@article{KruegerFriedrichFoersteretal.2012, author = {Krueger, Beate and Friedrich, Torben and F{\"o}rster, Frank and Bernhardt, J{\"o}rg and Gross, Roy and Dandekar, Thomas}, title = {Different evolutionary modifications as a guide to rewire two-component systems}, series = {Bioinformatics and Biology Insights}, volume = {6}, journal = {Bioinformatics and Biology Insights}, doi = {10.4137/BBI.S9356}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-123647}, pages = {97-128}, year = {2012}, abstract = {Two-component systems (TCS) are short signalling pathways generally occurring in prokaryotes. They frequently regulate prokaryotic stimulus responses and thus are also of interest for engineering in biotechnology and synthetic biology. The aim of this study is to better understand and describe rewiring of TCS while investigating different evolutionary scenarios. Based on large-scale screens of TCS in different organisms, this study gives detailed data, concrete alignments, and structure analysis on three general modification scenarios, where TCS were rewired for new responses and functions: (i) exchanges in the sequence within single TCS domains, (ii) exchange of whole TCS domains; (iii) addition of new components modulating TCS function. As a result, the replacement of stimulus and promotor cassettes to rewire TCS is well defined exploiting the alignments given here. The diverged TCS examples are non-trivial and the design is challenging. Designed connector proteins may also be useful to modify TCS in selected cases.}, language = {en} } @article{MergetKoetschanHackletal.2012, author = {Merget, Benjamin and Koetschan, Christian and Hackl, Thomas and F{\"o}rster, Frank and Dandekar, Thomas and M{\"u}ller, Tobias and Schultz, J{\"o}rg and Wolf, Matthias}, title = {The ITS2 Database}, series = {Journal of Visual Expression}, volume = {61}, journal = {Journal of Visual Expression}, number = {e3806}, doi = {10.3791/3806}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-124600}, year = {2012}, abstract = {The internal transcribed spacer 2 (ITS2) has been used as a phylogenetic marker for more than two decades. As ITS2 research mainly focused on the very variable ITS2 sequence, it confined this marker to low-level phylogenetics only. However, the combination of the ITS2 sequence and its highly conserved secondary structure improves the phylogenetic resolution1 and allows phylogenetic inference at multiple taxonomic ranks, including species delimitation. The ITS2 Database presents an exhaustive dataset of internal transcribed spacer 2 sequences from NCBI GenBank accurately reannotated. Following an annotation by profile Hidden Markov Models (HMMs), the secondary structure of each sequence is predicted. First, it is tested whether a minimum energy based fold (direct fold) results in a correct, four helix conformation. If this is not the case, the structure is predicted by homology modeling. In homology modeling, an already known secondary structure is transferred to another ITS2 sequence, whose secondary structure was not able to fold correctly in a direct fold. The ITS2 Database is not only a database for storage and retrieval of ITS2 sequence-structures. It also provides several tools to process your own ITS2 sequences, including annotation, structural prediction, motif detection and BLAST search on the combined sequence-structure information. Moreover, it integrates trimmed versions of 4SALE and ProfDistS for multiple sequence-structure alignment calculation and Neighbor Joining tree reconstruction. Together they form a coherent analysis pipeline from an initial set of sequences to a phylogeny based on sequence and secondary structure. In a nutshell, this workbench simplifies first phylogenetic analyses to only a few mouse-clicks, while additionally providing tools and data for comprehensive large-scale analyses.}, language = {en} } @article{BuchinBuchinByrkaetal.2012, author = {Buchin, Kevin and Buchin, Maike and Byrka, Jaroslaw and N{\"o}llenburg, Martin and Okamoto, Yoshio and Silveira, Rodrigo I. and Wolff, Alexander}, title = {Drawing (Complete) Binary Tanglegrams}, series = {Algorithmica}, volume = {62}, journal = {Algorithmica}, doi = {10.1007/s00453-010-9456-3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-124622}, pages = {309-332}, year = {2012}, abstract = {A binary tanglegram is a drawing of a pair of rooted binary trees whose leaf sets are in one-to-one correspondence; matching leaves are connected by inter-tree edges. For applications, for example, in phylogenetics, it is essential that both trees are drawn without edge crossings and that the inter-tree edges have as few crossings as possible. It is known that finding a tanglegram with the minimum number of crossings is NP-hard and that the problem is fixed-parameter tractable with respect to that number. We prove that under the Unique Games Conjecture there is no constant-factor approximation for binary trees. We show that the problem is NP-hard even if both trees are complete binary trees. For this case we give an O(n 3)-time 2-approximation and a new, simple fixed-parameter algorithm. We show that the maximization version of the dual problem for binary trees can be reduced to a version of MaxCut for which the algorithm of Goemans and Williamson yields a 0.878-approximation.}, language = {en} } @article{StaigerCadotKooteretal.2012, author = {Staiger, Christine and Cadot, Sidney and Kooter, Raul and Dittrich, Marcus and M{\"u}ller, Tobias and Klau, Gunnar W. and Wessels, Lodewyk F. A.}, title = {A Critical Evaluation of Network and Pathway-Based Classifiers for Outcome Prediction in Breast Cancer}, series = {PLoS One}, volume = {7}, journal = {PLoS One}, number = {4}, doi = {10.1371/journal.pone.0034796}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-131323}, pages = {e34796}, year = {2012}, abstract = {Recently, several classifiers that combine primary tumor data, like gene expression data, and secondary data sources, such as protein-protein interaction networks, have been proposed for predicting outcome in breast cancer. In these approaches, new composite features are typically constructed by aggregating the expression levels of several genes. The secondary data sources are employed to guide this aggregation. Although many studies claim that these approaches improve classification performance over single genes classifiers, the gain in performance is difficult to assess. This stems mainly from the fact that different breast cancer data sets and validation procedures are employed to assess the performance. Here we address these issues by employing a large cohort of six breast cancer data sets as benchmark set and by performing an unbiased evaluation of the classification accuracies of the different approaches. Contrary to previous claims, we find that composite feature classifiers do not outperform simple single genes classifiers. We investigate the effect of (1) the number of selected features; (2) the specific gene set from which features are selected; (3) the size of the training set and (4) the heterogeneity of the data set on the performance of composite feature and single genes classifiers. Strikingly, we find that randomization of secondary data sources, which destroys all biological information in these sources, does not result in a deterioration in performance of composite feature classifiers. Finally, we show that when a proper correction for gene set size is performed, the stability of single genes sets is similar to the stability of composite feature sets. Based on these results there is currently no reason to prefer prognostic classifiers based on composite features over single genes classifiers for predicting outcome in breast cancer.}, language = {en} } @article{NaseemDandekar2012, author = {Naseem, Muhammad and Dandekar, Thomas}, title = {The Role of Auxin-Cytokinin Antagonism in Plant-Pathogen Interactions}, series = {PLOS Pathogens}, volume = {8}, journal = {PLOS Pathogens}, number = {11}, doi = {10.1371/journal.ppat.1003026}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-131901}, pages = {e1003026}, year = {2012}, abstract = {No abstract available.}, language = {en} } @article{SchokraieWarnkenHotzWagenblattetal.2012, author = {Schokraie, Elham and Warnken, Uwe and Hotz-Wagenblatt, Agnes and Grohme, Markus A. and Hengherr, Steffen and F{\"o}rster, Frank and Schill, Ralph O. and Frohme, Marcus and Dandekar, Thomas and Schn{\"o}lzer, Martina}, title = {Comparative proteome analysis of Milnesium tardigradum in early embryonic state versus adults in active and anhydrobiotic state}, series = {PLoS One}, volume = {7}, journal = {PLoS One}, number = {9}, doi = {10.1371/journal.pone.0045682}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-134447}, pages = {e45682}, year = {2012}, abstract = {Tardigrades have fascinated researchers for more than 300 years because of their extraordinary capability to undergo cryptobiosis and survive extreme environmental conditions. However, the survival mechanisms of tardigrades are still poorly understood mainly due to the absence of detailed knowledge about the proteome and genome of these organisms. Our study was intended to provide a basis for the functional characterization of expressed proteins in different states of tardigrades. High-throughput, high-accuracy proteomics in combination with a newly developed tardigrade specific protein database resulted in the identification of more than 3000 proteins in three different states: early embryonic state and adult animals in active and anhydrobiotic state. This comprehensive proteome resource includes protein families such as chaperones, antioxidants, ribosomal proteins, cytoskeletal proteins, transporters, protein channels, nutrient reservoirs, and developmental proteins. A comparative analysis of protein families in the different states was performed by calculating the exponentially modified protein abundance index which classifies proteins in major and minor components. This is the first step to analyzing the proteins involved in early embryonic development, and furthermore proteins which might play an important role in the transition into the anhydrobiotic state.}, language = {en} } @article{BugaScholzKumaretal.2012, author = {Buga, Ana-Maria and Scholz, Claus J{\"u}rgen and Kumar, Senthil and Herndon, James G. and Alexandru, Dragos and Cojocaru, Gabriel Radu and Dandekar, Thomas and Popa-Wagner, Aurel}, title = {Identification of New Therapeutic Targets by Genome-Wide Analysis of Gene Expression in the Ipsilateral Cortex of Aged Rats after Stroke}, series = {PLoS One}, volume = {7}, journal = {PLoS One}, number = {12}, doi = {10.1371/journal.pone.0050985}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-130657}, pages = {e50985}, year = {2012}, abstract = {Background: Because most human stroke victims are elderly, studies of experimental stroke in the aged rather than the young rat model may be optimal for identifying clinically relevant cellular responses, as well for pinpointing beneficial interventions. Methodology/Principal Findings: We employed the Affymetrix platform to analyze the whole-gene transcriptome following temporary ligation of the middle cerebral artery in aged and young rats. The correspondence, heat map, and dendrogram analyses independently suggest a differential, age-group-specific behaviour of major gene clusters after stroke. Overall, the pattern of gene expression strongly suggests that the response of the aged rat brain is qualitatively rather than quantitatively different from the young, i.e. the total number of regulated genes is comparable in the two age groups, but the aged rats had great difficulty in mounting a timely response to stroke. Our study indicates that four genes related to neuropathic syndrome, stress, anxiety disorders and depression (Acvr1c, Cort, Htr2b and Pnoc) may have impaired response to stroke in aged rats. New therapeutic options in aged rats may also include Calcrl, Cyp11b1, Prcp, Cebpa, Cfd, Gpnmb, Fcgr2b, Fcgr3a, Tnfrsf26, Adam 17 and Mmp14. An unexpected target is the enzyme 3-hydroxy-3-methylglutaryl-Coenzyme A synthase 1 in aged rats, a key enzyme in the cholesterol synthesis pathway. Post-stroke axonal growth was compromised in both age groups. Conclusion/Significance: We suggest that a multi-stage, multimodal treatment in aged animals may be more likely to produce positive results. Such a therapeutic approach should be focused on tissue restoration but should also address other aspects of patient post-stroke therapy such as neuropathic syndrome, stress, anxiety disorders, depression, neurotransmission and blood pressure.