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  • 1.
    Agasthya, Lokahith
    et al.
    Indian Inst Sci Educ & Res, Pune 411008, Maharashtra, India.;Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India.;Univ Roma Tor Vergata, Dept Phys, Via Ric Sci 1, I-00133 Rome, Italy.;Univ Roma Tor Vergata, Ist Nazl Fis Nucl, Via Ric Sci 1, I-00133 Rome, Italy..
    Picardo, Jason R.
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India..
    Ravichandran, Siddharth
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, S-10691 Stockholm, Sweden..
    Govindarajan, Rama
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India..
    Ray, Samriddhi Sankar
    Tata Inst Fundamental Res, Int Ctr Theoret Sci, Bangalore 560089, Karnataka, India..
    Understanding droplet collisions through a model flow: Insights from a Burgers vortex2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 6, article id 063107Article in journal (Refereed)
    Abstract [en]

    We investigate the role of intense vortical structures, similar to those in a turbulent flow, in enhancing collisions (and coalescences) which lead to the formation of large aggregates in particle-laden flows. By using a Burgers vortex model, we show, in particular, that vortex stretching significantly enhances sharp inhomogeneities in spatial particle densities, related to the rapid ejection of particles from intense vortices. Furthermore our work shows how such spatial clustering leads to an enhancement of collision rates and extreme statistics of collisional velocities. We also study the role of polydisperse suspensions in this enhancement. Our work uncovers an important principle, which, if valid for realistic turbulent flows, may be a factor in how small nuclei water droplets in warm clouds can aggregate to sizes large enough to trigger rain.

  • 2. Agasthya, Lokahith
    et al.
    Picardo, Jason R.
    Sivaramakrishnan, Ravichandran
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Govindarajan, Rama
    Ray, Samriddhi Sankar
    Understanding droplet collisions through a model flow: Insights from a Burgers vortex2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 6, article id 063107Article in journal (Refereed)
    Abstract [en]

    We investigate the role of intense vortical structures, similar to those in a turbulent flow, in enhancing collisions (and coalescences) which lead to the formation of large aggregates in particle-laden flows. By using a Burgers vortex model, we show, in particular, that vortex stretching significantly enhances sharp inhomogeneities in spatial particle densities, related to the rapid ejection of particles from intense vortices. Furthermore our work shows how such spatial clustering leads to an enhancement of collision rates and extreme statistics of collisional velocities. We also study the role of polydisperse suspensions in this enhancement. Our work uncovers an important principle, which, if valid for realistic turbulent flows, may be a factor in how small nuclei water droplets in warm clouds can aggregate to sizes large enough to trigger rain.

  • 3. Agosta, L.
    et al.
    Metere, A.
    Dzugutov, Mikhail
    KTH.
    Hexatic smectic phase with algebraically decaying bond-orientational order2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 5, article id 052702Article in journal (Refereed)
    Abstract [en]

    The hexatic phase predicted by the theories of two-dimensional melting is characterized by the power-law decay of the orientational correlations, whereas the in-layer bond orientational order in all the hexatic smectic phases observed so far was found to be long range. We report a hexatic smectic phase where the in-layer bond orientational correlations decay algebraically, in quantitative agreement with the hexatic ordering predicted by the theory for two dimensions. The phase was formed in a molecular dynamics simulation of a one-component system of particles interacting via a spherically symmetric potential. The present results thus demonstrate that the theoretically predicted two-dimensional hexatic order can exist in a three-dimensional system.

  • 4.
    Agosta, Lorenzo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Metere, Alfredo
    Dzugutov, Mikhail
    Hexatic smectic phase with algebraically decaying bond-orientational order2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 5, article id 052702Article in journal (Refereed)
    Abstract [en]

    The hexatic phase predicted by the theories of two-dimensional melting is characterized by the power-law decay of the orientational correlations, whereas the in-layer bond orientational order in all the hexatic smectic phases observed so far was found to be long range. We report a hexatic smectic phase where the in-layer bond orientational correlations decay algebraically, in quantitative agreement with the hexatic ordering predicted by the theory for two dimensions. The phase was formed in a molecular dynamics simulation of a one-component system of particles interacting via a spherically symmetric potential. The present results thus demonstrate that the theoretically predicted two-dimensional hexatic order can exist in a three-dimensional system.

  • 5. Argun, Aykut
    et al.
    Soni, Jalpa
    Dabelow, Lennart
    Bo, Stefano
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Pesce, Giuseppe
    Eichhorn, Ralf
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Volpe, Giovanni
    Experimental realization of a minimal microscopic heat engine2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 5, article id 052106Article in journal (Refereed)
    Abstract [en]

    Microscopic heat engines are microscale systems that convert energy flows between heat reservoirs into work or systematic motion. We have experimentally realized a minimal microscopic heat engine. It consists of a colloidal Brownian particle optically trapped in an elliptical potential well and simultaneously coupled to two heat baths at different temperatures acting along perpendicular directions. For a generic arrangement of the principal directions of the baths and the potential, the symmetry of the system is broken, such that the heat flow drives a systematic gyrating motion of the particle around the potential minimum. Using the experimentally measured trajectories, we quantify the gyrating motion of the particle, the resulting torque that it exerts on the potential, and the associated heat flow between the heat baths. We find excellent agreement between the experimental results and the theoretical predictions.

  • 6. Argun, Aykut
    et al.
    Soni, Jalpa
    Dabelow, Lennart
    Bo, Stefano
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Pesce, Giuseppe
    Eichhorn, Ralf
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Volpe, Giovanni
    Experimental realization of a minimal microscopic heat engine2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 5, article id 052106Article in journal (Refereed)
    Abstract [en]

    Microscopic heat engines are microscale systems that convert energy flows between heat reservoirs into work or systematic motion. We have experimentally realized a minimal microscopic heat engine. It consists of a colloidal Brownian particle optically trapped in an elliptical potential well and simultaneously coupled to two heat baths at different temperatures acting along perpendicular directions. For a generic arrangement of the principal directions of the baths and the potential, the symmetry of the system is broken, such that the heat flow drives a systematic gyrating motion of the particle around the potential minimum. Using the experimentally measured trajectories, we quantify the gyrating motion of the particle, the resulting torque that it exerts on the potential, and the associated heat flow between the heat baths. We find excellent agreement between the experimental results and the theoretical predictions.

  • 7. Aslak, Ulf
    et al.
    Rosvall, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lehmann, Sune
    Constrained information flows in temporal networks reveal intermittent communities2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 6, article id 062312Article in journal (Refereed)
    Abstract [en]

    Many real-world networks represent dynamic systems with interactions that change over time, often in uncoordinated ways and at irregular intervals. For example, university students connect in intermittent groups that repeatedly form and dissolve based on multiple factors, including their lectures, interests, and friends. Such dynamic systems can be represented as multilayer networkswhere each layer represents a snapshot of the temporal network. In this representation, it is crucial that the links between layers accurately capture real dependencies between those layers. Often, however, these dependencies are unknown. Therefore, current methods connect layers based on simplistic assumptions that do not capture node-level layer dependencies. For example, connecting every node to itself in other layers with the same weight can wipe out dependencies between intermittent groups, making it difficult or even impossible to identify them. In this paper, we present a principled approach to estimating node-level layer dependencies based on the network structure within each layer. We implement our node-level coupling method in the community detection framework Infomap and demonstrate its performance compared to current methods on synthetic and real temporal networks. We show that our approach more effectively constrains information inside multilayer communities so that Infomap can better recover planted groups in multilayer benchmark networks that represent multiple modeswith different groups and better identify intermittent communities in real temporal contact networks. These results suggest that node-level layer coupling can improve the modeling of information spreading in temporal networks and better capture intermittent community structure.

