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  • 301. Fredriksson, Sverker
    et al.
    Enström, Daniel
    Hansson, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ekelin, Svante
    Kungliga tekniska högskolan, KTH.
    Nicolaidis, A.
    Is dark matter made up of massive quark objects?1999In: Dark matter in astrophysics and particle physics 1998: proceedings of the Second International Conference on Dark Matter in Astrophysics and Particle Physics / [ed] Hans Volker Klapdor-Kleingrothaus ; L. Baudis, Bristol: IOP Publishing Ltd , 1999, p. 651-658Conference paper (Refereed)
    Abstract [en]

    We suggest that dark matter is made up of massive quark objects that have survived from the Big Bang, representing the ground state of "baryonic'' matter. Hence, there was no overall phase transition of the original quark matter, but only a split-up into smaller objects. We speculate that normal hadronic matter comes about through enforced phase transitions when such objects merge or collide, which also gives rise to the cosmic gamma-ray bursts.

  • 302.
    Fredriksson, Sverker
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hansson, Johan
    Ekelin, Svante
    Kungliga tekniska högskolan, KTH.
    A potential diquark in the proton1997In: Zeitschrift für Physik C Particles and Fields, ISSN 0170-9739, E-ISSN 1431-5858, Vol. 75, no 1, p. 107-111Article in journal (Refereed)
    Abstract [en]

    A non-relativistic, QCD-based, potential quark model for the proton and the neutron inevitably predicts a spin-0 diquark structure with an rms radius of the order of 0.35rfm or smaller. We prove this by solving the (S wave) hamiltonian by De Rújula et al. with variational methods. It is essential to include all quark interactions and to use realistic test wave-functions. The protondelta mass difference, the magnetic moments and the nucleon charge radii can be reproduced only with wave functions that contain a mixture of quark-diquark and three-quark states. Approaches with just a quark-diquark component give incorrect magnetic moments, while those without diquarks lead to a too low proton-delta mass difference.

  • 303. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    A new indication of diquarks in baryons1982In: Zeitschrift für Physik C Particles and Fields, ISSN 0170-9739, E-ISSN 1431-5858, Vol. 14, no 1, p. 41-46Article in journal (Refereed)
    Abstract [en]

    In data from 100 GeV/c p d, 200 GeV/cpd and 200 GeV/cπ - d collisions there is evidence that the probability for a double-collisiondecreases slowly with increasing number of hadrons produced in the first projectile-nucleon collision. We argue that the presence of diquarks in baryons is the only plausible explanation of such an effect.

  • 304. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Demon deuteron: heavy or healthy?1982Report (Other academic)
  • 305. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Demon deuterons1981In: Berkeley 1981, Proceedings, High Energy Heavy Ion Study, 1981, p. 423-237Conference paper (Refereed)
  • 306. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Demon deuterons: dead or alive?1982Report (Other academic)
  • 307. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Demon nuclei: a closer look!1982Report (Other academic)
  • 308. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Kicking around with the deuteron1981In: Dubna HEP Seminar 1981:0250, 1981Conference paper (Refereed)
  • 309. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Probing the space-time structure of multiparticle production processes1981In: Zeitschrift für Physik C Particles and Fields, ISSN 0170-9739, E-ISSN 1431-5858, Vol. 10, no 2, p. 185-187Article in journal (Refereed)
    Abstract [en]

    It is shown that the models for highenergy multiparticle production in which the notion of a hadronicformation time plays a central role are in disagreement with recently published compilations of the rescatter probabilities in 100 GeV/c p d and 200 GeV/c p d collisions.

  • 310. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    The diquark deuteron1982In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 48, no 1, p. 14-16Article in journal (Refereed)
    Abstract [en]

    It is speculated that an almost stable state of hadronic and nuclear matter can be built from diquarks. It is suggested that this alternative form of matter has already revealed itself in existing experimental data in the form of a diquark "deuteron" with JP=0- and with several other anomalous properties.

  • 311. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Larsson, Tomas
    A new diquark model for deep inelastic structure functions1982In: Zeitschrift für Physik C Particles and Fields, ISSN 0170-9739, E-ISSN 1431-5858, Vol. 14, no 1, p. 35-39Article in journal (Refereed)
    Abstract [en]

    The bulk of data from deep inelasticep, eD, μp, μN, νp and νN scattering is fitted with a new diquark model of nucleons. The proton is found to be mostly in au(ud) 0 state, where the (ud)0 diquark has spin and isospin zero. There is hence no trace ofSU(6) symmetry among diquarks in nucleons.

  • 312. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Larsson, Tomas
    Are "Gluon Effects" caused by diquarks?1983In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 51, no 24, p. 2179-2182Article in journal (Refereed)
    Abstract [en]

    The possible importance of diquarks in high-energy physics is discussed and it is suggested that this nonperturbative phenomenon can explain the trends in high-energy data that are usually attributed to gluon processes as described by perturbative QCD. Several experimental tests are suggested for discriminating between gluon and diquark phenomena.

  • 313. Fredriksson, Sverker
    et al.
    Jändel, Magnus
    Larsson, Tomas
    Probing spin-1 diquarks in deep inelastic structure functions1983In: Zeitschrift für Physik C Particles and Fields, ISSN 0170-9739, E-ISSN 1431-5858, Vol. 19, no 1, p. 53-55Article in journal (Refereed)
    Abstract [en]

    Within the scope of a new diquark model for deep inelastic structure functions presented by us recently we use the existing data onF 1 ep (x,Q2) to learn about the admixture of spin-1 diquarks in nucleons. It turns out that they are so rare, heavy and extended compared to spin-0 diquarks that they are presumably accidental and not dynamical. Their number and form factors can be understood qualitatively within this picture. Still, the spin-1 diquarks give interesting structures in data and, together with quarks and spin-0 diquarks, carry enough momentum to account for the full nucleon energy. A gluon component is hence not needed in the nucleon!

  • 314. Fredriksson, Sverker
    et al.
    Larsson, Tomas
    A comment on diquark fragmentation1983In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 28, no 1, p. 255-256Article in journal (Other academic)
    Abstract [en]

    We discuss diquark fragmentation and suggest that a spectator uu system in deep-inelastic lepton-nucleon scattering has a larger breakup probability than a ud system. The reason for this is argued to be that half of the leftover ud systems are in bound (ud)0 diquark configurations, while no such bound uu diquarks exist.

  • 315.
    Frommhold, Lothar
    et al.
    University of Texas, Physics Department.
    Abel, Martin
    University of Texas, Physics Department.
    Wang, Fei
    Physics Department, Beijing Institute of Technology, China.
    Gustafsson, Magnus
    Department of Chemistry, University of Gothenburg.
    Li, Xiaoping
    Department of Chemistry, Michigan State University.
    Hunt, Katherine L.C.
    Department of Chemistry, Michigan State University.
    Infrared atmospheric emission and absorption by simple molecular complexes, from first principles2010In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 108, no 17, p. 2265-2272Article in journal (Refereed)
    Abstract [en]

    Quantum chemical methods are used to obtain the interaction-induced dipole surfaces (IDS) of complexes of two interacting (i.e. colliding) molecules, for example H2–H2, H2–He, etc., collisional complexes, along with their potential energy surfaces (PES). Eight H2 bond distances, from 0.942 to 2.801 bohr, are chosen for each H2 molecule to account for rotovibrational excitations. Rotovibrational matrix elements of these ID and PE surfaces are computed as necessary for the study of supermolecular (‘collision-induced’) absorption spectra of dense hydrogen gas, and of gaseous mixtures of hydrogen and helium, at temperatures up to several thousand kelvin and for frequencies from 0 to those of several H2 overtone bands. Rotovibrational state to state scattering calculations couple the collisional complex perturbatively to single photons. The absorption process causes rotovibrational transitions in one molecule, or simultaneous transitions in both molecules (when H2–H2 collisional complexes are considered). The spectral profiles of tens of thousands of such transitions are computed from first principles. Individual ‘lines’ are very broad so that they overlap substantially, forming a supermolecular quasi-continuum. The comparison of the computed collision-induced absorption (CIA) spectra with existing laboratory measurements at low temperatures (≤ 300 K) shows close agreement so that our results for higher temperatures, where laboratory experiments do not exist, may be used with confidence. Similar calculations of CIA spectra at high temperatures and frequencies are underway for other collisional systems (e.g. H2–H) of interest in astrophysical applications (e.g. ‘cool’ stellar atmospheres). Collision-induced Raman spectra (CIRS) have been similarly obtained; computed Raman spectra also compare favourably with existing laboratory measurements.

