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- Berggren, Magnus, et al.
(författare)
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Controlling inter-chain and intra-chain excitations of a poly(thiophene) derivative in thin films
- 1999
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Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 304:1-2, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- The decay of photoexcitations in polythiophene chains has been studied in solid solutions of the polymer from room temperature to 4 K. A strong blue shift of the emission spectrum is observed in the polymer blend, as compared to the homopolymer. Dispersion of the polythiophene suppresses the non-radiative processes, which are suggested to be correlated to close contacts of polymer chains. Quantum chemistry modeling of the excited state distributed on two chains corroborate this conclusion.
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| 4. |
- Fagerström, Daniel, 1965-
(författare)
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Spatio-Temporal Scale-Space Theory
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses two important topics in developing a systematic space-time geometric approach to real-time, low-level motion vision. The first one concerns measuring of image flow, while the second one focuses on how to find low level features. We argue for studying motion vision in terms of space-time geometry rather than in terms of two (or a few) consecutive image frames. The use of Galilean Geometry and Galilean similarity geometry for this purpose is motivated and relevant geometrical background is reviewed. In order to measure the visual signal in a way that respects the geometry of the situation and the causal nature of time, we argue that a time causal Galilean spatio-temporal scale-space is needed. The scale-space axioms are chosen so that they generalize popular axiomatizations of spatial scale-space to spatio-temporal geometries. To be able to derive the scale-space, an infinitesimal framework for scale-spaces that respects a more general class of Lie groups (compared to previous theory) is developed and applied. Perhaps surprisingly, we find that with the chosen axiomatization, a time causal Galilean scale-space is not possible as an evolution process on space and time. However, it is possible on space and memory. We argue that this actually is a more accurate and realistic model of motion vision. While the derivation of the time causal Galilean spatio-temporal scale-spaces requires some exotic mathematics, the end result is as simple as one possibly could hope for and a natural extension of spatial scale-spaces. The unique infinitesimally generated scale-space is an ordinary diffusion equation with drift on memory and a diffusion equation on space. The drift is used for velocity adaption, the "velocity adaption" part of Galilean geometry (the Galilean boost) and the temporal scale-space acts as memory. Lifting the restriction of infinitesimally generated scale spaces, we arrive at a new family of scale-spaces. These are generated by a family of fractional differential evolution equations that generalize the ordinary diffusion equation. The same type of evolution equations have recently become popular in research in e.g. financial and physical modeling. The second major topic in this thesis is extraction of features from an image flow. A set of low-level features can be derived by classifying basic Galilean differential invariants. We proceed to derive invariants for two main cases: when the spatio-temporal gradient cuts the image plane and when it is tangent to the image plane. The former case corresponds to isophote curve motion and the later to creation and disappearance of image structure, a case that is not well captured by the theory of optical flow. The Galilean differential invariants that are derived are equivalent with curl, divergence, deformation and acceleration. These invariants are normally calculated in terms of optical flow, but here they are instead calculated directly from the the spatio-temporal image.
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| 5. |
- Hagell, Peter, et al.
