TY  - JOUR
A1  - Abdo, A. A.
A1  - Ackermann, Margit
A1  - Ajello, M.
A1  - Allafort, A. J.
A1  - Baldini, L.
A1  - Ballet, J.
A1  - Barbiellini, G.
A1  - Baring, M. G.
A1  - Bastieri, D.
A1  - Bechtol, K. C.
A1  - Bellazzini, R.
A1  - Berenji, B.
A1  - Blandford, R. D.
A1  - Bloom, E. D.
A1  - Bonamente, E.
A1  - Borgland, A. W.
A1  - Bouvier, A.
A1  - Brandt, T. J.
A1  - Bregeon, Johan
A1  - Brez, A.
A1  - Brigida, M.
A1  - Bruel, P.
A1  - Buehler, R.
A1  - Buson, S.
A1  - Caliandro, G. A.
A1  - Cameron, R. A.
A1  - Cannon, A.
A1  - Caraveo, P. A.
A1  - Carrigan, Svenja
A1  - Casandjian, J. M.
A1  - Cavazzuti, E.
A1  - Cecchi, C.
A1  - Celik, O.
A1  - Charles, E.
A1  - Chekhtman, A.
A1  - Cheung, C. C.
A1  - Chiang, J.
A1  - Ciprini, S.
A1  - Claus, R.
A1  - Cohen-Tanugi, J.
A1  - Conrad, Jan
A1  - Cutini, S.
A1  - Dermer, C. D.
A1  - de Palma, F.
A1  - do Couto e Silva, E.
A1  - Drell, P. S.
A1  - Dubois, R.
A1  - Dumora, D.
A1  - Favuzzi, C.
A1  - Fegan, S. J.
A1  - Ferrara, E. C.
A1  - Focke, W. B.
A1  - Fortin, P.
A1  - Frailis, M.
A1  - Fuhrmann, L.
A1  - Fukazawa, Y.
A1  - Funk, S.
A1  - Fusco, P.
A1  - Gargano, F.
A1  - Gasparrini, D.
A1  - Gehrels, N.
A1  - Germani, S.
A1  - Giglietto, N.
A1  - Giordano, F.
A1  - Giroletti, M.
A1  - Glanzman, T.
A1  - Godfrey, G.
A1  - Grenier, I. A.
A1  - Guillemot, L.
A1  - Guiriec, S.
A1  - Hayashida, M.
A1  - Hays, E.
A1  - Horan, D.
A1  - Hughes, R. E.
A1  - Johannesson, G.
A1  - Johnson, A. S.
A1  - Johnson, W. N.
A1  - Kadler, M.
A1  - Kamae, T.
A1  - Katagiri, H.
A1  - Kataoka, J.
A1  - Knoedlseder, J.
A1  - Kuss, M.
A1  - Lande, J.
A1  - Latronico, L.
A1  - Lee, S. -H.
A1  - Lemoine-Goumard, M.
A1  - Longo, F.
A1  - Loparco, F.
A1  - Lott, B.
A1  - Lovellette, M. N.
A1  - Lubrano, P.
A1  - Madejski, G. M.
A1  - Makeev, A.
A1  - Max-Moerbeck, W.
A1  - Mazziotta, Mario Nicola
A1  - McEnery, J. E.
A1  - Mehault, J.
A1  - Michelson, P. F.
A1  - Mitthumsiri, W.
A1  - Mizuno, T.
A1  - Moiseev, A. A.
A1  - Monte, C.
A1  - Monzani, M. E.
A1  - Morselli, A.
A1  - Moskalenko, I. V.
A1  - Murgia, S.
A1  - Naumann-Godo, M.
A1  - Nishino, S.
A1  - Nolan, P. L.
A1  - Norris, J. P.
A1  - Nuss, E.
A1  - Ohsugi, T.
A1  - Okumura, A.
A1  - Omodei, N.
A1  - Orlando, E.
A1  - Ormes, J. F.
A1  - Paneque, D.
A1  - Panetta, J. H.
A1  - Parent, D.
A1  - Pavlidou, V.
A1  - Pearson, T. J.
A1  - Pelassa, V.
A1  - Pepe, M.
A1  - Pesce-Rollins, M.
A1  - Piron, F.
A1  - Porter, T. A.
A1  - Raino, S.
A1  - Rando, R.
A1  - Razzano, M.
A1  - Readhead, A.
A1  - Reimer, A.
A1  - Reimer, O.
A1  - Richards, J. L.
A1  - Ripken, J.
A1  - Ritz, S.
A1  - Roth, M.
A1  - Sadrozinski, H. F. -W.
A1  - Sanchez, D.
A1  - Sander, A.
A1  - Scargle, J. D.
A1  - Sgro, C.
A1  - Siskind, E. J.
A1  - Smith, P. D.
A1  - Spandre, G.
A1  - Spinelli, P.
A1  - Stawarz, L.
A1  - Stevenson, M.
A1  - Strickman, M. S.
A1  - Sokolovsky, K. V.
A1  - Suson, D. J.
A1  - Takahashi, H.
A1  - Takahashi, T.
A1  - Tanaka, T.
A1  - Thayer, J. B.
A1  - Thayer, J. G.
A1  - Thompson, D. J.
A1  - Tibaldo, L.
A1  - Torres, F.
A1  - Tosti, G.
A1  - Tramacere, A.
A1  - Uchiyama, Y.
A1  - Usher, T. L.
A1  - Vandenbroucke, J.
A1  - Vasileiou, V.
A1  - Vilchez, N.
A1  - Vitale, V.
A1  - Waite, A. P.
A1  - Wang, P.
A1  - Wehrle, A. E.
A1  - Winer, B. L.
A1  - Wood, K. S.
A1  - Yang, Z.
A1  - Ylinen, T.
A1  - Zensus, J. A.
A1  - Ziegler, M.
A1  - Aleksic, J.
A1  - Antonelli, L. A.
A1  - Antoranz, P.
A1  - Backes, Michael
A1  - Barrio, J. A.
A1  - Gonzalez, J. Becerra
A1  - Bednarek, W.
A1  - Berdyugin, A.
A1  - Berger, K.
A1  - Bernardini, E.
A1  - Biland, A.
A1  - Blanch Bigas, O.
A1  - Bock, R. K.
A1  - Boller, A.
A1  - Bonnoli, G.
A1  - Bordas, Pol
A1  - Tridon, D. Borla
A1  - Bosch-Ramon, Valentin
A1  - Bose, D.
A1  - Braun, I.
A1  - Bretz, T.
A1  - Camara, M.
A1  - Carmona, E.
A1  - Carosi, A.
A1  - Colin, P.
A1  - Colombo, E.
A1  - Contreras, J. L.
A1  - Cortina, J.
A1  - Covino, S.
A1  - Dazzi, F.
A1  - de Angelis, A.
A1  - del Pozo, E. De Cea
A1  - De Lotto, B.
A1  - De Maria, M.
A1  - De Sabata, F.
A1  - Mendez, C. Delgado
A1  - Ortega, A. Diago
A1  - Doert, M.
A1  - Dominguez, A.
A1  - Prester, Dijana Dominis
A1  - Dorner, D.
A1  - Doro, M.
A1  - Elsaesser, D.
A1  - Ferenc, D.
A1  - Fonseca, M. V.
A1  - Font, L.
A1  - Lopen, R. J. Garcia
A1  - Garczarczyk, M.
A1  - Gaug, M.
A1  - Giavitto, G.
A1  - Godinovi, N.
A1  - Hadasch, D.
A1  - Herrero, A.
A1  - Hildebrand, D.
A1  - Hoehne-Moench, D.
A1  - Hose, J.
A1  - Hrupec, D.
A1  - Jogler, T.
A1  - Klepser, S.
A1  - Kraehenbuehl, T.
A1  - Kranich, D.
A1  - Krause, J.
A1  - La Barbera, A.
A1  - Leonardo, E.
A1  - Lindfors, E.
A1  - Lombardi, S.
A1  - Lopez, M.
A1  - Lorenz, E.
A1  - Majumdar, P.
A1  - Makariev, E.
A1  - Maneva, G.
A1  - Mankuzhiyil, N.
A1  - Mannheim, K.
A1  - Maraschi, L.
A1  - Mariotti, M.
A1  - Martinez, M.
A1  - Mazin, D.
A1  - Meucci, M.
A1  - Miranda, J. M.
A1  - Mirzoyan, R.
A1  - Miyamoto, H.
A1  - Moldon, J.
A1  - Moralejo, A.
A1  - Nieto, D.
A1  - Nilsson, K.
A1  - Orito, R.
A1  - Oya, I.
A1  - Paoletti, R.
A1  - Paredes, J. M.
A1  - Partini, S.
A1  - Pasanen, M.
A1  - Pauss, F.
A1  - Pegna, R. G.
A1  - Perez-Torres, M. A.
A1  - Persic, M.
A1  - Peruzzo, J.
A1  - Pochon, J.
A1  - Moroni, P. G. Prada
A1  - Prada, F.
A1  - Prandini, E.
A1  - Puchades, N.
A1  - Puljak, I.
A1  - Reichardt, T.
A1  - Reinthal, R.
A1  - Rhode, W.
A1  - Ribo, M.
A1  - Rico, J.
A1  - Rissi, M.
A1  - Ruegamer, S.
A1  - Saggion, A.
A1  - Saito, K.
A1  - Saito, T. Y.
A1  - Salvati, M.
A1  - Sanchez-Conde, M.
A1  - Satalecka, K.
A1  - Scalzotto, V.
A1  - Scapin, V.
A1  - Schultz, C.
A1  - Schweizer, T.
A1  - Shayduk, M.
A1  - Shore, S. N.
A1  - Sierpowska-Bartosik, A.
A1  - Sillanpaa, A.
A1  - Sitarek, J.
A1  - Sobczynska, D.
A1  - Spanier, F.
A1  - Spiro, S.
A1  - Stamerra, A.
A1  - Steinke, B.
A1  - Storz, J.
A1  - Strah, N.
A1  - Struebig, J. C.
A1  - Suric, T.
A1  - Takalo, L. O.
A1  - Tavecchio, F.
A1  - Temnikov, P.
A1  - Terzic, T.
A1  - Tescaro, D.
A1  - Teshima, M.
A1  - Vankov, H.
A1  - Wagner, R. M.
A1  - Weitzel, Q.
A1  - Zabalza, V.
A1  - Zandanel, F.
A1  - Zanin, R.
A1  - Acciari, V. A.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Benbow, W.
A1  - Boltuch, D.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Cui, W.
A1  - Dickherber, R.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Gillanders, G. H.
A1  - Godambe, S.
A1  - Grube, J.
A1  - Guenette, R.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Huang, D.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Konopelko, A.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - Maier, G.
A1  - McArthur, S.
A1  - McCann, A.
A1  - McCutcheon, M.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Ong, R.
A1  - Otte, N.
A1  - Pandel, D.
A1  - Perkins, J. S.
A1  - Pichel, A.
A1  - Pohl, M.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Rovero, A. C.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Senturk, G. D.
A1  - Steele, D.
A1  - Swordy, S. P.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Varlotta, A.
A1  - Vincent, S.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Williams, D. A.
A1  - Wood, M.
A1  - Zitzer, B.
A1  - Villata, M.
A1  - Raiteri, C. M.
A1  - Aller, H. D.
A1  - Aller, M. F.
A1  - Arkharov, A. A.
A1  - Blinov, D. A.
A1  - Calcidese, P.
A1  - Chen, W. P.
A1  - Efimova, N. V.
A1  - Kimeridze, G.
A1  - Konstantinova, T. S.
A1  - Kopatskaya, E. N.
A1  - Koptelova, E.
A1  - Kurtanidze, O. M.
A1  - Kurtanidze, S. O.
A1  - Lahteenmaki, A.
A1  - Larionov, V. M.
A1  - Larionova, E. G.
A1  - Larionova, L. V.
A1  - Ligustri, R.
A1  - Morozova, D. A.
A1  - Nikolashvili, M. G.
A1  - Sigua, L. A.
A1  - Troitsky, I. S.
A1  - Angelakis, E.
A1  - Capalbi, M.
A1  - Carraminana, A.
A1  - Carrasco, L.
A1  - Cassaro, P.
A1  - de la Fuente, E.
A1  - Gurwell, M. A.
A1  - Kovalev, Y. Y.
A1  - Kovalev, Yu. A.
A1  - Krichbaum, T. P.
A1  - Krimm, H. A.
A1  - Leto, Paolo
A1  - Lister, M. L.
A1  - Maccaferri, G.
A1  - Moody, J. W.
A1  - Mori, Y.
A1  - Nestoras, I.
A1  - Orlati, A.
A1  - Pagani, C.
A1  - Pace, C.
A1  - Pearson, R.
A1  - Perri, M.
A1  - Piner, B. G.
A1  - Pushkarev, A. B.
A1  - Ros, E.
A1  - Sadun, A. C.
A1  - Sakamoto, T.
A1  - Tornikoski, M.
A1  - Yatsu, Y.
A1  - Zook, A.
T1  - Insights into the high-energy gamma-Ray emission of markarian 501 fromextensive multifrequency observations in the fermi era
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We report on the gamma-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) gamma-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 +/- 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 +/- 0.14, and the softest one is 2.51 +/- 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size less than or similar to 0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (similar or equal to 10(44) erg s(-1)) constitutes only a small fraction (similar to 10(-3)) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude.
KW  - acceleration of particles
KW  - BL Lacertae objects: general
KW  - BL Lacertae objects: individual (Mrk 501)
KW  - galaxies: active
KW  - gamma rays: general
KW  - radiation mechanisms: non-thermal
Y1  - 2011
U6  - https://doi.org/10.1088/0004-637X/727/2/129
SN  - 0004-637X
VL  - 727
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Abdo, A. A.
A1  - Ackermann, Margit
A1  - Ajello, M.
A1  - Allafort, A. J.
A1  - Baldini, L.
A1  - Ballet, J.
A1  - Barbiellini, G.
A1  - Baring, M. G.
A1  - Bastieri, D.
A1  - Bellazzini, R.
A1  - Berenji, B.
A1  - Blandford, R. D.
A1  - Bloom, E. D.
A1  - Bonamente, E.
A1  - Borgland, A. W.
A1  - Bouvier, A.
A1  - Brandt, T. J.
A1  - Bregeon, Johan
A1  - Brigida, M.
A1  - Bruel, P.
A1  - Buehler, R.
A1  - Buson, S.
A1  - Caliandro, G. A.
A1  - Cameron, R. A.
A1  - Caraveo, P. A.
A1  - Casandjian, J. M.
A1  - Cecchi, C.
A1  - Chaty, S.
A1  - Chekhtman, A.
A1  - Cheung, C. C.
A1  - Chiang, J.
A1  - Cillis, A. N.
A1  - Ciprini, S.
A1  - Claus, R.
A1  - Cohen-Tanugi, J.
A1  - Conrad, Jan
A1  - Corbel, S.
A1  - Cutini, S.
A1  - de Angelis, A.
A1  - de Palma, F.
A1  - Dermer, C. D.
A1  - Digel, S. W.
A1  - do Couto e Silva, E.
A1  - Drell, P. S.
A1  - Drlica-Wagner, A.
A1  - Dubois, R.
A1  - Dumora, D.
A1  - Favuzzi, C.
A1  - Ferrara, E. C.
A1  - Fortin, P.
A1  - Frailis, M.
A1  - Fukazawa, Y.
A1  - Fukui, Y.
A1  - Funk, S.
A1  - Fusco, P.
A1  - Gargano, F.
A1  - Gasparrini, D.
A1  - Gehrels, N.
A1  - Germani, S.
A1  - Giglietto, N.
A1  - Giordano, F.
A1  - Giroletti, M.
A1  - Glanzman, T.
A1  - Godfrey, G.
A1  - Grenier, I. A.
A1  - Grondin, M. -H.
A1  - Guiriec, S.
A1  - Hadasch, D.
A1  - Hanabata, Y.
A1  - Harding, A. K.
A1  - Hayashida, M.
A1  - Hayashi, K.
A1  - Hays, E.