}, language = {en} } @article{BoehlerCreignouGalotaetal.2012, author = {B{\"o}hler, Elmar and Creignou, Nadia and Galota, Matthias and Reith, Steffen and Schnoor, Henning and Vollmer, Heribert}, title = {Complexity Classifications for Different Equivalence and Audit Problems for Boolean Circuits}, series = {Logical Methods in Computer Science}, volume = {8}, journal = {Logical Methods in Computer Science}, number = {3:27}, doi = {10.2168/LMCS-8(3:27)2012}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-131121}, pages = {1 -- 25}, year = {2012}, abstract = {We study Boolean circuits as a representation of Boolean functions and conskier different equivalence, audit, and enumeration problems. For a number of restricted sets of gate types (bases) we obtain efficient algorithms, while for all other gate types we show these problems are at least NP-hard.}, language = {en} } @article{AtienzadeCastroCortesetal.2012, author = {Atienza, Nieves and de Castro, Natalia and Cort{\´e}s, Carmen and Garrido, M. {\´A}ngeles and Grima, Clara I. and Hern{\´a}ndez, Gregorio and M{\´a}rquez, Alberto and Moreno-Gonz{\´a}lez, Auxiliadora and N{\"o}llenburg, Martin and Portillo, Jos{\´e} Ram{\´o}n and Reyes, Pedro and Valenzuela, Jes{\´u}s and Trinidad Villar, Maria and Wolff, Alexander}, title = {Cover contact graphs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-78845}, year = {2012}, abstract = {We study problems that arise in the context of covering certain geometric objects called seeds (e.g., points or disks) by a set of other geometric objects called cover (e.g., a set of disks or homothetic triangles). We insist that the interiors of the seeds and the cover elements are pairwise disjoint, respectively, but they can touch. We call the contact graph of a cover a cover contact graph (CCG). We are interested in three types of tasks, both in the general case and in the special case of seeds on a line: (a) deciding whether a given seed set has a connected CCG, (b) deciding whether a given graph has a realization as a CCG on a given seed set, and (c) bounding the sizes of certain classes of CCG's. Concerning (a) we give efficient algorithms for the case that seeds are points and show that the problem becomes hard if seeds and covers are disks. Concerning (b) we show that this problem is hard even for point seeds and disk covers (given a fixed correspondence between graph vertices and seeds). Concerning (c) we obtain upper and lower bounds on the number of CCG's for point seeds.}, subject = {Informatik}, language = {de} } @article{WolffRutter2012, author = {Wolff, Alexander and Rutter, Iganz}, title = {Augmenting the Connectivity of Planar and Geometric Graphs}, series = {Journal of Graph Algorithms and Applications}, journal = {Journal of Graph Algorithms and Applications}, doi = {10.7155/jgaa.00275}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-97587}, year = {2012}, abstract = {In this paper we study connectivity augmentation problems. Given a connected graph G with some desirable property, we want to make G 2-vertex connected (or 2-edge connected) by adding edges such that the resulting graph keeps the property. The aim is to add as few edges as possible. The property that we consider is planarity, both in an abstract graph-theoretic and in a geometric setting, where vertices correspond to points in the plane and edges to straight-line segments. We show that it is NP-hard to � nd a minimum-cardinality augmentation that makes a planar graph 2-edge connected. For making a planar graph 2-vertex connected this was known. We further show that both problems are hard in the geometric setting, even when restricted to trees. The problems remain hard for higher degrees of connectivity. On the other hand we give polynomial-time algorithms for the special case of convex geometric graphs. We also study the following related problem. Given a planar (plane geometric) graph G, two vertices s and t of G, and an integer c, how many edges have to be added to G such that G is still planar (plane geometric) and contains c edge- (or vertex-) disjoint s{t paths? For the planar case we give a linear-time algorithm for c = 2. For the plane geometric case we give optimal worst-case bounds for c = 2; for c = 3 we characterize the cases that have a solution.}, language = {en} } @article{BuchheimKellerKoetschanetal.2011, author = {Buchheim, Mark A. and Keller, Alexander and Koetschan, Christian and F{\"o}rster, Frank and Merget, Benjamin and Wolf, Matthias}, title = {Internal Transcribed Spacer 2 (nu ITS2 rRNA) Sequence-Structure Phylogenetics: Towards an Automated Reconstruction of the Green Algal Tree of Life}, series = {PLoS ONE}, volume = {6}, journal = {PLoS ONE}, number = {2}, doi = {10.1371/journal.pone.0016931}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-140866}, pages = {e16931}, year = {2011}, abstract = {Background: Chloroplast-encoded genes (matK and rbcL) have been formally proposed for use in DNA barcoding efforts targeting embryophytes. Extending such a protocol to chlorophytan green algae, though, is fraught with problems including non homology (matK) and heterogeneity that prevents the creation of a universal PCR toolkit (rbcL). Some have advocated the use of the nuclear-encoded, internal transcribed spacer two (ITS2) as an alternative to the traditional chloroplast markers. However, the ITS2 is broadly perceived to be insufficiently conserved or to be confounded by introgression or biparental inheritance patterns, precluding its broad use in phylogenetic reconstruction or as a DNA barcode. A growing body of evidence has shown that simultaneous analysis of nucleotide data with secondary structure information can overcome at least some of the limitations of ITS2. The goal of this investigation was to assess the feasibility of an automated, sequence-structure approach for analysis of IT2 data from a large sampling of phylum Chlorophyta. Methodology/Principal Findings: Sequences and secondary structures from 591 chlorophycean, 741 trebouxiophycean and 938 ulvophycean algae, all obtained from the ITS2 Database, were aligned using a sequence structure-specific scoring matrix. Phylogenetic relationships were reconstructed by Profile Neighbor-Joining coupled with a sequence structure-specific, general time reversible substitution model. Results from analyses of the ITS2 data were robust at multiple nodes and showed considerable congruence with results from published phylogenetic analyses. Conclusions/Significance: Our observations on the power of automated, sequence-structure analyses of ITS2 to reconstruct phylum-level phylogenies of the green algae validate this approach to assessing diversity for large sets of chlorophytan taxa. Moreover, our results indicate that objections to the use of ITS2 for DNA barcoding should be weighed against the utility of an automated, data analysis approach with demonstrated power to reconstruct evolutionary patterns for highly divergent lineages.}, language = {en} } @phdthesis{Reitwiessner2011, author = {Reitwießner, Christian}, title = {Multiobjective Optimization and Language Equations}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-70146}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {Praktische Optimierungsprobleme beinhalten oft mehrere gleichberechtigte, sich jedoch widersprechende Kriterien. Beispielsweise will man bei einer Reise zugleich m{\"o}glichst schnell ankommen, sie soll aber auch nicht zu teuer sein. Im ersten Teil dieser Arbeit wird die algorithmische Beherrschbarkeit solcher mehrkriterieller Optimierungsprobleme behandelt. Es werden zun{\"a}chst verschiedene L{\"o}sungsbegriffe diskutiert und auf ihre Schwierigkeit hin verglichen. Interessanterweise stellt sich heraus, dass diese Begriffe f{\"u}r ein einkriterielles Problem stets gleich schwer sind, sie sich ab zwei Kriterien allerdings stark unterscheiden k{\"o}nen (außer es gilt P = NP). In diesem Zusammenhang wird auch die Beziehung zwischen Such- und Entscheidungsproblemen im Allgemeinen untersucht. Schließlich werden neue und verbesserte Approximationsalgorithmen f{\"u}r verschieden Varianten des Problems des Handlungsreisenden gefunden. Dabei wird mit Mitteln der Diskrepanztheorie eine Technik entwickelt, die ein grundlegendes Hindernis der Mehrkriteriellen Optimierung aus dem Weg schafft: Gegebene L{\"o}sungen so zu kombinieren, dass die neue L{\"o}sung in allen Kriterien m{\"o}glichst ausgewogen ist und gleichzeitig die Struktur der L{\"o}sungen nicht zu stark zerst{\"o}rt wird. Der zweite Teil der Arbeit widmet sich verschiedenen Aspekten von Gleichungssystemen f{\"u}r (formale) Sprachen. Einerseits werden konjunktive und Boolesche Grammatiken untersucht. Diese sind Erweiterungen der kontextfreien Grammatiken um explizite Durchschnitts- und Komplementoperationen. Es wird unter anderem gezeigt, dass man bei konjunktiven Grammatiken die Vereinigungsoperation stark einschr{\"a}nken kann, ohne dabei die erzeugte Sprache zu {\"a}ndern. Außerdem werden bestimmte Schaltkreise untersucht, deren Gatter keine Wahrheitswerte sondern Mengen von Zahlen berechnen. F{\"u}r diese Schaltkreise wird das {\"A}quivalenzproblem betrachtet, also die Frage ob zwei gegebene Schaltkreise die gleiche Menge berechnen oder nicht. Es stellt sich heraus, dass, abh{\"a}ngig von den erlaubten Gattertypen, die Komplexit{\"a}t des {\"A}quivalenzproblems stark variiert und f{\"u}r verschiedene Komplexit{\"a}tsklassen vollst{\"a}ndig ist, also als (parametrisierter) Vertreter f{\"u}r diese Klassen stehen kann.}, subject = {Mehrkriterielle Optimierung}, language = {en} } @phdthesis{Staehle2011, author = {Staehle, Barbara}, title = {Modeling and Optimization Methods for Wireless Sensor and Mesh Networks}, doi = {10.25972/OPUS-4967}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-64884}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {Im Internet der Zukunft werden Menschen nicht nur mit Menschen, sondern auch mit „Dingen", und sogar „Dinge" mit „Dingen" kommunizieren. Zus{\"a}tzlich wird das Bed{\"u}rfnis steigen, immer und {\"u}berall Zugang zum Internet zu haben. Folglich gewinnen drahtlose Sensornetze (WSNs) und drahtlose Mesh-Netze (WMNs) an Bedeutung, da sie Daten {\"u}ber die Umwelt ins Internet liefern, beziehungsweise einfache Internet-Zugangsm{\"o}glichkeiten schaffen. In den vier Teilen dieser Arbeit werden unterschiedliche Modellierungs- und Optimierungsmethoden f{\"u}r WSNs und WMNs vorgestellt. Der Energieverbrauch ist die wichtigste Metrik, wenn es darum geht die Kommunikation in einem WSN zu optimieren. Da sich in der Literatur sehr viele unterschiedliche Energiemodelle finden, untersucht der erste Teil der Arbeit welchen Einfluss unterschiedliche Energiemodelle auf die Optimierung von WSNs haben. Aufbauend auf diesen {\"U}berlegungen besch{\"a}ftigt sich der zweite Teil der Arbeit mit drei Problemen, die {\"u}berwunden werden m{\"u}ssen um eine standardisierte energieeffiziente Kommunikations-L{\"o}sung f{\"u}r WSNs basierend auf IEEE 802.15.4 und ZigBee zu realisieren. F{\"u}r WMNs sind beide Probleme von geringem Interesse, die Leistung des Netzes jedoch umso mehr. Der dritte Teil der Arbeit f{\"u}hrt daher Algorithmen f{\"u}r die Berechnung des Max-Min fairen (MMF) Netzwerk-Durchsatzes in WMNs mit mehreren Linkraten und Internet-Gateways ein. Der letzte Teil der Arbeit untersucht die Auswirkungen des LRA-Konzeptes. Dessen grundlegende Idee ist die folgende. Falls f{\"u}r einen Link eine niedrigere Datenrate als theoretisch m{\"o}glich verwendet wird, sinkt zwar der Link-Durchsatz, jedoch ist unter Umst{\"a}nden eine gr{\"o}ßere Anzahl von gleichzeitigen {\"U}bertragungen m{\"o}glich und der Gesamt-Durchsatz des Netzes kann sich erh{\"o}hen. Mithilfe einer analytischen LRA Formulierung und einer systematischen Studie kann gezeigt werden, dass eine netzwerkweite Zuordnung robusterer Datenraten als n{\"o}tig zu einer Erh{\"o}hung des MMF Netzwerk-Durchsatzes f{\"u}hrt. Desweitern kann gezeigt werden, dass sich LRA positiv auf die Leistungsf{\"a}higkeit eines IEEE 802.11 WMNs auswirkt und f{\"u}r die Optimierung des Netzes genutzt werden kann.