TY  - THES
A1  - Lunemann, Carolin
T1  - Quantum cryptography : security analysis of multiuser quantum communication with embedded authentication
N2  - Three quantum cryptographic protocols of multiuser quantum networks with embedded authentication, allowing quantum key distribution or quantum direct communication, are discussed in this work. The security of the protocols against different types of attacks is analysed with a focus on various impersonation attacks and the man-in-the-middle attack. On the basis of the security analyses several improvements are suggested and implemented in order to adjust the investigated vulnerabilities. Furthermore, the impact of the eavesdropping test procedure on impersonation attacks is outlined. The framework of a general eavesdropping test is proposed to provide additional protection against security risks in impersonation attacks.
N2  - In der Diplomarbeit werden drei verschiedene quantenkryptographische Protokolle mit dem Schwerpunkt auf authentifizierten Quantennetzwerken analysiert. Die Sicherheit der Protokolle gegenüber verschiedenen Angriffen wird untersucht, wobei der Fokus auf kompletten Personifikationsattacken („impersonation attacks“) liegt. Auf Basis der Sicherheitsanalyse und den Netzwerkanforderungen werden entsprechende Verbesserungen vorgeschlagen. Um die Gefahr von Personifikationen realistisch abschätzen zu können, wird außerdem der Einfluss des Testablaufs analysiert. Um zusätzlichen Schutz gegen Personifikationsattacken zu gewährleisten, werden die Rahmenbedingungen für eine allgemeine Testspezifikation festgelegt.
KW  - Kryptographie
KW  - Quantenkryptographie
KW  - Authentifizierung
KW  - Netzwerk
KW  - cryptography
KW  - quantum cryptography
KW  - authentication
KW  - multiuser
KW  - network
Y1  - 2006
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12756
ER  - 
TY  - THES
A1  - Stieglitz, Stefan
T1  - Steuerung Virtueller Communities : Instrumente, Mechanismen, Wirkungszusammenhänge
T1  - Governance of Virtual Communities : instruments, mechanisms, and interdependences
N2  - Virtuelle Communities bezeichnen Gemeinschaften von Individuen, die maßgeblich über das Internet miteinander kommunizieren und kollaborieren. Anders als in Unternehmen, in denen Motivationsstrukturen primär auf finanziellen Anreizen basieren, gilt für Virtuelle Communities, dass die Zuarbeit in diesen in der Regel freiwillig und ohne monetäre Interessen der Mitglieder stattfindet. Unternehmen nutzen Virtuelle Communities für Zwecke des Customer Relationship Management, des Wissensmanagement und des Customer Integration. Universitäten bilden virtuelle Lernnetzwerke, um die Interaktion zwischen Studierenden zu erhöhen und hierdurch Lernerfolge zu steigern. Die Potenziale Virtueller Communities werden jedoch in vielen Fällen nicht vollständig ausgeschöpft. Insbesondere der Frage nach einer systematischen Mitgliedersteuerung kommt aufgrund der vorherrschenden komplexen Motivationsstrukturen der freiwillig partizipierenden Mitglieder eine besondere Bedeutung zu. In bisherigen wissenschaftlichen Arbeiten wurde dieser Aspekt jedoch vernachlässigt. Das Untersuchungsdesign der Arbeit zielt darauf ab, diese Forschungslücke zu schließen und einen Ordnungsrahmen zu gestalten, der einen systematischen Aufbau, Betrieb und insbesondere eine Steuerung Virtueller Communities ermöglicht. Die Identifikation von Steuerungsinstrumenten wurde im Rahmen der Arbeit durch eine Analyse der Strukturen und Funktionsweisen in Open Source-Projekten vorgenommen, anschließend wurden diese auf andere Typen Virtueller Communities übertragen. Im Rahmen zweier Fallstudien wurde der entwickelte Ordnungsrahmen unter realen Bedingungen an einem Expertennetzwerk an der Börse Berlin AG und einem universitären Lernnetzwerk erprobt. Die anschließende Analyse gibt Aufschluss über die Wirkungsweisen wettbewerblicher, kooperativer und hierarchischer Steuerungsinstrumente in Virtuellen Communities.
