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  • 201.
    Blumenau, A.T.
    et al.
    Universität Paderborn.
    Frauenheim, T.
    Universität Paderborn.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Willems, B.
    University of Antwerp.
    Tendeloo, G. van
    University of Antwerp.
    Dislocation structures in diamond: density-functional based modelling and high-resolution electron microscopy2004Inngår i: Diffusion and defect data, solid state data. Part A, Defect and diffusion forum, ISSN 1012-0386, E-ISSN 1662-9507, Vol. 226-228, s. 11-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The core structures of perfect 60° and edge dislocations in diamond are investigated atomistically in a density-functional based tight-binding approach, and their dissociation is discussed both in terms of structure and energy. Furthermore, high resolution electron microscopy is performed on dislocation cores in high-temperature, high-pressure annealed natural brown diamond, and HRTEM image simulation allows a comparison of theoretically predicted and experimentally observed structures.

  • 202.
    Blumenau, A.T.
    et al.
    Department of Physics, Universität Paderborn.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Department of Physics, Universität Paderborn.
    Basal plane partial dislocations in silicon carbide2003Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 340, s. 160-164Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Under operating conditions (forward bias) bipolar 4H- and 6H-SiC devices are known to degrade rapidly through stacking fault formation and expansion in the basal plane. It has been suggested that a recombination-enhanced dislocation glide (REDG) mechanism allows the bordering Shockley partial dislocations to overcome their barrier to glide motion and thus results in the observed stacking fault growth. In this work, we investigate the structure and properties of the participating Shockley partials by means of density functional-based atomistic calculations. Their glide motion is modelled in a process involving the formation and subsequent migration of kinks. This in combination with an analysis of the electronic structure of the partials allows an identification of those types which will be affected by the REDG mechanism.

  • 203.
    Blumenau, A.T.
    et al.
    Department of Physics, Faculty of Science, University of Paderborn.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Department of Physics, University of Newcastle.
    Density functional based modelling of 30° partial dislocations in SiC2004Inngår i: Proceedings of the 10th International Conference on Silicon Carbide and Related Materials, ICSCRM 2003, Stafa-Zuerich: Trans Tech Publications Inc., 2004, Vol. 1, s. 453-456Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experiment has shown that 4H- and 6H-SiC pin diodes degrade rapidly during forward biased operation. This degradation is accompanied by the formation and expansion of stacking faults in the basal plane. It is believed that the observed rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations. In our work we investigate the structure and properties of basal plane 30° Shockley partials in SiC by means of density functional based calculations. Barriers to their glide motion, and thus the expansion of the accompanying stacking fault is modelled in a process involving the formation and subsequent migration of kinks in the dislocation. In combination with an analysis of the electronic structure of the partials and stacking faults, this allows an identification of those types of partials which will be affected by the REDG mechanism in this model.

  • 204.
    Blumenau, A.T.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Dislocation related photoluminescence in silicon2001Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 87, nr 18, s. 187404-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dislocation related photoluminescence in Si and SiGe is attributed to stable interstitial clusters bound to 60° dislocations. Density functional based total energy calculations in Si give binding energies between 1.5 and 3.6 eV for I3 and I4 clusters with 90° and 30° partials. They possess donor levels around Ev+0.4 eV which are consistent with deep level transient spectroscopic studies on p-Si. It is further suggested that the clusters would act as the obstacles to the movement of dislocations which may have been observed in recent transmission electron microscopy studies.

  • 205.
    Blumenau, A.T.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Frauenheim, T.
    Universität Paderborn.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Optical bands related to dislocations in Si2000Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, s. 10123-10129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principles calculations are used to investigate the interaction of self-interstitial aggregates with the 90° partial dislocation in Si. We find that I4 is bound to the line with an energy of around 3 eV. The defect causes deep levels to appear in the band gap and optical transitions between these levels may account for the luminescent bands relating to plastically deformed Si.

  • 206.
    Brasch, Thomas von
    et al.
    Statistisk sentralbyrå og NUPI.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lystad, Lars Petter
    Narvik University College, 8505 Narvik, Norway.
    Fibonaccirekken i økonomifaget2013Inngår i: Samfunnsøkonomen, ISSN 1890-5250, Vol. 127, nr 2, s. 10-15Artikkel i tidsskrift (Fagfellevurdert)
  • 207.
    Brasch, Thomas von
    et al.
    Statistisk sentralbyrå.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lystad, Lars Petter
    Narvik University College, 8505 Narvik, Norway.
    Optimal control and the fibonacci sequence2012Rapport (Annet vitenskapelig)
    Abstract [en]

    We bridge mathematical number theory with that of optimal control and show that a generalised Fibonacci sequence enters the control function of finite horizon dynamic optimisation problems with one state and one control variable. In particular, we show that the recursive expression describing the first-order approximation of the control function can be written in terms of a generalised Fibonacci sequence when restricting the final state to equal the steady state of the system. Further, by deriving the solution to this sequence, we are able to write the first-order approximation of optimal control explicitly. Our procedure is illustrated in an example often referred to as the Brock-Mirman economic growth model.

