基于分层核磁测试新技术的未冻水变化规律研究——以砂土冻融过程为例北大核心CSCD     

韩大伟  杨成松  张莲海  石亚军  尚飞 《冰川冻土》2022,44(2):667-683

土体冻融过程中的未冻水动态变化与冰-水相变过程密切相关,是冻融过程中非饱和土研究的重要基础。利用在线控温以及分层扫描的核磁共振新技术直观测试冻融过程中非饱和砂土的未冻水含量。结合T_(2)分布曲线(曲线上不同的T;值对应着孔隙水类别特性,曲线下方的面积对应试样水分含量)在冻融过程中的峰值大小和峰面积数据反演土体中含水量的大小与赋存的位置,而曲线的峰形态以及弛豫范围(各峰起始值以及终止值)等信息反演不同类型水分(吸附水与毛细水)以及土体结构的分布。在处理试验结果时,首先依据测试得到的冻结温度划分试样冻结区与未冻区。冻结区与未冻区未冻水含量及其孔隙变化差异明显,究其原因是冰水相变与水分迁移。在土样冻结区域冰水相变占主导地位,水分主要由未冻区向冻结锋面附近的e、f层迁移。首先以中大孔隙中毛细水迁移为主,其次以小孔隙中的吸附水迁移为辅。依据水相变成冰体积增大和孔隙体积占比数据分析可知,冻结区微小孔隙会在冻结过程中连通形成中大孔隙;而在未冻区水分迁移占主导地位。未冻区受固结作用中大孔隙压缩形成为小孔隙。试验过程中冻结锋面附近的e、f层孔隙变化最为剧烈。  相似文献   

Sentinel-3卫星双角度热红外数据的流域尺度地表蒸散发估算与验证     

薛可嘉  何苗  卞尊健  宋立生  徐艳豪  蒋浩 《遥感学报》2021,25(8):1683-1699

双层能量平衡模型TSEB（Two Source Energy Balance）常用于地表蒸散发的估算研究,对于干旱半干旱流域的水资源调控以及利用有着十分重要的意义。本文在流域尺度上分别利用Sentinel-3双角度观测热红外和近红外数据反演的地表温度LST（Land Surfacer Temperature）和地表组分温度LSCT（Land Surface Component Temperatures）分别驱动TSEB模型,估算了黑河流域不同土地覆盖类型下的瞬时地表通量,并利用流域内上、中、下游通量塔地面观测数据验证了两种模型估算的地表通量。结果表明：两种模型都在一定程度上高估了净辐射和潜热通量,在植被稀疏的高寒草甸以及河岸林土地覆被类型下,TSEB-PT模型表现更好,随着植被覆盖度的上升,TSEB-2T模型的优势更加明显。研究结果为黑河流域水资源合理利用提供一定的保障以及为水资源管理者提供流域尺度上更加准确的植被水分利用的估计值,并且为后期模型的优化提供了理论基础。  相似文献   

A long-term UBVRI photometric study of the pre-main sequence star V350 Cep     

Sunay Ibryamov  Evgeni Semkov  Stoyanka Peneva 《中国天文和天体物理学报》2014,(10)

Results from UBVRI optical photometric observations of the pre-main sequence star V350 Cep during the period 2004-2014 are presented.The star was discovered in 1977 due to its remarkable increase in brightness by more than 5 mag(R).In previous studies,V350 Cep was considered to be a potential FUor or EXor eruptive variable.Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations.Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors,similar to V1647 0ri.  相似文献   

Evapotranspiration models of different complexity for multiple land cover types     

Minha Choi  William P. Kustas  Ram L. Ray 《水文研究》2012,26(19):2962-2972

A comparison between half‐hourly and daily measured and computed evapotranspiration (ET) using three models of different complexity, namely, the Priestley–Taylor (P‐T), the reference Penman–Monteith (P‐M) and the Common Land Model (CLM), was conducted using three AmeriFlux sites under different land cover and climate conditions (i.e. arid grassland, temperate forest and subhumid cropland). Using the reference P‐M model with a semiempirical soil moisture function to adjust for water‐limiting conditions yielded ET estimates in reasonable agreement with the observations [root mean square error (RMSE) of 64–87 W m^?2 for half‐hourly and RMSE of 0.5–1.9 mm day^?1 for daily] and similar to the complex Common Land Model (RMSE of 60–94 W m^?2 for half‐hourly and RMSE of 0.4–2.1 mm day^?1 for daily) at the grassland and cropland sites. However, the semiempirical soil moisture function was not applicable particularly for the P‐T model at the forest site, suggesting that adjustments to key model variables may be required when applied to diverse land covers. On the other hand, under certain land cover/environmental conditions, the use of microwave‐derived soil moisture information was found to be a reliable metric of regional moisture conditions to adjust simple ET models for water‐limited cases. Further studies are needed to evaluate the utility of the simplified methods for different landscapes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Steady‐state solution for cylindrical penetrometers     

