| 1. |
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| 2. |
- Asplund, M, et al.
(författare)
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Line formation in solar granulation - I. Fe line shapes, shifts and asymmetries
- 2000
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Ingår i: ASTRONOMY AND ASTROPHYSICS. - : SPRINGER-VERLAG. - 0004-6361. ; 359:2, s. 729-742
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Tidskriftsartikel (refereegranskat)abstract
- Realistic ab-initio 3D, radiative-hydrodynamical convection simulations of the solar granulation have been applied to Fe I and Fe II line formation. In contrast to classical analyses based on hydrostatic ID model atmospheres the procedure contains no adju
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| 3. |
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| 4. |
- Assarsson, Maria, et al.
(författare)
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Restoring proper radical generation by azide binding to the iron site of the E238A mutant R2 protein of ribonucleotide reductase from Escherichia coli.
- 2001
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 276:29, s. 26852-26859
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Tidskriftsartikel (refereegranskat)abstract
- The enzyme activity of Escherichia coli ribonucleotide reductase requires the presence of a stable tyrosyl free radical and diiron center in its smaller R2 component. The iron/radical site is formed in a reconstitution reaction between ferrous iron and molecular oxygen in the protein. The reaction is known to proceed via a paramagnetic intermediate X, formally a Fe(III)-Fe(IV) state. We have used 9.6 GHz and 285 GHz EPR to investigate intermediates in the reconstitution reaction in the iron ligand mutant R2 E238A with or without azide, formate, or acetate present. Paramagnetic intermediates, i.e. a long-living X-like intermediate and a transient tyrosyl radical, were observed only with azide and under none of the other conditions. A crystal structure of the mutant protein R2 E238A/Y122F with a diferrous iron site complexed with azide was determined. Azide was found to be a bridging ligand and the absent Glu-238 ligand was compensated for by azide and an extra coordination from Glu-204. A general scheme for the reconstitution reaction is presented based on EPR and structure results. This indicates that tyrosyl radical generation requires a specific ligand coordination with 4-coordinate Fe1 and 6-coordinate Fe2 after oxygen binding to the diferrous site.
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| 5. |
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| 6. |
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| 7. |
- Brena, Barbara, et al.
(författare)
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Ultrafast Molecular Dissociation of Water in Ice
- 2004
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Ingår i: Physical Review Letters. - : The American Physical Society. - 1079-7114 .- 0031-9007. ; 93, s. 148302-148305
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Tidskriftsartikel (refereegranskat)abstract
- Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path.
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| 8. |
- Chin, Yung-Kang Robert, et al.
(författare)
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Thermal analysis - Lumped-circuit model and finite element analysis
- 2003
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Ingår i: IPEC 2003: Proceedings of the 6th International Power Engineering Conference. - SINGAPORE : NANYANG TECHNOLOGICAL UNIV. ; , s. 952-957
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents the thermal analysis of Permanent Magnet Synchronous Motors (PMSMs) for electric vehicle traction applications. Modem thermal design techniques can be classified into two general methods, analytical lumped circuit and numerical analysis. It is the aim of this paper to investigate the strengths and weaknesses of the two approaches. Two commercially available thermal design packages, Motor-CAD and FEMLAB, are used in our investigation. Motor-CAD is a 3-dimensional (3-D) lumped circuit analysis package dedicated to the thermal design of motors. FEMLAB is a multi-physics 2- and 3-dimensional finite element analysis (FEA) package.
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| 9. |
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| 10. |
- Nordlund, D., et al.
(författare)
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Surface structure of thin ice Ih films
- 2004
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 395:1-3, s. 161-165
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Tidskriftsartikel (refereegranskat)abstract
- An angular dependent X-ray absorption spectroscopy study of the surface of thin ice films grown on Pt(1 1 1) is presented. Using different probing depths together with spectral calculations based on density functional theory, the spectra are interpreted in terms of the structure of surface, subsurface and bulk regions. It is shown that the crystalline ice is terminated with a large abundance of isotropically distributed free O–H groups and a distorted subsurface.
