一种新的基于GPU实现的锥束CT正投影算法

锥束CT成像算法的正投影计算量大,消耗时间长.为此,本文提出了一种基于GPU实现的正投影加速算法.该算法在GPU的可编程管线中,通过纹理映射方法实现了圆轨迹锥束扫描模式下正投影计算.由于投影逐片并行计算,因此该算法具有较高的计算速率,且支持全浮点运算精度.在该正投影算法的基础上,本文还给出了三种算法优化方法.这些优化方法进一步提高了算法的执行效率.通过对Shepp-logan模型的正投影计算以及应用于迭代法进行三维图像重建等实验验证了本文算法的优点.     

基于整体变分降噪算法下的多频率超声衍射层析成像

 根据傅立叶衍射投影定理,不同频率超声波得到的投影数据的傅立叶变换分布在复平面为不同半径的圆弧,提出了多频率超声衍射层析成像思想,并进行了实验研究,重建的时间比单频率法短约70%.由于多频率投影数据傅立叶变换比单频率法在复平面上分布更加不均匀,故重建的噪声也更大,整体变分法将图像恢复的数学模型转化为带有整体变分正则化项的能量泛函问题,采用变分原理将其中的最小化问题转为偏微分方程的求解.降噪后的多频率超声图像的误差比降噪前的图像小约50%.     

P2P流媒体系统中层次化网络拓扑推断技术的研究

目前基于P2P技术的应用已经远远超过了传统互联网应用,成为占用互联网带宽最多的网络应用. 因此,如何减少P2P应用、特别是P2P流媒体播放系统对骨干网带宽的过度消耗,成为P2P技术中一个急需解决的问题.本文提出利用一种基于网络断层扫描的分层推断方法,以将P2P流媒体系统中的流量限制在较小的网络范围内,从而减少跨网流量、同网之间的骨干网带宽消耗,缓解网络拥塞.在OPNET上的仿真表明,该方法能够适应P2P流媒体的高动态性,有效降低跨网流量以及对骨干网的带宽消耗速度.     

Highly Tunable Thiol-Ene Photoresins for Volumetric Additive Manufacturing

Volumetric additive manufacturing (VAM) forms complete 3D objects in a single photocuring operation without layering defects, enabling 3D printed polymer parts with mechanical properties similar to their bulk material counterparts. This study presents the first report of VAM-printed thiol-ene resins. With well-ordered molecular networks, thiol-ene chemistry accesses polymer materials with a wide range of mechanical properties, moving VAM beyond the limitations of commonly used acrylate formulations. Since free-radical thiol-ene polymerization is not inhibited by oxygen, the nonlinear threshold response required in VAM is introduced by incorporating 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a radical scavenger. Tuning of the reaction kinetics is accomplished by balancing inhibitor and initiator content. Coupling this with quantitative measurements of the absorbed volumetric optical dose allows control of polymer conversion and gelation during printing. Importantly, this work thereby establishes the first comprehensive framework for spatial–temporal control over volumetric energy distribution, demonstrating structures 3D printed in thiol-ene resin by means of tomographic volumetric VAM. Mechanical characterization of this thiol-ene system, with varied ratios of isocyanurate and triethylene glycol monomers, reveals highly tunable mechanical response far more versatile than identical acrylate-based resins. This broadens the range of materials and properties available for VAM, taking another step toward high-performance printed polymers.     

Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (C_SC) region (C_SC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower C_SC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at C_SC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at C_SC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at C_SC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at C_SC = 85 wt.% in rheological measurements.     

Carbon Segregation in CoCrFeMnNi High-Entropy Alloy Driven by High-Pressure Torsion at Room and Cryogenic Temperatures

Herein, a CoCrFeMnNi high-entropy alloy with reduced Cr content and with the addition of 2 at% C interstitial is processed via high-pressure torsion (HPT) under 6.5 GPa by three turns at room and cryogenic temperatures. The microstructure is investigated by transmission electron microscopy (TEM) and atom probe tomography (APT). The results indicate that C atoms segregate at the boundaries of the nanograins in the sample processed at room temperature, while the sample processed at cryogenic temperature does not show any notable segregations of carbon.     

