source of finite size are characterized by a non-homogeneous field of density. It was speculated that this

inhomogeneity is due to the transient shape of the sediment during the process of construction of the

heap, thus reflecting the history of the creation of the heap. By comparison of structural characteristics of

the heap with sediments created on top of inclined planes exploiting the method of Minkowski tensors,

we provide further evidence to support this hypothesis. Moreover, for the case of sediments generated by

homogeneous rain on surfaces, we provide relationships between the inclination of the surface and the

Minkowski measures characterizing the isotropy of local particle environments.}, author = {Topic, Nikola and Schaller, Fabian and Schröder-Turk, Gerd and Pöschel, Thorsten}, doi = {10.1039/c5sm03114a}, faupublication = {yes}, journal = {Soft Matter}, peerreviewed = {Yes}, title = {{The} microscopic structure of mono-disperse granular heaps and sediments of particles on inclined surfaces}, year = {2016} } @article{faucris.114662724, abstract = {Downhill flows of granular matter colliding in the lowest point of a valley, may induce a selforganized jet. By means of a quasi two-dimensional experiment where fine grained sand flows in a vertically sinusoidally agitated cylinder, we show that the emergent jet, that is, a sheet of ejecta, does not follow the frequency of agitation but reveals subharmonic response. The order of the subharmonics is a complex function of the parameters of driving.}, author = {Kollmer, Jonathan and Pöschel, Thorsten}, doi = {10.1038/srep22520}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Subharmonic} instability of a self-organized granular jet}, volume = {6}, year = {2016} } @article{faucris.113990404, abstract = {We present an efficient event-driven algorithm for sequential ballistic deposition of complex-shaped rigid particles. Each of the particles is constructed from hard spheres (typically 5.1000) of variable radii. The sizes and relative positions of the spheres may mutually overlap and can be chosen such that the surface of the resulting particle appears relatively smooth. In the sequential deposition process, by performing steps of rolling and linear motion, the particles move along the steepest descent in a landscape formed by the boundaries and previously deposited particles. The computer time for the simulation of a deposition process depends on the total number of spheres but only weakly on the sizes and shapes of the particles. The proposed algorithm generalizes the Visscher-Bolsterli algorithm [1] which is frequently used for packing of spheres, to non-spherical particles. The proposed event-driven algorithm allows simulations of multi-million particle systems using desktop computers.}, author = {Topic, Nikola and Pöschel, Thorsten}, doi = {10.1016/j.jcp.2015.12.052}, faupublication = {yes}, journal = {Journal of Computational Physics}, keywords = {Complex shaped particles; Event-driven algorithm; Non-spherical particles; Steepest descent ballistic deposition}, pages = {421-437}, peerreviewed = {Yes}, title = {{Steepest} descent ballistic deposition of complex shaped particles}, url = {http://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84953267728&origin=inward}, volume = {308}, year = {2016} } @article{faucris.110020284, abstract = {We investigate the flow of granular material in a rotating cylinder numerically using molecular dynamics in two dimensions. The particles are described by a new model which allows to simulate geometrically complicated shaped grains. The results of the simulation agree significantly better with experiments than the results which are based on circular particles. © 1995.}, author = {Buchholtz, Volkhard and Pöschel, Thorsten and Tillemans, Hans-Jürgen}, doi = {10.1016/0378-4371(95)00045-9}, faupublication = {no}, journal = {Physica A-Statistical Mechanics and Its Applications}, pages = {199-212}, peerreviewed = {Yes}, title = {{Simulation} of rotating drum experiments using non-circular particles}, volume = {216}, year = {1995} } @article{faucris.110028204, abstract = {Experiments and numerical simulations of granular material under swirling motion of the container are presented. At low packing densities the material rotates in the same direction as the swirling motion of the container (rotation). At higher densities the cluster of granular material rotates in the opposite direction (reptation). The change of the direction of the motion of the cluster takes place at a critical packing density while the diffusion coefficient changes significantly. The measured critical density of the packing is in good agreement with results obtained by molecular-dynamics simulation.}, author = {Scherer, Michael A. and Buchholtz, Volkhard and Pöschel, Thorsten and Rehberg, Ingo}, doi = {10.1103/PhysRevE.54.R4560}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Swirling} granular matter: {From} rotation to reptation}, volume = {54}, year = {1996} } @article{faucris.119755944, author = {Wu, Chuan-Yu and Pöschel, Thorsten}, doi = {10.1007/s10035-013-0441-9}, faupublication = {yes}, journal = {Granular Matter}, pages = {389-390}, peerreviewed = {Yes}, title = {{Micro}-mechanics and dynamics of cohesive particle systems}, volume = {15}, year = {2013} } @article{faucris.109906984, abstract = {The coefficient of restitution of a spherical particle in contact with a flat plate is investigated as a function of the impact velocity. As an experimental observation we notice nontrivial (non-Gaussian) fluctuations of the measured values. For a fixed impact velocity, the probability density of the coefficient of restitution, p, is formed by two exponential functions (one increasing, one decreasing) of different slope. This behavior may be explained by a certain roughness of the particle which leads to energy transfer between the linear and rotational degrees of freedom. © 2011 American Physical Society.}, author = {Montaine, Marina and Heckel, Michael and Kruelle, Christof and Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.84.041306}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Coefficient} of restitution as a fluctuating quantity}, volume = {84}, year = {2011} } @article{faucris.109876404, abstract = {Antiperiodic oscillations forming infinite cascades of spirals were recently found experimentally and numerically in the control parameter space of an autonomous electronic circuit. They were discovered while recording one specific voltage of the circuit. Here, we show that such regular self-organization may be measured in any of the four variables of the circuit. Although the relative size of individual phases, their boundaries and the number of peaks of each characteristic oscillation depends on the physical quantity used to record them, the global structural organization of the complex phase diagrams is an invariant of the circuit. Tunable families of antiperiodic oscillations cast fresh light on new intricate behavior of nonlinear systems and open the possibility of studying hitherto unobserved phenomena.}, author = {Freire, J. G. and Cabeza, C. and Marti, A. C. and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1140/epjst/e2014-02299-2}, faupublication = {yes}, journal = {European Physical Journal: Special Topics}, pages = {2857-2867}, peerreviewed = {Yes}, title = {{Self}-organization of antiperiodic oscillations}, volume = {223}, year = {2014} } @article{faucris.109463904, abstract = {We investigate the residual distribution of structural defects in very tall packings of disks deposited randomly in large channels. By performing simulations involving the sedimentation of up to 50 × 10 9 particles we find all deposits to consistently show a non-zero residual density of defects obeying a characteristic power-law as a function of the channel width. This remarkable finding corrects the widespread belief that the density of defects should vanish algebraically with growing height. A non-zero residual density of defects implies a type of long-range spatial order in the packing, as opposed to only local ordering. In addition, we find deposits of particles to involve considerably less randomness than generally presumed.}, author = {Topic, Nikola and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1038/srep12703}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Residual} {Defect} {Density} in {Random} {Disks} {Deposits}}, url = {http://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84938513548&origin=inward}, volume = {5}, year = {2015} } @article{faucris.109957584, abstract = {The gravity-driven flow of granular material through a rough, narrow vertical pipe is described using the Langevin equation formalism. Above a critical particle density the homogeneous flow becomes unstable with respect to short-wave length perturbations. In correspondence with experimental observations, we find clogging and density waves in the flowing material.}, author = {Riethmüller, Tino and Schimansky-Geier, Lutz and Rosenkranz, Dirk and Pöschel, Thorsten}, doi = {10.1007/BF02180213}, faupublication = {no}, journal = {Journal of Statistical Physics}, keywords = {Flow of solids; Granular material; Stochastic processes}, pages = {421-430}, peerreviewed = {Yes}, title = {{Langevin} equation approach to granular flow in a narrow pipe}, volume = {86}, year = {1997} } @article{faucris.114387504, abstract = {We discuss several models for granular particles commonly used in Molecular Dynamics simulations of granular materials, including spheres with linear dashpot force, viscoelastic spheres and adhesive viscoelastic spheres. Starting from the vectorial interaction forces we derive the coefficients of normal and tangential restitution as functions of the vectorial impact velocity and of the material constants. We review the methods of measurements of the coefficients of restitution and characterize the coefficient of normal restitution as a fluctuating quantity. Moreover, the scaling behavior and the influence of different force laws on the dynamical system behavior are discussed. The powerful method of event-driven Molecular Dynamics is described and the algorithmic simulation technique is explained in detail. Finally we discuss the limitations of event-driven MD.}, author = {Pöschel, Thorsten and Brilliantov, Nikolai and Formella, Arno and Heckel, Michael and Kruelle, Christof and Müller, Patric and Salueña, Clara and Schwager, Thomas}, doi = {10.3166/ejece.12.827-870}, faupublication = {yes}, journal = {European Journal of Environmental and Civil Engineering}, pages = {827--870}, peerreviewed = {Yes}, title = {{Contact} of granular particles and the simulation of rapid flows using event-driven molecular dynamics}, volume = {12}, year = {2008} } @article{faucris.123382644, abstract = {We study the packing of fine glass powders of mean particle diameter in the range (4-52)μm both experimentally and by numerical DEM simulations. We obtain quantitative agreement between the experimental and numerical results, if both types of attractive forces of particle interaction, adhesion and non-bonded van der Waals forces are taken into account. Our results suggest that considering only viscoelastic and adhesive forces in DEM simulations may lead to incorrect numerical predictions of the behavior of fine powders. Based on the results from simulations and experiments, we propose a mathematical expression to estimate the packing fraction of fine polydisperse powders as a function of the average particle size.}, author = {Ribeiro Parteli, Eric Josef and Schmidt, Jochen and Blümel, Christina and Wirth, Karl-Ernst and Peukert, Wolfgang and Pöschel, Thorsten}, doi = {10.1038/srep06227}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Attractive} particle interaction forces and packing density of fine glass powders}, volume = {4}, year = {2014} } @article{faucris.109996964, abstract = {We report a striking effect observed experimentally in several granular materials when shaken horizontally: The material displays a recurrent alternation between a slow inflation phase, characterized by an increase in its volume, and a fast collapse phase, when the volume abruptly returns to its original value. The frequency of such phase alternations is totally decoupled from the frequency of the external drive. We argue that the inflation and collapse alternation arises from an interplay between the mechanical stability of the material and Reynolds dilatancy due to convective motion. © 2012 American Physical Society.}, author = {Pöschel, Thorsten and Rosenkranz, Dirk E. and Gallas, Jason}, doi = {10.1103/PhysRevE.85.031307}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Recurrent} inflation and collapse in horizontally shaken granular materials}, volume = {85}, year = {2012} } @article{faucris.106996164, abstract = {Stochastic rotation dynamics (SRD) is a widely used method for the

mesoscopic modeling of complex fluids, such as colloidal suspensions or

multiphase flows. In this method, however, the underlying Cartesian grid

defining the coarse-grained interaction volumes induces anisotropy. We

propose an isotropic, lattice-free variant of stochastic rotation

dynamics, termed iSRD. Instead of Cartesian grid cells, we employ

randomly distributed spherical interaction volumes. This eliminates the

requirement of a grid shift, which is essential in standard SRD to

maintain Galilean invariance. We derive analytical expressions for the

viscosity and the diffusion coefficient in relation to the model

parameters, which show excellent agreement with the results obtained in

iSRD simulations. The proposed algorithm is particularly suitable to

model systems bound by walls of complex shape, where the domain cannot

be meshed uniformly. The presented approach is not limited to SRD but is

applicable to any other mesoscopic method, where particles interact

within certain coarse-grained volumes.}, author = {Mühlbauer, Sebastian and Strobl, Severin and Pöschel, Thorsten}, doi = {10.1103/PhysRevFluids.2.124204}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Isotropic} stochastic rotation dynamics}, volume = {2}, year = {2017} } @article{faucris.109929204, abstract = {Given an equidistribution for probabilities p(i) -1/N, i = 1,...,N. What is the expected corresponding rank ordered frequency distribution f(i), i=1,...,N, if an ensemble of M events is drawn? © 2002 The American Physical Society.}, author = {Pöschel, Thorsten and Freund, Jan A.}, doi = {10.1103/PhysRevE.66.026103}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Finite}-sample frequency distributions originating from an equiprobability distribution}, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.66.026103}, volume = {66}, year = {2002} } @article{faucris.119660464, abstract = {Instruments for surgical and dental application based on oscillatory mechanics submit unwanted vibrations to the operator's hand. Frequently the weight of the instrument's body is increased to dampen its vibration. Based on recent research regarding the optimization of granular damping we developed a prototype granular damper that attenuates the vibrations of an oscillatory saw twice as efficiently as a comparable solid mass. © 2012 Elsevier B.V. All rights reserved.}, author = {Heckel, Michael and Sack, Achim and Kollmer, Jonathan and Pöschel, Thorsten}, doi = {10.1016/j.physa.2012.04.007}, faupublication = {yes}, journal = {Physica A-Statistical Mechanics and Its Applications}, keywords = {Dissipation mechanism; Granular damper; Granular system; Vibrations}, pages = {4442-4447}, peerreviewed = {Yes}, title = {{Granular} dampers for the reduction of vibrations of an oscillatory saw}, volume = {391}, year = {2012} } @article{faucris.122137004, abstract = {Granular pipe flows are characterized by intermittent behavior and large, potentially destructive solid fraction variations in the transport direction. By means of particle-based numerical simulations of gravity-driven flows in vertical pipes, we show that it is possible to obtain steady material transport by adding a helical texture to the inner-wall of the pipe. The helical texture leads to a more homogeneous mass flux along the pipe, prevents the emergence of large density waves and substantially reduces the probability of plug formation thus avoiding jamming of the particulate flow. We show that the granular mass flux Q through a pipe of diameter D with a helical texture of wavelength λ follows the equation Q = Q

