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Measurement of the ZZ production cross section and $\mathrm{ Z } \to {\ell^+\ell^-\ell^{\prime+}\ell^{\prime-}} $ branching fraction in pp collisions at $ \sqrt{s} = $ 13 TeV
https://cds.cern.ch/record/2202723
Four-lepton production in proton-proton collisions, ${\mathrm{ p }\mathrm{ p }} \to \left(\mathrm{Z} / \gamma^*\right)\left(\mathrm{Z}/ \gamma^*\right) \to {\ell^+\ell^-\ell^{\prime+}\ell^{\prime-}} $, where $\ell, \ell' = \mathrm{ e }$ or $\mu$, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.6 fb$^{-1}$. The ZZ production cross section, $\sigma(\mathrm{ p }\mathrm{ p } \to \mathrm{Z}\mathrm{Z}) =$ 14.6 $^{+1.9}_{-1.8}$ (stat) $^{+0.5}_{-0.3}$ (syst) $\pm$ 0.2 (theory) $\pm$ 0.4 (lumi) pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 $< m_{\ell^+\ell^-}, m_{\ell^{\prime +}\ell^{\prime -}} <$ 120 GeV. The Z boson branching fraction to four leptons is measured to be $\mathcal{B}(\mathrm{Z} \to {\ell^+\ell^-\ell^{\prime+}\ell^{\prime-}} ) =$ 4.9 $_{-0.7}^{+0.8}$ (stat) $_{-0.2}^{+0.3}$ (syst) $_{-0.1}^{+0.2}$ (theory) $\pm$ 0.1 (lumi) $\times 10^{-6}$ for the four-lepton invariant mass in the range 80 $< m_{{\ell^+\ell^-\ell^{\prime+}\ell^{\prime-}} } <$ 100 GeV and dilepton mass $m_{\ell^+\ell^{\prime -} } > $ 4 GeV for all opposite-sign lepton pairs. The results are in agreement with standard model predictions.CMS CollaborationFri, 29 Jul 2016 15:26:57 GMT29 Jul 2016CERN-EP-2016-174https://cds.cern.ch/record/22027232016174A measurement of the calorimeter response to single hadrons and determination of the jet energy scale uncertainty using LHC Run-1 $pp$-collision data with the ATLAS detector
https://cds.cern.ch/record/2202682
A measurement of the calorimeter response to isolated charged hadrons in the ATLAS detector at the LHC is presented. This measurement is performed with 3.2 nb$^{-1}$ of proton--proton collision data at $\sqrt{s}=7$ TeV from 2010 and 0.1 nb$^{-1}$ of data at $\sqrt{s}=8$ TeV from 2012. A number of aspects of the calorimeter response to isolated hadrons are explored. After accounting for energy deposited by neutral particles, there is a 5\% discrepancy in the modelling, using Geant4 physics lists, of the calorimeter response to isolated charged hadrons in the central calorimeter region. The description of the response to anti-protons at low momenta is found to be improved with respect to previous analyses. The electromagnetic and hadronic calorimeters are also examined separately, and the detector simulation is found to describe the response in the hadronic calorimeter well. The jet energy scale uncertainty and correlations in scale between jets of different momenta are derived based on these studies. The uncertainty is 2-5\% for jets with transverse momenta above 2 TeV, where this method provides the jet energy scale uncertainty for ATLAS.ATLAS CollaborationFri, 29 Jul 2016 12:25:58 GMT29 Jul 2016CERN-EP-2016-149https://cds.cern.ch/record/22026822016149Competition of tolerant strategies in the spatial public goods game
https://cds.cern.ch/record/2202622
Tolerance implies enduring trying circumstances with a fair and objective attitude. To determine whether evolutionary advantages might be stemming from diverse levels of tolerance in a population, we study a spatial public goods game, where in addition to cooperators, defectors, and loners, tolerant players are also present. Depending on the number of defectors within a group, a tolerant player can either cooperate in or abstain from a particular instance of the game. We show that the diversity of tolerance can give rise to synergistic effects, wherein players with a different threshold in terms of the tolerated number of defectors in a group compete most effectively against defection and default abstinence. Such synergistic associations can stabilise states of full cooperation where otherwise defection would dominate. We observe complex pattern formation that gives rise to an intricate phase diagram, where invisible yet stable strategy alliances require outmost care lest they are overlooked. Our results highlight the delicate importance of diversity and tolerance for the provisioning of public goods, and they reveal fascinating subtleties of the spatiotemporal dynamics that is due to the competition of subsystem solutions in structured populations.Szolnoki, AttilaPerc, MatjazFri, 29 Jul 2016 06:31:54 GMT28 Jul 2016arXiv:1607.08600https://cds.cern.ch/record/2202622['arXiv:1607.08600']arXiv:1607.08600Efficient modularity optimization by self-avoiding walk
