| 431. |
- Le Page, Yannick, et al.
(författare)
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Seasonality of vegetation fires as modified by human action : observing the deviation from eco-climatic fire regimes
- 2010
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Ingår i: Global Ecology and Biogeography. - : Blackwell Publishing Lt. - 1466-822X .- 1466-8238. ; 19:4, s. 575-588
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Tidskriftsartikel (refereegranskat)abstract
- Aim In any region affected, fires exhibit a strong seasonal cycle driven by the dynamic of fuel moisture and ignition sources throughout the year. In this paper we investigate the global patterns of fire seasonality, which we relate to climatic, anthropogenic, land-cover and land-use variables. Location Global, with detailed analyses from single 1°× 1° grid cells. Methods We use a fire risk index, the Chandler burning index (CBI), as an indicator of the ‘natural’, eco-climatic fire seasonality, across all types of ecosystems. A simple metric, the middle of the fire season, is computed from both gridded CBI data and satellite-derived fire detections. We then interpret the difference between the eco-climatic and observed metrics as an indicator of the human footprint on fire seasonality. Results Deforestation, shifting cultivation, cropland production or tropical savanna fires are associated with specific timings due to land-use practices, sometimes largely decoupled from the CBI dynamics. Detailed time series from relevant locations provide comprehensive information about these practices and how they are adapted to eco-climatic conditions. Main conclusions We find a great influence of anthropogenic activities on global patterns of fire seasonality. The specificity of the main fire practices and their easy identification from global observation is a potential tool to support land-use monitoring efforts. Our results should also prove valuable in the development of a methodological approach for improving the representation of anthropogenic fire practices in dynamic global vegetation models.
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| 432. |
- Lee, Boon Q, et al.
(författare)
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A stochastic cascade model for Auger-electron emitting radionuclides
- 2016
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Ingår i: International Journal of Radiation Biology. - : Taylor & Francis. - 0955-3002 .- 1362-3095. ; 92:11, s. 641-653
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Tidskriftsartikel (refereegranskat)abstract
- To benchmark a Monte Carlo model of the Auger cascade that has been developed at the Australian National University (ANU) against the literature data. The model is applicable to any Auger-electron emitting radionuclide with nuclear structure data in the format of the Evaluated Nuclear Structure Data File (ENSDF). Sch€onfeld’s algorithms and the BRICC code were incorporated to obtain initial vacancy distributions due to electron capture (EC) and internal conversion (IC), respectively. Atomic transition probabilities were adopted from the Evaluated Atomic Data Library (EADL) for elements with atomic number, Z¼1–100. Atomic transition energies were evaluated using a relativistic Dirac- Fock method. An energy-restriction protocol was implemented to eliminate energetically forbidden transitions from the simulations. Calculated initial vacancy distributions and average energy spectra of 123I, 124I, and 125I were compared with the literature data. In addition, simulated kinetic energy spectra and frequency distributions of the number of emitted electrons and photons of the three iodine radionuclides are presented. Some examples of radiation spectra of individual decays are also given. Good agreement with the published data was achieved except for the outer-shell Auger and Coster-Kronig transitions. Nevertheless, the model needs to be compared with experimental data in a future study.
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| 433. |
- Li, Jiguang, et al.
(författare)
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Effects of the electron correlation and Breit and hyperfine interactions on the lifetime of the 2p53s states in neutral neon
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : Americal Physical Society. - 1050-2947 .- 1094-1622. ; 86:5
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Tidskriftsartikel (refereegranskat)abstract
- In the framework of the multiconfiguration Dirac-Hartree-Fock method, we investigate the transition properties of four excited states in the 2p53s configuration of neutral neon. The electron correlation effects are taken into account systematically by using the active space approach. The effect of higher-order correlation on fine structures is shown. We also study the influence of the Breit interaction and find that it reduces the oscillator strength of the 3 P1o-1 S0 transition by 17%. It turns out that the inclusion of the Breit interaction is essential even for such a light atomic system. Our ab initio calculated line strengths, oscillator strengths, and transition rates are compared with other theoretical values and experimental measurements. Good agreement is found except for the 3 P2o-1 S0 M2 transition for which discrepancies of around 15% between theories and experiments remain. In addition, the impact of hyperfine interactions on the lifetimes of the 3 P0o and 3 P2o metastable states is investigated for the 21Ne isotope (I=3/2). We find that hyperfine interactions reduce the lifetimes drastically. For the 3 P0o state the lifetime is decreased by a factor of 630.
