| 1. |
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| 2. |
- Andersson, M, et al.
(författare)
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A presentation of three ab initio atomic structure calculation projects
- 2004
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Ingår i: 8th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS 8). ; , s. 22-22
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Konferensbidrag (refereegranskat)abstract
- Three theoretical atomic structure projects of interest for the astrophysical community and the lightning industry which are partially finished will be presented. Extensive ab initio calculations of properties of astrophysical interest has been done or are under its way for Ga I, Ga II, Ga III, In II and In III. The aim of the project is to also make calculations for In I, Tl I, Tl II and Tl III. Results will be presented for gf-values, hyperfine structure, hyperfine quenching, isotope shift and gf-factors for parts of the Ga I and Ga II systems to give a flavor of what we are doing. Large spectroscopic calculations of transition probabilities for some of the neutral noble gases has been done or are under its way. This project is done as a part of a fluorescent light project in which the goal is to simulate the plasma in a fluorescent tube. A large number of transition probabilities will be presented for Kr I. Developing of programs as a part of the MCHF and GRASP packages has been done for implementing the effects on ions in an external magnetic field. An example of our treatment will be given
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| 3. |
- Andersson, Martin, et al.
(författare)
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Analysis of the competition between forbidden and hyperfine-induced transitions in Ne-like ions
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate the decay of the |2p53sP03) state in neon-like ions along the isoelectronic sequence ranging from Z=10 to Z=35. In the absence of a nuclear spin, the magnetic dipole transition to |2p53sP13) is the dominating decay channel. However, for isotopes with a nuclear spin, the interaction between the nuclear magnetic dipole moment and the electronic field introduces a mixing of |2p53sP13) and |P11) into the |P03) state, which in turn opens up a competing hyperfine-induced electric dipole decay channel to the ground state. This hyperfine-induced transition channel clearly dominates over the magnetic dipole channel for the neutral end of the isoelectronic sequence, when present. We give values for the rates of both these competing channels and discuss how the introduction of the hyperfine-induced transition channel could have a dramatic influence on the spectrum, not only because it introduces a new line, but also since it can substantially decrease the intensity of the magnetic dipole 2p53sP03→2p53sP13 line and affect the predicted ionization balance in different plasmas.
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| 4. |
- Andersson, Martin, et al.
(författare)
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Effects on intercombination transition rates and branching ratios - the UV0.01 (3s(2)3p(2) P-3(1,2)-3s3p(3 5)S(2)) multiplet in SiI-like ions revisited
- 2007
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:4, s. 709-726
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Tidskriftsartikel (refereegranskat)abstract
- We report on large-scale ab initio calculations for intercombination lines in Si I-like ions. Two measurable quantities, the lifetime of the 3s3p(3 5)S(2) level and the branching ratio of the two lines are discussed, to infer the importance of different features of our calculations. The effects of core polarization, two-body spin-dependent operators and Dirac contra Breit-Pauli approaches are discussed. Earlier calculations are reviewed and evaluated. The calculated lifetimes are in good agreement with experiments, while a discrepancy persists for branching ratios.
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| 5. |
- Andersson, Martin, et al.
(författare)
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HYPERFINE-DEPENDENT gf -VALUES OF Mn i LINES IN THE 1.49–1.80 μm H BAND
- 2015
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 216:1
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Tidskriftsartikel (refereegranskat)abstract
- The three Mn I lines at 17325, 17339, and 17349 angstrom are among the 25 strongest lines (log(gf) > 0.5) in the H band. They are all heavily broadened due to hyperfine structure, and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infrared (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines cannot be described in the conventional way using the diagonal A and B hyperfine interaction constants. The off-diagonal hyperfine interaction not only has a large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and the gf-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, we achieved agreement between our synthetic and experimental spectra. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modeled in the relevant region, 1.73-1.74 mu m, using our theoretically predicted gf-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and gf-values for all the 3d(5)4s(S-7)4d e(6)D - 3d(5)4s(S-7)4f w(6)F hyperfine lines are available as supporting material, whereas only the stronger lines are presented and discussed in detail in this paper.
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| 6. |
- Andersson, M, et al.
(författare)
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Hyperfine-dependent lifetimes in Be-like ions
- 2009
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 79:3
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of hyperfine quenching of the two metastable levels 1s(2)2s2p P-3(0) and P-3(2) have been performed along the Be-like isoelectronic sequence for ions between Z=6-22. It is shown that the lifetime of the latter level is sensitive to hyperfine quenching in the beginning of the isoelectronic sequence, but the sensitivity decreases towards the high-Z end. It is also shown that the hyperfine dependent branching fraction between the 2s(2) S-1(0)-2s2p P-3(2) and the 2s2p P-3(1)-2s2p P-3(2) transitions can lead to some rather drastic changes in the spectra. Our predicted value of 0.677 s(-1) for the hyperfine-induced 2s(2) S-1(0)-2s2p P-3(0) transition rate for Ti-47(18+) are in disagreement with a recent experimental value of 0.56(3) s(-1). Our calculated values of this quenching are in agreement with other recent calculations all along the sequence.
