| 1. |
- Boikov, Iouri, 1949, et al.
(författare)
-
Strain-enhanced phase separation affecting electro- and magnetotransport in La0.67Ca0.33MnO3 films
- 2004
-
Ingår i: Journal of Applied Physics. ; 96:1, s. 435-442
-
Tidskriftsartikel (refereegranskat)abstract
- Biaxial strain during nucleation influences phase separation into ferromagnetic (metallic) and nonferromagnetic (insulating) regions and that, in turn, markedly affects the electric transport of a manganite film. A 40-nm-thick La0.67Ca0.33MnO3 film, coherently constrained by a (001)LaAlO3 substrate, possesses a noticeably contracted unit cell volume (Veff[approximate]56.70 Å3) as compared with that of a stoichiometric bulk sample. It corresponds to a higher relative concentration (45%) of tetravalent manganese ions in the manganite layer than that in the target (33%). The resistivity rho(T) curve of the strained film peaks twice in the range 4.2300 K. The charge transport of strained La0.67Ca0.33MnO3 films is non-ohmic at T
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| 2. |
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| 3. |
- Brucas, Rimantas, 1965, et al.
(författare)
-
Tunneling and charging effects in discontinuous superparamagnetic Ni81Fe19/Al2O3 multilayers
- 2010
-
Ingår i: Physical Review B - Condensed Matter and Materials Physics. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 1098-0121 .- 1550-235X. ; 81:22, s. 224437-
-
Tidskriftsartikel (refereegranskat)abstract
- The magnetic and transport properties of films based on discontinuous layers of Ni81Fe19 (Py) embedded in Al2O3 were investigated. In films with nominal Py thicknesses 6 and 8 angstrom superparamagnetic particles with median diameters D-med = 2.8 and 3.1 nm and distribution widths sigma(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 the charge transport occurs via tunneling; with the charging energy supplied by thermal fluctuations at high temperature, T >= 100 K, and by the electric field at low temperature, T
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| 4. |
- Demidov, V. V., et al.
(författare)
-
Magnetic anisotropy in strained manganite films and bicrystal junctions
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:16
-
Tidskriftsartikel (refereegranskat)abstract
- 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 degrees to 25 degrees. 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.
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| 5. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
A phenomenographic analysis of students’ use of base-ten material
- 2020
-
Konferensbidrag (refereegranskat)abstract
- Previous research indicates that manipulatives, like base-ten blocks, not necessarily strengthen students’ understanding of numerical place-value and the decimal numeral system. This study takes its starting point in the hypothesis that to create functional teaching situations with base-ten blocks, it is necessary to first know students’ prior understanding of such manipulatives. Therefore, here we present a phenomenographic analysis of students’ understanding how such manipulative material can be used to represent multidigit numbers. The data was collected from individual interviews with 58 students in grade 1 (6-7 years old).We identify six qualitatively different categories of students’ understanding, and, based on these, suggest implications for the design of teaching situations.
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| 6. |
- Gunnarsson, Robert, 1972
(författare)
-
Anisotropic spin-orbit interaction revealed by in-plane magnetoresistance in single-oriented SrRuO3 thin films
- 2012
-
Ingår i: Physical Review B - Condensed Matter and Materials Physics. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 1098-0121 .- 1550-235X. ; 85:23, s. 235409-
-
Tidskriftsartikel (refereegranskat)abstract
- 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
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| 7. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
Brackets and the structure sense
- 2014
-
Ingår i: Development of Mathematics Teaching: Design, Scale, Effects. - Linköping : Svensk förening för MatematikDidaktisk Forskning - SMDF. - 9789197393492 ; , s. 47-55
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Gunnarsson, Robert, 1972-
(författare)
-
En studie om elevers uppfattning om associativitet och hur det kan påverka algebraundervisningen
- 2022
-
Ingår i: The relation between mathematics education research and teachers’ professional development. - Göteborg : Svensk förening för MatematikDidaktisk Forskning - SMDF. - 9789198402452 ; , s. 131-131
-
Konferensbidrag (refereegranskat)abstract
- Denna presentation beskriver en pågående studie om hur associativitet kan uppfattas och hanteras i matematikundervisning. Studien syftar till att beskriva elevers olika sätt att förstå associativitet och utifrån dessa designa lämpliga undervisningsinslag för att främja elevernas algebraiska förståelse. Vissa delresultat beskrivs.
