| 47741. |
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| 47742. |
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| 47743. |
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| 47744. |
- Johansson, P., et al.
(författare)
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Primary energy use for heating in the Swedish building sector - Current trends and proposed target
- 2007
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Ingår i: Energy Policy. - : Elsevier BV. - 0301-4215. ; 35:2, s. 1386-1404
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Tidskriftsartikel (refereegranskat)abstract
- One goal of the Swedish energy policy is to reduce the amount of electricity used for heating in the building sector. This means to reduce the primary energy used for heating which in this paper is analyzed in the context of various heating technologies and CO2 emissions. The analysis is applied to a region in Sweden (southern Sweden) for which detailed information on the energy infrastructure (the capital stock of the buildings and heating systems together with geographical variations in heat intensity) is available from a previous work [Johansson, P., Nylander, A., Johnsson, F., 2005. Electricity dependency and CO2 emissions from heating in the Swedish building sector-current trends in conflict with governmental policy? Energy policy] and which is large enough to be assumed representative for Sweden as a whole. The detailed mapping of the energy infrastructure allows a good estimate on the rate at which the energy system can be expected to be replaced with respect to economical lifetime of the capital stock (the year 2025 in this case). Two scenarios are investigated; a: target scenario for which energy savings are employed (e.g. improving climate shell in buildings) and oil and most of the electricity used for heating purposes are phased out and a second for which the current trend in the heating market continues. In the target scenario it is shown that although only applying commercially competitive heating technologies, it is possible to achieve a 47% reduction in primary energy use for heating with a 34% decrease in heat demand together with significant reduction in CO2 emissions. However, the scenario which continues the current trends on the heating market instead yields an increase (of about 10%) in primary energy use (reduction in conversion efficiency) of the heating system of the region over the period studied, in spite of a slight decrease in heat demand (9%, mainly due to energy efficiency measures) as well as in CO2 emissions. In light of the recently proposed introduction of energy performance certification of buildings in Sweden (and in EU), it can be concluded that such a certification system must take into account the primary energy use and local conditions. A politically acceptable way to do so would be to propose municipalities to develop "best strategies" on development of the heating market for various house types and districts within the municipality which can then be included as recommendations in the energy performance certification of the buildings. (c) 2006 Elsevier Ltd. All rights reserved.
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| 47745. |
- Johansson, Robert, 1977, et al.
(författare)
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Influence of intraparticle gradients in modeling of fixed bed combustion
- 2007
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Ingår i: Combustion and Flame. ; 149, s. 49-62
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Tidskriftsartikel (refereegranskat)abstract
- The impact of using a porous media approximation, neglecting intraparticle gradients, for modeling fixed bed combustion has been investigated. This has been done by comparing the results from a bed model using the porous media approximation with the results from the same model, where the intraparticle gradients have been taken into account by a two-dimensional particle model. The particle model provides information on the internal heating of the solid particles and the internal rate of drying and devolatilization. The surface temperature of the particles, given by the porous bed model, is the boundary condition for the particle model. Fuel particles of sizes between 5 and 40 mm, consisting of wood, and inlet gas velocities ranging from 0.05 to 0.2 m/s are used. For large bed particles there are considerable differences between the two modeling approaches in the rates of release of volatiles and moisture. The temperature profile in the bed is also affected. For the smaller bed particles in the size range investigated, the differences are small. However, the difference in ignition rate and maximum temperature are small even for the largest particles, compared to uncertainties in the models and scattering of experimental data.
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| 47746. |
- Johansson, Robert, 1977, et al.
(författare)
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Sensitivity Analysis of a Fixed Bed Combustion Model
- 2007
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Ingår i: Energy & Fuels. ; 21:3, s. 1493-1503
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Tidskriftsartikel (refereegranskat)abstract
- The ability to model the combustion of biofuels in a fixed bed is evaluated by a sensitivity analysis. Theanalysis treats the uncertainty of model parameters related to heat transport, reaction rates, and composition ofvolatiles. The scatter of the parameters is estimated from the differences between several published correlations.The results are compared with measurement data and possible model simplifications are discussed. It is shownthat the bed model is able to reproduce the ignition rate and the maximum temperature. Prediction of theseproperties is relatively insensitive to the uncertainty of most of the parameters. Gas concentrations within thebed are more difficult to predict. They are greatly influenced by the composition of the volatile gas releasedduring devolatilization. Also the composition of the volatile gas has a significant influence on the ignition ofthe gas in the model, affecting the ignition rate, particularly at low airflows. Moreover, the investigation showsthat treatment of radiation can be simplified, and the number of gas species included in the model can berestricted without significant losses of model generality.
