| 1. |
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| 2. |
- Thomas, HS, et al.
(författare)
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- 2019
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swepub:Mat__t
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| 10. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 11. |
- Keable, Stephen M., et al.
(författare)
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Room temperature XFEL crystallography reveals asymmetry in the vicinity of the two phylloquinones in photosystem I
- 2021
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Photosystem I (PS I) has a symmetric structure with two highly similar branches of pigments at the center that are involved in electron transfer, but shows very different efficiency along the two branches. We have determined the structure of cyanobacterial PS I at room temperature (RT) using femtosecond X-ray pulses from an X-ray free electron laser (XFEL) that shows a clear expansion of the entire protein complex in the direction of the membrane plane, when compared to previous cryogenic structures. This trend was observed by complementary datasets taken at multiple XFEL beamlines. In the RT structure of PS I, we also observe conformational differences between the two branches in the reaction center around the secondary electron acceptors A1A and A1B. The π-stacked Phe residues are rotated with a more parallel orientation in the A-branch and an almost perpendicular confirmation in the B-branch, and the symmetry breaking PsaB-Trp673 is tilted and further away from A1A. These changes increase the asymmetry between the branches and may provide insights into the preferential directionality of electron transfer.
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| 12. |
- Olszewski, Adam J., et al.
(författare)
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Burkitt Lymphoma International Prognostic Index
- 2021
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Ingår i: Journal of clinical oncology : official journal of the American Society of Clinical Oncology. - 0732-183X. ; 39:10, s. 1129-1138
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Burkitt lymphoma (BL) has unique biology and clinical course but lacks a standardized prognostic model. We developed and validated a novel prognostic index specific for BL to aid risk stratification, interpretation of clinical trials, and targeted development of novel treatment approaches. METHODS: We derived the BL International Prognostic Index (BL-IPI) from a real-world data set of adult patients with BL treated with immunochemotherapy in the United States between 2009 and 2018, identifying candidate variables that showed the strongest prognostic association with progression-free survival (PFS). The index was validated in an external data set of patients treated in Europe, Canada, and Australia between 2004 and 2019. RESULTS: In the derivation cohort of 633 patients with BL, age ≥ 40 years, performance status ≥ 2, serum lactate dehydrogenase > 3× upper limit of normal, and CNS involvement were selected as equally weighted factors with an independent prognostic value. The resulting BL-IPI identified groups with low (zero risk factors, 18% of patients), intermediate (one factor, 36% of patients), and high risk (≥ 2 factors, 46% of patients) with 3-year PFS estimates of 92%, 72%, and 53%, respectively, and 3-year overall survival estimates of 96%, 76%, and 59%, respectively. The index discriminated outcomes regardless of HIV status, stage, or first-line chemotherapy regimen. Patient characteristics, relative size of the BL-IPI groupings, and outcome discrimination were consistent in the validation cohort of 457 patients, with 3-year PFS estimates of 96%, 82%, and 63% for low-, intermediate-, and high-risk BL-IPI, respectively. CONCLUSION: The BL-IPI provides robust discrimination of survival in adult BL, suitable for use as prognostication and stratification in trials. The high-risk group has suboptimal outcomes with standard therapy and should be considered for innovative treatment approaches.
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| 13. |
- Rabe, Patrick, et al.
(författare)
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X-ray free-electron laser studies reveal correlated motion during isopenicillin N synthase catalysis
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:34
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Tidskriftsartikel (refereegranskat)abstract
- Isopenicillin N synthase (IPNS) catalyzes the unique reaction of L-delta-(alpha-aminoadipoyl)-L-cysteinyl-D-valine (ACV) with dioxygen giving isopenicillin N (IPN), the precursor of all natural penicillins and cephalosporins. X-ray free-electron laser studies including time-resolved crystallography and emission spectroscopy reveal how reaction of IPNS:Fe(II):ACV with dioxygen to yield an Fe(III) superoxide causes differences in active site volume and unexpected conformational changes that propagate to structurally remote regions. Combined with solution studies, the results reveal the importance of protein dynamics in regulating intermediate conformations during conversion of ACV to IPN. The results have implications for catalysis by multiple IPNS-related oxygenases, including those involved in the human hypoxic response, and highlight the power of serial femtosecond crystallography to provide insight into long-range enzyme dynamics during reactions presently impossible for nonprotein catalysts.
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| 14. |
- Bhowmick, Asmit, et al.
(författare)
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Going around the Kok cycle of the water oxidation reaction with femtosecond X-ray crystallography
- 2023
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Ingår i: IUCrJ. - : International Union Of Crystallography. - 2052-2525. ; 10:6, s. 642-655
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Forskningsöversikt (refereegranskat)abstract
- The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.
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| 15. |
- Bhowmick, Asmit, et al.
