TY - JOUR A1 - Yang, Xiaohui A1 - Müller, David C. A1 - Neher, Dieter A1 - Meerholz, Klaus T1 - Highly efficient polymeric electrophosphorescent diodes N2 - Polymeric electrophosphorescent LEDs with internal quantum efficiencies approaching unity have been fabricated. Such performance levels are previously unknown for OLEDs. The key to this success is redox chemically doped oxetane- crosslinkable hole-transporting layers with multilayer capability (see figure). They improve hole injection and act as electron-blocking layers, without the need to include exciton-or hole-blocking layers Y1 - 2006 UR - 1960 = DOI: 10.1002/adma.200501867 ER - TY - JOUR A1 - Walther, T A1 - Wessel, Niels A1 - Malberg, Hagen A1 - Voss, Andreas A1 - Stepan, H A1 - Faber, R T1 - A combined technique for predicting pre-eclampsia : concurrent measurement of uterine perfusion and analysis of heart rate and blood pressure variability N2 - Objective Pre-eclampsia is a serious complication of pregnancy with high morbidity and mortality and an incidence of 3-5% in all pregnancies. Early prediction is still insufficient in clinical practice. Although most pre- eclamptic patients have pathological uterine perfusion in the second trimester, perfusion disturbance has a positive predictive accuracy (PPA) only of approximately 30%. Methods Non-invasive continuous blood pressure recordings were taken simultaneously via a finger cuff for 30 min. Time series of systolic as well as diastolic beat-to-beat pressure values were extracted to analyse heart rate and blood pressure variability and baroreflex sensitivity in 102 second- trimester pregnancies, to assess predictability for pre-eclampsia (n = 16). All women underwent Doppler investigations of the uterine arteries. Results We identified a combination of three variability and baroreflex parameters to best predict pre-eclampsia several weeks before clinical manifestation. The discriminant function of these three parameters classified patients with later pre-eclampsia with a sensitivity of 87.5%, a specificity of 83.7%, and a PPA of 50.0%. Combined with Doppler investigations of uterine arteries, PPA increased to 71.4%. Conclusions This technique of incorporating one-stop clinical assessment of uterine perfusion and variability parameters in the second trimester produces the most effective prediction of pre-eclampsia to date Y1 - 2006 ER - TY - JOUR A1 - Straube, Arthur V. A1 - Lyubimov, Dmitry V. A1 - Shklyaev, Sergey V. T1 - Averaged dynamics of two-phase media in a vibration field N2 - The averaged dynamics of various two-phase systems in a high-frequency vibration field is studied theoretically. The continuum approach is applied to describe such systems as solid particle suspensions, emulsions, bubbly fluids, when the volume concentration of the disperse phase is small and gravity is insignificant. The dynamics of the disperse system is considered by means of the method of averaging, when the fast pulsation and slow averaged motion can be treated separately. Two averaged models for both nondeformable and deformable particles, when the compressibility of the disperse phase becomes important, are obtained. A criterion when the compressibility of bubbles cannot be neglected is figured out. For both cases the developed models are applied to study the averaged dynamics of the disperse media in an infinite plane layer under the action of transversal vibration. (C) 2006 American Institute of Physics Y1 - 2006 UR - http://pof.aip.org/resource/1/phfle6/v18/i5/p053303_s1?view=fulltext U6 - https://doi.org/10.1063/1.2204057 ER - TY - JOUR A1 - Albers, Nicole A1 - Spahn, Frank T1 - The influence of particle adhesion on the stability of agglomerates in Saturn's rings N2 - In planetary rings, binary collisions and mutual gravity are the predominant particle interactions. Based on a viscoelastic contact model we implement the concept of static adhesion. We discuss the collision dynamics and obtain a threshold velocity for restitution or agglomeration to occur. The latter takes place within a range of a few cm s(-1) for icy grains at low temperatures. The stability of such two-body agglomerates bound by adhesion and gravity in a tidal environment is discussed and applied to the saturnian system. A maximal agglomerate size for a given orbit location is obtained. In this way we are able to resolve the borderline of the zone where agglomerates can exist as a function of the agglomerate size and thus gain an alternative to the classical Roche limit. An increasing ring grain size with distance to Saturn as observed by the VIMS-experiment on board the Cassini spacecraft can be found by our estimates and implications for the saturnian system will be addressed. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/00191035 U6 - https://doi.org/10.1016/j.icarus.2005.10.011 SN - 0019-1035 ER - TY - JOUR A1 - Wessel, Niels A1 - Schirdewan, Alexander T1 - Toward a prediction of sudden death in propofol-related infusion syndrome Y1 - 2006 ER - TY - JOUR A1 - Wegener, Michael A1 - Künstler, Wolfgang A1 - Gerhard, Reimund T1 - Poling behavior and optical absorption of partially dehydrofluorinated and uniaxially stretched polyvinylidene fluoride N2 - Polyvinylidene fluoride was dissolved together with solid sodium hydroxide as catalyst in a dimethylsulfoxide/ acetone mixture and moderately dehydrofluorinated. The dehydrofluorination leads to a partial degradation of the fluorohydrocarbons, and in particular to main-chain scission and to formation of carbon double or triple bonds. This enhances the absorption at UV-vis frequencies. The degradation process also generates a large amount of excess charges in the polymer, which influence the electrical polarization behavior of the dehydrofluorinated polymer. Uniaxial stretching of moderately dehydrofluorinated polyvinylidene fluoride leads to films in a polar phase. Dipole polarization in the degraded and stretched films is demonstrated by means of switching experiments Y1 - 2006 U6 - https://doi.org/10.1080/00150190600694761 ER - TY - JOUR A1 - Pikovskij, Arkadij A1 - Rosenau, Philip T1 - Phase compactons N2 - We study the phase dynamics of a chain of autonomous, self-sustained, dispersively coupled oscillators. In the quasicontinuum limit the basic discrete model reduces to a Korteveg-de Vries-like equation, but with a nonlinear dispersion. The system supports compactons - solitary waves with a compact support - and kovatons - compact formations of glued together kink-antikink pairs that propagate with a unique speed, but may assume an arbitrary width. We demonstrate that lattice solitary waves, though not exactly compact, have tails which decay at a superexponential rate. They are robust and collide nearly elastically and together with wave sources are the building blocks of the dynamics that emerges from typical initial conditions. In finite lattices, after a long time, the dynamics becomes chaotic. Numerical studies of the complex Ginzburg-Landau lattice show that the non-dispersive coupling causes a damping and deceleration, or growth and acceleration, of compactons. A simple perturbation method is applied to study these effects. (c) 2006 Elsevier B.V. All rights reserved Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/01672789 U6 - https://doi.org/10.1016/j.physd.2006.04.015 ER - TY - JOUR A1 - Montanari, Gian Carlo A1 - Fabiani, Davide A1 - Ciani, Franco A1 - Motori, Antonio A1 - Paajanen, Mika A1 - Gerhard, Reimund A1 - Wegener, Michael T1 - Charging properties and time-temperature stability of innovative polymeric cellular ferroelectrets N2 - After appropriate mechanical and electrical treatments, some cellular polymers become able to retain space charge for a long time, i.e. they acquire electret behavior. The electrical treatment consists of charging under high levels of DC electric field. The mechanical treatment, based on the application of stretching forces to cellular polymer slabs that were before expanded under pressurized gas, affects the cavity size and shape, and therefore also the effectiveness of the charging process itself. An investigation of charging mechanisms, as well as of mechanical treatment, is therefore fundamental for optimizing the ferro- and piezo-electret properties. The aim of this paper is to discuss the effect of the physical dimension of the cavities on the charging behavior of cellular ferroelectrets and to focus on the time-temperature stability for two families of polymeric cellular ferroelectrets based on polypropylene (PP) and on a cyclo-olefin copolymer (COC). Emphasis will be given to the stretching process and in particular to the expansion rate applied during the manufacturing process (which affects the radial dimension and the height of the cavities, respectively). Space-charge and partial-discharge measurements as a function of time and temperature are the main tools to infer the influence of the cavity size on charging and stability characteristics. Y1 - 2007 UR - http://ieeexplore.ieee.org/servlet/opac?punumber=94 U6 - https://doi.org/10.1109/TDEI.2007.302892 SN - 1070-9878 ER - TY - JOUR A1 - Saalfrank, Peter A1 - Nest, Mathias A1 - Andrianov, Igor V. A1 - Klamroth, Tillmann A1 - Kroner, Dominic A1 - Beyvers, Stephanie T1 - Quantum dynamics of laser-induced desorption from metal and semiconductor surfaces, and related phenomena N2 - Recent progress towards a quantum theory of laser-induced desorption and related phenomena is reviewed, for specific examples. These comprise the photodesorption of NO from Pt(111), the scanning tunnelling microscope and laser- induced desorption and switching of H at Si(100), and the electron stimulated desorption and dissociation of CO at Ru(0001). The theoretical methods used for nuclear dynamics range from open-system density matrix theory over nonadiabatically coupled multi-state models to electron-nuclear wavepackets. Also, aspects of time-dependent spectroscopy to probe ultrafast nonadiabatic processes at surfaces will be considered for the example of two-photon photoemission of solvated electrons in ice layers on Cu(111) Y1 - 2006 UR - http://iopscience.iop.org/0953-8984/18/30/S05/pdf/0953-8984_18_30_S05.pdf U6 - https://doi.org/10.1088/0953-8984/18/30/S05 SN - 1361-648X SN - 0953-8984 VL - 18 IS - 30 SP - S1425 EP - S1459 PB - IOP Publ. CY - Bristol ER - TY - JOUR A1 - Mittal, Rupal A1 - Porcas, Richard A1 - Wucknitz, Olaf A1 - Biggs, Andy D. A1 - Browne, Ian W. A. T1 - VLBI phase-reference observations of the gravitational lens JVAS B0218+357 N2 - We present the results of phase-referenced VLBA+Effelsberg observations at five frequencies of the double-image gravitational lens WAS B0218+357, made to establish the precise registration of the A and B lensed image positions. The motivation behind these observations is to investigate the anomalous variation of the image flux-density ratio (A[B) with frequency - this ratio changes by almost a factor of two over a frequency range from 1.65 GHz to 15.35 GHz. We investigate whether frequency dependent image positions, combined with a magnification gradient across the image field, could give rise to the anomaly. Our observations confirm the variation of image flux-density ratio with frequency. The results from Our phase-reference astrometry, taken together with the lens mass model of Wucknitz et al. (2004, MNRAS, 349, 14), show that shifts of the image peaks and centroids are too small to account for the observed frequency- dependent ratio Y1 - 2006 UR - http://www.edpsciences.org/docinfos/AAS/ U6 - https://doi.org/10.1051/0004-6361:20054012 ER - TY - JOUR A1 - Li, Changpin A1 - Sun, Weigang A1 - Kurths, Jürgen T1 - Synchronization of complex dynamical networks with time delays N2 - In the present paper, two kinds of dynamical complex networks are considered. The first is that elements of every node have different time delays but all nodes in Such networks have the same time-delay vector. The second is that different nodes have different time-delay vectors, and the elements of each node also have different time delays. Corresponding synchronization theorems are established. Numerical examples show the efficiency of the derived theorems. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/03784371 U6 - https://doi.org/10.1016/j.physa.2005.07.007 SN - 0378-4371 ER - TY - JOUR A1 - Leitenberger, Wolfram A1 - Pietsch, Ullrich T1 - A monolithic Fresnel bimirror for hard X-rays and its application for coherence measurements N2 - Experiments using a simple X-ray interferometer to measure the degree of spatial coherence of hard X-rays are reported. A monolithic Fresnel bimirror is used at small incidence angles to investigate synchrotron radiation in the energy interval 5-50 keV with monochromatic and white beam. The experimental setup was equivalent to a Young's double-slit experiment for hard X-rays with slit dimensions in the micrometre range. From the high-contrast interference pattern the degree of coherence was determined. Y1 - 2007 UR - http://journals.iucr.org/s/issues/2007/02/00/wl5137/wl5137.pdf U6 - https://doi.org/10.1107/S0909049507003846 SN - 0909-0495 ER - TY - JOUR A1 - Thiel, Marco A1 - Romano, Maria Carmen A1 - Kurths, Jürgen T1 - Spurious structures in recurrence plots induced by embedding N2 - In this paper we show that delay embedding produces spurious structures in a recurrence plot (RP) that are not present in the real attractor. We analyze typical sets of simulated data, such as white noise and data from the chaotic Rossler system to show the relevance of this effect. In the second part of the paper we show that the second order Renyi entropy and the correlation dimension are dynamical invariants that can be estimated from Recurrence Plots with arbitrary embedding dimension and delay Y1 - 2006 U6 - https://doi.org/10.1007/s11071-006-2010-9 ER - TY - JOUR A1 - Tino, G. M. A1 - Cacciapuoti, L. A1 - Bongs, K. A1 - Bordé, Ch. J. A1 - Bouyer, P. A1 - Dittus, H. A1 - Ertmer, W. A1 - Görlitz, A. A1 - Inguscio, M. A1 - Landragin, A. A1 - Lemonde, P. A1 - Lämmerzahl, C. A1 - Peters, A. A1 - Rasel, E. A1 - Reichel, J. A1 - Salomon, C. A1 - Schiller, S. A1 - Schleich, W. A1 - Sengstock, K. A1 - Sterr, U. A1 - Wilkens, Martin T1 - Atom interferometers and optical atomic clocks : new quantum sensors for fundamental physics experiments in space N2 - We present projects for future space missions using new quantum devices based on ultracold atoms. They will enable fundamental physics experiments testing quantum physics, physics beyond the standard model of fundamental particles and interactions, special relativity, gravitation and general relativity. Y1 - 2007 ER - TY - JOUR A1 - Goldobin, Denis S. A1 - Pikovskij, Arkadij T1 - Effects of delayed feedback on Kuramoto transition N2 - We develop a weakly nonlinear theory of the Kuramoto transition in an ensemble of globally coupled oscillators in presence of additional time-delayed coupling terms. We show that a linear delayed feedback not only controls the transition point, but effectively changes the nonlinear terms near the transition. A purely nonlinear delayed coupling does not effect the transition point, but can reduce or enhance the amplitude of collective oscillations Y1 - 2006 UR - http://www2.yukawa.kyoto-u.ac.jp/~ptpwww/link-supplement.html U6 - https://doi.org/10.1143/PTPS.161.43 SN - 0375-9687 ER - TY - JOUR A1 - Garnier, Sebastien A1 - Laschewsky, André A1 - Storsberg, J T1 - Polymeric surfactants : novel agents with exceptional properties N2 - This article presents recent progress in the field of polymeric surfactants made of permanently amphiphilic block copolymers or of stimulus-sensitive ones. We highlight key points in the design of amphiphilic macromolecules, to yield polymer surfactants with tailor-made properties, as well as recently developed and still challenging application fields for this new class of surfactants. The efficiency boosting of amphiphilic block copolymers as co-surfactants in microemulsions is discussed, as are surface modification by polymer surfactants, and stabilization of dispersions. Moreover, the use of block copolymers in nanosciences is presented, for instance as a tool for nanomaterial fabrication, or for biomedical and cosmetic applications in bio-nanotechnology. Finally, self-assembly and applications of some newly developed "exotic" amphiphilic block copolymer structures as new surface-active materials will be highlighted Y1 - 2006 UR - http://www.tsdjournal.com/ SN - 0932-3414 ER - TY - JOUR A1 - Zhang, Ning A1 - Hayer, Anna A1 - Al-Suti, Mohammed K. A1 - Al-Belushi, Rayya A. A1 - Khan, Muhammad S. A1 - Köhler, Anna T1 - The effect of delocalization on the exchange energy in meta- and para-linked Pt-containing carbazole polymers and monomers N2 - A series of novel platinum-containing carbazole monomers and polymers was synthesized and fully characterized by UV-VIS absorption, luminescence, and photoinduced absorption studies. In these compounds, a carbazole unit is incorporated into the main chain via either a para- or a meta-linkage. We discuss the effects of linkage and polymerization on the energy levels of S-1, T-1, and T-n. The S-1-T-1 splitting observed for the meta-linked monomer (0.4 eV) is only half of that in the para-linked monomer (0.8 eV). Upon polymerization, the exchange energy in the para- linked compound reduces, yet still remains larger than in the meta-linked polymer. We attribute the difference in exchange energy to the difference in wave function overlap between electron and hole in these compounds. (c) 2006 American Institute of Physics Y1 - 2006 UR - http://scitation.aip.org/getpdf/servlet/ GetPDFServlet?filetype=pdf&id=JCPSA6000124000024244701000001&idtype=cvips&doi=10.1063/1.2200351&prog=normal U6 - https://doi.org/10.1063/1.2200351 ER - TY - JOUR A1 - Boccaletti, Stefano A1 - Hwang, Dong-Uk A1 - Chavez, Mario A1 - Amann, Andreas A1 - Kurths, Jürgen A1 - Pecora, Louis M. T1 - Synchronization in dynamical networks : evolution along commutative graphs N2 - Starting from an initial wiring of connections, we show that the synchronizability of a network can be significantly improved by evolving the graph along a time dependent connectivity matrix. We consider the case of connectivity matrices that commute at all times, and compare several approaches to engineer the corresponding commutative graphs. In particular, we show that synchronization in a dynamical network can be achieved even in the case in which each individual commutative graphs does not give rise to synchronized behavior Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.74.016102 SN - 1539-3755 ER - TY - JOUR A1 - Goldobin, Denis S. A1 - Pikovskij, Arkadij T1 - Antireliability of noise-driven neurons N2 - We demonstrate, within the framework of the FitzHugh-Nagumo model, that a firing neuron can respond to a noisy driving in a nonreliable manner: the same Gaussian white noise acting on identical neurons evokes different patterns of spikes. The effect is characterized via calculations of the Lyapunov exponent and the event synchronization correlations. We construct a theory that explains the antireliability as a combined effect of a high sensitivity to noise of some stages of the dynamics and nonisochronicity of oscillations. Geometrically, the antireliability is described by a random noninvertible one-dimensional map Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.73.061906 SN - 1539-3755 ER - TY - JOUR A1 - Anishchenko, Vadim S. A1 - Nikolaev, S A1 - Kurths, Jürgen T1 - Winding number locking on a two-dimensional torus : synchronization of quasiperiodic motions N2 - We propose a new autonomous dynamical system of dimension N=4 that demonstrates the regime of stable two- frequency motions and period-doubling bifurcations of a two-dimensional torus. It is shown that the period-doubling bifurcation of the two-dimensional torus is not followed by the resonance phenomenon, and the two-dimensional ergodic torus undergoes a period-doubling bifurcation. The interaction of two generators is also analyzed. The phenomenon of external and mutual synchronization of two-frequency oscillations is observed, for which winding number locking on a two- dimensional torus takes place Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.73.056202 SN - 1539-3755 ER - TY - JOUR A1 - Nolte, Guido A1 - Meinecke, Frank C. A1 - Ziehe, Andreas A1 - Müller, Klaus-Robert T1 - Identifying interactions in mixed and noisy complex systems N2 - We present a technique that identifies truly interacting subsystems of a complex system from multichannel data if the recordings are an unknown linear and instantaneous mixture of the true sources. The method is valid for arbitrary noise structure. For this, a blind source separation technique is proposed that diagonalizes antisymmetrized cross- correlation or cross-spectral matrices. The resulting decomposition finds truly interacting subsystems blindly and suppresses any spurious interaction stemming from the mixture. The usefulness of this interacting source analysis is demonstrated in simulations and for real electroencephalography data Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.73.051913 ER - TY - JOUR A1 - Raab, Corinna A1 - Wessel, Niels A1 - Schirdewan, Alexander A1 - Kurths, Jürgen T1 - Large-scale dimension densities for heart rate variability analysis N2 - In this work, we reanalyze the heart rate variability (HRV) data from the 2002 Computers in Cardiology (CiC) Challenge using the concept of large-scale dimension densities and additionally apply this technique to data of healthy persons and of patients with cardiac diseases. The large-scale dimension density (LASDID) is estimated from the time series using a normalized Grassberger-Procaccia algorithm, which leads to a suitable correction of systematic errors produced by boundary effects in the rather large scales of a system. This way, it is possible to analyze rather short, nonstationary, and unfiltered data, such as HRV. Moreover, this method allows us to analyze short parts of the data and to look for differences between day and night. The circadian changes in the dimension density enable us to distinguish almost completely between real data and computer-generated data from the CiC 2002 challenge using only one parameter. In the second part we analyzed the data of 15 patients with atrial fibrillation (AF), 15 patients with congestive heart failure (CHF), 15 elderly healthy subjects (EH), as well as 18 young and healthy persons (YH). With our method we are able to separate completely the AF (rho(mu)(ls)=0.97 +/- 0.02) group from the others and, especially during daytime, the CHF patients show significant differences from the young and elderly healthy volunteers (CHF, 0.65 +/- 0.13; EH, 0.54 +/- 0.05; YH, 0.57 +/- 0.05; p < 0.05 for both comparisons). Moreover, for the CHF patients we find no circadian changes in rho(mu)(ls) (day, 0.65 +/- 0.13; night, 0.66 +/- 0.12; n.s.) in contrast to healthy controls (day, 0.54 +/- 0.05; night, 0.61 +/- 0.05; p=0.002). Correlation analysis showed no statistical significant relation between standard HRV and circadian LASDID, demonstrating a possibly independent application of our method for clinical risk stratification Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.73.041907 SN - 1539-3755 ER - TY - JOUR A1 - Ilnytskyi, Jaroslav A1 - Saphiannikova, Marina A1 - Neher, Dieter T1 - Photo-induced deformations in azobenzene-containing side-chain polymers : molecular dynamics study N2 - We perform molecular dynamics simulations of azobenzene containing side-chain liquid crystalline polymer subject to an external model field that mimicks the reorientations of the azobenzenes upon irradiation with polarized light. The smectic phase of the polymer is studied with the field applied parallel to the nematic director, forcing the trans isomers to reorient perpendicularly to the field (the direction of which can be assosiated with the light polarization). The coupling between the reorientation of azobenzenes and mechanical deformation of the sample is found to depend on the field strength. In a weak field the original smectic order is melted gradually with no apparent change in the simulation box shape, whereas in a strong field two regimes are observed. During the first one a rapid melting of the liquid crystalline order is accompanied by the contraction of the polymer along the field direction (the effect similar to the one observed experimentally in azopenzene containing elastomers). During the slower second regime, the smectic layers are rebuilt to accomodate the