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| 7. |
- Andersson, Martin, et al.
(författare)
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Hyperfine dependent lifetimes in Mg-like ions
- 2010
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:9
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of the hyperfine quenching of the two metastable levels 1s(2)2s(2)2p(6)3s3p P-3(0) and P-3(2) have been performed along the magnesium-like iso-electronic sequence ranging from Z = 12 to Z = 31. It is shown that the lifetime of the latter level is sensitive to hyperfine quenching in the beginning of the sequence, but that this sensitivity decreases going to higher Z. It is also shown that the branching fractions of the 3s(2) S-1(0)-3s3p P-3(2) and 3s3p P-3(1)-3s3p P-3(2) transitions are very sensitive to hyperfine quenching, which could lead to some dramatic effects in the spectrum. Our predicted transition rates of the hyperfine induced 3s(2) S-1(0)-3s3p P-3(0) transition are compared to earlier results and some disagreements are found and explained. The present predicted lifetime of 3s3p P-3(0) in Al-27(+) is slightly longer than the recent measurement, but in better agreement than earlier predictions.
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| 8. |
- Andersson, M., et al.
(författare)
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Hyperfine-interaction-dependent 4s4p P-3(2) lifetimes in Zn-like ions
- 2008
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 78:6
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical studies on hyperfine-interaction-dependent lifetimes of the 4s4p P-3(2) states of Zn-like ions are reported in this paper. A systematic investigation along the isoelectronic sequence shows that the lifetime of the 4s4p P-3(2) level is very sensitive to hyperfine interaction at the beginning of the sequence, but gets less sensitive going to the higher end. The intensity ratio between the 4s(2) S-1(0)-4s4p P-3(2) and the 4s4p P-3(1)-4s4p P-3(2) transitions was also investigated and it is shown that this ratio is very sensitive to hyperfine interaction. In some isotopes the two branches are dominated by transitions from different upper hyperfine levels. Our research also reveals that the hyperfine-induced electric dipole transitions contribute to the transitions of 4s(2) S-1(0)-4s4p P-3(2) at about the same level as, or even higher than, M2 transitions whenever the nucleus has a spin. This is true all along the isoelectronic sequence.
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| 9. |
- Andersson, M., et al.
(författare)
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Hyperfine-state-dependent lifetimes along the Ni-like isoelectronic sequence
- 2008
-
Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:4, s. 12-042509
-
Tidskriftsartikel (refereegranskat)abstract
- An investigation of the lifetime of the 3d(9)4s D-3(3) level along a part of the nickel-like isoelectronic sequence has been performed. The focus of this work has been to evaluate the importance of the hyperfine induced electric quadrupole channel of the 3d(10) S-1(0)-3d(9)4s D-3(3) transition for isotopes with nuclear spin. Comparisons between the magnetic octupole transition rate and the hyperfine-induced electric quadrupole transition rate shows that the hyperfine quenching is of importance along the whole isoelectronic sequence. At the low-Z end the hyperfine induced electric quadrupole transition channel dominates, being several orders of magnitude larger than the rate for the magnetic octupole transition channel, while for higher Z the two rates are of comparable size.
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| 10. |
- Andersson, Martin, et al.
(författare)
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Systematic studies of highly excited Rydberg states in ions with two valance electrons
- 2006
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:12, s. 2815-2826
-
Tidskriftsartikel (refereegranskat)abstract
- A method, based on the multiconfiguration Hartree-Fock approach, for ab initio calculations of Rydberg states has been developed. The method has been tested for a number of highly excited Rydberg states, with quantum numbers l = 4 - 8 and n <= 9, in Mg-like and Be-like ions. The results are compared with Hartree-Fock calculations to investigate the influence of correlation and, to a lesser extent, relativistic effects. The theoretical spectra for Cl VI and the lifetimes of the 2s6g-levels in O V are in excellent agreement with experimental results. More limited calculations have also been done for some Rydberg series in S V and Ar VII to illustrate the changing influence of perturbers along the isoelectronic sequence. The difficulties of using isoelectronic extrapolation/interpolation in making predictions for this kind of systems are discussed.
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| 11. |
- Beideck, DJ, et al.
