| 1. |
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| 2. |
- Andersson, Mats R., et al.
(author)
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Regioselective polymerization of 3-(4-octylphenyl)thiophene with FeCl3
- 1994
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In: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 27:22, s. 6503-6506
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Journal article (peer-reviewed)abstract
- We have shown that it is possible to regioselectively polymerize 3-(4-octylphenyl) thiophene with FeCl3. Adding FeCl3 slowly to the monomer leads to a soft and therefore regioselective polymerization. The head-to-tail content was determined by H-1 NMR to be 94 +/- 2%. Thin films of the polymer treated with chloroform vapor have an absorption maximum at 602 nm (2.06 eV) with clear vibronic fine structure. Free standing films have a conductivity of 4 S/cm, which is 100 times higher than for earlier prepared poly(3-(4-octylphenyl)thiophene). A mechanism for the regioregular polymerization is also proposed.
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| 3. |
- Andersson, Sebastian, et al.
(author)
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Establishing epistemic practices in students’ formulation of scientifically researchable questions in upper secondary science education
- 2019
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In: NOFA7 ABSTRACTS Stockholm University, 13 - 15 May 2019. ; , s. 24-24
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Conference paper (other academic/artistic)abstract
- The development of students' capability to engage in scientific inquiry is part of the science curricula across the educational system. However, previous research shows that laboratory and practical work in science education do not necessarily develop the capability to engage in scientific inquiry or contribute to developing an understanding of the nature of inquiry. The purpose of this study is to explore how teaching activities can be designed with a specific focus to develop students' capability to formulate questions for scientific inquiry. Some science education research points to that in order for students to develop an understanding of the nature of science inquiry, teaching has to include activities explicitly focusing aspects of inquiry such as asking questions, observing and making inferences. In this study we draw on the theoretical framework of epistemic practices to analyse and design teaching with the purpose of developing students' capabilities to formulate questions for scientific inquiry. Epistemic practices refer to the ways people in a specific community propose, justify, evaluate and legitimize knowledge claims within a disciplinary framework. From this perspective, formulating scientifically researchable questions makes sense only as part of epistemic practice in relation to a motive of knowledge production. The research question is: How can epistemic practices be established in upper-secondary school science where students are invited to participate in activities of formulating researchable questions?The study was carried out as a design-based research collaboration with a research team consisting of nine science teachers and four science education researchers. Data was collected in three cycles of design, intervention and analysis of research lessons with six classes in three different upper-secondary schools. The data consists of video-recordings of student interaction while engaging in tasks of formulating researchable scientific questions. The data is analysed using the didactical model of organizing purposes; distinguishing between overarching purposes and the student-orientated purposes emerging in interaction. The results indicate that the development of students’ capabilities to formulate researchable questions is situated in the processes of interaction with peers, and the conditions for situating the formulation of questions in a practice characterised by closeness to an epistemic object and gathering of observational data. Based on the results, we argue for a shift in science education from focusing students’ views of a generic nature of science or nature of science inquiry to focussing student participation in epistemic practices of various kinds.
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| 4. |
- Andersson, Sebastian, et al.
