Volker Ahlers

Hochschule Hannover · Faculty IV, Dept. of Computer Science

We present an approach towards a data acquisition system for digital twins that uses a 5G network for data transmission and localization. The current hardware setup, which utilizes stereo vision and LiDARfor 3D mapping, is explained together with two recorded point cloud data sets. Furthermore, a resulting digital twin comprised of voxelized point...

In this paper, we present a novel approach for real‐time rendering of soft eclipse shadows cast by spherical, atmosphereless bodies. While this problem may seem simple at first, it is complicated by several factors. First, the extreme scale differences and huge mutual distances of the involved celestial bodies cause rendering artifacts in practice....

Although machine learning (ML) for intrusion detection is attracting research, its deployment in practice has proven difficult. Major hindrances are that training a classifier requires training data with attack samples, and that trained models are bound to a specific network. To overcome these problems, we propose two new methods for anomaly-based...

Global urbanization for decades has led to unprecedented levels and growing demands for urban logistics. Thus, problems such as congestion, environmental noise, and urban sprawl are growing. As a result, many cities face problems of optimal decision-making regarding green and sustainable smart transportation systems and infrastructures. However, va...

Large scale 3D scenes in applications like space simulations are often subject to depth buffer related issues and visual artefacts like Z-fighting and spatial jittering. These issues are primarily a result of indistinguishable depth buffer values. To mitigate these issues, many techniques have been developed over time to better distribute depth val...

Global urbanization for decades has led to unprecedented levels and growing demands for urban logistics. Thus, problems such as congestion, environmental noise, and urban sprawl are growing. As a result, many cities face problems of optimal decision-making regarding green and sustainable smart transportation systems and infrastructures. However, va...

The network security framework VisITMeta allows the visual evaluation and management of security event detection policies. By means of a "what-if" simulation the sensitivity of policies to specific events can be tested and adjusted. This paper presents the results of a user study for testing the usability of the approach by measuring the correct co...

During the transition from conventional towards purely electrical, sustainable mobility, transitional technologies play a major part in the task of increasing adaption rates and decreasing range anxiety. Developing new concepts to meet this challenge requires adaptive test benches, which can easily be modified e.g. when progressing from one stage o...

OSGi is a Java-based framework intended for embedded systems. In this paper, we design, implement, evaluate and demonstrate an approach to enhancing OSGi with asynchronous messaging. Our approach is non-invasive. It guarantees reliable delivery of messages. Furthermore, our approach enables a remote asynchronous communication not only between OSGi...

In computer networks many components produce valuable information about themselves or other participants, especially security analysis relevant information. Although such information is intrinsically related as components are connected by a network, most of them still operate independently and do not share data amongst each other. Furthermore, the...

Monitoring a computer network's security state is a di cult task as network components rarely share their information. The IF-MAP speci fication de fines a client/server-based protocol that enables network components to share security information among each other, which is represented in a graph structure. Visualization of this data is challenging...

Background: Motion sensing input devices could provide a practical and low-cost alternative method for repeated range of motion measurements. This study aimed to assess the reliability, accuracy and time requirements of a motion sensing input device (Microsoft Kinect) for ROM measurements comparing it with goniometer based measurements and subject...

Computer graphics is a subject which is typically enjoyed by students and which has the potential to attract pupils to consider studying computer science. Although the programming methods used by computer graphics have significantly changed in recent years due to the integration of programmable shaders into the graphics rendering pipeline, a lot of...

Motivation: Recent exome-sequencing studies have successfully identified disease-causing sequence variants for several rare monogenic diseases by examining variants common to a group of patients. However, the current data analysis strategies are only insufficiently able to deal with confounding factors such as genetic heterogeneity, incomplete pen...

OSGi is a popular Java-based platform, which has its roots in the area of embedded systems. However, nowadays it is used more and more in enterprise systems. To fit this new application area, OSGi has recently been extended with the Remote Services specification. This specification enables distribution, which OSGi was previously lacking. However, t...

Metagenomic studies use high-throughput sequence data to investigate microbial communities in situ. However, considerable challenges remain in the analysis of these data, particularly with regard to speed and reliable analysis of microbial species as opposed to higher level taxa such as phyla. We here present Genometa, a computationally undemanding...

Distribution of Pseudomonas aeruginosa CHA reads mapped to the Herminiimonas arsenicoxydans genome. Mapped reads correspond to ORFs from the RGP27 island in P. aeruginosa PACS2. (TIF)

Distribution of human gut metagenome reads mapped to the Bifidobacterium longum NCC2705 genome. The widespread hits indicate the strain is present in the metagenome. Figures were produced with the statistical language R. (TIF)

Supplementary results and statistical algorithms for short reads. (DOC)

P-values (i.e. probability) that not one single overlap is observed for any possible pair of reads among a particular number of mapped reads for a sequence of length L bp. This table was calculated from equation 5 above. Underlined p-values are those where at least one pair of overlapping reads are expected (p≲0.5) for the given sequence length and...

