TY - JOUR A1 - Rychkov, Dmitry A1 - Yablokov, M. A1 - Rychkov, A. T1 - Chemical and physical surface modification of PTFE films-an approach to produce stable electrets JF - Applied physics : A, Materials science & processing N2 - The thermal stability of positive charge has been investigated in chemically and physically treated polytetrafluoroethylene (PTFE) films. It has been found that virgin films, oriented by the manufacturer, display an increase in thermal stability of positive charge with an increase of the initial value of surface potential. Such an anomalous behavior is explained by the influence of a negative tribocharge, trapped some small distance below the surface. In PTFE samples treated with orthophosphoric acid and with tetraethoxysilane, a considerable improvement of positive charge stability has been achieved, but no influence of the initial value of surface potential has been observed. However, this influence should be kept in mind when comparing charge stability in virgin and modified samples. In nonoriented PTFE films, no influence of the initial value of surface potential on charge stability has been observed. This could be due to the fact that these films did not possess a noticeable negative tribocharge. After the treatment in glow-discharge defluorination, oxidation and appearance of polar groups have been detected on the surface. These changes in chemical composition of a PTFE surface resulted in a noticeable improvement in thermal stability of positively charged electrets. This improvement is attributed to the formation of deeper traps on the modified surface. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-012-6834-5 SN - 0947-8396 VL - 107 IS - 3 SP - 589 EP - 596 PB - Springer CY - New York ER - TY - JOUR A1 - Garz, Andreas A1 - Sandmann, Michael A1 - Rading, Michael A1 - Ramm, Sascha A1 - Menzel, Ralf A1 - Steup, Martin T1 - Cell-to-cell diversity in a synchronized chlamydomonas culture as revealed by single-cell analyses JF - Biophysical journal N2 - In a synchronized photoautotrophic culture of Chlamydomonas reinhardtii, cell size, cell number, and the averaged starch content were determined throughout the light-dark cycle. For single-cell analyses, the relative cellular starch was quantified by measuring the second harmonic generation (SHG). In destained cells, amylopectin essentially represents the only biophotonic structure. As revealed by various validation procedures, SHG signal intensities are a reliable relative measure of the cellular starch content. During photosynthesis-driven starch biosynthesis, synchronized Chlamydomonas cells possess an unexpected cell-to-cell diversity both in size and starch content, but the starch-related heterogeneity largely exceeds that of size. The cellular volume, starch content, and amount of starch/cell volume obey lognormal distributions. Starch degradation was initiated by inhibiting the photosynthetic electron transport in illuminated cells or by darkening. Under both conditions, the averaged rate of starch degradation is almost constant, but it is higher in illuminated than in darkened cells. At the single-cell level, rates of starch degradation largely differ but are unrelated to the initial cellular starch content. A rate equation describing the cellular starch degradation Y1 - 2012 U6 - https://doi.org/10.1016/j.bpj.2012.07.026 SN - 0006-3495 VL - 103 IS - 5 SP - 1078 EP - 1086 PB - Cell Press CY - Cambridge ER - TY - JOUR A1 - Mattos, Thiago G. A1 - Mejia-Monasterio, Carlos A1 - Metzler, Ralf A1 - Oshanin, Gleb T1 - First passages in bounded domains When is the mean first passage time meaningful? JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - We study the first passage statistics to adsorbing boundaries of a Brownian motion in bounded two-dimensional domains of different shapes and configurations of the adsorbing and reflecting boundaries. From extensive numerical analysis we obtain the probability P(omega) distribution of the random variable omega = tau(1)/(tau(1) + tau(2)), which is a measure for how similar the first passage times tau(1) and tau(2) are of two independent realizations of a Brownian walk starting at the same location. We construct a chart for each domain, determining whether P(omega) represents a unimodal, bell-shaped form, or a bimodal, M-shaped behavior. While in the former case the mean first passage time (MFPT) is a valid characteristic of the first passage behavior, in the latter case it is an insufficient measure for the process. Strikingly we find a distinct turnover between the two modes of P(omega), characteristic for the domain shape and the respective location of absorbing and reflective boundaries. Our results demonstrate that large fluctuations of the first passage times may occur frequently in two-dimensional domains, rendering quite vague the general use of the MFPT as a robust measure of the actual behavior even in bounded domains, in which all moments of the first passage distribution exist. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevE.86.031143 SN - 1539-3755 VL - 86 IS - 3 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Makarava, Natallia A1 - Bettenbühl, Mario A1 - Engbert, Ralf A1 - Holschneider, Matthias T1 - Bayesian estimation of the scaling parameter of fixational eye movements JF - epl : a letters journal exploring the frontiers of physics N2 - In this study we re-evaluate the estimation of the self-similarity exponent of fixational eye movements using Bayesian theory. Our analysis is based on a subsampling decomposition, which permits an analysis of the signal up to some scale factor. We demonstrate that our approach can be applied to simulated data from mathematical models of fixational eye movements to distinguish the models' properties reliably. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/100/40003 SN - 0295-5075 VL - 100 IS - 4 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Aliu, E. A1 - Archambault, S. 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 - Ciupik, L. A1 - Collins-Hughes, E. A1 - Connolly, M. P. A1 - Cui, W. A1 - Decerprit, G. A1 - Dickherber, R. A1 - Duke, C. A1 - Dumm, J. A1 - Dwarkadas, Vikram V. A1 - Errando, M. A1 - Falcone, A. A1 - Feng, Q. 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 - Gyuk, G. A1 - Hanna, D. A1 - Holder, J. A1 - Huan, H. A1 - Hughes, G. A1 - Humensky, T. B. A1 - Kaaret, P. A1 - Karlsson, N. A1 - Kertzman, M. A1 - Khassen, Y. A1 - Kieda, D. A1 - Krawczynski, H. A1 - Krennrich, F. A1 - Lang, M. J. A1 - Lee, K. A1 - Maier, G. A1 - Majumdar, P. A1 - McArthur, S. A1 - McCann, A. A1 - Millis, J. A1 - Moriarty, P. A1 - Mukherjee, R. A1 - Nunez, P. D. A1 - Ong, R. A. A1 - Orr, M. A1 - Otte, A. N. A1 - Pandel, D. A1 - Park, N. A1 - Perkins, J. S. A1 - Pohl, M. 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 - Telezhinsky, Igor O. 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 - Weekes, T. C. A1 - Weinstein, A. A1 - Weisgarber, T. A1 - Welsing, R. A1 - Williams, D. A. A1 - Zitzer, B. T1 - Veritas observations of the nova in V407 CYGNI JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We report on very high energy (E > 100 GeV) gamma-ray observations of V407 Cygni, a symbiotic binary that underwent a nova outburst producing 0.1-10 GeV gamma rays during 2010 March 10-26. Observations were made with the Very Energetic Radiation Imaging Telescope Array System during 2010 March 19-26 at relatively large zenith angles due to the position of V407 Cyg. An improved reconstruction technique for large zenith angle observations is presented and used to analyze the data. We do not detect V407 Cygni and place a differential upper limit on the flux at 1.6 TeV of 2.3 x 10(-12) erg cm(-2) s(-1) (at the 95% confidence level). When considered jointly with data from Fermi-LAT, this result places limits on the acceleration of very high energy particles in the nova. KW - gamma rays: general KW - novae, cataclysmic variables KW - white dwarfs Y1 - 2012 U6 - https://doi.org/10.1088/0004-637X/754/1/77 SN - 0004-637X VL - 754 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Zurita-Sanchez, Jorge R. A1 - Henkel, Carsten T1 - Acoustic waves from mechanical impulses due to fluorescence resonant energy (Forster) transfer Blowing a whistle with light JF - epl : a letters journal exploring the frontiers of physics N2 - We present a momentum transfer mechanism mediated by electromagnetic fields that originates in a system of two nearby molecules: one excited (donor D*) and the other in ground state (acceptor A). An intermolecular force related to fluorescence resonant energy or Forster transfer (FRET) arises in the unstable D* A molecular system, which differs from the equilibrium van der Waals interaction. Due to the its finite lifetime, a mechanical impulse is imparted to the relative motion in the system. We analyze the FRET impulse when the molecules are embedded in free space and find that its magnitude can be much greater than the single recoil photon momentum, getting comparable with the thermal momentum (Maxwell-Boltzmann distribution) at room temperature. In addition, we propose that this FRET impulse can be exploited in the generation of acoustic waves inside a film containing layers of donor and acceptor molecules, when a picosecond laser pulse excites the donors. This acoustic transient is distinguishable from that produced by thermal stress due to laser absorption, and may therefore play a role in photoacoustic spectroscopy. The effect can be seen as exciting a vibrating system like a string or organ pipe with light; it may be used as an opto-mechanical transducer. Y1 - 2012 U6 - https://doi.org/10.1209/0295-5075/97/43002 SN - 0295-5075 VL - 97 IS - 4 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Haakh, Harald Richard A1 - Henkel, Carsten T1 - Magnetic near fields as a probe of charge transport in spatially dispersive conductors JF - The European physical journal : B, Condensed