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| 47747. |
- Johansson, Sven, 1981
(författare)
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Multiscale Modeling of Interfaces
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding strength and stability of interfaces between dissimilar materials or phases is a highly active field of contemporary materials research. Knowledge of interface structure and energetics is important for modeling of complex materials both on a mechanical and thermodynamical level as well as for many functional properties. Interfaces is a collective term including surfaces, interphase boundaries and grain boundaries. A general interface can be sharp or diffuse, planar or corrugated. The interface between two crystals is usually quite sharp, and can be classified as coherent, semicoherent or incoherent depending on the mismatch between the adjoining crystals.The goal of this Thesis is to obtain a better understanding of interfacial structures and energetics, in particular of semicoherent interfaces. Previous first-principles work in the field has often excluded the effect of misfit. Therefore, we present a simple model combining the interfacial interaction from first-principles methods with a continuum description to account for the elastic displacements. The accuracy of the model has been satisfactorily tested against atomistic modelling.We investigate the effect of misfit on interfaces in two classes of materials: steels and cemented carbides. In the first case, we study the interface between Fe and a VN precipitate. The results show that even a small misfit (2%) has a large influence on the interface energy. In the second case, we apply the method to the semicoherent Sigma=2 twist boundary found in both tungsten carbide powder and sintered cemented carbides. The results are discussed in the context of grain boundary evolution during sintering.
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| 47748. |
- John, Wolfgang, 1978, et al.
(författare)
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Analysis of Internet Backbone Traffic and Header Anomalies Observed
- 2007
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Ingår i: IMC '07: Proceedings of the 7th ACM SIGCOMM conference on Internet measurement. - 9781595939081 ; , s. 111-116
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Konferensbidrag (refereegranskat)abstract
- The dominating Internet protocols, IP and TCP, allow some flexibility in implementation, including a variety of optional features. To support research and further development of these protocols, it is crucial to know about current deployment of protocol specific features and accompanying anomalies. This work is intended to reflect the current characteristics of Internet backbone traffic and point out misbehaviors and potential problems. On 20 consecutive days in April 2006 bidirectional traffic was collected on an OC-192 backbone link. The analysis of the data provides a comprehensive summary about current protocol usage including comparisons to prior studies. Furthermore, header misbehaviors and anomalies were found within almost every aspect analyzed and are discussed in detail. These observations are important information for designers of network protocols, network application and network attack detection systems.
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| 47749. |
- John, Wolfgang, 1978, et al.
(författare)
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Differences between In- and Outbound Internet Backbone Traffic
- 2007
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Ingår i: TERENA Networking Conference 2007, Copenhagen, DK.
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Konferensbidrag (refereegranskat)abstract
- Contemporary backbone-traffic is analyzed with respect to behaviour differences between inbound and outbound Internet traffic. For the analysis, 146 traffic traces of 20 minutes duration have been collected in April 2006, carrying 10.7 billion frames and 7.5 TB of data. Significant directional differences, among others found in IP fragmentation, TCP termination behaviour and TCP options usage, are pointed out and discussed on different protocol levels (IP, TCP and UDP). The analysis includes a focus on TCP connection properties, yielding P2P and malicious traffic as main reasons for the differences. The results are relevant for a better understanding of how applied network protocols are used in an operative environment.Furthermore, a quantification of malicious traffic provides related research fields, such as network security or intrusion detection, with important insights.
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| 47750. |
- Johnson, Erland, 1962, et al.
(författare)
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Lateral spårstabilitet -- slutrapport
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Det gemensamma CHARMEC/SP-projektet Lateral spårstabilitet startade 2003 och avslutades under våren 2007. Det övergripande målet för projektet var att motverka uppkomsten av solkurvor. Detta skulle åstadkommas genom att öka möjligheten att besvara de två fundamentala frågorna när det gäller uppkomsten av solkurvor: Vilken kompressiv axialkraft verkar i rälen och vilket sidomotstånd har spåret? Detta övergripande mål bröts ned i tre delprojekt: · Utveckling av bättre metoder för mätning av spänningsfri temperatur · Numerisk simulering av ballastens sidomotstånd · Utveckling av en numerisk modell för prediktering av uppkomst av solkur- vor. Detta är en kortfattad sammanställning av vad som utförts och vilka resul- tat som uppnåtts. Detaljerad information finns i de hänvisade rapporterna.
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