preferential direction of chromophores perperdicular to the field. Y1 - 2006 UR - http://www.icmp.lviv.ua/journal/Contents.html SN - 1607-324X ER - TY - JOUR A1 - Heinmüller, Janine A1 - Petitjean, Patrick A1 - Ledoux, Cedric A1 - Caucci, Sara A1 - Srianand, Raghunathan T1 - Kinematics and star formation activity in the z(abs)=2.03954 damped Lyman-alpha system towards PKS 0458-020 N2 - We present UVES observations of the log N(H I) = 21.7 damped Lyman-alpha system at z(abs) = 2.03954 towards the quasar PKS 0458-020. Hi Lyman-alpha emission is detected in the center of the damped Lyman-alpha absorption trough. Metallicities are derived for Mg II, Si II, P II, Cr II, Mn II, Fe II and Zn II and are found to be -1.21 +/- 0.12, - 1.28 +/- 0.20, -1.54 +/- 0.11, -1.66 +/- 0.10, -2.05 +/- 0.11, -1.87 +/- 0.11, -1.22 +/- 0.10, respectively, relative to solar. The depletion factor is therefore of the order of [Zn/Fe] = 0.65. We observe metal absorption lines to be blueshifted compared to the Lyman-alpha emission up to a maximum of similar to 100 and 200 km s(-1) for low and high- ionization species respectively. This can be interpreted either as the consequence of rotation in a large (similar to 7 kpc) disk or as the imprint of a galactic wind. The star formation rate (SFR) derived from the Lyman-alpha emission, 1.6 M-circle dot yr(-1), is compared with that estimated from the observed C II* absorption. No molecular hydrogen is detected in our data, yielding a molecular fraction log f < -6.52. This absence of H-2 can be explained as the consequence of a high ambient UV flux which is one order of magnitude larger than the radiation field in the ISM of our Galaxy and originates in the observed emitting region Y1 - 2006 UR - http://www.aanda.org/ U6 - https://doi.org/10.1051/0004-6361:20053910 SN - 0004-6361 ER - TY - JOUR A1 - Tirok, Katrin A1 - Gaedke, Ursula T1 - Spring weather determines the relative importance of ciliates, rotifers and crustaceans for the initiation of the clear-water phase in a large, deep lake N2 - Clear-water phase (CWP) is an important event in seasonal plankton succession. We examined the influence of all herbivorous zooplankton on its initiation under different weather and climatic conditions using up to 19 years of observations from the large, deep Lake Constance (Europe) and estimates of relative clearance rates. A CWP occurred regularly, even if daphnid biomass was still very low. CWP was attributed to strong grazing either by a daphnid- dominated zooplankton community or by a diverse assemblage consisting of micro- and meso-zooplankton. Both types of zooplankton communities occurred with approximately the same frequency. The timing of the CWP was unrelated to the North Atlantic Oscillation (NAO) but correlated with the wind-dependent intensity of deep vertical mixing 3 months earlier, during early spring. Less mixing enabled early growth of phytoplankton, ciliates and rotifers despite low temperatures, which prevented daphnid development at this time. This resulted in enhanced grazing of ciliates and rotifers, which increased the importance of phytoplankton less edible for most ciliates, rotifers and daphnids. Ciliates clearly dominated the grazing pressure on phytoplankton throughout spring, maintaining high biomasses together with the phytoplankton for up to 2 months. A CWP was observed when herbivores grazing on larger phytoplankton developed in addition to ciliates Y1 - 2006 ER - TY - JOUR A1 - Brilliantov, Nikolai V. A1 - Pöschel, Thorsten T1 - Breakdown of the Sonine expansion for the velocity distribution of granular gases JF - Europhysics Letters N2 - The velocity distribution of a granular gas is analyzed in terms of the Sonine polynomials expansion. We derive an analytical expression for the third Sonine coefficient a(3). In contrast to frequently used assumptions this coefficient is of the same order of magnitude as the second Sonine coefficient a(2). For small inelasticity the theoretical result is in good agreement with numerical simulations. The next-order Sonine coefficients a(4), a(5) and a(6) are determined numerically. While these coefficients are negligible for small dissipation, their magnitude grows rapidly with increasing inelasticity for 0 < epsilon less than or similar to 0.6. We conclude that this behavior of the Sonine coefficients manifests the breakdown of the Sonine polynomial expansion caused by the increasing impact of the overpopulated high-energy tail of the distribution function Y1 - 2006 UR - http://iopscience.iop.org/0295-5075/ U6 - https://doi.org/10.1209/epl/i2005-10555-6 SN - 0295-5075 VL - 74 IS - 3 SP - 424 EP - 430 ER - TY - JOUR A1 - Cramer, Marcus A1 - Eisert, Jens A1 - Plenio, Martin B. A1 - Dreißig, Julian T1 - Entanglement-area law for general bosonic harmonic lattice systems N2 - We demonstrate that the entropy of entanglement and the distillable entanglement of regions with respect to the rest of a general harmonic-lattice system in the ground or a thermal state scale at most as the boundary area of the region. This area law is rigorously proven to hold true in noncritical harmonic-lattice systems of arbitrary spatial dimension, for general finite-ranged harmonic interactions, regions of arbitrary shape, and states of nonzero temperature. For nearest-neighbor interactions-corresponding to the Klein-Gordon case-upper and lower bounds to the degree of entanglement can be stated explicitly for arbitrarily shaped regions, generalizing the findings of Phys. Rev. Lett. 94, 060503 (2005). These higher-dimensional analogs of the analysis of block entropies in the one-dimensional case show that under general conditions, one can expect an area law for the entanglement in noncritical harmonic many-body systems. The proofs make use of methods from entanglement theory, as well as of results on matrix functions of block- banded matrices. Disordered systems are also considered. We moreover construct a class of examples for which the two- point correlation length diverges, yet still an area law can be proven to hold. We finally consider the scaling of classical correlations in a classical harmonic system and relate it to a quantum lattice system with a modified interaction. We briefly comment on a general relationship between criticality and area laws for the entropy of entanglement Y1 - 2006 UR - http://pra.aps.org/ U6 - https://doi.org/10.1103/Physreva.73.012309 ER - TY - JOUR A1 - Dana, Syamal Kumar A1 - Blasius, Bernd A1 - Kurths, Jürgen T1 - Experimental evidence of anomalous phase synchronization in two diffusively coupled Chua oscillators N2 - We study the transition to phase synchronization in two diffusively coupled, nonidentical Chua oscillators. In the experiments, depending on the used parameterization, we observe several distinct routes to phase synchronization, including states of either in-phase, out-of-phase, or antiphase synchronization, which may be intersected by an intermediate desynchronization regime with large fluctuations of the frequency difference. Furthermore, we report the first experimental evidence of an anomalous transition to phase synchronization, which is characterized by an initial enlargement of the natural frequency difference with coupling strength. This results in a maximal frequency disorder at intermediate coupling levels, whereas usual phase synchronization via monotonic decrease in frequency difference sets in only for larger coupling values. All experimental results are supported by numerical simulations of two coupled Chua models Y1 - 2006 UR - http://ojps.aip.org/chaos/ U6 - https://doi.org/10.1063/1.2197168 SN - 1054-1500 ER - TY - JOUR A1 - Kuzanyan, Kirill M. A1 - Pipin, Valerij V. A1 - Seehafer, Norbert T1 - The alpha effect and the observed twist and current helicity of solar magnetic fields N2 - We present a straightforward comparison of model calculations for the alpha-effect, helicities, and magnetic field line twist in the solar convection zone with magnetic field observations at atmospheric levels. The model calculations are carried out in a mixing-length approximation for the turbulence with a profile of the solar internal rotation rate obtained from helioseismic inversions. The magnetic field data consist of photospheric vector magnetograms of 422 active regions for which spatially-averaged values of the force-free twist parameter and of the current helicity density are calculated, which are then used to determine latitudinal profiles of these quantities. The comparison of the model calculations with the observations suggests that the observed twist and helicity are generated in the bulk of the convection zone, rather than in a layer close to the bottom. This supports two-layer dynamo models where the large-scale toroidal field is generated by differential rotation in a thin layer at the bottom while the alpha-effect is operating in the bulk of the convection zone. Our previous observational finding was that the moduli of the twist factor and of the current helicity density increase rather steeply from zero at the equator towards higher latitudes and attain a certain saturation at about 12 - 15 degrees. In our dynamo model with algebraic nonlinearity, the increase continues, however, to higher latitudes and is more gradual. This could be due to the neglect of the coupling between small-scale and large-scale current and magnetic helicities and of the latitudinal drift of the activity belts in the model Y1 - 2006 UR - http://www.springerlink.com/content/100339 U6 - https://doi.org/10.1007/s11207-006-1636-6 SN - 0038-0938 ER - TY - JOUR A1 - Franco, Olga A1 - Orgzall, Ingo A1 - Regenstein, Wolfgang A1 - Schulz, Burkhard T1 - Structural and spectroscopical study of a 2,5-diphenyl-1,3,4-oxadiazole polymorph under compression N2 - The x-ray pattern and the Raman and luminescence spectra of crystalline 2,5-diphenyl-1,3,4-oxadiazole in one of its polymorphic forms (DPO II) have been investigated under pressure up to 5 GPa. The behaviour of the lattice parameters under compression was determined and it was found that the Murnaghan equation of state provides a good description of the volume-pressure relationship of DPO II. The values for the bulk modulus and its pressure derivative are K-0 = 8.6 GPa and K-0' = 7.2. The analysis of the Raman spectrum under compression clearly shows the pressure- induced shift of the Raman modes to higher frequencies. The mode Gruneisen parameters for the lattice modes were determined. Additionally, it was found that the emission spectrum of DPO II moves to lower energies and that the luminescence intensity decreases when pressure is applied Y1 - 2006 UR - http://iopscience.iop.org/0953-8984 U6 - https://doi.org/10.1088/0953-8984/18/4/029 SN - 0953-8984 ER - TY - JOUR A1 - Vasconcelos, D. B. A1 - Lopes, S. R. A1 - Viana, R. L. A1 - Kurths, Jürgen T1 - Spatial recurrence plots N2 - We propose an extension of the recurrence plot concept to perform quantitative analyzes of roughness and disorder of spatial patterns at a fixed time. We introduce spatial recurrence plots (SRPs) as a graphical representation of the pointwise correlation matrix, in terms of a two-dimensional spatial return plot. This technique is applied to the study of complex patterns generated by coupled map lattices, which are characterized by measures of complexity based on SRPs. We show that the complexity measures we propose for SRPs provide a systematic way of investigating the distribution of spatially coherent structures, such as synchronization domains, in lattice profiles. This approach has potential for many more applications, e.g., in surface roughness analyzes Y1 - 2006 UR - http://pre.aps.org/pdf/PRE/v73/i5/e056207 U6 - https://doi.org/10.1103/Physreve.73.056207 ER - TY - JOUR A1 - Schulz, Burkhard A1 - Orgzall, Ingo A1 - Diez, Isabel A1 - Dietzel, Birgit A1 - Tauer, Klaus T1 - Template mediated formation of shaped polypyrrole particles N2 - The formation of different micro- and nanostructures during the chemical synthesis of polypyrrole is reviewed shortly based on the conceptions of hard- and soft-templating models. Contrary to other models that emphasize the role of micelles it is found here that during the oxidative polymerization of pyrole using sulfonic acid dopants a crystalline hard template is found in the