An experimental study on microscopic characteristics of gas-bearing sediments under different gas reservoir pressures

Gas-bearing sediments are widely distributed in five continents all over the world. Most of the gases exist in the soil skeleton in the form of discrete large bubbles. The existence of gas-phase may increase or decrease the strength of the soil skeleton. So far, bubbles’ structural morphology and evolution characteristics in soil skeleton lack research, and the influence of different gas reservoir pressures on bubbles are still unclear. The micro characteristics of bubbles in the same sediment sample were studied using an industrial CT scanning test system to solve these problems. Using the image processing software, the micro variation characteristics of gas-bearing sediments in gas reservoir pressure change are obtained. The results show that the number and volume of bubbles in different equivalent radius ranges will change regularly under different gas reservoir pressure. With the increase of gas reservoir pressure, the number and volume of tiny bubbles decrease. In contrast, the number and volume of large bubbles increase, and the gas content in different positions increases and occupies a dominant position, driving the reduction of pore water and soil skeleton movement.     

三维CT成像的数学模型

三维CT成像广泛应用于放疗模拟定位等临床实践。当扫描运动物体时三维图像存在的位移和形变,与扫描参数设置和被扫描物体的运动状态等关系密切。本文通过理论分析CT扫描过程,建立三维成像的数学模型,计算三维图像的时间分辨率、位移和形变等指标,并分析其变化规律,为将来进一步的实验研究奠定基础。     

GE VCT-高图像质量和低剂量的和谐

在本文中讨论了实现图像质量和X射线剂量的和谐和同一的重要性,介绍了GELightSpeedVCT在硬件,软件和临床应用上降低病人剂量的方法。VCT在实现各向同性高分辨率的同时努力提高X射线的有效利用率,降低病人剂量,真正实现了高图像质量和低剂量的和谐。     

用于颗粒土微观力学行为试验的微型三轴试验仪

颗粒土的微观力学行为（如土颗粒的运动与破碎等）决定着其宏观应力-应变行为,如应变局部化、应力硬化等。为研究颗粒土的微观力学行为,开发了一台微型三轴试验装置。它的轴向加载系统由伺服控制的步进转动马达与涡轮传动的减速器组成,围压由GDS压力控制器提供,压力室采用高透光率,高强度的轻质材料制成。借助于X射线显微CT及图像处理分析技术,该装置能实现对干砂土微尺寸试样（直径为8 mm,高度为16 mm）在三轴剪切条件下微观特性的无损检测。采用该三轴试验装置对粒径为0.60～1.18 mm 的LBS（Leighton Buzzard sand）试样在1.5 MPa的围压下进行了试验。结果显示,试验装置测得应力-应变曲线合理,显微CT 图像特征清晰,能够用于颗粒土体微观土力学行为的试验研究。     

颗粒形状对碎石料孔隙特性影响研究

颗粒形状是影响碎石料孔隙特性的主要因素之一,进而影响碎石料的渗透特性和力学行为。选取粒径为2~5 mm和5~10 mm的灰岩碎石颗粒填筑试样,同时与相同级配和孔隙率的玻璃球试样进行对比研究,采用CT扫描技术和图形处理软件获取多孔介质孔隙边界轮廓,选取0.5 mm开度阈值分割孔隙;每组试样选取3张扫描断面图像,取定量参数的平均值为研究对象,对孔隙特性进行定量分析。结果表明：玻璃球多孔介质孔隙形状的复杂性甚于碎石料;玻璃球多孔介质孔隙系统的连通度大于同粒组碎石料。     

New style of honeycomb structures revealed on 3D seismic data indicate widespread diagenesis offshore Great South Basin,New Zealand

