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  • 951.
    Zámečníková, Martina
    et al.
    Charles University.
    Soldán, Pavel
    Charles University.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Nyman, Gunnar
    University of Gothenburg.
    Formation of CO+ by radiative association2019Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 489, nr 2, s. 2954-2960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We theoretically estimate formation rate coefficients for CO+ through the radiative association of C+(2P) with O(3P). In 1989, Petuchowski et al. claimed radiative association to be the most important route for CO+ formation in SN 1987A. In 1990, Dalgarno, Du and You challenged this claim. Therefore, in this study, we improve previous estimates of the radiative association rate coefficients for forming CO+ from C+(2P) and O(3P). To do this, we perform quantum mechanically based perturbation theory calculations as well as semiclassical calculations, which are combined with Breit–Wigner theory in order to add the effect of shape resonances. We explicitly include four electronic transitions. The required potential energy and transition dipole-moment curves are obtained through large basis set multireference configuration interaction electronic structure calculations. We report cross-sections and from these we obtain rate coefficients in the range of 10 –10 000 K, finding that the CO+ formation rate coefficient is larger than the previous estimate by Dalgarno et al. Still our results support their claim that in SN 1987A, CO is mainly formed through radiative association and not through the charge transfer reaction CO+ + O → CO + Oas earlier suggested by Petuchowski et al.

  • 952.
    Århammar, Cecilia
    et al.
    AB Sandvik Coromant, Sandviken.
    Silvearv, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bergman, A.
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University.
    Norgren, Susanne M
    AB Sandvik Coromant, Sandviken.
    Pedersen, Henrik
    Department of Physics, Chemistry and Biology, Linköping University.
    Ahuja, Rajeev B.
    Division of Materials Theory, Department of Physics and Astronomy, Uppsala University.
    A theoretical study of possible point defects incorporated into α-alumina deposited by chemical vapor deposition2014Inngår i: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, nr 2, s. 1-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The energetics and electronic structure of carbon, chlorine, hydrogen, and sulfur in α-Al2O3 was investigated by first principles and thermodynamical calculations. These species are present in the gas phase during the synthesis of α-Al2O3 by chemical vapor deposition (CVD) but little is known of their solubility in this compound. The heat of formation from standard reference states of the elements varying the chemical potential of each element was calculated. An attempt to model the actual conditions in the CVD process was made, using the species and solid compounds present in a common CVD process as reference states. Our calculations suggest that sulfur from the catalyzing agent H2S will not solve in α-Al2O3 during deposition by CVD. It is found that the neutral chlorine and hydrogen interstitial defects display the lowest heat of formation, 281 and 280 kJ/mol, respectively, at the modeled CVD conditions. This energy is too high in order for neutral defects to form during CVD of α-Al2O3 at any significant amounts. The charged defects and their compensation were studied. Carbon substituting oxygen is found to be energetically favored under the modeled CVD conditions, considering carbon dioxide as competing species to solid solubility in α-Al2O3 at an energy of -128 kJ/mol. However, care needs to be taken when choosing the possible competing carbon-containing phases. Compensation of carbon substituting for oxygen by oxygen vacancies takes place at 110 kJ/mol from standard reference states, graphite, fcc-Al and O2. The carbon solubility in Al2O3 is difficult to measure with standard analysis techniques such as X-ray diffraction and energy dispersive X-ray spectroscopy, but several stable compounds in the Al-C-O are available in the literature

