共查询到19条相似文献，搜索用时 736 毫秒
1.
热中子数字成像系统的研制 总被引：2，自引：0，他引：2
成像系统是中子照相装置的关键组件之一.采用6LiFZnS(Ag)材料中子转换屏、长焦距、小视场专用微光镜头等光学组件,利用科学级CCD芯片、两级热电偶制冷技术、14bit模数转换技术研制了数字CCD摄像机,采用Visula C 和C Builder为工具,开发了双字节图像采集处理分析软件包,并设计了成像系统辐射防护装置,构成了热中子数字成像系统.实验证明:所采用的技术路线是合理的,达到了设计目的,成像质量可以与国外类似装置相媲美. 相似文献
2.
为了实现对板状构件的截面重建与缺陷检测,建立了X射线层析截面重建系统。对该系统的成像方法、重建精度、层析截面重建算法等进行研究。首先,提出并论述了采用特殊的成像方式获取X射线透视图像实现分层摄影功能的方法和层析截面重建原理。接着,对上述成像系统进行重建精度分析和运动系统校准。然后,根据上述成像方法获取已知形状检测工件的透视图像,并根据校准结果进行修正,对获取的图像按层析截面重建方法进行重建实验。最后,根据实验重建结果,进行仿真实验并优化重建参数。实验结果表明：探测器旋转步进角为0.5°时,重建图像伪影减小,使用S-L滤波器后,轮廓边缘更为清晰。该层析截面重建方法能有效重建X射线最大入射角内的信息,增大入射角并适当调整检测物角度,可获得清晰的截面图像。 相似文献
3.
热中子CT成像是一种极为重要的核成像技术,借以进行被检物的无损检测与无损评价.针对热中子CT成像过程中产生一系列导致CT图像降质的因素,本文在探讨了影响中子CT成像图像降质的一些因素基础上,提出了将成像过程中的图像预处理与后处理技术进行统一考察和集成处理的方案.研究结果表明,基于MATLAB GUI集成处理器,研究开发了一套集图像预处理与后处理技术于一体的处理程序分析方法,能够有效改善热中子CT成像的图像质量,为无损检测与评价提供可靠的保证,对热中子CT成像技术研究具有参考价值. 相似文献
4.
基于GPS信标观测数据重建电离层电子密度的时变三维电离层层析问题的数学基础，在简化电离层电子密度随时间变化的条件下，导出了三维平行束层析重建公式. 在二维情况下，本文导出的三维平行束层析重建公式与Yeh等给出的二维电离层层析重建公式相同. 文中还讨论了有限视角和有限接收机孔径对重建图像的影响. 根据文中给出的三维平行束层析重建公式，在这些非理想条件下，对一个脉冲源函数进行CT重建的结果表明，基于GPS信标观测数据重建电离层电子密度的时变三维电离层层析是可行的. 相似文献
5.
热中子CT成像是一种极为重要的核成像技术,借以进行被检物的无损检测与无损评价。针对热中子CT成像过程中产生一系列导致CT图像降质的因素,本文在探讨了影响中子CT成像图像降质的一些因素基础上,提出了将成像过程中的图像预处理与后处理技术进行统一考察和集成处理的方案。研究结果表明,基于MATLABGUI集成处理器,研究开发了一套集图像预处理与后处理技术于一体的处理程序分析方法,能够有效改善热中子CT成像的图像质量,为无损检测与评价提供可靠的保证,对热中子CT成像技术研究具有参考价值。 相似文献
6.
本文给出GPS地面台网和掩星观测结合的时变三维电离层层析的原理、算法和基于实测数据的反演结果.反演结果的比较表明,联合地基GPS与掩星观测数据进行重建,电子密度整体图像的重建质量特别是其垂直结构的重建质量得到了明显改善.在平静日和磁暴期间两种条件下利用实测数据的重建结果表明,GPS地面台网和掩星观测结合的电离层层析可以获得电离层电子密度在高度-纬度-经度-时间四维空间中的变化.重建结果清晰地显示了磁暴期间电离层负相暴效应,表明结合GPS地面台网和掩星观测的时变三维电离层层析可以有效地监测扰动条件下的大尺度电离层结构. 相似文献
7.
