Endre søk
Begrens søket
1234567 51 - 100 of 962
Referera
Referensformat
• apa
• harvard1
• ieee
• modern-language-association-8th-edition
• vancouver
• Annet format
Fler format
Språk
• de-DE
• en-GB
• en-US
• fi-FI
• nn-NO
• nn-NB
• sv-SE
• Annet språk
Fler språk
Utmatningsformat
• html
• text
• asciidoc
• rtf
Treff pr side
• 5
• 10
• 20
• 50
• 100
• 250
Sortering
• Standard (Relevans)
• Forfatter A-Ø
• Forfatter Ø-A
• Tittel A-Ø
• Tittel Ø-A
• Type publikasjon A-Ø
• Type publikasjon Ø-A
• Eldste først
• Nyeste først
• Disputationsdatum (tidligste først)
• Disputationsdatum (siste først)
• Standard (Relevans)
• Forfatter A-Ø
• Forfatter Ø-A
• Tittel A-Ø
• Tittel Ø-A
• Type publikasjon A-Ø
• Type publikasjon Ø-A
• Eldste først
• Nyeste først
• Disputationsdatum (tidligste først)
• Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
• 51.
Diamond Light Source Ltd., Diamond House, Harwell Science Campus, Didcot, Oxfordshire, United Kingdom.
Departamento de Física Aplicada-Instituto de Ciencia de Materiales, Matter at High Pressure (MALTA) Consolider Team, Universidad de Valencia, Edificio de Investigación, Valencia, Spain. AWE, Aldermaston, Reading, United Kingdom. SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions,The University of Edinburgh, Edinburgh, United Kingdom. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Diamond Light Source Ltd., Diamond House, Harwell Science Campus, Didcot, Oxfordshire, United Kingdom. AWE, Aldermaston, Reading, United Kingdom. Departmento de Física, Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez s/n, Tenerife, Spain. Institute of Earth Sciences Jaume Almera, CSIC, Barcelona, Spain. SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions,The University of Edinburgh, Edinburgh, United Kingdom. SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions,The University of Edinburgh, Edinburgh, United Kingdom. CELLS-ALBA Synchrotron Light Facility, Barcelona, Spain. DCITIMAC, MALTA Consolider Team, Universidad de Cantabria, Santander, Spain. AWE, Aldermaston, Reading, United Kingdom.
Phase diagram of calcium at high pressure and high temperature2018Inngår i: Physical review materials, ISSN 2475-9953, Vol. 2, nr 8, artikkel-id 083608Artikkel i tidsskrift (Fagfellevurdert)

Resistively heated diamond-anvil cells have been used together with synchrotron x-ray diffraction to investigate the phase diagram of calcium up to 50 GPa and 800 K. The phase boundaries between the Ca-I (fcc), Ca-II (bcc), and Ca-III (simple cubic, sc) phases have been determined at these pressure-temperature conditions, and the ambient temperature equation of state has been generated. The equation of state parameters at ambient temperature have been determined from the experimental compression curve of the observed phases by using third-order Birch-Murnaghan and Vinet equations. A thermal equation of state was also determined for Ca-I and Ca-II by combining the room-temperature Birch-Murnaghan equation of state with a Berman-type thermal expansion model.

• 52.
Solid State & Supramolecular Structural Chemistry Unit, Division of Organic Chemistry, National Chemical Laboratory.
Solid State & Supramolecular Structural Chemistry Unit, Division of Organic Chemistry, National Chemical Laboratory. Solid State & Supramolecular Structural Chemistry Unit, Division of Organic Chemistry, National Chemical Laboratory.
Supramolecular synthesis of some molecular adducts of 4,4′-bipyridine N,N′-dioxide2009Inngår i: New Journal of Chemistry, ISSN 1144-0546, E-ISSN 1369-9261, Vol. 33, nr 1, s. 57-63Artikkel i tidsskrift (Fagfellevurdert)

Molecular adducts (1a–1e) of 4,4′-bipyridine N,N′-dioxide, 1, respectively with cyanuric acid, trithiocyanuric acid, 1,3,5-trihydroxybenzene (phloroglucinol), 1,3-dihydroxybenzene (resorcinol) and 1,2,4,5-benzenetetracarboxylic acid have been reported. The major interactions observed in the structures 1a–1e are N–H⋯O, N–H⋯S, O–H⋯O and C–H⋯O, in the form of homomeric and heteromeric patterns of the constituents, either as a single or cyclic hydrogen-bonded motifs. While in the adduct 1a, both homomeric and heteromeric units of both the constituents were observed, no heteromeric interactions were observed in 1b and 1c. In addition, in 1b, homomeric aggregation of molecules of 1 occurred in association with water molecules. However, while heteromeric interactions prevail between the constituents in 1d and 1e, only one of the co-crystallizing species gave homomeric interactions (4,4′-bipyridine N,N′-dioxide in 1d; 1,2,4,5-benzenetetracarboxylic acid in 1e). Further, in either type of the patterns, the cyclic motifs are formed as a pair-wise hydrogen bonds comprising of strong and weak hydrogen bonds (N–H⋯O/C–H⋯O or O–H⋯O/C–H⋯O). In three-dimensions, the ensembles of molecules yield planar sheets, ladders and pseudorotaxane type assemblies

• 53. Arvanitidis, J.
High pressure study of the 2D polymeric phase of C60 by means of Raman spectroscopy2001Inngår i: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 18, nr 1-6, s. 145-151Artikkel i tidsskrift (Fagfellevurdert)

The effect of high hydrostatic pressure, up to 12GPa, on the intramolecular phonon frequencies and the material stability of the two-dimensional tetragonal Cm polymer has been studied by means of Raman spectroscopy in the spectral range of the radial intramolecular modes (200-800cm-1). A number of new Raman modes appear in the spectrum for pressures ≈ 1.4 and ≈ 5.0 GPa. The pressure coefficients for the majority of the phonon modes exhibit changes to lower values at P=4.0 GPa, which may be related to a structural modification of the 2D polymer to a more isotropic phase. The peculiarities observed in the Raman spectra are reversible and the material is stable in the pressure region investigated.

• 54. Arvanitidis, J.
Comparative Raman study of the 1D and 2D polymeric phases of C60 under pressure1999Inngår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 215, nr 1, s. 443-448Artikkel i tidsskrift (Fagfellevurdert)

The effect of symmetry lowering on the phonon spectra as well as the pressure effects on the vibrational spectrum of polymerized C60 were studied by Raman spectroscopy. Drastic changes related to the splitting of degenerate modes of the C60 molecule were observed together with selected softening of some of them. In spite of many similarities in the Raman spectra of the one- (1D) and two-dimensional (2D) polymeric forms of C60, some salient differences in the peak intensities and the appearance of complementary modes are evident. In the Raman spectrum of the 2D polymer under high pressure, new modes, which may be related to the deformations of molecular cages, appear. The observed pressure effects are reversible and the material remains stable for pressures up to 8.8 GPa.