(författare)
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Lifetimes of 5d96p and 5d86s6p levels in Hg iii
- 1993
-
Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 47:2, s. 884-889
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental and theoretical studies of lifetimes and transition probabilities for doubly ionized mercury, Hg III, are reported. Such data are currently of great astrophysical interest because observations with the Goddard high resolution spectrograph on board the Hubble space telescope have shown some 5d(9)6s-5d(9)6p transitions of Hg III in the spectrum of the chemically peculiar star chi Lupi. We now report experimental lifetimes for some selected 5d(9)6p and 5d(8)6s6p levels, determined by beam-foil spectroscopy, and compare the results with theoretical transition probabilities based on relativistic multiconfiguration Dirac-Fock calculations.
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| 12. |
- Bieron, Jacek, et al.
(författare)
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Computational Atomic Structure
- 2012
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Ingår i: Program and Abstracts. ; , s. 56-56
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There is an increasing demand for accurate atomic data due to advancements in experimental techniques and investments in large scale research facilities. In astrophysics the quality and resolution of solar and stellar spectra has so improved that the accuracy of atomic data is frequently a limiting factor in the interpretation. Accurate atomic data are also required in plasma physics and in other emerging areas such as laser spectroscopy on isotope separators, X-ray lithography, and lighting research. The needs include accurate transition energies, fine- and hyperfine structures, isotope shifts as well as parameters related to interaction with external magnetic fields. Also there is a constant need for transition rates between excited states. Data are needed for a wide range of elements and ionization stages. To meet the demands for accurate atomic data the COMPutational Atomic Structure (COMPAS) group has been formed. The group is involved in developing state of the art computer codes for atomic calculations in the non-relativistic scheme with relativistic corrections in the Breit-Pauli approximation [1] as well as in the fully relativistic domain. Here we describe new developments of the GRASP2K relativistic atomic structure code [2, 3]. We present results for a number of systems and properties to illustrate the potential and restriction of computational atomic structure. Among the properties are hyperfine structures and hyperfine quenched rates, Zeeman splittings in intermediate fields, isotope shifts and transition rates [4]. We also discuss plans for future code developments.
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| 13. |
- Brage, Tomas, et al.
(författare)
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A review of intercombination lines in beryllium-like ions
- 2000
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 98:16, s. 1057-1065
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Forskningsöversikt (refereegranskat)abstract
- Theoretical and experimental results for the 2s(2) S-1(0)-2s2p P-3(1) intercombination line in beryllium-like ions are reviewed and revised, and some new data are presented. The uncertainty in the resulting transition rate is estimated, by using convergence of systematic calculations, accuracy of energy properties and theoretical tests, and is used to evaluate the accuracy of present and other calculations, and arrive at a recommended theoretical value, with uncertainty estimates.
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| 14. |
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| 15. |
- Brage, Tomas, et al.
(författare)
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Atomic calculations inspired by the GHRS - gf-values, hyperfine structure constants, and isotope shifts for heavy elements
- 1998
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Ingår i: The Scientific Impact of the Goddard High Resolution Spectrograph (Astronomical Society of the Pacific Conference Series). - 1886733635 ; 143, s. 378-381
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Konferensbidrag (refereegranskat)abstract
- GHRS observations of chemically peculiar stars have initiated a new project for calculating atomic properties of heavy elements (Z approximate to 80). The method used is based on large-scale, fully relativistic MCDF, and the data involve accurate gf-values, hyperfine structure parameters, and relative isotope shifts.
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| 16. |
- Brage, Tomas, et al.
(författare)
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Core polarization effects on oscillator strengths in neutral zinc
- 1992
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 45:1, s. 43-48
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Tidskriftsartikel (refereegranskat)abstract
- The effect of core polarization on the oscillator strength for the resonance transition in neutral zinc is investigated using the multiconfiguration Hartree Fock approach. The use of model potentials and corrections to the dipole operator is compared to a method, where the core polarization is represented by including configuration state functions, with one hole in the 3d core subshell in the CI-expansion. The latter, which is labeled explicit CI, gives results in good agreement with experiment. The reason for deviations in earlier calculations is discussed, together with the validity of the comparison of length and velocity forms of oscillator strengths, as a test of accuracy. The dependence of the model potential results on the choice of cut-off radius is investigated.
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| 17. |
- Brage, Tomas, et al.