由投影重建图像的对称网格迭代算法 总被引：1，自引：0，他引：1
本文对于工业CT检测中常用的代数迭代重建算法提出了改进,利用投影射线之间存在的几何对称结构,提出了图像重建的对称网格迭代算法(简写为SM-IRT).该算法简化了投影系数矩阵的计算,调整了迭代算法逐线校正的迭代顺序.对模拟数据和工业CT实测数据进行了重建图像的数值实验,结果表明:与常规算法比较,本文提出的新算法重建速度快,成像精度高. 相似文献
8.
数字合成X射线体层成像技术能利用有限角度下的投影数据重建物体任意断层的图像.在数宁合成X射线体层成像重建算法研究中,模拟投影数据是重要的步骤,本文提出了一种基于GPU光线投射算法的数字合成X射线体层成像投影数据模拟方法.比较传统CPU模拟手段,GPU模拟方法计算速率快,且基于硬件支持的三线性插值能够得到更加接近实际的投... 相似文献
9.
医学图像三维表面模型重建 总被引：10，自引：0，他引：10
三维表面模型重建是医学图像处理的重要内容,是将CT和MRI等医疗影像设备获得的二维图像重建成三维立体表面显示图像的过程.本文重点研究了其重建算法的具体实现:(1)在建模上采用了基于体素的三维物体体积重建;(2)在显示上提出了基于Ray-Casting的三维物体二维直接显示技术.所以,和传统采用三角面拟合的方法相比,具有图像重建过程无需生成中间数据、无需进行3D物体的边界检测等优点,同时该算法并行性好,易于采用硬件方法实现加速.因此,本研究为医学图像三维表面模型重建应用软件的开发打下了理论基础. 相似文献
10.
一种基于数据外插改进的ART迭代算法 总被引：1，自引：0，他引：1
本文针对有限角度的投影数据的CT图像重建问题,提出了一种基于数据外插改进的ART算法.该算法的基本思想足运用已知角度的投影数据来补全未知角度的投影数据,再用ART算法进行图像重建.最后用模拟的投影数据进行了重建图像的数值实验.实验结果表明该算法不但提高了重建图像质量,同时也提高了图像达代的收敛速度. 相似文献
11.
C. Degueldre H. Pleinert P. Maguire E. Lehman J. Missimer J. Hammer K. Leenders H. Bck D. Townsend 《Earth and Planetary Science Letters》1996,140(1-4):213-225
This study demonstrates that positron emission tomography (PET) and neutron radiography (NR) techniques are complementary methods for determining the fluid pathway and porosity in crystalline rock. After preliminary injection of an organic solvent (e.g. isopropanol) front followed by the injection of the polymer solution (e.g. epoxy used for both techniques) and resin hardening, rock cutting may be performed. Flow pathway may be imaged by using a β+ emitter (e.g. 68Ga) in the resin. With a high-resolution PET camera, determination of the original water carrier features is possible in granodiorite pieces 20 cm in size and in simulated features with porosities of the order of 0.2. The use of a β+ tracer and the camera field, however, limit the lateral resolution of the technique (10 mm). Neutron radiography makes it possible to visualize the simulated porous phases by neutron transmission. The transmission process depends on the neutron scattering properties of the hydrogen-rich material (e.g. epoxy resin). Combination of 2D pictures may rebuild the 3D pattern. Lateral resolution may be in the range of 1 mm; however, the thickness of the rock sample must not exceed 10 cm. Complementarity of these techniques is discussed and they are compared with other methods used to determine porosity. 相似文献
12.
