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  • 1.
    Bielecki, Johan
    et al.
    Chalmers tekniska högskola, Göteborg.
    Rauer, Ralf
    Chalmers tekniska högskola, Göteborg.
    Zanghellini, Ezio
    Chalmers tekniska högskola, Göteborg.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Dörr, Katherine
    Institut für festkörper- und werkstofforschung, Dresden.
    Börjesson, Lars
    Chalmers tekniska högskola, Göteborg.
    Two-component heat diffusion observed in LaMnO3 and La0.7Ca0.3MnO32010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 6, p. 064434-Article in journal (Other academic)
    Abstract [en]

    We investigate the low-temperature electron, lattice, and spin dynamics of LaMnO3 (LMO) and La0.7Ca0.3MnO3 (LCMO) by resonant pump-probe reflectance spectroscopy. Probing the high-spin d-d transition as a function of time delay and probe energy, we compare the responses of the Mott insulator and the double-exchange metal to the photoexcitation. Attempts have previously been made to describe the subpicosecond dynamics of colossal magnetoresistance manganites in terms of a phenomenological three-temperature model describing the energy transfer between the electron, lattice, and spin subsystems followed by a comparatively slow exponential decay back to the ground state. However, conflicting results have been reported. Here we first show clear evidence of an additional component in the long-term relaxation due to film-to-substrate heat diffusion and then develop a modified three-temperature model that gives a consistent account for this feature. We confirm our interpretation by using it to deduce the band gap in LMO. In addition, we also model the nonthermal subpicosecond dynamics, giving a full account of all observed transient features both in the insulating LMO and the metallic LCMO.

  • 2.
    Brucas, Rimantas
    et al.
    Uppsala University.
    Hanson, Maj
    Chalmers University of Technology, Göteborg.
    Apell, Peter
    Chalmers University of Technology, Göteborg.
    Nordblad, Per
    Uppsala University.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Hjörvarsson, Björgvin
    Uppsala University.
    Tunneling and charging effects in discontinuous superparamagnetic Ni81Fe19/Al2O3 multilayers2010In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, no 22, p. 224437-Article in journal (Other academic)
    Abstract [en]

    The magnetic and transport properties of films based on discontinuous layers of Ni81Fe19 (Py) embedded inAl2O3 were investigated. In films with nominal Py thicknesses 6 and 8 Å superparamagnetic particles withmedian diameters Dmed=2.8 and 3.1 nm and distribution widths s_D=1.2 and 1.3 nm were formed. Current-voltage (IU) curves were measured with the current perpendicular to the film plane. The analyses show that thecharge transport occurs via tunneling; with the charging energy supplied by thermal fluctuations at hightemperature, T>100 K, and by the electric field at low temperature, T<10 K. The separation of the tworegimes allows independent estimates of the mean charging energy <EC>~40 meV for both samples; from theresistance R versus T analyzed in an effective-medium model at high temperature and from I versus U at 4 K.In order to obtain a consistent description of the transport properties, the size distributions must be included toaccount for the deviation from the single size behavior R~exp(EC/kBT) at high T. The scaling parameter inthe relation I \propto (U/Uth−1)^g, where Uth is the threshold for conduction, is estimated to g~2 at 4 K. The superparamagneticrelaxation of the particles becomes blocked below a temperature T~20 K respective 30 K for 6and 8 Å. The magnetic field (B) dependence of the resistance R(B) displays a single maximum of the ratio MR=[R(B)−R(2 T)] /R(2 T) in zero field at room temperature and a characteristic splitting of the peak at 4K, attributed to the blocking. The maxima, ~0.9% for 6 Å and 1.1% for 8 Å, are positioned at fields abouta factor of two to three higher than the coercive fields of the samples

  • 3.
    Demidov, V.V.
    et al.
    Institute of Radio Engineering and Electronics, Russian Academy of Sciences.
    Ovsyannikov, G.A.
    Institute of Radio Engineering and Electronics, Russian Academy of Sciences.
    Petrzhik, A.M.
    Institute of Radio Engineering and Electronics, Russian Academy of Sciences.
    Borisenko, I.V.
    Institute of Radio Engineering and Electronics, Russian Academy of Sciences.
    Shadrin, A.V.
    Institute of Radio Engineering and Electronics, Russian Academy of Sciences.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education. Chalmers University of Technology.
    Magnetic anisotropy in strained manganite films and bicrystal junctions2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 16, p. 163909-163909-10Article in journal (Refereed)
    Abstract [en]

