In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma,a new dynamical model of the L-H transition based on edge instability phase transition（E...In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma,a new dynamical model of the L-H transition based on edge instability phase transition（EIPT） has been developed.With the typical plasma parameters of the EAST tokamak,the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability,which indicates that the L-H transition can be caused by the stabilization of the edge instability through EIPT.The weak E？×？B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures,which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport.With the acceleration mechanism of E？×？B flow shear,fast L-H and H-L transitions are demonstrated under the control of the input heating power.Due to the simplified scrape-offlayer boundary condition applied,the ratio between the heating powers at the H-L and L-H transition respectively differs from the ratio by Nusselt number.The results of the modeling reveal a scaling of the power threshold of the L-H transition,P_（L-H）？∝？n^（0.76） B^（0.8） for deuterium plasma.It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.展开更多
We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the thre...We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.展开更多
The calculation time in the Monte Carlo simulations consistently represents an essential issue. It is often very long, and its decrease constitutes a challenge for the simulator. Generally, an MC simulation is qualifi...The calculation time in the Monte Carlo simulations consistently represents an essential issue. It is often very long, and its decrease constitutes a challenge for the simulator. Generally, an MC simulation is qualified as quality or not according to two main criteria: the calculation time and the accuracy of the results. However, in most cases, the optimization of one criterion affects negatively the other. Therefore, a compromise between both of them is always required in this kind of simulation. The present work aims at studying the impact of the production threshold(or cut) of the GEANT4 toolkit on the calculation of the power deposition in the MEGAPIE spallation target.The production threshold of secondaries is a GEANT4 intrinsic parameter. It indicates the limit of energy we can reach in the production of secondary particles. This study has allowed us to make the following conclusions. First,the influence of the cut on the calculation of the deposited power depends on the volume size, its arrangement and the importance of the electromagnetic processes occurring within. Second, the accuracy of the calculations can be acceptable only below a given value of the cut energy.Third, this accuracy remains almost unchangeable from a certain value of the cut. The study has also made it possible to explore the prevalence of certain interactions in the zone of spallation in the MEGAPIE target.展开更多
Ultrasound is used in various chemical reaction processes, and these reactions are influenced by ultrasonic frequency. A threshold power is required for the ultrasonic degradation reaction and oxidation reaction cause...Ultrasound is used in various chemical reaction processes, and these reactions are influenced by ultrasonic frequency. A threshold power is required for the ultrasonic degradation reaction and oxidation reaction caused by hydroxyl radicals, and the cavitation threshold power is also influenced by frequency generally. In this study, the effects of frequency on the threshold power of methylene blue degradation and KI oxidation were investigated in the range between 22.8 kHz and 1640 kHz. The threshold power of KI oxidation reaction increased with increasing frequency. This phenomenon well agrees with previous study, and it is revealed that the generation of I-3?ion is caused by oxidation reaction of Iˉ ions with hydroxyl radicals. On the other hand, the threshold power of methylene blue degradation reaction was not affected by frequency. The ultrasonic degradation of methylene blue is considered to be caused by hydroxyl radicals, and there is a linear relationship between degradation rate constant and sonochemical efficiency value. However, it is guessed that the degradation of methylene blue is occurred inside cavitation bubble by pyrolysis at high frequency regions.展开更多
