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Sökning: LAR1:cth > Högskolan i Gävle

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  • Amin, Shoaib, 1985-, et al. (författare)
  • Behavioral Modeling and Linearization of Crosstalk and Memory Effects in RF MIMO Transmitters
  • 2014
  • Ingår i: Ieee Transactions on Microwave Theory and Techniques. - 0018-9480. ; 62:4, s. 810-823
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper proposes three novel models for behavioral modeling and digital pre-distortion (DPD) of nonlinear 2$,times,$ 2 multiple-input multiple-output (MIMO) transmitters in the presence of crosstalk. The proposed models are extensions of the single-input single-output generalized memory polynomial model. Three types of crosstalk effects were studied and characterized as linear, nonlinear, and nonlinear & linear crosstalk. A comparative study was performed with previously published models for the linearization of crosstalk in a nonlinear 2 $,times,$2 MIMO transmitter. The experiments indicate that, depending on the type of crosstalk, the selection of the correct model in the transmitter is necessary for behavioral modeling and sufficient DPD performance. The effects of coherent and partially noncoherent signal generation on the performance of DPD were also studied. For crosstalk levels of ${-}{hbox{30}}$ dB, the difference in the normalized mean square error and adjacent channel power ratio was found to be 3–4 dB between coherent and partially noncoherent signal generation.
  • Andersson-Sköld, Yvonne, et al. (författare)
  • A framework for assessing urban greenery's effects and valuing its ecosystem services
  • 2018
  • Ingår i: Journal of Environmental Management. - Academic Press. - 0301-4797. ; 205, s. 274-285
  • Tidskriftsartikel (refereegranskat)abstract
    • Ongoing urban exploitation is increasing pressure to transform urban green spaces, while there is increasing awareness that greenery provides a range of important benefits to city residents. In efforts to help resolve associated problems we have developed a framework for integrated assessments of ecosystem service (ES) benefits and values provided by urban greenery, based on the ecosystem service cascade model. The aim is to provide a method for assessing the contribution to, and valuing, multiple ES provided by urban greenery that can be readily applied in routine planning processes. The framework is unique as it recognizes that an urban greenery comprises several components and functions that can contribute to multiple ecosystem services in one or more ways via different functional traits (e.g. foliage characteristics) for which readily measured indicators have been identified. The framework consists of five steps including compilation of an inventory of indicator; application of effectivity factors to rate indicators' effectiveness; estimation of effects; estimation of benefits for each ES; estimation of the total ES value of the ecosystem. The framework was applied to assess ecosystem services provided by trees, shrubs, herbs, birds, and bees, in green areas spanning an urban gradient in Gothenburg, Sweden. Estimates of perceived values of ecosystem services were obtained from interviews with the public and workshop activities with civil servants. The framework is systematic and transparent at all stages and appears to have potential utility in the existing spatial planning processes.
  • Arghand, Taha, et al. (författare)
  • An experimental investigation of the flow and comfort parameters for under-floor, confluent jets and mixing ventilation systems in an open-plan office
  • 2015
  • Ingår i: Building and Environment. - 0360-1323. ; 92, s. 48-60
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a new trend to convert the workplaces from individual office rooms to open offices for motivating money saving and better communication. With such a shift the ability of existing ventilation systems in meeting the new requirements is a challenging question for researchers. The available options could have an impact on workers' health in terms of providing acceptable levels of thermalcomfort and indoor air quality. Thus, this experimental investigation focuses on the performances of three different air distribution systems in an open-plan office space. The investigated systems were: mixing ventilation with ceiling-mounted inlets, confluent jets ventilation and underfloor air distribution with straight and curved vanes. Although this represents a small part of our more extensiveexperimental investigation, the results show that all the purposed stratified ventilation systems (CJV and UFAD) were more or less behaving as mixing systems with some tendency for displacement effects. Nevertheless, it is known that the mixing systems have a stable flow pattern but has the disadvantage of mixing contaminated air with the fresh supplied air which may produce lower performance and in worst cases occupants' illness. For the open-plan office we studied here, it will be shown that the new systems are capable of performing better than the conventional mixing systems. As expected, the higher air exchange efficiency in combination with lower local mean age of air for corner-mounted CJV and floor-mounted UFAD grills systems indicates that these systems are suitable for open-plan offices and are to be favored over conventional mixing systems.