}, subject = {Drahtloses Sensorsystem}, language = {en} } @phdthesis{Schmidt2011, author = {Schmidt, Marco}, title = {Ground Station Networks for Efficient Operation of Distributed Small Satellite Systems}, isbn = {978-3-923959-77-8}, doi = {10.25972/OPUS-4984}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-64999}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {The field of small satellite formations and constellations attracted growing attention, based on recent advances in small satellite engineering. The utilization of distributed space systems allows the realization of innovative applications and will enable improved temporal and spatial resolution in observation scenarios. On the other side, this new paradigm imposes a variety of research challenges. In this monograph new networking concepts for space missions are presented, using networks of ground stations. The developed approaches combine ground station resources in a coordinated way to achieve more robust and efficient communication links. Within this thesis, the following topics were elaborated to improve the performance in distributed space missions: Appropriate scheduling of contact windows in a distributed ground system is a necessary process to avoid low utilization of ground stations. The theoretical basis for the novel concept of redundant scheduling was elaborated in detail. Additionally to the presented algorithm was a scheduling system implemented, its performance was tested extensively with real world scheduling problems. In the scope of data management, a system was developed which autonomously synchronizes data frames in ground station networks and uses this information to detect and correct transmission errors. The system was validated with hardware in the loop experiments, demonstrating the benefits of the developed approach.}, subject = {Kleinsatellit}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {A Rule-based Statistical Classifier for Determining a Base Text and Ranking Witnesses In Textual Documents Collation Process}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-57465}, year = {2011}, abstract = {Given a collection of diverging documents about some lost original text, any person interested in the text would try reconstructing it from the diverging documents. Whether it is eclecticism, stemmatics, or copy-text, one is expected to explicitly or indirectly select one of the documents as a starting point or as a base text, which could be emended through comparison with remaining documents, so that a text that could be designated as the original document is generated. Unfortunately the process of giving priority to one of the documents also known as witnesses is a subjective approach. In fact even Cladistics, which could be considered as a computer-based approach of implementing stemmatics, does not present or recommend users to select a certain witness as a starting point for the process of reconstructing the original document. In this study, a computational method using a rule-based Bayesian classifier is used, to assist text scholars in their attempts of reconstructing a non-existing document from some available witnesses. The method developed in this study consists of selecting a base text successively and collating it with remaining documents. Each completed collation cycle stores the selected base text and its closest witness, along with a weighted score of their similarities and differences. At the end of the collation process, a witness selected more often by majority of base texts is considered as the probable base text of the collection. Witnesses' scores are weighted using a weighting system, based on effects of types of textual modifications on the process of reconstructing original documents. Users have the possibility to select between baseless and base text collation. If a base text is selected, the task is reduced to ranking the witnesses with respect to the base text, otherwise a base text as well as ranking of the witnesses with respect to the base text are computed and displayed on a histogram.}, subject = {Textvergleich}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Assisting Understanding, Retention, and Dissemination of Religious Texts Knowledge with Modeling, and Visualization Techniques: The Case of The Quran}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-55927}, year = {2011}, abstract = {Learning a book in general involves reading it, underlining important words, adding comments, summarizing some passages, and marking up some text or concepts. Once deeper understanding is achieved, one would like to organize and manage her/his knowledge in such a way that, it could be easily remembered and efficiently transmitted to others. In this paper, books organized in terms of chapters consisting of verses, are considered as the source of knowledge to be modeled. The knowledge model consists of verses with their metadata and semantic annotations. The metadata represent the multiple perspectives of knowledge modeling. Verses with their metadata and annotations form a meta-model, which will be published on a web Mashup. The meta-model with linking between its elements constitute a knowledge base. An XML-based annotation system breaking down the learning process into specific tasks, helps constructing the desired meta-model. The system is made up of user interfaces for creating metadata, annotating chapters' contents according to user selected semantics, and templates for publishing the generated knowledge on the Internet. The proposed software system improves comprehension and retention of knowledge contained in religious texts through modeling and visualization. The system has been applied to the Quran, and the result obtained shows that multiple perspectives of information modeling can be successfully applied to religious texts. It is expected that this short ongoing study would motivate others to engage in devising and offering software systems for cross-religions learning.}, subject = {Wissensmanagement}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Design and Implementation of Architectures for Interactive Textual Documents Collation Systems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-56601}, year = {2011}, abstract = {One of the main purposes of textual documents collation is to identify a base text or closest witness to the base text, by analyzing and interpreting differences also known as types of changes that might exist between those documents. Based on this fact, it is reasonable to argue that, explicit identification of types of changes such as deletions, additions, transpositions, and mutations should be part of the collation process. The identification could be carried out by an interpretation module after alignment has taken place. Unfortunately existing collation software such as CollateX1 and Juxta2's collation engine do not have interpretation modules. In fact they implement the Gothenburg model [1] for collation process which does not include an interpretation unit. Currently both CollateX and Juxta's collation engine do not distinguish in their critical apparatus between the types of changes, and do not offer statistics about those changes. This paper presents a model for both integrated and distributed collation processes that improves the Gothenburg model. The model introduces an interpretation component for computing and distinguishing between the types of changes that documents could have undergone. Moreover two architectures implementing the model in order to solve the problem of interactive collation are discussed as well. Each architecture uses CollateX library, and provides on the one hand preprocessing functions for transforming input documents into CollateX input format, and on the other hand a post-processing module for enabling interactive collation. Finally simple algorithms for distinguishing between types of changes, and linking collated source documents with the collation results are also introduced.}, subject = {Softwarearchitektur}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Assisting Analysis and Understanding of Quran Search Results with Interactive Scatter Plots and Tables}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-55840}, year = {2011}, abstract = {The Quran is the holy book of Islam consisting of 6236 verses divided into 114 chapters called suras. Many verses are similar and even identical. Searching for similar texts (e.g verses) could return thousands of verses, that when displayed completely or partly as textual list would make analysis and understanding difficult and confusing. Moreover it would be visually impossible to instantly figure out the overall distribution of the retrieved verses in the Quran. As consequence reading and analyzing the verses would be tedious and unintuitive. In this study a combination of interactive scatter plots and tables has been developed to assist analysis and understanding of the search result. Retrieved verses are clustered by chapters, and a weight is assigned to each cluster according to number of verses it contains, so that users could visually identify most relevant areas, and figure out the places of revelation of the verses. Users visualize the complete result and can select a region of the plot to zoom in, click on a marker to display a table containing verses with English translation side by side.}, subject = {Text Mining}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {A Knowledge-based Hybrid Statistical Classifier for Reconstructing the Chronology of the Quran}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-54712}, year = {2011}, abstract = {Computationally categorizing Quran's chapters has been mainly confined to the determination of chapters' revelation places. However this broad classification is not sufficient to effectively and thoroughly understand and interpret the Quran. The chronology of revelation would not only improve comprehending the philosophy of Islam, but also the easiness of implementing and memorizing its laws and recommendations. This paper attempts estimating possible chapters' dates of revelation through their lexical frequency profiles. A hybrid statistical classifier consisting of stemming and clustering algorithms for comparing lexical frequency profiles of chapters, and deriving dates of revelation has been developed. The classifier is trained using some chapters with known dates of revelation. Then it classifies chapters with uncertain dates of revelation by computing their proximity to the training ones. The results reported here indicate that the proposed methodology yields usable results in estimating dates of revelation of the Quran's chapters based on their lexical contents.}, subject = {Text Mining}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Using Machine Learning Algorithms for Categorizing Quranic Chaptersby Major Phases of Prophet Mohammad's Messengership}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-66862}, year = {2011}, abstract = {This paper discusses the categorization of Quranic chapters by major phases of Prophet Mohammad's messengership using machine learning algorithms. First, the chapters were categorized by places of revelation using Support Vector Machine and na{\"i}ve Bayesian classifiers separately, and their results were compared to each other, as well as to the existing traditional Islamic and western orientalists classifications. The chapters were categorized into Meccan (revealed in Mecca) and Medinan (revealed in Medina). After that, chapters of each category were clustered using a kind of fuzzy-single linkage clustering approach, in order to correspond to the major phases of Prophet Mohammad's life. The major phases of the Prophet's life were manually derived from the Quranic text, as well as from the secondary Islamic literature e.g hadiths, exegesis. Previous studies on computing the places of revelation of Quranic chapters relied heavily on features extracted from existing background knowledge of the chapters. For instance, it is known that Meccan chapters contain mostly verses about faith and related problems, while Medinan ones encompass verses dealing with social issues, battles…etc. These features are by themselves insufficient as a basis for assigning the chapters to their respective places of revelation. In fact, there are exceptions, since some chapters do contain both Meccan and Medinan features. In this study, features of each category were automatically created from very few chapters, whose places of revelation have been determined through identification of historical facts and events such as battles, migration to Medina…etc. Chapters having unanimously agreed places of revelation were used as the initial training set, while the remaining chapters formed the testing set. The classification process was made recursive by regularly augmenting the training set with correctly classified chapters, in order to classify the whole testing set. Each chapter was preprocessed by removing unimportant words, stemming, and representation with vector space model. The result of this study shows that, the two classifiers have produced useable results, with an outperformance of the support vector machine classifier. This study indicates that, the proposed methodology yields encouraging results for arranging Quranic chapters by phases of Prophet Mohammad's messengership.