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- Amloy, Supaluck, et al.
(författare)
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Excitons and biexcitons in InGaN quantum dot like localization centers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Indium segregation in a narrow InGaN single quantum well creates quantum dot (QD) like exciton localization centers. Cross section transmission electron microscopy reveals varying shapes and lateral sizes in the range ~1-5 nm of the QD-like features, while scanning near field optical microscopy demonstrates a highly inhomogeneous spatial distribution of optically active individual localization centers. Microphotoluminescence spectroscopy confirms the spectrally inhomogeneous distribution of localization centers, in which the exciton and the biexciton related emissions from single centers of varying geometry could be identified by means of excitation power dependencies. Interestingly, the biexciton binding energy (Ebxx) was found to vary from center to center, between 3 to -22 meV, in correlation with the exciton emission energy. Negative binding energies justify the three-dimensional quantum confinement, which confirms QD-like properties of the localization centers.! The observed energy correlation is proposed to be understood as variations of the lateral extension of the confinement potential, which would yield smaller values of Ebxx for reduced lateral extension and higher exciton emission energy. The proposed relation between lateral extension and Ebxx is further supported by the exciton and the biexciton recombination lifetimes of a single QD, which suggest a lateral extension of merely ~3 nm for a QD with strongly negative Ebxx = -15.5 meV.
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- Grönberg, Fredrik, et al.
(författare)
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Dimensionality and Background Cancellation in Energy Selective X-Ray Imaging
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Purpose: The set of linear attenuation coefficients that belong to materials in the human body is commonly assumed to be spanned by two basis functions in the range of clinical x-ray energies, even though there is evidence that the dimensionality of this set is greater than two. It has not yet been clear that the use of a third basis function could be beneficial in absence of contrast agents.Approach: In this work, the choice of the number of basis functions used in the basis decomposition method is studied for the task of producing an image where a third material is separated from a background of two other materials, in a case where none of the materials have a K-edge in the range of considered x-ray energies (20-140 keV). The case of separating iron from mixtures of liver and adipose tissue is studied with a simulated phantom which incorporates random and realistic tissue variability.Results: Inclusion of a third basis function improves the quantitative estimate of iron concentration by several orders of magnitude in terms of mean squared error in the resulting image.Conclusions: The inclusion of a third basis function in the basis decomposition is essential for the studied imaging task and could have potential application for quantitative estimation of iron concentration from material decomposed images.
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- Heljedal, Martin, et al.
(författare)
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Attitudes towards rail transportation among Swedish companies
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Rail freight, and consequently multimodal (where two or more transport modes are combined) road-and-rail transportation, constituted 15% of the total tonne-kilometres in the EU during 2009, to be compared to road transportation at 74%. In Sweden the numbers are slightly more in favour of rail transportation, but still a small share despite the fact that the European Committee promotes sustainable modes of transport. To reduce the environmental impact from the transport sector, and be able to promote the use of sustainable transport modes, it is important to gain an understanding of why the modal balance is disposed this way. A survey was used to contact 665 companies in central Sweden regarding their attitude towards transportation involving rail. The unfamiliarity regarding the attributes of rail transportation was surprisingly vast among respondents, while the required transhipment between modes was considered the most negative characteristic, since many companies believed that this creates extra costs and increased door-to-door time. The lesser environmental impact was the best known characteristic and also what respondents claimed would be the reason for them to consider this mode of transport. The distilled results of the study informs academy, policy makers and practitioners about the lack of knowledge regarding rail transportation and the specific aspects that the industry must put effort into improving if rail transportation are to be considered a advantageous option.
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