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- Leshchenko, Vyacheslav E., et al.
(författare)
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On-target temporal characterization of optical pulses at relativistic intensity
- 2019
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Ingår i: Light. - : Nature Publishing Group. - 2095-5545 .- 2047-7538. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- High-field experiments are very sensitive to the exact value of the peak intensity of an optical pulse due to the nonlinearity of the underlying processes. Therefore, precise knowledge of the pulse intensity, which is mainly limited by the accuracy of the temporal characterization, is a key prerequisite for the correct interpretation of experimental data. While the detection of energy and spatial profile is well established, the unambiguous temporal characterization of intense optical pulses, another important parameter required for intensity evaluation, remains a challenge, especially at relativistic intensities and a few-cycle pulse duration. Here, we report on the progress in the temporal characterization of intense laser pulses and present the relativistic surface second harmonic generation dispersion scan (RSSHG-D-scan)—a new approach allowing direct on-target temporal characterization of high-energy, few-cycle optical pulses at relativistic intensity.
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- Leshchev, Denis, et al.
(författare)
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Tracking the picosecond deactivation dynamics of a photoexcited iron carbene complex by time-resolved X-ray scattering
- 2018
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 9:2, s. 405-414
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Tidskriftsartikel (refereegranskat)abstract
- Recent years have seen the development of new iron-centered N-heterocyclic carbene (NHC) complexes for solar energy applications. Compared to typical ligand systems, the NHC ligands provide Fe complexes with longer-lived metal-to-ligand charge transfer (MLCT) states. This increased lifetime is ascribed to strong ligand field splitting provided by the NHC ligands that raises the energy levels of the metal centered (MC) states and therefore reduces the deactivation efficiency of MLCT states. Among currently known NHC systems, [Fe(btbip)2]2+ (btbip = 2,6-bis(3-tert-butyl-imidazol-1-ylidene)pyridine) is a unique complex as it exhibits a short-lived MC state with a lifetime on the scale of a few hundreds of picoseconds. Hence, this complex allows for a detailed investigation, using 100 ps X-ray pulses from a synchrotron, of strong ligand field effects on the intermediate MC state in an NHC complex. Here, we use time-resolved wide angle X-ray scattering (TRWAXS) aided by density functional theory (DFT) to investigate the molecular structure, energetics and lifetime of the high-energy MC state in the Fe-NHC complex [Fe(btbip)2]2+ after excitation to the MLCT manifold. We identify it as a 260 ps metal-centered quintet (5MC) state, and we refine the molecular structure of the excited-state complex verifying the DFT results. Using information about the hydrodynamic state of the solvent, we also determine, for the first time, the energy of the 5MC state as 0.75 ± 0.15 eV. Our results demonstrate that due to the increased ligand field strength caused by NHC ligands, upon transition from the ground state to the 5MC state, the metal to ligand bonds extend by unusually large values: by 0.29 Å in the axial and 0.21 Å in the equatorial direction. These results imply that the transition in the photochemical properties from typical Fe complexes to novel NHC compounds is manifested not only in the destabilization of the MC states, but also in structural distortion of these states.
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- Rivano Eckerdal, Johanna
(författare)
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Information sources at play: the apparatus of knowledge production in contraceptive counselling
- 2012
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Ingår i: Journal of Documentation. - : Emerald. - 0022-0418. ; 68:3, s. 278-298
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this article is to suggest that the information interaction between midwives and young women during counselling meetings about contraceptives can be approached as loci of knowledge production and discuss the consequences this has for the understanding of information practices. The overarching question is: how is knowledge produced during the interaction between the midwives and the young women and what roles do their bodies play in this interaction?Design/methodology/approachQualitative methods inspired by ethnography were used, including conversation transcripts of ten counselling meetings, 19 interviews and participatory observations at five youth centres in the South of Sweden. The study took place over a period of nine months. The feministic conceptual framework presented by Donna Haraway concerning knowledge production was used to analyse the material.FindingsAs they meet, both midwives and young women are information sources to each other, and the information conveyed is negotiated in both words and actions. Both parties are involved in a careful negotiation to establish what information is needed and appropriate for the situation at hand, but the midwives have the final say. However, the midwives balance between exerting a generalised expertise and entering in a situated dialogue with the young women.Practical implicationsThis study may contribute to awareness among information professionals of counselling meetings as information interactions where both words and actions are important as well as the inequality of power in that interaction.Originality/valueThis study contributes to library and information studies by broadening the understanding of what an information source may be and by exploring the usefulness of feminist researcher Donna Haraway's analytical tools for understanding information interactions as knowledge producing negotiations.
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