(författare)
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Structural evidence for intermediates during O2 formation in photosystem II
- 2023
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 617:7961, s. 629-636
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Tidskriftsartikel (refereegranskat)abstract
- In natural photosynthesis, the light-driven splitting of water into electrons, protons and molecular oxygen forms the first step of the solar-to-chemical energy conversion process. The reaction takes place in photosystem II, where the Mn4CaO5 cluster first stores four oxidizing equivalents, the S0 to S4 intermediate states in the Kok cycle, sequentially generated by photochemical charge separations in the reaction center and then catalyzes the O–O bond formation chemistry. Here, we report room temperature snapshots by serial femtosecond X-ray crystallography to provide structural insights into the final reaction step of Kok’s photosynthetic water oxidation cycle, the S3→[S4]→S0 transition where O2 is formed and Kok’s water oxidation clock is reset. Our data reveal a complex sequence of events, which occur over micro- to milliseconds, comprising changes at the Mn4CaO5 cluster, its ligands and water pathways as well as controlled proton release through the hydrogen-bonding network of the Cl1 channel. Importantly, the extra O atom Ox, which was introduced as a bridging ligand between Ca and Mn1 during the S2→S3 transition, disappears or relocates in parallel with Yz reduction starting at approximately 700 μs after the third flash. The onset of O2 evolution, as indicated by the shortening of the Mn1–Mn4 distance, occurs at around 1,200 μs, signifying the presence of a reduced intermediate, possibly a bound peroxide.
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| 16. |
- Hussein, Rana, et al.
(författare)
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Structural dynamics in the water and proton channels of photosystem II during the S2 to S3 transition
- 2021
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Light-driven oxidation of water to molecular oxygen is catalyzed by the oxygen-evolving complex (OEC) in Photosystem II (PS II). This multi-electron, multi-proton catalysis requires the transport of two water molecules to and four protons from the OEC. A high-resolution 1.89 Å structure obtained by averaging all the S states and refining the data of various time points during the S2 to S3 transition has provided better visualization of the potential pathways for substrate water insertion and proton release. Our results indicate that the O1 channel is the likely water intake pathway, and the Cl1 channel is the likely proton release pathway based on the structural rearrangements of water molecules and amino acid side chains along these channels. In particular in the Cl1 channel, we suggest that residue D1-E65 serves as a gate for proton transport by minimizing the back reaction. The results show that the water oxidation reaction at the OEC is well coordinated with the amino acid side chains and the H-bonding network over the entire length of the channels, which is essential in shuttling substrate waters and protons.
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| 17. |
- Ibrahim, Mohamed, et al.
(författare)
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Untangling the sequence of events during the S-2 -> S-3 transition in photosystem II and implications for the water oxidation mechanism
- 2020
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 117:23, s. 12624-12635
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Tidskriftsartikel (refereegranskat)abstract
- In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S-1, S-2, S-3, and S-0, showing that a water molecule is inserted during the S-2 -> S-3 transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O-2 formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S-2 -> S-3 transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QA and QB, are observed. At the donor site, tyrosine YZ and His190 H-bonded to it move by 50 mu s after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a "water wheel"-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (t of similar to 350 mu s) during the S-2 -> S-3 transition mirrors the appearance of OX electron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.
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| 18. |
- Ibrahim, Mohamed, et al.
(författare)
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Untangling the sequence of events during the S2 -> S3 transition in photosystem II and implications for the water oxidation mechanism
- 2020
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 117:23, s. 12624-12635
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Tidskriftsartikel (refereegranskat)abstract
- In oxygenic photosynthesis, light-driven oxidation of water to molecular oxygen is carried out by the oxygen-evolving complex (OEC) in photosystem II (PS II). Recently, we reported the room-temperature structures of PS II in the four (semi)stable S-states, S1, S2, S3, and S0, showing that a water molecule is inserted during the S2 -> S3 transition, as a new bridging O(H)-ligand between Mn1 and Ca. To understand the sequence of events leading to the formation of this last stable intermediate state before O2 formation, we recorded diffraction and Mn X-ray emission spectroscopy (XES) data at several time points during the S2 -> S3 transition. At the electron acceptor site, changes due to the two-electron redox chemistry at the quinones, QA and QB, are observed. At the donor site, tyrosine YZ and His190 H-bonded to it move by 50 μs after the second flash, and Glu189 moves away from Ca. This is followed by Mn1 and Mn4 moving apart, and the insertion of OX(H) at the open coordination site of Mn1. This water, possibly a ligand of Ca, could be supplied via a "water wheel"-like arrangement of five waters next to the OEC that is connected by a large channel to the bulk solvent. XES spectra show that Mn oxidation (τ of ∼350 μs) during the S2 -> S3 transition mirrors the appearance of OX electron density. This indicates that the oxidation state change and the insertion of water as a bridging atom between Mn1 and Ca are highly correlated.
