| 1. |
- Baranzahi, Amir, et al.
(författare)
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Chemical sensors with catalytic metal gates - Switching behavior and kinetic phase transitions
- 1998
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 145:10, s. 3401-3406
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Tidskriftsartikel (refereegranskat)abstract
- Rapid transitions in the response of platinum-based chemical sensors occurring at given hydrogen-oxygen concentration ratios are explained by kinetic phase transitions or switching phenomena on the catalytic metal surface. Below the transition point the response of platinum-insulator silicon carbide devices is small and above the transition it is large. It is found that the critical ratio depends on the operation temperature and the properties of the device. Three different cases are identified, namely, injection-, diffusion-, and reaction-rate-determined transitions. At sufficiently large temperatures the transition is injection limited and occurs at the stoichiometric ratio of hydrogen and oxygen in the gas mixture. The implications of the experimental observations on the applications of chemical sensors with catalytic sensing layers are discussed.
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| 2. |
- Baranzahi, Amir, et al.
(författare)
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Kinectic phase transitions and chemical sensors with catalytic metal gates
- 1997
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Ingår i: Chemical & Biological Sensors & Analytical Electrochemical Methods, 1997. - : Electrochemical Society. - 9781566771474 - 1566771471 ; , s. 1-15
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Rapid transitions in the response of platinum based chemical sensors occurring at given hydrogen-oxygen concentration ratios are explained by kinetic phase transitions or switching phenomena on the catalytic metal surface. Below the transition point the response of platinum-insulator silicon carbide devices is small and above the transition large and almost saturated. It is found that the critical ratio depends on the operation temperature and the properties of the device. Three different cases are identified, namely injection-, diffusion- and reaction rate determined transitions. At sufficiently large temperatures the transition is injection limited and occurs at the stoichiometric ratio of hydrogen and oxygen in the gas mixture. The implications of the experimental observations on the applications of chemical sensors with catalytic sensing layers are discussed.
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| 3. |
- Cullin, F., et al.
(författare)
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Economic considerations related to choice of intraocular lens (IOL) and posterior capsule opacification frequency - a comparison of three different IOLs
- 2014
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Ingår i: Acta Ophthalmologica. - : Wiley. - 1755-375X .- 1755-3768. ; 92:2, s. 179-183
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Tidskriftsartikel (refereegranskat)abstract
- Abstract. Purpose: To evaluate the posterior capsule opacification (PCO) rates in three different modern standard intraocular lenses (IOL) and analyse the related cost. Methods: Retrospective study of medical records from 1527 patients who underwent uneventful cataract surgery by phacoemulsification with posterior chamber implantation of either AcrySof SN60 (n = 375), Akreos Adapt (n = 350) or Tecnis Acryl IOL (n = 801). All surgeries were performed by the same surgeon using the same surgical technique and equipment. Primary end-point was neodymium:yttrium-aluminium-garnet (Nd:YAG) capsulotomy for visual impairment secondary to PCO. Cost of IOL material and Nd:YAG capsulotomy for PCO was then evaluated and compared between the IOLs. Results: Mean follow-up was 41.5 months, and the only statistically significant variable of developing PCO was IOL type and individual follow-up time. Nd:YAG capsulotomy was performed in 7.47% in the AcrySof group, 17.71% in the Akreos group and 3.75% in the Tecnis group. Average cost for Nd:YAG capsulotomy per surgery was euro18.75 in the AcrySof SN60 group, euro44.25 in the Akreos Adapt group and euro9.25 in the Tecnis Acryl group. The combined cost of cataract surgery and PCO treatment was euro9.81 higher in for the Akreos Adapt group than the other two combined. Conclusions: This retrospective study shows that the risk of PCO and Nd:YAG capsulotomy is significantly higher in hydrophilic Akreos IOL compared with both AcrySof and Tecnis hydrophobic IOLs. The increased risk of PCO in the hydrophilic IOL is related to higher total average costs for cataract surgery.
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| 4. |
- Dahlström, Tobias, et al.
(författare)
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Corruption and growth
- 2007
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The note adds to the growing body of studies analysing the relationship between corruption and growth. The novelty is that the study cleans the corruption data from the impact of a country’s institutional setting. This enables the authors to verify if it is the absence of corruption and/or the institutional standard of a country that cause growth. The conclusion drawn is that corruption is only a symptom and does not in itself lower the GDP growth rate of a country.
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| 5. |
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| 6. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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A dual-lattice hydrodynamic-thermal MRT-LBM model implemented on GPU for DNS calculations of turbulent thermal flows
- 2023
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Ingår i: International journal of numerical methods for heat & fluid flow. - : Emerald Group Publishing Limited. - 0961-5539 .- 1758-6585. ; 33:5, s. 1703-1725
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Tidskriftsartikel (refereegranskat)abstract
- PurposeThe purpose of this paper is to present a fast and bare bones implementation of a numerical method for quickly simulating turbulent thermal flows on GPUs. The work also validates earlier research showing that the lattice Boltzmann method (LBM) method is suitable for complex thermal flows.Design/methodology/approachA dual lattice hydrodynamic (D3Q27) thermal (D3Q7) multiple-relaxation time LBM model capable of thermal DNS calculations is implemented in CUDA.FindingsThe model has the same computational performance compared to earlier publications of similar LBM solvers. The solver is validated against three benchmark cases for turbulent thermal flow with available data and is shown to be in excellent agreement.Originality/valueThe combination of a D3Q27 and D3Q7 stencil for a multiple relaxation time -LBM has, to the authors’ knowledge, not been used for simulations of thermal flows. The code is made available in a public repository under a free license.