The development of reliable strategies to optimize part production in additive manufacturing technologies hinges, to a large extent, on the quantitative understanding of the mechanical behavior of the powder particles during the application process. Since it is difficult to acquire this understanding based on experiments alone, a particle- based numerical tool for the simulation of powder application is required. In the present work, we develop such a numerical tool and apply it to investigate the characteristics of the powder layer de posited onto the part using a roller as the coating system. In our simulations, the complex geometric shapes of the powder particles are taken explicitly into account. Our results show that increasing the coating speed leads to an increase in the surface roughness of the powder bed, which is known to affect part quality. We also find that, surprisingly, powders with broader size distributions may lead to larger values of surface roughness as the smallest particles are most prone to form large agglomerates thus increasing the packing’s porosity. Moreover, we find that the load on the part may vary over an order of magnitude during the coating process owing to the strong inhomogeneity of inter-particle forces in the granular packing. Our numerical tool can be used to assist — and partially replace — experimental investigations of the flowability and packing behavior of different powder systems as a function of material and process parameters.

}, author = {Ribeiro Parteli, Eric Josef and Pöschel, Thorsten}, doi = {10.1051/epjconf/201714015013}, faupublication = {yes}, journal = {EPJ Web of Conferences}, peerreviewed = {unknown}, title = {{Particle}-based simulations of powder coating in additive manufacturing suggest increase in powder bed roughness with coating speed}, volume = {140}, year = {2017} } @article{faucris.122877744, abstract = {The dynamics of dissipative soft-sphere gases obeys Newton's equations of motion, which are commonly solved numerically by (force-based) Molecular Dynamics (MD) schemes. With the assumption of instantaneous, pairwise collisions, the simulation can be accelerated considerably using event-driven MD, where the coefficient of restitution is derived from the interaction force between particles. Recently it was shown, however, that this approach may fail dramatically, that is, the obtained trajectories deviate significantly from the ones predicted by Newton's equations. In this paper, we generalize the concept of the coefficient of restitution and derive a numerical scheme which, in the case of dilute systems and frictionless interaction, allows us to perform highly efficient event-driven MD simulations even for noninstantaneous collisions. We show that the particle trajectories predicted by our scheme agree perfectly with the corresponding (force-based) MD, except for a short transient period whose duration corresponds to the duration of the contact. Thus, the new algorithm solves Newton's equations of motion like force-based MD while preserving the advantages of event-driven simulations. © 2013 American Physical Society.}, author = {Müller, Patric and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.87.033301}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Event}-driven molecular dynamics of soft particles}, volume = {87}, year = {2013} } @article{faucris.110032604, abstract = {The decay of temperature of a force-free granular gas in the homogeneous cooling state depends on the specific model for particle interaction. For the case of rough spheres, in recent experimental and theoretical work, the coefficient of restitution was characterized as a fluctuating quantity. We show that for such particles, the decay of temperature with time follows the law which deviates from Haff's law, T ∼ t, obtained for gases of particles interacting via a constant coefficient of restitution also from obtained for gases of viscoelastic particles. Our results are obtained from kinetic theory and are in very good agreement with Monte Carlo simulations. © IOP Publishing and Deutsche Physikalische Gesellschaft.}, author = {Gunkelmann, Nina and Serero, Dan and Pöschel, Thorsten}, doi = {10.1088/1367-2630/15/9/093030}, faupublication = {yes}, journal = {New Journal of Physics}, peerreviewed = {Yes}, title = {{Temperature} of a granular gas with regard to the stochastic nature of particle interactions}, volume = {15}, year = {2013} } @article{faucris.107381824, abstract = {The kinetic energy of a force-free granular gas decays monotonously due to inelastic collisions of the particles. For a homogeneous granular gas of identical particles, the corresponding decay of granular temperature is quantified by Haff’s law. Here, we report that for a granular gas of aggregating particles, the granular temperature does not necessarily decay but may even increase. Surprisingly, the increase of temperature is accompanied by the continuous loss of total gas energy. This stunning effect arises from a subtle interplay between decaying kinetic energy and gradual reduction of the number of degrees of freedom associated with the particles’ dynamics. We derive a set of kinetic equations of Smoluchowski type for the concentrations of aggregates of different sizes and their energies. We find scaling solutions to these equations and a condition for the aggregation mechanism predicting growth of temperature. Numerical direct simulation Monte Carlo results confirm the theoretical predictions.}, author = {Brilliantov, Nikolai and Formella, Arno and Pöschel, Thorsten}, doi = {10.1038/s41467-017-02803-7}, faupublication = {yes}, journal = {Nature Communications}, peerreviewed = {Yes}, title = {{Increasing} temperature of cooling granular gases}, volume = {9}, year = {2018} } @article{faucris.119476324, abstract = {

We show that the orientation and morphology of bedforms occurring on top of Pluto’s smooth ice coats are consistent with an aeolian origin under conditions of unidirectional flow. From scaling relations for dune size as a function of attributes of atmosphere and sediments, we find that the average diameter of the granular particles constituting such bedforms — assuming an aeolian origin — lies within the range 600 *μ*m< d < 750 *μ*m. Our findings show that, owing to the effect of hysteresis in the minimal threshold wind velocity for saltation, dune migration on Pluto can occur under wind speeds that are common to Earth and Mars.

}, author = {Ribeiro Parteli, Eric Josef and Pöschel, Thorsten}, doi = {10.1051/epjconf/201714014010}, faupublication = {yes}, journal = {EPJ Web of Conferences}, peerreviewed = {unknown}, title = {{Barchan} dunes on {Pluto}?}, volume = {140}, year = {2017} } @article{faucris.119943164, abstract = {

A flowing hourglass changes its weight in the course of time because of the accelerated motion of its center of mass. While this insight is not new, it is frequently said that the effect is tiny and hardly measurable. Here we present a simple experiment which allows to monitor the weight as a function of time revealing different stages, in quantitative agreement with theory.

