地基GNSS-R在复杂地形条件下的积雪探测

GNSS-R技术是一种以GNSS为信号源的全新遥感技术, 可用于监测海洋和陆地.在地基GNSS-R积雪探测研究中, 反射区域内的复杂地形不仅会引起积雪的不均匀分布, 还使得接收机能在同一时刻接收到来自多个反射界面的反射信号, 从而增加了积雪探测的难度.针对该问题, 本文利用北极圈内斯匹次卑尔根岛上布设的GNSS-R测站, 开展了复杂地形条件下的积雪探测研究.根据不同界面上的反射信号具有不同多普勒频移的特点, 本文提出了基于傅里叶变换的谱分析方法, 将不同界面的反射信号从混合信号中分离出来, 并根据特定多普勒频率段的功率来监测地表积雪变化.基于该方法, 本文分析了反射路径位于Schetelig山地区域的8颗卫星在2014年间的反射信号, 计算结果表明: 卫星PRN 2、12和28与积雪地面介电常数之间的相关系数分别为0.02、0.20和0.05, 表明这三颗卫星的反射信号与地面介电常数之间不相关; 卫星PRN 14和20与地面介电常数之间的相关系数分别为0.29和0.26, 为低度相关; PRN 17、18和25与地面介电常数之间的相关系数分别为0.43、0.54和0.44, 为中等程度相关.研究证明本文提出的方法, 可用于探测复杂地形下的地表积雪.

     

Pore pressure profiles in fractured and compliant rocks1

Fluid permeability in fractured rocks is sensitive to pore-pressure changes. This dependence can have large effects on the flow of fluids through rocks. We define the permeability compliance γ= 1/k(k/δp_p)_pc, which is the sensitivity of the permeability k to the pore pressure p_p at a constant confining pressure p_c, and solve the specific problems of constant pressure at the boundary of a half-space, a cylindrical cavity and a spherical cavity. The results show that when the magnitude of permeability compliance is large relative to other compliances, diffusion is masked by a piston-like pressure profile. We expect this phenomenon to occur in highly fractured and compliant rock systems where γ may be large. The pressure profile moves rapidly when fluids are pumped into the rock and very slowly when fluids are pumped out. Consequently, fluid pressure, its history and distribution around injection and production wells may be significantly different from pressures predicted by the linear diffusion equation. The propagation speed of the pressure profile, marked by the point where δp_p/δx is a maximum, decreases with time approximately as and the amplitude of the profile also dissipates with time (or distance). The effect of permeability compliance can be important for fluid injection into and withdrawal from reservoirs. For example, excessive drawdown could cause near-wellbore flow suffocation. Also, estimates of the storage capacity of reservoirs may be greatly modified when γ is large. The large near-wellbore pressure gradients caused during withdrawal by large γ can cause sanding and wellbore collapse due to excessive production rates.     

航磁异常轴向特征提取算法研究及其应用

通过分析航磁异常的空间分布特征，提出一种在平面等值线追踪基础上，根据封闭等值线之间的关系并应用离散卡洛变换，自动检测和绘制航磁异常轴向图的方法，将该方法用于新疆某地航磁异常分析，发现了断裂构造，有效地验证了算法的正确性。     

Numerical investigation of the seismic response of a UHV composite bypass switch retrofitted with wire rope isolators

An ultra-high voltage(UHV)composite bypass switch(BPS)faces increasing seismic challenges when UHV projects extend to high seismic intensity areas.The UHV composite BPS still generates excessive stress at the bottom section although hollow composite insulators with high flexural strength are adopted.Since the standard retrofitting strategy by using stiffer supports cannot reduce stress responses,wire rope isolation is introduced.The optimal design of isolation considers both stress and displacement responses since the slenderness and composite material of insulators contribute to significant displacement.The results show that properly designed isolation can significantly reduce stress without excessive displacement responses.A larger radius configuration helps to improve the applicability of small stiffness isolators under high winds.When the isolation still cannot satisfy the requirement,smaller stiffness isolators with a larger radius,or isolators with increased loops and smaller radius,can be introduced to gain better energy dissipation capacity and effectiveness in response mitigation.Accordingly,a three-step design procedure is proposed to increase the damping force but fix the rotational stiffness of isolation.Hence,the application of wire rope isolation can be extended to UHV composite BPS with a low natural frequency,but conductors with enough redundancy should be used.     

Microtremor-based analysis of the dynamic response characteristics of earth-fissured sites in the Datong basin,China

This study conducted microtremor testing along six survey lines that cross three typical earth fissures in the Datong basin to determine the dynamic response characteristics of earth fissure sites with regard to the Fourier amplitude spectrum, response spectrum, and Arias intensity. The results show the following.(1) The predominant frequency of an earth fissure site is mainly affected by the thickness and the shear wave velocity of the soil layer and is minimally effected by the presence of an earth fissure.(2) Earth fissures have a pronounced amplification effect on dynamic response. Fourier amplitude, response acceleration, and Arias intensity are high near an earth fissure and decrease with an increase in distance from the earth fissure, tending toward stability at a distance of 20 m.(3) The area that is seriously affected by this amplification is within 6–8 m of an earth fissure, and the general affected area is farther out than this, to a distance of 25 m.(4) New construction should be avoided in an area affected by the amplification, and existing buildings in general and seriously affected areas need to be reinforced to increase their seismic fortification intensity.     