  • 8.
    Aurell, Erik
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST). Aalto Univ, Dept Comp Sci, FIN-00076 Aalto, Finland.;Aalto Univ, Dept Appl Phys, FIN-00076 Aalto, Finland.
    Characteristic functions of quantum heat with baths at different temperatures2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 6, article id 062117Article in journal (Refereed)
    Abstract [en]

    This paper is about quantum heat defined as the change in energy of a bath during a process. The presentation takes into account recent developments in classical strong-coupling thermodynamics and addresses a version of quantum heat that satisfies quantum-classical correspondence. The characteristic function and the full counting statistics of quantum heat are shown to be formally similar. The paper further shows that the method can be extended to more than one bath, e.g., two baths at different temperatures, which opens up the prospect of studying correlations and heat flow. The paper extends earlier results on the expected quantum heat in the setting of one bath [E. Aurell and R. Eichhorn, New .J Phys. 17, 065007 (2015); E. Aurell, Entropy 19, 595 (2017)].

  • 9.
    Aurell, Erik
    KTH. Aalto Univ, Dept Comp Sci & Appl Phys, FIN-00076 Espoo, Aalto, Finland..
    Unified picture of strong-coupling stochastic thermodynamics and time reversals2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 4, article id 042112Article in journal (Refereed)
    Abstract [en]

    Strong-coupling statistical thermodynamics is formulated as the Hamiltonian dynamics of an observed system interacting with another unobserved system (a bath). It is shown that the entropy production functional of stochastic thermodynamics, defined as the log ratio of forward and backward system path probabilities, is in a one-to-one relation with the log ratios of the joint initial conditions of the system and the bath. A version of strong-coupling statistical thermodynamics where the system-bath interaction vanishes at the beginning and at the end of a process is, as is also weak-coupling stochastic thermodynamics, related to the bath initially in equilibrium by itself. The heat is then the change of bath energy over the process, and it is discussed when this heat is a functional of the system history alone. The version of strong-coupling statistical thermodynamics introduced by Seifert and Jarzynski is related to the bath initially in conditional equilibrium with respect to the system. This leads to heat as another functional of the system history which needs to be determined by thermodynamic integration. The log ratio of forward and backward system path probabilities in a stochastic process is finally related to log ratios of the initial conditions of a combined system and bath. It is shown that the entropy production formulas of stochastic processes under a general class of time reversals are given by the differences of bath energies in a larger underlying Hamiltonian system. The paper highlights the centrality of time reversal in stochastic thermodynamics, also in the case of strong coupling.

  • 10. Aurell, Erik
    et al.
    Bo, Stefano
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Steady diffusion in a drift field: A comparison of large-deviation techniques and multiple-scale analysis2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 3, article id 032140Article in journal (Refereed)
    Abstract [en]

    A particle with internal unobserved states diffusing in a force field will generally display effective advection-diffusion. The drift velocity is proportional to the mobility averaged over the internal states, or effective mobility, while the effective diffusion has two terms. One is of the equilibrium type and satisfies an Einstein relation with the effective mobility while the other is quadratic in the applied force. In this contribution we present two new methods to obtain these results, on the one hand using large deviation techniques and on the other by a multiple-scale analysis, and compare the two. We consider both systems with discrete internal states and continuous internal states. We show that the auxiliary equations in the multiple-scale analysis can also be derived in second-order perturbation theory in a large deviation theory of a generating function (discrete internal states) or generating functional (continuous internal states). We discuss that measuring the two components of the effective diffusion give a way to determine kinetic rates from only first and second moments of the displacement in steady state.

  • 11.
    Aurell, Erik
    et al.
    KTH. Departments of Information and Computer Science and Applied Physics, Aalto University, FIN-00076 Espoo, Finland.
    Bo, Stefano
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Steady diffusion in a drift field: A comparison of large-deviation techniques and multiple-scale analysis2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 3, article id 032140Article in journal (Refereed)
    Abstract [en]

    A particle with internal unobserved states diffusing in a force field will generally display effective advection-diffusion. The drift velocity is proportional to the mobility averaged over the internal states, or effective mobility, while the effective diffusion has two terms. One is of the equilibrium type and satisfies an Einstein relation with the effective mobility while the other is quadratic in the applied force. In this contribution we present two new methods to obtain these results, on the one hand using large deviation techniques and on the other by a multiple-scale analysis, and compare the two. We consider both systems with discrete internal states and continuous internal states. We show that the auxiliary equations in the multiple-scale analysis can also be derived in second-order perturbation theory in a large deviation theory of a generating function (discrete internal states) or generating functional (continuous internal states). We discuss that measuring the two components of the effective diffusion give a way to determine kinetic rates from only first and second moments of the displacement in steady state.

  • 12.
    Aurell, Erik
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Dominguez, Eduardo
    Univ Havana, Dept Theoret Phys, Grp Complex Syst & Stat Phys, Havana, Cuba..
    Machado, David
    Univ Havana, Dept Theoret Phys, Grp Complex Syst & Stat Phys, Havana, Cuba..
    Mulet, Roberto
    Univ Havana, Dept Theoret Phys, Grp Complex Syst & Stat Phys, Havana, Cuba..
    Exploring the diluted ferromagnetic p-spin model with a cavity master equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 5, article id 050103Article in journal (Refereed)
    Abstract [en]

    We introduce an alternative solution to Glauber multispin dynamics on random graphs. The solution is based on the recently introduced cavity master equation (CME), a time-closure turning the, in principle, exact dynamic cavity method into a practical method of analysis and of fast simulation. Running CME once is of comparable computational complexity as one Monte Carlo run on the same problem. We show that CME correctly models the ferromagnetic p-spin Glauber dynamics from high temperatures down to and below the spinoidal transition. We also show that CME allows an alternative exploration of the low-temperature spin-glass phase of the model.

  • 13.
    Aurell, Erik
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Montana, Federica
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Thermal power of heat flow through a qubit2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 4, article id 042130Article in journal (Refereed)
    Abstract [en]

    In this paper we consider the thermal power of a heat flow through a qubit between two baths. The baths are modeled as a set of harmonic oscillators initially at equilibrium, at two temperatures. Heat is defined as the change of energy of the cold bath, and thermal power is defined as expected heat per unit time, in the long-time limit. The qubit and the baths interact as in the spin-boson model, i.e., through qubit operator sigma(z). We compute thermal power in an approximation analogous to a "noninteracting blip" (NIBA) and express it in the polaron picture as products of correlation functions of the two baths, and a time derivative of a correlation function of the cold bath. In the limit of weak interaction we recover known results in terms of a sum of correlation functions of the two baths, a correlation functions of the cold bath only, and the energy split.

  • 14. Barfuss, Wolfram
    et al.
    Donges, Jonathan F.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Potsdam Institute for Climate Impact Research, Germany.
    Kurths, Jürgen
    Deterministic limit of temporal difference reinforcement learning for stochastic games2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 4, article id 043305Article in journal (Refereed)
    Abstract [en]

    Reinforcement learning in multiagent systems has been studied in the fields of economic game theory, artificial intelligence, and statistical physics by developing an analytical understanding of the learning dynamics (often in relation to the replicator dynamics of evolutionary game theory). However, the majority of these analytical studies focuses on repeated normal form games, which only have a single environmental state. Environmental dynamics, i.e., changes in the state of an environment affecting the agents' payoffs has received less attention, lacking a universal method to obtain deterministic equations from established multistate reinforcement learning algorithms. In this work we present a methodological extension, separating the interaction from the adaptation timescale, to derive the deterministic limit of a general class of reinforcement learning algorithms, called temporal difference learning. This form of learning is equipped to function in more realistic multistate environments by using the estimated value of future environmental states to adapt the agent's behavior. We demonstrate the potential of our method with the three well-established learning algorithms Q learning, SARSA learning, and actor-critic learning. Illustrations of their dynamics on two multiagent, multistate environments reveal a wide range of different dynamical regimes, such as convergence to fixed points, limit cycles, and even deterministic chaos.

