| 51. |
- Abdurrokhman, Iqbaal, 1991
(författare)
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Proton conducting ionic liquids-Binary mixtures and structural modifications
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proton conduction is a phenomenon of fundamental importance for biological and chemical systems, such as in photosynthesis and aerobic respiration. Proton conduction is also key in the proton exchange membrane fuel cell, a clean electrochemical device that converts chemical into electrical energy. The archetypical proton exchange membrane is currently a perfluorinated polymer with pending acidic groups. The fuel cell technology is presently at renewed focus in the commercial sector, and consequently also in the scope of research and development programs. In order to enable the development of more sustainable proton exchange membrane fuel cells, new requirements have been set that for instance target operation at higher temperatures and anhydrous conditions. In this context, protic ionic liquids have been highlighted as interesting next-generation electrolytes with the potential to assist proton conduction. Protic ionic liquids are a subset of ionic liquids, also known as low temperature molten salts, entirely composed of ions and displaying very low vapor pressures. Moreover, a protic ionic liquid has an exchangeable proton and is able to establish extended networks of hydrogen bonds. Understanding the dynamics of this local structures is fundamental to design new protic ionic liquids able to sustain a fast proton motion decoupled from the diffusion of the ionic species. To achieve such a dynamical behavior we have investigated two different approaches, that is i) mixing a protic ionic liquid candidate with a co-solvent (here ethylene glycol) able to participate in the hydrogen bonds and ii) modifying the molecular structure of the cation (here by alkyl chains of length (n) varying from ethyl (n=2) to dodecyl (n=12)) in a series of imidazolium based protic ionic liquids. The local intermolecular inter- actions, the nano-structuration as well as ionic and protonic dynamics have been investigated by suitable techniques that include vibrational spectroscopy, NMR spectroscopy, diffusion NMR, impedance spectroscopy and X-ray scattering.
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| 52. |
- Abedi, Hamidreza, 1979
(författare)
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Development of Vortex Filament Method for Aerodynamic Loads on Rotor Blades
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wind power is currently one of the most reliable new energy sources serving as an alternative tofossil fuel generated electricity and is known as a widely distributed clean and renewable sourceof energy. It is now the world’s fastest growing energy source and has also become one of themost rapidly expanding industries.The aerodynamics of a wind turbine are governed by the flow around the rotor, where theprediction of air loads on rotor blades in different operational conditions and its relation to rotorstructural dynamics is crucial for design purposes. One of the most important challenges in windturbine aerodynamics is therefore to accurately predict the forces on the blade, where the bladeand wake are modeled by different approaches such as the Blade Element Momentum (BEM)theory, the vortex method and Computational Fluid Dynamics (CFD). Here, the application ofthe vortex filament method for wind turbine aerodynamic performance is used. Different blademodels such as the lifting line and the lifting surface with prescribed and free wake models arestudied. The main purpose is to find the proper combination of blade and wake models for theaerodynamic loads as well as the computational time in order to develop an accurate and efficientaerodynamic tool. The results of the different approaches are compared with the BEM methodand GENUVP code (see the acknowledgments).
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| 53. |
- Abedi, Hamidreza, 1979
(författare)
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Development of Vortex Filament Method for Wind Power Aerodynamics
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wind power is currently one of the cleanest and widely distributed renewable energy sources serving as an alternative to fossil fuel generated electricity. Exponential growth of wind turbines all around the world makes it apt for different research disciplines. The aerodynamics of a wind turbine is governed by the flow around the rotor, where the prediction of air loads on rotor blades in different operational conditions and its relation to rotor structural dynamics is crucial for design, development and optimization purposes. This leads us to focus on high-fidelity modeling of the rotor and wake aerodynamics. There are different methods for modeling the aerodynamics of a wind turbine with different levels of complexity and accuracy, such as the Blade Element Momentum (BEM) theory, Vortex method and Computational Fluid Dynamics (CFD). Historically, the vortex method has been widely used for aerodynamic analysis of airfoils and aircrafts. Generally, it may stand between the CFD and BEM methods in terms of the reliability, accuracy and computational efficiency. In the present work, a free vortex filament method for wind turbine aerodynamics was developed. Among different approaches for modeling theblade (e.g. a lifting line or a lifting surface) and wake (e.g. a prescribed or a free wake model), the Vortex Lattice Free Wake (VLFW) model known as the most accurate and computationally expensive vortex method was implemented. Because of the less restrictive assumptions, it could be used for unsteady load calculations, especially for time-varying flow environment which are classified according to the atmospheric conditions, e.g. wind shear and turbulent inflow together with the turbine structure such as yaw misalignment, rotor tilt and blade elastic deformation. In addition to the standard potential methodfor aerodynamic load calculation using the VLFW method, two additional methods, namely the 2D static airfoil data model and the dynamic stall model were implemented to increase capability of the free vortex wake method to predict viscous phenomena such as drag and separation using tabulated airfoil data. The implemented VLFW methodwas validated against the BEM and CFD methods, the GENUVP code by National Technical University of Athens (NTUA), Hönö turbine measurement data and MEXICO wind tunnel measurements. The results showed that the VLFW model might be used as a suitable engineering method for wind turbine’s aerodynamics covering a broad range of operating conditions.