first steps of the reaction before the addition of the oxidant. This template is formed by a complex consisting of 2,5-bis(pyrrole-2-yl)pyrrolidine and the sulfonic acid anion. The acid catalyzed formation of this specific tripyrrole is discussed. (C) 2009 Elsevier B.V. All rights reserved. Y1 - 2010 U6 - https://doi.org/10.1016/j.colsurfa.2009.11.034 SN - 0927-7757 ER - TY - JOUR A1 - Orus, Roman A1 - Latorre, Jose Ignacio A1 - Eisert, Jens A1 - Cramer, Marcus T1 - Half the entanglement in critical systems is distillable from a single specimen N2 - We establish a quantitative relationship between the entanglement content of a single quantum chain at a critical point and the corresponding entropy of entanglement. We find that, surprisingly, the leading critical scaling of the single-copy entanglement with respect to any bipartitioning is exactly one-half of the entropy of entanglement, in a general setting of conformal field theory and quasifree systems. Conformal symmetry imposes that the single-copy entanglement scales as E-1(rho(L))=(c/6)ln L-(c/6)(pi(2)/ln L)+O(1/L), where L is the number of constituents in a block of an infinite chain and c denotes the central charge. This shows that from a single specimen of a critical chain, already half the entanglement can be distilled compared to the rate that is asymptotically available. The result is substantiated by a quantitative analysis for all translationally invariant quantum spin chains corresponding to all isotropic quasifree fermionic models. An example of the XY spin chain shows that away from criticality the above relation is maintained only near the quantum phase transition Y1 - 2006 UR - http://pra.aps.org/ U6 - https://doi.org/10.1103/Physreva.73.060303 ER - TY - JOUR A1 - Nest, Mathias T1 - Quantum carpets and correlated dynamics of several fermions N2 - We study theoretically the coherent and correlated motion of many fermions inside an infinite square well potential. We will look at electrons and He-3 atoms, which behave very differently not only because of their masses, but also because of their different interaction potential. Also, the level of theory and the role of approximations in the solution of the time-dependent Schrodinger equation will be discussed Y1 - 2006 UR - http://pra.aps.org/ U6 - https://doi.org/10.1103/Physreva.73.023613 ER - TY - JOUR A1 - Kurths, Jürgen A1 - Romano, Maria Carmen A1 - Thiel, Marco A1 - Osipov, Grigory V. A1 - Ivanchenko, Mikhail V. A1 - Kiss, Istvan Z. A1 - Hudson, John L. T1 - Synchronization analysis of coupled noncoherent oscillators N2 - We present two different approaches to detect and quantify phase synchronization in the case of coupled non- phase coherent oscillators. The first one is based on the general idea of curvature of an arbitrary curve. The second one is based on recurrences of the trajectory in phase space. We illustrate both methods in the paradigmatic example of the Rossler system in the funnel regime. We show that the second method is applicable even in the case of noisy data. Furthermore, we extend the second approach to the application of chains of coupled systems, which allows us to detect easily clusters of synchronized oscillators. In order to illustrate the applicability of this approach, we show the results of the algorithm applied to experimental data from a population of 64 electrochemical oscillators Y1 - 2006 UR - http://www.springerlink.com/content/102972 U6 - https://doi.org/10.1007/s11071-006-1957-x SN - 0924-090X ER - TY - JOUR A1 - Luszczynska, Beata A1 - Dobruchowska, Ewa A1 - Glowacki, Ireneusz A1 - Ulanski, Jacek A1 - Jaiser, Frank A1 - Yang, Xiaohui A1 - Neher, Dieter A1 - Danel, Andrzej T1 - Poly(N-vinylcarbazole) doped with a pyrazoloquinoline dye : a deep blue light-emitting composite for light- emitting diode applications N2 - We investigated the spectral properties of light-emitting diodes based on a deep blue-emitting pyrazoloquinoline dye doped into a poly(N-vinylcarbazole)-based matrix. Even though the electroluminescence (EL) of the host is redshifted and broadened with respect to the emission of the dye, the EL spectrum becomes fully dominated by the dye emission at concentrations of ca. 2 wt %. This is attributed to a competition of exciplex formation on the matrix and exciton formation on the dye. Y1 - 2006 UR - http://jap.aip.org/ U6 - https://doi.org/10.1063/1.2162268 SN - 0021-8979 ER - TY - JOUR A1 - Pasternak, Zohar A1 - Blasius, Bernd A1 - Abelson, Avigdor A1 - Achituv, Yair T1 - Host-finding behaviour and navigation capabilities of symbiotic zooxanthellae N2 - Past studies have shown that the initiation of symbiosis between the Red-Sea soft coral Heteroxenia fuscescens and its symbiotic dinoflagellates occurs due to the chemical attraction of the motile algal cells to substances emanating from the coral polyps. However, the resulting swimming patterns of zooxanthellae have not been previously studied. This work examined algal swimming behaviour, host location and navigation capabilities under four conditions: (1) still water, (2) in still water with waterborne host attractants, (3) in flowing water, and (4) in flow with host attractants. Algae were capable of actively and effectively locating their host in still water as well as in flow. When in water containing host attractants, swimming became slower, motion patterns straighter and the direction of motion was mainly towards the host-even if this meant advancing upstream against flow velocities of up to 0.5 mm s(-1)supercript stop. Coral-algae encounter probability decreased the further downstream of the host algae were located, probably due to diffusion of the chemical signal. The results show how the chemoreceptive zooxanthellae modify their swimming pattern, direction, velocity, circuity and turning rate to accommodate efficient navigation in changing environmental conditions Y1 - 2006 UR - http://www.springerlink.com/content/100407 U6 - https://doi.org/10.1007/s00338-005-0085-2 ER - TY - JOUR A1 - Schwager, Monika A1 - Johst, Karin A1 - Jeltsch, Florian T1 - Does red noise increase or decrease extinction risk? Single extreme events versus series of unfavorable conditions N2 - Recent theoretical studies have shown contrasting effects of temporal correlation of environmental fluctuations ( red noise) on the risk of population extinction. It is still debated whether and under which conditions red noise increases or decreases extinction risk compared with uncorrelated ( white) noise. Here, we explain the opposing effects by introducing two features of red noise time series. On the one hand, positive autocorrelation increases the probability of series of poor environmental conditions, implying increasing extinction risk. On the other hand, for a given time period, the probability of at least one extremely bad year ("catastrophe") is reduced compared with white noise, implying decreasing extinction risk. Which of these two features determines extinction risk depends on the strength of environmental fluctuations and the sensitivity of population dynamics to these fluctuations. If extreme ( catastrophic) events can occur ( strong noise) or sensitivity is high ( overcompensatory density dependence), then temporal correlation decreases extinction risk; otherwise, it increases it. Thus, our results provide a simple explanation for the contrasting previous findings and are a crucial step toward a general understanding of the effect of noise color on extinction risk Y1 - 2006 ER - TY - JOUR A1 - Gross, Thilo A1 - Feudel, Ulrike T1 - Generalized models as a universal approach to the analysis of nonlinear dynamical systems N2 - We present a universal approach to the investigation of the dynamics in generalized models. In these models the processes that are taken into account are not restricted to specific functional forms. Therefore a single generalized models can describe a class of systems which share a similar structure. Despite this generality, the proposed approach allows us to study the dynamical properties of generalized models efficiently in the framework of local bifurcation theory. The approach is based on a normalization procedure that is used to identify natural parameters of the system. The Jacobian in a steady state is then derived as a function of these parameters. The analytical computation of local bifurcations using computer algebra reveals conditions for the local asymptotic stability of steady states and provides certain insights on the global dynamics of the system. The proposed approach yields a close connection between modelling and nonlinear dynamics. We illustrate the investigation of generalized models by considering examples from three different disciplines of science: a socioeconomic model of dynastic cycles in china, a model for a coupled laser system and a general ecological food web Y1 - 2006 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.73.016205 SN - 1539-3755 ER - TY - JOUR A1 - Beyvers, Stephanie A1 - Ohtsuki, Y A1 - Saalfrank, Peter T1 - Optimal control in a dissipative system : vibrational excitation of CO/Cu(100) by IR pulses N2 - The question as to whether state-selective population of molecular vibrational levels by shaped infrared laser pulses is possible in a condensed phase environment is of central importance for such diverse fields as time-resolved spectroscopy, quantum computing, or "vibrationally mediated chemistry." This question is addressed here for a model system, representing carbon monoxide adsorbed on a Cu(100) surface. Three of the six vibrational modes are considered explicitly, namely, the CO stretch vibration, the CO-surface vibration, and a frustrated translation. Optimized infrared pulses for state-selective excitation of "bright" and "dark" vibrational levels are designed by optimal control theory in the framework of a Markovian open-system density matrix approach, with energy flow to substrate electrons and phonons, phase relaxation, and finite temperature accounted for. The pulses are analyzed by their Husimi "quasiprobability" distribution in time-energy space. Y1 - 2006 UR - http://jcp.aip.org/ U6 - https://doi.org/10.1063/1.2206593 SN - 0021-9606 ER - TY - JOUR A1 - Evans, Nicholas R. A1 - Devi, Lekshmi Sudha A1 - Mak, Chris S. K. A1 - Watkins, Scott E. A1 - Pascu, Sofia I. A1 - Köhler, Anna A1 - Friend, Richard H. A1 - Williams, Charlotte K. A1 - Holmes, Andrew B. T1 - Triplet energy back transfer in conjugated polymers with pendant phosphorescent iridium complexes N2 - The nature of Dexter triplet energy transfer between bonded systems of a red phosphorescent iridium complex 13 and a conjugated polymer, polyfluorene, has been investigated in electrophosphorescent organic light-emitting diodes. Red- emitting phosphorescent iridium complexes based on the [Ir(btp)2(acac)]fragment (where btp is 2-(2 '- benzo[b]thienyl)pyridinato and acac is acetylacetonate) have been attached either directly (spacerless) or through a - (CH2)(8)-chain (octamethylene-tethered) at the 9-position of a 9-octylfluorene host. The resulting dibromo- functionalized spacerless (8) or octamethylene-tethered (12) fluorene monomers were chain extended by Suzuki polycondensations using the bis(boronate)-terminated fluorene macromonomers 16 in the presence of end-capping chlorobenzene solvent to produce the statistical spacerless (17) and octamethylene-tethered ( 18) copolymers containing an even dispersion of the pendant phosphorescent fragments. The spacerless monomer 12 adopts a face-to-face conformation with a separation of only 3.6 angstrom between the iridium complex and fluorenyl group, as shown by X-ray analysis of a single crystal, and this facilitates intramolecular triplet energy transfer in the spacerless copolymers 17. The photo- and electroluminescence efficiencies of the octamethylene-tethered copolymers 18 are double those of the spacerless copolymers 17, and this is consistent with suppression of the back transfer of triplets from the red phosphorescent iridium complex to the polyfluorene backbone in 18. The incorporation of a -(CH2)(8)- chain between the polymer host and phosphorescent guest is thus an important design principle for achieving higher efficiencies in those electrophosphorescent organic light-emitting diodes for which the triplet energy levels of