2006年4月17日北京特大降尘的地球化学特征   总被引：5，自引：0，他引：5  

张崧  刘平  靳春胜  韩家懋  秦小光  刘东生 《海洋地质与第四纪地质》2008,28(3)

2006年4月17日北京遭遇了近年来最为严重的一次降尘天气。分析了降尘的主量、微量和稀土元素地球化学特征,并与洛川马兰黄土和几次北京降尘进行对比,结果显示本次北京降尘与洛川马兰黄土具有相似的元素分布模式,表明与黄土具有相似的物质组成,并在搬运过程中经历了充分的混合,同时,北京降尘与黄土相比具有一定程度的差异性,表现为北京降尘中Mg、Na相时富集,Ca明显亏损并含有较高的烧失量,降尘CIA值较低,表明降尘源区化学风化程度较弱,处于化学风化的初始阶段,降尘∑REE显著高于黄土,同时轻、重稀土分馏程度也较黄土高,4次北京降尘间稀土元素分布模式对比表明,粒度是影响重稀土元素间分馏程度不同的主要因素。  相似文献   

末次冰期低纬度西太平洋硅藻席沉积与生态特征   总被引：1，自引：0，他引：1  

翟滨  李铁刚 《海洋地质与第四纪地质》2009,(4)

硅藻在全球碳循环中发挥着重要的作用。"树荫种"硅藻在次表层水体中的勃发成席,并迅速埋藏成为硅藻席沉积,使人们逐渐意识到次表层生产在整个生产力及输出生产中起着重要作用。介绍了首次在低纬度西太平洋区域发现的硅藻席沉积的分布特征,硅藻席发现站位呈带状分布,大致呈北西-南东向展布,大部分散布在17.5°～20°N之间。采集到硅藻席沉积物的站位其水深在碳酸钙补偿深度(CCD)以下4837～6150m的深水区,多分布在较平坦的海底,且受风力和陆源物质输入影响相对较强的区域。该区域硅藻席的形成可能是由于末次冰期时该海区有大洋锋面的形成所致。该区域的成席硅藻Ethmodiscus rex(Wallich)Hendey为典型的"树荫种"硅藻,可以通过自身调节浮力的作用,在水体相对稳定的贫氧大洋中生存并勃发成席。末次冰期低纬度西太平洋硅藻席沉积的发生,可能使该区成为CO2的汇。  相似文献   

喜马拉雅山东南地区地质灾害发育规律初步研究   总被引：2，自引：0，他引：2  

童立强  祁生文  刘春玲 《工程地质学报》2007,15(6):721-729

利用遥感手段,结合MapGis,研究了喜马拉雅山东南地区地质灾害的发育情况,发现本区发育的主要地质灾害有滑坡、崩塌、泥石流、冰湖以及堰塞湖。其中崩塌、滑坡、泥石流斜坡地质灾害是本区最重要的地质灾害类型,占到总灾害数量的95.3%。在此基础上对喜马拉雅山东南地区地质灾害发育规律初步研究,发现本区地质灾害的发育在空间上的分布并非均匀,而是具有丛集性的特点。滑坡灾害主要发育在隆子和朗县。泥石流灾害比较严重的有米林、隆子和洛扎3县,而崩塌则主要集中在隆子县。研究发现,本区滑坡发育与地层、地形坡度以及土地类型关系密切,其中修康群、日当组和念青唐古拉群是本区的易滑地层。涅如组由于面积大,其中发育的滑坡较多,但是滑坡的发育率只略高于本区的平均水平。统计表明,16～30的坡度范围是滑坡最容易发生的。大于45以上的坡段很少发生滑坡。灌木林和天然草地这两种土地类型滑坡发育率最高。对于泥石流,研究表明,涅如组中泥石流发育面积最大,发育率也最高。泥石流发育的最适宜坡度也是16～30这样一个坡度范围。冰川和永久积雪区则最易发生泥石流。崩塌发育与地层类型、坡度的关系较为密切,崩塌主要发育在涅如组中,并且集中在坡度大于60以上的陡坡段中。这些初步成果的取得,是以后进行该区地质灾害空间预测的基础。  相似文献   

A unified CFD‐DEM approach for modeling of debris flow impacts on flexible barriers          下载免费PDF全文

