Jakob Zwiers

Action systems and action refinement in the development of parallel systems

A new notion of refinement and several other new operators are proposed that allow for a compositional algebraic characterization of action systems and serializability in distributed database systems. A simple design language is introduced and is provided with a semantics essentially based on partial order models.

Online and off-line visualization of meeting information and meeting support

In current meeting research we see modest attempts to visualize the information that has been obtained by either capturing and, probably more importantly, by interpreting the activities that take place during a meeting. The meetings being considered take place in smart meeting rooms. Cameras, microphones and other sensors capture meeting activities. Captured information can be stored and retrieved. Captured information can also be manipulated and in turn displayed on different media. We survey our research in this area, look at issues that deal with turn-taking and gaze behavior of meeting participants, influence and talkativeness, and virtual embodied representations of meeting participants. We stress that this information is interesting not only for real-time meeting support, but also for remote participants and off-line consultation of meeting information.

Mixed reality participants in smart meeting rooms and smart home environments

Human–computer interaction requires modeling of the user. A user profile typically contains preferences, interests, characteristics, and interaction behavior. However, in its multimodal interaction with a smart environment the user displays characteristics that show how the user, not necessarily consciously, verbally and nonverbally provides the smart environment with useful input and feedback. Especially in ambient intelligence environments we encounter situations where the environment supports interaction between the environment, smart objects (e.g., mobile robots, smart furniture) and human participants in the environment. Therefore it is useful for the profile to contain a physical representation of the user obtained by multi-modal capturing techniques. We discuss the modeling and simulation of interacting participants in a virtual meeting room, we discuss how remote meeting participants can take part in meeting activities and they have some observations on translating research results to smart home environments.

Presenting in Virtual Worlds: Towards an Architecture for a 3D Presenter explaining 2D-Presented Information

Meeting and lecture room technology is a burgeoning field. Such technology can provide real-time support for physically present participants, for online remote participation, or for offline access to meetings or lectures. Capturing relevant information from meetings or lectures is necessary to provide this kind of support.Multimedia presentation of this captured information requires a lot of attention. Our previous research has looked at including in these multimedia presentations a regeneration of meeting events and interactions in virtual reality. We developed technology that translates captured meeting activities into a virtual-reality version that lets us add and manipulate information.1 In that research, our starting point was the human presenter or meeting participant. Here, it’s a semiautonomous virtual presenter that performs in a virtual- reality environment (see figure 1). The presenter’s audience might consist of humans, humans represented by embodied virtual agents, and autonomous agents that are visiting the virtual lecture room or have roles in it. In this article, we focus on models and associated algorithms that steer the virtual presenter’s presentation animations. In our approach, we generate the presentations from a script describing the synchronization of speech, gestures, and movements. The script has also a channel devoted to presentation sheets (slides) and sheet changes, which we assume are an essential part of the presentation. This channel can also present material other than sheets, such as annotated paintings or movies.

Classifying motor imagery in presence of speech

In the near future, brain-computer interface (BCI) applications for non-disabled users will require multimodal interaction and tolerance to dynamic environment. However, this conflicts with the highly sensitive recording techniques used for BCIs, such as electroencephalography (EEG). Advanced machine learning and signal processing techniques are required to decorrelate desired brain signals from the rest. This paper proposes a signal processing pipeline and two classification methods suitable for multiclass EEG analysis. The methods were tested in an experiment on separating left/right hand imagery in presence/absence of speech. The analyses showed that the presence of speech during motor imagery did not affect the classification accuracy significantly and regardless of the presence of speech, the proposed methods were able to separate left and right hand imagery with an accuracy of 60%. The best overall accuracy achieved for the 5-class separation of all the tasks was 47% and both proposed methods performed equally well. In addition, the analysis of event-related spectral power changes revealed characteristics related to motor imagery and speech.

The compositional approach to sequential consistency and lazy caching

Summary. The lazy caching protocol proposed by Afek, Brown and Merritt [ABM93], is explained and formally proven correct by means of compositional methods. The protocol is decomposed into four simple protocols, which are of interest on their own. A top level proof is given that is to a large extent independent of the particular model used for the more detailed proofs and allows for a number of generalizations of the original lazy caching protocol. Detailed proofs of safety and liveness properties are given using CSP and trace logic.

Partial Order Based Design of Concurrent Systems

A partial order based graph model for concurrency is introduced, using hierarchical structured graphs with relations denoting concurrency, causal ordering, and temporal ordering. Both compositionally structured processes as well as partial order based structures describing the semantics of processes can be expressed in this unified framework. Thus we obtain a powerful calculus that allows to algebraically transform processes or to prove properties of them.

Synchronizing Clocked Transition Systems

A model related to the CTS model of [KMP96] is introduced that deals with distributed systems with clocks that are not perfectly synchonized. The basis of the system is temporal logic of actions [Lam91], which ensures that the model is easily integrated with other formalisms. Verification rules and refinement rules for timed modules are proposed, and applied to a clock synchronization algorithm derived from [CAS86].