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| 4. |
- Béland, Laurent Karim, et al.
(author)
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Accurate classical short-range forces for the study of collision cascades in Fe-Ni-Cr
- 2017
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In: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 219, s. 11-19
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Journal article (peer-reviewed)abstract
- The predictive power of a classical molecular dynamics simulation is largely determined by the physical validity of its underlying empirical potential. In the case of high-energy collision cascades, it was recently shown that correctly modeling interactions at short distances is necessary to accurately predict primary damage production. An ab initio based framework is introduced for modifying an existing embedded atom method FeNiCr potential to handle these short-range interactions. Density functional theory is used to calculate the energetics of two atoms approaching each other, embedded in the alloy, and to calculate the equation of state of the alloy as it is compressed. The pairwise terms and the embedding terms of the potential are modified in accordance with the ab initio results. Using this reparametrized potential, collision cascades are performed in Ni50Fe50, Ni80Cr20 and Ni33Fe33Cr33. The simulations reveal that alloying Ni and NiCr to Fe reduces primary damage production, in agreement with some previous calculations. Alloying Ni and NiFe to Cr does not reduce primary damage production, in contradiction with previous calculations.
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| 5. |
- Bläckberg, Lisa, et al.
(author)
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Assisted self-healing in ripped graphene
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:19, s. 195434-
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Journal article (peer-reviewed)abstract
- A monolayer of sp(2)-bonded carbon (graphene) is a material with great technological promise because of, for example, its transport, electrical, optical, and mechanical properties. In this work noble gas diffusion through ripped graphene sheets is explored. The motivation is improved detection systems used worldwide to verify compliance of the Comprehensive Nuclear-Test-Ban Treaty. It is demonstrated that even ripped graphene sheets and/or nonoverlapping graphene flakes inhibit noble gas diffusion. The latter has been shown for He and Xe where an infinitely long rip was constructed to have Stone-Wales edges. It is also shown that the ripped graphene layer self-heal in an alternating pentagon, hexagon, heptagon (5-6-7) and 7-6-5 pattern perpendicular to the rip. Moreover, the noble gas (He and Xe) assists in the healing process of wider rips.
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| 6. |
- Bläckberg, Lisa, et al.
(author)
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Effects of surface coatings on the light collection in plastic scintillators used for radioxenon detection
- 2012
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In: Physica Scripta. - 0031-8949 .- 1402-4896. ; T150, s. 014007-
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Journal article (peer-reviewed)abstract
- Atomic Layer Deposition coatings are under investigation to reduce diffusion of radioxenon into plastic scintillators. This paper investigates the impact of such surface coating on the light collection efficiency in a cylindrical geometry. A high and uniform light collection efficiency is important to preserve detector resolution. Monte Carlo simulations and measurements have been performed to study the influence of coating thickness, refractive index, and surface quality. It was found important to achieve a smooth coating, and a good optical match between the refractive indices of the coating and the plastic scintillator. Taking these considerations into account, the detector under study could be coated without significant degradation of its resolution.
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| 7. |
- Bläckberg, Lisa, et al.
(author)
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Investigations of surface coatings to reduce memory effect in plastic scintillator detectors used for radioxenon detection
- 2011
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 656:1, s. 84-91
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Journal article (peer-reviewed)abstract
- In this work Al(2)O(3) and SiO(2) coatings are tested as Xe diffusion barriers on plastic scintillator substrates. The motivation is improved beta-gamma coincidence detection systems, used to measure atmospheric radioxenon within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. One major drawback with the current setup of these systems is that the radioxenon tends to diffuse into the plastic scintillator material responsible for the beta detection, resulting in an unwanted memory effect. Here, coatings with thicknesses between 20 and 900 nm have been deposited onto plastic scintillators, and investigated using two different experimental techniques. The results show that all tested coatings reduce the Xe diffusion into the plastic. The reduction is observed to increase with coating thickness for both coating materials. The 425 nm Al(2)O(3) coating is the most successful one, presenting a diffusion reduction of a factor 100, compared to uncoated plastic. In terms of memory effect reduction this coating is thus a viable solution to the problem in question.
