高能电子和物质相互作用是一个级联簇射 (shower)物理过程 .空间飞行器防护系统就是利用这一原理 ,通过宇宙中的电子在飞行器中产生的 shower电子 ,来了解其中半导体器件的有关信息 .该文利用 Monte Carlo方法 ,采用 PENEL OPE(Penetrat...高能电子和物质相互作用是一个级联簇射 (shower)物理过程 .空间飞行器防护系统就是利用这一原理 ,通过宇宙中的电子在飞行器中产生的 shower电子 ,来了解其中半导体器件的有关信息 .该文利用 Monte Carlo方法 ,采用 PENEL OPE(Penetration and Energy L oss of Positrons and Electrons)软件包 ,对电子在飞行器中的运动过程进行模拟 ,给出球壳和半导体材料中的能量沉积分布 。展开更多
目的:基于光子计数探测器的X线CT(Photon Counting Computed Tomography,PCCT)较传统CT成像最突出的特点是可实现多参数成像,包括基物质成像和单能量成像等。然而,当前商用光子计数探测器的计数率低、能量分辨率有限,大大限制了PCCT更...目的:基于光子计数探测器的X线CT(Photon Counting Computed Tomography,PCCT)较传统CT成像最突出的特点是可实现多参数成像,包括基物质成像和单能量成像等。然而,当前商用光子计数探测器的计数率低、能量分辨率有限,大大限制了PCCT更为广泛的临床应用。为了更好地研究PCCT成像技术,本文系统地研究了基于光子计数探测器的X线CT蒙特卡罗仿真方法,深入探讨了K值效应及能量段宽度对成像质量的影响。方法:首先通过PENELOPE(Penetration and Energy Loss of Positrons and Electrons)仿真软件对PCCT成像系统进行设计,完成光子计数探测器的配置,其后基于仿真系统完成不同体模的能谱CT数据仿真。针对K值效应及能量段宽度对图像质量的影响,对相关数据进行了定量分析。结果:本研究设计的PCCT成像仿真系统能有效地实现能谱CT数据采集与成像性能分析,其中对比剂在K缘处的对比度噪声比较其在非K缘处高,并且对比剂在适当宽度的能量段里获得优质的图像。结论:本研究设计的PCCT成像仿真系统能有效地实现能谱CT数据采集与成像性能分析。展开更多
In this paper,the beam quality and percent depth dose curves for different field sizes of CyberKnife? system were investigated by Monte Carlo simulations using the PENELOPE code,which has been used to simulate 6 MV ph...In this paper,the beam quality and percent depth dose curves for different field sizes of CyberKnife? system were investigated by Monte Carlo simulations using the PENELOPE code,which has been used to simulate 6 MV photon beam.In water phantom,the absolute doses were calculated for Φ10–60 mm collimators,and percent depth dose curves were evaluated for Φ30–60 mm collimators.The agreement of dose distributions of the calculation with measurement was within 3.0%.The mean energy of photon spectrum was 1.46 MeV,and the beam quality index was 0.632,which was slightly smaller than that of measurement.展开更多
Background:Evidence suggests that wintering waterbirds have become conspicuously more concentrated at two largest lakes of the Yangtze River Floodplain,East Dong Ting Lake(Hunan Province,29°20′N,113°E)and P...Background:Evidence suggests that wintering waterbirds have become conspicuously more concentrated at two largest lakes of the Yangtze River Floodplain,East Dong Ting Lake(Hunan Province,29°20′N,113°E)and Poyang Lake(Jiangxi Province,29°N,116°20′E),relative to other lakes,despite the establishment of reserves elsewhere.While this relationship is likely due to greater extent of undisturbed habitats in larger lakes,we understand little of the drivers affecting individual behaviours behind this tendency.Methods:We tracked wintering movements of three duck species(Eurasian Wigeon Mareca penelope,Falcated Duck M.falcata and Northern Pintail Anas acuta)using GPS transmitters,examining differences between the two largest lakes and other smaller lakes in ducks’habitat use,duration of stay at each lake and the daily distances moved by the tagged birds while at these sites.Results:The Eurasian Wigeon and Falcated Duck stayed five times longer and almost exclusively used natural habitat types at the two large lakes(91‒95%of positions)compared to length of stay time at smaller lakes,where they spent 28‒33 days on average(excluding the capture site)and exploited many more different habitats(including c.50%outside lakes).Conclusions:Our study is the first to show that shorter length of stay and more varied habitat use by ducks at small lakes may contribute to explaining the apparent regional concentration of numbers present of these and other species at the largest lakes in recent years.This compares with their declining abundance at smaller lakes,where habitat loss and degradation has been more manifest than on the larger lakes.展开更多
