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  • 1.
    Bachinger, A.
    et al.
    Composite Structures, Swerea SICOMP AB.
    Marklund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Composite Structures, Swerea SICOMP AB.
    Rössler, J.
    Hellström, Pär
    Composite Structures, Swerea SICOMP AB.
    Asp, Leif
    Composite Structures, Swerea SICOMP AB.
    Stiffness-modifiable composite for pedestrian protection2014Ingår i: 16th European Conference on Composite Materials, ECCM 2014: Seville, Spain, 22 - 26 June 2014, European Conference on Composite Materials, ECCM , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    A novel functional material allowing stiffness-reduction upon external stimulation was developed. Implementation of such technology in the design of a car front has high potential to result in increased protection of vulnerable road users (VRUs). The composite material is obtained by coating carbon fibres with a thermoplastic polymer in a continuous process, followed by infusion with an epoxy resin. The process is scalable for industrial use. The coating process was optimized regarding coating efficiency, energy consumption, risks involved for operating personnel and environment, and tailored to gain the optimal coating thickness obtained from numerical calculations. A drastic decrease in transversal stiffness could be detected for the composite material by dynamic mechanical thermal analysis (DMTA), when the temperature was increased above the glass transition temperature of the thermoplastic interphase. The ability of the material to achieve such temperature and associated reduction in stiffness by the application of current was verified using a special 3-point bending setup developed for this task.

  • 2. Fredriksson, Andreas
    et al.
    Hellström, Pär
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Comparison between in situ total internal reflection vibrational spectroscopy of an adsorbed collector and spectra calculated by ab initio density functional theory methods2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 26, s. 9299-9304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this investigation, adsorbed heptyl xanthate on a Ge(111) surface was studied, as well as the free heptyl xanthate molecule, by means of first-principle density functional theory calculations. The modeled results were compared with the in situ total internal reflection vibrational spectroscopy spectra of heptyl xanthate adsorbed on a germanium internal reflection element and the transmission infrared spectrum of a heptyl xanthate ion in aqueous solution. The assignments of the vibrational frequencies were done for the adsorbed xanthate. The region between 1150 and 1000 cm(-1) seems suitable for discussing differences between an adsorbed xanthate and its corresponding ion. The modeled spectra for both the adsorbed xanthate and the xanthate ion are in good agreement with the experimentally retrieved spectra. This investigation shows the strength of using DFT calculations in the interpretation of absorption bands from molecules adsorbed at surfaces in situ.

  • 3. Hellström, Pär
    Ab initio modeling of xanthate adsorption on ZnS surfaces2005Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Modeling surface adsorption requires systems of hundreds of atoms. To model such systems at an ab initio level successfully, we need to avoid traditional quantum chemical methods. In the present work we have shown that density functional theory is a powerful modeling tool for large chemical systems especially in combinations with pseudopotentials This is validated by an initial study of ethyl and heptyl xanthates and their sodium/potassium salts. In this study, all electron calculations using both Hartree-Fock and density functional theory methods are compared with experimental infrared results. To do this the influence of basis sets and modeling approaches on the geometrical structure and the vibrational modes are examined. This includes comparing the pseudopotential and full electron potential approaches. Results obtained from pseudopotential methods are in close agreement with both all electron calculations as well as experimental results, here used to study adsorption of heptyl xanthate ZnS surfaces. Vibrational frequencies of the adsorbed species is presented, together with calculations of the tilt angles. The investigation of the tilt angles resulted in 20.3° 20.6° and 25.2° for the 100, 110 and 111 surfaces respectively. Heptyl xanthate forms a bridging confirmation on both the 110 and 111 surfaces and a bidentate confirmation on the 100 surface. Assignments of vibrational modes of ethyl/heptyl xanthate molecule and its corresponding potassium/sodium salts are also reported.