A1  - Horan, D.
A1  - Jackson, M. S.
A1  - Johannesson, G.
A1  - Johnson, A. S.
A1  - Kamae, T.
A1  - Katagiri, H.
A1  - Kataoka, J.
A1  - Kerr, M.
A1  - Knoedlseder, J.
A1  - Kuss, M.
A1  - Lande, J.
A1  - Latronico, L.
A1  - Lee, S. -H.
A1  - Lemoine-Goumard, M.
A1  - Longo, F.
A1  - Loparco, F.
A1  - Lovellette, M. N.
A1  - Lubrano, P.
A1  - Madejski, G. M.
A1  - Makeev, A.
A1  - Mazziotta, Mario Nicola
A1  - McEnery, J. E.
A1  - Michelson, P. F.
A1  - Mignani, R. P.
A1  - Mitthumsiri, W.
A1  - Mizuno, T.
A1  - Moiseev, A. A.
A1  - Monte, C.
A1  - Monzani, M. E.
A1  - Morselli, A.
A1  - Moskalenko, I. V.
A1  - Murgia, S.
A1  - Naumann-Godo, M.
A1  - Nolan, P. L.
A1  - Norris, J. P.
A1  - Nuss, E.
A1  - Ohsugi, T.
A1  - Okumura, A.
A1  - Orlando, E.
A1  - Ormes, J. F.
A1  - Paneque, D.
A1  - Parent, D.
A1  - Pelassa, V.
A1  - Pesce-Rollins, M.
A1  - Pierbattista, M.
A1  - Piron, F.
A1  - Pohl, Martin
A1  - Porter, T. A.
A1  - Raino, S.
A1  - Rando, R.
A1  - Razzano, M.
A1  - Reimer, O.
A1  - Reposeur, T.
A1  - Ritz, S.
A1  - Romani, R. W.
A1  - Roth, M.
A1  - Sadrozinski, H. F. -W.
A1  - Parkinson, P. M. Saz
A1  - Sgro, C.
A1  - Smith, D. A.
A1  - Smith, P. D.
A1  - Spandre, G.
A1  - Spinelli, P.
A1  - Strickman, M. S.
A1  - Tajima, H.
A1  - Takahashi, H.
A1  - Takahashi, T.
A1  - Tanaka, T.
A1  - Thayer, J. G.
A1  - Thayer, J. B.
A1  - Thompson, D. J.
A1  - Tibaldo, L.
A1  - Tibolla, O.
A1  - Torres, D. F.
A1  - Tosti, G.
A1  - Tramacere, A.
A1  - Troja, E.
A1  - Uchiyama, Y.
A1  - Vandenbroucke, J.
A1  - Vasileiou, V.
A1  - Vianello, G.
A1  - Vilchez, N.
A1  - Vitale, V.
A1  - Waite, A. P.
A1  - Wang, P.
A1  - Winer, B. L.
A1  - Wood, K. S.
A1  - Yamamoto, H.
A1  - Yamazaki, R.
A1  - Yang, Z.
A1  - Ziegler, M.
T1  - Observations of the young supernova remnant RX J1713.7-3946 with the fermi large area telescope
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present observations of the young supernova remnant (SNR) RX J1713.7-3946 with the Fermi Large Area Telescope (LAT). We clearly detect a source positionally coincident with the SNR. The source is extended with a best-fit extension of 0 degrees.55 +/- 0 degrees.04 matching the size of the non-thermal X-ray and TeV gamma-ray emission from the remnant. The positional coincidence and the matching extended emission allow us to identify the LAT source with SNR RX J1713.7-3946. The spectrum of the source can be described by a very hard power law with a photon index of Gamma = 1.5 +/- 0.1 that coincides in normalization with the steeper H. E. S. S.-detected gamma-ray spectrum at higher energies. The broadband gamma-ray emission is consistent with a leptonic origin as the dominant mechanism for the gamma-ray emission.
KW  - acceleration of particles
KW  - gamma rays: general
KW  - gamma rays: ISM
KW  - ISM: individual objects (RX J1713.7-3946)
KW  - ISM: supernova remnants
KW  - radiation mechanisms: non-thermal
Y1  - 2011
U6  - https://doi.org/10.1088/0004-637X/734/1/28
SN  - 0004-637X
VL  - 734
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Abdolvahab, Rouhollah Haji
A1  - Metzler, Ralf
A1  - Ejtehadi, Mohammad Reza
T1  - First passage time distribution of chaperone driven polymer translocation through a nanopore homopolymer and heteropolymer cases
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Peclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Peclet number. We investigate the effect of the chaperone size on the translocation process. In particular, for large chaperone size, the translocation progress and the mean waiting time as function of the reaction coordinate exhibit pronounced sawtooth-shapes. The effects of a heterogeneous polymer sequence on the translocation dynamics is studied in terms of the translocation velocity, the probability distribution for the translocation progress, and the monomer waiting times. (C) 2011 American Institute of Physics.
Y1  - 2011
U6  - https://doi.org/10.1063/1.3669427
SN  - 0021-9606
VL  - 135
IS  - 24
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Abel, M. W.
A1  - Shepelyansky, Dima L.
T1  - Google matrix of business process management
JF  - The European physical journal : B, Condensed matter and complex systems
N2  - Development of efficient business process models and determination of their characteristic properties are subject of intense interdisciplinary research. Here, we consider a business process model as a directed graph. Its nodes correspond to the units identified by the modeler and the link direction indicates the causal dependencies between units. It is of primary interest to obtain the stationary flow on such a directed graph, which corresponds to the steady-state of a firm during the business process. Following the ideas developed recently for the World Wide Web, we construct the Google matrix for our business process model and analyze its spectral properties. The importance of nodes is characterized by PageRank and recently proposed CheiRank and 2DRank, respectively. The results show that this two-dimensional ranking gives a significant information about the influence and communication properties of business model units. We argue that the Google matrix method, described here, provides a new efficient tool helping companies to make their decisions on how to evolve in the exceedingly dynamic global market.
Y1  - 2011
U6  - https://doi.org/10.1140/epjb/e2010-10710-y
SN  - 1434-6028
VL  - 84
IS  - 4
SP  - 493
EP  - 500
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Acciari, V. A.
A1  - Aliu, E.
A1  - Araya, M.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Cui, W.
A1  - Dickherber, R.
A1  - Duke, C.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Guenette, R.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Hughes, G.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Imran, A.
A1  - Kaaret, P.
A1  - Kertzman, M.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Madhavan, A. S.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - Moriarty, P.
A1  - Ong, R. A.
A1  - Otte, A. N.
A1  - Pandel, D.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pohl, Martin
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Saxon, D. B.
A1  - Sembroski, G. H.
A1  - Sentuerk, G. D.
A1  - Smith, A. W.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Varlotta, A.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Weng, S.
A1  - Williams, D. A.
A1  - Wood, M.
A1  - Zitzer, B.
T1  - Gamma-ray observations of the Be/Pulsar binary 1A 0535+262 during a Giant X-Ray outburst
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Giant X-ray outbursts, with luminosities of about 10(37) erg s(-1), are observed roughly every five years from the nearby Be/pulsar binary 1A 0535+262. In this article, we present observations of the source with VERITAS at very high energies (VHEs; E > 100 GeV) triggered by the X-ray outburst in 2009 December. The observations started shortly after the onset of the outburst and provided comprehensive coverage of the episode, as well as the 111 day binary orbit. No VHE emission is evident at any time. We also examined data from the contemporaneous observations of 1A 0535+262 with the Fermi/Large Area Telescope at high-energy photons (E > 0.1 GeV) and failed to detect the source at GeV energies. The X-ray continua measured with the Swift/X-Ray Telescope and the RXTE/PCA can be well described by the combination of blackbody and Comptonized emission from thermal electrons. Therefore, the gamma-ray and X-ray observations suggest the absence of a significant population of non-thermal particles in the system. This distinguishes 1A 0535+262 from those Be X-ray binaries (such as PSR B1259-63 and LS I +61 degrees 303) that have been detected at GeV-TeV energies. We discuss the implications of the results on theoretical models.
KW  - acceleration of particles
KW  - binaries: general
KW  - gamma rays: general
KW  - stars: individual (1A 0535+262)
Y1  - 2011
U6  - https://doi.org/10.1088/0004-637X/733/2/96
SN  - 0004-637X
VL  - 733
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Acciari, V. A.
A1  - Aliu, E.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Christiansen, J. L.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Duke, C.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Guenette, R.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Hughes, G.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Jackson, D. J.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - Madhavan, A. S.
A1  - Maier, G.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Moriarty, P.
A1  - Newbold, M. D.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pohl, Martin
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Ruppel, J.
A1  - Saxon, D. B.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Sentuerk, G. D.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Swordy, S. P.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Williams, D. A.
A1  - Wood, M.
T1  - Veritas observations of gamma-ray bursts detected by swift
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the results of 16 Swift-triggered Gamma-ray burst (GRB) follow-up observations taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) telescope array from 2007 January to 2009 June. The median energy threshold and response time of these observations were 260 GeV and 320 s, respectively. Observations had an average duration of 90 minutes. Each burst is analyzed independently in two modes: over the whole duration of the observations and again over a shorter timescale determined by the maximum VERITAS sensitivity to a burst with a t(-1.5) time profile. This temporal model is characteristic of GRB afterglows with high-energy, long-lived emission that have been detected by the Large Area Telescope on board the Fermi satellite. No significant very high energy (VHE) gamma-ray emission was detected and upper limits above the VERITAS threshold energy are calculated. The VERITAS upper limits are corrected for gamma-ray extinction by the extragalactic background light and interpreted in the context of the keV emission detected by Swift. For some bursts the VHE emission must have less power than the keV emission, placing constraints on inverse Compton models of VHE emission.
KW  - astroparticle physics
KW  - gamma-ray burst: general
Y1  - 2011
U6  - https://doi.org/10.1088/0004-637X/743/1/62
SN  - 0004-637X
VL  - 743
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Acciari, V. A.
A1  - Aliu, E.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Dickherber, R.
A1  - Duke, C.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Gillanders, G. H.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Guenette, R.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Hughes, G.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - LeBohec, S.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pohl, Martin
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Ruppel, J.
A1  - Saxon, D. B.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Senturk, G. D.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Williams, D. A.
A1  - Zitzer, B.
T1  - VERITAS OBSERVATIONS OF THE TeV BINARY LS I+61 degrees 303 DURING 2008-2010
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the results of observations of the TeV binary LS I + 61 degrees 303 with the VERITAS telescope array between 2008 and 2010, at energies above 300 GeV. In the past, both ground-based gamma-ray telescopes VERITAS and MAGIC have reported detections of TeV emission near the apastron phases of the binary orbit. The observations presented here show no strong evidence for TeV emission during these orbital phases; however, during observations taken in late 2010, significant emission was detected from the source close to the phase of superior conjunction (much closer to periastron passage) at a 5.6 standard deviation (5.6 sigma) post-trials significance. In total, between 2008 October and 2010 December a total exposure of 64.5 hr was accumulated with VERITAS on LS I + 61 degrees 303, resulting in an excess at the 3.3 sigma significance level for constant emission over the entire integrated data set. The flux upper limits derived for emission during the previously reliably active TeV phases (i.e., close to apastron) are less than 5% of the Crab Nebula flux in the same energy range. This result stands in apparent contrast to previous observations by both MAGIC and VERITAS which detected the source during these phases at 10% of the Crab Nebula flux. During the two year span of observations, a large amount of X-ray data were also accrued on LS I + 61 degrees 303 by the Swift X-ray Telescope and the Rossi X-ray Timing Explorer Proportional Counter Array. We find no evidence for a correlation between emission in the X-ray and TeV regimes during 20 directly overlapping observations. We also comment on data obtained contemporaneously by the Fermi Large Area Telescope.
KW  - binaries: general
KW  - gamma rays: general
KW  - X-rays: binaries
Y1  - 2011
U6  - https://doi.org/10.1088/0004-637X/738/1/3
SN  - 0004-637X
VL  - 738
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Acciari, V. A.
A1  - Aliu, E.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Cui, W.
A1  - Dickherber, R.
A1  - Duke, C.
A1  - Errando, M.
A1  - Finley, J. P.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Gillanders, G. H.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Guenette, R.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Hughes, J. P.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - LeBohec, S.
A1  - Madhavan, A. S.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Pandel, D.
A1  - Park, N. H.
A1  - Perkins, J. S.
A1  - Pohl, Martin
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Saxon, D. B.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Senturk, G. Demet
A1  - Slane, P.
A1  - Smith, A. W.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Williams, D. A.
A1  - Wood, M.
A1  - Zitzer, B.
T1  - Discovery of OF TeV Gamma-Ray emission from tycho's supernova remnant
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - We report the discovery of TeV gamma-ray emission from the Type Ia supernova remnant (SNR) G120.1+1.4, known as Tycho's SNR. Observations performed in the period 2008-2010 with the VERITAS ground-based gamma-ray observatory reveal weak emission coming from the direction of the remnant, compatible with a point source located at 00(h)25(m)27(s).0, +64 degrees 10'50 '' (J2000). The TeV photon spectrum measured by VERITAS can be described with a power law dN/dE = C(E/3.42 TeV)(-Gamma) with Gamma = 1.95 +/- 0.51(stat) +/- 0.30(sys) and C = (1.55 +/- 0.43(stat) +/- 0.47(sys)) x 10(-14) cm(-2) s(-1) TeV-1. The integral flux above 1 TeV corresponds to similar to 0.9% of the steady Crab Nebula emission above the same energy, making it one of the weakest sources yet detected in TeV gamma rays. We present both leptonic and hadronic models that can describe the data. The lowest magnetic field allowed in these models is similar to 80 mu G, which may be interpreted as evidence for magnetic field amplification.
KW  - gamma rays: general
KW  - ISM: individual objects (G120.1+01.4, Tycho=VER J0025+641)
Y1  - 2011
U6  - https://doi.org/10.1088/2041-8205/730/2/L20
SN  - 2041-8205
VL  - 730
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Ackermann, Margit
A1  - Ajello, M.
A1  - Allafort, A. J.
A1  - Baldini, L.
A1  - Ballet, J.
A1  - Barbiellini, G.
A1  - Bastieri, D.
A1  - Belfiore, A.
A1  - Bellazzini, R.
A1  - Berenji, B.
A1  - Blandford, R. D.
A1  - Bloom, E. D.
A1  - Bonamente, E.
A1  - Borgland, A. W.
A1  - Bottacini, E.
A1  - Brigida, M.
A1  - Bruel, P.
A1  - Buehler, R.
A1  - Buson, S.
A1  - Caliandro, G. A.
A1  - Cameron, R. A.
A1  - Caraveo, P. A.
A1  - Casandjian, J. M.
A1  - Cecchi, C.
A1  - Chekhtman, A.
A1  - Cheung, C. C.
A1  - Chiang, J.
A1  - Ciprini, S.
A1  - Claus, R.
A1  - Cohen-Tanugi, J.
A1  - de Angelis, A.
A1  - de Palma, F.
A1  - Dermer, C. D.
A1  - do Couto e Silva, E.
A1  - Drell, P. S.
A1  - Dumora, D.
A1  - Favuzzi, C.
A1  - Fegan, S. J.
A1  - Focke, W. B.
A1  - Fortin, P.
A1  - Fukazawa, Y.
A1  - Fusco, P.
A1  - Gargano, F.
A1  - Germani, S.
A1  - Giglietto, N.
A1  - Giordano, F.
A1  - Giroletti, M.
A1  - Glanzman, T.
A1  - Godfrey, G.
A1  - Grenier, I. A.
A1  - Guillemot, L.
A1  - Guiriec, S.
A1  - Hadasch, D.
A1  - Hanabata, Y.
A1  - Harding, A. K.
A1  - Hayashida, M.
A1  - Hayashi, K.
A1  - Hays, E.
A1  - Johannesson, G.
A1  - Johnson, A. S.
A1  - Kamae, T.
A1  - Katagiri, H.
A1  - Kataoka, J.
A1  - Kerr, M.
A1  - Knoedlseder, J.
