| 10111. |
- Andersson, Martin
(författare)
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Solid Oxide Fuel Cell Modeling at the Cell Scale - Focusing on Species, Heat, Charge and Momentum Transport as well as the Reaction Kinetics and Effects
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fuel cells are electrochemical devices that directly transform chemical energy into electricity. They are promising for future energy systems, since they are energy efficient, able to use renewable fuels and, when hydrogen is used as fuel, there are no direct emissions of greenhouse gases. Various improvements are made during the recent years, however the technology is still in the early phases of commercialisation. Fully coupled computational fluid dynamics (CFD) approaches based on the finite element method (with the software COMSOL Multiphysics) in two-dimensions are developed, in several steps, to describe an intermediate temperature SOFC single cell. Governing equations covering heat, gas-phase species, momentum, ion and electron transport are implemented and coupled to kinetics describing internal reforming and electrochemical reactions. Both ordinary and Knudsen diffusion are considered for the gas-phase species transport. For the heat transport a local temperature equilibrium approach is compared to a local temperature non-equilibrium approach, considering the solid- and gas-phases. The Darcy-Brinkman equation enables continuous pressure and velocity fields over the electrode/gas channel interfaces. The electrochemical reaction model is extended from zero-dimension (with only an average value defined) in the early models, to one-dimension covering the variation in current density along the flow direction. Finally a two-dimensional approach including the current density distribution, both along the flow direction and through the electrolyte-electrodes, is developed. The model relies on experimental data from a standard cell developed at Ningbo Institute of Material Technology & Engineering (NIMTE) in China. The anode microscopic structure and catalytic characteristics have a major impact on the internal reforming reaction rates and also on the cell performance. The large difference between the different activation energies and reaction kinetics found in the open literature may be due to the fact that several parameters probably have a significance influence on the reaction rate. Heat is generated due to ohmic, activation and concentration polarizations within the electrolyte and electrodes as well as change of entropy in the cathodic electrochemical reactions. Heat is consumed due to the change of entropy in the anodic electrochemical reactions and the steam reforming reactions within the anode. The activation polarizations in the electrodes and the ohmic polarization due to ion transport in the YSZ material are found to be the major part of the polarizations. The activation polarization is the most significant and as the electrochemical model is extended from one- to two-dimensions, the activation polarization within the cathode becomes smaller than the one within the anode. This difference might be explained by different current density per (active TPB) area and variable area-to-volume-ratios for the electrochemical reactions within the anode and cathode, respectively. The current density and the activation polarization are the highest at the electrolyte-electrode interface and decreases rapidly within the electrodes as the distance from the interface increases. However, the ohmic polarization by ion transfer increases for the positions away from the interface.
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| 10112. |
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| 10113. |
- Andersson, Martin, et al.
(författare)
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Spatial variations in financial constraints of SMEs-evidence from firm-level estimates of investment-cash flow sensitivities in Sweden
- 2023
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Ingår i: Small Business Economics. - : Springer. - 0921-898X .- 1573-0913. ; 60:4, s. 1683-1698
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Tidskriftsartikel (refereegranskat)abstract
- Plain English Summary We show that small- and medium-sized enterprises (SMEs) located outside the main city regions are more dependent on internal cash flow in their investments compared to SME urban city regions. Our findings clearly show that, as access to agglomerated economies decreases, financial constraints faced by the SMEs increase. The investment ability of SMEs in rural regions depends on own cash flow more but revenues in smaller regions tend to be smaller too-implying that the cash flow is likely to be lower. As a result, SMEs in smaller and more remote places would find it harder to invest and, therefore, to grow or increase productivity. The fact that such a consistent pattern of increasing investment-cash flow sensitivity is clearly observable in Sweden, one of the least regionally unequal countries, only reinforces the importance of considering the spatial dimension in policies targeted at closing SME financing gap. It is well established that there is uneven availability of credit across space, in particular for SMEs. The evidence on whether this translates into differences in actual business investments remains scarce. We assess this question by using firm-level data for Swedish firms and estimate the extent to which the average investment-cash flow sensitivities of firms vary across the urban-rural hierarchy. We find that the world of financing is not yet flat for the majority of Swedish SMEs. Companies located in non-metro regions are most dependent on own cash flow in their investments. The results hold for all firms, firms of different sizes, firms operating in low-end services, unaffiliated firms and those belonging to domestic corporations. In contrast, investment-cash flow sensitivity of firms operating in high-tech services and those belonging to a multinational enterprise does not differ geographically. On average, regional investment-cash flow sensitivity is lower in bigger, denser and more educated local labour market regions; it is higher in regions with greater concentration of SMEs.
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| 10114. |
- Andersson, Mats, et al.
(författare)
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Spectroscopic studies of wood-drying processes
- 2006
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Ingår i: Optics Express. - 1094-4087. ; 14:8, s. 3641-3653
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Tidskriftsartikel (refereegranskat)abstract
- By the use of wavelength-modulation diode laser spectroscopy, water vapor and oxygen are detected in scattering media nonintrusively, at 980 nm and 760 nm, respectively. The technique demonstrated is based on the fact that free gases have extremely sharp absorption structures in comparison with the broad features of bulk material. Water vapor and oxygen measurements have been performed during the drying process of wood. The results suggest that the demonstrated technique can give information about the drying process of wood to complement that of commercially available moisture meters. In particular, the time when all the free water has evaporated from the wood can be readily identified by a strong falloff in the water vapor signal accompanied by the reaching of a high-level plateau in the molecular oxygen signal. Furthermore, the same point is identified in the differential optical absorption signal for liquid water, with a sharp increase by an order of magnitude in the ratio of the signal intensities at 980 nm and 760 nm.
