The high level of noise is a special feature of the geomagnetic field on the territory of Slovenia. The tension of the Adriatic tectonic microplate, on which Slovenia entirely lies, was recognized as one of its source...The high level of noise is a special feature of the geomagnetic field on the territory of Slovenia. The tension of the Adriatic tectonic microplate, on which Slovenia entirely lies, was recognized as one of its sources. The interior of the Earth is also the source of geomagnetic jerks. They are impulses in the secular variation calculated on the basis of monthly or annual mean values of variation of the geomagnetic field. The paper presents an analysis of accelerations in a local magnetic field calculated on the bases of daily mean values of the magnetic field measured at PIA geomagnetic Observatory (Piran, Slovenia) in 2020. These accelerations indicate geomagnetic impulses at the regional level over days or weeks. Then these results are compared with the registered seismic activity in the West Balkans.展开更多
The significance of laser-driven polarized beam acceleration has been increasingly recognized in recent years.We propose an efficient method for generating polarized proton beams from a pre-polarized hydrogen halide g...The significance of laser-driven polarized beam acceleration has been increasingly recognized in recent years.We propose an efficient method for generating polarized proton beams from a pre-polarized hydrogen halide gas jet,utilizing magnetic vortex acceleration enhanced by a laser-driven plasma bubble.When a petawatt laser pulse passes through a pre-polarized gas jet,a bubble-like ultra-nonlinear plasma wave is formed.As a portion of the particles constituting this wave,background protons are swept by the acceleration field of the bubble and oscillate significantly along the laser propagation axis.Some of the pre-accelerated protons in the plasma wave are trapped by the acceleration field at the rear side of the target.This acceleration field is intensified by the transverse expansion of the laser-driven magnetic vortex,resulting in energetic polarized proton beams.The spin of energetic protons is determined by their precession within the electromagnetic field,which is described using the Thomas-Bargmann-Michel-Telegdi equation in analytical models and particle-in-cell simulations.Multidimensional simulations reveal that monoenergetic proton beams with an energy of hundreds of MeV,a beam charge of hundreds of pC,and a beam polarization of tens of percent can be produced at laser powers of several petawatts.Such laser-driven polarized proton beams have promise for application in polarized beam colliders,where they can be utilized to investigate particle interactions and to explore the properties of matter under extreme conditions.展开更多
This research work emphasizes the capability of delivering optically shaped targets through the interaction of nanosecond laser pulses with high-density gas-jet profiles,and explores proton acceleration in the near-cr...This research work emphasizes the capability of delivering optically shaped targets through the interaction of nanosecond laser pulses with high-density gas-jet profiles,and explores proton acceleration in the near-critical density regime via magnetic vortex acceleration(MVA).Multiple blast waves(BWs)are generated by laser pulses that compress the gas-jet into near-critical steep gradient slabs of a few micrometres thickness.Geometrical alternatives for delivering the laser pulses into the gas target are explored to efficiently control the characteristics of the density profile.The shock front collisions of the generated BWs are computationally studied by 3D magnetohydrodynamic simulations.The efficiency of the proposed target shaping method for MVA is demonstrated for TW-class lasers by a particle-in-cell simulation.展开更多
Coronal mass ejections(CMEs) and solar flares are the large-scale and most energetic eruptive phenomena in our solar system and able to release a large quantity of plasma and magnetic flux from the solar atmosphere in...Coronal mass ejections(CMEs) and solar flares are the large-scale and most energetic eruptive phenomena in our solar system and able to release a large quantity of plasma and magnetic flux from the solar atmosphere into the solar wind. When these high-speed magnetized plasmas along with the energetic particles arrive at the Earth, they may interact with the magnetosphere and ionosphere, and seriously affect the safety of human high-tech activities in outer space. The travel time of a CME to 1 AU is about 1–3 days, while energetic particles from the eruptions arrive even earlier. An efficient forecast of these phenomena therefore requires a clear detection of CMEs/flares at the stage as early as possible. To estimate the possibility of an eruption leading to a CME/flare, we need to elucidate some fundamental but elusive processes including in particular the origin and structures of CMEs/flares. Understanding these processes can not only improve the prediction of the occurrence of CMEs/flares and their effects on geospace and the heliosphere but also help understand the mass ejections and flares on other solar-type stars. The main purpose of this review is to address the origin and early structures of CMEs/flares, from multi-wavelength observational perspective. First of all, we start with the ongoing debate of whether the pre-eruptive configuration, i.e., a helical magnetic flux rope(MFR), of CMEs/flares exists before the eruption and then emphatically introduce observational manifestations of the MFR. Secondly, we elaborate on the possible formation mechanisms of the MFR through distinct ways. Thirdly, we discuss the initiation of the MFR and associated dynamics during its evolution toward the CME/flare. Finally, we come to some conclusions and put forward some prospects in the future.展开更多
