@article{LiuSachseSpahnetal.2016, author = {Liu, Xiaodong and Sachse, Manuel and Spahn, Frank and Schmidt, Jurgen}, title = {Dynamics and distribution of Jovian dust ejected from the Galilean satellites}, series = {Journal of geophysical research, Planets}, volume = {121}, journal = {Journal of geophysical research, Planets}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9097}, doi = {10.1002/2016JE004999}, pages = {1141 -- 1173}, year = {2016}, abstract = {In this paper, the dynamical analysis of the Jovian dust originating from the four Galilean moons is presented. High-accuracy orbital integrations of dust particles are used to determine their dynamical evolution. A variety of forces are taken into account, including the Lorentz force, solar radiation pressure, Poynting-Robertson drag, solar gravity, the satellites' gravity, plasma drag, and gravitational effects due to nonsphericity of Jupiter. More than 20,000 dust particles from each source moon in the size range from 0.05 \&\#956;m to 1 cm are simulated over 8000 (Earth) years until each dust grain hits a sink (moons, Jupiter, or escape from the system). Configurations of dust number density in the Jovicentric equatorial inertial frame are calculated and shown. In a Jovicentric frame rotating with the Sun the dust distributions are found to be asymmetric. For certain small particle sizes, the dust population is displaced towards the Sun, while for certain larger sizes, the dust population is displaced away from the Sun. The average lifetime as a function of particle size for ejecta from each source moon is derived, and two sharp jumps in the average lifetime are analyzed. Transport of dust between the Galilean moons and to Jupiter is investigated. Most of the orbits for dust particles from Galilean moons are prograde, while, surprisingly, a small fraction of orbits are found to become retrograde mainly due to solar radiation pressure and Lorentz force. The distribution of orbital elements is also analyzed.}, language = {en} } @article{PedatellaFangJinetal.2016, author = {Pedatella, Nick M. and Fang, T. -W. and Jin, Hao and Sassi, F. and Schmidt, H. and Chau, Jorge Luis and Siddiqui, Tarique Adnan and Goncharenko, L.}, title = {Multimodel comparison of the ionosphere variability during the 2009 sudden stratosphere warming}, series = {Journal of geophysical research : Space physics}, volume = {121}, journal = {Journal of geophysical research : Space physics}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1002/2016JA022859}, pages = {7204 -- 7225}, year = {2016}, abstract = {A comparison of different model simulations of the ionosphere variability during the 2009 sudden stratosphere warming (SSW) is presented. The focus is on the equatorial and low-latitude ionosphere simulated by the Ground-to-topside model of the Atmosphere and Ionosphere for Aeronomy (GAIA), Whole Atmosphere Model plus Global Ionosphere Plasmasphere (WAM+GIP), and Whole Atmosphere Community Climate Model eXtended version plus Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (WACCMX+TIMEGCM). The simulations are compared with observations of the equatorial vertical plasma drift in the American and Indian longitude sectors, zonal mean Fregion peak density (NmF2) from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites, and ground-based Global Positioning System (GPS) total electron content (TEC) at 75 degrees W. The model simulations all reproduce the observed morning enhancement and afternoon decrease in the vertical plasma drift, as well as the progression of the anomalies toward later local times over the course of several days. However, notable discrepancies among the simulations are seen in terms of the magnitude of the drift perturbations, and rate of the local time shift. Comparison of the electron densities further reveals that although many of the broad features of the ionosphere variability are captured by the simulations, there are significant differences among the different model simulations, as well as between the simulations and observations. Additional simulations are performed where the neutral atmospheres from four different whole atmosphere models (GAIA, HAMMONIA (Hamburg Model of the Neutral and Ionized Atmosphere), WAM, and WACCMX) provide the lower atmospheric forcing in the TIME-GCM. These simulations demonstrate that different neutral atmospheres, in particular, differences in the solar migrating semidiurnal tide, are partly responsible for the differences in the simulated ionosphere variability in GAIA, WAM+GIP, and WACCMX+TIMEGCM.}, language = {en} } @article{QuadeAbelShafietal.2016, author = {Quade, Markus and Abel, Markus and Shafi, Kamran and Niven, Robert K. and Noack, Bernd R.