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| 9. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
Evaluation of recipes for obtaining single terminated perovskite oxide substrates
- 2009
-
Ingår i: Surface Science. - : Elsevier. - 0039-6028 .- 1879-2758. ; 603:1, s. 151-157
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Gunnarsson, Robert, 1972, et al.
(författare)
-
Fabrication and characterisation of La0.67Sr0.33MnO3 submicron grain boundary junctions
- 2004
-
Ingår i: Annalen der Physik (Leipzig). ; 13:1-2, s. 101-102
-
Konferensbidrag (refereegranskat)abstract
- We have successfully fabricated LSMO grain boundary bicrystaljunctions with widths down to 200 nm. The grain boundaries aresymmetric with misorientation angles of 24degrees or 36.8degrees, and the microbridges are positioned across thosewith a precision better than 0.5 micro-meter. Grain boundary magnetoresistance is observed in the wider junctions but not in the most narrow junction.
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| 11. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
Identifying what is critical for learning ‘rate if change’ : Experiences from a learning study in Sweden
- 2019
-
Ingår i: Theory and practice of lesson study in mathematics. - Cham : Springer. - 9783030040307 - 9783030040314 ; , s. 441-456
-
Bokkapitel (refereegranskat)abstract
- 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.
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| 12. |
- Gunnarsson, Robert, 1972, et al.
(författare)
-
Low-field magnetoresistance in perovskite manganites: Magnetic field, temperature, and current dependence
- 2004
-
Ingår i: Physical Review B. ; 69:5, s. 054413-
-
Tidskriftsartikel (refereegranskat)abstract
- The low-field response from single bicrystal grain boundary junction of La0.7Sr0.3MnO3 has been investigated. We provide experimental data for the temperature, magnetic field and bias current dependence of its low-field magnetoresistance. We are then able to separate the contribution from anisotropic magnetoresistance, and the magnetization processes in the vicinity of the grain boundary. Our data indicate that with the magnetic field applied parallel to the grain boundary the magnetization process is dominated by domain wall motion, whereas with the field in the perpendicular direction the magnetoresistance is determinedby coherent rotation of magnetization directions.
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| 13. |
- Gunnarsson, Robert, 1972
(författare)
-
Magnetic Bicrystal Junctions - a Study of Half-Metallic Manganite Grain Boundaries
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents studies on magnetic bicrystal junctions. In these, films on either side of the junction are structurally and magnetically misoriented. This type of device enables us to study junction magnetoresistance and spin polarized charge transport between ferromagnets with well defined directions of magnetization. The ferromagnets subject to our studies are epitaxial films, prepared by pulsed laser deposition, of La0.7Sr0.3MnO3, suggested to possess half-metallic characteristics. The electrical transport through single and arrays of junctions have been measured as functions of magnetic field and temperature. We have demonstrated that the magnetization reversal processes responsible for the magnetoresistance observed in poly-crystalline films can be studied in detail by using single bicrystal grain boundary junctions. We have shown that when the field is applied perpendicular to a grain boundary, the magnetization reversal process can be well described by a Stoner-Wohlfarth model for coherent rotation of magnetization. Whereas, when the field is applied along the grain boundary, the magnetoresistance data suggest a stochastic reversal process, including splitting into domains. Coherent rotation of magnetization is an essential ingredient when modelling the magnetoresistance hysteresis. We have observed, by high resolution electron microscopy, that the region of structural disorder at the bicrystal interface can be small, with a width as small as down to a unit-cell. Different models have been discussed for the transport mechanism across the interface. Current-voltage characteristics of single junctions are close to Ohmic at low voltage, and become non-linear at voltages higher than 5 - 20 mV, depending on misorientation angle. However, they cannot be fitted to a simple parabolic function. The results are discussed in terms of a tunnelling model.
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| 14. |
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| 15. |
- Gunnarsson, Robert, 1972, et al.
(författare)
-
Magnetization reversal processes in magnetic bicrystal junctions
- 2006
-
Ingår i: Phys. Rev. B. ; 73, s. 014435-
-
Tidskriftsartikel (refereegranskat)abstract
- 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. The magnetoresistance hysteresis is interpreted directly into 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.