    Transport and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite thin films and bicrystal junctions were investigated. Epitaxial manganite films were grown on SrTiO3, LaAlO3, NdGaO3 (NGO), and (LaAlO3)0.3 + (Sr2AlTaO6)0.7 substrates, and their magnetic anisotropy were determined by two independent techniques of magnetic resonance spectroscopy. It was demonstrated that by using these techniques, a small (0.3%) anisotropy of crystal structure at the (110) surface plane of the orthorhombic NGO substrate leads to uniaxial magnetic anisotropy of the films in the plane of the substrate at least at the room temperature. It was found that on vicinal NGO substrates, the value of magnetic anisotropy strength can be varied in the range 100–200 Oe at T = 295 K by changing the substrate vicinal angle from 0° to 25°. Measurement of the magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetic spin subsystems for both types of bicrystal boundaries with tilting of basal plane of manganite tilted bicrystal (TB-junction) and with rotation of crystallographic axes (RB-junction) used for comparison. The magnetoresistance of TB-junctions increases with decreasing temperature and the misorientation angle. Variation of bicrystal misorientation angle does not lead to change of misorientation of easy magnetic axes in the film parts forming TB-junction. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms. The first one is the spin-flip of spin-polarized carriers due to the strong electron-electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the second one is spin-flip by antiferromagnetic magnons at high temperatures.

  • 4.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Anisotropic spin-orbit interaction revealed by in-plane magnetoresistance in single-oriented SrRuO3 thin films2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 85, no 23, article id 235409Article in journal (Refereed)
    Abstract [en]

    A detailed analysis of the in-plane magnetoresistance anisotropy in single orientation thin filmSrRuO3 grown on (001)SrTiO3 is presented. The resistivity is measured in strips along [001], [¯110]and [¯11¯1] with in-plane rotating magnetic field. The data show new details in the transfer fromnegative to positive magnetoresistance when the field is rotated in the plane. They show that themagnetoresistance is anisotropic with respect to the crystalline directions rather than with respectto the direction of the current. The data suggest an anisotropic spin-orbit interaction, and canpossibly be a sign of in-plane weak anti-localization.

  • 5.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Arithmetic expressions with multiple operations - How to solve it?2016In: Proceedings of the 40th Conference of the International Group for the Psychology of Mathematics Education, Volume 2, 2016, Vol. 1, p. 298-Conference paper (Refereed)
  • 6.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    The model of the particle nature of matter in science and science education2014Conference paper (Refereed)
    Abstract [en]

    The model of the particle nature of matter has been one of the fundaments in science and science education. This model describes matter as being composed of small hard solid entities - particles - often known as atoms and molecules, clinging to each other or moving around in empty space. However, from a scientific point of view there are problems with this model; for instance, quantum mechanics describes atoms as having both particle as well as wave properties implying that the entities are neither hard nor solid. The particle nature of matter model is also facing problems within science education. Students’ conceptions of the concept of particle appears to be limited.

    In this talk I will describe how science teachers’ understanding of the model of the particle nature of matter is limited too. Eleven secondary school science teachers were interviewed about their arguments for the particle nature of matter. Although the teachers appears to have an epistemological understanding of the concept of models in science they give vague arguments for the particle nature of matter model. Particularly, they have problems justifying the model from specific experiments. The model of the particle nature of matter is discussed in the light of these interview data, but also in the light of historical arguments and verifications of the model.

  • 7.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Ekdahl, Anna-Lena
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Landén, Josefine
    Jönköping University, School of Education and Communication.
    Tegnefur, Jenny
    Jönköping University, School of Education and Communication.
    Students’ strategies to continue geometric number sequences2016Conference paper (Refereed)
    Abstract [en]

    Number sequences can be useful tools for teaching generalization, functions, or variables, for instance. Consequently, there are many studies that have studied students’ perception of number sequences and the strategies used to continue those sequences. However, a large part of the studies have been using arithmetic or quadratic number sequences. In this paper we present a study of students’ strategies to continue non-contextualized geometric number sequences. Interview data from 18 students in grades 9 to 12(age 15-19) (in Sweden) was analysed. Five qualitatively different strategies have been discerned in the data. These strategies are not completely overlapping the strategies previously described in literature.

