共查询到18条相似文献，搜索用时 203 毫秒
1.
随着探测器技术的发展,具有能量分辨能力的光子计数探测器在X射线能谱CT成像中应用越来越广泛。能量与阈值的对应关系对能谱CT成像具有重要意义,受到实验条件的限制,目前的光子计数探测器的能量标定方法有一定的局限性。针对光子计数探测器的单像素标定问题,本文提出一种基于X射线光机连续谱的能量标定方法,通过建立和分析X光谱模型,利用光机连续谱中高能端的能量信息,得到阈值与能量之间的关系。实验结果表明该方法操作方便,对探测器单像素标定结果较为准确,对其他类型光子计数探测器的标定具有参考意义。 相似文献
2.
双能X射线骨密度仪系统具有测量精度高、时间短、剂量低等独特优势,是目前X射线骨密度测定技术的“金标准”。本文采用半导体CdZnTe探测器模块搭建半导体光子计数骨密度能谱测量平台,针对CdZnTe半导体探测器信号特点,使用移动最小二乘算法进行不同材料高低能拟合校正。移动最小二乘算法通过权函数改变目标数据点周围节点对其影响程度,可以让数据点的拟合方向更具灵活性。研究分析移动最小二乘算法对双能X射线骨密度测量数值的数据处理流程,完成基于移动最小二乘高低能拟合校正算法的骨密度测量实验。实验结果表明,本文所设计实现的基于移动最小二乘算法的骨密度双能拟合技术在实际应用中能达到较好的拟合误差精度,其中探测器像素单元在高能条件下拟合平均误差为0.032%,低能条件下拟合平均误差为0.036%。进一步数据分析表明,边缘像素单元与中心像素单元在高低能条件下的拟合误差差异仅为0.012%和0.011%。该算法能够有效提高半导体光子计数探测器的骨密度测量精度,降低探测器边缘像素单元信号不均匀性差异带来的误差影响,对目前线阵或面阵光子计数半导体探测器像素差异对骨密度诊断的影响具有良好的改善作用。 相似文献
3.
本文的目的是评估光子计数探测器对CT成像的性能的影响,我们对一款基于碲锌镉(CZT)的光子计数探测器进行了性能测试,并搭建一个成像平台。首先对探测器系统进行能量增益的校正以及坏像素点校正,以减少探测器响应的不均匀性对CT成像的影响。然后对探测器进行能量-阈值标定,以确定探测器的工作能量阈值。最终搭建成像系统,对X光能量分别大于36和45keV的数据,获得了模体的重建结果,并对结果进行了分析。 相似文献
4.
在工业X射线CT检测系统中,当对某一物体进行检测的时候,系统中的载物台机架会进行不断的旋转,在旋转过程中,机架将会伴随有机械径跳,径跳会影响到探测器接收到的光子数,最后对投影数据有一定的影响,进而影响重建出的物体图像。本文主要分析了载物台机架发生机械径跳的原因,以及径跳对探测器接收X射线光子的影响;在对以上原因进行分析的基础上,提出了在考虑CT机架径跳时的CT投影公式,并对这一投影进行仿真。 相似文献
5.
1）CT机的进展：CT机器自问世以来，随着计算机技术、探测器技术、X线技术的不断及发展以及新的微电子和显微技术不断的应用于CT机，从而提高了CT机的性能，标志着CT扫描从层面扫描到螺旋扫描的换代。2）图象后处理技术：螺旋CT的出现及计算机软件的开发，利用导航技术做出具有3D仿真内窥镜的图象，既（VE），这种新的影像学方法，引起了广泛的关注。 相似文献
6.
