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- Johansson, C. G. Mikael
(författare)
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Social and Organizational Aspects of Requirements Engineering Methods
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improving requirements engineering has been recognized as critical for the 1990s. Reported differences in theoretical reasoning vs. the practice of how methods are used suggest a need for further research. A way to proceed is to investigate how real-life system design situations can be supported the best way. An important area is to investigate social and organizational aspects of the design of requirements engineering methods. Also increasing the knowledge of what is regarded as important by the users of methods for requirements engineering is essential for progress and development of new knowledge in the field.The aim of this thesis is to develop knowledge of what social and organizational issues are important for the use and development of requirements engineering methods. The research is based on a qualitative research approach using different qualitative methods and instruments for data gathering and data analysis.The results include an outline of a preliminary method for requirements engineering (Action Design). A "handbook evaluation" shows motives and needs for requirement engineering methods. Quality characteristics recognized in requirements engineering as important by the participants are established and prioritized. Thereafter, the value of visualization of internal functions for an enterprise in participatory design projects is presented. Finally, an integration of techniques for enterprise modeling and prioritization of requirements is performed to analyze what value such integration has and how improvements can be achieved.This research suggests an alternative approach to requirements engineering where support and methods are grounded in the prerequisites for each situation. The results are mainly applicable to situations where multiprofessional participation is desired. It is concluded that the organizational context has to be taken into account in the improvement of methods used in-requirements engineering.
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| 2. |
- Johansson, Mikael
(författare)
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Piecewise Linear Control Systems
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats analysis and design of piecewise linear control systems. Piecewise linear systems capture many of the most common nonlinearities in engineering systems, and they can also be used for approximation of other nonlinear systems. Several aspects of linear systems with quadratic constraints are generalized to piecewise linear systems with piecewise quadratic constraints. It is shown how uncertainty models for linear systems can be extended to piecewise linear systems, and how these extensions give insight into the classical trade-offs between fidelity and complexity of a model. Stability of piecewise linear systems is investigated using piecewise quadratic Lyapunov functions. Piecewise quadratic Lyapunov functions are much more powerful than the commonly used quadratic Lyapunov functions. It is shown how piecewise quadratic Lyapunov functions can be computed via convex optimization in terms of linear matrix inequalities. The computations are based on a compact parameterization of continuous piecewise quadratic functions and conditional analysis using the S-procedure. A unifying framework for computation of a variety of Lyapunov functions via convex optimization is established based on this parameterization. Systems with attractive sliding modes and systems with bounded regions of attraction are also treated. Dissipativity analysis and optimal control problems with piecewise quadratic cost functions are solved via convex optimization. The basic results are extended to fuzzy systems, hybrid systems and smooth nonlinear systems. It is shown how Lyapunov functions with a discontinuous dependence on the discrete state can be computed via convex optimization. An automated procedure for increasing the flexibility of the Lyapunov function candidate is suggested based on linear programming duality. A Matlab toolbox that implements several of the results derived in the thesis is presented.
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| 3. |
- Johansson, Mikael
(författare)
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Scanning Tunnelling Microscopy and Spectroscopy of Adsorbates on Aluminium and Silicon
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main topic of this thesis is the investigation of atomic andmolecular adsorbates on single crystal surfaces of silicon and aluminiumusing the techniques of scanning tunnelling microscopy (STM) andspectroscopy (STS). The emphasis has been to use atomic-resolutionspectroscopy and imaging to determine the relationship between thesurfaces' geometric and electronic structures. The STM results have beenprofitably compared with synchrotron-based valence band and core levelphotoelectron spectroscopy (PES) data to provide a more complete picturethan any single technique could provide. On Si(001) a peak seen in valence band PES at Li coverages up to 0.4 MLwas explained by STM images showing a local perturbation of theSi(001)-2x1 reconstruction by the Li atoms. STM also showed that Liadsorption on p-type substrates created localised electron traps whichinduced negative differential resistance in tunnel spectra. The formation of 3D islands of metallic MoSi2 was shown to be a generalfeature of annealing 0.1 - 10 ML Mo films on Si(001) and Si(111) at 800 C.STM and STS showing the growth of the silicide islands at the expense ofatomic-scale features formed at lower temperatures was correlated withPES data showing the changes in the Si bonding on the surface. STS of Rb on Al(111) revealed that the (Root(3)xRoot(3))R30 overlayer formedat room temperature confined electrons to a 2D quantum well state. STM ofthe growing layer supported existing models for the (Root(3)xRoot(3))R30reconstruction and a complex structure formed at lower coverages, as well asdemonstrating the existence of kinetic barriers to atomic motion on thesurface. STM of C60 on Al(111) showed details of the growth of a (2Root(3)x2Root(3))R30ordered overlayer at room temperature. Spectroscopy of an annealedsurface proved that inequivalent molecules in its (6x6) unit cell havedifferent molecular energy levels and bonding to the substrate.
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