A1  - Kuss, M.
A1  - Lande, J.
A1  - Latronico, L.
A1  - Lee, S. -H.
A1  - Longo, F.
A1  - Loparco, F.
A1  - Lott, B.
A1  - Lovellette, M. N.
A1  - Lubrano, P.
A1  - Martin, P.
A1  - Mazziotta, Mario Nicola
A1  - McEnery, J. E.
A1  - Mehault, J.
A1  - Michelson, P. F.
A1  - Mitthumsiri, W.
A1  - Mizuno, T.
A1  - Monte, C.
A1  - Monzani, M. E.
A1  - Morselli, A.
A1  - Moskalenko, I. V.
A1  - Murgia, S.
A1  - Naumann-Godo, M.
A1  - Nolan, P. L.
A1  - Norris, J. P.
A1  - Nuss, E.
A1  - Ohsugi, T.
A1  - Okumura, A.
A1  - Orlando, E.
A1  - Ormes, J. F.
A1  - Ozaki, M.
A1  - Paneque, D.
A1  - Parent, D.
A1  - Pesce-Rollins, M.
A1  - Pierbattista, M.
A1  - Piron, F.
A1  - Pohl, Martin
A1  - Prokhorov, D.
A1  - Raino, S.
A1  - Rando, R.
A1  - Razzano, M.
A1  - Reposeur, T.
A1  - Ritz, S.
A1  - Parkinson, P. M. Saz
A1  - Sgro, C.
A1  - Siskind, E. J.
A1  - Smith, P. D.
A1  - Spinelli, P.
A1  - Strong, A. W.
A1  - Takahashi, H.
A1  - Tanaka, T.
A1  - Thayer, J. G.
A1  - Thayer, J. B.
A1  - Thompson, D. J.
A1  - Tibaldo, L.
A1  - Torres, D. F.
A1  - Tosti, G.
A1  - Tramacere, A.
A1  - Troja, E.
A1  - Uchiyama, Y.
A1  - Vandenbroucke, J.
A1  - Vasileiou, V.
A1  - Vianello, G.
A1  - Vitale, V.
A1  - Waite, A. P.
A1  - Wang, P.
A1  - Winer, B. L.
A1  - Wood, K. S.
A1  - Yang, Z.
A1  - Zimmer, S.
A1  - Bontemps, S.
T1  - A cocoon of freshly accelerated cosmic rays detected by fermi in the cygnus superbubble
JF  - Science
N2  - The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova shockwaves, but we know little of their escape from the shock and their evolution through the turbulent medium surrounding massive stars. Gamma rays can probe their spreading through the ambient gas and radiation fields. The Fermi Large Area Telescope (LAT) has observed the star-forming region of Cygnus X. The 1- to 100-gigaelectronvolt images reveal a 50-parsec-wide cocoon of freshly accelerated cosmic rays that flood the cavities carved by the stellar winds and ionization fronts from young stellar clusters. It provides an example to study the youth of cosmic rays in a superbubble environment before they merge into the older Galactic population.
Y1  - 2011
U6  - https://doi.org/10.1126/science.1210311
SN  - 0036-8075
VL  - 334
IS  - 6059
SP  - 1103
EP  - 1107
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
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A1  - Vink, J.
A1  - Vlahakis, N.
A1  - Vlahos, L.
A1  - Vogler, P.
A1  - Vollhardt, A.
A1  - Volpe, F.
A1  - Von Gunten, H. P.
A1  - Vorobiov, S.
A1  - Wagner, S.
A1  - Wagner, R. M.
A1  - Wagner, B.
A1  - Wakely, S. P.
A1  - Walter, P.
A1  - Walter, R.
A1  - Warwick, R.
A1  - Wawer, P.
A1  - Wawrzaszek, R.
A1  - Webb, N.
A1  - Wegner, P.
A1  - Weinstein, A.
A1  - Weitzel, Q.
A1  - Welsing, R.
A1  - Wetteskind, H.
A1  - White, R.
A1  - Wierzcholska, A.
A1  - Wilkinson, M. I.
A1  - Williams, D. A.
A1  - Winde, M.
A1  - Wischnewski, R.
A1  - Wisniewski, L.
A1  - Wolczko, A.
A1  - Wood, M.
A1  - Xiong, Q.
A1  - Yamamoto, T.
A1  - Yamaoka, K.
A1  - Yamazaki, R.
A1  - Yanagita, S.
A1  - Yoffo, B.
A1  - Yonetani, M.
A1  - Yoshida, A.
A1  - Yoshida, T.
A1  - Yoshikoshi, T.
A1  - Zabalza, V.
A1  - Zagdanski, A.
A1  - Zajczyk, A.
A1  - Zdziarski, A.
A1  - Zech, Alraune
A1  - Zietara, K.
A1  - Ziolkowski, P.
A1  - Zitelli, V.
A1  - Zychowski, P.
T1  - Design concepts for the Cherenkov Telescope Array CTA an advanced facility for ground-based high-energy gamma-ray astronomy
JF  - Experimental astronomy : an international journal on astronomical instrumentation and data analysis
N2  - Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
KW  - Ground based gamma ray astronomy
KW  - Next generation Cherenkov telescopes
KW  - Design concepts
Y1  - 2011
U6  - https://doi.org/10.1007/s10686-011-9247-0
SN  - 0922-6435
SN  - 1572-9508
VL  - 32
IS  - 3
SP  - 193
EP  - 316
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Aliu, E.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Boettcher, Markus
A1  - Bouvier, A.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Dickherber, R.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Gillanders, G. H.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Huan, H.
A1  - Hughes, G.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Madhavan, A. S.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pichel, A.
A1  - Pohl, Martin
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Ruppel, J.
A1  - Saxon, D. B.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Skole, C.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Williams, D. A.
T1  - Veritas observations of unusual extragalactic transient swift J164449.3+573451
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - We report on very high energy (>100 GeV) gamma-ray observations of Swift J164449.3+573451, an unusual transient object first detected by the Swift Observatory and later detected by multiple radio, optical, and X-ray observatories. A total exposure of 28 hr was obtained on Swift J164449.3+573451 with the Very Energetic Radiation Imaging Telescope Array System ( VERITAS) during 2011 March 28-April 15. We do not detect the source and place a differential upper limit on the emission at 500 GeV during these observations of 1.4 x 10(-12) erg cm(-2) s(-1) (99% confidence level). We also present time-resolved upper limits and use a flux limit averaged over the X-ray flaring period to constrain various emission scenarios that can accommodate both the radio-through-X-ray emission detected from the source and the lack of detection by VERITAS.
KW  - accretion, accretion disks
KW  - galaxies: active
KW  - gamma rays: galaxies
KW  - radiation mechanisms: non-thermal
Y1  - 2011
U6  - https://doi.org/10.1088/2041-8205/738/2/L30
SN  - 2041-8205
VL  - 738
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Aliu, E.
A1  - Arlen, T.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Bouvier, A.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Byrum, K.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Christiansen, J. L.
A1  - Ciupik, L.
A1  - Collins-Hughes, E.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Dickherber, R.
A1  - Duke, C.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Gibbs, K.
A1  - Gillanders, G. H.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Guenette, R.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Holder, J.
A1  - Huan, H.
A1  - Hughes, G.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Imran, A.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Lang, M. J.
A1  - Lyutikov, M.
A1  - Madhavan, A. S.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - McCann, A.
A1  - McCutcheon, M.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Nunez, P.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pizlo, F.
A1  - Pohl, Martin
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Ruppel, J.
A1  - Saxon, D. B.
A1  - Schroedter, M.
A1  - Sembroski, G. H.
A1  - Sentuerk, G. D.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Vincent, S.
A1  - Vivier, M.
A1  - Wakely, S. P.
A1  - Ward, J. E.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Weisgarber, T.
A1  - Williams, D. A.
A1  - Zitzer, B.
T1  - Detection of pulsed Gamma Rays Above 100 GeV from the Crab Pulsar
JF  - Science
N2  - We report the detection of pulsed gamma rays from the Crab pulsar at energies above 100 giga-electron volts (GeV) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) array of atmospheric Cherenkov telescopes. The detection cannot be explained on the basis of current pulsar models. The photon spectrum of pulsed emission between 100 mega-electron volts and 400 GeV is described by a broken power law that is statistically preferred over a power law with an exponential cutoff. It is unlikely that the observation can be explained by invoking curvature radiation as the origin of the observed gamma rays above 100 GeV. Our findings require that these gamma rays be produced more than 10 stellar radii from the neutron star.
Y1  - 2011
U6  - https://doi.org/10.1126/science.1208192
SN  - 0036-8075
VL  - 334
IS  - 6052
SP  - 69
EP  - 72
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Aliu, E.
A1  - Aune, T.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Boettcher, Markus
A1  - Bouvier, A.
A1  - Bradbury, S. M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Cannon, A.
A1  - Cesarini, A.
A1  - Ciupik, L.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Decerprit, G.
A1  - Dickherber, R.
A1  - Duke, C.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Feng, Q.
A1  - Finnegan, G.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Galante, N.
A1  - Gall, D.
A1  - Gillanders, G. H.
A1  - Godambe, S.
A1  - Griffin, S.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hanna, D.
A1  - Hivick, B.
A1  - Holder, J.
A1  - Huan, H.
A1  - Hughes, G.
A1  - Hui, C. M.
A1  - Humensky, T. B.
A1  - Kaaret, P.
A1  - Karlsson, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krawczynski, H.
A1  - Krennrich, F.
A1  - Maier, G.
A1  - Majumdar, P.
A1  - McArthur, S.
A1  - McCann, A.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Nelson, T.
A1  - Ong, R. A.
A1  - Orr, M.
A1  - Otte, A. N.
A1  - Park, N.
A1  - Perkins, J. S.
A1  - Pichel, A.
A1  - Pohl, Martin
A1  - Prokoph, H.
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reyes, L. C.
A1  - Reynolds, P. T.
A1  - Roache, E.
A1  - Rose, H. J.
A1  - Ruppel, J.
A1  - Saxon, D. B.
A1  - Sembroski, G. H.
A1  - Skole, C.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Tesic, G.
A1  - Theiling, M.
A1  - Thibadeau, S.
A1  - Tsurusaki, K.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Wakely, S. P.
A1  - Weekes, T. C.
A1  - Weinstein, A.
A1  - Williams, D. A.
A1  - Zitzer, B.
A1  - Ciprini, S.
A1  - Fumagalli, M.
A1  - Kaplan, K.
A1  - Paneque, D.
A1  - Prochaska, J. X.
T1  - Multiwavelenght observations of the previously unidentified blzar RX J0648.7+1516
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We report on the VERITAS discovery of very high energy (VHE) gamma-ray emission above 200 GeV from the high-frequency-peaked BL Lac (HBL) object RX J0648.7+1516 (GB J0648+1516), associated with 1FGL J0648.8+1516. The photon spectrum above 200 GeV is fitted by a power law dN/dE = F-0(E/E-0)(-Gamma) with a photon index Gamma of 4.4 +/- 0.8(stat) +/- 0.3(syst) and a flux normalization F-0 of (2.3 +/- 0.5(stat) +/- 1.2(sys)) x 10(-11) TeV-1 cm(-2) s(-1) with E-0 = 300 GeV. No VHE variability is detected during VERITAS observations of RX J0648.7+1516 between 2010 March 4 and April 15. Following the VHE discovery, the optical identification and spectroscopic redshift were obtained using the Shane 3 m Telescope at the Lick Observatory, showing the unidentified object to be a BL Lac type with a redshift of z = 0.179. Broadband multiwavelength observations contemporaneous with the VERITAS exposure period can be used to subclassify the blazar as an HBL object, including data from the MDM observatory, Swift-UVOT, and X-Ray Telescope, and continuous monitoring at photon energies above 1 GeV from the Fermi Large Area Telescope (LAT). We find that in the absence of undetected, high-energy rapid variability, the one-zone synchrotron self-Compton (SSC) model overproduces the high-energy gamma-ray emission measured by the Fermi-LAT over 2.3 years. The spectral energy distribution can be parameterized satisfactorily with an external-Compton or lepto-hadronic model, which have two and six additional free parameters, respectively, compared to the one-zone SSC model.
KW  - BL Lacertae objects: individual (RX J0648.7+1516, 1FGL J0648.8+1516, VER J0648+152)
KW  - gamma rays: galaxies
Y1  - 2011
U6  - https://doi.org/10.1088/0004-637X/742/2/127
SN  - 0004-637X
VL  - 742
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Arhammar, C.
A1  - Pietzsch, Annette
A1  - Bock, Nicolas
A1  - Holmstroem, Erik
A1  - Araujo, C. Moyses
A1  - Grasjo, Johan
A1  - Zhao, Shuxi
A1  - Green, Sara
A1  - Peery, T.
A1  - Hennies, Franz
A1  - Amerioun, Shahrad
A1  - Föhlisch, Alexander
A1  - Schlappa, Justine
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir N.
A1  - Niklasson, Gunnar A.
A1  - Wallace, Duane C.
A1  - Rubensson, Jan-Erik
A1  - Johansson, Borje
A1  - Ahuja, Rajeev C.
T1  - Unveiling the complex electronic structure of amorphous metal oxides
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - Amorphous materials represent a large and important emerging area of material's science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today's integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5-10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.
KW  - stochastic quench
KW  - X-ray absorption spectroscopy
KW  - ab initio
KW  - coating
Y1  - 2011
U6  - https://doi.org/10.1073/pnas.1019698108
SN  - 0027-8424
VL  - 108
IS  - 16
SP  - 6355
EP  - 6360
PB  - National Acad. of Sciences
CY  - Washington
ER  - 
TY  - THES
A1  - Avila, Gastón
T1  - Asymptotic staticity and tensor decompositions with fast decay conditions
T1  - Asymptotisch statische Anfangsdaten und Tensor-Zerlegungen mit starken Abfallbedingungen
N2  - Corvino, Corvino and Schoen, Chruściel and Delay have shown the existence of a large class of asymptotically flat vacuum initial data for Einstein's field equations which are static or stationary in a neighborhood of space-like infinity, yet quite general in the interior. The proof relies on some abstract, non-constructive arguments which makes it difficult to calculate such data numerically by using similar arguments. A quasilinear elliptic system of equations is presented of which we expect that it can be used to construct vacuum initial data which are asymptotically flat, time-reflection symmetric, and asymptotic to static data up to a prescribed order at space-like infinity. A perturbation argument is used to show the existence of solutions. It is valid when the order at which the solutions approach staticity is restricted to a certain range. Difficulties appear when trying to improve this result to show the existence of solutions that are asymptotically static at higher order. The problems arise from the lack of surjectivity of a certain operator. Some tensor decompositions in asymptotically flat manifolds exhibit some of the difficulties encountered above. The Helmholtz decomposition, which plays a role in the preparation of initial data for the Maxwell equations, is discussed as a model problem. A method to circumvent the difficulties that arise when fast decay rates are required is discussed. This is done in a way that opens the possibility to perform numerical computations. The insights from the analysis of the Helmholtz decomposition are applied to the York decomposition, which is related to that part of the quasilinear system which gives rise to the difficulties. For this decomposition analogous results are obtained. It turns out, however, that in this case the presence of symmetries of the underlying metric leads to certain complications. The question, whether the results obtained so far can be used again to show by a perturbation argument the existence of vacuum initial data which approach static solutions at infinity at any given order, thus remains open. The answer requires further analysis and perhaps new methods.