}, subject = {Koran}, language = {en} } @phdthesis{Schlosser2011, author = {Schlosser, Daniel}, title = {Quality of Experience Management in Virtual Future Networks}, doi = {10.25972/OPUS-5719}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-69986}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {Aktuell beobachten wir eine drastische Vervielf{\"a}ltigung der Dienste und Anwendungen, die das Internet f{\"u}r den Datentransport nutzen. Dabei unterscheiden sich die Anforderungen dieser Dienste an das Netzwerk deutlich. Das Netzwerkmanagement wird durch diese Diversit{\"a}t der nutzenden Dienste aber deutlich erschwert, da es einem Datentransportdienstleister kaum m{\"o}glich ist, die unterschiedlichen Verbindungen zu unterscheiden, ohne den Inhalt der transportierten Daten zu analysieren. Netzwerkvirtualisierung ist eine vielversprechende L{\"o}sung f{\"u}r dieses Problem, da sie es erm{\"o}glicht f{\"u}r verschiedene Dienste unterschiedliche virtuelle Netze auf dem gleichen physikalischen Substrat zu betreiben. Diese Diensttrennung erm{\"o}glicht es, jedes einzelne Netz anwendungsspezifisch zu steuern. Ziel einer solchen Netzsteuerung ist es, sowohl die vom Nutzer erfahrene Dienstg{\"u}te als auch die Kosteneffizienz des Datentransports zu optimieren. Dar{\"u}ber hinaus wird es mit Netzwerkvirtualisierung m{\"o}glich das physikalische Netz so weit zu abstrahieren, dass die aktuell fest verzahnten Rollen von Netzwerkbesitzer und Netzwerkbetreiber entkoppelt werden k{\"o}nnen. Dar{\"u}ber hinaus stellt Netzwerkvirtualisierung sicher, dass unterschiedliche Datennetze, die gleichzeitig auf dem gleichen physikalischen Netz betrieben werden, sich gegenseitig weder beeinflussen noch st{\"o}ren k{\"o}nnen. Diese Arbeit  besch{\"a}ftigt sich mit ausgew{\"a}hlten Aspekten dieses Themenkomplexes und fokussiert sich darauf, ein virtuelles Netzwerk mit bestm{\"o}glicher Dienstqualit{\"a}t f{\"u}r den Nutzer zu betreiben und zu steuern. Daf{\"u}r wird ein Top-down-Ansatz gew{\"a}hlt, der von den Anwendungsf{\"a}llen, einer m{\"o}glichen Netzwerkvirtualisierungs-Architektur und aktuellen M{\"o}glichkeiten der Hardwarevirtualisierung ausgeht. Im Weiteren fokussiert sich die Arbeit dann in Richtung Bestimmung und Optimierung der vom Nutzer erfahrenen Dienstqualit{\"a}t (QoE) auf Applikationsschicht und diskutiert M{\"o}glichkeiten zur Messung und {\"U}berwachung von wesentlichen Netzparametern in virtualisierten Netzen.}, subject = {Netzwerkmanagement}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Computing Generic Causes of Revelation of the Quranic Verses Using Machine Learning Techniques}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-66083}, year = {2011}, abstract = {Because many verses of the holy Quran are similar, there is high probability that, similar verses addressing same issues share same generic causes of revelation. In this study, machine learning techniques have been employed in order to automatically derive causes of revelation of Quranic verses. The derivation of the causes of revelation is viewed as a classification problem. Initially the categories are based on the verses with known causes of revelation, and the testing set consists of the remaining verses. Based on a computed threshold value, a na{\"i}ve Bayesian classifier is used to categorize some verses. After that, using a decision tree classifier the remaining uncategorized verses are separated into verses that contain indicators (resultative connectors, causative expressions…), and those that do not. As for those verses having indicators, each one is segmented into its constituent clauses by identification of the linking indicators. Then a dominant clause is extracted and considered either as the cause of revelation, or post-processed by adding or subtracting some terms to form a causal clause that constitutes the cause of revelation. Concerning remaining unclassified verses without indicators, a naive Bayesian classifier is again used to assign each one of them to one of the existing classes based on features and topics similarity. As for verses that could not be classified so far, manual classification was made by considering each verse as a category on its own. The result obtained in this study is encouraging, and shows that automatic derivation of Quranic verses' generic causes of revelation is achievable, and reasonably reliable for understanding and implementing the teachings of the Quran.}, subject = {Text Mining}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Design and Implementation of a Model-driven XML-based Integrated System Architecture for Assisting Analysis, Understanding, and Retention of Religious Texts:The Case of The Quran}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-65737}, year = {2011}, abstract = {Learning a book in general involves reading it, underlining important words, adding comments, summarizing some passages, and marking up some text or concepts. Once deeper understanding is achieved, one would like to organize and manage her/his knowledge in such a way that, it could be easily remembered and efficiently transmitted to others. This paper discusses about modeling religious texts using semantic XML markup based on frame-based knowledge representation, with the purpose of assisting understanding, retention, and sharing of knowledge they contain. In this study, books organized in terms of chapters made up of verses are considered as the source of knowledge to model. Some metadata representing the multiple perspectives of knowledge modeling are assigned to each chapter and verse. Chapters and verses with their metadata form a meta-model, which is represented using frames, and published on a web mashup. An XML-based annotation and visualization system equipped with user interfaces for creating static and dynamic metadata, annotating chapters' contents according to user selected semantics, and templates for publishing generated knowledge on the Internet, has been developed. The system has been applied to the Quran, and the result obtained shows that multiple perspectives of information modeling can be successfully applied to religious texts, in order to support analysis, understanding, and retention of the texts.}, subject = {Wissensrepr{\"a}sentation}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Computer-based Textual Documents Collation System for Reconstructing the Original Text from Automatically Identified Base Text and Ranked Witnesses}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-65749}, year = {2011}, abstract = {Given a collection of diverging documents about some lost original text, any person interested in the text would try reconstructing it from the diverging documents. Whether it is eclecticism, stemmatics, or copy-text, one is expected to explicitly or indirectly select one of the documents as a starting point or as a base text, which could be emended through comparison with remaining documents, so that a text that could be designated as the original document is generated. Unfortunately the process of giving priority to one of the documents also known as witnesses is a subjective approach. In fact even Cladistics, which could be considered as a computer-based approach of implementing stemmatics, does not present or recommend users to select a certain witness as a starting point for the process of reconstructing the original document. In this study, a computational method using a rule-based Bayesian classifier is used, to assist text scholars in their attempts of reconstructing a non-existing document from some available witnesses. The method developed in this study consists of selecting a base text successively and collating it with remaining documents. Each completed collation cycle stores the selected base text and its closest witness, along with a weighted score of their similarities and differences. At the end of the collation process, a witness selected more often by majority of base texts is considered as the probable base text of the collection. Witnesses' scores are weighted using a weighting system, based on effects of types of textual modifications on the process of reconstructing original documents. Users have the possibility to select between baseless and base text collation. If a base text is selected, the task is reduced to ranking the witnesses with respect to the base text, otherwise a base text as well as ranking of the witnesses with respect to the base text are computed and displayed on a bar diagram. Additionally this study includes a recursive algorithm for automatically reconstructing the original text from the identified base text and ranked witnesses.}, subject = {Textvergleich}, language = {en} } @unpublished{Nassourou2011, author = {Nassourou, Mohamadou}, title = {Philosophical and Computational Approaches for Estimating and Visualizing Months of Revelations of Quranic Chapters}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-65784}, year = {2011}, abstract = {The question of why the Quran structure does not follow its chronology of revelation is a recurring one. Some Islamic scholars such as [1] have answered the question using hadiths, as well as other philosophical reasons based on internal evidences of the Quran itself. Unfortunately till today many are still wondering about this issue. Muslims believe that the Quran is a summary and a copy of the content of a preserved tablet called Lawhul-Mahfuz located in the heaven. Logically speaking, this suggests that the arrangement of the verses and chapters is expected to be similar to that of the Lawhul-Mahfuz. As for the arrangement of the verses in each chapter, there is unanimity that it was carried out by the Prophet himself under the guidance of Angel Gabriel with the recommendation of God. But concerning the ordering of the chapters, there are reports about some divergences [3] among the Prophet's companions as to which chapter should precede which one. This paper argues that Quranic chapters might have been arranged according to months and seasons of revelation. In fact, based on some verses of the Quran, it is defendable that the Lawhul-Mahfuz itself is understood to have been structured in terms of the months of the year. In this study, philosophical and mathematical arguments for computing chapters' months of revelation are discussed, and the result is displayed on an interactive scatter plot.}, subject = {Text Mining}, language = {en} } @phdthesis{Selbach2011, author = {Selbach, Stefan}, title = {Hybride bitparallele Volltextsuche}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-66476}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2011}, abstract = {Der große Vorteil eines q-Gramm Indexes liegt darin, dass es m{\"o}glich ist beliebige Zeichenketten in einer Dokumentensammlung zu suchen. Ein Nachteil jedoch liegt darin, dass bei gr{\"o}ßer werdenden Datenmengen dieser Index dazu neigt, sehr groß zu werden, was mit einem deutlichem Leistungsabfall verbunden ist. In dieser Arbeit wird eine neuartige Technik vorgestellt, die die Leistung eines q-Gramm Indexes mithilfe zus{\"a}tzlicher M-Matrizen f{\"u}r jedes q-Gramm und durch die Kombination mit einem invertierten Index erh{\"o}ht. Eine M-Matrix ist eine Bit-Matrix, die Informationen {\"u}ber die Positionen eines q-Gramms enth{\"a}lt. Auch bei der Kombination von zwei oder mehreren Q-Grammen bieten diese M-Matrizen Informationen {\"u}ber die Positionen der Kombination. Dies kann verwendet werden, um die Komplexit{\"a}t der Zusammenf{\"u}hrung der q-Gramm Trefferlisten f{\"u}r eine gegebene Suchanfrage zu reduzieren und verbessert die Leistung des n-Gramm-invertierten Index. Die Kombination mit einem termbasierten invertierten Index beschleunigt die durchschnittliche Suchzeit zus{\"a}tzlich und vereint die Vorteile beider Index-Formate. Redundante Informationen werden in dem q-Gramm Index reduziert und weitere Funktionalit{\"a}t hinzugef{\"u}gt, wie z.B. die Bewertung von Treffern nach Relevanz, die M{\"o}glichkeit, nach Konzepten zu suchen oder Indexpartitionierungen nach Wichtigkeit der enthaltenen Terme zu erstellen.