Browsing by Subject "Network"

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Genetische Diversität von Echinococcus granulosus sensu stricto
(2017) Ebi, Dennis; Mackenstedt, Ute
The dog tapeworm Echinococcus granulosus sensu stricto, distributed worldwide, is the most important agent of human Cystic Echinococcosis, a zoonotic disease which is considered as one of the priority ‘neglected zoonotic diseases’ by the World Health Organisation. The parasite is known from a large number of host species and is conventionally subdivided into several genotypes. The epidemiological consequences of the variation, however, are still unknown. In the last years several studies on the intraspecific variation of this parasite were published. Most of these studies were based on small numbers of isolates from geographically restricted regions, so that the relevance of that diversity concerning pathogenicity, host specificity, transmission cycles and biogeography is still little understood. To achieve a comprehensive estimate of its genetic diversity, 1085 isolates of E. granulosus s.s. from humans and animal hosts originating from widely different regions of the world were analyzed for the sequence polymorphism of a 1609 bp fragment of the mitochondrial cox1 gene. For analysis haplotype networks, diversity and neutrality indices of subpopulations of different geographic origin were compared. To improve the analytical efficiency of the sequence-data, a LabVIEW application was written. It could be shown that most diverse sub-population is found in the Middle Eastern region and that the genetic diversity is lower in the other analyzed regions, which confirms a previous tentative hypothesis on the origin of the domestic cycle of E. granulosus s.s. in that region. Records of identical haplotypes in different regions, inclusion of published data, calculation of parameters of population genetics and haplotype network analysis led to hypotheses explaining the distribution history of E. granulosus s.s.. This in line with fossil and molecular data on domestic sheep as the principal final host. A set of new and easily calculable genetic diversity indices were developed and their added value was explained. Additionally, a statistical resampling experiment was programmed which showed that at least 40 well distributed samples are necessary to provide a reliable estimate of the genetic diversity of the parasite in a region. Using an extension for that software, it was shown that the newly developed diversity indices do not strongly depend on the number of analyzed samples, and provide appropriate tools to assess the genetic diversity of parasite populations.
Lokale Kommunikation und Lokalmedien im Online-Zeitalter : Kommunikationsräume im Stadt-Land-Vergleich
(2021) Brückner, Lara; Schweiger, Wolfgang
Although the theoretical importance of the municipal level is undisputed, little research has been done to date on how local communication spaces are shaped in the online age. This is where the present study comes in and comparatively examines local communication spaces in urban and rural contexts. To this end, a theoretical framework based on sociological theories and (more recent) theories of the public sphere has been developed; it distinguishes between a structuring and an action dimension of communication spaces. The structuring dimension comprises macro-, meso-, and micro-level communication structures (e.g., competition in the local newspaper market or communication resources of actors). The action dimension comprises observable communicative action and can be characterized by two aspects: the communication networks of actors and their public communication with a large audience. Subsequently, n=49 guideline interviews with journalists and interest-led actors (politicians, administrative staff, active citizens, etc.) have been conducted on a total of six topics in three municipalities – two large cities and one small town. The actors were asked how they communicate with other actors and citizens on local political issues and what role traditional local media (still) play in this process. In all the communication spaces studied, the local or regional daily newspaper domi-nates as the most important local medium. From the point of view of the actors, the newspaper is still the central medium with which they inform citizens and reach people outside their topic-specific communities and filter bubbles. They also attribute to the newspaper a great influence on public opinion and – especially in the large cities – political decision-making. At the same time, the actors perceive that the newspapers reach is constantly decreasing and that they hardly reach young people in particular. Even if they are not seen as a substitute for local newspapers, online-only offers and blogs are useful channels for actors to address younger people who are particularly interested in the topic. In rural communication areas, actors who focus their public relations on traditional media and the press dominate. Digital tools and channels are hardly used – neither for public relations nor for communicating with other actors in the field. On the one hand, the actors argue with concerns about the users’ privacy; on the other hand they argue a lack of resources. For example, there is a lack of time and personnel to use additional online channels and to observe or even moderate user discussions. Another aspect is the lack of know-how of the mostly older local politicians, administrative staff, and journalists in dealing with digital tools. Actors who deliberately orchestrate different communication channels (online and offline, earned and owned media), digitally bring together knowledge and expertise from local, regional, and national networks and use these networks strategically for their public relations work are generally rare and predominantly found in urban communication spaces. Interest-led actors and journalists should make even greater use of the network logic of todays communication spaces. This means, for example, that interest-led actors should not only focus on journalists in their communication work but also on other central network nodes such as bloggers, politicians, and active citizens, and regularly provide them with information via topic-specific mailing lists. Journalists should make themselves visible as contact persons, adapt their work to the requirements of the respective communication networks - e.g., strengthen the voice of actors who receive little attention, bring together the arguments and positions of actors who have not been in contact so far - and more thoroughly examine options for (project-related) cooperation with other media in order to pool resources and create new buying incentives for readers by offering investigative content.