The energy loss, produced by shielding effect of steel cage outside the source tube, is quite considerable. With PENELOPE software package, MC results have been obtained based on the simulation of different source con...The energy loss, produced by shielding effect of steel cage outside the source tube, is quite considerable. With PENELOPE software package, MC results have been obtained based on the simulation of different source con- formations. The result illustrates that the naked source tubes can improve the utilization ratio of the cobalt facilities. It demonstrates the applied value of the naked source tube in engineering.展开更多
Understanding that Homer＇s Odyssey （1998） has a feminine perspective, this paper intends to explore the Greek epic placing queen Penelope as the protagonist, observing, mainly, the narratological shifts in the stor...Understanding that Homer＇s Odyssey （1998） has a feminine perspective, this paper intends to explore the Greek epic placing queen Penelope as the protagonist, observing, mainly, the narratological shifts in the story grammar, duration and character elaboration. This study also uses Paul Ricoeur＇s The Rule of Metaphor （2008） to analyze the episode of the shroud in Homer＇s Odyssey. Ricoeur sees metaphor in three distinct levels： the level of lexis where he bases himself in the works of Aristotle; the level of phrase in which he recurs to the structuralist linguistician l^mile Benveniste; and the metaphor in the level of discourse, when Ricoeur himself devises an elaborate study of the figure of speech. Penelope＇s weaving can be understood as a representation of discourse and of the feminine. Such analogy transcends the stereotype she is often given and defines a new role for the character in the epic.展开更多
This paper discusses Penelope Maddy＇s （b. 1950） naturalistic philosophy of mathematics, which is one of the most influential forms of post-Quinean naturalism in the philosophy of mathematics. Two defining features ...This paper discusses Penelope Maddy＇s （b. 1950） naturalistic philosophy of mathematics, which is one of the most influential forms of post-Quinean naturalism in the philosophy of mathematics. Two defining features of Maddy＇s theory, namely the methodological autonomy of mathematics and the equivalence of Thin Realism and Arealism, are analyzed, and some criticisms of them are posed from within the naturalistic line of thought itself. In the course of this analysis and criticism, the paper will also consider Maddy＇s objections to the Quinean Indispensability Argument, which are the starting point of her own version of naturalism.展开更多
文摘高能电子和物质相互作用是一个级联簇射 (shower)物理过程 .空间飞行器防护系统就是利用这一原理 ,通过宇宙中的电子在飞行器中产生的 shower电子 ,来了解其中半导体器件的有关信息 .该文利用 Monte Carlo方法 ,采用 PENEL OPE(Penetration and Energy L oss of Positrons and Electrons)软件包 ,对电子在飞行器中的运动过程进行模拟 ,给出球壳和半导体材料中的能量沉积分布 。
文摘目的:基于光子计数探测器的X线CT(Photon Counting Computed Tomography,PCCT)较传统CT成像最突出的特点是可实现多参数成像,包括基物质成像和单能量成像等。然而,当前商用光子计数探测器的计数率低、能量分辨率有限,大大限制了PCCT更为广泛的临床应用。为了更好地研究PCCT成像技术,本文系统地研究了基于光子计数探测器的X线CT蒙特卡罗仿真方法,深入探讨了K值效应及能量段宽度对成像质量的影响。方法:首先通过PENELOPE(Penetration and Energy Loss of Positrons and Electrons)仿真软件对PCCT成像系统进行设计,完成光子计数探测器的配置,其后基于仿真系统完成不同体模的能谱CT数据仿真。针对K值效应及能量段宽度对图像质量的影响,对相关数据进行了定量分析。结果:本研究设计的PCCT成像仿真系统能有效地实现能谱CT数据采集与成像性能分析,其中对比剂在K缘处的对比度噪声比较其在非K缘处高,并且对比剂在适当宽度的能量段里获得优质的图像。结论:本研究设计的PCCT成像仿真系统能有效地实现能谱CT数据采集与成像性能分析。
基金Supported by Shanghai Science and Technology Committee (08JC1410200)Shanghai Leading Academic Disciplines (S30109)
文摘In this paper,the beam quality and percent depth dose curves for different field sizes of CyberKnife? system were investigated by Monte Carlo simulations using the PENELOPE code,which has been used to simulate 6 MV photon beam.In water phantom,the absolute doses were calculated for Φ10–60 mm collimators,and percent depth dose curves were evaluated for Φ30–60 mm collimators.The agreement of dose distributions of the calculation with measurement was within 3.0%.The mean energy of photon spectrum was 1.46 MeV,and the beam quality index was 0.632,which was slightly smaller than that of measurement.
