嘉陵江卵石粒度分布与最大干密度的分形特征

应用分形理论研究了卵石粒度分布的分形规律,建立了关于分维数（D）、小于10mm颗粒含量（P10）与卵石最大千密度（rdmax）的数学模型。研究表明,嘉陵江卵石颗粒粒径在10mm以上部分其粒度具有良好的分形结构,基于嘉陵江卵石特征所建立的数学模型对工程实践具有重要的指导意义。     

各向异性结构性砂土离散元分析

天然沉积砂土力学特性受各向异性及结构性影响明显,实际工程中不能忽视。为探究二者的影响,首先在二维离散元程序NS2D中采用椭圆颗粒模拟了重力场中颗粒长轴主方向为水平的各向异性净砂样,随后基于结构性砂土胶结厚度分布规律及室内试验提出了一个新的微观胶结接触模型并将其引入各向异性净砂样以模拟天然各向异性结构性砂土,最后对该离散元试样进行了双轴试验模拟,将模拟结果与室内试验结果对比以验证该模型的适用性,并对其微观力学特性变化进行研 究。分析结果表明,随着剪切进行,各向异性结构性砂土呈明显应变软化及剪胀现象;胶结接触逐渐减少,且主方向始终为竖向方向;胶结破坏速率及胶结破坏率变化情况与宏观力学响应较一致,且胶结物多为拉剪破坏;土颗粒排列主方向始终为水平向,且水平向排列颗粒所占比例略微增大。     

南京细颗粒物对城市热岛强度的影响

随着城市化和工业化进程的加快,南京城市热岛效应显著,细颗粒物污染加剧,对大气环境、气候变化和人体健康产生重要影响.本文基于观测资料,分析了南京市不同颗粒物浓度水平下城市热岛强度的变化特征;利用光学特性模型OPAC（optical properties of aerosols and clouds model）和辐射传输模型TUV（troposphere ultraviolet-visible model）估计了气溶胶的光学厚度及辐射强迫;定量分析了细颗粒物对城市热岛强度的影响及其可能机制.结果表明：南京城市热岛强度范围为-0.51.3K,冬季强于夏季.细颗粒物质量浓度范围为32 135 μg/m3,冬季高于夏季,城区和郊区差别不大;当大气中细颗粒物质量浓度较高时,城市热岛强度相对较弱;南京城郊气溶胶光学厚度变化范围为0.28 1.01,在地面产生的辐射强迫达-3.88-4.72 W＆#183;m-2;由于城区和郊区下垫面、人为热、细颗粒物浓度水平的差异,造成城郊近地面降温的不同,导致细颗粒物对城市热岛强度的削弱,夏季减弱0.1K,冬季减弱0.2K.     

基于粒子滤波的PDR/地磁指纹室内定位

针对行人航位推算(PDR)定位存在误差累积和地磁指纹不唯一导致的误匹配问题,本文改进了基于粒子滤波的PDR/地磁指纹室内定位方法.在PDR定位过程中利用地图信息控制粒子权重更新,得到较为准确的位置信息后,利用动态时间规整(DTW)算法在PDR推算位置基础上进行快速序列匹配,获取最优位置估计.试验结果表明,融合定位方法有...     

约束非负矩阵分解框架下高维自适应粒子群端元提取

传统基于约束非负矩阵分解NMF(Nonnegative Matrix Factorization)的高光谱端元提取算法一般存在两个问题:一方面,以固定惩罚系数方法处理端元提取的约束优化问题,难以较好权衡目标项与约束项间的关系,影响提取效果;另一方面,求解过程通常基于梯度算法,依赖于初始值和步长的设定,容易陷入局部最优。针对这些问题本文提出约束NMF框架下高维自适应粒子群端元提取算法HAPSO(High-dimension Adaptive Particle Swarm Optimization)。该算法在端元距离最小约束的NMF框架下,利用粒子群算法PSO替代原梯度算法以增强全局搜索能力;采用高维PSO方法解决了多波段高维问题,并结合种群信息构建自适应惩罚机制以实现端元提取中目标与约束的合理权衡。通过模拟影像和真实影像的实验,证实该算法与传统的NMF端元提取算法相比能够更合理地权衡约束和避免局部最优,具有较好的端元提取效果。     

Numerical simulation of particle plugging in hydraulic fracture by element partition method

Hydraulic fracturing (HF) treatment often involves particle migration and is applied for propping or plugging fractures. Particle migration behaviors, e.g., bridging, packing, and plugging, significantly affect the HF process. Hence, it is crucial to effectively simulate particle migration. In this study, a new numerical approach is developed based on a coupled element partition method (EPM). The EPM is used to model natural and hydraulic fractures, in which a fracture is allowed to propagate across an element, thereby avoiding remeshing in fracture simulations. To characterize the water flow process in a fracture, a fully hydromechanical coupled equation is adopted in the EPM. To model particle transportation in fractures with water flow, each particle is treated as a discrete element. The particles move in the fracture as a result of being dragged by fluid. Their movement, contact, and packing behaviors are simulated using the discrete element method. To reflect the plugging effect, an equivalent aperture approach is proposed. Using this method, the particle migration and its effect on water flow are well simulated. The simulation results show that this method can effectively reproduce particle bridging, plugging, and unblocking in a hydraulic fracture. Furthermore, it is demonstrated that particle plugging significantly affects water flow in a fracture and hence the propagation of hydraulic fracture. This method provides a simple and feasible approach for the simulation of particle migration in a hydraulic fracture.     

Unfilterable "geoaerosols", their use in the search for thermal, mineral and mineralized waters, and their possible influence on the origin of certain types of mineral waters

 Many articles describing the unusual mobility of solid particles in the subsurface layers of the Earth's crust have been published in the last decades, especially in the geological literature. In an attempt to explain this phenomenon, several hypotheses have been developed. The one closest to the behavior observed in nature is based on quantum mechanics. Based on this phenomenon, a new geological prospecting method called Molecular Form of Elements (MFE) was developed in former Czechoslovakia during the 1970s. It has been widely applied since for various types of prospecting, including the search for thermal and mineral waters. When using the MFE method for prospecting, the relationship between the ascending mineral springs and the four directions of structural faults was discovered. The possibility of whether a process, similar to the one acting during the absorption of elements when using the MFE method, can be a source of dissolved solid particles during the creation of mineral waters is also discussed. Received: 3 March 2000 · Accepted: 11 July 2000     

The role of organic material in atmospheric aerosols

An estimated budget of organic substances in the atmosphere is compiled to whow the importance of organics in the aerosol. The distribution of organic compounds in background aerosols is estimated and it will be shown that the Aitken particles probably consist of roughly one quarter of organic substances. This is important for the dynamics of the aerosol and calculations are presented to estimate the aerosol production distribution for gas-to-particle conversion processes.     

射流泵流场的PIV测量

利用粒子图像速度场仪(PIV)对射流泵渐缩锥形入口、等径直管内有限空间水射流进行测量。该射流泵喉管面积与喷嘴面积之比为4.75,基于射流泵喷嘴直径D和喷嘴出口流速计算的雷诺数为3.68×105。通过流量比在0.20～0.80之间的变化来研究流量比对流场的影响。获得了射流泵对称面流场的速度矢量、轴心速度分布和轴向速度等值线图。结果表明:当射流泵的面积比确定后,射流泵内有限空间射流结构只与射流泵的流量比有关,流量比愈小,其轴心速度衰减得愈快,高速射流区愈短。测量结果为射流泵理论研究和优化设计提供可靠依据。