https://cds.cern.ch/record/2202621
Different kinds of random walks have showed to be useful in the study of the structural properties of complex networks. Among them, the restricted dynamics of the self-avoiding random walk (SAW), which reaches only unvisited vertices in the same walk, has been succesfully used in network exploration. SAWs are therefore a promising tool to investigate community structures in networks. Despite its importance, community detection remains an open problem due to the high computational complexity of the associated optimization problem and a lack of a unique formal definition of communities. In this work, we propose a SAW-based modularity optimization algorithm to extract the community distribution of a network that achieves high modularity scores. We combined SAW with principal component analyses to define the dissimilarity measure and use agglomerative hierarchical clustering. To evaluate the performance of this algorithm we compare it with three popular methods for community detection: Girvan-Newman, Fastgreedy and Walktrap, using two types of synthetic networks and six well-known real world cases.Bagnato, Guilherme de GuzziRonqui, José Ricardo FurlanTravieso, GonzaloFri, 29 Jul 2016 06:31:54 GMT28 Jul 2016arXiv:1607.08597https://cds.cern.ch/record/2202621['arXiv:1607.08597']arXiv:1607.08597Detection of biomolecules and bioconjugates by monitoring rotated grating-coupled surface plasmon resonance
https://cds.cern.ch/record/2202620
Plasmonic biosensing chips were prepared by fabricating wavelength-scaled dielectric-metal interfacial gratings on thin polycarbonate films covered bimetal layers via two-beam interference laser lithography. Lysozyme (LYZ) biomolecules and gold nanoparticle (AuNP-LYZ) bioconjugates with 1:5 mass ratio were seeded onto the biochip surfaces. Surface plasmon resonance spectroscopy was performed before and after biomolecule seeding in a modified Kretschmann-arrangement by varying the azimuthal and polar angles to optimize the conditions for rotated grating-coupling. The shift of secondary and primary resonance peaks originating from rotated grating-coupling phenomenon was monitored to detect the biomolecule and bioconjugate adherence. Numerical calculations were performed to reproduce the measured reflectance spectra and the resonance peak shifts caused by different biocoverings. Comparison of measurements and calculations proved that monitoring the narrower secondary peaks under optimal rotated-grating coupling condition makes it possible to achieve enhanced sensitivity in biodetection. The sensitivity is further increased in case of bioconjugates due to coupled localized resonances on Au NPs. The enlarged resonance peak shift is resulted by the two-fold antisymmetric long-range plamonic modes propagating at the edge of the valleys and hills, which originate from Bragg scattered surface plasmon polaritons. Optimal configuration of ideal chips supporting rotated grating-coupled long-range plasmonic modes are proposed for biosensing.Szalai, AnikoToth, EmeseSomogyi, AnikoSzenes, AndrasBanhelyi, BalazsCsapo, EditDekany, ImreCsendes, TiborCsete, MariaFri, 29 Jul 2016 06:31:54 GMT28 Jul 2016arXiv:1607.08595https://cds.cern.ch/record/2202620['arXiv:1607.08595']arXiv:1607.08595A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators
https://cds.cern.ch/record/2202619
We present a study of the application of the Jagiellonian Positron Emission Tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the o-Ps$\to3\gamma$ decays with angular and energy resolution equal to $\sigma(\theta) \approx 0.4^{\circ}$ and $\sigma(E) \approx 4.1$ keV, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pileups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.Kamińska, DGajos, ACzerwiński, EAlfs, DBednarski, TBiałas, PCurceanu, CDulski, KGłowacz, BGupta-Sharma, NGorgol, MHiesmayr, B CJasińska, BKorcyl, GKowalski, PKrzemień, WKrawczyk, NKubicz, EMohammed, MNiedźwiecki, SzPawlik-Niedźwiecka, MRaczyński, LRudy, ZSilarski, MWieczorek, AWiślicki, WZgardzińska, BZieliński, MMoskal, PFri, 29 Jul 2016 06:31:54 GMT28 Jul 2016arXiv:1607.08588https://cds.cern.ch/record/2202619['arXiv:1607.08588']arXiv:1607.08588Enhanced dipolar transport in one-dimensional waveguide arrays
https://cds.cern.ch/record/2202618
