Influence of glacier hydrology on the dynamics of a large Quaternary ice sheet

The influence of glacier hydrology on the time-dependent morphology and flow behaviour of the late Weichselian Scandinavian ice sheet is explored using a simple one-dimensional ice sheet model. The model is driven by orbitally induced radiation variations, ice-albedo feedback and eustatic sea-level change. The influence of hydrology is most marked during deglaciation and on the southern side of the ice sheet, where a marginal zone of rapid sliding, thin ice and low surface slopes develops. Such a zone is absent when hydrology is omitted from the model, and its formation results in earlier and more rapid deglaciation than occurs in the no-hydrology model. The final advance to the glacial maximum position results from an increase in the rate of basal sliding as climate warms after 23000 yr BP. Channelised subglacial drainage develops only episodically, and is associated with relatively low meltwater discharges and high hydraulic gradients. The predominance of iceberg calving as an ablation mechanism on the northern side of the ice sheet restricts the occurrence of surface melting. Lack of meltwater penetration to the glacier bed in this area means that ice flow is predominantly by internal deformation and the ice sheet adopts a classical parabolic surface profile.     

在耀斑-日球电流片坐标系中——研究耀斑-激波相应地磁扰动的分布特征（Ⅱ）

本文采用一种新的坐标系--耀斑-日球电流片坐标系,对1966-1982年间由耀斑-激波所引起的277个耀斑-地磁扰动事件进行了分析.初步结果是:1.耀斑-地磁扰动事件在该坐标系中相对日球电流片的随机分布呈高斯分布,极大值在电流片附近;2.当地球和耀斑位于日球电流片同侧时,地磁扰动事件频次远高于异侧;3.地磁扰动强弱在该坐标系中的分布,亦呈现了同侧高于异侧,且极大值多在日球电流片附近;4.耀斑-激波能流密度ρ₂V₂³及其跃变量ρ₂V₂³-ρ₁V₁³在该坐标系中具有十分类似于相应磁扰水平的分布,其离散程度后者略大于前者. 根据本文的结果可以看出,对耀斑-地磁扰动研究来说,近太阳日球电流片的存在是一个重要的特征面,它对耀斑-地磁扰动的产生和强弱水平有重要影响,使太阳耀斑活动与地磁活动效应之间的对应关系变得复杂化了.     

Combining geomorphological and geodetic data to determine postglacial tilting in Manitoba

Estimates of postglacial rebound in central North America from Laurentide deglaciation to the present time are uncertain as a result of lack of data from the continental interior. A more precise knowledge of postglacial tilt history will assist studies of the evolution of the major lakes in Manitoba and will facilitate the engineering and environmental management of the present-day hydrological system. This paper explores the benefits of combining geomorphological data with high-precision, real-time geodetic data (GPS positioning and absolute gravity) and lake-gauge tilt data now being collected for postglacial rebound studies in Manitoba and adjacent regions in the US. Presently-available data sets representing these data types are (1) tilting of the 9.5 kyr B.P. Campbell strand line south and west of Lake Winnipeg, (2) the rate of decrease in absolute gravity values measured from 1987 to 1995 at Churchill, Manitoba, and (3) the present-day regional tilt rate derived from water-level gauges in southern Manitoba lakes. These data are compared to theoretical predictions based on the published ICE-3G loading history and on a model of Earth rheology characterized by a 1066B density and elastic structure, an upper-mantle viscosity of 10 ²¹Pa s, a lower-mantle viscosity of 2 × 10 ²¹Pa s, and a lithosphere thickness of 120 km (Tushingham & Peltier, 1991). All three data types show disagreement in Manitoba with ICE-3G and the standard Earth model. ICE-4G does better but could not be investigated in any detail. The constraints on model parameters provided by the different data types were investigated by varying, one at a time, three key parameters, (1) the thickness of the lithosphere in excess of 120 km, (2) the lower mantle viscosity, and (3) the thickness of Laurentide ice over the Prairies, to obtain better fits to the data. The present data do not appear to constrain lithosphere thickness in excess of 120 km very well. While both the Campbell strand line data and the Churchill absolute gravity data are consistent with an increase in lower-mantle viscosity, the present-day, lake-gauge data are not. All three data types are consistent with a thinning of the Laurentide ice-sheet over the Prairies relative to the ICE-3G model. Simultaneous adjustment of model parameters with the advantage of anticipated new data in Manitoba and adjacent regions in the US will lead to better understanding of the trade-offs between Earth rheology and ice sheet history and hence to an improved Laurentide postglacial rebound model.     