(författare)
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Measurement properties of the Minimal Insomnia Symptom Scale (MISS) as an insomnia screening tool among adults and the elderly
- 2015
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Ingår i: The 6th International Conference on Probabilistic Models for Measurement in Education.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Background: The Minimal Insomnia Symptom Scale (MISS) has been suggested as a brief 3-item screening tool for detecting insomnia. Each item has an ordered 5-category (0-4) response scale and the instrument yields a total score between 0-12 (higher scores = more insomnia). Available MISS evaluations have been based on classical test theory (CTT) approaches. Different cut-offs for identifying insomnia have been suggested for adults (aged 20-64) and elderly (aged 65+). For adults, a cut-off of ≥6 has been suggested, while a cut-off of ≥7 has been suggested for the elderly, as determined from applications of the Youden index. Aim: To test the measurement properties of the MISS using the Rasch measurement model, with special emphasis on Differential Item Functioning (DIF) by age, and to explore implications for the two suggested cut-off scores. Design: Cross-sectional MISS data from adult (n=1075) and elderly (n=548) populations were analysed by the unrestricted polytomous Rasch measurement model using the RUMM2030 software program. To avoid an inflated type I error rate, sample size was algebraically adjusted to 500 in the calculation of P-values while leaving all other aspects of data (e.g., locations, fit residuals) unaltered. Results: Mean person location was -1.095 (SD, 1.28), i.e. items tend to represent more severe levels of insomnia than that experienced by the sample. However, for the purpose of screening this may be considered acceptable. There were no statistically significant deviations from model expectations, with a non-significant overall item-trait interaction (χ2 = 26.94, P=0.173). Reliability (PSI) was 0.59 suggesting that the MISS can separate approximately two statistically distinct groups of people (1.92 strata). The highest Information Function (IF) was found at -0.2 logits. There were no disordered response category thresholds. There was uniform DIF by age for all three items, which disappeared following adjustment (split by age group) for the most pronounced DIF, suggesting that DIF was artificial for two items. Examination of raw scores-to-location estimates between the two age groups revealed differences at the lower and higher ends of the scale. The raw score cut-off of ≥6 was associated with a smaller logit difference between age groups than the ≥7 cut-off (0.09 vs. 0.23). That is, at a raw score of 6 the two age groups were comparable regarding their logit location estimates. This raw score (representing a logit value of -0.03 for the pooled sample) was also the one closest to the location of the highest IF (i.e., -0.2 logits). Summary and implications: This study provides general support for the measurement properties of the MISS. However, caution should be exercised in comparing MISS scores between age groups, but applying a ≥6 raw score cut-off appears to allow for valid comparisons between adults and elderly regarding the presence of insomnia. Nevertheless, additional studies are needed to determine the clinically optimal cut-score for identification of insomnia.
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- Westerberg, Håkan, et al.
(författare)
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Modeling the drift of European (Anguilla anguilla) and American (Anguilla rostrata) eel larvae during the year of spawning
- 2018
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 75, s. 224-234
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Tidskriftsartikel (refereegranskat)abstract
- © 2018, Canadian Science Publishing. All rights reserved. The distribution of the leptocephalus larvae of European (Anguilla anguilla) and American (Anguilla rostrata) eels collected during recent Sargasso Sea surveys was used to model larval drift. The drift trajectories of individual larva were back-calculated to the estimated time of spawning, using current data from two global oceanographic assimilation models. The results of both models give the same overall result; widespread spawning extended in time from December to March. The drift was also calculated forwards for approximately 1 year. The forward drift modelling showed that most leptocephali remained in the area south of the Subtropical Frontal Zone. One conclusion is that the majority of leptocephali remain trapped and possibly die in the retention area. A small proportion of leptocephali are entrained into the Gulf Stream system. An implication is that the spawning success may be highly sensitive to oceanographic and climatic factors that alter the dispersion of leptocephali out from the retention area. An alternative interpretation is that the surveys were made too late after the peak spawning period and that the core spawning area was missed.
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| 7. |
- Westergren, Albert, et al.
(författare)
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Measurement properties of the minimal insomnia symptom scale as insomnia screening tool for adults and the elderly
- 2015
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Ingår i: Sleep Medicine. - : Elsevier. - 1389-9457 .- 1878-5506. ; 16:3, s. 379-384
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Tidskriftsartikel (refereegranskat)abstract
- Background The psychometric properties of the three-item Minimal Insomnia Symptom Scale (MISS) were evaluated using the classical test theory. Different cut-offs for identifying insomnia were suggested in two age groups (≥6 and ≥7 among adult and elderly people, respectively). The aim of the present study was to test the measurement properties of the MISS using the Rasch measurement model, with special emphasis on differential item functioning by gender and age. Methods Cross-sectional MISS data from adult (age 20–64 years, n = 1075) and elderly (age 65+, n = 548) populations were analysed using the Rasch measurement model. Results Data generally met Rasch model requirements and the scale could separate between two distinct groups of people. Differential item functioning was found by age but not gender. The difference between the adult and elderly samples was lower for the originally recommended ≥6 points cut-off (0.09 logits) than for the ≥7 points cut-off (0.23 logits), but greater at the lower and higher ends of the scale. Conclusions This study provides general support for the measurement properties of the MISS. Caution should be exercised in comparing raw MISS scores between age groups, but applying a ≥6 cut-off appears to allow for valid comparisons between adults and the elderly regarding the presence of insomnia. Nevertheless, additional studies are needed to determine the clinically optimal cut-score for identification of insomnia.
