Characterization of humic substances by advanced solid state NMR spectroscopy: Demonstration of a systematic approach   总被引：2，自引：0，他引：2  

Jingdong Mao  Na ChenXiaoyan Cao 《Organic Geochemistry》2011,42(8):891-902

Characterization of humic substances is challenging due to their structural complexity and heterogeneity. Solid state nuclear magnetic resonance (NMR) is regarded as one of the best tools for elucidating structures of humic substances. The primary solid state NMR technique that has been used so far is the routine ¹³C cross polarization-magic angle spinning (CP-MAS) technique. Although this technique has markedly advanced our understanding of humic substances, the full potential of NMR for characterizing humic substances has yet to be realized. Recent technical developments and applications of advanced solid state NMR have revealed the promise to provide deeper insights into structures of humic substances. In this paper, we summarized and demonstrated the systematic solid state NMR protocol for characterization of humic substances using a humic acid as an example. This protocol included (1) identification of specific functional groups using spectral editing techniques, occasionally assisted by ¹H¹³C two-dimensional heteronuclear correlation (2D HETCOR) NMR, (2) quantification of specific functional groups based on direct polarization-magic angle spinning (DP-MAS) and DP-MAS with recoupled dipolar dephasing, combined with spectral editing techniques, (3) determination of connectivities and proximities of specific functional groups by ¹H¹³C 2D HETCOR or 2D HETCOR combined with spectral editing techniques, and (4) examination of domains and heterogeneities by ¹H¹³C 2D HETCOR with ¹H spin diffusion. We used a soil humic acid as an example to demonstrate how this protocol was applied to the characterization of humic substances step by step. Afterwards, based on typical ¹³C NMR spectra of humic substances we described how we could combine different NMR techniques to identify specific functional groups band by band from downfield to upfield. Finally, we briefly mentioned the potential new NMR techniques that could be developed to enrich the current systematic protocol. This systematic protocol is not only applicable to humic substances but also to other natural organic matter samples.  相似文献   

CMMB信号抗多径性能的分析与仿真     

李俊俊  华宇  黄长江 《时间频率学报》2012,35(4):244-249

从CMMB（中国移动多媒体广播）体系结构入手,研究了CMMB信号抗多径性能。以信号中有、无循环前缀（CP）为例给出了抗多径性能的详细推导,通过Matlab 7．1对该系统在典型动态多径信道情况下的性能进行了仿真。结果表明：该系统有很强的抗多径能力,在信噪比为30dB时接收CMMB信号与接收普通OFDM（正交频分复用）信号相比,误码率有2个量级的改善,有利于提高导航定位的精度。  相似文献   

高速铁路轨道控制网精密测量数据处理   总被引：2，自引：0，他引：2  

周东卫 《测绘科学》2013,38(1):118-121

高速铁路无砟轨道施工建设需要布设高精度的轨道控制网(CPIII),要求相邻点平面相对精度优于1mm,同精度复测较差优于3mm。本文针对轨道控制网测量工程的特点,提出一种适合轨道控制网精密测量数据的处理方法,并采用国内某客专的实测数据进行了分析验证。实验结果表明,采用本文提出的方法能有效提高轨道控制网的平差精度、可靠性和计算效能。  相似文献   

