Katharina Hahn

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In this paper we examine data dissemination in MANETs using various push and pull based protocols and a combination of both. We evaluate the protocols considering the load for each node and the resulting data freshness. Furthermore we introduce an adaptive pull protocol which enhances dissemination and saves up to 13% of the network load achieving the same(More)
Service oriented computing provides suitable means to technically support distributed collaboration of heterogeneous devices such as in mobile environments. However, wireless communication links are unstable. When supporting collaboration in such environments, failures have to be optimistically coped with in order to still provide suitable correctness(More)
With the emergence of wireless sensor networks, the issues of event recognition and processing have been partially shifted into the embedded domain. New processing capabilities on small devices allow for physically close event monitoring and fast filtering without having to set up a wired infrastructure beforehand. This opportunity for flexible deployments,(More)
Service oriented computing provides suitable means to technically support distributed collaboration of heterogeneous devices, for example those present in mobile environments. E.g., many applications are built on composite Web-Services. However, when executing these applications in dynamic environments, failures of participating entities have to be(More)
When supporting ad-hoc collaboration in heterogeneous environments, one has to be able to optimistically cope with failures in order to support reliable cooperation. Composite services technically provide suitable means to implement ad-hoc cooperations. We explore transactional properties of services at runtime to ensure correct execution of workflows by(More)
With the encapsulation of functionality in services, many applications are nowadays built on composite Web-Services. Those are specified using workflow execution languages, such as BPEL, which represent the structure of the composition. However, they do not integrate transactional guarantees such as failure-atomicity. It is up to the application designer to(More)
Mobile ad-hoc networks (MANETs) are unstable. Link errors, which are considered as an exception in fixed-wired networks must be assumed to be the default case in MANETs. Hence designing fault tolerant systems efficiently offering transactional guarantees in these unstable environments is considerably more complex. The efficient support for such guarantees(More)
Applications deployed in mobile peer-to-peer systems have to cope with mobility and fluctuation of nodes. These dynamics restrict the reliability of communication links as well as the availability of certain nodes, services, and resources. Exploring the context of nodes can be used to anticipate these shortages. Context-awareness enables improvement of(More)
The exchange of electronic information, goods or functionality is an attractive application for mobile ad-hoc networks. However, users will only take part in such systems, if the probability of a successful exchange is high enough. Exchanges may fail either because of communication failures or due to unfair behavior. Both obstacles need to be overcome to(More)
Photon counting detector (PCD)-based computed tomography (CT) is an emerging imaging technique. Compared to conventional energy integrating detector (EID)-based CT, PCD-CT is able to exclude electronic noise that may severely impair image quality at low photon counts. This work focused on comparing the noise performance at low doses between the PCD and EID(More)