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961.
石漠化地区基岩裸露、砾石堆积,水土流失严重,土壤与植被覆盖率低,因此引发一系列的生态恶化问题,而客土恢复植被是一项快速有效的治理途径。本试验在贵州毕节地区实施,以当地黄壤客土(T1,黄壤与砾石比为1∶1;T2,黄壤与砾石比为2∶1;T3,黄壤与砾石比为3∶1;T4,黄壤与砾石比为1∶0)改良石漠化,从耐瘠薄的灌木——沙棘(Hippophae rhamnoides)为试材,探究其幼苗在客土改良后的石漠化土壤中的适应性,栽种期为2年。结果表明:客土处理对沙棘幼苗的冠幅、粗根的根长密度、粗根根重密度均无显著影响;百分之百客土即T4会显著抑制沙棘株高、根系生物量,显著促进细根比根长的增长;当黄壤与砾石比例1/2—2/3时,2年后沙棘细根的根重密度与土壤含水量均会显著增加;当黄壤与砾石比大于2/3时会显著抑制沙棘根系长度总和的增加,且2年后对土壤水分改善作用不显著;沙棘根系指标与2年后的土壤含水量呈现出显著的相关关系。在贵州毕节地区客土改良石漠化时,并非客土越多越好,当黄壤与砾石的比例在1/2—2/3时,栽种沙棘2年可显著改善土壤含水量。 相似文献
962.
Developing a comprehensive understanding of inter-city interactions is crucial for regional planning.We therefore examined spatiotemporal patterns of population migration across the Qinghai-Tibet Plateau(QTP)using migration big data from Tencent for the period between 2015 and 2019.We initially used decomposition and breakpoint detection methods to examine time-series migration data and to identify the two seasons with the strongest and weakest population migration levels,between June 18th and August 18th and between Oc-tober 8th and February 15th,respectively.Population migration within the former period was 2.03 times that seen in the latter.We then used a variety of network analysis methods to examine population flow directions as well as the importance of each individual city in migra-tion.The two capital cities on the QTP,Lhasa and Xining,form centers for population migra-tion and are also transfer hubs through which migrants from other cities off the plateau enter and leave this region.Data show that these two cities contribute more than 35％of total population migration.The majority of migrants tend to move within the province,particularly during the weakest migration season.We also utilized interactive relationship force and ra-diation models to examine the interaction strength and the radiating energy of each individual city.Results show that Lhasa and Xining exhibit the strongest interactions with other cities and have the largest radiating energies.Indeed,the radiating energy of the QTP cities cor-relates with their gross domestic product(GDP)(Pearson correlation coefficient:0.754 in the weakest migration season,WMS versus 0.737 in the strongest migration season,SMS),while changes in radiating energy correlate with the tourism-related revenue(Pearson correlation coefficient:0.685).These outcomes suggest that level of economic development and level of tourism are the two most important factors driving the QTP population migration.The results of this analysis provide critical clarification guidance regarding huge QTP development dif-ferences. 相似文献
963.
Due to large deserts on Earth surface a thorough understanding of climate change, landscape evolution and geomorphological processes having occurred in deserts is crucial for Earth System Science. The landscapes in deserts are, however, diverse and different over the globe with regard to their geomorphological nature, human activities and geological histories. In the last decades a great number of efforts have been put to the investigation of the initial timing of the occurrence of arid climate, e. g. in northwestern China. Silty sediments in the downwind directions have been used to deduce the histories of deserts. In general, there is a lack of knowledge about processes and landscapes in Chinese drylands between the initial Miocene silt sedimentation at desert margins and the late Quaternary multiple occurrences of wetter climate with assumed large lakes in many of the deserts in northern China. The geomorphological concept of three primary triggering factors, i.e., the sediment supply, sediment availability and transport capacity of wind, and additionally the underground geology need to be fully considered for a better understanding of the environmental histories of sand seas which should not be viewed as equivalent for deserts because sand seas cover between < 1% and ca. 45% of the desert areas in various continents dependent on a complex interaction between various processes of both exogenous and endogenous origins. 相似文献
964.
965.
Summary This paper presents a systematic procedure for determining fracture toughness of an anisotropic marble using the diametral
compression test (Brazilian test) with a central crack on the discs. Additionally, a novel formulation to increase the accuracy
in Stress Intensity Factor (SIF) calculations using Boundary Element Method (BEM) is applied to determine the stress intensity
factors and the fracture toughness of anisotropic rocks under mixed-mode loading. The numerical results show that the SIFs
for both isotropic and anisotropic problems are in good agreement with those reported by previous authors. The marble with
clear white-black foliation from Hualien (in eastern Taiwan), was selected for the Brazilian tests. Diametral loading was
conducted on the Cracked Straight Through Brazilian Disc (CSTBD) specimens to evaluate their fracture toughness. In addition,
a new fracture criterion was developed to predict pure mode I, pure mode II or mixed mode (I–II) fracture toughness of the
anisotropic marble. The new fracture criterion is based on the examination of mode I, mode II and mixed mode (I–II) fracture
toughness for different crack angles and anisotropic orientation.