}, author = {Sack, Achim and Pöschel, Thorsten}, doi = {10.1119/1.4973527}, faupublication = {yes}, journal = {American Journal of Physics}, month = {Jan}, peerreviewed = {Yes}, title = {{Weight} of an {Hourglass} – {Theory} and {Experiment} in {Quantitative} {Comparison}}, volume = {85}, year = {2017} } @article{faucris.109942184, abstract = {We propose a new method for the calculation of the statistical properties, e.g., the entropy, of unknown generators of symbolic sequences. The probability distribution p(k) of the elements k of a population can be approximated by the frequencies f(k) of a sample provided the sample is long enough so that each element k occurs many times. Our method yields an approximation if this precondition does not hold. For a given f(k) we recalculate the Zipf-ordered probability distribution by optimization of the parameters of a guessed distribution. We demonstrate that our method yields reliable results. © 1995 Plenum Publishing Corporation.}, author = {Pöschel, Thorsten and Ebeling, Werner and Rose, Helge}, doi = {10.1007/BF02179880}, faupublication = {no}, journal = {Journal of Statistical Physics}, keywords = {Entropy estimation; information science}, pages = {1443-1452}, peerreviewed = {Yes}, title = {{Guessing} probability distributions from small samples}, volume = {80}, year = {1995} } @article{faucris.122896004, abstract = {The coefficient of restitution of colliding viscoelastic spheres is known analytically as a complete series expansion in terms of the impact velocity where all (infinitely many) coefficients are known. While being analytically exact, this result is not suitable for applications in efficient event-driven molecular dynamics (eMD) or direct simulation Monte Carlo (DSMC) methods. Based on the analytic result, here we derive expressions for the coefficient of restitution that allow for application in efficient eMD and DSMC simulations of granular systems. © 2011 American Physical Society.}, author = {Müller, Patric and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.84.021302}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Collision} of viscoelastic spheres: {Compact} expressions for the coefficient of normal restitution}, volume = {84}, year = {2011} } @incollection{faucris.218986067, abstract = {Matter appears on our planet, in the solar system and in the rest of Universe in rather different forms.}, author = {Ebeling, Werner and Pöschel, Thorsten}, booktitle = {Lectures on Quantum Statistics}, doi = {10.1007/978-3-030-05734-3_1}, faupublication = {yes}, isbn = {978-3-030-05734-3}, note = {CRIS-Team Scopus Importer:2019-05-28}, pages = {1-17}, peerreviewed = {unknown}, publisher = {Springer Verlag}, series = {Lecture Notes in Physics}, title = {{Basic} physics of gases and plasmas}, volume = {953}, year = {2019} } @article{faucris.109920844, abstract = {Assume in a sample of size M one finds M representatives of species i with i = 1 ⋯ N*. The normalized frequency p* ≡ M/M, based on the finite sample, may deviate considerably from the true probabilities p. We propose a method to infer rank-ordered true probabilities r from measured frequencies M. We show that the rank-ordered probabilities provide important informations on the system, e.g., the true number of species, the Shannon- and the Renyi-entropies. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2004.}, author = {Pöschel, Thorsten and Ebeling, Werner and Frömmel, Cornelius and Ramirez, Rosa}, doi = {10.1140/epje/e2004-00025-4}, faupublication = {no}, journal = {European Physical Journal E}, pages = {531-541}, peerreviewed = {Yes}, title = {{Correction} algorithm for finite sample statistics}, volume = {12}, year = {2003} } @book{faucris.109848904, abstract = {A remarkably regular organization of spirals converging to a focal point in control parameter space was recently predicted and then observed in a nonlinear circuit containing two diodes. Such spiral organizations are relatively hard to observe experimentally because they usually emerge very compressed. Here we show that a circuit with a tunnel diode displays not one but two large spiral cascades. We show such cascades to exist over wide parameter ranges and, therefore, we expect them to be easier to observe experimentally. © Springer-Verlag Berlin Heidelberg 2013.}, author = {Francke, Ricardo and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1007/978-3-642-34560-9-9}, faupublication = {yes}, isbn = {9783642345593}, pages = {161-177}, peerreviewed = {Yes}, title = {{Infinite} networks of hubs, spirals, and zig-zag patterns in self-sustained oscillations of a tunnel diode and of an erbium-doped fiber-ring laser}, volume = {459}, year = {2013} } @article{faucris.122088824, abstract = {The decision whether a measured distribution complies with an equidistribution is a central element of many biostatistical methods. High throughput differential expression measurements, for instance, necessitate to judge possible over-representation of genes. The reliability of this judgement, however, is strongly affected when rarely expressed genes are pooled. We propose a method that can be applied to frequency ranked distributions and that yields a simple but efficient criterion to assess the hypothesis of equiprobable expression levels. By applying our technique to surrogate data we exemplify how the decision criterion can differentiate between a true equidistribution and a triangular distribution. The distinction succeeds even for small sample sizes where standard tests of significance (e.g. χ) fail. Our method will have a major impact on several problems of computational biology where rare events baffle a reliable assessment of frequency distributions. The program package is available upon request from the authors. © 2003 Elsevier Science Ireland Ltd. All rights reserved.}, author = {Pöschel, Thorsten and Freund, Jan A.}, doi = {10.1016/S0303-2647(03)00030-3}, faupublication = {no}, journal = {Biosystems}, keywords = {Biometrics; Finite sample statistics; Hypothesis testing; Microarray analysis}, pages = {63-72}, peerreviewed = {Yes}, title = {{How} to decide whether small samples comply with an equidistribution}, url = {http://www.sciencedirect.com/science/article/pii/S0303264703000303}, volume = {69}, year = {2003} } @article{faucris.109106844, abstract = {This paper reports a detailed numerical investigation of the geometrical and structural properties of three-dimensional heaps of particles. Our goal is the characterization of very large heaps produced by ballistic deposition from extended circular dropping areas. First, we provide an in-depth study of the formation of monodisperse heaps of particles. We find very large heaps to contain three new geometrical characteristics: they may display two external angles of repose, one internal angle of repose, and four distinct packing fraction (density) regions. Such features are found to be directly connected with the size of the dropping zone. We derive a differential equation describing the boundary of an unexpected triangular packing fraction zone formed under the dropping area.We investigate the impact that noise during the deposition has on the final heap structure. In addition, we perform two complementary experiments designed to test the robustness of the novel features found. The first experiment considers changes due to polydispersity. The second checks what happens when letting the extended dropping zone to become a point-like source of particles, the more common type of source.}, author = {Gallas, Jason and Pöschel, Thorsten and Topic, Nikola}, doi = {10.1080/14786435.2013.797618}, faupublication = {yes}, journal = {Philosophical Magazine}, pages = {4090-4107}, peerreviewed = {unknown}, title = {{Characteristics} of large threedimensional heaps of particles produced by ballistic deposition from extended sources}, volume = {93}, year = {2013} } @article{faucris.119477644, abstract = {Unsaturated wet granular media are usually modelled using force laws based on analytical and empirical results of liquid bridge forces between pairs of grains. These models make ad-hoc assumptions on the liquid volume present in the bridges and its distribution. The force between grains and rupture criterion of the bridge are a function of this assumed volume of liquid, in addition to other parameters like contact angle of the liquid, geometry of the grains and the inter grain distance. To study the initial volume and morphology of liquid bridges, hydrodynamic simulation of dynamic effects leading to formation of liquid bridges at grain scale are indispensable. We use a Smoothed Particle Hydrodynamics algorithm to simulate the hydrodynamics of the evolution of the free surface using a novel freesurface-capillary model, inspired by the molecular basis of surface tension. We present validations for the model and simulations of formation and rupture of liquid bridges.}, author = {Nair, Prapanch and Pöschel, Thorsten}, doi = {10.1051/epjconf/201714009005}, faupublication = {yes}, journal = {EPJ Web of Conferences}, peerreviewed = {unknown}, title = {{Structural} changes in wet granular matter due to drainage}, volume = {140}, year = {2017} } @article{faucris.121151624, abstract = {We investigate the average turbulent wind field over a barchan dune by means of Computational Fluid Dynamics. We find that the fractional speed-up ratio of the wind velocity over the three-dimensional barchan shape differs from the one obtained from two-dimensional calculations of the airflow over the longitudinal cut along the dune's symmetry axis - that is, over the equivalent transverse dune of same size. This finding suggests that the modeling of the airflow over the central slice of barchan dunes is insufficient for the purpose of the quantitative description of barchan dune dynamics as three-dimensional flow effects cannot be neglected.}, author = {Michelsen, Britt and Strobl, Severin and Ribeiro Parteli, Eric Josef and Pöschel, Thorsten}, doi = {10.1038/srep16572}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Two}-dimensional airflow modeling underpredicts the wind velocity over dunes}, url = {http://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84947790766&origin=inward}, volume = {5}, year = {2015} } @inproceedings{faucris.109579404, abstract = {Part of the optimization steps for additive manufacturing is related to the correct understanding of the mechanical behavior of the powder used in the process. Obtain this understanding based purely on experiments might be a difficult and sometimes prohibitive task. A particle-based numerical tool can provide critical information for correct understanding of powder deposition process. Numerical simulations through the Discrete Element Method (DEM) provide a useful mean to investigate the additive manufacturing process, given the possibility to study particle-scale information that are difficult to access experimentally. The characteristics of the recoated powder bed are investigated in the packed bed region and onto the manufactured part using PA12 commercial powder. Particle size distribution, contact and non-contact cohesive forces are incorporated in the numerical model. Furthermore, the non-spherical shape of real particles is taken explicitly into account in numerical simulations. A blade-type recoating system is used to form the powder bed and its roughness is calculated. Experimental measurements are performed by fringe projection. Several areas of the recoated powder layers can be scanned with this optical measurement method. Thus, the analyzed surface roughness can be compared with the simulated quantities to validate the numerical model. The sintered part is modelled as a prescribed rigid static region in the simulated system. The powder recoated in the sintered region may have different characteristics (packing, roughness) compared to the powder bed region. Recoating process is modelled using two different shapes for the sintered region. The amount of material recoated and the surface roughness are then calculated for the powder bed as well as for the sintered region}, author = {Schiochet Nasato, Daniel and Heinl, Martin and Hausotte, Tino and Pöschel, Thorsten}, booktitle = {International Conference on Particle based Methods}, date = {2017-09-26/2017-09-28}, editor = {V International Conference on Particle-based Methods – Fundamentals and Applications PARTICLES 2017}, faupublication = {yes}, keywords = {Granular Materials; DEM; Additive Manufacturing; Surface Roughness; Numerical simulation}, pages = {429-439}, peerreviewed = {unknown}, title = {{Numerical} and experimental study of the powder bed characteristics in the recoated bed of the additive manufacturing process}, venue = {Hannover}, year = {2017} } @article{faucris.107702584, abstract = {When a narrow tube inserted into a static container filled with particles is subjected to vertical vibration, the particles rise in the tube, much resembling the ascending motion of a liquid column in a capillary tube. To gain insights on the particle dynamics dictating this phenomenon – which we term

In this work, we examine theoretically the cooling dynamics of binary mixtures of spheres and rods. To this end, we introduce a generalized mean field analytical theory, which describes the free cooling behavior of the mixture. The relevant characteristic time scale for the cooling process is derived, depending on the mixture composition and the aspect ratio of the rods. We simulate mixtures of spherocylinders and spheres using a molecular dynamics algorithm implemented on graphics processing unit (GPU) architecture. We systematically study mixtures composed of spheres and rods with several aspect ratios and varying the mixture composition. A homogeneous cooling state, where the time dependence of the system’s intensive variables occurs only through a global granular temperature, is identified. We find cooling dynamics in excellent agreement with Haff’s law, when using an adequate time scale. Using the scaling properties of the homogeneous cooling dynamics, we estimated numerically the efficiency of the energy interchange between rotational and translational degrees of freedom for collisions between spheres and rods.