M. R. Deinert J. -Y. Parlange T. Steenhuis J. Throop K. Ünlü K. B. Cady 《Journal of Hydrology》2004,290(3-4):192-201
Few methods exist for measuring rapidly changing fluid contents at the pore scale that simultaneously allow whole flow field visualization. We present a method for using real-time neutron radiography to measure rapidly changing moisture profiles in porous media. The imaging technique monitors the attenuation of a thermal neutron beam as it traverses a flow field and provides measurements every 30 ms with an image area >410 cm2 and a spatial resolution 0.05 cm. The technique is illustrated by measuring the variation in moisture content across a wetting front moving at constant velocity through SiO2 sand. The relative contributions of the hydraulic conductivity and diffusivity terms in Richards' equation to the total fluid flux within the wetting front region were also measured. The diffusivity was found to rise from zero to a peak value within the wetting front region before falling off while the conductivity was found to rise monotonically. The reliability of the technique was checked via mass balance. 相似文献
13.
— The internal structure of rock samples studied in laboratory experiments can be described by a variety of physical parameters. Some of them, like the velocity of acoustic waves, enhanced velocity or quality factor can be reconstructed by means of ultrasonic tomography. This article presents the results of classical velocity tomography imaging, accompanied by the results of attenuation tomography and recently introduced enhanced velocity tomography obtained for a Lac Du Bonnet granite sample subjected to thermal stresses. To invert acoustic data recorded during six heating cycles, a Bayesian inversion scheme accompanied by a genetic algorithm optimization approach and the robust Cauchy norm have been used. To obtain the highest possible spatial resolution of images the inversion was performed in two steps. In the first step a crude parameterization of the sample was used. The result of this stage was next taken as an a priori model for a final inversion with refined parameterization. The choice of parameterization (cell sizes) and damping parameters at both stages was based on an analysis of the resolution operator. Both velocity and enhanced velocity tomography accurately imaged changes in the rock microstructure caused by thermal stresses. However, enhanced velocity tomography gave a much better spatial resolution than velocity tomography. On the other hand, attenuation tomography based on inversion of pulse rise times was able to image only a rough structure of the sample and it has difficulty with reasonable imaging of the crack formed in the sixth heating cycle. 相似文献
14.
在定量中子照相散射校正时需要考虑中子转换屏对不同角度入射中子的响应,中子转换屏的角度响应研究在中子照相散射校正中具有很重要的意义。本文在理论上推导中子转换屏的角度响应的解析式,并利用蒙特卡罗程序MCNP5对该解析式进行验证。利用蒙特卡罗方法对中子转换屏角度响应的影响因素进行研究。给出中子转换屏的角度响应与转换屏厚度以及入射中子能量之间的关系,中子转换屏的角度响应随着转换屏的厚度增大而增大,随着入射中子能量的增大而减小,并得到6LiF-ZnS(Ag)转换屏的最佳厚度为0.3mm。 相似文献
15.
The soil water retention function is needed for modeling multiphase flow in porous media. Traditional techniques for measuring the soil water retention function, such as the hanging water column or pressure cell methods, yield average water retention data which have to be modeled using inverse procedures to extract relevant point parameters. In this study, we have developed a technique for directly measuring multiple point (pixel-scale) water retention curves for a repacked sand material using 2-D neutron radiography. Neutron radiographic images were obtained under quasi-equilibrium conditions at nine imposed basal matric potentials during monotonic drying of Flint sand at the High Flux Isotope Reactor (HFIR) Cold Guide (CG) 1D beamline at Oak Ridge National Laboratory. All of the images were normalized with respect to an image of the oven dry sand column. Volumetric water contents were computed on a pixel by pixel basis using an empirical calibration equation after taking into account beam hardening and geometric corrections. Corresponding matric potentials were calculated from the imposed basal matric potential and pixel elevations. Volumetric water content and matric potential data pairs corresponding to 120 selected pixels were used to construct 120 point water retention curves. Each curve was fitted to the Brooks and Corey equation using segmented non-linear regression in SAS. A 98.5% convergence rate was achieved resulting in 115 estimates of the four Brooks and Corey parameters. A single Brooks and Corey point water retention function was constructed for Flint sand using the median values of these parameter estimates. This curve corresponded closely with the point Brooks and Corey function inversely extracted from the average water retention data using TrueCell. Forward numerical simulations performed using HYDRUS 1-D showed that the cumulative outflows predicted using the point Brooks and Corey functions from both the direct (neutron radiography) and inverse (TrueCell) methods were in good agreement with independent measurements of cumulative outflow determined with a transducer. Our results indicate that neutron radiography can be used to quantify the point water retention curve of homogeneous mineral particles. Further research will be needed to extend this approach to more heterogeneous porous media. 相似文献
16.