N2  - A virtual community can be understood as a group of people sharing common interests, ideas, and feelings by using the internet or other collaborative networks. In contrast to companies where contributors are mainly motivated by financial incentives, virtual communities are based on voluntarily participation and non-monetary benefits. Companies build up virtual communities to support customer relationship management, customer integration or knowledge management. Universities use virtual learning communities to increase knowledge transfer among students. However, the potential of virtual communities can not completely tapped without efficient and systematic approaches of community engineering. Members usually participate voluntarily in virtual community and therefore are characterized by a complex motivational structure. This aspect has not been discussed in scientific literature intensively. The research design of this contribution aims on developing a framework that can be used to systematically build up a virtual community. By analyzing open source projects several instruments of member management were identified and transferred to different types of virtual communities. By developing a case study design the practical relevance of the theoretical model was measured. A network of experts at Berlin stock exchange and a learning network at University of Potsdam were analysed. Surveys, interviews as well as data examinations were used to evaluate the effects of instruments of a systematic member management and different types of coordination such as hierarchy, competition and cooperation.
KW  - Virtuelle Community
KW  - Steuerung
KW  - Open Source
KW  - Lernnetzwerk
KW  - Expertennetzwerk
KW  - Virtual Community
KW  - Governance
KW  - Open Source
KW  - network
KW  - member
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16671
ER  - 
TY  - THES
A1  - Gause, Clemens
T1  - Das System der Strategie : ein Vergleich zwischen Strategien biologischer Systeme und militärischen Strategien ; eine Modellentwicklung
T1  - The system of strategy : a comparison between strategies of biological systems and military strategies ; a model development
N2  - Das vorliegende Buch vergleicht Strategien biologischer Systeme mit militärischen Strategien. Die zentrale Fragestellung ist dabei darauf gerichtet, ob es neben systemischen Gemeinsamkeiten auch gemeinsame oder ähnliche Strukturmuster und ähnliche Prozessabläufe beispielsweise sowohl im biologischen Abwehrmechanismus des Immunsystems und bei Insektenstaaten als auch bei Prozessen im Militär gibt. Vor diesem Hintergrund klaffen in der Theorie der Strategie, speziell in den Militärwissenschaften Lücken, denn der Systemansatz wird nicht konsequent beachtet, wie in diesem Buch mehrfach nachgewiesen ist. Von einem allgemeinen Verständnis der Strategie als bewusstem planerischem Vorgehen ist Abstand zu nehmen. Ausgehend von der Methode der Analogie und des Vergleichs wird im theoretischen Teil dieses Buches die Allgemeine Systemtheorie erläutert. Dabei werden der Begriff der Strategie ebenso wie die Begriffe Struktur und Prozess und Ansätze aus der Kriegsphilosophie von Clausewitz untersucht. Den Ausgangspunkt und schließlich auch wieder den Endpunkt der Überlegungen bilden neben dem notwendigen weiten Verständnis von Strategie, vor allem der Begriff der Organisation, ihrer Umwelt und der in diesem Zusammenhang bestehenden Wechselwirkung. Sowohl die Wechselwirkung von Umwelt und System als auch ihre Abhängigkeit durch strukturelle Kopplung werden beschrieben. Das Zusammenspiel und die daraus entstehende Komplexität der fünf Komponenten der Wahrnehmung, der Information und der Führung im Zusammenhang der Komponenten von Raum und Zeit in einem sozialen System lassen die klassische Ziel-Mittel-Zweck-Beziehung Clausewitz´scher Strategiedefinition verkürzt erscheinen. Anhand eines kurzen Rekurses der Methoden der Sozialen Netzwerkanalyse (SNA) wird der breite und tiefgehende Analyserahmen der Messung und Transparenzerreichung in Organisationen vorgestellt. Die SNA wird als Ausprägung der Netzwerk- und Graphentheorie, in die Allgemeine Systemtheorie integriert. Sie bildet eine zukunftsweisende Methode der Untersuchung von Netzwerken wie etwa dem Internet (Facebook, Xing etc.). Der aufgezeigte Theorierahmen bildet dabei zugleich eine Methode für den Systemvergleich und kann als Vorgehensmodell künftiger Strategieentwicklung genutzt werden. Der anschließende Systemvergleich wird mit mehreren Beispielen durchgeführt. Ausgehend von der Zelle als Grundeinheit werden Strukturen und Prozesse des