  • 8.
    Gunnarsson, Robert
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Hanson, Maj
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Magnetization reversal processes in magnetic bicrystal junctions2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, no 1, p. 014435-Article in journal (Refereed)
    Abstract [en]

    We provide experimental data for the magnetoresistance in epitaxial ferromagnetic manganite (La0.7Sr0.3MnO3) bicrystals with various angles. Experiments were conducted using samples with in-plane magnetization as well as with out-of-plane magnetization. From the shape of the magnetoresistance hysteresis we draw conclusions on the different magnetization reversal processes. We show that it is possible to set the electrode magnetization at remanence such that the spins at the bicrystal interface are either parallel or inclined to each other at an angle determined by the crystal orientations. Finally, we demonstrate the feasibility of using epitaxial magnetic bicrystals to probe the transport properties in magnetic junctions with well-determined angles of magnetization.

  • 9.
    Gunnarsson, Robert
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Hanson, Maj
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Misorientation angle dependence of bicrystal magnetoresistance within the model of coherent rotation2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 21, p. 3761-3768Article in journal (Refereed)
    Abstract [en]

    Bicrystal magnetoresistance hysteresis is studied within the model of coherent rotation of magnetization. The magnetoresistance hysteresis is calculated numerically in the limit of fully spin polarized current for symmetric bicrystal junctions with biaxial magnetic anisotropy and of varying misorientation angles. The shape of the curves obtained from the model displays different characteristic features, depending on the angular relationships, which are consistent with experimental data from the literature. The results show a magnetoresistance increasing with increasing misorientation angle. The influence of biaxial magnetocrystalline anisotropy is reflected in a hump in the maximum magnetoresistance curve at around a misorientation angle of 25°. This structure is absent in the case of uniaxial anisotropy.

  • 10.
    Gunnarsson, Robert
    et al.
    Chalmers tekniska högskola, Göteborg.
    Hanson, Maj
    Chalmers tekniska högskola, Göteborg.
    Dubourdieu, Catherine
    Laboratoire des Mattériaux et du Génie Physique, CNRS, St. Martin d'Hères.
    Magnetoresistance in bicrystal grain-boundary junctions analyzed within the Stoner-Wohlfarth model2005In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 290-291, no 1, p. 761-763Article in journal (Refereed)
  • 11.
    Gunnarsson, Robert
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Hanson, Maj
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Dubourdieu, Catherine
    Laboratiore des Matériaux et du Génie Physique, CNRS, St. Martin d'Hères.
    Stoner-Wohlfarth model applied to bicrystal magnetoresistance hysteresis2004In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 96, no 1, p. 482-485Article in journal (Refereed)
    Abstract [en]

    We calculate numerically the magnetization direction as function of magnetic field in the Stoner–Wohlfarth theory and are able to reproduce the shape of the low-field magnetoresistance hysteresis observed in manganite grain boundary junctions. Moreover, we show that it is necessary to include biaxial magnetocrystalline anisotropy to fully describe the grain boundary magnetoresistance in La0.7Sr0.3MnO3/SrTiO3 bicrystal tunnel junctions.

  • 12.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF).
    Hellquist, Björn
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF).
    Strömdahl, Helge
    Zelic, Dusan
    Jönköping University, School of Education and Communication.
    Secondary school science teachers’ arguments for the particulate nature of matter2018In: Journal of Research in Science Teaching, ISSN 0022-4308, E-ISSN 1098-2736, Vol. 55, no 4, p. 503-525Article in journal (Refereed)
    Abstract [en]

    How do secondary school science teachers justify the model of a particulate nature of matter, and how do the arguments they use relate to historical arguments? To find out, we individually interviewed 11 in-service secondary school science teachers (certified to teach chemistry and/or physics in secondary school, and with 2–30 years of teaching experience) regarding their arguments for the particulate nature of matter and experiments that could demonstrate the existence of particles. The collected data were qualitatively analyzed. Three qualitatively different categories of arguments could be constructed from data: philosophical argumentsindirect experimental arguments, and direct experimental arguments. The indirect experimental arguments, which is the largest category, could be further divided into qualitatively different subcategories: non-specific research and experiments, and chemical, physical and subatomic experiments. Even though several experiments and arguments were suggested by the informants in our study, the arguments regarding the validity of the experiments were quite uncertain and vague. The experiments and arguments were used to corroborate the particulate nature of matter and taken for granted in advance rather than used to justify a model with particles. The outcome was discussed in relation to scientific arguments and experiments and in view of results from previous science education research. Based on our data, teacher education and in-service teacher training, as well as teacher guides, were suggested to be more elaborate regarding contemporary knowledge, with direct experimental evidence for the particulate nature of matter being presented. 