the host and guest are similar Y1 - 2006 UR - http://pubs.acs.org/journal/jacsat U6 - https://doi.org/10.1021/Ja0584267 SN - 0002-7863 ER - TY - JOUR A1 - Yang, X. H. A1 - Jaiser, Frank A1 - Klinger, S A1 - Neher, Dieter T1 - Blue polymer electrophosphorescent devices with different electron-transporting oxadiazoles N2 - We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert- butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at similar to 40 wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd/A and 8.8 lm/W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component. (c) 2006 American Institute of Physics Y1 - 2006 UR - http://scitation.aip.org/getpdf/servlet/ GetPDFServlet?filetype=pdf&id=APPLAB000088000002021107000001&idtype=cvips&doi=10.1063/1.2162693&prog=normal U6 - https://doi.org/10.1063/1.2162693 ER - TY - JOUR A1 - Ostermeyer, Martin A1 - Mudge, Damien A1 - Veitch, Peter John A1 - Munch, Jesper T1 - Thermally induced birefringence in Nd : YAG slab lasers N2 - We study thermally induced birefringence in crystalline Nd:YAG zigzag slab lasers and the associated depolarization losses. The optimum crystallographic orientation of the zigzag slab within the Nd:YAG boule and photoelastic effects in crystalline Nd:YAG slabs are briefly discussed. The depolarization is evaluated using the temperature and stress distributions, calculated using a finite element model, for realistically pumped and cooled slabs of finite dimensions. Jones matrices are then used to calculate the depolarization of the zigzag laser mode. We compare the predictions with measurements of depolarization, and suggest useful criteria for the design of the gain media for such lasers. Y1 - 2006 UR - http://www.opticsinfobase.org/ U6 - https://doi.org/10.1364/AO.45.005368 ER - TY - JOUR A1 - Jechow, Andreas A1 - Raab, Volker A1 - Menzel, Ralf T1 - High cw power using an external cavity for spectral beam combining of diode laser-bar emission N2 - In extension to known concepts of wavelength-multiplexing diode laser arrays, a new external cavity is presented. The setup simultaneously improves the beam quality of each single emitter of a standard 25 emitter broad-area stripe laser bar and spectrally superimposes the 25 beams into one. By using this external resonator in an "off-axis" arrangement, beam qualities of M-slow(2) < 14 and M-fast(2) < 3 with optical powers in excess of 10 W in cw operation are obtained. Y1 - 2006 UR - http://www.opticsinfobase.org/ao/browse.cfm U6 - https://doi.org/10.1364/AO.45.003545 SN - 0003-6935 ER - TY - JOUR A1 - Charron, Eric A1 - Cirone, M. A. A1 - Negretti, Antonio A1 - Schmiedmayer, Jörg A1 - Calarco, Tommaso T1 - Theoretical analysis of a realistic atom-chip quantum gate N2 - We present a detailed, realistic analysis of the implementation of a proposal for a quantum phase gate based on atomic vibrational states, specializing it to neutral rubidium atoms on atom chips. We show how to create a double-well potential with static currents on the atom chips, using for all relevant parameters values that are achieved with present technology. The potential barrier between the two wells can be modified by varying the currents in order to realize a quantum phase gate for qubit states encoded in the atomic external degree of freedom. The gate performance is analyzed through numerical simulations; the operation time is similar to 10 ms with a performance fidelity above 99.9%. For storage of the state between the operations the qubit state can be transferred efficiently via Raman transitions to two hyperfine states, where its decoherence is strongly inhibited. In addition we discuss the limits imposed by the proximity of the surface to the gate fidelity. Y1 - 2006 UR - http://pra.aps.org/ SN - 1050-2947 ER - TY - JOUR A1 - Winterhalder, Matthias A1 - Schelter, B A1 - Kurths, Jürgen A1 - Schulze-Borthage, A A1 - Timmer, Jens T1 - Sensitivity and specificity of coherence and phase synchronization analysis N2 - In this Letter, we show that coherence and phase synchronization analysis are sensitive but not specific in detecting the correct class of underlying dynamics. We propose procedures to increase specificity and demonstrate the power of the approach by application to paradigmatic dynamic model systems. (c) 2006 Elsevier B.V. All rights reserved Y1 - 2006 UR - http://www.sciencedirect.com/science/article/pii/S0375960106004002 ( 11.07.2011] U6 - https://doi.org/10.1016/j.physleta.2006.03.018 ER - TY - JOUR A1 - Schwabedal, Justus T. C. A1 - Pikovskij, Arkadij T1 - Effective phase description of noise-perturbed and noise-induced oscillations N2 - An effective dynamical description of a general class of stochastic phase oscillators is presented. For this, the effective phase velocity is defined either by the stochastic phase oscillators invariant probability density or its first passage times. Using the first approach the effective phase exhibits the correct frequency and invariant distribution density, whereas the second approach models the proper phase resetting curve. The discrepancy of the effective models is most pronounced for noise-induced oscillations and is related to non-monotonicity of the stochastic phase variable due to fluctuations. Y1 - 2010 U6 - https://doi.org/10.1140/epjst/e2010-01271-6 SN - 1951-6355 ER - TY - JOUR A1 - Wegener, Michael A1 - Bergweiler, Steffen A1 - Zscherpel, Detlef A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Detection of elliptical oscillations and monopole breathing of organ-pipe bodies with piezoelectric polymer sensors N2 - In this paper, a measuring technique is presented for the detection of radial oscillations of tube walls excited by changes in internal air pressure. On organ pipes, the oscillations were investigated by means of piezoelectric polymer films slightly tensioned around the pipe bodies. Employing sensors with patterned electrodes, the well-known elliptical oscillation of the cross section as well as an additional monopole breathing of the organ-pipe body were detected. For the monopole breathing, a close relationship between the pressure distribution of the air-column resonances inside the pipe and the circumference variations along the pipe was observed Y1 - 2006 ER - TY - JOUR A1 - Wu, Ye A1 - Zhou, Changsong A1 - Chen, Maoyin A1 - Xiao, Jinghua A1 - Kurths, Jürgen T1 - Human comment dynamics in on-line social systems N2 - Human comment is studied using data from 'tianya' which is one of the most popular on-line social systems in China. We found that the time interval between two consecutive comments on the same topic, called inter-event time, follows a power-law distribution. This result shows that there is no characteristic decay time on a topic. It allows for very long periods without comments that separate bursts of intensive comments. Furthermore, the frequency of a different ID commenting on a topic also follows a power-law distribution. It indicates that there are some "hubs" in the topic who lead the direction of the public opinion. Based on the personal comments habit, a model is introduced to explain these phenomena. The numerical simulations of the model fit well with the empirical results. Our findings are helpful for discovering regular patterns of human behavior in on-line society and the evolution of the public opinion on the virtual as well as real society. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/03784371 U6 - https://doi.org/10.1016/j.physa.2010.08.049 SN - 0378-4371 ER - TY - JOUR A1 - Henkel, Carsten A1 - Joulain, Karl T1 - Electromagnetic field correlations near a surface with a nonlocal optical response N2 - The coherence length of the thermal electromagnetic field near a planar surface has a minimum value related to the nonlocal dielectric response of the material. We perform two model calculations of the electric energy density and the field's degree of spatial coherence. Above a polar crystal, the lattice constant gives the minimum coherence length. It also gives the upper limit to the near field energy density, cutting off its 1/z(3) divergence. Near an electron plasma described by the semiclassical Lindhard dielectric function, the corresponding length scale is fixed by plasma screening to the Thomas-Fermi length. The electron mean free path, however, sets a larger scale where significant deviations from the local description are visible Y1 - 2006 UR - http://www.springerlink.com/content/100502 U6 - https://doi.org/10.1007/s00340-006-2219-9 SN - 0946-2171 ER - TY - JOUR A1 - Schwabedal, Justus T. C. A1 - Pikovskij, Arkadij T1 - Effective phase dynamics of noise-induced oscillations in excitable systems N2 - We develop an effective description of noise-induced oscillations based on deterministic phase dynamics. The phase equation is constructed to exhibit correct frequency and distribution density of noise-induced oscillations. In the simplest one-dimensional case the effective phase equation is obtained analytically, whereas for more complex situations a simple method of data processing is suggested. As an application an effective coupling function is constructed that quantitatively describes periodically forced noise-induced oscillations. Y1 - 2010 UR - http://link.aps.org/doi/10.1103/PhysRevE.81.046218 U6 - https://doi.org/10.1103/Physreve.81.046218 SN - 1539-3755 ER - TY - JOUR A1 - Abel, Markus A1 - Bergweiler, Steffen A1 - Gerhard, Reimund T1 - Synchronization of organ pipes : experimental observations and modeling N2 - We report measurements on the synchronization properties of organ pipes. First, we investigate influence of an external acoustical signal from a loudspeaker on the sound of an organ pipe. Second, the mutual influence of two pipes with different pitch is analyzed. In analogy to the externally driven, or mutually coupled self-sustained oscillators, one observes a frequency locking, which can be explained by synchronization theory. Further, we measure the dependence of the frequency of the signals emitted by two mutually detuned pipes with varying distance between the pipes. The spectrum shows a broad '' hump '' structure, not found for coupled oscillators. This indicates a complex coupling of the two organ pipes leading to nonlinear beat phenomena. Y1 - 2006 UR - http://scitation.aip.org/jasa/ U6 - https://doi.org/10.1121/1.217044 SN - 0001-4966 ER - TY - JOUR A1 - Varykhalov, Andrei A1 - Gudat, Wolfgang A1 - Adamchuk, V. K. A1 - Rader, Oliver T1 - Magic numbers in two-dimensional self-organization of C-60 molecules N2 - Employing the chemically passive carbon reconstruction W(110)/C-R(15x3) as substrate for deposition of C-60 molecules, we have discovered by scanning tunneling microscopy two-dimensional self-assembly of fullerenes into uniform molecular nanoclusters with "magic" numbers. Our photoemission measurements determine van der Waals forces as the dominating interaction in this self-organizing two-dimensional molecular gas. Based on this, a theoretical determination of the cluster structures in the framework of the Girifalco model gives perfect agreement with the experiment Y1 - 2006 UR - http://prb.aps.org/pdf/PRB/v73/i24/e241404 U6 - https://doi.org/10.1103/Physrevb.73.241404 ER - TY - JOUR A1 - Mellinger, Axel A1 - Wegener, Michael A1 - Wirges, Werner A1 - Mallepally, Rajendar Reddy A1 - Gerhard, Reimund T1 - Thermal and temporal stability of ferroelectret films made from cellular polypropylene/air composites N2 - Ferroelectrets are thin films of polymer foams, exhibiting piezoelectric properties after electrical charging. Ferroelectret foams usually consist of a cellular polymer structure filled with air. Polymer-air composites are elastically soft due to their high air content as well as due to the size and shape of the polymer walls. Their elastically soft composite structure is one essential key for the working principle of ferroelectrets, besides the permanent trapping of electric charges inside the polymer voids. The elastic properties allow large deformations of the electrically charged voids. However, the composite structure can also possibly limit the stability and consequently the range of applications because of, e. g., penetration of gas and liquids accompanied by discharge phenomena or because of a mechanical pre-load which may be required during the application. Here, we