With the discovery of high-TC superconducting materials like Yttrium Barium Cupric Oxide, Bismuth Strontium Calcium Copper Oxide and Thallium Calcium Barium Copper Oxide, tremendous interest has developed over the pas...With the discovery of high-TC superconducting materials like Yttrium Barium Cupric Oxide, Bismuth Strontium Calcium Copper Oxide and Thallium Calcium Barium Copper Oxide, tremendous interest has developed over the past two years in understanding these materials as well as utilizing them in a variety of applications. The thin films of these materials are expected to play an important role in the area of microelectronics, especially for interconnects in integrated circuits, Josephson junctions, magnetic field sensors and optical detectors. Here, the authors designed a new nanocrystalline ceramic type II high-TC superconductor, Gadolinium Barium Copper Oxide (GdBaCuO/GBCO). The GBCO perovskite phase structure was prepared by the conventional solid state thermochemical reaction technique involving mixing, milling, calcination and sintering. In GBCO system, the method for controlling microstructure and superconducting state is related to oxygen content consideration because small changes in oxygen concentration can often?lead to huge change in Tc. In order to show the viability of the proposed method, super-conducting powder was prepared in special furnace. The sample was analyzed by X-Ray Diffraction (XRD), an indispensible non-destructive tool for structural materials characterization and quality control which makes use of the Debye-Scherrer method. The comparison of XRD results with JCPDS files confirmed the orthorhombic structure of the sample. Micro-structural features are studied using Scanning Electron Microscopy (SEM) which revealed that its particle size is in the nanometer range. It also confirmed the calculated value of particle size from Debye Scherrer’s formula. EDX plot shows the presence of all the constituents. X-ray instrumental peak broadening analysis was used to evaluate the size and lattice strain by the Williamson-Hall Plot method.展开更多
Transformer‐rectifier flux pumps are DC superconducting power supplies capable of charging superconducting magnets to high currents and stored magnetic energies.Here,we demonstrate a full‐wave superconducting flux p...Transformer‐rectifier flux pumps are DC superconducting power supplies capable of charging superconducting magnets to high currents and stored magnetic energies.Here,we demonstrate a full‐wave superconducting flux pump assembled from high‐temperature superconducting(HTS)wire that utilizes superconducting switches controlled by applied magnetic field.A negative DC offset occurs in the superconducting secondary of the circuit during operation which is related to the output load current.A feedback control system is proposed and demonstrated to account for the negative DC offset.Increasing the primary current proportional to the load current during operation allowed for the maximum output of the flux pump to be increased from 35 A to more than 275 A.These results are reproduced using a coupled electrical‐and magnetic–circuit model formulated in the MATLAB Simulink®package.展开更多
This study proposes an image-based visual servoing(IBVS)method based on a velocity observer for an unmanned aerial vehicle(UAV)for tracking a dynamic target in Global Positioning System(GPS)-denied environments.The pr...This study proposes an image-based visual servoing(IBVS)method based on a velocity observer for an unmanned aerial vehicle(UAV)for tracking a dynamic target in Global Positioning System(GPS)-denied environments.The proposed method derives the simplified and decoupled image dynamics of underactuated UAVs using a constructed virtual camera and then considers the uncertainties caused by the unpredictable rotations and velocities of the dynamic target.A novel image depth model that extends the IBVS method to track a rotating target with arbitrary orientations is proposed.The depth model ensures image feature accuracy and image trajectory smoothness in rotating target tracking.The relative velocities of the UAV and the dynamic target are estimated using the proposed velocity observer.Thanks to the velocity observer,translational velocity measurements are not required,and the control chatter caused by noise-containing measurements is mitigated.An integral-based filter is proposed to compensate for unpredictable environmental disturbances in order to improve the antidisturbance ability.The stability of the velocity observer and IBVS controller is analyzed using the Lyapunov method.Comparative simulations and multistage experiments are conducted to illustrate the tracking stability,anti-disturbance ability,and tracking robustness of the proposed method with a dynamic rotating target.展开更多
The reconstruction of images from their corresponding noisy Radon transform is a typical example of an ill-posed linear inverse problem as arising in the application of computerized tomography(CT).As the(naive)solutio...The reconstruction of images from their corresponding noisy Radon transform is a typical example of an ill-posed linear inverse problem as arising in the application of computerized tomography(CT).As the(naive)solution does not depend on the measured data continuously,regularization is needed to reestablish a continuous dependence.In this work,we investigate simple,but yet still provably convergent approaches to learning linear regularization methods from data.More specifically,we analyze two approaches:one generic linear regularization that learns how to manipulate the singular values of the linear operator in an extension of our previous work,and one tailored approach in the Fourier domain that is specific to CT-reconstruction.We prove that such approaches become convergent regularization methods as well as the fact that the reconstructions they provide are typically much smoother than the training data they were trained on.Finally,we compare the spectral as well as the Fourier-based approaches for CT-reconstruction numerically,discuss their advantages and disadvantages and investigate the effect of discretization errors at differentresolutions.展开更多
