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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Antarctic Station-based Pressure Reconstructions from 1905-2011 using Principal Component Regression

Lee, Ming Yeung 13 June 2013 (has links)
No description available.
42

Comparison of different aluminium casting processes from an environmental perspective : Case study on plaster mould castings produced in Mid Sweden

Schaub, Henning January 2018 (has links)
While Aluminium has lots of unique properties and is seen as a material of the future, its production and manufacturing has significant environmental impacts. For complex and dimensional shapes casting remains the main manufacturing method and in this study the environmental pressure of different casting techniques is compared. A screening LCA is conducted to determine the environmental impacts of plaster mould castings in a case study at the Ventana Hackås AB foundry in Mid Sweden. The findings are compared to models of sand, pressure die and lost wax castings, based on literature datasets. The most relevant factors for the environmental performance are identified as the production of the aluminium alloy and the amount and source of energy. For plaster mould castings additionally the plaster consumption is significant, while lost wax castings are dominated by the mould production and general processes. Under similar circumstances a relatively similar performance was found for all casting techniques except the lost wax process, which is at least 3 times more emission intensive. Of the remaining techniques pressure die castings performed the best and plaster mould castings the worst, but different sources of uncertainties have been identified in this comparison. In addition a carbon footprint interface is created based on these findings, to enable specific comparisons of different casting method setups. Customizable variables allow the adaptation of three scenarios to real world conditions. As the main influencing factors the aluminium alloy, source of electricity and casting technique have been identified. / <p>2018-10-10</p>
43

Hållbart byggande för konstruktörer : Beslutunderlag för minskad miljöpåverkan i tidiga skeden / Sustainable construction for structural engineers : Decisions basis for reduced environmental impact in early stages

Barmicho, Romil, Flensburg, Olle January 2020 (has links)
Hållbarhet är något som påverkar alla. Det är en utmaning att minska överutnyttjandet av jordens resurser samtidigt som befolkningsmängden ökar. Byggsektorn har en stor påverkan på samhället och står inför flera utmaningar i sitt arbete med att minska klimat- och miljöpåverkan. Materialval är en viktig del då de största utsläppen oftast sker vid tillverkning av byggnadsmaterial.Detta arbete gjordes för att belysa hur viktig konstruktörernas del i hållbarhetsarbetet är och visa att de kan vara med och påverka beställarens beslut. Syftet med examensarbetet var att underlätta hållbarhetsarbetet i projekteringsskedet vid val av stomsystem. Konstruktörer ska kunna visa att grundläggande hänsyn tagits till minskad miljö- och klimatpåverkan. Syftet var också att utreda hur hållbarhetskonsulters analyser av konstruktörers arbete lättare kan utföras.I detta arbete utfördes semistrukturerade intervjuer tillsammans med en enkät för att utreda vilka delar som behövde utvecklas mellan projekteringsprogam och LCA-verktyg för att förenkla utförandet av en livscykelanalys (LCA). Utöver utredningen gjordes en fallstudie på ett referensobjekt i form av tre framtagna alternativ för stommar. Fallstudien utfördes genom en förenklad LCA i projekteringsprogrammet Revit. Den data som användes för de ingående materialen sammanställdes först i en lista med emissionsvärden för klimatpåverkan, ozonnedbrytning, försurning och övergödning. Dessa värden hämtades från olika miljövarudeklarationer (EPD:er) som fanns publicerade i publika databaser. Därefter formades ett ”Schedule” i Revit för att visa miljöpåverkan från de olika stomalternativen direkt i programmet. Listan utformades som en informationsguide och framtagningen av ett ”Schedule” i Revit förklaras grundligt för att konstruktörer ska kunna ta hjälp av detta vid framtida projekteringar för en minskad miljöpåverkan.Resultatet av utredningen visar att många av de utmaningar som tidigare studier har visat fortfarande är aktuella. Bland dessa är kravställandet på projekteringen en av de punkter som nämns mest. Flera förslag på hur kravställandet kan gå till nämns bl.a. genom en matris som vanligtvis används vid kravställande i projekt med BIM-samordning. Vidare ansåg intervjupersonerna att en kravställningsmall bör tas fram för att kunna användas i samtliga projekt, även om inte en LCA ska utföras.Det resultat som fallstudien visar var att stomalternativet i stål är det som påverkar miljön mest i alla kategorier som jämfördes. Träalternativet visade sig inte vara nämnvärt mycket lägre än betongalternativet ur klimatpåverkansperspektiv. Detta på grund av de avväxlingsbalkar i stål som användes för att avlasta det befintliga planet som stommen skulle byggas på. Det visas genom ett cirkeldiagram och analyseras vidare i diskussionen. / Sustainability is something that affect us all. It´s challenging to reduce the over-utilization of the earth’s resources at the same time as the population is increasing. The building sector has a big impact on the society and faces several challenges in the work to reduce climate and environmental impacts. Material choice is an important part because the largest emissions comes from the manufacturing phase.This study was made to highlight the importance of structural engineer’s part in the sustainability work and the impact on the purchaser’s decision. The purpose of this degree project was to support the sustainability work in the design stage when choosing a load bearing structure. The structural engineer could show that basic consideration was taken to reduce the environmental and climate impacts. The purpose was also to investigate how to facilitate sustainability consultants’ assessments of the work delivered by structural engineers.Semi-structured interviews were conducted together with a survey to investigate the parts in need of further development between design programs and LCA-applications in the process to execute and simplify sustainability analysis. Besides the investigation, a case study was made on a reference object. The object had three alternatives of load bearing structures. The case study was performed through a simplified LCA in Revit. The data that was used for the included materials was compiled to a schedule with emission values of climate influences, ozone decomposition, acidification and overfertilization. These emission values were retrieved from different EPD:s hat was published in open access databases. After the emissions were retrieved a schedule was made in Revit that showed the environmental impact for the different structural alternatives.The schedule was designed as a guide and the development of a schedule in Revit is explained thoroughly as guidance for structural engineers in future projects to reduce the environmental impact.The results of the investigation show that a lot of challenges that former studies have shown are still valid. Among these challenges, most of the respondents mentioned the prerequisites for projects to be one of the main points. One of the many proposals on how the setting requirements would take place was through a matrix that often is used in projects with BIM-coordination. Furthermore, the interviewers felt that the requirements for data should be developed for all projects, even though an LCA-analyze is not required.The results from the case study show that structures in steel affected the environment most in all the categories that was compared. The wood option showed that it was not that much lower from a climate impact perspective compared to the concrete option. This was because of the members in steel that was used to unload the existing floor which the structure would build on. This is shown with a pie chart and is further analyzed in the chapter of discussion.
44