discuss various stability aspects related to the piezoelectric properties of polypropylene ferroelectrets. Near and below room temperature, the piezoelectric effect and the stability of the trapped charges are practically independent from humidity during long-time storage in a humid atmosphere or water, or from operating conditions, such as continuous mechanical excitation. Thermal treatment of cellular polypropylene above -10 degrees C leads to a softening of the voided structure which is apparent from the decreasing values of the elastic modulus. This decrease results in an increase of the piezoelectric activity. Heating above 60 degrees C, however, leads to a decrease in piezoelectricity Y1 - 2006 ER - TY - JOUR A1 - Mikelskis, Helmut F. T1 - Chaosphysik Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Mikelskis, Helmut F. T1 - Die Nanowelt Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Mikelskis, Helmut F. T1 - Offener Physikunterricht Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Mikelskis, Helmut F. T1 - Die Rolle des Physikbuches beim Unterrichten und Lernen von Physik Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Mikelskis, Helmut F. T1 - Physikunterricht als Beitrag zur Bewältigung gesellschaftlicher Schlüsselprobleme Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Shklyaev, Sergey A1 - Straube, Arthur V. T1 - Superexponential droplet fractalization as a hierarchical formation of dissipative compactons N2 - We study the dynamics of a thin film over a substrate heated from below in a framework of a strongly nonlinear one-dimensional Cahn-Hilliard equation. The evolution leads to a fractalization into smaller and smaller scales. We demonstrate that a primitive element in the appearing hierarchical structure is a dissipative compacton. Both direct simulations and the analysis of a self-similar solution show that the compactons appear at superexponentially decreasing scales, which means vanishing dimension of the fractal. Y1 - 2010 UR - http://pre.aps.org/ U6 - https://doi.org/10.1103/Physreve.82.020601 SN - 1539-3755 ER - TY - JOUR A1 - Klamroth, Tillmann T1 - Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone N2 - We report time-dependent configuration interaction singles calculations for the ultrafast laser driven many- electron dynamics in a polyatomic molecule, N-methyl-6-quinolone. We employ optimal control theory to achieve a nearly state-selective excitation from the S-0 to the S-1 state, on a time scale of a few (approximate to 6) femtoseconds. The optimal control scheme is shown to correct for effects opposing a state-selective transition, such as multiphoton transitions and other, nonlinear phenomena, which are induced by the ultrashort and intense laser fields. In contrast, simple two-level pi pulses are not effective in state-selective excitations when very short pulses are used. Also, the dependence of multiphoton and nonlinear effects on the number of states included in the dynamical simulations is investigated. Y1 - 2006 UR - http://jcp.aip.org/ U6 - https://doi.org/10.1063/1.2185633 SN - 0021-9606 ER - TY - JOUR A1 - Mellinger, Axel A1 - Flores Suárez, Rosaura A1 - Singh, Rajeev A1 - Wegener, Michael A1 - Wirges, Werner A1 - Lang, Sidney B. A1 - Gerhard, Reimund T1 - High-resolution space-charge and polarization tomography with thermal pulses N2 - Die Arbeit wurde am 13.03.2006 mit dem "BEST PAPER AWARD" des deutschen IEEE Instrumentation and Measurement (I&M) Chapter ausgezeichnet. Y1 - 2006 SN - 3-8007-2939-3 ER - TY - JOUR A1 - Rabe, Thorid T1 - Motivation, Interesse und Selbstkonzept im Physikunterricht Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Starauschek, Erich T1 - Zur Rolle der Sprache beim Lernen von Physik Y1 - 2006 SN - 3-589-22148-8 ER - TY - JOUR A1 - Beim Graben, Peter A1 - Atmanspacher, Harald T1 - Complementarity in classical dynamical systems N2 - The concept of complementarity, originally defined for non-commuting observables of quantum systems with states of non-vanishing dispersion, is extended to classical dynamical systems with a partitioned phase space. Interpreting partitions in terms of ensembles of epistemic states (symbols) with corresponding classical observables, it is shown that such observables are complementary to each other with respect to particular partitions unless those partitions are generating. This explains why symbolic descriptions based on an ad hoc partition of an underlying phase space description should generally be expected to be incompatible. Related approaches with different background and different objectives are discussed Y1 - 2006 UR - http://www.springerlink.com/content/101591 U6 - https://doi.org/10.1007/s10701-005-9013-0 SN - 0015-9018 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Tiersch, Brigitte T1 - Porous polytetrafluoroethylene (PTFE) electret films : porosity and time dependent charging behaviour of the free surface N2 - Electrically charged porous polytetrafluoroethylene (PTFE) films are often discussed as active layers for electromechanical transducers. Here, the electric charging behavior of open-porous PTFE films with different porosities is investigated. Optimized electric charging of porous PTFE films is determined by variation of charging parameters such as electric fields and charging times. Maximum surface potentials are depending on the porosity of the PTFE films. Suitable charging leads to high surface potentials observed on non-stretched or slightly stretched porous PTFE films. Further increase of charging fields yields decreasing values of the surface potential accompanied with an increase of conductivity. Y1 - 2006 UR - http://www.springerlink.com/content/601u86x365560515/ U6 - https://doi.org/10.1007/s10934-006-9015-0 ER - TY - JOUR A1 - Qiu, Xunlin A1 - Mellinger, Axel A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Dielectric barrier discharges during the generation of ferroelectrets : optical spectroscopy for process monitoring Y1 - 2007 SN - 978-1-4244-1482-6 ER - TY - JOUR A1 - Basso, Heitor Cury A1 - Altafim, Ruy Alberto Pisani A1 - Altafim, Ruy Alberto Pisani A1 - Mellinger, Axel A1 - Fang, Peng A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Three-layer ferroelectrets from perforated Teflon-PTFE films fused between two homogeneous Teflon-FEP films Y1 - 2007 SN - 978-1-4244-1482-6 ER - TY - JOUR A1 - Wegener, Michael A1 - Wirges, Werner A1 - Paajanen, Mika A1 - Gerhard, Reimund T1 - Charging behaviour and thermal stability of porous and non-porous polytetrafluoroethylene (PTFE) electrets Y1 - 2007 SN - 978-1-4244-1482-6 ER - TY - JOUR A1 - Qiu, Xunlin A1 - Mellinger, Axel A1 - Wegener, Michael A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Barrier discharges in cellular polypropylene ferroelectrets : how do they influence the electromechanical properties? Y1 - 2007 ER - TY - JOUR A1 - Reddy, Raghavendra V. A1 - Puranik, Shikha A1 - Gupta, Ajay A1 - Leitenberger, Wolfram T1 - Study of FePt films prepared by reactive sputtering Y1 - 2007 UR - http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TW4-4N49VG1-1- 9&_cdi=5552&_user=1584062&_orig=search&_coverDate=05%2F25%2F2007&_sk=999189990&view=c&wchp=dGLbVtb- zSkzS&md5=d04c9f9f7492f4ef5fb605bfbaf ER - TY - JOUR A1 - Seehafer, Norbert A1 - Fuhrmann, M. A1 - Valori, Gherardo A1 - Kliem, Bernhard T1 - Force-free magnetic fields in the solar atmosphere Y1 - 2007 UR - http://www3.interscience.wiley.com/cgi-bin/abstract/117872628/ABSTRACT ER - TY - JOUR A1 - Mikelskis-Seifert, Silke A1 - Rabe, Thorid T1 - Der darbietende Unterricht : Darstellung und Präsentation durch Lehrerinnen Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Kasper, Lutz T1 - Textarbeit und Narration : Naration Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Rabe, Thorid T1 - Textarbeit und Narration : Textarbeit Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Mikelskis-Seifert, Silke A1 - Leisner-Bodenthin, Antje T1 - Unterrichtsansätze zu den Methoden physikalischer Erkenntnisgewinnung : die Modellmethode Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Rabe, Thorid T1 - Schülerzentierte Unterrichtsansätze : Kooperatives Lernen in Gruppen Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Menzel, Ralf T1 - Photonics : linear and nonlinear interactions of laser light and matter Y1 - 2007 SN - 978-540-67074-2 PB - Springer CY - Berlin ER - TY - JOUR A1 - Palus, Milan A1 - Kurths, Jürgen A1 - Schwarz, Udo A1 - Seehafer, Norbert A1 - Novotna, Dagmar A1 - Charvatova, Ivanka T1 - The solar activity cycle is weakly synchronized with the solar inertial motion N2 - We study possible interrelations between the 300-year record of the yearly sunspot numbers and the solar inertial motion (SIM) using the recently developed technique of synchronization analysis. Phase synchronization of the sunspot cycle and the SIM is found and statistically confirmed in three epochs (1734-1790, 1855-1875 and 1907-1960) of the whole period 1700-2000. These results give quantitative support to the hypothesis that there is a weak interaction between the solar activity and the SIM. Y1 - 2007 UR - http://www.sciencedirect.com/ science?_ob=GatewayURL&_method=citationSearch&_urlVersion=4&_origin=SDVIALERTHTML&_version=1&_uoikey=B6TVM-4MYVG5S- 1&md5=92d1fc7094be5195504f17e1afb4f0d1 U6 - https://doi.org/10.1016/j.physleta.2007.01.039 ER - TY - JOUR A1 - Mikelskis, Helmut F. T1 - Unterrichtsprinzipien : exemplarisch - genetisch - sokratisch Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Mikelskis-Seifert, Silke A1 - Rabe, Thorid T1 - Der darbietende Unterricht : darbieten - was und wie? Y1 - 2007 SN - 978-3-589-22377-0 ER - TY - JOUR A1 - Kofod, Guggi A1 - Wirges, Werner A1 - Paajanen, Mika A1 - Bauer, Siegfried T1 - Energy minimization for self-organized structure formation and actuation N2 - An approach for creating complex structures with embedded actuation in planar manufacturing steps is presented. Self-organization and energy minimization are central to this approach, illustrated with a model based on minimization of the hyperelastic free energy strain function of a stretched elastomer and the bending elastic energy of a plastic frame. A tulip-shaped gripper structure illustrates the technological potential of the approach. Advantages are simplicity of manufacture, complexity of final structures, and the ease with which any electroactive material can be exploited as means of actuation. (c) 2007 American Institute of Physics. Y1 - 2007 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.2695785 SN - 0003-6951 ER - TY - JOUR A1 - Kowarik, Stefan A1 - Gerlach, Andreas A1 - Leitenberger, Wolfram A1 - Hu J, Witte A1 - Wöll, Christoph A1 - Schreiber, Frank T1 - Energy-dispersive X-ray reflectivity and GID for real-time growth studies of pentacene thin films N2 - We use energy-dispersive X-ray reflectivity and grazing incidence diffraction (GID) to follow the growth of the crystalline organic semiconductor pentacene on silicon oxide in-situ and in real-time. The technique allows for monitoring Bragg reflections and measuring X-ray growth oscillations with a time resolution of 1 min in a wide q-range in reciprocal space extending over 0.25-0.80 angstrom(-1), i.e. sampling a large number of Fourier components simultaneously. A quantitative analysis of growth oscillations at several q-points yields the evolution of the surface roughness, showing a marked transition from layer-by-layer growth to strong roughening after four monolayers of pentacene have been deposited. (c) 2006 Elsevier B.V. All rights reserved. Y1 - 2007 UR - http://www.sciencedirect.com/science/journal/00406090 U6 - https://doi.org/10.1016/j.tsf.2006.12.020 SN - 0040-6090 ER - TY - JOUR A1 - Qiu, Xunlin A1 - Mellinger, Axel A1 - Wirges, Werner A1 - Gerhard, Reimund T1 - Spectroscopic study of dielectric barrier discharges in cellular polypropylene ferroelectrets N2 - The transient light emission from the dielectric barrier discharges (DBDs) in cellular polypropylene ferroelectrets subjected to high electric poling fields was spectroscopically measured. The spectrum shows strong emission from the second positive system of molecular nitrogen, N-2(C (3)Pi(u))-> N-2(B (3)Pi(g)), and the first negative system of N-2(+), N-2(+)(B (2)Sigma(+)(u))-> N-2(+)(X (2)Sigma(+)(g)), consistent with a