N2  - Corvino, Corvino und Schoen als auch Chruściel und Delay haben die Existenz einer grossen Klasse asymptotisch flacher Anfangsdaten für Einsteins Vakuumfeldgleichungen gezeigt, die in einer Umgebung des raumartig Unendlichen statisch oder stationär aber im Inneren der Anfangshyperfläche sehr allgemein sind. Der Beweis beruht zum Teil auf abstrakten, nicht konstruktiven Argumenten, die Schwierigkeiten bereiten, wenn derartige Daten numerisch berechnet werden sollen. In der Arbeit wird ein quasilineares elliptisches Gleichungssystem vorgestellt, von dem wir annehmen, dass es geeignet ist, asymptotisch flache Vakuumanfangsdaten zu berechnen, die zeitreflektionssymmetrisch sind und im raumartig Unendlichen in einer vorgeschriebenen Ordnung asymptotisch zu statischen Daten sind. Mit einem Störungsargument wird ein Existenzsatz bewiesen, der gilt, solange die Ordnung, in welcher die Lösungen asymptotisch statische Lösungen approximieren, in einem gewissen eingeschränkten Bereich liegt. Versucht man, den Gültigkeitsbereich des Satzes zu erweitern, treten Schwierigkeiten auf. Diese hängen damit zusammen, dass ein gewisser Operator nicht mehr surjektiv ist. In einigen Tensorzerlegungen auf asymptotisch flachen Räumen treten ähnliche Probleme auf, wie die oben erwähnten. Die Helmholtzzerlegung, die bei der Bereitstellung von Anfangsdaten für die Maxwellgleichungen eine Rolle spielt, wird als ein Modellfall diskutiert. Es wird eine Methode angegeben, die es erlaubt, die Schwierigkeiten zu umgehen, die auftreten, wenn ein schnelles Abfallverhalten des gesuchten Vektorfeldes im raumartig Unendlichen gefordert wird. Diese Methode gestattet es, solche Felder auch numerisch zu berechnen. Die Einsichten aus der Analyse der Helmholtzzerlegung werden dann auf die Yorkzerlegung angewandt, die in den Teil des quasilinearen Systems eingeht, der Anlass zu den genannten Schwierigkeiten gibt. Für diese Zerlegung ergeben sich analoge Resultate. Es treten allerdings Schwierigkeiten auf, wenn die zu Grunde liegende Metrik Symmetrien aufweist. Die Frage, ob die Ergebnisse, die soweit erhalten wurden, in einem Störungsargument verwendet werden können um die Existenz von Vakuumdaten zu zeigen, die im räumlich Unendlichen in jeder Ordnung statische Daten approximieren, bleibt daher offen. Die Antwort erfordert eine weitergehende Untersuchung und möglicherweise auch neue Methoden.
KW  - Einsteins Feldgleichungen
KW  - Zwangsgleichungen
KW  - Tensor-Zerlegungen
KW  - raumartige Unendliche
KW  - elliptisches Gleichungssystem
KW  - Einstein's field equations
KW  - constraint equations
KW  - tensor decompositions
KW  - space-like infinity
KW  - elliptic systems
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-54046
ER  - 
TY  - JOUR
A1  - Bagnich, Sergey A.
A1  - Unger, Th.
A1  - Jaiser, Frank
A1  - Neher, Dieter
A1  - Thesen, M. W.
A1  - Krüger, H.
T1  - Efficient green electrophosphorescence based on ambipolar nonconjugated polymers evaluation of transport and emission properties
JF  - Journal of applied physics
N2  - New materials for polymer organic light-emitting diodes based on a polymer matrix doped with phosphorescent dyes are presented. The matrix system is based on a polystyrene backbone bearing either electron or hole transporting units at the 4-position of each repeat unit. Random copolymers and polymer blend systems of the homopolymers are prepared, both with 62 wt.% electron transporting and 38 wt.% hole transporting moieties. Adding a green electrophosphorescent dye to the polymer matrix leads to efficient electroluminescence with a maximum current efficiency of 35 cd/A and a maximum external quantum efficiency of up to 10%. The mobilities of electrons and holes in the dye-doped copolymer, as measured by transient electroluminescence, are around 5 x 10(-5) and 5 x 10(-6) cm(2)/Vs, respectively, while the blend of the two homopolymers exhibits slightly lower mobilities of both types of carriers. Despite the pronounced imbalance of charge transport, the device performance is almost entirely limited by the phosphorescence efficiency of the dye, implying balanced flow of holes and electrons into the active region. Also, devices made with either the copolymer or the blend yielded very similar device efficiencies, despite the noticeable difference in electron and hole mobility. It is proposed that electrons are efficiently blocked at the interlayer and that the so-formed space charge assists the balanced injection of holes.
Y1  - 2011
U6  - https://doi.org/10.1063/1.3618681
SN  - 0021-8979
SN  - 1089-7550
VL  - 110
IS  - 3
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - THES
A1  - Barbosa Pfannes, Eva Katharina
T1  - Probing the regulatory mechanisms of the actomyosin system in motile cells
T1  - Erforschung von Regulationsmechanismen des Aktomyosinsystems in bewegliche Zellen
N2  - Actin-based directional motility is important for embryonic development, wound healing, immune responses, and development of tissues. Actin and myosin are essential players in this process that can be subdivided into protrusion, adhesion, and traction. Protrusion is the forward movement of the membrane at the leading edge of the cell. Adhesion is required to enable movement along a substrate, and traction finally leads to the forward movement of the entire cell body, including its organelles. While actin polymerization is the main driving force in cell protrusions, myosin motors lead to the contraction of the cell body. The goal of this work was to study the regulatory mechanisms of the motile machinery by selecting a representative key player for each stage of the signaling process: the regulation of Arp2/3 activity by WASP (actin system), the role of cGMP in myosin II assembly (myosin system), and the influence of phosphoinositide signaling (upstream receptor pathway). The model organism chosen for this work was the social ameba Dictyostelium discoideum, due to the well-established knowledge of its cytoskeletal machinery, the easy handling, and the high motility of its vegetative and starvation developed cells. First, I focused on the dynamics of the actin cytoskeleton by modulating the activity of one of its key players, the Arp2/3 complex. This was achieved using the carbazole derivative Wiskostatin, an inhibitor of the Arp2/3 activator WASP. Cells treated with Wiskostatin adopted a round shape, with no of few pseudopodia. With the help of a microfluidic cell squeezer device, I could show that Wiskostatin treated cells display a reduced mechanical stability, comparable to cells treated with the actin disrupting agent Latrunculin A. Furthermore, the WASP inhibited cells adhere stronger to a surface and show a reduced motility and chemotactic performance. However, the overall F-actin content in the cells was not changed. Confocal microscopy and TIRF microscopy imaging showed that the cells maintained an intact actin cortex. Localized dynamic patches of increased actin polymerization were observed that, however, did not lead to membrane deformation. This indicated that the mechanisms of actin-driven force generation were impaired in Wiskostatin treated cells. It is concluded that in these cells, an altered architecture of the cortical network leads to a reduced overall stiffness of the cell, which is insufficient to support the force generation required for membrane deformation and pseudopod formation. Second, the role of cGMP in myosin II dynamics was investigated. Cyclic GMP is known to regulate the association of myosin II with the cytoskeleton. In Dictyostelium, intracellular cGMP levels increase when cells are exposed to chemoattractants, but also in response to osmotic stress. To study the influence of cyclic GMP on actin and myosin II dynamics, I used the laser-induced photoactivation of a DMACM-caged-Br-cGMP to locally release cGMP inside the cell. My results show that cGMP directly activates the myosin II machinery, but is also able to induce an actin response independently of cAMP receptor activation and signaling. The actin response was observed in both vegetative and developed cells. Possible explanations include cGMP-induced actin polymerization through VASP (vasodilator-stimulated phosphoprotein) or through binding of cGMP to cyclic nucleotide-dependent kinases. Finally, I investigated the role of phosphoinositide signaling using the Polyphosphoinositide-Binding Peptide (PBP10) that binds preferentially to PIP2. Phosphoinositides can recruit actin-binding proteins to defined subcellular sites and alter their activity. Neutrophils, as well as developed Dictyostelium cells produce PIP3 in the plasma membrane at their leading edge in response to an external chemotactic gradient. Although not essential for chemotaxis, phosphoinositides are proposed to act as an internal compass in the cell. When treated with the peptide PBP10, cells became round, with fewer or no pseudopods. PH-CRAC translocation to the membrane still occurs, even at low cAMP stimuli, but cell motility (random and directional) was reduced. My data revealed that the decrease in the pool of available PIP2 in the cell is sufficient to impair cell motility, but enough PIP2 remains so that PIP3 is formed in response to chemoattractant stimuli. My data thus highlights how sensitive cell motility and morphology are to changes in the phosphoinositide signaling. In summary, I have analyzed representative regulatory mechanisms that govern key parts of the motile machinery and characterized their impact on cellular properties including mechanical stability, adhesion and chemotaxis.
N2  - Das Ziel der Arbeit war es, die regulatorischen Mechanismen der Zellmotilität zu untersuchen. Dazu habe ich für jedes Stadium dieses Prozesses einen repräsentativen regulatorischen Schritt ausgewählt und genauer untersucht: Die Regelung des Arp2/3 Komplexes durch WASP (Aktinsystem), die Rolle von cGMP in der Myosin II-Regulation (Myosinsystem) und der Einfluss von Phosphoinositiden im intrazellulären Signalprozess (Rezeptor-Signalweg). Die soziale Amöbe Dictyostelium discoideum wurde als Modellorganismus für diese Arbeiten gewählt. Gründe für diese Wahl waren die bereits vorliegenden detaillierten Kenntnisse über das Zytoskelett dieser Zellen, ihre einfache Handhabbarkeit im Labor, und die hohe Motilität der Zellen im vegetativen und entwickelten Zustand. Als Erstes analysierte ich die Dynamik des Aktin-Zytoskeletts durch Modulation der Aktivität des Arp2/3-Komplexes. Dafür benutzte ich das Carbazol-Derivat Wiskostatin, ein Inhibitor des Arp2/3-Aktivators WASP. Zellen, die mit Wiskostatin behandelt wurden, zeigten eine runde Form mit wenigen oder keinen Pseudopodien. Mit Hilfe des mikrofluidischen cell squeezer device konnte ich zeigen, dass Wiskostatin-behandelte Zellen eine geringere mechanische Stabilität aufweisen, vergleichbar mit Zellen unter dem Einfluss des Aktin-depolymerisierenden Wirkstoffes Latrunculin A. Darüber hinaus zeigen Wiskostatin behandelten Zellen eine erhöhte Substratadhäsion und eine verringerte Motilität und chemotaktische Effizienz. Der F-Aktingehalt der Zelle insgesamt blieb jedoch unverändert. Konfokal- und TIRF-mikroskopische Aufnahmen zeigten, dass die Zellen einen intakten Aktinkortex aufweisen. Es konnten lokalisierte dynamische Regionen erhöhter Aktinpolymerisation beobachtet werden, die jedoch nicht zur Ausbildung von Membrandeformationen führten. Daraus kann man rückschließen, dass die Mechanismen der Krafterzeugung im Aktin-Zytoskelett in WASP-inhibierten Zellen beeinträchtigt sind. Vermutlich liegt in diesen Zellen eine veränderte Mikroarchitektur des kortikalen Netzwerks vor, die zu einer verminderten Steifigkeit der Zelle führt, so dass die zur Bildung von Pseudopodien erforderlichen Kräfte nicht entfaltet werden können. Als Zweites wurde die Rolle von cGMP in der Myosin II-Dynamik untersucht. Es ist bekannt, dass cGMP die Assoziation von Myosin II mit dem Zytoskelett reguliert. In Dictyostelium steigt die intrazelluläre Konzentration von cGMP in Gegenwart von chemoattraktiven Lockstoffen sowie in Antwort auf osmotischen Stress. Um den Einfluss von cGMP auf die Aktin und Myosin II -Dynamik zu untersuchen, benutzte ich laserinduzierte Photoaktivierung von DMACM-caged-Br-cGMP, um cGMP lokal innerhalb der Zelle freizusetzen. Meine Ergebnisse zeigten, dass intrazelluläres cGMP direkt zur Aktivierung von Myosin II führt, jedoch auch Aktinantworten unabhängig vom cAMP-Rezeptorsignalweg induzieren kann. Die Aktinreaktion wurde sowohl in vegetativen als auch in entwickelten Zellen beobachtet. Eine mögliche Erklärung könnte die cGMP-induzierte Aktinpolymerisation über VASP (vasodilator-stimulated phosphoprotein) sein oder über die Bindung von cGMP an Nukleotid-abhängige Proteinkinasen. Als dritten Punkt meiner Arbeit untersuchte ich die Rolle der Phosphoinositide mit Hilfe des Phosphoinositide-bindenden Proteins PBP10, das bevorzugt an PIP2 bindet. Phosphoinositiden können Aktin-bindende Proteine zu definierten subzellulären Orten rekrutieren und ihre Aktivität verändern. Sowohl Neutrophile als auch entwickelte Dictyostelium Zellen produzieren PIP3 in der Plasmamembran an ihrer leading edge in Antwort auf externe Gradienten chemischer Lockstoffe. Obwohl Zellen auch ohne PIP3 chemotaktisches Verhalten zeigen, werden Phosphoinositide im Allgemeinen mit dem inneren chemotaktischen Kompass der Zelle in Verbindung gebracht. Mit dem Peptid PBP10 behandelte Zellen nahmen eine runde Form an, mit wenigen oder keinen Pseudopodien. PH-CRAC -Translokation zur Membran konnte in PBP10-behandelten Zellen selbst bei geringen cAMP-Stimuli weiterhin beobachtet werden. Ungerichtete wie auch gerichtete Zellmotiliät waren jedoch beeinträchtigt. Meine Daten zeigen, dass die Abnahme des PIP2-Pools in der Zelle durch PBP10 ausreicht, um die Zellmotilität zu beeinträchtigen, dass jedoch genug PIP2 erhalten bleibt um in Folge einer Rezeptorstimulation PIP3 zu produzieren. Die Ergebnisse demonstrieren daher, wie empfindlich Zellmotilität und -morphologie gegenüber Modifikationen im Phosphoinositid-Signalweg sind. Zusammenfassend habe ich mehrere repräsentative Beispiele für regulatorische Mechanismen der Zellmotilität untersucht und deren Auswirkung auf Eigenschaften der Zelle wie mechanische Stabilität, Zelladhäsion und Chemotaxis charakterisiert.
KW  - Dictyostelium
KW  - Aktomyosin
KW  - Wiskostatin
KW  - cGMP
KW  - PBP10
KW  - Dictyostelium
KW  - actomyosin
KW  - Wiskostatin
KW  - cGMP
KW  - PBP10
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-57812
ER  - 
TY  - JOUR
A1  - Baumgärtel, Hellmut
T1  - A Characteristic decay semigroup for the resonances of trace class perturbations with analyticity conditions of semibounded hamiltonians
JF  - International journal of theoretical physic
N2  - To asymptotic complete scattering systems {M(+) + V, M(+)} on H(+) := L(2)(R(+), K, d lambda), where M(+) is the multiplication operator on H(+) and V is a trace class operator with analyticity conditions, a decay semigroup is associated such that the spectrum of the generator of this semigroup coincides with the set of all resonances (poles of the analytic continuation of the scattering matrix into the lower half plane across the positive half line), i.e. the decay semigroup yields a "time-dependent" characterization of the resonances. As a counterpart a "spectral characterization" is mentioned which is due to the "eigenvalue-like" properties of resonances.
KW  - Resonances
KW  - Scattering theory
KW  - Lax-Phillips theory
KW  - Decay semigroups
Y1  - 2011
U6  - https://doi.org/10.1007/s10773-010-0533-9
SN  - 0020-7748
VL  - 50
IS  - 7
SP  - 2002
EP  - 2008
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Baushev, Anton N.
T1  - Principal properties of the velocity distribution of dark matter particles on the outskirts of the Solar system
JF  - Monthly notices of the Royal Astronomical Society
N2  - The velocity distribution of the dark matter particles on the outskirts of the Solar system remains unclear. We suggest to determine it using experimentally found properties of the oldest halo objects. Indeed, the oldest halo stars and globular clusters form a collisionless system, as well as dark matter particles do, and they evolved in the same gravitational field. If we accept this analogy, we can show that the velocity distribution of the dark matter particles should be highly anisotropic and have a sharp maximum near upsilon similar to 500 km s(-1). The distribution is totally different from the Maxwell one.