  • 208.
    Brasch, Thomas von
    et al.
    Research Department, Unit for Macroeconomics, Statistics Norway.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lystad, Lars Petter
    Department of Technology, Narvik University College.
    Optimal control and the Fibonacci sequence2012Inngår i: Journal of Optimization Theory and Applications, ISSN 0022-3239, E-ISSN 1573-2878, Vol. 154, nr 3, s. 857-878Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We bridge mathematical number theory with optimal control and show that a generalised Fibonacci sequence enters the control function of finite-horizon dynamic optimisation problems with one state and one control variable. In particular, we show that the recursive expression describing the first-order approximation of the control function can be written in terms of a generalised Fibonacci sequence when restricting the final state to equal the steady-state of the system. Further, by deriving the solution to this sequence, we are able to write the first-order approximation of optimal control explicitly. Our procedure is illustrated in an example often referred to as the Brock-Mirman economic growth model

  • 209.
    Breuer, S J
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Interstitial hydrogen and enhanced dissociation of C-H complexes in GaAs1996Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 53, nr 24, s. 16289-16296Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Local-density-functional-based ab initio calculations are used to investigate hydrogen and carbon-hydrogen defects in GaAs. The equilibrium structure for both the C-H and C-H- complexes are shown to be similar, with the hydrogen located at a C-Ga bond-centered site. The dissociation of these complexes is investigated and it is found that the energy barrier of 1.84 eV for the process C-H → C- + H+ is substantially lowered to 0.88 eV in the presence of an electron resonantly bound to the defect. This is in good quantitative agreement with recent experiments. Isolated interstitial hydrogen is found to lie at a Ga-As bond-centered site for both H+ and H0 and at an antibonding site relative to a Ga atom for H-. It is also found that the stable form of the hydrogen dimer is a H2 molecule, the dissociation energy of which is 1.64 eV, and that interstitial hydrogen is a negative-U defect. Finally, a mechanism for minority-carrier-induced device degradation is proposed.

  • 210.
    Breuer, S.J.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Interstitial hydrogen and the dissociation of C-H defects in GaAs1995Inngår i: Proceedings of the 18th International Conference on Defects in Semiconductors: ICDS-18; Sendai, Japan, July 23 - 28, 1995 / [ed] Masashi Suezawa, Trans Tech Publications Inc., 1995, s. 951-956Konferansepaper (Fagfellevurdert)
  • 211.
    Briddon, Patrick
    et al.
    School of Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Rayson, Mark
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Accurate Kohn–Sham DFT with the speed of tight binding: Current techniques and future directions in materials modelling2011Inngår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 248, nr 6, s. 1309-1318Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a review of methodological and implementation details of the AIMPRO Kohn–Sham density functional code. It is demonstrated that full Kohn–Sham density functional theory calculations can be performed in a time only marginally greater than tight binding implementations and a route is opened to achieve full and demonstrable convergence with respect to basis size. Topics covered will include both the kernel and functionality of the current code, a discussion of recent developments as well as future research directions and perspectives. Also, a broad discussion regarding the application of these methods is made that, it is hoped, will serve as a useful guide to application specialists.

  • 212.
    Buchukuri, Tengiz
    et al.
    A. Razmadze Mathematical Institute, Tbilisi State University.
    Dudachava, Roland
    A. Razmadze Mathematical Institute, Tbilisi State University.
    Tephnadze, George
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Laplace–Beltrami equation on hypersurfaces and Γ-convergence2017Inngår i: Mathematical methods in the applied sciences, ISSN 0170-4214, E-ISSN 1099-1476, Vol. 40, nr 13, s. 4637-4657Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A mixed boundary value problem for the stationary heat transfer equation in a thin layer around a surface C with the boundary is investigated. The main objective is to trace what happens in Γ-limit when the thickness of the layer converges to zero. The limit Dirichlet BVP for the Laplace–Beltrami equation on the surface is described explicitly, and we show how the Neumann boundary conditions in the initial BVP transform in the Γ-limit. For this, we apply the variational formulation and the calculus of Günter's tangential differential operators on a hypersurface and layers, which allow global representation of basic differential operators and of corresponding boundary value problems in terms of the standard Euclidean coordinates of the ambient space Rn.