}, author = {Hidalgo, Raúl Cruz and Serero, Dan and Pöschel, Thorsten}, doi = {10.1063/1.4954670}, faupublication = {yes}, journal = {Physics of Fluids}, peerreviewed = {unknown}, title = {{Homogeneous} cooling of mixtures of particle shapes}, url = {http://www.mss.cbi.fau.de/content/uploads/Homogeneous_cooling_Physics_of_fluids_2016.pdf}, volume = {28}, year = {2016} } @article{faucris.116698384, author = {Behringer, Robert and Jenkins, James and Miloh, Touvia and Orszag, Steven and Pöschel, Thorsten and Rosenau, Philip and Savage, Stuart and Schuss, Zeev and Shemer, Lev}, faupublication = {yes}, journal = {Journal of Fluid Mechanics}, pages = {1 - 2}, peerreviewed = {Yes}, title = {{Obituary}: {PROFESSOR} {ISAAC} {GOLDHIRSCH} 11 {October} 1949–29 {April} 2010}, volume = {655}, year = {2010} } @article{faucris.122036024, abstract = {Some dynamical properties for a dissipative time-dependent Lorentz gas are studied. We assume that the size of the scatterers change periodically in time. We show that for some combination of the control parameters the particles come to a complete stop between the scatterers, but for some other cases, the average velocity grows unbounded. This is the first time that the unlimited energy growth is observed in a dissipative system. Finally, we study the behavior of the average velocity as a function of the number of collisions and we show that the system is scaling invariant with scaling exponents well defined. © 2013 Elsevier B.V. All rights reserved.}, author = {Fregolente Mendes de Oliveira, Diego and Pöschel, Thorsten}, doi = {10.1016/j.physleta.2013.06.029}, faupublication = {yes}, journal = {Physics Letters A}, keywords = {Billiards; Chaos; Dissipation; Lorentz gas; Scaling}, pages = {2052-2057}, peerreviewed = {Yes}, title = {{Competition} between unlimited and limited energy growth in a two-dimensional time-dependent billiard}, volume = {377}, year = {2013} } @article{faucris.109843844, author = {Meerson, Baruch and Pöschel, Thorsten and Sasorov, Pavel V. and Schwager, Thomas}, doi = {10.1103/PhysRevE.69.059905}, faupublication = {no}, journal = {Physical Review E}, pages = {059905-1}, peerreviewed = {Yes}, title = {{Erratum}: {Giant} fluctuations at a granular phase separation threshold ({Physical} {Review} {E} (2004) 69 (021302))}, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.69.059905}, volume = {69}, year = {2004} } @article{faucris.119186804, abstract = {With the assumption of a linear-dashpot interaction force, the coefficient of restitution, ε (k, γ), can be computed as a function of the elastic and dissipative material constants, k and γ by integrating Newton's equation of motion for an isolated pair of colliding particles. If we require further that the particles interact exclusively repulsive, which is a common assumption in granular systems, we obtain an expression ε (k, γ) which differs even qualitatively from the known result ε (k, γ). The expression ε (k, γ) allows to relate Molecular Dynamics simulations to event-driven Molecular Dynamics for a widely used collision model. © 2007 Springer-Verlag.}, author = {Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1007/s10035-007-0065-z}, faupublication = {no}, journal = {Granular Matter}, keywords = {Coefficient of restitution; Particle collisions}, pages = {465-469}, peerreviewed = {Yes}, title = {{Coefficient} of restitution and linear-dashpot model revisited}, volume = {9}, year = {2007} } @article{faucris.109997844, abstract = {We show that two basic mechanical processes, the collision of particles and rolling motion of a sphere on a plane, are intimately related. According to our recent findings, the restitution coefficient for colliding spherical particles ε, which characterizes the energy loss upon collision, is directly related to the rolling friction coefficient μ for a viscous sphere on a hard plane. We quantify both coefficients in terms of material constants which allows to determine either of them provided the other is known. This relation between the coefficients may give rise to a novel experimental technique to determine alternatively the coefficient of restitution or the coefficient of rolling friction.}, author = {Brilliantov, Nikolai and Pöschel, Thorsten}, doi = {10.1007/s100510051007}, faupublication = {no}, journal = {European Physical Journal B}, keywords = {81.05.Rm Porous materials; granular materials; 83.70.Fn Granular solids}, pages = {299-301}, peerreviewed = {Yes}, title = {{Rolling} as a "continuing collision"}, volume = {12}, year = {1999} } @article{faucris.122956724, abstract = {The collision of frictional granular particles may be described by an interaction force whose normal component is that of viscoelastic spheres while the tangential part is described by the model by Cundall and Strack (G´ eotechnique 29, 47 (1979)) being the most popular tangential collision model in Molecular Dynamics simulations. Albeit being a rather complicatedmodel, governed by 5 phenomenological parameters and 2 independent initial conditions, we find that it is described by 3 independent parameters only. Surprisingly, in a wide range of parameters the corresponding coefficient of tangential restitution, εt, is well described by the simple Coulomb law with a cut-off at εt = 0. A more complex behavior of the coefficient of restitution as a function on the normal and tangential components of the impact velocity, gn and gt, including negative values of εt, is found only for very small ratio gt/gn. For the analysis presented here we neglect dissipation of the interaction in normal direction.}, author = {Schwager, Thomas and Becker, Volker and Pöschel, Thorsten}, doi = {10.1140/epje/i2007-10356-3}, faupublication = {yes}, journal = {European Physical Journal E}, pages = {107--114}, peerreviewed = {Yes}, title = {{Coefficient} of tangential restitution for viscoelastic spheres}, volume = {27}, year = {2008} } @article{faucris.110013464, abstract = {The coefficient of self-diffusion for a homogeneously cooling granular gas changes significantly if the impact-velocity dependence of the restitution coefficient ε is taken into account. For the case of a constant ε the particles spread logarithmically slowly with time, whereas a velocity-dependent coefficient yields a power law time dependence. The impact of the difference in these time dependences on the properties of a freely cooling granular gas is discussed.}, author = {Brilliantov, Nikolai and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.61.1716}, faupublication = {no}, journal = {Physical Review E}, pages = {1716-1721}, peerreviewed = {Yes}, title = {{Self}-diffusion in granular gases}, volume = {61}, year = {2000} } @book{faucris.122766204, abstract = {Computer simulations not only belong to the most important methods for the theoretical investigation of granular materials, but also provide the tools that have enabled much of the expanding research by physicists and engineers. The present book is intended to serve as an introduction to the application of numerical methods to systems of granular particles. Accordingly, emphasis is placed on a general understanding of the subject rather than on the presentation of the latest advances in numerical algorithms. Although a basic knowledge of C++ is needed for the understanding of the numerical methods and algorithms in the book, it avoids usage of elegant but complicated algorithms to remain accessible for those who prefer to use a different programming language. While the book focuses more on models than on the physics of granular material, many applications to real systems are presented. © Springer-Verlag Berlin Heidelberg 2005.}, author = {Pöschel, Thorsten and Schwager, Thomas}, doi = {10.1007/3-540-27720-X}, faupublication = {no}, isbn = {9783540214854}, pages = {1-322}, publisher = {Springer Berlin Heidelberg}, title = {{Computational} granular dynamics: {Models} and algorithms}, year = {2005} } @article{faucris.109988384, abstract = {We investigate the transport of proteins inside the proteasome and propose an active-transport mechanism based on a spatially asymmetric interaction potential of peptide chains. The transport is driven by fluctuations which are always present in such systems. We compute the peptide-size-dependent transport rate which is essential for the functioning of the proteasome. In agreement with recent experiments, varying temperature changes the transport mechanism qualitatively. © EDP Sciences.}, author = {Zaikin, A. and Pöschel, Thorsten}, doi = {10.1209/epl/i2004-10426-8}, faupublication = {no}, journal = {EPL - Europhysics Letters}, pages = {725-731}, peerreviewed = {Yes}, title = {{Peptide}-size-dependent active transport in the proteasome}, volume = {69}, year = {2005} } @article{faucris.109900604, abstract = {The velocity distribution of a granular gas is analyzed in terms of the Sonine polynomials expansion. We derive an analytical expression for the third Sonine coefficient a. In contrast to frequently used assumptions this coefficient is of the same order of magnitude as the second Sonine coefficient a. For small inelasticity the theoretical result is in good agreement with numerical simulations. The next-order Sonine coefficients a, and a are determined numerically. While these coefficients are negligible for small dissipation, their magnitude grows rapidly with increasing inelasticity for 0 < ε ≲ 0.6. We conclude that this behavior of the Sonine coefficients manifests the breakdown of the Sonine polynomial expansion caused by the increasing impact of the overpopulated high-energy tail of the distribution function. © EDP Sciences.}, author = {Brilliantov, Nikolai V. and Pöschel, Thorsten}, doi = {10.1209/epl/i2005-10555-6}, faupublication = {no}, journal = {EPL - Europhysics Letters}, pages = {424-430}, peerreviewed = {Yes}, title = {{Breakdown} of the {Sonine} expansion for the velocity distribution of granular gases}, volume = {74}, year = {2006} } @article{faucris.109947244, abstract = {We investigate numerically the interaction of a stream of granular particles with a resting obstacle in two dimensions. For the case of high stream velocity we find that the force acting on the obstacle is proportional to the square of the stream velocity, the density and the obstacle size. This behaviour is equivalent to that of noninteracting hard spheres. For low stream velocity a gap between the obstacle and the incoming stream particles appears which is filled with granular gas of high temperature and low density. As soon as the gap appears the force does not depend on the square of velocity of the stream but the dependency obeys another law.}, author = {Buchholtz, Volkhard and Pöschel, Thorsten}, doi = {10.1007/PL00010908}, faupublication = {no}, journal = {Granular Matter}, pages = {33-41}, peerreviewed = {Yes}, title = {{Interaction} of a granular stream with an obstacle}, volume = {1}, year = {1998} } @article{faucris.106891444, abstract = {The investigation of regular and irregular patterns in nonlinear oscillators is an outstanding problem in physics and in all natural sciences. In general, regularity is understood as tantamount to periodicity. However, there is now a flurry of works proving the existence of "antiperiodicity", an unfamiliar type of regularity. Here we report the experimental observation and numerical corroboration of antiperiodic oscillations. In contrast to the isolated solutions presently known, we report infinite hierarchies of antiperiodic waveforms that can be tuned continuously and that form wide spiral-shaped stability phases in the control parameter plane. The waveform complexity increases towards the focal point common to all spirals, a key hub interconnecting them all.}, author = {Freire, J. G. and Cabeza, C. and Marti, A. C. and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1038/srep01958}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Antiperiodic} oscillations}, volume = {3}, year = {2013} } @article{faucris.109177024, abstract = {Cylindrical containers with a rotating bottom disk (so-called split-bottom geometry) are well established devices to shear granular materials in a continuous way, and to generate well-defined localized shear bands in the granular bed. When material composed of shape-anisotropic grains is sheared in such a container, a secondary flow is generated that leads to the formation of a considerable heap of material near the rotation center. We demonstrate that this effect can be found not only with prolate grains, as shown in a previous study, but also for oblate particle shapes. In addition, the quantitative influence of geometric and dynamic parameters is studied systematically. It is shown that the fill height of the container has considerable influence on the time scale for heap formation, but much less effect on the heap height. Results of numerical simulations agree with the experimental findings and provide insight in the particle dynamics.}, author = {Börzsönyi, Tamás and Fischer, David and Schiochet Nasato, Daniel and Pöschel, Thorsten and Stannarius, Ralf}, doi = {10.1088/1367-2630/18/11/113006}, faupublication = {yes}, journal = {New Journal of Physics}, peerreviewed = {Yes}, title = {{Heaping} and secondary flows in sheared granular materials}, volume = {18}, year = {2016} } @article{faucris.109964404, abstract = {We investigate autogenous fragmentation of dry granular material in rotating cylinders using two-dimensional molecular dynamics. By evaluation of spatial force distributions achieved numerically for various rotation velocities we argue that comminution occurs mainly due to the existence of these force chains. A statistical analysis of these force chains explains the spatial distribution of comminution efficiency in ball mills as measured experimentally by ROTHKEGEL and ROLF.}, author = {Buchholtz, V. and Freund, Jan A. and Pöschel, Thorsten}, doi = {10.1007/PL00011052}, faupublication = {no}, journal = {Bulk Solids Handling}, pages = {159-171}, peerreviewed = {Yes}, title = {{Molecular} dynamics of comminution in ball mills}, volume = {20}, year = {2000} } @article{faucris.217940857, abstract = {We present an enhanced version of our previously engineered MyoRobot system for reliable, versatile and automated investigations of skeletal muscle or linear polymer material (bio)mechanics. That previous version already replaced strenuous manual protocols to characterize muscle biomechanics properties and offered automated data analysis. Here, the system was further improved for precise control over experimental temperature and muscle single fiber sarcomere length. Moreover, it also now features the calculation of fiber cross-sectional area via on-the-fly optical diameter measurements using custom-engineered microscope optics. With this optical systems integration, the MyoRobot 2.0 allows to tailor a wealth of recordings for relevant physiological parameters to be sequentially executed in living single myofibers. Research questions include assessing temperature-dependent performance of active or passive biomechanics, or automated control over length-tension or length-velocity relations. The automatically obtained passive stress-strain relationships and elasticity modules are important parameters in (bio)material science. From the plethora of possible applications, we validated the improved MyoRobot 2.0 by assessing temperature-dependent myofibrillar Ca

We describe the velocity distribution function of a granular gas of electrically charged particles by means of a Sonine polynomial expansion and study the decay of its granular temperature. We find a dependence of the first non trivial Sonine coefficient, *a _{2}* , on time through the value of temperature. In particular, we find a sudden drop of

}, author = {Takada, Satoshi and Serero, Dan and Pöschel, Thorsten}, doi = {10.1063/1.4993620}, faupublication = {yes}, journal = {Physics of Fluids}, peerreviewed = {unknown}, title = {{Homogeneous} cooling state of dilute granular gases of charged particles}, volume = {29}, year = {2017} } @article{faucris.212766115, abstract = {Fluidized beds with secondary gas injection enjoy great popularity in process industry. Owing to their characteristic properties such as intense mixing of solids, excellent mass and heat transfer conditions as well as easy handling of solids, this type of apparatus is applied in various fields of process engineering nowadays. In the past decades research concerning fluidized beds with secondary gas injection has focused on understanding how solid particles and the injected gas are distributed within the apparatus. With the aid of invasive measurement techniques the region surrounding the injector nozzle was investigated with respect to the penetration depth of the gas jet above the nozzle orifice as well as the jet opening angle. A major drawback of the previously used measurement techniques consists in their invasive nature. Penetration of the injection zone by a probe can severely influence the local flow pattern and consequently has a detrimental effect on the reliability of the measured data. Therefore in the presented work for the first time the solids distribution as well as the motion of a single particle in a fluidized bed with secondary gas injection has been investigated by positron emission particle tracking (PEPT). This non-invasive technique is based on labeling one single particle, randomly selected from the bulk, radioactively, which allows for tracking its motion with high temporal and spatial resolution. The obtained data are compared with results derived from invasive measurements. Moreover PEPT-data have been used to perform investigations on the residence time behavior of particles within the jet region and the suspended phase. It could be found that the combination of invasive measurements and PEPT provide valuable information for the design and optimization of fluidized bed reactors with a well-defined injection zone.}, author = {Hensler, Timo and Tupy, Martin and Strer, Timo and Pöschel, Thorsten and Wirth, Karl-Ernst}, doi = {10.1016/j.proeng.2015.01.204}, faupublication = {yes}, journal = {Procedia Engineering}, note = {EAM Import::2019-03-08}, pages = {850-857}, peerreviewed = {unknown}, title = {{Particle} {Tracking} in {Fluidized} {Beds} with {Secondary} {Gas} {Injection}}, volume = {102}, year = {2015} } @article{faucris.109954064, abstract = {A modified single-stage low pressure impactor is described to measure the coefficient of normal restitution e for nanoparticles. The device is analysed numerically using CFD, and the gas flow inside the structured impaction plate is studied. A formula for the calculation of e is derived and first measurements of e for spherical silver particles are presented together with numerical data obtained from force-based molecular dynamics simulations. Furthermore, the simulation data for e and the sticking probability are investigated in detail for the elastic, and partly for the plastic impaction regime. Particle collisions are of great importance for the modeling of fundamental processes in a wide range of interests. So far it was not possible to determine the coefficient of restitution for nanoparticles experimentally. Here, a new measurement technique is described. The results are compared to and extended by a numerical study for detailed analysis. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.}, author = {Schöner, Christian and Rennecke, Stephan and Weber, Alfred P. and Pöschel, Thorsten}, doi = {10.1002/cite.201300132}, faupublication = {yes}, journal = {Chemie Ingenieur Technik}, keywords = {Coefficient of restitution; Impaction; Molecular dynamics; Nanoparticle; Product design; Rebound}, pages = {365-374}, peerreviewed = {Yes}, title = {{Introduction} of a new technique to measure the coefficient of restitution for nanoparticles}, volume = {86}, year = {2014} } @article{faucris.109808424, abstract = {We consider the transition of a horizontally vibrated monodisperse granular monolayer between its condensed state and its three-dimensional gaseous state as a function of the vibration parameters, amplitude, and frequency as well as particle number density. The transition is characterized by an abrupt change of the dynamical state which leaves its fingerprints in several measurable quantities including dissipation rate, sound emission, and a gap size which characterizes the sloshing motion of the material. The transition and its pronounced hysteresis is explained through the energy due to the collective motion of the particles relative to the container.}, author = {Heckel, Michael and Sack, Achim and Kollmer, Jonathan and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.91.062213}, faupublication = {yes}, journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics}, peerreviewed = {Yes}, title = {{Fluidization} of a horizontally driven granular monolayer}, url = {http://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84936984912&origin=inward}, volume = {91}, year = {2015} } @article{faucris.119404604, abstract = {The homogenization of granular flows through narrow pipes is important for a broad range of technological and industrial applications. Here we show, by means of molecular dynamics simulations, that such homogenization can be achieved by adding a helical inner-wall texture to the pipe, without the need for energy input from any external source. By using such a texture, jamming is prevented and the granular flux can be predicted using a modified Beverloo equation that accounts for the wavelength of the helical texture.}, author = {Verbücheln, Felix and Ribeiro Parteli, Eric Josef and Pöschel, Thorsten}, doi = {10.1051/epjconf/201714003069}, faupublication = {yes}, journal = {EPJ Web of Conferences}, peerreviewed = {unknown}, title = {{Homogenization} of granular pipe flow by means of helical inner-wall texture}, volume = {140}, year = {2017} } @article{faucris.120048324, abstract = {A numerical study that aims to analyze the thermal mechanisms of unsteady, supersonic granular flow by means of hydrodynamic simulations of the Navier-Stokes granular equation is reported in this paper. For this purpose, a paradigmatic problem in granular dynamics such as the Faraday instability is selected. Two different approaches for the Navier-Stokes transport coefficients for granular materials are considered, namely the traditional Jenkins-Richman theory for moderately dense quasi-elastic grains and the improved Garzó-Dufty-Lutsko theory for arbitrary inelasticity, which we also present here. Both the solutions are compared with event-driven simulations of the same system under the same conditions, by analyzing the density, temperature and velocity field. Important differences are found between the two approaches, leading to interesting implications. In particular, the heat transfer mechanism coupled to the density gradient, which is a distinctive feature of inelastic granular gases, is responsible for a major discrepancy in the temperature field and hence in the diffusion mechanisms. © IOP Publishing and Deutsche Physikalische Gesellschaft.}, author = {Garzó, Vicente and Almazán Torres, Lidia and Carrillo, José A. and Salueña, Clara and Pöschel, Thorsten}, doi = {10.1088/1367-2630/15/4/043044}, faupublication = {yes}, journal = {New Journal of Physics}, peerreviewed = {Yes}, title = {{A} numerical study of the {Navier}-{Stokes} transport coefficients for two-dimensional granular hydrodynamics}, volume = {15}, year = {2013} } @article{faucris.109998944, abstract = {A first-principle continuum-mechanics expression for the rolling friction coefficient is obtained for the rolling motion of a viscoelastic sphere on a hard plane. It relates the friction coefficient to the viscous and elastic constants of the sphere material. The relation obtained refers to the case when the deformation of the sphere ξ is small, the velocity of the sphere V is much less than the speed of sound in the material and when the characteristic time ξ/V is much larger than the dissipative relaxation times of the viscoelastic material. To our knowledge this is the first "first-principle" expression of the rolling friction coefficient which does not contain empirical parameters.}, author = {Brilliantov, Nikolai and Pöschel, Thorsten}, doi = {10.1209/epl/i1998-00281-7}, faupublication = {no}, journal = {EPL - Europhysics Letters}, pages = {511-516}, peerreviewed = {Yes}, title = {{Rolling} friction of a viscous sphere on a hard plane}, volume = {42}, year = {1998} } @article{faucris.109909184, abstract = {We perform a dimension analysis for colliding viscoelastic spheres to show that the coefficient of normal restitution ε depends on the impact velocity g as ε=1-γg+γg+ ⋯, in accordance with recent findings. We develop a simple theory to find explicit expressions for coefficients γ and γ. Using these and few next expansion coefficients for ε(g) we construct a Padé approximation for this function which may be used for a wide range of impact velocities where the concept of the viscoelastic collision is valid. The obtained expression reproduces quite accurately the existing experimental dependence ε(g) for ice particles.}, author = {Ramirez, Rosa and Pöschel, Thorsten and Brilliantov, Nikolai and Schwager, Thomas}, doi = {10.1103/PhysRevE.60.4465}, faupublication = {no}, journal = {Physical Review E}, pages = {4465-4472}, peerreviewed = {Yes}, title = {{Coefficient} of restitution of colliding viscoelastic spheres}, volume = {60}, year = {1999} } @article{faucris.107138064, abstract = {Ratchets are simple mechanical devices which combine spatial asymmetry and nonequilibrium to produce counterintuitive transport of particles. The operation and properties of