}, title = {Prediction of dynamical systems by symbolic regression}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {94}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, address = {Bethesda}, issn = {2470-0045}, doi = {10.1103/PhysRevE.94.012214}, pages = {15}, year = {2016}, abstract = {We study the modeling and prediction of dynamical systems based on conventional models derived from measurements. Such algorithms are highly desirable in situations where the underlying dynamics are hard to model from physical principles or simplified models need to be found. We focus on symbolic regression methods as a part of machine learning. These algorithms are capable of learning an analytically tractable model from data, a highly valuable property. Symbolic regression methods can be considered as generalized regression methods. We investigate two particular algorithms, the so-called fast function extraction which is a generalized linear regression algorithm, and genetic programming which is a very general method. Both are able to combine functions in a certain way such that a good model for the prediction of the temporal evolution of a dynamical system can be identified. We illustrate the algorithms by finding a prediction for the evolution of a harmonic oscillator based on measurements, by detecting an arriving front in an excitable system, and as a real-world application, the prediction of solar power production based on energy production observations at a given site together with the weather forecast.}, language = {en} } @article{PiattiIvanovRubeleetal.2016, author = {Piatti, Andres E. and Ivanov, Valentin D. and Rubele, Stefano and Marconi, Marcella and Ripepi, Vincenzo and Cioni, Maria-Rosa L. and Oliveira, Joana M. and Bekki, Kenji}, title = {The VMC Survey - XXI. New star cluster candidates discovered from infrared photometry in the Small Magellanic Cloud}, series = {Monthly notices of the Royal Astronomical Society}, volume = {460}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw1000}, pages = {383 -- 395}, year = {2016}, language = {en} } @article{BodrovaChechkinCherstvyetal.2016, author = {Bodrova, Anna S. and Chechkin, Aleksei V. and Cherstvy, Andrey G. and Safdari, Hadiseh and Sokolov, Igor M. and Metzler, Ralf}, title = {Underdamped scaled Brownian motion: (non-)existence of the overdamped limit in anomalous diffusion}, series = {Scientific reports}, volume = {6}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep30520}, pages = {16}, year = {2016}, abstract = {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.}, language = {en} } @article{KopyshevGalvinPatiletal.2016, author = {Kopyshev, Alexey and Galvin, Casey J. and Patil, Rohan R. and Genzer, Jan and Lomadze, Nino and Feldmann, David and Zakrevski, Juri and Santer, Svetlana}, title = {Light-Induced Reversible Change of Roughness and Thickness of Photosensitive Polymer Brushes}, series = {Applied physics : A, Materials science \& processing}, volume = {8}, journal = {Applied physics : A, Materials science \& processing}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.6b06881}, pages = {19175 -- 19184}, year = {2016}, abstract = {We investigate light-induced changes in thickness and roughness of photosensitive polymer brushes containing azobenzene cationic surfactants by atomic force microscopy (AFM) in real time during light irradiation. Because the cis-state of azobenzene unit requires more free volume than its trans counterpart, the UV light-induced expansion of polymer thin films associated with the trans-to-cis isomerism of azobenzene groups is expected to occur. This phenomenon is well documented in physisorbed polymer films containing azobenzene groups. In contrast, photosensitive polymer brushes show a decrease in thickness under UV irradiation. We have found that the azobenzene surfactants in their trans-state form aggregates within the brush. Under irradiation, the surfactants undergo photoisomerization to the cis-state, which is more hydrophilic. As a consequence, the aggregates within the brush are disrupted, and the polymer brush contracts. When subsequently irradiated with blue light the polymer brush thickness returns back to its initial value. This behavior is related to isomerization of the surfactant to the more hydrophobic trans-state and subsequent formation of surfactant aggregates within the polymer brush. The photomechanical function of the dry polymer brush, i.e., contraction and expansion, was found to be reversible with repeated irradiation cycles and requires only a few seconds for switching. In addition to the thickness change, the roughness of the brush also changes reversibly between a few Angstroms (blue light) and several nanometers (UV light). Photosensitive polymer brushes represent smart films with light responsive thickness and roughness that could be used for generating dynamic fluctuating surfaces, the function of which can be turned on and off in a controllable manner on a nanometer length scale.