  • 316.
    Furustig, Joel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Dobryden, Illia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    The measurement of wear using AFM and wear interpretation using a contact mechanics coupled wear model2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 350-351, p. 74-81Article in journal (Refereed)
    Abstract [en]

    Detailed understanding of wear processes is required to improve the wear resistance and lifetime of machine components. Atomic force microscopy (AFM) is used to measure surface height profiles with high precision, before and after a wear experiment. The distribution and depth of wear on steel surfaces is then calculated using a relocation method. A numerical investigation of wear based on Archard's equation is conducted on the same measured surfaces. A good correlation was found between the model and experiment for wear larger than a hundred nm. The wear mechanisms considered in the numerical simulation was thus found to be the cause of the majority of the wear. On the scale of tens of nm the correlation was limited, but the measured wear was still analysed in detail.

  • 317.
    Gahn, G. F.
    et al.
    Stockholm Observatory, AlbaNova University Centre, Stockholm University.
    Grenman, Tiia
    Fredriksson, Sverker
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Kristen, H.
    Imminent Training Technol AB.
    Globulettes as seeds of brown dwarfs and free-floating planetary-mass objects2007In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 133, no 4, p. 1795-1809Article in journal (Refereed)
    Abstract [en]

    Some H II regions surrounding young stellar clusters contain tiny dusty clouds, which on photos look like dark spots or teardrops against a background of nebular emission. From our collection of Hα images of 10 H II regions gathered at the Nordic Optical Telescope, we found 173 such clouds, which we call "globulettes," since they are much smaller than normal globules and form a distinct class of objects. Many globulettes are quite isolated and located far from the molecular shells and elephant trunks associated with the regions. Others are attached to the trunks (or shells), suggesting that globulettes may form as a consequence of erosion of these larger structures. None of our objects appear to contain stellar objects. The globulettes were measured for position, dimension, and orientation, and we find that most objects are smaller than 10 kAU. The Rosette Nebula and IC 1805 are particularly rich in globulettes, for which the size distributions peak at mean radii of ∼2.5 kAU, similar to what was found by Reipurth and coworkers and De Marco and coworkers for similar objects in other regions. We estimate total mass and density distributions for each object from extinction measures and conclude that a majority contain <13 MJ, corresponding to planetary-mass objects. We then estimate the internal thermal and potential energies and find, when also including the effects from the outer pressure, that a large fraction of the globulettes could be unstable and would contract on short timescales, < 106 yr. In addition, the radiation pressure and ram pressure exerted on the side facing the clusters would stimulate contraction. Since the globulettes are not screened from stellar light by dust clouds farther in, one would expect photoevaporation to dissolve the objects. However, surprisingly few objects show bright rims or teardrop forms. We calculate the expected lifetimes against photoevaporation. These lifetimes scatter around 4 × 10 6 yr, much longer than estimated in previous studies and also much longer than the free-fall time. We conclude that a large number of our globulettes have time to form central low-mass objects long before the ionization front, driven by the impinging Lyman photons, has penetrated far into the globulette. Hence, the globulettes may be one source in the formation of brown dwarfs and free-floating planetary-mass objects in the galaxy.

  • 318.
    Galstyan, V.
    et al.
    CNR IDASC SENSOR Lab.
    Comini, E.
    CNR IDASC SENSOR Lab.
    Faglia, G.
    CNR IDASC SENSOR Lab.
    Vomiero, Alberto
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Brisotto, M.
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, E.
    INSTM and Chemistry for Technologies Laboratory.
    Sberveglieri, G.
    CNR IDASC SENSOR Lab.
    Fabrication of TiO 2 and TiO 2 nanotubular arrays and their gas sensing properties2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 25, p. 757-760Article in journal (Refereed)
    Abstract [en]

    Pure TiO 2 and TiO 2 nanotubular arrays were successfully sensitized. Nanotubular arrays were prepared by electrochemical anodization of thin films of Ti and of Ti-Nb deposited on alumina substrates with two different roughness. Morphological characterization and functional properties are presented. The gas sensing properties of TiO 2 and TiO 2 nanotubes with different gases have been tested in a wide range of operating temperatures. © 2011 Published by Elsevier Ltd.

  • 319.
    Galstyan, V.
    et al.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Comini, E.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Vomiero, Alberto
    SENSOR Lab, Department of Chemistry and Physics, Brescia University and CNR-IDASC.
    Ponzoni, A.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Concina, Isabella
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Brisotto, M.
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, E.
    INSTM and Chemistry for Technologies Laboratory.
    Faglia, G.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Sberveglieri, G.
    Department of Physics, Chemistry and Biology (IFM), Linköping University.
    Fabrication of pure and Nb-TiO 2 nanotubes and their functional properties2012In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 536, no SUPPL.1, p. S488-S490Article in journal (Refereed)
    Abstract [en]

    TiO 2 and Nb-doped TiO 2 nanotubes were obtained on flexible polymeric substrates (Kapton HN) and alumina with high roughness (alumina substrate with granular surface). Nanotubes were prepared by electrochemical anodization of a Ti thick film. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the morphology of the structures and the roughness of the substrates. The functional properties of tubular arrays obtained on flexible and rough substrates were investigated towards two applications, namely, chemoresistive gas sensors and flexible dye sensitized solar cells. © 2011 Elsevier B.V. All rights reserved.

  • 320.
    Galstyan, V.
    et al.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Vomiero, Alberto
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Comini, E.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Faglia, G.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Sberveglieri, G.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    TiO 2 nanotubular and nanoporous arrays by electrochemical anodization on different substrates2011In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 1, no 6, p. 1038-1044Article in journal (Refereed)
    Abstract [en]

    The preparation of nanotubular arrays on different substrates and nanoporous structures on titanium foil by means of electrochemical anodization of titanium layer has been investigated. Highly aligned nanotubes of TiO 2 on flexible, rough and flat substrates are reported. Modification of anodization conditions of titanium on specific substrates such as polyethylene terephthalate (PET), conducting glass and granular alumina was found to affect the morphology of TiO 2 nanotubes. Two different kinds of aqueous electrolytes have been applied, containing either glycerol or H 2SO 4, in order to investigate the effect of ion mobility on anodization process. Galvanostatic and potentiostatic anodization modes have been investigated: transition from nanotubes to nanoporous structures has been highlighted in galvanostatic mode, depending on the intensity of anodization current density. These results pave the way for massive production of TiO 2 nanotubes over, in principle, whatever substrate, enabling exploitation of new functional properties derived from the combination of tubes and substrates. This journal is © The Royal Society of Chemistry 2011.