为了改善传统岩性密度测井仪的缺陷,本文基于传统的双 源距探测器密度测井仪,提出在负源距范围内增加一个反散射探测器,构成新的三探测器密 度测井仪器. 利用Monte Carlo方法通用程序MCNP(3B),从光子与地层相互作用的机理出发 ,计算得到了反散射探测器、长源距探测器和短源距探测器的光子通量的能谱分布、光子通 量与源距的关系、光子通量与地层密度的关系、源距与探测深度的关系以及计数能窗等. 从 结果看,三探测器密度测井仪的长、短源距探测器对地层的响应关系与双源距密度测井仪的 长、短源距探测器一致,而反散射探测器对地层具有明确的响应关系,其响应关系与长、短 源距探测器近似相反,且其计数率很高. 因此,在负源距范围内增加第三个探测器是可行的 ,这将有利于提高密度测井的测量精度和垂向分辨率. 同时表明了Monte Carlo方法在核测 井仪器早期研制中的有效性,对仪器设计具有指导作用. 相似文献
7.
为弥补传统双源距密度测井仪器纵向分辨率低、受井眼影响大的缺陷以及碘化钠(NaI(Tl))探测器的不足,提高密度测井识别油气层的能力,我们采用MCNP5蒙特卡罗模拟程序模拟研究了密度测井在负源距下增加溴化镧(LaBr_3(Ce))探测器.首先对比研究了LaBr_3(Ce)探测器与NaI(Tl)探测器的探测效率、能谱和响应特征;然后模拟计算LaBr_3(Ce)探测器源距与光子通量的关系、负源距光子通量能谱、负源距探测深度与源距的关系、气层负源距光子通量与密度的关系.结果表明:LaBr_3(Ce)探测器在密度测井中比NaI(Tl)探测器探测效率高、能峰高、峰总比大;负源距探测器与传统长、短源距探测器的响应规律近似相反;负源距探测器源距小,纵向分辨率高;探测深度浅,主要反映泥饼的性质,从而为泥饼校正提供丰富数据.因此,在双源距密度测井负源距区增加LaBr_3(Ce)探测器可以提高地层密度的灵敏度、测量精度、纵向分辨率和改善泥饼及薄层校正效果,为有效勘探开发油气藏提供测井技术支持. 相似文献
8.
ＣＴ图象出现的编织状伪影，根据扫描部位变化有时又会呈水波纹状及无规划放射状伪影，这种伪影的产生原因是因机器使用日久，探测器管球和光栏间的位置发生了相对位移，破坏了机器出厂前调整好的线性关系，按程序重新调整后故障伪影全部排除。 相似文献
9.
《地震工程与工程振动》2021,41(3)
为研究T形双波纹钢板混凝土组合剪力墙的抗震性能,以轴压比、波纹钢板形式、翼缘宽度和剪跨比为变化参数,完成了5个试件的拟静力加载试验。基于试验中观测的破坏形态和滞回曲线,对T形双波纹钢板混凝土组合剪力墙的破坏规律和抗震性能进行了分析。试验结果表明:在低周反复荷载作用下试件破坏形态表现为压屈和受拉破坏,破坏发生在腹板端柱底部,滞回曲线呈捏拢的S形,具有非对称性;波纹形状对试件整体抗震性能影响不大;随着轴压比的提高,核心混凝土的约束作用得到加强,水平承载力提升较大,破坏时位移减小,延性变差;增大翼缘宽度可以减小强度退化程度;减小剪跨比可以显著提高试件的初始刚度和水平承载力,但耗能能力变差。 相似文献
10.
周光湖 《CT理论与应用研究》1990,(1)
(一) 图象重显卷积算法 CT中最常用的图象重显算法之一是卷积法,它易于实现、计算量小、且重显质量好。图1中L为投影线,它穿过物体后收集的投影值为P(l,0)。设当l≥E时P(l,0)=0, 相似文献
11.
Nedavia Bethlahmy 《Journal of Hydrology》1973,20(2):155-169
In steep, mountainous terrain of the western United States, where summer rains are negligible and annual runoff is primarily dependent on melting snow, the runoff distribution is such that a high energy recipient (HE) watershed generally yields more water per unit area than a low energy recipient (LE) watershed except during the latter's flood peak period, at which time the ratio of yields is reversed. HE watersheds peak sooner than their corresponding LE watersheds, but also vary more in their peaking date. The ratio of maximum peak flows may be greater or less than 1.0 depending on environmental circumstances. 相似文献
12.
