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Sökning: WFRF:(Fransson Thomas)

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1.
  • Lundgren, Markus, et al. (författare)
  • Analgesic antipyretic use among young children in the TEDDY study : No association with islet autoimmunity
  • 2017
  • Ingår i: BMC Pediatrics. - : Springer Science and Business Media LLC. - 1471-2431. ; 17:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: The use of analgesic antipyretics (ANAP) in children have long been a matter of controversy. Data on their practical use on an individual level has, however, been scarce. There are indications of possible effects on glucose homeostasis and immune function related to the use of ANAP. The aim of this study was to analyze patterns of analgesic antipyretic use across the clinical centers of The Environmental Determinants of Diabetes in the Young (TEDDY) prospective cohort study and test if ANAP use was a risk factor for islet autoimmunity. Methods: Data were collected for 8542 children in the first 2.5 years of life. Incidence was analyzed using logistic regression with country and first child status as independent variables. Holm's procedure was used to adjust for multiplicity of intercountry comparisons. Time to autoantibody seroconversion was analyzed using a Cox proportional hazards model with cumulative analgesic use as primary time dependent covariate of interest. For each categorization, a generalized estimating equation (GEE) approach was used. Results: Higher prevalence of ANAP use was found in the U.S. (95.7%) and Sweden (94.8%) compared to Finland (78.1%) and Germany (80.2%). First-born children were more commonly given acetaminophen (OR 1.26; 95% CI 1.07, 1.49; p = 0.007) but less commonly Non-Steroidal Anti-inflammatory Drugs (NSAID) (OR 0.86; 95% CI 0.78, 0.95; p = 0.002). Acetaminophen and NSAID use in the absence of fever and infection was more prevalent in the U.S. (40.4%; 26.3% of doses) compared to Sweden, Finland and Germany (p < 0.001). Acetaminophen or NSAID use before age 2.5 years did not predict development of islet autoimmunity by age 6 years (HR 1.02, 95% CI 0.99-1.09; p = 0.27). In a sub-analysis, acetaminophen use in children with fever weakly predicted development of islet autoimmunity by age 3 years (HR 1.05; 95% CI 1.01-1.09; p = 0.024). Conclusions: ANAP use in young children is not a risk factor for seroconversion by age 6 years. Use of ANAP is widespread in young children, and significantly higher in the U.S. compared to other study sites, where use is common also in absence of fever and infection.
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2.
  • Young, Iris D., et al. (författare)
  • Structure of photosystem II and substrate binding at room temperature
  • 2016
  • Ingår i: Nature. - : Macmillan Publishers Ltd.. - 0028-0836 .- 1476-4687. ; 540:7633, s. 453-457
  • 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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4.
  • Fuller, Franklin D, et al. (författare)
  • Drop-on-demand sample delivery for studying biocatalysts in action at X-ray free-electron lasers
  • 2017
  • Ingår i: Nature Methods. - : Macmillan Publishers Ltd.. - 1548-7091 .- 1548-7105. ; 14, s. 443-449
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray crystallography at X-ray free-electron laser sources is a powerful method for studying macromolecules at biologically relevant temperatures. Moreover, when combined with complementary techniques like X-ray emission spectroscopy, both global structures and chemical properties of metalloenzymes can be obtained concurrently, providing insights into the interplay between the protein structure and dynamics and the chemistry at an active site. The implementation of such a multimodal approach can be compromised by conflicting requirements to optimize each individual method. In particular, the method used for sample delivery greatly affects the data quality. We present here a robust way of delivering controlled sample amounts on demand using acoustic droplet ejection coupled with a conveyor belt drive that is optimized for crystallography and spectroscopy measurements of photochemical and chemical reactions over a wide range of time scales. Studies with photosystem II, the phytochrome photoreceptor, and ribonucleotide reductase R2 illustrate the power and versatility of this method.
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5.
  • Joffrin, E., et al. (författare)
  • Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
  • 2019
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
  • Forskningsöversikt (refereegranskat)abstract
    • For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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6.
  • Kern, Jan, et al. (författare)
  • Structures of the intermediates of Kok’s photosynthetic water oxidation clock
  • 2018
  • Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 563, s. 421-425
  • 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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8.
  • Rabe, Patrick, et al. (författare)
  • X-ray free-electron laser studies reveal correlated motion during isopenicillin N synthase catalysis
  • 2021
  • Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:34
  • 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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9.