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| 11. |
- Nordlund, J., et al.
(författare)
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The influence of electrode morphology on the performance of a DMFC anode
- 2002
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Ingår i: Journal of Applied Electrochemistry. - 0021-891X .- 1572-8838. ; 32:3, s. 259-265
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Tidskriftsartikel (refereegranskat)abstract
- For low concentrations of methanol, mass transfer in the electrode is a limiting parameter for the direct methanol fuel cell (DMFC). To improve mass transfer, it is possible to induce convection in the gas backing layer or even in the porous electrode. In this study electrodes with different amounts of PTFE were compared to observe the influence of morphology on the anode performance. The hypothesis was that adding PTFE to the anode may make the morphology more favourable for carbon dioxide to evolve as a gas by creating the necessary pore sizes. Electrode performance was characterized electrochemically and the anode layer structure was studied using SEM, Hg-porosimetry and the van der Pauw method for measuring electric conductivity. Pores smaller than 0.04 mum were unaffected by adding PTFE while the volume fraction of pores of 0.04-1.0 mum diameter increased. Electrodes with 50% PTFE also performed as nonhydrophobized, despite the much higher ohmic losses and thickness. This implies that, above a certain amount, adding PTFE has a positive effect and that optimizing the electrode with PTFE may give better performance than electrodes without PTFE. The results suggest that gas evolves within the electrode, giving improved mass transfer in the liquid phase.
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| 12. |
- Ogasawara, H., et al.
(författare)
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Structure and Bonding of Water on Pt(111)
- 2002
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Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114. ; 89:27, s. 276102-276105
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Tidskriftsartikel (refereegranskat)abstract
- We address the adsorption of water on Pt(111) using x-ray absorption, x-ray emission, and x-ray photoelectron spectroscopy along with calculations in the framework of density functional theory. Using the direct relationship between the electronic structure and adsorbate geometry, we show that in the first layer all the molecules bind directly to the surface and to each other through the in-layer H bonds without dissociation, creating a nearly flat overlayer. The water molecules are adsorbed through alternating metal-oxygen (M-O) and metal-hydrogen (M-HO) bonds.
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| 13. |
- O'Shea, J. N., et al.
(författare)
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Hydrogen-bond induced surface core-level shift in pyridine carboxylic acids
- 2001
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 486:3, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular hydrogen bonding in thick films of pyridine carboxylic acids (isonicotinic; picolinic and bi-isonicotinic acid) evaporated onto rutile TiO2(1 1 0) has been investigated with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. These molecules are shown to be strongly H-bonded in the condensed phase, and a surface core-level shift is observed due to the presence of non-H-bonded nitrogen atoms in the surface layer. Density functional theory calculations are used to relate the experimental data to the proposed bonding configurations based on the surface termination of the known equilibrium solid-state structure. A kinetic barrier, attributed to the high degree of molecular orientation required for the formation of extended H-bonding networks, has also been investigated.
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| 14. |
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| 15. |
- Rieutord, M, et al.
(författare)
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A simulation of solar convection at supergranulation scale
- 2002
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Ingår i: Nuovo Cimento C. Colloquia on Physics. - 1124-1896. ; 25:5-6, s. 523-528
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Tidskriftsartikel (refereegranskat)abstract
- We present here numerical simulations of surface solar convection which cover a box of 30 x 30 x 3.2 Mm(3) with a resolution of 315 x 315 x 82, which is used to investigate the dynamics of scales larger than granulation. No structure resembling supergranulation is present; possibly higher Reynolds numbers (i.e. higher numerical resolution), or magnetic fields, or greater depth are necessary. The results also show interesting aspects of granular dynamics which are briefly presented, like extensive p-mode ridges in the k-w diagram and a ringlike distribution of horizontal vorticity around granules. At large scales, the horizontal velocity is much larger than the vertical velocity and the vertical motion is dominated by p-mode oscillations.