Magnetic Resonance Imaging(MRI)serves as a crucial diagnostic tool in medical practice,yet its lengthy acquisition times pose challenges for patient comfort and clinical efficiency.Current deep learning approaches for...Magnetic Resonance Imaging(MRI)serves as a crucial diagnostic tool in medical practice,yet its lengthy acquisition times pose challenges for patient comfort and clinical efficiency.Current deep learning approaches for accelerating MRI acquisition face difficulties in managing data variability caused by different scanner vendors or imaging protocols.This research investigates the use of transfer learning in variational deep learning models to enhance generalization capabilities.We collect 135 ACR phantom samples from 3.0T GE and SIEMENS MRI scanners,following standard ACR guidelines,to study vendor-specific generalization.Additionally,the fastMRI brain dataset,a recognized benchmark for MRI acceleration,is utilized to evaluate performance across diverse acquisition sequences.Through comprehensive testing,we identify vendor and sequence inconsistencies as key hurdles for accelerated MRI generalization.To overcome these challenges,we introduce a feature refinement-based transfer learning method,achieving significant gains over baseline models in both vendor and sequence generalization tasks.Moreover,we incorporate experience replay to mitigate catastrophic forgetting,resulting in notable performance stability.For vendor generalization,our approach reduces Peak Signal Noise-to-Ratio(PSNR)and Structural SIMilarity(SSIM)degradation by 25.55%and 9.5%,respectively.Similarly,for sequence transfer,forgetting is reduced by 3.5%(PSNR)and 2%(SSIM),establishing a robust framework with substantial improvements.展开更多
The fast extraction kicker system is one of the most important accelerator components and the main source of impedance in the Rapid Cycling Synchrotron of the China Spallation Neutron Source. It is necessary to unders...The fast extraction kicker system is one of the most important accelerator components and the main source of impedance in the Rapid Cycling Synchrotron of the China Spallation Neutron Source. It is necessary to understand the kicker impedance before its installation into the tunnel. Conventional and improved wire methods are employed in the impedance measurement. The experimental results for the kicker impedance are explained by comparison with simulation using CST PARTICLE STUDIO. The simulation and measurement results confirm that the window-frame ferrite geometry and the end plate are the important structures causing coupling impedance. It is proved in the measurements that the mismatching from the power form network to the kicker leads to a serious oscillation sideband of the longitudinal and vertical impedance and the oscillation can be reduced by ferrite absorbing material.展开更多
文摘The high level of noise is a special feature of the geomagnetic field on the territory of Slovenia. The tension of the Adriatic tectonic microplate, on which Slovenia entirely lies, was recognized as one of its sources. The interior of the Earth is also the source of geomagnetic jerks. They are impulses in the secular variation calculated on the basis of monthly or annual mean values of variation of the geomagnetic field. The paper presents an analysis of accelerations in a local magnetic field calculated on the bases of daily mean values of the magnetic field measured at PIA geomagnetic Observatory (Piran, Slovenia) in 2020. These accelerations indicate geomagnetic impulses at the regional level over days or weeks. Then these results are compared with the registered seismic activity in the West Balkans.
基金supported by the National Natural Science Foundation of China(Grant Nos.12075081 and 12404395)the Innovation Group Project of the Natural Science Foundation of Hubei Province of China(Grant No.2024AFA038)Bin Liu acknowledges the support of Guangdong High Level Innovation Research Institute Project,Grant No.2021B0909050006.
文摘The significance of laser-driven polarized beam acceleration has been increasingly recognized in recent years.We propose an efficient method for generating polarized proton beams from a pre-polarized hydrogen halide gas jet,utilizing magnetic vortex acceleration enhanced by a laser-driven plasma bubble.When a petawatt laser pulse passes through a pre-polarized gas jet,a bubble-like ultra-nonlinear plasma wave is formed.As a portion of the particles constituting this wave,background protons are swept by the acceleration field of the bubble and oscillate significantly along the laser propagation axis.Some of the pre-accelerated protons in the plasma wave are trapped by the acceleration field at the rear side of the target.This acceleration field is intensified by the transverse expansion of the laser-driven magnetic vortex,resulting in energetic polarized proton beams.The spin of energetic protons is determined by their precession within the electromagnetic field,which is described using the Thomas-Bargmann-Michel-Telegdi equation in analytical models and particle-in-cell simulations.Multidimensional simulations reveal that monoenergetic proton beams with an energy of hundreds of MeV,a beam charge of hundreds of pC,and a beam polarization of tens of percent can be produced at laser powers of several petawatts.Such laser-driven polarized proton beams have promise for application in polarized beam colliders,where they can be utilized to investigate particle interactions and to explore the properties of matter under extreme conditions.
基金The authors acknowledge support of this work by the project‘ELI-LASERLAB Europe Synergy,HiPER&IPERIONCH.gr’(MIS 5002735),which is implemented under the action‘Reinforcement of the Research and Innovation Infrastructure’,funded by the Operational programme‘Competitiveness,Entrepreneurship and Innovation’(NSRF 2014-2020)and co-financed by Greece and the European Union(European Regional Development Fund)supported by computational time granted by the Greek Research and Technology Network(GRNET)in the National HPC facility-ARIS-under project ID pr011027-LaMPIOS+1 种基金This work has been carried out within the framework of the EUROfusion Consortium,funded by the European Union via the Euratom Research and Training Programme(grant agreement No.101052200-EUROfusion)the Hellenic National Program of Controlled Thermonuclear Fusion.