  • Arushanyan, Yevgeniya, et al. (författare)
  • Environmental Assessment of Possible Future Waste Management Scenarios
  • 2017
  • Ingår i: Energies. - MDPI AG. - 1996-1073. ; 10:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Waste management has developed in many countries and will continue to do so. Changes towards increased recovery of resources in order to meet climate targets and for society to transition to a circular economy are important driving forces. Scenarios are important tools for planning and assessing possible future developments and policies. This paper presents a comprehensive life cycle assessment (LCA) model for environmental assessments of scenarios and waste management policy instruments. It is unique by including almost all waste flows in a country and also allow for including waste prevention. The results show that the environmental impacts from future waste management scenarios in Sweden can differ a lot. Waste management will continue to contribute with environmental benefits, but less so in the more sustainable future scenarios, since the surrounding energy and transportation systems will be less polluting and also because less waste will be produced. Valuation results indicate that climate change, human toxicity and resource depletion are the most important environmental impact categories for the Swedish waste management system. Emissions of fossil CO2 from waste incineration will continue to be a major source of environmental impacts in these scenarios. The model is used for analyzing environmental impacts of several policy instruments including weight based collection fee, incineration tax, a resource tax and inclusion of waste in a green electricity certification system. The effect of the studied policy instruments in isolation are in most cases limited, suggesting that stronger policy instruments as well as combinations are necessary to reach policy goals as set out in for example the EU action plan on circular economy.
  • Elgammal, Karim, et al. (författare)
  • Density functional calculations of graphene-based humidity and carbon dioxide sensors : effect of silica and sapphire substrates
  • 2017
  • Ingår i: Surface Science. - Elsevier. - 0039-6028. ; 663, s. 23-30
  • Tidskriftsartikel (refereegranskat)abstract
    • We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 (A) over circle. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.
  • Eriksson, Ola, et al. (författare)
  • Life cycle assessment of fuels for district heating: A comparison of waste incineration, biomass- and natural gas combustion
  • 2007
  • Ingår i: Energy Policy. - 0301-4215. ; 35:2, s. 1346-1362
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this consequential life cycle assessment (LCA) is to compare district heating based on waste incineration with combustion of biomass or natural gas. The study comprises two options for energy recovery (combined heat and power (CHP) or heat only), two alternatives for external, marginal electricity generation (fossil lean or intense), and two alternatives for the alternative waste management (landfill disposal or material recovery). A secondary objective was to test a combination of dynamic energy system modelling and LCA by combining the concept of complex marginal electricity production in a static, environmental systems analysis. Furthermore, we wanted to increase the methodological knowledge about how waste can be environmentally compared to other fuels in district-heat production. The results indicate that combustion of biofuel in a CHP is environmentally favourable and robust with respect to the avoided type of electricity and waste management. Waste incineration is often (but not always) the preferable choice when incineration substitutes landfill disposal of waste. It is however, never the best choice (and often the worst) when incineration substitutes recycling. A natural gas fired CHP is an alternative of interest if marginal electricity has a high fossil content. However, if the marginal electricity is mainly based on non-fossil sources, natural gas is in general worse than biofuels.
  • Finnveden, Göran, et al. (författare)
  • Policy Instruments towards a Sustainable Waste Management
  • 2013
  • Ingår i: Sustainability. - Basel : MDPI AG. - 2071-1050. ; 5:3, s. 841-881
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this paper is to suggest and discuss policy instruments that could lead towards a more sustainable waste management. The paper is based on evaluations from a large scale multi-disciplinary Swedish research program. The evaluations focus on environmental and economic impacts as well as social acceptance. The focus is on the Swedish waste management system but the results should be relevant also for other countries. Through the assessments and lessons learned during the research program we conclude that several policy instruments can be effective and possible to implement. Particularly, we put forward the following policy instruments: “Information”; “Compulsory recycling of recyclable materials”; “Weight-based waste fee in combination with information and developed recycling systems”; “Mandatory labeling of products containing hazardous chemicals”, “Advertisements on request only and other waste minimization measures”; and “Differentiated VAT and subsidies for some services”. Compulsory recycling of recyclable materials is the policy instrument that has the largest potential for decreasing the environmental impacts with the configurations studied here. The effects of the other policy instruments studied may be more limited and they typically need to be implemented in combination in order to have more significant impacts. Furthermore, policy makers need to take into account market and international aspects when implementing new instruments. In the more long term perspective, the above set of policy instruments may also need to be complemented with more transformational policy instruments that can significantly decrease the generation of waste.