  • 213.
    Budde, M.
    et al.
    Institute of Physics and Astronomy, University of Aarhus.
    Nielsen, B. Bach
    Institute of Physics and Astronomy, University of Aarhus.
    Leary, P.
    Department of Physics, University of Exeter.
    Goss, J.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Breuer, ¨S.J.
    Edinburgh Parallel Computing Centre, University of Edinburgh.
    The hydrogen-saturated self-interstitial in silicon and germanium1997Inngår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 35-40Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Infrared absorption spectroscopy is used to study H-related point defects in H+-implanted Si (Si:H) and Ge (Ge:H). The absorption lines at 743.1, 748.0, 1986.5 and 1989.4 cm-1 in Si:H and at 700.3, 705.5, 1881.8 and 1883.5 cm-1 in Ge:H are shown to originate from the same defect containing two equivalent H atoms. Uniaxial stress experiments show that the defects have monoclinic-II symmetry, and the orientations of the two Si-H or Ge-H bonds are determined. The structure and the local vibrational modes of the self-interstitial binding two H atoms (IH2) are calculated with LDF cluster theory. The symmetry, bond-orientations and isotopic frequency-shifts calculated for IH2 are in excellent agreement with those observed for the 743.1-, 748.0-, 1986.5- and 1989.4-cm-1 modes in Si:H and for the 700.3-, 705.5-, 1881.8- and 1883.5-cm-1 modes in Ge:H.

  • 214.
    Budde, M
    et al.
    University of Aarhus.
    Nielsen, B Bech
    University of Aarhus.
    Jones, R
    University of Exeter.
    Goss, J
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Local modes of the H2* dimer in germanium1996Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 54, nr 8, s. 5485-5494Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Local vibrational modes of the H2* defect in crystalline germanium are identified by a combination of infrared-absorption spectroscopy, uniaxial stress measurements, and ab initio theory. Germanium crystals are implanted with protons and/or deuterons at 30 K, and subsequently annealed at room temperature. A number of local vibrational modes of hydrogen are revealed by infrared-absorption spectroscopy. In particular, modes at 765, 1499, 1774, and 1989 cm-1 originate from the same defect which has trigonal symmetry according to the uniaxial stress measurements. The 765-cm-1 mode is two dimensional, while the 1774- and 1989-cm-1 modes are one dimensional. Measurements on samples coimplanted with protons and deuterons show that the defect contains a pair of weakly coupled and inequivalent hydrogen atoms. The 765-, 1499-, 1774-, and 1989-cm-1 modes are ascribed to the H2* defect. The 765-cm-1 mode is a Ge-H bend mode with an overtone at 1499 cm-1 and the modes at 1774 and 1989 cm-1 are Ge-H stretch modes. An excellent fit to the stretch frequencies is obtained with a simple model based on two coupled Morse-potential oscillators. In addition, the model gives intensity ratios in fair agreement with those observed. The structure, the local-mode frequencies, and the isotope shifts of H2* are calculated with ab initio local-density-functional cluster theory. The theoretical frequencies are consistently 5-10 % too high, as expected from the theory which often leads to overbinding. The isotope shifts, however, are in fair agreement with observations. These results provide additional support for our assignments, and show that the 765- and 1774-cm-1 modes primarily involve the hydrogen at the antibonding site, while the 1989-cm-1 mode is related mainly to vibration of the hydrogen near the bond-center site

  • 215.
    Budde, M
    et al.
    University of Aarhus.
    Nielsen, B Bech
    University of Aarhus.
    Leary, P
    University of Exeter.
    Goss, J
    University of Exeter.
    Jones, R
    University of Exeter.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Breuer, S J
    University of Edinburgh.
    Identification of the hydrogen-saturated self-interstitials in silicon and germanium1998Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 57, nr 18, s. 4397-4412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to the excitation of hydrogen-related local vibrational modes. The lines at 743.1, 748.0, 1986.5, and 1989.4 cm-1 in silicon and at 700.3, 705.5, 1881.8, and 1883.5 cm-1 in germanium originate from the same defect in the two materials. Measurements on samples coimplanted with protons and deuterons show that the defect contains two equivalent hydrogen atoms. Uniaxial stress measurements are carried out and a detailed analysis of the results is presented. It is shown that the defect has monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect are determined. Ab initio local-density-functional theory is used to calculate the structure and local vibrational modes of the self-interstitial binding one and two hydrogen atoms in silicon and germanium together with the structure of the self-interstitial itself. The observed properties of the defect are in excellent agreement with those calculated for the self-interstitial binding two hydrogen atoms.

