A dual-tone technique is used to produce multi-samples in optimising calibration of six-port junction. More accurate results are achieved by using the least-square method and excluding those samples which may cause bi...A dual-tone technique is used to produce multi-samples in optimising calibration of six-port junction. More accurate results are achieved by using the least-square method and excluding those samples which may cause bigger errors. A 0.80 -1.10 GHz microwave integrated circuit （MIC） six-port reflectometer is constructed. Nine test samples are used in the measurement. With Engen＇s calibration procedure, the difference between the HP8510 and the six-port reflectrometer is in the order of 0.20 dB/1.5° for most cases, above 0.50 dB/5.0° at boundary frequency. With the optimised method, the difference is less than 0. 10 dB/1.0° for most cases, and the biggest error is 0.42 dB/2.1° for boundary frequencies.展开更多
Using the density functional theory and the nonequilibrium Green＇s function method, we studied the finite-bias quan- tum transport in a Cr/graphene/Cr magnetotunnel junction （MTJ） constructed by a single graphene l...Using the density functional theory and the nonequilibrium Green＇s function method, we studied the finite-bias quan- tum transport in a Cr/graphene/Cr magnetotunnel junction （MTJ） constructed by a single graphene layer sandwiched be- tween two semi-infinite Cr（111 ） electrodes. We found that the tunneling magnetoresistance （TMR） ratio in this MTJ reached 108%, which is close to that of a perfect spin filter. Under an external positive bias, we found that the TMR ratio remained constant at 65%, in contrast to MgO-based MTJs, the TMR ratios of which decrease with increasing bias. These results indicate that the Cr/graphene/Cr MTJ is a promising candidate for spintronics applications.展开更多
Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3...Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3D TIs).In this work,we further generalize that method to the circumstance with radio frequency(rf)irradiation.We find that with the increase of the rf power,the measured minigap becomes broadened and extends to higher energies in a way similar to the rf power dependence of the outer border of the Shapiro step region.We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction(RSJ)model and the Blonder–Tinkham–Klapwijk(BTK)theory.Our findings could be useful when using the contact-resistancemeasurement method to study the Majorana-related physics in topological insulator-based Josephson junctions under rf irradiation.展开更多
The flow instability through the side branch of a T-junction is analyzed in a numerical simulation. In a previous experimental study, the authors clarified the mechanism of fluid-induced vibration in the side branch o...The flow instability through the side branch of a T-junction is analyzed in a numerical simulation. In a previous experimental study, the authors clarified the mechanism of fluid-induced vibration in the side branch of the T-junction in laminar steady flow through the trunk. However, in that approach there were restrictions with respect to extracting details of flow behavior such as the flow instability and the distribution of wall shear stress along the wall. Here the spatial growth of the velocity perturbation at the upstream boundary of the side branch is investigated. The simulation result indicates that a periodic velocity fluctuation introduced at the upstream boundary is amplified downstream, in good agreement with experimental result. The fluctuation in wall shear stress because of the flow instability shows local extrema in both the near and distal walls. From the numerical simulation, the downstream fluid oscillation under a typical condition has a Strouhal number of 1.05, which approximately agrees with the value obtained in experiments. Therefore, this periodic oscillation motion is a universal phenomenon in the side branch of a T-junction.展开更多
The coupling properties of a transverse slot in the common wall between two buttingrectangular waveguides are discussed.By means of Galerkin’s method which takes into accountthe wall thickness,equivalent magnetic cur...The coupling properties of a transverse slot in the common wall between two buttingrectangular waveguides are discussed.By means of Galerkin’s method which takes into accountthe wall thickness,equivalent magnetic currents on the aperture surface of the slot are obtained,and then the general formulae of scattering fields and of equivalent parameters are derived.Thedimensions as well as seats of those two waveguides and the slot,and the thickness of the wall arearbitrary.For example,the transforming coefficients and the VSWRs of numerical calculationand experimental results are given.They are in good agreement.展开更多
For discrimination of the common W-junction and Y-junction in the labels of line drawing for a three-dimensional manifold plane surface with trihedral vertices, the existing algorithms are almost using angles between ...For discrimination of the common W-junction and Y-junction in the labels of line drawing for a three-dimensional manifold plane surface with trihedral vertices, the existing algorithms are almost using angles between two adjacent lines and W-junction and Y- junction＇s definitions, and other complex methods. This passage gives four methods with their detailed mathematical inference processes in order to use these algorithms implemented by computer. The algorithms listed are Angle Summation method and Points to the Line method, Triangle methods which are the Triangle Area method and the Cross method. When the computer programs discriminate junctions, by comparison, the Angle Summation method and Points to the Line method are less efficacious than the Triangle method, and Cross method is more efficacious than the Triangle Area method in the Triangle method.展开更多
Open channel junctions are encountered in urban water treatment plants, irrigation and drainage canals, and natural river systems. Junctions are very important in municipal sewerage systems and river engineering. Adeq...Open channel junctions are encountered in urban water treatment plants, irrigation and drainage canals, and natural river systems. Junctions are very important in municipal sewerage systems and river engineering. Adequate theoretical description of flow through an open channel junction is difficult because numerous variables are to be considered. Equations of junction models are based on mass and momentum or mass and energy conservation. The objective of this study is to compare two junction models for subcritical flows. In channel branches, we solve numerically the Saint-Venant hyperbolic system by combining Preissmann scheme and double sweep method. We validate our results with HEC-RAS using Nash and Sutcliffe efficiency. In junction models, equality of water stage and complete energy conservation equation from HEC-RAS are compared. Outcome of the research clearly indicates that the complete conservation energy model is more suitable in flow through junction than equality of water stage model in serious situations.展开更多
基金The National Natural Science Foundation of China (No.60441006)
文摘A dual-tone technique is used to produce multi-samples in optimising calibration of six-port junction. More accurate results are achieved by using the least-square method and excluding those samples which may cause bigger errors. A 0.80 -1.10 GHz microwave integrated circuit （MIC） six-port reflectometer is constructed. Nine test samples are used in the measurement. With Engen＇s calibration procedure, the difference between the HP8510 and the six-port reflectrometer is in the order of 0.20 dB/1.5° for most cases, above 0.50 dB/5.0° at boundary frequency. With the optimised method, the difference is less than 0. 10 dB/1.0° for most cases, and the biggest error is 0.42 dB/2.1° for boundary frequencies.