(författare)
-
Core values work in academia : – with experiences from Lund University
- 2016
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Rapport (populärvet., debatt m.m.)abstract
- What are core values and what use are they? How can the central governmentcore values translate to academia? Why do the ‘statutory’, political valuesend up in conflict with academic values based on the specific culture ofuniversities? What methods and what examples exist for active and effectivecore values work at a university? And how do you implement core values sothat they are present and meaningful within the organisation? This report from the “Core values project at Lund University” attempts to answer these questions, problematise various values and provide support for core values work at a ‘typical’ university. The book contains the history of core values, their legaland cultural background in general and at Lund University in particular.It provides examples of methods which can be applied in core values work, such as a deeper understanding of discrimination and master suppression techniques, norm criticism and inclusive teaching. It concludes with an inventory of relevant projects at Lund University
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| 18. |
- Brage, Tomas, et al.
(författare)
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Determination of hyperfine-induced transition rates from observations of a planetary nebula
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 89:28
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Tidskriftsartikel (refereegranskat)abstract
- Observations of the planetary nebula NGC3918 made with the STIS instrument on the Hubble Space Telescope reveal the first unambiguous detection of a hyperfine-induced transition 2s2p P-3(0)o-->2s(2) S-1(0) in the berylliumlike emission line spectrum of N IV at 1487.89 Angstrom. A nebular model allows us to confirm a transition rate of 4x10(-4) sec(-1)+/-33% for this line. The measurement represents the first independent confirmation of the transition rate of hyperfine-induced lines in low ionization stages, and it provides support for the techniques used to compute these transitions for the determination of very low densities and isotope ratios.
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| 19. |
- Brage, Tomas, et al.
(författare)
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Effects of Core-valence and Core-core Correlation On the Line-strength of the Resonance Lines In Li-i and Na-i
- 1994
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 49:3, s. 2181-2184
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Tidskriftsartikel (refereegranskat)abstract
- The resonance lines in Li I and Na I both exhibit a puzzling discrepancy between experiment and accurate ab initio calculations. Only results from a semiempirical method, that in principal neglects core-core correlation, agree with the experiments. The agreement with a multiconfiguration Hartree-Fock calculation, including only core-valence correlation, shows that this might be fortuitous. A method for including some core-core correlation is designed and gives results in excellent agreement with other accurate ab initio methods.
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| 20. |
- Brage, Tomas, et al.
(författare)
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Experimental and theoretical study of core-excited states of Mg II
- 1991
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 44:4, s. 336-342
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Tidskriftsartikel (refereegranskat)abstract
- The 2p(5)3s3p, 3p2, 3s4s, 3s3d, and 3s4f core-excited configurations of Mg II have been studied experimentally by beam-foil spectroscopy and theoretically by multiconfiguration Hartree-Fock calculations with Breit-Pauli relativistic corrections. The previously established energy levels belonging to the former four configurations have been reexamined leading to significant corrections of the 3p2 4D and 3s4s 4P levels. Many previously unidentified spectral lines have now been assigned allowing a confident set of energy levels of the nearly degenerate 3p2, 3s4s, and 3s3d configurations to be established. in addition, the higher lying 3s4f states have been studied allowing the assignment of the prominent, but unidentified line at 3480 angstrom to the 3s4f 4G11/2 --> 3s3d 4F9/2 transition, and the establishment of some 3s3d states which primarily decay by autoionization.
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| 21. |
- Brage, Tomas, et al.
(författare)
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Forbidden and Unexpected atomic transitions
- 2009
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Ingår i: AIP Conference Proceedings (ICAMDATA-2008). - : AIP. - 0094-243X .- 1551-7616. ; 1125, s. 18-28
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Konferensbidrag (refereegranskat)abstract
- This paper includes a discussion and classification of what is generally referred to as '"Forbidden lines"' in atomic physics. Historical and important examples are reviewed, in light of their challenge to computations and remaining disagreements between experiment and theory. We also review some recent results on what could be labeled the third generation of unexpected transitions, induced by hyperfine quenching.
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| 22. |
- Brage, Tomas, et al.
(författare)
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Hyperfine induced transitions as diagnostics of isotopic composition and densities of low-density plasmas
- 1998
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 500:1, s. 507-521
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Tidskriftsartikel (refereegranskat)abstract
- The J = 0 --> J' = 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperfine (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the nsnp P-3(J)0 --> nS(2 1)S(J'= 0) transitions in ions of the Be (n = 2) and Mg (n = 3) isoelectronic sequences. The HPF induced decay rates for the J = 0 --> J' = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes, and when present are typically 1 or 2 orders of magnitude smaller than the decay rates of the magnetic quadrupole (J = 2 --> J' = 0) transitions for these ions. Several HPF induced transitions are potentially of astrophysical interest in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission-line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV and EUV solar and nebular data in light of these new results and suggest possible applications for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2, we derive an upper limit of 0.1 for C-13/C-12 from Goddard High-Resolution Spectrograph data obtained by Clegg. It is likely that more stringent limits could be obtained using newer data with higher sensitivities in a variety of objects.