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| 19. |
- John, Juliane, et al.
(författare)
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Redox-controlled reorganization and flavin strain within the ribonucleotide reductase R2b–NrdI complex monitored by serial femtosecond crystallography
- 2022
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Ingår i: eLIFE. - 2050-084X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Redox reactions are central to biochemistry and are both controlled by and induce protein structural changes. Here, we describe structural rearrangements and crosstalk within the Bacillus cereus ribonucleotide reductase R2b–NrdI complex, a di-metal carboxylate-flavoprotein system, as part of the mechanism generating the essential catalytic free radical of the enzyme. Femtosecond crystallography at an X-ray free electron laser was utilized to obtain structures at room temperature in defined redox states without suffering photoreduction. Together with density functional theory calculations, we show that the flavin is under steric strain in the R2b–NrdI protein complex, likely tuning its redox properties to promote superoxide generation. Moreover, a binding site in close vicinity to the expected flavin O2 interaction site is observed to be controlled by the redox state of the flavin and linked to the channel proposed to funnel the produced superoxide species from NrdI to the di-manganese site in protein R2b. These specific features are coupled to further structural changes around the R2b–NrdI interaction surface. The mechanistic implications for the control of reactive oxygen species and radical generation in protein R2b are discussed.
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| 20. |
- John, Juliane, et al.
(författare)
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Redox-controlled reorganization and flavin strain within the ribonucleotide reductase R2b–NrdI complex monitored by serial femtosecond crystallography
- 2022
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Redox reactions are central to biochemistry and are both controlled by and induce protein structural changes. Here, we describe structural rearrangements and crosstalk within the Bacillus cereus ribonucleotide reductase R2b–NrdI complex, a di-metal carboxylate-flavoprotein system, as part of the mechanism generating the essential catalytic free radical of the enzyme. Femtosecond crystallography at an X-ray free electron laser was utilized to obtain structures at room temperature in defined redox states without suffering photoreduction. Together with density functional theory calculations, we show that the flavin is under steric strain in the R2b–NrdI protein complex, likely tuning its redox properties to promote superoxide generation. Moreover, a binding site in close vicinity to the expected flavin O2 interaction site is observed to be controlled by the redox state of the flavin and linked to the channel proposed to funnel the produced superoxide species from NrdI to the di-manganese site in protein R2b. These specific features are coupled to further structural changes around the R2b–NrdI interaction surface. The mechanistic implications for the control of reactive oxygen species and radical generation in protein R2b are discussed.
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| 21. |
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| 22. |
- Simon, Philipp S., et al.
(författare)
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Capturing the sequence of events during the water oxidation reaction in photosynthesis using XFELs
- 2023
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Ingår i: FEBS Letters. - : John Wiley & Sons. - 0014-5793 .- 1873-3468. ; 597:1, s. 30-37
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Tidskriftsartikel (refereegranskat)abstract
- Ever since the discovery that Mn was required for oxygen evolution in plants by Pirson in 1937 and the period-four oscillation in flash-induced oxygen evolution by Joliot and Kok in the 1970s, understanding of this process has advanced enormously using state-of-the-art methods. The most recent in this series of innovative techniques was the introduction of X-ray free-electron lasers (XFELs) a decade ago, which led to another quantum leap in the understanding in this field, by enabling operando X-ray structural and X-ray spectroscopy studies at room temperature. This review summarizes the current understanding of the structure of Photosystem II (PS II) and its catalytic centre, the Mn4CaO5 complex, in the intermediate Si (i = 0–4)-states of the Kok cycle, obtained using XFELs.
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| 23. |
- Young, Iris D., et al.
(författare)
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Structure of photosystem II and substrate binding at room temperature
- 2016
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Ingår i: Nature. - : Macmillan Publishers Ltd.. - 0028-0836 .- 1476-4687. ; 540:7633, s. 453-457
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Tidskriftsartikel (refereegranskat)abstract
- Light-induced oxidation of water by photosystem II (PS II) in plants, algae and cyanobacteria has generated most of the dioxygen in the atmosphere. PS II, a membrane-bound multi-subunit pigment protein complex, couples the one-electron photochemistry at the reaction centre with the four-electron redox chemistry of water oxidation at the Mn4CaO5 cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S0 to S4)1, in which S1 is the dark-stable state and S3 is the last semi-stable state before O–O bond formation and O2 evolution2,3. A detailed understanding of the O–O bond formation mechanism remains a challenge, and will require elucidation of both the structures of the OEC in the different S-states and the binding of the two substrate waters to the catalytic site4–6. Here we report the use of femtosecond pulses from an X-ray free electron laser (XFEL) to obtain damage-free, room temperature structures of dark-adapted (S1), two-flash illuminated (2F; S3-enriched), and ammonia-bound two-flash illuminated (2F-NH3; S3-enriched) PS II. Although the recent 1.95 Å resolution structure of PS II at cryogenic temperature using an XFEL7 provided a damage-free view of the S1 state, measurements at room temperature are required to study the structural landscape of proteins under functional conditions8,9, and also for in situ advancement of the S-states. To investigate the water-binding site(s), ammonia, a water analogue, has been used as a marker, as it binds to the Mn4CaO5 cluster in the S2 and S3 states10. Since the ammonia-bound OEC is active, the ammonia-binding Mn site is not a substrate water site10–13. This approach, together with a comparison of the native dark and 2F states, is used to discriminate between proposed O–O bond formation mechanisms.