}, language = {en} } @article{KunnusZhangDelceyetal.2016, author = {Kunnus, Kristjan and Zhang, Wenkai and Delcey, Mickael G. and Pinjari, Rahul V. and Miedema, Piter S. and Schreck, Simon and Quevedo, Wilson and Schr{\"o}der, Henning and F{\"o}hlisch, Alexander and Gaffney, Kelly J. and Lundberg, Marcus and Odelius, Michael and Wernet, Philippe}, title = {Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {120}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.6b04751}, pages = {7182 -- 7194}, year = {2016}, abstract = {The valence-excited states of ferric and ferrous hexacyanide ions in aqueous solution were mapped by resonant inelastic X-ray scattering (RIXS) at the Fe L-2,L-3 and N K edges. Probing of both the central Fe and the ligand N atoms enabled identification of the metal-and ligand-centered excited states, as well as ligand-to-metal and metal-to-ligand charge-transfer excited states. Ab initio calculations utilizing the RASPT2 method were used to simulate the Fe L-2,L-3-edge RIXS spectra and enabled quantification of the covalencies of both occupied and empty orbitals of pi and sigma symmetry. We found that pi back-donation in the ferric complex is smaller than that in the ferrous complex. This is evidenced by the relative amounts of Fe 3d character in the nominally 2 pi CN- molecular orbital of 7\% and 9\% in ferric and ferrous hexacyanide, respectively. Utilizing the direct sensitivity of Fe L-3-edge RIXS to the Fe 3d character in the occupied molecular orbitals, we also found that the donation interactions are dominated by sigma bonding. The latter was found to be stronger in the ferric complex, with an Fe 3d contribution to the nominally 5 sigma CN- molecular orbitals of 29\% compared to 20\% in the ferrous complex. These results are consistent with the notion that a higher charge at the central metal atom increases donation and decreases back-donation.}, language = {en} } @article{ThomasFeldmeier2016, author = {Thomas, Timon and Feldmeier, Achim}, title = {Radiative waves in stellar winds with line scattering}, series = {Monthly notices of the Royal Astronomical Society}, volume = {460}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw1008}, pages = {1923 -- 1933}, year = {2016}, abstract = {Photospheric radiation can drive winds from hot, massive stars by direct momentum transfer through scattering in bound-bound transitions of atmospheric ions. The line radiation force should cause a new radiative wave mode. The dispersion relation from perturbations of the line force was analysed so far either in Sobolev approximation or for pure line absorption. The former does not include the line-driven instability, and the latter cannot account for upstream propagating, radiative waves. We consider a non-Sobolev line force that includes scattering in a simplified way, accounting however for the important line-drag effect. We derive a new dispersion relation for radiative waves, and analyse wave propagation using Fourier methods, and by numerical solution of an integro-differential equation. The existence of an upstream propagating, dispersive radiative wave mode is demonstrated.}, language = {en} } @article{GeigerFrielerLevermann2016, author = {Geiger, Tobias and Frieler, Katja and Levermann, Anders}, title = {High-income does not protect against hurricane losses}, series = {Environmental research letters}, volume = {11}, journal = {Environmental research letters}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1748-9326}, doi = {10.1088/1748-9326/11/8/084012}, pages = {10}, year = {2016}, abstract = {Damage due to tropical cyclones accounts for more than 50\% of all meteorologically-induced economic losses worldwide. Their nominal impact is projected to increase substantially as the exposed population grows, per capita income increases, and anthropogenic climate change manifests. So far, historical losses due to tropical cyclones have been found to increase less than linearly with a nation's affected gross domestic product (GDP). Here we show that for the United States this scaling is caused by a sub-linear increase with affected population while relative losses scale super-linearly with per capita income. The finding is robust across a multitude of empirically derived damage models that link the storm's wind speed, exposed population, and per capita GDP to reported losses. The separation of both socio-economic predictors strongly affects the projection of potential future hurricane losses. Separating the effects of growth in population and per-capita income, per hurricane losses with respect to national GDP are projected to triple by the end of the century under unmitigated climate change, while they are estimated to decrease slightly without the separation.