  • 15.
    Bhatnagar, Akshay
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Statistics of relative velocity for particles settling under gravity in a turbulent flow2020In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 101, no 3, article id 033102Article in journal (Refereed)
    Abstract [en]

    We study the joint probability distributions of separation R and radial component of the relative velocity V-R of particles settling under gravity in a turbulent flow. We also obtain the moments of these distributions and analyze their anisotropy using spherical harmonics. We find that the qualitative nature of the joint distributions remains the same as no-gravity case. Distributions of V-R for fixed values of R show a power-law dependence on V-R for a range of V-R; the exponent of the power law depends on the gravity. Effects of gravity are also manifested in the following ways: (a) Moments of the distributions are anisotropic; degree of anisotropy depends on particle's Stokes number, but does not depend on R for small values of R. (b) Mean velocity of collision between two particles is decreased for particles having equal Stokes numbers but increased for particles having different Stokes numbers. For the later, collision velocity is set by the difference in their settling velocities.

  • 16.
    Bhatnagar, Akshay
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Indian Institute of Science, India.
    Gupta, Anupam
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Pandit, Rahul
    Heavy inertial particles in turbulent flows gain energy slowly but lose it rapidly2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 3, article id 033102Article in journal (Refereed)
    Abstract [en]

    We present an extensive numerical study of the time irreversibility of the dynamics of heavy inertial particles in three-dimensional, statistically homogeneous, and isotropic turbulent flows. We show that the probability density function (PDF) of the increment, W(tau), of a particle's energy over a time scale tau is non-Gaussian, and skewed toward negative values. This implies that, on average, particles gain energy over a period of time that is longer than the duration over which they lose energy. We call this slow gain and fast loss. We find that the third moment of W(tau) scales as tau(3) for small values of tau. We show that the PDF of power-input p is negatively skewed too; we use this skewness Ir as a measure of the time irreversibility and we demonstrate that it increases sharply with the Stokes number St for small St; this increase slows down at St similar or equal to 1. Furthermore, we obtain the PDFs of t(+) and t(-), the times over which p has, respectively, positive or negative signs, i.e., the particle gains or loses energy. We obtain from these PDFs a direct and natural quantification of the slow gain and fast loss of the energy of the particles, because these PDFs possess exponential tails from which we infer the characteristic loss and gain times t(loss) and t(gain), respectively, and we obtain t(loss) < t(gain) for all the cases we have considered. Finally, we show that the fast loss of energy occurs with greater probability in the strain-dominated region than in the vortical one; in contrast, the slow gain in the energy of the particles is equally likely in vortical or strain-dominated regions of the flow.

  • 17.
    Bhatnagar, Akshay
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Gupta, Anupam
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Pandit, Rahul
    Heavy inertial particles in turbulent flows gain energy slowly but lose it rapidly2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 3, article id 033102Article in journal (Refereed)
    Abstract [en]

    We present an extensive numerical study of the time irreversibility of the dynamics of heavy inertial particles in three-dimensional, statistically homogeneous, and isotropic turbulent flows. We show that the probability density function (PDF) of the increment, W(tau), of a particle's energy over a time scale tau is non-Gaussian, and skewed toward negative values. This implies that, on average, particles gain energy over a period of time that is longer than the duration over which they lose energy. We call this slow gain and fast loss. We find that the third moment of W(tau) scales as tau(3) for small values of tau. We show that the PDF of power-input p is negatively skewed too; we use this skewness Ir as a measure of the time irreversibility and we demonstrate that it increases sharply with the Stokes number St for small St; this increase slows down at St similar or equal to 1. Furthermore, we obtain the PDFs of t(+) and t(-), the times over which p has, respectively, positive or negative signs, i.e., the particle gains or loses energy. We obtain from these PDFs a direct and natural quantification of the slow gain and fast loss of the energy of the particles, because these PDFs possess exponential tails from which we infer the characteristic loss and gain times t(loss) and t(gain), respectively, and we obtain t(loss) < t(gain) for all the cases we have considered. Finally, we show that the fast loss of energy occurs with greater probability in the strain-dominated region than in the vortical one; in contrast, the slow gain in the energy of the particles is equally likely in vortical or strain-dominated regions of the flow.

  • 18.
    Bhatnagar, Akshay
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Indian Institute of Science, India.
    Gupta, Anupam
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Perlekar, Prasad
    Wilkinson, Michael
    Pandit, Rahul
    Deviation-angle and trajectory statistics for inertial particles in turbulence2016In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 94, no 6, article id 063112Article in journal (Refereed)
    Abstract [en]

    Small particles in suspension in a turbulent fluid have trajectories that do not follow the pathlines of the flow exactly. We investigate the statistics of the angle of deviation phi between the particle and fluid velocities. We show that, when the effects of particle inertia are small, the probability distribution function (PDF) P-phi of this deviation angle shows a power-law region in which P-phi similar to phi(-4). We also find that the PDFs of the trajectory curvature. and modulus theta of the torsion theta have power-law tails that scale, respectively, as P-kappa similar to kappa (-5/2), as kappa -> infinity, and P-phi similar to phi(-3), as theta -> infinity: These exponents are in agreement with those previously observed for fluid pathlines. We propose a way to measure the complexity of heavy-particle trajectories by the number N-I(t, St) of points (up until time t) at which the torsion changes sign. We present numerical evidence that n(I)(St) lim(t ->infinity) N-I(t, St)/t similar to St(-Delta) for large St, with Lambda similar or equal to 0.5.

  • 19.
    Bhatnagar, Akshay
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Gustavsson, K.
    Mehlig, B.
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Relative velocities in bidisperse turbulent aerosols: Simulations and theory2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 6, article id 063107Article in journal (Refereed)
    Abstract [en]

    We perform direct numerical simulations of a bidisperse suspension of heavy spherical particles in forced, homogeneous, and isotropic three-dimensional turbulence. We compute the joint distribution of relative particle distances and longitudinal relative velocities between particles of different inertia. For a pair of particles with small difference in their inertias we compare our results with recent theoretical predictions [Meibohm et al., Phys. Rev. E 96, 061102 (2017)] for the shape of this distribution. We also compute the moments of relative velocities as a function of particle separation and compare with the theoretical predictions. We observe good agreement. For a pair of particles that are very different from each other-one is heavy and the other one has negligible inertia-we give a theory to calculate their root-mean-square relative velocity. This theory also agrees well with the results of our simulations.

  • 20.
    Bhatnagar, Akshay
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Gustavsson, K.
    Gothenburg Univ, Dept Phys, S-41296 Gothenburg, Sweden..
    Mehlig, B.
    Gothenburg Univ, Dept Phys, S-41296 Gothenburg, Sweden..
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Relative velocities in bidisperse turbulent aerosols: Simulations and theory2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 6, article id 063107Article in journal (Refereed)
    Abstract [en]

    We perform direct numerical simulations of a bidisperse suspension of heavy spherical particles in forced, homogeneous, and isotropic three-dimensional turbulence. We compute the joint distribution of relative particle distances and longitudinal relative velocities between particles of different inertia. For a pair of particles with small difference in their inertias we compare our results with recent theoretical predictions [Meibohm et al., Phys. Rev. E 96, 061102 (2017)] for the shape of this distribution. We also compute the moments of relative velocities as a function of particle separation and compare with the theoretical predictions. We observe good agreement. For a pair of particles that are very different from each other-one is heavy and the other one has negligible inertia-we give a theory to calculate their root-mean-square relative velocity. This theory also agrees well with the results of our simulations.

