Performance of ground penetrating radar in root detection and its application in root diameter estimation under controlled conditions

A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root systems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excavation/drilling location is of prime importance. Ground penetrating radar (GPR) provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the performance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled environment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radargrams were subject to the influence of the following factors: size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T ₂ (p<0.001, r=0.795). Because GPR root detection is highly site-specific, this study provides a local reference for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.     

大兴安岭南部乌拉盖地区满克头鄂博组火山岩年代学、地球化学研究及构造环境分析

[研究目的]通过查明大兴安岭乌拉盖地区火山岩的年龄、地球化学特征,探讨火山岩形成的时代、成因及构造背景,为研究大兴安岭南部地区的岩浆活动和构造演化过程提供依据.[研究方法]选取大兴安岭乌拉盖地区满克头鄂博组火山岩,系统开展LA-MC-ICP-MS锆石U-Pb年代学和岩石地球化学研究.[研究结果]研究区满克头鄂博组火山岩...     

冰川物质平衡线的估算方法

冰川物质平衡线高度(ELA)与气候变化, 特别是与气温和降水的变化关系密切, 是重建古气候和反映冰川积累和消融变化的重要代用指标.直接观测方法可以获得较为精准的ELA, 但不能大范围展开.因此, ELA的间接估算方法, 如赫斯法(Hess)、 积累区面积比率法(AAR)、 面积–高程平衡率法(AABR)、 末端至冰斗后壁比率法(THAR)、 终碛到最高峰高差比率法(TSAM)、 侧碛最大高度法(MELM)、 冰斗底部高程法(CF)、 冰川作用阈值法(GT)等, 得到了广泛的发展与应用.然而, 由于受到雪崩或风吹雪补给、 表碛覆盖、 冰川类型和形态等因素的影响, 单一使用某种方法易受到算法本身的限制, 误差较大, 需综合考虑各种算法的适用性和选取参数的差异, 以提高计算的精度, 同时也要考虑到后期构造抬升等的影响.     

不同粗糙度的节理直剪颗粒流分析

利用二维颗粒流程序生成5种不同粗糙程度的节理模型,并对5种节理模型进行了5种不同法向恒定荷载作用下的直剪试验,从细观角度分析了不同粗糙程度的节理模型在法向荷载下的形貌损伤情况和裂纹演化机制。与此同时,分析了节理JRC值和节理面颗粒摩擦系数对节理抗剪强度影响,并反推出了节理面抗剪强度参数Cj与?j与JRC值的关系。结果为：法向恒定荷载越大时,节理峰值抗剪应力越大,剪胀现象越小,节理形貌损伤范围越大。随着剪切的进行,上下节理面接触范围减小,微裂纹开始主要沿节理面产生,随着剪切位移的继续增加微裂纹数量显著增加,并且不局限于节理面附近而深入到模型内部。随着节理粗糙程度（JRC值）和节理面颗粒摩擦系数的增加节理峰值抗剪应力也增大。节理抗剪强度参数Cj与?j随着JRC值的增大而增大。所得结果可以为室内试验和工程应用提供参考和依据。     

SHRIMP zircon U-Pb dating of a small tonalite intrusion in metamorphic belt of Chinese Altai orogen and its geological implication

Small granitic intrusions occur in the progressive metamorphic belts of the Chinese Ahai orogen. SHRIMP U-Pb analyses were performed on zircons separated from a tonalite intrusion and yielded a concordant age of 409.6±3.7 Ma （ MSWD = 0.93 ）, restricting the emplacement and crystallization of the tonalite intru- sion to the Early Devonian. Combined with the existing geological data of the contemporary large granitic plutons in the Chinese Altai orogen, the tonalite is considered to be formed together with other granitic rocks in a continental arc setting. The tonalite intrusion has consistent foliation with its country rocks, indicating the strain resuiting in the regional deformation should be very strong during or after the early Devonian.     

Slope stability and landslides in proglacial varved clays of western Estonia

During the last decade the frequency of landslides at river valley slopes eroding into the glaciolacustrine plain in western Estonia has grown considerably. We studied in detail nine recent landslides out of 25 known and recorded sliding events in the area. All landslides occurred at the river banks in otherwise almost entirely flat areas of proglacial deposits capped with marine sands. Glaciolacustrine varved clay is the weakest soil type in the area and holds the largest landslides. Slope stability modelling shows that critical slope gradient for the clay is ≥ 10° and for the marine sand ≥ 20°. Fluvial erosion is the main process in decreasing slope stability at the outer bends of the river meanders. An extra shear stress generated by groundwater flow following the high stand of the groundwater level or rapid water level drawdown in the river channels are responsible for triggering the landslides. Consecutive occurrence of small-scale slides has a direct effect in triggering the large, retrogressive complexes of slides in the glaciolacustrine clay. A landslide hazard zonation map was composed based on digital elevation model and the data on spatial distribution of glaciolacustrine clays and marine sands, and on existing and critical slope angles of these deposits.     

Impending HRT wave precursors to the Wenchuan M_s8.0 earthquake and methods of earthquake impending prediction by using HRT wave

We deployed four geo-electric monitoring stations in Sichuan and Yunnan provinces from 2004, using the new generation of equipment (PS-100) and technologies to capture the HRT wave earthquake precursor. Before the Wenchuan Ms8.0 earthquake, we recorded the HRT wave precursor at the only operating station in Hongge (HG, Δ=465 km) and found that significant impending signal had been recorded at the station in the early morning ( 0―5 am) of 12th of May, 2008. The precursor for this earthquake is consistent wit...     

热红外目标的多标度分形识别模型

利用机载热红外成像光谱仪（TASI）获取的热红外图像,进行了温度与比辐射率分离,然后采用多标度分形模型进行阈值分割,建立了一种新的热红外影像目标探测方法。实验结果表明,温度的空间分布具有多标度分形特征,即对lgL（r）与lgr进行分段拟合。利用多标度分形模型提取的温度阈值进行城市热红外影像的精细目标识别,并成功提取了建筑物目标。     

陕西省宁陕县香子坪金矿矿床地质特征及找矿标志

香子坪金矿床位于秦岭造山带南秦岭构造亚带北缘,北西向断裂带控制着含金构造蚀变带及金矿体的分布,硅化、绢云母化、黄铁矿化、绿泥石化、褐铁矿化等蚀变为找矿标志,蚀变矿物愈多、组合愈复杂,金、银的品位往往越高。金矿成因类型为脉型及蚀变岩型金矿。     

X射线极光强度与亚暴指数AE的相关关系

研究了Polar卫星的极区电离层X射线成像仪（PIXIE）得到的极光X射线成像强度AI（Auroral Intensity）与磁层亚暴指数的相关关系.本文发现,在所选取的1997年至2001年的部分数据中,从完整的X射线图像得到的极光X射线总强度和AE指数有很好的线性相关关系,在全部83组数据中有566％的数据的线性相关系数都在060以上（相关系数最大为097）.所以本文认为极光X射线总强度可以作为新的磁层亚暴卫星实时监测指数.