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| 16. |
- Gunnarsson, Robert, 1972, et al.
(författare)
-
Magnetoresistance in bicrystal grain-boundary junctions analyzed within the Stoner-Wohlfarth model
- 2005
-
Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 290-291:part 1, s. 761-763
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental data of bicrystal grain boundary magnetoresistance hysteresis shows that the resistance at remanence after saturation depends on whether the magnetic field was applied parallel or perpendicular to the grain boundary. In the latter case the behaviour can be described by the Stoner-Wohlfarth magnetization reversal model for coherent rotation of the magnetization, which leads to an alignment along the easy magnetization directions of the bicrystal in zero field. In the parallel configuration themagnetization directions of the two grains remain parallel in zero field. We have used this information to deduce an effective spin-polarization of P ~ 40 % of the grain boundary in a bicrystal of La0.7Sr0.3MnO3.
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| 17. |
- Gunnarsson, Robert, 1972, et al.
(författare)
-
Misorientation angle dependence of bicrystal magnetoresistance within the model of coherent rotation
- 2004
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. ; 16:21, s. 3761-3768
-
Tidskriftsartikel (refereegranskat)abstract
- The 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 increasingmisorientation angle. The influence of biaxial magnetocrystalline anisotropy is reflected in a hump in the maximum magnetoresistance curve at around a misorientation angle of 25 degrees. This structure is absent in the case of uniaxial anisotropy.
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| 18. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
On the use of emphasizing brackets when learning precedence rules
- 2012
-
Ingår i: Evaluation and comparison of mathematical achievement: Dimensions and perspectives. - Linköping : Svensk förening för matematikdidaktisk forskning (SMDF). - 9789197393485 ; , s. 209-210
-
Konferensbidrag (refereegranskat)
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| 19. |
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| 20. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
Secondary school science teachers’ arguments for the particulate nature of matter
- 2018
-
Ingår i: Journal of Research in Science Teaching. - : John Wiley & Sons. - 0022-4308 .- 1098-2736. ; 55:4, s. 503-525
-
Tidskriftsartikel (refereegranskat)abstract
- 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 arguments, indirect 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.
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| 21. |
- Gunnarsson, Robert, 1972, et al.
(författare)
-
Stoner-Wohlfarth model applied to bicrystal magnetoresistance hysteresis
- 2004
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:1, s. 482-485
-
Tidskriftsartikel (refereegranskat)abstract
- We calculate numerically the magnetization direction as function of magnetic field in the StonerWohlfarth 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.
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| 22. |
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| 23. |
- Gunnarsson, Robert, 1972-
(författare)
-
The model of the particle nature of matter in science and science education
- 2014
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 24. |
- Gunnarsson, Robert, 1972-, et al.
(författare)
-
Useless brackets in arithmetic expressions with mixed operations
- 2012
-
Ingår i: Proceedings of the 36th Conference of the International Group for the Psychology of Mathematics Education. - : The International Group for the Psychology of mathematics Education. ; , s. 2-275-2-282
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 25. |
- Håkansson, Per, et al.
(författare)
-
Frågan är vad frågan gör – olika frågeställningars betydelse för hur elever uttrycker och använder förändringstakt i matematik
- 2018
-
Ingår i: Forskning om undervisning och lärande. - : Stiftelsen SAF i samverkan med Lärarförbundet. - 2000-9674 .- 2001-6131. ; 6:2, s. 44-62
-
Tidskriftsartikel (refereegranskat)abstract
- Syftet med denna studie är att jämföra olika frågeställningars betydelse för hur elever relaterar och uttrycker relationer mellan olika storheter i uppgifter om förändringstakt i matematik. Genom en kvalitativ analys jämför vi hur elever i årskurs 9 besvarar två olika typer av uppgifter om hur snabbt vätskevolymen i två medicinska droppåsar förändras. Analysen pekar bland annat på att en jämförande uppgift (”vilken förändras snabbast?”) kan öppna ett brett utfallsrum, där vi kunde observera fem kvalitativt skilda sätt att lösa uppgiften. Vidare verkar en uppgift som efterfrågar ett värde (”hur snabbt förändras den?”) kunna leda eleverna mot multiplikativa jämförelser, som ligger nära den vedertagna matematiska innebörden i begreppet förändringstakt. Avslutningsvis diskuterar vi de olika frågeställningarnas potential för att lyfta olika aspekter av begreppet förändringstakt och hur de skulle kunna användas av lärare för olika syften i undervisningen.