(author)
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Students’ capabilities to formulate scientifically researchable questions in upper secondary science education
- 2019
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In: NOFA7 ABSTRACTS Stockholm University, 13 - 15 May 2019. ; , s. 25-25
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Conference paper (other academic/artistic)abstract
- A goal for science education is to develop student capabilities to participate in scientific inquiry. This includes various aspects of inquiry; formulating scientifically researchable questions as well as planning, performing, analyzing and presenting science investigations. In science education practices, there is a tradition of using practical or laboratory work to illustrate science concepts; focussing correct answers and reproduction of ready-made scientific knowledge, rather than engaging students in inquiry. Previous research shows that inquiry teaching predominantly engage students in investigating science questions as formulated beforehand by the teacher or a textbook. Little attention has been paid to what might characterize the capability of formulating scientifically researchable questions in school. In this study we draw on a theoretical framework of epistemic practices. Epistemic practices refer to the ways people in a specific community propose, justify, evaluate and legitimize knowledge claims within a disciplinary framework. From this perspective, formulating and developing scientifically researchable questions makes sense only in relation to a motive of knowledge production. The aim of this study is to explore what might characterize students’ capabilities to formulate and develop scientifically researchable questions in upper secondary science education.The collected data consists of video-recordings of student interaction in group-work focussing formulating and developing scientifically researchable questions. Data was collected as part of a design-based study with six classes in three different schools. The video-recordings were transcribed in verbatim and analysed by the means of qualitative content analysis. The preliminary results suggest three themes: Formulation of scientifically researchable questions as:1) Working with the specification of the epistemic object. The theme illustrates how the students elaborated on the meaning of related scientific concepts and discussed cause and effect. 2) Specifying researchability by focussing on how to operationalize the epistemic object. The theme illustrates how the students reformulate their questions as part of a process of discussing e.g. measurability and variables.3) Making value-judgements of epistemic objects. The theme illustrates how the students distinguish between scientific and non-scientific questions and make value-judgements about relevance. The results contribute to an understanding of what the capability to engage in scientific inquiry as participation in collective epistemic work in an upper-secondary school science classroom might entail. The themes are related to the establishing of a specific scientific epistemic object. The results are discussed in relation to previous research in science education and the development of resources for teaching inquiry framing capabilities of inquiry as generic.
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| 5. |
- Berggren, Magnus, et al.
(author)
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Controlling colour by voltage in polymer light emitting diodes
- 1995
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In: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2185-2186
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Journal article (peer-reviewed)abstract
- We report electroluminescence using different substituted polythiophenes as the emitting mterial. Different substituents cause different sterical interacion which force the thiophene rings out of planarity. This results in different bandgaps. Colours from blue to near infrared have been demonstrated in electroluminescent devices. We also demonstrate voltage controlled electroluminescence using mixtures of these polymers.
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| 6. |
- Berggren, Magnus, et al.
(author)
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Green Electroluminescence in Poly-(3-cyclohexylthiophene) light-emitting diodes
- 1994
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In: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 6:6, s. 488-490
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Journal article (peer-reviewed)abstract
- Electoluminescent devices based on polythiophene-system this films have been demonstrated that together span the entire visible range, steric hindrance being used to vary the bandgap between compunds. Poly-(3-cyclohexylthiophene), see Figures, exhibits green electoluminescence. Possible interpretations of this observation are proposed.
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| 7. |
- Berggren, Magnus, et al.
(author)
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Thermal control of near‐infrared and visible electroluminescence in alkyl‐phenyl substituted polythiophenes
- 1994
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In: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 65:12, s. 1489-1491
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Journal article (peer-reviewed)abstract
- We report electroluminescence from a regioregular alkyl-phenyl substituted polythiophene. The polymer film exists in two forms, giving widely different optical absorption, as well as photoluminescence and electroluminescence spectra. In the low-bandgap form, we observe high emission intensity centered at 1.55 eV (800 nm), well into the infrared, while the high-bandgap form gives a maximum at 1.85 eV (670 nm). The conversion from the high-bandgap form to the low-bandgap form can be done by thermal treatment of the polymer light emitting diodes.
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| 8. |
- Dyreklev, Peter, et al.
(author)
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Polarized electroluminescence from an oriented substituted polythiophene in a light emitting diode
- 1995
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In: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 7:1, s. 43-45
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Journal article (peer-reviewed)abstract
- Polarized light sources based on stretch-oriented conjugated polymers are reported. The devices, based on poly 3(4-octylphenyl)-2,2′-bithiophene, show an external quantum efficiency of 0.1% and are produced using a very simple method which may be easily extended to other polymers. The fabrication of the devices is described and factors such as the emission and spectral differences parallel and prependicular to the stretching direction discussed.
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| 9. |
- Hansson, Sverker, 1946, et al.
(author)
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Dimercapto-succinic acid scintigraphy instead of voiding cystourethrography for infants with urinary tract infection.