  • 21.
    Bhatnagar, Akshay
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Gustavsson, K.
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 2, article id 023105Article in journal (Refereed)
    Abstract [en]

    We use direct numerical simulations to calculate the joint probability density function of the relative distance R and relative radial velocity component V-R for a pair of heavy inertial particles suspended in homogeneous and isotropic turbulent flows. At small scales the distribution is scale invariant, with a scaling exponent that is related to the particle-particle correlation dimension in phase space, D-2. It was argued [K. Gustavsson and B. Mehlig, Phys. Rev. E 84, 045304 (2011); J. Turbul. 15, 34 (2014)] that the scale invariant part of the distribution has two asymptotic regimes: (1) vertical bar V-R vertical bar << R, where the distribution depends solely on R, and (2) vertical bar V-R vertical bar >> R, where the distribution is a function of vertical bar V-R vertical bar alone. The probability distributions in these two regimes are matched along a straight line: vertical bar V-R vertical bar = z*R. Our simulations confirm that this is indeed correct. We further obtain D-2 and z* as a function of the Stokes number, St. The former depends nonmonotonically on St with aminimum at about St approximate to 0.7 and the latter has only a weak dependence on St.

  • 22.
    Bhatnagar, Akshay
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.
    Gustavsson, K.
    Mitra, Dhrubaditya
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.
    Statistics of the relative velocity of particles in turbulent flows: Monodisperse particles2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 2, article id 023105Article in journal (Refereed)
    Abstract [en]

    We use direct numerical simulations to calculate the joint probability density function of the relative distance R and relative radial velocity component V-R for a pair of heavy inertial particles suspended in homogeneous and isotropic turbulent flows. At small scales the distribution is scale invariant, with a scaling exponent that is related to the particle-particle correlation dimension in phase space, D-2. It was argued [K. Gustavsson and B. Mehlig, Phys. Rev. E 84, 045304 (2011); J. Turbul. 15, 34 (2014)] that the scale invariant part of the distribution has two asymptotic regimes: (1) vertical bar V-R vertical bar << R, where the distribution depends solely on R, and (2) vertical bar V-R vertical bar >> R, where the distribution is a function of vertical bar V-R vertical bar alone. The probability distributions in these two regimes are matched along a straight line: vertical bar V-R vertical bar = z*R. Our simulations confirm that this is indeed correct. We further obtain D-2 and z* as a function of the Stokes number, St. The former depends nonmonotonically on St with aminimum at about St approximate to 0.7 and the latter has only a weak dependence on St.

  • 23.
    Bo, Stefano
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Schmidt, Falko
    Eichhorn, Ralf
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Volpe, Giovanni
    Measurement of anomalous diffusion using recurrent neural networks2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 100, no 1, article id 010102Article in journal (Refereed)
    Abstract [en]

    Anomalous diffusion occurs in many physical and biological phenomena, when the growth of the mean squared displacement (MSD) with time has an exponent different from one. We show that recurrent neural networks (RNNs) can efficiently characterize anomalous diffusion by determining the exponent from a single short trajectory, outperforming the standard estimation based on the MSD when the available data points are limited, as is often the case in experiments. Furthermore, the RNNs can handle more complex tasks where there are no standard approaches, such as determining the anomalous diffusion exponent from a trajectory sampled at irregular times, and estimating the switching time and anomalous diffusion exponents of an intermittent system that switches between different kinds of anomalous diffusion. We validate our method on experimental data obtained from subdiffusive colloids trapped in speckle light fields and superdiffusive microswimmers.

  • 24.
    Bo, Stefano
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, Dresden, DE-01187, Germany.
    Schmidt, Falko
    Eichhorn, Ralf
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Volpe, Giovanni
    Measurement of anomalous diffusion using recurrent neural networks2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 100, no 1, article id 010102Article in journal (Refereed)
    Abstract [en]

    Anomalous diffusion occurs in many physical and biological phenomena, when the growth of the mean squared displacement (MSD) with time has an exponent different from one. We show that recurrent neural networks (RNNs) can efficiently characterize anomalous diffusion by determining the exponent from a single short trajectory, outperforming the standard estimation based on the MSD when the available data points are limited, as is often the case in experiments. Furthermore, the RNNs can handle more complex tasks where there are no standard approaches, such as determining the anomalous diffusion exponent from a trajectory sampled at irregular times, and estimating the switching time and anomalous diffusion exponents of an intermittent system that switches between different kinds of anomalous diffusion. We validate our method on experimental data obtained from subdiffusive colloids trapped in speckle light fields and superdiffusive microswimmers.

  • 25.
    Borlenghi, Simone
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Boman, Magnus
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. RISE SICS, Electrum 229, SE-16429 Kista, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Modeling reservoir computing with the discrete nonlinear Schrodinger equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052101Article in journal (Refereed)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrodinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 26.
    Borlenghi, Simone
    et al.
    KTH Royal Institute of Technology, Sweden.
    Boman, Magnus
    RISE - Research Institutes of Sweden, ICT, SICS. KTH Royal Institute of Technology, Sweden.
    Delin, Anna
    KTH Royal Institute of Technology, Sweden.
    Modeling reservoir computing with the discrete nonlinear Schrödinger equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052101Article in journal (Refereed)
    Abstract [en]

    We formulate, using the discrete nonlinear Schrödinger equation (DNLS), a general approach to encode and process information based on reservoir computing. Reservoir computing is a promising avenue for realizing neuromorphic computing devices. In such computing systems, training is performed only at the output level by adjusting the output from the reservoir with respect to a target signal. In our formulation, the reservoir can be an arbitrary physical system, driven out of thermal equilibrium by an external driving. The DNLS is a general oscillator model with broad application in physics, and we argue that our approach is completely general and does not depend on the physical realization of the reservoir. The driving, which encodes the object to be recognized, acts as a thermodynamic force, one for each node in the reservoir. Currents associated with these thermodynamic forces in turn encode the output signal from the reservoir. As an example, we consider numerically the problem of supervised learning for pattern recognition, using as a reservoir a network of nonlinear oscillators.

  • 27.
    Borlenghi, Simone
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Iubini, Stefano
    Univ Firenze, Dipartimento Fis & Astron, Via G Sansone 1, I-50019 Sesto Fiorentino, Italy.;Ist Nazl Fis Nucl, Sez Firenze, Via G Sansone 1, I-50019 Sesto Fiorentino, Italy..
    Lepri, Stefano
    Ist Nazl Fis Nucl, Sez Firenze, Via G Sansone 1, I-50019 Sesto Fiorentino, Italy.;CNR, Ist Sistemi Complessi, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy..
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Entropy production for complex Langevin equations2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 1, article id 012150Article in journal (Refereed)
    Abstract [en]

    We study irreversible processes for nonlinear oscillators networks described by complex-valued Langevin equations that account for coupling to different thermochemical baths. Dissipation is introduced via non-Hermitian terms in the Hamiltonian of the model. We apply the stochastic thermodynamics formalism to compute explicit expressions for the entropy production rates. We discuss in particular the nonequilibrium steady states of the network characterized by a constant production rate of entropy and flows of energy and particle currents. For two specific examples, a one-dimensional chain and a dimer, numerical calculations are presented. The role of asymmetric coupling among the oscillators on the entropy production is illustrated.