DBD in air. When a dc voltage is applied stepwise to the ferroelectret film, light emission starts above a threshold, coinciding with the threshold voltage in obtaining piezoelectricity. From selected vibronic band strength ratios, the electric field in the discharge was determined and found to agree with Townsend breakdown. Y1 - 2007 UR - http://apl.aip.org/ U6 - https://doi.org/10.1063/1.2786597 ER - TY - JOUR A1 - Feudel, Fred A1 - Tuckerman, L. S. A1 - Gellert, Marcus A1 - Seehafer, Norbert T1 - Bifurcations of rotating waves in rotating spherical shell convection JF - Physical Review E N2 - The dynamics and bifurcations of convective waves in rotating and buoyancy-driven spherical Rayleigh-Benard convection are investigated numerically. The solution branches that arise as rotating waves (RWs) are traced by means of path-following methods, by varying the Rayleigh number as a control parameter for different rotation rates. The dependence of the azimuthal drift frequency of the RWs on the Ekman and Rayleigh numbers is determined and discussed. The influence of the rotation rate on the generation and stability of secondary branches is demonstrated. Multistability is typical in the parameter range considered. KW - nonsymmetric linear-systems KW - thermal-convection KW - fluid shells KW - hopf-bifurcation KW - onset KW - magnetoconvection KW - number KW - flow Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevE.92.053015 SN - 1539-3755 SN - 1550-2376 VL - 92 IS - 5 PB - American Physical Society CY - Woodbury ER - TY - JOUR A1 - Feldmann, David A1 - Maduar, Salim R. A1 - Santer, Mark A1 - Lomadze, Nino A1 - Vinogradova, Olga I. A1 - Santer, Svetlana T1 - Manipulation of small particles at solid liquid interface BT - light driven diffusioosmosis JF - Scientific reports N2 - The strong adhesion of sub-micron sized particles to surfaces is a nuisance, both for removing contaminating colloids from surfaces and for conscious manipulation of particles to create and test novel micro/nano-scale assemblies. The obvious idea of using detergents to ease these processes suffers from a lack of control: the action of any conventional surface-modifying agent is immediate and global. With photosensitive azobenzene containing surfactants we overcome these limitations. Such photo-soaps contain optical switches (azobenzene molecules), which upon illumination with light of appropriate wavelength undergo reversible trans-cis photo-isomerization resulting in a subsequent change of the physico-chemical molecular properties. In this work we show that when a spatial gradient in the composition of trans- and cis- isomers is created near a solid-liquid interface, a substantial hydrodynamic flow can be initiated, the spatial extent of which can be set, e.g., by the shape of a laser spot. We propose the concept of light induced diffusioosmosis driving the flow, which can remove, gather or pattern a particle assembly at a solid-liquid interface. In other words, in addition to providing a soap we implement selectivity: particles are mobilized and moved at the time of illumination, and only across the illuminated area. KW - genomic DNA conformation KW - photosensitive surfactants KW - optical manipulation KW - photocontrol KW - azobenzene KW - films KW - gradients KW - transport KW - tracking KW - brushes Y1 - 2016 U6 - https://doi.org/10.1038/srep36443 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - de Carvalho, Sidney J. A1 - Metzler, Ralf A1 - Cherstvy, Andrey G. T1 - Critical adsorption of polyelectrolytes onto planar and convex highly charged surfaces BT - the nonlinear Poisson–Boltzmann approach JF - New journal of physics : the open-access journal for physics N2 - We study the adsorption–desorption transition of polyelectrolyte chains onto planar, cylindrical and spherical surfaces with arbitrarily high surface charge densities by massive Monte Carlo computer simulations. We examine in detail how the well known scaling relations for the threshold transition—demarcating the adsorbed and desorbed domains of a polyelectrolyte near weakly charged surfaces—are altered for highly charged interfaces. In virtue of high surface potentials and large surface charge densities, the Debye–Hückel approximation is often not feasible and the nonlinear Poisson–Boltzmann approach should be implemented. At low salt conditions, for instance, the electrostatic potential from the nonlinear Poisson–Boltzmann equation is smaller than the Debye–Hückel result, such that the required critical surface charge density for polyelectrolyte adsorption σc increases. The nonlinear relation between the surface charge density and electrostatic potential leads to a sharply increasing critical surface charge density with growing ionic strength, imposing an additional limit to the critical salt concentration above which no polyelectrolyte adsorption occurs at all. We contrast our simulations findings with the known scaling results for weak critical polyelectrolyte adsorption onto oppositely charged surfaces for the three standard geometries. Finally, we discuss some applications of our results for some physical–chemical and biophysical systems. KW - polyelectrolyte adsorption KW - electrostatic interactions KW - critical phenomena KW - Debye screening Y1 - 2016 U6 - https://doi.org/10.1088/1367-2630/18/8/083037 SN - 1367-2630 VL - 18 PB - IOP Publ. CY - London ER - TY - JOUR A1 - Reppert, Alexander von A1 - Puddell, J. A1 - Koc, A. A1 - Reinhardt, M. A1 - Leitenberger, Wolfram A1 - Dumesnil, K. A1 - Zamponi, Flavio A1 - Bargheer, Matias T1 - Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet JF - Structural dynamics N2 - We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost. Y1 - 2016 U6 - https://doi.org/10.1063/1.4961253 SN - 2329-7778 VL - 3 PB - AIP Publishing LLC CY - Melville, NY ER - TY - JOUR A1 - Bodrova, Anna S. A1 - Chechkin, Aleksei V. A1 - Cherstvy, Andrey G. A1 - Safdari, Hadiseh A1 - Sokolov, Igor M. A1 - Metzler, Ralf T1 - Underdamped scaled Brownian motion BT - (non-)existence of the overdamped limit in anomalous diffusion JF - Scientific reports N2 - It is quite generally assumed that the overdamped Langevin equation provides a quantitative description of the dynamics of a classical Brownian particle in the long time limit. We establish and investigate a paradigm anomalous diffusion process governed by an underdamped Langevin equation with an explicit time dependence of the system temperature and thus the diffusion and damping coefficients. We show that for this underdamped scaled Brownian motion (UDSBM) the overdamped limit fails to describe the long time behaviour of the system and may practically even not exist at all for a certain range of the parameter values. Thus persistent inertial effects play a non-negligible role even at significantly long times. From this study a general questions on the applicability of the overdamped limit to describe the long time motion of an anomalously diffusing particle arises, with profound consequences for the relevance of overdamped anomalous diffusion models. We elucidate our results in view of analytical and simulations results for the anomalous diffusion of particles in free cooling granular gases. Y1 - 2016 U6 - https://doi.org/10.1038/srep30520 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Cherstvy, Andrey G. A1 - Metzler, Ralf T1 - Anomalous diffusion in time-fluctuating non-stationary diffusivity landscapes JF - Physical chemistry, chemical physics : PCCP ; a journal of European chemical societies N2 - We investigate the ensemble and time averaged mean squared displacements for particle diffusion in a simple model for disordered media by assuming that the local diffusivity is both fluctuating in time and has a deterministic average growth or decay in time. In this study we compare computer simulations of the stochastic Langevin equation for this random diffusion process with analytical results. We explore the regimes of normal Brownian motion as well as anomalous diffusion in the sub- and superdiffusive regimes. We also consider effects of the inertial term on the particle motion. The investigation of the resulting diffusion is performed for unconfined and confined motion. Y1 - 2016 U6 - https://doi.org/10.1039/C6CP03101C SN - 1463-9084 SN - 1463-9076 VL - 18 SP - 23840 EP - 23852 PB - RSC Publ. CY - Cambridge ER - TY - JOUR A1 - Ghosh, Surya K. A1 - Cherstvy, Andrey G. A1 - Petrov, Eugene P. A1 - Metzler, Ralf T1 - Interactions of rod-like particles on responsive elastic sheets JF - Soft matter N2 - What are the physical laws of the mutual interactions of objects bound to cell membranes, such as various membrane proteins or elongated virus particles? To rationalise this, we here investigate by extensive computer simulations mutual interactions of rod-like particles adsorbed on the surface of responsive elastic two-dimensional sheets. Specifically, we quantify sheet deformations as a response to adhesion of such filamentous particles. We demonstrate that tip-to-tip contacts of rods are favoured for relatively soft sheets, while side-by-side contacts are preferred for stiffer elastic substrates. These attractive orientation-dependent substrate-mediated interactions between the rod-like particles on responsive sheets can drive their aggregation and self-assembly. The optimal orientation of the membrane-bound rods is established via responding to the elastic energy profiles created around the particles. We unveil the phase diagramme of attractive–repulsive rod–rod interactions in the plane of their separation and mutual orientation. Applications of our results to other systems featuring membrane-associated particles are also discussed. Y1 - 2016 U6 - https://doi.org/10.1039/C6SM01522K SN - 1744-6848 SN - 1744-683X PB - RSC CY - London ER - TY - JOUR A1 - Kopyshev, Alexey A1 - Lomadze, Nino A1 - Feldman, David A1 - Genzer, Jan A1 - Santer, Svetlana T1 - Making polymer brush photosensitive with azobenzene containing surfactants JF - Polymer : the international journal for the science and technology of polymers N2 - We report on rendering polyelectrolyte brushes photosensitive by loading them with azobenzene-containing cationic surfactants. Planar poly(methacrylic acid) (PMAA) brushes are synthesized using the “grafting from” free-radical polymerization scheme followed by exposure to a solution of photosensitive surfactants consisting of positively-charged head groups and hydrophobic tails into which azobenzene moieties are inserted. In this study the length of the hydrophobic methylene spacer connecting the azobenzene and the charged head group ranges from 4 to 10 CH2 groups. Under irradiation with UV light, the photo-isomerization of azobenzene integrated into a surfactant results in a change in size, geometry, dipole moment and free volume of the whole molecule. When the brush loaded with photosensitive surfactants is exposed to irradiation with UV interference patterns, the topography of the brush deforms following the distribution of the light intensity, exhibiting surface relief gratings (SRG). Since SRG formation is accompanied by a local rupturing of polymer chains in areas from which the polymer material is receding, most of the polymer material is removed from the surface during treatment with good solvent, leaving behind characteristic patterns of lines or dots. The azobenzene molecules still integrated within the polymer film can be removed by washing the brush with water. The remaining nano-structured brush can then be re-used for further functionalization. Although the opto-mechanically induced rupturing occurs for all surfactants, larger species do not penetrate deep enough into the brush such that after rupturing a leftover layer of polymer material remains on the substrate. This indicates that rupturing occurs predominantly in regions of high surfactant density. KW - Azobenzene containing cationic surfactants KW - Photosensitive polymer brushes KW - Opto-mechanically induced scission of polymer chains Y1 - 2015 U6 - https://doi.org/10.1016/j.polymer.2015.09.023 SN - 0032-3861 VL - 79 SP - 65 EP - 72 PB - Elsevier Science CY - Oxford ER - TY - JOUR A1 - Kurpiers, Jona A1 - Neher, Dieter T1 - Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend JF - Scientific reports N2 - Recombination