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| 24. |
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| 25. |
- Bayram Özdemir, Sevgi, 1981-, et al.
(författare)
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Conceptualization and assessment of multiple forms of social withdrawal in Turkey
- 2015
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Ingår i: Social development (Oxford. Print). - : Wiley. - 0961-205X .- 1467-9507. ; 24:1, s. 142-165
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Tidskriftsartikel (refereegranskat)abstract
- We examined the meaning, assessment, and implications of different forms of social withdrawal in Turkey across two studies. In study 1, semi-structured interviews were conducted with children, mothers, and teachers to identify descriptors of social withdrawal. Shyness and unsociability were confirmed through content analyses, and regulated withdrawal, a new subtype characterized by overregulation of behaviors and suppression of own desires during social interactions, was revealed. Based on these findings, the child social preference scale, an established North American measure of social withdrawal, was revised. In study 2, a confirmatory factor analysis on a sample of 599 9–11-year-old children revealed three distinct forms of social withdrawal. Shyness was related to a wider range of child adjustment difficulties than unsociability and regulated withdrawal, although all forms of withdrawal were associated with child adjustment difficulties, providing support for the importance of children's active involvement in social relationships for their positive development and well-being.
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| 26. |
- Bayram Özdemir, Sevgi, 1981-, et al.
(författare)
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Mothers’ Reactions to Preschoolers’ Proactive and Reactive Aggressive Behaviors
- 2017
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Ingår i: Infant and Child Development. - : John Wiley & Sons. - 1522-7227 .- 1522-7219. ; 26:2
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Tidskriftsartikel (refereegranskat)abstract
- The present study was designed to examine mothers' emotional reactions, causal attributions, and socialization strategies in response to preschool children's engagement in proactive and reactive physical aggression with peers during free play at school. Participants were 84 mothers (Mage=31.83, SD=4.48) with preschool-aged children (Mage=4.92, SD=0. 97), residing in Ankara, Turkey. Supporting our expectations, mothers reacted with negative emotions to both functions of aggressive behaviours, with less anxiety, disappointment, embarrassment, and guilt for reactive aggression. They also believed that reactive aggression is more contextually dependent and intentional and reported more indirect (e.g., asking the child, teacher, or other children to find out more about the situation and aggressive episode) and other-oriented strategies (e.g., telling the other child to behave properly) to address these behaviours. Overall, our findings suggest that Turkish mothers' feelings, perceptions, and socialization approaches to childhood aggression vary depending on the functions of aggression, and mothers perceive preschool-aged children's engagement in reactive aggression in the school setting as relatively more acceptable than proactive aggression.
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| 27. |
- Bayram Özdemir, Sevgi, 1981-, et al.
(författare)
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Processes and conditions underlying the link between shyness and school adjustment among Turkish children
- 2017
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Ingår i: British Journal of Developmental Psychology. - Hoboken NJ, USA : John Wiley & Sons. - 0261-510X .- 2044-835X. ; 35:2, s. 218-236
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Tidskriftsartikel (refereegranskat)abstract
- This study examined the underlying processes and conditions that contribute to the school adjustment of shy children in Turkey, where children's interpersonal relationships in social settings and academic achievement are highly emphasized. First, we examined the unique mediating roles of children's feelings of social anxiety, depressive symptoms, and loneliness in the associations between shyness and indices of school outcomes (academic achievement and school liking/avoidance). Second, we explored the moderating role of children's peer acceptance in these associations. Fourth- and fifth-grade children (N = 599; Mage = 10.11 years, SD = 0.65; 48% girls) provided information on shyness, social anxiety, depressive symptoms, loneliness, and school liking/avoidance. Head teachers in each classroom reported on students' academic performance. The peer nomination method was used to assess children's peer relationships. Results revealed that when children displayed shy behaviours, they reported more depressive symptoms that were, in turn, associated with poorer academic performance, less school liking, and higher school avoidance. Moreover, shyness negatively predicted school liking at low levels of peer acceptance, suggesting that difficulties in peer relationships increased shy children's risk of school dissatisfaction. Overall, our findings support the importance of the interpersonal relationship context for children's adjustment within the Turkish cultural context. Statement of contribution What is already known on this subject? Shy children have difficulties initiating and maintaining social interactions, which put them at risk for a wide range of socio-emotional difficulties. Shy children have poor academic performance and experience school adjustment difficulties in North America. What does this study add? Shyness is an important risk factor for poorer academic performance and adjustment among children in Turkey. The association between shyness and difficulties at school is explained by children's experience of depressive symptoms. Difficulties with peer relationships increase shy children's risk of school dissatisfaction.
