多层螺旋 CT 评价心肌桥及其与动脉粥样硬化的关系?          下载免费PDF全文

崔润河  刘慧  邢桂荣 《CT理论与应用研究》2016,(4):477-484

目的：探讨壁冠状动脉（MCA）于舒张中、晚期的显示规律,并分析壁冠状动脉于舒张中、晚期的狭窄程度与载心肌桥厚度以及动脉粥样硬化的发生等的相关关系。方法：对754例临床疑似冠心病患者进行冠状动脉 CT 成像,在独立工作站上进行多平面重组（MPR,包括 CPR）,观察冠状动脉与心肌的空间关系,确认完全性心肌桥。按照 MB 近、远端血管形态可分为两组：平滑弧形组和迂曲成角组。并按 MB 的厚度是否大于2 mm 进行分组,在重组成像中测量壁冠状动脉的狭窄程度,并进行两组间 t 检验。按 MCA 近端有无斑块形成分为斑块组和无斑块组,对 MCA狭窄程度分别作两组间独立样本 t 检验。对斑块组和非斑块组成角迂曲的发生概率作χ2检验。分析81 MCA 患者静态心电图、心绞痛以及迂曲成角发生率与心肌桥厚度以及 MCA 近端有无斑块之间的相关性。结果：在总计754例受检者中发现完全性心肌桥81例。心肌桥较厚（>2 mm）时,舒张期 MCA 狭窄程度较走行正常者严重,两组间 t 检验结果有显著统计学差异（P <0.05）。斑块组舒张期 MCA 狭窄程度较无斑块组重,两组间 t 检验结果有显著统计学差异（P <0.05）。斑块组和非斑块组成角迂曲的发生概率作四格表χ2检验有显著统计学差异（P <0.05）。对81例受检者分析其静态心电图,迂曲成角组静态心电图 ST-T 段改变以及心绞痛发生的比率明显高于正常组（P <0.05）。结论：心肌桥可能与动脉粥样硬化病变的发展相关。舒张期 MCA 狭窄程度与 MB 厚度以及近端有无粥样硬化斑块有关,>2 mm 组舒张期狭窄程度大于≤2 mm 组,近端有斑块组舒张期狭窄程度大于无斑块组。MCA 近端有斑块时,动脉粥样硬化更易发生成角迂曲,且迂曲成角组受检者静态心电图 ST-T 段改变以及心绞痛发生率均高于平滑弧形组。  相似文献   

Effects of seismic isolation on the seismic response of a California high‐speed rail prototype bridge with soil‐structure and track‐structure interactions          下载免费PDF全文

Yong Li  Joel P. Conte 《地震工程与结构动力学》2016,45(15):2415-2434

With the launch of the high‐speed train project in California, the seismic risk is a crucial concern to the stakeholders. To investigate the seismic behavior of future California High‐Speed Rail (CHSR) bridge structures, a 3D nonlinear finite‐element model of a CHSR prototype bridge is developed. Soil‐structure and track‐structure interactions are accounted for in this comprehensive numerical model used to simulate the seismic response of the bridge and track system. This paper focuses on examining potential benefits and possible drawbacks of the a priori promising application of seismic isolation in CHSR bridges. Nonlinear time history analyses are performed for this prototype bridge subjected to two bidirectional horizontal historical earthquake ground motions each scaled to two different seismic hazard levels. The effect of seismic isolation on the seismic performance of the bridge is investigated through a detailed comparison of the seismic response of the bridge with and without seismic isolation. It is found that seismic isolation significantly reduces the deck acceleration and the force demand in the bridge substructure (i.e., piers and foundations), especially for high‐intensity earthquakes. However, seismic isolation increases the deck displacement (relative to the pile cap) and the stresses in the rails. These findings imply that seismic isolation can be promisingly applied to CHSR bridges with due consideration of balancing its beneficial and detrimental effects through using appropriate isolators design. The optimum seismic isolator properties can be sought by solving a performance‐based optimum seismic design problem using the nonlinear finite‐element model presented herein. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Investigating the influence of minor hydraulic structures on modeling flood events in lowland areas   总被引：1，自引：0，他引：1       下载免费PDF全文

Freegzi Mehari Hailemariam  Luigia Brandimarte  Francesco Dottori 《水文研究》2014,28(4):1742-1755

