@incollection{MiddelPoppRaptisetal., author = {Middel, Luise and Popp, Christof and Raptis, Georgios and Sutter, Tamara and Gutbrod, Max}, title = {Konzeption und Aufbau einer technischen Telepr{\"a}senzrobotik-Plattform f{\"u}r die Unterst{\"u}tzung von Schlaganfallpatient*innen in der Pflege, Logop{\"a}die und Physiotherapie}, series = {Digitale Technik f{\"u}r ambulante Pflege und Therapie}, booktitle = {Digitale Technik f{\"u}r ambulante Pflege und Therapie}, publisher = {de Gruyter}, address = {Berlin}, doi = {10.1515/9783839462355-002}, pages = {19 -- 58}, language = {de} } @inproceedings{BraunSchildgenDessloch, author = {Braun, Stefan and Schildgen, Johannes and Deßloch, Stefan}, title = {Visualization of NoSQL transformations using sampling techniques | Visualisierung von NoSQL-Transformationen unter der Verwendung von Sampling-Techniken}, series = {Proceedings of the LWA 2015 workshops: KDML, FGWM, IR, and FGDB : Trier, Germany, October 7-9, 2015}, booktitle = {Proceedings of the LWA 2015 workshops: KDML, FGWM, IR, and FGDB : Trier, Germany, October 7-9, 2015}, publisher = {RWTH Aachen}, address = {Aachen}, pages = {427 -- 438}, abstract = {Analysen auf NoSQL-Datenbanken sind oft langdauernd und die Ergebnisse fur den Benutzer haufig schwer verst ̈andlich. Wir prasentieren eine M{\"o}glichkeit, Datenmengen aus Wide-Column Stores mittels der Transformationssprache NotaQL zu transformieren sowie zu aggregieren und die Ergebnisse in Form von Diagrammen dem Benutzer darzustellen. Dabei kommen Sampling-Techniken zum Einsatz, um die Berechnung auf Kosten der Genauigkeit zu beschleunigen. Das von uns verwendete iterative Samplingverfahren sorgt fur eine kontinuierliche Verbesserung der Berechnungsgenauigkeit und bietet zudem M{\"o}glichkeiten zur Genauigkeitsabsch{\"a}tzung, die in Form von Konfidenzintervallen in den Diagrammen dargestellt werden kann.}, language = {en} } @article{HaertlLoeschelReppetal., author = {Haertl, Petra Maria and L{\"o}schel, Rainer and Repp, Natalia and Pohl, Fabian and K{\"o}lbl, Oliver and Dobler, Barbara}, title = {Frameless fractionated stereotactic radiation therapy of intracranial lesions: Impact of cone beam CT based setup correction on dose distribution}, series = {Radiation Oncology}, volume = {8}, journal = {Radiation Oncology}, number = {1}, publisher = {BioMed Central}, address = {London}, doi = {10.1186/1748-717X-8-153}, abstract = {Background The purpose of this study was to evaluate the impact of Cone Beam CT (CBCT) based setup correction on total dose distributions in fractionated frameless stereotactic radiation therapy of intracranial lesions. Methods Ten patients with intracranial lesions treated with 30 Gy in 6 fractions were included in this study. Treatment planning was performed with Oncentra® for a SynergyS® (Elekta Ltd, Crawley, UK) linear accelerator with XVI® Cone Beam CT, and HexaPOD™ couch top. Patients were immobilized by thermoplastic masks (BrainLab, Reuther). After initial patient setup with respect to lasers, a CBCT study was acquired and registered to the planning CT (PL-CT) study. Patient positioning was corrected according to the correction values (translational, rotational) calculated by the XVI® system. Afterwards a second CBCT study was acquired and registered to the PL-CT to confirm the accuracy of the corrections. An in-house developed software was used for rigid transformation of the PL-CT to the CBCT geometry, and dose calculations for each fraction were performed on the transformed CT. The total dose distribution was achieved by back-transformation and summation of the dose distributions of each fraction. Dose distributions based on PL-CT, CBCT (laser set-up), and final CBCT were compared to assess the influence of setup inaccuracies. Results The mean displacement vector, calculated over all treatments, was reduced from (4.3 ± 1.3) mm for laser based setup to (0.5 ± 0.2) mm if CBCT corrections were applied. The mean rotational errors around the medial-lateral, superior-inferior, anterior-posterior axis were reduced from (-0.1 ± 1.4)°, (0.1 ± 1.2)° and (-0.2 ± 1.0)°, to (0.04 ± 0.4)°, (0.01 ± 0.4)° and (0.02 ± 0.3)°. As a consequence the mean deviation between planned and delivered dose in the planning target volume (PTV) could be reduced from 12.3\% to 0.4\% for D95 and from 5.9\% to 0.1\% for Dav. Maximum deviation was reduced from 31.8\% to 0.8\% for D95, and from 20.4\% to 0.1\% for Dav. Conclusion Real dose distributions differ substantially from planned dose distributions, if setup is performed according to lasers only. Thermoplasic masks combined with a daily CBCT enabled a sufficient accuracy in dose distribution.