Xingyue Li  Jidong Zhao 《国际地质力学数值与分析法杂志》2018,42(14):1643-1670

This paper presents a unified modeling framework to investigate the impacts of debris flow on flexible barriers, based on coupled computational fluid dynamics and discrete element method (CFD‐DEM). We consider a debris flow as a mixture of fluid and particles where the fluid and particle phases are modeled by the CFD and the DEM, respectively. The fluid‐particle coupling is considered by the exchange of interaction forces between CFD and DEM calculations. The flexible barrier is simulated by the DEM as a network of bonded particles with remote interactions. The proposed coupled CFD‐DEM approach enables us to conveniently handle the complicated three‐way interactions among the fluid, the particles, and the flexible barrier structure for debris flow impact simulations. The proposed approach is first used to investigate the influences of channel inclination and the volumetric solid fraction in a debris mixture on the impact force, the resultant deformation, and the retained mass in a flexible barrier. The predictions agree well with existing experimental and numerical studies. We further examine the possible failure modes of a flexible barrier under debris flow impact and their underlying mechanisms. The performance of different components in a flexible barrier system, including single wires, double twists and cables, and their load sharing mechanisms, are carefully evaluated. The proposed unified framework offers a novel, promising pathway towards physically based, quantitative analysis and design of flexible barriers for debris flow mitigation.  相似文献   

The back-barrier and barrier depositional history of Romney Marsh,Walland Marsh and Dungeness,Kent, England     

Antony J. Long  James B. Innes 《第四纪科学杂志》1995,10(3):267-283

Previous stratigraphical investigations of Romney Marsh have tended to be local in scale, and this has hindered efforts to establish a unifying stratigraphical framework for this area. This paper addresses this problem, by describing the results of a 12-km transect across Romney Marsh, linking previously studied back- and fore-marsh sites (Horsemarsh Sewer and Broomhill respectively), and presenting additional pollen, diatom and radiocarbon data from an intermediate, mid-marsh site (Brookland). One main organic unit is recorded across much of Romney Marsh, although its age, altitude and composition varies. Microfossil and radiocarbon data from Brookland and elsewhere on Romney Marsh show that this organic unit accumulated under a general removal and return of marine conditions that took place between ca. 5100 and 2000 yr BP. A recently proposed model of barrier development is used to investigate the history of back-barrier sedimentation in Romney and Walland Marshes. This model suggests a three-phase life-history for gravel barriers, which consists of initiation, stability and breakdown. Although there are problems in relating back-barrier deposits directly to barrier dynamics, nevertheless the Romney Marsh data do, for the most part, agree with the expected number and sequence of sea-level tendencies predicted by this model. The back-barrier stratigraphical data suggest that initiation, stability and breakdown of the Dungeness foreland occurred between ca. 6000 and 5000 yr BP, 5000 and 2000 yr BP and 2000 yr BP and present, respectively.  相似文献   

Impact of SST Anomaly Events over the Kuroshio-Oyashio Extension on the “Summer Prediction Barrier”     

Yujie WU  Wansuo DUAN 《大气科学进展》2018,35(4):397-409

The "summer prediction barrier"(SPB) of SST anomalies(SSTA) over the Kuroshio–Oyashio Extension(KOE) refers to the phenomenon that prediction errors of KOE-SSTA tend to increase rapidly during boreal summer, resulting in large prediction uncertainties. The fast error growth associated with the SPB occurs in the mature-to-decaying transition phase,which is usually during the August–September–October(ASO) season, of the KOE-SSTA events to be predicted. Thus, the role of KOE-SSTA evolutionary characteristics in the transition phase in inducing the SPB is explored by performing perfect model predictability experiments in a coupled model, indicating that the SSTA events with larger mature-to-decaying transition rates(Category-1) favor a greater possibility of yielding a more significant SPB than those events with smaller transition rates(Category-2). The KOE-SSTA events in Category-1 tend to have more significant anomalous Ekman pumping in their transition phase, resulting in larger prediction errors of vertical oceanic temperature advection associated with the SSTA events. Consequently, Category-1 events possess faster error growth and larger prediction errors. In addition, the anomalous Ekman upwelling(downwelling) in the ASO season also causes SSTA cooling(warming), accelerating the transition rates of warm(cold) KOE-SSTA events. Therefore, the SSTA transition rate and error growth rate are both related with the anomalous Ekman pumping of the SSTA events to be predicted in their transition phase. This may explain why the SSTA events transferring more rapidly from the mature to decaying phase tend to have a greater possibility of yielding a more significant SPB.  相似文献   

