| 21. |
- Aasa, Annika, 1963
(författare)
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User Defined Syntax
- 1992
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes two examples of user defined syntax. The first, and most thoroughly investigated, is a new datatype construction, the conctype, the elements of which have a very flexible syntax. An embedded language can easily be introduced into a programming language using conctypes and computations are easily expressed using the concrete syntax and a special pattern matching form. The second example is user defined distfix operators which give a user possibility to extend the syntax for expressions in a programming language. We describe both a user's view and the implementation of these two examples. In both cases, context-free grammars serve as a basis for the definition of the new syntax. A problem that is investigated is how to disambiguate grammars with precedences. To see how this should be done we investigate which language a grammar together with precedence rules defines. For a sub-class of context-free grammars we give a predicate that defines the precedence correct syntax trees according to some precedence rules. We also give an algorithm that transforms such a grammar to an ordinary unambiguous context-free grammar and prove the correctness of the algorithm. We use the algorithm in our implementation of distfix operators. For more general grammars, we isolate one kind of ambiguity which is suitable to resolve with precedence rules. We define the generated language for such a grammar by an attribute grammar. This approach of resolving ambiguity is used in the implementation of conctypes.
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| 22. |
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| 23. |
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| 24. |
- Abadei, Saeed, 1961
(författare)
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Ferroelectric Thin Films on Si-substrate for Tunable Microwave Applications
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis presents the development of microwave tunable devices based onferroelectric thin films. The main tasks in this work are the fabrication, optimization, andintegration of ferroelectric thin film into Si-MMIC. This work has been motivated byincreased interest on advanced tunable microwave components which meet therequirements of low microwave losses, high tunability, easy to integrate to largersystems, and low cost.Dielectric permittivity, tunability, and loss tangent are the most important parameters,characterizing ferroelectrics for application in tunable microwave devices. Most of theefforts in this work have been devoted to the optimization of film fabrication processes interms of microwave loss reduction. Experimental investigations of these parameters forNa0.5K0.5NbO3 (NKN), (SrTiO3) STO, Ba0.25Sr0.75TiO3 (BSTO) and (Pb, Zr) TiO3 (PZT)films are carried out in a wide frequency, DC bias, and temperature ranges. Thesemeasurements give important information about dispersion, temperature, and dc-fielddependencies of dielectric permittivity and losses. The latter are useful for understandingthe basic physical processes in ferroelectric films and help to optimize film depositionand device fabrication processes in terms of low losses, high tunability, and temperaturestability.Coplanar-plate structure is used to integrate the ferroelectric films into the siliconcircuits. Planar varactors are fabricated by depositing tunable ferroelectric films onSi/SiO2 substrates using laser ablation, RF magnetron sputtering, and sol-gel technique,followed by metal electrode deposition. Different varactor designs based on as straightgap, interdigital gap, and circular gap have been investigated and further used in thecomponents. Experiments show the capability and potential of tunable devices based onferroelectric thin films and confirm that they are competitive with other technologies likesemiconductors at frequency above 20 GHz. It is shown that NKN films in polar phaseare also useful for tunable microwave applications demonstrating low loss and goodtunability in a frequency above 20 GHz. BSTO films, which are in paraelectric phase atroom temperature, are used to fabricate microwave varactors. These varactors are used intwo different phase shifters designs. These tunable devices show more than 60°/dB figureof merit, which is one the best value reported so far.
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| 25. |
- Abadei, S., et al.
(författare)
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Microwave properties of tunable capacitors basee on magnetron sputtered ferroelectric Na0.5K0.5NbO3 film on low and high resistivity silicon substrates
- 2001
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 39:1-4, s. 359-366
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, small signal DC voltage dependent dielectric permittivity, loss tangent, and tuneability of magnetron sputtered epitaxial Na0.5K0.5NO3 films are studied experimentally. (100)-oriented Na0.5K0.5NbO3 films are deposited onto SiO2-buffered CMOS grade low resistivity (p = 10-20 cm) and high resistivity (p = 15-45 kcm) silicon substrates. Planar capacitors with 2 or 4 m gaps between electrodes have been fabricated on top of ferroelectric films. These devices have been characterized in the frequency range 1.0 MHz to 50 GHz at temperatures 30 - 300K. Na0.5K0.5NbO3/SiO2/Si structures on high resistivity silicon substrate exhibit C-V performances typical for Metal-Insulator- Semiconductor (MIS) capacitors. At low frequencies, f 1.0 GHz, the large tuneability and large losses are associated with the MIS structure, while at higher microwave frequencies the tuneability is mainly associated with the ferroelectric, film. At 1.0 MHz and room temperature, the tuneability of Na0.5K0.5NbO3/SiO2/Si structures more than 90%, reducing to 10-15 % at 50 GHz. The losses decrease with increasing the DC bias and frequency. A Q-factor more than 15 at 50 GHz is observed. The dielectric permittivity of the Na0.5K0.5NbO3 film is in the range 50-150 at frequencies 0.045-50 GHz. On low resistivity substrate the performance of Na0.5K0.5NbO3 films is completely screened by the high losses in silicon, and the tuneability is negligible. © 2001 Taylor and Francis.