}, language = {en} } @article{HoegeleDoblerKoelbletal., author = {H{\"o}gele, Wolfgang and Dobler, Barbara and K{\"o}lbl, Oliver and Beard, Clair and Zygmanski, Piotr and L{\"o}schel, Rainer}, title = {Stochastic triangulation for prostate positioning during radiotherapy using short CBCT arcs}, series = {Radiotherapy and Oncology}, volume = {106}, journal = {Radiotherapy and Oncology}, number = {2}, publisher = {Elsevier}, doi = {10.1016/j.radonc.2013.01.005}, pages = {241 -- 249}, abstract = {Background and purpose: Fast and reliable tumor localization is an important part of today's radiotherapy utilizing new delivery techniques. This proof-of-principle study demonstrates the use of a method called herein 'stochastic triangulation' for this purpose. Stochastic triangulation uses very short imaging arcs and a few projections. Materials and methods: A stochastic Maximum A Posteriori (MAP) estimator is proposed based on an uncertainty-driven model of the acquisition geometry and inter-/intra-fractional deformable anatomy. The application of this method was designed to use the available linac-mounted cone-beam computed tomography (CBCT) and/or electronic portal imaging devices (EPID) for the patient setup based on short imaging arcs. For the proof-of-principle clinical demonstration, the MAP estimator was applied to 5 CBCT scans of a prostate cancer patient with 2 implanted gold markers. Estimation was performed for several (18) very short imaging arcs of 5° with 10 projections resulting in 90 estimations. Results: Short-arc stochastic triangulation led to residual radial errors compared to manual inspection with a mean value of 1.4mm and a standard deviation of 0.9 mm (median 1.2mm, maximum 3.8mm) averaged over imaging directions all around the patient. Furthermore, abrupt intra-fractional motion of up to 10mm resulted in radial errors with a mean value of 1.8mm and a standard deviation of 1.1mm (median 1.5mm, maximum 5.6mm). Slow periodic intra-fractional motions in the range of 12 mm resulted in radial errors with a mean value of 1.8mm and a standard deviation of 1.1mm (median 1.6mm, maximum 4.7 mm). Conclusion: Based on this study, the proposed stochastic method is fast, robust and can be used for inter- as well as intra-fractional target localization using current CBCT units.}, language = {en} } @article{HoegeleZygmanskiDobleretal., author = {H{\"o}gele, Wolfgang and Zygmanski, Piotr and Dobler, Barbara and Kroiss, M. and K{\"o}lbl, Oliver and L{\"o}schel, Rainer}, title = {Localization of deformable tumors from short-arc projections using Bayesian estimation}, series = {Medical Physics}, volume = {39}, journal = {Medical Physics}, number = {12}, publisher = {Wiley}, doi = {10.1118/1.4764483}, pages = {7205 -- 7214}, abstract = {Purpose: The authors present a stochastic framework for radiotherapy patient positioning directly utilizing radiographic projections. This framework is developed to be robust against anatomical nonrigid deformations and to cope with challenging imaging scenarios, involving only a few cone beam CT projections from short arcs. Methods: Specifically, a Bayesian estimator (BE) is explicitly derived for the given scanning geometry. This estimator is compared to reference methods such as chamfer matching (CM) and the minimization of the median absolute error adapted as tools of robust image processing and statistics. In order to show the performance of the stochastic short-arc patient positioning method, a CIRS IMRT thorax phantom study is presented with movable markers and the utilization of an Elekta Synergy® XVI system. Furthermore, a clinical prostate CBCT scan of a Varian® On-Board Imager® system is utilized to investigate the robustness of the method for large variations of image quality (anterior-posterior vs lateral views). Results: The results show that the BE shifts reduce the initial setup error of up to 3 cm down to 3 mm at maximum for an imaging arc as short as 10° while CM achieves residual errors of 7 mm at maximum only for arcs longer than 40°. Furthermore, the BE can compensate robustly for low image qualities using several low quality projections simultaneously. Conclusions: In conclusion, an estimation method for marker-based patient positioning for short imaging arcs is presented and shown to be robust and accurate for deformable anatomies.}, language = {en} } @article{aufderHeideSchindelhauerVolbertetal., author = {auf der Heide, Friedhelm Meyer and Schindelhauer, Christian and Volbert, Klaus and Gr{\"u}newald, Matthias}, title = {Congestion, dilation, and energy in radio networks}, series = {Theory of Computing Systems}, volume = {37}, journal = {Theory of Computing Systems}, number = {3}, publisher = {Springer Nature}, doi = {10.1007/s00224-004-1124-z}, pages = {343 -- 370}, abstract = {We investigate the problem of path selection in radio networks for a given static set of n sites in two- and three-dimensional space. For static point-to-point communication we define measures for congestion, dilation, and energy consumption that take interferences among communication links into account. We show that energy-optimal path selection for radio networks can be computed in polynomial time. Then we introduce the diversity g(V) of a set V ⫅ ℝd for any constant d. It can be used to upper bound the number of interfering edges. For real-world applications it can be regarded as Θ(log n). A main result is that a c-spanner construction as a communication network allows one to approximate the congestion-optimal path system by a factor of O(g(V)2). Furthermore, we show that there are vertex sets where only one of the performance parameters congestion, dilation, and energy can be optimized at a time. We show trade-offs lower bounding congestion × dilation and dilation × energy. The trade-off between congestion and dilation increases with switching from two-dimensional to three-dimensional space. For congestion and energy the situation is even worse. It is only possible to find a reasonable approximation for either congestion or energy minimization, while the other parameter is at least a polynomial factor worse than in the optimal network.