  • 216.
    Burtseva, Evgeniya
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Singular Integral Operators in Generalized Morrey Spaces on Curves in the Complex Plane2017Inngår i: Mediterranean Journal of Mathematics, ISSN 1660-5446, E-ISSN 1660-5454, Vol. 14, nr 5, artikkel-id 203Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the boundedness of the Cauchy singular integral operators on curves in complex plane in generalized Morrey spaces. We also consider the weighted case with radial weights. We apply these results to the study of Fredholm properties of singular integral operators in weighted generalized Morrey spaces.

  • 217.
    Burtseva, Evgeniya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lundberg, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper. UiT, The Arctic University of Norwa.
    Samko, Natasha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Multi–dimensional Hardy type inequalities in Hölder spaces2018Inngår i: Journal of Mathematical Inequalities, ISSN 1846-579X, E-ISSN 1848-9575, Vol. 12, nr 3, s. 719-729Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most Hardy type inequalities concern boundedness of the Hardy type operators in Lebesgue spaces. In this paper we prove some new multi-dimensional Hardy type inequalities in Hölder spaces.

  • 218. Burtseva, Evgeniya
    et al.
    Lundberg, Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Samko, Natasha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Potential type operators in PDEs and their applications2017Inngår i: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 1798, artikkel-id 020178Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     We prove the boundedness of Potential operator in weighted generalized Morrey space in terms of Matuszewska-Orlicz indices of weights and apply this result to the Hemholtz equation in r3 with a free term in such a space. We also give a short overview of some typical situations when Potential type operators arise when solving PDEs.

  • 219.
    Burtseva, Evgeniya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper. UiT, The Arctic University of Norway, Narvik, Norway.
    Samko, Natasha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Necessary and sufficient conditions for the boundedness of weighted Hardy operators in Hölder spaces2018Inngår i: Mathematische Nachrichten, ISSN 0025-584X, E-ISSN 1522-2616, Vol. 291, nr 11-12, s. 1655-1665Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study one‐ and multi‐dimensional weighted Hardy operators on functions with Hölder‐type behavior. As a main result, we obtain necessary and sufficient conditions on the power weight under which both the left and right hand sided Hardy operators map, roughly speaking, functions with the Hölder behavior only at the singular point to functions differentiable for and bounded after multiplication by a power weight. As a consequence, this implies necessary and sufficient conditions for the boundedness in Hölder spaces due to the corresponding imbeddings. In the multi‐dimensional case we provide, in fact, stronger Hardy inequalities via spherical means. We also separately consider the case of functions with Hölder‐type behavior at infinity (Hölder spaces on the compactified ).

  • 220.
    Burtseva, Evgeniya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Samko, Natasha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    On weighted generalized fractional and Hardy-type operators acting between Morrey-type spaces2017Inngår i: Fractional Calculus and Applied Analysis, ISSN 1311-0454, E-ISSN 1314-2224, Vol. 20, nr 6, s. 1545-1566Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study weighted generalized Hardy and fractional operators acting from generalized Morrey spaces Lp,φ,(n) into Orlicz-Morrey spaces LΦ,φ,(n). We deal with radial quasi-monotone weights and assumptions imposed on weights are given in terms of Zigmund-type integral conditions. We find conditions on φ,Φ, the weight w and the kernel of the fractional operator, which insures such a boundedness. We prove some pointwise estimates for weighted generalized fractional operators via generalized Hardy operators, which allow to obtain the weighted boundedness for fractional operators from those for Hardy operators. We provide also some easy to check numerical inequalities to verify the obtained conditions.

  • 221.
    Burtseva, Evgeniya
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Samko, Natasha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Weighted Adams type theorem for the Riesz fractional integral in generalized Morrey Space2016Inngår i: Fractional Calculus and Applied Analysis, ISSN 1311-0454, E-ISSN 1314-2224, Vol. 19, nr 4, s. 954-972Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We prove the boundedness of the Riesz fractional integration operator from a generalized Morrey space L-p,L-phi to a certain Orlicz-Morrey space L-Phi,L-phi which covers the Adams result for Morrey spaces. We also give a generalization to the case of weighted Riesz fractional integration operators for some class of weights.

