TY - JOUR A1 - Turner, Sarah T. A1 - Pingel, Patrick A1 - Steyrleuthner, Robert A1 - Crossland, Edward J. W. A1 - Ludwigs, Sabine A1 - Neher, Dieter T1 - Quantitative analysis of bulk heterojunction films using linear absorption spectroscopy and solar cell performance JF - Advanced functional materials N2 - A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non-optimized (chloroform cast) and nearly optimized (solvent-annealed o-dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H-aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent-annealed o-dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra- and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges. KW - Organic electronics KW - morphology KW - solar cells KW - mobility KW - absorption spectroscopy Y1 - 2011 U6 - https://doi.org/10.1002/adfm.201101583 SN - 1616-301X VL - 21 IS - 24 SP - 4640 EP - 4652 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Tremblay, Jean Christophe A1 - Monturet, Serge A1 - Saalfrank, Peter T1 - The Effects of electron-hole pair coupling on the infrared laser-controlled vibrational excitation of NO on Au(111) JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - In this work, we present theoretical simulations of laser-driven vibrational control of NO adsorbed on a gold surface. Our goal is to tailor laser pulses to selectively excite specific modes and vibrational eigenstates, as well as to favor photodesorption of the adsorbed molecule. To this end, various control schemes and algorithms are applied. For adsorbates at metallic surfaces, the creation of electron hole pairs in the substrate is known to play a dominant role in the transfer of energy from the system to the surroundings. These nonadiabatic couplings are included perturbatively in our reduced density matrix simulations using a generalization of the state-resolved position-dependent anharmonic rate model we recently introduced. An extension of the reduced density matrix is also proposed to provide a sound model for photodesorption in dissipative systems. Y1 - 2011 U6 - https://doi.org/10.1021/jp205902k SN - 1089-5639 VL - 115 IS - 39 SP - 10698 EP - 10707 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Townsley, Leisa K. A1 - Broos, Patrick S. A1 - Corcoran, Michael F. A1 - Feigelson, Eric D. A1 - Gagne, Marc A1 - Montmerle, Thierry A1 - Oey, M. S. A1 - Smith, Nathan A1 - Garmire, Gordon P. A1 - Getman, Konstantin V. A1 - Povich, Matthew S. A1 - Evans, Nancy Remage A1 - Naze, Yael A1 - Parkin, E. R. A1 - Preibisch, Thomas A1 - Wang, Junfeng A1 - Wou, Scott J. A1 - Chu, You-Hua A1 - Cohen, David H. A1 - Gruendl, Robert A. A1 - Hamaguchi, Kenji A1 - King, Robert R. A1 - Mac Low, Mordecai-Mark A1 - McCaughrean, Mark J. A1 - Moffat, Anthony F. J. A1 - Oskinova, Lida A1 - Pittard, Julian M. A1 - Stassun, Keivan G. A1 - Ud-Doula, Asif A1 - Walborn, Nolan R. A1 - Waldron, Wayne L. A1 - Churchwell, Ed A1 - Nictiols, J. S. A1 - Owocki, Stanley P. A1 - Schulz, Norbert S. T1 - An introduction to the chandra carina complex project JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series N2 - The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of > 14,000 X-ray point sources;> 9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results. KW - H II regions KW - stars: massive KW - stars: pre-main sequence KW - X-rays: individual (Carina) KW - X-rays: ISM KW - X-rays: stars Y1 - 2011 U6 - https://doi.org/10.1088/0067-0049/194/1/1 SN - 0067-0049 VL - 194 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Todt, Helge Tobias A1 - Peña, Miriam A1 - Zühlke, Julia A1 - Oskinova, Lida A1 - Hamann, Wolf-Rainer A1 - Gräfener, Götz T1 - Weak emission line central stars of planetary nebulae T2 - Planetary Nebulae: an Eye to the Future N2 - To understand the evolution and morphology of planetary nebulae, a detailed knowledge of their central stars is required. Central stars that exhibit emission lines in their spectra, indicating stellar mass-loss allow to study the evolution of planetary nebulae in action. Emission line central stars constitute about 10 % of all central stars. Half of them are practically hydrogen-free Wolf-Rayet type central stars of the carbon sequence, [WC], that show strong emission lines of carbon and oxygen in their spectra. In this contribution we address the weak emission-lines central stars (wels). These stars are poorly analyzed and their hydrogen content is mostly unknown. We obtained optical spectra, that include the important Balmer lines of hydrogen, for four weak emission line central stars. We present the results of our analysis, provide spectral classification and discuss possible explanations for their formation and evolution. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 462 KW - stars: AGB and post-AGB KW - stars: Wolf-Rayet KW - stars: abundances Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-413775 ER - TY - JOUR A1 - Tepper-Garcia, Thorsten A1 - Richter, Philipp A1 - Schaye, Joop A1 - Booth, C. M. A1 - Vecchia, Claudio Dalla A1 - Theuns, Tom A1 - Wiersma, Robert P. C. T1 - Absorption signatures of warm-hot gas at low redshift o vi JF - Monthly notices of the Royal Astronomical Society N2 - We investigate the origin and physical properties of O vi absorbers at low redshift (z = 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening O vi absorbers are believed to trace shock-heated gas in the warm-hot intergalactic medium (WHIM) and may thus play a key role in the search for the missing baryons in the present-day Universe. When compared to observations, the predicted distributions of the different O vi line parameters (column density, Doppler parameter, rest equivalent width W-r) from our simulations exhibit a lack of strong O vi absorbers, a discrepancy that has also been found by Oppenheimer & Dave. This suggests that physical processes on subgrid scales (e.g. turbulence) may strongly influence the observed properties of O vi systems. We find that the intervening O vi absorption arises mainly in highly metal enriched (10-1 < Z/Z(circle dot) less than or similar to 1) gas at typical overdensities of 1 < /<<>> less than or similar to 102. One-third of the O vi absorbers in our simulation are found to trace gas at temperatures T < 105 K, while the rest arises in gas at higher temperatures, most of them around T = 105.3 +/- 0.5 K. These temperatures are much higher than inferred by Oppenheimer & Dave, probably because that work did not take the suppression of metal-line cooling by the photoionizing background radiation into account. While the O vi resides in a similar region of (, T)-space as much of the shock-heated baryonic matter, the vast majority of this gas has a lower metal content and does not give rise to detectable O vi absorption. As a consequence of the patchy metal distribution, O vi absorbers in our simulations trace only a very small fraction of the cosmic baryons (< 2 per cent) and the cosmic metals. Instead, these systems presumably trace previously shock-heated, metal-rich material from galactic winds that is now mixing with the ambient gas and cooling. The common approach of comparing O vi and H i column densities to estimate the physical conditions in intervening absorbers from QSO observations may be misleading, as most of the H i (and most of the gas mass) is not physically connected with the high-metallicity patches that give rise to the O vi absorption. KW - methods: numerical KW - galaxies: formation KW - intergalactic medium KW - quasars: absorption lines KW - cosmology: theory Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2966.2010.18123.x SN - 0035-8711 VL - 413 IS - 1 SP - 190 EP - 212 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Sun, Zhuanlan A1 - Zhang, Xiaoqing A1 - Xia, Zhongfu A1 - Qiu, Xunlin A1 - Wirges, Werner A1 - Gerhard, Reimund A1 - Zeng, Changchun A1 - Zhang, Chuck A1 - Wang, Ben T1 - Polarization and piezoelectricity in polymer films with artificial void structure JF - Applied physics : A, Materials science & processing N2 - Laminated polymer-film systems with well-defined void structures were prepared from fluoroethylenepropylene (FEP) and polytetrafluoroethylene (PTFE) layers. First the PTFE films were patterned and then fusion-bonded with the FEP films. The laminates were subjected to either corona or contact charging in order to obtain the desired piezoelectricity. The build-up of the "macro-dipoles" in the laminated films was studied by recording the electric hysteresis loops. The resulting electro-mechanical properties were investigated by means of dielectric resonance spectroscopy (DRS) and direct measurements of the stress-strain relationship. Moreover, the thermal stability of the piezoelectric d (33) coefficient was investigated at elevated temperatures and via thermally stimulated discharge (TSD) current measurements in short circuit. For 150 mu m thick laminated films, consisting of one 25 mu m thick PTFE layer, two 12.5 mu m thick FEP layers, and a void of 100 mu m height, the critical voltage necessary for the build-up of the "macro-dipoles" in the inner voids was approximately 1400 V, which agrees with the value calculated from the Paschen Law. A quasi-static piezoelectric d (33) coefficient up to 300 pC/N was observed after corona charging. The mechanical properties of the film systems are highly anisotropic. At room temperature, the Young's moduli of the laminated film system are around 0.37 MPa in the thickness direction and 