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| 8. |
- Bläckberg, Lisa, et al.
(author)
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Measurements of memory effect and resolution for an Al2O3 coated plastic scintillator used for radioxenon detection
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Other publication (other academic/artistic)abstract
- A cylindrical plastic scintillator cell, used for radioxenon monitoring within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty, has been coated with 425 nm Al2O3 using low temperature Atomic Layer Deposition, and its performance has been evaluated. The motivation is to reduce the memory effect caused by radioxenon diffusing into the plastic scintillator material during measurements, resulting in an elevated detection limit. Measurements of the coated detector show a resolution comparable to uncoated detectors, and a memory effect reduction of a factor of 1000. If these results are reproducible, and the quality of the detector is maintained for a longer period of time, the Al2O3 coating method is believed to be viable solution to the memory effect problem in question.
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| 9. |
- Bläckberg, Lisa, et al.
(author)
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Memory effect, resolution, and efficiency measurements of an Al2O3 coated plastic scintillator used for radioxenon detection
- 2013
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 714, s. 128-135
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Journal article (peer-reviewed)abstract
- A cylindrical plastic scintillator cell, used for radioxenon monitoring within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty, has been coated with 425 nm Al2O3 using low temperature Atomic Layer Deposition, and its performance has been evaluated. The motivation is to reduce the memory effect caused by radioxenon diffusing into the plastic scintillator material during measurements, resulting in an elevated detection limit. Measurements with the coated detector show both energy resolution and efficiency comparable to uncoated detectors, and a memory effect reduction of a factor of 1000. Provided that the quality of the detector is maintained for a longer period of time, Al2O3 coatings are believed to be a viable solution to the memory effect problem in question.
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| 11. |
- Bläckberg, Lisa
(author)
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Surface Coatings as Xenon Diffusion Barriers for Improved Detection of Clandestine Nuclear Explosions
- 2014
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Doctoral thesis (other academic/artistic)abstract
- This thesis investigates surface coatings as xenon diffusion barriers on plastic scintillators. The motivation for the work is improved radioxenon detection systems, used within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT).One type of radioxenon detection systems used in this context is the Swedish SAUNA system. This system uses a cylindrical plastic scintillator cell to measure the beta decay from radioxenon isotopes. The detector cell also acts as a container for the xenon sample during the measurement.One problem with this setup is that part of the xenon sample diffuses into the plastic scintillator material during the measurement, resulting in residual activity left in the detector during subsequent measurements. This residual activity is here referred to as the memory effect.It is here proposed, and demonstrated, that it is possible to coat the plastic scintillator material with a transparent oxide coating, working as a xenon diffusion barrier. It is found that a 425 nm Al2O3 coating, deposited with Atomic Layer Deposition, reduces the memory effect by a factor of 1000, compared an uncoated detector. Furthermore, simulations show that the coating might also improve the light collection in the detector. Finally, the energy resolution of a coated detector is studied, and no degradation is observed.The focus of the thesis is measurements of the diffusion barrier properties of Al2O3 films of different thicknesses deposited on plastic scintillators, as well as an evaluation of the expected effect of a coating on the energy resolution of the detector. The latter is studied through light transport simulations. As a final step, a complete coated plastic scintillator cell is evaluated in terms of memory effect, efficiency and energy resolution.In addition, the xenon diffusion process in the plastic material is studied, and molecular dynamics simulations of the Xe-Al2O3 system are performed in order to investigate the reason for the need for a rather thick coating to significantly reduce the memory effect.