Immunsystems mit solchen in militärischen Strukturen, weil sie im Lauf der Evolution enorme Leistungen in Reaktion, Anpassung und Optimierung vollbracht haben. Der Vergleich geht der Frage nach, ob in diesen Bereichen der Strategie und Organisation systemische Grundregeln existieren. Das Beispiel der Wechselwirkung zwischen Parasit und Wirt zeigt, dass jeder Fortschritt und Sieg angesichts der Systemeinbettung von Strategie nur relativ wirken kann. Die Analogie zwischen Viren und Bakterien sowie die Entwicklung des Begriffs der sozialen Mimikry führen zu einem erweiterten Verständnis der Strategie von Terroristen in sozialen Systemen. Verdeutlicht wird das Grundschema des Täuschens und Eindringens in Systeme sowie die Beeinflussung und Umsteuerung von Prozessen und Strukturen in einem System durch Kommunikation und Implementation von Codes. Am Beispiel des Immunsystems und der Bildung verschiedener Kommunikations- und Steuerungsmechanismen von Zellsystemen sowie Beispielen von Schwarmbildung und der Organisation sozialer Insekten werden eine Vielzahl heuristischer Hinweise für neue Ansätze für die Organisation von Streitkräften und ihrer Steuerung gefunden. Neben der Erarbeitung eines grundlegenden Strategiebegriffs anhand von Wahrnehmung und Selektion als Grundprozess der Erzeugung von Strategie wird eine differenzierte Betrachtung von Begriffen wie Redundanz und Robustheit sowie eine relativierende Sichtweise von Risiko, Gefahr und Schaden gewonnen. Der Vergleich mit dem Immunsystems zeigt einfache Beispiele der Informationsspeicherung und -übertragung, die zudem Bypassfähigkeiten sowie dezentrale Eskalations- und Deeskalationsprinzipien veranschaulichen. Dies eröffnet in Analogie dieser Prinzipien einen weiten Raum Sicherheitsarchitekturen zu überdenken und neu zu strukturieren. Zudem kann die räumliche Ausbreitung von Information und Kräften als ein gemeinsames Grundproblem der Entwicklung und Wirksamkeit von Strategien sowohl in der Natur, als auch im Militär identifiziert werden. Die Betrachtung zeigt zudem wie Zellen mit fehlgeleiteten Prozessen und Strukturen umgehen. Die Analogie deutet auf das Erfordernis einer Veränderung im Umgang mit Fehlern und ihrer Rückführ- und Umkehrbarkeit im weitesten Sinne. Das Buch eröffnet überdies ein neues Verständnis von Staat, Gewaltenteilung und Institutionen in einem sozialen System. Die Ergebnisse sind auch auf andere Forschungsbereiche, Organisationen und unterschiedlichste soziale Systeme übertragbar. Es eröffnet sich ein breites Anwendungsspektrum für künftige strategische Untersuchungen.
N2  - This book compares strategies of biological systems to military strategies. The central question is directed to whether there are systemic similarities, common or similar structures and similar patterns Processes, for example, both the biological defense mechanism Immune system and in insect societies as well as processes are in the military.
KW  - Strategie
KW  - System
KW  - Militär
KW  - Netzwerk
KW  - Biologie
KW  - strategy
KW  - system
KW  - military
KW  - network
KW  - biology
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-50068
ER  - 
TY  - JOUR
A1  - Stollenwerk, Eric
A1  - Dörfler, Thomas
A1  - Schibberges, Julian
T1  - Taking a new perspective
BT  - Mapping the Al Qaeda network through the eyes of the UN security council
JF  - Terrorism and political violence
N2  - Network analysis has attracted significant attention when researching the phenomenon of transnational terrorism, particularly Al Qaeda. While many scholars have made valuable contributions to mapping Al Qaeda, several problems remain due to a lack of data and the omission of data provided by international organizations such as the UN. Thus, this article applies a social network analysis and subsequent mappings of the data gleaned from the Security Council's consolidated sanctions list, and asks what they can demonstrate about the structure and organizational characteristics of Al Qaeda. The study maps the Al Qaeda network on a large scale using a newly compiled data set. The analysis reveals that the Al Qaeda network consists of several hundred individual and group nodes connecting almost all over the globe. Several major nodes are crucial for the network structure, while simultaneously many other nodes only weakly and foremost regionally connect to the network. The article concludes that the findings tie in well to the latest research pointing to local and simultaneously global elements of Al Qaeda, and that the new data is a valuable source for further analyses, potentially in combination with other data.