274 MPa in the lateral direction, respectively. Using these values, the theoretical shape anisotropy ratio of the void was calculated, which agrees well with experimental observation. Compared with films that do not exhibit structural regularity, the laminates showed improved thermal stability of the d (33) coefficients. The thermal stability of d (33) can be further improved by pre-aging. E.g., the reduction of the d (33) value in the sample pre-aged at 150A degrees C for 5 h was less than 5% after annealing for 30 h at a temperature of 90A degrees C. Y1 - 2011 U6 - https://doi.org/10.1007/s00339-011-6481-2 SN - 0947-8396 VL - 105 IS - 1 SP - 197 EP - 205 PB - Springer CY - New York ER - TY - JOUR A1 - Sun, Zhongkui A1 - Yang, Xiaoli T1 - Generating and enhancing lag synchronization of chaotic systems by white noise JF - Chaos : an interdisciplinary journal of nonlinear science N2 - In this paper, we study the crucial impact of white noise on lag synchronous regime in a pair of time-delay unidirectionally coupled systems. Our result demonstrates that merely via white-noise-based coupling lag synchronization could be achieved between the coupled systems (chaotic or not). And it is also demonstrated that a conventional lag synchronous regime can be enhanced by white noise. Sufficient conditions are further proved mathematically for noise-inducing and noise-enhancing lag synchronization, respectively. Additionally, the influence of parameter mismatch on the proposed lag synchronous regime is studied, by which we announce the robustness and validity of the new strategy. Two numerical examples are provided to illustrate the validity and some possible applications of the theoretical result. Y1 - 2011 U6 - https://doi.org/10.1063/1.3623440 SN - 1054-1500 SN - 1089-7682 VL - 21 IS - 3 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Sun, Y. -P. A1 - Hennies, Franz A1 - Pietzsch, Annette A1 - Kennedy, B. A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Andersson, Joakim A1 - Berglund, Martin A1 - Rubensson, Jan-Erik A1 - Aidas, K. A1 - Gel'mukhanov, F. A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Intramolecular soft modes and intermolecular interactions in liquid acetone JF - Physical review : B, Condensed matter and materials physics N2 - Resonant inelastic x-ray scattering spectra excited at the O1s(-1)pi* resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevB.84.132202 SN - 1098-0121 VL - 84 IS - 13 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Sun, Y-P A1 - Pietzsch, Annette A1 - Hennies, Franz A1 - Rinkevicius, Z. A1 - Karlsson, Hans O. A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Andersson, Joakim A1 - Kennedy, B. A1 - Schlappa, J. A1 - Föhlisch, Alexander A1 - Gel'mukhanov, F. A1 - Rubensson, Jan-Erik T1 - Internal symmetry and selection rules in resonant inelastic soft x-ray scattering JF - Journal of physics : B, Atomic, molecular and optical physics N2 - Resonant inelastic soft x-ray scattering spectra excited at the dissociative 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O(2) are presented and discussed in terms of state-of-the-art molecular theory. A new selection rule due to internal spin coupling is established, facilitating a deep analysis of the valence excited final states. Furthermore, it is found that a commonly accepted symmetry selection rule due to orbital parity breaks down, as the core hole and excited electron swap parity, thereby opening the symmetry forbidden 3 sigma(g) decay channel. Y1 - 2011 U6 - https://doi.org/10.1088/0953-4075/44/16/161002 SN - 0953-4075 VL - 44 IS - 16 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Straube, Arthur V. A1 - Pikovskij, Arkadij T1 - Pattern formation induced by time-dependent advection JF - Mathematical modelling of natural phenomena N2 - We study pattern-forming instabilities in reaction-advection-diffusion systems. We develop an approach based on Lyapunov-Bloch exponents to figure out the impact of a spatially periodic mixing flow on the stability of a spatially homogeneous state. We deal with the flows periodic in space that may have arbitrary time dependence. We propose a discrete in time model, where reaction, advection, and diffusion act as successive operators, and show that a mixing advection can lead to a pattern-forming instability in a two-component system where only one of the species is advected. Physically, this can be explained as crossing a threshold of Turing instability due to effective increase of one of the diffusion constants. KW - pattern formation KW - reaction-advection-diffusion equation Y1 - 2011 U6 - https://doi.org/10.1051/mmnp/20116107 SN - 0973-5348 VL - 6 IS - 1 SP - 138 EP - 148 PB - EDP Sciences CY - Les Ulis ER -