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| 26. |
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| 27. |
- Håkansson, Per
(författare)
-
Rate as the relation of changes in two quantities : A variation theory perspective of learning rate of change
- 2020
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis comprises three original papers about learning rate of change in school mathematics. The overall aim of the thesis is to contribute with knowledge in this particular area of research. Within this aim, each of the original papers contribute with its own perspective. The theoretical framework used in the thesis is variation theory of learning (Marton & Booth, 1997; Marton, 2015), by which learning is seen as experiencing a phenomenon in a new way. This theoretical point of departure is reflected in the research question of the thesis: What is critical to discern to use and express rate as a measure of the relation of changes in two quantities? The empirical study was conducted as a learning study (Pang & Marton, 2003). A learning study is an iterative, interventional research arrangement in which teachers and researchers collaboratively explore a specific ability, the object of learning, worthwhile for the students to learn. The object of learning related to this thesis, ‘to express the quantitative rate of change of a linear relation’, was explored in a series of three research lessons at a secondary school. Data consists of students’ responses to written pre- and post-tests, and lesson videos. Some data have been analysed during the on-going empirical study and some data have been analysed after it was concluded. Principles from variation theory have been used as tools for analysis throughout the study. Main results of Paper I demonstrate how two critical aspects are identified and revised through the process of learning study. In Paper II the results indicate that qualitatively different questions in a task may affect students’ ways to relate changes in two quantities. The results of Paper III suggest how different perspectives of slope may promote homogeneity as an aspect of rate. Results also comprise six critical aspects of the object of learning, four of which was identified by revisiting the results of Paper II. In summary, the critical aspects also specify the meaning of a covariational perspective of rate. Results are discussed in relation to previous educational research about rate of change, covariation of quantities and students’ conceptions of rate and slope. Further research directions are suggested.
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| 28. |
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| 29. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
-
Cationic Disorder and Phase Segregation in LaAlO3/SrTiO3 Heterointerfaces Evidenced by Medium-Energy Ion Spectroscopy
- 2009
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 103:14, s. 146101-
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 30. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
-
Effect of oxygen vacancies in the SrTiO3 substrate on the electrical properties of the LaAlO3/SrTiO3 interface
- 2007
-
Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 75:12, s. 121404(R)-
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 31. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
-
Electrical and structural properties of ABO3/SrTiO3 interfaces
- 2012
-
Ingår i: Materials Research Society Symposium Proceedings. - Warrendale, Pa. : Springer Science and Business Media LLC. - 0272-9172. - 9781605114316 ; 1454, s. 167-172, s. 167-172
-
Konferensbidrag (refereegranskat)abstract
- 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.
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| 32. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
-
Inhomogeneous Microstructure and Electrical Transport Properties at the LaAlO3/SrTiO3 Interface
- 2012
-
Ingår i: Japanese Journal of Applied Physics. - 1347-4065 .- 0021-4922. ; 51:11(spec.issue), s. article no. 11PG10 -
-
Tidskriftsartikel (refereegranskat)abstract
- Medium-energy ion spectroscopy (MEIS), scanning transmission electron microscopy (STEM) and X-ray photoemission spectroscopy (XPS) were used to investigate the composition and microstructure of LaAlO3/SrTiO3 (LAO/STO) interfaces grown by pulsed laser deposition of LAO on TiO2-terminated STO substrates under different oxidizing conditions. MEIS and XPS indicated Sr/La and Al/Ti intermixing within several atomic layers at all studied interfaces. XPS and STEM revealed that La diffuses deeper than Al. Analysis of the MEIS data suggests inhomogeneous lateral 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.
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| 33. |
- Karlsson, Annasara, et al.