  • Schmith, Anika, et al. (författare)
  • A host factor supports retrotransposition of the TRE5-A population in Dictyostelium cells by suppressing an Argonaute protein
  • 2015
  • Ingår i: Mobile DNA. - : Springer Science and Business Media LLC. - 1759-8753. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: In the compact and haploid genome of Dictyostelium discoideum control of transposon activity is of particular importance to maintain viability. The non-long terminal repeat retrotransposon TRE5-A amplifies continuously in D. discoideum cells even though it produces considerable amounts of minus-strand (antisense) RNA in the presence of an active RNA interference machinery. Removal of the host-encoded C-module-binding factor (CbfA) from D. discoideum cells resulted in a more than 90 % reduction of both plus-and minus-strand RNA of TRE5-A and a strong decrease of the retrotransposition activity of the cellular TRE5-A population. Transcriptome analysis revealed an approximately 230-fold overexpression of the gene coding for the Argonaute-like protein AgnC in a CbfA-depleted mutant. Results: The D. discoideum genome contains orthologs of RNA-dependent RNA polymerases, Dicer-like proteins, and Argonaute proteins that are supposed to represent RNA interference pathways. We analyzed available mutants in these genes for altered expression of TRE5-A. We found that the retrotransposon was overexpressed in mutants lacking the Argonaute proteins AgnC and AgnE. Because the agnC gene is barely expressed in wild-type cells, probably due to repression by CbfA, we employed a new method of promoter-swapping to overexpress agnC in a CbfA-independent manner. In these strains we established an in vivo retrotransposition assay that determines the retrotransposition frequency of the cellular TRE5-A population. We observed that both the TRE5-A steady-state RNA level and retrotransposition rate dropped to less than 10 % of wild-type in the agnC overexpressor strains. Conclusions: The data suggest that TRE5-A amplification is controlled by a distinct pathway of the Dictyostelium RNA interference machinery that does not require RNA-dependent RNA polymerases but involves AgnC. This control is at least partially overcome by the activity of CbfA, a factor derived from the retrotransposon's host. This unusual regulation of mobile element activity most likely had a profound effect on genome evolution in D. discoideum.
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10.
  • Sundqvist, Bertil, et al. (författare)
  • Physical properties of pressure polymerized C60
  • 1996
  • Ingår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, volume 3. - Pennington, NJ : The Electrochemical Society. - 1566771625 ; , s. 1014-1028
  • Konferensbidrag (refereegranskat)abstract
    • We present in this paper an overview of the physical properties of the high pressure polymerized C60 phase commonly known as "soft fcc". This phase has been studied by several methods over wide ranges in temperature T and/or pressure, p. We present here experimental information about the specific heat capacity, the thermal expansion coefficient, the lattice structure, and the thermal conductivity, and we also show results obtained by NMR and Raman spectroscopy. All data presented agree with the accepted model that the individual molecules in this phase are covalently bound to form linear molecular chains. In particular, the NMR data show clearly the presence of covalent bonds, and the Raman data exhibit several new lines at very low energies connected with chain vibrations. Thermal conductivity data obtained during polymerization show both the time dependence of the process and that polymerization occurs at lower p and T than observed previously for this phase.
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12.
  • Wang, Xiaofeng, et al. (författare)
  • Evidence for type ia supernova diversity from ultraviolet observations with the hubble space telescope
  • 2012
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 749:2, s. 126-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This data set provides unique spectral time series down to 2000 angstrom. Significant diversity is seen in the near-maximum-light spectra (similar to 2000-3500 angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminositiesmeasured in the uvw1/F250W filter are found to correlate with the B-band light-curve shape parameter Delta m(15)(B), but with much larger scatter relative to the correlation in the broadband B band (e.g., similar to 0.4 mag versus similar to 0.2 mag for those with 0.8 mag < Delta m(15)(B) < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by similar to 0.9 mag and similar to 2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.
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13.