• 55. Arvantidis, J.
Raman modes of the two-dimensional tetragonal polymeric phase of C60 under high pressure2001Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 114, nr 20, s. 9099-9104Artikkel i tidsskrift (Fagfellevurdert)

The effect of high hydrostatic pressure, up to 12 GPa, on the phonon spectrum and the material stability of the two-dimensional (2D) tetragonal C60 polymer have been studied by means of Raman spectroscopy in the frequency range 100-2000 cm-1. A number of Raman modes appear in the spectrum for pressures above ~1.4 GPa, whose intensities increase with pressure. The pressure coefficients of the majority of the phonon modes change gradually to lower values for pressures around 4.0 GPa. The deformation of the C60 molecular cage along with the change of the material to a more isotropic state (as far as its elastic properties are concerned) resulting from the application of high pressure may be causing the observed effects in the Raman spectra. These effects are reversible upon pressure release and therefore the material is stable in the pressure region investigated.

• 56.
Luleå tekniska universitet.
Luleå tekniska universitet.
The NN-1, π and ΔN-1 delta decay modes in the nuclear medium1994Inngår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 572, nr 3-4, s. 600-620Artikkel i tidsskrift (Fagfellevurdert)

The dependence of the Δ-width on the Δ-decay channels is studied in the nuclear medium. We calculate the decay of the delta into a nucleon and a general pisobar mode consisting of NN-1-, π- and dN-1-modes. For the case of no width of the Δ in the pisobar we present partial contributions to the Δ-width from the Δ-decay channels: Δ→N+NN-1, Δ→N+π and Δ→N+ΔN-1. Results for a self-consistent treatment of the Δ-width in the pisobar is presented. The self-consistent treatment only modifies the results with no width in the pisobar to a small extent. It is found that NN-1 channel is not only dominating the decay at low energies of the Δ-resonance but at high densities (ρ>1.5ρ0) this channel also dominates the decay at higher energies. Qualitative agreement with inclusive and exclusive (p,n) and (3He,T) experiments is achieved

• 57.
Department of Physics and I3N, University of Aveiro, Aveiro, Portugal.
Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 142290 Moscow Region, Russian Federation. Department of Physics and I3N, University of Aveiro, Aveiro, Portugal. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 142290 Moscow Region, Russian Federation. Physics Faculty, Southern Federal University, Rostov-on-Don 344090, Russian Federation.
Optoelectronics and defect levels in hydroxyapatite by first-principles2018Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, nr 15, artikkel-id 154706Artikkel i tidsskrift (Fagfellevurdert)

Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.

• 58. Axelsson, O.
Reactive evaporation of potassium in CO2 and the formation of bulk intermediates1994Inngår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 12, nr 1, s. 158-160Artikkel i tidsskrift (Fagfellevurdert)

Potassium vapor condensed in CO2 has been studied by transmission infrared spectroscopy and by total pressure thermal desorption spectroscopy. The results are compared with surface spectroscopic data for CO2 adsorbed on alkali metal overlayers. Both systems show the formation of bulk coordinated oxalate species at cryogenic temperatures and the conversion to carbonate intermediates upon annealing.

• 59. Axelsson, O.
A theoretical and experimental study of reaction pathways for the interaction of CO2 with alkali-modified surfaces1995Inngår i: Journal of Physical Chemistry, ISSN 0022-3654, Vol. 99, nr 18, s. 7028-7035Artikkel i tidsskrift (Fagfellevurdert)
• 60.
Turkish Atomic Energy Authority, Ankara Nuclear Research and Training Center.
Turkish Atomic Energy Authority, Ankara Nuclear Research and Training Center. Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
Leaching of radioactive isotopes from ash2003Konferansepaper (Annet vitenskapelig)

The aim of the study is to reduce the environmental impact of ash deposits. Ash from coal and biomass combustion, containing uranium and thorium from Yatagan-Silopi and Tuncbilek coal; cesium-137 from forests in northeastern Turkey and central Sweden. Turkey is dependent on coal for power generation and huge volumes of ash (>15 Mton/yr) are produced every year. Because of that certain coals, in particular Yatagan, with known problems from Mo and U leaching to the ground water, and Silopi oil shales/asphaltites were studied. Biomass ash comes from branches, bark and other unused parts of the trees and plants. This ash has low concentration of environmentally hazardous metals, but {sup 137}Cs is a problem in certain regions and it is of interest to investigate the possibilities to leach this metal from the ash. Washing ash through rapid chemical leaching at low pH reduces the slow release of metals from ash due to precipitation and besides it may lead to metal recovery from the ash. Initial experiments were done in batch form, in which the neutralizing capacity at pH 1-1.5 was measured by adding sulfuric acid to maintain pH for mixtures of ash and water. Subsequent experiments were done in bench scale. The process also reduced the metal content of the ash, due to chemical leaching of metal oxides and ion exchange at the surfaces of stable oxides. This means that treated ash will not release further metals and, eventually, relaxes the requirements on depositories and allows the ash from coal to be used as an admixture in cement, and to be used as a fertilizer following after treatment of ash from biomass

• 61.
Luleå tekniska universitet, Institutionen för system- och rymdteknik.
Ion Temperature Anisotropies in the Venus Plasma Environment2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

Velocity distributions are a key to understanding the interplay between particles and waves in a plasma. Any deviation from a Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer MAG on-board Venus Express,  ion distributions in the plasma environment of Venus are studied. The focus lies on temperature anisotropy, that is, the difference between the ion temperature parallel and perpendicular to the background magnetic field. This study presents spatial maps of the average ratio between the perpendicular temperature $T_\perp$ and parallel temperature $T_\parallel$, both for proton and heavy ions (atomic oxygen, molecularoxygen and carbon dioxide). Furthermore average values of $T_\perp$ and $T_\parallel$ are calculated for different spatial areas around Venus. The results show that proton $T_\perp$ and $T_\parallel$ are nearly equal in the solar wind. At the bow shock and in the magnetosheath, the ratio $T_\perp/T_\parallel$ increases to provide conditions favoring mirror mode wave generation. An even higher anisotropy is found in the magnetotail with $T_\perp/T_\parallel\approx 2$ for both protons and heavy ions.

• 62.
Luleå tekniska universitet. Swedish Institute of Space Physics, Kiruna, Sweden. Physics, Lancaster University, Lancaster, United Kingdom.
Swedish Institute of Space Physics, Kiruna, Sweden. Swedish Institute of Space Physics, Uppsala, Sweden. Swedish Institute of Space Physics, Kiruna, Sweden. Swedish Institute of Space Physics, Kiruna, Sweden. Swedish Institute of Space Physics, Kiruna, Sweden. Department of Physics, Umeå Universitet, Umeå, Sweden. Swedish Institute of Space Physics, Kiruna, Sweden. Space Research Institute, Austrian Academy of Science, Graz, Austria.
Proton Temperature Anisotropies in the Plasma Environment of Venus2019Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 5, s. 3312-3330Artikkel i tidsskrift (Fagfellevurdert)

Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T⊥) and parallel (T‖) to the background magnetic field. We calculate average values of T⊥ and T‖ for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T⊥/T‖ > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near‐subsolar magnetosheath (T⊥/T‖≈3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere.