Besides its importance for science and engineering, the process of drop formation from a homogeneous jet or at a nozzle is of great aesthetic appeal. In this paper, we introduce a low-cost setup for classroom use to produce quasi-high-speed recordings with high temporal and spatial resolution of the formation of drops at a nozzle. The visualization of the process can be used for quantitative analysis of the underlying physical phenomena.

}, author = {Sack, Achim and Pöschel, Thorsten}, doi = {10.1119/1.4979657}, faupublication = {yes}, journal = {American Journal of Physics}, peerreviewed = {Yes}, title = {{Dripping} faucet in extreme spatial and temporal resolution}, volume = {85}, year = {2017} } @incollection{faucris.218985571, abstract = {The development of a systematic statistical theory for systems with Coulomb interactions is related to characteristic problems: 1.Debye’s screening problem, 2.Wigner’s problem of lattice formation,3.Herzfeld’s bound state problem.}, author = {Ebeling, Werner and Pöschel, Thorsten}, booktitle = {Lectures on Quantum Statistics}, doi = {10.1007/978-3-030-05734-3_6}, faupublication = {yes}, isbn = {978-3-030-05734-3}, note = {CRIS-Team Scopus Importer:2019-05-28}, pages = {171-210}, peerreviewed = {unknown}, publisher = {Springer Verlag}, series = {Lecture Notes in Physics}, title = {{Quantum} statistics of dilute plasmas}, volume = {953}, year = {2019} } @incollection{faucris.218985819, abstract = {From the classical kinetic theory of gases we know the equation of state of the ideal gas, βp = n (see Chap. 1). For real gases, the interaction forces between the molecules lead to corrections to the ideal gas equation of state. We mention the classical theory by van der Waals and the systematic expansions with respect to density, called virial expansions.}, author = {Ebeling, Werner and Pöschel, Thorsten}, booktitle = {Lectures on Quantum Statistics}, doi = {10.1007/978-3-030-05734-3_5}, faupublication = {yes}, isbn = {978-3-030-05734-3}, note = {CRIS-Team Scopus Importer:2019-05-28}, pages = {141-170}, peerreviewed = {unknown}, publisher = {Springer Verlag}, series = {Lecture Notes in Physics}, title = {{Real} gas quantum statistics}, volume = {953}, year = {2019} } @article{faucris.109802924, abstract = {A recent study claimed that heavy use of equations impedes communication among biologists, as measured by the ability to attract citations from peers. It was suggested that to increase the probability of being cited one should reduce the density of equations in papers, that equations should be moved to appendices, and that math training among biologists should be improved. Here, we report a detailed study of the citation habits among physicists, a community that has traditionally strong training and dependence on mathematical formulations. Is it possible to correlate statistical citation patterns and fear of mathematics in a community whose work strongly depends on equations? By performing a systematic analysis of the citation counts of papers published in one of the leading journals in physics covering all its disciplines, we find striking similarities with distribution of citations recorded in biological sciences. However, based on the standard deviations in citation data of both communities, biologists and physicists, we argue that trends in statistical indicators are not reliable to unambiguously blame mathematics for the existence or lack of citations. We digress briefly about other statistical trends that apparently would also enhance citation success.}, author = {Kollmer, Jonathan and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1088/1367-2630/17/1/013036}, faupublication = {yes}, journal = {New Journal of Physics}, keywords = {citation strategies; science communication; social physics}, peerreviewed = {Yes}, title = {{Are} physicists afraid of mathematics?}, url = {http://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84922245151&origin=inward}, volume = {17}, year = {2015} } @article{faucris.110024464, abstract = {The static as well as the dynamic behavior of granular material are determined by dynamic and static friction. There are well known methods to inlcude static friction in molecular dynamics simulations using scarcely understood forces. We propose an ansatz based on the geometrical shape of nonspherical particles which does not involve an explicit expression for static friction. It is shown that the simulations based on this model are close to experimental results. © 1993 The American Physical Society.}, author = {Pöschel, Thorsten and Buchholtz, Volkhard}, doi = {10.1103/PhysRevLett.71.3963}, faupublication = {no}, journal = {Physical Review Letters}, pages = {3963-3966}, peerreviewed = {Yes}, title = {{Static} friction phenomena in granular materials: {Coulomb} law versus particle geometry}, volume = {71}, year = {1993} } @article{faucris.122887864, abstract = {A two-dimensional cellular automaton is introduced to model the flow and jamming of vehicular traffic in cities. Each site of the automaton represents a crossing where a finite number of cars can wait approaching the crossing from each of the four directions. The flow of cars obeys realistic traffic rules. We investigate the dependence of the average velocity of cars on the global traffic density. At a critical threshold for the density the average velocity reduces drastically caused by jamming. For the low-density regime we provide analytical results which agree with the numerical results. © 1995.}, author = {Freund, Jan A. and Pöschel, Thorsten}, doi = {10.1016/0378-4371(95)00170-C}, faupublication = {no}, journal = {Physica A-Statistical Mechanics and Its Applications}, pages = {95-113}, peerreviewed = {Yes}, title = {{A} statistical approach to vehicular traffic}, volume = {219}, year = {1995} } @article{faucris.106954804, abstract = {Background: For many applications one wishes to decide whether a certain set of numbers originates from an equiprobability distribution or whether they are unequally distributed. Distributions of relative frequencies may deviate significantly from the corresponding probability distributions due to finite sample effects. Hence, it is not trivial to discriminate between an equiprobability distribution and non-equally distributed probabilities when knowing only frequencies. Results: Based on analytical results we provide a software tool which allows to decide whether data correspond to an equiprobability distribution. The tool is available at http://bioinf.charite.de/ equifreq/. Conclusions: Its application is demonstrated for the distribution of point mutations in coding genes. © 2003 Pöschel et al; licensee BioMed Central Ltd.}, author = {Pöschel, Thorsten and Frömmel, Cornelius and Gille, Christoph}, doi = {10.1186/1471-2105-4-58}, faupublication = {no}, journal = {Bmc Bioinformatics}, peerreviewed = {Yes}, title = {{Online} tool for the discrimination of equi-distributions}, url = {http://www.biomedcentral.com/1471-2105/4/58}, volume = {4}, year = {2003} } @article{faucris.109917764, abstract = {In horizontally shaken granular material different types of pattern formation have been reported. We want to deal with the convection instability which has been observed in experiments and which recently has been investigated numerically. Using two dimensional molecular dynamics we show that the convection pattern depends crucially on the inelastic properties of the material. The concept of restitution coefficient provides arguments for the change of the behaviour with varying inelasticity.}, author = {Salueña, Clara and Pöschel, Thorsten}, doi = {10.1007/s101890050006}, faupublication = {no}, journal = {European Physical Journal E}, pages = {55-59}, peerreviewed = {Yes}, title = {{Convection} in horizontally shaken granular material}, volume = {1}, year = {2000} } @article{faucris.122902824, abstract = {The phase separation instability that occurs in a system of nearly elastically colliding hard spheres driven by a thermal wall was investigated. It was demonstrated that if the aspect ratio of the confining box exceeded a threshold value the phase separation could be predicted by granular hydrostatics. It was found that in a wide region of aspect ratios around the threshold, the system was dominated by fluctuations. The two possible scenarios of the origin of the giant fluctuations were also discussed.}, author = {Meerson, Baruch and Pöschel, Thorsten and Sasorov, Pavel V. and Schwager, Thomas}, doi = {10.1103/PhysRevE.69.021302}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Giant} fluctuations at a granular phase separation threshold}, volume = {69}, year = {2004} } @article{faucris.109944604, abstract = {The hydrodynamics of granular gases of viscoelastic particles were derived. Collisions of viscoelastic particles were characterized by an impact velocity dependent coefficient of restitution. The Chapman-Enskog approach was used together with an adiabatic approximation for the velocity distribution function, which assumes that the shape of the velocity distribution function follows adiabatically the decaying temperature. Numerical solutions for temperature T(t) and for the second Sonine coefficient a(t) were compared with the corresponding adiabatic approximations.}, author = {Brilliantov, Nikolai and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.67.061304}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Hydrodynamics} and transport coefficients for dilute granular gases}, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.67.061304}, volume = {67}, year = {2003} } @article{faucris.122041524, abstract = {Sand dunes are ubiquitous in deserts, on coasts, on the sea bottom, and on the surface of Mars, Venus and Titan. The quantitative understanding of dune dynamics is thus of relevance for a broad range of physical, geological and planetary sciences. A morphodynamic model for dunes, which combines an analytical description of the average turbulent wind field over the topography with a continuum saltation model, has proven successful to quantitatively reproduce the shape of aeolian dunes of different types. We present a short review on the physics of dune formation and the model development, as well as some future plans for further developments and applications.}, author = {Ribeiro Parteli, Eric Josef and Kroy, Klaus and Tsoar, Haim and Andrade, José S. and Pöschel, Thorsten}, doi = {10.1140/epjst/e2014-02263-2}, faupublication = {yes}, journal = {European Physical Journal: Special Topics}, pages = {2269-2283}, peerreviewed = {Yes}, title = {{Morphodynamic} modeling of aeolian dunes: {Review} and future plans}, volume = {223}, year = {2014} } @article{faucris.124183884, abstract = {We study the diffusion of tracers (self-diffusion) in a homogeneously cooling gas of dissipative particles, using the Green-Kubo relation and the Chapman-Enskog approach. The dissipative particle collisions are described by the coefficient of restitution ε which for realistic material properties depends on the impact velocity. First, we consider self-diffusion using a constant coefficient of restitution, ε=const, as frequently used to simplify the analysis. Second, self-diffusion is studied for a simplified (stepwise) dependence of ε on the impact velocity. Finally, diffusion is considered for gases of realistic viscoelastic particles. We find that for ε=const both methods lead to the same result for the self-diffusion coefficient. For the case of impact-velocity dependent coefficients of restitution, the Green-Kubo method is, however, either restrictive or too complicated for practical application, therefore we compute the diffusion coefficient using the Chapman-Enskog method. We conclude that in application to granular gases, the Chapman-Enskog approach is preferable for deriving kinetic coefficients. © 2005 American Institute of Physics.}, author = {Brilliantov, Nikolai V. and Pöschel, Thorsten}, doi = {10.1063/1.1889266}, faupublication = {no}, journal = {Chaos}, peerreviewed = {Yes}, title = {{Self}-diffusion in granular gases: {Green}-{Kubo} versus {Chapman}-{Enskog}}, volume = {15}, year = {2005} } @article{faucris.120500204, abstract = {The coefficient of restitution may be determined from the sound signal emitted by a sphere bouncing repeatedly off the ground. Although there is a large number of publications exploiting this method, so far, there is no quantitative discussion of the error related to this type of measurement. Analyzing the main error sources, we find that even tiny deviations of the shape from the perfect sphere may lead to substantial errors that dominate the overall error of the measurement. Therefore, we come to the conclusion that the well-established method to measure the coefficient of restitution through the emitted sound is applicable only for the case of nearly perfect spheres. For larger falling height, air drag may lead to considerable error, too.