matter and complex systems N2 - We calculate magnetic field fluctuations above a conductor with a nonlocal response (spatial dispersion) and consider a large range of distances. The cross-over from ballistic to diffusive charge transport leads to a reduced noise spectrum at distances below the electronic mean free path, as compared to a local description. We also find that the mean free path provides a lower limit to the correlation (coherence) length of the near field fluctuations. The short-distance behaviour is common to a wide range of materials, including semiconductors and superconductors. Our discussion is aimed at atom chip experiments where spin-flip transitions give access to material properties with mesoscopic spatial resolution. The results also hint at fundamental limits to the coherent operation of miniaturised atom traps and matter-wave interferometers. Y1 - 2012 U6 - https://doi.org/10.1140/epjb/e2011-20567-1 SN - 1434-6028 VL - 85 IS - 1 PB - Springer CY - New York ER - TY - JOUR A1 - Bödecker, Geesche A1 - Henkel, Carsten T1 - Validity of the quantum regression theorem for resonance fluorescence in a photonic crystal JF - Annalen der Physik N2 - Correlation functions of a driven two-level system embedded in a photonic crystal are analyzed. The spectral density of the photonic bands near a gap makes this system non-Markovian. The equations of motion for two-time correlations are derived by two different methods, the quantum regression theorem and the fluctuation dissipation theorem, and found to be the same. KW - Resonance fluorescence KW - fluctuation dissipation theorem KW - quantum regression theorem KW - non-Markovian dynamics KW - open quantum system KW - photonic bandgap Y1 - 2012 U6 - https://doi.org/10.1002/andp.201200135 SN - 0003-3804 VL - 524 IS - 12 SP - 805 EP - 813 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Wirges, Werner A1 - Raabe, Sebastian A1 - Qiu, Xunlin T1 - Dielectric elastomer and ferroelectret films combined in a single device how do they reinforce each other? JF - Applied physics : A, Materials science & processing N2 - Dielectric elastomers (DE) are soft polymer materials exhibiting large deformations under electrostatic stress. When a prestretched elastomer is stuck to a flat plastic frame, a complex structure that can be used as an actuator (DEA) is formed due to self-organization and energy minimization. Here, such a DEA was equipped with a ferroelectret film. Ferroelectrets are internally charged polymer foams or void-containing polymer-film systems combining large piezoelectricity with mechanical flexibility and elastic compliance. In their dielectric spectra, ferroelectrets show piezoelectric resonances that can be used to analyze their electromechanical properties. The antiresonance frequencies ( ) of ferroelectret films not only are directly related to their geometric parameters, but also are sensitive to the boundary conditions during measurement. In this paper, a fluoroethylenepropylene (FEP) ferroelectret film with tubular void channels was glued to a plastic frame prior to the formation of self-organized minimum-energy DEA structure. The dielectric resonance spectrum (DRS) of the ferroelectret film was measured in-situ during the actuation of the DEA under applied voltage. It is found that the antiresonance frequency is a monotropic function of the bending angle of the actuator. Therefore, the actuation of DEAs can be used to modulate the of ferroelectrets, while the can also be taken for in-situ diagnosis and for precise control of the actuation of the DEA. Combination of DEAs and ferroelectrets brings a number of possibilities for application. Y1 - 2012 U6 - https://doi.org/10.1007/s00339-012-6833-6 SN - 0947-8396 SN - 1432-0630 VL - 107 IS - 3 SP - 583 EP - 588 PB - Springer CY - New York ER - TY - JOUR A1 - Jeon, Jae-Hyung A1 - Metzler, Ralf T1 - Inequivalence of time and ensemble averages in ergodic systems: exponential versus power-law relaxation in confinement JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Single-particle tracking has become a standard tool for the investigation of diffusive properties, especially in small systems such as biological cells. Usually the resulting time series are analyzed in terms of time averages over individual trajectories. Here we study confined normal as well as anomalous diffusion, modeled by fractional Brownian motion and the fractional Langevin equation, and show that even for such ergodic systems time-averaged quantities behave differently from their ensemble-averaged counterparts, irrespective of how long the measurement time becomes. Knowledge of the exact behavior of time averages is therefore fundamental for the proper physical interpretation of measured time series, in particular, for extraction of the relaxation time scale from data. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevE.85.021147 SN - 1539-3755 VL - 85 IS - 2 PB - American Physical Society CY - College Park ER -