• 63.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Polar Geophysical Institute, Murmansk. Swedish Institute of Space Physics / Institutet för rymdfysik. Swedish Institute of Space Physics / Institutet för rymdfysik.
Electron density profiles in the quiet lower ionosphere based on the results of modeling and experimental data2012Inngår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 30, nr 9, s. 1345-1360Artikkel i tidsskrift (Fagfellevurdert)

The theoretical PGI (Polar Geophysical Institute) model for the quiet lower ionosphere has been applied for computing the ionization rate and electron density profiles in the summer and winter D-region at solar zenith angles less than 80Â° and larger than 99Â° under steady state conditions. In order to minimize possible errors in estimation of ionization rates provided by solar electromagnetic radiation and to obtain the most exact values of electron density, each wavelength range of the solar spectrum has been divided into several intervals and the relations between the solar radiation intensity at these wavelengths and the solar activity index F10.7 have been incorporated into the model. Influence of minor neutral species (NO, H2O, O, O3) concentrations on the electron number density at different altitudes of the sunlit quiet D-region has been examined. The results demonstrate that at altitudes above 70 km, the modeled electron density is most sensitive to variations of nitric oxide concentration. Changes of water vapor concentration in the whole altitude range of the mesosphere influence the electron density only in the narrow height interval 73-85 km. The effect of the change of atomic oxygen and ozone concentration is the least significant and takes place only below 70 km. Model responses to changes of the solar zenith angle, solar activity (low-high) and season (summer-winter) have been considered. Modeled electron density profiles have been evaluated by comparison with experimental profiles available from the rocket measurements for the same conditions. It is demonstrated that the theoretical model for the quiet lower ionosphere is quite effective in describing variations in ionization rate, electron number density and effective recombination coefficient as functions of solar zenith angle, solar activity and season. The model may be used for solving inverse tasks, in particular, for estimations of nitric oxide concentration in the mesosphere

• 64.
School of Chemistry, University of Bath.
School of Physics and Astronomy, University of Nottingham. School of Physics and Astronomy, University of Nottingham. Department of Physics and Energy, Materials and Surface Science Institute, University of Limerick. Fritz Haber Institute of the Max-Planck Society. School of Chemistry, the University of Nottingham. School of Chemistry, the University of Nottingham. School of Physics and Astronomy, University of Nottingham. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
A Case of Unusually Large Density of States Changes For Physisorption - TetraPhenyl-Porphyrins on Cu(111)2015Konferansepaper (Annet vitenskapelig)

Conformational changes caused by surface adsorption can dramatically affect a molecule’s properties. The conformational flexibility of the porphyrin family of molecules has been exploited particularly well in a number of contexts, including prototypical molecular switches. Despite this level of study, however, the exact mechanisms underpinning conformational switching are often unclear. We show that the conformation of the tetra(4-bromophenyl) porphyrin (Br4TPP) on Cu(111) depends critically on the precise adsorption site of the molecule, and that, remarkably, large conformational changes are driven entirely by van der Waals (vdW) interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, low temperature single molecule manipulation, dispersion-corrected density functional theory (DFT) and molecular dynamics (MD) simulations shows that van der Waals forces dominate the adsorption of TPP molecules, causing significant distortions of the molecular architecture so that the porphyrin can adopt one of two low energy conformations. In addition, scanning probe manipulation has been used to translate and switch the Br4TPP molecule between conformations via an intermediary, ‘hybrid’ structure. We have used the generalized gradient approximation (GGA) parameterization by Perdew—Burke—Ernzerhof (PBE), and the sparse-matter optBP86b-vdW20 (vdW-DFT) exchange and correlation functional to account for the missing dispersion forces. In order to check for the presence of chemical bonding we have analyzed the molecule-surface complexes using electron localization function (ELF) and Bader charges. We find that vdW-forces alone are capable of causing large shifts in the molecular density of states, despite the complete absence of chemical interactions.

• 65.
Tyndall National Institute, University College Cork.
Tyndall National Institute, University College Cork. Division of Materials Theory, Department of Physics and Astronomy, Uppsala University. Division of Materials Theory, Department of Physics and Astronomy, Uppsala University.
On the stability of single-walled carbon nanotubes and their binding strengths2012Inngår i: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 131, nr 9, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)

We have studied the relative stability of hydrogen-terminated single-walled carbon nanotubes (SWNTs) segments, and open-ended SWNT fragments of varying diameter and chirality that are present at the interface of the catalytic metal particles during growth. We have found that hydrogen-terminated SWNTs differ by <1 eV in stability among different chiralities, which presents a challenge for selective and property-controlled growth. In addition, both zigzag and armchair tubes can be the most stable chirality of hydrogen-terminated SWNTs, which is a fundamental obstacle for property-controlled growth utilizing thermodynamic stability. In contrast, the most armchair-like open-ended SWNTs segments are always the most stable ones, followed in sequence by chiral index up to the least stable zigzag segments. We explain the ordering by triple bond stabilization of the carbon dangling bonds at the open ends, which is a fragment stabilization effect that is only manifested when all bonds between two layers are broken. We show convincingly that the bond strength difference between zigzag and armchair tubes is not present when individual bonds are broken or formed

• 66.
Tyndall National Institute, University College Cork.
Structure and energetics of shuttlecock-shaped tin-phthalocyanine on Ag(111: A density functional study employing dispersion correction2012Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, s. 9487-9497Artikkel i tidsskrift (Fagfellevurdert)

• 67.
Tyndall National Institute, University College Cork.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
Theoretical insights into adsorption of cobalt phthalocyanine on Ag(111): A combination of chemical and van der Waals bonding2013Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 45, s. 23887-23898Artikkel i tidsskrift (Fagfellevurdert)

In this article we study in detail the interaction of cobalt phthalocyanine (CoPc) with the Ag(111) surface by means of density functional theory calculations (DFT). We discuss the electronic and geometric differences of the adsorbed CoPc as it interacts with the different binding sites of the surface, yielding deeper insight into the adsorption mechanism of organometallic molecules with noble metal surfaces. We interpret the experimentally observed 4-fold to 2-fold symmetry reduction upon interaction of phthalocyanine molecules with metal surfaces as caused by electronic effects originating from nonsymmetric interactions between the molecule and the surface. To asses the role of dispersion forces in bonding of CoPc to the surface we employ a semiempirical dispersion correction to standard DFT and compare the obtained molecule-surface separation with experimental measurements. We show that, in the case of CoPc, the molecule bonds to the surface mostly due to covalent bonding between Co and Ag, but with a considerable contribution from van der Waals bonding between the Pc ligand and the surface. We show in this case where the molecule-surface separation is mostly governed by covalent bonding between the central metal atom and the surface atoms that standard DFT performs reasonably well, as compared to the available experimental data.

• 68.
University of Brescia.
University of Brescia. University of Brescia. University of Brescia. University of Brescia. University of Brescia, CNR-INFM SENSOR Laboratory. University of Brescia.
Transparent Metal Oxide Semiconductors as Gas Sensors2010Inngår i: Transparent Electronics: From Synthesis to Applications, John Wiley and Sons , 2010, s. 417-442Kapittel i bok, del av antologi (Fagfellevurdert)
• 69.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
Numerical & physical modelling of fluid flow in a continuous casting mould: Flow dynamics studies for flexible operation of continuous casters2016Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave

The current demands on Swedish steel industry to produce low quantity batches of specialized products requires research on steel casting processes. There are several physical processes that need be taken into account for this problem to be viewed in full light such as thermal-processes, solidiﬁcation and ﬂuid dynamics. This work focuses on the ﬂuid-dynamics part; more speciﬁcally, the dependence of ﬂow quality within the caster on nozzle and mould geometry.

