| 1. |
- Schirmer, M. D., et al.
(författare)
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White matter hyperintensity quantification in large-scale clinical acute ischemic stroke cohorts - The MRI-GENIE study
- 2019
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Ingår i: Neuroimage-Clinical. - : Elsevier BV. - 2213-1582. ; 23
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Tidskriftsartikel (refereegranskat)abstract
- White matter hyperintensity (WMH) burden is a critically important cerebrovascular phenotype linked to prediction of diagnosis and prognosis of diseases, such as acute ischemic stroke (AIS). However, current approaches to its quantification on clinical MRI often rely on time intensive manual delineation of the disease on T2 fluid attenuated inverse recovery (FLAIR), which hinders high-throughput analyses such as genetic discovery. In this work, we present a fully automated pipeline for quantification of WMH in clinical large-scale studies of AIS. The pipeline incorporates automated brain extraction, intensity normalization and WMH segmentation using spatial priors. We first propose a brain extraction algorithm based on a fully convolutional deep learning architecture, specifically designed for clinical FLAIR images. We demonstrate that our method for brain extraction outperforms two commonly used and publicly available methods on clinical quality images in a set of 144 subject scans across 12 acquisition centers, based on dice coefficient (median 0.95; inter-quartile range 0.94-0.95; p < 0.01) and Pearson correlation of total brain volume (r = 0.90). Subsequently, we apply it to the large-scale clinical multi-site MRI-GENIE study (N = 2783) and identify a decrease in total brain volume of -2.4 cc/year. Additionally, we show that the resulting total brain volumes can successfully be used for quality control of image preprocessing. Finally, we obtain WMH volumes by building on an existing automatic WMH segmentation algorithm that delineates and distinguishes between different cerebrovascular pathologies. The learning method mimics expert knowledge of the spatial distribution of the WMH burden using a convolutional auto-encoder. This enables successful computation of WMH volumes of 2533 clinical AIS patients. We utilize these results to demonstrate the increase of WMH burden with age (0.950 cc/year) and show that single site estimates can be biased by the number of subjects recruited.
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| 2. |
- Wannberg, Gudmund, et al.
(författare)
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EISCAT_3D - a next-generation European radar system for upper atmosphere and geospace research
- 2010
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Ingår i: Radio Science Bulletin. - 1024-4530. ; :333, s. 75-88
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Tidskriftsartikel (refereegranskat)abstract
- The EISCAT Scientifi c Association, together with a number of collaborating institutions, has recently completed a feasibility and design study for an enhanced performance research radar facility to replace the existing EISCAT UHF and VHF systems. This study was supported by EU Sixth-Framework funding. The new radar retains the powerful multi-static geometry of the EISCAT UHF, but will employ phased arrays, direct-sampling receivers, and digital beamforming and beam steering. Design goals include, inter alia, a tenfold improvement in temporal and spatial resolution, an extension of the instantaneous measurement of full-vector ionospheric drift velocities from a single point to the entire altitude range of the radar, and an imaging capability to resolve small-scale structures. Prototype receivers and beamformers are currently being tested on a 48-element, 224 MHz array (the "Demonstrator") erected at the Kiruna EISCAT site, using the EISCAT VHF transmitter as an illuminator.
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| 3. |
- Domeij, Martin, et al.
(författare)
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2.2 kV SiC BJTs with low V(CESAT) fast switching and short-circuit capability
- 2010
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2. ; , s. 1033-1036
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Konferensbidrag (refereegranskat)abstract
- This paper reports large active area (15 mm(2)) 4H-SiC BJTS with a low V(CESAT)=0.6 V at 1(C)=20 A (J(C)=133 A/cm(2)) and an open-base breakdown voltage BV(CEO)=2.3 kV at T=25 degrees C. The corresponding room temperature specific on-resistance R(SP.ON)=4.5 m Omega cm(2) is to the authors knowledge the lowest reported value for a large area SiC BJT blocking more than 2 kV. The onstate and blocking characteristics were analyzed by device simulation and found to be in good agreement with measurements. Fast switching with VcE rise- and fall-times in the range of 20-30 ns was demonstrated for a 6 A 1200 V rated SiC BJT. It was concluded that high dynamic base currents are essential for fast switching to charge the BJT parasitic base-collector capacitance. In addition, 10 mu s short-circuit capability with V(CE)=800 V was shown for the 1200 V BJT.