  • Glaumann, Mauritz, et al. (författare)
  • Miljöklassning av byggnader : Slutrapport april 2008
  • 2008
  • Rapport (populärvet., debatt m.m.)abstract
    • Den här rapporten presenterar en metod för att miljöklassa byggnader med avseende på energi, innemiljö och kemiska ämnen. Rapporten presenterar också några särskilda miljökrav för byggnader med eget VA-system.Det övergripande syftet med ett nationellt miljöklassningssystem är att bidra till en hållbar bygg- och fastighetssektor. Arbetet ska resultera i en praktiskt tillämpbar metod för miljöklassning av byggnader som är väl förankrad i byggsektorn och hos myndigheterna. En allmänt accepterad miljöklassning av yggnader kan bli ett starkt incitament för byggherrar, fastighetsägare, fastighetsförvaltare och bebyggelsens användare att påskynda en utveckling mot en miljöanpassad och hälsoinriktad byggsektor.En av de viktigaste utgångspunkterna för arbetet med att ta fram ett miljöklassningssystem har varit Bygga-bo-dialogens1 mål att alla nya hus och 30 procent av det befintliga byggnadsbeståndet ska vara miljöklassade senast år 2009. Denna ambition har medfört att enkelhet har varit ett viktigt mål för miljöklassningsarbetet. Balansen mellan trovärdighet ochenkelhet har varit viktigt för arbetet.
  • Kazmierczak, Karolina, et al. (författare)
  • An integrated analysis of ergonomics and time consumption in Swedish "craft-type' car disassembly
  • 2005
  • Ingår i: Applied Ergonomics. - Elsevier. - 1872-9126. ; 36:3, s. 263-273
  • Tidskriftsartikel (refereegranskat)abstract
    • Car disassembly is at the edge of extensive rationalisations due to increased legislative demands for recycling. This study focused on (1) assessing Current mechanical exposures (physical work loads) for comparison with future rationalised systems, with particular emphasis on time aspects, (2) analysing disassembly work in terms of time consumption and exposures in constituent tasks as defined by a loss analysis technique, and (3) predicting the consequences of car disassembly rationalisation for mechanical exposures. The study showed that disassembly implied pronounced circulatory loads, and that more walking and higher lumbar peak loads were found than in studies of assembly work. Value-adding tasks comprised 30% of the total working time, and implied higher postural exposures for the head, arm, trunk and wrist, as well as less opportunities to recover, as compared to non-value-adding tasks. Organisational-type rationalisations can be expected to increase the time spent in value-adding work, thus increasing local exposures for the average worker, while a concurrent increase in mechanisation level might reduce circulatory exposures, the amount of walking, and peak lumbar loads.
  • Keus van de Poll, Marijke, et al. (författare)
  • Unmasking the effects of masking on performance the potential of multiple-voice masking in the office environment
  • 2015
  • Ingår i: Journal of the Acoustical Society of America. - 0001-4966. ; 138:2, s. 807-816
  • Tidskriftsartikel (refereegranskat)abstract
    • Broadband noise is often used as a masking sound to combat the negative consequences of background speech on performance in open-plan offices. As office workers generally dislike broadband noise, it is important to find alternatives that are more appreciated while being at least not less effective. The purpose of experiment 1 was to compare broadband noise with two alternatives—multiple voices and water waves—in the context of a serial short-term memory task. A single voice impaired memory in comparison with silence, but when the single voice was masked with multiple voices, performance was on level with silence. Experiment 2 explored the benefits of multiple-voice masking in more detail (by comparing one voice, three voices, fivevoices, and seven voices) in the context of word processed writing (arguably a more office-relevant task). Performance (i.e., writing fluency) increased linearly from worst performance in the one-voice condition to best performance in the seven-voice condition. Psychological mechanisms underpinning these effects are discussed.
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