| 21001. |
- Rossi, Barbara, et al.
(författare)
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Life Cycle Impacts Assessment of Steel, Composite, Concrete and Wooden Columns
- 2011
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Ingår i: Proceedings of the final conference in Innsbruck. - Malta : University of Malta. ; , s. 277-284
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a comparative study showing the environmental profile of structural members used in the construction domain. The functional unit is a column that is realistic in terms of dimensions and load bearing capacity, made of steel or high strength steel sections, steel and concrete (composite), reinforced concrete, solid wood and glue-laminated wood. The design of the columns is made following the Eurocodes. Several environmental impacts are assessed, such as the global warming potential and energy consumption while also focusing on the acidification potential. The results are presented in the forms of bar charts for each considered column. For steel and concrete, depending on the source of information, the inventory can vary substantially e.g. the CO and CH4 emissions. Several sources of information are provided and used to perform a brief sensitivity analysis. The influence of the recycling of steel taking into account the IISI methodology will also be discussed.
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| 21002. |
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| 21003. |
- Rossi Espagnet, Alberto, et al.
(författare)
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Techno-economic assessment of Thermal Energy Storage integration into Low Temperature District Heating networks
- 2016
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Ingår i: Book of abstracts. - : Aalborg Universitetsforlag.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Thermal energy storage (TES) systems are technologies with the potential to enhance the efficiency and the flexibility of the coming 4th generation low temperature district heating (LTDH). Their integration would enable the creation of smarter, more efficient networks, benefiting both the utility and the end consumers. This study aims to develop a comparative assessment of TES systems, both latent and sensible heat based. First, a techno-economic analysis of several TES systems is conducted to evaluate their suitability to be integrated into LTDH. Then, potential scenarios of TES integration are analysed in a case study of a LTDH network. This is complemented with a review of current DH legislation focused on the Swedish case, with the aim of taking into consideration the present situation, and changes that may support some technologies over others. The results of the analysis show that sensible heat storage is still preferred to latent heat when coupled with LTDH: the cost per kWh stored is still 15% higher for latent heat in systems below 5MWh of storage size; though, they require just half of the volume. However, it is expected that the cost of latent heat storage systems will decline in the future, making them more competitive. From a system perspective, the introduction of TES systems into the network results in an increase in flexibility leading to lower heat production costs by load shifting: by running the production units with lower marginal heat production costs for longer periods and with high efficiency, and thus reducing the operating hours of the other more expensive operating units during peak load conditions. These results may also be extended to the case when heat generation is replaced by renewable, intermittent energy sources; thus increasing profits, reducing fuel consumption, and consequently emissions. This study represents a step forward in the development of a more efficient DH system through the integration of TES which will play a crucial role in future smart energy system.
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| 21004. |
- Rossitto, Chiara, 1976-
(författare)
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Managing Work at Several Places : Understanding Nomadic Practices in Student Groups
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Within Swedish universities students are often required to work in groups to collaborate on projects or to write essays. A salient feature characterizing this type of work is the lack of a stable and fixed location wherein project- related activities can be carried out and accomplished. Thus, by regarding students as instances of nomadic workers, this thesis investigates the nomadic practices in the context of their group work, with particular attention to issues related to collaborative and coordinative aspects. Although the lack of a stable office has, somehow, always characterized students’ activities, the spread of mobile technologies raises relevant analytical issues concerning the relationships between individuals’ practices, the use of particular technologies and the physical environments in which interactions may occur. In this regard, this thesis provides an example of how a philosophical conceptualization of place as the product of human experience can assist in exploring: (a) the relationships between students’ activities, the locales they work at, and the situated use of specific technological artifacts; (b) how students occupy and experience places, by investing them with activities, meanings and values; (c) how different physical environments constrain and shape the way activities are performed. The data were collected by means of ethnographically-informed methods during two different field studies for which two design courses, held at a technical university, had been chosen as settings. Within both of them, the participants were to develop a prototype of novel IT technologies, and to account for the evolution of their projects by means of a report. The two studies aimed at understanding: (a) how students organize their activities at a number of locations, and how it reflects on the activities they engage with; (b) the strategies they adopt and the technologies they use to overcome problems deriving from the lack of a stable workplace, (c) the different ways a workplace is practically created, how it emerges from students’ interactions with the environment they inhabit, and how it is mediated by the technology they use (place-making). Observations, field-notes, video-recordings, semi-structured interviews were used during the phase of data collection. Some participants were also asked to fill in a diary and to take pictures of the different sites used for their project activities. In addition, a workshop, organized as a focus group, was arranged in order to unpack issues concerning students’ usage of various technologies, with respect to number of people involved, ongoing activities and the related chosen locations. The data analysis suggests that taking into account the way a place is disassembled and the way nomadic workers manage to move out of it is central to an understanding of their work practices. Moreover, it shows that the participants experienced planning the division of work as essential in order to manage coordination and collaboration within the groups, to organize collaborative and individual activities, and to allocate them to differing physical places. Furthermore, this thesis outlines in what way a focus on place may assist designers in reflecting on the design of educational environments, and of technological artifacts enabling students to share and integrate heterogeneous sources of information.
