@article{StoyanovKolloscheRisseetal.2011, author = {Stoyanov, Hristiyan and Kollosche, Matthias and Risse, Sebastian and McCarthy, Denis N. and Kofod, Guggi}, title = {Elastic block copolymer nanocomposites with controlled interfacial interactions for artificial muscles with direct voltage control}, series = {Soft matter}, volume = {7}, journal = {Soft matter}, number = {1}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1744-683X}, doi = {10.1039/c0sm00715c}, pages = {194 -- 202}, year = {2011}, abstract = {Soft, physically crosslinking, block copolymer elastomers were filled with surface-treated nanoparticles, in order to evaluate the possibility for improvement of their properties when used as soft dielectric actuators. The nanoparticles led to improvements in dielectric properties, however they also reinforced the elastomer matrix. Comparing dielectric spectra of composites with untreated and surface-treated particles showed a measurable influence of the surface on the dielectric loss behaviour for high filler amounts, strongly indicating an improved host-guest interaction for the surface-treated particles. Breakdown strength was measured using a test bench and was found to be in good agreement with the results from the actuation measurements. Actuation responses predicted by a model for prestrained actuators agreed well with measurements up to a filler amount of 20\%(vol). Strong improvements in actuation behaviour were observed, with an optimum near 15\%(vol) nanoparticles, corresponding to a reduction in electrical field of 27\% for identical actuation strains. The use of physically crosslinking elastomer ensured the mechanical properties of the matrix elastomer were unchanged by nanoparticles effecting the crosslinking reaction, contrary to similar experiments performed with chemically crosslinking elastomers. This allows for a firm conclusion about the positive effects of surface-treated nanoparticles on actuation behavior.}, language = {en} } @phdthesis{Stoyanov2011, author = {Stoyanov, Hristiyan}, title = {Soft nanocomposites with enhanced electromechanical response for dielectric elastomer actuators}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-51194}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {Electromechanical transducers based on elastomer capacitors are presently considered for many soft actuation applications, due to their large reversible deformation in response to electric field induced electrostatic pressure. The high operating voltage of such devices is currently a large drawback, hindering their use in applications such as biomedical devices and biomimetic robots, however, they could be improved with a careful design of their material properties. The main targets for improving their properties are increasing the relative permittivity of the active material, while maintaining high electric breakdown strength and low stiffness, which would lead to enhanced electrostatic storage ability and hence, reduced operating voltage. Improvement of the functional properties is possible through the use of nanocomposites. These exploit the high surface-to-volume ratio of the nanoscale filler, resulting in large effects on macroscale properties. This thesis explores several strategies for nanomaterials design. The resulting nanocomposites are fully characterized with respect to their electrical and mechanical properties, by use of dielectric spectroscopy, tensile mechanical analysis, and electric breakdown tests. First, nanocomposites consisting of high permittivity rutile TiO2 nanoparticles dispersed in thermoplastic block copolymer SEBS (poly-styrene-coethylene-co-butylene-co-styrene) are shown to exhibit permittivity increases of up to 3.7 times, leading to 5.6 times improvement in electrostatic energy density, but with a trade-off in mechanical properties (an 8-fold increase in stiffness). The variation in both electrical and mechanical properties still allows for electromechanical improvement, such that a 27 \% reduction of the electric field is found compared to the pure elastomer. Second, it is shown that the use of nanofiller conductive particles (carbon black (CB)) can lead to a strong increase of relative permittivity through percolation, however, with detrimental side effects. These are due to localized enhancement of the electric field within the composite, which