别添加Cu(NO3_)_2、Pb(NO_3)_2,使试验田中心污染源铜元素和铅元素的分别达到2.6×103 mg/kg和4.0×10~3 mg/kg。设置3组不同的灌溉量,每组设2个平行试验,分别于d 7、14、31、49进行采样,之后利用电感耦合等离子体发射光谱仪(ICP-OES)、原子吸收分光光度计检测这2种重金属元素含量,研究铜、铅在土壤中的迁移规律。结果检测结果显示铜、铅2种元素在土壤中的横向迁移速度差异较大。铜元素横向扩散速度较快,在d 49时监测位点的铜元素浓度趋于稳定,接近最大值;而铅元素较慢,监测位点的铅元素浓度基本没有发生变化。结论单一的取样点难以同时满足铜、铅2种重金属元素的风险评估工作需要,建议对这2种重金属元素的取样检测工作应尽量区别开展。     

Corrosion Behavior of Friction Stir-Processed and Gas Tungsten Arc-Welded Ti-6Al-4V

The corrosion behavior of the investment-cast Ti-6Al-4V alloy in 5-pct HCl solution was investigated after gas tungsten arc welding and friction stir (FS) processing. The FS-processed samples exhibited superior corrosion behavior compared with the base metal and the arc-welded samples. The inferior corrosion resistance of the arc weldment was attributed to the acicular α and β microstructure and the alloying element partitioning between the phases. This was confirmed by scanning electron microscopy evaluations of the surface of specimens that had been immersed 50 hours in 20-pct HCl at 308 K (35 °C). In addition, the results indicated that vanadium as an alloying element has a detrimental effect on the corrosion performance of Ti-6Al-4V alloy in an HCl solution.     

一种QoS保证的移动自组网低能耗资源发现协议

如何在大规模的移动自组网络中快速地找到所需的资源是一个迫切需要解决的问题.提出了一种称为EAQOS(Energy Aware QoS)的资源发现协议,本协议将资源查询请求过程同路由协议紧密结合,通过合并资源请求、QoS探测以及路径请求信息能够快速定位网络中的最优QoS的资源供应者并进行访问,同时有效降低了网络中的通信量以及能量消耗.最后通过NS2进行模拟实验,与两种不同的Qos资源发现协议相比,结果表明所提出协议的性能,包括查询延迟、通信代价以及能量消耗都有显著的提高.     

PDSOI SRAM单元的单粒子加固方法

通过MEDICI的二维器件模拟,提出不仅在正栅下的体区受到单粒子入射后释放电荷外,漏极也可以在受到单粒子入射后释放干扰电荷.对SOI SRAM单元中器件的漏极掺杂浓度进行优化,可以减小漏极受到单粒子入射所释放的电荷.改进了SOI SRAM的单元结构,可以提高SRAM抗单粒子翻转(SEU)的能力.     

Extension of a graphical approach to time-varying system analysis

Time-varying system parameters and control inputs are assumed constant over small intervals of time and corresponding incremental time transition matrices are determined from l-invariant system theory. A sequence of incremental convolution operations determining incremental state responses yields the overall-time state response in a discretized form, and is shown to correspond to the continuous integral-convolution response equation from analytical theory. The incremental time response synthesis is extended to a derivation of Neumann's Series and discrepancies relevant to numerical work are noted. At appropriate stages in the development results obtained from high order transition matrices are related to those of the first order finite difference method. The graphical approach elucidates problem structure and contributes to a clearer understanding of lvarying system analysis for the benefit of both tutorial and practical numerical work on non-singular systems.     

Decadal Changes in Climatological Intraseasonal Fluctuation of Subseasonal Evolution of Summer Precipitation over the Korean Peninsula in the mid-1990s

T Decadal changes in the subseasonal evolution and the phase-locked climatological intraseasonal fluctuation of summertime rainfall over the Korean Peninsula before and after the mid-1990s are investigated. The activity and the migration speed of the monsoon rain band over the East Asian region are altered in the recent decade, resulting in the drier conditions in late spring and the earlier onset of Changma. In early August when a climatological monsoon break was clear in the earlier decade, the precipitation has increased dramatically with a meridional coherency. The response to the enhanced convection over the South China Sea and southeastern China provides a favorable condition for more precipitation in early August through the changes in moisture transport and tropical cyclone passage.