| 95091. |
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| 95092. |
- Johansson, Jan, 1961
(författare)
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Bengalisk deg
- 1995
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Ingår i: Sydasien. - 0282-0463. ; :4
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 95093. |
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| 95094. |
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| 95095. |
- Johansson, Jan, 1961
(författare)
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Bland spindlar och människor
- 1997
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Ingår i: Göteborgs Posten. ; :1997.11.08
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 95096. |
- Johansson, Jens, et al.
(författare)
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Brain diffusion MRI with multiplexed sensitivity encoding for reduced distortion in a pediatric patient population
- 2022
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Ingår i: Magnetic Resonance Imaging. - : Elsevier BV. - 0730-725X. ; 87, s. 97-103
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Tidskriftsartikel (refereegranskat)abstract
- Background: Diffusion-weighted imaging (DWI) is a valuable tool for routine imaging of the pediatric brain. However, the commonly used single-shot (ss) echo-planar imaging (EPI) DWI sequence is prone to geometric distortions and T2*-blurring. This study aimed to investigate in a pediatric population the benefits of using multiplexed sensitivity-encoding (MUSE) without and with reversed polarity gradients (RPG) instead. Methods: This retrospective study compared image quality, geometric distortions, and diffusion values between three different approaches for DWI (ssEPI, MUSE, and RPG-MUSE) in 14 patients (median age = 4 (0.6–15) years, 11 males). Distortion levels were quantified and compared in two brain regions, i.e., the brain stem and the temporal lobes, using the Dice Coefficient and the Hausdorff Distance, with T2-weighted images as reference. Expected geometrical distortion was further evaluated by comparing the effective echo spacing between the DWI sequences. Apparent diffusion coefficient (ADC) values were determined in the genu of the corpus callosum and the optic nerves. Two raters graded overall image quality and image distortions on a Likert scale. Results: Distortion levels assessed with Dice coefficient and Hausdorff distance were significantly lower for MUSE (p < 0.05) and RPG-MUSE (p < 0.01) compared to ssEPI. No significant difference in ADC values was observed between methods. The RPG-MUSE method was graded by one rater as significantly higher in overall image quality than ssEPI (p < 0.05) and by both raters as significantly lower in levels of image distortions than both MUSE (p < 0.05) and ssEPI (p < 0.05). These results were in agreement with the reduced effective echo spacing was that was attained with MUSE and RPG-MUSE. Conclusion: For imaging of the pediatric brain, MUSE and even more so RPG-MUSE offers both improved geometric fidelity and image quality compared to ssEPI. © 2022 The Authors
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| 95097. |
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| 95098. |
- Johansson, Jonas, et al.
(författare)
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Diffuse gas in retired galaxies: nebular emission templates and constraints on the sources of ionization
- 2016
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 461:4, s. 4505-4516
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Tidskriftsartikel (refereegranskat)abstract
- We present emission-line templates for passively-evolving ('retired') galaxies, useful for investigation of the evolution of the interstellar medium in these galaxies, and characterization of their high-temperature source populations. The templates are based on high signal-to-noise (> 800) co-added spectra (3700-6800 angstrom) of similar to 11 500 gas-rich Sloan Digital Sky Survey galaxies devoid of star formation and active galactic nuclei. Stacked spectra are provided for the entire sample and sub-samples binned by mean stellar age. In our previous paper, Johansson et al., these spectra provided the first measurements of the He II 4686 angstrom line in passively-evolving galaxies, and the observed He II/H beta ratio constrained the contribution of accreting white dwarfs (the 'single-degenerate' scenario) to the Type Ia supernova rate. In this paper, the full range of unambiguously detected emission lines are presented. Comparison of the observed [OI] 6300 angstrom/H alpha ratio with photoionization models further constrains any high-temperature single-degenerate scenario for Type Ia supernovae (with 1.5 less than or similar to T/10(5) K less than or similar to 10) to less than or similar to 3-6 per cent of the observed rate in the youngest age bin (i.e. highest SN Ia rate). Hence, for the same temperatures, in the presence of an ambient population of post-asymptotic giant branch stars, we exclude additional high-temperature sources with a combined ionizing luminosity of approximate to 1.35 x 10(30) L-circle dot/M-circle dot,(*) for stellar populations with mean ages of 1-4 Gyr. Furthermore, we investigate the extinction affecting both the stellar and nebular continuum. The latter shows about five times higher values. This contradicts isotropically distributed dust and gas that renders similar extinction values for both cases.