A. Papafotiou R. Helmig J. Schaap P. Lehmann A. Kaestner H. Flühler I. Neuweiler R. Hassanein B. Ahrenholz J. Tölke A. Peters W. Durner 《Advances in water resources》2008
A well-controlled 3-D experiment with pre-defined block heterogeneities is conducted, where neutron tomography is used to map 3-D water distribution after two successive drainage steps. The material and hydraulic properties of the two sands are first measured in the laboratory with multistep outflow experiments. Additionally, the pore structure of the sands is acquired by means of image analysis of synchrotron tomography data and the structure is used for pore-scale simulation of one- and two-phase flow with Lattice-Boltzmann methods. This gives us another set of material and hydraulic parameters of the sands. The two sets of hydraulic properties (from the lab scale and from the pore scale) are then used in numerical simulations of the 3-D experiment. 相似文献
17.
John H. Kramer Stephen J. Cullen Lome G. Everett 《Ground Water Monitoring & Remediation》1992,12(3):177-187
The neutron moisture probe is widely applicable to vadose zone monitoring problems which require measuring variable moisture contents. Neutron data are proportional to hydrogen density (modified by local chemistry) and sensitive to wetting fronts as well as changing volumes of hydrocarbon liquids. They cannot, however, be used to confirm contaminant chemistry, nor to detect steady-state flow. Neutron data are amenable to statistical analysis, providing a measure of the significance of data variations. Detection of incipient moisture changes at numerous monitoring locations is more practical using raw neutron data than data calibrated for moisture content because calibrations suffer from uncertainties associated with soil heterogeneities. When properly applied, the neutron probe is an effective monitoring tool as illustrated by three example applications described in this paper: (1) neutron moisture logs are used to detect subtle lithologic changes and identify monitoring horizons; (2) sequential neutron data are used to track induced saturation at a soil flushing pilot study; and (3) neutron logs from a horizontal access tube beneath a waste facility are used to pinpoint moisture anomalies. 相似文献
18.
The Gd isotopic composition in 19 lunar rock and soil samples from three Apollo sites is reported. The analytical techniques and the high precision mass spectrometric measurements are discussed. Enrichments in158GdO/157GdO due to neutron capture range up to 0.75%. Integrated ‘thermal’ neutron fluxes derived from the isotopic anomalies of Gd are compared with spallation Kr data from aliquot samples to construct a model which gives both average cosmic-ray irradiation depths and effective neutron exposure ages (Tn) for some rocks. In the case of rock 12053, this yields an average sample location of ∼300 g/cm2 below the lunar surface and an effective irradiation age of ∼230 my, compared to 99 my obtained by the81Kr-Kr method. Rock 14310 is the first lunar sample where Kr anomalies due to resonance neutron capture in Br are observed. A81Kr-Kr exposure age of 262 ± 7 my is calculated for this rock. 相似文献
19.
卫星遥感热红外辐射与川滇强震探讨 总被引：10，自引：0，他引：10
为了使卫星空间监测技术在地震监测预报的应用研究由理论性、实验性阶段进入实用性阶段，进行了探索和尝试。按照地震前兆资料常规处理的格式和要求，对收集的部分卫星遥感热红外辐射观测资料进行了处理。处理过程中使用了包含数据格式转换、数据预处理、异常挑选等内容的计算机工作软件。在此基础上，根据卫星遥感数据资料所具有的二维均匀分布的特性，应用平面和立体的数据图像处理软件，对卫星遥感热红外辐射观测资料的异常场信息进行了研究。同时，开发出了使用卫星遥感热红外辐射观测资料的数据接口软件。卫星空间监测技术的应用将给地震监测预报带来全新的思维方式及更加快捷实用的数据采集、传送、处理和分析方法。 相似文献