}, language = {en} } @article{HoegeleLoeschelDobleretal., author = {H{\"o}gele, Wolfgang and L{\"o}schel, Rainer and Dobler, Barbara and K{\"o}lbl, Oliver and Zygmanski, Piotr}, title = {Bayesian estimation applied to stochastic localization with constraints due to interfaces and boundaries}, series = {Mathematical Problems in Engineering}, volume = {213}, journal = {Mathematical Problems in Engineering}, publisher = {HIndawi}, issn = {1563-5147}, doi = {10.1155/2013/960421}, pages = {17}, abstract = {Purpose We present a systematic Bayesian formulation of the stochastic localization/triangulation problem close to constraining interfaces. Methods For this purpose, the terminology of Bayesian estimation is summarized suitably for applied researchers including the presentation of Maximum Likelihood (ML), Maximum A Posteriori (MAP), and Minimum Mean Square Error (MMSE) estimation. Explicit estimators for triangulation are presented for the linear 2D parallel beam and the nonlinear 3D cone beam model. The priors in MAP and MMSE optionally incorporate (A) the hard constraints about the interface and (B) knowledge about the probability of the object with respect to the interface. All presented estimators are compared in several simulation studies for live acquisition scenarios with 10,000 samples each. Results First, the presented application shows that MAP and MMSE perform considerably better, leading to lower Root Mean Square Errors (RMSEs) in the simulation studies compared to the ML approach by typically introducing a bias. Second, utilizing priors including (A) and (B) is very beneficial compared to just including (A). Third, typically MMSE leads to better results than MAP, by the cost of significantly higher computational effort. Conclusion Depending on the specific application and prior knowledge, MAP and MMSE estimators strongly increase the estimation accuracy for localization close to interfaces.}, language = {en} } @article{HecknerMuehlbacherWolff, author = {Heckner, Markus and M{\"u}hlbacher, Susanne and Wolff, Christian}, title = {Tagging tagging. Analysing user keywords in scientific bibliography management systems}, series = {Journal of Digital Information}, volume = {9}, journal = {Journal of Digital Information}, number = {2}, publisher = {Multimedia Research Group}, pages = {19}, abstract = {In this paper, an empirical study of tagging behaviour in web-based bibliographic annotation systems is presented. Starting from an initial category finding phase in which tags attributed to selected articles from Connotea were classified we have set up a category model for linguistic and functional aspects of tag usage as well as for the relationship between tags and document full text. In a second phase this model is applied to approx. 500 tagged articles from the information and computer technology domain randomly selected from Connotea. Our findings show significant differences to other tagging research which was primarily conducted using popular (non-scientific) tagging platforms like Flickr or Delicious. We observe a great overlap of tag material and document text and rather few non-content related tags. The comparison of user tags with author keywords shows that users tend to use less and more general tags. Finally, system functionality seems to play a role for users' tagging behaviour.}, language = {en} } @article{HagerFinkeSeitzetal., author = {Hager, Markus and Finke, Thomas and Seitz, Jochen and Waas, Thomas}, title = {Software-based management for Ethernet networks}, series = {Wireless Personal Communications}, volume = {74}, journal = {Wireless Personal Communications}, number = {3}, publisher = {Springer Nature}, doi = {10.1007/s11277-013-1341-3}, pages = {1021 -- 1032}, abstract = {An adequate network management is an essential part for each network permitting to keep the network performance at a suitable level. In this paper, we present our work focusing on an Ethernet network which is used as background interconnection technology for a smart home system in large buildings like tenements or an office block. In this case the network is larger and especially the applications are quite heterogeneous as compared to a private smart home system. Therefore, it is hard to supply a fair and quality of service aware network meeting all the demands. This is especially challenging in the case of an Ethernet network because this technology was intended to use it as a transparent connection system without the feature to support hard quality of service. We present how this problem could be solved by a middleware which best meets the special requirement of the mentioned use case. Finally, we discuss possible design improvements of this solution and present the recent Ethernet standards that could help solve this problem in an alternative way.