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| 21005. |
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| 21006. |
- Rostami, Jowan
(författare)
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Functional Low-Density Materials from Cellulose Fibers and Fibrils
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose-based aerogels are emerging bio-based materials for a range of applications in the quest toward a circular and carbon-neutral society. Owing to their lightweight nature, high porosity, high specific surface area, biocompatibility, and biodegradability, cellulose aerogels are suitable for packaging, insulation, wound care products, hygiene products, and water purification. However, their commercial use is hampered by complicated time- and energy-consuming fabrication processes. Hence, industrially relevant processes with upscaling opportunities need to be developed for cellulose-based aerogels to reach their full potential. This thesis explores different scalable and simple methods for preparing and designing highly porous aerogels with high wet integrity using cellulose-rich fibers and cellulose nanofibrils (CNFs). As wet integrity is crucial for specific applications and enables further functionalization of the aerogels using water-based chemistry, different methods were developed to achieve wet integrity without complicated crosslinking procedures. The effects of the raw materials and processing methods on the final material properties were also carefully studied to optimize the performance for the targeted applications. Moreover, the role of the network-forming ability of CNFs in the development of functional materials with structural integrity was explored by incorporating small amounts of CNFs in aerogel systems based on macroscopic cellulose-rich fibers and nanosized metal-organic frameworks. Finally, the potential of the different developed cellulose-based or cellulose-reinforced aerogels with high wet integrity was demonstrated in applications for which the aerogels’ structural integrity and physical and mechanical properties are highly advantageous, such as biomedical applications, gas storage and separation, flame retardancy, and hygiene products. As demonstrated in this thesis, these functional aerogel materials could be a bio-based alternative for today’s fossil-based materials.
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| 21007. |
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| 21008. |
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| 21009. |
- Roth, Olivia, 1978-
(författare)
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Physical and Chemical Aspects of Radiation Induced Oxidative Dissolution of UO2
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Denna licensiatavhandling behandlar oxidativ upplösning av UO2. Upplösning av UO2 studeras huvudsakligen då UO2-matrisen hos använt kärnbränsle förväntas fungera som en barriär mot frigörande av radionuklider i ett framtida djupförvar. Lösligheten av U(IV) är mycket låg under i djupförvaret rådande förhållanden emedan U(VI) har betydligt högre löslighet. Oxidation av UO2-matrisen kommer därför att påverka dess löslighet och därmed dess funktion som barriär. I denna avhandling studeras den relativa effektiviteten av en- och två-elektronoxidanter för upplösning av UO2. Vid låga oxidantkoncentrationer är utbytet för upplösningen för en-elektronoxidanter signifikant lägre än för två-elektronoxidanter. För en-elektronoxidanter ökar dock utbytet med ökande oxidanthalt, vilket kan förklaras av den ökade sannolikheten för två konsekutiva en-elektronoxidationer av samma reaktionssite och den ökade möjligheten till disproportionering. Radikaler och molekylära radiolysprodukters relativa inverkan på oxidativ upplösning av UO2 studeras också i denna avhandling genom mätning av mängden upplöst U(VI) i γ-bestrålade system som dominerades av olika oxidanter. Dessa studier visade att upplösningshastigheten av UO2 kan uppskattas från oxidantkoncentrationer framtagna genom simuleringar av radiolys i motsvarande homogena system och hastighetskonstanterna för ytreaktionerna. Simuleringarna visar att de molekylära oxidanterna kommer vara de viktigaste oxidanterna i alla system i denna studie vid långa bestrålningstider (>10 timmar). Vid liknande simuleringar av α-bestrålade system fanns att vid förhållanden relevanta för ett djupförvar för använt kärnbränsle, är det endast de molekylära oxidanterna (i huvudsak H2O2) som är av betydelse för upplösningen av bränslematrisen. Då använt kärnbränsle innehåller en mängd radionuklider som utsätter UO2-matrisen för kontinuerlig bestrålning, är det av vikt att undersöka hur bestrålning påverkar reaktiviteten av UO2. Bestrålningseffekten på reaktionen mellan UO2 och MnO4- studerades. Dessa försök visade att bestrålning av UO2 vid doser >40 kGy leder till att reaktiviteten ökar upp till 1.3 gånger reaktiviteten av obestrålad UO2. Den ökade reaktiviteten kvarstår efter bestrålningen och effekten kan därför möjligen tillskrivas permanenta förändringar i materialet. Vid uppskattning av reaktiviteten hos använt kärnbränsle måste hänsyn tas till denna effekt då bränslet redan efter ett par dagar i reaktor blivit utsatt för doser >40 kGy. Det har tidigare föreslagits att hastigheten för en heterogen västka/fast-fas reaktion är beroende av partikelstorleken hos det fasta materialet, vilket har studerats för UO2-partiklar i denna avhandling. Experimentellt bestämda kinetiska parametrar jämförs med de föreslagna ekvationerna för fyra storleksfraktioner av UO2-pulver och en UO2-pellet. Studien visade partikelstorleksberoendet av andra ordningens hastighetskonstant och aktiveringsenergin för oxidation av UO2 med MnO4- beskrivs relativt väl av de föreslagna ekvationerna.
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| 21010. |
- Roth, Olivia, 1978-
(författare)
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Redox Chemistry in Radiation Induced Dissolution of Spent Nuclear Fuel : from Elementary Reactions to Predictive Modeling
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this doctoral thesis is the redox chemistry involved in radiation induced oxidative dissolution of spent nuclear fuel and UO2 (as a model substance for spent nuclear fuel). It is shown that two electron oxidants are more efficient than one electron oxidants in oxidative dissolution of UO2 at low oxidant concentrations. Furthermore, it is shown that H2O2 is the only oxidant that has to be taken into account in radiation induced dissolution of UO2 under deep repository conditions (granite groundwater dominated by α-radiolysis). Previously determined rate constants for oxidation of UO2 by H2O2 and O2, and rate constants for dissolution of U(VI) from the surface are successfully used to reproduce numerous UO2 dissolution rates reported in the literature. The impact of reactive solutes (Fe(II)(aq), 2-propanol and chloride) and Pd-inclusions (as a model for ε-particles) in combination with H2, on radiation induced oxidative dissolution of UO2 is investigated. It is shown that both the studied reactive solutes (under oxygen free conditions) and the combination of Pd inclusions and H2 inhibit the dissolution. Calculations (based on the fuel inventory) show that 1 µM Fe(II)(aq) decreases the dissolution rate by a factor of ~50 and that 1 ppm surface coverage of ε-particles is sufficient to completely stop the dissolution of 100 year old fuel (assuming 40 bar H2).The dissolution behavior of NpO2 and PuO2 in H2O2 containing aqueous solution without complexing agent is studied and compared to UO2. Based on the measured dissolution rates, we would not expect the dissolution of the actinides to be congruent. Instead, in a system without complexing agent, the rates Np and Pu are expected to be lower than the U release rate. The effect of ionizing irradiation on the UO2 reactivity is studied in order to elucidate the effect of self-irradiation on the reactivity of the spent fuel matrix. It is shown that a threshold dose must be achieved before any effect of irradiation can be seen. Beyond the threshold the reactivity seems to increase with increasing dose. Furthermore, the effect appears to be permanent. The effect of particle size on the reactivity of UO2 powder is studied in view of proposed theories suggesting a particle size dependence of both the pre-exponential factor and the activation energy for redox reactions. The rate constant and activation energy for oxidation of UO2 by MnO4- seems to agree with the proposed equations. The radiation chemical synthesis of UO2 nanoparticles is studied. It is shown that U(VI) released by dissolution of spent nuclear fuel could be reduced to UO2 nanoparticles.These particles could, due to their high reactivity towards H2O2, act as oxidant scavenger in a future deep repository for spent nuclear fuel.
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