  • 222. Bylund, Nicklas
    et al.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Reiterated homogenization with applications to autopart construction2001Inngår i: ICCE 8: Eight Annual International Conference on Composites Engineering / [ed] David Hui, 2001, s. 31-34Konferansepaper (Fagfellevurdert)
  • 223.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Correctors for some nonlinear monotone operators2001Inngår i: Journal of Nonlinear Mathematical Physics, ISSN 1402-9251, E-ISSN 1776-0852, Vol. 8, nr 1, s. 8-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we study homogenization of quasi-linear partial differential equations of the form -div (a (x, x/εh,Duh)) = fh on Ω with Dirichlet boundary conditions. Here the sequence (εh) tends to 0 as h→∞ and the map a (x, y, ξ) is periodic in y, monotone in ξ and satisfies suitable continuity conditions.W e prove that uh → u weakly in W1,p 0 (Ω) as h → ∞, where u is the solution of a homogenized problem of the form -div (b (x,Du)) = f on Ω. We also derive an explicit expression for the homogenized operator b and prove some corrector results, i.e. we find (Ph) such that Duh -Ph (Du) → 0 in Lp (Ω,Rn). () 0 in (Ω).

  • 224.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Correctors for some nonlinear monotone operators: Appendix with proofs1999Rapport (Annet vitenskapelig)
    Abstract [en]

    Contains appendix with proofs to the publeshed article "J. Byström. Correctors for some nonlinear monotone operators. J. Nonlinear Math. Phys., ISSN: 1402-9251, 8:1 (2001), 8-30."

  • 225.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Influence of the inclusions distribution on the effective properties of heterogeneous media2003Rapport (Annet vitenskapelig)
  • 226.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Influence of the inclusions distribution on the effective properties of heterogeneous media2003Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 34, nr 7, s. 587-592Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we investigate the effective conductivity of composite materials by means of the homogenization method. We concentrate on composites with circular or elliptic cylindrical inclusions. In particular, we are interested in the effect of the distribution of the cylinders in the continuous material on the effective properties. We compare rectangular and hexagonal distributions with random distributions for different volume fractions of the inclusions. We also study the effect of the number of inclusions in each periodic cell for the random structure as well as shape influence of the elliptical inclusions.

  • 227.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Mathematical modelling of composites using the homogenization method2003Inngår i: Proceedings of the conference "MathTools-2003" / [ed] George Osipenko, 2003, s. 32-Konferansepaper (Fagfellevurdert)
  • 228.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Sharp constants for some inequalities connected to the p-Laplace operator2005Inngår i: Journal of Inequalities in Pure and Applied Mathematics, ISSN 1443-5756, E-ISSN 1443-5756, Vol. 6, nr 2, artikkel-id 56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we investigate a set of structure conditions used in the existence theory of differential equations. More specific, we find best constants for the corresponding inequalities in the special case when the differential operator is the p-Laplace operator.

  • 229.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Some mathematical and engineering aspects of the homogenization theory2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is devoted to some problems connected to the theory of homogenization of partial differential operators. The thesis consists of an elementary introduction and five different parts, A-E. In the introduction we give an elementary presentation of the basic ideas in the homogenization theory. Moreover, the introduction also serves as an overview of the field and points out where the results contained in this thesis fit in. The first part, Part A, consists of two papers with a complementary appendix and deals some purely theoretical parts of homogenization theory. Part B consists of one paper dealing with bounds of the homogenized operator. The third part, Part C, consists of two papers concerning some computational aspects of homogenization. Part D consists of two papers which show how the theoretical results from the homogenization theory can be practically used in composites engineering. Finally, Part E consists of two papers presented at international conferences, which consider some further mathematical and engineering aspects of the homogenization method.

  • 230.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Some new developments and applications of the homogenization theory1999Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is devoted to some problems connected to the theory of homogenization of partial differential operators. The thesis consists of an introduction and three different parts, A-C. In the introduction we give an elementary presentation of the basic ideas in the homogenization theory. Moreover, the introduction also serves as an overview of the field and points out where the results contained in this thesis fit in. The first part, Part A, consists of one paper with a complementary appendix and deals with the limit behavior of the solutions of a sequence of quasi-linear equations. Part B consists of one paper with a complementary appendix in which the homogenization theory is used for the evaluation of different semi-analytical models used in the determination of the elastic properties of woven composites. The third part, Part C, consists of three papers which consider some further mathematical and engineering aspects of the homogenization method. Several numerical and experimental results are also presented and compared with theoretical results.

