双能光子吸收法提高CT衬度(密度)分辨率的研究

目的：提高CT衬度的分辨率，30年来，医学CT经历了原始的第一代CT发展至目前第5代高分辨率CT和高速电子束CT，其成像的空间分辨率和时间分辨率均有明显提高，但CT成像的衬度（密度）分辨率提高并不显著，而衬度分辨率与图像的灰度等级（灰阶）密切相关，是图像清晰度的重要参数。本文对应用双能量光子扫描吸收法以提高CT衬度（密度）分辨率的原理进行分析，并探讨其实际应用的可行性。     

渤海北部东岸海风锋活动及其触发对流特征分析

利用常规观测、雷达、卫星及加密自动气象站等资料,对2015年、2018年和2019年渤海北部东岸海风锋活动及其触发的对流特征进行统计分析.结果表明:不同年份渤海北部东岸海风锋活动的差异较大,海风锋主要出现在6—8月,其中7月最多;海风锋可分为沿山型、北部沿海型和混合型3种,其中沿山型占比70％以上,海风锋东移到达沿山地...     

Vertical and horizontal vibrations of a rigid disc on a multilayered transversely isotropic half-space

A half-space containing horizontally multilayered regions of different transversely isotropic elastic materials as well as a homogeneous half-space as the lowest layer is considered such that the axes of material symmetries of different layers and the lowest half-space to be as depth-wise. A rigid circular disc rested on the free surface of the whole half-space is considered to be under a forced either vertical or horizontal vibration of constant amplitudes. Because of the involved integral transforms, the mixed boundary value problems due to mixed condition at the surface of the half-space are changed to some dual integral equations, which are reduced to Fredholm integral equations of second kind. With the help of contour integration, the governing Fredholm integral equations are numerically solved. Some numerical evaluations are given for different combinations of transversely isotropic layers to show the effect of degree of anisotropy of different layers on the response of the inhomogeneous half-space.     

Numerical study on screening of surface waves using a pair of softer backfilled trenches

Vibration screening effectiveness of a pair of in-filled trenches is numerically studied under conditions of plane strain using PLAXIS 2D in a linear elastic, isotropic, and homogeneous half-space acted upon by a steady-state vertical excitation. Barrier efficiency is analyzed in terms of reduction of vertical and horizontal vibration components with respect to the variations in barrier geometry and in-fill material parameters. The geometric features are normalized with respect to Rayleigh wavelength of vibration in soil. The in-fill trench material is considered to be softer and accordingly assigned lower shear wave velocities than the half-space. Non-dimensional design charts are developed and the key parameters participating in wave screening process are identified. Some recommendations are made regarding the optimal selection of these parameters. Comparison with a few published results shows close agreement. Such an isolation scheme may be advantageous in circumstances where a single trench requires unrealistic depth.     

双参数展开CRP叠加和速度分析方法研究

椭圆展开共反射点(CRP)方法可以获得比常规倾角时差校正(DMO)方法更近似的零偏移距时间剖面和相应CRP速度场.大量研究和实践证实,在非均质性较弱的地区,该方法取得的成果显著.但由于该方法没有考虑速度的横向变化和转换波等情况,当地下介质存在较强非均质性时,该方法不再准确,需要引进反映速度横向变化的双参数(上行波与下行波的平均速度和速度比)进行改进.本文详细推导了引入双参数后的叠加和速度分析算法,并通过数值模型和地震资料处理证实,修正后的算法可以更好地解决地质复杂地区速度建模和叠加成像问题.     

Spatial and temporal mapping of water in soil by magnetic resonance imaging

Experiments on model and real soil blocks designed to assess the feasibility of using magnetic resonance imaging for three-dimensional mapping of the time-varying spatial distribution of water in structured soils are reported. The results show that, notwithstanding inherent problems in imaging natural soils with a significant iron content, experimental parameters can be identified which allow satisfactory images to be obtained. Magnetic resonance imaging may therefore provide important information on soil structure and water movement in dual porosity soils, with attendant benefits for the calibration of models of non-Darcian flow in such soils.     