leads to sharp reductions in electric field strength. Hence, the increase in permittivity does not make up for the reduction in breakdown strength in relation to stored electrical energy, which may prohibit their practical use. Third, a completely new approach for increasing the relative permittivity and electrostatic energy density of a polymer based on 'molecular composites' is presented, relying on chemically grafting soft π-conjugated macromolecules to a flexible elastomer backbone. Polarization caused by charge displacement along the conjugated backbone is found to induce a large and controlled permittivity enhancement (470 \% over the elastomer matrix), while chemical bonding, encapsulates the PANI chains manifesting in hardly any reduction in electric breakdown strength, and hence resulting in a large increase in stored electrostatic energy. This is shown to lead to an improvement in the sensitivity of the measured electromechanical response (83 \% reduction of the driving electric field) as well as in the maximum actuation strain (250 \%). These results represent a large step forward in the understanding of the strategies which can be employed to obtain high permittivity polymer materials with practical use for electro-elastomer actuation.}, language = {en} } @article{StoofLeichsenringJungingerOlakaetal.2011, author = {Stoof-Leichsenring, Kathleen Rosemarie and Junginger, Annett and Olaka, Lydia A. and Tiedemann, Ralph and Trauth, Martin H.}, title = {Environmental variability in Lake Naivasha, Kenya, over the last two centuries}, series = {Journal of paleolimnolog}, volume = {45}, journal = {Journal of paleolimnolog}, number = {3}, publisher = {Springer}, address = {Dordrecht}, issn = {0921-2728}, doi = {10.1007/s10933-011-9502-4}, pages = {353 -- 367}, year = {2011}, abstract = {Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea, flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon concentrations in the sediments. Core chronology was established by (210)Pb dating and covered a similar to 186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm(-2) year(-1) correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century. The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified two major periods in the lake's history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted those of natural climate variation.}, language = {en} } @phdthesis{StoofLeichsenring2011, author = {Stoof-Leichsenring, Kathleen Rosemarie}, title = {Genetic analysis of diatoms and rotifers in tropical Kenyan lake sediments}, address = {Potsdam}, year = {2011}, language = {en} } @article{StojanovicMarkovicKleinpeteretal.2011, author = {Stojanovic, Milovan and Markovic, Rade and Kleinpeter, Erich and Baranac-Stojanovic, Marija}, title = {Endo-Mode cyclizations of vinylogous N-acyliminium ions as a route to the synthesis of condensed thiazolidines}, series = {Tetrahedron}, volume = {67}, journal = {Tetrahedron}, number = {49}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2011.10.011}, pages = {9541 -- 9554}, year = {2011}, abstract = {endo-Mode cyclizations of vinylogous N-acyliminium ions incorporating heteroatom-based nucleophiles have been examined as a route to the synthesis of condensed thiazolidines. The scope of these reactions and stereochemical outcome are discussed and explained using quantum chemical calculations.}, language = {en} } @article{StojanovicMarkovicKleinpeteretal.2011, author = {Stojanovic, Milovan and Markovic, Rade and Kleinpeter, Erich and Baranac-Stojanovic, Marija}, title = {endo-Mode cyclizations of vinylogous N-acyliminium ions as a route to the synthesis of condensed thiazolidines}, issn = {0040-4020}, year = {2011}, language = {en} } @article{StockhorstEvert2011, author = {Stockhorst, Stefanie and Evert, Felix}, title = {Preussische Gastlichkeit : Friedrich Nicolai und die Wirtshauskultur des 18. Jahrhunderts}, isbn = {978-3-89693-553-3}, year = {2011}, language = {de} } @article{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Signals from the past forms and functions of the traditional behavior in Thomas Kling's essay}, series = {Zeitschrift f{\"u}r Germanistik}, volume = {21}, journal = {Zeitschrift f{\"u}r Germanistik}, number = {1}, publisher = {Lang}, address = {Bern}, issn = {0323-7982}, doi = {10.3726/92132_114}, pages = {114 -- 130}, year = {2011}, language = {de} } @misc{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Reed, T. J., Mehr Licht in Deutschland. Eine kleine Geschichte der Aufkl{\"a}rung; M{\"u}nchen, Beck, 2009}, issn = {0722-740X}, year = {2011}, language = {de} } @phdthesis{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Einf{\"u}hrung in das Werk Gotthold Ephraim Lessings}, series = {Einf{\"u}hrungen Germanistik}, journal = {Einf{\"u}hrungen Germanistik}, publisher = {WBG}, address = {Darmstadt}, isbn = {978-3-534-22984-0}, pages = {143 S.