  • 13.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Hernell, Bernt
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Sönnerhed, Wang Wei
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    On the use of emphasizing brackets when learning precedence rules2012In: Evaluation and comparison of mathematical achievement: Dimensions and perspectives: Proceedings of Madif 8 / [ed] C Bergsten, E Jablonka, M Raman, Linköping: Svensk förening för matematikdidaktisk forskning (SMDF) , 2012, p. 209-210Conference paper (Refereed)
  • 14.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Hernell, Bernt
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Sönnerhed, Wang Wei
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Useless brackets in arithmetic expressions with mixed operations2012In: Proceedings of the 36th Conference of the International Group for the Psychology of Mathematics Education / [ed] T.Y. Tso, The International Group for the Psychology of mathematics Education , 2012, p. 2-275-2-282Conference paper (Refereed)
    Abstract [en]

    There can be different intentions with brackets in mathematical expressions. It has previously been suggested that mathematically useless brackets can be educationally useful when learning the order of operations in expressions with mixed operations. This paper reports how students (12-13 years) deal with the implicit mental conflict between brackets as a necessary part of the order of operations and brackets to emphasize precedence. The students taking part in this quasi-experimental study were instructed on the order of operations, but were also indirectly exposed to different use of brackets. It is concluded that emphasizing brackets impede the transfer from a left-to-right computation strategy to the use of precedence rules.

  • 15.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, Disciplinary Research. Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Kalabukhov, Alexei
    Chalmers tekniska högskola.
    Winkler, Dag
    Chalmers tekniska högskola.
    Evaluation of recipes for obtaining single terminated perovskite oxide substrates2009In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 603, no 1, p. 151-157Article in journal (Refereed)
    Abstract [en]

    We have re-assessed different methods to obtain single terminated perovskite oxide substrate surfaces of SrTiO3, LaAlO3 and NdGaO3. The surfaces have been probed by a combination of atomic and lateral force microscopy, X-ray photoelectron spectroscopy and reflection high-energy electron diffraction. (0 0 1)SrTiO3 surfaces were prepared with HF or plasma etching and annealing, (0 0 1)LaAlO3 surfaces were prepared with or without HCl etching and a consecutive annealing at 750–1100 °C, and (1 1 0)NdGaO3 surfaces were only annealed. Two of the recipes have previously been suggested to result in A-site terminated surfaces. However, except for the case of high-temperature annealed LaAlO3 where we observe a double-terminated surface, our data suggest that the single terminated surfaces obtained by these methods were of B-site type.

  • 16.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Karlsson, Annasara
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Brackets and the structure sense2014In: Development of Mathematics Teaching: Design, Scale, Effects: Proceedings of MADIF 9, The Ninth Swedish Mathematics Research Seminar / [ed] O. Helenius, A. Engström, T. Meaney, P. Nilsson, E. Norén, J. Sayers & M. Österholm., Linköping: Svensk förening för MatematikDidaktisk Forskning - SMDF, 2014, p. 47-55Conference paper (Refereed)
    Abstract [en]

    Brackets are essential structure elements in mathematics expressions. However, students have shown to have scattered understanding of the concept of brackets and how they are used in mathematical expressions. In this paper we present data that illustrate students’ perceptions of the word “brackets” and how these perceptions influence their use of brackets in numerical expressions. Based on our data we argue that the teaching of the concept of brackets also need to describe brackets as ordered pairs where each symbol has a unique counterpart and that insertion of brackets can, but does not have to, modify the structure of an expression.

  • 17.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    Papadopoulos, I.
    Pairing numbers: An unconventional way of evaluating arithmetic expressions2019Conference paper (Refereed)
  • 18.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    Papadopoulos, Ioannis
    Aristotle University, Thessaloniki, Greece.
    The impact of number pairing on students' ideas on how to evaluate numerical expressions2018In: Proceedings of the 42nd Conference of the International Group for the Psychology of Mathematics Education: Vol. 5 / [ed] E. Bergqvist, M. Österholm, C. Granberg & L. Sumpter, Umeå: PME , 2018, p. 238-238Conference paper (Refereed)
  • 19.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    Runesson, Ulla
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    Håkansson, Per
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research. Vasaskolan, Skövde.
    Identifying what is critical for learning ‘rate if change’: Experiences from a learning study in Sweden2019In: Theory and practice of lesson study in mathematics: An international perspective / [ed] R. Huang, A. Takahashi & J. P. da Ponte, Cham: Springer, 2019, p. 441-456Chapter in book (Refereed)
    Abstract [en]