}, language = {en} } @article{HecknerNeubauerWolff, author = {Heckner, Markus and Neubauer, Tanja and Wolff, Christian}, title = {Tree, funny, to-read, google: What are tags supposed to achieve?: A comparative analysis of user keywords for different digital resource types}, series = {Proceedings of the 2008 ACM workshop on Search in social media (SSM '08), Napa Valley California, USA, 30 October 2008}, journal = {Proceedings of the 2008 ACM workshop on Search in social media (SSM '08), Napa Valley California, USA, 30 October 2008}, publisher = {ACM}, doi = {10.1145/1458583.1458589}, pages = {3 -- 10}, abstract = {Social tagging systems have become increasingly popular over the past years. Users' tagging practices have been little studied and understood so far. However, understanding tagging behaviour can contribute towards a thorough understanding of the tagging phenomenon from multiple perspectives. In the present paper, results of a comparative analysis of tag characteristics on the tagging platforms connotea.org (scientific articles), del.icio.us (bookmarks), flickr.com (photos), and youtube.com (videos) are presented. Results show that differences in tagging behaviour can be observed for different digital resource types. Finally, a short discussion of the possible implications of the results for the design of future tagging systems is presented.}, language = {en} } @article{LukovszkiSchindelhauerVolbert, author = {Lukovszki, Tamas and Schindelhauer, Christian and Volbert, Klaus}, title = {Resource efficient maintenance of wireless network topologies}, series = {Journal of Universal Computer Science}, volume = {12}, journal = {Journal of Universal Computer Science}, number = {9}, publisher = {Verlag der Technischen Universit{\"a}t Graz}, doi = {10.3217/jucs-012-09-1292}, pages = {1292 -- 1311}, abstract = {Multiple hop routing in mobile ad hoc networks can minimize energy consumption and increase data throughput. Yet, the problem of radio interferences remain. However if the routes are restricted to a basic network based on local neighborhoods, these interferences can be reduced such that standard routing algorithms can be applied. We compare different network topologies for these basic networks, i.e. the Yao-graph (aka. Θ-graph) and some also known related models, which will be called the SymmYgraph (aka. YS-graph), the SparsY-graph (aka. YY-graph) and the BoundY-graph. Further, we present a promising network topology called the HL-graph (based on Hierarchical Layers). We compare these topologies regarding degree, spanner-properties, and communication features. We investigate how these network topologies bound the number of (uni- and bidirectional) interferences and whether these basic networks provide energy-optimal or congestion-minimal routing. Then, we compare the ability of these topologies to handle dynamic changes of the network when radio stations appear and disappear. For this we measure the number of involved radio stations and present distributed algorithms for repairing the network structure.}, language = {en} } @inproceedings{RuehrupSchindelhauerVolbert, author = {R{\"u}hrup, Stefan and Schindelhauer, Christian and Volbert, Klaus}, title = {Performance analysis of the hierarchical layer graph for wireless networks}, series = {4th International Conference, ADHOC-NOW 2005, Cancun, Mexico, October 6-8, 2005}, booktitle = {4th International Conference, ADHOC-NOW 2005, Cancun, Mexico, October 6-8, 2005}, publisher = {Springer}, address = {Berlin ; Heidelberg}, isbn = {978-3-540-29132-9}, doi = {10.1007/11561354_21}, pages = {244 -- 257}, abstract = {The Hierarchical Layer Graph (HL graph) is a promising network topology for wireless networks with variable transmission ranges. It was introduced and analyzed by Meyer auf der Heide et al. 2004. In this paper we present a distributed, localized and resource-efficient algorithm for constructing this graph. The qualtiy of the HL graph depends on the domination radius and the publication radius, which affect the amount of interference in the network. These parameters also determine whether the HL graph is a c-spanner, which implies an energy-efficient topology. We investigate the performance on randomly distributed node sets and show that the restrictions on these parameters derived from a worst case analysis are not so tight using realistic settings. Here, we present the results of our extensive experimental evaluation, measuring congestion, dilation and energy. Congestion includes the load that is induced by interfering edges. We distinguish between congestion and realistic congestion where we also take the signal-to-interference ratio into account. Our experiments show that the HL graph contains energy-efficient paths as well as paths with a few number of hops while preserving a low congestion.}, language = {en} }