The simulations are carried out using a scale-resolving method, in speciﬁc LES (Large Eddy Simulation) which is coupled with a DPM (Discrete Phase Model) to model Argon behaviour. The results of these simulations are presented and validated against physical experiment and data from industrial trials. Conclusions are drawn regarding optimal nozzle types in respect to diﬀerent mould geometries.

The mould eigenfrequencies are shown to exhibit a connection with the casting velocity. This results in so called sweet spots in casting velocity where ﬂow irregularities due to sloshing is minimal. It is shown that the mountain type nozzle is preferable for smaller geometries whilst comparatively larger geometries beneﬁt from a cup type.

• 70. Baricordi, S.
Institute for High Energy Physics. Institute for High Energy Physics. University of Trento, Department of Materials Engineering and Industrial Technologies. Petersburg Institute for Nuclear Physics. INFN. CERN. Department of Physics, University of Padova.
Low-energy-channeling surface analysis on silicon crystals designed for high-energy-channeling in accelerators2005Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, nr 9, artikkel-id 94102Artikkel i tidsskrift (Fagfellevurdert)

Channeling of relativistic particles in bent Si crystals is a powerful technique for use with accelerators. Its efficiency can be found to be highly dependent on the state of the surface of the crystal steering the particles. We investigated the morphology and structure of the surface of the samples that have been used with high efficiency for channeling in accelerators. Low-energy channeling of 2 MeVα particles or protons was used as a probe. We found that mechanical treatment of the samples leads to a superficial damaged layer, which is correlated to efficiency limitations of the crystal in accelerators. In contrast, chemical etching, which was used to treat the surface of the most efficient crystals, leaves a surface with superior perfection. © 2005 American Institute of Physics.

• 71.
Institut National de la Recherche Scientifique-Énergie, Matériaux et Télécommunications, Université du Québec, Varennes.
Institut National de la Recherche Scientifique-Énergie, Matériaux et Télécommunications, Université du Québec, Varennes. Institut National de la Recherche Scientifique Energie Varennes, Institut National de la Recherche Scientifique-Énergie, Matériaux et Télécommunications, Université du Québec, Varennes. Institut National de la Recherche Scientifique Energie Varennes, Institut National de la Recherche Scientifique-Énergie, Matériaux et Télécommunications, Université du Québec, Varennes. Institut National de la Recherche Scientifique-Énergie, Matériaux et Télécommunications, Université du Québec, Varennes. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Institut National de la Recherche Scientifique Energie Varennes, Institut National de la Recherche Scientifique-Énergie, Matériaux et Télécommunications, Université du Québec, Varennes.
Enhanced photovoltaic properties in dye sensitized solar cells by surface treatment of SnO2 photoanodes2016Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, artikkel-id 23312Artikkel i tidsskrift (Fagfellevurdert)

We report the fabrication and testing of dye sensitized solar cells (DSSC) based on tin oxide (SnO2) particles of average size ~20 nm. Fluorine-doped tin oxide (FTO) conducting glass substrates were treated with TiOx or TiCl4 precursor solutions to create a blocking layer before tape casting the SnO2 mesoporous anode. In addition, SnO2 photoelectrodes were treated with the same precursor solutions to deposit a TiO2 passivating layer covering the SnO2 particles. We found that the modification enhances the short circuit current, open-circuit voltage and fill factor, leading to nearly 2-fold increase in power conversion efficiency, from 1.48% without any treatment, to 2.85% achieved with TiCl4 treatment. The superior photovoltaic performance of the DSSCs assembled with modified photoanode is attributed to enhanced electron lifetime and suppression of electron recombination to the electrolyte, as confirmed by electrochemical impedance spectroscopy (EIS) carried out under dark condition. These results indicate that modification of the FTO and SnO2 anode by titania can play a major role in maximizing the photo conversion efficiency

• 72.
Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
Department of Physics and I3N, University of Aveiro, Campus Santiag, Aveiro, Portugal. Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway. Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden. Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway. Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway. Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway.
Anisotropic and plane-selective migration of the carbon vacancy in SiC: Theory and experiment2019Inngår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 1, artikkel-id 014103Artikkel i tidsskrift (Fagfellevurdert)

We investigate the migration mechanism of the carbon vacancy (VC) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The VC, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for VC removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that VC migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, VC(h), and pseudocubic, VC(k)] and their consequences for VC migration have not been considered so far. The first part of the paper presents a theoretical study of VC migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for VC migration. In 3C-SiC, VC is found to migrate with an activation energy of EA=4.0 eV. In 4H-SiC, on the other hand, we anticipate that VC migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of EA=4.2 eV, and a striking preference for basal migration within the h plane with a barrier of EA=3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of VC in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z1/2 electron trap in annealed samples that were subject to ion implantation. Activation energies of EA=(4.4±0.3) eV and EA=(3.6±0.3) eV were found for VC migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D0=0.54cm2/s and 0.017cm2/s are in line with a simple jump process, as expected for a primary vacancy point defect.

• 73.
LCP-A2MC, Université de Lorraine.
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, LCPME UMR 7564 CNRS-Université de Lorraine. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Laboratoire de Synthèse Organométallique et Réactivité, Université Henri Poincaré - Nancy, Laboratoire de Structure et Réactivité des Systèmes Moléculaires Complexes, Nancy Université, SRSMC UMR 7565 CNRS-Université de Lorraine, Faculté des Sciences et Techniques. LCP-A2MC, Université de Lorraine. LCP-A2MC, Université de Lorraine. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
Mild covalent functionalization of single-walled carbon nanotubes highlighted by spectroscopic ellipsometry2016Inngår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 96, s. 557-564Artikkel i tidsskrift (Fagfellevurdert)

Single-walled carbon nanotubes (SWCNT) synthesized using the HiPco® process and purified thereafter were submitted to two covalent functionalization processes: i) a mild oxidation in a concentrated HNO3 solution using microwave irradiation and ii) a radical functionalization to graft methoxyphenyl groups. The samples were analyzed by Raman spectroscopy and spectroscopic ellipsometry in the energy window 0.07-4.96 eV. The complex dielectric function was analytically calculated in order to extract the real (εr) and imaginary (εi) parts of this function vs. the incident energy of the light. The ellipsometric data in the infrared part of the spectrum revealed that process i) mainly affected the amorphous carbon deposited on the surface of SWCNTs while process ii) strongly changed the electronic nature of the film due to a charge transfer between methoxyphenyl groups and SWCNTs. These results demonstrate the richness of information that spectroscopic ellipsometry is able to bring about on an entire carbon nanotube ensemble compared to Raman spectroscopy, while not suffering from limitation on their electronic structure and/or aggregate state/presence of surfactants.