    Learning study is an adapted version of lesson study developed in Hong Kong and Sweden. It has commonalities with lesson study but is framed within a specific pedagogical learning theory – variation theory. Central in variation theory is the object of learning and what is critical for students’ learning. Hence, as with lesson study, it is a collective and iterative work where teachers explore how they can make the object of learning available to students, but what characterises learning study is the use of a specific learning theory. In this process, special attention is paid to the critical aspects of the object of learning. We argue that to identify the aspects that are critical, the aspects need to be verified and refined in classrooms. In this chapter, we demonstrate how teachers gain knowledge about such critical aspects. Particularly, we show how these critical aspects cannot be extracted only from the mathematical content or the students pre-understanding alone, but evolve during the learning study cycles. For this we use a learning study about the mathematical topic of rate of change in grade 9 in Sweden as an illustration. We describe how an analysis of how students solved tasks in pre- and post-test and during the lessons, as well as how the mathematical content was presented in lessons, helped the teachers identify what was critical for learning to understand and express the rate of change for a dynamic situation.

  • 20.
    Gunnarsson, Robert
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Wei Sönnerhed, Wang
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Hernell, Bernt
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Does it help to use mathematically superfluous brackets when teaching the rules for the order of operations?2016In: Educational Studies in Mathematics, ISSN 0013-1954, E-ISSN 1573-0816, Vol. 92, no 1, p. 91-105Article in journal (Refereed)
    Abstract [en]

    The hypothesis that mathematically superfluous brackets can be useful when teaching the rules for the order of operations is challenged. The idea of the hypothesis is that with brackets it is possible to emphasize the order priority of one operation over another. An experiment was conducted where expressions with mixed operations were studied, focusing specifically on expressions of the type a ± (b × c) with brackets emphasizing the multiplication compared to expressions of the type a ± b × c without such brackets. Data were collected from pen and paper tests, before and after brief (about 7 min) instructions, of 169 Swedish students in year 6 and 7 (aged 12 to 13). The data do not seem to support the use of brackets to detach the middle number (b) from the first operation (±) in a ± b × c type of expressions.

  • 21.
    Håkansson, Per
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research. Vasaskolan, Skövde.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    Frågan är vad frågan gör – olika frågeställningars betydelse för hur elever uttrycker och använder förändringstakt i matematik2018In: Forskning om undervisning och lärande, ISSN 2000-9674, E-ISSN 2001-6131, Vol. 6, no 2, p. 44-62Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to compare the impact of different phrasings of questions as of how students relate and express relations between different quantities in student tasks concerning rate of change. Through a qualitative analysis we compare how students in ninth grade (age 15) respond to two different framings of questions, concerning how fast the volume of fluid in two medicine bags change. The analysis indicates that a comparing question (”which changes fastest?”) can open up a wide outcome space, in which we could observe five qualitatively distinct ways of solving the task. Furthermore, a question that requests a value (“how fast does it change?”) seem to encourage students to make multiplicative comparisons, which is close to the mathematical meaning of rate of change. Finally, we discuss the potential of each question for pointing to different aspects of rate of change, and how they could be used by teachers for different purposes in teaching situations.

  • 22.
    Håkansson, Per
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    KEY ASPECTS OF EXPRESSING THE RATE OF CHANGE IN LOWER SECONDARY SCHOOL MATHEMATICS2017Conference paper (Refereed)
  • 23.
    Håkansson, Per
    et al.
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research. Vasaskolan, Skövde.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    What is critical in order to learn the average rate of change?2018In: Proceedings of the 42nd Conference of the International Group for the Psychology of Mathematics Education: Vol. 5 / [ed] E. Bergqvist, M. Österholm, C. Granberg & L. Sumpter, Umeå: PME , 2018, p. 55-55Conference paper (Refereed)
  • 24.
    Kalabukhov, Alexei
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Boikov, Yuri
    Ioffe Physico-Technical Institute, Sankt Petersburg.
    Serenkov, I. T.
    Ioffe Physico-Technical Institute, Sankt Petersburg.
    Sakharov, V. I.
    Ioffe Physico-Technical Institute, Sankt Petersburg.
    Popok, Vladimir
    Göteborgs universitet, Institutionen för fysik.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Disciplinary Research. Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Börjesson, Johan
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Ljustina, Nikolina
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Olsson, Eva
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Winkler, Dag
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Claeson, Tord
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Cationic disorder and phase segregation in LaAlO3/SrTiO3 heterointerfaces evidenced by medium-energy ion spectroscopy2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 14, p. 146101-Article in journal (Refereed)
    Abstract [en]