- 2004
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In: The Journal of urology. - : Ovid Technologies (Wolters Kluwer Health). - 0022-5347 .- 1527-3792. ; 172:3
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Journal article (peer-reviewed)abstract
- PURPOSE: We study the ability of dimercapto-succinic acid (DMSA) scintigraphy to predict the presence of dilating vesicoureteral reflux (VUR) in infants with urinary tract infection (UTI) to simplify the evaluation protocol. MATERIALS AND METHODS: A retrospective analysis of the records of 303 children younger than 2 years with initial UTI investigated with DMSA scintigraphy and voiding cystourethrography (VCU) within 3 months after UTI was performed. RESULTS: In 156 of the 303 children (51%) DMSA scintigraphy showed renal lesions. VUR was found in 80 patients (26%) and VUR grade significantly correlated with the presence of renal lesions. A normal DMSA scintigraphy and dilating VUR (grade III) occurred in 7 infants. At followup after 1 to 2 years, 6 of these 7 patients had normal DMSA scans and 1 had a scarred duplex kidney. VUR resolved spontaneously in 5 and improved spontaneously to grade 1 in 2 patients. None of the 7 children had recurrent UTI. CONCLUSIONS: DMSA scintigraphy in infants with UTI may replace VCU as a first line investigation. A strategy to perform VCU in only patients with renal lesions is proposed. In this study 147 of 303 VCUs would have been unnecessary as only 1 child with a damaged kidney was missed.
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| 10. |
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| 11. |
- Planting-Bergloo, Sara, 1978-, et al.
(author)
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Att utveckla elevers förmåga att formulera undersökningsbara frågor i naturvetenskap : Mangling av en didaktisk modell
- 2021
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In: LUMAT. - : LUMA Centre Finland. - 2323-7112. ; 9:1, s. 774-803
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Journal article (peer-reviewed)abstract
- En viktig målsättning för naturvetenskaplig undervisning är att utveckla förmågan att formulera undersökningsbara frågor. Syftet med den här studien är att undersöka hur undervisning som utformats med hjälp av metoden Question Formulation Technique (QFT) kan stödja utveckling av elevers förmåga att formulera naturvetenskapligt undersökningsbara frågor. QFT är en modell för att utveckla elevers förmåga att formulera och värdera sina egna frågor i allmänhet. I studien prövas QFT i en svensk skolkontext och inom ramen för naturvetenskaplig undervisning. Studien genomfördes som en interventionsstudie i gymnasieskolan och inom ramen för kursen Gymnasiearbete. I kursen ska eleverna genomföra en egen naturvetenskaplig undersökning. QFT användes för att utforma undervisning som del av introduktionen till kursen. Data består av videoinspelningar av elevsamtal från undervisning som har analyserats utifrån ett pragmatiskt ramverk med organiserande syften och praktisk epistemologisk analys. Resultaten visar vilka närliggande syften som etableras i elevernas samtal om undersökningsbara frågor i undervisningen: (A) att producera så många frågor som möjligt, (B) att bedöma vilka frågor som är mest relevanta, (C) att kategorisera frågor, (D) att hitta och specificera ett undersökningsobjekt och (E) att planera för att genomföra en undersökning. Slutsatsen är att QFT kan fungera som stöd för lärares planering av undervisning om naturvetenskapligt undersökningsbara frågor under förutsättning att läraren aktivt stödjer eleverna i att uppmärksamma centrala kvaliteter avseende undersökningsbarhet och genom att binda samman närliggande syften med det övergripande syftet.
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| 12. |
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| 13. |
- Wennerström, Hjalmar, 1984-, et al.
(author)
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A Long-Term Study on the Effects of Meteorological Conditions on 802.15.4 Links
- 2012
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In: 8th Swedish National Computer Networking Workshop, Stockholm, June 7-8.
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Conference paper (peer-reviewed)abstract
- Remote monitoring of natural phenomena using wireless sensor networks requires these networks to successfully operate while being exposed to the surrounding environment. Weather conditions are an essential aspect of the environment, therefore it is important to understand the effects of weather on sensor networks. This understanding is especially important since weather varies strongly over time and affects the communication between sensor nodes. In our ongoing work we study how different meteorological conditions influence radio links in outdoor wireless sensor networks that use IEEE 802.15.4 for communication. We deploy an experimental setup next to a meteorological research station and aim to run experiments over several months in order to capture both short- and long-term changes in the link characteristics. We show some initial measurements of the deployment, highlighting influences on packet reception rate and signal strength.
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| 14. |
- Wennerström, Håkan, et al.
