共查询到18条相似文献,搜索用时 125 毫秒
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北京奥运期间石化工业区多组分污染气体的开放光程FTIR监测 总被引:1,自引:0,他引:1
利用自行研制的开放光程傅里叶变换红外光谱(FTIR)测量系统于2008奥运期间对北京燕山地区大气中的HCHO,CH4,CH3OH,C2H6,C2H4,C2H2和CH3COCH3气体进行了连续监测,介绍了系统的组成及光谱数据处理方法,并对浓度测量结果进行了分析。研究结果显示,7月20日限行措施实施后,除C2H4外,其他气体日平均浓度均有明显下降,平均幅度约29%,奥运期间平均降幅达34%,受局部气象条件引起的本底浓度暂时性波动影响,监测指标物中,C2H4平均浓度分别增加6.09%和19.66%,但其日变化幅度明显下降,表明北京市奥运期间的控制减排措施有效。 相似文献
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传统差分吸收光谱法(DOAS)对于H2S气体浓度检测原理简单,检测精准,反应速度较快,但在低浓度、光程较短的环境中会产生较大的误差。本文在传统的差分吸收算法的基础上,采用遗传算法对低浓度H2S气体进行反演,但遗传算法容易发生过早收敛,从而陷入局部最优,因此设计了灾变优化后的遗传算法对H2S气体浓度进行反演。结果表明,该方法对低浓度H2S气体有较高的测量精确度,与传统的差分吸收光谱法结合可得到更宽的检测范围。 相似文献
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CO2和H2O是大气中两种重要的温室气体,对生态系统中CO2和H2O的浓度进行在线监测可用于分析环境及气候变化。选择CO2和H2O的近红外吸收谱线,利用可调谐半导体激光吸收光谱技术结合自动增益调节技术设计了开放式CO2和H2O在线检测仪。在中国科学院禹城综合试验站进行了1238m光程下,20Hz时间分辨率的连续观测实验,结果表明自动增益调节解决了开放光路检测时探测信号幅度大幅变化问题。监测点的CO2浓度具有白天低,夜间高的日变化周期性。与同场地涡度相关系统的LI-7500对比测量,数据一致性较好。该检测技术灵敏度高、响应速度快、免采样,实现了大尺度区域生态系统中CO2和H2O浓度的稳定、连续、在线检测。 相似文献
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工业革命以来,温室效应引起的全球气候变迁问题越来越受到人们的关注。人类活动相关的主要温室气体是CO2,CH4,N2O和CO,对其浓度进行连续测量,获取浓度随时间的变化规律对大气环境科学具有重要意义。使用多次反射池FTIR系统在浙江地区对这四种气体进行了监测,通过对测量的气体吸收光谱进行光谱定量分析,获取了待测组分的浓度信息,并对其变化规律进行了分析。同时对仪器的性能进行了检测,结果表明,多次反射池FTIR是进行环境气体监测的一种快速有效直接的监测手段。 相似文献
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Electron mobility models for 4H, 6H, and 3C SiC [MESFETs] 总被引:2,自引:0,他引:2
Models for the electron mobility in the three most important silicon carbide (SiC) polytypes, namely, 4H, 6H, and 3C SiC are developed. A large number of experimental mobility data and Monte Carlo (MC) results reported in the literature have been evaluated and serve as the basis for the model development. The proposed models describe the dependence of the electron mobility on doping concentration, temperature, and electric field. The low-field mobility in 4H SiC is much higher than in 6H and 3C in the doping range interesting for RF power transistors (1016 cm-3 ...1018 cm -3), whereas the saturation velocities in the three polytypes investigated are nearly the same (slightly above 2×107 cm/s at 300 K). The models developed can be easily incorporated into numerical device simulators 相似文献
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C-H体系CVD金刚石薄膜取向生长的热力学分析 总被引:1,自引:0,他引:1
化学气相淀积金刚石薄膜过程中 ,CH3 和C2 H2 是金刚石生长的主要前驱基团。C2 H2 与CH3 浓度比 ( [C2 H2 ]/[CH3 ])的变化将影响金刚石薄膜的生长取向。用非平衡热力学耦合模型计算了C H体系CVD金刚石薄膜生长过程中C2 H2 浓度和CH3浓度随淀积条件的变化 ,并进一步获得了 [C2 H2 ]/[CH3 ]随衬底温度和CH4浓度的变化关系 ,从理论上探讨了金刚石薄膜 ( 1 1 1 )面和 ( 1 0 0 )面取向生长与淀积条件的关系。在衬底温度和CH4浓度由低到高的变化过程中 ,[C2 H2 ]/[CH3 ]逐渐升高 ,导致金刚石薄膜的形貌从 ( 1 1 1 )晶面转为 ( 1 0 0 )晶面。 相似文献
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N. Nordell A. Schöner K. Rottner P. O. Å. Persson Q. Wahab L. Hultman M. K. Linnarsson E. Olsson 《Journal of Electronic Materials》1998,27(7):833-837
Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×1016 cm−3 and 2×1018 cm−3. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron
microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated
with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during
regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects
could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows
the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up
at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point
defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer
at a concentration of below 2×1016 cm−3, with a diffusion constant estimated to 1.3×10−12 cm2s−1. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation
shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device
structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region.
A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B. 相似文献
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The latest international video-coding standard H.264/AVC significantly achieves better coding performance compared to prior
video coding standards such as MPEG-2 and H.263, which have been widely used in today’s digital video applications. To provide
the interoperability between different coding standards, this paper proposes an efficient architecture for MPEG-2/H.263/H.264/AVC
to H.264/AVC intra frame transcoding, using the original information such as discrete cosine transform (DCT) coefficients
and coded mode type. Low-frequency components of DCT coefficients and a novel rate distortion cost function are used to select
a set of candidate modes for rate distortion optimization (RDO) decision. For H.263 and H.264/AVC, a mode refinement scheme
is utilized to eliminate unlikely modes before RDO mode decision, based on coded mode information. The experimental results,
conducted on JM12.2 with fast C8MB mode decision, reveal that average 58%, 59% and 60% of computation (re-encoding) time can
be saved for MPEG-2, H.263, H.264/AVC to H.264/AVC intra frame transcodings respectively, while preserving good coding performance
when compared with complex cascaded pixel domain transcoding (CCPDT); or average 88% (a speed up factor of 8) when compared
with CCPDT without considering fast C8MB. The proposed algorithm for H.264/AVC homogeneous transcoding is also compared to
the simple cascaded pixel domain transcoding (with original mode reuse). The results of this comparison indicate that the
proposed algorithm significantly outperforms the mode reuse algorithm in coding performance, with only slightly higher computation. 相似文献