  • 321.
    Galstyan, Vardan
    et al.
    CNR IDASC SENSOR Lab.
    Comini, Elisabetta
    CNR IDASC SENSOR Lab.
    Faglia, Guido
    CNR IDASC SENSOR Lab.
    Vomiero, Alberto
    CNR IDASC SENSOR Lab.
    Borgese, Laura
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, Elza
    INSTM and Chemistry for Technologies Laboratory.
    Sberveglieri, Giorgio
    CNR IDASC SENSOR Lab.
    Fabrication and investigation of gas sensing properties of Nb-doped TiO 2 nanotubular arrays2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 23, article id 235706Article in journal (Refereed)
    Abstract [en]

    Synthesis of Nb-containing titania nanotubular arrays at room temperature by electrochemical anodization is reported. Crystallization of pure and Nb-doped TiO 2 nanotubes was carried out by post-growth annealing at 400°C. The morphology of the tubes obtained was characterized by scanning electron microscopy (SEM). Crystal structure and composition of tubes were investigated by glancing incidence x-ray diffraction (GIXRD) and total reflection x-ray fluorescence (TXRF). For the first time gas sensing characteristics of Nb-doped TiO 2 nanotubes were investigated and compared to those of undoped nanotubes. The functional properties of nanotubular arrays towards CO, H 2, NO 2, ethanol and acetone were tested in a wide range of operating temperature. The introduction of Nb largely improves conductivity and enhances gas sensing performances of TiO 2 nanotubes. © 2012 IOP Publishing Ltd.

  • 322.
    Galstyan, Vardan
    et al.
    CNR IDASC SENSOR Lab.
    Vomiero, Alberto
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Concina, Isabella
    CNR IDASC SENSOR Lab.
    Braga, Antonio
    CNR IDASC SENSOR Lab.
    Brisotto, Mariangela
    INSTM and Chemistry for Technologies Laboratory.
    Bontempi, Elza
    INSTM and Chemistry for Technologies Laboratory.
    Faglia, Guido
    CNR IDASC SENSOR Lab.
    Sberveglieri, Giorgio
    CNR IDASC SENSOR Lab.
    Vertically aligned TiO 2 nanotubes on plastic substrates for flexible solar cells2011In: Small, ISSN 1613-6810, E-ISSN 1613-6829, Vol. 7, no 17, p. 2437-2442Article in journal (Refereed)
    Abstract [en]

    Electrochemical anodization of a titanium film on a Kapton HN substrate leads to the formation of closely packed aligned nanotubes, whose shape can be finely tuned by tailoring the anodization parameters. An amorphous-to-anatase phase transition is induced on nanotubes by annealing at 350 °C. The nanotubes are applied as photoanodes in flexible dye-sensitized solar cells (N719 dye; I 3 -/I - redox couple), resulting in a photoconversion efficiency of up to 3.5% under simulated sunlight irradiation air mass 1.5 global (AM 1.5G). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • 323.
    Ganemi, B.
    et al.
    Kungliga tekniska högskolan, KTH.
    Björnbom, E.
    Kungliga tekniska högskolan, KTH.
    Demirel, B.
    Center for Applied Energy Research, Lexington, KY.
    Paul, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zeolite Cu-ZSM-5: material characteristics and NO decomposition2000In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 38, no 2-3, p. 287-300Article in journal (Refereed)
    Abstract [en]

    Zeolite ZSM-5 (SiO2/Al2O3 ratio 53:1) ion exchanged with Cu2+ to 0%, 74% and 160% was characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Infrared (IR) spectroscopy, Electron spectroscopy for chemical analysis (ESCA) and ammonia desorption. A more limited set of data was obtained for Cu-ZSM-5-33, ion exchanged with 0%, 104% and 210% Cu2+ ions. All catalysts lose water below 100°C. More strongly bound water, approximately two molecules per Cu2+ ion, emerge at a higher temperature. This corresponds either to an incomplete hydration shell for zeolite-bound Cu2+ ions or to the decomposition of Cu(OH)2 and simultaneous reactive adsorption of copper ions on the inner surface of the zeolite. The process occurs in the same temperature range, 150-350°C, where XRD reveals rearrangements in the H-form of the catalyst. Reactions between the exchangeable cations and the zeolite appear critical for lattice changes and possibly the formation and dispersion of catalytically active centers at these temperatures. Dehydroxylation and water desorption are observed between 350°C and 450°C for H-ZSM-5. This temperature range overlaps with the light-off temperature for direct NO decomposition over Cu-ZSM-5. This coincidence can be rationalized in terms of two effects of enhanced ionic mobility and dynamics of the zeolitic framework. ESCA shows that partial reduction, cupric to cuprous, occurs as a result of annealing in the same temperature range. It has been suggested that NO-derived surface intermediates act as site blockers for the direct decomposition below the light-off temperature until destabilized by lattice movements. The lower stability and thus higher mobility of low SiO2/Al2O3 ratio ZSM-5 zeolites would then rationalize an advantage of these materials as supports in catalysts for direct NO decomposition.

  • 324.
    Ganemi, B.
    et al.
    Kungliga tekniska högskolan, KTH.
    Björnbom, E.
    Kungliga tekniska högskolan, KTH.
    Paul, Jan
    Conversion and in situ FTIR studies of direct NO decomposition over Cu-ZSM51998In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 17, no 4, p. 293-311Article in journal (Refereed)
    Abstract [en]

    Copper ion-exchanged zeolites ZSMS with SiO2:Al2O3 molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560-5400 h(-1)). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO2 formation in the gas phase. A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO2:Al2O3 ratio, enhances the conversion of NO. A vibrational band at 1631 cm(-1) is observed below the light-off temperature and interpreted as a bridged nitrate group bound to Cu2+-O-Cu2+ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrate groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N2O3, also binds in a bridge configuration to the same Cu2+-O-Cu2+ dimers.A second nitrate group with unidentate coordination and vibrational bands at 1598/1575 cm(-1) probes isolated copper ions.A third infrared band at 2130 cm(-1) confirms previous observations of NO2+-ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for NO2+ adsorption are blocked by Cu2+ ion-exchange. The 2130 cm(-1) species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice.Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers.A high SiO2:Al2O3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites.

  • 325.
    Gergely, Andras
    et al.
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Szabó, Péter
    Department of General and Inorganic Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Krojer, Antal
    Department of Inspection and Maintenance, Mol Nyrt., Olajmunkás, Hungary .
    Nagy, Bence
    Refining Research and Innovation, Mol Nyrt., Hungary .
    Kristof, Tamas
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia, Egyetem, Hungary .
    Hydrogen Sulfide Corrosion of Carbon and Stainless Steel Alloys in Mixtures of Renewable Fuel Sources under Co-Processing Conditions2018In: Modern Applied Science, ISSN 1913-1844, E-ISSN 1913-1852, Vol. 12, no 4, p. 227-255Article in journal (Refereed)
    Abstract [en]

    Corrosion rates of steel alloys were investigated in gas oil and its mixture with waste cooking oil and animal waste lard over 1, 3, 7 and 21 days under desulfurizing condition. Co-processing conditions were attempted to simulate by batch-reactor experiment at temperatures between 200 and 300oC and pressures between 20 and 90 bar in the presence of 2 volume% hydrogen sulfide. Integral and differential corrosion rates were defined by weight losses. Intense sulfide corrosion of carbon steels was less impacted by the biomass sources. Thinner scales in gas oil was probably due to frequent cohesive failure, whereas thicker layers in biomass mixtures were allowed to form to afford limited physical protection. The high corrosion rate of low alloy steel with temperature over time is related to inefficient protection by the metal sulfide scales. Greater activation energy and enthalpy balance in the formation of activated complex is expected to reflect in thick cohesive scales. Loose layers and the less unfavorable entropy balance in the transition state did not lead to valuable barrier protection. High sulfide corrosion resistance of stainless steels is in chemical in nature markedly impacted by the biomass fuel sources and contributed especially by the acidic species. Corrosion rates increased with temperature by magnitude similar to those of carbon steels, which probably owes to the less unfavorable entropy and free energy balance between the initial and transition states of the reactants.