多能谱X射线成像技术及其在CT中的应用 总被引：1，自引：0，他引：1
随着探测器技术的不断发展,具有能谱分辨能力的光子计数探测器成为人们研究的焦点,并在X射线成像领域开始得到应用.使用该种探测器,可以将具有较宽能谱分布的X射线分为不同的能区分别进行计数,获得详细的能谱信息及不同能量射线的衰减信息,由此引出了"多能谱成像"的概念.本义介绍了近些年来光子计数探测器技术的发展及其在X射线成像中... 相似文献
13.
A novel method for parameterizing the morphology of seafloor ripples with fingerprint analysis numerical techniques is presented. This fully automated analysis tool identifies rippled areas in two-dimensional imagery of the seafloor, and returns ripple orientation and wavelength as well as a new morphological parameter, the spatial density of ripple defects. In contrast to widely used manual and spectral parameterization methods, this new technique yields a unique probability distribution for each derived parameter, which describes its spatial variability across the sampled domain. Here we apply this new analysis technique to synthetic and field collected side-scan sonar seafloor images in order to assess the methods capacity to define bed geometry across a wide range of simulated and observed morphological conditions. The resulting orientation and wavelength values compare favorably with those of the existing manual and spectral parameterization methods, and are superior under environmental conditions characterized by low signal to noise ratios as well as high planform ripple sinuosity. Furthermore, the resulting ripple defect density values demonstrate correlation with ripple orientation, wave direction, and the Shields parameter, which is consistent with recent investigations that have theoretically linked this parameter to hydrodynamic forcing conditions. The presented fingerprint analysis method surpasses the capacity of existing methods for ripple parameterization and promises to yield greater insight into theoretical and applied problems associated with the temporal and spatial variability of ripple morphology across a wide spectrum of marine environments. 相似文献
14.
This study examined the UV/H2O2 decolorization efficiency under high UV photon flux (intensity normalized by photon energy) irradiation; the incident UV was ranging from 3.13 × 10?8 to 3.13 × 10?6 einstein cm?2 s?1. The experimental results showed that complete decolorization of 20 mg L?1 methylene blue (MB) can be achieved within 5 s and 99% decolorization of 1000 mg L?1 MB can be achieved in 180 s under the best condition of high UV intensity UV/H2O2 process. To the best of our knowledge, UV/H2O2 decolorization process in such a short time has not been reported. The electrical energy per order of the process was 16.21 kWh m?3 order?1 and it is relatively economical compared with other advanced oxidation processes. The kinetics of decolorization follows pseudo‐first order. There is a linear relationship between rate constant and UV intensity, which indicates that increasing UV intensity does not cause decline in light utilization efficiency. The experiment related to initial substrate concentration shows decolorization rate of different substrate concentration (20–1000 mg L?1) are closed to each other. Besides, optimal H2O2 concentration, comparative study with low photon flux light, decolorization of other types of dyes and TOC removal were also studied. 相似文献
15.
参照并综合应用国内外相关资料、实验和研究成果，建立了一种涉及多种环境因素的模型，分析了不同因素对构造运动能量指标的影响．其中包括地壳纵向结构、断层产状、岩性条件、地壳应力状态、孔隙压力和地温条件等．模型计算结果表明，断裂的剪切破裂能随深度增加通常呈现先上升，在某一深度上达到峰值后逐渐衰减的形态．在诸多因素中，孔隙压力和地温条件对能量指标的影响相对显著．高孔隙压力和地温环境可导致剪切破裂能曲线的峰值降低、峰值和铃腰值所在的深度下移．这种效应限制了强震事件，而适于中小地震活动或低能量释放的断层活动，其震源深度分布的下限较低．反之，低孔隙压力和低地温环境使剪切破裂能曲线的峰值加大、形态变陡，其结果利于高强度、高能量积累的闭锁段的形成．如果这两种段落在断裂带上相邻，则可能促进断裂带不同段落之间的能量转换，从而形成能量积累程度高而邻区锁定强度低的孕震环境．红河断裂北西段温泉密度和热储温度分布与该地区的地震频度、强度和震源深度分布之间的关系与模型结果基本相符，从而为模型的主要推论提供了佐证． 相似文献
16.