  • Wigsten, Emma, 1984, et al. (författare)
  • Comparing Quality of Life of Patients Undergoing Root Canal Treatment or Tooth Extraction
  • 2020
  • Ingår i: Journal of Endodontics. - : Elsevier BV. - 0099-2399 .- 1878-3554. ; 46:105, s. 19-28
  • Tidskriftsartikel (refereegranskat)abstract
    • Introduction: The knowledge of patient-centered outcomes concerning the consequences of root canal treatment in daily life is limited. The treatment option is often tooth extraction with possible prosthetic replacement. This study aimed to achieve a greater understanding of the patient perspective by evaluating the effect of root canal treatment in terms of quality of life and quality-adjusted life year (QALY) weights in comparison with patients who underwent tooth extraction. Methods: Patients with either root canal treatment or extraction were recruited from 6 clinics in the general public dental service during a predetermined period of 8 weeks. Three different instruments were used: the Oral Health Impact Profile evaluating the oral health related quality of life (OHRQOL), the EQ-5D-5L evaluating health-related quality of life (HRQOL) and QALY weights, and a disease-specific questionnaire evaluating satisfaction regarding the root canal treatment. The evaluation was assessed at the initiation of treatment and after 1 month. Patient-based and tooth-specific characteristics were obtained from the dental records. Results: Eighty-five patients were included. The distribution between sexes was even, with 43 women and 42 men. The mean age was 51.1 years. Forty-eight patients (56.5%) had a tooth extraction, and 37 patients (43.5%) initiated root canal treatment. The response rate for the questionnaire at baseline was 95.3%, and at the 1-month follow-up, it was 74.1%. Two relevant and comparable groups were obtained after exclusion of the extracted third molars (n = 20), resulting in 65 patients for further analyses. At follow-up, the patients who initiated root canal treatment registered a significant improvement in perceived HRQOL according to the QALY weights (P = .02 and P < .01, respectively). Patients initiating root canal treatment reported generally high satisfaction. Conclusions: A cohort of patients either initiating root canal treatment or tooth extraction as a control group was established. Initiating root canal treatment had a positive impact on perceived HRQOL. The included patients in general dental practice registered overall high satisfaction regarding root canal treatment.
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14.
  • Alfredsson, P. Henrik, et al. (författare)
  • The diagnostic plot : a new way to appraise turbulent boundary-layer data
  • 2009
  • Ingår i: ADVANCES IN TURBULENCE XII. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642030840 ; , s. 609-612
  • Konferensbidrag (refereegranskat)abstract
    • During the last decade there has been a renewed interest in how averaged quantities of the turbulent boundary layer vary in the direction normal to the wall, especially with regard to the mean and fluctuation velocity distributions (see e.g. [1, 2]). Comparing data from different facilities and/or different techniques are, however, often inconclusive since the inaccuracies of the measured quantities may be larger than the trends one wants to investigate.
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15.
  • Alp, Dennis, et al. (författare)
  • The 30 Year Search for the Compact Object in SN 1987A
  • 2018
  • Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 864:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.
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16.
  • Alp, Dennis, et al. (författare)
  • X-Ray Absorption in Young Core-collapse Supernova Remnants
  • 2018
  • Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 864:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The material expelled by core-collapse supernova (SN) explosions absorbs X-rays from the central regions. We use SN models based on three-dimensional neutrino-driven explosions to estimate optical depths to the center of the explosion, compare different progenitor models, and investigate the effects of explosion asymmetries. The optical depths below 2 keV for progenitors with a remaining hydrogen envelope are expected to be high during the first century after the explosion due to photoabsorption. A typical optical depth is 100 t(4)(-2 )E(-2), where t(4) is the time since the explosion in units of 10,000 days (similar to 27 years) and E is the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity at similar to 1000 days at 1 MeV. The optical depths are approximately an order of magnitude lower for hydrogen-stripped progenitors. The metallicity of the SN ejecta is much higher than that in the interstellar medium, which enhances photoabsorption and makes absorption edges stronger. These results are applicable to young SN remnants in general, but we explore the effects on observations of SN 1987A and the compact object in Cas A in detail. For SN 1987A, the absorption is high and the X-ray upper limits of similar to 100 L-circle dot on a compact object are approximately an order of magnitude less constraining than previous estimates using other absorption models. The details are presented in an accompanying paper. For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature.
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17.
