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- Andersen, S.J., et al.
(författare)
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Comparison of Engineering Wake Models with CFD Simulations
- 2014
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 524, s. 012161-
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Tidskriftsartikel (refereegranskat)abstract
- The engineering wake models by Jensen [1] and Frandsen et al. [2] are assessed for different scenarios simulated using Large Eddy Simulation and the Actuator Line method implemented in the Navier-Stokes equations. The scenarios include the far wake behind a single wind turbine, a long row of turbines in an atmospheric boundary layer, idealised cases of an infinitely long row of wind turbines and infinite wind farms with three different spacings. Both models include a wake expansion factor, which is calibrated to fit the simulated wake velocities. The analysis highlights physical deficiencies in the ability of the models to universally predict the wake velocities, as the expansion factor can be fitted for a given case, but with not apparent transition between the cases. 1.
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| 4. |
- Anrup, Roland, et al.
(författare)
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Centrala universitetsvärden hotas av bolagiseringsidén
- 2013
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Ingår i: Dagens nyheter. - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Högskolestiftelser. Förslaget att driva svenska universitet i stiftelseform öppnar för bolagisering. Men det är ingen riktig utredning, utan en politisk pamflett utan eftertanke. Privatisering av universitet hotar både oberoendet, forskningskvaliteten och samhällsnyttan, skriver 36 forskare vid svenska högskolor och universitet.
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| 5. |
- Antoni, Gunnar, et al.
(författare)
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In Vivo Visualization of Amyloid Deposits in the Heart with C-11-PIB and PET
- 2013
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 1535-5667 .- 2159-662X. ; 54:2, s. 213-220
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Tidskriftsartikel (refereegranskat)abstract
- Cardiac amyloidosis is a differential diagnosis in heart failure and is associated with high mortality. There is currently no noninvasive imaging test available for specific diagnosis. N-[methyl-C-11]2-(4'-methylamino-phenyl)-6-hydroxybenzothiazole (C-11-PIB) PET is used in the evaluation of brain amyloidosis. We evaluated the potential use of C-11-PIB PET in systemic amyloidosis affecting the heart. Methods: Patients (n = 10) diagnosed with systemic amyloidosis-including heart involvement of either monoclonal immunoglobulin light-chain (AL) or transthyretin (ATTR) type- and healthy volunteers (n = 5) were investigated with PET/CT using C-11-PIB to study cardiac amyloid deposits and with C-11-acetate to measure myocardial blood flow to study the impact of global and regional perfusion on PIB retention. Results: Myocardial C-11-PIB uptake was visually evident in all patients 15-25 min after injection and was not seen in any volunteer. A significant difference in C-11-PIB retention in the heart between patients and healthy controls was found. The data indicate that myocardial amyloid deposits in patients diagnosed with systemic amyloidosis could be visualized with C-11-PIB. No correlation between C-11-PIB retention index and myocardial blood flow as measured with C-11-acetate was found on the global level, whereas a positive correlation on the segmental level was seen in a single patient. Conclusion: C-11-PIB and PET could be a method to study systemic amyloidosis of type AL and ATTR affecting the heart and should be investigated further both as a diagnostic tool and as a noninvasive method for treatment follow-up.
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| 7. |
- Axelsson, Jan, 1966-, et al.
