| 55821. |
- Yuan, Jinliang, et al.
(författare)
-
Analysis of chemical-reaction-coupled mass and heat transport phenomena in a methane reformer duct for PEMFCs
- 2007
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 50:3-4, s. 687-701
-
Tidskriftsartikel (refereegranskat)abstract
- Mass, heat and momentum transport processes are coupled with catalytic chemical reactions in a methane steam reforming duct. it is often found that endothermic and exothermic reactions in the ducts are strongly integrated by heat transfer from adjacent catalytic combustion ducts. In this paper, a three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, and the effects on various transport processes in a steam reforming duct. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The predicted results are presented and discussed for a composite duct consisting of a porous catalyst reaction layer, the fuel gas flow duct and solid layers. Parametric studies are conducted to reveal the importance of reformer designs and operating conditions. The results show that the variables, such as porous layer configuration, temperature and catalyst loading, have significant effects on the transport processes and reformer performance.
|
|
| 55822. |
- Yuan, Jinliang, et al.
(författare)
-
Analysis of Parameter Effects on Transport Phenomena in Conjunction with Chemical Reactions in Ducts Relevant for Methane Reformers
- 2007
-
Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 32:16, s. 3887-3898
-
Tidskriftsartikel (refereegranskat)abstract
- Various transport phenomena in conjunction with chemical reactions are strongly affected by reformer configurations and properties of involved porous catalyst layers. The considered composite duct is relevant for a methane steam reformer and consists of a porous layer for the catalytic chemical reactions, the fuel gas flow duct and solid plate. In this paper, a fully three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, with purpose to reveal the importance of design and operating parameters grouped as three characteristic ratios. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The results show that the characteristic ratios have significant effects on the transport phenomena and overall reforming reaction performance.
|
|
| 55823. |
- Yuan, Jinliang, et al.
(författare)
-
CFD Approach to Analyze Transport Phenomena Coupled Chemical Reactions Relevant for Methane Reformers
- 2007
-
Ingår i: Proceedings of the Fifth Internation Conference Hydrogen Economy and Hydrogen Treatment of Materials. ; 1, s. 176-183
-
Konferensbidrag (refereegranskat)abstract
- Various transport phenomena in conjunction with chemical reactions are strongly affected by reformer configurations and properties of involved porous catalyst layers. The considered composite duct is relevant for a methane steam reformer and consists of a porous layer for the catalytic chemical reactions, the fuel gas flow duct and solid plate. In this paper, a fully three-dimensional calculation method is developed to simulate and analyze reforming reactions of methane, with purpose to reveal the importance of design and operating parameters. The reformer conditions such as mass balances associated with the reforming reactions and gas permeation to/from the porous catalyst reforming layer are applied in the analysis. The results show that the characteristic parameters have significant effects on the transport phenomena and overall reforming reaction performance.
|
|
| 55824. |
- Yuan, Jinliang, et al.
(författare)
-
Simulation of Heat Transfer and Effects on Reaction-Coupled Transport Processes in SOFCs
- 2007
-
Ingår i: Proceedings of 2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference. - 0791842754 ; 2, s. 5-14
-
Konferensbidrag (refereegranskat)abstract
- For anode-supported plate solid oxide fuel cells (SOFCs), the size of the porous anode is bigger than that of the fuel gas flow duct in terms of thickness and cross-sectional area. The heat transfer rates are controlled by various operating and design parameters, and have significant effects on chemical reactions and coupled transport processes. In this study, the considered composite duct is relevant for an intermediate temperature (600-800oC) plate design and consists of a porous anode layer for the internal reforming reactions of methane, the fuel gas flow duct and solid plate. A fully three-dimensional calculation method is developed to simulate and analyze heat transfer and combined effects on internal reforming/ electrochemical reactions and the coupled transport processes, with purpose to reveal the importance of various parameters. The results show that the operating temperatures have significant effects on the chemical reactions, fuel gas distribution and overall performance.
|
|
| 55825. |
- Yuan, Jinliang, et al.
(författare)
-
Transport Phenomena Coupled by Chemical Reactions in Methane Reforming Ducts
- 2007
-
Konferensbidrag (refereegranskat)abstract
- Mass, heat and momentum transport processes are strongly coupled with catalytic chemical reactions in a methane steam reforming duct. In this paper, a threedimensional calculation method is developed to simulate and analyze reforming reactions of methane, and the effects on various transport processes in a steam reforming duct. The results show that the design and operating parameters grouped as characteristic ratios have significant effects on the transport phenomena.
|
|
| 55826. |
- Yurova, Alla, et al.