}, author = {Heckel, Michael and Glielmo, Aldo and Gunkelmann, Nina and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.93.032901}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Can} we obtain the coefficient of restitution from the sound of a bouncing ball?}, url = {http://link.aps.org/doi/10.1103/PhysRevE.93.032901}, volume = {93}, year = {2016} } @article{faucris.119189004, abstract = {The flow of granular material in a rotating cylinder was simulated by molecular dynamics in two dimensions using spherical as well as nonspherical grains. At very low but constant angular velocity we found that the flow varies irregularly with time. The particles move in a stick-slip mode, i.e. there are avalanches of different size at the surface of the granular material. Observing the traces of the particles we found that there are unstable convection cells. Our results agree with recent experiments by Rajchenbach and Rolf. © 1995.}, author = {Pöschel, Thorsten and Buchholtz, Volkhard}, doi = {10.1016/0960-0779(94)00193-T}, faupublication = {no}, journal = {Chaos Solitons & Fractals}, peerreviewed = {Yes}, title = {{Complex} flow of granular material in a rotating cylinder}, volume = {5}, year = {1995} } @article{faucris.109981564, abstract = {When granular systems are modeled by hard spheres, particle-particle collisions are considered as instantaneous events. This implies that while the velocities change according to the collision rule, the positions of the particles are the same before and after such an event. We show that depending on the material and system parameters, this assumption may fail. For the case of viscoelastic particles we present a universal condition which allows to assess whether hard-spheremodeling and, thus, event-driven Molecular Dynamics simulations are justified. © Springer-Verlag 2012.}, author = {Müller, Patric and Pöschel, Thorsten}, doi = {10.1007/s10035-012-0324-5}, faupublication = {yes}, journal = {Granular Matter}, keywords = {Coefficient of normal restitution; Event-driven molecular dynamics; Granular gases; Hard sphere model; Viscoelastic spheres}, pages = {115-120}, peerreviewed = {Yes}, title = {{Oblique} impact of frictionless spheres: {On} the limitations of hard sphere models for granular dynamics}, volume = {14}, year = {2012} } @article{faucris.118441224, abstract = {We apply positron emission particle tracking (PEPT) to a gas-solid fluidized bed with injection of a secondary gas through a centrally arranged nozzle and present a method to compute stationary fluid-dynamic characteristics of the system from the trajectories of a test particle. In order to evaluate this non-invasive method we compare the field of density obtained by PEPT with the density obtained by a traditional, well-established and approved, yet invasive, measurement technique to find good agreement. Besides the penetration depth of the jet region and the opening angle of the jet which are inferred from the density field, we use PEPT to measure quantities whose measurement using traditional methods is rather sophisticated, including the residence time of particles in the jet region and the suspended phase, the coefficients of axial and radial dispersion and the material flux across the jet boundaries. We conclude that PEPT is a reliable and at the same time versatile technique to measure stationary fluid-dynamic properties of dynamical particle systems at spatial resolution only limited by the duration of the measurement.}, author = {Hensler, Timo and Tupy, Martin and Strer, Timo and Pöschel, Thorsten and Wirth, Karl-Ernst}, doi = {10.1016/j.powtec.2015.04.005}, faupublication = {yes}, journal = {Powder Technology}, keywords = {Dispersion coefficient; Fluidized bed; Measurement technology; Positron emission particle tracking; Residence time; Secondary gas injection}, pages = {113-122}, peerreviewed = {Yes}, title = {{Positron} emission particle tracking in fluidized beds with secondary gas injection}, volume = {279}, year = {2015} } @article{faucris.106904424, abstract = {

We consider electroconvection as the response of nematic liquid crystal to an external electric AC field, in the absence of free charge carriers. Previous experimental and theoretical results emphasized charge carriers as a necessary precondition of electroconvection because free-charges in the fluid can response to the external electric field. Therefore, ionized molecules are considered as responsible for the driving of electroconvective flows. In experiments, finite conductivity is achieved by adding charge-carrying dye molecules or in non-dyed liquid crystals by impurities of the samples. The phenomenon of electroconvection is explained by the Carr-Helfrich theory, supported by numerical simulations. In the present paper, we show that electroconvection may occur also in pure nematic liquid crystals. By means of particle-based numerical simulation we found that bound charges emerge by alignment of polarized liquid crystal molecules in response to the external electric field. In our simulations we could reproduce the characteristic features of electroconvection, such as directorflow patterns, the phase-transition in the voltage-frequency diagram, and dislocation climb/glide motion, which are well known from experiments and hydrodynamic simulations under the assumption of free charge carriers.

}, author = {Lee, Kuang-Wu and Pöschel, Thorsten}, doi = {10.1039/C7SM02055D}, faupublication = {yes}, journal = {Soft Matter}, pages = {8816-8823}, peerreviewed = {unknown}, title = {{Electroconvection} of {Pure} {Nematic} {Liquid} {Crystals} without {Free} {Charge} {Carriers}}, volume = {120}, year = {2017} } @article{faucris.109906764, abstract = {We investigate the cooling rate of a gas of inelastically interacting particles. When we assume velocity-dependent coefficients of restitution the material cools down slower than with constant restitution. This behavior might have a large influence to clustering and structure formation processes.}, author = {Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.57.650}, faupublication = {no}, journal = {Physical Review E}, pages = {650-654}, peerreviewed = {Yes}, title = {{Coefficient} of normal restitution of viscous particles and cooling rate of granular gases}, volume = {57}, year = {1998} } @article{faucris.107033124, abstract = {

Grid based fluid simulation methods are not able to solve complex non-linear dynamics like the rupture of a dynamic liquid bridge between freely colliding solids–an exemplary scenario of capillary forces competing with inertial forces in engineering applications–using a monolithic formulation for the solid and liquid phases present. We introduce a new Incompressible Smoothed Particle Hydrodynamics method for simulating three dimensional fluid-solid interaction flows with capillary (wetting and surface tension) effects at free surfaces. This meshless approach presents significant advantages over grid based approaches in terms of being monolithic and in handling interaction with free solids. The method is validated for accuracy and stability in dynamic scenarios involving surface tension and wetting. We then present three dimensional simulations of crown forming instability following the splash of a liquid drop, and the rupture of a liquid bridge between two colliding solid spheres, to show the method’s advantages in the study of dynamic micromechanical phenomena involving capillary flows.

}, author = {Nair, Prapanch and Pöschel, Thorsten}, doi = {10.1016/j.ces.2017.10.042}, faupublication = {yes}, journal = {Chemical Engineering Science}, pages = {192-204}, peerreviewed = {Yes}, title = {{Dynamic} capillary phenomena using {Incompressible} {SPH}}, volume = {176}, year = {2017} } @article{faucris.119196924, abstract = {Our study examines the long-time behaviour of a force-free granular gas of viscoelastic particles, for which the coefficient of restitution depends on the impact velocity, as it follows from the solution of the impact problem for viscoelastic spheres. Starting from the Boltzmann equation, we derived the hydrodynamic equations and obtained microscopic expressions for the transport coefficients in terms of the elastic and dissipative parameters of the particle material. We performed the stability analysis of the linearized set of equations and found that any inhomogeneities and vortices vanish after a long time and the system approaches the flow-free stage of homogeneous density. This behaviour is in contrast to that of a gas consisting of particles which interact via a (non-realistic) constant coefficient of restitution, for which inhomogeneities (clusters) and vortex patterns have been proven to arise and to continuously develop.}, author = {Brilliantov, Nikolai and Pöschel, Thorsten}, doi = {10.1098/rsta.2001.0940}, faupublication = {no}, journal = {Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences}, keywords = {Clustering; Dissipative gases; Granular gases; Hydrodynamics; Inelastic collisions; Structure formation}, pages = {415-428}, peerreviewed = {Yes}, title = {{Hydrodynamics} of granular gases of viscoelastic particles}, volume = {360}, year = {2002} } @article{faucris.110035904, abstract = {The kinetic energy distribution function satisfying the Boltzmann equation is studied analytically and numerically for a system of inelastic hard spheres in the case of binary collisions. Analytically, this function is shown to have a similarity form in the simple cases of uniform or steady-state flows. This determines the region of validity of hydrodynamic description. The latter is used to construct the phase diagram of granular systems and discriminate between clustering instability and inelastic collapse. The molecular dynamics results support analytical results, but also exhibit a novel fluctuational breakdown of mean-field descriptions.}, author = {Pöschel, Thorsten and Esipov, Sergei E.}, doi = {10.1007/BF02183630}, faupublication = {no}, journal = {Journal of Statistical Physics}, keywords = {Boltzmann equation; Granular hydrodynamics; Granular temperature}, pages = {1385-1395}, peerreviewed = {Yes}, title = {{The} granular phase diagram}, volume = {86}, year = {1997} } @incollection{faucris.218987059, abstract = {Quantum statistics is a many body theory describing macroscopic matter. Let us first summarize concepts of classical many body theory and subsequently concepts of many body quantum theory, just what we need in the following. After this we will proceed to the simplest quantum statistical ensembles.}, address = {Cham}, author = {Ebeling, Werner and Pöschel, Thorsten}, booktitle = {Lectures on Quantum Statistics}, doi = {10.1007/978-3-030-05734-3_2}, faupublication = {yes}, isbn = {978-3-030-05733-6}, note = {CRIS-Team Scopus Importer:2019-05-28}, pages = {19-53}, peerreviewed = {unknown}, publisher = {Springer Verlag}, series = {Lecture Notes in Physics}, title = {{Elements} of quantum statistical theory}, volume = {953}, year = {2019} } @article{faucris.122915804, abstract = {A representation of the genetic code as a six-dimensional Boolean hypercube is described. This structure is the result of the hierarchical order of the interaction energies of the bases in codon-anticodon recognition. In this paper it is applied to study molecular evolution in vivo and in vitro. In the first case we compared aligned positions in homologous protein sequences and found two different behaviors: (a) There are sites in which the different amino acids may be explained by one or two 'attractor nodes' (coding for the dominating amino acid(s)) and their one-bit neighbors in the codon hypercube; and (b) There are sites in which the amino acids correspond to codons located in closed paths in the hypercube. In the second case we studied the 'Sexual PCR' experiment described by Stemmer and found that the success of this combination of usual PCR and recombination is in part due to the Gray code structure of the genetic code.}, author = {Jiménez-Montaño, Miguel A. and de la Mora-Basáñez, Carlos R. and Pöschel, Thorsten}, doi = {10.1016/0303-2647(96)01605-X}, faupublication = {no}, journal = {Biosystems}, keywords = {Genetic code; In vitro and in vivo; Molecular evolution; Six dimensional Boolean hypercube}, pages = {117-125}, peerreviewed = {Yes}, title = {{The} hypercube structure of the genetic code explains conservative and non-conservative aminoacid substitutions in vivo and in vitro}, volume = {39}, year = {1996} } @article{faucris.107356744, abstract = {We engineered an automated biomechatronics system,

By means of particle-based numerical simulations using the discrete element method, we address the

question of how the performance of granular dampers is affected by the shape of the granular particles.