(författare)
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The 2D Hotelling filter : a quantitativenoise-reducing principal-component filter fordynamic PET data, with applications in patientdose reduction
- 2013
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Ingår i: BMC Medical Physics. - : BioMed Central (BMC). - 1756-6649. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: In this paper we apply the principal-component analysis filter (Hotelling filter) to reduce noise fromdynamic positron-emission tomography (PET) patient data, for a number of different radio-tracer molecules. Wefurthermore show how preprocessing images with this filter improves parametric images created from suchdynamic sequence.We use zero-mean unit variance normalization, prior to performing a Hotelling filter on the slices of a dynamictime-series. The Scree-plot technique was used to determine which principal components to be rejected in thefilter process. This filter was applied to [11C]-acetate on heart and head-neck tumors, [18F]-FDG on liver tumors andbrain, and [11C]-Raclopride on brain. Simulations of blood and tissue regions with noise properties matched to realPET data, was used to analyze how quantitation and resolution is affected by the Hotelling filter. Summing varyingparts of a 90-frame [18F]-FDG brain scan, we created 9-frame dynamic scans with image statistics comparable to 20MBq, 60 MBq and 200 MBq injected activity. Hotelling filter performed on slices (2D) and on volumes (3D) werecompared.Results: The 2D Hotelling filter reduces noise in the tissue uptake drastically, so that it becomes simple to manuallypick out regions-of-interest from noisy data. 2D Hotelling filter introduces less bias than 3D Hotelling filter in focalRaclopride uptake. Simulations show that the Hotelling filter is sensitive to typical blood peak in PET prior to tissueuptake have commenced, introducing a negative bias in early tissue uptake. Quantitation on real dynamic data isreliable. Two examples clearly show that pre-filtering the dynamic sequence with the Hotelling filter prior toPatlak-slope calculations gives clearly improved parametric image quality. We also show that a dramatic dosereduction can be achieved for Patlak slope images without changing image quality or quantitation.Conclusions: The 2D Hotelling-filtering of dynamic PET data is a computer-efficient method that gives visuallyimproved differentiation of different tissues, which we have observed improve manual or automated regionof-interest delineation of dynamic data. Parametric Patlak images on Hotelling-filtered data display improved clarity,compared to non-filtered Patlak slope images without measurable loss of quantitation, and allow a dramaticdecrease in patient injected dose.
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| 8. |
- Borges, João Batista, et al.
(författare)
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Ventilation Distribution Studies Comparing Technegas and "Gallgas" Using (GaCl3)-Ga-68 as the Label
- 2011
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 1535-5667 .- 2159-662X. ; 52:2, s. 206-209
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Tidskriftsartikel (refereegranskat)abstract
- Ventilation distribution can be assessed by SPECT with Technegas. This study was undertaken in piglets with different degrees of ventilation inhomogeneity to compare PET using Ga-68-labeled pseudogas or "Gallgas" with Technegas. Methods: Twelve piglets were studied in 3 groups: control, lobar obstruction, and diffuse airway obstruction. Two more piglets were assessed for lung volume (functional residual capacity). Results: In controls, SPECT and PET images showed an even distribution of radioactivity. With lobar obstruction, the absence of ventilation of the obstructed lobe was visible with both techniques. In diffuse airway obstruction, SPECT images showed an even distribution of radioactivity, and PET images showed more varied radioactivity over the lung. Conclusion: PET provides detailed ventilation distribution images and a better appreciation of ventilation heterogeneity. Gallgas with PET is a promising new diagnostic tool for the assessment of ventilation distribution.
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| 9. |
- Bülow, Fredrik, 1980-
(författare)
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A Generator Perspective on Vertical Axis Wind Turbines
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The wind energy conversion system considered in this thesis is based on a vertical axis wind turbine with a cable wound direct drive PM generator. Diode rectifiers are used to connect several such units to a single DC-bus and a single inverter controls the power flow from the DC-bus to a utility grid. This work considers the described system from a generator perspective i.e. the turbine is primarily seen as a torque and the inverter is seen as a controlled load.A 12 kW VAWT prototype with a single turbine has been constructed within the project. The power coefficient of this turbine has been measured when the turbine is operated at various tip speed ratios. This measurement determines both how much energy the turbine can convert in a given wind and at what speed the turbine should be operated in order to maximise the energy capture. The turbine torque variation during the revolution of the turbine has also been studied.A PM generator prototype has been constructed in order to study power loss in the stator core at low electrical frequencies. Heat exchange between the stator and the air-gap between the stator and the rotor has been studied. Heat exchange between the stator and the air-gap is increased by turbulence caused by the rotor. The generator was also used in a demonstration of a DC-grid where two diode rectified PM generators supplied power to a single DC load. An initial study of an inverter suitable for grid connection of the 12 kW PM generator has been performed.Several turbine control strategies are evaluated in simulations. The control strategies only require the parameter "turbine speed" to determine the optimal system load.
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| 10. |
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Challenging the aid paradigm: Western Currents and Asian Alternatives
- 2010
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- Challenging the Aid Paradigm critically examines central aspects of Western international aid policy, while at the same time exploring non-western, especially Chinese, aid and assesses to what extent these may be competitive or complementary.
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