配电线路长期暴露于自然环境下,易受强对流天气影响而发生故障。2022年4月19日午后,受大风、雷电等高影响天气影响,陇南市13条配电线路先后出现故障。利用陇南市自动气象观测站的极大风速和闪电定位数据以及风云4A(FY-4A)红外云图、探...配电线路长期暴露于自然环境下,易受强对流天气影响而发生故障。2022年4月19日午后,受大风、雷电等高影响天气影响,陇南市13条配电线路先后出现故障。利用陇南市自动气象观测站的极大风速和闪电定位数据以及风云4A(FY-4A)红外云图、探空资料、多普勒天气雷达等资料,对此次强对流天气过程及其对电网影响进行分析。结果表明:(1)此次强对流天气以雷电、雷暴大风天气为主,西和、礼县、武都、康县等县(区)出现大面积用户停电和电力负荷损失等不利影响。(2)强对流发展主要受高原槽和切变线共同影响,在“上冷下暖”的大气层结不稳定条件下,由地面辐合线触发较强的雷暴大风天气;卫星云图和雷达回波也显示对流云团的发生发展与地面雷暴大风相吻合。(3)陇南市配电线路故障范围分布与强对流天气发生时间和过境路径基本一致,利用逐10 min极大风速和闪电定位数据,探讨得出当极大风速值超过15.0 m·s^(-1)、或正地闪电流强度超过43 k A、或负地闪电流强度超过26 k A时,配电线路发生故障的可能性较大。展开更多
在图像拼接过程中,使用固定阈值的旋转不变性二进制描述(Oriented fast and rotated brief,ORB)算法检测出的特征点在特征匹配阶段会产生较多误匹配,从而导致拼接的图像在拼接缝处产生重影。针对此问题,提出一种基于改进ORB的图像拼接...在图像拼接过程中,使用固定阈值的旋转不变性二进制描述(Oriented fast and rotated brief,ORB)算法检测出的特征点在特征匹配阶段会产生较多误匹配,从而导致拼接的图像在拼接缝处产生重影。针对此问题,提出一种基于改进ORB的图像拼接算法。首先,使用自适应算法将ORB的固定阈值替换为动态阈值对特征点进行检测;然后,使用K近邻(K-nearest neighbor,KNN)算法进行特征点粗匹配,再用随机抽样一致性(Random sampling consensus,RANSAC)算法对特征点进行精匹配;最后,通过最佳缝合线法和渐入渐出法对图像进行拼接。实验结果表明,相较于传统的ORB算法,利用所提出的算法时所需的特征点检测时间、匹配时间明显减少,匹配正确率明显提高,拼接缝重影被有效消除。展开更多
基金supported by National Natural Science Foundation of China under Contract Nos.11575235 and 11422546China Postdoctoral Science Foundation under Contract No.2016M602043+2 种基金the National Magnetic Confinement Fusion Science Program of China under Contract No.2015GB101002Key Research Program of Frontier Sciences,CAS,Grant No.QYZDB-SSW-SLH001K C Wong Education Foundation
文摘In order to understand the mechanism of the confinement bifurcation and H-mode power threshold in magnetically confined plasma,a new dynamical model of the L-H transition based on edge instability phase transition（EIPT） has been developed.With the typical plasma parameters of the EAST tokamak,the self-consistent turbulence growth rate is analyzed using the simplest case of pressure-driven ballooning-type instability,which indicates that the L-H transition can be caused by the stabilization of the edge instability through EIPT.The weak E？×？B flow shear in L-mode is able to increase the ion inertia of the electrostatic motion by increasing the radial wave number of the tilted turbulence structures,which play an important role for accelerating the trigger process of EIPT rather than directly to suppress the turbulent transport.With the acceleration mechanism of E？×？B flow shear,fast L-H and H-L transitions are demonstrated under the control of the input heating power.Due to the simplified scrape-offlayer boundary condition applied,the ratio between the heating powers at the H-L and L-H transition respectively differs from the ratio by Nusselt number.The results of the modeling reveal a scaling of the power threshold of the L-H transition,P_（L-H）？∝？n^（0.76） B^（0.8） for deuterium plasma.It is found finite Larmor radius induces an isotope effect of the H-mode power threshold.
基金Supported by the National Basic Research Program of China under Grant Nos 2013CB632801 and 2013CB632803the National Natural Science Foundation of China under Grant Nos 61435014,61306058 and 61274094the Beijing Natural Science Foundation under Grant No 4144086
文摘We report on the room-temperature cascade laser （QCL） at λ -4.7μm. cw operation of a surface grating Both grating design and material distributed feedback （DFB） quantum optimization are used to decrease the threshold current density and to increase the output power. For a high-reflectivity-coated 13-μm-wide and 4- mm-long laser, high wall-plug efficiency of 6% is obtained at 20℃ from a single facet producing over I W of ew output power. The threshold current density of DFB QCL is as low as 1.13kA/cm^2 at 10℃ and 1.34kA/cm2 at 30℃ in cw mode. Stable single-mode emission with a side-mode suppression ratio of about 30 dB is observed in tile working temperature range of 20-50℃.
