| 1. |
- Ali, Safdar, et al.
(författare)
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Electron-ion recombination of H- and He-like sulfur
- 2011
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 44:22, s. 225203-
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Tidskriftsartikel (refereegranskat)abstract
- Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombination (DR) cross sections up to n = 5 for H-like and He-like sulfur ions by observing the x-rays from the trapped ions. A fully relativistic distorted wave approximation method was used for calculating the DR cross sections, while the resonance energies were obtained with a multiconfiguration Dirac-Fock approach using the GRASP II code. The calculations agree with the experimental results within the experimental error bars. Additionally, the obtained total DR resonance strengths were used to check the behaviour of a scaling formula for low-Z, He-like iso-electronic sequence (Watanabe et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 5095).
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| 2. |
- Ali, Safdar, et al.
(författare)
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Electron-ion recombination rate coefficients for C II forming C I
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 753:2, s. 132-
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Tidskriftsartikel (refereegranskat)abstract
- We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (∆n = 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 103-106 K. The derived temperature dependent plasma recombination rate coefficients are presented graphically to compare with the theoretical data available in literature and parameterized by using a fit formula for convenient use in plasma modelling codes. In the temperature range of 103-2×104 K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2×104 K the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.
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| 3. |
- Ali, Safdar, et al.
(författare)
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Experimental recombination rate coefficients of Be-like Frecombining into B-like F
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Recombination spectra of F VI forming F V have been investigated with high-energy resolution, using the CRYRING heavy-ion storage ring. The absolute recombination rate coefficients are derived in the center-of-mass energy range of 0-25 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations for 2s-2p (∆n=0) core excitation and show a very good agreement in the resonance energy positions and intensities. Trielectronic recombination with 2s2-2p2 transitions are clearly identified in the spectrum. Metastable ion contributions are considered and found negligible. The energy dependent recombination spectra are convoluted with Maxwell-Boltzmann energy distribution in the 10-106 K temperature range. The resulting temperature dependent rate coefficients are compared with theoretical results from literature. In the 103-104 K range the calculated data significantly underestimates the plasma recombination rate coefficients. Above ~105 K, our AUTOSTRUCTURE results and plasma rate coefficients from Colgan et al. (2003) show an agreement better than 20% with the experimental results.
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| 4. |
- Ali, Safdar, et al.
(författare)
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Photo-recombination studies at R-EBIT with a Labview control and data = quisition system
- 2011
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 6, s. C01016-
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Tidskriftsartikel (refereegranskat)abstract
- Equipment at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) was developed for photo-recombination studies. A LabView-based event mode data acquisition and R-EBIT control system was implemented. The energies of KLL dielectronic recombination resonances in Li- to C-like argon ions were determined and compared with theoretical calculations performed using a distorted wave approximation. The theoretical and experimental peak positions for Li-, Be-, and C-like argon ions agree within the error bars. For B-like argon we observe an energy shift of 9 eV between the experimentally obtained peak position and the calculated result.
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| 5. |
- Bauer, Margit, et al.
(författare)
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Assessment of the in vivo biomechanical properties of the human uterine cervix in pregnancy using the aspiration test A feasibility study
- 2009
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Ingår i: European Journal of Obstetrics, Gynecology, and Reproductive Biology. - : Elsevier BV. - 0301-2115 .- 1872-7654. ; 144, s. S77-S81
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To date no diagnostic tool is yet available to objectively assess the in vivo biomechanical properties of the uterine cervix during gestation. Methods: We show the first clinical application of an aspiration device to assess the in vivo biomechanical properties of the cervix in pregnancy with the aim to describe the physiological biomechanical changes throughout gestation in order to eventually detect pregnant women at risk for cervical insufficiency (CI). Results: Out of 15 aspiration measurements, 12 produced valid results. The stiffness values were in the range between 0.013 and 0.068 bar/mm. The results showed a good reproducibility of the aspiration test. In our previous test series on non-pregnant cervices our repetitive measurements showed a standard deviation of > 20% compared to <+/- 10% to our data on pregnant cervices. Stiffness values are decreasing with gestational age which indicates a progressive softening of cervical tissue towards the end of pregnancy. Three pregnant women had two subsequent measurements within a time interval of four weeks. Decreasing stiffness values in the range of 20% were recorded. Discussion: This preliminary study on the clinical practicability of aspiration tests showed promising results in terms of reproducibility (reliability) and clinical use (feasibility). Ongoing studies will provide further insights on its usefulness in clinical practice and in the detection of substantial changes of the cervix in pregnancy indicative for threatened preterm birth or cervical insufficiency.