(författare)
-
Students' perceptions of brackets
- 2013
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Ingår i: Proceedings of the 37th Conference of the International Group for the Psychology of Mathematics Education, vol. 5. - Kiel, Germany : IGPME. ; , s. 85-
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Konferensbidrag (refereegranskat)
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| 34. |
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| 35. |
- Lee, Arthur, et al.
(författare)
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Distinguishing more precise objects of learning through comparison of two mathematics lessons
- 2021
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Ingår i: The Earli Sig 9 Conference, 10-11 February 2021. ; , s. 20-20
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Konferensbidrag (refereegranskat)abstract
- Understanding the object of learning is a significant, yet often elusive, part of analysing a lesson through the lens of variation theory of learning. It involves not only specifying the usual learning objectives in terms of content and how to handle it, but also through identification of critical aspects to be discerned. The role of critical aspects in formulating the object of learning in an elaborate and useful way is the focus of this discussion paper. This is explored by comparing two mathematics lessons in China, designed and conducted by two teachers skilfully with bianshi pedagogy. As the content, textbook resources and students’ characteristics are basically the same, the subtle difference in the observed objects of learning becomes apparent. This difference is reflected in two contrasting sets of critical aspects that are structuring the lessons. In Marton (2015), “the object of learning is described primarily in terms of critical aspects and features to be discerned” for a better precision. Our analysis may contribute to a further discussion about how far the critical aspects constitute the meanings behind the content, which is not commonly addressed when a lesson is mainly analysed in terms of patterns of variation in a mechanical manner.
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
- Mårtensson, Pernilla, 1969-, et al.
(författare)
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Att planera och undervisa om tal i bråkform utifrån Shanghai-traditionen
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Världens blickar har under de två senaste decennierna riktas mot östra Asien när lärande och undervisning i matematik står i centrum för diskussioner. En anledning till det ökade intresset är troligtvis att dessa regioner, gång efter annan, placerar sig i topp i olika internationella mätningar som TIMMS och Pisa medan Sverige och många andra OECD-länder hamnar på en mer blygsam placering. Det finns flera tänkbara förklaringar till sådana skillnader. En avgörande faktor för undervisningskvalitet och som ofta lyfts fram är den kinesiska undervisningstraditionen Bianshi Jiaoxue—undervisa utifrån variation av ämnesinnehållet. Denna tradition erbjuder flera intressanta begrepp som kan användas som verktyg för att planera och genomföra undervisning, speciellt med avseende på hur uppgifter kan sammanlänkas för att skapa effektivt och fördjupat lärande i matematik. Vi illustrerar några centrala begrepp inom traditionen genom att lyfta några exempel från en lektion om addition och subtraktion med tal i bråkform genomförd i Shanghai samt från en intervju genomförd med den undervisande läraren. Lektions- och intervjudata kommer från ett av samarbetsprojekt, finansierat av Vetenskapsrådet, mellan forskare från Jönköping University och Hong Kong University. Utgångspunkten relaterat konferensens tema är att en praktisk teori är en viktig komponent för undervisning på vetenskaplig grund.
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| 42. |
- Papadopoulos, Ioannis, et al.
(författare)
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Exploring the way rational expressions trigger the use of “mental” brackets by primary school students
- 2020
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Ingår i: Educational Studies in Mathematics. - : Springer. - 0013-1954 .- 1573-0816. ; 103:2, s. 191-207
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Tidskriftsartikel (refereegranskat)abstract
- When a number sentence includes more than one operation, students are taught to follow the rules for the order of operations to get the correct result. In this context, brackets are used to determine the operations that should be calculated first. However, it seems that the written format of an arithmetical expression has an impact on the way students evaluate this expression. It also seems that a connection exists between this way of evaluation and an understanding of structure. Both issues are examined in this paper. A number of arithmetical expressions in a rational form were given to primary school students from Greece and Sweden. The collected findings strengthen our hypothesis that this rational form of the arithmetical expressions was of critical importance for the students’ decision on how to evaluate these expressions. They temporarily put aside their knowledge about the rules for the order of operations. Instead, the way they evaluated the expressions indicates an implicit use of what we call in this paper “mental” brackets. It is very likely that the use of these “mental” brackets is closely connected with students’ structure sense.
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| 43. |
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| 44. |
- Popok, Vladimir, 1966, et al.