  • 28.
    Calatayud, Joaquín
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bernardo-Madrid, Ruben
    Neuman, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rojas, Alexis
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Rosvall, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Exploring the solution landscape enables more reliable network community detection2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 100, no 5, article id 052308Article in journal (Refereed)
    Abstract [en]

    To understand how a complex system is organized and functions, researchers often identify communities in the system's network of interactions. Because it is practically impossible to explore all solutions to guarantee the best one, many community-detection algorithms rely on multiple stochastic searches. But for a given combination of network and stochastic algorithms, how many searches are sufficient to find a solution that is good enough? The standard approach is to pick a reasonably large number of searches and select the network partition with the highest quality or derive a consensus solution based on all network partitions. However, if different partitions have similar qualities such that the solution landscape is degenerate, the single best partition may miss relevant information, and a consensus solution may blur complementary communities. Here we address this degeneracy problem with coarse-grained descriptions of the solution landscape. We cluster network partitions based on their similarity and suggest an approach to determine the minimum number of searches required to describe the solution landscape adequately. To make good use of all partitions, we also propose different ways to explore the solution landscape, including a significance clustering procedure. We test these approaches on synthetic networks and a real-world network using two contrasting community-detection algorithms: The algorithm that can identify more general structures requires more searches, and networks with clearer community structures require fewer searches. We also find that exploring the coarse-grained solution landscape can reveal complementary solutions and enable more reliable community detection.

  • 29. Chen, Xiaolong
    et al.
    Zhou, Tianshou
    Feng, Ling
    Liang, Junhao
    Liljeros, Fredrik
    Stockholm University, Faculty of Social Sciences, Department of Sociology.
    Havlin, Shlomo
    Hu, Yanqing
    Nontrivial resource requirement in the early stage for containment of epidemics2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 100, no 3, article id 032310Article in journal (Refereed)
    Abstract [en]

    During epidemic control, containment of the disease is usually achieved through increasing a devoted resource to reduce the infectiousness. However, the impact of this resource expenditure has not been studied quantitatively. For disease spread, the recovery rate can be positively correlated with the average amount of resource devoted to infected individuals. By incorporating this relation we build a novel model and find that insufficient resource leads to an abrupt increase in the infected population size, which is in marked contrast with the continuous phase transitions believed previously. Counterintuitively, this abrupt phase transition is more pronounced in less contagious diseases. Furthermore, we find that even for a single infection source, the public resource needs to be available in a significant amount, which is proportional to the total population size, to ensure epidemic containment. Our findings provide a theoretical foundation for efficient epidemic containment strategies in the early stage.

  • 30.
    Cirillo, Emilio
    et al.
    Sapienza Univ Roma, Dipartimento Sci Base & Appl Ingn, Via A Scarpa 16, I-00161 Rome, Italy.
    Krehel, Oleh
    Eindhoven Univ Technol, ICMS, Dept Math & Comp Sci, POB 513, NL-5600 MB Eindhoven, Netherlands.
    Muntean, Adrian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    van Santen, Rutger
    Eindhoven Univ Technol, Fac Chem Engn, ICMS, POB 513, NL-5600 MB Eindhoven, Netherlands.
    Lattice model of reduced jamming by a barrier2016In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 94, no 4, article id 042115Article in journal (Refereed)
  • 31.
    Cirillo, Emilio N. M.
    et al.
    Sapienza Univ Roma, Dipartimento Sci Base & Appl Ingn, Via A Scarpa 16, I-00161 Rome, Italy.
    Colangeli, Matteo
    Gran Sasso Sci Inst, Viale F Crispi 7, I-00167 Laquila, Italy.
    Muntean, Adrian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Blockage-induced condensation controlled by a local reaction2016In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 94, no 4Article in journal (Refereed)
    Abstract [en]

    We consider the setup of stationary zero range models and discuss the onset of condensation induced by a local blockage on the lattice. We show that the introduction of a local feedback on the hopping rates allows us to control the particle fraction in the condensed phase. This phenomenon results in a current versus blockage parameter curve characterized by two nonanalyticity points.

  • 32.
    Corbetta, Alessandro
    et al.
    Eindhoven University of Technology.
    Lee, Chung-Min
    California State University Long Beach.
    Benzi, Roberto
    University of Rome Tor Vergata.
    Muntean, Adrian
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Toschi, Federico
    Eindhoven University of Technology.
    Fluctuations around mean walking behaviors in diluted pedestrian flows2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 95, no 3Article in journal (Refereed)
    Abstract [en]

    Understanding and modeling the dynamics of pedestrian crowds can help with designing and increasing the safety of civil facilities. A key feature of a crowd is its intrinsic stochasticity, appearing even under very diluted conditions, due to the variability in individual behaviors. Individual stochasticity becomes even more important under densely crowded conditions, since it can be nonlinearly magnified and may lead to potentially dangerous collective behaviors. To understand quantitatively crowd stochasticity, we study the real-life dynamics of a large ensemble of pedestrians walking undisturbed, and we perform a statistical analysis of the fully resolved pedestrian trajectories obtained by a yearlong high-resolution measurement campaign. Our measurements have been carried out in a corridor of the Eindhoven University of Technology via a combination of Microsoft Kinect 3D range sensor and automatic head-tracking algorithms. The temporal homogeneity of our large database of trajectories allows us to robustly define and separate average walking behaviors from fluctuations parallel and orthogonal with respect to the average walking path. Fluctuations include rare events when individuals suddenly change their minds and invert their walking directions. Such tendency to invert direction has been poorly studied so far, even if it may have important implications on the functioning and safety of facilities. We propose a model for the dynamics of undisturbed pedestrians, based on stochastic differential equations, that provides a good agreement with our field observations, including the occurrence of rare events.

  • 33.
    Cozzani, Giulia
    et al.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France.;Univ Pisa, Dipartimento Fis E Fermi, I-56127 Pisa, Italy..
    Retino, A.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France..
    Califano, F.
    Univ Pisa, Dipartimento Fis E Fermi, I-56127 Pisa, Italy..
    Alexandrova, A.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France..
    Contel, O. Le
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France..
    Khotyaintsev, Y.
    Swedish Inst Space Phys, SE-75121 Uppsala, Sweden..
    Vaivads, Andris
    Swedish Inst Space Phys, SE-75121 Uppsala, Sweden..
    Fu, H. S.
    Beihang Univ, Sch Space & Environm, Beijing 100083, Peoples R China..
    Catapano, F.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France.;Univ Calabria, Dipartimento Fis, I-87036 Arcavacata Di Rende, CS, Italy..
    Breuillard, H.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France.;Univ Orleans, UMR 7328, CNRS, Lab Phys & Chim Environm & Espace, F-45071 Orleans, France..
    Ahmadi, N.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90095 USA..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Fuseher, S.
    Southwest Res Inst, San Antonio, TX 78238 USA.;Univ Texas San Antonio, San Antonio, TX 78238 USA..
    Mauk, B. H.
    Johns Hopkins Univ, Appl Phys Lab, Johns Hopkins Rd, Laurel, MD 20723 USA..
    Moore, T.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    In situ spacecraft observations of a structured electron diffusion region during magnetopause reconnection2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 4, article id 043204Article in journal (Refereed)
    Abstract [en]

    The electron diffusion region (EDR) is the region where magnetic reconnection is initiated and electrons are energized. Because of experimental difficulties, the structure of the EDR is still poorly understood. A key question is whether the EDR has a homogeneous or patchy structure. Here we report Magnetospheric Multiscale (MMS) spacecraft observations providing evidence of inhomogeneous current densities and energy conversion over a few electron inertial lengths within an EDR at the terrestrial magnetopause, suggesting that the EDR can be rather structured. These inhomogenenities are revealed through multipoint measurements because the spacecraft separation is comparable to a few electron inertial lengths, allowing the entire MMS tetrahedron to be within the EDR most of the time. These observations are consistent with recent high-resolution and low-noise kinetic simulations.