We study the transport properties of fundamental and dipolar (first-excited) modes on one-dimensional coupled waveguide arrays. By modulating an optical beam, we are able to generate fundamental and dipolar modes to study discrete diffraction (single-site excitation) and gaussian beam propagation (multi-site excitation \& phase gradient). We find that dipolar modes experience a coupling constant more than two times larger than the one for fundamental modes. This implies an enhanced transport of energy for dipoles in a tight-binding lattice. Additionally, we study disordered systems and find that while fundamental modes are already trapped in a weakly disorder array, dipoles still diffract across the lattice.Cantillano, CamiloMorales-Inostroza, LuisReal, BastiánRojas-Rojas, SantiagoDelgado, AldoSzameit, AlexanderVicencio, Rodrigo AFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08575https://cds.cern.ch/record/2202618['arXiv:1607.08575']arXiv:1607.08575Inverse problem for multi-body interaction of nonlinear waves
https://cds.cern.ch/record/2202617
The inverse problem is studied in multi-body systems with nonlinear dynamics representing, e.g., phase-locked wave systems, standard multimode and random lasers. Using a general model for four-body interacting complex-valued variables we test two methods based on pseudolikelihood, respectively with regularization and with decimation, to determine the coupling constants from sets of measured configurations. We test statistical inference predictions for increasing number of sampled configurations and for an externally tunable {\em temperature}-like parameter mimicing real data noise and helping minimization procedures. Analyzed models with phasors and rotors are generalizations of problems of real-valued spherical problems (e.g., density fluctuations), discrete spins (Ising and vectorial Potts) or finite number of states (standard Potts): inference methods presented here can, then, be straightforward applied to a large class of inverse problems.Marruzzo, AlessiaTyagi, PayalAntenucci, FabrizioPagnani, AndreaLeuzzi, LucaFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08549https://cds.cern.ch/record/2202617['arXiv:1607.08549']arXiv:1607.08549Spontaneous symmetry breaking in a split potential box
https://cds.cern.ch/record/2202616
We report results of the analysis of the spontaneous symmetry breaking (SSB) in the basic (actually, simplest) model which is capable to produce the SSB phenomenology in the one-dimensional setting. It is based on the Gross-Pitaevskii - nonlinear Schroedinger equation with the cubic self-attractive term and a double-well-potential built as an infinitely deep potential box split by a narrow (delta-functional) barrier. The barrier's strength, epsilon, is the single free parameter of the scaled form of the model. It may be implemented in atomic Bose-Einstein condensates and nonlinear optics. The SSB bifurcation of the symmetric ground state (GS) is predicted analytically in two limit cases, viz., for deep or weak splitting of the potential box by the barrier. For the generic case, a variational approximation (VA) is elaborated. The analytical findings are presented along with systematic numerical results. Stability of stationary states is studied through the calculation of eigenvalues for small perturbations, and by means of direct simulations. The GS always undergoes the SSB bifurcation of the supercritical type, as predicted by the VA at moderate values of epsilon, although the VA fails at small epsilon, due to inapplicability of the underlying ansatz in that case. However, the latter case is correctly treated by the approximation based on a soliton ansatz. On top of the GS, the first and second excited states are studied too. The antisymmetric mode (the first excited state) is destabilized at a critical value of its norm. The second excited state undergoes the SSB bifurcation, like the GS, but, unlike it, the bifurcation produces an unstable asymmetric mode. All unstable modes tend to spontaneously reshape into the asymmetric GS.Shamriz, EladDror, NirMalomed, Boris AFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08532https://cds.cern.ch/record/2202616['arXiv:1607.08532']arXiv:1607.08532Multivalued fundamental diagrams of traffic flow in the kinetic Fokker-Planck limit
https://cds.cern.ch/record/2202615
Starting from interaction rules based on two levels of stochasticity we study the influence of the microscopic dynamics on the macroscopic properties of vehicular flow. In particular, we study the qualitative structure of the resulting flux-density and speed-density diagrams for different choices of the desired speeds. We are able to recover multivalued diagrams as a result of the existence of a one-parameter family of stationary distributions, whose expression is analytically found by means of a Fokker-Planck approximation of the initial Boltzmann-type model.Visconti, GiuseppeHerty, MichaelPuppo, GabriellaTosin, AndreaFri, 29 Jul 2016 06:31:53 GMT27 Jul 2016arXiv:1607.08530https://cds.cern.ch/record/2202615['arXiv:1607.08530']arXiv:1607.08530Toy models of ice formation in turbulent overcooled water