Flood inundation models have been recognized to be a valuable tool to reproduce flow dynamics in a given area and support decision‐making processes on flood management measures. In many cases, in the simulation of flood events, only the main river channel and the associated structures are represented within the model. However, during flood events involving lowland areas, the minor drainage network – and the associated hydraulic structures – may have an important role in conveying flow and determining which areas will be flooded. The objective of this study is to investigate whether – and to what extent – small hydraulic structures in drainage networks have an influence in flooding on lowland areas. The case study for this research is the 1990 flood event which occurred in the lowland plain of the Reno River, in Northern Italy. The study area is mainly used for agricultural purposes and has a drainage system with several small bridges and culverts. The influence of the minor hydraulic structures on flood dynamics was analyzed through a combined use of one‐dimensional (1D) and two‐dimensional (2D) hydraulic models. First, a number of detailed and simplified approaches to represent hydraulic structures in the computational grids were analyzed by means of the HECRAS 1D model. Second, these approaches were implemented and tested in several 2D simulations of the flood event. The simulated inundation extents and flood levels were then compared with the observed data and with each other. The analysis of results showed that simplified schematizations were sufficient to obtain good model predictions of peak inundation extent and flood levels, at least for the present case study. Moreover, the influence of the structures on the peak flood inundation extent and flood levels was found to be limited, whereas it showed to be more significant during the drainage phase of the flood. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

安居富民工程在2008 年、2014 年于田7. 3 级地震中的减灾效益对比分析     

刘军  胡伟华  李志强  宋立军  谭明  古丽孜帕 《中国地震》2014,30(2):243-248

2014 年2 月12 日17 时19 分(北京时间),新疆于田县发生7. 3 级地震。根据现场调查,本次地震最大烈度为Ⅸ度。灾区曾遭受过2008 年于田7. 3 级地震灾害的严重影响,之后近6 年来大力推进的安居富民工程发挥的重要作用,是本次地震没有造成人员伤亡的重要原因。通过将2008 年、2014 年两次于田7. 3 级地震抗震安居房和安居富民房面积替换为安居工程改造前的简易房屋计算抗震房减灾效益可以看出,相对于2008 年于田7. 3 级地震,本次地震由于灾区覆盖率较高,居住房的经济损失减少3. 8 亿元,恢复重建经费减少12. 9 亿元,失去住所户数减少1 万户。  相似文献   

基于运营环境和提升小波变换的桥梁损伤检测研究   总被引：1，自引：0，他引：1  

孙增寿  ;张耀  ;王希东 《地震学刊》2014,(6):718-724

根据损伤桥梁在车辆荷载作用下的动力响应特点,以及提升小波变换对信号突变信息的放大功能,提出了利用桥梁运营荷载作用下加速度响应提升小波变换系数的分布特性对结构损伤进行识别的方法。首先,采集桥梁在行车荷载作用下的加速度响应信号;然后,对加速度响应信号进行提升小波变换,分别利用加速度响应信号、加速度响应信号差,提升小波变换系数空间变化的峰值识别损伤位置;最后,对行车速度、损伤位置、损伤程度和测量噪声对损伤识别效果的影响进行了分析讨论。结果表明：在行车速度8m/s以下、测量噪声不高于5%情况下,利用运营荷载作用下桥梁单点动力响应信号提升小波变换,可以实现桥梁多处损伤的检测和识别。  相似文献   

A European digital accelerometric database:statistical analysis of engineering parameters of small to moderate magnitude events   总被引：1，自引：1，他引：0  

Carlos S.Oliveira  Gerard Gassol  Xavier Goula  Teresa Susagna 《地震工程与工程振动(英文版)》2014,(4)

During the NERIES Project, an accelerometric database containing European digital information was developed. Besides event and station metadata, ground motion parameters, computed in a homogeneous manner, were assembled:PGA, PGV, AI, TD, CAV, HI and PSV(f,5%)(19,961 components, 2629 events, 547 stations). Merging small and moderate magnitude events produced a unique database capable of providing important information such as:(i) Correlations between several ground motion parameters follow analogous trends as in previous worldwide datasets, with slight corrections.(ii) Although PGA attenuations with distance show great uncertainties, four recent GMPEs recommended for Europe fit quite well the central 50% data interval for the distance range 10 R 200 km; outside these distances, they do not fit.(iii) Soil amplification ratios indicate that weak motion(low magnitudes and larger distances) shows larger amplification than strong motion(short distances and large magnitudes) as represented in UBC97 for the USA, but not in EC8 for Europe.(iv) Average spectral shapes are smaller than in the EC8.(v) Differences in amplification factors for PGA, PGV and HI for EC8 soil classes B and C, and differences in spectral shapes for these soil classes, indicate that EC8, Type 2 S-coefficient should be frequency dependent, as in UBC97.  相似文献   