Texture, mineralogy, and rock strength in horizontal stress-related coal mine roof falls   总被引：1，自引：0，他引：1  

S.E. Phillipson   《International Journal of Coal Geology》2008,75(3):175-184

Geologic structures can represent planes of preferential weakness that, by dismembering the roof beam, may contribute to the failure of roof spans. However, beam deflection and roof failure also occur in rocks where no visible geologic discontinuities are present. This suggests that roof failure may depend on rock strength, which in turn depends on intrinsic textural properties inherent to the rock. In this study, rock samples were collected from horizontal stress-related roof fall material in coal mines for petrographic characterization and compressive strength testing. Brittle, stress failure-prone rock types include thinly interlaminated siltstone and shale, and black shale that had been lightly recrystallized. Samples exhibit a narrow range of density values between approximately 2.5–3.0 g/cm³ but exhibit a wide range of unconfined compressive strength values, between approximately 20–70 MPa. Results of laboratory observations suggest that for samples of coal mine immediate roof shale, compressive strength is not well correlated with density, grain size, sutured grain boundaries, or quartz content. These results for shale are generally at odds with the results of similar studies for sandstone. The great variability of strength, texture, and mineralogy documented in these samples may be an indication of their complexity and the need for specialized methodology in the study of shale strength.  相似文献   

Three-dimensional analysis of the screening effectiveness of hollow pile barriers for foundation-induced vertical vibration   总被引：2，自引：0，他引：2  

Pei-hsun Tsai  Zheng-yi Feng  Tin-lon Jen 《Computers and Geotechnics》2008,35(3):489-499

The study applies the three-dimensional boundary element method in frequency domain to investigate the screening effectiveness of circular piles in a row for a massless square foundation subject to harmonic vertical loading. Four types of piles were studied: steel pipe piles, concrete hollow piles, concrete solid piles and timber piles. A parametric study was undertaken to examine the effects of pile dimensions, operational frequency, and source distance on the screening effectiveness. The results showed that screening effectiveness of steel pipe piles is generally better than that of solid piles, and that a concrete hollow pile barrier can be ineffective due to its stiffness. The influence of pile length on screening effectiveness is more significant than that of pile spacing and the distance between the vibrating foundation and the pile barrier.  相似文献   

Research on the temperature field of a partially freezing sand barrier with groundwater seepage     

LiYan Lao  ZhiQiang Ji  LiangLiang Huang  ShangJing Li 《寒旱区科学》2017,9(3):280-288

To study the distribution characteristics and variation regularity of the temperature field during the process of seepage freezing,a simulated-freezing test with seepage of Xuzhou sand was completed by using a model test developed in-house equipment.By means of three group freezing tests with different seepage velocities,we discovered the phenomenon of the asymmetry of the temperature field under the influence of seepage.The temperature upstream was obviously higher than that downstream.The temperature gradient upstream was also steeper than that downstream.With a higher seepage velocity,the asymmetry of the temperature field is more pronounced.The asymmetry for the interface temperature profile is more strongly manifest than for the main surface temperature profile.The cryogenic barrier section is somewhat"heartshaped".With the increasing velocity of the seepage flow,the cooling rate of the soil decreases.It takes much time to reach the equilibrium state of the soil mass.In our study,seepage flow velocities of 0 m/d,7.5 m/d,and 15 m/d showed the soilcooling rate of 4.35°C/h,4.96°C/h,and 1.72°C/h,respectively.  相似文献   

周口分县短期天气预报系统     

霍传秀  王洪涛等 《河南气象》2001,(2):6-7

利用ECMMF格点预报产品和14年历史实况资料，在预报后日前后10天左右找相似，采用VC＋＋4．0和VB5．0编程，制作周口分县24h天气预报。经试验，预报准确率为68．6％。  相似文献