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| 23. |
- Brage, Tomas, et al.
(författare)
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Intercombination and allowed transitions in O IV
- 1996
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 464:2, s. 1030-1043
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Tidskriftsartikel (refereegranskat)abstract
- We report on large-scale ab initio multiconfiguration Hartree-Fock calculations for important multiplets including the UV 0.01 multiplet, 2s(2)2p(2)P(J-)2s2p(24)P(J'), in O IV. The resulting transition probabilities should be accurate to +/- 5%-10% for intersystem lines and 1% or better for permitted lines. We present new calculations of line emission coefficients using these transition probabilities and collisional rate coefficients published by Zhang, Graziani, & Pradhan in 1994. We readdress the use of these lines as diagnostics of electron densities, paying particular attention to uncertainties in density determinations. We find (1) the absolute uncertainties in derived densities are difficult to assess, but are at least +/-40%, controlled by uncertainties in collision strengths; (2) our new calculations bring observed and computed line ratios into better agreement (earlier papers yielding systematically different densities make the agreement worse); (3) there is additional evidence for strong blends in the 1404.8 emission feature, as argued by other authors, and/or evidence for inaccurate laboratory wavelengths; and (4) the computed branching ratios are in good agreement with observed ratios to within observational uncertainties of +/-7%. We determine electron densities in a variety of solar features from HRTS data from the first and second flights of this instrument. The derived electron densities vary remarkably little between quiet Sun network and active regions, but resonance line intensities vary dramatically, and we discuss reasons for this. Finally, we discuss how new high-quality data from the SUMER instrument to be flown on Solar and Heliosphereic Observatory (SOHO) could be used to address outstanding problems concerning blends and heating of the solar transition region.
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| 24. |
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| 25. |
- Brage, Tomas, et al.
(författare)
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MCHF calculations of autoionization widths in two- and three-electron systems
- 1993
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 26:4, s. 621-640
-
Tidskriftsartikel (refereegranskat)abstract
- We present calculations of autoionization widths using a fully numerical multiconfigurational Hartree-Fock method (MCHF). Energy positions and autoionization rates are given for several doubly-excited states lying below the n = 2 threshold in He I and H-. Particular attention is given to orthogonality considerations in the computation of the autoionization widths. The method is extended to the 1s2p2 2D, 1s2s(3S)3d 2D and 1s2s(3S)4d 2D states of Li I. To the authors' knowledge, our MCHF value, 12.5 meV, is the first result obtained for the autoionization width of the 1s2s(3S)4d 2D state. Comparison is made with other theoretical results and with experimental values and we point out several inconsistencies between the two sets of results.
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| 26. |
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| 27. |
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| 28. |
- Brage, Tomas, et al.
(författare)
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Resolving a discrepancy between experimental and theoretical lifetimes in atomic negative ions
- 2017
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:2
-
Tidskriftsartikel (refereegranskat)abstract
- A recent measurement of the lifetime of the excited 3p5 state in the S- negative ion, which is dominated by a forbidden magnetic dipole transition to the 2 P3/ 2 ground state, reveals a discrepancy with earlier theoretical predictions. To investigate this we have performed systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations for this system. After including a careful treatment of correlation and relativistic effects, we predict a well-converged value for this lifetime, with an uncertainty considerably less than 1%, thereby removing the apparent conflict between theory and experiment. We also show that this result corresponds to the non-relativistic limit in the LS coupling approximation for the magnetic dipole transition within this 2 P term. In addition we demonstrate the usefulness of the latter approach for 2 P transitions in O-, Se- and Te-, as well as for analogous M1 transitions within 2 D terms in Ni- and Pt- ions.
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| 29. |
- Brage, Tomas, et al.
(författare)
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Spectral lines for polarization measurements of the coronal magnetic field. III. Atomic data for SiIX
- 2000
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 540:2, s. 1114-1118
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Tidskriftsartikel (refereegranskat)abstract
- We report on large-scale ab initio multiconfiguration Dirac-Fock (MCDF) calculations for spectral lines of Si IX, with emphasis on the forbidden transitions 2p(2) P-3(J-->J'). The J = 0 --> J' = 1 transition at 3.9346 mu m holds promise as a diagnostic of coronal magnetic fields if and when future coronagraphic instruments can measure the polarized light at this wavelength.
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| 30. |
- Brage, Tomas, et al.
(författare)
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The 1s2s2p2 5P-1s2p3 5S transition in Be I-like ions
- 1988
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 21:14, s. 2563-2569
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Tidskriftsartikel (refereegranskat)
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| 31. |
- Brage, Tomas, et al.