  • 231.
    Byström, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    The homogenization method applied to the computation of effective thermal conductivities of composite materials1996Independent thesis Advanced level (degree of Master (Two Years)), 40 poäng / 60 hpOppgave
    Abstract [en]

    To solve boundary value problems of stationary heat distribution in composite materials, one has to solve partial differential equations with rapidly oscillating coefficients. These equations are in general impossible to solve numerically by standard methods. Instead, one wants to find constants, effective conductivities and solve the corresponding boundary value problem to get an approximate solution of the original problem. To compute these effective conductivities, we have developed a finite element computer program with integrated homogenization routines.

  • 232.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Dasht, Johan
    Wall, Peter
    A numerical study of stochastic homogenization2003Inngår i: Proceedings of the International Conference on Composites Engineering: ICCE/10 / [ed] David Hui, 2003Konferansepaper (Fagfellevurdert)
  • 233. Byström, Johan
    et al.
    Dasht, Johan
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A numerical study of the convergence in stochastic homogenization2004Inngår i: Journal of Analysis and Applications, ISSN 0972-5954, Vol. 2, nr 3, s. 159-171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This note makes the link between theoretical results on stochastic homogenization and effective computation of averaged coefficients for diffusion operators in random media. Examples of how to construct relevant random media and numerical results on the effective coefficients are given.

  • 234. Byström, Johan
    et al.
    Engström, Jonas
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Bounds and numerical results for the homogenized degenerated p-Poisson equation2004Inngår i: Applications of Mathematics, ISSN 0862-7940, E-ISSN 1572-9109, Vol. 49, nr 2, s. 111-122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we derive upper and lower bounds on the homogenized energy density functional corresponding to degenerated p-Poisson equations. Moreover, we give some non-trivial examples where the bounds are tight and thus can be used as good approximations of the homogenized properties. We even present some cases where the bounds coincide and also compare them with some numerical results.

  • 235.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Engström, Jonas
    Wall, Peter
    Periodic approximation of elastic properties in random media2006Inngår i: Advances in Algebra and Analysis, ISSN 0973-2306, Vol. 1, nr 2, s. 103-113Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most papers on stochastic homogenization either deal with theoretical aspects or with questions regarding computational issues. Since the theoretical analysis involves the solution of a problem which is stated in a abstract probability space, it is not clear how the two areas are connected. In previous works this problem has not been considered. However, recently Bourgeat and Piatnitski investigated this connection in the scalar case for second order operators of divergence form. They proved that in the limit, the method of periodic approximation gives the same effective properties as in stochastic homogenization. In this paper we prove similar results for the vector valued case, which appears in e.g. the theory of elasticity. Moreover, we provide a numerical analysis of the results.

  • 236.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Engström, Jonas
    Wall, Peter
    Reiterated homogenization of degenerate nonlinear elliptic equations2002Inngår i: Chinese Annals of Mathematics. Series B, ISSN 0252-9599, E-ISSN 1860-6261, Vol. 23, nr 3, s. 325-334Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The authors study homogenization of some nonlinear partial differential equations of the form _ div (a (hx, h2 x, Duh)) = f , where a is periodic in the rst two arguments and monotone in the third. In particular the case where a satis es degenerated structure conditions is studied. It is proved that uh converges weakly in W0 1,1 (Ω) to the unique solution of a limit problem as h → ∞ . Moreover, explicit expressions for the limit problem are obtained.

  • 237. Byström, Johan
    et al.
    Engström, Jonas
    Wall, Peter
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Reiterated homogenization of degenerate nonlinear monotone operators2004Inngår i: Frontiers in Mathematical Analysis and Numerical Methods: In Memory of Jacques-Louis Lions, Singapore: World Scientific and Engineering Academy and Society, 2004, s. 83-96Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 238.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Helsing, Johan
    Kungliga tekniska högskolan, KTH.
    Meidell, Annette
    Narvik University College, 8505 Narvik, Norway.
    Some computational aspects of iterated structures2001Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 32, nr 6, s. 485-490Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider some computational aspects of effective properties for some multi-scale structures. In particular, we discuss iterated square honeycombs and another type of square honeycombs containing up to 4000 small discs randomly distributed inside each square. We present some numerical methods for estimating the effective conductivity with good control of the accuracy.