IntroductionThe tectono-physical background and dynamic environmental features of strong earthquakes have long been studied from different viewpoints by seismologists both in domestic and abroad. Many controlling factors include the crust structure, lithological environment, tectonic conditions, the stress state, heat flow distribution and hydrodynamic effects at depth, etc. Some of the studies have established a foundation for researching and recognizing the spatial distribution of potential … 相似文献
17.
The velocities with which grains were observed to emerge from a sand bed after an intersaltation collision at u* = 40 cm s?1 are reported for four bed attitudes, from horizontal bed to adverse bed slope 15°. The principal effect of bed angle is to alter the magnitude and direction of the ricochet velocity. However, emergent velocities of dislodged grains are consistent with reptation path lengths comparable to the length of the upwind face of ripples in the corresponding wind. Calculations of the loss of forward momentum at collision, using the data for the range of bed attitudes studied suggest that creep is most vigorous on the sloping upwind face of the ripple and diminishes at the crest. As a result, the crest would be expected to accumulate the coarse material which moves predominantly by creep. The saltations originating in ricochet from the sloping back of the ripple are more vigorous and more concentrated in plan than are those originating at the crest. However, the saltation path length is at least an order of magnitude greater than the ripple wavelength and the probability distribution of path lengths is quite dispersed. Consequently it is very unlikely that these spatial patterns of ricochet are preserved sufficiently distinctly in the saltation cloud and subsequent collision distribution to be the agent of ripple development. This study therefore supports a view of moving grain interaction with the bed in which saltation provides the power to mobilize grains but ripple growth is associated with reptation and particularly with a pattern of impact which develops with the bed relief. Creep is more active on upwind facing slopes than at the crest, which therefore is a zone of net creep grain deposition. 相似文献
18.
A model, in which various seismic environmental factors are involved, has been developed in the paper on the bases of relevant
data. The environmental factors include the crust structure, lithological conditions, fault plan attitude, the crust stress
state, pore-fluid pressure and geothermal conditions, etc. The effect of each of the factors on the tectonic movement energy index has been analyzed. The model calculation results
indicate that shear fracture energy of a fault generally increases with depth; it reached a peak value at a certain depth,
then turns gradually attenuated. Of all the factors, the effects of pore-fluid pressure and geothermal conditions on the energy
index are of prominence. High pore-fluid pressure and high temperature circumstance may result in decline of the peak value
of the shear fracture energy curve, making the depths of the peak value and of the bell-waist value deepened. Such effects
restrict strong seismic events, but suitable for micro-seismic activity and/or fault creep. The lower limit of focal depth
under such an environment is relatively deep. Contrarily, low pore-fluid pressure and low geothermal temperature circumstance
result in increase of the peak value of the shear fracture energy curve, and the curve becoming steep. The later circumstance
is favorable to the formation of locked segment where possesses high strength and high-energy accumulation. If these two kind
of segments are arranged interactively along a fault zone, such arrangement would boost the energy transition among the segments,
forming mechanical circumstance of energy highly accumulated in one segment with adjacent segment(s) less-locked. Such contrast
of the strength and energy would provide conditions for strong earthquakes with high stress drop. An analysis of the northwest
segment of the Honghe fault has provided some evidence for the modeling results.
Foundation item: Chinese Joint Seismological Science Foundation (No. 9507424). 相似文献