(author)
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A Quantum Description of the Stern–Gerlach Experiment
- 2017
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In: Entropy. - Basel : MDPI. - 1099-4300. ; 19:5
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Journal article (peer-reviewed)abstract
- A detailed analysis of the classic Stern–Gerlach experiment is presented. An analytical simple solution is presented for the quantum description of the translational and spin dynamics of a silver atom in a magnetic field with a gradient along a single z-direction. This description is then used to obtain an approximate quantum description of the more realistic case with a magnetic field gradient also in a second y-direction. An explicit relation is derived for how an initial off center deviation in the y-direction affects the final result observed at the detector. This shows that the “mouth shape” pattern at the detector observed in the original Stern–Gerlach experiment is a generic consequence of the gradient in the y-direction. This is followed by a discussion of the spin dynamics during the entry of the silver atom into the magnet. An analytical relation is derived for a simplified case of a field only along the z-direction. A central question for the conceptual understanding of the Stern–Gerlach experiment has been how an initially unpolarized spin ends up in a polarized state at the detector. It is argued that this can be understood with the use of the adiabatic approximation. When the atoms first experience the magnetic field outside the magnet, there is in general a change in the spin state, which transforms from a degenerate eigenstate in the absence of a field into one of two possible non-degenerate states in the field. If the direction of the field changes during the passage through the device, there is a corresponding adiabatic change of the spin state. It is shown that an application of the adiabatic approximation in this way is consistent with the previously derived exact relations.
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| 15. |
- Wennerström, Håkan, et al.
(author)
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On Stern-Gerlach coincidence measurements and their application to Bell's theorem
- 2013
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In: Physics Essays. - Ottawa : Physics Essays Publication. - 0836-1398. ; 26:2, s. 174-180
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Journal article (peer-reviewed)abstract
- We analyze a coincidence Stem-Gerlach measurement often discussed in connection with the derivation and illustration of Bell's theorem. The treatment is based on our recent analysis of the original Stern-Gerlach experiment [H. Wennerstrom and P.-O. Westlund, Phys. Chem. Chem. Phys. 14, 1677 (2012)1, where it is concluded that it is necessary to include a spin relaxation process to account for the experimental observations. We consider two limiting cases of a coincidence measurement using both an analytical and a numerical description. In one limit, relaxation effects are neglected. In this case, the correlation between the two spins present in the initial state is conserved during the passage through the magnets. However, at exit the z-coordinate along the magnetic field gradient is randomly distributed between the two extreme values. In the other limit, T-2 relaxation is assumed to be fast relative to the time of flight through the magnet. In this case, the z-coordinate takes one of two possible values as observed in the original Stern-Gerlach experiment. Due to the presence of a relaxation process involving transfer of angular momentum between particle and magnet, the initially entangled spin state changes character leading to a loss of correlation between the two spins. In the original derivations of Bell's theorem based on a coincidence Stem-Gerlach setup, one assumes both a perfect correlation between the spins and only two possible values for the z-coordinate on exit. According to the present calculations, one can satisfy either of these conditions but not both simultaneously. (C) 2013 Physics Essays Publication.
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| 16. |
- Wennerström, Håkan, et al.
(author)
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The Stern-Gerlach experiment and the effects of spin relaxation
- 2012
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In: Physical Chemistry, Chemical Physics - PCCP. - : RSC Publishing. - 1463-9076 .- 1463-9084. ; 14, s. 1677-1684
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Journal article (peer-reviewed)abstract
- The classical Stern-Gerlach experiment is analyzed with an emphasis on the spin dynamics. The central question asked is whether there occurs a relaxation of the spin angular momentum during the time the particle passes through the Stern-Gerlach magnet. We examine in particular the transverse relaxation, involving angular momentum exchange between the spin of the particles and the spins of the magnet. A method is presented describing relaxation effects at an individual particle level. This leads to a stochastic equation of motion for the spins. This is coupled to a classical equation of motion for the particle translation. The experimental situation is then modeled through simulations of individual trajectories using two sets of parameter choices and three different sets of initial conditions. The two main conclusions are: (A) if the coupling between the magnet and the spin is solely described by the Zeeman interaction with the average magnetic field the simulations show a clear disagreement with the experimental observation of Stern and Gerlach. (B) If one, on the other hand, also allows for a T(2) relaxation time shorter than the passage time one can obtain a practically quantitative agreement with the experimental observations. These conclusions are at variance with the standard textbook explanation of the Stern-Gerlach experiment.
