Aquatic vegetation(AV)is vital for maintaining the health of lake ecosystems,with submerged aquatic vegetation(SAV)and floating/emergent aquatic vegetation(FEAV)representing clear and shaded states,respectively.Howeve...Aquatic vegetation(AV)is vital for maintaining the health of lake ecosystems,with submerged aquatic vegetation(SAV)and floating/emergent aquatic vegetation(FEAV)representing clear and shaded states,respectively.However,global SAV and FEAV dynamics are poorly understood due to data scarcity.To address this gap,we developed an innovative AV mapping algorithm and workflow using satellite imagery(1.4 million Landsat images)from 1989 to 2021 and created a global database of AV across 5,587 shallow lakes.Our findings suggest that AV covers 108,186 km2 on average globally,accounting for 28.9%(FEAV,15.8%;SAV,13.1%)of the total lake area.Over two decades,we observed a notable transition:SAV decreased by 30.4%,while FEAV increased by 15.6%,leading to a substantial net loss of AV.This global trend indicates a shift from clear to shaded conditions,increasingly progressing toward turbid states dominated by phytoplankton.We found that human-induced eutrophication was the primary driver of change until the early 2010s,after which global warming and rising lake temperatures became the dominant drivers.These trends serve as a warning sign of deteriorating lake health worldwide.With future climate warming and intensified eutrophication,these ongoing trends pose a significant risk of disrupting lake ecosystems.展开更多
High-order harmonic generation below ionization threshold of He atom in the laser field is investigated by solving the three-dimensional time-dependent Schrodinger equation. An angular momentum-dependent model potenti...High-order harmonic generation below ionization threshold of He atom in the laser field is investigated by solving the three-dimensional time-dependent Schrodinger equation. An angular momentum-dependent model potential of He atom was used for getting the accurate energy levels of singlet states. The satellite-peak structures of the below-threshold harmonic generation(BTHG) of He are observed. We analyze the emission properties of the BTHG by employing a synchrosqueezing transform technique. We find that the satellite-peak structures have two types related to two kinds of transitions. One is the transition of the dressed states of the excited states, the other is the transition between the excited states and the ground state in the field-free case. Furthermore, our results show that the maximum Stark shift of the 2 p state is about 0.9 Up(penderomotive energy), and that of the 4 p state is about 1.0 Up. It indicates that the energy difference between some satellite-and main-peaks of the BTHG can be used to measure the maximum Stark shift of the excited states of He atom in the laser field.展开更多
Accurate isotope shift factors of the 2s2p^（3,1）P_1~o–2s^2 ~1S_0 transitions in B II, obtained with the multi-configuration Dirac–Hartree–Fock and the relativistic configuration interaction methods, are reported....Accurate isotope shift factors of the 2s2p^（3,1）P_1~o–2s^2 ~1S_0 transitions in B II, obtained with the multi-configuration Dirac–Hartree–Fock and the relativistic configuration interaction methods, are reported. We found a linear correlation relation between the mass shift factors and the energies for the transitions concerned, considering all-order electron correlations. This relation is important for estimating the uncertainty in the calculation of isotope shift factors. These atomic data can be used to extract the nuclear mean-square charge radii of the boron isotopes with halo structures or to resolve the high precise spectroscopy of B II in astronomical observation.展开更多
This paper presents the operation of LCL type resonant arc welding power supply with fixed frequency and its steady state mathematical model. Using MathCAD to get the results and compared it to the results of the SP...This paper presents the operation of LCL type resonant arc welding power supply with fixed frequency and its steady state mathematical model. Using MathCAD to get the results and compared it to the results of the SPICE simulative experiment, we verify this mathematical model is correct.展开更多
We have developed an open-source cross-platform software toolkit entitled ACCEPT-NMR (Automated Crystal Contact Extrapolation/Prediction Toolkit for NMR) as a helpful tool to automate many of the complex tasks require...We have developed an open-source cross-platform software toolkit entitled ACCEPT-NMR (Automated Crystal Contact Extrapolation/Prediction Toolkit for NMR) as a helpful tool to automate many of the complex tasks required to find and visualize crystal contacts in structures of biomolecules and biomolecular assemblies. This toolkit provides many powerful features geared toward NMR spectroscopy and related disciplines, such as isotopic labeling, advanced visualization options, and reporting tools. Using this software, we have undertaken a survey of available chemical shift data in the literature and deposited in the BMRB, and show that the mere presence of one or more crystal contacts to a residue confers an approximately 65% likelihood of significant chemical shift perturbations (relative to solution NMR chemical shifts). The presence of each additional crystal contact subsequently increases this probability, resulting in predictive accuracies in excess of 80% in many cases. Conversely, the presence of a significant experimental chemical shift perturbation indicates a >60% likelihood of finding one or more crystal contacts to a particular residue. Pinpointing sites likely to experience large CSPs is critical to mapping solution NMR chemical shifts onto solid-state NMR data as a basis for preliminary assignments, and can thus simplify the assignment process for complex biomolecules. Mapping observed CSPs onto the molecular structure, on the other hand, can indicate the presence of crystal interfaces where no crystal structure is available. Finally, by detecting sites critical to intermolecular interfaces, ACCEPT-NMR can help guide experimental approaches (e.g. isotopic labeling schemes) to detect and probe specific inter-subunit interactions.展开更多
基金supported by the National Natural Science Foundation of China(42425104,42271377,and 42271114)the Key Laboratory of Lake and Watershed Science for Water Security(NKL2023-KP02 and NIGLAS2022GS09)+4 种基金the PIFI Project of the Chinese Academy of Sciences(2024PG0017 and 2024DC0005)the International Research Center of Big Data for Sustainable Development Goals(CBAS)(CBASYX0906)the TÜBITAK program BIDEB2232(118C250)the UKRI Natural Environment Research Council(NERC)Independent Research Fellowship(NE/T011246/1)the UK EO Climate Information Service(NE/X019071/1).