基金supported by the National Natural Science Foundation of China(Grant Nos.10874143,10974166,and 11574260)the Program for New Century Excellent Talents in University,China(Grant No.NCET-10-0169)+1 种基金the National Innovation Foundation for Graduate,China(Grant No.201310530003)the Computational Support from Shanghai Super-computer Center,China
文摘Using the density functional theory and the nonequilibrium Green＇s function method, we studied the finite-bias quan- tum transport in a Cr/graphene/Cr magnetotunnel junction （MTJ） constructed by a single graphene layer sandwiched be- tween two semi-infinite Cr（111 ） electrodes. We found that the tunneling magnetoresistance （TMR） ratio in this MTJ reached 108%, which is close to that of a perfect spin filter. Under an external positive bias, we found that the TMR ratio remained constant at 65%, in contrast to MgO-based MTJs, the TMR ratios of which decrease with increasing bias. These results indicate that the Cr/graphene/Cr MTJ is a promising candidate for spintronics applications.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0300601,2017YFA0304700,and 2015CB921402)the National Natural Science Foundation China(Grant Nos.11527806,91221203,11174357,91421303,and 11774405)+1 种基金the Strategic Priority Research Program B of the Chinese Academy of Sciences(Grant Nos.XDB07010100 and XDB28000000)the Beijing Municipal Science&Technology Commission,China(Grant No.Z191100007219008)
文摘Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3D TIs).In this work,we further generalize that method to the circumstance with radio frequency(rf)irradiation.We find that with the increase of the rf power,the measured minigap becomes broadened and extends to higher energies in a way similar to the rf power dependence of the outer border of the Shapiro step region.We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction(RSJ)model and the Blonder–Tinkham–Klapwijk(BTK)theory.Our findings could be useful when using the contact-resistancemeasurement method to study the Majorana-related physics in topological insulator-based Josephson junctions under rf irradiation.
文摘The flow instability through the side branch of a T-junction is analyzed in a numerical simulation. In a previous experimental study, the authors clarified the mechanism of fluid-induced vibration in the side branch of the T-junction in laminar steady flow through the trunk. However, in that approach there were restrictions with respect to extracting details of flow behavior such as the flow instability and the distribution of wall shear stress along the wall. Here the spatial growth of the velocity perturbation at the upstream boundary of the side branch is investigated. The simulation result indicates that a periodic velocity fluctuation introduced at the upstream boundary is amplified downstream, in good agreement with experimental result. The fluctuation in wall shear stress because of the flow instability shows local extrema in both the near and distal walls. From the numerical simulation, the downstream fluid oscillation under a typical condition has a Strouhal number of 1.05, which approximately agrees with the value obtained in experiments. Therefore, this periodic oscillation motion is a universal phenomenon in the side branch of a T-junction.
文摘The coupling properties of a transverse slot in the common wall between two buttingrectangular waveguides are discussed.By means of Galerkin’s method which takes into accountthe wall thickness,equivalent magnetic currents on the aperture surface of the slot are obtained,and then the general formulae of scattering fields and of equivalent parameters are derived.Thedimensions as well as seats of those two waveguides and the slot,and the thickness of the wall arearbitrary.For example,the transforming coefficients and the VSWRs of numerical calculationand experimental results are given.They are in good agreement.
文摘For discrimination of the common W-junction and Y-junction in the labels of line drawing for a three-dimensional manifold plane surface with trihedral vertices, the existing algorithms are almost using angles between two adjacent lines and W-junction and Y- junction＇s definitions, and other complex methods. This passage gives four methods with their detailed mathematical inference processes in order to use these algorithms implemented by computer. The algorithms listed are Angle Summation method and Points to the Line method, Triangle methods which are the Triangle Area method and the Cross method. When the computer programs discriminate junctions, by comparison, the Angle Summation method and Points to the Line method are less efficacious than the Triangle method, and Cross method is more efficacious than the Triangle Area method in the Triangle method.
文摘Open channel junctions are encountered in urban water treatment plants, irrigation and drainage canals, and natural river systems. Junctions are very important in municipal sewerage systems and river engineering. Adequate theoretical description of flow through an open channel junction is difficult because numerous variables are to be considered. Equations of junction models are based on mass and momentum or mass and energy conservation. The objective of this study is to compare two junction models for subcritical flows. In channel branches, we solve numerically the Saint-Venant hyperbolic system by combining Preissmann scheme and double sweep method. We validate our results with HEC-RAS using Nash and Sutcliffe efficiency. In junction models, equality of water stage and complete energy conservation equation from HEC-RAS are compared. Outcome of the research clearly indicates that the complete conservation energy model is more suitable in flow through junction than equality of water stage model in serious situations.