https://cds.cern.ch/record/2202614
A study of ice formation in stationary turbulent conditions is carried out in various limit regimes with regard to crystal growth rate, overcooling and ice entrainment at the water surface. Analytical expressions of the temperature, salinity and ice concentration mean profiles are provided, and the role of fluctuations in ice production is numerically quantified. A lower bound on the ratio of sensible heat flux to latent heat flux to the atmosphere is derived.De Santi, FrancescaOlla, PieroFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08528https://cds.cern.ch/record/2202614['arXiv:1607.08528']arXiv:1607.08528Pairwise adaptive thermostats for improved accuracy and stability in dissipative particle dynamics
https://cds.cern.ch/record/2202613
We examine the formulation and numerical treatment of dissipative particle dynamics (DPD) and momentum-conserving molecular dynamics. We show that it is possible to improve both the accuracy and the stability of DPD by employing a pairwise adaptive Langevin thermostat that precisely matches the dynamical characteristics of DPD simulations (e.g., autocorrelation functions) while automatically correcting thermodynamic averages using a negative feedback loop. In the low friction regime, it is possible to replace DPD by a simpler momentum-conserving variant of the Nos\'{e}--Hoover--Langevin method based on thermostatting only pairwise interactions; we show that this method has an extra order of accuracy for an important class of observables (a superconvergence result), while also allowing larger timesteps than alternatives. All the methods mentioned in the article are easily implemented. Numerical experiments are performed in both equilibrium and nonequilibrium settings; using Lees--Edwards boundary conditions to induce shear flow.Leimkuhler, BenedictShang, XiaochengFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08510https://cds.cern.ch/record/2202613['arXiv:1607.08510']arXiv:1607.08510Mitochondrial Ca2+ uptake in skeletal muscle health and disease
https://cds.cern.ch/record/2202612
Muscle uses Ca2+ as a messenger to control contraction and relies on ATP to maintain the intracellular Ca2+ homeostasis. Mitochondria are the major sub-cellular organelle of ATP production. With a negative inner membrane potential, mitochondria take up Ca2+ from their surroundings, a process called mitochondrial Ca2+ uptake. Under physiological conditions, Ca2+ uptake into mitochondria promotes ATP production. Excessive uptake causes mitochondrial Ca2+ overload, which activates downstream adverse responses leading to cell dysfunction. Moreover, mitochondrial Ca2+ uptake could shape spatio-temporal patterns of intracellular Ca2+ signaling. Malfunction of mitochondrial Ca2+ uptake is implicated in muscle degeneration. Unlike non-excitable cells, mitochondria in muscle cells experience dramatic changes of intracellular Ca2+ levels. Besides the sudden elevation of Ca2+ level induced by action potentials, Ca2+ transients in muscle cells can be as short as a few milliseconds during a single twitch or as long as minutes during tetanic contraction, which raises the question whether mitochondrial Ca2+ uptake is fast and big enough to shape intracellular Ca2+ signaling during excitation-contraction coupling and creates technical challenges for quantification of the dynamic changes of Ca2+ inside mitochondria. This review focuses on characterization of mitochondrial Ca2+ uptake in skeletal muscle and its role in muscle physiology and diseases.Zhou, JingsongDhakal, KamalYi, JianxunFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08507https://cds.cern.ch/record/2202612['arXiv:1607.08507']arXiv:1607.08507On Varying Topology of Complex Networks and Performance Limitations of Community Detection Algorithms
https://cds.cern.ch/record/2202611