OSGi is a popular Java-based platform that was originally intended for embedded systems. But today OSGi is used more and more in enterprise systems. To fit this new application area, OSGi is continuously extended by the OSGi Enterprise Expert Group (EEG). For example, recently, support for remote services has been added to OSGi. But this support im...

Voice portals are widely used to guide users interactively through an application. Recent portals provide a growing number of functions in one application, thus increasing their complexity. This work presents flow-map-based techniques for the comparative visualization of user flows at different time frames, in order to enable dialog designers to an...

Traditionally, web services were used in large distributed systems. In this paper, we propose an approach to using web services in embedded systems, which have small memory footprints. At the heart of our approach lay: (1) the use of Apache CXF to extend the OSGi framework with distribution; and (2) the adaption of Apache CXF to embedded system pla...

Die CAD/CAM-basierte Herstellung von Zahnersatz ermöglicht die effiziente Verarbeitung hochwertiger keramischer Materialien; sie basiert auf 3D-Messdaten der präparierten Kiefersituation. Die vorliegende Arbeit beschreibt ein Verfahren zur vollautomatischen Extraktion der Präparationsgrenze (der unteren Grenzlinie zwischen Zahnersatz und präpariert...

Due to the increasing demand for high-quality ceramic crowns and bridges, the CAD/CAM-based production of dental restorations has been a subject of intensive research during the last fifteen years. A prerequisite for the efficient processing of the D measurement of prepared teeth with a minimal amount of user interaction is the automatic determinat...

A simple one-dimensional microscopic model of the depinning transition of an interface from an attractive hard wall is introduced and investigated. Upon varying a control parameter, the critical behavior observed along the transition line changes from a directed-percolation type to a multiplicative-noise type. Numerical simulations allow for a quan...

We investigate Anderson localization in a quasi–one-dimensional disordered system consisting of weakly coupled statistically independent channels. The dependence of the localization length on the coupling κ is shown to be singular: proportional to 1/|ln κ|. Numerical evidence is given for coupled random chains with different statistics of site pote...

We study two coupled spatially extended dynamical systems which exhibit space-time chaos. The transition to the synchronized state is treated as a nonequilibrium phase transition, where the average synchronization error is the order parameter. The transition in one-dimensional systems is found to be generically in the universality class of the Kard...

The behavior of the Lyapunov exponents (LEs) of a disordered system consisting of mutually coupled chaotic maps with different parameters is studied. The LEs are demonstrated to exhibit avoided crossing and level repulsion, qualitatively similar to the behavior of energy levels in quantum chaos. Recent results for the coupling dependence of the LEs...

Subject of this work is the investigation of universal scaling laws which are observed in coupled chaotic systems. Progress is made by replacing the chaotic fluctuations in the perturbation dynamics by stochastic processes. First, a continuous-time stochastic model for weakly coupled chaotic systems is introduced to study the scaling of the Lyapuno...

We use linear stochastic Langevin equations to describe the Lyapunov exponents in coupled chaotic systems. The largest Lyapunov exponent is calculated analytically, using the stationary solution of the Fokker-Planck equation. For small couplings we reproduce the singularity which was first described by Daido as the effect of coupling sensitivity of...

We develop a statistical theory of the coupling sensitivity of chaos. The effect was first described by Daido [Prog. Theor. Phys. 72, 853 (1984)]; it appears as a logarithmic singularity in the Lyapunov exponent in coupled chaotic systems at very small couplings. Using a continuous-time stochastic model for the coupled systems we derive a scaling r...

We develop a statistical theory of the coupling sensitivity of chaos. The effect was first described by Daido [Prog. Theor. Phys. 72, 853 (1984)]; it appears as a logarithmic singularity in the Lyapunov exponent in coupled chaotic systems at very small couplings. Using a continuous-time stochastic model for the coupled systems we derive a scaling r...

. The effect of coupling sensitivity of chaos is known as logarithmic singular behavior of the Lyapunov exponents of coupled chaotic systems at small values of the coupling parameter. In order to study it analytically, we use a continuous-time stochastic model which can be treated by means of the Fokker-Planck equation. One main result is that the...

Two unidirectionally coupled external cavity semiconductor lasers showing chaotic intensity fluctuations are studied by numerically solving the LangKobayashi model equations [IEEE J. Quantum Electron. QE-16, 347 (1980)]. The systems are shown to synchronize when operating in the regime of lowfrequency fluctuations which is characterized by a very h...