}, language = {en} } @article{RoshchupkinOrtegaPlotitcynaetal.2016, author = {Roshchupkin, Dmitry and Ortega, Luc and Plotitcyna, Olga and Erko, Alexei and Zizak, Ivo and Vadilonga, Simone and Irzhak, Dmitry and Emelin, Evgenii and Buzanov, Oleg and Leitenberger, Wolfram}, title = {Piezoelectric Ca3NbGa3Si2O14 crystal: crystal growth, piezoelectric and acoustic properties}, series = {Journal of geophysical research : Space physics}, volume = {122}, journal = {Journal of geophysical research : Space physics}, publisher = {Springer}, address = {New York}, issn = {0947-8396}, doi = {10.1007/s00339-016-0279-1}, pages = {2803 -- 2812}, year = {2016}, abstract = {Ca3NbGa3Si2O14 (CNGS), a five-component crystal of lanthanum-gallium silicate group, was grown by the Czochralski method. The parameters of the elementary unit cell of the crystal were measured by powder diffraction. The independent piezoelectric strain coefficients d(11) and d(14) were determined by the triple-axis X-ray diffraction in the Bragg and Laue geometries. Excitation and propagation of surface acoustic waves (SAW) were studied by high-resolution X-ray diffraction at BESSY II synchrotron radiation source. The velocity of SAW propagation and power flow angles in the Y-, X-and yxl/+36 degrees-cuts of the CNGS crystal were determined from the analysis of the diffraction spectra. The CNGS crystal was found practically isotropic by its acoustic properties.}, language = {en} } @article{XuYanLazarian2016, author = {Xu, Siyao and Yan, Huirong and Lazarian, A.}, title = {DAMPING OF MAGNETOHYDRODYNAMIC TURBULENCE IN PARTIALLY IONIZED PLASMA: IMPLICATIONS FOR COSMIC RAY PROPAGATION}, series = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, volume = {826}, journal = {The astrophysical journal : an international review of spectroscopy and astronomical physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0004-637X}, doi = {10.3847/0004-637X/826/2/166}, pages = {32}, year = {2016}, abstract = {We study the damping processes of both incompressible and compressible magnetohydrodynamic (MHD) turbulence in a partially ionized medium. We start from the linear analysis of MHD waves, applying both single-fluid and two-fluid treatments. The damping rates derived from the linear analysis are then used in determining the damping scales of MHD turbulence. The physical connection between the damping scale of MHD turbulence and the cutoff boundary of linear MHD waves is investigated. We find two branches of slow modes propagating in ions and neutrals, respectively, below the damping scale of slow MHD turbulence, and offer a thorough discussion of their propagation and dissipation behavior. Our analytical results are shown to be applicable in a variety of partially ionized interstellar medium (ISM) phases and the solar chromosphere. The importance of neutral viscosity in damping the Alfvenic turbulence in the interstellar warm neutral medium and the solar chromosphere is demonstrated. As a significant astrophysical utility, we introduce damping effects to the propagation of cosmic rays in partially ionized ISM. The important role of turbulence damping in both transit-time damping and gyroresonance is identified.}, language = {en} } @article{RipollLoridanCunninghametal.2016, author = {Ripoll, Jean-Fran{\c{c}}ois and Loridan, Vivien and Cunningham, G. S. and Reeves, Geoffrey D. and Shprits, Yuri}, title = {On the time needed to reach an equilibrium structure of the radiation belts}, series = {Journal of geophysical research : Space physics}, volume = {121}, journal = {Journal of geophysical research : Space physics}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1002/2015JA022207}, pages = {7684 -- 7698}, year = {2016}, abstract = {In this study, we complement the notion of equilibrium states of the radiation belts with a discussion on the dynamics and time needed to reach equilibrium. We solve for the equilibrium states obtained using 1-D radial diffusion with recently developed hiss and chorus lifetimes at constant values of Kp = 1, 3, and 6. We find that the equilibrium states at moderately low Kp, when plotted versus L shell (L) and energy (E), display the same interesting S shape for the inner edge of the outer belt as recently observed by the Van Allen Probes. The S shape is also produced as the radiation belts dynamically evolve toward the equilibrium state when initialized to simulate the buildup after a massive dropout or to simulate loss due to outward diffusion from a saturated state. Physically, this shape, intimately linked with the slot structure, is due to the dependence of electron loss rate (originating from wave-particle interactions) on both energy and L shell. Equilibrium electron flux profiles are governed by the Biot number (tau(Diffusion)/tau(loss)), with large Biot number corresponding to low fluxes and low Biot number to large fluxes. The time it takes for the flux at a specific (L, E) to reach the value associated with the equilibrium state, starting from these different initial states, is governed by the initial state of the belts, the property of the dynamics (diffusion coefficients), and the size of the domain of computation. Its structure