Ralf Ackermann

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Following the vision of an Internet of Things (IoT) real world objects are integrated into the Internet to provide data as sensors and to manipulate the real world as actors. While current IoT approaches focus on the integration of things based on service technologies, scenarios in domains like smart cities, automotive or crisis management require service(More)
Remodeling of photosynthetic machinery induced by growing spinach plants under low light intensities reveals an up-regulation of light-harvesting complexes and down-regulation of photosystem II and cytochrome b6f complexes in intact thylakoids and isolated grana membranes. The antenna size of PSII increased by 40-60% as estimated by fluorescence induction(More)
Firewalls are a widely used security mechanism to provide access control and auditing at the border between " open " and private networks or administrative domains. As part of the network infrastructure they are strongly affected by the development and deployment of new communication paradigms and applications.Currently we experience a very fast rise in the(More)
Digital watermarking is well known as enabling technology to prove ownership on copyrighted material, detect originators of illegally made copies, monitor the usage of the copyrighted multimedia data and analyze the spread spectrum of the data over networks and servers. Research has shown that data hiding techniques can be applied successfully to other(More)
Collaborative Virtual Environments (CVEs) support the coexistence of many users in shared virtual worlds, permitting a productive collaboration among them. Due to the inherit complexity of their distributed nature and their big demands on 3D content modeling, CVEs are hard to be developed. The maintenance of CVEs, integrated with naturally captured media(More)
Intrusion detection systems (IDS) provide security for network systems. They are used in computer networks to detect violations against security policies or unusual events that could lead towards a security thread. Telephone networks based on the internet protocol (IP) called IP telephony (IPT) are a recent development in network usage and will become a(More)
Within the traditional telephone system a certain level of quality and security has been established over the years. If we try to use IP Telephony systems as a core part of our future communication infrastructure (e.g. as classical PBX enhancement or replacement) continuous high availability , stable and error-free operation and the protection of the(More)
The tremendous recent efforts to develop and deploy ubiquitous mobile communication possibilities are changing the demands but also possibilities for establishing new business and commerce relationships. Within this paper we show our innovative approach for integrating watermark and cryptography based methods within a framework of new application scenarios(More)
The initiation and propagation of a filament generated by ultrashort laser pulses in turbulent air is investigated experimentally. A filament can be generated and propagated even after the beam has propagated through strongly turbulent regions, with structure parameters C(n)2 as many as 5 orders of magnitude larger than those encountered in the usual(More)