  • 34.
    Cozzani, Giulia
    et al.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France;Univ Pisa, Dipartimento Fis E Fermi, I-56127 Pisa, Italy.
    Retino, A.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France.
    Califano, F.
    Univ Pisa, Dipartimento Fis E Fermi, I-56127 Pisa, Italy.
    Alexandrova, A.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France.
    Contel, O. Le
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France.
    Khotyaintsev, Yuri V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fu, H. S.
    Beihang Univ, Sch Space & Environm, Beijing 100083, Peoples R China.
    Catapano, F.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France;Univ Calabria, Dipartimento Fis, I-87036 Arcavacata Di Rende, CS, Italy.
    Breuillard, H.
    Univ Paris Sud, Sorbonne Univ, Observ Paris, Lab Phys Plasmas,CNRS,Ecole Polytech, F-91128 Palaiseau, France;Univ Orleans, UMR 7328, CNRS, Lab Phys & Chim Environm & Espace, F-45071 Orleans, France.
    Ahmadi, N.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Lindqvist, P-A
    KTH Royal Inst Technol, SE-10044 Stockholm, Sweden.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA.
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA.
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90095 USA.
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria.
    Fuseher, S.
    Southwest Res Inst, San Antonio, TX 78238 USA;Univ Texas San Antonio, San Antonio, TX 78238 USA.
    Mauk, B. H.
    Johns Hopkins Univ, Appl Phys Lab, Johns Hopkins Rd, Laurel, MD 20723 USA.
    Moore, T.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA.
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX 78238 USA.
    In situ spacecraft observations of a structured electron diffusion region during magnetopause reconnection2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 4, article id 043204Article in journal (Refereed)
    Abstract [en]

    The electron diffusion region (EDR) is the region where magnetic reconnection is initiated and electrons are energized. Because of experimental difficulties, the structure of the EDR is still poorly understood. A key question is whether the EDR has a homogeneous or patchy structure. Here we report Magnetospheric Multiscale (MMS) spacecraft observations providing evidence of inhomogeneous current densities and energy conversion over a few electron inertial lengths within an EDR at the terrestrial magnetopause, suggesting that the EDR can be rather structured. These inhomogenenities are revealed through multipoint measurements because the spacecraft separation is comparable to a few electron inertial lengths, allowing the entire MMS tetrahedron to be within the EDR most of the time. These observations are consistent with recent high-resolution and low-noise kinetic simulations.

  • 35.
    Ekman, Robin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Asenjo, F. A.
    Zamanian, Jens
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Relativistic kinetic equation for spin-1/2 particles in the long-scale-length approximation2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 2, article id 023207Article in journal (Refereed)
    Abstract [en]

    In this paper, we derive a fully relativistic kinetic theory for spin-1/2 particles and its coupling to Maxwell's equations, valid in the long-scale-length limit, where the fields vary on a scale much longer than the localization of the particles; we work to first order in (h) over bar. Our starting point is a Foldy-Wouthuysen (FW) transformation, applicable to this regime, of the Dirac Hamiltonian. We derive the corresponding evolution equation for the Wigner quasidistribution in an external electromagnetic field. Using a Lagrangian method we find expressions for the charge and current densities, expressed as free and bound parts. It is furthermore found that the velocity is nontrivially related to the momentum variable, with the difference depending on the spin and the external electromagnetic fields. This fact that has previously been discussed as "hidden momentum" and is due to that the FW transformation maps pointlike particles to particle clouds for which the prescription of minimal coupling is incorrect, as they have multipole moments. We express energy and momentum conservation for the system of particles and the electromagnetic field, and discuss our results in the context of the Abraham-Minkowski dilemma.

  • 36. Elperin, T.
    et al.
    Kleeorin, N.
    Liberman, Michael A.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholms University, Sweden.
    Lipatnikov, A. N.
    Rogachevskii, I.
    Yu, R.
    Turbulent diffusion of chemically reacting flows: Theory and numerical simulations2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 5, article id 053111Article in journal (Refereed)
    Abstract [en]

    The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014)] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damkohler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.

  • 37. Elperin, T.
    et al.
    Kleeorin, N.
    Liberman, Michael
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Lipatnikov, A. N.
    Rogachevskii, I.
    Yu, R.
    Turbulent diffusion of chemically reacting flows: Theory and numerical simulations2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 5, article id 053111Article in journal (Refereed)
    Abstract [en]

    The theory of turbulent diffusion of chemically reacting gaseous admixtures developed previously [T. Elperin et al., Phys. Rev. E 90, 053001 (2014)] is generalized for large yet finite Reynolds numbers and the dependence of turbulent diffusion coefficient on two parameters, the Reynolds number and Damkohler number (which characterizes a ratio of turbulent and reaction time scales), is obtained. Three-dimensional direct numerical simulations (DNSs) of a finite-thickness reaction wave for the first-order chemical reactions propagating in forced, homogeneous, isotropic, and incompressible turbulence are performed to validate the theoretically predicted effect of chemical reactions on turbulent diffusion. It is shown that the obtained DNS results are in good agreement with the developed theory.

  • 38. Fouxon, Itzhak
    et al.
    Ge, Zhouyang
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Leshansky, Alexander
    Integral representation of channel flow with interacting particles2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 6, article id 063110Article in journal (Refereed)
    Abstract [en]

    We construct a boundary integral representation for the low-Reynolds-number flow in a channel in the presence of freely suspended particles (or droplets) of arbitrary size and shape. We demonstrate that lubrication theory holds away from the particles at horizontal distances exceeding the channel height and derive a multipole expansion of the flow which is dipolar to the leading approximation. We show that the dipole moment of an arbitrary particle is a weighted integral of the stress and the flow at the particle surface, which can be determined numerically. We introduce the equation of motion that describes hydrodynamic interactions between arbitrary, possibly different, distant particles, with interactions determined by the product of the mobility matrix and the dipole moment. Further, the problem of three identical interacting spheres initially aligned in the streamwise direction is considered and the experimentally observed "pair exchange" phenomenon is derived analytically and confirmed numerically. For nonaligned particles, we demonstrate the formation of a configuration with one particle separating from a stable pair. Our results suggest that in a dilute initially homogenous particulate suspension flowing in a channel the particles will eventually separate into singlets and pairs.

  • 39.
    Gao, Chen-Yi
    et al.
    Chinese Acad Sci, Inst Theoret Phys, Key Lab Theoret Phys, Beijing 100190, Peoples R China.;Univ Chinese Acad Sci, Sch Phys Sci, Beijing 100049, Peoples R China..
    Zhou, Hai-Jun
    Chinese Acad Sci, Inst Theoret Phys, Key Lab Theoret Phys, Beijing 100190, Peoples R China.;Univ Chinese Acad Sci, Sch Phys Sci, Beijing 100049, Peoples R China.;Hunan Normal Univ, Synerget Innovat Ctr Quantum Effects & Applicat, Changsha 410081, Hunan, Peoples R China..
    Aurell, Erik
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB. Aalto Univ, Dept Appl Phys, Aalto 00076, Finland.;Aalto Univ, Dept Comp Sci, Aalto 00076, Finland..
    Correlation-compressed direct-coupling analysis2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 3, article id 032407Article in journal (Refereed)
    Abstract [en]

    Learning Ising or Potts models from data has become an important topic in statistical physics and computational biology, with applications to predictions of structural contacts in proteins and other areas of biological data analysis. The corresponding inference problems are challenging since the normalization constant (partition function) of the Ising or Potts distribution cannot be computed efficiently on large instances. Different ways to address this issue have resulted in a substantial amount of methodological literature. In this paper we investigate how these methods could be used on much larger data sets than studied previously. We focus on a central aspect, that in practice these inference problems are almost always severely under-sampled, and the operational result is almost always a small set of leading predictions. We therefore explore an approach where the data are prefiltered based on empirical correlations, which can be computed directly even for very large problems. Inference is only used on the much smaller instance in a subsequent step of the analysis. We show that in several relevant model classes such a combined approach gives results of almost the same quality as inference on the whole data set. It can therefore provide a potentially very large computational speedup at the price of only marginal decrease in prediction quality. We also show that the results on whole-genome epistatic couplings that were obtained in a recent computation-intensive study can be retrieved by our approach. The method of this paper hence opens up the possibility to learn parameters describing pairwise dependences among whole genomes in a computationally feasible and expedient manner.