  • Alp, Dennis, MSc, 1992-, et al. (författare)
  • X-Ray and Gamma-Ray Emission from Core-collapse Supernovae : Comparison of Three-dimensional Neutrino-driven Explosions with SN 1987A
  • 2019
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 882:1
  • Tidskriftsartikel (refereegranskat)abstract
    • During the first few hundred days after the explosion, core-collapse supernovae (SNe) emit down-scattered X-rays and gamma-rays originating from radioactive line emissions, primarily from the Ni-56 -> Co-56 -> Fe-56 chain. We use supernova (SN) models based on three-dimensional neutrino-driven explosion simulations of single stars and mergers to compute this emission and compare the predictions with observations of SN 1987A. A number of models are clearly excluded, showing that high-energy emission is a powerful way of discriminating between models. The best models are almost consistent with the observations, but differences that cannot be matched by a suitable choice of viewing angle are evident. Therefore, our self-consistent models suggest that neutrino-driven explosions are able to produce, in principle, sufficient mixing, although remaining discrepancies may require small changes to the progenitor structures. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor envelope. The main effect of asymmetries is to vary the flux level by a factor of similar to 3. For the more asymmetric models, the shapes of the light curves also change. In addition to the models of SN 1987A, we investigate two models of SNe II-P and one model of a stripped-envelope SN IIb. The Type II-P models have observables similar to those of the models of SN 1987A, but the stripped-envelope SN model is significantly more luminous and evolves faster. Finally, we make simple predictions for future observations of nearby SNe.
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18.
  • Bergström, Malin, et al. (författare)
  • Mental health in Swedish children living in joint physical custody and their parents' life satisfaction : A cross-sectional study
  • 2014
  • Ingår i: Scandinavian Journal of Psychology. - : Wiley. - 0036-5564 .- 1467-9450. ; 55:5, s. 433-439
  • Tidskriftsartikel (refereegranskat)abstract
    • This study compared the psychological symptoms of 129 children in joint physical custody with children in single care and nuclear families, using a nationally representative 2011 survey of 1,297 Swedish children aged between four and 18 years. The outcome measure was the Strengths and Difficulties Questionnaire (SDQ) and its association with three dimensions of parental life satisfaction was investigated. Linear regression analyses showed higher SDQ-scores for children in joint physical custody (B=1.4, p<0.001) and single care (B=2.2, p<0.001) than in nuclear families, after adjustment for socio-demographic variables. The estimates decreased to 1.1 and 1.3, respectively, after being adjusted for parental life satisfaction (p<0.01). Our findings confirm previous research that showed lower symptom scores for children in nuclear families than children in single care and joint physical custody. Parental life satisfaction should be investigated further as a possible explanation of differences in symptom load between children in different living arrangements.
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19.
  • Bhandary, Sumanta, et al. (författare)
  • Controlling Electronic Structure and Transport Properties of Zigzag Graphene Nanoribbons by Edge Functionalization with Fluorine
  • 2015
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:36, s. 21227-21233
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we report a detailed study of the electronic structure and transport properties of mono- and difluorinated edges of zigzag graphene nanoribbons (ZGNR) using density functional theory (DFT). The calculated formation energies at 0 K indicate that the stability of the nanoribbons increases with the increase in the concentration of difluorinated edge C atoms along with an interesting variation of the energy gaps between 0.0 to 0.66 eV depending on the concentration. This gives a possibility of tuning the band gaps by controlling the concentration of F for terminating the edges of the nanoribbons. The DFT results have been reproduced by density functional tight binding method. Using the nonequilibrium Green functional method, we have calculated the transmission coefficients of several mono- and difluorinated ZGNR as a function of unit cell size and degree of homogeneous disorder caused by the random placement of mono and difluorinated C atoms at the edges.
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20.
  • Bhandary, Sumanta, 1985-, et al. (författare)
  • Controlling electronic structure and transport properties of zigzag graphene nanoribbons by mono- and difluorinated edge functionalization
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • In this work, we report a detailed study of the electronic structure and transport properties of mono- and di-fluorinated edges of zigzag graphene nanoribbons (ZGNR) using density functional theory (DFT). The calculated formation energies at 0K indicate that the stability of the nanoribbons increases with the increase in the concentration of di-fluorinated edge C atoms along with an interesting variation of the energy gaps between 0.0 to 0.66 eV depending on the concentration. This gives a possibility of tuning the band gaps by controlling the concentration of F for terminating the edges of the nanoribbons. The DFT results have been reproduced by single band tight binding as well as density functional tight binding methods. Using non-equilibrium Green functional method, we have calculated the transmission coecients of several mono and di-fluorinated ZGNR as a function of unit cell size and degree of homogeneous disorder caused by the random placement of mono and di-fuorinated C atoms at the edges.
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21.
  • Bhowmick, Asmit, et al. (författare)
  • Going around the Kok cycle of the water oxidation reaction with femtosecond X-ray crystallography
  • 2023
  • Ingår i: IUCrJ. - : International Union Of Crystallography. - 2052-2525. ; 10:6, s. 642-655
  • 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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22.