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| 26. |
- Abadikhah, Hossein, 1987
(författare)
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Dynamic higher order equations
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis is to derive and evaluate governing equations and correspondingboundary conditions for solid cylinders and rectangular plates, where the materialconstituting the cylinder or plate are governed by classical elasticity, micropolar elasticityor a functionally graded case of the previously mentioned models. This is achieved by asystematic power series expansion approach, by either adopting a generalized Hamilton'sprinciple or a direct approach.For the solid cylinders a power series expansion in the radial coordinate for the sought fields are adopted. Equations of motion together with consistent sets of end boundaryconditions are derived in a systematic fashion up to arbitrary order using a generalizedHamilton's principle. Governing equations are obtained for longitudinal, torsional, andexural modes. In the case of the rectangular plate, a power series expansion of thesought fields are adopted in the thickness coordinate. Governing equations of motion, forextensional and exural case, together with consistent sets of edge boundary conditionsare derived in a systematic fashion up to arbitrary order with use of the direct approach.Both the governing equations for the solid cylinder and the rectangular plate areasymptotically correct to all studied orders. Numerical examples are presented fordifferent sorts of problems, using exact theory, the present series expansion theories ofdifferent order, various classical theories and other newly developed approximate theories.These results cover dispersion curves, eigenfrequencies, various curves of cross sectionalquantities such as displacements, stresses and micro-rotations, as well as fixed frequencymotion due to prescribed end displacement or lateral distributed forces. The resultsillustrate that the present approach may render benchmark solutions provided higher ordertruncations are used, and act as engineering equations when using low order truncations.
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| 27. |
- Abadikhah, Hossein, 1987
(författare)
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Dynamic higher order equations for structural elements
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis is to derive and evaluate governing equations and corresponding boundary conditions for solid isotropic cylinders and isotropic micropolar rectangular plates. This is achieved by a systematic power series expansion approach, by either adopting a generalized Hamilton's principle or a direct approach.For the solid cylinders a power series expansion in the radial coordinate is adopted. Equations of motion together with consistent sets of end boundary conditions are derived in a systematic fashion up to arbitrary order using a generalized Hamilton's principle. Governing equations are obtained for longitudinal, torsional, and flexural modes. In the case of the isotropic micropolar plate a power series expansion of the displacements and micro-rotations are adopted in the thickness coordinate. Governing equations of motion, for extensional and flexural case, together with consistent sets of edge boundary conditions are derived in a systematic fashion up to arbitrary order with use of the direct approach.Both the governing equations for the solid cylinder and the micropolar plate are asymptotically correct to all studied orders. Numerical examples are presented for different sorts of problems, using exact theory, the present series expansion theories of different order, various classical theories and other newly developed approximate theories. These results cover dispersion curves, eigenfrequencies, various curves of cross sectional quantities such as displacements, stresses and micro-rotations, as well as fixed frequency motion due to prescribed end displacement or lateral distributed forces. The results illustrate that the present approach may render benchmark solutions provided higher order truncations are used, and act as engineering equations using low order truncation.
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| 28. |
- Abadikhah, Marie, 1992
(författare)
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Influence of electrode material and stochastic factors on the performance and microbial community assembly in microbial electrochemical systems
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Microbial electrolysis cells (MECs) are systems with microbial communities in the form of biofilms on electrode surfaces. The electrogenic bacteria in the anode biofilm act as catalysts for the oxidization of organic compounds, leading to release of electrons, generation of electrical current, and production of hydrogen and methane at the cathode. In addition to production of energy carriers, MECs can be used for other applications as well; for example, as biosensors to monitor biochemical oxygen demand or toxicity. The performance of MECs is determined by both deterministic and stochastic factors influencing the microbial communities on the electrode surfaces, most of which as still poorly understood. In this thesis, the effects of electrode materials on microbial community assembly and MEC performance was investigated. Two experiments were carried out. In the first, three cathode materials (carbon nanoparticles, titanium, and steel) were compared. In the second, three anode materials (carbon cloth, graphene, and nickel) were compared. The cathode materials had no significant effect on the performance of the MECs, as opposed to the anode materials where carbon cloth MECs had the highest current density and the shortest lag time during startup. The differences seen in lag time of replicate systems at the start of the experiment indicated a stochastic initial attachment of the electrogenic bacteria on the anode. Different microbial communities develop in the biofilms on the anodes and cathodes. Electrogens from the Desulfobacterota phylum dominated the anode, while various hydrogenotrophic methanogens, e.g., Methanobacterium, were found to dominate on the cathodes. Diversity and null model analysis of the electrode communities highlighted stochasticity and not electrode material as the important factor in the community assembly. Network analysis showed that the cathode communities had fewer negative interactions between taxa in comparison to the anode. Since hydrogen gas generated at the cathode surface can diffuse through the biofilm, all microorganisms on the cathode have access to the substrate, reducing the need for competition between species. In contrast, electrogens require a short distance to the anode to be able to use it as electron acceptor. Limited space on the anode and competition between electrogens shaped the anode communities and explain the higher number of negative interactions observed. Based on the findings in this thesis, it is suggested that stochastic factors have more influence than electrode material on the anode community even though there is a selective pressure for electrogenic bacteria.
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