  • 326.
    Gergely, András
    et al.
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia.
    Locskai, Roland
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia.
    Szabo, Peter
    Krójer, Antal
    Department of Inspection and Maintenance.
    Kristóf, Tamás
    Department of Physical Chemistry, Institute of Chemistry, University of Pannonia.
    Hydrogen Sulphide Corrosion of Carbon and Stainless Steel Alloys Immersed in Mixtures of Renewable Fuel Sources and Tested Under Co-processing Conditions2016In: Hungarian Journal of Industry and Chemistry, ISSN 2450-5102, Vol. 44, no 1, p. 55-70Article in journal (Refereed)
    Abstract [en]

    In accordance with modern regulations and directives, the use of renewable biomass materials as precursors for the production of fuels for transportation purposes is to be strictly followed. Even though, there are problems related to processing, storage and handling in wide range of subsequent uses, since there must be a limit to the ratio of biofuels mixed with mineral raw materials. As a key factor with regards to these biomass sources pose a great risk of causing multiple forms of corrosion both to metallic and non-metallic structural materials. To assess the degree of corrosion risk to a variety of engineering alloys like low-carbon and stainless steels widely used as structural metals, this work is dedicated to investigating corrosion rates of economically reasonable engineering steel alloys in mixtures of raw gas oil and renewable biomass fuel sources under typical co-processing conditions. To model a desulphurising refining process, corrosion tests were carried out with raw mineral gasoline and its mixture with used cooking oil and animal waste lard in relative quantities of 10% (g/g). Co-processing was simulated by batch-reactor laboratory experiments. Experiments were performed at temperatures between 200 and 300ºC and a pressure in the gas phase of 90 bar containing 2% (m3/m3) hydrogen sulphide. The time span of individual tests were varied between 1 and 21 days so that we can conclude about changes in the reaction rates against time exposure of and extrapolate for longer periods of exposure. Initial and integral corrosion rates were defined by a weight loss method on standard size of coupons of all sorts of steel alloys. Corrosion rates of carbon steels indicated a linear increase with temperature and little variation with composition of the biomass fuel sources. Apparent activation energies over the first 24-hour period remained moderate, varying between 35.5 and 50.3 kJ mol−1. Scales developed on carbon steels at higher temperatures were less susceptible to spall and detach. Nonetheless, moderate deceleration of corrosion rates as a function of time are due to the less coherent, frequently spalling and low compactness, higher porosity of the scales evolved at lower and higher temperatures, respectively. On the surface of high alloy steels, sulphide scales of an enhanced barrier nature formed during the induction periods and the layer formation mechanism was found to be assisted by the increasing temperature as initial reaction rates considerably decreased over time. Nevertheless, corrosion-related sulphide conversion of metals and mass loss of the high alloys are strongly affected by the composition of the biomass fuel sources especially animal waste lard. Thermal activation in the first 24 hours decreased from 68.9 to 35.2 kJ mol−1. A greater degree of failure to develop protective sulphide scales was experienced by changing to composition of the biomass fuel sources than the impact of thermal activation between a narrow temperature range at around 100ºC. In accordance with the literature, high free fatty acid contents lead to high corrosion rates accounted for direct corrosion of high alloy steels and assisted solubilisation of corrosion products. In addition, the pronounced acceleration of sulphide corrosion is connected to the diminishing inhibition effect of the sulphide scales

  • 327.
    Ghamgosar, Pedram
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Advanced Metal Oxide Semiconductors for Solar Energy Harvesting and Solar Fuel Production2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Increasing energy consumption and its environmental impacts make it necessary to look for alternative energy sources. Solar energy as huge energy source which is able to cover the terms sustainability is considered as a favorable alternative. Solar cells and solar fuels are two kinds of technologies, which make us able to harness solar energy and convert it to electricity and/or store it chemically.

    Metal oxide semiconductors (MOSs) have a major role in these devices and optimization of their properties (composition, morphology, dimensions, crystal structure) makes it possible to increase the performance of the devices. The light absorption, charge carriers mobility, the time scale between charge injection, regeneration and recombination processes are some of the properties critical to exploitation of MOSs in solar cells and solar fuel technology.

    In this thesis, we explore two different systems. The first one is a NiO mesoporous semiconductor photocathode sensitized with a biomimetic Fe-Fe catalyst and a coumarin C343 dye, which was tested in a solar fuel device to produce hydrogen. This system is the first solar fuel device based on a biomimetic Fe-Fe catalyst and it shows a Faradic efficiency of 50% in hydrogen production. Cobalt catalysts have higher Faradic efficiency but their performance due to hydrolysis in low pH condition is limited. The second one is a photoanode based on the nanostructured hematite/magnetite film, which was tested in a photoelectrochemical cell. This hybrid electrode improved the photoactivity of the photoelectrochemical cell for water splitting. The main mechanism for the improvement of the functional properties relies with the role of the magnetite phase, which improves the charge carrier mobility of the composite system, compared to pure hematite, which acts as good light absorber semiconductor.

    By optimizing the charge separation and mobility of charge carriers of MOSs, they can be a promising active material in solar cells and solar fuel devices due to their abundance, stability, non-toxicity, and low-cost. The future work will be focused on the use of nanostructured MOSs in all-oxide solar cell devices. We have already obtained some preliminary results on 1-dimensional heterojunctions, which we report in Chapter 3.3. While they are not conclusive, they give an idea about the future direction of the present research. 

  • 328.
    Ghamgosar, Pedram
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rigoni, Federica
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Morales, Edgar Abarca
    Luleå University of Technology.
    Mazzaro, Raffaello
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Morandi, Vittorio
    Institute for Microelectronics and Microsystems Section of Bologna , National Research Council , Bologna , Italy..
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Self-Powered Photodetectors Based on Core-Shell ZnO-Co3O4 Nanowire Heterojunctions2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 26, p. 23454-23462Article in journal (Refereed)
    Abstract [en]

    Self-powered photodetectors operating in the UV–visible–NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation without external power sources. In this study, we propose a new p–n junction nanostructure, based on a ZnO–Co3O4 core–shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV–visible–NIR p–n heterojunction photodetector. Ultrathin Co3O4 films (in the range 1–15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al2O3 buffer layer between ZnO and Co3O4 was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO–Al2O3–Co3O4 system at zero bias is 6 times higher compared to that of ZnO–Co3O4. The responsivity (R) and specific detectivity (D*) of the best device were 21.80 mA W–1and 4.12 × 1012 Jones, respectively. These results suggest a novel p–n junction structure to develop all-oxide UV–vis photodetectors based on stable, nontoxic, low-cost materials.

  • 329.
    Ghamgosar, Pedram
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rigoni, Federica
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    You, Shujie
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dobryden, Iliya
    Division of Surface and Corrosion Science, KTH Royal Institute of Technolog.
    Gilzad Kohan, Mojtaba
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Pellegrino, Anna Lucia
    Dipartimento Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania.
    Concina, Isabella
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Almqvist, Nils
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Malandrino, Graziella
    Dipartimento Scienze Chimiche, Università degli Studi di Catania, INSTM UdR-Catania.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 51, p. 308-316Article in journal (Refereed)
    Abstract [en]

    In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

  • 330.
    Gisenti, A
    et al.
    Dipartimento di Scienze Chimiche, Università di Padova.
    Frasson, A
    Dipartimento di Scienze Chimiche, Università di Padova.
    Galenda, A
    Dipartimento di Scienze Chimiche, Università di Padova.
    Ferroni, Matteo
    CNR IDASC SENSOR Lab.
    Concina, Isabella
    CNR IDASC SENSOR Lab.
    Natilea, M.M.
    Dipartimento di Scienze Chimiche, Università di Padova.
    Synthesis and characterization of Ag/CeO2 nanocomposites2010In: Materials Research Society Symposium Proceedings, Materials Research Society, 2010, Vol. 1257, p. 323-328Conference paper (Refereed)
    Abstract [en]