of free charge is a key process limiting the performance of solar cells. For low mobility materials, such as organic semiconductors, the kinetics of non-geminate recombination (NGR) is strongly linked to the motion of charges. As these materials possess significant disorder, thermalization of photogenerated carriers in the inhomogeneously broadened density of state distribution is an unavoidable process. Despite its general importance, knowledge about the kinetics of NGR in complete organic solar cells is rather limited. We employ time delayed collection field (TDCF) experiments to study the recombination of photogenerated charge in the high-performance polymer:fullerene blend PCDTBT:PCBM. NGR in the bulk of this amorphous blend is shown to be highly dispersive, with a continuous reduction of the recombination coefficient throughout the entire time scale, until all charge carriers have either been extracted or recombined. Rapid, contact-mediated recombination is identified as an additional loss channel, which, if not properly taken into account, would erroneously suggest a pronounced field dependence of charge generation. These findings are in stark contrast to the results of TDCF experiments on photovoltaic devices made from ordered blends, such as P3HT:PCBM, where non-dispersive recombination was proven to dominate the charge carrier dynamics under application relevant conditions. Y1 - 2016 U6 - https://doi.org/10.1038/srep26832 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Neher, Dieter A1 - Kniepert, Juliane A1 - Elimelech, Arik A1 - Koster, L. Jan Anton T1 - A New Figure of Merit for Organic Solar Cells with Transport-limited Photocurrents JF - Scientific reports N2 - Compared to their inorganic counterparts, organic semiconductors suffer from relatively low charge carrier mobilities. Therefore, expressions derived for inorganic solar cells to correlate characteristic performance parameters to material properties are prone to fail when applied to organic devices. This is especially true for the classical Shockley-equation commonly used to describe current-voltage (JV)-curves, as it assumes a high electrical conductivity of the charge transporting material. Here, an analytical expression for the JV-curves of organic solar cells is derived based on a previously published analytical model. This expression, bearing a similar functional dependence as the Shockley-equation, delivers a new figure of merit α to express the balance between free charge recombination and extraction in low mobility photoactive materials. This figure of merit is shown to determine critical device parameters such as the apparent series resistance and the fill factor. KW - Electronic and spintronic devices KW - Semiconductors Y1 - 2016 U6 - https://doi.org/10.1038/srep24861 SN - 2045-2322 VL - 6 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Rätzel, Dennis A1 - Wilkens, Martin A1 - Menzel, Ralf T1 - Gravitational properties of light BT - the gravitational field of a laser pulse JF - New journal of physics : the open-access journal for physics N2 - The gravitational field of a laser pulse of finite lifetime, is investigated in the framework of linearized gravity. Although the effects are very small, they may be of fundamental physical interest. It is shown that the gravitational field of a linearly polarized light pulse is modulated as the norm of the corresponding electric field strength, while no modulations arise for circular polarization. In general, the gravitational field is independent of the polarization direction. It is shown that all physical effects are confined to spherical shells expanding with the speed of light, and that these shells are imprints of the spacetime events representing emission and absorption of the pulse. Nearby test particles at rest are attracted towards the pulse trajectory by the gravitational field due to the emission of the pulse, and they are repelled from the pulse trajectory by the gravitational field due to its absorption. Examples are given for the size of the attractive effect. It is recovered that massless test particles do not experience any physical effect if they are co-propagating with the pulse, and that the acceleration of massless test particles counter-propagating with respect to the pulse is four times stronger than for massive particles at rest. The similarities between the gravitational effect of a laser pulse and Newtonian gravity in two dimensions are pointed out. The spacetime curvature close to the pulse is compared to that induced by gravitational waves from astronomical sources. KW - gravity KW - general relativity KW - laser pulses KW - electromagnetic radiation KW - linearized gravity KW - pp-wave solutions Y1 - 2016 U6 - https://doi.org/10.1088/1367-2630/18/2/023009 SN - 1367-2630 VL - 18 SP - 1 EP - 16 PB - IOP Science CY - London ER - TY - JOUR A1 - Pulkkinen, Otto A1 - Metzler, Ralf T1 - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation JF - Scientific reports N2 - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E.coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations. Y1 - 2015 U6 - https://doi.org/10.1038/srep17820 SN - 2045-2322 IS - 5 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Metzler, Ralf A1 - Bauer, Maximilian A1 - Rasmussen, Emil S. A1 - Lomholt, Michael A. T1 - Real sequence effects on the search dynamics of transcription factors on DNA JF - Scientific Reports N2 - Recent experiments show that transcription factors (TFs) indeed use the facilitated diffusion mechanism to locate their target sequences on DNA in living bacteria cells: TFs alternate between sliding motion along DNA and relocation events through the cytoplasm. From simulations and theoretical analysis we study the TF-sliding motion for a large section of the DNA-sequence of a common E. coli strain, based on the two-state TF-model with a fast-sliding search state and a recognition state enabling target detection. For the probability to detect the target before dissociating from DNA the TF-search times self-consistently depend heavily on whether or not an auxiliary operator (an accessible sequence similar to the main operator) is present in the genome section. Importantly, within our model the extent to which the interconversion rates between search and recognition states depend on the underlying nucleotide sequence is varied. A moderate dependence maximises the capability to distinguish between the main operator and similar sequences. Moreover, these auxiliary operators serve as starting points for DNA looping with the main operator, yielding a spectrum of target detection times spanning several orders of magnitude. Auxiliary operators are shown to act as funnels facilitating target detection by TFs. KW - gene regulatory networks KW - biological physics Y1 - 2015 U6 - https://doi.org/10.1038/srep10072 SN - 2045-2322 VL - 5 IS - 10072 PB - Nature Publishing Group CY - London ER - TY - JOUR A1 - Metzler, Ralf A1 - Cherstvy, Andrey G. A1 - Chechkin, Aleksei V. A1 - Bodrova, Anna S. T1 - Ultraslow scaled Brownian motion JF - New journal of physics : the open-access journal for physics N2 - We define and study in detail utraslow scaled Brownian motion (USBM) characterized by a time dependent diffusion coefficient of the form . For unconfined motion the mean squared displacement (MSD) of USBM exhibits an ultraslow, logarithmic growth as function of time, in contrast to the conventional scaled Brownian motion. In a harmonic potential the MSD of USBM does not saturate but asymptotically decays inverse-proportionally to time, reflecting the highly non-stationary character of the process. We show that the process is weakly non-ergodic in the sense that the time averaged MSD does not converge to the regular MSD even at long times, and for unconfined motion combines a linear lag time dependence with a logarithmic term. The weakly non-ergodic behaviour is quantified in terms of the ergodicity breaking parameter. The USBM process is also shown to be ageing: observables of the system depend on the time gap between initiation of the test particle and start of the measurement of its motion. Our analytical results are shown to agree excellently with extensive computer simulations. KW - anomalous diffusion KW - stochastic processes KW - ageing Y1 - 2015 U6 - https://doi.org/10.1088/1367-2630/17/6/063038 SN - 1367-2630 VL - 17 IS - 063038 PB - Dt. Physikalische Ges., IOP CY - Bad Honnef, London ER - TY - JOUR A1 - Goychuk, Igor A1 - Goychuk, Andriy T1 - Stochastic Wilson BT - Cowan models of neuronal network dynamics with memory and delay JF - New journal of physics N2 - We consider a simple Markovian class of the stochastic Wilson–Cowan type models of neuronal network dynamics, which incorporates stochastic delay caused by the existence of a refractory period of neurons. From the point of view of the dynamics of the individual elements, we are dealing with a network of non-Markovian stochastic two-state oscillators with memory, which are coupled globally in a mean-field fashion. This interrelation of a higher-dimensional Markovian and lower-dimensional non-Markovian dynamics is discussed in its relevance to the general problem of the network dynamics of complex elements possessing memory. The simplest model of this class is provided by a three-state Markovian neuron with one refractory state, which causes firing delay with an exponentially decaying memory within the two-state reduced model. This basic model is used to study critical avalanche dynamics (the noise sustained criticality) in a balanced feedforward network consisting of the excitatory and inhibitory neurons. Such avalanches emerge due to the network size dependent noise (mesoscopic noise). Numerical simulations reveal an intermediate power law in the distribution of avalanche sizes with the critical exponent around −1.16. We show that this power law is robust upon a variation of the refractory time over several orders of magnitude. However, the avalanche time distribution is biexponential. It does not reflect any genuine power law dependence. KW - neuronal networks KW - stochastic models KW - memory and delay KW - critical avalanche dynamics Y1 - 2015 U6 - https://doi.org/10.1088/1367-2630/17/4/045029 SN - 1367-2630 VL - 17 IS - 4 PB - Deutsche Physikalische Gesellschaft, Institute of Physics CY - Bad Honnef, London ER - TY - JOUR A1 - Goychuk, Igor A. A1 - Kharchenko, Vasyl O. A1 - Metzler, Ralf T1 - Molecular motors pulling cargos in the viscoelastic cytosol: how power strokes beat subdiffusion JF - Physical Chemistry Chemical Physics N2 - The discovery of anomalous diffusion of larger biopolymers and submicron tracers such as endogenous granules, organelles, or virus capsids in living cells, attributed to the viscoelastic nature of the cytoplasm, provokes the question whether this complex environment equally impacts the active intracellular transport of submicron cargos by molecular motors such as kinesins: does the passive anomalous diffusion of free cargo always imply its anomalously slow active transport by motors, the mean transport distance along microtubule growing sublinearly rather than linearly in time? Here we analyze this question within the widely used two-state Brownian ratchet model of kinesin motors based on the continuous-state diffusion along microtubules driven by a flashing binding potential, where the cargo particle is elastically attached to the motor. Depending on the cargo size, the loading force, the amplitude of the binding potential, the turnover frequency of the molecular motor enzyme, and the linker stiffness we demonstrate that the motor transport may turn out either normal or anomalous, as indeed measured experimentally. We show how a highly efficient normal active transport mediated by motors may emerge despite the passive anomalous diffusion of the cargo, and study the intricate effects of the elastic linker. Under different, well specified conditions the microtubule-based motor transport becomes anomalously slow and thus significantly less efficient. KW - royal soc chemistry KW - thomas graham house KW - science park KW - milton rd KW - cambridge cb4 0wf KW - cambs KW - england Y1 - 2014 SN - 1463-9076 IS - 16 SP - 16524 EP - 16535 PB - the Royal Society of Chemistry CY - Cambridge ER -