Analysis of Particle Precipitation and Development of the Atmospheric Ionization Module OSnabrück - AIMOS

Wissing, Jan Maik 31 August 2011 (has links)
The goal of this thesis is to improve our knowledge on energetic particle precipitation into the Earth’s atmosphere from the thermosphere to the surface. The particles origin from the Sun or from temporarily trapped populations inside the magnetosphere. The best documented influence of solar (high-) energetic particles on the atmosphere is the Ozone depletion in high latitudes, attributed to the generation of HOx and NOx by precipitating particles (Crutzen et al., 1975; Solomon et al., 1981; Reid et al., 1991). In addition Callis et al. (1996b, 2001) and Randall et al. (2005, 2006) point out the importance of low-energetic precipitating particles of magnetospheric origin, creating NOx in the lower thermosphere, which may be transported downwards where it also contributes to Ozone depletion. The incoming particle flux is dramatically changing as a function of auroral/geomagnetical activity and in particular during solar particle events. As a result, the degree of ionization and the chemical composition of the atmosphere are substantially affected by the state of the Sun. Therefore the direct energetic or dynamical influences of ions on the upper atmosphere depend on solar variability at different time scales. Influences on chemistry have been considered so far with simplified precipitation patterns, limited energy range and restrictions to certain particle species, see e.g. Jackman et al. (2000); Sinnhuber et al. (2003b, for solar energetic protons and no spatial differentiation), and Callis et al. (1996b, 2001, for magnetospheric electrons only). A comprehensive atmospheric ionization model with spatially resolved particle precipitation including a wide energy range and all main particle species as well as a dynamic magnetosphere was missing. In the scope of this work, a 3-D precipitation model of solar and magnetospheric particles has been developed. Temporal as well as spatial ionization patterns will be discussed. Apart from that, the ionization data are used in different climate models, allowing (a) simulations of NOx and HOx formation and transport, (b) comparisons to incoherent scatter radar measurements and (c) inter-comparison of the chemistry part in different models and comparison of model results to MIPAS observations. In a bigger scope the ionization data may be used to better constrain the natural sources of climate change or consequences for atmospheric dynamics due to local temperature changes by precipitating particles and their implications for chemistry. Thus the influence of precipitating energetic particles on the composition and dynamics of the atmosphere is a challenging issue in climate modeling. The ionization data is available online and can be adopted automatically to any user specific model grid.

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