相位展开是磁共振成像技术应用中最关键的环节之一,可以为磁共振的某些重要临床应用提供精确的相位信息。然而,由于临床磁共振成像过程中,部分区域真实的相位存在急剧变化,同时伴有不同性态的噪声污染,导致相位展开时存在信息的高度不...相位展开是磁共振成像技术应用中最关键的环节之一,可以为磁共振的某些重要临床应用提供精确的相位信息。然而,由于临床磁共振成像过程中,部分区域真实的相位存在急剧变化,同时伴有不同性态的噪声污染,导致相位展开时存在信息的高度不一致性。为了有效地解决上述难题,基于马尔可夫-最大后验(Markov Random Field& Maximum A Posterioi,MRF-MAP)模型,首次将相位展开看作计算机视觉中的标记问题,并结合磁共振相位数据的特点,设计出相位图的模糊质量图,完成相位展开的能量函数构建。针对能量函数的优化求解,采用高效的图割算法进行。展开更多
【目的】建立一种准确、快速测定香蕉果实单胺类及其前体物质(Monoamines and their precursors,MAPs)的方法,明确香蕉果实发育过程中MAPs各组分的含量变化规律,为下一步解析其合成代谢机理提供参考依据。【方法】以巴西香蕉、粉杂1号...【目的】建立一种准确、快速测定香蕉果实单胺类及其前体物质(Monoamines and their precursors,MAPs)的方法,明确香蕉果实发育过程中MAPs各组分的含量变化规律,为下一步解析其合成代谢机理提供参考依据。【方法】以巴西香蕉、粉杂1号粉蕉和东莞大蕉3个香蕉品种的果实为试验材料,采用反相高效液相色谱—紫外检测(RPHPLC-UV)方法测定断蕾后15~75 d的果肉和果皮中MAPs含量,研究其在香蕉果实发育过程中的变化规律。【结果】RP-HPLC-UV色谱条件:采用C_(18)色谱柱(4.6×250 mm,5μm),甲醇为流动相A、0.1%三氟乙酸水溶液为流动相B,定量检测到去甲肾上腺素(NE)、多巴胺(DA)、左旋多巴(L-dopa)、酪胺(TYRA)、酪氨酸(Tyr)、血清素(SERO)、色胺(TRM)和色氨酸(Trp)等8种MAPs含量。其加标回收率为95.3%~106.1%;日内精密度范围为0.37%~0.82%,日间精密度范围为0.35%~0.83%;检测限为0.0012~0.0016 mg/100 g,定量限为0.0040~0.0053 mg/100 g;一个样品在14 min内可以完成检测。3个香蕉品种果实发育过程中,果皮TRM、TYRA、L-dopa、NE和DA含量均高于果肉。东莞大蕉和粉杂1号粉蕉果皮中SERO、Trp和Tyr含量高于果肉,而巴西香蕉果皮中Trp和Tyr含量低于果肉。在果实发育前期,巴西香蕉果肉中大部分MAPs物质的含量有一个快速升高的过程,在断蕾后30 d达峰值,NE、DA、TYRA、Tyr、Trp和TRM含量分别为22.14、239.81、118.29、43.74、46.41和5.33 mg/100 g,之后含量持续下降,NE、DA、TYRA和TRM在果实成熟时达最低值,含量分别为3.17、7.08、12.58和1.04 mg/100 g,而Tyr和Trp含量最低值出现在断蕾后45 d。东莞大蕉和粉杂1号粉蕉中TYRA和SERO含量在果实发育过程中呈下降趋势。【结论】建立的RP-HPLC-UV方法准确、灵敏、快速,可用于香蕉果实中MAPs的定量检测;3个香蕉品种不同发育阶段的果肉和果皮中均可检测到NE、DA、L-dopa、TYRA、Tyr、SERO、TRM和Trp等8种MAPs物质,且其含量在巴西香蕉果实中表现出区别于东莞大蕉和粉杂1号粉蕉的变化规律。展开更多
Based on the analysis of the spurious introduced by phase accumulation truncation which was made by Nicholas, a new simplified algorithm for spurious spectrum in the presence of phase truncation is presented by using ...Based on the analysis of the spurious introduced by phase accumulation truncation which was made by Nicholas, a new simplified algorithm for spurious spectrum in the presence of phase truncation is presented by using the mapping mathematics and number theoretic method, it is possible to precisely analyze the spurious location and the spurious amplitude introduced by phase truncation in practical applications by computer.展开更多
This paper studies a queueing model with the finite buffer of capacity K in wireless cellular networks, which has two types of arriving calls--handoff and originating calls, both of which follow the Markov arriving pr...This paper studies a queueing model with the finite buffer of capacity K in wireless cellular networks, which has two types of arriving calls--handoff and originating calls, both of which follow the Markov arriving process with different rates. The channel holding times of the two types of calls follow different phase-type distributions. Firstly, the joint distribution of two queue lengths is derived, and then the dropping and blocking probabilities, the mean queue length and the mean waiting time from the joint distribution are gotten. Finally, numerical examples show the impact of different call arrival rates on the performance measures.展开更多
文摘相位展开是磁共振成像技术应用中最关键的环节之一,可以为磁共振的某些重要临床应用提供精确的相位信息。然而,由于临床磁共振成像过程中,部分区域真实的相位存在急剧变化,同时伴有不同性态的噪声污染,导致相位展开时存在信息的高度不一致性。为了有效地解决上述难题,基于马尔可夫-最大后验(Markov Random Field& Maximum A Posterioi,MRF-MAP)模型,首次将相位展开看作计算机视觉中的标记问题,并结合磁共振相位数据的特点,设计出相位图的模糊质量图,完成相位展开的能量函数构建。针对能量函数的优化求解,采用高效的图割算法进行。
文摘Based on the analysis of the spurious introduced by phase accumulation truncation which was made by Nicholas, a new simplified algorithm for spurious spectrum in the presence of phase truncation is presented by using the mapping mathematics and number theoretic method, it is possible to precisely analyze the spurious location and the spurious amplitude introduced by phase truncation in practical applications by computer.
基金supported by the Postgraduate Innovation Project of Jiangsu University (CX10B 003X)
文摘This paper studies a queueing model with the finite buffer of capacity K in wireless cellular networks, which has two types of arriving calls--handoff and originating calls, both of which follow the Markov arriving process with different rates. The channel holding times of the two types of calls follow different phase-type distributions. Firstly, the joint distribution of two queue lengths is derived, and then the dropping and blocking probabilities, the mean queue length and the mean waiting time from the joint distribution are gotten. Finally, numerical examples show the impact of different call arrival rates on the performance measures.