Multiagent resource allocation in service networks
(2014) Karänke, Paul; Kirn, Stefan
The term service network (SN) denotes a network of software services in which complex software applications are provided to customers by aggregating multiple elementary services. These networks are based on the service-oriented computing (SOC) paradigm, which defines the fundamental technical concepts for software services over electronic networks, e.g., Web services and, most recently, Cloud services. For the provision of software services to customers, software service providers (SPs) have to allocate their scarce computational resources (i.e., hardware and software) of a certain quality to customer requests. The SOC paradigm facilitates interoperability over organizational boundaries by representing business relationships on the software system level. Composite software services aggregate multiple software services into software applications. This aggregation is denoted as service composition. The loose coupling of services leads to SNs as dynamic entities with changing interdependencies between services. For composite software services, these dependencies exist across SN tiers; they result from the procurement of services, which are themselves utilized to produce additional services, and constitute a major problem for resource allocation in SNs. If these dependencies are not considered, the fulfillment of agreements may become unaccomplishable (overcommitment). Hence, the consideration of service dependencies is crucial for the allocation of service providers resources to fulfill customer requests in SNs. However, existing resource allocation methods, which could consider these dependencies -- such as combinatorial auctions with a central auctioneer for the whole SN -- are not applicable, since there are no central coordinating entities in SNs. The application of an allocation mechanism that does not consider these dependencies might negatively affect the actual service delivery; results are penalty payments as well as a damage to the reputation of the providers. This research is conducted in accordance to the design science paradigm in information system research. It is a problem-solving paradigm, which targets the construction and evaluation of IT artifacts. The objectives of this research are to develop and evaluate an allocation protocol, which can consider multi-tier service dependencies without the existence of central coordinating entities. Therefore, an interaction protocol engineering (IPE) perspective is applied to solve the problem of multi-tier dependencies in resource allocation. This approach provides a procedure model for designing interaction protocols for multiagent systems, and is closely related to the well-established area of communication protocol engineering. Automated resource allocation in SNs is analyzed in this research by representing the actors as autonomous software agents in the software system. The actors delegate their objectives to their software agents, which conduct the negotiations for service provision on their behalf. Thus, these agents communicate concerning the resource allocation; in this process, the sequence of communication interactions is crucial to the problem addressed. Interaction protocols define a structured exchange of defined messages between agents; they facilitate agent conversations. When multiple agents have to reach agreements by negotiation and bargaining, such as in case with allocating scarce resources, game theory provides means to formalize and analyze the most rational choice of actions for the interacting agents. Based on a formal framework for resource allocation in SNs, this research first performs a game-theoretic problem analysis; it is concerned with the existence, as well as the complexity of computing optimal allocations. In addition, Nash equilibria are analyzed for optimal allocations. Second, a distributed, auction-based allocation protocol, which prevents overcommitments and guarantees socially optimal allocations for single customer requests under certain assumptions, is proposed. Therefore, a game-theoretic model and an operationizable specification of the protocol are presented. Third, it is formally verified that the protocol enables multi-tier resource allocation and avoids overcommitments by proofs for the game-theoretic model and by model checking for the interaction protocol specification; using the model checker Spin, safety properties like the absence of deadlock are as well formally verified as the protocol enabling multi-tier resource allocation. Fourth, the efficacy and the benefits of the proposed protocol are demonstrated by multiagent simulation for concurrent customers. The experimental evaluation provides evidence of the protocols efficiency compared to the socially optimal allocation as a centralized benchmark in different settings, e.g., network topologies and different bidding policies.
