Tree-ring crossdates for a First Millennium AD advance of Tebenkof Glacier, southern Alaska     

David J. Barclay  Gregory C. Wiles 《Quaternary Research》2009,71(1):22-26

Tree-ring crossdates from glacially killed logs show that Tebenkof Glacier advanced into a forefield forest in the AD 710s and 720s. Recession from this First Millennium AD (FMA) advance occurred before the 950s, after which the ice margin readvanced in the 1280s to 1320s at the start of the Little Ice Age (LIA). A more extensive LIA advance was underway from the 1640s to 1670s, and the terminus stayed at or near its LIA maximum until the 1890s. These are the first absolute tree-ring crossdates for a FMA glacier advance in North America and support growing evidence from northwestern North America and Europe for a significant cool interval in the centuries around AD 500.  相似文献   

全球大变局、大考验、大合作与地理学大作为——在首届世界地理大会上的主旨讲演     

郑必坚 《世界地理研究》2023,32(1):1-4

全球正面临百年未有之大变局。人类进入21世纪的第三个10年,一场席卷全球的大疫灾及逆全球化浪潮使得全球局势“变上加变”。“大变局”同时也意味着对世界各国是否能坚持“大合作”的“大考验”,即在全球范围内,各个地区各个国家之间,能否抵御单边主义、封闭和对抗的倾向,从而逐步实现“大合作”。地理学能够在问题意识、理论框架和研究方法上连通自然与社会,贯穿时间与空间,揭示人与自然和谐共生的科学机理,捕捉世界各区域的自然和人文地理特征,因此可以为全球可持续发展与人类命运共同体建设提供学理支撑。中国地理学研究要“赶上时代”和“引领时代”,关键在于坚持创新,坚持把创新作为中国地理学研究的核心。首届世界地理大会的召开,就是中国地理学家走向世界的新起点。世界地理大会未来要形成机制,定期举办,广泛邀请海内外学者参与,努力将世界地理大会打造成为具有广泛国际影响力的合作交流平台。  相似文献   

Some aspects of the British Geological Survey’s contribution to the war effort at the Western Front, 1914–1918     

David G. Bate  Andrew L. Morrison 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(1):3-11

The application of geology to warfare in regard to questions of water supply, ground conditions and access to strategic minerals has long been appreciated, and much has already been written on these aspects of the science. During the Great War of 1914–1918 the services of the British Geological Survey, under the directorship of Aubrey Strahan, were called upon to advise on such matters both at home and abroad. Surviving archived files at the Geological Survey allow us to examine some rather more unexpected applications of the science, particularly in regard to the European theatre of war. These files provide only a partial record of the full range of war-related activities undertaken by the Survey, but they do reveal more especially the application of petrography to aircraft compass design, forensic geology, and the choice of stone for war graves.  相似文献   

Extended model of topological relations between spatial objects in geographic information systems     

《International Journal of Applied Earth Observation and Geoinformation》2007,9(3):264-275

This paper presents an extended model for describing topological relations between two sets (objects) in geographic information systems (GIS). First, based on the definition of the topological relations between two objects, we uncover a sequence of topological relations between two convex sets.Second, an extended model for topological relations between two sets is proposed based on the new definition. The topological relations between two convex sets are expressed as a sequence of 4 × 4 matrices, which are the topological properties of A^o ∩ B^o, A^o\B, B^o\A, ∂A ∩ ∂B. The model is also extended for handling the properties of the topological relations between two non-convex sets, where the factor of first fundamental group is added to A ∪ B to handle these complex relations.The results show that the number of topological relations between the two sets is not as simple as finite but infinite and can be approximated by a sequence of matrices.  相似文献   

昆明滇池盆地新近纪象类化石     

胡绍锦 《云南地质》2005,24(3):321-327

记述滇池盆地含煤层中首次发现的上新世剑齿象化石,包括脊棱齿象属的一个新种昆明脊棱齿象(Stegolophodon kunm ingensissp..nov.)、似元谋剑齿象(Stegodonaff.yuan-m ouensis)、玉溪剑齿象、师氏剑齿象等。这一剑齿象化石组合的发现,对研究新生代象类和滇池盆地的演化史,重新划分盆地煤系地层具有重要意义。  相似文献   