To produce fusion reactions efficiently,thermonuclear plasmas have to reach extremely high temperatures,which is incompatible with their coming into contact with material surfaces.Confinement of plasmas using magnetic...To produce fusion reactions efficiently,thermonuclear plasmas have to reach extremely high temperatures,which is incompatible with their coming into contact with material surfaces.Confinement of plasmas using magnetic fields has progressed significantly in the last years,particularly in the tokamak configuration.Unfortunately,all tokamak devices,and particularly metallic ones,are plagued by catastrophic events called disruptions.Many disruptions are preceded by anomalies in the radiation patterns,particularly in ITER-relevant scenarios.These specific forms of radiation emission either directly cause or reveal the approaching collapse of the configuration.Detecting the localization of these radiation anomalies in real time requires an innovative and specific elaboration of bolometric measurements,confirmed by visible cameras and the inversion of sophisticated tomographic algorithms.The information derived from these measurements can be interpreted in terms of local power balances,which suggest a new quantity,the radiated power divided by the plasma internal energy,to determine the criticality of the plasma state.Combined with robust indicators of the temperature profile shape,the identified anomalous radiation patterns allow determination of the sequence of macroscopic events leading to disruptions.A systematic analysis of JET campaigns at high power in deuterium,full tritium,and DT,for a total of almost 2000 discharges,proves the effectiveness of the approach.The warning times are such that,depending on the radiation anomaly and the available actuators,the control system of future devices is expected to provide enough notice to enable deployment of effective prevention and avoidance strategies.展开更多
The detailed density perturbations provided by the advanced polarimeter-interferometer system(Polaris) during sawtooth collapse on the Joint Texas Experimental Tokamak(J-TEXT) are reported in this article.During a saw...The detailed density perturbations provided by the advanced polarimeter-interferometer system(Polaris) during sawtooth collapse on the Joint Texas Experimental Tokamak(J-TEXT) are reported in this article.During a sawtooth collapse and the crash of plasma pressure at the center,it is found that the increase in density in the region between the inversion radius and mixing radius is poloidally asymmetrical,while the increase in temperature is poloidally symmetrical.The poloidal location where the density increases is dependent on the phase of the precursory m/n=1/1 kink mode.It is always out of phase with the hot core of the m/n=1/1 mode.The behaviors of density perturbations during sawtooth collapse observed in J-TEXT are beyond the expectations of the standard model,and this can shed new light on the understanding of sawtooth collapse.展开更多
文摘With the discovery of high-TC superconducting materials like Yttrium Barium Cupric Oxide, Bismuth Strontium Calcium Copper Oxide and Thallium Calcium Barium Copper Oxide, tremendous interest has developed over the past two years in understanding these materials as well as utilizing them in a variety of applications. The thin films of these materials are expected to play an important role in the area of microelectronics, especially for interconnects in integrated circuits, Josephson junctions, magnetic field sensors and optical detectors. Here, the authors designed a new nanocrystalline ceramic type II high-TC superconductor, Gadolinium Barium Copper Oxide (GdBaCuO/GBCO). The GBCO perovskite phase structure was prepared by the conventional solid state thermochemical reaction technique involving mixing, milling, calcination and sintering. In GBCO system, the method for controlling microstructure and superconducting state is related to oxygen content consideration because small changes in oxygen concentration can often?lead to huge change in Tc. In order to show the viability of the proposed method, super-conducting powder was prepared in special furnace. The sample was analyzed by X-Ray Diffraction (XRD), an indispensible non-destructive tool for structural materials characterization and quality control which makes use of the Debye-Scherrer method. The comparison of XRD results with JCPDS files confirmed the orthorhombic structure of the sample. Micro-structural features are studied using Scanning Electron Microscopy (SEM) which revealed that its particle size is in the nanometer range. It also confirmed the calculated value of particle size from Debye Scherrer’s formula. EDX plot shows the presence of all the constituents. X-ray instrumental peak broadening analysis was used to evaluate the size and lattice strain by the Williamson-Hall Plot method.
基金supported in part by the New Zealand Ministry of Business,Innovation and Employment(MBIE RTVU1916)has been part‐funded by STEP,a UKAEA programme to design and build a prototype fusion energy plant and a path to commercial fusion.
文摘Transformer‐rectifier flux pumps are DC superconducting power supplies capable of charging superconducting magnets to high currents and stored magnetic energies.Here,we demonstrate a full‐wave superconducting flux pump assembled from high‐temperature superconducting(HTS)wire that utilizes superconducting switches controlled by applied magnetic field.A negative DC offset occurs in the superconducting secondary of the circuit during operation which is related to the output load current.A feedback control system is proposed and demonstrated to account for the negative DC offset.Increasing the primary current proportional to the load current during operation allowed for the maximum output of the flux pump to be increased from 35 A to more than 275 A.These results are reproduced using a coupled electrical‐and magnetic–circuit model formulated in the MATLAB Simulink®package.