In consistence with previous experiments performed with nearly spherical particles we

fi

nd that

independently of the particles

’

shape, the granular system is characterized by a gas-like regime for

small amplitudes of the container

’

s oscillation and by a collect-and-collide regime for large amplitude

forcing. Both regimes are separated by an optimal operation mode

—

the critical amplitude of the

damping oscillation for which the energy dissipation is maximal

—

which is independent of the particle

shape for given conditions of particle mass, material properties and number of particles. However, in

the gas-like regime, we

fi

nd that spherical particles lead to more ef

fi

cient energy dissipation compared

to complex shaped particles of the same mass. In this regime, a dependence on the damper

’

sef

fi

ciency

on the particle shape is found.

},
author = {Pourtavakoli, Hamzeh and Ribeiro Parteli, Eric Josef and Pöschel, Thorsten},
doi = {10.1088/1367-2630/18/7#/073049},
faupublication = {yes},
journal = {New Journal of Physics},
keywords = {granular matter, numerical simulations, discrete element method, granular dampers},
peerreviewed = {Yes},
title = {{Granular} dampers: does particle shape matter?},
volume = {18},
year = {2016}
}
@article{faucris.122142504,
abstract = {In dense, static, polydisperse granular media under isotropic pressure, the probability density and the correlations of particle-wall contact forces are studied. Furthermore, the probability density functions of the populations of pressures measured with different sized circular pressure cells are examined. The questions answered are: (i) What is the number of contacts that has to be considered so that the measured pressure lies within a certain error margin from its expectation value? (ii) What is the statistics of the pressure probability density as function of the size of the pressure cell? Astonishing non-random correlations between contact forces are evidenced that lead to a rapid decay of the width of the distribution and range at least 10-15 particle diameters. Finally, an experiment is proposed to tackle and better understand this issue. © 2010 Elsevier B.V. All rights reserved.},
author = {Müller, Micha-Klaus and Luding, Stefan and Pöschel, Thorsten},
doi = {10.1016/j.chemphys.2010.07.020},
faupublication = {yes},
journal = {Chemical Physics},
keywords = {DEM simulations; Dense static granular packings; Force and stress correlations; Pressure cells},
pages = {600-605},
peerreviewed = {Yes},
title = {{Force} statistics and correlations in dense granular packings},
volume = {375},
year = {2010}
}
@article{faucris.119404164,
abstract = {The theory of homogeneously driven granular gases of hard particles predicts that the stationary state is characterized by a velocity distribution function with overpopulated high-energy tails as compared to the exponential decay valid for molecular gases. While this fundamental theoretical result was confirmed by numerous numerical simulations, an experimental confirmation is still missing. Using self-rotating active granular particles, we find a power-law decay of the velocity distribution whose exponent agrees well with the theoretic prediction.

}, author = {Scholz, Christian and Pöschel, Thorsten}, doi = {10.1103/PhysRevLett.118.198003}, faupublication = {yes}, journal = {Physical Review Letters}, peerreviewed = {unknown}, title = {{Velocity} distribution of a homogeneously driven two-dimensional granular gas}, volume = {118}, year = {2017} } @incollection{faucris.218986315, abstract = {In this chapter, we will introduce useful tools of Quantum Statistics. Most of them will be used in later chapters of this book to solve concrete problems. Our survey covers, of course, the most prominent methods such as density operators introduced by von Neumann and Landau, Wigner’s phase-space functions method, and Bogolyubov’s method of reduced density operators. Matsubara’s thermodynamical Green’s functions and real-time Green’s functions are important methods in the field of quantum plasmas but are discussed here only rather briefly.}, author = {Ebeling, Werner and Pöschel, Thorsten}, booktitle = {Lectures on Quantum Statistics}, doi = {10.1007/978-3-030-05734-3_4}, faupublication = {yes}, isbn = {978-3-030-05734-3}, note = {CRIS-Team Scopus Importer:2019-05-28}, pages = {91-140}, peerreviewed = {unknown}, publisher = {Springer Verlag}, series = {Lecture Notes in Physics}, title = {{Density} operators and other tools of quantum statistics}, volume = {953}, year = {2019} } @article{faucris.107385564, abstract = {We report evidence of a surprising systematic onset of periodic patterns in very tall piles of disks deposited randomly between rigid walls. Independently of the pile width, periodic structures are always observed in monodisperse deposits containing up to 107 disks. The probability density function of the lengths of disordered transient phases that precede the onset of periodicity displays an approximately exponential tail. These disordered transients may become very large when the channel width grows without bound. For narrow channels, the probability density of finding periodic patterns of a given period displays a series of discrete peaks, which, however, are washed out completely when the channel width grows.

}, author = {Topic, Nikola and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1103/PhysRevLett.120.148002}, faupublication = {yes}, journal = {Physical Review Letters}, peerreviewed = {unknown}, title = {{Systematic} {Onset} of {Periodic} {Patterns} in {Random} {Disk} {Packings}}, volume = {120}, year = {2018} } @book{faucris.113993044, abstract = {This chapter contains sections titled: Introduction Forces Between Granular Particles Elastic Forces Viscous Forces Adhesion of Contacting Particles Collision of Granular Particles Coefficient of Restitution Dimensional Analysis Coefficient of Restitution for Spheres Coefficient of Restitution for Adhesive Collisions Conclusion References.}, author = {Pöschel, Thorsten and Brilliantov, Nikolai}, doi = {10.1002/352760362X.ch8}, faupublication = {yes}, isbn = {9783527403738}, keywords = {Collision of adhesive viscoelastic particles; Collision of granular particles; Dense granular flow; Forces between granula particles; Physics of granular media}, pages = {189-209}, peerreviewed = {Yes}, publisher = {wiley}, title = {{Collision} of {Adhesive} {Viscoelastic} {Particles}}, year = {2005} } @article{faucris.109912924, abstract = {We investigate the collision of adhesive viscoelastic spheres in quasistatic approximation where the adhesive interaction is described by the Johnson, Kendall, and Roberts (JKR) theory. The collision dynamics, based on the dynamic contact force, describes both restitutive collisions quantified by the coefficient of restitution ε as well as aggregative collisions, characterized by the critical aggregative impact velocity gcr. Both quantities ε and gcr depend sensitively on the impact velocity and particle size. Our results agree well with laboratory experiments. © 2007 The American Physical Society.}, author = {Brilliantov, Nikolai V. and Albers, Nicole and Spahn, Frank and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.76.051302}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Collision} dynamics of granular particles with adhesion}, volume = {76}, year = {2007} } @inproceedings{faucris.106255204, abstract = {The properties of dense granular systems are analyzed from a hydrodynamical point of view, based on conservation laws for the particle number density and linear momentum. We discuss averaging problems associated with the nature of such systems and the peculiarities of the sources of noise. We perform a quantitative study by combining analytical methods and numerical results obtained by ensemble-averaging of data on creep during compaction and molecular dynamics simulations of convective flow. We show that numerical integration of the hydrodynamic equations gives the expected evolution for the time-dependent fields.}, address = {Bellingham, WA, United States}, author = {Salueña, Clara and Esipov, Sergei E. and Pöschel, Thorsten}, booktitle = {Smart Structures and Materials 1997: Passive Damping and Isolation}, doi = {10.1117/12.274205}, faupublication = {no}, isbn = {0819424587}, pages = {2-11}, publisher = {Society of Photo-Optical Instrumentation Engineers}, title = {{Hydrodynamic} fluctuations and averaging problems in dense granular flows}, venue = {San Diego, CA, USA}, volume = {3045}, year = {1997} } @article{faucris.109973424, abstract = {The response of an oscillating granular damper to an initial perturbation is studied using experiments performed in microgravity and granular dynamics simulations. High-speed video and image processing techniques are used to extract experimental data. An inelastic hard sphere model is developed to perform simulations and the results are in excellent agreement with the experiments. In line with previous work, a linear decay of the amplitude is observed. Although this behavior is typical for a friction-damped oscillator, through simulation it is shown that this effect is still present even when friction forces are absent. A simple expression is developed which predicts the optimal damping conditions for a given amplitude and is independent of the oscillation frequency and particle inelasticities. © 2011 American Physical Society.}, author = {Bannerman, Marcus and Kollmer, Jonathan and Sack, Achim and Heckel, Michael and Müller, Patric and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.84.011301}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Movers} and shakers: {Granular} damping in microgravity}, volume = {84}, year = {2011} } @article{faucris.107384684, abstract = {

Stochastic Rotation Dynamics (SRD) is a valuable numerical tool extensively used in many domains of hydrodynamics simulations including colloidal suspensions. We investigate the dynamics of two colloidal particles in the regime of low Reynolds number by means of SRD in 3D. In contrast to well-known analytical and experimental results, no long-range interaction between the suspended particles could be found, independent of the size of the particles and the Mach and Péclet numbers. We attribute this behavior to the compressible nature and low sound velocity in the SRD solvent. The inability of representing long-range interactions poses an important limitation to the applicability of SRD to certain physical systems. We provide an estimation of typical length scales for which SRD can be applied.