In the Great South Basin, within the Eocene section, at time-depths around 700–900 ms two way time below the seafloor, unusual features are observed on 3D seismic data closely associated with polygonal faults. The features, referred to as honeycomb structures (HS), cover an area of ∼600 km², are packed circular, oval, to polygonal depressions 150–400 m across in plan view and several to 10 + m in amplitude. Polygonal faults rapidly die out at the Marshall Paraconformity, which is overlain by the Oligocene Penrod Formation. Hence the polygonal faults are inferred to have formed prior to the Marshall Paraconformity, and they cross-cut HS features. Consequently the top of the HS probably formed at burial depths of around 375–500 m, which is their decompacted depth below the paraconformity. The interval containing HS is about 125 m vertical thick. There are several possible origins for the HS. The most probable is related to bulk contraction of the sediment volume accompanied by fluid expulsion, which suggests a diagenetic origin, in particular the opal-A/CT transition. There are actually two polygonal fault systems (PFS) present in the area. The Southern Tier 1 PFS lies laterally to the HS and overlaps with it. The Northern PFS (Tier 2) lies above the HS, appears to be independent of the HS, and formed in the upper 200–300 m of the sediment column. The Tier 1 PFS probably formed by shear failure related to the same diagenetic effects that caused the HS.     

基于CT三维重建与逆向工程技术的煤体数字模型的建立

为了建立能够表征煤体真实孔隙结构的数字模型,进而进行数值模拟研究,通过μCT225kVFCB高精度CT系统扫描得到了大柳塔煤矿长焰煤CT数据,可观测到的最小孔隙直径为1.94 μm。使用基于Matlab语言的三维重建程序结合逆向工程技术,提出了一种将煤体CT三维数据转换为CAD数字模型的方法。以Ansys建立的煤体有限元模型为例,对煤体瓦斯渗流进行了模拟,分析了煤体孔隙内的速度及压力分布规律,并计算了沿X、Y、Z方向的渗透系数。计算结果表明：在微观尺度下（< 100 μm）煤体渗透系数呈现各向异性,其受煤体结构的影响较明显。提出的基于CT三维重建结合逆向工程技术构建的煤体CAD数字模型不仅可进行有限元分析,同时也可以被EDEM等离散元分析软件所使用,拓宽了煤体CT三维数据的应用范围,丰富了煤体在微观尺度上的研究方法。     

多排螺旋CT对结核性腹膜炎与癌性腹膜炎的鉴别诊断

目的：探讨结核性腹膜炎（TBP）及癌性腹膜炎（CP）的多排螺旋CT（MSCT）表现,为两者的诊断及鉴别提供依据。方法：搜集2010年9月～2011年9月的24例TBP和47例CP患者的CT影像资料,全部病例经手术和病理进行确诊,采用χ2检验比较各种CT征象在两种病变中的发生率,结合病理变化、临床症状进行分析。结果：TBP组及CP组患者大量腹水,所占比例差异有统计学意义（41.7%、72.3%,χ2=9.695,P〈0.05）。TBP组以壁层腹膜均匀光滑增厚、肠系膜污垢样改变为主,CP组壁层腹膜以不规则、结节、块样增厚为主。结论：以壁层腹膜改变为基础,综合大网膜、肠系膜、腹水及淋巴结改变CT征象进行对两种病变的诊断及鉴别诊断具有重要意义。     

箱包CT检测系统弱信号情况下的CT成像实验研究

在箱包CT检测中,当放射源活度很低的情况时,对CT成像进行了实验研究。利用多次累加的方法降低统计涨落和噪声的影响,使CT图像质量得到提高。实验证明对于弱信号情况下,利用多次累加的方法,CT成像具有比较高的质量,能够实现物性判别的要求。另外对于A/D量化误差也进行了分析。     

肺泡蛋白沉着症支气管肺泡灌洗术前后胸部CT主要表现

目的：探讨肺泡蛋白沉积症（PAP）支气管肺泡灌洗术（BAL）前后的主要CT表现,以提高对本病的认识及评价BAL后的效果。方法：回顾性分析25例经病理证实为PAP的CT表现,观察病灶的范围、形态、边界及对比BAL前后的变化。结果：PAP的CT表现呈多样化,主要归纳为：地图征、碎石路征、肺水肿样及肺实变征。BAL后15例显著改善。结论：CT能直观显示PAP的影像特征,对该病有较高的诊断价值,同时可评价本病BAL后的效果,确诊依赖病理学证实。