(författare)
-
Carbon storage in the organic layers of boreal forest soils under various moisture conditions: A model study for Northern Sweden sites
- 2007
-
Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800. ; 204:3-4, s. 475-484
-
Tidskriftsartikel (refereegranskat)abstract
- A typical feature of the boreal forest landscape is a gradient from dry to wet sites, with associated increases in the depth of the soil organic layers. In this study, the coupled ecosystem-soil biogeochemistry model GUESS-ROMUL is used to explore how the specific features of soil organic matter decomposition and vegetation dynamics account for an observed difference between the soils formed under contrasting moisture conditions. Two sites, one mesic and one mesic-to-wet, representative of the natural forest in Northern Sweden, are simulated. In addition to the assumptions underlying the GUESS-ROMUL model, it is assumed that the fire frequency was higher at the mesic site. The model shows that with a natural fire regime, the soil organic layers at the mesic-to-wet site store 6.0 kg C m(-2) compared to 3.1 kg C m(-2) at the mesic site. Forty-seven percent of the difference between the sites in this respect is explained by suppressed decomposition under higher moisture conditions, 37% by the decreased litter input into the soil (more frequently disturbed ecosystems have lower productivity) and 16% by direct consumption of the forest floor in fires. It is predicted that due to anthropogenic fire suppression the organic soil layers of mesic sites will, in the future, sequester carbon at an average rate of 0.0103 kg C m(-2) year(-1) and have an equilibrium storage capacity of 5.4 kg C m(-2). For the mesic-to-wet site, the model predicts an extremely slow sequestration rate of 0.0022 kg C m(-2) year(-1). The effect of increased precipitation on the carbon storage at the landscape level is also investigated.
|
|
| 55827. |
- Yurova, Alla
(författare)
-
Hydrological aspects of the carbon balance in a boreal catchment: A model study
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- AbstractThe cycling of carbon in its gaseous, solid and dissolved forms is of central importance to ecosystem science, particularly, when the natural carbon cycle has been perturbed by human activity. Mathematical models are commonly used to asses and predict global and regional patterns of terrestrial carbon exchange. At the same time, processes operating on smaller (sub-grid) scales are usually outside the scope of the large-scale models exploring climate?biosphere interactions. However, if a sub-grid feature is found repeatedly in a large number of particular realizations, we may expect that its characteristic dynamics are likely to be important even at larger scales. This work examines some of these phenomena. First, a boreal landscape differentiated into forests and peatlands is investigated. Second, the export of dissolved organic carbon (DOC) in peatland streams is assessed.The work described herein mainly addresses methodology, i.e. how approaches to hydrology and ecosystem modelling can be combined. Specifically, the general ecosystem model GUESS was modified and supplied with new modules to be used for peatland simulations. The model was also designed to reproduce soil moisture and related ecosystem properties along a topographical catena. In addition, a completely new model of DOC production, transport and transformation in peat was developed. The data for model development and validation came from boreal catchments in the Vindelns Forest Research Parks, The Swedish University of Agricultural Sciences, Northern Sweden. A relatively good fit between the modelled and measured NEE at the Degerö Stormyr peatland was demonstrated for 2001-2003. Further, the model was used to demonstrate that the NEE was quite insensitive to changes in water table level within the ranges typical for the dominant mire plant community. The newly constructed model was able to reproduce DOC concentrations measured at the outlet of the Kallkälsmyren peatland for 1993-2001. The model suggested that the main drivers for interannual variability in DOC concentrations were the rates of microbially mediated DOC production and mineralization and the flow intensity in the active surface layer of the peatland. The amount of DOC in the peat water at a particular time was mainly determined by (much larger) amounts of soluble carbon sorbed on the peat matrix. A dynamic, rather than static, description of the adsorption and desorption processes was advocated.The work makes some contribution to filling the gap that currently exists between field observations at the plot scale and large-scale model analysis of the climate?biosphere interaction.
|
|
| 55828. |
- Zackrisson, Sophia, et al.