shows a rather complex scissor form in the (L, E) plane. The equilibrium value (phase space density or flux) is practically reachable only for selected regions in (L, E) and geomagnetic activity. Convergence to equilibrium requires hundreds of days in the inner belt for E>300 keV and moderate Kp (<= 3). It takes less time to reach equilibrium during disturbed geomagnetic conditions (Kp = 3), when the system evolves faster. Restricting our interest to the slot region, below L = 4, we find that only small regions in (L, E) space can reach the equilibrium value: E similar to [200, 300] keV for L= [3.7, 4] at Kp= 1, E similar to[0.6, 1] MeV for L = [3, 4] at Kp = 3, and E similar to 300 keV for L = [3.5, 4] at Kp = 6 assuming no new incoming electrons.}, language = {en} } @article{BoydSpenceHuangetal.2016, author = {Boyd, A. J. and Spence, Harlan E. and Huang, Chia-Lin and Reeves, Geoffrey D. and Baker, Daniel N. and Turner, D. L. and Claudepierre, Seth G. and Fennell, Joseph F. and Blake, J. Bernard and Shprits, Yuri}, title = {Statistical properties of the radiation belt seed population}, series = {Journal of geophysical research : Space physics}, volume = {121}, journal = {Journal of geophysical research : Space physics}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9380}, doi = {10.1002/2016JA022652}, pages = {7636 -- 7646}, year = {2016}, abstract = {We present a statistical analysis of phase space density data from the first 26 months of the Van Allen Probes mission. In particular, we investigate the relationship between the tens and hundreds of keV seed electrons and >1 MeV core radiation belt electron population. Using a cross-correlation analysis, we find that the seed and core populations are well correlated with a coefficient of approximate to 0.73 with a time lag of 10-15 h. We present evidence of a seed population threshold that is necessary for subsequent acceleration. The depth of penetration of the seed population determines the inner boundary of the acceleration process. However, we show that an enhanced seed population alone is not enough to produce acceleration in the higher energies, implying that the seed population of hundreds of keV electrons is only one of several conditions required for MeV electron radiation belt acceleration.}, language = {en} } @article{XiongStolleLuehr2016, author = {Xiong, Chao and Stolle, Claudia and L{\"u}hr, Hermann}, title = {The Swarm satellite loss of GPS signal and its relation to ionospheric plasma irregularities}, series = {Space Weather: The International Journal of Research and Applications}, volume = {14}, journal = {Space Weather: The International Journal of Research and Applications}, publisher = {American Geophysical Union}, address = {Washington}, issn = {1542-7390}, doi = {10.1002/2016SW001439}, pages = {563 -- 577}, year = {2016}, abstract = {In this study we investigated conditions for loss of GPS signals observed by the Swarm satellites during a 2 year period, from December 2013 to November 2015. Our result shows that the Swarm satellites encountered most of the total loss of GPS signal at the ionization anomaly crests, between +/- 5 degrees and +/- 20 degrees magnetic latitude, forming two bands along the magnetic equator, and these low-latitude events mainly appear around postsunset hours from 19: 00 to 22: 00 local time. By further checking the in situ electron density measurements of Swarm, we found that practically, all the total loss of GPS signal events at low latitudes are related to equatorial plasma irregularities (EPIs) that show absolute density depletions larger than 10 x 10(11) m(-3); then, the Swarm satellites encountered for up to 95\% loss of GPS signal for at least one channel and up to 45\% tracked less than four GPS satellites (making precise orbit determination impossible). For those EPIs with density depletions less than 10 x 10(11) m(-3), the chance of tracked GPS signals less than four reduces to only 1.0\%. Swarm also observed total loss of all GPS signal at high latitudes, mainly around local noon, and these events are related to large spatial density gradients due to polar patches or increased geomagnetic/auroral activities. We further found that the loss of GPS signals were less frequent after appropriate settings of the Swarm GPS receivers had been updated. However, the more recent period of the mission, e.g., after the GPS receiver settings have been updated, also coincides with less severe electron density depletions due to the declining solar cycle, making GPS loss events less likely. We conclude that both lower electron density gradients and appropriate GPS receiver settings reduce the probability for Swarm satellites loss of GPS signals.}, language = {en} } @misc{WuesthoffSohl2016, author = {Wuesthoff, Martin and Sohl, F.}, title = {Obliquity tides have an impact in diurnal tidal stresses on the Moon.