 We analyse the influence of the distribution function on the results of dark matter detection experiments. It is found that the direct detection signal should differ noticeably from the one calculated from the Maxwell distribution with <upsilon > similar or equal to 220 km s(-1), which is conventional for direct detection experiments (the ratio depends on the detector properties and typically falls within the range between 6 and 0.2). Moreover, the sharp distinction from the Maxwell distribution can be very essential to the observations of dark matter annihilation.
KW  - elementary particles
KW  - methods: analytical
KW  - dark matter
Y1  - 2011
U6  - https://doi.org/10.1111/j.1745-3933.2011.01125.x
SN  - 0035-8711
VL  - 417
IS  - 1
SP  - L83
EP  - L87
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Belova, Valentina
A1  - Shchukin, Dmitry G.
A1  - Gorin, Dmitry A.
A1  - Kopyshev, Alexey
A1  - Moehwald, Helmuth
T1  - A new approach to nucleation of cavitation bubbles at chemically modified surfaces
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm (2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation.
Y1  - 2011
U6  - https://doi.org/10.1039/c1cp20218a
SN  - 1463-9076
VL  - 13
IS  - 17
SP  - 8015
EP  - 8023
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Berenstein, Igal
A1  - Beta, Carsten
T1  - Flow-induced control of chemical turbulence
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - We report spatiotemporal chaos in the Oregonator model of the Belousov-Zhabotinsky reaction. Spatiotemporal chaos spontaneously develops in a regime, where the underlying local dynamics show stable limit cycle oscillations (diffusion-induced turbulence). We show that spatiotemporal chaos can be suppressed by a unidirectional flow in the system. With increasing flow velocity, we observe a transition scenario from spatiotemporal chaos via a regime of travelling waves to a stationary steady state. At large flow velocities, we recover the known regime of flow distributed oscillations.
KW  - chaos
KW  - chemical equilibrium
KW  - chemically reactive flow
KW  - reaction kinetics theory
KW  - spatiotemporal phenomena
KW  - turbulence
Y1  - 2011
U6  - https://doi.org/10.1063/1.3656248
SN  - 0021-9606
VL  - 135
IS  - 16
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - THES
A1  - Bergner, André
T1  - Synchronization in complex systems with multiple time scales
T1  - Synchronisation in komplexen Systemen mit mehreren Zeitskalen
N2  - In the present work synchronization phenomena in complex dynamical systems exhibiting multiple time scales have been analyzed. Multiple time scales can be active in different manners. Three different systems have been analyzed with different methods from data analysis. The first system studied is a large heterogenous network of bursting neurons, that is a system with two predominant time scales, the fast firing of action potentials (spikes) and the burst of repetitive spikes followed by a quiescent phase. This system has been integrated numerically and analyzed with methods based on recurrence in phase space. An interesting result are the different transitions to synchrony found in the two distinct time scales. Moreover, an anomalous synchronization effect can be observed in the fast time scale, i.e. there is range of the coupling strength where desynchronization occurs. The second system analyzed, numerically as well as experimentally, is a pair of coupled CO₂ lasers in a chaotic bursting regime. This system is interesting due to its similarity with epidemic models. We explain the bursts by different time scales generated from unstable periodic orbits embedded in the chaotic attractor and perform a synchronization analysis of these different orbits utilizing the continuous wavelet transform. We find a diverse route to synchrony of these different observed time scales. The last system studied is a small network motif of limit cycle oscillators. Precisely, we have studied a hub motif, which serves as elementary building block for scale-free networks, a type of network found in many real world applications. These hubs are of special importance for communication and information transfer in complex networks. Here, a detailed study on the mechanism of synchronization in oscillatory networks with a broad frequency distribution has been carried out. In particular, we find a remote synchronization of nodes in the network which are not directly coupled. We also explain the responsible mechanism and its limitations and constraints. Further we derive an analytic expression for it and show that information transmission in pure phase oscillators, such as the Kuramoto type, is limited. In addition to the numerical and analytic analysis an experiment consisting of electrical circuits has been designed. The obtained results confirm the former findings.
N2  - In der vorliegenden Arbeit wurden Synchronisationsphänomene in komplexen Systemen mit mehreren Zeitskalen untersucht. Es gibt mehrere Möglichkeiten wie diese verschiedenen Zeitskalen vorkommen können. Drei verschiedene Systeme, jedes mit einer anderen Art von zeitlicher Multiskalität, wurden mit unterschiedlichen Methoden der Datenanalyse untersucht. Das erste untersuchte System ist ein ausgedehntes heterogenes Netzwerk von Neuronen mit zwei dominanten Zeitskalen, zum einen die schnelle Folge von Aktionspotenzialen und zum anderen einer abwechselnden Folge von einer Phase von Aktionspotenzialen und einer Ruhephase. Dieses System wurde numerisch integriert und mit Methoden der Phasenraumrekurrenz untersucht. Ein interessantes Ergebnis ist der unterschiedliche Übergang zur Synchronisation der Neuronen auf den beiden verschiedenen Zeitskalen. Des weiteren kann auf der schnellen Zeitskala eine anomale Synchronisation beobachtet werden, d.h. es gibt einen Bereich der Kopplungsstärke in dem es zu einer Desynchronisation kommt. Als zweites wurde, sowohl numerisch als auch experimentell, ein System von gekoppelten CO₂ Lasern untersucht, welche in einem chaotischen bursting Modus arbeiten. Dieses System ist auch durch seine Äquivalenz zu Epidemiemodellen interessant. Wir erklären die Bursts durch unterschiedliche Zeitskalen, welche durch in den chaotischen Attraktor eingebettete instabile periodische Orbits generiert werden. Wir führen eine Synchronisationsanalyse mit Hilfe der kontinuierlichen Wavelettransformation durch und finden einen unterschiedlichen Übergang zur Synchronisation auf den unterschiedlichen Zeitskalen. Das dritte analysierte System ist ein Netzwerkmotiv von Grenzzyklusoszillatoren. Genauer handelt es sich um ein Nabenmotiv, welches einen elementaren Grundbaustein von skalenfreien Netzwerken darstellt, das sind Netzwerke die eine bedeutende Rolle in vielen realen Anwendungen spielen. Diese Naben sind von besonderer Bedeutung für die Kommunikation und den Informationstransport in komplexen Netzwerken. Hierbei wurde eine detaillierte Untersuchung des Synchronisationsmechanismus in oszillatorischen Netzwerken mit einer breiten Frequenzverteilung durchgeführt. Insbesondere beobachten wir eine Fernsynchronisation von Netzwerkknoten, die nur indirekt über andere Oszillatoren miteinander gekoppelt sind. Wir erklären den zu Grunde liegenden Mechanismus und zeigen dessen Grenzen und Bedingungen auf. Des weiteren leiten wir einen analytischen Ausdruck für den Mechanismus her und zeigen, dass eine Informationsübertragung in reinen Phasenoszillatoren, wie beispielsweise vom Kuramototyp, eingeschränkt ist. Diese Ergebnisse konnten wir durch Experimente mit elektrischen Schaltkreisen bestätigen.
KW  - Komplexe Systeme
KW  - Synchronisation
KW  - Nichtlineare Dynamik
KW  - Datenanalyse
KW  - complex systems
KW  - synchronization
KW  - nonlinear dynamics
KW  - data analysis
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53407
ER  - 
TY  - JOUR
A1  - Beta, Carsten
A1  - Bodenschatz, Eberhard
T1  - Microfluidic tools for quantitative studies of eukaryotic chemotaxis
JF  - European journal of cell biology
N2  - Over the past decade, microfluidic techniques have been established as a versatile platform to perform live cell experiments under well-controlled conditions. To investigate the directional responses of cells, stable concentration profiles of chemotactic factors can be generated in microfluidic gradient mixers that provide a high degree of spatial control. However, the times for built-up and switching of gradient profiles are in general too slow to resolve the intracellular protein translocation events of directional sensing of eukaryotes. Here, we review an example of a conventional microfluidic gradient mixer as well as the novel flow photolysis technique that achieves an increased temporal resolution by combining the photo-activation of caged compounds with the advantages of microfluidic chambers.
KW  - Eukaryotic chemotaxis
KW  - Dictyostelium discoideum
KW  - Microfluidics
KW  - Caged compounds
KW  - Numerical simulations
Y1  - 2011
U6  - https://doi.org/10.1016/j.ejcb.2011.05.006
SN  - 0171-9335
VL  - 90
IS  - 10
SP  - 811
EP  - 816
PB  - Elsevier
CY  - Jena
ER  - 
TY  - JOUR
A1  - Beye, Martin
A1  - Föhlisch, Alexander
T1  - A soft X-ray approach to electron-phonon interactions beyond the Born-Oppenheimer approximation
JF  - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
N2  - With modern soft X-ray methods, the whole field of electron-phonon interactions becomes accessible directly in the ultrafast time domain with ultrashort pulsed X-ray sources, as well as in the energy domain through modern highly resolving spectrometers. The well-known core-hole clock approach plays an intermediate role, resolving energetic and temporal features at the same time. In this perspective paper, we review several experiments to illustrate the modern advances in the selective study of electron-phonon interactions as fundamentally determining ingredients for materials properties. We present the different complementary approaches that can be taken with soft X-ray methods to conquer this field beyond the Born-Oppenheimer approximation.
KW  - Electron-phonon coupling
KW  - Resonant inelastic X-ray scattering
KW  - X-ray emission spectroscopy
KW  - Near edge X-ray absorption fine structure
Y1  - 2011
U6  - https://doi.org/10.1016/j.elspec.2010.12.032
SN  - 0368-2048
VL  - 184
IS  - 3-6
SP  - 313
EP  - 317
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - THES
A1  - Bierbaum, Veronika
T1  - Chemomechanical coupling and motor cycles of the molecular motor myosin V
T1  - Chemomechanische Kopplung und Motorzyklen für den molekularen Motor Myosin V
N2  - In the living cell, the organization of the complex internal structure relies to a large extent on molecular motors. Molecular motors are proteins that are able to convert chemical energy from the hydrolysis of adenosine triphosphate (ATP) into mechanical work. Being about 10 to 100 nanometers in size, the molecules act on a length scale, for which thermal collisions have a considerable impact onto their motion. In this way, they constitute paradigmatic examples of thermodynamic machines out of equilibrium. This study develops a theoretical description for the energy conversion by the molecular motor myosin V, using many different aspects of theoretical physics. Myosin V has been studied extensively in both bulk and single molecule experiments. Its stepping velocity has been characterized as a function of external control parameters such as nucleotide concentration and applied forces. In addition, numerous kinetic rates involved in the enzymatic reaction of the molecule have been determined. For forces that exceed the stall force of the motor, myosin V exhibits a 'ratcheting' behaviour: For loads in the direction of forward stepping, the velocity depends on the concentration of ATP, while for backward loads there is no such influence. Based on the chemical states of the motor, we construct a general network theory that incorporates experimental observations about the stepping behaviour of myosin V. The motor's motion is captured through the network description supplemented by a Markov process to describe the motor dynamics. This approach has the advantage of directly addressing the chemical kinetics of the molecule, and treating the mechanical and chemical processes on equal grounds. We utilize constraints arising from nonequilibrium thermodynamics to determine motor parameters and demonstrate that the motor behaviour is governed by several chemomechanical motor cycles. In addition, we investigate the functional dependence of stepping rates on force by deducing the motor's response to external loads via an appropriate Fokker-Planck equation. For substall forces, the dominant pathway of the motor network is profoundly different from the one for superstall forces, which leads to a stepping behaviour that is in agreement with the experimental observations. The extension of our analysis to Markov processes with absorbing boundaries allows for the calculation of the motor's dwell time distributions. These reveal aspects of the coordination of the motor's heads and contain direct information about the backsteps of the motor. Our theory provides a unified description for the myosin V motor as studied in single motor experiments.
N2  - Die hier vorgelegte Arbeit entwickelt unter Verwendung vieler verschiedener Aspekte der statistischen Physik eine Theorie der chemomechanischen Kopplung für den Energieumsatz des molekularen Motors Myosin V. Das Myosin V ist sowohl in chemokinetischen wie in Einzelmolekülexperimenten grundlegend untersucht worden. Seine Schrittgeschwindigkeit ist in Abhängigkeit verschiedener externer Parameter, wie der Nukleotidkonzentration und einer äußeren Kraft, experimentell bestimmt. Darüber hinaus ist eine große Anzahl verschiedener chemokinetischer Raten, die an der enzymatischen Reaktion des Moleküls beteiligt sind, quantitativ erfasst. Unter der Wirkung externer Kräfte, die seine Anhaltekraft überschreiten, verhält sich der Motor wie eine Ratsche: Für Kräfte, die entlang der Schrittbewegung des Motors wirken, hängt seine Geschwindigkeit von der ATP-Konzentration ab, für rückwärts angreifende Kräfte jedoch ist die Bewegung des Motors unabhängig von ATP. Auf der Grundlage der chemischen Zustände des Motors wird eine Netzwerktheorie aufgebaut, die die experimentellen Beobachtungen des Schrittverhaltens für Myosin V einschließt. Diese Netzwerkbeschreibung dient als Grundlage für einen Markovprozess, der die Dynamik des Motors beschreibt. Die Verwendung diskreter Zustände bietet den Vorteil der direkten Erfassung der chemischen Kinetik des Moleküls. Darüber hinaus werden chemische und mechanische Eigenschaften des Motors in gleichem Maße im Modell berücksichtigt. Durch die Erfassung der Enzymkinetik mittels eines stochastischen Prozesses lässt sich die Motordynamik mit Hilfe des stationären Zustands der Netzwerkdarstellung beschreiben. Um diesen zu bestimmen, verwenden wir eine graphentheoretische Methode, die auf Kirchhoff zurückgreift. Wir zeigen in Einklang mit den Gesetzen der Thermodynamik für Nichtgleichgewichtssysteme, dass das Schrittverhalten des Motors von mehreren chemomechanischen Zyklen beeinflusst wird. Weiterhin untersuchen wir das funktionale Verhalten mechanischer Schrittraten in Abhängigkeit der äußeren Kraft unter Verwendung einer geeigneten Fokker-Planck-Gleichung. Hierfür wird auf die Theorie einer kontinuierlichen Beschreibung von molekularen Methoden zurückgegriffen. Wir berechnen Größen wie die mittlere Schrittgeschwindigkeit, das Verhältnis von Vorwärts- und Rückwärtsschritten, und die Lauflänge des Motors in Abhängigkeit einer äußeren angreifenden Kraft sowie der Nukleotidkonzentration, und vergleichen diese mit experimentellen Daten. Für Kräfte, die kleiner als die Anhaltekraft des Motors sind, unterscheidet sich der chemomechanische Zyklus grundlegend von demjenigen, der für große Kräfte dominiert. Diese Eigenschaft resultiert in einem Schrittverhalten, das mit den experimentellen Beobachtungen übereinstimmt. Es ermöglicht weiterhin die Zerlegung des Netzwerks in einzelne Zyklen, die die Bewegung des Motors für verschiedene Bereiche externer Kräfte erfassen. Durch die Erweiterung unseres Modells auf Markovprozesse mit absorbierenden Zuständen können so die Wartezeitenverteilungen für einzelne Zyklen des Motors analytisch berechnet werden. Sie erteilen Aufschluss über die Koordination des Motors und enthalten zudem direkte Informationen über seine Rückwärtsschritte, die experimentell nicht erfasst sind. Für das gesamte Netzwerk werden die Wartezeitenverteilungen mit Hilfe eines Gillespie-Algorithmus bestimmt. Unsere Theorie liefert eine einheitliche Beschreibung der Eigenschaften von Myosin V, die in Einzelmolekülexperimenten erfasst werden können.
KW  - statistische Physik
KW  - Markov-Prozesse
KW  - molekulare Motoren
KW  - statistical physics
KW  - markov processes
KW  - molecular motors
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-53614
ER  - 
TY  - JOUR
A1  - Blaha, Karen A.
A1  - Pikovskij, Arkadij
A1  - Rosenblum, Michael
A1  - Clark, Matthew T.
A1  - Rusin, Craig G.
A1  - Hudson, John L.