(författare)
-
Improved survival rate for women with interval breast cancer - results from the breast cancer screening programme in Malmo, Sweden 1976-1999
- 2007
-
Ingår i: Journal of Medical Screening. - : SAGE Publications. - 1475-5793 .- 0969-1413. ; 14:3, s. 138-143
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Breast cancers detected between screening examinations can influence the sensitivity of a screening programme. Studies of the prognosis of these so-called interval breast cancers show diverging results. We investigated the course of interval breast cancer over time in the Malmo Mammographic Screening Trial (MMST) 1976-86 and the Malmo Mammographic Service Screening Programme (MMSSP) 1990-99. MATERIAL AND METHODS: Stage distribution and survival of interval cancers in MMSSP were compared with screen-detected and non-attender cancer cases in MMSSP, with interval cancers in MMST and with breast cancer cases in a non-screened population five years before the start of MMSSP (pre-screening cancer cases). RESULTS: In MMSSP 1990-99, the interval cancers did not differ in stage distribution or survival compared with cancer cases in non-attenders, while screen-detected cancer cases had more favourable stage distribution and rate of survival than had the interval cancer cases. The MMST interval cancer cases, 1976-1986, had more favourable stage distribution but higher overall case fatality rate, relative risks (RR) 1.78 (1.00-3.20), and breast cancer case fatality rate, RR 2.05 (1.05-4.00), compared with the more recent MMSSP interval cancer cases. No significant difference in five-year survival was seen in the MMSSP interval cancer cases compared with pre-screening cancer cases not exposed to screening. CONCLUSION: In this urban population invited to mammographic screening, the survival rate for women with interval cancer has improved over a period of 20 years. Further studies are needed to assess what factors might explain changes in the course of interval breast cancer.
|
|
| 55829. |
- Zackrisson, Sophia, et al.
(författare)
-
Social predictors of non-attendance in an urban mammographic screening programme: A multilevel analysis
- 2007
-
Ingår i: Scandinavian Journal of Public Health. - : SAGE Publications. - 1651-1905 .- 1403-4948. ; 35:5, s. 548-554
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: Rate of non-attendance following invitation for breast cancer screening is related to several socioeconomic conditions. To what extent this reflects differences with regard to individual and environmental circumstances, respectively, has received little attention. The purpose of this study was to investigate the effect of individual socioeconomic and area-level determinants on variations in non-attendance among geographic areas in an urban mammographic service screening programme. Methods: The study population consisted of 32,119 women invited for mammographic screening in 1990-93, residing in 97 neighbourhoods in the city of Malmo in Sweden. The influence of the individual factors age, marital status, education, housing accommodation, household income, and area-level circumstances, e. g. rate of migration and rate of being gainfully employed, on the rate of non-attendance was assessed by multilevel analysis. Results: Area rates of non-attendance ranged from 18% to 63%. Of the total variability in non-attendance, 4.3% was between neighbourhoods. This effect was significantly reduced when adjusting for the individual factors. The area-level factors, migration, and rate of being gainfully employed reduced and almost erased the neighbourhood variance in non-attendance. Conclusion: In addition to individual socioeconomic factors, area-level factors seem to be important determinants of neighbourhood rates of non-attendance in an urban mammographic screening programme. In a public health perspective neighbourhoods may be targeted in order to affect the problem of non-attendance in mammographic screening.
|
|
| 55830. |
- Zaehle, S, et al.
(författare)
-
Projected changes in terrestrial carbon storage in Europe under climate and land use change, 1990-2100
- 2007
-
Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 10, s. 380-401
-
Forskningsöversikt (refereegranskat)abstract
- Changes in climate and land use, caused by socio-economic changes, greenhouse gas emissions, agricultural policies and other factors, are known to affect both natural and managed ecosystems, and will likely impact on the European terrestrial carbon balance during the coming decades. This study presents a comprehensive European Union wide (EU15 plus Norway and Switzerland, EU*) assessment of potential future changes in terrestrial carbon storage considering these effects based on four illustrative IPCC-SRES storylines (A1FI, A2, B1, B2). A process-based land vegetation model (LPJ-DGVM), adapted to include a generic representation of managed ecosystems, is forced with changing fields of land-use patterns from 1901 to 2100 to assess the effect of land-use and cover changes on the terrestrial carbon balance of Europe. The uncertainty in the future carbon balance associated with the choice of a climate change scenario is assessed by forcing LPJ-DGVM with output from four different climate models (GCMs: CGCM2, CSIRO2, HadCM3, PCM2) for the same SRES storyline. Decrease in agricultural areas and afforestation leads to simulated carbon sequestration for all land-use change scenarios with an average net uptake of 17-38 Tg C/year between 1990 and 2100, corresponding to 1.9-2.9% of the EU*s CO2 emissions over the same period. Soil carbon losses resulting from climate warming reduce or even offset carbon sequestration resulting from growth enhancement induced by climate change and increasing atmospheric CO2 concentrations in the second half of the twenty-first century. Differences in future climate change projections among GCMs are the main cause for uncertainty in the cumulative European terrestrial carbon uptake of 4.4-10.1 Pg C between 1990 and 2100.
|
|