厄尔尼诺事件对中国夏季水汽输送和降水分布影响的新研究   总被引：1，自引：0，他引：1       下载免费PDF全文

吴萍  丁一汇  柳艳菊 《Acta Meteorologica Sinica》2017,75(3):371-383

基于1961-2016年中国地面台站降水观测资料和多种再分析资料,分析了东部型和中部型两类厄尔尼诺事件对中国夏季水汽输送和降水的不同影响。结果表明：（1）厄尔尼诺事件对中国夏季降水的影响在发生当年和次年有明显的不同,主要影响是在其发生的次年,中国大部分地区的夏季降水明显偏多。（2）东部型厄尔尼诺事件当年夏季,西北太平洋副热带高压（副高）偏东偏弱,水汽输送条件较弱,不利于中国大范围降水的发生;中部型事件当年夏季,低纬度印度洋和西太平洋蒸发异常偏强,来自阿拉伯海、孟加拉湾和西北太平洋向华南地区的水汽输送和净水汽收支增加,有利于华南地区降水的异常增多。（3）东部型厄尔尼诺事件次年夏季,副热带太平洋蒸发异常偏强,副高西伸,由于东亚-太平洋（EAP）遥相关型的建立,副高西侧的强西南气流将来自太平洋蒸发的大量水汽持续输送至中国中东部地区。此外,在东亚-太平洋遥相关型影响下中高纬度地区建立了亚洲双阻型环流,其间的低槽冷涡与上游阻高之间的强偏北气流有利于北冰洋的水汽持续输送到西北和华北北部地区,中国大部分地区净水汽收支均增加,中国北方和南方地区的降水均产生了明显的同步性增多响应,形成了南北两条异常雨带。中部型厄尔尼诺事件次年夏季,副高较常年偏西且偏北,来自太平洋蒸发的大量水汽输送到江淮地区,使其净水汽收支增加和降水偏多。因此,厄尔尼诺事件的发生不仅对长江流域和淮河流域等南方地区的降水有重要影响,对华北、东北和西北地区的降水异常也有相当的作用。  相似文献   

基于精密测量技术的高速铁路运营安全监测研究     

曾庆伟  晁召波 《测绘与空间地理信息》2016,(5):79-82

高速铁路运营阶段,可借助CPⅢ控制网对其轨道平顺性进行监测,以保障列车运行安全。CPⅢ控制点的稳定性和位置精度决定运营安全监测的可靠性。本文提出了基于精密测量技术的CPⅢ控制点稳定性检测方法,以发现存在较大点位误差的控制点,确保参与监测的CPⅢ控制点精度。  相似文献   

Cause of Extreme Heavy and Persistent Rainfall over Yangtze River in Summer 2020     

Xiao PAN  Tim LI  Ying SUN  Zhiwei ZHU 《大气科学进展》2021,38(12):1994-2009

Record-breaking heavy and persistent precipitation occurred over the Yangtze River Valley (YRV) in June-July (JJ) 2020. An observational data analysis has indicated that the strong and persistent rainfall arose from the confluence of southerly wind anomalies to the south associated with an extremely strong anomalous anticyclone over the western North Pacific (WNPAC) and northeasterly anomalies to the north associated with a high-pressure anomaly over Northeast Asia. A further observational and modeling study has shown that the extremely strong WNPAC was caused by both La Ni?a-like SST anomaly (SSTA) forcing in the equatorial Pacific and warm SSTA forcing in the tropical Indian Ocean (IO). Different from conventional central Pacific (CP) El Ni?os that decay slowly, a CP El Ni?o in early 2020 decayed quickly and became a La Ni?a by early summer. This quick transition had a critical impact on the WNPAC. Meanwhile, an unusually large area of SST warming occurred in the tropical IO because a moderate interannual SSTA over the IO associated with the CP El Ni?o was superposed by an interdecadal/long-term trend component. Numerical sensitivity experiments have demonstrated that both the heating anomaly in the IO and the heating anomaly in the tropical Pacific contributed to the formation and maintenance of the WNPAC. The persistent high-pressure anomaly in Northeast Asia was part of a stationary Rossby wave train in the midlatitudes, driven by combined heating anomalies over India, the tropical eastern Pacific, and the tropical Atlantic.  相似文献   

南印度洋副热带偶极子型海温异常与全球环流和我国降水变化的关系   总被引：9，自引：1，他引：9  

杨秋明 《海洋学报》2006,28(3):47-56

用1951~2001年观测资料,研究了南印度洋副热带偶极子型(IOSD)海温异常对全球500hPa环流和我国降水的影响.结果表明,冬季IOSD激发出极显著的南北半球环绕太平洋的波列结构(CP),其年际变化周期是2.0和6.5 a,与赤道中东太平洋海温也有密切联系.北半球冬季异常峰值后的第二年春季欧亚中高纬度地区500 hPa环流出现显著的EUP型低频流型持续异常,同时中太平洋和北美地区出现CPNP流型和澳大利亚南部的南半球中高纬地区呈现极显著的西南太平洋遥相关型(SWP).当冬季赤道南印度洋副热带呈极显著的西负东正海温距平分布时,后期春季欧亚中高纬地区负EUP型遥相关波列持续偏强,导致东亚大槽明显偏弱,长江以北地区(特别是黄河中上游地区)多雨.反之,春季东亚大槽加强且稳定,我国东部地区大范围少雨.它反映了南印度洋地区海气系统相互作用与东亚热带内外环流低频变化的联系.因此,上一年冬季南印度洋副热带偶极子型(IOSD)海温异常强度是预测春季华北地区旱涝变化的重要因子之一.  相似文献   