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| 7. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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Non-Stokesian flow through ordered thin porous media imaged by tomographic-PIV
- 2021
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Ingår i: Experiments in Fluids. - : Springer. - 0723-4864 .- 1432-1114. ; 62:3
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Tidskriftsartikel (refereegranskat)abstract
- The 3D flow-fields in a staggered and cubic arrangement of mono-radii cylinders are investigated using tomographic-PIV. The cylinder Reynolds-number is in the range of ≈10 to ≈800 giving an almost complete overview of the transition region. Two pore-scale effects are discovered. The first, visible in the cubic packing, is a spatially alternating lateral velocity field, which has a significant impact on the pressure drop and transversal dispersion. The second effect, present in the staggered array, is an example of a disturbance propagation effect that takes place in the laminar steady region; this manifests as a peculiar and complex flow-pattern. In accordance with other studies, it is shown that Darcy’s law can, from an engineering point of view be valid far beyond the limit for Stokesian flow.
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| 8. |
- Forslund, Tobias O.M. 1992-, et al.
(författare)
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Steady-State Transitions in Ordered Porous Media
- 2023
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Ingår i: Transport in Porous Media. - : Springer Nature. - 0169-3913 .- 1573-1634. ; 149:2, s. 551-577
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Tidskriftsartikel (refereegranskat)abstract
- Previously performed experiments on flow through an ordered porous media cell with tomographic particle image velocimetry reveal a complex three-dimensional steady-state flow pattern. This flow pattern emerge in the region where inertial structures have been previously reported for a wide range of packings. The onset of these steady-state inertial flow structures is here scrutinized for three different types of packing using a finite difference method. It is concluded that the onset of the flow structure coincides with a symmetry break in the flow field and discontinuities in the pressure drop, volume averaged body forces and heat transfer. A quantity for identifying the transition is proposed, namely the pressure integral across the solid surfaces. It is also shown that the transition can both increase and decrease the heat transfer dependent on the actual geometry of the porous medium.
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| 9. |
- Forslund, Tobias O. M., 1992-, et al.
(författare)
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The Effects of Periodicity Assumptions in Porous Media Modelling
- 2021
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Ingår i: Transport in Porous Media. - : Springer. - 0169-3913 .- 1573-1634. ; 137:3, s. 769-797
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Tidskriftsartikel (refereegranskat)abstract
- The effects of periodicity assumptions on the macroscopic properties of packed porous beds are evaluated using a cascaded Lattice-Boltzmann method model. The porous bed is modelled as cubic and staggered packings of mono-radii circular obstructions where the bed porosity is varied by altering the circle radii. The results for the macroscopic properties are validated using previously published results. For unsteady flows, it is found that one unit cell is not enough to represent all structures of the fluid flow which substantially impacts the permeability and dispersive properties of the porous bed. In the steady region, a single unit cell is shown to accurately represent the fluid flow across all cases studied
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| 10. |
- Forslund, Tobias, 1992-
(författare)
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Transitional flow in ordered porous media
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Porous media, here defined as any permeable structure allowing a fluid to flow through, are relevant to a multitude of engineering applications and natural processes. The observed macroscopic properties of the porous media such as mixing, heat transfer and apparent permeability are properties which are affected by the flow and especially the type of flow, or flow region. The flow regions are characterized by the ratio of the convective to viscous forces, called the Reynolds number (Re). Of these regions the transition from inertial laminar flow to fully turbulent flow is the least understood. In comparison to flows in straight pipes the onset of inertial and unsteady phenomena in porous beds do not coincide, also the transition region stretches over orders of magnitude in Re for most porous beds. In porous media this domain is characterized by temporally long-lived and spatially large scale flow structures which interact in unpredictable ways leading to dramatic shifts of the behavior of the macroscopic properties. To improve the understanding of this transitional domain, ordered materials, that reduce geometrically induced flow complexities, are studied with both numerical and experimental methods.In Paper A two types of ordered porous media with the same porosity but varying tortuosity are investigated using tomographic Particle Image Velocimetry and pressure measurements. The variation of Re gives an almost complete overview from the onset of inertial effects up to the start of the turbulent region. Two pore-scale phenomena were disclosed from the complex flow patterns that appeared. The first is an inertial steady effect first assumed to be caused by wall effects. In Paper D it was, however, discovered that the phenomenon materializes independently of wall effects. Instead it is a specific case of a more general inertial transition occurring for a wide range of porous media. A second pore-scale effect is a form of inertial core symmetry break-up that occurs in low-tortuosity porous media. This symmetry break-up is correlated to a sharp increase in the average pressure drop. The second flow structure was reproduced using numerical methods in Paper B forming the basis of a more comprehensive discussion on how these structures impact the usage of periodic conditions when modelling porous media.The possibility of using high performance Graphics Processing Unit (GPU) implementations of the Lattice Boltzmann Method (LBM) for simulating thermal turbulent flows in porous media has also been investigated in Paper C. It is concluded that the GPU LBM implementations provide fast, efficient and accurate simulations of thermal turbulent flows in porous media, as well as for a wide range of other flows. Furthermore, in Paper E, a multiple GPU implementation of a hydrodynamic LBM model is presented.
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