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| 28. |
- Bayram Özdemir, Sevgi, 1981-, et al.
(författare)
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Turkish mothers’ parenting beliefs in response to preschoolers’ aggressive and socially withdrawn behaviors
- 2015
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Ingår i: Journal of Child and Family Studies. - : Springer Science and Business Media LLC. - 1062-1024 .- 1573-2843. ; 24:3, s. 687-702
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Tidskriftsartikel (refereegranskat)abstract
- The present study aimed to examine Turkish mothers’ reactive parenting beliefs (reactive emotional appraisals, causal attributions, anticipated strategies, and underlying goals for their anticipated strategies) in response to children’s aggressive and socially withdrawn behaviors. Participants included 84 mothers with preschool-aged children residing in Ankara, Turkey. Supporting our expectations, the results showed that the degree of mothers’ negative emotional responses varied based on the child maladaptive behaviors. Moreover, mothers perceived aggressive behaviors as more temporary and contextually dependent, but intentional than withdrawn behaviors. More directive strategies and parent-centered goals were reported for aggression, whereas more indirect strategies and emphatic goals were reported for social withdrawal. Overall, the present study provided evidence that Turkish mothers’ perceptions and evaluations of maladaptive behaviors may have universal characteristics as well as aspects that are particular to the Turkish socio-cultural context.
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| 29. |
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| 30. |
- Boniolo, Manuel, et al.
(författare)
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Water Oxidation by Pentapyridyl Base Metal Complexes? : A Case Study
- 2022
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 61:24, s. 9104-9118
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Tidskriftsartikel (refereegranskat)abstract
- The design of molecular water oxidation catalysts (WOCs) requires a rational approach that considers the intermediate steps of the catalytic cycle, including water binding, deprotonation, storage of oxidizing equivalents, O–O bond formation, and O2 release. We investigated several of these properties for a series of base metal complexes (M = Mn, Fe, Co, Ni) bearing two variants of a pentapyridyl ligand framework, of which some were reported previously to be active WOCs. We found that only [Fe(Py5OMe)Cl]+ (Py5OMe = pyridine-2,6-diylbis[di-(pyridin-2-yl)methoxymethane]) showed an appreciable catalytic activity with a turnover number (TON) = 130 in light-driven experiments using the [Ru(bpy)3]2+/S2O82– system at pH 8.0, but that activity is demonstrated to arise from the rapid degradation in the buffered solution leading to the formation of catalytically active amorphous iron oxide/hydroxide (FeOOH), which subsequently lost the catalytic activity by forming more extensive and structured FeOOH species. The detailed analysis of the redox and water-binding properties employing electrochemistry, X-ray absorption spectroscopy (XAS), UV–vis spectroscopy, and density-functional theory (DFT) showed that all complexes were able to undergo the MIII/MII oxidation, but none was able to yield a detectable amount of a MIV state in our potential window (up to +2 V vs SHE). This inability was traced to (i) the preference for binding Cl– or acetonitrile instead of water-derived species in the apical position, which excludes redox leveling via proton coupled electron transfer, and (ii) the lack of sigma donor ligands that would stabilize oxidation states beyond MIII. On that basis, design features for next-generation molecular WOCs are suggested.
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| 31. |
- Cheah, Charissa S. L., et al.
(författare)
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Chinese Malaysian Adolescents’ Social Cognitive Reasoning regarding Filial Piety Dilemmas
- 2018
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Ingår i: Child Development. - : John Wiley & Sons. - 0009-3920 .- 1467-8624. ; 89:2, s. 383-396
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Tidskriftsartikel (refereegranskat)abstract
- This study examined the social-cognitive reasoning of 52 Chinese Malaysian preadolescents (9-12 years old; M = 11.02, SD = 0.94) and 68 adolescents (13-18 years old; M = 14.76, SD = 1.39) in resolving filial dilemmas within the personal and moral domain. Preadolescents deferred to parental authority, whereas adolescents endorsed filial obligation reasoning to justify compliance in the personal domain. Both appealed to filial obligation, pragmatic, or welfare and safety reasoning to justify compliance but fairness or rights reasoning to justify their noncompliance, for the moral issue. Distinctions between authoritarian and reciprocal filial piety reasoning were revealed. Findings demonstrated complex decision-making and cognitive reasoning processes among Chinese Malaysian adolescents as they negotiate their filial obligations and autonomy development.