(författare)
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Theoretical oscillator strengths and hyperfine structure in HgII
- 1999
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 513:1, s. 524-534
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical model ion for Hg II, including oscillator strengths and hyperfine structure constants for a large number of transitions and levels. Different computational models have been used, depending on the observability of the lines and their importance in spectral synthesis of stellar atmospheres. For the resonance lines, we use highly systematic, accurate, and fully relativistic multiconfiguration Dirac-Fock methods. These methods are well suited to an accurate treatment of both the relativistic problem and the strong correlation effects in this ion. The predicted gf-values are probably accurate to within a few percent. A larger number of transitions are treated with a more flexible, but less accurate, version of the method. This is based on the idea of crosswise optimization to represent a number of states in the same calculation. The results are used in stellar atmosphere models, assuming local thermodynamic equilibrium (LTE), where a line-by-line investigation is important. A larger set of levels are treated with semiempirical methods, for use in large scale non-LTE calculations. The lower accuracy of these are well-suited to a more statistical treatment of the structure of the ion. We discuss the importance of a correct treatment of core-valence correlation and relativistic effects for predicting accurate oscillator strengths. These tend to reduce their values by as much as a factor of 2 for the resonance line.
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| 32. |
- Brage, Tomas, et al.
(författare)
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Theoretical oscillator strengths for Sr II and Y III, with application to abundances in the HgMn-type star chi Lupi
- 1998
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 496:2, s. 1051-1057
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Tidskriftsartikel (refereegranskat)abstract
- Oscillator strengths for selected transitions of Sr II and Y III have been determined using ab initio multiconfiguration Hartree-Fock techniques. The importance of including an accurate treatment of the core-valence correlation is emphasized. The results are used to determine the abundances of Sr and Y in the chemically peculiar star chi Lupi from HST/GHRS Echelle spectra. Overabundances of 2.09 dex for Sr and 2.8 dex for Y relative to the solar abundance are derived, and an ionization imbalance of +1.1 dex is evident from abundance determinations using Y III and Y II.
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| 33. |
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| 34. |
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| 35. |
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| 36. |
- Brandt, JC, et al.
(författare)
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A Goddard High Resolution Spectrograph atlas of echelle observations of the HgMn star chi Lupi
- 1999
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Ingår i: The Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 117:3, s. 1505-1548
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Tidskriftsartikel (refereegranskat)abstract
- Observations of the ultra-sharp-lined, chemically peculiar star chi Lupi taken by the Goddard High Resolution Spectrograph in echelle mode are presented. Thirty-six intervals of the spectral region between 1249 and 2688 Angstrom are covered with resolving powers in the range 75,000-93,000. Line identifications are provided, and the observed spectra are compared with synthetic spectra calculated using the SYNTHE program and associated line lists with changes to the line lists. The significance of these spectra for the chi Lupi Pathfinder Project and the closely related atomic physics effort is discussed in a companion paper.
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| 37. |
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| 38. |
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| 39. |
- Chen, Yajie, et al.
(författare)
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Application of a Magnetic-field-induced Transition in Fe x to Solar and Stellar Coronal Magnetic Field Measurements
- 2023
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 23:2
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars. Routine and accurate measurements of the magnetic fields at all the atmospheric layers are of critical importance to understand these magnetic activities, but in the solar and stellar coronae such a measurement is still a challenge due to the weak field strength and the high temperature. Recently, a magnetic-field-induced transition (MIT) of Fe x at 257.26 Å has been proposed for the magnetic field measurements in the solar and stellar coronae. In this review, we present an overview of recent progresses in the application of this method in astrophysics. We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe x lines. We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields. We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling. Furthermore, we discuss the application of the MIT method to the existing spectroscopic observations obtained by the Extreme-ultraviolet Imaging Spectrometer onboard Hinode. This novel technique provides a possible way for routine measurements of the magnetic fields in the solar and stellar coronae, but still requires further efforts to improve its accuracy. Finally, the challenges and prospects for future research on this topic are discussed.
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| 40. |
- Clementson, Joel, et al.
(författare)
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Atomic data and theoretical X-ray spectra of Ge-like through V-like W ions
- 2014
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Ingår i: Atomic Data and Nuclear Data Tables. - : Elsevier BV. - 0092-640X. ; 100:2, s. 577-649
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structure and spectra of ten tungsten ions have been calculated using the Flexible Atomic Code. The calculations yield energy levels, radiative lifetimes, spectral line positions, transition probability rates, and oscillator strengths for the tungsten ions isoelectronic to germanium, W42+, through vanadium, W51+. Collisional-radiative models for high-temperature, low-density plasmas have been implemented to produce line emissivities for X-ray transitions in the 1-4 keV (3-12 angstrom) spectral interval. The Ge-like through V-like W ions are important in nuclear fusion research where their spectra may provide diagnostic information on magnetically confined plasmas. (C) 2013 Elsevier Inc. All rights reserved.