One of the most widely studied problem in mining and analysis of complex networks is the detection of community structures. The problem has been extensively studied by researchers due to its high utility and numerous applications in various domains. Many algorithmic solutions have been proposed for the community detection problem but the quest to find the best algorithm is still on. More often than not, researchers focus on developing fast and accurate algorithms that can be generically applied to networks from a variety of domains without taking into consideration the structural and topological variations in these networks. In this paper, we evaluate the performance of different clustering algorithms as a function of varying network topology. Along with the well known LFR model to generate benchmark networks with communities,we also propose a new model named Naive Scale Free Model to study the behavior of community detection algorithms with respect to different topological features. More specifically, we are interested in the size of networks, the size of community structures, the average connectivity of nodes and the ratio of inter-intra cluster edges. Results reveal several limitations of the current popular network clustering algorithms failing to correctly find communities. This suggests the need to revisit the design of current clustering algorithms that fail to incorporate varying topological features of different networks.Pasta, Muhammad QasimZaidi, FarazMelançon, GuyFri, 29 Jul 2016 06:31:53 GMT28 Jul 2016arXiv:1607.08497https://cds.cern.ch/record/2202611['arXiv:1607.08497']arXiv:1607.08497Design of a new tracking device for on-line dose monitor in ion therapy
https://cds.cern.ch/record/2202610
Charged Particle Therapy is a technique for cancer treatment that exploits hadron beams, mostly protons and carbons. A critical issue is the monitoring of the dose released by the beam to the tumor and to the surrounding tissues. We present the design of a new tracking device for monitoring on-line the dose in ion therapy through the detection of secondary charged particles produced by the beam interactions in the patient tissues. In fact, the charged particle emission shape can be correlated with the spatial dose release and the Bragg peak position. The detector uses the information provided by 12 layers of scintillating fibers followed by a plastic scintillator and a small calorimeter made of a pixelated Lutetium Fine Silicate crystal. Simulations have been performed to evaluate the achievable spatial resolution and a possible application of the device for the monitoring of the dose pro?le in a real treatment is presented.Traini, GiacomoBattistoni, GiuseppeBollella, AngelaCollamati, FrancescoDe Lucia, ErikaFaccini, RiccardoFerroni, FernandoFrallicciardi, Paola MariaMancini-Terracciano, CarloMarafini, MichelaMattei, IlariaMiraglia, FedericoMuraro, SilviaParamatti, RiccardoPiersanti, LucaPinci, DavideRucinski, AntoniRussomando, AndreaSarti, AlessioSciubba, AdalbertoSenzacqua, MartinaSolfaroli-Camillocci, ElenaToppi, MarcoVoena, CeciliaPatera, VincenzoFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08493https://cds.cern.ch/record/2202610['arXiv:1607.08493']arXiv:1607.08493A large eddy simulation (LES) study of inertial deposition of particles onto in-line tube-banks
https://cds.cern.ch/record/2202609
We study deposition and impact of heavy particles onto an in-line tube-banks within a turbulent cross flow through Lagrangian particle tracking coupled with an LES modelling framework. The flow Reynolds number based on the cylinder diameter D and flow velocity between the gap of two vertically adjacent cylinders is 33960. We examine the flow structures across the tube bank and report surface pressure characteristics on cylinders. Taking into account particle-wall impact and bounce, we study dispersion and deposition of three sets of particles (St = 0.35, 0.086, 0.0075) based on 107 particles tracked through the turbulent flow resolved by LES. The deposition efficiency for the three sets of particles are reported across the tube-banks. Positions of particle deposited onto tube-banks shows that significantly more of smaller particles deposit onto the back-side of the back-banks. This suggests that the smaller particles are easier to be entrained into the wake and impact onto the back-side of cylinders.Jin, CPotts, ISwailes, D CReeks, M WFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08475https://cds.cern.ch/record/2202609['arXiv:1607.08475']arXiv:1607.08475An algorithm for motif-based network design
https://cds.cern.ch/record/2202608