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| 12. |
- Bläckberg, Lisa, 1982-
(author)
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Surface coatings as xenon diffusion barriers on plastic scintillators : Improving Nuclear-Test-Ban Treaty verification
- 2011
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Licentiate thesis (other academic/artistic)abstract
- This thesis investigates the ability of transparent surface coatings to reduce xenon diffusion into plastic scintillators. The motivation for the work is improved radioxenon monitoring equipment, used with in the framework of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty. A large part of the equipment used in this context incorporates plastic scintillators which are in direct contact with the radioactive gas to be detected. One problem with such setup is that radioxenon diffuses into the plastic scintillator material during the measurement, resulting in an unwanted memory effect consisting of residual activity left in the detector. In this work coatings of Al2O3 and SiO2, with thicknesses between 20 and 400 nm have been deposited onto flat plastic scintillator samples, and tested with respect to their Xe diffusion barrier capabilities. All tested coatings were found to reduce the memory effect, and 425 nm of Al2O3 showed the most promise. This coating was deposited onto a complete detector. Compared to uncoated detectors, the coated one presented a memory effect reduction of a factor of 1000. Simulations and measurements of the expected light collection efficiency of a coated detector were also performed, since it is important that this property is not degraded by the coating. It was shown that a smooth coating, with a similar refractive index as the one of the plastic, should not significantly affect the light collection and resolution. The resolution of the complete coated detector was also measured, showing a resolution comparable to uncoated detectors. The work conducted in this thesis proved that this coating approach is a viable solution to the memory effect problem, given that the results are reproducible, and that the quality of the coating is maintained over time.
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| 13. |
- Brandell, D, et al.
(author)
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Calculation of the optical absorption spectrum of ErCl3 in poly(ethylene oxide) (PEO)
- 2000
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In: INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY. - : JOHN WILEY & SONS INC. - 0020-7608. ; 80:4-5, s. 799-806
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Journal article (peer-reviewed)abstract
- The optical absorption spectrum for the rare-earth ion Er3+ in a, amorphous polymer host poly(ethylene oxide) (PEO) has been calculated. A modified Judd-Ofelt theory has been exploited to calculate the oscillator strengths for the electric-dipole transiti
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| 14. |
- Butorin, Sergei, et al.
(author)
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Effect of Ag Doping on Electronic Structure of Cluster Compounds AgxMo9Se11 (x = 3.4, 3.9)
- 2018
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:8, s. 4032-4039
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Journal article (peer-reviewed)abstract
- The electronic structure of AgxMo9Se11 as a potential material for thermoelectric applications was studied using high-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) and the resonant inelastic X-ray scattering (RIXS) technique. The experiments were supported by first-principle calculations using density functional theory (DFT). The analysis of obtained spectra indicate the presence of subvalent (less than 1+) Ag in AgxMo9Se11. The advanced HERFD-XAS measurements allowed us to resolve the contribution of the electronic states at the Fermi level of AgxMo9Se11 and to monitor its dependence on the x value. A comparison of the experimental data with the results of the DFT calculations suggests the importance of the Ag2-type sites with the shortest Ag–Se distance for affecting the properties of AgxMo9Se11.
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| 15. |
- Caleman, Carl, et al.
(author)
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Radiation damage in biological material : electronic properties and electron impact ionization in urea
- 2009
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In: Europhysics letters. - : IOP. - 0295-5075 .- 1286-4854. ; 85:1, s. 18005-
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Journal article (peer-reviewed)abstract
- Radiation damage is an unavoidable process when performing structural investigations of biological macromolecules with X-rays. In crystallography this process can be limited through damage distribution in a crystal, while for single molecular imaging it can be outrun by employing short intense pulses. Secondary electron generation is crucial during damage formation and we present a study of urea, as model for biomaterial. From first principles we calculate the band structure and energy loss function, and subsequently the inelastic electron cross-section in urea. Using Molecular Dynamics simulations, we quantify the damage and study the magnitude and spatial extent of the electron cloud coming from an incident electron, as well as the dependence with initial energy.
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| 16. |
- Costa, Marcio, et al.