    Two Ag/CeO2 nanocomposite samples were prepared by deposition-precipitation (Ag/Ce nominal atomic ratio = 0.03 and 0.12). XPS data suggest the possible presence of traces of Ce(III). Beside Ag (0), oxidized silver species are also revealed in the Ag/CeO2 sample with lower metal content. The deposition of metal increases surface hydroxylation and carbonation. Methanol interacts molecularly and dissociatively with the samples; oxidation products are observed from low temperature and depend on Ag content. Both the samples reveal a high activity in methanol complete oxidation; traces of partial oxidation products are observed in the sample with lower Ag content

  • 331.
    Glaz, Waldemar
    et al.
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań.
    Bancewicz, Tadeusz
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University.
    Godet, Jean Luc
    Laboratoire de Photonique D'Angers, Université D'Angers.
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Haskopoulos, Anastasios
    Department of Chemistry, University of Patras.
    Maroulis, George
    Department of Chemistry, University of Patras.
    Effects of anisotropic interaction-induced properties of hydrogen-rare gas compounds on rototranslational Raman scattering spectra: Comprehensive theoretical and numerical analysis2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 3, article id 34303Article in journal (Refereed)
    Abstract [en]

    A comprehensive study is presented of many aspects of the depolarized anisotropic collision induced (CI) component of light scattered by weakly bound compounds composed of a dihydrogen molecule and a rare gas (Rg) atom, H2-Rg. The work continues a series of earlier projects marking the revival of interest in linear light scattering following the development of new highly advanced tools of quantum chemistry and other theoretical, computational, and experimental means of spectral analyses. Sophisticated ab initio computing procedures are applied in order to obtain the anisotropic polarizability component's dependence on the H2-Rg geometry. These data are then used to evaluate the CI spectral lines for all types of Rg atoms ranging from He to Xe (Rn excluded). Evolution of the properties of CI spectra with growing polarizability/masses of the complexes studied is observed. Special attention is given to the heaviest, Kr and Xe based, scatterers. The influence of specific factors shaping the spectral lines (e.g., bound and metastable contribution, potential anisotropy) is discussed. Also the share of pressure broadened allowed rotational transitions in the overall spectral profile is taken into account and the extent to which it is separable from the pure CI contribution is discussed. We finish with a brief comparison between the obtained results and available experimental data

  • 332.
    Gobbi, Emanuela
    et al.
    Univ Udine.
    Falasconi, Matteo
    CNR IDASC SENSOR Lab, University of Brescia.
    Concina, Isabella
    CNR IDASC SENSOR Lab.
    Mantero, G
    Biodivers SPA, Brescia,.
    Bianchi, F
    Univ Studi Parma, Dipartimento Chim Gen & Inorgan,.
    Mattarozzi, M
    Univ Studi Parma, Dipartimento Chim Gen & Inorgan,.
    Musci, M
    Univ Studi Parma, Dipartimento Chim Gen & Inorgan,.
    Sberveglieri, Giorgio
    SENSOR Lab, Department of Information Engineering, University of Brescia.
    Electronic nose and Alicyclobacillus spp. spoilage of fruit juices: An emerging diagnostic tool2010In: Food Control, ISSN 0956-7135, E-ISSN 1873-7129, Vol. 21, no 10, p. 1374-1382Article in journal (Refereed)
    Abstract [en]

    The application of an electronic nose equipped with a Metal Oxide Semiconductor sensor array for the detection of Alicyclobacillus acidoterrestris and A. acidocaldarius artificially inoculated in peach, orange and apple fruit juices is described in this study. Overall the system was able to detect the presence of Alicyclobacillus spp. in all the tested fruit juices at 24 h from inoculation. The electronic nose could detect bacterial concentration as low as <10(2) colony forming unit/ml and it was also able to classify bacterial contamination independently of the Alicyclobacillus species. The gas chromatography-mass spectrometry characterization of the volatile profile of orange juices confirmed the existence of quantitatively different patterns between contaminated and uncontaminated samples.

  • 333.
    Goliath, Martin
    et al.
    Stockholms Universitet.
    Nilsson, Ulf S.
    Stockholms Universitet.
    Uggla, Claes
    Luleå tekniska universitet.
    Spatially self-similar spherically symmetric perfect-fluid models1998In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 15, no 1, p. 167-186Article in journal (Refereed)
    Abstract [en]

    Einstein's field equations for spatially self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively with the theory of dynamical systems

  • 334.
    Goliath, Martin
    et al.
    Department of Physics, Stockholm University.
    Nilsson, Ulf S.
    Department of Physics, Stockholm University.
    Uggla, Claes
    Luleå tekniska universitet.
    Timelike self-similar spherically symmetric perfect-fluid models1998In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 15, no 9, p. 2841-2863Article in journal (Refereed)
    Abstract [en]

    Einstein's field equations for timelike self-similar spherically symmetric perfect-fluid models are investigated. The field equations are rewritten as a first-order system of autonomous differential equations. Dimensionless variables are chosen in such a way that the number of equations in the coupled system is reduced as far as possible and so that the reduced phase space becomes compact and regular. The system is subsequently analysed qualitatively using the theory of dynamical systems

  • 335.
    Golubev, Nikolay V.
    et al.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Gustafsson, Magnus
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Antipov, Sergey V.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Formation of the SiP radical through radiative association2013In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 117, no 34, p. 8184-8188Article in journal (Refereed)
    Abstract [en]

    Formation of the SiP radical through radiative association of Si( 3P) and P(4S) atoms is studied using classical and quantum dynamics. Rate coefficients for formation in the two lowest doublet states and the two lowest quartet states are calculated for T = 10-20 000 K. Breit-Wigner theory is used to properly account for contribution from quantum mechanical resonances.

  • 336.
    Gonella, F.
    et al.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Canton, P.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Cattaruzza, E.
    CNR-IDASC SENSOR Lab and Dipartimento di Chimica e Fisica per l'Ingegneria e per i Materiali.
    Quaranta, A.
    Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali, Università di Trento.
    Sada, C.
    Dipartimento di Fisica Sperimentale, Università di Torino.
    Vomiero, Alberto
    CNR-INFM SENSOR Laboratory.
    Field-assisted ion diffusion of transition metals for the synthesis of nanocomposite silicate glasses2006In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 26, no 5-7, p. 1087-1091Article in journal (Refereed)
    Abstract [en]

    Field-assisted ion diffusion of metals was realized for the controlled doping of silicate glasses. Metallic films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. In particular, cobalt was, for the first time, introduced into a soda-lime glass by field-assisted ion exchange, giving rise to diffusion profiles that were observed to depend on the preparation parameters, namely, temperature and electric field intensity across the samples. This technique, which allowed to dope the glass matrix with high metal concentration values, can be used as the first step in combined methodologies for the preparation of nanostructured glass composites. The shape of the measured Co diffusion profiles indicates that the migration process depends not only on the experimental parameters but also on the behavior of alkali ions within the glass. Chemical phenomena occurring at the metal/glass interface also play a significant role in the penetration of the Co ions. The possibility of doping the glass with two different metal species was also investigated, with the aim to create the condition for the formation of core-shell or alloy nanoclusters. In particular, preliminary results on Co + Au field-assisted co-diffusion are presented. © 2005 Elsevier B.V. All rights reserved.