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| 434. |
- Li, Jiguang, et al.
(författare)
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Hyperfine induced 1s2s^1S_0 -> 1s^2^1S_0 M1 transition of He-like ions
- 2009
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Ingår i: European Physical Journal D. - : EDP Sciences. - 1434-6060 .- 1434-6079. ; 51:3, s. 313-317
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Tidskriftsartikel (refereegranskat)abstract
- Hyperfine induced SS0 M1 transition probabilities of He-like ions have been calculated from relativistic configuration interaction wavefunctions including the frequency independent Breit interaction and QED effects. Present results for 151Eu and 155Gd are in good agreement with previous calculations [L.N. Labzowsky et al., Phys. Rev. A 63, 054105 (2001)]. Electronic data are given in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine induced decay rates to be estimated for any isotope. The results should be helpful for future experimental investigations on QED and parity non-conservation effects.
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| 435. |
- Li, Jiguang, et al.
(författare)
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Hyperfine-induced 2s2p3 3Po 0 - 2s22p2 3P0 transitions in C-like ions
- 2012
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Ingår i: Book of Abstracts. ; , s. 218-218
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Hyperfine-induced transitions (HIT) have recently attracted a lot of attention especially for its applications in astrophysics [1, 2]. Owing to their nature, HIT can be used to determine the relative isotope abundances and for low-density plasma diagnostics. For C-like ions, the fine structure interval between the 2s2p3 3Po0 and 2s2p3 3Po1 levels is quite small [3, 4], which results in strong state mixing in the presence of the hyperfine interactions. Consequently, large HIT probabilities are expected for many elements through the isoelectronic sequence. Using the GRASP2K package [5] and the MCDF-GME program [6] we calculate the HIT rates for a few abundant elements in stars. Stress is put on the interference effects between individual transition amplitudes that contribute to the HIT. In addition, some possible experiments will be suggested for a promising isotope analysis in stars.
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| 436. |
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| 437. |
- Li, Jiguang, et al.
(författare)
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Hyperfine induced transitions in He-like, Be-like and Mg-like ions
- 2009
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Ingår i: Journal of Physics, Conference Series. - : Bibliopolis, Edizioni di Filosofia e Scienze. - 1742-6588 .- 1742-6596. ; 194:15
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Tidskriftsartikel (refereegranskat)abstract
- Hyperfine quenching rates for 1s2s 1S0 → 1s2 1S0 M1 transition of He-like ions, 2s2p 3P0 → 3P2 → 2s2 1S0 E1 transition of Be-like ions and 3s3p 3P0 → 3s2 S0 E1 transition of Mg-like ions have been calculated from relativistic configuration interaction wavefunctions including the frequency independent Breit interaction and QED effects. The present study not only supply accurate theoretical values for developing atomic clocks, diagnosing low-density plasma, probing nuclear properties, exploring weak interaction beyond standard model, but also to analyze some characteristics in hyperfine induced transitions.
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| 438. |
- Li, Jiguang, et al.