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| 41. |
- Curtis, LJ, et al.
(författare)
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Relativistic empirical specification of transition probabilities from measured lifetime and energy level data
- 1997
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Ingår i: Physica Scripta. Topical Issues. - : IOP Publishing. - 0281-1847. ; 56:3, s. 240-244
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Tidskriftsartikel (refereegranskat)abstract
- A relativistic extension is made of methods by which intermediate coupling amplitudes are deduced from measured energy levels and combined with measured lifetimes to obtain transition probabilities within a multiplet between two pure configurations. A procedure for incorporating the relativistic j-dependence of the radial transition integral into the empirical data reduction is presented and applied to the isoelectronic formulation of the 2s(2)-2s2p transitions in the Be sequence and the 6s(2)6p(2)-6s(2)6p7s transitions in the Pb sequence.
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| 42. |
- Du, Weijie, et al.
(författare)
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Lifetimes of the hyperfine levels of 3d(9)4s D-3(3) in high-Z Ni-like ions
- 2013
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:14
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Tidskriftsartikel (refereegranskat)abstract
- Based on the multi-configuration Dirac-Hartree-Fock method and using the GRASPVU package, a theoretical investigation was performed to study the lifetimes of hyperfine levels of the first excited level 3d(9)4s D-3(3) in Ni-like ions (Z = 72-79) for all stable isotopes with nuclear spin. Comparisons between hyperfine-induced electric quadrupole transition rates and the pure magnetic octupole transition rates show that the extra electric quadrupole transition channel caused by the nuclear magnetic dipole and electric quadrupole hyperfine interaction is important for most hyperfine levels in each individual ion. Lifetimes of most hyperfine levels are sensitive to this extra decay channel. Extreme cases are found in Ta-181, Re-185 and Re-187, where lifetimes of some hyperfine levels are shortened by more than an order of magnitude.
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| 43. |
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| 44. |
- Fei, Z., et al.
(författare)
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Experimental and theoretical study of the ground-state M1 transition in Ag-like tungsten
- 2012
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 86:6
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental and theoretical study of the F-2(5/2) -> F-2(7/2) M1 transition in Ag-like W (W27+). The experiments employed the Shanghai permanent magnet electron beam ion trap, which has been developed especially for assisting spectroscopic diagnostics of edge plasmas for magnetic fusion devices. The theoretical value was obtained using the GRASP2K set of computer codes and included a comprehensive correlation study. The experimental M1 wavelength was measured as 3377.43 +/- 0.26 angstrom (3378.43 angstrom vacuum wavelength), whereas the calculated wavelength is in good agreement at 3381.80 angstrom. This good agreement shows the importance of fully understanding the electron correlation effects to predict the energy of the fine structure even in this, for tungsten, relatively simple case.
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| 45. |
- Fei, Z., et al.
(författare)
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Forbidden-line spectroscopy of the ground-state configuration of Cd-like W
- 2014
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 90:5
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Tidskriftsartikel (refereegranskat)abstract
- only using electric-dipole forbidden emission lines, in what we label forbidden-line spectroscopy, we identified several energy levels in cadmium-like tungsten, W26+. The spectrum was recorded at the Shanghai permanentmagnet electron beam ion trap in the visible region. The identifications were supported by large-scale multiconfiguration Dirac-Hartree-Fock calculations which involved careful investigations of core-valence and core-core correlation effects, and by relativistic many-body perturbation theory calculations. With this novel method we identified in all seven lines and measured their wavelengths. From this we can determine the relative position of seven energy levels. Due to the close degeneracy of two levels, we give alternative energies for three of the levels.
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| 46. |
- Fischer, Charlotte Froese, et al.
(författare)
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Advanced multiconfiguration methods for complex atoms : I. Energies and wave functions
- 2016
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:18
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Forskningsöversikt (refereegranskat)abstract
- Multiconfiguration wave function expansions combined with configuration interaction methods are a method of choice for complex atoms where atomic state functions are expanded in a basis of configuration state functions. Combined with a variational method such as the multiconfiguration Hartree-Fock (MCHF) or multiconfiguration Dirac-Hartree-Fock (MCDHF), the associated set of radial functions can be optimized for the levels of interest. The present review updates the variational MCHF theory to include MCDHF, describes the multireference single and double process for generating expansions and the systematic procedure of a computational scheme for monitoring convergence. It focuses on the calculations of energies and wave functions from which other atomic properties can be predicted such as transition rates, hyperfine structures and isotope shifts, for example.