(author)
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Large magnetic anisotropy of Fe2P investigated via ab initio density functional theory calculations
- 2012
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:8, s. 085125-
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Journal article (peer-reviewed)abstract
- We present an investigation of the large magnetic anisotropy of Fe2P, based on ab initio density functional theory calculations, with a full-potential linear muffin-tin orbital basis. We obtain a uniaxial magnetic anisotropy energy (MAE) of 664 mu eV/f.u., which is in decent agreement with experimental observations. Based on a band structure analysis the microscopic origin of the large magnetic anisotropy is explained. We also show that by straining the crystal structure, the MAE can be enhanced further.
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| 17. |
- de Almeida, J. S., et al.
(author)
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On the dynamical stability and metallic behavior of YH3 under pressure
- 2009
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:25, s. 251913-
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Journal article (peer-reviewed)abstract
- Wereport on the behavior of structural and electronic properties ofyttrium trihydride under pressure using first principles calculations. We showthat YH3 undergoes a structural transformation and its high pressurephase is dynamically stable under pressure since the peak atthe imaginary frequencies of the phonon density of states, whichaccount for the structural instability disappears at high pressure. Additionally,our GW calculations indicate a metallization of the high pressurecubic phase of YH3.
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| 18. |
- Derenzo, S. E., et al.
(author)
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Scintillation studies of CdS(In): effects of various semiconductor doping strategies
- 2005
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002. ; 537:1-2, s. 261-
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Journal article (peer-reviewed)abstract
- We present room-temperature photoluminescence and pulsed X-ray measurements of powder samples of CdS(In) codoped with three hole traps (Te, Ag, and Na). Te is an isoelectronic hole trap and Ag, and Na are acceptor hole traps. The emission of CdS(In) excited at 430 nm is centered at approximate to 520 nm (near the band edge) with approximate to 20 nm FWHM. The emissions from CdS(Te) and the three codoped samples are shifted to longer wavelengths and are characterized by broad emission bands peaking near 630 nm. Whereas the decay of the CdS(Te) emission is nonexponential with times > 10 its, the decay of CdS(In, Te) is 3.3 ns and exponential over three decades. The decay of the acceptor-doped samples CdS(In,Ag) and CdS(In, Na) are also fast, 2.5 and 2.8 ns, respectively. These results show the potential for developing fast inorganic scintillators based on direct-gap semiconductors that can be codoped to provide fast radiative recombination. Additional work is needed to increase the luminosity.
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| 20. |
- Edvardsson, Sverker, et al.
(author)
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The use of CI calculated polarizabilities to study rare-earth CFP dependencies in the laser host RE:YLF
- 1999
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In: Materials Science Forum. - 0255-5476. ; 315/317, s. 407-414
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Journal article (peer-reviewed)abstract
- It has earlier been shown that the Sternheimer method is appropriate in deriving crystal field parameters (CFP) for Pr3+ and Nd3+ doped in YLF or Nd3+ in YAG. In this connection, the dipole (αD) and quadrupole (αQ) polarizabilities for the whole rare-earth (RE) series will be presented. These are needed for the self consistent lattice summations performed. The various rare-earth wavefunctions needed for the computations are derived from the well known relativistic full Hartree-Fock code by R. D. Cowan. The main CFP behaviour for the various RE dopants in YLF are seen to agree fairly well with the experimentally fitted parameters. Covalency effects are, as expected, observed to be more important for higher order parameters. It is also seen that the contribution to the crystal field due to covalency is approximately constant for a given Btp. This observation is also supported by calculations of Newman. The shielding, nuclear antishielding factors and radial integrals for the whole RE series are also presented.
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| 21. |
- Edvardsson, Sverker, et al.