KW  - Al Qaeda
KW  - network
KW  - social network analysis
KW  - terrorism
KW  - UN
Y1  - 2016
U6  - https://doi.org/10.1080/09546553.2014.987341
SN  - 0954-6553
SN  - 1556-1836
VL  - 28
IS  - 5
SP  - 950
EP  - 970
PB  - Taylor & Francis
CY  - London
ER  - 
TY  - JOUR
A1  - Groth, Detlef
T1  - Modeling a secular trend by Monte Carlo simulation of height biased migration in a spatial network
JF  - Anthropologischer Anzeiger : journal of biological and clinical anthropology ; Mitteilungsorgan der Gesellschaft für Anthropologie
N2  - Background: In a recent Monte Carlo simulation, the clustering of body height of Swiss military conscripts within a spatial network with characteristic features of the natural Swiss geography was investigated. In this study I examined the effect of migration of tall individuals into network hubs on the dynamics of body height within the whole spatial network. The aim of this study was to simulate height trends. Material and methods: Three networks were used for modeling, a regular rectangular fishing net like network, a real world example based on the geographic map of Switzerland, and a random network. All networks contained between 144 and 148 districts and between 265-307 road connections. Around 100,000 agents were initially released with average height of 170 cm, and height standard deviation of 6.5 cm. The simulation was started with the a priori assumption that height variation within a district is limited and also depends on height of neighboring districts (community effect on height). In addition to a neighborhood influence factor, which simulates a community effect, body height dependent migration of conscripts between adjacent districts in each Monte Carlo simulation was used to re-calculate next generation body heights. In order to determine the direction of migration for taller individuals, various centrality measures for the evaluation of district importance within the spatial network were applied. Taller individuals were favored to migrate more into network hubs, backward migration using the same number of individuals was random, not biased towards body height. Network hubs were defined by the importance of a district within the spatial network. The importance of a district was evaluated by various centrality measures. In the null model there were no road connections, height information could not be delivered between the districts. Results: Due to the favored migration of tall individuals into network hubs, average body height of the hubs, and later, of the whole network increased by up to 0.1 cm per iteration depending on the network model. The general increase in height within the network depended on connectedness and on the amount of height information that was exchanged between neighboring districts. If higher amounts of neighborhood height information were exchanged, the general increase in height within the network was large (strong secular trend). The trend in the homogeneous fishnet like network was lowest, the trend in the random network was highest. Yet, some network properties, such as the heteroscedasticity and autocorrelations of the migration simulation models differed greatly from the natural features observed in Swiss military conscript networks. Autocorrelations of district heights for instance, were much higher in the migration models. Conclusion: This study confirmed that secular height trends can be modeled by preferred migration of tall individuals into network hubs. However, basic network properties of the migration simulation models differed greatly from the natural features observed in Swiss military conscripts. Similar network-based data from other countries should be explored to better investigate height trends with Monte Carlo migration approach.