  • 239.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jekabsons, Normunds
    Persson, Lars-Erik
    A comparison of different homogenization models and experimental results1999Inngår i: ICCE 6: Sixth Annual International Conference on Composites Engineering / [ed] David Hui, 1999, s. 97-98Konferansepaper (Fagfellevurdert)
  • 240.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jekabsons, Normunds
    Luleå tekniska universitet.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    An evaluation of different models for prediction of elastic properties of woven composites2000Inngår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 31, nr 1, s. 7-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A critical analysis of two simple and convenient analytical models for calculation of elastic properties of woven fabric composites is performed. Predictions of these models are compared with results obtained using the method of reiterated homogenization and with experimental data for plain weave glass fiber and carbon fiber polyester composites. Three different scales are identified in the analysis. The first scale predictions, which are the tow properties (obtained by applying Hashin's concentric cylinder model, the Halpin-Tsai expressions or mathematical homogenization technique), are the most critical because they form the input information for woven composite modeling. It appears that the uncertainty in this information causes larger differences in predictions than the deviations between models of different degree of accuracy. This fact sets limits on the required accuracy of the models. Model comparisons reveal that the woven compoiste model based on isostrain assumption in the compoiste plane and isostress assumption for out-of-plane components is in very good agreement with both experimental data and the reiterated homogenization method, whereas the modified mosaic parallel model fails to describe composites with large interlaced regions.

  • 241.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Kuzmin, Leonid
    Cross section dependence on ski pole stiffness2013Rapport (Fagfellevurdert)
    Abstract [en]

    Ski equipment producer SWIX has recently presented a new pair of ski poles,called SWIX Triac, which di¤ers from conventional (round) ski poles by having atriangular cross section. SWIX claims that the main objective for this design is thatit has superior sti¤ness to weight ratio compared to common ski poles. We provein this paper that this claim in general is not true. More speci…c, we show thatfor thin walled cross sections, a hollow circular cross section has up to 36% bettersti¤ness to weight ratio than a corresponding triangular cross section.

  • 242.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Lystad, Lars Petter
    Department of Technology, Narvik University College.
    Nyman, Per-Ole
    Department of Technology, Narvik University College.
    Using generalized Fibonacci sequences for solving the one-dimensional LQR problem and its discrete-time Riccati equation2010Inngår i: Modeling, Identification and Control, ISSN 0332-7353, E-ISSN 1890-1328, Vol. 31, nr 1, s. 1-18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article we develop a method of solving general one-dimensional Linear Quadratic Regulator (LQR) problems in optimal control theory, using a generalized form of Fibonacci numbers. We find the solution R (k) of the corresponding discrete-time Riccati equation in terms of ratios of generalized Fibonacci numbers. An explicit Binet type formula for R (k) is also found, removing the need for recursively finding the solution at a given timestep. Moreover, we show that it is also possible to express the feedback gain, the penalty functional and the controller state in terms of these ratios. A generalized golden ratio appears in the corresponding in finite horizon problem. Finally, we show the use of the method in a few examples.

  • 243.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Random versus periodic cells in homogenization2002Inngår i: ICCE 9: Ninth Annual International Conference on Composites Engineering / [ed] David Hui, 2002, s. 83-84Konferansepaper (Fagfellevurdert)
  • 244.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Tillämpad matematik: en populär introduktion för lärare och ingenjörer2004Inngår i: Kvinnor och matematik : konferens den 12-14 april 2002: konferensrapport / [ed] Barbro Grevholm; Lisbeth Lindberg, Kristianstad: Högskolan Kristianstad , 2004, s. 37-48Konferansepaper (Annet vitenskapelig)
  • 245.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Persson, Lars-Erik
    Jekabsons, Normunds
    Luleå tekniska universitet.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Using reiterated homogenization for stiffness computation of woven composites1998Inngår i: ICCE 5: Fifth International Conference on Composites Engineering / [ed] David Hui, 1998, s. 133-134Konferansepaper (Fagfellevurdert)
  • 246.
    Byström, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Wall, Peter
    Heat conductivity bounds by Halpin-Tsai type equations and homogenization2000Inngår i: Proceedings of the Seventh International Conference on Composites Engineering: ICCE/7 / [ed] David Hui, 2000, s. 97-98Konferansepaper (Fagfellevurdert)
  • 247. Börjesson, Per Ola
    et al.
    Feichtinger, Hans G
    NUHAG (Numerical Harmonic Analysis Group), Dept. of Mathematics, University of Vienna.
    Grip, Niklas
    Isaksson, Mikael
    Telia Research AB.
    Kaiblinger, Norbert
    NUHAG (Numerical Harmonic Analysis Group), Dept. of Mathematics, University of Vienna.
    Ödling, Per
    Persson, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A low-complexity PAR-reduction method for DMT-VDSL1999Inngår i: Proceedings of the 5th International Symposium on Digital Signal Processing for Communication Systems: DSPCS'99, Perth, Australia, Feb. 1999, 1999, s. 164-169Konferansepaper (Fagfellevurdert)
    Abstract [en]