A determinant property of the structure of a biological network is the distribution of local connectivity patterns, i.e., network motifs. In this work, a method for creating directed, unweighted networks while promoting a certain combination of motifs is presented. This motif-based network algorithm starts with an empty graph and randomly connects the nodes by advancing or discouraging the formation of chosen motifs. The in- or out-degree distribution of the generated networks can be explicitly chosen. The algorithm is shown to perform well in producing networks with high occurrences of the targeted motifs, both ones consisting of 3 nodes as well as ones consisting of 4 nodes. Moreover, the algorithm can also be tuned to bring about global network characteristics found in many natural networks, such as small-worldness and modularity.Mäki-Marttunen, TuomoFri, 29 Jul 2016 06:31:52 GMT13 May 2016arXiv:1607.08472https://cds.cern.ch/record/2202608['arXiv:1607.08472']arXiv:1607.08472Reconstruction of Sub-Surface Velocities from Satellite Observations Using Iterative Self-Organizing Maps
https://cds.cern.ch/record/2202607
In this letter a new method based on modified self-organizing maps is presented for the reconstruction of deep ocean current velocities from surface information provided by satellites. This method takes advantage of local correlations in the data-space to improve the accuracy of the reconstructed deep velocities. Unlike previous attempts to reconstruct deep velocities from surface data, our method makes no assumptions regarding the structure of the water column, nor the underlying dynamics of the flow field. Using satellite observations of surface velocity, sea-surface height and sea-surface temperature, as well as observations of the deep current velocity from autonomous Argo floats to train the map, we are able to reconstruct realistic high--resolution velocity fields at a depth of 1000m. Validation reveals extremely promising results, with a speed root mean squared error of ~2.8cm/s, a factor more than a factor of two smaller than competing methods, and direction errors consistently smaller than 30 degrees. Finally, we discuss the merits and shortcomings of this methodology and its possible future applications.Chapman, ChristopherCharantonis, Anastase AlexandreFri, 29 Jul 2016 06:31:52 GMT26 Jul 2016arXiv:1607.08469https://cds.cern.ch/record/2202607['arXiv:1607.08469']arXiv:1607.08469Waves of DNA: Propagating Excitations in Extended Nanoconfined Polymers
https://cds.cern.ch/record/2202606
We use a nanofluidic system to investigate the emergence of thermally driven collective phenomena along a single polymer chain. In our approach, a single DNA molecule is confined in a nanofluidic slit etched with arrays of embedded nanocavities; the cavity lattice is designed so that a single chain occupies multiple cavities. Fluorescent video-microscopy data shows that waves of excess fluorescence propagate across the cavity-straddling molecule, corresponding to propagating fluctuations of contour overdensity in the cavities. The waves are quantified by examining the correlation in intensity fluctuations between neighbouring cavities. Correlations grow from an anti-correlated minimum to a correlated maximum before decaying, corresponding to a transfer of contour between neighbouring cavities at a fixed transfer time-scale. The observed dynamics can be modelled using Langevin dynamics simulations and a minimal lattice model of coupled diffusion. This study shows how confinement-based sculpting of the polymer equilibrium configuration, by renormalizing the physical system into a series of discrete cavity states, can lead to new types of dynamic collective phenomena.Klotz, Alexander Rde Haan, Hendrick WReisner, Walter WFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08431https://cds.cern.ch/record/2202606['arXiv:1607.08431']arXiv:1607.08431From a thin film model for passive suspensions towards the description of osmotic biofilm spreading
https://cds.cern.ch/record/2202605
Biofilms are ubiquitous macro-colonies of bacteria that develop at various interfaces (solid-liquid, solid-gas or liquid-gas). The formation of biofilms starts with the attachment of individual bacteria to an interface, where they proliferate and produce a slimy polymeric matrix - two processes that result in colony growth and spreading. Recent experiments on the growth of biofilms on agar substrates under air have shown that for certain bacterial strains, the production of the extracellular matrix and the resulting osmotic influx of nutrient-rich water from the agar into the biofilm are more crucial for the spreading behaviour of a biofilm than the motility of individual bacteria. We present a model which describes the biofilm evolution and the