Environmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 (90Sr) and technetium-99 (99Tc), are only found on Earth as a result of human a...Environmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 (90Sr) and technetium-99 (99Tc), are only found on Earth as a result of human activity, and some, like potassium-40 (40K), are only present due to natural processes, a few isotopes, e.g. tritium (3H), result from both natural processes and human activities. The concentration and location of some natural isotopes, particularly uranium-238 (238U), can be affected by human activity because of the constant exposure of Human beings to radiation caused by terrestrial, extra-terrestrial and anthropogenic radio nuclides, it is necessary to determine and estimate the activity of various radio nuclides in environmental media such as vegetation, soil, and water. In the present research, the activities of 226Ra, 232Th and 40K are measured in soil, vegetation and water samples, collected from Yangdong District, Yangxi County, and Yangjiang County of Guangdong Province, China using an HPGe based gamma spectrometry system. The measured mean activity of 226Ra, 232Th and 40K in soil samples was found to be 31.19 ± 1.2, 47.00 ± 2.30 and 589.31 ± 17.52 Bqkg-1, respectively. The measured mean activity of these radionuclides in all water samples was found to be below minimum detectable activity. The measured mean activity of 226Ra, 232Th and 40K in vegetation samples was 19.92 ± 3.09, 25.36 ± 8.11 and 4982.94 ± 85.68 Bqkg-1, respectively. No anthropogenic 137Cs was detected in these environmental samples. Mean radium equivalent activity (Raeq), external radiation hazard index (Hex), internal radiation hazard index (Hin) and absorbed dose rate (D) for the area under study were determined as 142.92 Bqkg-1, 0.38, 0.47 and 66.47 nGyh-1, respectively. The annual effective dose equivalent (AEDE) varied in the range from 0.03 to 0.12 mSvy-1. It is concluded that the surveyed area do not pose any significant radiological risk to the population and environment.展开更多
The enhancement of the precision of phase estimation in quantum metrology is investigated by employing weak measurement （WM） and quantum measurement reversal （QMR）. We derive the exact expressions of the optimal q...The enhancement of the precision of phase estimation in quantum metrology is investigated by employing weak measurement （WM） and quantum measurement reversal （QMR）. We derive the exact expressions of the optimal quantum Fisher information （QFI） and success probability of phase estimation for an exactly solving model consisting of a qubit interacting with a structured reservoir. We show that the QFI can be obviously enhanced by means of the WM and QMR in different regimes. In addition, we also show that the magnitude of the decoherence involved in the WM and QMR can be a general complex number, which extends the applicable scope of the WM and QMR approach.展开更多
针对基于车辆响应的间接测量法进行桥梁模态识别时,桥面不平度的影响难以滤除、高阶模态识别准确率较低等问题,提出一种基于盲源分离算法来分离车桥接触点响应信号中的桥面不平度效应与桥梁振动响应,进而实现桥梁模态识别的方法.首先,...针对基于车辆响应的间接测量法进行桥梁模态识别时,桥面不平度的影响难以滤除、高阶模态识别准确率较低等问题,提出一种基于盲源分离算法来分离车桥接触点响应信号中的桥面不平度效应与桥梁振动响应,进而实现桥梁模态识别的方法.首先,详细阐述了应用二阶盲识别(Second Order Blind Identification,SOBI)算法,以两组车桥接触点加速度响应信号作为输入信号,进而获取桥梁振动估计信号的原理和方法.然后,采用信号带通滤波和Hilbert变换并结合支点数据延拓的振型修正策略,建立了基于车辆响应的桥梁模态识别技术流程和框架.最后,依托数值算例对所提出方法的适用性和有效性进行了验证,并分析了车辆间距、桥面不平度和车辆频率等参数对方法适用性的影响.结果表明,所提出方法能有效滤除桥面不平度的影响,实现桥梁高阶模态的准确识别,且对多种关键因素的影响具有鲁棒性,具有精度高、操作简便和适用性强等特点,可为基于车辆响应的桥梁模态识别提供一种新思路.展开更多