(författare)
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Magnetic-field-dependent angular distributions and linear polarizations of emissions from the 2p53s 3P2 state in Ne-like ions
- 2014
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 90
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effect of an external magnetic field on the angular distribution and the linear polarization of the 2s22p53s 3Po 2 → 2s22p6 1S0 emission line in Ne-like ions. Since an electric dipole decay channel is opened by the magnetic field and competes with the inherent magnetic quadrupole transition, these properties strongly depend on the magnetic field strength, B. As an example, we discuss in some detail this transition in neonlike magnesium. This is of special interest, since the B-dependent angular distributions and linear polarization degrees are potentially unique diagnostic tools for the magnetic field in different plasmas.
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| 439. |
- Li, Jiguang, et al.
(författare)
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Mass and field isotope shift parameters for the 2s-2p resonance doublet of Lithium-like ions
- 2012
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Ingår i: Book of Abstracts. ; , s. 219-219
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Recently, it was shown that the dielectronic recombination measurements can be used for accurately inferring changes in the nuclear mean-square charge radii of highly-charged lithium-like neodymium [1]. To make use of this method for other elements and isotopes, mass and field isotope shift calculations are required in order to derive information about the nuclear charge distributions. In this work [2], we estimate the relativistic mass and field isotope shift factors for the two 2s2 S1/2−2p 2Po 1/2,3/2 transitions along the lithium isoelectronic sequence using the GRASP2K package [3, 4] based on the multiconfiguration Dirac-Hartree-Fock method. The detailed comparisons with the MCDF-gme [5] calculations and others will be illustrated. Adopting the calculated electronic parameters of isotope shifts, we analyze the competition between the mass and field shift contributions for the 2s − 2p resonance doublet along the isoelectronic sequence, with the assistance of the empirical relations between Z and the nuclear properties. It is found that the mass shifts and the field shifts possess similar orders of magnitude in the Z < 40 range, so that one should consider both of them for a relevant analysis of isotope shifts. The field shift contribution grows rapidly towards the high-Z region and becomes quickly dominant. Discussions are also made for the 2s 2S1/2 − 2p 2Po 1/2,3/2 line isotope shifts in the case of 150,142 Nd 57+ where the experimental values are available. The present results show that the higher-order nuclear moments often neglected in the calculation of the field shift should be considered for very highly charged ions in order to extract the δ⟨r2⟩ values from experiments.
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| 440. |
- Li, Jiguang, et al.
(författare)
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Mass and field isotope shift parameters for the 2s - 2p resonance doublet of lithium-like ions (Göteborg)
- 2012
-
Ingår i: Europhysics Conference Abstracts;36C. - : European Physical Society. ; , s. 76-76, s. 92-92
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Dielectronic recombination measurements have been proven to be a sensitive tool for deducing changes in the nuclear mean-square charge radii of highly-charged lithium-like neodymium. To make use of this method for other elements and isotopes, mass and field isotope shift calculations are required in order to derive information about the nuclear charge distributions. In this work, we estimate and discuss the relativistic mass and field isotope shift factors for the two 2s 2S1/2−2p 2Po 1/2,3/2 transitions along the lithium isoelectronic sequence. Using the GRASP2K package based on the multi-configuration Dirac-Fock method, the electron correlation and the Breit interaction are taken systematically into account in all the calculations. Adopting the calculated electronic parameters of isotope shifts, we qualitatively analyze the competition between the mass and field shift contributions for the 2s − 2p resonance doublet along the isoelectronic sequence, with the assistance of some empirical relations between Z and the nuclear properties. It is found that the mass shifts and the field shifts possess similar orders of magnitude in the Z < 40 range, so that one should consider both of them for a relevant analysis of isotope shifts, especially for extracting the nuclear mean-square charge radii. The field shift contribution grows rapidly towards the high-Z region and becomes quickly dominant. Quantitative discussions are also made for the 2s 2S1/2 − 2p 2Po 1/2,3/2 line isotope shifts in the case of 150,142Nd57+ for which experimental values are available. The present results show that the higher-order nuclear moments often neglected in the calculation of the field shift should be considered for very highly charged ions in order to extract the δhr2i values from experiments. The consistency between GRASP2K and MCDF-gme results will be illustrated.
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