  • 40. Hertz, John
    et al.
    Tyrcha, Joanna
    Stockholm University, Faculty of Science, Department of Mathematics.
    Correales, Alvaro
    Stochastic activation in a genetic switch model2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 5, article id 052403Article in journal (Refereed)
    Abstract [en]

    We study a biological autoregulation process, involving a protein that enhances its own transcription, in a parameter region where bistability would be present in the absence of fluctuations. We calculate the rate of fluctuation-induced rare transitions between locally stable states using a path integral formulation and Master and Chapman-Kolmogorov equations. As in simpler models for rare transitions, the rate has the form of the exponential of a quantity S-0 (a barrier) multiplied by a prefactor eta. We calculate S-0 and eta first in the bursting limit (where the ratio gamma of the protein and mRNA lifetimes is very large). In this limit, the calculation can be done almost entirely analytically, and the results are in good agreement with simulations. For finite gamma numerical calculations are generally required. However, S-0 can be calculated analytically to first order in 1/gamma, and the result agrees well with the full numerical calculation for all gamma > 1. Employing a method used previously on other problems, we find we can account qualitatively for the way the prefactor eta varies with gamma, but its value is 15-20% higher than that inferred from simulations.

  • 41. Holkundkar, Amol R.
    et al.
    Brodin, Gert
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Transition from wakefield generation to soliton formation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 4, article id 043204Article in journal (Refereed)
    Abstract [en]

    It is well known that when a short laser pulse propagates in an underdense plasma, it induces longitudinal plasma oscillations at the plasma frequency after the pulse, typically referred to as the wakefield. However, for plasma densities approaching the critical density, wakefield generation is suppressed, and instead the EM-pulse (electromagnetic pulse) undergoes nonlinear self-modulation. In this article we have studied the transition from the wakefield generation to formation of quasi-solitons as the plasma density is increased. For this purpose we have applied a one-dimensional relativistic cold fluid model, which has also been compared with particle-in-cell simulations. A key result is that the energy loss of the EM-pulse due to wakefield generation has its maximum for a plasma density of the order 10% of the critical density, but that wakefield generation is sharply suppressed when the density is increased further.

  • 42. Honkonen, J.
    et al.
    Lučivjanský, T.
    Škultéty, Viktor
    Stockholm University, Faculty of Science, Department of Physics.
    Influence of turbulent mixing on critical behavior of directed percolation process: Effect of compressibility2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 2, article id 022123Article in journal (Refereed)
    Abstract [en]

    Universal behavior is a typical emergent feature of critical systems. A paramount model of the nonequilibrium critical behavior is the directed bond percolation process that exhibits an active-to-absorbing state phase transition in the vicinity of a percolation threshold. Fluctuations of the ambient environment might affect or destroy the universality properties completely. In this work, we assume that the random environment can be described by means of compressible velocity fluctuations. Using field-theoretic models and renormalization group methods, we investigate large-scale and long-time behavior. Altogether, 11 universality classes are found, out of which 4 are stable in the infrared limit and thus macroscopically accessible. In contrast to the model without velocity fluctuations, a possible candidate for a realistic three-dimensional case, a regime with relevant short-range noise, is identified. Depending on the dimensionality of space and the structure of the turbulent flow, we calculate critical exponents of the directed percolation process. In the limit of the purely transversal random force, critical exponents comply with the incompressible results obtained by previous authors. We have found intriguing nonuniversal behavior related to the mutual effect of compressibility and advection.

  • 43. Jovanovic, Stojan
    et al.
    Hertz, John
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Copenhagen, Denmark.
    Rotter, Stefan
    Cumulants of Hawkes point processes2015In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 91, no 4, article id 042802Article in journal (Refereed)
    Abstract [en]

    We derive explicit, closed-form expressions for the cumulant densities of a multivariate, self-exciting Hawkes point process, generalizing a result of Hawkes in his earlier work on the covariance density and Bartlett spectrum of such processes. To do this, we represent the Hawkes process in terms of a Poisson cluster process and show how the cumulant density formulas can be derived by enumerating all possible family trees, representing complex interactions between point events. We also consider the problem of computing the integrated cumulants, characterizing the average measure of correlated activity between events of different types, and derive the relevant equations.

  • 44. Klamser, Pascal P.
    et al.
    Wiedermann, Marc
    Donges, Jonathan F.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Potsdam Institute for Climate Impact Research, Germany.
    Donner, Reik V.
    Zealotry effects on opinion dynamics in the adaptive voter model2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 96, no 5, article id 052315Article in journal (Refereed)
    Abstract [en]

    The adaptive voter model has been widely studied as a conceptual model for opinion formation processes on time-evolving social networks. Past studies on the effect of zealots, i.e., nodes aiming to spread their fixed opinion throughout the system, only considered the voter model on a static network. Here we extend the study of zealotry to the case of an adaptive network topology co-evolving with the state of the nodes and investigate opinion spreading induced by zealots depending on their initial density and connectedness. Numerical simulations reveal that below the fragmentation threshold a low density of zealots is sufficient to spread their opinion to the whole network. Beyond the transition point, zealots must exhibit an increased degree as compared to ordinary nodes for an efficient spreading of their opinion. We verify the numerical findings using a mean-field approximation of the model yielding a low-dimensional set of coupled ordinary differential equations. Our results imply that the spreading of the zealots' opinion in the adaptive voter model is strongly dependent on the link rewiring probability and the average degree of normal nodes in comparison with that of the zealots. In order to avoid a complete dominance of the zealots' opinion, there are two possible strategies for the remaining nodes: adjusting the probability of rewiring and/or the number of connections with other nodes, respectively.

  • 45.
    Kleeorin, Nathan
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel; University of Helsinki, Finland.
    Rogachevskii, Igor
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel; University of Helsinki, Finland.
    Soustova, I. A.
    Troitskaya, Yu.
    Ermakova, O. S.
    Zilitinkevich, S.
    Internal gravity waves in the energy and flux budget turbulence-closure theory for shear-free stably stratified flows2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 6, article id 063106Article in journal (Refereed)
    Abstract [en]

    We have advanced the energy and flux budget turbulence closure theory that takes into account a two-way coupling between internal gravity waves (IGWs) and the shear-free stably stratified turbulence. This theory is based on the budget equation for the total (kinetic plus potential) energy of IGWs, the budget equations for the kinetic and potential energies of fluid turbulence, and turbulent fluxes of potential temperature for waves and fluid flow. The waves emitted at a certain level propagate upward, and the losses of wave energy cause the production of turbulence energy. We demonstrate that due to the nonlinear effects more intensive waves produce more strong turbulence, and this, in turn, results in strong damping of IGWs. As a result, the penetration length of more intensive waves is shorter than that of less intensive IGWs. The anisotropy of the turbulence produced by less intensive IGWs is stronger than that caused by more intensive waves. The low-amplitude IGWs produce turbulence consisting up to 90% of turbulent potential energy. This resembles the properties of the observed high-altitude tropospheric strongly anisotropic (nearly two-dimensional) turbulence.