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| 54. |
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| 55. |
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| 56. |
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| 57. |
- Abel, Enno, 1935, et al.
(författare)
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Byggnaden som system
- 2006
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Bok (övrigt vetenskapligt/konstnärligt)
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| 58. |
- Abel, Frida, 1974
(författare)
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Genetic studies of neuroblastoma with emphasis on the apoptotic pathway
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aim: The objective of this thesis was to find genes and chromosomal regions involved in neuroblastoma (NB) tumor progression. NB is a childhood tumor of the sympathetic nervous system that generally occurs spontaneously. Biologically, NB has a complex heterogeneity from tumor progression to tumor regression, dependent on clinical stage and age at diagnosis. The main genetic markers, which are also of prognostic value in NB, are amplification of the oncogene MYCN, deletion of chromosome arm 1p and gain of chromosome arm 17q. Results: We have been shown using fluorescence in situ hybridization (FISH) on a Scandinavian tumor material, that 17q gain is present in approximately 65% of all NB stages, is significantly associated with poor prognosis and predicts survival. The gene encoding somatostatin receptor 2 (SSTR2), localized in chromosome region 17q24, was not found to be mutated in any NB, when analyzed with PCR-based single stranded conformation polymorphism/heteroduplex (SSCP/HD) and DNA sequencing. In a tentative effort of defining of the location of a general embryonal tumor suppressor gene (TSG) on 1p, we combined the smallest region of overlap (SRO) of 1p deletions in NB tumors and germ cell tumors (GCTs). We thus delimited the NB/GCT SRO to approximately 5 cM between markers D1S508 and D1S244, and fine-mapped this region by radiation hybrid mapping and construction of a bacterial artificial chromosome (BAC) contig. A homozygously deleted region in an NB cell line was found to partially overlap the proximal part of the 5 cM-SRO defined by us, which further focused our search for a TSG to a 500 kb candidate region in 1p36.22. Two attractive candidate NB TSGs, DFFA and CASP9, are both located in 1p36.2 and encode key apoptotic mediators. In fact, DFFA resides in the 500 kb TSG candidate region. Via sequence analysis of the entire tumor material, we found three different coding alterations in DFFA which all affect the highly conserved N-terminal regulatory domain of DFF45. Using RT-PCR and real-time RT-PCR (TaqMan) studies, we were able to show that both DFFA and CASP9 are preferably expressed in NB tumors with favorable outcome. It has been proposed that lack of apoptosis plays an important role in tumor progression. We therefore screened an array with cDNAs involved in the apoptotic process, to find genes differentially expressed in NB tumors with unfavorable versus favorable biology. Using real-time RT-PCR analysis, we verified the differential expression of several transcripts encoding mitochondrial apoptotic mediators. Conclusions: We have shown that 17q gain is the most frequently detected alteration in NB and that it is associated with established prognostic factors. We narrowed down the TSG candidate region on 1p and found mutations in a gene localized in the region possessing fundamental functions in apoptosis. Our results also suggest that the mitochondrial apoptotic pathway is suppressed at multiple steps in advanced stages of NB tumors, due to imbalance between anti-apoptotic and pro-apoptotic mediators.
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| 59. |
- Abeywickrama, Nilanga, 1976
(författare)
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Effect of Dielectric and Magnetic Material Characteristics on Frequency Response of Power Transformers
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Frequency response analysis (FRA) technique has become increasingly popular for the assessment of mechanicalintegrity in power transformers. This method is based on the fact that the shape of the frequency response at higher frequencies is uniquely determined by the geometrical construction of the transformer. However, characteristics of the insulation system (pressboard, paper and oil) and the laminated ferromagnetic core may influence the distributed inductances and capacitances, resulting in deviations of the frequency response.The main goal of this thesis is to investigate the influence of properties of the core and insulation materials on the frequency response of power transformers. To be able to realize this goal, a small-signal high frequency model based on lumped circuit approach, of which all the circuit parameters are calculated by considering the frequency dependent phenomena related to transformer insulation and core materials, is developed. Capacitances and conductances are calculated based on analytical expressions derived from approximated geometrical parameters and measured frequency dependent permittivities of paper and pressboard. Hierarchical multi-scale modelling approach is adaptedfor the purpose of calculating inductances and resistances,including anisotropic properties of the core and diamagneticproperties of the windings. Complex permeability of silicon steel laminations, which is a vital input parameter in inductance calculations, is estimated using an optimization algorithm as well as by means of a single sheet tester.The developed circuit model is implemented in MATLAB as a state space model, which is used to quantify the influence of insulation condition on the frequency response and to explore a possibility of using FRA technique for characterization of the transformer insulation. According to the model prediction, the moisture content in transformer insulation can influence the response most, since it modifies both the real part of dielectric permittivityand the losses.Measurements were performed on two transformers at differentmagnetization levels to show effects of remanent magnetization in the core due to removal of 3-phase supply, relaxation demagnetization and DC flux on the frequency response of winding impedance. It was found that the low frequency response (
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| 60. |
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