  • 337.
    Gorbatov, Oleg
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden. Laboratory for Mechanics of Gradient Nanomaterials, Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia.
    Stroev, A. Yu.
    National Research Centre, Kurchatov Institute, Moscow, Russia. Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, Russia.
    Gornostyrev, Yu. N.
    Institute of Metal Physics, Ural Division RAS, Ekaterinburg, Russia. Institute of Quantum Materials Science, Ekaterinburg, Russia.
    Korzhavyi, P. A.
    Department of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm, Sweden. Institute of Metal Physics, Ural Division RAS, Ekaterinburg, Russia.
    Effective cluster interactions and pre–precipitate morphology in binary Al-based alloys2019In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 179, p. 70-84Article in journal (Refereed)
    Abstract [en]

    The strengthening by coherent, nano-sized particles of metastable phases (pre-precipitates) continues to be the main design principle for new high-performance aluminium alloys. To describe the formation of such pre-precipitates in Al–Cu, Al–Mg, Al–Zn, and Al–Si alloys, we carry out cluster expansions of ab initio calculated energies for supercell models of the dilute binary Al-rich solid solutions. Effective cluster interactions, including many-body terms and strain-induced contributions due to the lattice relaxations around solute atoms, are thus systematically derived. Monte Carlo and statistical kinetic theory simulations, parameterized with the obtained effective cluster interactions, are then performed to study the early stages of decomposition in the binary Al-based solid solutions. We show that this systematic approach to multi-scale modelling is capable of incorporating the essential physical contributions (usually referred to as atomic size and electronic structure factors) to the free energy, and is therefore able to correctly describe the ordering temperatures, atomic structures, and morphologies of pre-precipitates in the four studied alloy systems.

  • 338.
    Gowda, Vasantha
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Experimental and Computational Magnetic Resonance Studies of Selected Rare Earth and Bismuth Complexes2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The rare-earth elements (REEs) and bismuth, being classified as the ‘most critical raw materials’ (European Raw Materials Initiatives, 2017), have a high economic importance to the EU combined with a high relative supply risk. REEs are highly important for the evolving technologies such as clean-energy applications, high-technology components, rechargeable batteries, permanent magnets, electric and hybrid vehicles, and phosphors monitors.This scientific research work aims at building a fundamental knowledge base concerning the electronic/molecular structure and properties of rare-earth element (REE) and bismuth complexes with dithiocarbamate (DTC) and 1,10-phenanthroline (PHEN) by employing state-of-the-art experimental techniques such as nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction (XRD) techniques together with ab initioquantum mechanical computational methods. This combination of methods has played a vital role in analysing the direct and significant effect of the heavy metal ions on the structural and magnetic resonance properties of the complexes, thereby, providing a framework of structure elucidation. This is of special importance for REEs, which are known to exhibit similar chemical and physical properties. The objectives of the work involve i) a systematic investigation of series of REE(III) as well as bismuth(III) complexes to get a profound understanding of the structure-properties relationship and ii) to find an appropriate theoretical modelling and NMR calculation methods, especially, for heavy metal systems in molecular and/or solid-state. This information can later be used in surface interaction studies of REE/bismuth minerals with DTC as well as in design and development of novel ligands for extraction/separation of metal ions.The REE(III) and bismuth(III) complexes with DTC and PHEN ligands have all provided aunique NMR fingerprint of the metal centre both in liquid and solid phase. The solid-state 13C and 15NNMR spectra of the diamagnetic REE(III) and bismuth(III) complexes were in accord with their structural data obtained by single crystal XRD. The density functional theory (DFT) methods were used to get complementary and refined structural and NMR parameters information for all diamagnetic complexes in the solid-state. The relativistic contributions due to scalar and spin-orbit correlations for the calculated 1H/13C/15N chemical shifts of REE complexes were analysed using two-component zeroth-order regular approximation (ZORA)/DFT while the ‘crystal-lattice’ effects on the NMR parameters were calculated by combining DFT calculations on molecular and periodic solid-state models. The paramagnetic REE complexes display huge differences in their 1H and 13C NMR spectral patterns. The experimental paramagnetic NMR (pNMR) chemical shifts, as well as the sizable difference of the 1H and 13C NMR shifts for these isoelectronic complexes, are well reproduced by the advanced calculations using ab initio/DFT approach. The accuracy of this approach is very promising for further applications to demanding pNMR problems involving paramagnetic f-block elements.The results presented in this thesis demonstrate that a multidisciplinary approach of combined experimental NMR and XRD techniques along with computational modelling and property calculations is highly efficient in studying molecular complexes and solids containing heavy metal systems, such as rare-earths and bismuth.

  • 339.
    Gowda, Vasantha
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Sarma, Bipul
    Department of Chemical Sciences, Division of Chemical Engineering, Tezpur University, Tezpur, Assam.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Telkki, Ville-Veikko
    University of Oulu, NMR Research Group, Division of Chemical Engineering, Faculty of Science, University of Oulu.
    Larsson, Anna-Carin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Lantto, Perttu
    University of Oulu, NMR Research Group, Division of Chemical Engineering, Faculty of Science, University of Oulu.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Structure Elucidation of an Yttrium Diethyldithiocarbamato-Phenanthroline Complex by X-ray Crystallography, Solid-State NMR, and ab-initio Quantum Chemical Calculations2016In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, Vol. 20, p. 3278-3291Article in journal (Refereed)
    Abstract [en]

    We present a structural analysis method for molecular and electronic structure of yttrium diethyldithiocarbamato-phenanthroline complex {[Y(S2CNR2)3PHEN] with R = C2H5 and PHEN = 1,10-phenanthroline} combining solid-state NMR spectroscopy, XRD, and first principles DFT calculations. Replacing the Nd3+ ion with Y3+ in the reported crystal structure of [Nd(S2CNR2)3PHEN] complex generated an approximate 3D structure of the title complex. The structure was then subjected to first principles quantum chemical geometry optimisation using periodic DFT method. The quality of the method is discussed by comparing predicted and experimental powder XRD patterns. Full assignment of 13C and 15N solid-state CP-MAS NMR spectra as well as analyses of the principal values of the chemical shift tensors were carried out using periodic scalar relativistic DFT modelling. Spin-orbit relativistic effects, estimated by SO-ZORA formalism for one molecular unit, were evaluated. Finally, the X-ray structure of the title complex was determined, which proved that the former procedure is appropriate. The most important orbital interactions were investigated by Natural Bond Orbital analysis. The isotropic shielding values for S2CN-carbons were analysed by Natural Localised Molecular Orbital analysis. The present approach can be further extended to study other rare earth metal complexes, particularly those having similar but not yet solved crystal structures

  • 340.
    Grenman, Tiia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Dusty Globules and Globulettes2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Interstellar gas and dust can condense into clouds of very different size, ranging from giant molecular cloud complexes to massive, isolated, dark cloudlets, called globules with a few solar masses.

    This thesis focuses on a new category of small globules, named globulettes.These have been found in the bright surroundings of H II regions of young, massive stellar clusters. The globulettes are much smaller and less massive than normal globules. The analysis is based on H-alpha images ofe.g., the Rosette Nebula and the Carina Nebula collected with the Nordic Optical Tele-scope and the Hubble Space Telescope.

    Most globulettes found in different H II regions have distinct contours and are well isolated from the surrounding molecular shell structures. Masses and densities were derived from the extinction of light through the globulettes and the measured shape of the objects. A majority of the globulettes have planetary masses,<13MJ (Jupiter masses). Very few objects have masses above 100MJ≈0.1M(Solar masses). Hence, there is no smooth overlap between globulettes and globules, which makes us conclude that globulettes represent a distinct, new class of objects.

    Globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. At a later stage, globulettes expand, disrupt or evaporate. However, preliminary calculations of their lifetimes show that some might survive for a relatively long time, in several cases even longer than their estimated contraction time.

    The tiny high density globulettes in the Carina Nebula indicate that they are in a more evolved state than those in the Rosette Nebula, and hence they may have survived for a longer time. It is possible that the globulettes could host low mass brown dwarfs or planets.

    Using the virial theorem on the Rosette Nebula globulettes and including only the thermal and gravitational potential energy indicated that the 133 found globulettes are all either expanding or disrupting. When the ram and the radiation pressure were included, we found that about half of our objectsare gravitationally bound or unstable to contraction and could collapse to form brown dwarfs or free floating planets.

    We also estimated the amount of globulettes and the number of free floating planetary mass objects, originating from globulettes, during the history of the Milky Way. We found that a conservative value of the number of globulettes formed is 5.7×1010. A less conservative estimate gave 2×1011globulettes andif 10% of these forms free floating planets then the globulettes have contributed about 0.2 free floating planets per star.