}, year = {2011}, language = {de} } @article{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Friedrich Nicolai (1733 - 1811) : zum 200. Todestag des Berliner Aufkl{\"a}rers}, year = {2011}, language = {de} } @article{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Le raccolte di saggi "Itinerar" (1997) e "Botenstoffe" (2001) di Thomas Kling archeologo del linguaggio}, isbn = {978-88-15-14700-4}, year = {2011}, language = {it} } @misc{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Weimarer Klassik}, isbn = {978-3- 476-02004-8}, year = {2011}, language = {de} } @article{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Ethische Aufr{\"u}stung : zur Konvergenz von Landlebensdichtung und Neustoizismus im Zeichen des Dreissigj{\"a}hrigen Krieges am Beispiel von J. G. Schottelius' Lamentatio Germaniae exspirantis (1640)}, year = {2011}, language = {de} } @article{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Signale aus der Vergangenheit : zu Formen und Funktionen des Traditionsverhaltens in Thomas Klings Essayistik}, year = {2011}, language = {de} } @misc{Stockhorst2011, author = {Stockhorst, Stefanie}, title = {Friedrich Nicolai (1733-1811). - on the two hundreth Anniversary of the Berlin Enlightenment writer and bookseller has works published}, series = {Zeitschrift f{\"u}r Germanistik}, volume = {21}, journal = {Zeitschrift f{\"u}r Germanistik}, number = {1}, publisher = {Lang}, address = {Bern}, issn = {0323-7982}, pages = {153 -- 159}, year = {2011}, language = {de} } @article{Stillmark2011, author = {Stillmark, Katja}, title = {Affekt der Straße in zeitgen{\"o}ssischen autobiographischen Texten und dystopischen Romanen}, isbn = {978-3-8376-1404-6}, year = {2011}, language = {de} } @article{Stillmark2011, author = {Stillmark, Hans-Christian}, title = {Das Geschichtsdrama : ein Erbst{\"u}ck der DDR-Literatur}, year = {2011}, abstract = {Der Aufsatz besch{\"a}ftigt sich mit dem Genre des Geschichtsdramas und verweist auf das Problem des Dramas wie auf das der Geschichte im Verlaufe der DDR-Entwicklung und danach. Untersucht werden die Abweichung und Aufloesungserscheinungen des aristotelischen Dramas unter den Bedingung einer geschwundenen Geschichtsutopie.}, language = {de} } @article{Stillmark2011, author = {Stillmark, Hans-Christian}, title = {Transformationsr{\"a}ume im Werk Wolfgang Hilbigs}, isbn = {978-3-8376-1404-6}, year = {2011}, abstract = {Der Beitrag untersucht bestimmte Raeume, die in Wolfgang Hilbigs Prosawerk wiederholt auftauchen und die mit einer bestimmten affektiven Ladung ausgestattet sind. Es sind dies die Kuechen, die in Hilbigs Werk einer Geschlechtsverwandlung von einem ehemals weiblichen in einen maennlichen Arbeitsraum unterzogen werden. Auch werden idyllische Waldsiedlungen in Hilbigs Geschichten zu Staetten, die vom Judenmord durchzogen werden. Generall kann verallgemeinert werden, dass Hilbigs Raeume Transformationen unterliegen, die Verwandlungen bewirken.}, language = {de} } @article{Stillmark2011, author = {Stillmark, Hans-Christian}, title = {Zu Kleists theatralischer Transformation der K{\"o}rper}, isbn = {978- 3-939888-93-2}, year = {2011}, abstract = {Der Beitrag untersucht Kleists Dramentexte vor allem im Hinblick auf den "Skandal" des Koerpers und versucht dafuer eine Erklaerung zu finden. Diese besteht zunaechst im Herausfall aus dem Paradigma des aesthetischem Koerpers als einem schoenen Koerper. Zum zweiten aber auch darin, das Kleist mit seinen literarischen Mitteln eine drastische Performation des Koerpers fuer das Buehnenstueck vornahm ohne dafuer eine theatralische Praxis zu haben. Der Einsatz des Koerpers als ein Zeichen im Buehnenspiel ist daher strategisch vom Autor Kleist zu einer Aussage performiert worden, die neben den Aussagen des sprachlichen Textes eine weitere koerpersprachliche Textur konstruiert.}, language = {de} }