• 74.
Laboratoire des Solides Irradiés, CNRS-UMR 7642 & CEA/DSM/DRECAM, Ecole Polytechnique, Palaiseau cedex.
Institut Néel, Grenoble. Institut Néel, Grenoble. Commissariat à l'Energie Atomique, Grenoble. Kungliga tekniska högskolan, KTH. University of Rochester. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
Thermodynamics of a heavy-ion-irradiated superconductor: the zero-field transition2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 10Artikkel i tidsskrift (Fagfellevurdert)

Specific heat measurements show that the introduction of amorphous columnar defects considerably affects the transition from the normal to the superconducting state in zero magnetic field. Experimental results are compared to numerical simulations of the three-dimensional XY model for both the pure system and the system containing random columnar disorder. The numerics reproduce the salient features of experiment, showing in particular that the specific heat peak changes from cusplike to smoothly rounded when columnar defects are added. By considering the specific heat critical exponent α, we argue that such behavior is consistent with recent numerical work [A. Vestergren et al., Phys. Rev. B 70, 054508 (2004)] showing that the introduction of columnar defects changes the universality class of the transition.

• 75.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Solar Wind Dynamics within The Atmosphere of comet 67P/Churyumov-Gerasimenko2018Doktoravhandling, med artikler (Annet vitenskapelig)

In this thesis, we explore the dynamics of the solar wind as it perme-ates and flows through a tenuous cometary atmosphere, with a focuson the interaction observed at comet 67P/Churyumov–Gerasimenko.

Seven comets had already been visited by nine different probes when the European spacecraft Rosetta reached comet Churyumov–Gerasimenko in August 2014. The mission was however the first to orbit its host comet, which it did for a total duration of more than two years, corre-sponding to a large part of the comet’s orbit around the Sun. This en-abled to study how the dynamics of the plasma environment evolvedas the comet itself was transformed from one of the smallest obstaclesto the solar wind in the Solar System when far away from the Sun, toa well-established magnetosphere at perihelion.

Most of our efforts tackle the early part of this transformation, when the creation of new-born cometary ions starts to induce significant disturbances to the incident flow. During this stage, a kinetic descrip-tion of the interaction is necessary, as the system of interest cannot be reduced to a hydrodynamic problem. This contrasts with the situation closer to the Sun, where a fluid treatment can be used, at Churyumov–Gerasimenko as well as at previously visited comets.

Rosetta was not a mission dedicated to plasma studies, however. It directly translates into a limited spatial coverage of the cometary plasma environment, which by its nature extends over several spatial scales. An approach solely based on the analysis of in-situ data cannot properly address the major questions on the nature and physics of the plasma environment of Churyumov–Gerasimenko. This thesis there-fore largely exploits the experimental–analytical–numerical triad of approaches. In Chapters 3 and 4 we propose simple models of the ion dynamics and of the cometary plasma environment, and these are tested against experimental and numerical data. Used together,they give a global description of the solar wind ion dynamics through the cometary atmosphere, that we explore in the 2-dimensional and 3-dimensional cases (Chapter 5). In Chapter 6, we propose a view onthe interaction and its fluid aspects when closer to the Sun.

• 76.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna. Aalto University, School of Electrical Engineering, Department of Electronics and Nanoengineering, Finland. Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Germany. Jet Propulsion Laboratory, California Institute of Technology, USA.
The birth and growth of a solar wind cavity around a comet: Rosetta observations2017Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, nr Suppl. 2, s. S369-S403Artikkel i tidsskrift (Fagfellevurdert)

The Rosetta mission provided detailed observations of the growth of a cavity in the solar wind around comet 67P/Churyumov–Gerasimenko. As the comet approached the Sun, the plasma of cometary origin grew enough in density and size to present an obstacle to the solar wind. Our results demonstrate how the initial slight perturbations of the solar wind prefigure the formation of a solar wind cavity, with a particular interest placed on the discontinuity (solar wind cavity boundary) passing over the spacecraft. The slowing down and heating of the solar wind can be followed and understood in terms of single particle motion. We propose a simple geometric illustration that accounts for the observations, and shows how a cometary magnetosphere is seeded from the gradual steepening of an initially slight solar wind perturbation. A perspective is given concerning the difference between the diamagnetic cavity and the solar wind cavity.

• 77.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna. LPC2E, CNRS, Orléans. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris. IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris. Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
The root of a comet tail: Rosetta ion observations at comet 67P/Churyumov–Gerasimenko2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, artikkel-id A21Artikkel i tidsskrift (Fagfellevurdert)

Context.The first 1000 km of the ion tail of comet 67P/Churyumov–Gerasimenko were explored by the EuropeanRosettaspacecraft,2.7 au away from the Sun.Aims.We characterised the dynamics of both the solar wind and the cometary ions on the night-side of the comet’s atmosphere.Methods.We analysed in situ ion and magnetic field measurements and compared the data to a semi-analytical model.Results.The cometary ions are observed flowing close to radially away from the nucleus during the entire excursion. The solar windis deflected by its interaction with the new-born cometary ions. Two concentric regions appear, an inner region dominated by theexpanding cometary ions and an outer region dominated by the solar wind particles.Conclusions.The single night-side excursion operated byRosettarevealed that the near radial flow of the cometary ions can beexplained by the combined action of three different electric field components, resulting from the ion motion, the electron pressuregradients, and the magnetic field draping. The observed solar wind deflection is governed mostly by the motional electric field−uion×B.

• 78.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna.
LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna.
Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko2018Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, nr 2, s. 1570-1575Artikkel i tidsskrift (Fagfellevurdert)

When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream electric field orientation and sense, the cometary pick-up ions are drifting towards the dawn side of the coma, while the solar wind ions are drifting towards the dusk side of the coma, independent of the heliocentric distance. The dynamics of the interaction is not taking place in a plane, as often assumed in previous works.

• 79.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna.
LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris. IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris. LPC2E, CNRS, Orléans. Laboratory for Atmospheric and Space Physics (LASP), University of Colorado Boulder. Umeå University, Department of Physics. Swedish Institute of Space Physics, Kiruna. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna.
Solar wind dynamics around a comet: A 2D semi-analytical kinetic model2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, artikkel-id A35Artikkel i tidsskrift (Fagfellevurdert)

Aims.We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometaryatmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics.Methods.We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-stateis assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced byindividual solar wind protons during the interaction.Results.A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to acomet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r2. The solar winddeflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular regionis found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, togetherwith the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of theRosettamission.Conclusions.The qualitative match between the model and thein situdata highlights how dominant the motional electric field isthroughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic descriptionof how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical modelfor a systematic quantitative comparison to the data.

• 80.
INFN.
Dipartimento di Fisica Sperimentale, Università di Torino. Dipartimento di Fisica Sperimentale, Università di Torino. Istituto di Fisica Generale Applicata. INFN. Dipartimento di Fisica Sperimentale, Università di Torino. Dipartimento di Fisica Sperimentale, Università di Torino. Centro de Fısica Nuclear da Universidade de Lisboa. Laboratori Nazionali del Gran Sasso. Institute of Nuclear Research (ATOMKI), Debrecen. Dipartimento di Fisica Sperimentale, Università di Torino. Istituto di Fisica Generale Applicata. Laboratori Nazionali del Gran Sasso. Institute of Nuclear Research (ATOMKI), Debrecen. Dipartimento di Scienze Fisiche, Universitá Federico II. Centro de Fısica Nuclear da Universidade de Lisboa. Laboratori Nazionali del Gran Sasso. Dipartimento di Scienze Fisiche, Universitá Federico II. INFN. Dipartimento di Fisica Sperimentale, Università di Torino. Dipartimento di Scienze Fisiche, Universitá Federico II. Seconda Università di Napoli. Institut Für Experimentalphysik III. Dipartimento di Scienze Fisiche, Universitá Federico II. INFN. INFN Laboratori Nazionali di Legnaro.
Feasibility of low-energy radiative-capture experiments at the LUNA underground accelerator facility2005Inngår i: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 24, nr 2, s. 313-319Artikkel i tidsskrift (Fagfellevurdert)