文摘Environmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 (90Sr) and technetium-99 (99Tc), are only found on Earth as a result of human activity, and some, like potassium-40 (40K), are only present due to natural processes, a few isotopes, e.g. tritium (3H), result from both natural processes and human activities. The concentration and location of some natural isotopes, particularly uranium-238 (238U), can be affected by human activity because of the constant exposure of Human beings to radiation caused by terrestrial, extra-terrestrial and anthropogenic radio nuclides, it is necessary to determine and estimate the activity of various radio nuclides in environmental media such as vegetation, soil, and water. In the present research, the activities of 226Ra, 232Th and 40K are measured in soil, vegetation and water samples, collected from Yangdong District, Yangxi County, and Yangjiang County of Guangdong Province, China using an HPGe based gamma spectrometry system. The measured mean activity of 226Ra, 232Th and 40K in soil samples was found to be 31.19 ± 1.2, 47.00 ± 2.30 and 589.31 ± 17.52 Bqkg-1, respectively. The measured mean activity of these radionuclides in all water samples was found to be below minimum detectable activity. The measured mean activity of 226Ra, 232Th and 40K in vegetation samples was 19.92 ± 3.09, 25.36 ± 8.11 and 4982.94 ± 85.68 Bqkg-1, respectively. No anthropogenic 137Cs was detected in these environmental samples. Mean radium equivalent activity (Raeq), external radiation hazard index (Hex), internal radiation hazard index (Hin) and absorbed dose rate (D) for the area under study were determined as 142.92 Bqkg-1, 0.38, 0.47 and 66.47 nGyh-1, respectively. The annual effective dose equivalent (AEDE) varied in the range from 0.03 to 0.12 mSvy-1. It is concluded that the surveyed area do not pose any significant radiological risk to the population and environment.
基金supported by the National Natural Science Foundation of China(Grants No.11247294)the Research Foundation of Education Bureau of Hunan Province,China(Grant No.12C0826)+2 种基金the Doctor Foundation Startup from Hunan University of Arts and Science,China(Grant No.13101039)the Key Laboratory of Photoelectricity Information Integration and Optics Manufacture Technology in Hunan Province,Chinathe Construct Program of the Key Discipline in Hunan University of Arts and Science(Optics),China
文摘The enhancement of the precision of phase estimation in quantum metrology is investigated by employing weak measurement （WM） and quantum measurement reversal （QMR）. We derive the exact expressions of the optimal quantum Fisher information （QFI） and success probability of phase estimation for an exactly solving model consisting of a qubit interacting with a structured reservoir. We show that the QFI can be obviously enhanced by means of the WM and QMR in different regimes. In addition, we also show that the magnitude of the decoherence involved in the WM and QMR can be a general complex number, which extends the applicable scope of the WM and QMR approach.
文摘针对基于车辆响应的间接测量法进行桥梁模态识别时,桥面不平度的影响难以滤除、高阶模态识别准确率较低等问题,提出一种基于盲源分离算法来分离车桥接触点响应信号中的桥面不平度效应与桥梁振动响应,进而实现桥梁模态识别的方法.首先,详细阐述了应用二阶盲识别(Second Order Blind Identification,SOBI)算法,以两组车桥接触点加速度响应信号作为输入信号,进而获取桥梁振动估计信号的原理和方法.然后,采用信号带通滤波和Hilbert变换并结合支点数据延拓的振型修正策略,建立了基于车辆响应的桥梁模态识别技术流程和框架.最后,依托数值算例对所提出方法的适用性和有效性进行了验证,并分析了车辆间距、桥面不平度和车辆频率等参数对方法适用性的影响.结果表明,所提出方法能有效滤除桥面不平度的影响,实现桥梁高阶模态的准确识别,且对多种关键因素的影响具有鲁棒性,具有精度高、操作简便和适用性强等特点,可为基于车辆响应的桥梁模态识别提供一种新思路.