腾冲老厂坪子地区铜多金属矿

老厂坪子地区已发现十余个矿床(点),矿体赋存于花岗岩与碳酸盐岩接触带及其附近的断裂破碎带中,并受其双重控制。矿石品位较富,矽卡岩型和热液型成因,矿质来源于二叠系、三叠系碳酸盐岩及燕山早期岩浆岩。     

一次飑线过程的动力和微物理结构及滴谱变化对降水估测的影响研究

雨滴谱的变化和回波强度的垂直变化是影响雷达估测降水的重要原因.文章利用美国KOUN双线偏振雷达观测的一次飑线过程资料,用模糊逻辑的方法、β方法和约束条件下的Λ方法,分析了飑线过程降水粒子相态和雨区雨滴谱分布及其相态混合区冰雹融化过程,结合四维变分方法风场反演方法,研究了雨滴谱变化与飑线过程风场中尺度结构的关系,及其对双线偏振雷达不同估测降水方法的影响.结果表明:处在气旋中的飑线存在中低层辐合线,低层辐合带及强烈上升形成强回波,飑线后部的层状云中存在下沉气流,而飑线的前部存在下沉气流形成的边界层辐合线.飑线中对流单体组成的强回波带和后侧的层状云降水的雨滴谱分布有明显的变化,大雨滴区往往在飑线前部,在东南气流中新生的对流单体也常常有大雨滴区存在.ZH、ZDR随高度变化比较明显,而KDP基本不随高度变化,高度的选取对传统的Z-R关系方法、(ZH,ZDP)方法估测降水量影响很大,但KDP方法几乎不受高度变化的影响.本次过程雨滴谱变化非常明显,这对Z-R关系估测降水将产生重要影响,(ZH、ZDR)方法和KDP方法估测的降水比较接近,而Z-R关系方法在对流中心降水估测值偏大.小于30 dBz回波的KDP脉动很大,出现的不正常值对降水估测有一定影响,采用综合降水估测方法是必要的.     

双极化Sentinel-1数据在昆明市沉降监测中的应用

针对多数学者用VV极化的Sentinel-1数据对城市区域进行监测而忽略VH极化数据的问题,本文利用SBAS-InSAR方法,结合28景双极化(VV极化和VH极化)Sentinel-1数据,得到了昆明市2018年8月—2019年7月间的地面沉降情况,并且对两种极化的沉降监测结果进行对比.结果表明昆明市主城区存在着较为明显的沉降现象,部分区域沉降严重形成明显的沉降漏斗.最大年平均沉降速率达到-53.63 mm/a(VV极化)和-53.67 mm/a (VH极化).对两种极化的数据集进行对比,发现在SDFP点的筛选和获取方面,VV极化数据集要优于VH极化数据集;其次,VV极化数据和VH极化数据的沉降速率、沉降分布及趋势等结果呈现出一致性,但是二者在同一时间段的各个监测节点的沉降时序变化存在着差异.     

Planning of municipal solid waste management systems under dual uncertainties: a hybrid interval stochastic programming approach

In this study, a random-boundary-interval linear programming (RBILP) method is developed and applied to the planning of municipal solid waste (MSW) management under dual uncertainties. In the RBILP model, uncertain inputs presented as interval numbers can be directly communicated into the optimization process; besides, intervals with uncertain lower and upper bounds can be handled through introducing the concept of random boundary interval. Consequently, robustness of the optimization process can be enhanced. To handle uncertainties with such complex presentations, an integrated chance-constrained programming and interval-parameter linear programming approach (ICCP) is proposed. ICCP can help analyze the reliability of satisfying (or risk of violating) system constraints under uncertainty. The applicability of the proposed RBILP and ICCP approach is validated through a case study of MSW management. Violations for capacity constraints are allowed under a range of significant levels. Interval solutions associated with different risk levels of constraint violation are obtained. They can be used for generating decision alternatives and thus helping waste managers to identify desired policies under various environmental, economic, and system-reliability constraints.