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| 47. |
- Gedoz Tieppo, Maria, et al.
(författare)
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Classrooms of the present and practices of the past : The importance of understanding physics teachers’ embodied practices as a possible locus for social change
- 2023
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Ingår i: International Gender for Excellence in Research Conference Proceedings : Part 2: Selected Papers and Abstracts June 10-11, 2023 - Part 2: Selected Papers and Abstracts June 10-11, 2023. - 9789180397810 - 9789180397827 ; 2, s. 104-120
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Konferensbidrag (refereegranskat)abstract
- Physics classrooms are still clearly marked by practices belonging to a certaineducational past, while teachers are increasingly being asked to teach in lignment with current equality, diversity and inclusion agendas. At the core of this temporal disconnect are teachers’ practices, which are strongly marked by normative regimes in terms of gender, race, ethnicity, class and other social factors. Moreover, certainpractices more than others are constantly being transmitted, validated and legitimized as the normative ways of teaching. Drawing upon post-structuralist and feminist perspectives on teaching, practices, knowledge and subjectivities, in this theoretical paper I discuss the implications of understanding teachers’ practices as embodied practices. Doing so brings to the fore the normative dynamics of physics teachers’ taken-for-granted and invisible practices. Building on Vick and Martinez’s argument about the centrality of the body in teachers’ practices, I argue for the importance of understanding physics teachers’ embodied practices, because it bridges the gap between the equality that teachers strive to achieve in and through education, and what they end up doing in practice.
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| 48. |
- Grumer, Jon, et al.
(författare)
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Coronal lines and the importance of deep-core-valence correlation in Ag-like ions
- 2014
-
Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 89:6
-
Tidskriftsartikel (refereegranskat)abstract
- We report on large-scale and critically evaluated ab initio multiconfiguration Dirac-Hartree-Fock calculations of the wavelength and transition rate of the "coronal," M1 transition 4f F-2(5/2)o-F-2(7/2)o in Ag-like ions. The transition between these two fine-structure levels, which makes up the ground term for Z >= 62 in the isoelectronic sequence, has recently been observed in Yb23+ and W27+, where the latter could be of great importance for fusion plasma diagnostics. We present values for all members of the sequence between Z = 50 and 94, which are supported by excellent agreement with values from recent experiments. The importance of including core-valence correlation with the n = 3 shell in the theoretical model is emphasized. The results show close-to-spectroscopic accuracy for these forbidden lines.
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| 49. |
- Grumer, Jon, et al.
(författare)
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Hyperfine induced intensity redistribution in In II
- 2010
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:7
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical investigation of the hyperfine structure of the 5s5d D-3(2)-5s4f F-3(2,3)0 transitions in In II. Earlier work has failed in determining hyperfine constants for the upper levels of these transitions. We show that this is due to strong off-diagonal hyperfine interaction, which not only changes the position of the individual hyperfine lines but also introduces large intensity redistributions among the different hyperfine levels. We present hyperfine dependent gf-values and show that off-diagonal hyperfine interaction reduces some of the gf-values by two orders of magnitude, while others are increased by up to more than a factor of 6. We also discuss the influence on the hyperfine structure of an accurate representation of the level-splitting of the 5s4f configuration. We show that the hyperfine interaction in F-3(3)0 and F-1(3)0 is very hard to determine accurately even in a large-scale calculation, and we derive a semi-empirical method for adjusting our results using an experimentally known, diagonal hyperfine constant for 5s4f F-1(3)0. The resulting theoretical synthetic spectra reproduce the experimental values to high accuracy and facilitate the identification of all observed lines.
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| 50. |
- Grumer, Jon, et al.
(författare)
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Magnetic field induced transition rates in Ne- and Be-like ions for plasma diagnostics and E1M1 two-photon decay rate determination
- 2014
-
Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 488, s. 152005-152005
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We report on theoretical results of magnetic field induced transitions (MITs) in Ne- and Be-like ions without nuclear spin for two applicalions. Firstly, MITs are promising candidates in the determination of magnetic fields in plasmas. In our work on Ne-like ions we present accurate theoretical MIT rates for 2p(6 1)S(O) - 2p(5)3s 3P(O),2 [11. Purthermore, for Be-like ions, it has been proposed to extract the rate of the BIM1 two-photon transition 2s(2 1)S(O) - 2s2p P-3(O) by measuring the lifetime of the 'Po state using a storage ring, which involves an external magnetic field. The MIT rates are carefully evaluated and shown to be of the same order as the ElMI rates [2].
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