文摘The calculation time in the Monte Carlo simulations consistently represents an essential issue. It is often very long, and its decrease constitutes a challenge for the simulator. Generally, an MC simulation is qualified as quality or not according to two main criteria: the calculation time and the accuracy of the results. However, in most cases, the optimization of one criterion affects negatively the other. Therefore, a compromise between both of them is always required in this kind of simulation. The present work aims at studying the impact of the production threshold(or cut) of the GEANT4 toolkit on the calculation of the power deposition in the MEGAPIE spallation target.The production threshold of secondaries is a GEANT4 intrinsic parameter. It indicates the limit of energy we can reach in the production of secondary particles. This study has allowed us to make the following conclusions. First,the influence of the cut on the calculation of the deposited power depends on the volume size, its arrangement and the importance of the electromagnetic processes occurring within. Second, the accuracy of the calculations can be acceptable only below a given value of the cut energy.Third, this accuracy remains almost unchangeable from a certain value of the cut. The study has also made it possible to explore the prevalence of certain interactions in the zone of spallation in the MEGAPIE target.
文摘Ultrasound is used in various chemical reaction processes, and these reactions are influenced by ultrasonic frequency. A threshold power is required for the ultrasonic degradation reaction and oxidation reaction caused by hydroxyl radicals, and the cavitation threshold power is also influenced by frequency generally. In this study, the effects of frequency on the threshold power of methylene blue degradation and KI oxidation were investigated in the range between 22.8 kHz and 1640 kHz. The threshold power of KI oxidation reaction increased with increasing frequency. This phenomenon well agrees with previous study, and it is revealed that the generation of I-3?ion is caused by oxidation reaction of Iˉ ions with hydroxyl radicals. On the other hand, the threshold power of methylene blue degradation reaction was not affected by frequency. The ultrasonic degradation of methylene blue is considered to be caused by hydroxyl radicals, and there is a linear relationship between degradation rate constant and sonochemical efficiency value. However, it is guessed that the degradation of methylene blue is occurred inside cavitation bubble by pyrolysis at high frequency regions.
文摘配电线路长期暴露于自然环境下,易受强对流天气影响而发生故障。2022年4月19日午后,受大风、雷电等高影响天气影响,陇南市13条配电线路先后出现故障。利用陇南市自动气象观测站的极大风速和闪电定位数据以及风云4A(FY-4A)红外云图、探空资料、多普勒天气雷达等资料,对此次强对流天气过程及其对电网影响进行分析。结果表明:(1)此次强对流天气以雷电、雷暴大风天气为主,西和、礼县、武都、康县等县(区)出现大面积用户停电和电力负荷损失等不利影响。(2)强对流发展主要受高原槽和切变线共同影响,在“上冷下暖”的大气层结不稳定条件下,由地面辐合线触发较强的雷暴大风天气;卫星云图和雷达回波也显示对流云团的发生发展与地面雷暴大风相吻合。(3)陇南市配电线路故障范围分布与强对流天气发生时间和过境路径基本一致,利用逐10 min极大风速和闪电定位数据,探讨得出当极大风速值超过15.0 m·s^(-1)、或正地闪电流强度超过43 k A、或负地闪电流强度超过26 k A时,配电线路发生故障的可能性较大。
文摘在图像拼接过程中,使用固定阈值的旋转不变性二进制描述(Oriented fast and rotated brief,ORB)算法检测出的特征点在特征匹配阶段会产生较多误匹配,从而导致拼接的图像在拼接缝处产生重影。针对此问题,提出一种基于改进ORB的图像拼接算法。首先,使用自适应算法将ORB的固定阈值替换为动态阈值对特征点进行检测;然后,使用K近邻(K-nearest neighbor,KNN)算法进行特征点粗匹配,再用随机抽样一致性(Random sampling consensus,RANSAC)算法对特征点进行精匹配;最后,通过最佳缝合线法和渐入渐出法对图像进行拼接。实验结果表明,相较于传统的ORB算法,利用所提出的算法时所需的特征点检测时间、匹配时间明显减少,匹配正确率明显提高,拼接缝重影被有效消除。