Assaf Klar  Shmulik Pinkert 《国际地质力学数值与分析法杂志》2010,34(6):645-659

This paper suggests a new method for obtaining steady‐state solutions for ‘full‐flow’ penetrometers. The method is based on the numerical solution of the small strain plastic‐flow problem (i.e. rigid plastic material) with an inhomogeneous strength field, which is determined by converting changes of material properties over time in a stationary frame of reference into spatial distribution of strength in a moving frame of reference. Rather than building streamlines from back integration of soil element distortion, as previous methods have suggested, the method treats the domain as continuous with the associated field equations. The method employs an upstream weighting technique for the determination of information flow within the domain. The execution order for the calculation is based on topological ordering. This results in the calculation having a complexity of O(N), as compared with O(N^1.5) for the strain path or streamline methods (N is the number of discretized points), which significantly reduces the calculation time. The formulation is presented for the cylindrical (T‐bar) penetrometer, and includes aspects of soil strength degradation, strain rate effects, strength anisotropy, and interface strength law. Comparison to previously published values, based on large displacement finite element simulations with remeshing, showed good agreement, indicating on the correctness of the suggested approach. Investigation into the soil rigid‐body rotation and the remolding effect on anisotropy characteristics showed an interesting behavior, where the decrease of strength anisotropy due to remolding has a greater influence when the soil strength is higher in the vertical direction. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

GEM模型、RF模型和M5T模型的无人机DEM测点插值算法比较     

孙国强  潘学鹏  张祥燊 《北京测绘》2020,(3):361-364

无人机技术作为现如今测量的先进技术,已被逐渐广泛应用,由于DEM数据在实测过程中只能形成点数据,因此对点数据的插值计算一直是测绘专业研究的热点。为找出适用于无人机DEM测点插值计算的最优模型,本文基于GEM模型、RF模型和M5T模型,以降雨、经纬度和海拔为输入参数,对不同模型下的DEM进行了插值计算,结果表明:GEM模型表现的精度最高,该模型RMSE仅为11.72 m,RRMSE为12.7%,R2为0.964,Ens为0.946,MAE为11.28 m,该模型可作为无人机DEM测点插值计算的标准模型使用。  相似文献   

基于岩石物理参数转换模型的页岩气含气量评价新方法研究          下载免费PDF全文

郭宇航  刘财  潘保芝  张丽华  郭怀志  龚劲松  李宁 《地球物理学报》2019,62(7):2724-2731

页岩气在储层中主要以游离气和吸附气的形式存在,其含气量主要通过现场解吸和测井方法计算.由于页岩储层十分致密,并且常伴有微裂缝发育,这就造成了页岩储层的储集空间从纳米级孔隙到微米-毫米级的微裂缝并存的特殊情况.针对微孔和介孔段(50nm以内)的等温吸附方法,以及针对宏孔(50nm以上)的高压压汞方法在表征页岩孔隙结构上都存在着局限性.而核磁(NMR)T2分布本身虽然能够表征孔径分布,但是需要精确刻度横向弛豫时间与孔径的关系.本文在现有方法的基础上,结合上述方法的优势,采用拼接的方式表征页岩整体孔径分布,并将核磁T2分布刻度为孔径分布.基于横向弛豫时间和孔径的关系,结合T2-I转换模型,采用动态参数计算页岩储层含水饱和度和含气量,这为页岩储层含气量评价提供了新的可靠的方法.  相似文献   

JCZ-1T超宽频带地震计常见故障分析     

荆涛  孙艺  方禹心  顾强强  安峻峰  万芳 《地震地磁观测与研究》2019,41(1):85-90

对JCZ-1T超宽频带地震计的多种故障进行分类,故障主要包括仪器记录波形异常、仪器标定波形异常、地震计工作状态异常等,并对故障原因进行分析,给出相应解决方法。此外,对沈阳地震基准台JCZ-1T地震计1例故障的现象、原因排查、维修方法等进行了详细介绍。  相似文献   

基于核磁共振双截止值的致密砂岩渗透率评价新方法          下载免费PDF全文

范宜仁  刘建宇  葛新民  邓少贵  刘洪亮  顾定娜 《地球物理学报》2018,61(4):1628-1638

对比分析致密砂岩岩心在完全含水状态和束缚水状态下的核磁共振T₂谱,明确了致密砂岩孔隙中流体的赋存状态和渗流规律,指出常规核磁共振方法预测渗透率的局限性并提出核磁共振双截止值的概念.基于核磁共振双截止值,将储集空间细分为完全可动、完全束缚、部分可动等三部分,分析不同孔隙组分对渗透率的影响,并应用三组分法建立了核磁共振渗透率表征新模型.研究表明：致密砂岩渗透率与完全可动流体饱和度、部分可动流体T₂几何平均值、核磁孔隙度成正比,与完全束缚流体饱和度成反比.在此基础上,结合完全含水核磁共振T₂谱的二阶差分得到了双截止值的自适应确定方法,可以连续地计算储层双截止值.将该研究成果应用于生产实践,渗透率计算精度有较大的提高.  相似文献   

Variability of emission lines in the optical spectra of the Herbig Be binary system HD 200775     

Anastasia P.Bisyarina  ANDrey M.Sobolev  Stanislav Yu.Gorda  Anatoly S.Miroshnichenko 《天文和天体物理学研究(英文版)》2019,(3):31-34

In our previous papers we have improved the value of the orbital period of the binary Herbig Be star HD 200775 and showed that the [O I] and Si II 6347 and 6371 ?A emission lines displayed variations which correlate with the orbital period. In this paper we provide evidences that other broad emission lines of metals in the spectra of HD 200775 also exhibit variability, which is probably related to the orbital cycle of the binary. Analysis was performed based on the high-resolution spectral data collected over a time span of 6 years at the Kourovka Astronomical Observatory of the Ural Federal University(Russia) and the Three College Observatory of the University of North Carolina at Greensboro(USA) as well as archival spectral data compiled since 1994. We report new data points in the radial velocity curve of the He I 5876 ?A line near the extremal values of the radial velocity.  相似文献