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| 32. |
- Cheah, Charissa S. L., et al.
(författare)
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Parenting hassles mediate predictors of Chinese and Korean immigrants' psychologically controlling parenting
- 2016
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Ingår i: Journal of applied developmental psychology. - : Elsevier. - 0193-3973 .- 1873-7900. ; 47, s. 13-22
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Tidskriftsartikel (refereegranskat)abstract
- We examined: (1) the mediating role of parenting daily hassles in the associations between three predictors (child temperament, maternal psychological well-being, and marital quality) and psychologically controlling practices in two Asian immigrant samples. We also explored the moderating role of maternal acculturation in the path from parenting daily hassles to psychological control. Participants were 152 Chinese and 165 Korean immigrant mothers with preschool children in the U.S. Multi-group path analysis revealed that easier child temperament, higher psychological well-being, and better marital quality were each associated with fewer parenting daily hassles, which in turn were associated with less psychological control. These general mediating effects held for both groups. However, the indirect effects of child temperament, maternal psychological well-being, and marital quality through parenting daily hassles were further moderated by acculturation for Chinese immigrant mothers, but not Korean immigrant mothers. The culturally similar and different findings across the two groups were discussed.
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| 33. |
- Cheah, Charissa S. L., et al.
(författare)
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Predicting filial behaviors of Chinese-Malaysian adolescents from perceived parental investments, filial emotions, and parental warmth and support
- 2012
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Ingår i: Journal of Adolescence. - : Wiley. - 0140-1971 .- 1095-9254. ; 35:3, s. 628-637
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Tidskriftsartikel (refereegranskat)abstract
- The present study examined the mediating role of perceived parental warmth and support in predicting Chinese Malaysian adolescents' filial behaviors from their age, perceived parental investments, and positive filial emotions toward their parents. The effects of these predictors were examined separately for mothers and fathers. Participants included 122 Chinese adolescents (. M = 13.14 years; . SD = 2.22) in Malaysia. Adolescents' perceived parental investments, filial emotions, and warmth and support from each parent were positively, and age was negatively associated with their filial behaviors. No gender differences were found. Perceived maternal warmth and support significantly mediated the effect of age, perceived investments from, and filial emotions toward mothers on adolescents' filial behaviors, but perceived paternal warmth and support did not have a mediating role. The present study sheds light on the unique maternal versus paternal filial role, and important familial processes in Chinese-Malaysian children and adolescents from a cultural perspective.
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| 34. |
- Cheah, S.K, et al.
(författare)
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Nanostructure Electrodes for 3D Li-ion Microbatteries
- 2008
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Ingår i: Junior Euromat 2008 14-18 July, Lausanne (CH) oral presentation.
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The vast development of surface micromachining technology has brought the proliferation of MEMS devices. However, the issue of powering the MEMS devices still remains as a great challenge. Although the conventional thin film 2D batteries seems promising for achieving high power density, however, relatively large area is required for having sufficient capacity. The drawbacks of 2D batteries can be overcome by using 3D architecture of Li-ion microbatteries.The 3D architecture of Li-ion microbatteries will have the advantages of short diffusion path as the electrode active materials are just tenth of nanometer deposited on the current collectors. The short diffusion path guarantees the high power performance. Besides that, the capacity of the microbatteries can be enhanced by just increasing the length of the electrode while keeping the areal footprint. This is what makes the 3D microbatteries a more promising power supply for MEMS.Our approach to synthesize a 3D Li-ion microbattery is starting with the synthesis of a nanostructure current collector using a template method. An anodized aluminium oxide (AAO) membrane is used as template for the electrodeposition of an aluminium current collector. AAO with defined pore sizes and inter-pores spacing are synthesized with a suitable diameter and interspacing where an aluminium current collector can grow within the template. The following step is the deposition of electrode active materials on the current collector. In this example Atomic Layer Deposition (ALD) is employed in order to achieve a well deposited layer of, in this case, a TiO2 cathode material. By controlling the deposition parameters, the crystal structure and the thickness of TiO2 layer can be altered to give a better electrochemical performance. Our results will be discussed in the light of the complexity of the deposition mechanisms of both the aluminium current collector nano-rods and the TiO2 layer.
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| 35. |
- Fransson, Thomas, et al.