反应谱对构造环境剪应力场的依赖性   总被引：2，自引：0，他引：2       下载免费PDF全文

李保昆  陈培善  白彤霞 《地震学报》2005,27(3):292-300

在以前理论工作的基础上, 导出了构造环境剪应力值对反应谱的影响. 在美国知名学者Boore等建立的预测公式BJF94的基础上, 提出了新的预测公式CLB20. 在CLB20中引进了应力场量值tau;0对SA的影响项. BJF94主要是基于美国西部的强震观测资料作出的经验预测公式, 而SEA99是基于全球张性地区的强震观测资料作出的预测公式. 我们把两者的预测结果进行了全面的比较, 发现BJF94的预测值lg(Y) 减去0.16个对数单位后, 与SEA99的预测值十分接近. 这说明张性地区的 lg(Y) 较小; 地区性差异主要表现在构造环境剪应力场的差异上. 如果这个因素在预测公式中能得到适当体现, 同时预测公式中的震级标度都用全球统一的矩震级, 距离都使用多数人倾向使用的断层投影距, 那么预测公式的地区性差异将大大减轻, 以至最后消失, 有可能构造出全球适用的预测公式. 我们的抗震设计直接引用美国研究者发表的反应谱衰减结果（例如BJF94和SEA99）, 不会导致太大的误差.    相似文献   

迎接大气科学发展即将到来的新飞跃   总被引：7，自引：3，他引：4  

叶笃正  季劲钧 《地球科学进展》2005,20(10):1047-1052

一门学科中新的事实的发现、新的观测手段和新技术的应用都会引发新理论,从而促进这门学科一个大发展。大气科学发展的历史,就是沿上述道路前进的。近10多年来,对大气、海洋、陆面、生物和冰雪圈进行了大规模、四维的观测,获得了海量的资料。同时,组织了丰富多彩的多项国际和地区的研究计划。通过对观测资料的深入分析和研究,必将发现许多新事实和新现象。这是大气科学即将到来的一个飞跃时期的事实基础。 展望未来10~20年大气科学重大发展,预估将会有多方面的重大突破。新事实和新现象将催生大气科学新理论出现;对气候系统中各种过程的深入了解,巨型计算机的发展,使得新气候环境模式将会出现;这将是一个集地球系统中物理、化学和生物学等自然过程和人类社会经济活动的综合的模拟系统;对于人类生活环境有重大影响的气候突变现象的发生发展机理的了解将会比现在前进一大步;能够发现一些气候突变的阈值和一些气候突变的前期信号;对于未来气候的稳定性、极端气候的发生、海平面升高的程度都将会有比较确切的回答;气候预测的精度也将大大提高。  相似文献   

多维地震激励作用下大跨度钢管混凝土提篮拱桥的随机响应   总被引：8，自引：4，他引：4  

赵灿晖  周志祥 《地震工程与工程振动》2005,25(3):87-92

以某大跨度钢管混凝土提篮拱桥为例,分别研究了大跨度钢管混凝土提篮拱桥的自振特性及其在纵向激励、纵 竖向激励、纵 横向激励、纵 竖 横向激励作用下的地震响应特性。结果表明,横向激励对提篮拱桥地震响应特性有较大影响,对于多维激励情况,提篮拱桥的抗震性能并不优于平行拱,并进一步分析了原因。  相似文献   

电子航道图标准建设与应用     

罗睿  李晓雨 《测绘地理信息》2022,47(1):56-58

电子航道图的标准建设与生产应用关系到内河航运的高质量发展动能.分析了电子航道图标准的现状及存在的问题,建立了现有电子航道图标准体系及内河航道地理信息要素的分类方法,结合电子航道图核心要素,建立了典型应用场景,通过完善电子航道图数据标准体系和精细化生产应用,不断提升综合立体交通网的水运比较优势.  相似文献