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| 10115. |
- Andersson, Mats, et al.
(författare)
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Stabilisation of chloroperoxidase towards peroxide dependent inactivation
- 2000
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Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 18:6, s. 457-469
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Tidskriftsartikel (refereegranskat)abstract
- The addition of polyethyleneimine with a molecular weight of 2000 to chloroperoxidase from Caldariomyces fumago dramatically improved the stability of the enzyme towards peroxide dependent inactivation. The rate constant for the H 2 O 2 -dependent inactivation of chloroperoxidase decreased from 0.0016s -1 to 1.1 * 10 -5 s -1 in the presence of 1% polyethyleneimine. The stabilising effect towards tert-butyl hydroperoxide was even more impressive. The half-life of the chloroperoxidase when exposed to a solution of 40 mM tert-butyl hydroperoxide increased from 3.2 minutes to ≥ 70 hours in presence of 0.1% polyethyleneimine.
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| 10116. |
- Andersson, Michael, et al.
(författare)
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Stabilization of evanescent wave propagation operators
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a stabilized scheme that solves the wave propagation problem in a general bianisotropic, stratified medium. The method utilizes the concept of propagators, i.e., the wave propagation operators that map the total tangential electric and magnetic fields from one plane in the slab to another. The scheme transforms the propagator approach into a scattering matrix form, where a spectral decomposition of the propagator enables separation of the exponentially growing and decaying terms in order to obtain a well-conditioned formulation. Multilayer structures can be handled in a stable manner using the dissipative property of the Redheffer star product for cascading scattering matrices. The reflection and transmission dyadics for a general bianisotropic medium with an isotropic half space on both sides of the slab are presented in a coordinate-independent dyadic notation, as well as the reflection dyadic for a bianisotropic slab with perfect electric conductor backing (PEC). Several numerical examples that illustrate the performance of the stabilized algorithm are presented.
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| 10117. |
- Andersson, Michael, et al.
(författare)
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Stabilization of Evanescent Wave Propagation Operators
- 2023
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Ingår i: Progress In Electromagnetics Research B. - 1937-6472. ; 101, s. 17-44
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a stabilized scheme that solves the wave propagation problem in a general bianisotropic, stratified medium. The method utilizes the concept of propagators, i.e., the wave propagation operators that map the total tangential electric and magnetic fields from one plane in the slab to another. The scheme transforms the propagator approach into a scattering matrix form, where a spectral decomposition of the propagator enables separation of the exponentially growing and decaying terms in order to obtain a well-conditioned formulation. Multilayer structures can be handled in a stable manner using the dissipative property of the Redheffer star product for cascading scattering matrices. The re ection and transmission dyadics for a general bianisotropic medium with an isotropic half space on both sides of the slab are presented in a coordinate-independent dyadic notation, as well as the re ection dyadic for a bianisotropic slab with perfect electric conductor backing (PEC). Several numerical examples that illustrate the performance of the stabilized algorithm are presented.
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| 10118. |
- Andersson, Martin
(författare)
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Staten i utvecklingsprocessen
- 2024
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Ingår i: Statsvetenskaplig tidskrift. - 0039-0747. ; 2024:1
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Tidskriftsartikel (refereegranskat)
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| 10119. |
- Andersson, Magnus, et al.
(författare)
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Stochastic Depth Buffer Compression using Generalized Plane Encoding
- 2013
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Ingår i: Computer Graphics Forum. - : Wiley. - 1467-8659 .- 0167-7055. ; 32:2, s. 103-112
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we derive compact representations of the depth function for a triangle undergoing motion or defocus blur. Unlike a static primitive, where the depth function is planar, the depth function is a rational function in time and the lens parameters. Furthermore, we show how these compact depth functions can be used to design an efficient depth buffer compressor/decompressor, which significantly lowers total depth buffer bandwidth usage for a range of test scenes. In addition, our compressor/decompressor is simpler in the number of operations needed to execute, which makes our algorithm more amenable for hardware implementation than previous methods.
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| 10120. |
- Andersson, Martin, et al.
(författare)
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Structural change and income inequality – Agricultural development and inter-sectoral dualism in the developing world, 1960–2010
- 2016
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Ingår i: OASIS. Observatorio de Analisis de los Sistemas Internacionales. - : Universidad Externado de Colombia. - 2346-2132. ; :23
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Tidskriftsartikel (refereegranskat)abstract
- Structural change consists of the long-term changes in the sectoral composition of output and employment. We introduce a structural change perspective to the study of income inequality in 27 countries of the developing world for the period 1960–2010. The service sector has become the main employer, but the agricultural sector is central to the income distribution because poverty is mostly rural, and the labor surplus is high. We decompose the sectoral composition of aggregate labor productivity at the country level, divide the countries into agrarian, dual (beginner, intermediate and advanced) and mature economies and use the inter-sectoral productivity gap to test the effect of structural change on income inequality. We confirm increases in agricultural productivity everywhere and find that the inter-sectoral gap is positively associated with income inequality. The effect is negligible in agrarian and advanced economies but powerful in dual beginner economies: an increase of 1% in the inter-sectoral gap increases income inequality by 0.5%. The effect peters out in dual intermediate economies and disappears completely in dual advanced economies. Finally, redistribution has been the key to compensating the losers in the income changes, particularly for those entering the non-agricultural economy.
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