}, subject = {Information Retrieval}, language = {de} } @article{MandelHoernleinIflandetal.2011, author = {Mandel, Alexander and H{\"o}rnlein, Alexander and Ifland, Marianus and L{\"u}neburg, Edeltraud and Deckert, J{\"u}rgen and Puppe, Frank}, title = {Aufwandsanalyse f{\"u}r computerunterst{\"u}tzte Multiple-Choice Papierklausuren}, series = {GMS Journal for Medical Education}, volume = {28}, journal = {GMS Journal for Medical Education}, number = {4}, doi = {10.3205/zma000767}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-134386}, pages = {1-15, Doc55}, year = {2011}, abstract = {Introduction: Multiple-choice-examinations are still fundamental for assessment in medical degree programs. In addition to content related research, the optimization of the technical procedure is an important question. Medical examiners face three options: paper-based examinations with or without computer support or completely electronic examinations. Critical aspects are the effort for formatting, the logistic effort during the actual examination, quality, promptness and effort of the correction, the time for making the documents available for inspection by the students, and the statistical analysis of the examination results. Methods: Since three semesters a computer program for input and formatting of MC-questions in medical and other paper-based examinations is used and continuously improved at Wuerzburg University. In the winter semester (WS) 2009/10 eleven, in the summer semester (SS) 2010 twelve and in WS 2010/11 thirteen medical examinations were accomplished with the program and automatically evaluated. For the last two semesters the remaining manual workload was recorded. Results: The cost of the formatting and the subsequent analysis including adjustments of the analysis of an average examination with about 140 participants and about 35 questions was 5-7 hours for exams without complications in the winter semester 2009/2010, about 2 hours in SS 2010 and about 1.5 hours in the winter semester 2010/11. Including exams with complications, the average time was about 3 hours per exam in SS 2010 and 2.67 hours for the WS 10/11. Discussion: For conventional multiple-choice exams the computer-based formatting and evaluation of paper-based exams offers a significant time reduction for lecturers in comparison with the manual correction of paper-based exams and compared to purely electronically conducted exams it needs a much simpler technological infrastructure and fewer staff during the exam."}, language = {de} } @article{Zeeshan2010, author = {Zeeshan, Ahmed}, title = {Towards Performance Measurement and Metrics Based Analysis of PLA Applications}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-68188}, year = {2010}, abstract = {This article is about a measurement analysis based approach to help software practitioners in managing the additional level complexities and variabilities in software product line applications. The architecture of the proposed approach i.e. ZAC is designed and implemented to perform preprocessesed source code analysis, calculate traditional and product line metrics and visualize results in two and three dimensional diagrams. Experiments using real time data sets are performed which concluded with the results that the ZAC can be very helpful for the software practitioners in understanding the overall structure and complexity of product line applications. Moreover the obtained results prove strong positive correlation between calculated traditional and product line measures.}, subject = {Programmierbare logische Anordnung}, language = {en} } @phdthesis{Oechsner2010, author = {Oechsner, Simon}, title = {Performance Challenges and Optimization Potential of Peer-to-Peer Overlay Technologies}, doi = {10.25972/OPUS-4159}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-50015}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {In today's Internet, building overlay structures to provide a service is becoming more and more common. This approach allows for the utilization of client resources, thus being more scalable than a client-server model in this respect. However, in these architectures the quality of the provided service depends on the clients and is therefore more complex to manage. Resource utilization, both at the clients themselves and in the underlying network, determine the efficiency of the overlay application. Here, a trade-off exists between the resource providers and the end users that can be tuned via overlay mechanisms. Thus, resource management and traffic management is always quality-of-service management as well. In this monograph, the three currently significant and most widely used overlay types in the Internet are considered. These overlays are implemented in popular applications which only recently have gained importance. Thus, these overlay networks still face real-world technical challenges which are of high practical relevance. We identify the specific issues for each of the considered overlays, and show how their optimization affects the trade-offs between resource efficiency and service quality. Thus, we supply new insights and system knowledge that is not provided by previous work.}, subject = {Overlay-Netz}, language = {en} } @phdthesis{Henjes2010, author = {Henjes, Robert}, title = {Performance Evaluation of Publish/Subscribe Middleware Architectures}, doi = {10.25972/OPUS-4536}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-53388}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {While developing modern applications, it is necessary to ensure an efficient and performant communication between different applications. In current environments, a middleware software is used, which supports the publish/subscribe communication pattern. Using this communication pattern, a publisher sends information encapsulated in messages to the middleware. A subscriber registers its interests at the middleware. The monograph describes three different steps to determine the performance of such a system. In a first step, the message throughput performance of a publish/subscribe in different scenarios is measured using a Java Message Service (JMS) based implementation. In the second step the maximum achievable message throughput is described by adapted models depending on the filter complexity and the replication grade. Using the model, the performance characteristics of a specific system in a given scenario can be determined. These numbers are used for the queuing model described in the third part of the thesis, which supports the dimensioning of a system in realistic scenarios. Additionally, we introduce a method to approximate an M/G/1 system numerically in an efficient way, which can be used for real time analysis to predict the expected performance in a certain scenario. Finally, the analytical model is used to investigate different possibilities to ensure the scalability of the maximum achievable message throughput of the overall system.}, subject = {Middleware}, language = {en} } @inproceedings{OPUS4-4233, title = {9. Fachgespr{\"a}ch Sensornetze der GI/ITG Fachgruppe Kommunikation und Verteilte Systeme}, editor = {Kolla, Reiner}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-51106}, year = {2010}, abstract = {J{\"a}hrliches Fachgespr{\"a}ch zu Sensornetzen der GI/ITG Fachgruppe Kommunikation und Verteilte Systeme, 16. - 17. September 2010, Universit{\"a}t W{\"u}rzburg}, subject = {Drahtloses Sensorsystem}, language = {mul} } @phdthesis{Zeiger2010, author = {Zeiger, Florian}, title = {Internet Protocol based networking of mobile robots}, isbn = {978-3-923959-59-4}, doi = {10.25972/OPUS-4661}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-54776}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {This work is composed of three main parts: remote control of mobile systems via Internet, ad-hoc networks of mobile robots, and remote control of mobile robots via 3G telecommunication technologies. The first part gives a detailed state of the art and a discussion of the problems to be solved in order to teleoperate mobile robots via the Internet. The focus of the application to be realized is set on a distributed tele-laboratory with remote experiments on mobile robots which can be accessed world-wide via the Internet. Therefore, analyses of the communication link are used in order to realize a robust system. The developed and implemented architecture of this distributed tele-laboratory allows for a smooth access also with a variable or low link quality. The second part covers the application of ad-hoc networks for mobile robots. The networking of mobile robots via mobile ad-hoc networks is a very promising approach to realize integrated telematic systems without relying on preexisting communication infrastructure. Relevant civilian application scenarios are for example in the area of search and rescue operations where first responders are supported by multi-robot systems. Here, mobile robots, humans, and also existing stationary sensors can be connected very fast and efficient. Therefore, this work investigates and analyses the performance of different ad-hoc routing protocols for IEEE 802.11 based wireless networks in relevant scenarios. The analysis of the different protocols allows for an optimization of the parameter settings in order to use these ad-hoc routing protocols for mobile robot teleoperation. Also guidelines for the realization of such telematics systems are given. Also traffic shaping mechanisms of application layer are presented which allow for a more efficient use of the communication link. An additional application scenario, the integration of a small size helicopter into an IP based ad-hoc network, is presented. The teleoperation of mobile robots via 3G telecommunication technologies is addressed in the third part of this work. The high availability, high mobility, and the high bandwidth provide a very interesting opportunity to realize scenarios for the teleoperation of mobile robots or industrial remote maintenance. This work analyses important parameters of the UMTS communication link and investigates also the characteristics for different data streams. These analyses are used to give guidelines which are necessary for the realization of or industrial remote maintenance or mobile robot teleoperation scenarios. All the results and guidelines for the design of telematic systems in this work were derived from analyses and experiments with real hardware.}, subject = {Robotik}, language = {en} } @phdthesis{Sauer2010, author = {Sauer, Markus}, title = {Mixed-Reality for Enhanced Robot Teleoperation}, isbn = {978-3-923959-67-9}, doi = {10.25972/OPUS-4666}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-55083}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {In den letzten Jahren ist die Forschung in der Robotik soweit fortgeschritten, dass die Mensch-Maschine Schnittstelle zunehmend die kritischste Komponente f{\"u}r eine hohe Gesamtperformanz von Systemen zur Navigation und Koordination von Robotern wird. In dieser Dissertation wird untersucht wie Mixed-Reality Technologien f{\"u}r Nutzerschnittstellen genutzt werden k{\"o}nnen, um diese Gesamtperformanz zu erh{\"o}hen. Hierzu werden Konzepte und Technologien entwickelt, die durch Evaluierung mit Nutzertest ein optimiertes und anwenderbezogenes Design von Mixed-Reality Nutzerschnittstellen erm{\"o}glichen. Er werden somit sowohl die technische Anforderungen als auch die menschlichen Faktoren f{\"u}r ein konsistentes Systemdesign ber{\"u}cksichtigt. Nach einer detaillierten Problemanalyse und der Erstellung eines Systemmodels, das den Menschen als Schl{\"u}sselkomponente mit einbezieht, wird zun{\"a}chst die Anwendung der neuartigen 3D-Time-of-Flight Kamera zur Navigation von Robotern, aber auch f{\"u}r den Einsatz in Mixed-Reality Schnittstellen analysiert und optimiert. Weiterhin wird gezeigt, wie sich der Netzwerkverkehr des Videostroms als wichtigstes Informationselement der meisten Nutzerschnittstellen f{\"u}r die Navigationsaufgabe auf der Netzwerk Applikationsebene in typischen Multi-Roboter Netzwerken mit dynamischen Topologien und Lastsituation optimieren l{\"a}sst. Hierdurch ist es m{\"o}glich in sonst in sonst typischen Ausfallszenarien den Videostrom zu erhalten und die Bildrate zu stabilisieren. Diese fortgeschrittenen Technologien werden dann auch dem entwickelten Konzept der generischen 3D Mixed Reality Schnittselle eingesetzt. Dieses Konzept erm{\"o}glicht eine integrierte 3D Darstellung der verf{\"u}gbaren Information, so dass r{\"a}umliche Beziehungen von Informationen aufrechterhalten werden und somit die Anzahl der mentalen Transformationen beim menschlichen Bediener reduziert wird. Gleichzeitig werden durch diesen Ansatz auch immersive Stereo Anzeigetechnologien unterst{\"u}tzt, welche zus{\"a}tzlich das r{\"a}umliche Verst{\"a}ndnis der entfernten Situation f{\"o}rdern. Die in der Dissertation vorgestellten und evaluierten Ans{\"a}tze nutzen auch die Tatsache, dass sich eine lokale Autonomie von Robotern heute sehr robust realisieren l{\"a}sst. Dies wird zum Beispiel zur Realisierung eines Assistenzsystems mit variabler Autonomie eingesetzt. Hierbei erh{\"a}lt der Fernbediener {\"u}ber eine Kraftr{\"u}ckkopplung kombiniert mit einer integrierten Augmented Reality Schnittstelle, einen Eindruck {\"u}ber die Situation am entfernten Arbeitsbereich, aber auch {\"u}ber die aktuelle Navigationsintention des Roboters. Die durchgef{\"u}hrten Nutzertests belegen die signifikante Steigerung der Navigationsperformanz durch den entwickelten Ansatz. Die robuste lokale Autonomie erm{\"o}glicht auch den in der Dissertation eingef{\"u}hrten Ansatz der pr{\"a}diktiven Mixed-Reality Schnittstelle. Die durch diesen Ansatz entkoppelte Regelschleife {\"u}ber den Menschen erm{\"o}glicht es die Sichtbarkeit von unvermeidbaren Systemverz{\"o}gerungen signifikant zu reduzieren. Zus{\"a}tzlich k{\"o}nnen durch diesen Ansatz beide f{\"u}r die Navigation hilfreichen Blickwinkel in einer 3D-Nutzerschnittstelle kombiniert werden - der exozentrische Blickwinkel und der egozentrische Blickwinkel als Augmented Reality Sicht.