    In the Crab Nebula, which is a supernova remnant from the explosion of a massive old star, one can find dusty globules appearing as dark spots against the background nebulosity. These globules are very similar to the globulettes we have found in H II regions. The total mass of dust in globules was estimated to be 4.5×10−4M, which corresponds to.2% of the total dust content of the nebula. These globules move outward from the center with transversal velocities of 60–1600 km s−1. Using the extinction law for globules, we found that the dust grains are similar to the interstellar dust grains. This means that they contribute to the ISM dust population. We concluded that the majority of the globules are not located in bright filaments and we proposed that these globules may be products of cell-like blobs or granules in the atmosphere of the progenitor star. Theses blobs collapse and form globules during the passage of the blast wave during the explosion.

  • 341.
    Grenman, Tiia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Globulettes: a new class of very small and dense interstellar clouds2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The space between stars is not empty, but filled with a thin gas and microscopic dust grains, together forming the so-called interstellar medium. Matter is concentrated into clouds of very different sizes, ranging from giant molecular cloud complexes to massive isolated dark small isolated cloudlets, called globules. In bright emission regions, surrounding young massive stars, one can find many tiny, isolated and cold objects appearing as dark spots against the background nebulosity. These objects are much smaller and less massive than normal globules. Such small clouds are the topic of the present Licentiate thesis, where they have been baptised globulettes. The analysis is based on H-alpha images of the Rosette Nebula and IC 1805 Nebula, collected with the Nordic Optical Telescope in the years 1999 and 2000. In total 151 globulettes in these two regions were catalogued, measured and analysed. Positions, orientations, sizes, masses, densities and pressures were derived, as well as their present condition with regard to gravitational stability. From these data, their origins and possible evolutionary history were discussed. Most globulettes are sharp-edged and well isolated from the surrounding. The size distributions are quite similar in the two studied nebulae. The masses and densities were derived from the extinction of light and the measured shape of the objects. In a few cases the masses have been estimated earlier by another team, from radio emission of CO gas, and our values are in line with their estimates for these particular globulettes. A majority of the objects have masses < 20 Jupiter masses, and the mass distribution drops rapidly towards higher values. Very few objects have masses above 100 Jupiter masses, which we define as the lower mass limit for normal globules. However, there is no smooth overlap between the two types of clouds, which makes us conclude that globulettes represent a distinct, new class of objects. The column density profile of a typical globulette was found to be rather uniform in the central parts, but flattens at the periphery, as compared to what is expected from a sphere of constant volume density. The virial theorem, including only the kinetic and gravitational energy, indicates that all 133 globulettes are expanding or disrupting. However, other forces, such as outer gas and radiation pressures, can help to confine the globulettes. Our results show that about half of these objects are gravitationally bound and even unstable against contraction, which opens some evolutionary scenarios not expected in the first place. Some massive globulettes could therefore collapse to form stars with very low masses, for instance, so-called brown dwarfs, while the low-mass globulettes could contract to free-floating planets. Globulettes might have been formed either by the fragmentation of larger filaments, or by the disintegration of large molecular clouds originally hosting compact and small cores. At a later stage even the confine globulettes might disrupt because of evaporation form the action of external radiation and gas flows. or evaporate. However, preliminary calculations of their lifetimes show that some might survive for a relatively long time and even longer than their estimated contraction time. No evidence of embedded infrared-emitting sources was found in independent IR studies, but one cannot exclude that globulettes already host low-mass brown dwarfs or planets.

  • 342.
    Grenman, Tiia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Elfgren, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    History of Globulettes in the Milky Way2018In: Astrophysics and Space Science, ISSN 0004-640X, E-ISSN 1572-946X, Vol. 363, no 2, article id 28Article in journal (Refereed)
    Abstract [en]

    Globulettes are small (radii $< 10$ kAU) dark dust clouds, seen against the background of bright nebulae.

    A majority of the objects have planetary mass.

    These objects may be a source of brown dwarfs and free floating planetary mass objects in the galaxy.

    In this paper we investigate how many globulettes could have formed in the Milky Way and how they could contribute to the total population of free floating planets.

    In order to do that we examine H-alpha images of 27 H~II regions. In these images, we find 778 globulettes.

    We find that a conservative value of the number of globulettes formed is $5.7\times 10^{10}$.

    If 10 \% of the globulettes form free floating planets then they have contributed with $5.7\times 10^{9}$ free floating planets in the Milky Way. A less conservative number of globulettes would mean that the globulettes could contribute $2.0\times 10^{10}$ free floating planets.

    Thus the globulettes could represent a non-negligible source of free floating planets in the Milky Way.

  • 343.
    Grenman, Tiia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gahm, Gösta F.
    Stockholm Observatory, AlbaNova University Centre, Stockholm University.
    The tiny globulettes in the Carina nebula2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 565, article id A107Article in journal (Refereed)
    Abstract [en]

    Context. Small molecular cloudlets are abundant in many H ii regions surrounding newborn stellar clusters. In optical images these so-called globulettes appear as dark silhouettes against the bright nebular background. Aims. We aim to make an inventory of the population of globulettes in the Carina nebula complex, and to derive sizes and masses for comparisons with similar objects found in other H ii regions. Methods. The globulettes were identified from Hα images collected at the Hubble Space Telescope. Results. We have located close to 300 globulettes in the Carina complex, more than in any other region surveyed so far. The objects appear as well-confined dense clumps and, as a rule, lack thinner envelopes and tails. Objects with bright rims are in the minority, but more abundant than in other regions surveyed. Some globulettes are slightly elongated with their major axes oriented in the direction of young clusters in the complex. Many objects are quite isolated and reside at projected distances >1.5 pc from other molecular structures in the neighbourhood. No globulette coincides in position with recognized pre-main-sequence objects in the area. The objects are systematically much smaller, less massive, and much denser than those surveyed in other H ii regions. Practically all globulettes are of planetary mass, and most have masses less than one Jupiter mass. The average number densities exceed 105 cm-3 in several objects. We have found a statistical relation between density and radius (mass) in the sense that the smallest objects are also the densest. Conclusions. The population of small globulettes in Carina appears to represent a more advanced evolutionary state than those investigated in other H ii regions. The objects are subject to erosion in the intense radiation field, which would lead to a removal of any thinner envelope and an unveiling of the core, which becomes more compact with time. We discuss the possibility that the core may become gravitationally unstable, in which case free-floating planetary mass objects can form.

  • 344.
    Grenman, Tiia
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gahm, Gösta F.
    Stockholm Observatory, AlbaNova University Centre, Stockholm University.
    Elfgren, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Dusty globules in the Crab Nebula2017In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 599, article id A110Article in journal (Refereed)
    Abstract [en]

    Context. Dust grains are widespread in the Crab Nebula. A number of small, dusty globules, are visible as dark spots against the background of continuous synchrotron emission in optical images. Aims. Our aim is to catalogue such dusty globules and investigate their properties. Methods. From existing broad-band images obtained with the Hubble Space Telescope, we located 92 globules, for which we derived positions, dimensions, orientations, extinctions, masses, proper motions, and their distributions. Results. The globules have mean radii ranging from 400 to 2000 AU and are not resolved in current infrared images of the nebula. The extinction law for dust grains in these globules matches a normal interstellar extinction law. Derived masses of dust range from 1 to 60 × 10-6M, and the total mass contained in globules constitute a fraction of approximately 2% or less of the total dust content of the nebula. The globules are spread over the outer part of the nebula, and a fraction of them coincide in position with emission filaments, where we find elongated globules that are aligned with these filaments. Only 10% of the globules are coincident in position with the numerous H2-emitting knots found in previous studies. All globules move outwards from the centre with transversal velocities of 60 to 1600 km s-1, along with the general expansion of the remnant. We discuss various hypotheses for the formation of globules in the Crab Nebula