基金supported in part by the National Key Research and Development Program of China(2021ZD0114503,2022YFB4701800,and 2021YFB1714700)the National Natural Science Foundation of China(62273098,62027810,61971071,62133005,62273138,and 62103140)+9 种基金the Major Research Plan of the National Natural Science Foundation of China(92148204)the Newton International Fellowships 2022 funded by the Royal Society,UK(NIF\R1\221089)Hunan Leading Talent of Technological Innovation(2022RC3063)Hunan Science Fund for Distinguished Young Scholars(2021JJ10025)the Hunan Key Research and Development Program(2021GK4011 and 2022GK2011)the Changsha Science and Technology Major Project(kh2003026)the Natural Science Foundation of Hunan Province(2021JJ20029 and 2021JJ40124)the Science and Technology Innovation Program of Hunan Province(2021RC3060)the Joint Open Foundation of the State Key Laboratory of Robotics(2021-KF-22-17)the China University Industry-University-Research Innovation Fund(2020HYA06006).
文摘This study proposes an image-based visual servoing(IBVS)method based on a velocity observer for an unmanned aerial vehicle(UAV)for tracking a dynamic target in Global Positioning System(GPS)-denied environments.The proposed method derives the simplified and decoupled image dynamics of underactuated UAVs using a constructed virtual camera and then considers the uncertainties caused by the unpredictable rotations and velocities of the dynamic target.A novel image depth model that extends the IBVS method to track a rotating target with arbitrary orientations is proposed.The depth model ensures image feature accuracy and image trajectory smoothness in rotating target tracking.The relative velocities of the UAV and the dynamic target are estimated using the proposed velocity observer.Thanks to the velocity observer,translational velocity measurements are not required,and the control chatter caused by noise-containing measurements is mitigated.An integral-based filter is proposed to compensate for unpredictable environmental disturbances in order to improve the antidisturbance ability.The stability of the velocity observer and IBVS controller is analyzed using the Lyapunov method.Comparative simulations and multistage experiments are conducted to illustrate the tracking stability,anti-disturbance ability,and tracking robustness of the proposed method with a dynamic rotating target.
基金the support of the German Research Foundation,projects BU 2327/19-1 and MO 2962/7-1support from the EPSRC grant EP/R513106/1support from the Alan Turing Institute.
文摘The reconstruction of images from their corresponding noisy Radon transform is a typical example of an ill-posed linear inverse problem as arising in the application of computerized tomography(CT).As the(naive)solution does not depend on the measured data continuously,regularization is needed to reestablish a continuous dependence.In this work,we investigate simple,but yet still provably convergent approaches to learning linear regularization methods from data.More specifically,we analyze two approaches:one generic linear regularization that learns how to manipulate the singular values of the linear operator in an extension of our previous work,and one tailored approach in the Fourier domain that is specific to CT-reconstruction.We prove that such approaches become convergent regularization methods as well as the fact that the reconstructions they provide are typically much smoother than the training data they were trained on.Finally,we compare the spectral as well as the Fourier-based approaches for CT-reconstruction numerically,discuss their advantages and disadvantages and investigate the effect of discretization errors at differentresolutions.
文摘To produce fusion reactions efficiently,thermonuclear plasmas have to reach extremely high temperatures,which is incompatible with their coming into contact with material surfaces.Confinement of plasmas using magnetic fields has progressed significantly in the last years,particularly in the tokamak configuration.Unfortunately,all tokamak devices,and particularly metallic ones,are plagued by catastrophic events called disruptions.Many disruptions are preceded by anomalies in the radiation patterns,particularly in ITER-relevant scenarios.These specific forms of radiation emission either directly cause or reveal the approaching collapse of the configuration.Detecting the localization of these radiation anomalies in real time requires an innovative and specific elaboration of bolometric measurements,confirmed by visible cameras and the inversion of sophisticated tomographic algorithms.The information derived from these measurements can be interpreted in terms of local power balances,which suggest a new quantity,the radiated power divided by the plasma internal energy,to determine the criticality of the plasma state.Combined with robust indicators of the temperature profile shape,the identified anomalous radiation patterns allow determination of the sequence of macroscopic events leading to disruptions.A systematic analysis of JET campaigns at high power in deuterium,full tritium,and DT,for a total of almost 2000 discharges,proves the effectiveness of the approach.The warning times are such that,depending on the radiation anomaly and the available actuators,the control system of future devices is expected to provide enough notice to enable deployment of effective prevention and avoidance strategies.
基金supported by the National MCF Energy R&D Program of China (No.2018YFE0310300)National Natural Science Foundation of China (No.51821005)。
文摘The detailed density perturbations provided by the advanced polarimeter-interferometer system(Polaris) during sawtooth collapse on the Joint Texas Experimental Tokamak(J-TEXT) are reported in this article.During a sawtooth collapse and the crash of plasma pressure at the center,it is found that the increase in density in the region between the inversion radius and mixing radius is poloidally asymmetrical,while the increase in temperature is poloidally symmetrical.The poloidal location where the density increases is dependent on the phase of the precursory m/n=1/1 kink mode.It is always out of phase with the hot core of the m/n=1/1 mode.The behaviors of density perturbations during sawtooth collapse observed in J-TEXT are beyond the expectations of the standard model,and this can shed new light on the understanding of sawtooth collapse.
基金supported by the National Natural Science Foundation of China(50773009)Science and Technology Commission of Shanghai Municipality,China(08JC1400600)~~