猪小肠粘膜碱性磷酸酶的分离纯化及性质研究

猪小肠粘膜经过Tris-HCl缓冲液(pH8.5)充分溶解、正丁醇除脂、冷冻离心、真空冻干等步骤处理后,先后经过Phenyl High Performance疏水层析/DEAE Fast Flow 阴离子层析/Sephacryl S-200凝胶层析纯化后得到猪小肠粘膜ALP(碱性磷酸酶),并对其蛋白二级结构及理化性质进行研究。结果表明:该酶经过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)分离得到ALP蛋白带,分子量约为57.0 kDa。该酶纯化倍数为68.2,比活力倍数为19.1 U/mg。利用圆二色性光谱测定纯化后蛋白二级结构,发现α-螺旋3.6%、β-折叠41.8%、β-转角21.5%、无规则卷曲33.1%。ALP在催化底物对硝基苯磷酸二钠(p-NPP)作用下最佳温度30 ℃、最佳pH为9.5;金属离子对ALP起到激活的离子为Mg²⁺和Ca²⁺,起到抑制的离子为Zn²⁺和EDTA。     

基于X射线无损研究霉变对小麦籽粒三维结构的影响

食品微观结构在确定其最终产品性能方面起着至关重要的作用,霉菌又是粮食储藏期危害非常严重的微生物类群,目前对粮粒感染霉菌后的研究多是间接的、破坏性的,无损的研究食品感染霉菌后内部微观结构的变化非常困难。X射线断层扫描技术提供了一个极好的工具来无损的评估食品内部的组分,本文利用X射线断层扫描法实现了小麦籽粒发霉后内部特征的三维可视化和定量分析。利用图像滤波、阈值分割、重建算法对X射线断层扫描获取的图像进行重建和渲染,实现了感染籽粒及内部孔隙的三维可视化,除了可视化还获取了如籽粒体积、籽粒内部孔隙率等参数。X射线断层扫描是一种强有力的工具,可以用于粮食储藏期间易发霉部位如(粮仓墙壁附近、粮粒表层)以及粮食在深加工前是否霉变的区分检测,用于无损检测单颗小麦籽粒等生物材料的损伤和微观结构组织的变化。     

Agreement and reliability in measuring central corneal thickness with a rotating Scheimpflug–Placido system and ultrasound pachymetry

PurposeWe compare the agreement and the reliability in measuring central corneal thickness (CCT) using two different technologies.MethodThe right eyes of 35 healthy individuals who had a negative history of ophthalmic disease, or ocular surgery were examined. The CCT was determined sequentially with a rotating Scheimpflug camera (Sirius; CSO), and an ultrasound pachymeter (P-1; Takagi). For statistical analysis, we used the methods suggested by Bland and Altman.ResultsThe mean values of CCT obtained from Sirius, and ultrasound were 537 ± 28 μm, and 550 ± 35 μm, respectively. There was a high correlation between Sirius and ultrasound (r = 0.92; p < 0.001), but the difference between the two measurements was statistically significant (t = −5.7; p < 0.00001). The precision of Sirius and ultrasound were 9.4 and 15.9 μm; repeatability 13.3 and 22.4 μm, and coefficient of variation 0.9% and 1.5%, respectively. The intraclass correlation coefficient was 0.97 for Sirius and 0.95 for ultrasound.ConclusionsThe average difference between corneal thickness measured with Sirius and ultrasound pachymetry was small but clinically significant. This means that the two instruments cannot be used interchangeably. Sirius showed precision and repeatability almost twice as much as ultrasound pachymetry. Confidence interval of 13.3 μm for Sirius can show variations in corneal thickness with an uncertainty value lower than 2.5% in 95% of cases. The simplicity of use, the possibility to obtain pachymetric maps, and less invasiveness make this instrument potentially useful in contact lens practice.