  • Bhowmick, Asmit, et al. (författare)
  • Structural evidence for intermediates during O2 formation in photosystem II
  • 2023
  • Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 617:7961, s. 629-636
  • 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.
  •  
23.
  • Bogacz, Isabel, et al. (författare)
  • Room temperature X-ray absorption spectroscopy of metalloenzymes with drop-on-demand sample delivery at XFELs
  • 2023
  • Ingår i: Pure and Applied Chemistry. - 0033-4545. ; 95:8, s. 891-897
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray crystallography and X-ray spectroscopy using X-ray free electron lasers plays an important role in understanding the interplay of structural changes in the protein and the chemical changes at the metal active site of metalloenzymes through their catalytic cycles. As a part of such an effort, we report here our recent development of methods for X-ray absorption spectroscopy (XAS) at XFELs to study dilute biological samples, available in limited volumes. Our prime target is Photosystem II (PS II), a multi subunit membrane protein complex, that catalyzes the light-driven water oxidation reaction at the Mn4CaO5 cluster. This is an ideal system to investigate how to control multi-electron/proton chemistry, using the flexibility of metal redox states, in coordination with the protein and the water network. We describe the method that we have developed to collect XAS data using PS II samples with a Mn concentration of <1 mM, using a drop-on-demand sample delivery method.
  •  
24.
  • Brodén, Joséphine, et al. (författare)
  • Cost-effectiveness of pulp capping and root canal treatment of young permanent teeth
  • 2019
  • Ingår i: Acta Odontologica Scandinavica. - : Taylor & Francis. - 0001-6357 .- 1502-3850. ; 77:4, s. 2751-7
  • Tidskriftsartikel (refereegranskat)abstract
    • OBJECTIVE: To contribute with information on cost-effectiveness of pulp capping and root canal treatment of posterior permanent vital teeth in children and adolescents with pulp exposures due to caries. MATERIAL AND METHODS: Cost-effectiveness by means of a Markov simulation model was studied in a Scandinavian setting. In a simulated 12-year-old patient, treatment of pulpal exposure of a permanent tooth, either by the initial treatment pulp capping or root canal treatment, was followed for 9 years until the patient was 21. The model was based on outcome data obtained from published literature and cost data based on reference prices. RESULTS: In the simulated case, with the annual failure probalility (AFP) of 0.034 for pulp capping, the total cost for an initial treatment with pulp capping and any anticipated following treatments during the 9 years, was 367 EUR lower than for a root canal treatment as the initial treatment. After an initial treatment with pulp capping 10.4% fewer teeth, compared with initial root canal treatment, were anticipated to be extracted. Pulp capping was thus considered to be the cost-effective alternative. The sensitivity analyses showed that the AFP of a tooth requiring a root canal treatment after an initial pulp capping needed to be 0.2 before root canal treatment may be considered being the cost-effective treatment. CONCLUSIONS: This model analysis indicated initial treatment by pulp capping to be cost-effective compared to root canal treatment in children and adolescents with pulp exposures due to caries.
  •  
25.
  • Brodén, Joséphine, et al. (författare)
  • Health economic evaluation of pulp capping versus root canal treatment in young permanent teeth
  • 2018
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Objective. There is a lack of knowledge regarding the health economic consequences of pulp capping and root canal treatment in order to treat children’s and adolescents’ permanent teeth with pulp exposures due to caries. Therefore, the aim of this study was to study the cost effectiveness of performing a pulp capping compared to a root canal treatment in children and adolescents with pulp exposures due to caries. Methods. The cost effectiveness was studied by the use of a Markov simulation model where a simulated 12-year-old patient with a pulp exposure in a permanent tooth was followed for 9 years. The probability of making a transition from one health state to another was calculated from data retrieved after literature searches of published clinical studies. The outcome was measured as avoided extractions until the subject was 21 years old. The time spent on the two treatments was studied by sending a survey to general dentists. Costs were discounted with 3% annually. Results. Based on the answers from the general dentists, the cost for a pulp capping as the initial treatment was 138 EUR and the cost for a root canal treatment as the initial treatment was 608 EUR during the 9 years. We found that less teeth were extracted after a pulp capping than after a root canal treatment in this age group. Pulp capping was found to be cost effective (dominant) compared to root canal treatment as the initial treatment.
  •  
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