On collusive behavior - models of cartel formation, organizational structure, and destabilization
(2011) Fischer, Julia; Schwalbe, Ulrich
This dissertation contributes to the theoretical literature on cartel formation, organizational structure, and destabilization in Cournot competitive markets. Cartel formation in Cournot competitive markets may take place as a sequential process even if the merger paradox applies. This conclusion was reached after giving up the assumption of symmetric information in cartel formation processes: it is assumed that outside firms are not informed about new cartel agreements and face a time lag by adjusting to changing behavior of some of the market participants. Furthermore, an extension to the standard cartel stability models is presented to capture the influence of communication and organizational structure in a cartel by modeling cartels as social networks. Despite the fact that communication in cartels is costly because contacts between members might be detected by antitrust authorities, it is shown that intensive contacts are possibly stabilizing within a cartel. Both aspects, the costs and benefits of communication in cartels, contribute to the players' valuation of collusion and therefore change cartel stability conditions. Additionally, this model accounts for the influence of leniency programs and fines. A theoretical explanation is given for differences between explicit and tacit collusion on the basis of this network model. Additionally, this dissertation examines whether collusive behavior might be deterred in vertical structures if dominant firms are allowed to apply specific discount schemes. It is shown that the profit maximizing behavior of a monopolistic upstream firm might lead to the deterrence of collusive behavior of downstream firms if the upstream firm is allowed to implement all-units discount schemes. All-units discounts, despite the fact that they are sometimes considered anticompetitive, possess welfare improving effects that are not generally shared by other pricing schemes.
Prediction of protein-protein complexes by combining size exclusion chromatography and mass spectrometric analysis
(2021) Gilbert, Max; Schulze, Waltraud
Two major objectives were pursued and met in this study. First, the goal was to add to the scientific toolbox a diligent method for uncovering PPi dynamics on a proteomic scale, with a focus on plant membranes. There are large-scale or high-throughput approaches, but they rely on genetically modified proteins or heterologous expression systems to describe PPi outside of their natural context. Similarly, those methods are incapable of describing the dynamics of protein interactions. In course of this study, a co-elution based approach was combined with modern mass spectrometric label free quantification in order to investigate PPi and interaction dynamics on a proteomic scale. A rigorous data processing pipeline was developed to not only address known fallacies of using co-elution based methods (such as for example random co elution), but also to access and utilize meta-information in form of protein abundance and protein network connectivity to draw conclusions not only on proteomic scale, but also for individual proteins. In total, 6.928 individual proteins extracted from Arabidopsis thaliana root membranes were detected under different nutritional conditions (full nutrition, nitrogen starvation and nitrogen resupply). The data processing pipeline described in this study was used to predict and discover connectivity information for at least 2.058 of these proteins. Each step in data processing was validated by comparison to database confirmed interactions to improve filtering criteria. Protein abundance was evaluated through a unique ranking system, allowing a seamless integration as network attributes for each condition. From the suggested interaction data, an interactome network of the various nutritional conditions was reconstructed. Using different network parameters from graph theory, protein significance and dynamic conditional changes were described. Second, this study applied the aforementioned approach to identify relevant proteins involved in nitrogen signaling in Arabidopsis thaliana root membranes. Through correlation analysis and network reconstruction, receptor kinase AT5G49770 was identified as a component of the nitrogen signaling network that collaborates with co-receptor QSK1, BAK1, the nitrogen transporter NRT2.1 and proton pump AHA2. In response to nitrogen deficiency, the network parameters of AT5G49770 reacted strongly and its involvement was demonstrated by a phenotypic similarity to knock-out lines of NRT2.1, NRT1.1 and AHA2 during a root growth assay of Arabidopsis seedlings. The interaction between QSK1 and BAK1 was further confirmed using FRET/FLIM microscopy and pulldown assays. These findings show that combining a co-elution based approach with a rigorous data processing pipeline and network analysis is suitable to study the protein interaction environment and signal response dynamics in plant root membranes. The modular experimental design allows for a simple adaptation to study different stimuli and the unbiased proteomic approach yields results for proteins regardless of the individual scientific focus. Meta-information such as protein abundance and network connectivity parameters can be used to prospect and identify important proteins involved in stress response dynamics. The author of this study is confident that the proteomic data produced can be utilized in further research and contributes to the understanding of nitrogen signaling in plant root membranes. Through integration of the data processing pipeline and adaptation to different scientific scenarios, valuable information beyond protein interaction is gained. Thus, this work makes an important contribution to the advancement of proteomic analysis and data interpretation methodology.