Structural modifications of vitrinite and alginite concentrates during pyrolitic maturation at different heating rates. A combined infrared, C NMR and microscopical study     

H.J. Schenk  E.G. Witte  R. Littke  K. Schwochau 《Organic Geochemistry》1990,16(4-6)

Immature vitrinite samples from a Miocene lignite seam of western Germany (H/C = 1.14, O/C = 0.41) and alginite concentrates from a Tasmanite deposit of Australia (H/C = 1.60, O/C = 0.10) were pyrolyzed in a stream of argon at heating rates of 0.1 and 2.0°C/min up to temperatures varying from 200 to 670°C. The solid maceral residues were subjected to elemental and microscopical analysis and studied by IR and ¹³C CP/MAS NMR spectroscopy with respect to structural modifications.The maximum pyrolytic weight loss amounts to 60% of the initial organic matter in the case of vitrinite and to 85% for alginite, the onset of degradation reactions being shifted to higher temperatures with increasing rate of heating. Both infrared and NMR spectra of the vitrinite samples indicate a rapid decomposition of the cellulose component upon heating whereas lignin related structures such as aromatic ether linkages remain remarkably stable. The main hydrocarbon release from vitrinite occurs at very early evolution stages (T_max = 296°C, R_m = 0.20% at 0.1°C/min; T_max = 337°C, R_m = 0.23 at 2.0°C/min). Hydrocarbon generation from alginite requires higher temperatures (T_max = 388 and 438°C) and is completed within a distinctly narrower temperature range.The pronounced increase of vitrinite reflectance between 350 and 670°C seems to be associated with a rather time-consuming reorganization of the residual organic material. The concomitant growth of polyaromatic units is illustrated by the increasing intensity ratio of the aromatic ring stretching vibration bands at 1600 and 1500 cm⁻¹. These reactions are moreover marked by increasing loss of phenolic oxygen and by increasing conversion of aliphatic carbon into fixed aromatic carbon.  相似文献   

两类厄尔尼诺事件对中国东部冬季气溶胶的影响     

李海燕  孙家仁  胡东明  谌志刚  曾琳  叶希莹 《气象学报》2018,76(5):699-713

利用MERRA-2再分析气溶胶光学厚度及气象观测资料,在剔除人为排放长期变化产生的气溶胶光学厚度扰动的基础上,从气候学角度探讨了两类厄尔尼诺事件对中国东部冬季气溶胶的影响。结果表明,东部型厄尔尼诺事件使绝大部分区域气溶胶光学厚度呈正异常分布,尤其对华北至东北的气溶胶污染加剧作用显著;而中部型厄尔尼诺事件使气溶胶光学厚度异常由南至北呈显著的“+-”双极型分布。进一步成因分析发现,虽然两类厄尔尼诺事件都具有削弱冬季风从而减弱北方气溶胶向南传输的作用,但中部型对水平流场的削弱作用不显著,尤其是东北地区没有通过90%的显著性检验。同时二者对北方大气垂直扰动和气溶胶的湿清除作用相反,其中东部型表现为大气垂直扰动和对流有效位能减弱,降水减少,湿清除减弱;而中部型则表现为垂直扰动和对流有效位能增强,降水增多,湿清除增强。对于南方,强东部型事件引发的强降水可能是产生该区域气溶胶污染影响不稳定的主因,而中部型则主要通过气流削弱作用加剧长江中下游地区气溶胶的局地污染。   相似文献   

基于 PDA 的 CPⅢ轨道控制网数据采集系统的设计与实现     

陈爱梅  吴昊  吴北平 《全球定位系统》2014,(5):82-85

为了提高C PⅢ轨道控制测量数据采集的效率,结合PD A 与测量机器人联合作业的技术特点,以Visual studio 2008和Visual C＃．NET 为开发平台和开发语言,采用串口通信和多线程技术,设计了基于PD A的C PⅢ轨道控制网数据采集系统。系统解决了国内外同类软件彼此间平台不统一、数据不兼容的问题,实现了在任意一款基于Windows Mobile操作系统的手簿上进行项目管理、数据通信、自动测量、质量控制和成果输出的功能。  相似文献