T1  - Reconstruction of two-dimensional phase dynamics from experiments on coupled oscillators
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Phase models are a powerful method to quantify the coupled dynamics of nonlinear oscillators from measured data. We use two phase modeling methods to quantify the dynamics of pairs of coupled electrochemical oscillators, based on the phases of the two oscillators independently and the phase difference, respectively. We discuss the benefits of the two-dimensional approach relative to the one-dimensional approach using phase difference. We quantify the dependence of the coupling functions on the coupling magnitude and coupling time delay. We show differences in synchronization predictions of the two models using a toy model. We show that the two-dimensional approach reveals behavior not detected by the one-dimensional model in a driven experimental oscillator. This approach is broadly applicable to quantify interactions between nonlinear oscillators, especially where intrinsic oscillator sensitivity and coupling evolve with time.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevE.84.046201
SN  - 1539-3755
VL  - 84
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Blakesley, James C.
A1  - Neher, Dieter
T1  - Relationship between energetic disorder and open-circuit voltage in bulk heterojunction organic solar cells
JF  - Physical review : B, Condensed matter and materials physics
N2  - We simulate organic bulk heterojunction solar cells. The effects of energetic disorder are incorporated through a Gaussian or exponential model of density of states. Analytical models of open-circuit voltage (V(OC)) are derived from the splitting of quasi-Fermi potentials. Their predictions are backed up by more complex numerical device simulations including effects such as carrier-density-dependent charge-carrier mobilities. It is predicted that the V(OC) depends on: (1) the donor-acceptor energy gap; (2) charge-carrier recombination rates; (3) illumination intensity; (4) the contact work functions (if not in the pinning regime); and (5) the amount of energetic disorder. A large degree of energetic disorder, or a high density of traps, is found to cause significant reductions in V(OC). This can explain why V(OC) is often less than expected in real devices. Energetic disorder also explains the nonideal temperature and intensity dependence of V(OC) and the superbimolecular recombination rates observed in many real bulk heterojunction solar cells.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevB.84.075210
SN  - 1098-0121
VL  - 84
IS  - 7
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Blakesley, James C.
A1  - Schubert, Marcel
A1  - Steyrleuthner, Robert
A1  - Chen, Zhihua
A1  - Facchetti, Antonio
A1  - Neher, Dieter
T1  - Time-of-flight measurements and vertical transport in a high electron-mobility polymer
JF  - Applied physics letters
N2  - We investigate charge transport in a high-electron mobility polymer, poly(N, N-bis 2-octyldodecyl-naphthalene-1,4,5,8-bis dicarboximide-2,6-diyl-alt-5,5-2,2-bithiophene) [P(NDI2OD-T2), Polyera ActivInk (TM) N2200]. Time-of-flight measurements reveal electron mobilities approaching those measured in field-effect transistors, the highest ever recorded in a conjugated polymer using this technique. The modest temperature dependence and weak dispersion of the transients indicate low energetic disorder in this material. Steady-state electron-only current measurements reveal a barrier to injection of about 300 meV. We propose that this barrier is located within the P(NDI2OD-T2) film and arises from molecular orientation effects.
Y1  - 2011
U6  - https://doi.org/10.1063/1.3657827
SN  - 0003-6951
VL  - 99
IS  - 18
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - THES
A1  - Boeche, Corrado
T1  - Chemical gradients in the Milky Way from unsupervised chemical abundances measurements of the RAVE spectroscopic data set
T1  - Chemische Gradienten in der Milchstraße aus unüberwachten chemischen Häufigkeitsmessungen aus dem RAVE spektroskopischen Datenset
N2  - The present thesis was born and evolved within the RAdial Velocity Experiment (RAVE) with the goal of measuring chemical abundances from the RAVE spectra and exploit them to investigate the chemical gradients along the plane of the Galaxy to provide constraints on possible Galactic formation scenarios. RAVE is a large spectroscopic survey which aims to observe spectroscopically ~10^6 stars by the end of 2012 and measures their radial velocities, atmospheric parameters and chemical abundances. The project makes use of the UK Schmidt telescope at Australian Astronomical Observatory (AAO) in Siding Spring, Australia, equipped with the multiobject spectrograph 6dF. To date, RAVE collected and measured more than 450,000 spectra. The precision of the chemical abundance estimations depends on the reliability of the atomic and atmosphere parameters adopted (in particular the oscillator strengths of the absorption lines and the effective temperature, gravity, and metallicity of the stars measured). Therefore we first identified 604 absorption lines in the RAVE wavelength range and refined their oscillator strengths with an inverse spectral analysis. Then, we improved the RAVE stellar parameters by modifying the RAVE pipeline and the spectral library the pipeline rely on. The modifications removed some systematic errors in stellar parameters discovered during this work. To obtain chemical abundances, we developed two different processing pipelines. Both of them perform chemical abundances measurements by assuming stellar atmospheres in Local Thermodynamic Equilibrium (LTE). The first one determines elements abundances from equivalent widths of absorption lines. Since this pipeline showed poor sensibility on abundances relative to iron, it has been superseded. The second one exploits the chi^2 minimization technique between observed and model spectra. Thanks to its precision, it has been adopted for the creation of the RAVE chemical catalogue. This pipeline provides abundances with uncertains of about ~0.2dex for spectra with signal-to-noise ratio S/N>40 and ~0.3dex for spectra with 20>S/N>40. For this work, the pipeline measured chemical abundances up to 7 elements for 217,358 RAVE stars. With these data we investigated the chemical gradients along the Galactic radius of the Milky Way. We found that stars with low vertical velocities |W| (which stay close to the Galactic plane) show an iron abundance gradient in agreement with previous works (~-0.07$ dex kpc^-1) whereas stars with larger |W| which are able to reach larger heights above the Galactic plane, show progressively flatter gradients. The gradients of the other elements follow the same trend. This suggests that an efficient radial mixing acts in the Galaxy or that the thick disk formed from homogeneous interstellar matter. In particular, we found hundreds of stars which can be kinetically classified as thick disk stars exhibiting a chemical composition typical of the thin disk. A few stars of this kind have already been detected by other authors, and their origin is still not clear. One possibility is that they are thin disk stars kinematically heated, and then underwent an efficient radial mixing process which blurred (and so flattened) the gradient. Alternatively they may be a transition population" which represents an evolutionary bridge between thin and thick disk. Our analysis shows that the two explanations are not mutually exclusive. Future follow-up high resolution spectroscopic observations will clarify their role in the Galactic disk evolution.
N2  - Die vorliegende Doktorarbeit wurde im Rahmen des RAdial Velocity Experiment (RAVE) angefertigt. Ihr Ziel ist es, chemische Elementhäufigkeiten an RAVE-Spektren zu messen und zur Untersuchung chemischer Gradienten in der Milchstrassenebene zu benutzen, um verschieden Szenarien der Galaxienentstehung einzugrenzen. RAVE ist eine große spektrokopische Durchmusterung, deren Ziel es ist, bis zum Ende des Jahres 2012 insgesamt 10^6 Sterne zu spektroskopieren, um deren Radialgeschwindigkeiten, sternatmosphärische Parameter und chemische Häufigkeiten zu messen. Das Projekt benutzt das UK Schmidt Teleskop am Australian Astronomical Observatory (AAO) in Siding Spring, Australien, welches mit dem Multiobjekt-Spektrographen 6dF bestückt ist. Bis heute hat RAVE die Spektren von mehr als 450,000 Sternen gesammelt und untersucht. Die Genauigkeit, mit der die Elementhäufigkeiten abgeschätzt werden können, hängt von der Zuverlässigkeit der verwendeten Parameter, (insbesondere der Oszillatorstärken der Absorptionslinien sowie von der effektiven Temperatur, Schwerebeschleunigung und der Metallizität des gemessenen Sterns) ab. Daher identifizierten wir zunächst 604 Absorptionslinien im Wellenlängenbereich von RAVE und verbesserten deren Oszillatorstärken durch eine inverse Spektralanalyse. Dann wurden die stellaren Parameter von RAVE verbessert, indem die RAVE Pipeline und die stellaren Parameter, auf denen sie beruht, modifiziert wurden. Die Änderungen eliminierten einen Teil der systematischen Fehler von stellaren Parametern, die im Laufe dieser Arbeit gefunden wurden. Um Elementhäufigkeiten zu bestimmen, haben wir zwei verschiedene Prozessierungs-Pipelines entwickelt. Beide berechnen die Elementhäufigkeiten unter der Annahme von Sternatmosphären im lokalen thermischen Gleichgewicht (local thermal equilibrium, LTE). Die erste Pipeline berechnete Elemenhäufigkeiten anhand der Äquivalentbreiten von Absorptionslinien. Da diese Methode eine geringe Empfindlichkeit für die Elementhäufigeiten relativ zu Eisen erreichte, wurde sie ersetzt. Die neue Pipeline benutzt chi^2-Fits von Modellspektren an die beobachteten Spektren. Dank Ihrer Präzision wurde diese für die Erstellung des RAVE-Katalogs von Elementhäufigkeiten verwendet. Diese Pipeline liefert Elementhäufigkeiten mit einer Genauigkeit von ~0.2dex, während für Spektren mit 20>S/N>40 immerhin noch ~0.3dex Genauigkeit erreicht werden. Für die vorliegende Arbeit wurden für 217.358 Sterne die Häufigkeiten von sieben chemischen Elementen bestimmt. Mit diesen Daten wurde der radiale chemische Gradient unserer Milchstraße untersucht. Wir finden, dass Sterne mit kleinen vertikalen Geschwindigkeiten |W|, die also nahe der galaktischen Ebene bleiben, einen radialen Gradienten der Eisenhäufigkeit zeigen, der mit früheren Studien übereinstimmt (~-0.07 dex Kpc^-1), während Sterne mit großen |W|, also solche, die größere galaktische Höhen erreichen, einen progressiv flachere Gradienten zeigen. Die Gradienten der anderen Element folgen dem gleichen Trend. Das lässt darauf schließen, dass entweder die Durchmischung der galaktischen dicken Scheibe effizient arbeitet oder aber dass die dicke Scheibe aus interstellarer Materie gebildet wurde, die chemisch recht homogen war. Speziell fanden wir hunderte von Sternen, die zwar kinematisch als zur dicken Scheibe zugehörig klassifiziert werden können, die aber die typische chemische Zusammensetzung der dünnen Scheibe aufweisen. Einige wenige dieser Sterne wurden bereits von anderen Autoren entdeckt, aber ihre Herkunft bleibt immer noch unklar. Eine Möglichkeit ist, dass die Sterne der dünnen Scheibe kinematische geheizt werden, sodass sie effizienter radial gemischt werden, was die chemischen Gradienten verwischt und auch flacher macht. Alternativ dazu könnten diese Sterne einer "Übergangspopulation" angehören, welche hinsichtlich der Scheibenevolution die Verbindung zwischen der dünnen und der dicken Scheibe darstellt. Unsere Untersuchung zeigt, dass sich diese beiden Erklärungen gegenseitig nicht ausschließen. Künftige Nachspektroskopierung mit hoher Auflösung wird die Rolle dieser Sterne in der Entwicklungsgeschichte der galaktischen Scheibe aufklären.
KW  - Galaxie
KW  - Milchstraße
KW  - Spektroskopie
KW  - chemische Häufigkeiten
KW  - Galaxy
KW  - Milky Way
KW  - Spectroscopy
KW  - Chemical Abundances
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-52478
ER  - 
TY  - JOUR
A1  - Brandao, F. G. S. L.
A1  - Eisert, Jens
A1  - Horodecki, M.
A1  - Yang, Dong
T1  - Entangled inputs cannot make imperfect quantum channels perfect
JF  - Physical review letters
N2  - Entangled inputs can enhance the capacity of quantum channels, this being one of the consequences of the celebrated result showing the nonadditivity of several quantities relevant for quantum information science. In this work, we answer the converse question (whether entangled inputs can ever render noisy quantum channels to have maximum capacity) to the negative: No sophisticated entangled input of any quantum channel can ever enhance the capacity to the maximum possible value, a result that holds true for all channels both for the classical as well as the quantum capacity. This result can hence be seen as a bound as to how "nonadditive quantum information can be.'' As a main result, we find first practical and remarkably simple computable single-shot bounds to capacities, related to entanglement measures. As examples, we discuss the qubit amplitude damping and identify the first meaningful bound for its classical capacity.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevLett.106.230502
SN  - 0031-9007
VL  - 106
IS  - 23
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - BOOK
A1  - Brehmer, Ludwig
T1  - Die Brandeburgische Landeshochschule zu Potsdam im Jahre eins : die Hochschule in Potsdamer Schulen ; Daten und Fakten ; Kommentare und Dokumente
Y1  - 2011
SN  - 978-3-00-034135-9
VL  - 4
PB  - Eigenverl. des Verf
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Burylko, Oleksandr
A1  - Pikovskij, Arkadij
T1  - Desynchronization transitions in nonlinearly coupled phase oscillators
JF  - Physica :D, Nonlinear phenomena
N2  - We consider the nonlinear extension of the Kuramoto model of globally coupled phase oscillators where the phase shift in the coupling function depends on the order parameter. A bifurcation analysis of the transition from fully synchronous state to partial synchrony is performed. We demonstrate that for small ensembles it is typically mediated by stable cluster states, that disappear with creation of heteroclinic cycles, while for a larger number of oscillators a direct transition from full synchrony to a periodic or a quasiperiodic regime occurs.
KW  - Coupled oscillators
KW  - Oscillator ensembles
KW  - Kuramoto model
KW  - Nonlinear coupling
KW  - Bifurcations
Y1  - 2011
U6  - https://doi.org/10.1016/j.physd.2011.05.016
SN  - 0167-2789
VL  - 240
IS  - 17
SP  - 1352
EP  - 1361
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Campbell, Earl T.
T1  - Catalysis and activation of magic states in fault-tolerant architectures
JF  - Physical review : A, Atomic, molecular, and optical physics
N2  - In many architectures for fault-tolerant quantum computing universality is achieved by a combination of Clifford group unitary operators and preparation of suitable nonstabilizer states, the so-called magic states. Universality is possible even for some fairly noisy nonstabilizer states, as distillation can convert many noisy copies into fewer purer magic states. Here we propose protocols that exploit multiple species of magic states in surprising ways. These protocols provide examples of previously unobserved phenomena that are analogous to catalysis and activation well known in entanglement theory.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevA.83.032317
SN  - 1050-2947
VL  - 83
IS  - 3
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Cockburn, S. P.
A1  - Negretti, Antonio
A1  - Proukakis, N. P.
A1  - Henkel, Carsten
T1  - Comparison between microscopic methods for finite-temperature Bose gases
JF  - Physical review : A, Atomic, molecular, and optical physics
N2  - We analyze the equilibrium properties of a weakly interacting, trapped quasi-one-dimensional Bose gas at finite temperatures and compare different theoretical approaches. We focus in particular on two stochastic theories: a number-conserving Bogoliubov (NCB) approach and a stochastic Gross-Pitaevskii equation (SGPE) that have been extensively used in numerical simulations. Equilibrium properties like density profiles, correlation functions, and the condensate statistics are compared to predictions based upon a number of alternative theories. We find that due to thermal phase fluctuations, and the corresponding condensate depletion, the NCB approach loses its validity at relatively low temperatures. This can be attributed to the change in the Bogoliubov spectrum, as the condensate gets thermally depleted, and to large fluctuations beyond perturbation theory. Although the two stochastic theories are built on different thermodynamic ensembles (NCB, canonical; SGPE, grand-canonical), they yield the correct condensate statistics in a large Bose-Einstein condensate (BEC) (strong enough particle interactions). For smaller systems, the SGPE results are prone to anomalously large number fluctuations, well known for the grand-canonical, ideal Bose gas. Based on the comparison of the above theories to the modified Popov approach, we propose a simple procedure for approximately extracting the Penrose-Onsager condensate from first-and second-order correlation functions that is both computationally convenient and of potential use to experimentalists. This also clarifies the link between condensate and quasicondensate in the Popov theory of low-dimensional systems.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevA.83.043619
SN  - 1050-2947
SN  - 1094-1622
VL  - 83
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Delahaye, T.
A1  - Fiasson, A.