KW  - secular trend
KW  - body height
KW  - simulation
KW  - community effect
KW  - Monte Carlo method
KW  - network
Y1  - 2017
U6  - https://doi.org/10.1127/anthranz/2017/0703
SN  - 0003-5548
SN  - 2363-7099
VL  - 74
IS  - 1
SP  - 81
EP  - 88
PB  - Schweizerbart
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - Fritz, Amelie
A1  - Makeyeva, Angelina
A1  - Staub, Kaspar
A1  - Groth, Detlef
T1  - Influence of network properties on a migration induced secular height trend by Monte Carlo simulation
JF  - Journal of biological and clinical anthropology : Anthropologischer Anzeiger ; Mitteilungsorgan der Gesellschaft für Anthropologie
N2  - Background: Recent research reported height biased migration of taller individuals and a Monte Carlo simulation showed that such preferential migration of taller individuals into network hubs can induce a secular trend of height. In the simulation model taller agents in the hubs raise the overall height of all individuals in the network by a community effect. However, it could be seen that the actual network structure influences the strength of this effect. In this paper the background and the influence of the network structure on the strength of the secular trend by migration is investigated. Material and methods: Three principal network types are analyzed: networks derived from street connections in Switzerland, more regular fishing net like networks and randomly generated ones. Our networks have between 10 and 152 nodes and between 20 and 307 edges connecting the nodes. Depending on the network size between 5.000 and 90.000 agents with an average height of 170 cm (SD 6.5 cm) are initially released into the network. In each iteration new agents are regenerated based on the actual average body height of the previous iteration and, to a certain proportion, corrected by body heights in the neighboring nodes. After generating new agents, a certain number of them migrated into neighbor nodes, the model let preferentially taller agents migrate into network hubs. Migration is balanced by back migration of the same number of agents from nodes with high centrality measures to less connected nodes. The latter is random as well, but not biased by the agents height. Furthermore the distribution of agents per node and their correlation to the centrality of the nodes is varied in a systematic manner. After 100 iterations, the secular trend, i.e. the gain in body height for the different networks, is investigated in relation to the network properties. Results: We observe an increase of average agent body height after 100 iterations if height biased migration is enabled. The increase rate depends on the height of the neighboring factor, the population distribution, the relationship between population in the nodes and their centrality as well as on the network topology. Networks with uniform like distributions of the agents in the nodes, uncorrelated associations between node centrality and agent number per node, as well as very heterogeneous networks with very different node centralities lead to biggest gains in average body height. Conclusion: Our simulations show, that height biased migration into network hubs can possibly contribute to the secular trend of height increase in the human population. The strength of this "tall by migration" event depends on the actual properties of the underlying network. There is a possible significance of this mechanism for social networks, when hubs are represented by individuals and edges as their personal relationships. However, the required high number of iterations to achieve significant effects in more natural network structures in our models requires further studies to test the relevance and real effect sizes in real world scenarios.
KW  - secular trend
KW  - body height
KW  - simulation
KW  - community effect
KW  - Monte Carlo method
KW  - network
KW  - centrality measures
Y1  - 2019
U6  - https://doi.org/10.1127/anthranz/2019/1032
SN  - 0003-5548
VL  - 76
IS  - 5
SP  - 433
EP  - 443
PB  - Schweizerbart
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - Distelmeyer, Jan
T1  - From object to process
BT  - Interface politics of networked computerization
JF  - Artnodes
N2  - One of the most difficult tasks today is trying to grasp the presence of computing. The almost ubiquitous and diverse forms of networked computers (in all their stationary, mobile, embedded, and autonomous modes) create a nearly overwhelming complexity. To speak of what is here evading and present at the same time, the paper proposes to reconsider the concept of interface, its historical roots, and its heuristic advantages for an analysis and critique of the current and especially everyday spread of computerization. The question of interfaces leads to isolable conditions and processes of conduction, as well as to the complexity of the cooperation formed by them. It opens both an investigative horizon and a mode of analysis, which always asks for further interface levels involved in the phenomenon I am currently investigating. As an example, the paper turns to the displacement of the file with the launch of the iPhone in 2007 and its comeback in 2017 with the "Files" apps. Both developments are profoundly related to the establishment of computers as permanently networked machines, whereby their functionality, depresentations, and ideology come into focus.
KW  - interface
KW  - conduction
KW  - network
KW  - ideology
KW  - depresentation
KW  - digital objects
Y1  - 2019
U6  - https://doi.org/10.7238/a.v0i24.3300
SN  - 1695-5951
IS  - 24
SP  - 83
EP  - 90
PB  - Universitat Oberta de Catalunya
CY  - Barcelona
ER  - 
TY  - JOUR
A1  - Jelken, Joachim
A1  - Santer, Svetlana
T1  - Light induced reversible structuring of photosensitive polymer films
JF  - RSC Advances
N2  - In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be “set in motion” like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices.