(författare)
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Effects of x-ray free-electron laser pulse intensity on the Mn K beta(1,3) x-ray emission spectrum in photosystem II-A case study for metalloprotein crystals and solutions
- 2021
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- In the last ten years, x-ray free-electron lasers (XFELs) have been successfully employed to characterize metalloproteins at room temperature using various techniques including x-ray diffraction, scattering, and spectroscopy. The approach has been to outrun the radiation damage by using femtosecond (fs) x-ray pulses. An example of an important and damage sensitive active metal center is the Mn4CaO5 cluster in photosystem II (PS II), the catalytic site of photosynthetic water oxidation. The combination of serial femtosecond x-ray crystallography and K beta x-ray emission spectroscopy (XES) has proven to be a powerful multimodal approach for simultaneously probing the overall protein structure and the electronic state of the Mn4CaO5 cluster throughout the catalytic (Kok) cycle. As the observed spectral changes in the Mn4CaO5 cluster are very subtle, it is critical to consider the potential effects of the intense XFEL pulses on the K beta XES signal. We report here a systematic study of the effects of XFEL peak power, beam focus, and dose on the Mn K beta(1,3) XES spectra in PS II over a wide range of pulse parameters collected over seven different experimental runs using both microcrystal and solution PS II samples. Our findings show that for beam intensities ranging from & SIM;5 x 10(15) to 5 x 10(17) W/cm(2) at a pulse length of & SIM;35 fs, the spectral effects are small compared to those observed between S-states in the Kok cycle. Our results provide a benchmark for other XFEL-based XES studies on metalloproteins, confirming the viability of this approach.& nbsp;
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| 36. |
- Fransson, Thomas, et al.
(författare)
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Effects of x-ray free-electron laser pulse intensity on the Mn K β 1,3x-ray emission spectrum in photosystem II - A case study for metalloprotein crystals and solutions
- 2021
-
Ingår i: Structural Dynamics. - : American Institute of Physics (AIP). - 2329-7778. ; 8:6
-
Tidskriftsartikel (refereegranskat)abstract
- In the last ten years, x-ray free-electron lasers (XFELs) have been successfully employed to characterize metalloproteins at room temperature using various techniques including x-ray diffraction, scattering, and spectroscopy. The approach has been to outrun the radiation damage by using femtosecond (fs) x-ray pulses. An example of an important and damage sensitive active metal center is the Mn4CaO5 cluster in photosystem II (PS II), the catalytic site of photosynthetic water oxidation. The combination of serial femtosecond x-ray crystallography and Kβ x-ray emission spectroscopy (XES) has proven to be a powerful multimodal approach for simultaneously probing the overall protein structure and the electronic state of the Mn4CaO5 cluster throughout the catalytic (Kok) cycle. As the observed spectral changes in the Mn4CaO5 cluster are very subtle, it is critical to consider the potential effects of the intense XFEL pulses on the Kβ XES signal. We report here a systematic study of the effects of XFEL peak power, beam focus, and dose on the Mn Kβ1,3 XES spectra in PS II over a wide range of pulse parameters collected over seven different experimental runs using both microcrystal and solution PS II samples. Our findings show that for beam intensities ranging from ∼5 × 1015 to 5 × 1017 W/cm2 at a pulse length of ∼35 fs, the spectral effects are small compared to those observed between S-states in the Kok cycle. Our results provide a benchmark for other XFEL-based XES studies on metalloproteins, confirming the viability of this approach.
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| 37. |
- Jakobsen, Lasse H., et al.
(författare)
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Minimal relapse risk and early normalization of survival for patients with Burkitt lymphoma treated with intensive immunochemotherapy : an international study of 264 real-world patients
- 2020
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Ingår i: British Journal of Haematology. - : Wiley. - 0007-1048 .- 1365-2141. ; 189:4, s. 661-671
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Tidskriftsartikel (refereegranskat)abstract
- Non-endemic Burkitt lymphoma (BL) is a rare germinal centre B-cell-derived malignancy with the genetic hallmark of MYC gene translocation and with rapid tumour growth as a distinct clinical feature. To investigate treatment outcomes, loss of lifetime and relapse risk in adult BL patients treated with intensive immunochemotherapy, retrospective clinic-based and population-based lymphoma registries from six countries were used to identify 264 real-world patients. The median age was 47 years and the majority had advanced-stage disease and elevated LDH. Treatment protocols were R-CODOX-M/IVAC (47%), R-hyper-CVAD (16%), DA-EPOCH-R (11%), R-BFM/GMALL (25%) and other (2%) leading to an overall response rate of 89%. The two-year overall survival and event-free survival were 84% and 80% respectively. For patients in complete remission/unconfirmed, the two-year relapse risk was 6% but diminished to 0·6% for patients reaching 12 months of post-remission event-free survival (pEFS12). The loss of lifetime for pEFS12 patients was 0·4 (95% CI: −0·7 to 2) months. In conclusion, real-world outcomes of adult BL are excellent following intensive immunochemotherapy. For pEFS12 patients, the relapse risk was low and life expectancy similar to that of a general population, which is important information for developing meaningful follow-up strategies with increased focus on survivorship and less focus on routine disease surveillance.
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| 38. |
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| 39. |
- Kern, Jan, et al.