}, subject = {Mobiler Roboter}, language = {en} } @unpublished{Nassourou2010, author = {Nassourou, Mohamadou}, title = {Markup overlap: Improving Fragmentation Method}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-49084}, year = {2010}, abstract = {Overlapping is a common word used to describe documents whose structural dimensions cannot be adequately represented using tree structure. For instance a quotation that starts in one verse and ends in another verse. The problem of overlapping hierarchies is a recurring one, which has been addressed by a variety of approaches. There are XML based solutions as well as Non-XML ones. The XML-based solutions are: multiple documents, empty elements, fragmentation, out-of-line markup, JITT and BUVH. And the Non-XML approaches comprise CONCUR/XCONCUR, MECS, LMNL ...etc. This paper presents shortly state-of-the-art in overlapping hierarchies, and introduces two variations on the TEI fragmentation markup that have several advantages.}, subject = {XML}, language = {en} } @phdthesis{Klein2010, author = {Klein, Alexander}, title = {Performance Issues of MAC and Routing Protocols in Wireless Sensor Networks}, doi = {10.25972/OPUS-4465}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-52870}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {The focus of this work lies on the communication issues of Medium Access Control (MAC) and routing protocols in the context of WSNs. The communication challenges in these networks mainly result from high node density, low bandwidth, low energy constraints and the hardware limitations in terms of memory, computational power and sensing capabilities of low-power transceivers. For this reason, the structure of WSNs is always kept as simple as possible to minimize the impact of communication issues. Thus, the majority of WSNs apply a simple one hop star topology since multi-hop communication has high demands on the routing protocol since it increases the bandwidth requirements of the network. Moreover, medium access becomes a challenging problem due to the fact that low-power transceivers are very limited in their sensing capabilities. The first contribution is represented by the Backoff Preamble-based MAC Protocol with Sequential Contention Resolution (BPS-MAC) which is designed to overcome the limitations of low-power transceivers. Two communication issues, namely the Clear Channel Assessment (CCA) delay and the turnaround time, are directly addressed by the protocol. The CCA delay represents the period of time which is required by the transceiver to detect a busy radio channel while the turnaround time specifies the period of time which is required to switch between receive and transmit mode. Standard Carrier Sense Multiple Access (CSMA) protocols do not achieve high performance in terms of packet loss if the traffic is highly correlated due to the fact that the transceiver is not able to sense the medium during the switching phase. Therefore, a node may start to transmit data while another node is already transmitting since it has sensed an idle medium right before it started to switch its transceiver from receive to transmit mode. The BPS-MAC protocol uses a new sequential preamble-based medium access strategy which can be adapted to the hardware capabilities of the transceivers. The protocol achieves a very low packet loss rate even in wireless networks with high node density and event-driven traffic without the need of synchronization. This makes the protocol attractive to applications such as structural health monitoring, where event suppression is not an option. Moreover, acknowledgments or complex retransmission strategies become almost unnecessary since the sequential preamble-based contention resolution mechanism minimizes the collision probability. However, packets can still be lost as a consequence of interference or other issues which affect signal propagation. The second contribution consists of a new routing protocol which is able to quickly detect topology changes without generating a large amount of overhead. The key characteristics of the Statistic-Based Routing (SBR) protocol are high end-to-end reliability (in fixed and mobile networks), load balancing capabilities, a smooth continuous routing metric, quick adaptation to changing network conditions, low processing and memory requirements, low overhead, support of unidirectional links and simplicity. The protocol can establish routes in a hybrid or a proactive mode and uses an adaptive continuous routing metric which makes it very flexible in terms of scalability while maintaining stable routes. The hybrid mode is optimized for low-power WSNs since routes are only established on demand. The difference of the hybrid mode to reactive routing strategies is that routing messages are periodically transmitted to maintain already established routes. However, the protocol stops the transmission of routing messages if no data packets are transmitted for a certain time period in order to minimize the routing overhead and the energy consumption. The proactive mode is designed for high data rate networks which have less energy constraints. In this mode, the protocol periodically transmits routing messages to establish routes in a proactive way even in the absence of data traffic. Thus, nodes in the network can immediately transmit data since the route to the destination is already established in advance. In addition, a new delay-based routing message forwarding strategy is introduced. The forwarding strategy is part of SBR but can also be applied to many routing protocols in order to modify the established topology. The strategy can be used, e.g. in mobile networks, to decrease the packet loss by deferring routing messages with respect to the neighbor change rate. Thus, nodes with a stable neighborhood forward messages faster than nodes within a fast changing neighborhood. As a result, routes are established through nodes with correlated movement which results in fewer topology changes due to higher link durations.}, subject = {Routing}, language = {en} } @unpublished{Nassourou2010, author = {Nassourou, Mohamadou}, title = {Understanding the Vex Rendering Engine}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-51333}, year = {2010}, abstract = {The Visual Editor for XML (Vex)[1] used by TextGrid [2]and other applications has got rendering and layout engines. The layout engine is well documented but the rendering engine is not. This lack of documenting the rendering engine has made refactoring and extending the editor hard and tedious. For instance many CSS2.1 and upcoming CSS3 properties have not been implemented. Software developers in different projects such as TextGrid using Vex would like to update its CSS rendering engine in order to provide advanced user interfaces as well as support different document types. In order to minimize the effort of extending Vex functionality, I found it beneficial to write a basic documentation about Vex software architecture in general and its CSS rendering engine in particular. The documentation is mainly based on the idea of architectural layered diagrams. In fact layered diagrams can help developers understand software's source code faster and easier in order to alter it, and fix errors. This paper is written for the purpose of providing direct support for exploration in the comprehension process of Vex source code. It discusses Vex software architecture. The organization of packages that make up the software, the architecture of its CSS rendering engine, an algorithm explaining the working principle of its rendering engine are described.}, subject = {Cascading Style Sheets}, language = {en} } @unpublished{Nassourou2010, author = {Nassourou, Mohamadou}, title = {Reference Architecture, Design of Cascading Style Sheets Processing Model}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-51328}, year = {2010}, abstract = {The technique of using Cascading Style Sheets (CSS) to format and present structured data is called CSS processing model. For instance a CSS processing model for XML documents describes steps involved in formatting and presenting XML documents on screens or papers. Many software applications such as browsers and XML editors have their own CSS processing models which are part of their rendering engines. For instance each browser based on its CSS processing model renders CSS layout differently, as a result an inconsistency in the support of CSS features arises. Some browsers support more CSS features than others, and the rendering itself varies. Moreover the W3C standards are not even adhered by some browsers such as Internet Explorer. Test suites and other hacks and filters cannot definitely solve these problems, because these solutions are temporary and fragile. To palliate this inconsistency and browser compatibility issues with respect to CSS, a reference CSS processing model is needed. By extension it could even allow interoperability across CSS rendering engines. A reference architecture would provide common software architecture and interfaces, and facilitate refactoring, reuse, and automated unit testing. In [2] a reference architecture for browsers has been proposed. However this reference architecture is a macro reference model which does not consider separately individual components of rendering and layout engines. In this paper an attempt to develop a reference architecture for CSS processing models is discussed. In addition the Vex editor [3] rendering and layout engines, as well as an extended version of the editor used in TextGrid project [5] are also presented in order to validate the proposed reference architecture.}, subject = {Cascading Style Sheets}, language = {en} } @unpublished{Nassourou2010, author = {Nassourou, Mohamadou}, title = {Empirical Study on Screen Scraping Web Service Creation: Case of Rhein-Main-Verkehrsverbund (RMV)}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-49396}, year = {2010}, abstract = {Internet is the biggest database that science and technology have ever produced. The world wide web is a large repository of information that cannot be used for automation by many applications due to its limited target audience. One of the solutions to the automation problem is to develop wrappers. Wrapping is a process whereby unstructured extracted information is transformed into a more structured one such as XML, which could be provided as webservice to other applications. A web service is a web page whose content is well structured so that a computer program can consume it automatically. This paper describes steps involved in constructing wrappers manually in order to automatically generate web services.}, subject = {HTML}, language = {en} } @unpublished{Nassourou2010, author = {Nassourou, Mohamadou}, title = {Java Web Frameworks Which One to Choose?}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-49407}, year = {2010}, abstract = {This article discusses web frameworks that are available to a software developer in Java language. It introduces MVC paradigm and some frameworks that implement it. The article presents an overview of Struts, Spring MVC, JSF Frameworks, as well as guidelines for selecting one of them as development environment.