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| 17. |
- Westlund, Per-Olof, et al.
(author)
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Disentanglement of a Singlet Spin State in a Coincidence Stern-Gerlach Device
- 2019
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In: Journal of Modern Physics. - : Scientific Research Publishing, Inc.. - 2153-1196 .- 2153-120X. ; 10:10, s. 1247-1254
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Journal article (peer-reviewed)abstract
- We analyze the spin coincidence experiment considered by Bell in the derivation of Bells theorem. We solve the equation of motion for the spin system with a spin Hamiltonian, Hz, where the magnetic field is only in the z-direction. For the specific case of the coincidence experiment where the two magnets have the same orientation the Hamiltonian Hz commutes with the total spin Iz, which thus emerges as a constant of the motion. Bells argument is then that an observation of spin up at one magnet A necessarily implies spin down at the other B. For an isolated spin system A-B with classical translational degrees of freedom and an initial spin singlet state there is no force on the spin particles A and B. The spins are fully entangled but none of the spin particles A or B are deflected by the Stern-Gerlach magnets. This result is not compatible with Bells assumption that spin 1/2 particles are deected in a Stern-Gerlach device. Assuming a more realistic Hamiltonian Hz + Hx including a gradient in x direction the total Iz is not conserved and fully entanglement is not expected in this case. The conclusion is that Bells theorem is not applicable to spin coincidence measurement originally discussed by Bell.
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| 18. |
- Westlund, Per-Olof, 1952-, et al.
(author)
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Electron spin relaxation at low field
- 2010
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 12:1, s. 201-206
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Journal article (peer-reviewed)abstract
- The low field ESR lineshape and the electron spin-lattice relaxation correlation function are calculated using the stochastic Liouville theory for an effective electron spin quantum number S = 1. When an axially symmetric permanent zero field splitting provides the dominant relaxation mechanism, and when it is much larger than the rotational diffusion constant, it is shown that both electron spin correlation functions S(0)S(t) (n = 0,1) are characterized by the same relaxation time tau(S) = (4D(R))(-1). This confirms the conjectures made by Schaefle and Sharp, J. Chem. Phys., 2004, 121, 5287 and by Fries and Belorizky, J. Chem. Phys., 2005, 123, 124510, based on numerical results using a different formalism. The stochastic Liouville approach also gives the paramagnetically enhanced nuclear spin relaxation time constants, T(1) and T(2), and the ESR lineshape function I(omega). In particular, the L-band (B(0) = 0.035 T) ESR spectrum of a low symmetry Ni(ii)-complex with a cylindrical ZFS tensor is shown to be detectable at sufficiently slowly reorientation of the complex. The analysis shows that the L-band spectrum becomes similar to the zero-field spectrum with a electron spin relaxation time tau(S) = (4D(R))(-1).
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| 19. |
- Westlund, Per-Olof, et al.
(author)
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Photon emission from translational energy in atomic collisions: A dynamic Casimir-Polder effect
- 2005
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In: PHYSICAL REVIEW A. - 1050-2947. ; A 71:062106, s. 1-5
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Journal article (peer-reviewed)abstract
- It is demonstrated, using a Liouville formalism, that the relative motion of two atoms can result in the emission of photons and conversely that photons can be absorbed to excite the relative translational motion. The mechanism responsible for the energy transfer between the radiation field and the translational motion of the atoms is a dynamic version of the long-range Casimir-Polder interaction between two fixed atoms. The phenomenon is analogous to the dynamic Casimir effect discussed for moving macro- (or meso)scopic objects and we term it the dynamic Casimir-Polder effect. The absorption or emission is a two-photon process and we find that the transition probability is proportional to the spectral density of a correlation function involving the relative translational motion of two atoms. An energy transfer only occurs for photons with energies smaller than or of the same magnitude as the thermal energy. The effect provides a microscopic mechanism for establishing thermal equilibrium between the radiation field and a gas. A sufficiently large volume of gas would be perceived as a black-body radiator. Applications of the dynamic Casimir-Polder effect might be found in the microscopic description of the cosmic low-temperature black-body radiation.
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