    Medium-energy ion spectroscopy (MEIS) has been used to study the depth profile and deduce the distribution of possible cationic substitutions in LaAlO3/SrTiO3 (LAO/STO) heterointerfaces. Analysis of La and Sr peaks in aligned and random MEIS spectra indicates that the surface layers of LAO on an STO substrate are not homogeneous and stoichiometric if the film thickness is less than 4 unit cell layers. This is possibly caused by a redistribution of La and Sr at the interface. Kelvin probe force microscopy reveals an inhomogeneous distribution of the surface potential in a 4 unit cell LAO film, indicating micrometer-sized regions of different compositions. Our findings provide a novel view on the microstructural origin of the electrically conductive interfaces.

  • 25.
    Kalabukhov, Alexei
    et al.
    MC2, Chalmers tekniska högskola.
    Claeson, Tord
    MC2, Chalmers tekniska högskola.
    Aurino, Pier Paulo
    MC2, Chalmers tekniska högskola.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Winkler, Dag
    MC2, Chalmers tekniska högskola.
    Olsson, Eva
    Tillämpad fysik, Chalmers tekniska högskola.
    Tuzla, Nicolina
    Tillämpad fysik, Chalmers tekniska högskola.
    Börjesson, Johan
    Tillämpad fysik, Chalmers tekniska högskola.
    Boikov, Yuri
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Serenkov, I.T.
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Sakharov, V.I.
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Volkov, M.P.
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Electrical and structural properties of ABO3/SrTiO3 interfaces2012In: MRS Online Proceedings Library, vol 1454: 2012 MRS Spring Meeting - Symposium HH – Nanocomposites, Nanostructures and Heterostructures of Correlated Oxide Systems, Warrendale, Pa.: Materials Research Society, 2012, p. 167-172Conference paper (Refereed)
    Abstract [en]

    Electrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2- terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.

  • 26.
    Kalabukhov, Alexei
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Disciplinary Research. Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Börjesson, Johan
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Olsson, Eva
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Winkler, Dag
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Claeson, Tord
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Effect of various deposition conditions on the electrical properties of LAO/STO hetero interfaces2008In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no 8, p. 082039-Article in journal (Refereed)
    Abstract [en]

    We have examined the effects of partial oxygen pressure and laser energy density on the electrical transport properties of thin LAO films grown on (100) TiO2-terminated SrTiO3 substrates. Films were grown by pulsed laser deposition monitored by in-situ reflection high-energy electron diffraction (RHEED). Layer-by-layer growth, as indicated by clear RHEED oscillations, can be obtained in a wide range of oxygen partial pressures from 10−6 to 5×10−2 mbar. Transmission electron microscopy (TEM) analysis shows that the interface is coherent and atomically sharp for all deposition conditions. The STO substrate is oxygen self reduced at an oxygen pressure of 10−6 mbar and the electrical properties of the interface are dominated by the presence of oxygen vacancies. By increasing the oxygen pressure above 10−4 mbar, the substrate itself is insulating but the interface still shows metallic conductivity. However, the interface becomes insulating at an oxygen pressure of 5×10−2 mbar. We also found that the interface exhibits insulator-to-metal transition by changing the laser fluence during the deposition of the film. The interface prepared at 5×10−2 mbar shows metallic conductivity at high fluence, above 3.5 J/cm2.

  • 27.
    Kalabukhov, Alexei
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Disciplinary Research. Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Winkler, Dag
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Claeson, Tord
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Börjesson, Johan
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Ljustina, Nikolina
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Olsson, Eva
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Boikov, Yuri
    Ioffe Physio-Technocal institute, St. Petersburg.
    Serenkov, I
    Ioffe Physio-Technocal institute, St. Petersburg.
    Sakharov, V
    Ioffe Physio-Technocal institute, St. Petersburg.
    Popok, Vladimir
    Göteborgs universitet, Institutionen för fysik.
    Correlation between cationic defects and electrical conductivity of LAO-STO interfaces2009Conference paper (Other academic)
  • 28.
    Kalabukhov, Alexey
    et al.
    MC2, Chalmers tekniska högskola.
    Claeson, Tord
    MC2, Chalmers tekniska högskola.
    Aurino, Pier Paolo
    MC2, Chalmers tekniska högskola.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Winkler, Dag
    MC2, Chalmers tekniska högskola.
    Olsson, Eva
    Tillämpad fysik, Chalmers tekniska högskola.
    Tuzla, Nikolina
    Tillämpad fysik, Chalmers tekniska högskola.
    Börjesson, Johan
    Tillämpad fysik, Chalmers tekniska högskola.
    Cao, Yu
    Material- och tillverkningsteknik, Chalmers tekniska högskola.
    Nyborg, Lars
    Material- och tillverkningsteknik, Chalmers tekniska högskola.
    Boikov, Yuri
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Serenkov, Igor
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Sakharov, Vladimir
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Volkov, Mikhail
    Ioffe Physio-Technical Institute, St Petersburg, Ryssland.
    Inhomogeneous Microstructure and Electrical Transport Properties at the LaAlO3/SrTiO3 Interface2012In: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 51, no 11, p. 11PG10-Article in journal (Refereed)
    Abstract [en]