    DMT-VDSL signals have a high peak-to-average power ratio (PAR). In the transmitters, the PAR governs the necessary resolution of the digital-to-analog converter (DAC) and is an important factor for the power consumption of the line-driver. Aiming at implementation in a specific system, we propose a low complexity PAR-reduction method based on the iterative algorithm derived in [5, 20, 24, 25]. We maintain good performance while stressing a straigthforward and low-complex implementation. Key elements of the method are: low latency; no loss in data rate; precalculated and stored peak-cancellation waveform; and bit-shifts (multiplication with powers of two) replacing the scaling of the waveform. Computer simulations show that, for a DMT frame length of 4096 samples and a frame clip rate of 10-4, the PAR can be reduced about 1.5 to 2.0 dB, depending on the number of peaks cancelled. When multiplication is replaced by bit-shifts, the reduction is still 1.5-1.7 dB.

  • 248.
    Calogero, F.
    et al.
    Dipartimento di Fisica, Università di Roma “La Sapienza”, Rome.
    Euler, Marianna
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Euler, Norbert
    New evolution PDEs with many isochronous solutions2009Inngår i: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 353, nr 2, s. 481-488Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Certain nonlinear evolution PDEs in 1 + 1 variables (time and space) are identified, featuring a positive parameter ω and evolving, for a large class of initial data, periodically with the fixed period T = 2 π / ω (or perhaps over(T, ̃) = p T with p a small integer). They are autonomous (i.e., they do not feature any explicit dependence on the time variable), but they generally (although not quite all of them) depend explicitly on the space variable hence are not translation-invariant. They are integrable, having been obtained by applying an appropriate change of dependent and independent variables to certain nonlinear evolution PDEs whose integrable character has been recently ascertained. Solutions of some of these PDEs are exhibited.

  • 249.
    Camps, I.
    et al.
    Universidade Federal de Alfenas—Unifal-MG.
    Coutinho, J.
    University of Aveiro.
    Mir, M.
    Universidade Federal de Alfenas—Unifal-MG.
    Rayson, Mark
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, Patrick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Elastic and optical properties of Cu2ZnSn(SexS1 − x)4 alloys: density functional calculations2012Inngår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 27, nr 11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cu2ZnSn(S1 − xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 − xGaxSe2 (CIGS) as the absorber layer for thin film solar cells. The former compound has the important advantage of using abundant Zn and Sn instead of the expensive In and Ga. A better understanding of the properties of CZT(S, Se) is being sought through experimental and theoretical means. Thus far, however, very little is known about the fundamental properties of the CZT(S, Se) alloys. In this work, theoretical studies on the structural, elastic, electronic and optical properties of CZT(S, Se) alloys through first-principles calculations are reported. We use a density functional code (aimpro), along with the Padé parametrization for the local density approximation to the exchange correlation potential. For the alloying calculations we employed 64 atom supercells (approximately cubic) with a 2 × 2 × 2 k-point sampling set. These supercells possess a total of 32 chalcogen species and the CZTSexS1 − x alloys are described by using the ordered alloy approximation. Accordingly, to create a perfectly diluted alloying host, the species type of the 32 chalcogen sites is selected randomly with uniform probability x and 1 − x for Se and S, respectively. Properties of alloys (structural, elastic, electronic and optical) are obtained by averaging the results of ten supercell configurations generated for each composition. For each configuration, lattice vectors and atomic positions were allowed to relax (although enforcing the tetragonal lattice type) and the Murnaghan equation of state was fitted to the total energy data. The results presented here permit a better understanding of the properties of the CZT(S, Se) alloys which in turn result in the design of more efficient solar cells.

  • 250.
    Carro, Maria J.
    et al.
    Department of Applied Mathematics and Analysis, University of Barcelona.
    Ericsson, Stefan
    Persson, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Real interpolation for divisible cones1999Inngår i: Proceedings of the Edinburgh Mathematical Society, ISSN 0013-0915, E-ISSN 1464-3839, Vol. 42, nr 2, s. 285-304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We give necessary and sufficient conditions on a general cone of positive functions to satisfy the Decomposition Property (DP) introduced in [5] and connect the results with the theory of interpolation of cones introduced by Sagher [9]. One of our main result states that if Q satisfies DP or equivalently is divisible, then for the quasi-normed spaces E0 and E1, According to this formula, it yields that the interpolation theory for divisible cones can be easily obtained from the classical theory

2345678 201 - 250 of 1366
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