KW  - surface-relief gratings
KW  - induced deformation
KW  - mass-transport
KW  - azobenzene elastomers
KW  - thin-films
KW  - birefringence
KW  - roughness
KW  - network
KW  - erasure
Y1  - 2019
U6  - https://doi.org/10.1039/C9RA02571E
SN  - 2046-2069
VL  - 9
IS  - 35
SP  - 20295
EP  - 20305
PB  - RSC Publishing
CY  - London
ER  - 
TY  - GEN
A1  - Jelken, Joachim
A1  - Santer, Svetlana
T1  - Light induced reversible structuring of photosensitive polymer films
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - In this paper we report on photoswitchable polymer surfaces with dynamically and reversibly fluctuating topographies. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes to form a surface relief grating. In the simplest case, the film shape mimics the intensity distribution and deforms into a wave like, sinusoidal manner with amplitude that may be as large as the film thickness. This process takes place in the glassy state without photo-induced softening. Here we report on an intriguing discovery regarding the formation of reliefs under special illumination conditions. We have developed a novel setup combining the optical part for creating interference patterns, an AFM for in situ acquisition of topography changes and diffraction efficiency signal measurements. In this way we demonstrate that these gratings can be “set in motion” like water waves or dunes in the desert. We achieve this by applying repetitive polarization changes to the incoming interference pattern. Such light responsive surfaces represent the prerequisite for providing practical applications ranging from conveyer or transport systems for adsorbed liquid objects and colloidal particles to generation of adaptive and dynamic optical devices.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 750 
KW  - surface-relief gratings
KW  - induced deformation
KW  - mass-transport
KW  - azobenzene elastomers
KW  - thin-films
KW  - birefringence
KW  - roughness
KW  - network
KW  - erasure
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436432
SN  - 1866-8372
IS  - 750
SP  - 20295
EP  - 20305
ER  - 
TY  - JOUR
A1  - Wilhelmi, Ilka
A1  - Grunwald, Stephan
A1  - Gimber, Niclas
A1  - Popp, Oliver
A1  - Dittmar, Gunnar
A1  - Arumughan, Anup
A1  - Wanker, Erich E.
A1  - Laeger, Thomas
A1  - Schmoranzer, Jan
A1  - Daumke, Oliver
A1  - Schürmann, Annette
T1  - The ARFRP1-dependent Golgi scaffolding protein GOPC is required for insulin secretion from pancreatic 13-cells
JF  - Molecular metabolism
N2  - Objective: Hormone secretion from metabolically active tissues, such as pancreatic islets, is governed by specific and highly regulated signaling pathways. Defects in insulin secretion are among the major causes of diabetes. The molecular mechanisms underlying regulated insulin secretion are, however, not yet completely understood. In this work, we studied the role of the GTPase ARFRP1 on insulin secretion from pancreatic 13-cells. <br /> Methods: A 13-cell-specific Arfrp1 knockout mouse was phenotypically characterized. Pulldown experiments and mass spectrometry analysis were employed to screen for new ARFRP1-interacting proteins. Co-immunoprecipitation assays as well as super-resolution microscopy were applied for validation. <br /> Results: The GTPase ARFRP1 interacts with the Golgi-associated PDZ and coiled-coil motif-containing protein (GOPC). Both proteins are co localized at the trans-Golgi network and regulate the first and second phase of insulin secretion by controlling the plasma membrane localization of the SNARE protein SNAP25. Downregulation of both GOPC and ARFRP1 in Min6 cells interferes with the plasma membrane localization of SNAP25 and enhances its degradation, thereby impairing glucose-stimulated insulin release from 13-cells. In turn, overexpression of SNAP25 as well as GOPC restores insulin secretion in islets from 13-cell-specific Arfrp1 knockout mice. <br /> Conclusion: Our results identify a hitherto unrecognized pathway required for insulin secretion at the level of trans-Golgi sorting. (c) 2020 The Authors. Published by Elsevier GmbH. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
KW  - Insulin secretion
KW  - Endosomal sorting
KW  - SNARE proteins
KW  - trans-Golgi
KW  - network
Y1  - 2020
U6  - https://doi.org/10.1016/j.molmet.2020.101151
SN  - 2212-8778
VL  - 45
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Crawford, Tim
A1  - Karamat, Fazeelat
A1  - Lehotai, Nóra
A1  - Rentoft, Matilda
A1  - Blomberg, Jeanette
A1  - Strand, Åsa
A1  - Björklund, Stefan
T1  - Specific functions for mediator complex subunits from different modules in the transcriptional response of arabidopsis thaliana to abiotic stress
JF  - Scientific reports
N2  - Adverse environmental conditions are detrimental to plant growth and development. Acclimation to abiotic stress conditions involves activation of signaling pathways which often results in changes in gene expression via networks of transcription factors (TFs). Mediator is a highly conserved co-regulator complex and an essential component of the transcriptional machinery in eukaryotes. Some Mediator subunits have been implicated in stress-responsive signaling pathways; however, much remains unknown regarding the role of plant Mediator in abiotic stress responses. Here, we use RNA-seq to analyze the transcriptional response of Arabidopsis thaliana to heat, cold and salt stress conditions. We identify a set of common abiotic stress regulons and describe the sequential and combinatorial nature of TFs involved in their transcriptional regulation. Furthermore, we identify stress-specific roles for the Mediator subunits MED9, MED16, MED18 and CDK8, and putative TFs connecting them to different stress signaling pathways. Our data also indicate different modes of action for subunits or modules of Mediator at the same gene loci, including a co-repressor function for MED16 prior to stress. These results illuminate a poorly understood but important player in the transcriptional response of plants to abiotic stress and identify target genes and mechanisms as a prelude to further biochemical characterization.
