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Abstract. Mobile devices are more and more used for mobile interactions with things, places and people in the real world. However, so far no studies have discussed which interaction techniques are preferred by users in different contexts. This paper presents an experimental comparison of four different physical mobile interaction techniques: touching, pointing, scanning and usermediated object interaction. To evaluate these techniques across different scenarios and to collect real usage data, four prototypes were implemented: a system for mobile interaction in smart environments, a mobile tourist guide, a mobile museum guide and a prototype for mobile interaction with advertisement posters. In each setting an experimental comparison was performed. Based on the results of these studies, which involved over 60 participants in total, advantages and disadvantages of these interaction techniques are described. Context-specific user preferences are presented for the interaction techniques, to help application designers and developers decide which interaction technique(s) to integrate into their application and which consequences this decision has.

Organic Computing (OC) systems differ from classical software systems as the topology and the participating components of the system are not predefined and therefore are subject to unforeseeable change during the systems' runtime. Thus, completely new challenges to the verification and validation of such systems as well as for interactions between system components and, of course, between the system and the user arise. These challenges can be subsumed by the terms trustworthiness or trust.This paper proposes -after exploring the notions and principles of trust in the literature -a definition of trust which encompasses all aspects that define the trustworthiness of an Organic Computing system. It then outlines the different research challenges that have to be tackled in order to provide an understanding of trust in OC-systems and gives perspectives on how this endeavour can be taken on. Current research initiatives in the area of trust in computing systems are reviewed and discussed.

To reach a good user-friendliness, knowledge about user requirements is crucial in the development process of a product. The sooner the knowledge is achieved via user evaluations, the more money and time can be saved. In this paper we investigate an approach called hybrid simulation for the early stages evaluation of mobile applications where real mobile phones are used as interaction devices to a virtualised simulation of a pervasive environment. On the first sight, the method is cheap, easy and quick to use as well as more realistic compared to a virtual simulation only approach. In order to receive a more detailed insight in potential benefits and problems of the method, we performed a user study and compared results of a traditional laboratory study with the results of a study performed with the hybrid simulation.