| 21. |
- Birgisson, Ragnar, et al.
(författare)
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Bounds on Test Effort for Event-Triggered Real-Time Systems
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The test effort required for full test coverage is much higher in an event-triggered than in a time-triggered real-time system. This makes it difficult to attain confidence in the correctness of event-triggered real-time applications by testing, which is a necessary complement to other verification methods. We present a more general upper bound on the test effort of constrained event-triggered real-time systems, assuming multiple resources (a refinement of previous results). The emphasis is on system level testing of application timeliness, assuming that sufficient confidence in its functional correctness has been attained. Covered fault types include incorrect assumptions about temporal attributes of application and execution environment, and synchronization faults. An analysis of the effects that our constraints have on predictability and efficiency shows that the use of designated preemption points is required. A key factor in this approach is the ability to reduce the number of required test cases while maintaining full test coverage.
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| 22. |
- Biro, Zoltan, et al.
(författare)
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Evolution of visually-guided approach behaviour in recurrent artificial neural network robot controllers
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Analysis of internal structures of embodied and situated agents may provide insights into the mechanisms underlying adaptive behaviour. This paper is concerned with the evolution and analysis of visually-guided approach behaviour in a simulated robotic agent controlled by a recurrent artificial neural network, whose connection weights have been evolved using evolutionary algorithms. Analysis of the evolved behaviours and their network-internal mechanisms reveals a behavioural structure and organization resembling a Brooksian subsumption architecture. The task decomposition, as well as the resulting individual behaviours and their integration, however, are realized as network-internal state space dynamics, evolved in the course of agent-environment interaction, i.e. with a minimum of designer intervention.
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| 23. |
- Bodén, Mikael
(författare)
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A Connectionist Variation on Inheritance
- 1996
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A connectionist architecture is outlined which makes use of RAAM to generate representations for objects in inheritance networks and extended learning to make such representations context-sensitive. The architecture embodies inheritance quite differently by relying on associative similarities and regions in representational space. The model avoids many of the problems identified for traditional inheritance.
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| 24. |
- Bodén, Mikael, et al.
(författare)
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Features of distributed representations for tree-structures : A study of RAAM
- 1995
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an in-depth analysis of properties of patterns, generated by the Recursive Auto-Associative Memory, based on the idea that representational features can be detected by a classification network. The intension of this analysis is to examine the actual reasons for the success of connectionist processes acting on super-positional activity vectors generated in the fashion described. We show that the structure supplied during training is maintained and is extractable from the generated pattern. Further, we show that the influence of the actual constituents in the structures supplied during training is not necessarily available, in the generated patterns, for holistic processing. The outlook for holistic processing is therefore limited unless new forms can be found which take into account, what Sharkey and Jackson call, `whole net' representations.
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| 25. |
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| 26. |
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| 27. |
- Ejdebäck, Mikael, 1969-, et al.
(författare)
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Effects of codon usage and vector-host combinations on the expression of spinach plastocyanin in Escherichia coli
- 1997
-
Ingår i: Protein Expression and Purification. - : Elsevier. - 1046-5928 .- 1096-0279. ; 11:1, s. 17-25
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Tidskriftsartikel (refereegranskat)abstract
- Spinach plastocyanin has been expressed in Escherichia coli and exported to the periplasmic space. The effects of codon usage, expression system, growth length, and temperature on expression levels in LB medium were investigated. A stretch of codons, rare in E. coli, was identified and replaced with highly expressed codons, increasing the yield by at least 20%. Plastocyanin was more efficiently expressed under the T7 promoter than under the lac promoter. Maximum yields were obtained at 37 degrees C when growing the cells for 16 h after induction. The optimized expression system produced 38 mg holoprotein per liter culture. In this system it was also possible to express plastocyanin in minimal medium, at a yield of 10 mg per liter. N-terminal sequencing and mass spectrometry showed that plastocyanin was correctly processed. The expressed plastocyanin was purified to homogeneity, as shown by an A278/A597 ratio of 1.0, and together with amino acid analysis and the determination of oxidized and total copper contents, both the absorption coefficients for epsilon 278 and for epsilon 597 were determined to be 4700 M-1 cm-1.
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| 28. |
- Ejdebäck, Mikael, 1969-
(författare)
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Studies on spinach plastocyanin and mutants : Expression in Escherichia coli, folding and function
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Photosynthesis is a process in which photons from sunlight excite chlorophylls in the thylakoid membranes of plants, algae and cyanobacteria. The photo-oxidised reaction centre chlorophyll P700 is re-reduced by an electron transferred from the soluble, blue copper protein plastocyanin. The oxidised plastocyanin dissociates and binds to the cytochrome b6f complex, where it accepts an electron and a new redox cycle can begin. Plastocyanin has three regions of importance for the interaction with its redox partners, a hydrophobic patch and two acidic (negatively charged) patches. Electrostatic interactions between opposite charges are important for the association and the specificity and stability of the formed complexes.In this work the interactions with photosystem 1 and cytochrome c have been studied using mutants of plastocyanin. The mutations introduced in the small acidic patch and position 88 of plastocyanin had small effects on the binding to photosystem 1 as compared to the weak binding reported for mutants in the large acidic patch. The affinity was increased by the Glu60Gln, Glu60Lys and Asp61Lys mutations and a more efficient electron transfer was observed for the Gln88Lys mutation. The association between Pc mutated in the small acidic patch and cytochrome c was weakened and the rearrangement hindered by lysines in positions 59 and 60.The development of an efficient expression system for spinach plastocyanin in the bacterium Escherichia coli made it possible to produce sufficient amounts of isotopically labelled plastocyanin for NMR experiments. This technique was used for solving the structure of the complex between plastocyanin and cytochrome f. The hydrophobic patch on plastocyanin binds to an area close to the heme on cytochrome f. Electrostatic interactions between opposite charges on the two proteins are also important. The short distance from the heme to the copper ligand His87 suggests an electron transfer from the heme via Tyr1 or Phe4 on cytochrome f.The involvement of specific amino-acid residues in copper binding or folding of plastocyanin has also been examined by site-directed mutagenesis. The copper-binding histidines have been replaced by other amino acids, but no blue protein could be produced. The stability of the different redox forms of copper plastocyanin as well as the zinc protein has also been determined by guanidinium-induced unfolding.
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| 29. |
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| 30. |
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