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231.
运动目标阴影在很大程度上会影响运动目标跟踪、行为识别的正确性和有效性.为此,文中提出了一种基于混合高斯模型和马尔科夫随机场的自适应阴影检测方法.该方法首先对混合高斯模型进行改进,使其可以自适应调整参数学习率以消除浅阴影;然后采用马尔科夫随机场综合邻域的空间依赖性信息进行精确的阴影检测.为了提高基于马尔科夫随机场的阴影检... 相似文献
232.
利用一维粒子模拟程序研究和比较了斜入射和垂直入射激光脉冲与稠密等离子体相互作用得到的阿秒脉冲以及激光强度对阿秒脉冲转换比率的影响.同样参数下,斜入射的阿秒脉冲转换比率明显高于垂直入射的情况,滤波后得到的阿秒脉冲振幅比较大,而脉冲串中阿秒脉冲的个数则是垂直入射时的一半.根据振荡镜面模型对两种情况进行了分析,由镜面振荡方程可以对结果给出解释.保持等离子体密度不变,增大入射激光强度时,随着滤波次数的增加,斜入射与垂直入射的阿秒脉冲的转换比率逐渐趋于相同.300次以上高通滤波后我们得到了处于X射线范围的阿秒脉冲. 相似文献
233.
The flame-holding mechanism in hypersonic propulsion technology is the most important factor in prolonging the duration time of hypersonic vehicles.The two-dimensional coupled implicit Reynolds-averaged Navier-Stokes equations,the shear-stress transport k-ω turbulence model and the finite-rate/eddy-dissipation reaction models were used to simulate the combustion flow field of a typical strut-based scramjet combustor.We investigated the effects of the hydrogen-air reaction mechanism and fuel injection temperature and pressure on the parametric distributions in the combustor.The numerical results show qualitative agreement with the experimental data.The hydrogen-air reaction mechanism makes only a slight difference in parametric distributions along the walls of the combustor,and the expansion waves and shock waves exist in the combustor simultaneously.Furthermore,the expansion wave is formed ahead of the shock wave.A transition occurs from the shock wave to the normal shock wave when the injection pressure or temperature increases,and the reaction zone becomes broader.When the injection pressure and temperature both increase,the waves are pushed out of the combustor with subsonic flows.When the waves are generated ahead of the strut,the separation zone is formed in double near the walls of the combustor because of the interaction of the shock wave and the boundary layer.The separation zone becomes smaller and disappears with the disappearance of the shock wave.Because of the horizontal fuel injection,the vorticity is generated near the base face of the strut,and this region is the main origin for turbulent combustion. 相似文献
234.
WenJue Zhong DongHong Wang XiaoWei Xu BingYi Wang Qian Luo Satyanarayanan Senthil Kumaran ZiJian Wang 《科学通报(英文版)》2011,56(3):275-284
Phenolic compounds exist widely in the influents and effluents of sewage treatment plants (STPs) and most are un-regulated.
In this study, a gas chromatography-mass spectrometry (GC-MS) method for the simultaneous analysis of 50 phenolic compounds
in wastewater was developed. Deconvolution technology was used to identify contaminants that are covered by co-extracted materials.
A mass spectral library containing all 50 silylated phenolic compounds was first established and used for deconvolution. Twelve
typical phenolic compounds were selected to optimize the sample preparation procedures. Solid-phase extraction using a C18
cartridge coupled with an HLB cartridge was used for pre-concentration and dichloromethane was used for elution. The solutes
were derivatized and analyzed by GC-MS. The blank and matrix spike recoveries ranged from 57.46% to 136.4% and 47.87% to 114.8%,
respectively. Method detection limits ranged from 3.64 to 97.64 ng L−1. The relative standard deviations of all the recovery experiments were lower than 13.6%. The instrument limits of quantification
ranged from 0.7 to 87.7 pg. The method has been applied to analyze the influents and effluents of 5 Chinese STPs. Except for
regulated phenolic compounds (phenol and 2,4,6-trichlorophenol), three un-regulated phenolic compounds, including 2-chlorophenol,
2,5-dichlorophenol and 2,4-dichloro-3-ethyl-6-nitrophenol were identified in the effluent wastewater. The detected concentrations
of un-regulated phenolic compounds could possibly cause environmental effects, indicating that immediate attention is required
to prevent complications. 相似文献
235.