Authors’ address: Associate Professor Chao-Shi Chen, Department of Resources Engineering, National Cheng Kung University,
No. 1 Dasyue Rd., East District, Tainan 701, Taiwan 相似文献
966.
HU Shixue LI Yong LUO Huilin FU Xiaoping YOU Ting PANG Jiyuan LIU Qi Michael Steiner 《《地质学报》英文版》2008,82(2):244-248
A new palaeoscolecid, Guanduscolex minor Hu, Luo et Fu gen. et sp. nov., with preserved soft parts of introvert and intestines comes from the Lower Cambrian Guanshan fauna of Yunnan, South China. Microstructural details of the cuticle revealed by scanning electron microscopy （SEM） show that each annulation bears three rows of plates and each plate bears 9-10 marginal and 4-5 central nodes. This discovery sheds new light on the relationships and evolutionary pathway of the palaeoscolecids and other early priapulids. 相似文献
967.
SEDEX-type lead-zinc deposits in the southern belt of the Xicheng Devonian basin, Gansu Province has been already identified. However, the sedimentary environment of the limestone and philite of the Xihanshui Group within which the lead-zinc deposits occur is littoral and shallow sea. This is different from those in the northern belt such as the Changba-Lijiagou lead-zinc deposits, which were formed in deep sea. The reef and bioclastic limestone are widespread in the southern belt. Particularly they are associated with lead-zinc ores and there are no striae and banding but massive or disseminated structures. It is discovered that the black chimney consists of sphalerite, ankerite, pyrite and galena, in which black, coarse and radial sphalerite occurs as irregularly veins or cylindricality with a width of 10-40 cm in the center, and it is surround by fine ankerite and minor celestite with ribbon structure. The immediate wall rock of the chimney, reef limestone, was unaltered and the outside reef and bioclastic limestone were intensively silicified. Those silicified reef and bioclastic limestone host disseminated lead-zinc ores of the Luoba and Bijiashan type. It is concluded that the exhalative system occurred in a shallow sea in the Givetian of the middle Devonian. Brine is boiled due to low pressure, and a great deal of lead and zinc was dispersed in the interface between the limestone and phyllite and formed a source bed. In the Triassic period, meta-hydrothermal fluids leached and extracted metals from the source bed, and then moved and mineralized in open space such as arches and inverse limbs of anticlines, and formed massive and vein ores such as the Jianyagou and Dengjiashan type deposits. 相似文献
968.
LIU Xiaoping 《《地质学报》英文版》2008,(3)
Ordovician fracture-cavity carbonate reservoir beds are the major type of producing formations in the Tahe oilfield,Tarim Basin.The seismic responses of these beds clearly changes depending on the different distance of the fracture-cavity reservoir bed from the top of the section.The seismic reflection becomes weak or is absent when the fracture-cavity reservoir beds are less than 20 ms below the top Ordovician.The effect on top Ordovician reflection became weaker with deeper burial of fracture-cavity reservoir beds but the developed deep fracture-cavity reservoir beds caused stronger reflection in the interior of the Ordovician.This interior reflection can be divided into strong long-axis, irregular and bead string reflections,and was present 80 ms below the top Ordovician.Aimed at understanding reflection characteristics,the spectral decomposition technique,which uses frequency to"tune-in"bed thickness,was used to predict Ordovician fracture-cavity carbonate formations in the Tahe oilfield.Through finely adjusting the processing parameters of spectral decomposition,it was found that the slice at 30 Hz of the tuned data cube can best represent reservoir bed development.Two large N-S-trending strong reflection belts in the mid-western part of the study area along wells TK440- TK427-TK417B and in the eastern part along wells TK404-TK409 were observed distinctly on the 30 Hz slice and 4-D time-frequency data cube carving.A small N-S trending reflection belt in the southern part along wells T403-TK446B was also clearly identified.The predicted reservoir bed development area coincides with the fracture-cavities connection area confirmed by drilling pressure testing results. Deep karst cavities occur basically in three reservoir bed-development belts identified by the Ordovician interior strong reflection.Spectral decomposition proved to be a useful technique in identifying fracture-cavity reservoir beds. 相似文献
969.
曲流河是冲积平原河流中的重要河型之一,曲流河的河道演变对冲积平原的建设与演化起着非常重要的作用。地处江汉平原的长江中游藕池口至城陵矶段河道是最典型的曲流河段,其曲流河道的几何形态和变化过程较为复杂,对该段河道演化过程的研究在河流的开发利用及水利工程建设中具有很好的理论指导意义。本研究通过对历史资料和多期卫星遥感影像的解译与分析,表明长江中游藕池口至城陵矶河段的曲流河道演化在受自然和人类活动双重影响的情况下,该河段河道的演化仍然维持曲流河特征。受大洪水的切滩作用及松滋口、太平口和藕池口3个分流口对洞庭湖的分水分沙的影响,该段河道的演化过程较为复杂。自然裁弯取直和人工裁弯取直在一定程度上改变着河道演化的进程,但由裁弯取直及上游水利工程引起的纵坡降增加产生的冲淤变化将会维持河道的稳定,同时在该河段实施的护岸工程也会抑制河流的横向侵蚀,曲流河段河道演化进入自调整和自组织过程。 相似文献
970.