The geography and co-location of european technology-specific co-inventorship networks
(2010) Christ, Julian P.
This paper contributes with empirical findings to European co-inventorship location and geographical coincidence of co-patenting networks. Based on EPO co-patenting information for the reference period 2000-2004, we analyze the spatial configuration of 44 technology-specific co-inventorship networks. European co-inventorship (co-patenting) activity is spatially linked to 1259 European NUTS3 units (EU25+CH+NO) and their NUTS1 regions by inventor location. We extract 7.135.117 EPO co-patenting linkages from our own relational database that makes use of the OECD RegPAT (2009) files. The matching between international Patent Classification (IPC) subclasses and 44 technology fields is based on the ISI-SPRU-OST-concordance. We confirm the hypothesis that the 44 co-inventorship networks differ in their overall size (nodes, linkages, self-loops)and that they are dominated by similar groupings of regions. The paper offers statistical evidence for the presence of highly localized European co-inventorship networks for all 44 technology fields, as the majority of linkages between NUTS3 units (counties and districts) are within the same NUTS1 regions. Accordingly, our findings helps to understand general presence of positive spatial autocorrelation in regional patent data. Our analysis explicitly accounts for different network centrality measures (betweenness, degree, eigenvector). Spearman rank correlation coefficients for all 44 technology fields confirm that most co-patenting networks co-locate in those regions that are central in several technology-specfic co-patenting networks. These findings support the hypothesis that leading European regions are indeed multi-field network nodes and that most research collaboration is taking place in dense co-patenting networks.
The geography and co-location of european technology-specific co-inventorship networks
(2010) Christ, Julian P.
This paper contributes with empirical findings to European co-inventorship location and geographical coincidence of co-patenting networks. Based on EPO co-patenting information for the reference period 2000-2004, we analyze the spatial configuration of 44 technology-specific co-inventorship networks. European co-inventorship (co-patenting) activity is spatially linked to 1259 European NUTS3 units (EU25+CH+NO) and their NUTS1 regions by inventor location. We extract 7.135.117 EPO co-patenting linkages from our own relational database that makes use of the OECD RegPAT (2009) files. The matching between International Patent Classification (IPC) subclasses and 44 technology fields is based on the ISI-SPRU-OST-concordance. We confirm the hypothesis that the 44 co-inventorship networks differ in their overall size (nodes, linkages, self-loops) and that they are dominated by similar groupings of regions. The paper offers statistical evidence for the presence of highly localized European co-inventorship networks for all 44 technology fields, as the majority of linkages between NUTS3 units (counties and districts) are within the same NUTS1 regions. Accordingly, our findings helps to understand general presence of positive spatial autocorrelation in regional patent data. Our analysis explicitly accounts for different network centrality measures (betweenness, degree, eigenvector). Spearman rank correlation coefficients for all 44 technology fields confirm that most co-patenting networks co-locate in those regions that are central in several technology-specific co-patenting networks. These findings support the hypothesis that leading European regions are indeed multi-filed network nodes and that most research collaboration is taking place in dense co-patenting networks.