  • 953.
    Öberg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Adjizian, Jean-Joseph
    Department of Chemistry, University of Sussex, Falmer, Brighton , Nanoscopic Physics (NAPS), Université catholique de Louvain.
    Erbahar, D.
    Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Rio, J.
    Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Humbert, Bernard
    Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Nancy Université, Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Dossot, Manuel
    Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Nancy Université, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, UMR 7564, CNRS–University of Lorraine.
    Soldatov, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Lefrant, S.
    Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Mevellec, J-Y
    Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Briddon, Patrick R.
    Department of Physics, University of Newcastle, School of Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne, School of Natural Science, University of Newcastle upon Tyne, Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Rayson, Mark
    Department of Chemistry, The University of Surrey, Guildford, School of Electrical and Electronic Engineering, Newcastle University, Newcastle upon Tyne.
    Ewels, Christopher P.
    Department of Physics, University of Exeter, CPES, University of Sussex, Falmer, Brighton, Université de Nantes, Institut des Mat´eriaux Jean Rouxel (IMN), Universit´e de Nantes, Centre national de la recherche scientifique (CNRS).
    Effect of functionalization and charging on resonance energy and radial breathing modes of metallic carbon nanotubes2016Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 93, nr 4, artikkel-id 45408Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    While changes in resonant Raman scattering measurements are commonly used to measure the effect of chemical functionalization on single-walled carbon nanotubes, the precise effects of functionalization on these spectra have yet to be clearly identified. In this density functional theory study, we explore the effects of functionalization on both the nanotube resonance energy and frequency shifts in radial breathing mode. Charge transfer effects cause a shift in the first Van Hove singularity spacings, and hence resonance excitation energy, and lead to a decrease in the radial breathing mode frequency, notably when the Fermi level decreases. By varying stochastically the effective mass of carbon atoms in the tube, we simulate the mass effect of functionalization on breathing mode frequency. Finally, full density functional calculations are performed for different nanotubes with varying functional group distribution and concentration using fluorination and hydrogenation, allowing us to determine overall effect on radial breathing mode and charge transfer. The results concur well with experiment, and we discuss the importance when using Raman spectroscopy to interpret experimental functionalization treatments

  • 954.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Polarization-resolved dual-view holographic system for 3D inspection of scattering particles2019Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 58, nr 34, s. G31-G40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel dual-view polarization-resolved pulsed holographic system for particle measurements is presented. Both dual-view configuration and polarization-resolved registration are well suited for particle holography. Dual-view registration improves the accuracy in the detection of 3D position and velocities, and polarization-resolved registration provides polarization information about individual particles. The necessary calibrations are presented, and aberrations are compensated for by mapping the positions in the two views to positions in a global coordinate system. The system is demonstrated on a sample consisting of 7 μm spherical polystyrene particles dissolved in water in a cuvette. The system is tested with different polarizations of the illumination. It is found that the dual view improves the accuracy significantly in particle tracking. It is also found that by having polarization-resolved holograms, it is possible to separate naturally occurring sub-micrometer particles from the larger, 7 μm seeding particles.

  • 955.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Axial Particle Positioning by Wavefront Parameterization using Chebyshev Polynomials and Off-axis Digital Holography2017Inngår i: Digital Holography and Three-Dimensional Imaging, Washington: The Optical Society , 2017, artikkel-id M4A.3Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A particle can be axially positioned where its scattered light has a plane wavefront. The phase anomaly compared to a plane wave is fitted to 3D Chebyshev polynomial, where coefficients correspond to the axial position.

  • 956.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Improved particle position accuracy from off-axis holograms using a Chebyshev model2018Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, nr 1, s. A157-A163Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Side scattered light from micrometer-sized particles is recorded using an off-axis digital holographic setup. From holograms, a volume is reconstructed with information about both intensity and phase. Finding particle positions is non-trivial, since poor axial resolution elongates particles in the reconstruction. To overcome this problem, the reconstructed wavefront around a particle is used to find the axial position. The method is based on the change in the sign of the curvature around the true particle position plane. The wavefront curvature is directly linked to the phase response in the reconstruction. In this paper we propose a new method of estimating the curvature based on a parametric model. The model is based on Chebyshev polynomials and is fit to the phase anomaly and compared to a plane wave in the reconstructed volume. From the model coefficients, it is possible to find particle locations. Simulated results show increased performance in the presence of noise, compared to the use of finite difference methods. The standard deviation is decreased from 3–39 μm to 6–10 μm for varying noise levels. Experimental results show a corresponding improvement where the standard deviation is decreased from 18 μm to 13 μm.

  • 957.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Polarization Resolved Dual-View Holographic System for Investigation of Microparticles2019Inngår i: OSA Technical Digest (Optical Society of America, 2019), 2019, artikkel-id Th2A.5Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A dual-view polarization resolved digital-holographic system is presented. The necessary calibration for both polarization and spatial coordinates are outlined. As an example the system is is used to track spherical microparticles in a cuvette.

