Functional and metabolic consequences of aortic valve replacement

4. Conclusions Severe aortic valve stenosis leads to a decreased myocardial PCr/ATP, and to impairment of LV diastolic function. Following aortic valve replacement, myocardial PCr/ATP normalizes completely, whereas LV diastolic function improves significantly. Moreover, there is an association between altered myocardial HEP metabolism and impaired LV diastolic function.     

基于性能的支撑钢框架结构方案对比分析

采用Pushover能力谱法对8层钢框架建筑进行基于性能的结构方案设计,考虑偏心支撑钢框架、隅撑支撑钢框架、纯钢框架3种结构体系,对结构自振特性、层间位移角及楼层侧移变化规律、结构刚度及耗能特征以及投资-收益等进行详细对比分析.结果表明:隅撑支撑钢框架和偏心支撑钢框架具有良好的结构性能,同样性能目标下,两者的经济效益相差不大,均可比纯钢框架节省近40%的用钢量,隅撑支撑钢框架的损失期望比例最小.     

双窗K空间权重导航技术在3.0T磁共振冠脉成像中的应用

提出了一种新的K空间权重导航技术(DKWN),该技术有利于缩短磁共振冠脉成像扫描时间同时获得好的图像质量.并将该导航技术应用到25位健康志愿者.经过实验分析,相比于常规固定窗导航技术而言,DKWN可以使导航效率提高30%(P＜0.05),同时平均扫描时间由2.12 min缩短至1.64 min(P＜0.05),并且图像质量相当.冠脉的直径和长度没有显著差异.     

Accelerating Advanced MRI Reconstructions on GPUs

Computational acceleration on graphics processing units (GPUs) can make advanced magnetic resonance imaging (MRI) reconstruction algorithms attractive in clinical settings, thereby improving the quality of MR images across a broad spectrum of applications. This paper describes the acceleration of such an algorithm on NVIDIA's Quadro FX 5600. The reconstruction of a 3D image with 128(3) voxels achieves up to 180 GFLOPS and requires just over one minute on the Quadro, while reconstruction on a quad-core CPU is twenty-one times slower. Furthermore, relative to the true image, the error exhibited by the advanced reconstruction is only 12%, while conventional reconstruction techniques incur error of 42%.     

Applications of in situ magnetic resonance techniques in chemical reaction engineering

NMR spectroscopy is now a well‐established technique for the in situ study of surface chemistry and the chemical processes occurring during catalytic reactions. Developments in probe design are making the sample environments ever closer to the operating conditions of the catalyst in industrial use. In parallel with these advances there is an increasing interest in the application of field gradient magnetic resonance techniques, namely pulsed gradient spin echo (PGSE) NMR and magnetic resonance imaging (MRI), to in situ studies of mass transport processes in catalysts and reactors. An overview of the recent developments in in situ NMR spectroscopy, PGSE NMR and MRI studies in application to catalysis and reaction engineering is presented and the potential of these techniques in the numerical modelling of catalytic processes and reactor design is highlighted. This revised version was published online in August 2006 with corrections to the Cover Date.     

基于剪力比的黏弹性阻尼腋撑-RC框架结构设计方法

现有减震设计方法需进行繁琐的迭代,其效率有待提高。基于剪力比的概念,采用黏弹性阻尼腋撑,设置罕遇地震下腋撑与框架结构的耗能比,提出了基于剪力比的黏弹性阻尼腋撑-RC框架结构抗震设计方法。选取7条地震动记录,根据不同剪力比 α 对6层、9层、12层模型设置不同参数的腋撑,进行罕遇地震下弹塑性动力时程分析。研究了腋撑耗能占地震输入结构总能量的关系,并将各模型最大层间位移角与GB 50011—2010《建筑抗震设计规范》的规定值进行了对比。从层间位移角、层剪力、顶层最大位移值、顶层峰值加速度等方面比较了结构的减震效果。研究结果表明：对于高40m以下的框架结构,耗能比为0.6时,剪力比 α 的合理取值范围在0.10~0.20之间;剪力比α取0.15时,RC框架结构的最大层间位移角、顶层最大位移值均减少34%~45%,层剪力、顶层加速度峰值均减少19%~23%。     

冻融后花岗岩孔隙发育特征与单轴抗压强度的关联分析

为了研究冻融后岩石的孔隙特征与力学性质之间的关系,对冻融后的花岗岩进行了核磁共振测试和力学试验,分别分析了NMR孔隙度和谱面积与单轴抗压强度之间的关系,并将岩石核磁共振成像结果与力学破坏特性进行了关联分析。研究结果表明：孔隙的发育程度对岩石的力学损伤有重要的影响,岩石的NMR孔隙度和谱面积与单轴抗压强度之间的关系式均为指数分布,岩石内部的孔隙分布情况与其力学性质和宏观破坏特征之间存在一定的联系;采用分形理论对冻融后花岗岩的孔隙发育特征进行了描述,得出了冻融花岗岩孔隙发育的分形维数。分析表明,冻融作用下岩体内的裂隙产生及其演化具有自相似性,分形维数值越大,孔隙越发育,其单轴抗压强度就越小。     

基于SolidWorks和VC＋＋的人工膝关节参数化设计

针对膝关节设计过程繁琐的问题,提出膝关节参数化设计方法。以Visual Studio 2008为开发工具,利用SolidWorks外部模式的二次开发技术,先对膝关节零件和装配体尺寸进行批量编辑、修改或智能获取,再对模型进行更新和干涉检查,最后预览模型并输出模型文件及其几何信息。利用该思路和方法,在Solid Works平台下编写了膝关节参数化设计程序,实现自动建模和膝关节参量的自动提取,并为膝关节的优化设计提供参考。