advancing biofilm edge for this spreading mechanism. The model is based on a gradient dynamics formulation for thin films of biologically passive liquid mixtures and suspensions, supplemented by bioactive processes which play a decisive role in the osmotic spreading of biofilms. It explicitly includes the wetting properties of the biofilm on the agar substrate via a disjoining pressure and can therefore give insight into the interplay between passive surface forces and bioactive growth processes.Trinschek, SarahJohn, KarinThiele, UweFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08425https://cds.cern.ch/record/2202605['arXiv:1607.08425']arXiv:1607.08425Stochastic chaos in a turbulent swirling flow
https://cds.cern.ch/record/2202604
We report the experimental evidence of the existence of a random attractor in a fully developed turbulent swirling flow. By defining a global observable which tracks the asymmetry in the flux of angular momentum imparted to the flow, we can first reconstruct the associated turbulent attractor and then follow its route towards chaos. We further show that the experimental attractor can be modeled by stochastic Duffing equations, that match the quantitative properties of the experimental flow, namely the number of quasi-stationary states and transition rates among them, the effective dimensions, and the continuity of the first Lyapunov exponents. Such properties can neither be recovered using deterministic models nor using stochastic differential equations based on effective potentials obtained by inverting the probability distributions of the experimental global observables. Our findings open the way to low dimensional modeling of systems featuring a large number of degrees of freedom and multiple quasi-stationary states.Faranda, DavideSato, YuzuruSaint-Michel, BriceWiertel, CecilePadilla, VincentDubrulle, BerengereDaviaud, FrancoisFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08409https://cds.cern.ch/record/2202604['arXiv:1607.08409']arXiv:1607.08409Stabilization and frequency control of a DFB laser with a tunable optical reflector integrated in a Silicon Photonics PIC
https://cds.cern.ch/record/2202603
We investigate the effect of tunable optical feedback on a commercial DFB laser edge coupled to a Silicon Photonics planar integrated circuit in which a tunable reflector has been implemented by means of a ring resonator based add-drop multiplexer. Controlled optical feedback allows for fine-tuning of the laser oscillation frequency. Under certain conditions it also allows suppression of bifurcation modes triggered by reflections occurring elsewhere on the chip. A semi-analytical model describing laser dynamics under combined optical feedback from the input facet of the edge coupler and from the tunable on-chip reflector fits the measurements. Compensation of detrimental effects from reflections induced elsewhere on a transceiver chip may allow moving isolators downstream in future communications systems, facilitating direct hybrid laser integration in Silicon Photonics chips, provided a suitable feedback signal for a control system can be identified. Moreover, the optical frequency tuning at lower feedback levels can be used to form a rapidly tunable optical oscillator as part of an optical phase locked loop, circumventing the problem of the thermal to free carrier effect crossover in the FM response of injection current controlled semiconductor laser diodes.Hauck, JohannesSchrammen, MatthiasRomero-García, SebastíanMüller, JulianaShen, BinRichter, JensMerget, FlorianWitzens, JeremyFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08407https://cds.cern.ch/record/2202603['arXiv:1607.08407']arXiv:1607.08407Variational perturbation and extended Plefka approaches to dynamics on random networks: the case of the kinetic Ising model
https://cds.cern.ch/record/2202602
We describe and analyze some novel approaches for studying the dynamics of Ising spin glass models. We first briefly consider the variational approach based on minimizing the Kullback-Leibler divergence between independent trajectories and the real ones and note that this approach only coincides with the mean field equations from the saddle point approximation to the generating functional when the dynamics is defined through a logistic link function, which is the case for the kinetic Ising model with parallel update. We then spend the rest of the paper developing two ways of going beyond the saddle point approximation to the generating functional. In the first one, we develop a