  • 4.
    Hellström, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Ab initio modelling of xanthates adsorbed on Ge and ZnS surfaces2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The motivation for this modelling work, in close collaboration with experimentalists, is to contribute to the understanding of xanthate adsorption on ZnS surfaces in the flotation process. Adsorption of xanthates on Ge surfaces is investigated, which also have been studied experimentally in the Agricola Research Centre. Furthermore, results for dibutyldithiophosphates—which are important in the flotation process—are reported. Modelling surface adsorption requires systems including hundreds of atoms. To model such systems at an ab initio level successfully, fast and accurate methods must be used.In the present work we use density functional theory (DFT) combined with pseudopotentials, which is a powerful modelling approach for large chemical systems. The results obtained in an initial study of ethyl and heptyl xanthates and their sodium or potassium salts using all electron Hartree-Fock and DFT calculations are used to validate the pseudopotential method used for modelling adsorption of xanthates on surfaces. Both geometrical and vibrational properties, as well as computer resources needed, are examined and compared. Results obtained using DFT and pseudopotentials are in close agreement with both experimental results and all electron potential calculations, while being obtained much faster. Hence, the pseudopotential approach is chosen to study ethyl/heptyl xanthate adsorbed on Ge and ZnS surfaces. The surfaces are modelled using periodically repeated supercells containing more than one hundred atoms. The geometrical structure and vibrational frequencies are calculated and the modes are described. The results are compared with attenuated total reflection infrared observations. The influence of additional atoms at the surface in the surrounding of the adsorbed xanthate are also investigated.

  • 5. Hellström, Pär
    et al.
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    An ab initio study of ethyl xanthate adsorbed on Ge(111) surfaces2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 45, s. 16920-16926Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction between adsorbed ethyl xanthate on a clean Ge(111) surface and a hydroxylated surface was studied, using first-principle density functional theory. Geometrically optimized structures are presented and discussed. Results suggest a bidentate bridging conformation on a clean Ge(111) surface, whereas a monodentate bonding is preferred when the surface is saturated by hydrogen atoms. Then the interaction with a hydroxylated surface was considered. The lowest energy configuration was obtained when xanthate binds with one sulfur to the surface and with the other to an OH group adsorbed on the surface. A marker for this configuration was found in the vibrational spectra at 3200 cm-1. Vibrational frequencies down to 250 cm-1 were calculated and assigned to vibrational modes and presented together with the calculated infrared spectra. The tilt angle of the hydrocarbon chain was also investigated.

  • 6. Hellström, Pär
    et al.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Fredriksson, Andreas
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    A theoretical and experimental study of vibrational properties of alkyl xanthates2006Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy, ISSN 1386-1425, E-ISSN 1873-3557, Vol. 65, nr 3-4, s. 887-895Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Geometrical structure and vibrational modes of potassium and sodium ethyl/heptyl xanthates were studied, using both theoretical and experimental methods. Both Hartree-Fock and density functional theory were used. The experimental method used was infrared absorption spectroscopy (FTIR). Our work showed that vibrational frequencies calculated with density functional theory, using the local density approximation, are in very good agreement with experiments. The results were not improved by using the more sophisticated and computationally demanding B3LYP functional.

  • 7.
    Larsson, Anna-Carin
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Hellström, Pär
    Fredriksson, Andreas
    Holmgren, Allan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Study of potassium O,O′-dibutyldithiophosphate combining DFT, 31P CP/MAS NMR and infrared spectroscopy2008Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, nr 46, s. 11777-11783Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dithiophosphates are used in many different industrial applications. To explain their functions and properties in these applications, a fundamental understanding on a molecular level is needed. Potassium O,O′-Dibutyldithiophosphate and its anion have been investigated by means of a combination of DFT and 31P CP/MAS NMR and infrared spectroscopy. Several low-energy conformations were studied by DFT. Three different conformations with significantly different torsion angles of the O-C bond relative to the O-P-O plane were selected for further studies of infrared frequencies and 31P NMR chemical-shift tensors. A good agreement between theoretical and experimental results was obtained, especially when the IR spectra or 31P chemical shift tensor parameters of all three conformations were added, indicating that, because of the low energy difference between the conformations, the molecules are rapidly fluctuating between them.

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