文摘Aquatic vegetation(AV)is vital for maintaining the health of lake ecosystems,with submerged aquatic vegetation(SAV)and floating/emergent aquatic vegetation(FEAV)representing clear and shaded states,respectively.However,global SAV and FEAV dynamics are poorly understood due to data scarcity.To address this gap,we developed an innovative AV mapping algorithm and workflow using satellite imagery(1.4 million Landsat images)from 1989 to 2021 and created a global database of AV across 5,587 shallow lakes.Our findings suggest that AV covers 108,186 km2 on average globally,accounting for 28.9%(FEAV,15.8%;SAV,13.1%)of the total lake area.Over two decades,we observed a notable transition:SAV decreased by 30.4%,while FEAV increased by 15.6%,leading to a substantial net loss of AV.This global trend indicates a shift from clear to shaded conditions,increasingly progressing toward turbid states dominated by phytoplankton.We found that human-induced eutrophication was the primary driver of change until the early 2010s,after which global warming and rising lake temperatures became the dominant drivers.These trends serve as a warning sign of deteriorating lake health worldwide.With future climate warming and intensified eutrophication,these ongoing trends pose a significant risk of disrupting lake ecosystems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674268,11764038,and 11765018)the Scientific Research Foundation of Physics of CPEE–NWNU and NWNU-LKQN-17-1,China
文摘High-order harmonic generation below ionization threshold of He atom in the laser field is investigated by solving the three-dimensional time-dependent Schrodinger equation. An angular momentum-dependent model potential of He atom was used for getting the accurate energy levels of singlet states. The satellite-peak structures of the below-threshold harmonic generation(BTHG) of He are observed. We analyze the emission properties of the BTHG by employing a synchrosqueezing transform technique. We find that the satellite-peak structures have two types related to two kinds of transitions. One is the transition of the dressed states of the excited states, the other is the transition between the excited states and the ground state in the field-free case. Furthermore, our results show that the maximum Stark shift of the 2 p state is about 0.9 Up(penderomotive energy), and that of the 4 p state is about 1.0 Up. It indicates that the energy difference between some satellite-and main-peaks of the BTHG can be used to measure the maximum Stark shift of the excited states of He atom in the laser field.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91436103,11404025,and 91536106)the Research Program of National University of Defense Technology,China(Grant No.JC15-0203)the China Postdoctoral Science Foundation(Grant No.2014M560061)
文摘Accurate isotope shift factors of the 2s2p^（3,1）P_1~o–2s^2 ~1S_0 transitions in B II, obtained with the multi-configuration Dirac–Hartree–Fock and the relativistic configuration interaction methods, are reported. We found a linear correlation relation between the mass shift factors and the energies for the transitions concerned, considering all-order electron correlations. This relation is important for estimating the uncertainty in the calculation of isotope shift factors. These atomic data can be used to extract the nuclear mean-square charge radii of the boron isotopes with halo structures or to resolve the high precise spectroscopy of B II in astronomical observation.
文摘This paper presents the operation of LCL type resonant arc welding power supply with fixed frequency and its steady state mathematical model. Using MathCAD to get the results and compared it to the results of the SPICE simulative experiment, we verify this mathematical model is correct.
文摘We have developed an open-source cross-platform software toolkit entitled ACCEPT-NMR (Automated Crystal Contact Extrapolation/Prediction Toolkit for NMR) as a helpful tool to automate many of the complex tasks required to find and visualize crystal contacts in structures of biomolecules and biomolecular assemblies. This toolkit provides many powerful features geared toward NMR spectroscopy and related disciplines, such as isotopic labeling, advanced visualization options, and reporting tools. Using this software, we have undertaken a survey of available chemical shift data in the literature and deposited in the BMRB, and show that the mere presence of one or more crystal contacts to a residue confers an approximately 65% likelihood of significant chemical shift perturbations (relative to solution NMR chemical shifts). The presence of each additional crystal contact subsequently increases this probability, resulting in predictive accuracies in excess of 80% in many cases. Conversely, the presence of a significant experimental chemical shift perturbation indicates a >60% likelihood of finding one or more crystal contacts to a particular residue. Pinpointing sites likely to experience large CSPs is critical to mapping solution NMR chemical shifts onto solid-state NMR data as a basis for preliminary assignments, and can thus simplify the assignment process for complex biomolecules. Mapping observed CSPs onto the molecular structure, on the other hand, can indicate the presence of crystal interfaces where no crystal structure is available. Finally, by detecting sites critical to intermolecular interfaces, ACCEPT-NMR can help guide experimental approaches (e.g. isotopic labeling schemes) to detect and probe specific inter-subunit interactions.