variational perturbative approximation to the generating functional by expanding the action around a quadratic function of the local fields and conjugate local fields whose parameters are optimized. We derive analytical expressions for the optimal parameters and show that when the optimization is suitably restricted, we recover the mean field equations that are exact for the fully asymmetric random couplings (M\'ezard and Sakellariou, 2011). However, without this restriction the results are different. We also describe an extended Plefka expansion in which in addition to the magnetization, we also fix the correlation and response functions. Finally, we numerically study the performance of these approximations for Sherrington-Kirkpatrick type couplings for various coupling strengths, degrees of coupling symmetry and external fields. We show that the dynamical equations derived from the extended Plefka expansion outperform the others in all regimes, although it is computationally more demanding. The unconstrained variational approach does not perform well in the small coupling regime, while it approaches dynamical TAP equations of (Roudi and Hertz, 2011) for strong couplings.Bachschmid-Romano, LudovicaBattistin, ClaudiaOpper, ManfredRoudi, YasserFri, 29 Jul 2016 06:31:52 GMT28 Jul 2016arXiv:1607.08379https://cds.cern.ch/record/2202602['arXiv:1607.08379']arXiv:1607.08379Isobaric first-principles molecular dynamics of liquid water with nonlocal van der Waals interactions
https://cds.cern.ch/record/2202601
We investigate the structural properties of liquid water at near ambient conditions using first-principles molecular dynamics simulations based on a semilocal density functional augmented with nonlocal van der Waals interactions. The adopted scheme offers the advantage of simulating liquid water at essentially the same computational cost of standard semilocal functionals. Applied to the water dimer and to ice Ih, we find that the hydrogen-bond energy is only slightly enhanced compared to a standard semilocal functional. We simulate liquid water through molecular dynamics in the NpH statistical ensemble allowing for fluctuations of the system density. The structure of the liquid departs from that found with a semilocal functional leading to more compact structural arrangements. This indicates that the directionality of the hydrogen-bond interaction has a diminished role as compared to the overall attractions, as expected when dispersion interactions are accounted for. This is substantiated through a detailed analysis comprising the study of the partial radial distribution functions, various local order indices, the hydrogen-bond network, and the selfdiffusion coefficient. The explicit treatment of the van der Waals interactions leads to an overall improved description of liquid water.Miceli, Giacomode Gironcoli, StefanoPasquarello, AlfredoFri, 29 Jul 2016 06:31:51 GMT28 Jul 2016arXiv:1607.08377https://cds.cern.ch/record/2202601['arXiv:1607.08377']arXiv:1607.08377Growing complex network of citations of scientific papers -- measurements and modeling
https://cds.cern.ch/record/2202600
To quantify the mechanism of a complex network growth we focus on the network of citations of scientific papers and use a combination of the theoretical and experimental tools to uncover microscopic details of this network growth. Namely, we develop a stochastic model of citation dynamics based on copying/redirection/triadic closure mechanism. In a complementary and coherent way, the model accounts both for statistics of references of scientific papers and for their citation dynamics. Originating in empirical measurements, the model is cast in such a way that it can be verified quantitatively in every aspect. Such verification is performed by measuring citation dynamics of Physics papers. The measurements revealed nonlinear citation dynamics, the nonlinearity being intricately related to network topology. The nonlinearity has far-reaching consequences including non-stationary citation distributions, diverging citation trajectory of similar papers, runaways or "immortal papers" with infinite citation lifetime etc. Thus, our most important finding is nonlinearity in complex network growth. In a more specific context, our results can be a basis for quantitative probabilistic prediction of citation dynamics of individual papers and of the journal impact factor.Golosovsky, MSolomon, SFri, 29 Jul 2016 06:31:51 GMT28 Jul 2016arXiv:1607.08370https://cds.cern.ch/record/2202600['arXiv:1607.08370']arXiv:1607.08370