    Medium-energy ion spectroscopy (MEIS), scanning transmission electron microscopy (STEM) and X-ray photoemission spectroscopy (XPS) wereused to investigate the composition and microstructure of LaAlO3/SrTiO3 (LAO/STO) interfaces grown by pulsed laser deposition of LAO onTiO2-terminated STO substrates under different oxidizing conditions. MEIS and XPS indicated Sr/La and Al/Ti intermixing within several atomiclayers at all studied interfaces. XPS and STEM revealed that La diffuses deeper than Al. Analysis of the MEIS data suggests inhomogeneouslateral distribution of the diffused elements. This is further supported by the observation of a large positive magneto-resistance at low temperatures. We discuss the role of lateral inhomogeneities on the formation of the electron gas at the LAO/STO interface.

  • 29.
    Kalabukhov, Alexey
    et al.
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Gunnarsson, Robert
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Börjesson, Johan
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Olsson, Eva
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Claeson, Tord
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Winkler, Dag
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Effect of oxygen vacancies in the SrTiO3 substrate on the electrical properties of LaAlO3/SrTiO3 interface2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 75, no 12, p. 121404(R)-Article in journal (Refereed)
    Abstract [en]

    We experimentally investigated optical, electrical, and microstructural properties of heterointerfaces between two thin-film perovskite insulating materials, SrTiO3 (STO) and LaAlO3 (LAO), deposited at different oxygen pressure conditions. Cathode and photoluminescence experiments show that oxygen vacancies are formed in the bulk STO substrate during the growth of LAO films, resulting in high electrical conductivity and mobility values. In both high and low oxygen pressure interfaces, the electrical Hall mobilities follow a similar power-law dependence as observed in oxygen reduced STO bulk samples. The results are confirmed on a microscopic level by local strain fields at the interface reaching 10  nm into the STO substrate.

  • 30.
    Karlsson, Annasara
    et al.
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Mathematics Education Research.
    Students' perceptions of brackets2013In: Proceedings of the 37th Conference of the International Group for the Psychology of Mathematics Education, vol. 5 / [ed] A.M. Lindmeier & A. Heinze, Kiel, Germany: IGPME , 2013, p. 85-Conference paper (Refereed)
  • 31.
    Ljustina, Nikolina
    et al.
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Börjesson, Johan
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Kalabukhov, Alexei
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education. Jönköping University, School of Education and Communication, HLK, Disciplinary Research.
    Winkler, Dag
    Chalmers tekniska högskola, Institutionen för mikroteknologi och nanovetenskap.
    Olsson, Eva
    Chalmers tekniska högskola, Institutionen för tillämpad fysik.
    Intermixing at the interface between epitaxial LaAlO3 thin films on (001) SrTiO3 substrates2009Conference paper (Other academic)
  • 32.
    Papadopoulos, Ioannis
    et al.
    Aristotle University, Thessaloniki, Greece.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Praktiknära utbildningsforskning (PUF), Mathematics Education Research.
    The use of ‘mental’ brackets when calculating arithmetic expressions2018In: Proceedings of the 42nd Conference of the International Group for the Psychology of Mathematics Education: Vol. 3 / [ed] E. Bergqvist, M. Österholm, C. Granberg & L. Sumpter, Umeå: PME , 2018, p. 451-458Conference paper (Refereed)
  • 33.
    Popok, Vladimir
    et al.
    Chalmers University of Technology, Göteborg.
    Kalabukhov, Alexey
    Chalmers University of Technology, Göteborg.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, Disciplinary Research. Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education.
    Lemeshko, Sergey
    NT-MDT Europe B.V., Eindhoven.
    Claeson, Tord
    Chalmers University of Technology, Göteborg.
    Winkler, Dag
    Chalmers University of Technology, Göteborg.
    Kelvin Probe Force Microscopy Study of LaAlO3/SrTiO3 Heterointerfaces2010In: Journal of Advanced Microscopy Research, ISSN 2156-7573, E-ISSN 2156-7581, Vol. 5, no 1, p. 26-30Article in journal (Refereed)
    Abstract [en]