一种平面薄片零件单目视觉测量方法

针对传统的零件质量测量手段操作复杂、效率低等问题,该文提出基于大像幅非量测数码相机的单目视觉检测方法。首先基于二维直接线性变换和光束法平差进行相机内参数的标定;其次基于平面控制点信息进行单幅影像外方位元素的解算;然后进行影像的畸变纠正和垂直纠正;最后基于轮廓线的多特征提取方法求解零件特征参数等。将大像幅非量测数码相机用于较大平面薄片类零件检测的结果与三坐标量测仪的检测数据对比,实验结果表明,其量测误差小于0.1mm,满足较大幅平面薄片类零件尺寸量测的要求。     

A New Model for Ice Forces on A Conical Structure

The ice force is an important factor to be taken into account for offshore structures in cold regions, and the calculation method of the ice force is meaningful for the offshore structure design. The cone is now used as an optimal ice-resistant structure because it can cause bending failure of the ice sheet. The interaction between an ice sheet and a conical structure is studied in this paper and Croasdale‘s model is modified based on field observations. The newly built model separates the ice sheet into the emersed part and the floating part, and the equilibrium analyses are canied out respectively. The bending moment distribution of the ice sheet is analyzed for the determination of the position of bending failure, which serves as a supplementary restraint. The analytic solution of the ice foree on a conical structure is obtained it is verified with the experimental data of previous researches.     

Stone pillar rockfall in Danxia landform area,Mt. Langshan,Hunan Province,China

A typical Danxia stone pillar, Leipishi I, in the World Natural Heritage site at Mt. Langshan, China, collapsed on 2 November 2009. To understand the mechanism controlling this rockfall event, uniaxial compressive strength, tensile strength, resistance against sulfuric acid, and freezing and thawing properties were analyzed from 44 sandstone and conglomerate cores collected from the Lanlong Formation, the only exposed formation on Mt. Langshan. In addition, four rock slices were created for analysis under a polarizing microscope. A detailed reconstruction of the geometry and restraint conditions of the stone pillar in place before the rockfall occurred permitted an estimation of the stress state before collapse using 3D finite-element code. The results show that the rapid retreat of soft, intercalated rock layers due to weathering can profoundly change the stress state within the rock body, causing compressive or tensile stresses to rise above compressive or tensile strengths in specific sections of a rock body, and causing partial or complete collapse.     

OSL ages on glaciofluvial sediment in northern Lower Michigan constrain expansion of the Laurentide ice sheet

We report new ages on glaciofluvial (outwash) sediment from a large upland in northern Lower Michigan—the Grayling Fingers. The Fingers are cored with > 150 m of outwash, which is often overlain by the (informal) Blue Lake till of marine isotope stage (MIS) 2. They are part of an even larger, interlobate upland comprised of sandy drift, known locally as the High Plains. The ages, determined using optically stimulated luminescence (OSL) methods, indicate that subaerial deposition of this outwash occurred between 25.7 and 29.0 ka, probably associated with a stable MIS 2 ice margin, with mean ages of ca. 27 ka. These dates establish a maximum-limiting age of ca. 27 ka for the MIS 2 (late Wisconsin) advance into central northern Lower Michigan. We suggest that widespread ice sheet stabilization at the margins of the northern Lower Peninsula, during this advance and later during its episodic retreat, partly explains the thick assemblages of coarse-textured drift there. Our work also supports the general assumption of a highly lobate ice margin during the MIS 2 advance in the Great Lakes region, with the Fingers, an interlobate upland, remaining ice-free until ca. 27 ka.     

利用ArcGIS构建地形图分幅空间数据库

本文利用ArcGIS绑定的脚本语言Python和AML及其空间分析功能,设计了简单可行的算法,并编制了相应的程序,构建了国家基本比例尺地形图分幅空间数据库。首先生成图幅分幅格网,以及对应的网格标识点、图幅编号文件,将标识点与图幅编号文件关联后再与图幅网格叠加即可。该方法充分利用了GIS的空间叠加功能,仅用了极少量的程序代码,没有编程经验的人员可以比较容易掌握,对于各行业应用领域的工作者有很大帮助。     

新版渔业用图的设计

新版渔业用图在数学基础的确定、表示的主要内容和生产方式上都发生了一定变化,针对新版渔业用图的设计特点,介绍了其表示的主要内容、数据结构设计以及版面设计方法.     

冰芯和台站记录的近50 a来东南极冰盖边缘地区气候变化格局

对取自东南极冰盖Lambert冰流东、西两侧共支雪芯,恢复了过去50 a来稳定同位素温度序列和积累率序列.对比发现,位于Lambert冰流东侧,即位于Wilks地和Princess Elizabeth 地的5支雪芯(GC₃0, GD03, GD15, DT001和DT085),过去50 a来积累率总体为上升趋势,δ¹⁸O上升速率介于0.34～2.6 kg·m^-2·a^-1; 稳定同位素显示其气温亦呈整体上升趋势, 上升速率介于0‰～0.02‰·a^-1. 但对位于Lamb ert冰流西侧, 即位于Dronning Maud地、Mizuho高原和Kamp地的5支雪芯(Core E,DML 05,W2 00, LGB16和MGA),过去50 a来积累率总体为下降趋势,下降速率介于-0.01～-2.3 6 kg·m^-2·a^-1; 稳定同位素温度变化则十分复杂:Dronning Maud 地西侧为上升, Mizuho高原和Kamp地为下降或变化不明显. 分布于LGB两侧沿岸气象站记录也印证了上述格局. 这种格局可能是南大洋独特的环流形式-环南极波(ACW)-在特殊地形( 如大的冰盆)影响下, 在南极冰盖边缘的表现形式.