永德梯子坡剖面丁家寨组发现早二叠世牙形石   总被引：4，自引：0，他引：4  

赵成峰 《云南地质》2003,22(2):196-199

测制永德县梯子坡剖面时，首次于丁家寨组顶部灰色亮晶生物碎屑灰岩层中发现丰富的早二叠世牙形石。根据牙形石组合，提出丁家寨组上部(至少顶部)存在下二叠统沉积。  相似文献   

An X-ray diffraction study of shock-wave-densified SiO<Subscript>2</Subscript> glasses     

Y. Shimada  M. Okuno  Y. Syono  M. Kikuchi  K. Fukuoka  N. Ishizawa 《Physics and Chemistry of Minerals》2002,29(4):233-239

 The densification and structural changes in SiO₂ glass compressed up to 43.4 GPa by shock experiments are investigated quantitatively by the X-ray diffraction technique. Direct structural data (average Si–O and Si–Si distances and Si–O–Si angles, coordination number of the Si atom) of these shock-densified SiO₂ glasses have been obtained by analyzing the radial distribution function curves, RDF(r), calculated with X-ray diffraction data. The coordination number of all densified glasses is about 4 and shows almost no pressure variation. The SiO₂ glass has shown density increase of 11% at a shock compression of 26.3 GPa. This density evolution could not be explained by the coordination change. The reduction of the average Si–O–Si angle (144° at 0 GPa to 136° at 26.3 GPa) obtained from RDF(r) data may account for this density increase. This Si–O–Si angle change may be caused by shrinkage of the network structure and the increase of small rings of SiO₄ tetrahedra. For higher shock pressure, a decrease in the Si–O–Si angle to 140° was observed. This is consistent with the decrease in density at 32.0 and 43.2 GPa. This decrease in the Si–O–Si angle and density could be attributed to an annealing effect due to high after-shock residual temperature. This pressure dependence of average Si–O–Si angles in shock-densified SiO₂ glass agrees with the results of our previous Raman spectroscopic study. On the other hand, the pressure variation for the first sharp diffraction peak (FSDP) was analyzed to estimate the evolution of intermediate range structures. It is suggested that the mean d value (d _m ) obtained from the position of FSDP strongly depends on the shock and residual temperature, as well as shock pressure. Received: 29 June 2001 / Accepted: 14 November 2001  相似文献   

Effect of three different boundary-layer parameterisations in a regional atmospheric model on the simulation of summer monsoon circulation     

K. V. J. Potty  U. C. Mohanty  S. Raman 《Boundary-Layer Meteorology》1997,84(3):363-381

Bulk, first-order and turbulent kinetic energy (TKE) closure schemes are used to parameterise the boundary-layer physics in a high resolution, limited area model. The model was used to simulate the summer monsoon circulations over India. The domain selected included the monsoon trough over northern India, a region of mesoscale convection. A monsoon depression was present at the time of the simulation. The results indicate that the TKE closure scheme combined with the Monin–Obukhov surface-layer similarity relation provided the best 48-hour simulation of the circulation and the rainfall associated with the monsoon depression.  相似文献   

云南地区地震序列早期地震波动力学特征     

蔡静观  雷素华  王兴辉  张喜玲 《地震》1996,(2)

研究了云南地区各类型地震序列的早期地震波动力学特征——地震波垂直分量P波初动和P、S波最大振幅比,结果表明:前震序列振幅比为过原点的直线,比值稳定,P波初动一致;双震型地震序列在第一主震后P波初动出现一组时,仍有一类波形(“大头波”或“小头波”)的振幅比保持为过原点的直线,第一主震后P波初动出现两组时,仍有初动相同的一组地震振幅比保持为过原点的直线,或者两组初动的地震振幅比分别、共同成过原点的直线;主余震地震序列在非大震孕育期间,地震振幅比离散,与大震孕育有关的主余震地震序列振幅比仍可为过原点的直线。地震波动力学特征在上述三类地震序列的早期判断能力分别为75％、55％—73％、90％。  相似文献   

变密度界面模型重力异常反演的B样条函数法   总被引：3，自引：0，他引：3  

王硕儒  汪炳柱 《地球物理学进展》1996,11(3):40-52

重力异常反演是一个求解第一类非线性积分方程的问题。当三维界面起伏满足│Δｈ│〈０．４１４ｈ０和二维界面起伏满足－ｈ０〈Δｈ〈０．４１４ｈ０时，积分方程的被积函数可Δｈ的级级数形式。  相似文献