The LUNA (Laboratory Underground for Nuclear Astrophysics) facility has been designed to study nuclear reactions of astrophysical interest. It is located deep underground in the Gran Sasso National Laboratory, Italy. Two electrostatic accelerators, with 50 and 400 kV maximum voltage, in combination with solid and gas target setups allowed to measure the total cross-sections of the radiative-capture reactions 2H2H(p, γ) 3He3Heand 14N14N(p, γ) 15O15Owithin their relevant Gamow peaks. We report on the gamma background in the Gran Sasso laboratory measured by germanium and bismuth germanate detectors, with and without an incident proton beam. A method to localize the sources of beam-induced background using the Doppler shift of emitted gamma rays is presented. The feasibility of radiative-capture studies at energies of astrophysical interest is discussed for several experimental scenarios. © Società Italiana di Fisica/Springer-Verlag 2005.

• 81.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
A.A. Baikov Institute of Metallurgy and Materials Science (IMET), Moscow, Baikov Institute of Metallurgy and Materials Science (IMET), Russian Academy of Sciences. A.A. Baikov Institute of Metallurgy and Materials Science (IMET), Moscow. A.A. Baikov Institute of Metallurgy and Materials Science (IMET), Moscow. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
Raman and electron microscopy study of C60 collapse/transformation to a nanoclustered graphene-based disordered carbon phase at high pressure/temperature2015Inngår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, nr 11, s. 2626-2629Artikkel i tidsskrift (Fagfellevurdert)

Transformation of C60 polymers to a superelastic hard carbon (nanoclustered graphene phase (NGP)) occurring in metal matrix at 5 GPa in a temperature interval of 1000–1100 K was studied by optical, scanning electron microscopy (SEM), and Raman spectroscopy. Raman spectral scan across the sample surface allowed us to identify different stages of the structural transformation. The SEM and Raman spectroscopy data testify for the NGP appearance at the defects concentration sites in the parent fullerite structure. We propose that the buckyballs collapse/formation of the NGP is governed by nucleation and growth (diffusive) mechanism unlike earlier discussed in the literature possibility of the martensitic-type (displacive) character of this transformation.

• 82.
INRS Centre for Energy, Materials and Telecommunications, 1650 Boulevard Lionel-Boulet, Varennes, Québec, J3X 1S2, Canada..
INRS Centre for Energy, Materials and Telecommunications, 1650 Boulevard Lionel-Boulet, Varennes, Québec, J3X 1S2, Canada.. INRS Centre for Energy, Materials and Telecommunications, 1650 Boulevard Lionel-Boulet, Varennes, Québec, J3X 1S2, Canada.. INRS Centre for Energy, Materials and Telecommunications, 1650 Boulevard Lionel-Boulet, Varennes, Québec, J3X 1S2, Canada.. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
Direct Measurement of Electronic Band Structure in Single Quantum Dots of Metal Chalcogenide Composites.2018Inngår i: Small (Weinheim an der Bergstrasse, Germany), ISSN 1613-6810, Vol. 14, nr 51, artikkel-id 1801668Artikkel i tidsskrift (Fagfellevurdert)

Metal chalcogenide quantum dots (QDs) are among the most promising materials as light harvesters in all-inorganic systems for applications in solar cells and production of solar fuels. The electronic band structure of composite QDs formed by lead and cadmium chalcogenides directly grafted on highly oriented pyrolytic graphite surfaces through successive ionic layer absorption and reaction is investigated. Atomic force microscopy and Kelvin probe force microscopy (KPFM) are applied to investigate PbS, CdS, and PbS/CdS QD systems. The variation of the surface potential of individual QDs is measured, investigating the evolution of the electronic band structure as a function of QD size and composition. A shift of the Fermi level toward more negative values occurs when QD size is increased. The shift is more pronounced in CdS than in PbS, while the composite PbS/CdS exhibits an intermediate behavior. The calculated shift is in good agreement with the experiments. These results highlight the ability of KPFM to directly measure the electronic band structure in individual QDs of metal chalcogenide composites. This feature regulates charge dynamics in composite systems, thereby affecting device performance. This work provides valuable insights for applications in several fields, in which charge injection plays a major role.

• 83.
INRS Centre for Energy, Materials and Telecommunications.
INRS Centre for Energy, Materials and Telecommunications. Département de Génie Électrique, École de Technologie Supérieure, Montréal. INRS Centre for Energy, Materials and Telecommunications, CNR-INO SENSOR Lab. Département de Génie Électrique, École de Technologie Supérieure, Montréal. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. INRS Centre for Energy, Materials and Telecommunications, Institute for Fundamental and Frontier Science University of Electronic 15 Science and Technology of China, Center for Self-Assembled Chemical Structures, McGill University.
Functionalized multi-wall carbon nanotubes/TiO2 composites as efficient photoanodes for dye sensitized solar cells2016Inngår i: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 4, nr 16, s. 3555-3562Artikkel i tidsskrift (Fagfellevurdert)

We report on the effects of incorporation of different concentrations of carboxyl group (COOH)-functionalized multi-wall carbon nanotubes (F-MWCNTs) into TiO2 active layers for dye-sensitized solar cells (DSSCs). Standard DSSCs with bare TiO2 exhibit a photo-conversion efficiency (PCE) of 6.05% and a short circuit current density (Jsc) of 13.3 mA cm−2. The presence of 2 wt% F-MWCNTs in the photoanodes increases the PCE up to 7.95% and Jsc up to 17.5 mA cm−2. The photoanodes were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The electrochemical behaviour of the solar cells was investigated by electrochemical impedance spectroscopy (EIS). We attribute the improved performances to the combined effect of increased dye loading and reduced charge recombination (as clarified by dye loading and EIS measurements), due to the conformal coverage of F-MWCNTs, which allows fast and efficient charge collection in operating solar cells. These results can help in improving the PCE in DSSCs in an elegant and straightforward way, minimizing the need of additional steps (e.g. pre- and post-treatment with TiCl4) for photoanode preparation.