正确使用X—CT球管的技术探讨

本文报道了我院连续六只Ｘ－ＣＴ球管的使用情况。寿命最长的曝光达３５８３００秒，而最短的只有１３５０００秒，其主要原因是缺乏正确地使用和维护知识，要想延长球管使用寿命，首先需加强对使用人员的专业素质训练，其次，在保证图像质量的前提下，降低ｍＡｓ；第三，保持扫描室恒业的温湿度；第四，定期检查球管的冷却散热系统。     

Isotopic evidence of TSR origin for natural gas bearing high H_2S contents within the Feixianguan Formation of the northeastern Sichuan Basin, southwestern China

Isotopic evidence of TSR origin for natural gas bearing high H2S contents 1961 As the hazardous component of natural gas, the ex-istence of H2S, due to its extremely strong toxicity and corrosivity, not only decreases the percentage of hy-drocarbon gas within natural gas and reduces its in-dustrial value, it also threatens each aspect of drilling and exploitation. It frequently causes serious safety accidents[1] and leads to the E&P cost and risk of natural gas with higher H2S contents be…     

Least-squares wave-path migration

We present a new least-squares migration method called least-squares wave-path migration. The proposed method combines an iterative conjugate-gradient solver with a stationary-phase wave-path migration operator. Numerical tests demonstrate that (i) least-squares wave-path migration is computationally more efficient than and almost as accurate as Kirchhoff least-squares migration, and (ii) many of the artefacts seen in wave-path migration images are suppressed after several conjugate-gradient iterations. Previous results have shown that 3D wave-path migration is up to 100 times faster than a standard 3D Kirchhoff migration, but sometimes at the cost of reduced quality. With the proposed least-squares wave-path migration method, the image quality in wave-path migration can be improved at an acceptable increase in computational cost.     

Assessing spatial likelihood of flooding hazard using naïve Bayes and GIS: a case study in Bowen Basin,Australia

Flooding hazard evaluation is the basis of flooding risk assessment which has significances to natural environment, human life and social economy. This study develops a spatial framework integrating naïve Bayes (NB) and geographic information system (GIS) to assess flooding hazard at regional scale. The methodology was demonstrated in the Bowen Basin in Australia as a case study. The inputs into the framework are five indices: elevation, slope, soil water retention, drainage proximity and density. They were derived from spatial data processed in ArcGIS. NB as a simplified and efficient type of Bayesian methods was used, with the assistance of remotely sensed flood inundation extent in the sampling process, to infer flooding probability on a cell-by-cell basis over the study area. A likelihood-based flooding hazard map was output from the GIS-based framework. The results reveal elevation and slope have more significant impacts on evaluation than other input indices. Area of high likelihood of flooding hazard is mainly located in the west and the southwest where there is a high water channel density, and along the water channels in the east of the study area. High likelihood of flooding hazard covers 45 % of the total area, medium likelihood accounts for about 12 %, low and very low likelihood represents 19 and 24 %, respectively. The results provide baseline information to identify and assess flooding hazard when making adaptation strategies and implementing mitigation measures in future. The framework and methodology developed in the study offer an integrated approach in evaluation of flooding hazard with spatial distributions and indicative uncertainties. It can also be applied to other hazard assessments.     

肾上皮样血管平滑肌脂肪瘤影像表现及病理对照

目的:探讨肾上皮样血管平滑肌脂肪瘤(EAML)的影像学特征及病理学特点,提高对该疾病的认识。材料和方法:回顾性分析2008年1月至2014年4月间本院7例经手术病理证实为肾脏EAML的影像学表现及病理特点。结果:7个病例8个病灶,其中5个病灶部分突出肾轮廓外,2个病灶突入肾窦,1个病灶同时突出肾轮廓外及肾窦;CT平扫3例呈稍高密度,2例呈等密度,1例MRI呈稍长T1短T2;增强扫描2例病灶呈“快进快出”,2例呈“快进慢出”;5例见“皮质掀起征”,5例见“黑星征”,其中4例同时出现“皮质掀起征”及“黑星征”;2例病理有恶性表现。组织学表现:肿瘤主要由上皮样细胞、平滑肌、厚壁血管及脂肪组成。免疫组化:常表达肿瘤细胞S-100、瘤细胞Vim、HMB-45、HHF-35及CD34。结论:肾上皮样血管平滑肌脂肪瘤的影像学表现多样化,影像学表现难与其他疾病相鉴别,当肿瘤部分突出肾轮廓外或向肾窦内生长,CT平扫密度呈稍高或等密度应考虑有EAML可能。