}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {51}, journal = {Macromolecules : a publication of the American Chemical Society}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1086-9379}, pages = {A672 -- A672}, year = {2016}, language = {en} } @article{VlasovRosenblumPikovskij2016, author = {Vlasov, Vladimir and Rosenblum, Michael and Pikovskij, Arkadij}, title = {Dynamics of weakly inhomogeneous oscillator populations: perturbation theory on top of Watanabe-Strogatz integrability}, series = {Journal of physics : A, Mathematical and theoretical}, volume = {49}, journal = {Journal of physics : A, Mathematical and theoretical}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1751-8113}, doi = {10.1088/1751-8113/49/31/31LT02}, pages = {8}, year = {2016}, abstract = {As has been shown by Watanabe and Strogatz (WS) (1993 Phys. Rev. Lett. 70 2391), a population of identical phase oscillators, sine-coupled to a common field, is a partially integrable system: for any ensemble size its dynamics reduce to equations for three collective variables. Here we develop a perturbation approach for weakly nonidentical ensembles. We calculate corrections to the WS dynamics for two types of perturbations: those due to a distribution of natural frequencies and of forcing terms, and those due to small white noise. We demonstrate that in both cases, the complex mean field for which the dynamical equations are written is close to the Kuramoto order parameter, up to the leading order in the perturbation. This supports the validity of the dynamical reduction suggested by Ott and Antonsen (2008 Chaos 18 037113) for weakly inhomogeneous populations.}, language = {en} } @article{SchleussnerDongesEngemannetal.2016, author = {Schleussner, Carl-Friedrich and Donges, Jonathan and Engemann, Denis A. and Levermann, Anders}, title = {Clustered marginalization of minorities during social transitions induced by co-evolution of behaviour and network structure}, series = {Scientific reports}, volume = {6}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep30790}, pages = {3407 -- 3417}, year = {2016}, abstract = {Large-scale transitions in societies are associated with both individual behavioural change and restructuring of the social network. These two factors have often been considered independently, yet recent advances in social network research challenge this view. Here we show that common features of societal marginalization and clustering emerge naturally during transitions in a co-evolutionary adaptive network model. This is achieved by explicitly considering the interplay between individual interaction and a dynamic network structure in behavioural selection. We exemplify this mechanism by simulating how smoking behaviour and the network structure get reconfigured by changing social norms. Our results are consistent with empirical findings: The prevalence of smoking was reduced, remaining smokers were preferentially connected among each other and formed increasingly marginalized clusters. We propose that self-amplifying feedbacks between individual behaviour and dynamic restructuring of the network are main drivers of the transition. This generative mechanism for co-evolution of individual behaviour and social network structure may apply to a wide range of examples beyond smoking.}, language = {en} } @article{AldorettaStLouisRichardsonetal.2016, author = {Aldoretta, E. J. and St-Louis, N. and Richardson, N. D. and Moffat, Anthony F. J. and Eversberg, T. and Hill, G. M. and Shenar, Tomer and Artigau, E. and Gauza, B. and Knapen, J. H. and Kubat, Jiř{\´i} and Kubatova, Brankica and Maltais-Tariant, R. and Munoz, M. and Pablo, H. and Ramiaramanantsoa, T. and Richard-Laferriere, A. and Sablowski, D. P. and Simon-Diaz, S. and St-Jean, L. and Bolduan, F. and Dias, F. M. and Dubreuil, P. and Fuchs, D. and Garrel, T. and Grutzeck, G. and Hunger, T. and Kuesters, D. and Langenbrink, M. and Leadbeater, R. and Li, D. and Lopez, A. and Mauclaire, B. and Moldenhawer, T. and Potter, M. and dos Santos, E. M. and Schanne, L. and Schmidt, J. and Sieske, H. and Strachan, J. and Stinner, E. and Stinner, P. and Stober, B. and Strandbaek, K. and Syder, T. and Verilhac, D. and Waldschlaeger, U. and Weiss, D. and Wendt, A.