Fan Yu Jun Xiao XiangYang Liang ShaoJun Liu GongJian Zhou KaiKun Luo Yun Liu Wei Hu YaPing Wang ZuoYan Zhu 《科学通报(英文版)》2011,56(16):1679-1684
Triploid carp (100%) with 150 (3n=150) chromosomes were obtained by crossing the females of improved tetraploid hybrids (♀,
4n=200) of red crucian carp (♀)×common carp (♂) with the males of diploid yellow river carp (♂, 2n=100). The crosses yielded
transgenic triploid carp (positive triploid fish, 44.2% of the progeny) and non-transgenic triploid carp (negative triploid
fish). Histological examination of the gonads of 24-month-old positive triploid fish suggested they were sterile and the fish
were not able to produce mature gametes during the breeding season. Morphologically, both the positive and negative triploid
fish were similar. They had a spindle-shaped, laterally compressed, steel grey body with two pairs of barbells. Most of the
quantifiable traits of the triploid carp were intermediate between those of the two parents. The positive and negative triploid
fish were raised in the same pond for 2 years. The mean body weight of the positive triploid fish was 2.3 times higher than
the negative triploid fish. The weight of the largest positive triploid fish was 2.91 times higher than that of the largest
negative triploid fish. Thus, we produced fast-growing transgenic triploid carp that have a reduced ecological risk because
of their inability to mate and produce progeny. 相似文献
236.
The strontium isotopic compositions (87Sr/86Sr) of samples including soils, bedrock, soil waters, drip waters and their corresponding speleothems in the Qixing Cave (QXC), Guizhou Province, China, were systemically measured and analyzed. The results indicate that there are significant Sr isotopic differences among samples. The mean 87Sr/86Sr ratios in drip water for the samples 1#, 4# and 9# were 0.709568, 0.709139 and 0.708761, respectively, which possibly result from different flow paths, residence times, and other hydrogeological processes in the unsaturated zone overlying QXC. Meanwhile, levels of 40.8%, 57.6% and 72.4% of Sr in drip waters for 1#, 4# and 9#, respectively, were derived from bedrock dissolution, which was calculated by the mixture model of the two end-members (soil and bedrock). There is, however, no positive correlation between the relative proportion from bedrock dissolution (δ13C value is 1.8‰) and drip water δ13CDIC values. The mean drip water δ13CDIC value in 1# is the heaviest (–4.5‰) with the lowest contribution rate of bedrock dissolution, whereas the value in 9# is the lightest (–9.3‰) with the highest contribution rate of bedrock dissolution. The proportion from host rock dissolution in 4# is higher than that in 1# and lower than that in 9#, while its mean drip water δ13CDIC value (–8.6‰) is higher than that of 9# and lower than that for 1#. This suggests that the prior calcite precipitation (PCP) processes in the unsaturated zone overlying the cave are responsible for the δ13CDIC value differences between different drip waters, and not bedrock dissolution. Furthermore, this study also demonstrates that the 87Sr/86Sr ratios of speleothems in the 1# and 4# mainly reflect the variation in the relative proportions from the soil system (soil water) and bedrock dissolution overlying the cave. It is, therefore, feasible to use the strontium isotopic signals of speleothems as an indicator for soil chemical weathering intensity, and consequently as a monsoon proxy in the study area. 相似文献
237.
中国工程院院士、华东师范大学河口海岸研究院陈吉余教授最近建议在长江河口缔造一个500公里2的新地,来缓解上海市土地、港口、水资源紧缺之困境,为上海市的长远发展提出了极其重要的宏伟设想. 相似文献
238.
239.
文章主要探讨造成加气混凝土砌块墙体裂缝;加气混凝土外墙渗水和加气混凝土填充墙抹灰层空鼓、脱落等三大问题的原因,并就这三大问题提出了具体的防治措施,为以后的施工提供借鉴。 相似文献
240.
池塘养鱼对池塘水源、面积、水深、形状和方向、底质、环境等重要因素进行具体分析,提出养鱼水质对鱼类和水生生物的水温适应范围及最适生长温度、改造方法,为池塘养鱼高产提供参考。 相似文献