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| 6. |
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| 7. |
- Mahmood, Sultan, 1969-
(författare)
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Interaction of atomic ions with electrons : Recombination rate coefficients for C1+, F5+, Ne5+, S14+,S15
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concentrates on electron-ion interaction studies, in particular focusing on dielectronic recombination (DR) of highly charged ions relevant to astrophysics and plasma physics. The measurements were performed at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) and at the CRYRING heavy-ion storage ring. For the R-EBIT measurements a newly developed time-of-flight (TOF) technique for separation of ions and detecting the charge state distribution was utilized. By using ion intensities derived from the TOF spectra as input parameters in the rate equations, energy dependent DR rate coefficients for S15+ and S14+ ions were obtained for the first time. Resonance energies and cross sections calculated within the relativistic many-body perturbation theory for S15+ agree well with the experimental data. In addition to the TOF spectra, the x-ray spectra have been also collected. The combination of these two measurements allows us to separate the photo-recombination and the excitation spectra, from which the excitation rate coefficients for S15+ and S14+ ions were extracted.From the storage ring measurements absolute recombination rate coefficients for C1+, F5+, and Ne5+ions as a function of electron-ion collision energy were obtained. These were reported for the first time with high energy resolution. The experimental results were compared with results obtained from AUTOSTRUCTURE calculations. Temperature dependent rate coefficients have been also derived for the studied ions and compared with calculations available in the literature.
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| 8. |
- Mahmood, Sultan, 1969-, et al.
(författare)
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Recombination and electron impact excitation rate coefficients for S XV AND S XVI
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 754:2, s. 86-
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Tidskriftsartikel (refereegranskat)abstract
- Recombination and electron impact excitation of S14+ and S15+ ions was measured at the Stockholm refrigerated electron beam ion trap. The collision energy range was 1.4-3 keV, where we covered the KLL, KLM, KLN, and KLO dielectronic recombination resonances resulting in S13+ and S14+ ions. The recombination rates were obtained by detecting the charge state distribution with a newly developed time-of-flight technique. Resonance energies and cross sections calculated within the relativistic many-body perturbation theory for S15+ agree well with the experimental data. The temperature dependent rate coefficients have been extracted from the measured rates and compared with calculations from literature used for studies of collisionally ionized astrophysical plasmas. A good agreement for S15+ was obtained, while the plasma rates for S14+ were 23% lower than the so far published values. In addition to the time-of-flight spectra, the x-ray spectra, produced mainly by photo-recombination and excitation, have been also collected. The combination of these two measurements allowed us to separate the photo-recombination and the excitation spectra, and the excitation rate coefficients for summed intensities with known fractions of S14+ and S15+ ions were extracted.
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| 9. |
- Mahmood, Sultan, et al.
(författare)
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RECOMBINATION RATE COEFFICIENTS OF BORON-LIKE Ne
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 771:2, s. 78-
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Tidskriftsartikel (refereegranskat)abstract
- Recombination of Ne5+ was measured in a merged-beam type experiment at the heavy-ion storage ring CRYRING. In the collision energy range 0-110 eV resonances due to 2s(2)2p -> 2s2p(2) (Delta n=0) and 2s(2)2p -> 2s(2)3l (Delta n=1), core excitations were observed. The experimentally derived rate coefficients agree well with the calculations obtained using AUTOSTRUCTURE. At low energies, recombination is dominated by resonances belonging to the spin-forbidden 2s2p(2)(P-4(J))nl series. The energy-dependent rate coefficients were convoluted with a Maxwell-Boltzmann electron energy distribution to obtain plasma recombination rate coefficients. The data from the literature deviate from the measured results at low temperature.
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| 10. |
- Orban, Istvan, 1980-, et al.
(författare)
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Excitation and recombination studies with silicon and sulphur ions at an EBIT
- 2024
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Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 57:9
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of electron-impact excitation and recombination rate coefficients of highly charged Si and S ions at the Stockholm electron beam ion trap are reported. The experimental method was a combination of photon detection from the trapped ions during probing and subsequently extraction and time-of-flight (TOF) charge analysis of these ions. The TOF technique allows to measure recombination rate coefficients separately for every charge state, and together with the photon spectra of these ions also the excitation rate coefficients. In this paper, we present more details of the experimental procedure and summarize the experimental results in comparison with two different state-of-the-art calculations of recombination and excitation rates for Si10+–Si13+ and S12+–S15+ ions. One of these uses a relativistic configuration interaction approach (flexible atomic code) and the other is a relativistic many-body perturbation theory. A good to excellent agreement with both of them is found in energy and resonance strength for the investigated ions.
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