    Surface potential distribution in ultra-thin (0.8-3.9 nm) LaAlO3 layers deposited on SrTiO3 substrates is studied. It is found that the potential distribution evolves from island-like to a homogeneous one with increasing LaAlO3 thickness. It is suggested that the observed islands are caused by locally enhanced concentration of mobile charge carriers at the interface that is in turn related to non-stoichiometry of the layers with thickness bellow 4 unit cells. Transition to a homogeneous potential distribution with increasing LAO thickness (≥ 4 unit cells) corresponds to the formation of a quasi-2-dimensional electron gas. The results agree with a percolation model explaining the insulator-to-metal transition that occurs at the LaAlO3/SrTiO3 heterointerface.

  • 34.
    Stepantsov, E.A.
    et al.
    Shubnikov Institute of Crystallography, Moskva.
    Kazakov, S.M.
    Moscow State University, Moskva.
    Belikov, V.V.
    Moscow State University, Moskva.
    Makarova, I.P.
    Shubnikov Institute of Crystallography, Mosva.
    Arpaia, R.
    Chalmers University of Technology.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education. Chalmers University of Technology.
    Lombardi, Floriana
    Chalmers University of Technology.
    Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe0.92-FeSe0.5Te0.5 system2013In: Crystallography reports (Print), ISSN 1063-7745, E-ISSN 1562-689X, Vol. 58, no 5, p. 735-738Article in journal (Refereed)
    Abstract [en]

    Thin films of FeSe0.92 and FeSe0.5Te0.5 iron chalcogenide superconductors and solid solutions containing these components in different ratios have been grown on the surface of LaAlO3 (10 1¯ 2) crystals by pulsed laser deposition. Films of solid solutions have been deposited by simultaneous laser ablation from two targets of the FeSe0.92 and FeSe0.5Te0.5 stoichiometric compositions onto one substrate. An X-ray diffraction study of the film structure shows that the films grown are epitaxial and their lattice parameters regularly vary with the ratio of the deposited components, which was controllably varied by changing the ablation intensities from the targets.

  • 35.
    Stepantsov, Evgeny
    et al.
    Shubnikov Institute of Crystallography, RAS, Moskva.
    Kazakov, S.M.
    Moscow State University.
    Belikov, V.V.
    Moscow State University.
    Makarova, I.P.
    Shubnikov Institute of Crystallography, RAS, Moskva.
    Arpaia, R.
    Chalmers tekniska högskola.
    Gunnarsson, Robert
    Jönköping University, School of Education and Communication, HLK, School Based Research, Sustainable Development and Science education. Chalmers tekniska högskola.
    Lombardi, Floriana
    Chalmers tekniska högskola.
    Ablation replacement of iron with Co, Mn, Ni, and Cu during growth of iron-based superconductor films in the Fe0.9M0.1Se0.92 system2014In: Crystallography reports (Print), ISSN 1063-7745, E-ISSN 1562-689X, Vol. 59, no 5, p. 739-743Article in journal (Refereed)
    Abstract [en]

    Thin films of ironbased chalcogenide superconductors FeSe0.92, with iron partially replaced (atleast up to 10 at %) by elements such as cobalt, nickel, manganese, or copper, have been grown on the surfaceof (10 2) LaAlO3 crystals. Growth is performed by the laser ablation of a target prepared in the form of aceramic pellet by hightemperature synthesis and the sintering of preliminarily pressed stoichiometric mixture of powders. Iron in these ceramics is replaced with an alloying metal by no more than 3 at %. The rest(7 at %) of the metal is in the form of precipitates of other phases. Xray diffraction analysis of the grown filmshas shown that they are singlecrystal and free of any precipitates of other crystallographic orientations andphases. This is evidence of the complete (10 at %) replacement of iron with a doping metal in the film structure. This circumstance indicates that the synthesis of components occurs more actively and completely during laser ablation (than in solidphase chemical reactions) as a result of the transformation of multicomponent target material into plasma. Thus, one can fabricate film materials in a wider range of chemical compositions than in the form of solidphase synthesized ceramics.

1 - 35 of 35
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