(author)
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Use of polarized optical absorption to obtain structural information for Na1/Nd31 b9-alumina
- 1996
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In: Physical Review B, Condensed matter. - 0163-1829. ; 54:24, s. 17476-17 485
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Journal article (peer-reviewed)abstract
- Part of the optical absorption spectrum is calculated for the Nd31-doped Na1 b9-alumina using a moleculardynamics-~MD! based approach. The Judd/Ofelt ~J/O! theory is modified ~and several approximations removed! to treat polarized transition intensities for rare-earth ions in a solid host. Stark-level energies and eigenfunctions of the ground state ~4I9/2! and excited multiplets (4F3/2,2P1/2) are also calculated for the local environments involved. Energies and polarized transition intensities between individual Stark levels are thus calculated simultaneously for several hundreds of MD-generated environments; summation gives the total bandshape. A high proportion of Beevers-Ross-site occupation ~.50%! is indicated for low Nd31 concentrations in b9-alumina. The contrary is observed experimentally for high Nd31 concentrations, i.e., then midoxygen site occupation dominates. It is demonstrated that ions in different local environments contribute differently to the absorption spectrum and, particularly, how the polarization of the various transitions changes for ions occupying different sites. Temperature dependence aspects are also considered
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| 22. |
- Fiori, G., et al.
(author)
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Simulation of hydrogenated graphene field-effect transistors through a multiscale approach
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:15, s. 153404-
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Journal article (peer-reviewed)abstract
- In this work, we present a performance analysis of field-effect transistors (FETs) based on recently fabricated 100% hydrogenated graphene (the so-called graphane) and theoretically predicted semihydrogenated graphene (i.e., graphone). The approach is based on accurate calculations of the energy bands by means of GW approximation, subsequently fitted with a three-nearest neighbor sp(3) tight-binding Hamiltonian, and finally used to compute ballistic transport in transistors based on functionalized graphene. Due to the large energy gap, the proposed devices have many of the advantages provided by one-dimensional graphene nanoribbon FETs, such as large I-on and I-on/I-off ratios, reduced band-to-band tunneling, without the corresponding disadvantages in terms of prohibitive lithography and patterning requirements for circuit integration.
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| 24. |
- Freyhult, Lisa, 1977-, et al.
(author)
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Working with context rich problems to teach problem solving
- 2017
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In: Transforming patterns through the scholarship of teaching and learning.
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Conference paper (peer-reviewed)abstract
- The ability to solve problems is an important ability for scientists as well as engineers and something we identify as a key competence for our students. Problem solving is often examined but still students complain about the difficulty of the examination, describing the problems as more difficult than the problems they have encountered previously.Our study suggests that our students often use inefficient strategies for problem solving, like pattern matching or trying to find a mathematical formula that fits the situation. It is clear that these strategies will not work and they become less and less useful the further the students get in their education.To train problem solving and to prepare students to handle unknown problems and situations cooperative problem solving and context rich problems have been identified as efficient strategies [1,2]. These methods have specifically been used in early courses in mechanics and similar experiences with open ended but shorter problems have been described in [3,4,5]. We have applied these strategies in a more advanced course in Lagrangian mechanics. Students perceive this topic as somewhat abstract and disconnected from everyday experience and lack a clear relevance to their professional role. We describe our work as a team of teachers and our experience introducing a new methodology in the course with the goal to teach in a way that discourages inefficient problem solving strategies.ReferencesHeller, P och Heller, K (2010) Cooperative Problem Solving in Physics A User’s ManualHeller, P, Keith, R och Andersson (1992), Teaching problem solving through cooperative grouping. Part 1: Group versus individual problem solving, S, Am. J. Phys. 60, 627; Heller, P och Hollabaugh, M (1992), Teaching problem solving through cooperative grouping. Part 2: Designing problems and structuring groups, Am. J. Phys. 60, 637Maloney, D., Research on problem solving in physics, in D. Gabel (ed.) (1994), Handbook of research in science teaching and learning, New YorkWedelin, D., Adawi, T., Jahan T. and Andersson, S., (2015), Investigating and developing engineering students’ mathematical modelling and problem-solving skills, European Journal of Engineering Education, 40:5, pp. 557-572Wedelin, D. och Adawi, D. (2015), Warming up for PBL: a course in mathematical modelling and problem solving for engineering students Högre utbildning Vol. 5, No. 1, pp. 23-34
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