  • 345.
    Grip, Carl-Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Elfgren, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Söderström, Mats
    Linköping University, Energy Systems.
    Thollander, Patrik
    Linköping University, Energy Systems.
    Berntsson, Thore
    Chalmers University of Technology, Department of Energy and Environment, Division of Heat and Power Technology.
    Åsblad, Anders
    CIT Industriell Energi.
    Wang, Chuan
    Swerea MEFOS AB.
    Possibilities and problems in using exergy expressions in process integration2011In: Proceedings of the World Renewable Energy Congress 2011 (WREC 2011): 9-13 May, Linköping, Linköping: Linköping University Electronic Press, 2011Conference paper (Refereed)
    Abstract [en]

    Industrial energy systems are complicated networks, where changes in one process influence its neighboring processes. Saving energy in one unit does not necessarily lead to energy savings for the total system. A study has been carried out on the possibility to use the exergy concept in the analysis of industrial energy systems. The exergy concept defines the quality of an amount of energy in relation to its surrounding, expressing the part that could be converted into work. The study consists of literature studies and general evaluations, an extensive case study and an interview study. In the latter it was found that non technical factors are major obstacles to the introduction of exergy.

  • 346.
    Grishin, A.
    et al.
    Kungliga tekniska högskolan, KTH.
    Niska, John
    Luleå tekniska universitet.
    Loberg, Bengt
    Weber, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Straightened voltage effect in high-Tc superconductors1994In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 76, no 10, p. 6947-6949Article in journal (Refereed)
    Abstract [en]

    A new effect called ``ac-current straightening'' has been observed in ceramic (Bi,Pb)-2223 slabs carrying ac current Idc+Iac cos(ωt). The current-voltage (I-V) characteristics of the ceramic were measured at 77 K at frequencies ranging from 50 to 20 000 Hz. A spectrum analyzer showed a series of high harmonics in the voltage signal as well as a constant voltage drop. The full set of experimental data has been explained theoretically using the Bean-Kim critical state model with a magnetic field dependent critical current jc(H)=jc(0)/(1+H/H0). A low transport ac current gives a voltage linearly proportional to the frequency and quadratically proportional to the ac-current amplitude Iac. It consists of odd harmonics only. If a bias dc current is switched on, then even harmonics and a dc-voltage drop appear. Their amplitudes are proportional to the small parameter Iac/cH0 and depend on the Idc/Iac ratio.

  • 347.
    Groth, Margareta Ring
    et al.
    Luleå tekniska universitet.
    Mannelquist, Anders
    Luleå tekniska universitet.
    Comparison of fractal analyses methods and fractal dimension for pre-treated stainless steel surfaces and the correlation to adhesive joint strength2001In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 73, no 3, p. 347-355Article in journal (Refereed)
    Abstract [en]

    The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength. All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light microscope (,0.5-100 7m). The AFM method was excluded in this comparison, since the limitation in the z-direction for the AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic average difference, Ra, but only weakly to the fractal dimension. Hence, traditional parameters, such as Ra, tell us very little about the spatial distribution of the elevation data

  • 348.
    Grånäs, Oscar
    et al.
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Marco, Igor di
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Eriksson, Olle
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Nordström, Lars
    Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
    Etz, Corina
    Department of Physics and Astronomy, Uppsala University.
    Electronic structure, cohesive properties, and magnetism of SrRuO32014In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 90, article id 165130Article in journal (Refereed)
    Abstract [en]

    We have performed an extensive test of the ability of density functional theory within several approximations for the exchange-correlation functional, local density approximation + Hubbard U, and local density approximation + dynamic mean field theory to describe magnetic and electronic properties of SrRuO3. We focus on the ferromagnetic phase, illustrating differences between the orthorhombic low-temperature structure versus the cubic high-temperature structure. We assess how magnetism, spectral function, and cohesive properties are affected by methodology, onsite Hubbard U, and double-counting corrections. Further, we compare the impact of the impurity solver on the quasiparticle weight Z, which is in turn compared to experimental results. The spectral functions resulting from the different treatments are also compared to experimental data. Finally, the impact of spin-orbit coupling is studied, allowing us to determine the orbital moments. In the orthorhombic phase, the orbital moments are found to be tilted with respect to the spin moments, emphasizing the importance of taking into account the distortion of the oxygen octahedra

  • 349.
    Guidi, V.
    et al.
    University of Ferrara.
    Antonini, A.
    University of Ferrara.
    Baricordi, S.
    University of Ferrara.
    Logallo, F.
    University of Ferrara.
    Malagù, C.
    University of Ferrara.
    Milan, E.
    University of Ferrara.
    Ronzoni, A.
    University of Ferrara.
    Stefancich, M.
    University of Ferrara.
    Martinelli, G.
    University of Ferrara.
    Vomiero, Alberto
    INFN Laboratori Nazionali di Legnaro.
    Tailoring of silicon crystals for relativistic-particle channeling2005In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 234, no 1-2, p. 40-46Article in journal (Refereed)
    Abstract [en]

    In the last years, the research on channeling of relativistic particles has progressed considerably. A significant contribution has been provided by the development of techniques for quality improvement of the crystals. In particular, a planar etching of the surfaces of the silicon crystals proved useful to remove the superficial layer, which is a region very rich in imperfections, in turn leading to greater channeling efficiency. Micro-fabrication techniques, borrowed from silicon technology, may also be useful: micro-indentation and deposition of tensile or compressive layers onto silicon samples allow one to impart an even curvature to the samples. In this way, different topologies may be envisaged, such as a bent crystal for deflection of protons and ions or an undulator to force coherent oscillations of positrons and electrons. © 2005 Elsevier B.V. All rights reserved.

  • 350.
    Guidi, V.
    et al.
    University of Ferrara, INFN.
    Baricordi, S.
    University of Ferrara, INFN.
    Fiorini, M.
    University of Ferrara, INFN.
    Martinelli, G.
    University of Ferrara, INFN.
    Mazzolari, A.
    University of Ferrara, INFN.
    Milan, E.
    University of Ferrara, INFN.
    Scandale, W.
    CERN.
    Chesnokov, Y.
    IHEP Protvino.
    Marchi, E. Boscolo
    INFN-LNL.
    Mea, G. Della
    INFN-LNL.
    Milan, R.
    INFN-LNL.
    Todros, S.
    INFN-LNL.
    Vomiero, Alberto
    INFN Laboratori Nazionali di Legnaro.
    Ivanov, Y. M.
    PNPI.
    Carnera, A.
    University of Padova.
    Salvador, D. De
    University of Padova.
    Sambo, A.
    University of Padova.
    Characterization of crystals for steering of protons through channelling in hadronic accelerators2006In: EPAC 2006: 10th European Particle Accelerator Conference EPAC 2006 ; a Europhysics conference ; Edinburgh, Scotland, International Conference Centre (EICC), 26 - 30 June 2006, Edinburgh: European Physical Society Accelerator Group (EPS-AG) , 2006, p. 1523-1525Conference paper (Refereed)
    Abstract [en]

    Channeling of relativistic particles through a crystal may be useful for many applications in accelerators, and particularly for collimation in hadronic colliders. Efficiency proved to be dependent on the state of the crystal surface and hence on the method used for preparation. We investigated the morphology and structure of the surface of the samples that have been used in accelerators with high efficiency. We found that crystal fabrication by only mechanical methods (dicing, lapping, and others) leads to a superficial damaged layer, which is correlated to performance limitation in accelerators. A planar chemical etching was studied and applied in order to remove the superficial damaged layer. RBS channeling analysis with low-energy protons and 4He + highlighted better crystal perfection at surface, as a result of the etching. A protocol for preparation and characterization of crystal for channelling has been developed, which may be of interest for reliable operation with crystals in accelerators.

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