}, subject = {Java Frameworks}, language = {en} } @unpublished{Nassourou2010, author = {Nassourou, Mohamadou}, title = {Doing Webservices Composition by Content-based Mashup: Example of a Web-based Simulator for Itinerary Planning}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-50036}, year = {2010}, abstract = {Webservices composition is traditionally carried out using composition technologies such as Business Process Execution Language (BPEL) [1] and Web Service Choreography Interface (WSCI) [2]. The composition technology involves the process of web service discovery, invocation, and composition. However these technologies are not easy and flexible enough because they are mainly developer-centric. Moreover majority of websites have not yet embarked into the world of web service, although they have very important and useful information to offer. Is it because they have not understood the usefulness of web services or is it because of the costs? Whatever might be the answers to these questions, time and money are definitely required in order to create and offer web services. To avoid these expenditures, wrappers [7] to automatically generate webservices from websites would be a cheaper and easier solution. Mashups offer a different way of doing webservices composition. In web environment a Mashup is a web application that brings together data from several sources using webservices, APIs, wrappers and so on, in order to create entirely a new application that was not provided before. This paper presents first an overview of Mashups and the process of web service invocation and composition based on Mashup, then describes an example of a web-based simulator for navigation system in Germany.}, subject = {Mashup }, language = {en} } @article{VainshteinSanchezBrazmaetal.2010, author = {Vainshtein, Yevhen and Sanchez, Mayka and Brazma, Alvis and Hentze, Matthias W. and Dandekar, Thomas and Muckenthaler, Martina U.}, title = {The IronChip evaluation package: a package of perl modules for robust analysis of custom microarrays}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-67869}, year = {2010}, abstract = {Background: Gene expression studies greatly contribute to our understanding of complex relationships in gene regulatory networks. However, the complexity of array design, production and manipulations are limiting factors, affecting data quality. The use of customized DNA microarrays improves overall data quality in many situations, however, only if for these specifically designed microarrays analysis tools are available. Results: The IronChip Evaluation Package (ICEP) is a collection of Perl utilities and an easy to use data evaluation pipeline for the analysis of microarray data with a focus on data quality of custom-designed microarrays. The package has been developed for the statistical and bioinformatical analysis of the custom cDNA microarray IronChip but can be easily adapted for other cDNA or oligonucleotide-based designed microarray platforms. ICEP uses decision tree-based algorithms to assign quality flags and performs robust analysis based on chip design properties regarding multiple repetitions, ratio cut-off, background and negative controls. Conclusions: ICEP is a stand-alone Windows application to obtain optimal data quality from custom-designed microarrays and is freely available here (see "Additional Files" section) and at: http://www.alice-dsl.net/evgeniy. vainshtein/ICEP/}, subject = {Microarray}, language = {en} } @article{SchmidSchindelinCardonaetal.2010, author = {Schmid, Benjamin and Schindelin, Johannes and Cardona, Albert and Longair, Martin and Heisenberg, Martin}, title = {A high-level 3D visualization API for Java and ImageJ}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-67851}, year = {2010}, abstract = {Background: Current imaging methods such as Magnetic Resonance Imaging (MRI), Confocal microscopy, Electron Microscopy (EM) or Selective Plane Illumination Microscopy (SPIM) yield three-dimensional (3D) data sets in need of appropriate computational methods for their analysis. The reconstruction, segmentation and registration are best approached from the 3D representation of the data set. Results: Here we present a platform-independent framework based on Java and Java 3D for accelerated rendering of biological images. Our framework is seamlessly integrated into ImageJ, a free image processing package with a vast collection of community-developed biological image analysis tools. Our framework enriches the ImageJ software libraries with methods that greatly reduce the complexity of developing image analysis tools in an interactive 3D visualization environment. In particular, we provide high-level access to volume rendering, volume editing, surface extraction, and image annotation. The ability to rely on a library that removes the low-level details enables concentrating software development efforts on the algorithm implementation parts. Conclusions: Our framework enables biomedical image software development to be built with 3D visualization capabilities with very little effort. We offer the source code and convenient binary packages along with extensive documentation at http://3dviewer.neurofly.de.}, subject = {Visualisierung}, language = {en} } @phdthesis{Fehler2010, author = {Fehler, Manuel}, title = {Kalibrierung Agenten-basierter Simulationen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-64762}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {In der vorliegenden Arbeit wird das Problem der Kalibrierung Agenten-basierter Simulationen (ABS) behandelt, also das Problem, die Parameterwerte eines Agenten-basierten Simulationsmodells so einzustellen, dass valides Simulationsverhalten erreicht wird. Das Kalibrierungsproblem f{\"u}r Simulationen an sich ist nicht neu und ist im Rahmen klassischer Simulationsparadigmen, wie z.B. der Makro-Simulation, fester Bestandteil der Forschung. Im Vergleich zu den dort betrachteten Kalibrierungsproblemen zeichnet sich das Kalibrierungsproblem f{\"u}r ABS jedoch durch eine Reihe zus{\"a}tzlicher Herausforderungen aus, welche die direkte Anwendung existierender Kalibrierungsverfahren in begrenzter Zeit erschweren, bzw. nicht mehr sinnvoll zulassen. Die L{\"o}sung dieser Probleme steht im Zentrum dieser Dissertation: Das Ziel besteht darin, den Nutzer bei der Kalibrierung von ABS auf der Basis von unzureichenden, potentiell fehlerhaften Daten und Wissen zu unterst{\"u}tzen. Dabei sollen drei Hauptprobleme gel{\"o}st werden: 1)Vereinfachung der Kalibrierung großer Agenten-Parametermengen auf der Mikro- Ebene in Agenten-basierten Simulationen durch Ausnutzung der spezifischen Struktur von ABS (n{\"a}mlich dem Aufbau aus einer Menge von Agentenmodellen). 2)Kalibrierung Agenten-basierter Simulationen, so dass auf allen relevanten Beobachtungsebenen valides Simulationsverhalten erzeugt wird (mindestens Mikro und Makro-Ebene). Als erschwerende Randbedingung muss die Kalibrierung unter der Voraussetzung einer Makro-Mikro-Wissensl{\"u}cke durchgef{\"u}hrt werden. 3)Kalibrierung Agenten-basierter Simulationen auf der Mikro-Ebene unter der Voraussetzung, dass zur Kalibrierung einzelner Agentenmodelle nicht ausreichend und potentiell verf{\"a}lschte Daten zur Verhaltensvalidierung zur Verf{\"u}gung stehen. Hierzu wird in dieser Arbeit das sogenannte Makro-Mikro-Verfahren zur Kalibrierung von Agenten-basierten Simulationen entwickelt. Das Verfahren besteht aus einem Basisverfahren, das im Verlauf der Arbeit um verschiedene Zusatzverfahren erweitert wird. Das Makro-Mikro-Verfahren und seine Erweiterungen sollen dazu dienen, die Modellkalibrierung trotz stark verrauschter Daten und eingeschr{\"a}nktem Wissen {\"u}ber die Wirkungszusammenh{\"a}nge im Originalsystem geeignet zu erm{\"o}glichen und dabei den Kalibrierungsprozess zu beschleunigen: 1) Makro-Mikro-Kalibrierungsverfahren: Das in dieser Arbeit entwickelte Makro- Mikro-Verfahren unterst{\"u}tzt den Nutzer durch eine kombinierte Kalibrierung auf der Mikro- und der Makro-Beobachtungsebene, die gegebenenfalls durch Zwischenebenen erweitert werden kann. Der Grundgedanke des Verfahrens besteht darin, das Kalibrierungsproblem in eines auf aggregierter Verhaltensebene und eines auf der Ebene des Mikro-Agentenverhaltens aufzuteilen. Auf der Makro-Ebene wird nach validen idealen aggregierten Verhaltensmodellen (IVM) der Agenten gesucht. Auf der Mikro-Ebene wird versucht die individuellen Modelle der Agenten auf Basis des erw{\"u}nschten Gesamtverhaltens und der ermittelten IVM so zu kalibrieren, das insgesamt Simulationsverhalten entsteht, das sowohl auf Mikro- als auch auf Makro-Ebene valide ist. 2) Erweiterung 1: Robuste Kalibrierung: Um den Umgang mit potentiell verrauschten Validierungskriterien (d.h. mit verrauschten Daten {\"u}ber ein Originalsystem, auf denen die Validierungskriterien der Simulation beruhen) und Modellteilen w{\"a}hrend der Kalibrierung von ABS zu erm{\"o}glichen, wird eine robuste Kalibrierungstechnik zur Anwendung im Makro-Mikro-Verfahren entwickelt. 3) Erweiterung 2: Kalibrierung mit Heterogenit{\"a}tssuche: Als zweite Erweiterung des Makro-Mikro-Verfahrens wird ein Verfahren entwickelt, das das Problem des unklaren Detaillierungsgrades von ABS auf der Ebene der Parameterwerte adressiert. Prinzipiell kann zwar jeder Agent unterschiedliche Parameterwerte verwenden, obwohl eine geringere Heterogenit{\"a}t zur Erzeugung validen Verhaltens ausreichend w{\"a}re. Die entwickelte Erweiterung versucht, w{\"a}hrend der Kalibrierung, eine geeignete Heterogenit{\"a}tsauspr{\"a}gung f{\"u}r die Parameterwerte der Agenten zu ermitteln. Unter einer Heterogenit{\"a}tsauspr{\"a}gung wird dabei eine Einteilung der simulierten Agenten in Gruppen mit jeweils gleichen Parameterwerten verstanden. Die Heterogenit{\"a}tssuche dient dazu, einen Kompromiss zu finden zwischen der Notwendigkeit, sehr große Parametersuchr{\"a}ume durchsuchen zu m{\"u}ssen und gleichzeitig den Suchraum so klein wie m{\"o}glich halten zu wollen.}, subject = {Computersimulation}, language = {de} } @phdthesis{Pries2010, author = {Pries, Jan Rastin}, title = {Performance Optimization of Wireless Infrastructure and Mesh Networks}, doi = {10.25972/OPUS-3723}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46097}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2010}, abstract = {Future broadband wireless networks should be able to support not only best effort traffic but also real-time traffic with strict Quality of Service (QoS) constraints. In addition, their available resources are scare and limit the number of users. To facilitate QoS guarantees and increase the maximum number of concurrent users, wireless networks require careful planning and optimization. In this monograph, we studied three aspects of performance optimization in wireless networks: resource optimization in WLAN infrastructure networks, quality of experience control in wireless mesh networks, and planning and optimization of wireless mesh networks. An adaptive resource management system is required to effectively utilize the limited resources on the air interface and to guarantee QoS for real-time applications. Thereby, both WLAN infrastructure and WLAN mesh networks have to be considered. An a-priori setting of the access parameters is not meaningful due to the contention-based medium access and the high dynamics of the system. Thus, a management system is required which dynamically adjusts the channel access parameters based on the network load. While this is sufficient for wireless infrastructure networks, interferences on neighboring paths and self-interferences have to be considered for wireless mesh networks. In addition, a careful channel allocation and route assignment is needed. Due to the large parameter space, standard optimization techniques fail for optimizing large wireless mesh networks. In this monograph, we reveal that biology-inspired optimization techniques, namely genetic algorithms, are well-suitable for the planning and optimization of wireless mesh networks. Although genetic algorithms generally do not always find the optimal solution, we show that with a good parameter set for the genetic algorithm, the overall throughput of the wireless mesh network can be significantly improved while still sharing the resources fairly among the users.