}, title = {An extensive spectroscopic time series of three Wolf-Rayet stars - I. The lifetime of large-scale structures in the wind of WR 134}, series = {Monthly notices of the Royal Astronomical Society}, volume = {460}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw1188}, pages = {3407 -- 3417}, year = {2016}, abstract = {During the summer of 2013, a 4-month spectroscopic campaign took place to observe the variabilities in three Wolf-Rayet stars. The spectroscopic data have been analysed for WR 134 (WN6b), to better understand its behaviour and long-term periodicity, which we interpret as arising from corotating interaction regions (CIRs) in the wind. By analysing the variability of the He ii lambda 5411 emission line, the previously identified period was refined to P = 2.255 +/- 0.008 (s.d.) d. The coherency time of the variability, which we associate with the lifetime of the CIRs in the wind, was deduced to be 40 +/- 6 d, or similar to 18 cycles, by cross-correlating the variability patterns as a function of time. When comparing the phased observational grey-scale difference images with theoretical grey-scales previously calculated from models including CIRs in an optically thin stellar wind, we find that two CIRs were likely present. A separation in longitude of Delta I center dot a parts per thousand integral 90A degrees was determined between the two CIRs and we suggest that the different maximum velocities that they reach indicate that they emerge from different latitudes. We have also been able to detect observational signatures of the CIRs in other spectral lines (C iv lambda lambda 5802,5812 and He i lambda 5876). Furthermore, a DAC was found to be present simultaneously with the CIR signatures detected in the He i lambda 5876 emission line which is consistent with the proposed geometry of the large-scale structures in the wind. Small-scale structures also show a presence in the wind, simultaneously with the larger scale structures, showing that they do in fact co-exist.}, language = {en} } @article{SantosdeLimaYandeGouveiaDalPinoetal.2016, author = {Santos de Lima, Reinaldo and Yan, Huirong and de Gouveia Dal Pino, E. M. and Lazarian, A.}, title = {Limits on the ion temperature anisotropy in the turbulent intracluster medium}, series = {Monthly notices of the Royal Astronomical Society}, volume = {460}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw1079}, pages = {2492 -- 2504}, year = {2016}, abstract = {Turbulence in the weakly collisional intracluster medium (ICM) of galaxies is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic pressure magnetohydrodynamic (AMHD) turbulence shows a very different statistical behaviour from the standard MHD one and is unable to amplify seed magnetic fields. This is in contrast to previous cosmological MHD simulations that are successful in explaining the observed magnetic fields in the ICM. On the other hand, temperature anisotropies can also drive plasma instabilities that can relax the anisotropy. This work aims to compare the relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasi-linear theory to estimate the ion scattering rate resulting from the parallel firehose, mirror and ion-cyclotron instabilities, for a set of plasma parameters resulting from AMHD simulations of the turbulent ICM. We show that the ICM turbulence can sustain only anisotropy levels very close to the instability thresholds. We argue that the AMHD model that bounds the anisotropies at the marginal stability levels can describe the Alfv,nic turbulence cascade in the ICM.}, language = {en} } @article{FeldmannLevermann2016, author = {Feldmann, Johannes and Levermann, Anders}, title = {Similitude of ice dynamics against scaling of geometry and physical parameters}, series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union}, volume = {10}, journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1994-0416}, doi = {10.5194/tc-10-1753-2016}, pages = {1753 -- 1769}, year = {2016}, abstract = {The concept of similitude is commonly employed in the fields of fluid dynamics and engineering but rarely used in cryospheric research. Here we apply this method to the problem of ice flow to examine the dynamic similitude of isothermal ice sheets in shallow-shelf approximation against the scaling of their geometry and physical parameters. Carrying out a dimensional analysis of the stress balance we obtain dimensionless numbers that characterize the flow. Requiring that these numbers remain the same under scaling we obtain conditions that relate the geometric scaling factors, the parameters for the ice softness, surface mass balance and basal friction as well as the ice-sheet intrinsic response time to each other. We demonstrate that these scaling laws are the same for both the (two-dimensional) flow-line case and the three-dimensional case. The theoretically predicted ice-sheet scaling behavior agrees with results from numerical simulations that we conduct in flow-line and three-dimensional conceptual setups. We further investigate analytically the implications of geometric scaling of ice sheets for their response time. With this study we provide a framework which, under several assumptions, allows for a fundamental comparison of the ice-dynamic behavior across different scales. It proves to be useful in the design of conceptual numerical model setups and could also be helpful for designing laboratory glacier experiments. The concept might also be applied to real-world systems, e.g., to examine the response times of glaciers, ice streams or ice sheets to climatic perturbations.}, language = {en} }