文摘This research work emphasizes the capability of delivering optically shaped targets through the interaction of nanosecond laser pulses with high-density gas-jet profiles,and explores proton acceleration in the near-critical density regime via magnetic vortex acceleration(MVA).Multiple blast waves(BWs)are generated by laser pulses that compress the gas-jet into near-critical steep gradient slabs of a few micrometres thickness.Geometrical alternatives for delivering the laser pulses into the gas target are explored to efficiently control the characteristics of the density profile.The shock front collisions of the generated BWs are computationally studied by 3D magnetohydrodynamic simulations.The efficiency of the proposed target shaping method for MVA is demonstrated for TW-class lasers by a particle-in-cell simulation.
基金supported by the Fundamental Research Funds for the Central Universitiesthe National Natural Science Foundation of China (Grant Nos. 11303016, 11373023, 11533005, 11203014)National Key Basic Research Special Foundation (Grant No. 2014CB744203)
文摘Coronal mass ejections(CMEs) and solar flares are the large-scale and most energetic eruptive phenomena in our solar system and able to release a large quantity of plasma and magnetic flux from the solar atmosphere into the solar wind. When these high-speed magnetized plasmas along with the energetic particles arrive at the Earth, they may interact with the magnetosphere and ionosphere, and seriously affect the safety of human high-tech activities in outer space. The travel time of a CME to 1 AU is about 1–3 days, while energetic particles from the eruptions arrive even earlier. An efficient forecast of these phenomena therefore requires a clear detection of CMEs/flares at the stage as early as possible. To estimate the possibility of an eruption leading to a CME/flare, we need to elucidate some fundamental but elusive processes including in particular the origin and structures of CMEs/flares. Understanding these processes can not only improve the prediction of the occurrence of CMEs/flares and their effects on geospace and the heliosphere but also help understand the mass ejections and flares on other solar-type stars. The main purpose of this review is to address the origin and early structures of CMEs/flares, from multi-wavelength observational perspective. First of all, we start with the ongoing debate of whether the pre-eruptive configuration, i.e., a helical magnetic flux rope(MFR), of CMEs/flares exists before the eruption and then emphatically introduce observational manifestations of the MFR. Secondly, we elaborate on the possible formation mechanisms of the MFR through distinct ways. Thirdly, we discuss the initiation of the MFR and associated dynamics during its evolution toward the CME/flare. Finally, we come to some conclusions and put forward some prospects in the future.
基金supported by the following grants:the National Institutes of Health(Nos.RF1AG073424 and P30AG072980)the Arizona Department of Health Services(No.CTR057001).
文摘Magnetic Resonance Imaging(MRI)serves as a crucial diagnostic tool in medical practice,yet its lengthy acquisition times pose challenges for patient comfort and clinical efficiency.Current deep learning approaches for accelerating MRI acquisition face difficulties in managing data variability caused by different scanner vendors or imaging protocols.This research investigates the use of transfer learning in variational deep learning models to enhance generalization capabilities.We collect 135 ACR phantom samples from 3.0T GE and SIEMENS MRI scanners,following standard ACR guidelines,to study vendor-specific generalization.Additionally,the fastMRI brain dataset,a recognized benchmark for MRI acceleration,is utilized to evaluate performance across diverse acquisition sequences.Through comprehensive testing,we identify vendor and sequence inconsistencies as key hurdles for accelerated MRI generalization.To overcome these challenges,we introduce a feature refinement-based transfer learning method,achieving significant gains over baseline models in both vendor and sequence generalization tasks.Moreover,we incorporate experience replay to mitigate catastrophic forgetting,resulting in notable performance stability.For vendor generalization,our approach reduces Peak Signal Noise-to-Ratio(PSNR)and Structural SIMilarity(SSIM)degradation by 25.55%and 9.5%,respectively.Similarly,for sequence transfer,forgetting is reduced by 3.5%(PSNR)and 2%(SSIM),establishing a robust framework with substantial improvements.
基金Supported by National Natural Science Foundation of China(11175193,11275221)
文摘The fast extraction kicker system is one of the most important accelerator components and the main source of impedance in the Rapid Cycling Synchrotron of the China Spallation Neutron Source. It is necessary to understand the kicker impedance before its installation into the tunnel. Conventional and improved wire methods are employed in the impedance measurement. The experimental results for the kicker impedance are explained by comparison with simulation using CST PARTICLE STUDIO. The simulation and measurement results confirm that the window-frame ferrite geometry and the end plate are the important structures causing coupling impedance. It is proved in the measurements that the mismatching from the power form network to the kicker leads to a serious oscillation sideband of the longitudinal and vertical impedance and the oscillation can be reduced by ferrite absorbing material.