基金supported by National Key Research and Development Program(2016YFC0500406)the National Natural Science Foundation of China(Grant Nos.31661143027,31670424,31870369)+1 种基金the Chinese Academy of Sciences Key Strategic Program,Water Ecological Security Assessment,the Major Research Strategy for Middle and Lower Yangtze River(Grant No.ZDRW-ZS-2017-3-3)China Biodiversity Observation Networks(Sino BON)
文摘Background:Evidence suggests that wintering waterbirds have become conspicuously more concentrated at two largest lakes of the Yangtze River Floodplain,East Dong Ting Lake(Hunan Province,29°20′N,113°E)and Poyang Lake(Jiangxi Province,29°N,116°20′E),relative to other lakes,despite the establishment of reserves elsewhere.While this relationship is likely due to greater extent of undisturbed habitats in larger lakes,we understand little of the drivers affecting individual behaviours behind this tendency.Methods:We tracked wintering movements of three duck species(Eurasian Wigeon Mareca penelope,Falcated Duck M.falcata and Northern Pintail Anas acuta)using GPS transmitters,examining differences between the two largest lakes and other smaller lakes in ducks’habitat use,duration of stay at each lake and the daily distances moved by the tagged birds while at these sites.Results:The Eurasian Wigeon and Falcated Duck stayed five times longer and almost exclusively used natural habitat types at the two large lakes(91‒95%of positions)compared to length of stay time at smaller lakes,where they spent 28‒33 days on average(excluding the capture site)and exploited many more different habitats(including c.50%outside lakes).Conclusions:Our study is the first to show that shorter length of stay and more varied habitat use by ducks at small lakes may contribute to explaining the apparent regional concentration of numbers present of these and other species at the largest lakes in recent years.This compares with their declining abundance at smaller lakes,where habitat loss and degradation has been more manifest than on the larger lakes.
文摘The energy loss, produced by shielding effect of steel cage outside the source tube, is quite considerable. With PENELOPE software package, MC results have been obtained based on the simulation of different source con- formations. The result illustrates that the naked source tubes can improve the utilization ratio of the cobalt facilities. It demonstrates the applied value of the naked source tube in engineering.
文摘Understanding that Homer＇s Odyssey （1998） has a feminine perspective, this paper intends to explore the Greek epic placing queen Penelope as the protagonist, observing, mainly, the narratological shifts in the story grammar, duration and character elaboration. This study also uses Paul Ricoeur＇s The Rule of Metaphor （2008） to analyze the episode of the shroud in Homer＇s Odyssey. Ricoeur sees metaphor in three distinct levels： the level of lexis where he bases himself in the works of Aristotle; the level of phrase in which he recurs to the structuralist linguistician l^mile Benveniste; and the metaphor in the level of discourse, when Ricoeur himself devises an elaborate study of the figure of speech. Penelope＇s weaving can be understood as a representation of discourse and of the feminine. Such analogy transcends the stereotype she is often given and defines a new role for the character in the epic.
文摘This paper discusses Penelope Maddy＇s （b. 1950） naturalistic philosophy of mathematics, which is one of the most influential forms of post-Quinean naturalism in the philosophy of mathematics. Two defining features of Maddy＇s theory, namely the methodological autonomy of mathematics and the equivalence of Thin Realism and Arealism, are analyzed, and some criticisms of them are posed from within the naturalistic line of thought itself. In the course of this analysis and criticism, the paper will also consider Maddy＇s objections to the Quinean Indispensability Argument, which are the starting point of her own version of naturalism.