(författare)
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Structures of the intermediates of Kok’s photosynthetic water oxidation clock
- 2018
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 563, s. 421-425
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Tidskriftsartikel (refereegranskat)abstract
- Inspired by the period-four oscillation in flash-induced oxygen evolution of photosystem II discovered by Joliot in 1969, Kok performed additional experiments and proposed a five-state kinetic model for photosynthetic oxygen evolution, known as Kok’s S-state clock or cycle1,2. The model comprises four (meta)stable intermediates (S0, S1, S2 and S3) and one transient S4 state, which precedes dioxygen formation occurring in a concerted reaction from two water-derived oxygens bound at an oxo-bridged tetra manganese calcium (Mn4CaO5) cluster in the oxygen-evolving complex3–7. This reaction is coupled to the two-step reduction and protonation of the mobile plastoquinone QB at the acceptor side of PSII. Here, using serial femtosecond X-ray crystallography and simultaneous X-ray emission spectroscopy with multi-flash visible laser excitation at room temperature, we visualize all (meta)stable states of Kok’s cycle as high-resolution structures (2.04–2.08 Å). In addition, we report structures of two transient states at 150 and 400 µs, revealing notable structural changes including the binding of one additional ‘water’, Ox, during the S2→S3 state transition. Our results suggest that one water ligand to calcium (W3) is directly involved in substrate delivery. The binding of the additional oxygen Ox in the S3 state between Ca and Mn1 supports O–O bond formation mechanisms involving O5 as one substrate, where Ox is either the other substrate oxygen or is perfectly positioned to refill the O5 position during O2 release. Thus, our results exclude peroxo-bond formation in the S3 state, and the nucleophilic attack of W3 onto W2 is unlikely.
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| 40. |
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| 41. |
- Seo, You Jung, et al.
(författare)
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The Mediating Role of Korean Immigrant Mothers' Psychological Well-Being in the Associations between Social Support and Authoritarian Parenting Style
- 2018
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Ingår i: Journal of Child and Family Studies. - : Springer. - 1062-1024 .- 1573-2843. ; 27:3, s. 979-989
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Tidskriftsartikel (refereegranskat)abstract
- We examined the mediating role of Korean immigrant mothers' psychological well-being in the associations between mothers' emotional vs. instrumental support received from their kin, and their authoritarian parenting style with their preschoolers using longitudinal data. First-generation Korean immigrant mothers with preschool-aged children (N = 158; M (maternal age) = 36.11 years, SD = 3.90; M (child age) = 4.43 years, SD = 1.10) residing in Maryland, U.S., participated in three assessment waves. Each assessment wave was 6 months apart. Mothers reported on the amount of perceived emotional and instrumental support they received from their kin, their behavioral acculturation towards the American culture, and their family demographic information at Wave 1, their psychological well-being at Wave 2, and their authoritarian parenting style at Wave 3. The results revealed that higher levels of perceived instrumental support (but not emotional support) received from kin predicted higher levels of maternal psychological well-being 6 months later, which in turn predicted lower levels of reported authoritarian parenting style 6 months later. Our findings highlighted the importance of psychological well-being as a mechanism that explains how instrumental support can impact Korean immigrant mothers' parenting style, and the importance of distinguishing between types of support. Services providing instrumental support (e.g., childcare assistance) for first-generation immigrant mothers, particularly those with smaller or less effective kin networks, appear important to implement.
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| 42. |
- Shin, Ji Youn, et al.
(författare)
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The parenting practices and child outcomes of Korean immigrant mothers with different acculturative strategies
- 2010
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Ingår i: Korean Journal of Child Studies. - : Korean Association of Child Studies. - 1226-1688 .- 2234-408X. ; 31:1, s. 179-195
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Tidskriftsartikel (refereegranskat)abstract
- Downloadable article in English: http://ocean.kisti.re.kr/downfile/volume/kacs/ODHHBP/2010/v31n1/ODHHBP_2010_v31n1_179.pdf미국의한국계이민가정이해마다증가하고있으나부모의문화적응과자녀양육에관한연구는미흡한실정이다.본연구는미국동부지역의88명의한인이민어머니와(M=35.9세SD=3.77)2-6세유아를(M=4.29세SD=1.06;49.4%여아)대상으로실시되었다.어머니의문화적응유형에따라1)양육실제에어떠한차이가있는지,2)유아의사회ᆞ정서적행동에는어떠한차이가있는지,3)양육실제와아동의사회ᆞ정서적행동간에어떠한상관이있는지를살펴보았다.연구결과,한국과미국문화를균형지게통합한어머니들이미국문화에서고립되거나,두문화에서모두소외된어머니들보다자녀에게더욱긍정적인(애정표현,합리적문제해결,자율성격려)양육실제를사용하였으며자녀들또한정서적문제행동은적은반면친사회적행동은높은것으로나타났다
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| 43. |
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| 44. |
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