A1  - Pohl, Martin
A1  - Salati, P.
T1  - The GeV-TeV Galactic gamma-ray diffuse emission I. Uncertainties in the predictions of the hadronic component
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. The Galactic gamma-ray diffuse emission is currently observed in the GeV-TeV energy range with unprecedented accuracy by the Fermi satellite. Understanding this component is crucial because it provides a background to many different signals, such as extragalactic sources or annihilating dark matter. It is timely to reinvestigate how it is calculated and to assess the various uncertainties that are likely to affect the accuracy of the predictions.
 Aims. The Galactic gamma-ray diffuse emission is mostly produced above a few GeV by the interactions of cosmic ray primaries impinging on the interstellar material. The theoretical error on that component is derived by exploring various potential sources of uncertainty. Particular attention is paid to cosmic ray propagation. Nuclear cross sections, the proton and helium fluxes at the Earth's position, the Galactic radial profile of supernova remnants, and the hydrogen distribution can also severely affect the signal.
 Methods. The propagation of cosmic ray species throughout the Galaxy is described in the framework of a semi-analytic two-zone diffusion/convection model. The gamma-ray flux is reliably and quickly determined. This allows conversion of the constraints set by the boron-to-carbon data into a theoretical uncertainty on the diffuse emission. New deconvolutions of the HI and CO sky maps are also used to get the hydrogen distribution within the Galaxy.
 Results. The thickness of the cosmic ray diffusive halo is found to have a significant effect on the Galactic gamma-ray diffuse emission, while the interplay between diffusion and convection has little influence on the signal. The uncertainties related to nuclear cross sections and to the primary cosmic ray fluxes at the Earth are significant. The radial distribution of supernova remnants along the Galactic plane turns out to be a key ingredient. As expected, the predictions are extremely sensitive to the spatial distribution of hydrogen within the Milky Way.
 Conclusions. Most of the sources of uncertainty are likely to be reduced in the near future. The stress should be put (i) on better determination of the thickness of the cosmic ray diffusive halo; and (ii) on refined observations of the radial profile of supernova remnants.
KW  - gamma rays: diffuse background
KW  - cosmic rays
KW  - methods: analytical
KW  - gamma rays: ISM
Y1  - 2011
U6  - https://doi.org/10.1051/0004-6361/201116647
SN  - 0004-6361
VL  - 531
IS  - 4
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - DiGuglielmo, J.
A1  - Samblowski, A.
A1  - Hage, B.
A1  - Pineda, Carlos
A1  - Eisert, Jens
A1  - Schnabel, R.
T1  - Experimental Unconditional Preparation and Detection of a Continuous Bound Entangled State of Light
JF  - Physical review letters
N2  - Among the possibly most intriguing aspects of quantum entanglement is that it comes in free and bound instances. The existence of bound entangled states certifies an intrinsic irreversibility of entanglement in nature and suggests a connection with thermodynamics. In this Letter, we present a first unconditional, continuous-variable preparation and detection of a bound entangled state of light. We use convex optimization to identify regimes rendering its bound character well certifiable, and continuously produce a distributed bound entangled state with an extraordinary and unprecedented significance of more than 10 standard deviations away from both separability and distillability. Our results show that the approach chosen allows for the efficient and precise preparation of multimode entangled states of light with various applications in quantum information, quantum state engineering, and high precision metrology.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevLett.107.240503
SN  - 0031-9007
VL  - 107
IS  - 24
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Donges, Jonathan
A1  - Donner, Reik Volker
A1  - Trauth, Martin H.
A1  - Marwan, Norbert
A1  - Schellnhuber, Hans Joachim
A1  - Kurths, Jürgen
T1  - Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - Potential paleoclimatic driving mechanisms acting on human evolution present an open problem of cross-disciplinary scientific interest. The analysis of paleoclimate archives encoding the environmental variability in East Africa during the past 5 Ma has triggered an ongoing debate about possible candidate processes and evolutionary mechanisms. In this work, we apply a nonlinear statistical technique, recurrence network analysis, to three distinct marine records of terrigenous dust flux. Our method enables us to identify three epochs with transitions between qualitatively different types of environmental variability in North and East Africa during the (i) Middle Pliocene (3.35-3.15 Ma B. P.), (ii) Early Pleistocene (2.25-1.6 Ma B. P.), and (iii) Middle Pleistocene (1.1-0.7 Ma B. P.). A deeper examination of these transition periods reveals potential climatic drivers, including (i) large-scale changes in ocean currents due to a spatial shift of the Indonesian throughflow in combination with an intensification of Northern Hemisphere glaciation, (ii) a global reorganization of the atmospheric Walker circulation induced in the tropical Pacific and Indian Ocean, and (iii) shifts in the dominating temporal variability pattern of glacial activity during the Middle Pleistocene, respectively. A reexamination of the available fossil record demonstrates statistically significant coincidences between the detected transition periods and major steps in hominin evolution. This result suggests that the observed shifts between more regular and more erratic environmental variability may have acted as a trigger for rapid change in the development of humankind in Africa.
KW  - African climate
KW  - Plio-Pleistocene
KW  - climate-driven evolution
KW  - dynamical transitions
KW  - nonlinear time series analysis
Y1  - 2011
U6  - https://doi.org/10.1073/pnas.1117052108
SN  - 0027-8424
VL  - 108
IS  - 51
SP  - 20422
EP  - 20427
PB  - National Acad. of Sciences
CY  - Washington
ER  - 
TY  - THES
A1  - Dosche, Carsten
T1  - Funktionale Farbstoffe und ihre Photophysik und Anwendung in komplexen Matrizes
Y1  - 2011
CY  - Potsdam
ER  - 
TY  - JOUR
A1  - Douce, Laurent
A1  - Suisse, Jean-Moise
A1  - Guillon, Daniel
A1  - Taubert, Andreas
T1  - Imidazolium-based liquid crystals a modular platform for versatile new materials with finely tuneable properties and behaviour
JF  - Liquid crystals : an international journal of science and technology
N2  - Ionic liquid Crystals constitute highly versatile materials that have drawn much interest these past few years in the fields of academic research and industrial development. In this respect, the present article is intended as an update of K. Binnemans review published in 2005, but focusing exclusively on the imidazolium cation - the most widely studied. Herein, imidazolium-containing thermotropic liquid crystalline materials will be sorted by molecular structure (mono-, bis-, poly-imidazolium compounds, with symmetrical and non-symmetrical structures) and discussed. Their physico-chemical properties will be exposed in order to adduce the relevancy and potential of the imidazolium platform in various fields of research.
KW  - imidazolium
KW  - liquid crystal
KW  - ionic liquid
Y1  - 2011
U6  - https://doi.org/10.1080/02678292.2011.610474
SN  - 0267-8292
VL  - 38
IS  - 11-12
SP  - 1653
EP  - 1661
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - THES
A1  - Döring, Sebastian
T1  - Oberflächengitter in azobenzenhaltigen Schichten für organische DFB-Laser
T1  - Surface relief gratings in azobenzene containing layers for organic DFB lasers
N2  - Ein neuentwickeltes azobenzenhaltiges Material, das auf einem supramolekularen Konzept basiert, wird bezüglich seiner Strukturbildung während einer holografischen Belichtung bei 488 nm untersucht. Im Mittelpunkt stehen dabei eindimensionale, sinusförmige Reliefs mit Periodizitäten kleiner 500 nm. Es wird gezeigt, wie der Grad der Vernetzung der photosensitiven Schicht die Strukturbildung in diesem Größenbereich beeinflusst. Zur Maximierung der Strukturtiefe werden gezielt Prozessparameter der Belichtung sowie Materialparameter variiert. Unter Standardbedingungen und moderaten Belichtungsintensitäten von ca. 200 mW/cm² bilden sich innerhalb weniger Minuten bei einer Periode von 400 nm Strukturtiefen von bis zu 80nm aus. Durch die Beeinflussung von Materialparametern, wie Oberflächenspannung und Viskosität, wird die maximale Strukturtiefe auf 160nm verdoppelt. Durch Mehrfachbelichtungen wird auch die Bildung von zweidimensionalen Gittern untersucht. Die Originalstrukturen werden in einem Abformverfahren kopiert und in Schichten von unter UV-Licht aushärtenden Polymeren übertragen. Durch das Abformen kommt es zu einer geringfügigen Verschlechterung der Oberflächenqualität sowie Abnahme der Strukturtiefe. Dieser Verlust wird durch eine Verringerung der Prozesstemperatur verringert. Mithilfe kopierter Oberflächengitter werden organische Distributed Feedback-(DFB)-Laser zweiter Ordnung hergestellt, um den Einfluss von Gitterparametern auf die Emissionseigenschaften dieser Laser zu untersuchen. Dazu erfolgt zunächst die Charakterisierung der optischen Verstärkungseigenschaften ausgewählter organischer Emittermaterialien mittels der Variablen Strichlängenmethode. Das mit dem Laserfarbstoff Pyrromthen567 (PM567) dotierte Polystyrol (PS) zeigt dabei trotz konzentrationsbedingter geringer Absorption eine vergleichsweise geringe Gewinnschwelle von 50µJ/cm² bei ca. 575 nm. Das aktive Gast-Wirt-System der konjugierten Polymere MEH-PPV und F8BT* weist eine hohe Absorption und eine kleine Gewinnschwelle von 2,5 µJ/cm² bei 630 nm auf. Dieses Verhalten spiegelt sich auch in den Emissionseigenschaften der damit hergestellten DFB-Laser wieder. Die Dicke der aktiven Schichten liegen im Bereich hunderter Nanometer und wird so eingestellt, dass sich nur die transversalen Grundmoden im Wellenleiter ausbreiten können. Die Gitterperiode sind so gewählt, dass ein Lichtmode im Verstärkungsbereich des Emittermaterials liegt. Die Emissionslinien der Laser sind mit FWHM-Werten von bis zu 0,3 nm spektral sehr schmalbandig und weisen auf eine sehr gute Gitterqualität hin. Die Untersuchungen liefern minimale Laserschwellen und maximale differentielle Effizienzen von 4,0µJ/cm² und 8,4% für MEH-PPV in F8BT* (bei ca. 640nm) sowie 80 µJ/cm² und 0,9% für PM567 in PS (bei ca. 575 nm). Die Vergrößerung der Strukturtiefe von 40nm auf 80nm in mit MEH-PPV dotierten F8BT*-Lasern zu einem deutlichen Anstieg der ausgekoppelten Energie sowie der differentiellen Effizienz und einem geringen Absinken der Laserschwelle. Dies ist ein Resultat der erhöhten Kopplung von Lasermode und Gitter. Die Emission von DFB-Lasern mit zweidimensionalen Oberflächengittern zeigen eine Verringerung der Divergenz aber kein Einfluss auf die Laserschwelle. Abschließend erfolgt eine Vermessung der Photostabilität von DFB-Lasern unter verschiedenen Bedingungen. Das Einbringen eines konjugierten Polymers in eine aktive Matrix sowie der Betrieb in einer Stickstoffatmosphäre führen dabei zu einer Erhöhung der Lebensdauer auf über eine Million Pulse. Durch die Kombination von Oberflächengittern in PDMS-Filmen mit elektroaktiven Substraten wird eine elektrisch steuerbare Deformation des Beugungsgitters erreicht und auf einen DFB-Laser übertragen. Die spannungsinduzierte Verformung wird zunächst in Beugungsexperimenten charakterisiert und ein optimaler Arbeitspunkt bestimmt. Mit den beiden Elastomeren SEBS12 und VHB4910 werden in den Gittern maximale Periodenänderungen von 1,3% bzw. 3,4% bei einer Steuerspannung von 2 kV erreicht. Der Unterschied resultiert aus den verschiedenen Elastizitätsmoduln der Materialien. Übertragen auf DFB-Laser resultiert eine Variation der Gitterperiode senkrecht zu den Gitterlinien in einer kontinuierlichen Verschiebung der Emissionswellenlänge. Mit einem Spannungssignal von 3,25 kV wird die schmalbandige Emission eines elastischen DFB-Lasers kontinuierlich um fast 50nm von 604 nm zu 557 nm hin verschoben. Aus dem Deformationsverhalten sowohl der reinen Beugungsgitter als auch der Laser werden Rückschlüsse auf die Elastizität der verwendeten Materialien gezogen und erlauben Verbesserungen der Bauteile.
N2  - The photoinduced surface relief formation in a newly developed azobenzene containing material is investigated. A photosensitive film based on a supramolecular material concept is illuminated in a holographic setup with light at 488 nm leading to sinusoidal surface structures. It can be shown how the degree of network formation within the material influences structure formation at periods below 500nm. Different material and process parameters are varied to determine maximum possible structure amplitude. At moderate recording conditions and illumination intensities of 200 mW/cm² maximum structure amplitudes of 80 nm are formed within several minutes at periods of approximately 400 nm. Changing material parameters like surface tension and viscosity leads to an increase of maximum amplitude to 160 nm. Additionally, twodimensional structures are fabricated by multiple recording steps. Original surface structures are copied by soft lithography methods into films of UV cured polymers. This replication leads to a decrease of structure contrast and increase of surface roughness. It is shown that structure contrast is preserved by reduction of process temperature. Organic second order distributed feedback (DFB) lasers are prepared with the help of replicated surface gratings covered with organic active layers with thicknesses of several hundred nanometers. The lasers are investigated regarding the influence of grating amplitude on laser threshold and slope efficiency. For this, the optical gain of two green/red emitter materials, polystyrene (PS) doped with laser dye pyrromethene567 (PM567) and active guest host system of conjugated polymers MEH-PPV and F8BT*, is measured. PS doped with PM567 shows relatively low gain threshold of 50 µJ/cm² at 575 nm caused by the low dye concentration while F8BT* doped with MEH-PPV shows threshold gain of 2.5 µJ/cm² at 630 nm. Similar behavior is observed during laser action. Following Bragg-condition grating periods at approximately 400nm lead to laser emission within the gain spectra of the materials. DFB lasers show single mode narrow line emission with FWHMs of down to 0.3nm. This is a result of high grating quality. Lasers based on MEH-PPV-F8BT* exhibit laser thresholds and slope efficiencies of 4.0µJ/cm² and 8.4%, respectively. PM567-PS lasers exhibit 80 µJ/cm² and 0.9%. An increase of grating amplitude of a MEH-PPV-F8BT*-DFB laser from 40nm to 80nm leads to a considerable increase of energy output and a slight decrease of laser threshold. This is a result of an increase of coupling between light mode and grating which relates to an increase of reflectivity. The use of a two dimensional grating leads to a decrease of divergence angle of laser emission but shows no influence on laser threshold. Finally, laser lifetime is observed under different conditions. Doping the conjugated polymer MEH-PPV in an active matrix in combination with the allocation of nitrogen atmosphere leads to an prolongation of half life time to several million pulses. The combination of elastic surface relief gratings with electro active substrates enables electrical controlled deformation of the surface structure. This deformation is characterized by diffraction measurements. At optimal working conditions electro active substrates based on elastomers SEBS12 and VHB4910 show maximum grating deformation of 1.3% und 3.4% at actuation voltages of 2kV, respectively. The different results are caused by the different elastic modulus of the elastomer materials. The transfer of deformation principle to elastic DFB lasers leads to a continuously shift of emission wavelength. At an actuation voltage of 3.25kV an elastic DFB laser based on polyvinylacetate doped with PM567 shows a shift of nearly 50 nm, from 604 nm to 557 nm. Deformation behavior of grating and laser allow to draw conclusions on elasticity of the material and with this is tool for the improvement of the device.