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| 95099. |
- Johansson, Jens
(författare)
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Diffusion MRI: Aspects of Reproducibility and Novel Segmented 2D and 3D Approaches for Higher Resolution and Geometric Fidelity
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diffusion-weighted imaging (DWI) is a very useful tool for non-invasive imaging and clinical investigation of the human body. It provides data of the water diffusion process. Applied to biological tissues in a clinical setting it provides information that can aid diagnosis and characterization of lesions, as well as longitudinal monitoring of disease, mapping of fiber architecture for surgical planning, and much more. While DWI is a valuable clinical tool, it suffers from several limitations such as low spatial resolution, image distortion and inaccurate quantification of the diffusion process. These limitations prevent the DWI method to reach its full clinical potential. The work presented in this thesis aims to investigate limitations associated with DWI and develop novel methods to reduce them. The first study compared a new multi-shot DWI method called MUSE to a conventional single-shot approach in a clinical setting for a pediatric population (n=14). Improved resolution, geometric fidelity and image quality was demonstrated using MUSE, both with and without a method termed reverse polarity gradient acquisition. The second study investigated the influence of acquisition parameters on the apparent diffusion coefficient (ADC) using the standard clinical PGSE sequence on a modern clinical scanner with high gradient performance. Diffusion time, echo time and gradient amplitude dependence of the ADC was explored in healthy brain (n=10) and in brain tumors (n=10). Only minor ADC changes were observed in healthy tissue at group level. For tumors, however, the observed ADC changes with diffusion-time and/or echo time exceeded the repeatability coefficient in several individual subjects. This suggests that such dependencies should be considered when using the ADC as a quantitative biomarker. Even though considerable effort has been devoted by others to improve the image resolution and geometric fidelity in DWI, there is still improvement needed to reach the overall quality that is considered the standard in conventional T1- and T2-weighted imaging. The third and fourth study aimed to develop and test a novel DWI approach for 3D-DWI in healthy brain. A 3D imaging approach allows for high isotropic spatial resolution at superior signal-to-noise ratio (SNR) compared to its 2D counterpart. In Study III, single thick-slab 3D-DWI was demonstrated using motion-compensated diffusion encoding gradients to minimize shot-to-shot motion induced phase errors at the source. In Study IV, this sequence was further improved by incorporating three orthogonal 1D phase navigators to monitor and correct for phase variations stemming from higher order motion terms.
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| 95100. |
- Johansson, Jan-Erik, et al.
(författare)
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Att skriva och lösa problem i grundskolans tre första årskurser. : Uppföljning av en försöksverksamhet i förskolan
- 1997
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Ingår i: Paper presenterat vid Nordisk förening för pedagogisk forskning (NFPF) Jubileumskongress, Göteborg, 6-9 mars.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Under åren 1991-1992 deltog 77 barn i en förskoleverksamhet som arbetade enligt en fenomenografiskt inspirerad pedagogik vid sex förskolor, med tonvikt lagd på att utveckla barns tänkande och förståelse för olika fenomen omvärlden. När dessa barn slutade i förskolan följdes huvuddelen av dem in skolan genom ett projekt kallat "Att möta skolans värld", finansierat av Skolverket. Syftet med projektet var dels att beskriva och utvärdera barns möte med skolans värld, dels att studera hur barn som gått i en "traditionell", dvs den vanligast förekommande förskoleverksamheten respektive hur barn som deltagit i en fenomenografiskt inspirerad förskoleverksamhet klarar skolan. Barnen har följts genom observationer och intervjuer. I slutet av årskurs 1, årskurs 2 och årskurs 3 har barnen deltagit i ett flertal kunskapsprov. Genom kunskapsproven har man sökt ta reda på hur barnen som deltagit i den försöksverksamheten klarar några ämnen i skolan i jämförelse med sina klasskamrater som fungerar som kontrollgrupp. I detta bidrag kommer resultat från barnens färdigheter inom matematik och skrivning att redovisas och diskuteras. Inom området skrivning uppvisar flickorna bättre resultat än pojkarna både inom försöksgruppen och kontrollgruppen. Samma tendens kan observeras även inom de matematiska färdigheterna även om skillnaderna via en statisktisk prövning visar sig vara relativt små. I provresultaten från kunskapsproven i matematisk problemlösning i årskurs 1 och 2 uppvisar barnen från försöksverksamheten generellt bättre resultat än barnen från kontrollgruppen. I årskurs 3 har denna skillnad ebbat ut.
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