(författare)
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Kelvin Probe Force Microscopy Study of LaAlO3/SrTiO3 Heterointerfaces
- 2010
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Ingår i: Journal of Advanced Microscopy Research. - : American Scientific Publishers. - 2156-7581 .- 2156-7573. ; 5:1, s. 26-30
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Tidskriftsartikel (refereegranskat)abstract
- Surface potential distributions in ultra-thin (0.8-3.9 nm) LaAlO3 layers deposited on SrTiO3 substrates are 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 a 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.
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| 45. |
- Roy, Pierre, et al.
(författare)
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Interface magnetic properties of La0.7Sr0.3MnO3 thin films
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. ; 272-276:Part 2, s. 1207-1209
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Konferensbidrag (refereegranskat)abstract
- Magnetic properties of La0.7Sr0.3MnO3 thin films with various capping layers have been investigated by SQUID magnetometry and X-ray magnetic circular dichroism. Results on the temperature dependence of the magnetization, orbital to spin moment ratios and the magnetocrystalline anisotropy are presented. xxxx
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| 46. |
- Stepantsov, E.A., et al.
(författare)
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Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe0.92-FeSe0.5Te0.5 system
- 2013
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Ingår i: Crystallography reports (Print). - 1063-7745 .- 1562-689X. ; 58:5, s. 735-738
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 47. |
- Stepantsov, Evgeny, et al.
(författare)
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Ablation replacement of iron with Co, Mn, Ni, and Cu during growth of iron-based superconductor films in the Fe0.9M0.1Se0.92 system
- 2014
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Ingår i: Crystallography reports (Print). - 1063-7745 .- 1562-689X. ; 59:5, s. 739-743
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 48. |
- Stepantsov, Evgeni, 1951, et al.
(författare)
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Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe0.92-FeSe0.5Te0.5 system
- 2013
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Ingår i: Crystallography Reports. - : Pleiades Publishing Ltd. - 1562-689X .- 1063-7745. ; 58:5, s. 735-738
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Tidskriftsartikel (refereegranskat)abstract
- 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 (102) 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.
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| 49. |
- Wessley, O, et al.
(författare)
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Final state effects in the X-ray absorption spectra of La0.7Sr0.3MnO3
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:3, s. 1780-1781
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Tidskriftsartikel (refereegranskat)abstract
- We present a comparison of theoretical calculations of the electronic structure of La0.7Sr0.3MnO3 with measurements of the unoccupied local density of states for Mn obtained from X-ray absorption spectroscopy (XAS). We compare two different theoretical calculations of the Mn XAS spectra, one based on the local spin density approximation (LSDA) and the other one based on an atomic Hartree–Fock calculation for the Mn ions. In the atomic calculation the solid state effects are introduced through a cubic crystal field where the crystal field strength is obtained from the LSDA calculation. It is found that the atomic calculations agree better with experimental data.
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| 50. |
- Östholm Balkhed, Åse, 1972-, et al.
(författare)
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An investigation of household dogs as the source in a case of human bacteraemia caused by Staphylococcus pseudintermedius
- 2023
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Ingår i: Infection Ecology & Epidemiology. - : Co-Action Publishing. - 2000-8686. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Staphylococcus pseudintermedius is a commensal and an opportunistic pathogen in dogs, and is also an opportunistic pathogen in humans. Here we report about a case of bacteraemia with a fatal outcome in a 77-year-old co-morbid male likely caused by a S. pseudintermedius and the investigation into the possible transmission from the two dogs in the patient's household. The two dogs carried the same S. pseudintermedius strain, but this dog strain was unrelated to the strain from the patient. In contrast to the patient strain, the dog strain showed reduced susceptibility to several antibiotics and both dogs had received antibiotic treatment prior to sampling. So, it is conceivable that these treatments can have eliminated the patient's strain between the transmission event and the dog sampling. It is also worth noting that the patient strain was positive for the expA gene, which encodes an exfoliative toxin closely related to the S. aureus exfoliative toxin B. This toxin has been linked to canine pyoderma, but its effect on humans remains unknown. Transmission of S. pseudintermedius was confirmed in the household between the dogs. However, we could not verify that the dogs were the source for the S. pseudintermedius in the patient.
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