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| 4. |
- Rao, Akhila, et al.
(författare)
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Team communication strategy for collaborative exploration by autonomous vehicles
- 2016
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Ingår i: 2016 IEEE International Conference on Communications, ICC 2016. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479966646
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Konferensbidrag (refereegranskat)abstract
- Exploring a large area can be conveniently performed by a team of small autonomous vehicles for different applications, such as search and rescue, cleaning, or lawn mowing. The efficiency and performance of such autonomous exploration depends on the exploration algorithm implemented by the vehicles, and can be enhanced with a better communication and collaboration strategy within the team. In this paper, a new algorithm is proposed and evaluated where vehicles with a limited communication range pro-actively seek their teammates to exchange information about the explored area. Simulations show that this approach allows the vehicles to finish the exploration and return to their base station 18% faster, without consuming more energy.
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| 5. |
- Rue, H., et al.
(författare)
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Spatial modeling with R-INLA: A review
- 2018
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Ingår i: Wiley Interdisciplinary Reviews-Computational Statistics. - : Wiley. - 1939-0068 .- 1939-5108. ; 10:6
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Forskningsöversikt (refereegranskat)abstract
- Coming up with Bayesian models for spatial data is easy, but performing inference with them can be challenging. Writing fast inference code for a complex spatial model with realistically-sized datasets from scratch is time-consuming, and if changes are made to the model, there is little guarantee that the code performs well. The key advantages of R-INLA are the ease with which complex models can be created and modified, without the need to write complex code, and the speed at which inference can be done even for spatial problems with hundreds of thousands of observations. R-INLA handles latent Gaussian models, where fixed effects, structured and unstructured Gaussian random effects are combined linearly in a linear predictor, and the elements of the linear predictor are observed through one or more likelihoods. The structured random effects can be both standard areal model such as the Besag and the BYM models, and geostatistical models from a subset of the Matern Gaussian random fields. In this review, we discuss the large success of spatial modeling with R-INLA and the types of spatial models that can be fitted, we give an overview of recent developments for areal models, and we give an overview of the stochastic partial differential equation (SPDE) approach and some of the ways it can be extended beyond the assumptions of isotropy and separability. In particular, we describe how slight changes to the SPDE approach leads to straight-forward approaches for nonstationary spatial models and nonseparable space-time models. This article is categorized under: Statistical and Graphical Methods of Data Analysis > Bayesian Methods and Theory Statistical Models > Bayesian Models Data: Types and Structure > Massive Data
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| 6. |
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| 7. |
- Deckner, F., et al.
(författare)
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Jordförstärkning
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Larsson, Cecilia, et al.
(författare)
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Measurement and modeling of residual stress in a welded Haynes® 25 cylinder
- 2005
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 399:1-2, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynes® 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 mm parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model.
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| 9. |
- Persson, Tobias A, 1975, et al.
(författare)
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Major oil exporters may profit rather than lose, in a carbon-constrained world.
- 2007
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Ingår i: Energy Policy. - : Elsevier BV. - 0301-4215. ; 35:12, s. 6346-6353
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Tidskriftsartikel (refereegranskat)abstract
- The Organization of Petroleum Exporting Countries (OPEC) claims compensation for losses in expected oil export revenues due to CO2 mitigation measures in developing countries. These losses are expected for two primary reasons: a reduction in the consumption of oil in importing countries and a reduction in the producer price of oil (taxation in an importing country implies a transfer of rents from producers to consumers). So far, most studies have focused on these two mechanisms and corroborated that revenue losses for OPEC are to be expected. However, there are also mechanisms that may be expected to raise the price of oil products. In a cost-effective regime for dealing with climate change, i.e., a regime in which all or most countries participate and in which the same carbon price is applied on all carbon-emitting activities, the cost of using unconventional oil, or synthetic diesel from coal, will increase even more than the cost of using conventional oil. Given that reserves of conventional oil are expected to dwindle over time, heavy oils and coal to liquids might set the long-run price for liquid fuels, which means that the price of oil would increase beyond the carbon fee; i.e., the rent on conventional oil would increase. We use an energy-economic optimization model to analyze these three mechanisms. We find that the net present value of OPEC revenue from conventional oil increases slightly (at most by 4 percent) with a global CO2 restriction regime. We also consider conditions under which this result does not hold.
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| 10. |
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