Effect factors of the absorption of the source,air,entrance window,and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles,along with statistical noise and other factors tha...Effect factors of the absorption of the source,air,entrance window,and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles,along with statistical noise and other factors that collectively cause the alpha spectrum to exhibit a well-known low-energy tail.Therefore,the estabUshment of an alpha spectrum detector response function from the perspective of a signaling system must consider the various factors mentioned above.The detector response function is the convolution of an alphaparticle pulse function,two exponential functions,and a Gaussian function,followed by calculation of the parameters of the detector response function using the weighted leastsquares fitting method as proposed in this paper.In our experiment,^(239)Pu alpha spectra were measured by a highresolution,passivated implanted planar silicon(PIPS)detector at 10 levels of vacuum and 10 source-detector distances.The spectrum-fitting results were excellent as evaluated by reduced Chi-square(x^2) and correlation coefficients.Finally,the variation of parameters with vacuum level and source-detector distance was studied.Results demonstrate that σ,τ_1,and τ_2 exhibit no obvious trend of variation with vacuum in the range 2000-20,000 mTorr,and at a confidence level of 95%,the values of τ_1 and τ_2 decline in a similar fashion with source-detector distance by the power exponential function,while the value of a declines linearly.展开更多
为了充分利用背景干扰频谱分布信息以提高变换域通信系统(transform domain communication system,TDCS)抗干扰性能,提出了一种TDCS基于权系数的基函数幅度谱设计方法。在背景干扰存在的情况下,通过给采样后每个干扰频点幅值乘以一个权...为了充分利用背景干扰频谱分布信息以提高变换域通信系统(transform domain communication system,TDCS)抗干扰性能,提出了一种TDCS基于权系数的基函数幅度谱设计方法。在背景干扰存在的情况下,通过给采样后每个干扰频点幅值乘以一个权系数生成基函数各个频点的幅度谱值,并对系统传输误码性能进行理论分析,推导出系统最优误码性能时权系数的表达式。仿真结果表明,与传统二元判决系统相比,基于权系数系统具有更好的抗干扰性能,在干信比为29 d B、误码率为10-4时,信噪比增益为1.5 d B;在干信比为35 d B、信噪比为0 d B时,仍可以有效的建立通信。展开更多
目的利用静息态功能磁共振成像(resting-state functional magnetic resonance imaging,rs-fMRI)技术联合机器学习算法对自闭症患者进行分类,试图为早期识别自闭症提供参考依据。材料与方法对24例自闭症患者和25例健康人的rs-fMRI数据...目的利用静息态功能磁共振成像(resting-state functional magnetic resonance imaging,rs-fMRI)技术联合机器学习算法对自闭症患者进行分类,试图为早期识别自闭症提供参考依据。材料与方法对24例自闭症患者和25例健康人的rs-fMRI数据进行预处理;然后,以偏相关性的功能连接(functional connection,FC)构建网络矩阵,并使用GRETNA软件选取稀疏度空间为0.05~0.50,以步长为0.05搭建脑功能网络,分别计算患者和健康人的4个局部节点指标;最后,将每类指标分类准确率所占比重作为权重系数进行特征融合,以此构建特征向量,输入到支持向量机中分类并进行交叉验证以检验融合效果。结果特征加权融合方法平均准确率可达89.47%,比单一特征提高了21.05%,比无加权的融合方法提高了4.74%。结论文中提出的特征加权融合法为rs-fMRI检测自闭症提供了新指标和新方法。展开更多
酒精使用障碍(alcohol use disorder,AUD)问题遍布全球,是最常见的成瘾性障碍。长期大量饮酒可造成躯体、精神及家庭社会危害,是人类重要的死亡原因之一。尽管越来越多的研究提示AUD患者大脑存在功能损伤,然而这种异常仍鲜有系统的论述...酒精使用障碍(alcohol use disorder,AUD)问题遍布全球,是最常见的成瘾性障碍。长期大量饮酒可造成躯体、精神及家庭社会危害,是人类重要的死亡原因之一。尽管越来越多的研究提示AUD患者大脑存在功能损伤,然而这种异常仍鲜有系统的论述。现回顾目前国内外有关AUD基于磁共振的功能影像学研究进展,总结影像学特征性表现,以期帮助临床医生较充分地了解AUD患者的功能影像学变化,有助于临床诊治工作。展开更多
基金supported by the National Natural Science Foundation of China(Nos.41374130 and 41604154)Opening Foundation of Sichuan Provincial Key Lab of Applied Nuclear Techniques in Geosciences(No.gnzds2014003)the Open Fund of Robot Technology Used for Special Environment Key Laboratory of Sichuan Province(13zxtk04)
文摘Effect factors of the absorption of the source,air,entrance window,and dead layer of a detector must be considered in the measurement of monoenergetic alpha particles,along with statistical noise and other factors that collectively cause the alpha spectrum to exhibit a well-known low-energy tail.Therefore,the estabUshment of an alpha spectrum detector response function from the perspective of a signaling system must consider the various factors mentioned above.The detector response function is the convolution of an alphaparticle pulse function,two exponential functions,and a Gaussian function,followed by calculation of the parameters of the detector response function using the weighted leastsquares fitting method as proposed in this paper.In our experiment,^(239)Pu alpha spectra were measured by a highresolution,passivated implanted planar silicon(PIPS)detector at 10 levels of vacuum and 10 source-detector distances.The spectrum-fitting results were excellent as evaluated by reduced Chi-square(x^2) and correlation coefficients.Finally,the variation of parameters with vacuum level and source-detector distance was studied.Results demonstrate that σ,τ_1,and τ_2 exhibit no obvious trend of variation with vacuum in the range 2000-20,000 mTorr,and at a confidence level of 95%,the values of τ_1 and τ_2 decline in a similar fashion with source-detector distance by the power exponential function,while the value of a declines linearly.
文摘为了充分利用背景干扰频谱分布信息以提高变换域通信系统(transform domain communication system,TDCS)抗干扰性能,提出了一种TDCS基于权系数的基函数幅度谱设计方法。在背景干扰存在的情况下,通过给采样后每个干扰频点幅值乘以一个权系数生成基函数各个频点的幅度谱值,并对系统传输误码性能进行理论分析,推导出系统最优误码性能时权系数的表达式。仿真结果表明,与传统二元判决系统相比,基于权系数系统具有更好的抗干扰性能,在干信比为29 d B、误码率为10-4时,信噪比增益为1.5 d B;在干信比为35 d B、信噪比为0 d B时,仍可以有效的建立通信。
文摘酒精使用障碍(alcohol use disorder,AUD)问题遍布全球,是最常见的成瘾性障碍。长期大量饮酒可造成躯体、精神及家庭社会危害,是人类重要的死亡原因之一。尽管越来越多的研究提示AUD患者大脑存在功能损伤,然而这种异常仍鲜有系统的论述。现回顾目前国内外有关AUD基于磁共振的功能影像学研究进展,总结影像学特征性表现,以期帮助临床医生较充分地了解AUD患者的功能影像学变化,有助于临床诊治工作。