}, subject = {IEEE 802.11}, language = {en} } @inproceedings{SchlosserJarschelDuellietal.2010, author = {Schlosser, Daniel and Jarschel, Michael and Duelli, Michael and Hoßfeld, Tobias and Hoffmann, Klaus and Hoffmann, Marco and Morper, Hans Jochen and Jurca, Dan and Khan, Ashiq}, title = {A Use Case Driven Approach to Network Virtualization}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-55611}, year = {2010}, abstract = {In today's Internet, services are very different in their requirements on the underlying transport network. In the future, this diversity will increase and it will be more difficult to accommodate all services in a single network. A possible approach to cope with this diversity within future networks is the introduction of support for running isolated networks for different services on top of a single shared physical substrate. This would also enable easy network management and ensure an economically sound operation. End-customers will readily adopt this approach as it enables new and innovative services without being expensive. In order to arrive at a concept that enables this kind of network, it needs to be designed around and constantly checked against realistic use cases. In this contribution, we present three use cases for future networks. We describe functional blocks of a virtual network architecture, which are necessary to support these use cases within the network. Furthermore, we discuss the interfaces needed between the functional blocks and consider standardization issues that arise in order to achieve a global consistent control and management structure of virtual networks.}, subject = {Virtualisierung}, language = {en} } @phdthesis{Spoerhase2009, author = {Spoerhase, Joachim}, title = {Competitive and Voting Location}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-52978}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2009}, abstract = {We consider competitive location problems where two competing providers place their facilities sequentially and users can decide between the competitors. We assume that both competitors act non-cooperatively and aim at maximizing their own benefits. We investigate the complexity and approximability of such problems on graphs, in particular on simple graph classes such as trees and paths. We also develop fast algorithms for single competitive location problems where each provider places a single facilty. Voting location, in contrast, aims at identifying locations that meet social criteria. The provider wants to satisfy the users (customers) of the facility to be opened. In general, there is no location that is favored by all users. Therefore, a satisfactory compromise has to be found. To this end, criteria arising from voting theory are considered. The solution of the location problem is understood as the winner of a virtual election among the users of the facilities, in which the potential locations play the role of the candidates and the users represent the voters. Competitive and voting location problems turn out to be closely related.}, subject = {Standortproblem}, language = {en} } @phdthesis{Saska2009, author = {Saska, Martin}, title = {Trajectory planning and optimal control for formations of autonomous robots}, isbn = {978-3-923959-56-3}, doi = {10.25972/OPUS-4622}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-53175}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2009}, abstract = {In this thesis, we present novel approaches for formation driving of nonholonomic robots and optimal trajectory planning to reach a target region. The methods consider a static known map of the environment as well as unknown and dynamic obstacles detected by sensors of the formation. The algorithms are based on leader following techniques, where the formation of car-like robots is maintained in a shape determined by curvilinear coordinates. Beyond this, the general methods of formation driving are specialized and extended for an application of airport snow shoveling. Detailed descriptions of the algorithms complemented by relevant stability and convergence studies will be provided in the following chapters. Furthermore, discussions of the applicability will be verified by various simulations in existing robotic environments and also by a hardware experiment.}, subject = {Autonomer Roboter}, language = {en} } @phdthesis{Hossfeld2009, author = {Hoßfeld, Tobias}, title = {Performance Evaluation of Future Internet Applications and Emerging User Behavior}, doi = {10.25972/OPUS-3067}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-37570}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2009}, abstract = {In future telecommunication systems, we observe an increasing diversity of access networks. The separation of transport services and applications or services leads to multi-network services, i.e., a future service has to work transparently to the underlying network infrastructure. Multi-network services with edge-based intelligence, like P2P file sharing or the Skype VoIP service, impose new traffic control paradigms on the future Internet. Such services adapt the amount of consumed bandwidth to reach different goals. A selfish behavior tries to keep the QoE of a single user above a certain level. Skype, for instance, repeats voice samples depending on the perceived end-to-end loss. From the viewpoint of a single user, the replication of voice data overcomes the degradation caused by packet loss and enables to maintain a certain QoE. The cost for this achievement is a higher amount of consumed bandwidth. However, if the packet loss is caused by congestion in the network, this additionally required bandwidth even worsens the network situation. Altruistic behavior, on the other side, would reduce the bandwidth consumption in such a way that the pressure on the network is released and thus the overall network performance is improved. In this monograph, we analyzed the impact of the overlay, P2P, and QoE paradigms in future Internet applications and the interactions from the observing user behavior. The shift of intelligence toward the edge is accompanied by a change in the emerging user behavior and traffic profile, as well as a change from multi-service networks to multi-networks services. In addition, edge-based intelligence may lead to a higher dynamics in the network topology, since the applications are often controlled by an overlay network, which can rapidly change in size and structure as new nodes can leave or join the overlay network in an entirely distributed manner. As a result, we found that the performance evaluation of such services provides new challenges, since novel key performance factors have to be first identified, like pollution of P2P systems, and appropriate models of the emerging user behavior are required, e.g. taking into account user impatience. As common denominator of the presented studies in this work, we focus on a user-centric view when evaluating the performance of future Internet applications. For a subscriber of a certain application or service, the perceived quality expressed as QoE will be the major criterion of the user's satisfaction with the network and service providers. We selected three different case studies and characterized the application's performance from the end user's point of view. Those are (1) cooperation in mobile P2P file sharing networks, (2) modeling of online TV recording services, and (3) QoE of edge-based VoIP applications. The user-centric approach facilitates the development of new mechanisms to overcome problems arising from the changing user behavior. An example is the proposed CycPriM cooperation strategy, which copes with selfish user behavior in mobile P2P file sharing system. An adequate mechanism has also been shown to be efficient in a heterogeneous B3G network with mobile users conducting vertical handovers between different wireless access technologies. The consideration of the user behavior and the user perceived quality guides to an appropriate modeling of future Internet applications. In the case of the online TV recording service, this enables the comparison between different technical realizations of the system, e.g. using server clusters or P2P technology, to properly dimension the installed network elements and to assess the costs for service providers. Technologies like P2P help to overcome phenomena like flash crowds and improve scalability compared to server clusters, which may get overloaded in such situations. Nevertheless, P2P technology invokes additional challenges and different user behavior to that seen in traditional client/server systems. Beside the willingness to share files and the churn of users, peers may be malicious and offer fake contents to disturb the data dissemination. Finally, the understanding and the quantification of QoE with respect to QoS degradations permits designing sophisticated edge-based applications. To this end, we identified and formulated the IQX hypothesis as an exponential interdependency between QoE and QoS parameters, which we validated for different examples. The appropriate modeling of the emerging user behavior taking into account the user's perceived quality and its interactions with the overlay and P2P paradigm will finally help to design future Internet applications.}, subject = {Leistungsbewertung}, language = {en} } @phdthesis{Hess2009, author = {Hess, Martin}, title = {Motion coordination and control in systems of nonholonomic autonomous vehicles}, isbn = {978-3-923959-55-6}, doi = {10.25972/OPUS-3794}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46442}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2009}, abstract = {This work focuses on coordination methods and the control of motion in groups of nonholonomic wheeled mobile robots, in particular of the car-like type. These kind of vehicles are particularly restricted in their mobility. In the main part of this work the two problems of formation motion coordination and of rendezvous in distributed multi-vehicle systems are considered. We introduce several enhancements to an existing motion planning approach for formations of nonholonomic mobile robots. Compared to the original method, the extended approach is able to handle time-varying reference speeds as well as adjustments of the formation's shape during reference trajectory segments with continuously differentiable curvature. Additionally, undesired discontinuities in the speed and steering profiles of the vehicles are avoided. Further, the scenario of snow shoveling on an airfield by utilizing multiple formations of autonomous snowplows is discussed. We propose solutions to the subproblems of motion planning for the formations and tracking control for the individual vehicles. While all situations that might occur have been tested in a simulation environment, we also verified the developed tracking controller in real robot hardware experiments. The task of the rendezvous problem in groups of car-like robots is to drive all vehicles to a common position by means of decentralized control laws. Typically there exists no direct interaction link between all of the vehicles. In this work we present decentralized rendezvous control laws for vehicles with free and with bounded steering. The convergence properties of the approaches are analyzed by utilizing Lyapunov based techniques. Furthermore, they are evaluated within various simulation experiments, while the bounded steering case is also verified within laboratory hardware experiments. Finally we introduce a modification to the bounded steering system that increases the convergence speed at the expense of a higher traveled distance of the vehicles.}, subject = {Robotik}, language = {en} } @misc{Kaempgen2009, type = {Master Thesis}, author = {Kaempgen, Benedikt}, title = {Deskriptives Data-Mining f{\"u}r Entscheidungstr{\"a}ger: Eine Mehrfachfallstudie}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46343}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2009}, abstract = {Das Potenzial der Wissensentdeckung in Daten wird h{\"a}ufig nicht ausgenutzt, was haupts{\"a}chlich auf Barrieren zwischen dem Entwicklerteam und dem Endnutzer des Data-Mining zur{\"u}ckzuf{\"u}hren ist. In dieser Arbeit wird ein transparenter Ansatz zum Beschreiben und Erkl{\"a}ren von Daten f{\"u}r Entscheidungstr{\"a}ger vorgestellt. In Entscheidungstr{\"a}ger-zentrierten Aufgaben werden die Projektanforderungen definiert und die Ergebnisse zu einer Geschichte zusammengestellt. Eine Anforderung besteht dabei aus einem tabellarischen Bericht und ggf. Mustern in seinem Inhalt, jeweils verst{\"a}ndlich f{\"u}r einen Entscheidungstr{\"a}ger. Die technischen Aufgaben bestehen aus einer Datenpr{\"u}fung, der Integration der Daten in einem Data-Warehouse sowie dem Generieren von Berichten und dem Entdecken von Mustern wie in den Anforderungen beschrieben. Mehrere Data-Mining-Projekte k{\"o}nnen durch Wissensmanagement sowie eine geeignete Infrastruktur voneinander profitieren. Der Ansatz wurde in zwei Projekten unter Verwendung von ausschließlich Open-Source-Software angewendet.}, subject = {Data Mining}, language = {de} }