  • 958.
    Öhman, L. O.
    et al.
    Umeå universitet.
    Ganemi, B.
    Kungliga tekniska högskolan, KTH.
    Björnbom, E.
    Kungliga tekniska högskolan, KTH.
    Rahkamaa, K.
    Åbo Akademi.
    Keiski, R. L.
    Uleåborg universitet.
    Paul, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Catalyst preparation through ion-exchange of zeolite Cu-, Ni-, Pd-, CuNi- and CuPd-ZSM-52002Inngår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 73, nr 2-3, s. 263-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ion-exchanged zeolite ZSM-5 is the best known catalyst for direct NOx decomposition and a viable candidate for NOx reduction with methane. The preparation is crucial for the efficiency of the conversion and this paper describes the ion-exchange, with Cu2+, Ni2+ or Pd2+, and the dual exchange, with Cu2+/Ni2+ or Cu2+/Pd2+, under appropriate pH and ion concentrations for maximum dispersion.

  • 959.
    Öhman, L.O.
    et al.
    Umeå universitet.
    Paul, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Materials aspects of titanium-doped aluminas: 14%Ti/γ-Al2O3/Cu and sulfided Al2O3-TiO2/NiMo2002Inngår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 73, nr 2-3, s. 242-251Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Materials aspects of titanium-doped alumina catalysts are discussed in light of a partly new synthesis route, ion exchange reactions and sulfidation. Starting with a solution of the isopropoxides of aluminum and titanium, we aimed at an Al:Ti ratio of 6:1, which corresponds to the maximum acidity of the final product. Transmission electron micrographs showed that the synthesis gave a product of nearly monodisperse, rectangular particles and X-ray diffractograms revealed an amorphous to nano-crystalline structure reminiscent of γ-Al2O3. The Brunauer-Emmet-Teller area was 340 m2 g-1 and the H+ titration found 3 acidic sites nm-2. These numbers indicate that the titanium modification may fourfold increase the ion exchange capacity of a regular alumina. The importance of titanium modification for catalysis is discussed in connection with selective catalytic reduction with hydrocarbon reactions over Cu/14%Ti-Al2O3 and hydrogenation of 1-Me-naphthalene over sulfided NiMo/Al2O3-TiO2. The Ti4+ ions in the alumina lattice are almost irreducible, but infrared spectra suggested that these ions act as dispersion agents not only for adsorbed Cu2+ ions, but also for a supported phase of sulfided NiMo. Finally, we show that a simple weight control can be used to monitor the sulfidation and to indicate if the synthesis has produced a separate, reducible titania phase.

  • 960.
    Öström, Jonatan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Erratum: “Reaction rate constant for radiative association of CF+” [J. Chem. Phys. 144, 044302 (2016)]2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 24, artikkel-id 249901Artikkel i tidsskrift (Fagfellevurdert)
  • 961.
    Öström, Jonatan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Reaction rate constant for radiative association of CF+2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, nr 4, artikkel-id 44302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C+) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 11Π → X1Σ+ and rovibrational transitions on the X1Σ+ and a3Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit–Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius–Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10–250 K, the rate constant is about 10−21 cm3 s−1, rising toward 10−16 cm3 s−1 for a temperature of 30 000 K.

  • 962.
    Öztas, Ahmet M.
    et al.
    Hacettepe University, Ankara.
    Smith, Michael L.
    Anabolic Laboratories, Inc., Tempe, AZ.
    Paul, Jan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Spacetime curvature is important for cosmology constrained with supernova emissions2008Inngår i: International journal of theoretical physics, ISSN 0020-7748, E-ISSN 1572-9575, Vol. 47, nr 9, s. 2464-2478Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate universe expansion models as functions of emission frequency ratio decline rather than redshift z, using the latest on-line, self-consistent data from 192 supernovae. We present results for simpler and some current models of cosmology, including those with dark energy (standard model) and a recent model correcting for the effect of a small time-dependent, emission frequency increase with lookback. This new model, with a gentle lookback decline of the Planck constant, and the standard model fit the data with similar confidence according to Bayesian Information Criteria. The standard model tends towards solutions high in matter density while remaining flat, but models without dark energy tend towards dilute universes with significant spacetime and curvature and a smaller Hubble constant. We conclude the normalized spacetime parameter, Ω k , should not be ignored and it includes the combined contributions of huge spacetime magnitude and curvature.

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