• 84.
INRS Centre for Energy, Materials and Telecommunications, Varennes, Québec, Canada.
Department of Applied Chemistry, Institute of Molecular Science and Center for Emergent Functional Matter Science, National Chiao Tung University, Hsinchu, Taiwan. Center for Emergent Functional Matter Science, National Chiao Tung University, Taiwan. Department of Applied Chemistry, Institute of Molecular Science and Center for Emergent Functional Matter Science, National Chiao Tung University, Taiwan. Department of Applied Chemistry, Institute of Molecular Science and Center for Emergent Functional Matter Science, National Chiao Tung University, Taiwan. INRS Centre for Energy, Materials and Telecommunications, Varennes, Québec, Canada. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Department of Applied Chemistry, Institute of Molecular Science and Center for Emergent Functional Matter Science, National Chiao Tung University, Hsinchu, Taiwan. Center for Emergent Functional Matter Science, National Chiao Tung University, Taiwan. INRS Centre for Energy, Materials and Telecommunications, Varennes, Québec, Canada. Institute of Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu, China.
Hole-extraction and photostability enhancement in highly efficient inverted perovskite solar cells through carbon dot-based hybrid material2019Inngår i: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 62, s. 781-790Artikkel i tidsskrift (Fagfellevurdert)

We report the effect of the integration of carbon dots (Cdots) in high-performance inverted planar-heterojunction (PHJ) perovskite solar cells (PSCs). We used Cdots to modify the hole-transport layer in planar PSC devices. By introducing Cdots on graphene oxide (GO) as hole-transporting layer, the efficiency of the PSC improved significantly from 14.7% in the case of bare GO to 16.2% of the best device with optimized Cdots content. When applying Cdots with an engineered absorption in the UV range as downshifting layer, the device performance was further improved, attaining a maximum PCE of 16.8% (+14%); the stability of the device was also enhanced of more than 20%. Kelvin probe force microscopy (KPFM) and cyclic voltammetry (CV) were employed to analyze the electronic band alignment at the interface between GO/Cdots and the perovskite film. Holes were extracted and transferred to the conductive substrate more efficiently in the presence of Cdots, thus delaying charge recombination. Photoluminescence (PL), transient PL decays and transient photovoltage (TPV) decays investigated the charge-transfer kinetics and proved the retardation of charge recombination. This work reveals an effective enhancement of the performance of planar PSCs by using Cdots/GO as hole transport material.

• 85.
Swedish Institute of Space Physics, Kiruna.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Swedish Institute of Space Physics, Kiruna. Technische Universität Braunschweig, Institute for Geophysics and Extraterrestrial Physics.
Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period2018Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)

Aims.Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma.We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in theterminator plane.Methods.We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly usingplasma moments). We propose a statistical approach over a period of one month.Results.On average, two populations were observed, separated in phase space. The motion of the first is governed by its interactionwith the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatiblewith an ambipolar electric field. Both populations display a consistent anti-sunward velocity component.Conclusions.Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative tothe nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometaryion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. Thereis no corresponding signature in the average magnetic field strengt

• 86.
Department of Applied Mathematics and High-performance ComputingM.V.Lomonosov Northern (Arctic) Federal University, Arkhangelsk.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
Computational study of the CO adsorption and diffusion in zeolites: validating the Reed–Ehrlich model2018Inngår i: Adsorption, ISSN 0929-5607, E-ISSN 1572-8757, Vol. 24, nr 4, s. 403-413Artikkel i tidsskrift (Fagfellevurdert)

Molecular simulations have been employed to explore at the microscopic scale the adsorption of CO in zeolites (MFI, CHA and DDR). On the basis of classical force fields, grand canonical Monte Carlo simulations are performed to predict the adsorption properties (isotherms) of these types of zeolites up to high pressure. Subsequent careful analysis yields details the microscopic mechanism in play, along the whole adsorption process, together with a considering of the arrangements of CO in MFI at high pressure. This work also summarizes an approach which uses single component diffusion data in prediction of multicomponent diffusion.

• 87.
Luleå tekniska universitet, Institutionen för system- och rymdteknik.
Testing of micro-fluidic systems for Raman spectroscopic measurements on biological cells2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave

Pulmonary Artery Hypertension (PAH) is a condition that can affect people as a consequence of infections or diseases such as lung disease, high blood pressure or pneumonia. When afflicted by these diseases, low oxygen content in the lung tissue causes the pulmonary arterial soft muscle cells (PASMC) located in the walls of the pulmonary arteries to chronically swell up. As a result, the arteries are constantly narrowed. This can in many cases be fatal as the arteries become clogged and the heart is forced to pump more blood to the lungs, causing an enlargement of the right heart chamber which eventually may lead to heart failure. This irreversible swelling of the PASMC is the cause for PAH. To find a treatment for this incurable disease, the mechanisms of the vasoconstriction need to be investigated.

Spectroscopy is the study of the interactions between light and matter and is a tool that can be used to gain knowledge in the matter of the expansions of the PASMC. In particular, Raman spectroscopy that targets the inelastic interactions can be used since it registers dynamic changes of cells.

To simulate an oxygen deprived environment, a micro-fluidic system designed for use in cellular experiments has been developed. Tests of the prototypes showed strong Raman signals from the polymeric material of the system itself. These signals overshadowed the signals from the observed sample. The objective of the experiments presented in this report was to test whether the signals from the micro-fluidic system could be eliminated by adding spacing between the polymer and the sample.

The experiment was conducted by collecting data of samples from baker's yeast prepared in the micro-fluidic system at different z-distances. By this the optimal spacing between the polymer of the micro-fluidic system and the sample could be determined. This experiment concluded that the sample needed to be placed 1.54 mm further from the micro-fluidic system in order to test human lung tissue at 2 mW laser intensity.

• 88.
Luleå tekniska universitet, Institutionen för system- och rymdteknik.
Europa's Hydrogen Corona in a Large Set of HST Lyman-Alpha Images2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave

Far-ultraviolet (FUV) spectral images of Jupiter's moon Europa were obtained by the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) on 20 occasions between the years 1999 and 2015. In this thesis these data are analyzed to look for Lyman-alpha emissions from a hydrogen corona. This hydrogen corona was recently discovered in absorption, also from HST Lyman-alpha images but with Europa in transit of Jupiter, and the aim of this study is to confirm the existence of the corona also in emission. Europa's thin atmosphere is dominated by molecular oxygen, mainly produced by radiolysis and sputtering of the icy surface. Atomic hydrogen, the main target for this study, is produced by sputtering from the surface and the dissociation of H2 and H2O. It quickly escapes the gravity of Europa. To study the hydrogen corona in the spectral STIS images the data need to be processed to remove the other Lyman-alpha contributions to the image. These other contributions include emissions from the geocorona, emissions from the interplanetary medium (IPM), dark current in the detector and sunlight reflected from the surface of Europa. To estimate the contribution to the image from the hydrogen corona, a basic model of the expected emissions from the corona is developed. By fitting this model to the processed STIS data values of the hydrogen density and the surface Lyman-alpha albedo of the moon are obtained. The results confirm the presence of a hydrogen corona, with varying densities between the different observations but generally about twice as large as the results from the previous study. The uncertainty for the results is however large and there is a clear correlation between hydrogen density and background level in the image, for which the reason is poorly understood. No hemispheric variability or connections to the true anomaly of the moon are found, but the hydrogen density seems to be increasing during the time of the observations. The results for the albedo is consistent with previous results, indicating a lower albedo on the leading than on the trailing hemisphere.

• 89.
KTH, Royal Institute of Technology, Department of Materials and Nano Physics.
Department of Physics and Astronomy, Uppsala University. Department of Physics and Astronomy, Uppsala University. Department of Physics and Astronomy, Uppsala University. Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
Atomistic spin dynamics of low-dimensional magnets2013Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 87, artikkel-id 144401Artikkel i tidsskrift (Fagfellevurdert)

We investigate the magnetic properties of a range of low-dimensional ferromagnets using a combination of first-principles calculations and atomistic spin dynamics simulations. This approach allows us to evaluate the ground state and finite temperature properties of experimentally well characterized systems such as Co/Cu(111), Co/Cu(001), Fe/Cu(001) and Fe/W(110), for different thicknesses of the magnetic layer. We compare our calculated spin wave spectra with experimental data available in the literature, and find a good quantitative agreement. We also predict magnon spectra for systems for which no experimental data exist at the moment, and estimate the role of temperature effects

• 90. Bergström, Lars
Backward production on nuclei and the tube model1980Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 21, nr 1, s. 305-307Artikkel i tidsskrift (Fagfellevurdert)

It is shown that the recent data from Burke et al. on backward production in 200-GeV/c nA collisions are in good agreement with expectations from the collective tube model with tube fragmentation taken into account.