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| 8. |
- Westergren, Albert, et al.
(författare)
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Measurement properties of the Minimal Insomnia Symptom Scale (MISS) as an insomnia screening tool among adults and the elderly
- 2015
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Ingår i: Sleep Medicine. - : Elsevier BV. - 1389-9457 .- 1878-5506. ; 16:3, s. 379-384
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Tidskriftsartikel (refereegranskat)abstract
- Background: The psychometric properties of the 3-item Minimal Insomnia Symptom Scale (MISS) have been evaluated using classical test theory. Different cut-offs for identifying insomnia have been suggested in two age groups (≥6 and ≥7 among adult and elderly people, respectively). The aim of this study was to test the measurement properties of the MISS using the Rasch measurement model, with special emphasis on differential item functioning by gender and age.Methods: Cross-sectional MISS data from adult (age 20-64 years; n=1075) and elderly (age 65+; n=548) populations were analysed by the Rasch measurement model.Results: Data generally met Rasch model requirements and the scale could separate between two distinct groups of people, but there was differential item functioning by age. The difference between the adult and elderly samples was lower for the originally recommended ≥6 points cut-off (0.09 logits) than for the ≥7 points cut-off (0.23 logits), but greater at the lower and higher ends of the scale.Conclusions: This study provides support for the measurement properties of the MISS. However, caution should be exercised in comparing raw MISS scores between age groups, but applying a ≥6 cut-off appears to allow for valid comparisons between adults and elderly
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| 9. |
- Åkerlind, Christina, et al.
(författare)
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Evaluation criteria for spectral design of camouflage
- 2015
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Ingår i: Proc. SPIE 9653, Target and Background Signatures. - : SPIE - International Society for Optical Engineering. - 9781628418637 ; , s. Art.no: 9653-2-
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Konferensbidrag (refereegranskat)abstract
- In development of visual (VIS) and infrared (IR) camouflage for signature management, the aim is the design of surface properties of an object to spectrally match or adapt to a background and thereby minimizing the contrast perceived by a threatening sensor. The so called 'ladder model" relates the requirements for task measure of effectiveness with surface structure properties through the steps signature effectiveness and object signature. It is intended to link materials properties via platform signature to military utility and vice versa. Spectral design of a surface intends to give it a desired wavelength dependent optical response to fit a specific application of interest. Six evaluation criteria were stated, with the aim to aid the process to put requirement on camouflage and for evaluation. The six criteria correspond to properties such as reflectance, gloss, emissivity, and degree of polarization as well as dynamic properties, and broadband or multispectral properties. These criteria have previously been exemplified on different kinds of materials and investigated separately. Anderson and Åkerlind further point out that the six criteria rarely were considered or described all together in one and same publication previously. The specific level of requirement of the different properties must be specified individually for each specific situation and environment to minimize the contrast between target and a background. The criteria or properties are not totally independent of one another. How they are correlated is part of the theme of this paper. However, prioritization has been made due to the limit of space. Therefore all of the interconnections between the six criteria will not be considered in the work of this report. The ladder step previous to digging into the different material composition possibilities and choice of suitable materials and structures (not covered here), includes the object signature and decision of what the spectral response should be, when intended for a specific environment. The chosen spectral response should give a low detection probability (DP). How detection probability connects to image analysis tools and implementation of the six criteria is part of this work.
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