KW  - Oberflächengitter
KW  - Azobenzen
KW  - Holografie
KW  - DFB-Laser
KW  - Wellenlängenverschiebung
KW  - surface relief grating
KW  - azobenzene
KW  - holography
KW  - DFB laser
KW  - wavelength shift
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-59211
ER  - 
TY  - JOUR
A1  - Döring, Sebastian
A1  - Kollosche, Matthias
A1  - Rabe, Torsten
A1  - Stumpe, Joachim
A1  - Kofod, Guggi
T1  - Electrically tunable polymer DFB laser
JF  - Advanced materials
Y1  - 2011
U6  - https://doi.org/10.1002/adma.201102465
SN  - 0935-9648
VL  - 23
IS  - 37
SP  - 4265
EP  - 4269
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Eichler, David
A1  - Pohl, Martin
T1  - Can ultrahigh-energy cosmic rays come from Gamma-ray bursts? - cosmic rays below the ankle and galactic gamma-ray bursts
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - The maximum cosmic-ray energy achievable by acceleration by a relativistic blast wave is derived. It is shown that forward shocks from long gamma-ray bursts (GRBs) in the interstellar medium accelerate protons to large enough energies, and have a sufficient energy budget, to produce the Galactic cosmic-ray component just below the ankle at 4 x 10(18) eV, as per an earlier suggestion. It is further argued that, were extragalactic long GRBs responsible for the component above the ankle as well, the occasional Galactic GRB within the solar circle would contribute more than the observational limits on the outward flux from the solar circle, unless an avoidance scenario, such as intermittency and/or beaming, allows the present-day local flux to be less than 10(-3) of the average. Difficulties with these avoidance scenarios are noted.
KW  - cosmic rays
KW  - galaxies: general
KW  - gamma-ray burst: general
Y1  - 2011
U6  - https://doi.org/10.1088/2041-8205/738/2/L21
SN  - 2041-8205
VL  - 738
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Evans, Nancy Remage
A1  - DeGioia-Eastwood, Kathleen
A1  - Gagne, Marc
A1  - Townsley, Leisa
A1  - Broos, Patrick S.
A1  - Wolk, Scott J.
A1  - Naze, Yael
A1  - Corcoran, Michael
A1  - Oskinova, Lida
A1  - Moffat, Anthony F. J.
A1  - Wang, Junfeng
A1  - Walborn, Nolan R.
T1  - The search for low-mass companions of b stars in the Carina Nebula cluster trumpler 16
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Supplement series
N2  - We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of eta Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M-circle dot are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M-circle dot) primaries, such as would be found by random pairing from the initial mass function.
KW  - open clusters and associations: individual (Trumpler 16)
KW  - stars: massive
Y1  - 2011
U6  - https://doi.org/10.1088/0067-0049/194/1/13
SN  - 0067-0049
VL  - 194
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Fang, Peng
A1  - Wang, Feipeng
A1  - Wirges, Werner
A1  - Gerhard, Reimund
A1  - Basso, Heitor Cury
T1  - Three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films
JF  - Applied physics : A, Materials science & processing
N2  - A process for preparing three-layer piezoelectrets from fluorinated ethylene-propylene (FEP) copolymer films is introduced. Samples are made from commercial FEP films by means of laser cutting, laser bonding, electrode evaporation, and high-field poling. The observed dielectric-resonance spectra demonstrate the piezoelectricity of the FEP sandwiches. Piezoelectric d (33) coefficients up to a few hundred pC/N are achieved. Charging at elevated temperatures can increase the thermal stability of the piezoelectrets. Isothermal experiments for approximately 15 min demonstrate that samples charged at 140A degrees C keep their piezoelectric activity up to at least 120A degrees C and retain 70% of their initial d (33) even at 130A degrees C. Acoustical measurements show a relatively flat frequency response in the range between 300 Hz and 20 kHz.
Y1  - 2011
U6  - https://doi.org/10.1007/s00339-010-6008-2
SN  - 0947-8396
SN  - 1432-0630
VL  - 103
IS  - 2
SP  - 455
EP  - 461
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Fechner, Cora
T1  - Reconstructing the intergalactic UV background with QSO absorption lines
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We present a new approach to observationally constraining the spectral energy distribution of the intergalactic UV background by studying metal absorption systems. We study single-component metal line systems that exhibit various well-measured species. Among the observed transitions, at least two ratios of ionization stages from the same element are required, e. g. C III/C IV and Si III/Si IV. For each system photoionization models are constructed by varying the spectrum of the ionizing radiation. The spectral energy distribution can then be constrained by comparing the models with the observed column density ratios. Extensive tests with artificial absorbers show that the spectrum of the ionizing radiation cannot be reconstructed unambiguously, but it is possible to constrain the main characteristics of the spectrum. Furthermore, the resulting physical parameters of the absorber, such as ionization parameter, metallicity, and relative abundances, may depend strongly on the adopted ionizing spectrum. Even in case of well-fitting models, the uncertainties can be as high as similar to 0.5 dex for the ionization parameter and up to similar to 1.5 dex for the metallicity. Therefore, it is essential to know the hardness of the UV background when estimating the metallicity of the intergalactic medium. Applying the procedure to a small sample of 3 observed single-component metal line systems yields a soft ionizing radiation at z > 2 and a slightly harder spectrum at z < 2. The resulting energy distributions exhibit strong He II Lya re-emission features, suggesting that reprocessing by intergalactic He II is important. Comparing the observed systems to UV background spectra from the literature indicates that a recent model that includes sawtooth modulation due to reprocessing by intergalactic He II with delayed helium reionization fits the investigated systems very well.
KW  - intergalactic medium
KW  - quasars: absorption lines
KW  - diffuse radiation
Y1  - 2011
U6  - https://doi.org/10.1051/0004-6361/201117080
SN  - 0004-6361
VL  - 532
IS  - 2
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - GEN
A1  - Federici, S.
A1  - Pohl, Martin
A1  - Ruppel, J.
A1  - Telezhinsky, Igor O.
A1  - Hofmann, Werner
A1  - Martinez, M.
A1  - Knapp, J.
T1  - Design concepts for the Cherenkov Telescope Array CTA
BT  - an advanced facility for ground-based high-energy gamma-ray astronomy
T2  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1325 
KW  - ground based gamma ray astronomy
KW  - next generation Cherenkov telescopes
KW  - design concepts
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-430149
SN  - 1866-8372
VL  - 32
IS  - 1325
ER  - 
TY  - JOUR
A1  - Feudel, Fred
A1  - Bergemann, Kay
A1  - Tuckerman, Laurette S.
A1  - Egbers, C.
A1  - Futterer, B.
A1  - Gellert, Marcus
A1  - Hollerbach, Rainer
T1  - Convection patterns in a spherical fluid shell
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Symmetry-breaking bifurcations have been studied for convection in a nonrotating spherical shell whose outer radius is twice the inner radius, under the influence of an externally applied central force field with a radial dependence proportional to 1/r(5). This work is motivated by the GeoFlow experiment, which is performed under microgravity condition at the International Space Station where this particular central force can be generated. In order to predict the observable patterns, simulations together with path-following techniques and stability computations have been applied. Branches of axisymmetric, octahedral, and seven-cell solutions have been traced. The bifurcations producing them have been identified and their stability ranges determined. At higher Rayleigh numbers, time-periodic states with a complex spatiotemporal symmetry are found, which we call breathing patterns.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevE.83.046304
SN  - 1539-3755
VL  - 83
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Fiehler, Katja
A1  - Bannert, Michael M.
A1  - Bischoff, Matthias
A1  - Blecker, Carlo
A1  - Stark, Rudolf
A1  - Vaitl, Dieter
A1  - Franz, Volker H.
A1  - Roesler, Frank
T1  - Working memory maintenance of grasp-target information in the human posterior parietal cortex
JF  - NeuroImage : a journal of brain function
N2  - Event-related functional magnetic resonance imaging was applied to identify cortical areas involved in maintaining target information in working memory used for an upcoming grasping action. Participants had to grasp with their thumb and index finger of the dominant right hand three-dimensional objects of different size and orientation. Reaching-to-grasp movements were performed without visual feedback either immediately after object presentation or after a variable delay of 2-12 s. The right inferior parietal cortex demonstrated sustained neural activity throughout the delay, which overlapped with activity observed during encoding of the grasp target. Immediate and delayed grasping activated similar motor-related brain areas and showed no differential activity. The results suggest that the right inferior parietal cortex plays an important functional role in working memory maintenance of grasp-related information. Moreover, our findings confirm the assumption that brain areas engaged in maintaining information are also involved in encoding the same information, and thus extend previous findings on working memory function of the posterior parietal cortex in saccadic behavior to reach-to-grasp movements.
Y1  - 2011
U6  - https://doi.org/10.1016/j.neuroimage.2010.09.080
SN  - 1053-8119
VL  - 54
IS  - 3
SP  - 2401
EP  - 2411
PB  - Elsevier
CY  - San Diego
ER  - 
TY  - JOUR
A1  - Filimon, Marlena
A1  - Kopf, Ilona
A1  - Schmidt, Dietrich A.
A1  - Bruendermann, Erik
A1  - Rühe, Jürgen
A1  - Santer, Svetlana
A1  - Havenith, Martina
T1  - Local chemical composition of nanophase-separated polymer brushes
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - Using scattering scanning nearfield infrared microscopy (s-SNIM), we have imaged the nanoscale phase separation of mixed polystyrene-poly(methyl methacrylate) (PS-PMMA) brushes and investigated changes in the top layer as a function of solvent exposure. We deduce that the top-layer of the mixed brushes is composed primarily of PMMA after exposure to acetone, while after exposure to toluene this changes to PS. Access to simultaneously measured topographic and chemical information allows direct correlation of the chemical morphology of the sample with topographic information. Our results demonstrate the potential of s-SNIM for chemical mapping based on distinct infrared absorption properties of polymers with a high spatial resolution of 80 nm x 80 nm.
Y1  - 2011
U6  - https://doi.org/10.1039/c0cp02756a
SN  - 1463-9076
VL  - 13
IS  - 24
SP  - 11620
EP  - 11626
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - THES
A1  - Flores Suárez, Rosaura
T1  - Three-dimensional polarization probing in polymer ferroelectrics, polymer-dispersed liquid crystals, and polymer ferroelectrets
T1  - Dreidimensionale Polarisationsmessung in polymeren Ferroelektrika, polymerdispergierten Flüssigkristallen und polymeren Ferroelektreten
N2  - A key non-destructive technique for analysis, optimization and developing of new functional materials such as sensors, transducers, electro-optical and memory devices is presented. The Thermal-Pulse Tomography (TPT) provides high-resolution three-dimensional images of electric field and polarization distribution in a material. This thermal technique use a pulsed heating by means of focused laser light which is absorbed by opaque electrodes. The diffusion of the heat causes changes in the sample geometry, generating a short-circuit current or change in surface potential, which contains information about the spatial distribution of electric dipoles or space charges. Afterwards, a reconstruction of the internal electric field and polarization distribution in the material is possible via Scale Transformation or Regularization methods. In this way, the TPT was used for the first time to image the inhomogeneous ferroelectric switching in polymer ferroelectric films (candidates to memory devices). The results shows the typical pinning of electric dipoles in the ferroelectric polymer under study and support the previous hypotheses of a ferroelectric reversal at a grain level via nucleation and growth. In order to obtain more information about the impact of the lateral and depth resolution of the thermal techniques, the TPT and its counterpart called Focused Laser Intensity Modulation Method (FLIMM) were implemented in ferroelectric films with grid-shaped electrodes. The results from both techniques, after the data analysis with different regularization and scale methods, are in total agreement. It was also revealed a possible overestimated lateral resolution of the FLIMM and highlights the TPT method as the most efficient and reliable thermal technique. After an improvement in the optics, the Thermal-Pulse Tomography method was implemented in polymer-dispersed liquid crystals (PDLCs) films, which are used in electro-optical applications. The results indicated a possible electrostatic interaction between the COH group in the liquid crystals and the fluorinate atoms of the used ferroelectric matrix. The geometrical parameters of the LC droplets were partially reproduced as they were compared with Scanning Electron Microscopy (SEM) images. For further applications, it is suggested the use of a non-strong-ferroelectric polymer matrix. In an effort to develop new polymerferroelectrets and for optimizing their properties, new multilayer systems were inspected. The results of the TPT method showed the non-uniformity of the internal electric-field distribution in the shaped-macrodipoles and thus suggested the instability of the sample. Further investigation on multilayers ferroelectrets was suggested and the implementation of less conductive polymers layers too.
N2  - In dieser Arbeit wird eine zerstörungsfreie Technik zur Analyse, Optimierung, und Entwicklung neuer funktioneller Materialien für Sensoren, Wandler, Speicher und elektrooptische Anwendungen vorgestellt. Die Wärmepuls-Tomographie (engl. Thermal-Pulse Tomography, TPT) liefert dreidimensionale Abbildungen hoher Auflösung von elektrischen Feldern und Polarisationsverteilungen eines Materials. Bei dieser thermischen Methode wird ein fokussierter, gepulster Laserstrahl durch eine undurchsichtige Oberflächenelektrode absorbiert, welche sich dadurch aufheizt. Die einsetzende Wärmediffusion führt – aufgrund der Wärmeausdehnung des Materials – zu Änderungen der Probengeometrie, welche in pyroelektrischen Materialien einen Kurzschlussstrom oder eine Änderung des Oberflächenpotentials zur Folge hat. Diese wiederum enthalten wichtige Informationen über die räumliche Verteilung elektrischer Dipole und Raumladungen im untersuchten Material. Aus dem gemessenen Kurzsschlussstrom kann anschließend das interne elektrische Feld und die Polarisationsverteilung im Material mittels verschiedener Skalentransformations- und Regularisierungsmethoden rekonstruiert werden. Auf diese Weise ermöglichte die TPT-Methode erstmals die Darstellung inhomogener ferroelektrischer Schaltvorgänge in polymeren ferroelektrischen Filmen, welche mögliche Materialien für die Datenspeicherung sind. Die Ergebnisse zeigen eine typische Haftschicht im ferroelektrischen Polymer und unterstützen die Hypothese einer ferroelektrischen Umpolung auf einer der Korngröße äquivalenten Längenskala über Keimbildung und anschließendes Wachstum. Um die Lateral- und Tiefenauflösung zu untersuchen, wurden sowohl die TPT-Methode als auch die äquivalente Methode in der Zeitdomäne (Focused Laser Intensity Modulation Method, FLIMM) auf ferroelektrischen Filme mit Gitterelektroden angewendet. Die Ergebnisse beider Techniken zeigen nach der Datenauswertung mit unterschiedlichen Regularisierungs- und Scale-Methoden eine vollkommene Übereinstimmung. Des Weiteren stellte sich heraus, dass bisherige Untersuchungen der lateralen Auflösung von FLIMM diese möglicherweise überschätzen. Damit behauptet sich TPT als effiziente und verlässliche thermische Methode. Nach einer Optimierung der Optik wurde die TPT-Methode in polymerdispergierten Flüssigkristallen (polymer-dispersed liquid crystals, PDLC), welche in elektrooptischen Anwendungen von Interesse sind, angewendet. Die Ergebnisse deuten auf eine mögliche elektrostatischeWechselwirkung zwischen den COH-Gruppen des Flüssigkristalls und den Fluoratomen der verwendeten ferroelektrischen Matrix hin. Die durch rasterelektronenmikroskopische Aufnahmen (scanning electron microscopy, SEM) gewonnenen geometrischen Parameter der Flüssigkristalltröpfchen konnten mittels TPT reproduziert werden. Für weitere Anwendungen werden schwach ferroelektrische Polymermatrices vorgeschlagen. Im Bestreben neue polymere Ferroelektrete zu entwickeln und deren Eigenschaften zu optimieren, wurden neuartige Mehrschichtsysteme untersucht. Die Ergebnisse aus der TPT-Methode zeigen eine Abweichung der Uniformität der inneren Verteilung des elektrischen Feldes in den geformten Makrodipolen, was auf eine Instabilität der Probe hindeutet. Ebenfalls wurden weitere Untersuchungen an Mehrschicht-Ferroelektreten und die Anwendung von halbleitenden Polymerschichten vorgeschlagen.
KW  - Ferroelektrik
KW  - Ferroelektrete
KW  - Wärmepuls-Tomographie
KW  - Polarisationsverteilung
KW  - Flüssigkristalle
KW  - Polarization distribution
KW  - Ferroelectrics
KW  - PDLC
KW  - Ferroelectrets
KW  - Thermal-Pulse Tomography
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-60173
ER  -