  • 46.
    Kleeorin, Nathan
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Ben Gurion Univ Negev, Dept Mech Engn, POB 653, IL-8410530 Beer Sheva, Israel.;Nordita Stockholm Univ, S-10691 Stockholm, SwedenUniv Helsinki, Inst Atmospher & Earth Syst Res, Helsinki 00014, Finland..
    Rogachevskii, lgor
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Ben Gurion Univ Negev, Dept Mech Engn, POB 653, IL-8410530 Beer Sheva, Israel.;Nordita Stockholm Univ, S-10691 Stockholm, SwedenUniv Helsinki, Inst Atmospher & Earth Syst Res, Helsinki 00014, Finland..
    Soustova, I. A.
    Russian Acad Sci, Inst Appl Phys, Nizhnii Novgorod 603950, Russia..
    Troitskaya, Yu, I
    Russian Acad Sci, Inst Appl Phys, Nizhnii Novgorod 603950, Russia..
    Ermakova, O. S.
    Russian Acad Sci, Inst Appl Phys, Nizhnii Novgorod 603950, Russia..
    Zilitinkevich, S.
    Univ Helsinki, Inst Atmospher & Earth Syst Res, Helsinki 00014, Finland.;Finnish Meteorol Inst, Helsinki 00101, Finland.;Moscow MV Lomonosov State Univ, Fac Geog, Moscow 119234, Russia.;Tyumen State Univ, Tyumen 625003, Russia..
    Internal gravity waves in the energy and flux budget turbulence-closure theory for shear-free stably stratified flows2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 6, article id 063106Article in journal (Refereed)
    Abstract [en]

    We have advanced the energy and flux budget turbulence closure theory that takes into account a two-way coupling between internal gravity waves (IGWs) and the shear-free stably stratified turbulence. This theory is based on the budget equation for the total (kinetic plus potential) energy of IGWs, the budget equations for the kinetic and potential energies of fluid turbulence, and turbulent fluxes of potential temperature for waves and fluid flow. The waves emitted at a certain level propagate upward, and the losses of wave energy cause the production of turbulence energy. We demonstrate that due to the nonlinear effects more intensive waves produce more strong turbulence, and this, in turn, results in strong damping of IGWs. As a result, the penetration length of more intensive waves is shorter than that of less intensive IGWs. The anisotropy of the turbulence produced by less intensive IGWs is stronger than that caused by more intensive waves. The low-amplitude IGWs produce turbulence consisting up to 90% of turbulent potential energy. This resembles the properties of the observed high-altitude tropospheric strongly anisotropic (nearly two-dimensional) turbulence.

  • 47.
    Korolkovas, Airidas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Inst Laue Langevin, 71 Rue Martyrs, F-38000 Grenoble, France.
    Gutfreund, Philipp
    Inst Laue Langevin, 71 Rue Martyrs, F-38000 Grenoble, France.
    Chenneviere, Alexis
    Univ Paris Sud, Lab Phys Solides, CNRS, F-91405 Orsay, France.
    Ankner, John F.
    Oak Ridge Natl Lab, Spallat Neutron Source, Oak Ridge, TN 37830 USA.
    Adlmann, Franz
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Wolff, Max
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Barrat, Jean-Louis
    Univ Grenoble Alpes, LiPhy, F-38402 St Martin Dheres, France.
    Shear deformation of low-density polymer brushes in a good solvent2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 98, no 3, article id 032501Article in journal (Refereed)
    Abstract [en]

    Self-consistent field approach is used to model a single end-tethered polymer chain on a substrate subject to various forces in three dimensions. Starting from a continuous Gaussian chain model, the following perturbations are considered: (i) hydrodynamic interaction with an externally imposed shear flow for which an alternative theoretical framework is formulated; (ii) excluded volume effect in a good solvent, treated in a mean field approximation; (iii) monomer-substrate repulsion. While the chain stretches along the flow, the change of the density profile perpendicular to the substrate is negligible for any reasonable simulation parameters. This null effect is in agreement with multiple neutron scattering studies.

  • 48.
    Kozlov, Vladimir
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Vakulenko, Sergey
    Russian Academic Science, Russia; St Petersburg National Research University of Informat Technology Mech, Russia.
    Wennergren, Uno
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, Faculty of Science & Engineering.
    Biodiversity, extinctions, and evolution of ecosystems with shared resources2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 95, no 3, article id 032413Article in journal (Refereed)
    Abstract [en]

    We investigate the formation of stable ecological networks where many species share the same resource. We show that such a stable ecosystem naturally occurs as a result of extinctions. We obtain an analytical relation for the number of coexisting species, and we find a relation describing how many species that may become extinct as a result of a sharp environmental change. We introduce a special parameter that is a combination of species traits and resource characteristics used in the model formulation. This parameter describes the pressure on the system to converge, by extinctions. When that stress parameter is large, we obtain that the species traits are concentrated at certain values. This stress parameter is thereby a parameter that determines the level of final biodiversity of the system. Moreover, we show that the dynamics of this limit system can be described by simple differential equations.

  • 49.
    Liberman, Michael
    et al.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Kleeorin, Nathan
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel.
    Rogachevskii, Igor
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel.
    Haugen, Nils Erland L.
    Mechanism of unconfined dust explosions: Turbulent clustering and radiation-induced ignition2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 95, no 5, article id 051101Article in journal (Refereed)
    Abstract [en]

    It is known that unconfined dust explosions typically start off with a relatively weak primary flame followed by a severe secondary explosion. We show that clustering of dust particles in a temperature stratified turbulent flow ahead of the primary flame may give rise to a significant increase in the radiation penetration length. These particle clusters, even far ahead of the flame, are sufficiently exposed and heated by the radiation from the flame to become ignition kernels capable to ignite a large volume of fuel-air mixtures. This efficiently increases the total flame surface area and the effective combustion speed, defined as the rate of reactant consumption of a given volume. We show that this mechanism explains the high rate of combustion and overpressures required to account for the observed level of damage in unconfined dust explosions, e.g., at the 2005 Buncefield vapor-cloud explosion. The effect of the strong increase of radiation transparency due to turbulent clustering of particles goes beyond the state of the art of the application to dust explosions and has many implications in atmospheric physics and astrophysics.

  • 50.
    Liberman, Michael
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Kleeorin, Nathan
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden; Ben-Gurion University of the Negev, Israel.
    Rogachevskii, Igor
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden; Ben-Gurion University of the Negev, Israel.
    Haugen, Nils Erland L.
    Mechanism of unconfined dust explosions: Turbulent clustering and radiation-induced ignition2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 95, no 5, article id 051101Article in journal (Refereed)
    Abstract [en]

    It is known that unconfined dust explosions typically start off with a relatively weak primary flame followed by a severe secondary explosion. We show that clustering of dust particles in a temperature stratified turbulent flow ahead of the primary flame may give rise to a significant increase in the radiation penetration length. These particle clusters, even far ahead of the flame, are sufficiently exposed and heated by the radiation from the flame to become ignition kernels capable to ignite a large volume of fuel-air mixtures. This efficiently increases the total flame surface area and the effective combustion speed, defined as the rate of reactant consumption of a given volume. We show that this mechanism explains the high rate of combustion and overpressures required to account for the observed level of damage in unconfined dust explosions, e.g., at the 2005 Buncefield vapor-cloud explosion. The effect of the strong increase of radiation transparency due to turbulent clustering of particles goes beyond the state of the art of the application to dust explosions and has many implications in atmospheric physics and astrophysics.

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