KW  - regulate gene expression
KW  - signal transduction
KW  - circadian clock
KW  - plant Mediator
KW  - salicylic-acid
KW  - activation
KW  - jasmonate
KW  - network
KW  - defense
KW  - MED16
Y1  - 2020
U6  - https://doi.org/10.1038/s41598-020-61758-w
SN  - 2045-2322
VL  - 10
IS  - 1
SP  - 1
EP  - 18
PB  - Macmillan Publishers Limited, part of Springer Nature
CY  - London
ER  - 
TY  - JOUR
A1  - Lehr, Christian
A1  - Lischeid, Gunnar
T1  - Efficient screening of groundwater head monitoring data for anthropogenic effects and measurement errors
JF  - Hydrology and Earth System Sciences
N2  - Groundwater levels are monitored by environmental agencies to support the sustainable use of groundwater resources. For this purpose continuous and spatially comprehensive monitoring in high spatial and temporal resolution is desired. This leads to large datasets that have to be checked for quality and analysed to distinguish local anthropogenic influences from natural variability of the groundwater level dynamics at each well. Both technical problems with the measurements as well as local anthropogenic influences can lead to local anomalies in the hydrographs. We suggest a fast and efficient screening method for the identification of well-specific peculiarities in hydrographs of groundwater head monitoring networks. The only information required is a set of time series of groundwater heads all measured at the same instants of time. For each well of the monitoring network a reference hydrograph is calculated, describing expected "normal" behaviour at the respective well as is typical for the monitored region. The reference hydrograph is calculated by multiple linear regression of the observed hydrograph with the "stable" principal components (PCs) of a principal component analysis of all groundwater head series of the network as predictor variables. The stable PCs are those PCs which were found in a random subsampling procedure to be rather insensitive to the specific selection of the analysed observation wells, i.e. complete series, and to the specific selection of measurement dates. Hence they can be considered to be representative for the monitored region in the respective period. The residuals of the reference hydrograph describe local deviations from the normal behaviour. Peculiarities in the residuals allow the data to be checked for measurement errors and the wells with a possible anthropogenic influence to be identified. The approach was tested with 141 groundwater head time series from the state authority groundwater monitoring network in northeastern Germany covering the period from 1993 to 2013 at an approximately weekly frequency of measurement.