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Walther, Sten, et al.
(författare)
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Multicentre study of validity and interrater reliability of the modified Nursing Care Recording System (NCR11) for assessment of workload in the ICU
- 2004
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Ingår i: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172 .- 1399-6576. ; 48:6, s. 690-696
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Tidskriftsartikel (refereegranskat)abstract
- Background: Reliable assessment of nursing workload is necessary for the quantitative approach to staffing of intensive care units. The Nursing Care Recording System (NCR11) scores both the nursing contribution to patient care and those related to medical procedures. The purpose of the present work was to compare NCR11 scoring with the Therapeutic Intervention Scoring System (TISS) and Nine Equivalents of Nurse Manpower use Score (NEMS) and to examine the interrater reliability of NCR11 scoring. Methods: Bias and precision of workload scores (NCR11 vs. TISS or NEMS) were assessed for 6126 consecutive admissions (23910 ICU-days) at three intensive care units. Inter-rater reliability was analyzed by having nurses at nine ICUs score workload using NCR11 for three dummy intensive care patient cases presented over a 3-year period. Variability in scoring was analyzed using the coefficient of variation. Results: Agreement between NCR11 and TISS or NEMS was poor and limits of agreement were wide. Linear relationships between NCR11 and TISS or NEMS scores differed between units. Variability in NCR11 scoring decreased significantly from 10.4% to 5.9% between dummy cases 1 and 2 and remained low for patient case 3. Conclusion: The NCR11 does not measure the same elements of workload in the ICU as do TISS and NEMS. Inter-rater reliability with NCR11 is good, showing little variation in scoring between nurses.
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| 20. |
- Wernet, Ph., et al.
(författare)
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The Structure of the First Coordination Shell in Liquid Water
- 2004
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 304:5673, s. 995-999
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen-bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen-bonded tetrahedral structure in ice. Upon heating from 25°C to 90°C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen-bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed.
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| 21. |
- Öström, Henrik, et al.
(författare)
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Geometric structure and chemical bonding of acetylene adsorbed on Cu(110)
- 2004
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 565:2-3, s. 206-222
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Tidskriftsartikel (refereegranskat)abstract
- The chemical bonding and geometric structure of acetylene adsorbed on Cu(I 10) is analyzed using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES) in combination with density functional theory (DFT) total energy geometry optimizations and spectral calculations. XPS reveals two different adsorbed species at liquid nitrogen temperature. The molecular alignment is deduced from angle-resolved XAS, revealing that in one site the molecules are aligned with the C-C axis along the [0 0 1] direction and in the other site with an average angle of 35degrees to the Cu rows. The position of the shape resonance is used to deduce a C-C bond length of 1.35 Angstrom, which is close to the values obtained from the DFT geometry optimizations. XES reveals strong sigma-pi mixing and new occupied states close to the Fermi level, originating from the out-of-plane pi* orbital, which becomes occupied upon adsorption in agreement with the Dewar-Chatt-Duncanson model of the bonding.
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| 22. |
- Öström, H., et al.
(författare)
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Orbital rehybridization in n-octane adsorbed on Cu(110)
- 2003
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606. ; 118:8, s. 3782-3789
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the local electronic structure of n-octane adsorbed on the Cu(110) surface using symmetry-resolved x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) in combination with density functional theory (DFT) spectrum calculations. We found new adsorption-induced states in the XE spectra, which we assign to interaction between the bonding CH orbitals and the metal surface. By performing a systematic investigation of the influence of different structural parameters on the XA and XE spectra, we conclude that the molecular geometry is significantly distorted relative to the gas-phase structure. The bonding to the surface leads to a strengthening of the carbon–carbon bonds and a weakening of the carbon–hydrogen bonds, consistent with a rehybridization of the carbons from sp3 to sp2.8. ©2003 American Institute of Physics.
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