• 91. Bergström, Lars
Estimates of recoil nucleon spectra in high-energy hadron-nucleus collisions1977Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 68, nr 2, s. 177-179Artikkel i tidsskrift (Fagfellevurdert)

It is shown that recent data on the recoil nucleon spectrum in 10.5 GeV/c pion-neon collisions are in excellent agreement with a parameter free estimate from the so called tube model for high-energy hadron-nucleus collisions. A simple independent collision model is also treated.

• 92. Bergström, Lars
Is the recently published counterproof of the tube model credible?1978Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 78, nr 2-3, s. 337-341Artikkel i tidsskrift (Fagfellevurdert)

It is shown that recent data from pion and proton collision with emulsion nuclei at 200 GeV/c are in perfect agreement with expectations from the collective tube model. The opposite conclusion in publications by Azimov et al. came about because the authors ignored the important effects of target fragmentation.

• 93. Bergström, Lars
The deuteron in high-energy physics1980Inngår i: Reviews of Modern Physics, ISSN 0034-6861, E-ISSN 1539-0756, Vol. 51, nr 4, s. 675-697Artikkel i tidsskrift (Fagfellevurdert)

The deuterium nucleus plays an important role in several branches of high-energy physics. We review its present status as a neutron source, a relativistic bound state, a collective six-quark state and a double scatterer.

• 94.
Luleå tekniska universitet.
Sveptunnelmikroskopet: ett nytt sätt att se in i atomernas värld1989Rapport (Annet vitenskapelig)
• 95.
Luleå tekniska universitet.
Synchrotron radiation in soft X-ray and electron spectroscopy1990Rapport (Annet vitenskapelig)
• 96. Beton, P.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
A study for the construction of a quantum information precessing device using doped fullerenes2000Konferansepaper (Fagfellevurdert)
• 97.
INFN Sezione di Roma, Roma, Italy; Sapienza Università di Roma, Roma, Italy.
Luleå tekniska universitet. Stockholm University, Stockholm, Sweden. Lawrence Berkeley National Laboratory, University of California, Berkeley, CA, USA; Department of Physics, University of California, Berkeley, CA, USA.
A design for an electromagnetic filter for precision energy measurements at the tritium endpoint2019Inngår i: Progress in Particle and Nuclear Physics, ISSN 0146-6410, E-ISSN 1873-2224, Vol. 106, s. 120-131Artikkel i tidsskrift (Fagfellevurdert)

We present a detailed description of the electromagnetic filter for the PTOLEMY project to directly detect the Cosmic Neutrino Background (CNB). Starting with an initial estimate for the orbital magnetic moment, the higher-order drift process of E×B is configured to balance the gradient-B drift motion of the electron in such a way as to guide the trajectory into the standing voltage potential along the mid-plane of the filter. As a function of drift distance along the length of the filter, the filter zooms in with exponentially increasing precision on the transverse velocity component of the electron kinetic energy. This yields a linear dimension for the total filter length that is exceptionally compact compared to previous techniques for electromagnetic filtering. The parallel velocity component of the electron kinetic energy oscillates in an electrostatic harmonic trap as the electron drifts along the length of the filter. An analysis of the phase-space volume conservation validates the expected behavior of the filter from the adiabatic invariance of the orbital magnetic moment and energy conservation following Liouville's theorem for Hamiltonian systems.

• 98.
Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
Uppsala universitet, Department of Physics and Astronomy, Uppsala University. School of Applied Sciences, University of Huddersfield, Queensgate. Uppsala universitet, Department of Physics and Astronomy, Uppsala University. Institut für Experimentalphysik, Freie Universität Berlin. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen. Department of Physics and Astronomy, Uppsala University. Institut für Experimentalphysik, Freie Universität Berlin. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen. Uppsala universitet, Department of Physics and Astronomy, Uppsala University. Uppsala universitet, Department of Physics and Astronomy, Uppsala University.
Manipulation of spin state of iron porphyrin by chemisorption on magnetic substrates2013Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 88, nr 2, artikkel-id 24401Artikkel i tidsskrift (Fagfellevurdert)
• 99.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Institut für Kartographie, Technische Universität Dresden. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Martian slope streaks as plausible indicators of transient water activity2017Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, nr 1, artikkel-id 7074Artikkel i tidsskrift (Fagfellevurdert)

Slope streaks have been frequently observed in the equatorial, low thermal inertia and dusty regions of Mars. The reason behind their formation remains unclear with proposed hypotheses for both dry and wet mechanisms. Here, we report an up-to-date distribution and morphometric investigation of Martian slope streaks. We find: (i) a remarkable coexistence of the slope streak distribution with the regions on Mars with high abundances of water-equivalent hydrogen, chlorine, and iron; (ii) favourable thermodynamic conditions for transient deliquescence and brine development in the slope streak regions; (iii) a significant concurrence of slope streak distribution with the regions of enhanced atmospheric water vapour concentration, thus suggestive of a present-day regolith-atmosphere water cycle; and (iv) terrain preferences and flow patterns supporting a wet mechanism for slope streaks. These results suggest a strong local regolith-atmosphere water coupling in the slope streak regions that leads to the formation of these fluidised features. Our conclusions can have profound astrobiological, habitability, environmental, and planetary protection implications

• 100.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
Discovery of recurring slope lineae candidates in Mawrth Vallis, Mars2019Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikkel-id 2040Artikkel i tidsskrift (Fagfellevurdert)

utside of established RSL regions and further prompt the inclusion of a new geographical region within the RSL candidate group. Our inferences on the RSL candidates are based on several morphological and geophysical evidences and analogies: (i) the dimensions of the RSL candidates are consistent with confirmed mid-latitude RSL; (ii) albedo and thermal inertia values are comparable to those of other mid-latitude RSL sites; and (iii) features are found in a summer season image and on the steep and warmest slopes. These results denote the plausible presence of transient liquid brines close to the previously proposed landing ellipse of the ExoMars rover, rendering this site particularly relevant to the search of life. Further investigations of Mawrth Vallis carried out at higher spatial and temporal resolutions are needed to identify more of such features at local scales to maximize the scientific return from the future Mars rovers, to prevent probable biological contamination during rover operations, to evade damage to rover components as brines can be highly corrosive, and to quantify the ability of the regolith at mid-latitudes to capture atmospheric water which is relevant for in-situ-resource utilization.

1234567 51 - 100 of 962
Referera
Referensformat
• apa
• harvard1
• ieee
• modern-language-association-8th-edition
• vancouver
• Annet format
Fler format
Språk
• de-DE
• en-GB
• en-US
• fi-FI
• nn-NO
• nn-NB
• sv-SE
• Annet språk
Fler språk
Utmatningsformat
• html
• text
• asciidoc
• rtf