KW  - streamflow variability
KW  - principal components
KW  - united states
KW  - time-seriesa
KW  - water
KW  - network
KW  - nonstationarity
KW  - fluctuations
KW  - rotation
Y1  - 2020
U6  - https://doi.org/10.5194/hess-24-501-2020
SN  - 1027-5606
SN  - 1607-7938
VL  - 24
IS  - 2
SP  - 501
EP  - 513
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - GEN
A1  - Crawford, Tim
A1  - Karamat, Fazeelat
A1  - Lehotai, Nóra
A1  - Rentoft, Matilda
A1  - Blomberg, Jeanette
A1  - Strand, Åsa
A1  - Björklund, Stefan
T1  - Specific functions for mediator complex subunits from different modules in the transcriptional response of arabidopsis thaliana to abiotic stress
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Adverse environmental conditions are detrimental to plant growth and development. Acclimation to abiotic stress conditions involves activation of signaling pathways which often results in changes in gene expression via networks of transcription factors (TFs). Mediator is a highly conserved co-regulator complex and an essential component of the transcriptional machinery in eukaryotes. Some Mediator subunits have been implicated in stress-responsive signaling pathways; however, much remains unknown regarding the role of plant Mediator in abiotic stress responses. Here, we use RNA-seq to analyze the transcriptional response of Arabidopsis thaliana to heat, cold and salt stress conditions. We identify a set of common abiotic stress regulons and describe the sequential and combinatorial nature of TFs involved in their transcriptional regulation. Furthermore, we identify stress-specific roles for the Mediator subunits MED9, MED16, MED18 and CDK8, and putative TFs connecting them to different stress signaling pathways. Our data also indicate different modes of action for subunits or modules of Mediator at the same gene loci, including a co-repressor function for MED16 prior to stress. These results illuminate a poorly understood but important player in the transcriptional response of plants to abiotic stress and identify target genes and mechanisms as a prelude to further biochemical characterization.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1399 
KW  - regulate gene expression
KW  - signal transduction
KW  - circadian clock
KW  - plant Mediator
KW  - salicylic-acid
KW  - activation
KW  - jasmonate
KW  - network
KW  - defense
KW  - MED16
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-513666
SN  - 1866-8372
IS  - 1
ER  - 
TY  - GEN
A1  - Lehr, Christian
A1  - Lischeid, Gunnar
T1  - Efficient screening of groundwater head monitoring data for anthropogenic effects and measurement errors
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Groundwater levels are monitored by environmental agencies to support the sustainable use of groundwater resources. For this purpose continuous and spatially comprehensive monitoring in high spatial and temporal resolution is desired. This leads to large datasets that have to be checked for quality and analysed to distinguish local anthropogenic influences from natural variability of the groundwater level dynamics at each well. Both technical problems with the measurements as well as local anthropogenic influences can lead to local anomalies in the hydrographs. We suggest a fast and efficient screening method for the identification of well-specific peculiarities in hydrographs of groundwater head monitoring networks. The only information required is a set of time series of groundwater heads all measured at the same instants of time. For each well of the monitoring network a reference hydrograph is calculated, describing expected “normal” behaviour at the respective well as is typical for the monitored region. The reference hydrograph is calculated by multiple linear regression of the observed hydrograph with the “stable” principal components (PCs) of a principal component analysis of all groundwater head series of the network as predictor variables. The stable PCs are those PCs which were found in a random subsampling procedure to be rather insensitive to the specific selection of the analysed observation wells, i.e. complete series, and to the specific selection of measurement dates. Hence they can be considered to be representative for the monitored region in the respective period. The residuals of the reference hydrograph describe local deviations from the normal behaviour. Peculiarities in the residuals allow the data to be checked for measurement errors and the wells with a possible anthropogenic influence to be identified. The approach was tested with 141 groundwater head time series from the state authority groundwater monitoring network in northeastern Germany covering the period from 1993 to 2013 at an approximately weekly frequency of measurement.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1424 
KW  - streamflow variability
KW  - principal components
KW  - united states
KW  - time-series
KW  - water
KW  - network
KW  - nonstationarity
KW  - fluctuations
KW  - rotation
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-511992
SN  - 1866-8372
IS  - 2
ER  - 
TY  - JOUR
A1  - Binder, Julia
A1  - Mettenberger, Tobias
T1  - Schlüsselfiguren in ländlichen Netzwerken
JF  - KWI-Schriften
KW  - Schlüsselfiguren
KW  - ländliche Räume
KW  - Netzwerk
KW  - Akteure
KW  - Pioniere
KW  - leader
KW  - rural areas
KW  - network
KW  - actor
KW  - pioneer
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-631133
SN  - 978-3-86956-571-2
SN  - 1867-951X
SN  - 1867-9528
IS  - 14
SP  - 39
EP  - 50
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Bembnista, Kamil
A1  - Mettenberger, Tobias
A1  - Zscherneck, Julia
T1  - Soziale Netzwerke als Ressourcenzugänge für Digitale Pioniere
JF  - KWI-Schriften
KW  - Netzwerk
KW  - soziales Netzwerk
KW  - Ressource
KW  - Digitalisierung
KW  - Pioniere
KW  - Akteure
KW  - network
KW  - social network
KW  - resource
KW  - digitalization
KW  - pioneer
KW  - actor
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-631156
SN  - 978-3-86956-571-2
SN  - 1867-951X
SN  - 1867-9528
IS  - 14
SP  - 51
EP  - 72
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  -