}, author = {Shakeri, Ali and Lee, Kuang-Wu and Pöschel, Thorsten}, doi = {10.1063/1.5008812}, faupublication = {yes}, journal = {Physics of Fluids}, month = {Jan}, peerreviewed = {unknown}, title = {{Limitation} of stochastic rotation dynamics to represent hydrodynamic interaction between colloidal particles}, volume = {30}, year = {2018} } @article{faucris.119756164, abstract = {The evolution of a pile of granular material is investigated by molecular dynamics using a new model including nonsphericity of the particles instead of introducing static friction terms. The angle of repose of the piles as well as the avalanche statistics gathered by the simulation agree with experimental results. The angle of repose of the pile is determined by the shape of the grains. Our results are compared with simulations using spherical grains and static friction. © 1994.}, author = {Buchholtz, Volkhard and Pöschel, Thorsten}, doi = {10.1016/0378-4371(94)90467-7}, faupublication = {no}, journal = {Physica A-Statistical Mechanics and Its Applications}, pages = {390-401}, peerreviewed = {Yes}, title = {{Numerical} investigations of the evolution of sandpiles}, volume = {202}, year = {1994} } @article{faucris.215447040, abstract = {An impressive ping-pong ball cannon can be made by placing a bottle of liquid nitrogen at the bottom of a container and quickly covering it with, say, 1500 ping-pong balls. The liquid turns rapidly into a gas whose mounting pressure explodes the bottle, sending a swarm of balls upward out of the container. Surprisingly, the container also moves upward. This is a counterintuitive effect because the balance of forces, that is, Newton's third law does not seem to allow the container to move upwards. We explain the effect as a consequence of granular jamming in combination with Coulomb's friction law. (C) 2019 American Association of Physics Teachers.}, author = {Pöschel, Thorsten and Nasato, Daniel S. and Parteli, Eric J. R. and Gallas, Jason and Müller, Patric}, doi = {10.1119/1.5088805}, faupublication = {yes}, journal = {American Journal of Physics}, note = {CRIS-Team WoS Importer:2019-04-04}, pages = {255-263}, peerreviewed = {Yes}, title = {{Ping}-pong ball cannon: {Why} do barrel and balls fly in the same direction?}, volume = {87}, year = {2019} } @article{faucris.117458924, abstract = {We study experimentally the dissipation of energy in a rotating cylinder which is partially filled by granular material. We consider the range of angular velocity corresponding to continous and stationary flow of the granulate. In this regime, the stationary state depends on the angular velocity and on the filling mass. For a wide interval of filling levels we find a universal behavior of the driving torque required to sustain the stationary state as a function of the angular velocity. The result may be of relevance to industrial applications, e.g. to understand the power consumption of ball mills or rotary kilns and also for damping applications where mechanical energy has to be dissipated in a controlled wa}, author = {Sack, Achim and Pöschel, Thorsten}, doi = {10.1038/srep26833}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Dissipation} of {Energy} by {Dry} {Granular} {Matter} in a {Rotating} {Cylinder}}, volume = {6}, year = {2016} } @article{faucris.123696144, author = {Brey, Javier and Goldhirsch, Isaac and Pöschel, Thorsten}, faupublication = {yes}, journal = {European Physical Journal-Special Topics}, peerreviewed = {Yes}, title = {{Granular} {Gases}: {Beyond} the {Dilute} {Limit}}, volume = {179}, year = {2009} } @article{faucris.123486264, abstract = {We propose a new scheme for the two-way coupling of incompressible fluids and deformable bodies, where we focus on a medical application; in particular, secondary bone healing. Our method allows for accurate simulation and visualisation of the secondary bone healing process, which is used to optimise clinical treatment of bone fractures. In our simulation, the soft tissues are simulated as elastic materials using Strain Based Dynamics (SBD), and fluid is simulated using Incompressible Smoothed Particle Hydrodynamics (ISPH). The interaction model we propose works with any type of deformation technique as long as the object surface is represented by a polygonal mesh and the fluid by Lagrangian particles.}, author = {Aburumman, Nadine and Müller, Patric and Nair, Prapanch and Pöschel, Thorsten}, faupublication = {yes}, journal = {Eurographics technical report series}, peerreviewed = {No}, title = {{Coupled} {Simulation} of {Deformable} {Bodies} and {ISPH} {Fluids} for {Secondary} {Bone} {Healing}}, year = {2017} } @article{faucris.119735484, abstract = {We simulate the dynamical behavior of M elevators serving N floors of a building in which a Poisson distribution of persons call elevators. Our simulation reproduces the jamming effect typically seen in large buildings when a large number of persons decide to leave the building simultaneously. The collective behavior of the elevators involves characteristics similar to those observed in systems of coupled oscillators. In addition, there is an apparently rule-free critical population density above which elevators start to arrive synchronously at the ground floor. © 1994 The American Physical Society.}, author = {Pöschel, Thorsten and Gallas, Jason A.}, doi = {10.1103/PhysRevE.50.2654}, faupublication = {no}, journal = {Physical Review E}, pages = {2654-2659}, peerreviewed = {Yes}, title = {{Synchronization} effects in the dynamical behavior of elevators}, volume = {50}, year = {1994} } @article{faucris.122138764, abstract = {We consider the attenuation of the oscillation of a flat spring due to the action of a granular damper. The efficiency of the damper is quantified by evaluating the position of the oscillator as a function of time using a Hall effect based position sensor. Performing experiments for a large abundance of parameters under conditions of microgravity, we confirm a recent theory for granular damping (Kollmer et al. in New J Phys 15:093023, 2013) and show that the theory remains approximately valid even beyond the limits of its derivation.}, author = {Sack, Achim and Heckel, Michael and Kollmer, Jonathan and Pöschel, Thorsten}, doi = {10.1007/s10035-014-0539-8}, faupublication = {yes}, journal = {Granular Matter}, keywords = {Dissipation; Granular systems; Vibration damping}, pages = {73-82}, peerreviewed = {Yes}, title = {{Probing} the validity of an effective-one-particle description of granular dampers in microgravity}, volume = {17}, year = {2014} } @article{faucris.109959124, abstract = {A gas of particles which collide inelastically if their impact velocity exceeds a certain value is investigated. In difference to common granular gases, cluster formation occurs only as a transient phenomenon. We calculate the decay of temperature due to inelastic collisions. In spite of the drastically reduced dissipation at low temperature the temperature surprisingly converges to zero. © 2003 Published by Elsevier Science B.V.}, author = {Pöschel, Thorsten and Brilliantov, Nikolai and Schwager, Thomas}, doi = {10.1016/S0378-4371(03)00206-1}, faupublication = {no}, journal = {Physica A-Statistical Mechanics and Its Applications}, keywords = {Cluster formation; Granular gas; Molecular dynamics; Velocity dependent coefficient of restitution}, pages = {274-283}, peerreviewed = {Yes}, title = {{Long}-time behavior of granular gases with impact-velocity dependent coefficient of restitution}, url = {http://www.sciencedirect.com/science/article/pii/S0378437103002061}, volume = {325}, year = {2003} } @article{faucris.123972464, abstract = {By means of particle-based numerical simulations using the discrete element method, we address the question of how the performance of granular dampers is affected by the shape of the granular particles. In consistence with previous experiments performed with nearly spherical particles we find that independently of the particles‘ shape, the granular system is characterized by a gas-like regime for small amplitudes of the container’s oscillation and by a collect-and-collide regime for large amplitude forcing. Both regimes are separated by an optimal operation mode—the critical amplitude of the damping oscillation for which the energy dissipation is maximal—which is independent of the particle shape for given conditions of particle mass, material properties and number of particles. However, in the gas-like regime, we find that spherical particles lead to more efficient energy dissipation compared to complex shaped particles of the same mass. In this regime, a dependence on the damper’s efficiency on the particle shape is found.}, author = {Pourtavakoli, Hamzeh and Ribeiro Parteli, Eric Josef and Pöschel, Thorsten}, doi = {10.1088/1367-2630/18/7/073049}, faupublication = {yes}, journal = {New Journal of Physics}, peerreviewed = {Yes}, title = {{Effect} of particle shape on the efficiency of granular dampers}, volume = {18}, year = {2016} } @inproceedings{faucris.122054504, abstract = {We report a numerical investigation of the structural properties of very large three-dimensional heaps of granular material produced by ballistic deposition from extended circular dropping areas. Very large heaps are found to contain three new geometrical characteristics not observed before: they may have two external angles of repose, an internal angle of repose, and four distinct packing fraction (density) regions. Such characteristics are shown to be directly correlated with the size of the dropping zone. In addition, we also describe how noise during the deposition affects the final heap structure.}, author = {Gallas, Jason and Pöschel, Thorsten and Topic, Nikola}, booktitle = {Proceed. XXIII ICTAM}, date = {2012-08-19/2012-08-24}, faupublication = {yes}, peerreviewed = {unknown}, title = {{Structure} of granular packings}, venue = {Beijing, China}, year = {2012} } @article{faucris.114764804, abstract = {An algorithm for the exact calculation of the overlap volume of a sphere and a tetrahedron, wedge, or hexahedron is described. The method can be used to determine the exact local solid fractions for a system of spherical, non-overlapping particles contained in a complex mesh, a question of significant relevance for the numerical solution of many fluid-solid interaction problems. While challenging due to the limited machine precision, a numerically robust version of the calculation maintaining high computational efficiency is devised. The method is evaluated with respect to the numerical precision and computational cost. It is shown that the exact calculation is only limited by the machine precision and can be applied to a wide range of size ratios, contrary to previously published methods. Eliminating this constraint enables the usage of meshes with higher resolution near the system boundaries for coupled CFD-DEM simulations. The numerical robustness is further illustrated by applying the method to highly deformed mesh elements. The full source code of the reference implementation is made available under an open-source license.}, author = {Strobl, Severin and Formella, Arno and Pöschel, Thorsten}, doi = {10.1016/j.jcp.2016.02.003}, faupublication = {yes}, journal = {Journal of Computational Physics}, keywords = {Local solid fraction; Numerical robustness; Overlap volume; Sphere-mesh overlap}, pages = {158-172}, peerreviewed = {Yes}, title = {{Exact} calculation of the overlap volume of spheres and mesh elements}, volume = {311}, year = {2016} } @article{faucris.123019644, abstract = {By means of experiments in microgravity conditions, we show that granular systems subjected to sinusoidal vibrations respond either by harmonic or gaslike dynamics, depending on the parameters of the vibration, amplitude and frequency, and the container size, while subharmonic response is unstable, except for extreme material properties and particular initial conditions. The absence of subharmonic response in vibrated granular systems implies that granular dampeners cannot reveal higher-order resonances, which makes them even more attractive for technical applications. Extensive molecular dynamics simulations support our findings.}, author = {Kollmer, Jonathan and Tupy, Martin and Heckel, Michael and Sack, Achim and Pöschel, Thorsten}, doi = {10.1103/PhysRevApplied.3.024007}, faupublication = {yes}, journal = {Physical Review Applied}, peerreviewed = {Yes}, title = {{Absence} of subharmonic response in vibrated granular systems under microgravity conditions}, url = {http://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84951752550&origin=inward}, volume = {3}, year = {2015} } @inproceedings{faucris.122142944, abstract = {We perform two-dimensional hydrodynamic simulations on a paradigmatic problem of granular dynamics, the Faraday instability, using two different approximations to the Navier-Stokes granular equations: the constitutive equations and kinetic coefficients derived from the assumption of vanishing inelasticity (Jenkins-Richman approach) obtained by solving the Enskog equation disks by means of Grad's method, and the ones obtained by solving the Enskog equation with the Chapman-Enskog method (Garzó-Dufty-Lutsko approach). The comparison reveals important qualitative and quantitative differences with respect to the hydrodynamic fields obtained by averaging results from particle simulations of the same system. © 2012 American Institute of Physics.}, author = {Almazán Torres, Lidia and Salueña, Clara and Garzó, Vicente and Carrillo, José A. and Pöschel, Thorsten}, booktitle = {28th International Symposium on Rarefied Gas Dynamics 2012, RGD 2012}, doi = {10.1063/1.4769650}, faupublication = {yes}, isbn = {9780735411159}, keywords = {Faraday instability; hydrodynamic simulations; molecular dynamics; Rapid granular flows}, pages = {993-1000}, title = {{Hydrodynamics} at the {Navier}-{Stokes} level applied to fast, transient, supersonic granular flows}, venue = {Zaragoza}, volume = {1501}, year = {2012} } @article{faucris.106400624, abstract = {

As an environment for rich pattern formation, the electroconvection (EC) of nematic liquid crystals (LCs) is studied via fully nonlinear simulations for the first time. Previously, EC was mostly studied by experiments or

by linear/weakly nonlinear hydrodynamic theory for its instability criteria. While the negative dielectric LCs are used in most EC analytical and experimental investigations, EC with positive dielectric LCs is limited to

experiments only, due to their more complex nonlinear behavior. In this work we take a step beyond the existing weakly nonlinear EC research by using a fully nonlinear particle-based simulation. To investigate

the distinct dynamics of positive and negative dielectric LCs, we modified the molecular potential in the LC stochastic rotational model (LC SRD) [Lee et al., J. Chem. Phys., 2015, 142, 164110] to incorporate the

dielectric characteristics and the field-particle interaction. As a result, different convection patterns known in the EC experiments were observed in our simulations, for which those patterns appeared orderly, as a function of external field strength. The simulated director and flow fields correspond to each other well, as found in our experiments. For the positive dielectric LC, we discovered a net directional flow accompanying the travelling EC rolls. This numerical model and its hydrodynamic analysis could be used for precise flow control at the micro-scale, such as nematic colloidal transportation in microfluidics.

}, author = {Lee, Kuang-Wu and Pöschel, Thorsten}, doi = {10.1039/C7RA06757G}, faupublication = {yes}, journal = {RSC Advances}, peerreviewed = {unknown}, title = {{Field}-driven pattern formation in nematic liquid crystals: mesoscopic simulations of electroconvection}, volume = {7}, year = {2017} } @article{faucris.109805124, abstract = {We consider the motion of an aspherical inelastic particle of dumbbell type bouncing repeatedly on a horizontal flat surface. The coefficient of restitution of such a particle depends not only on material properties and impact velocity but also on the angular orientation at the instant of the collision whose variance is considerable, even for small eccentricity. Assuming random angular orientation of the particle at the instant of contact we characterize the measured coefficient of restitution as a fluctuating quantity and obtain a wide probability density function including a finite probability for negative values of the coefficient of restitution. This may be understood from the partial exchange of translational and rotational kinetic energy.}, author = {Glielmo, Aldo and Gunkelmann, Nina and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.90.052204}, faupublication = {yes}, journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics}, peerreviewed = {Yes}, title = {{Coefficient} of restitution of aspherical particles}, volume = {90}, year = {2014} } @article{faucris.109910724, abstract = {The linear dashpot model for the inelastic normal force between colliding spheres leads to a constant coefficient of normal restitution, εn =const, which makes this model very popular for the investigation of dilute and moderately dense granular systems. For two frequently used models for the tangential interaction force we determine the coefficient of tangential restitution, εt, both analytically and by numerical integration of Newton's equation. Although εn =const for the linear-dashpot model, we obtain pronounced and characteristic dependences of the tangential coefficient on the impact velocity, εt = εt (g). The results may be used for event-driven simulations of granular systems of frictional particles. © 2008 The American Physical Society.}, author = {Becker, Volker and Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.77.011304}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Coefficient} of tangential restitution for the linear dashpot model}, volume = {77}, year = {2008} } @article{faucris.119713044, author = {Pöschel, Thorsten and Wolf, Dietrich}, faupublication = {yes}, journal = {Granular Matter}, peerreviewed = {Yes}, title = {{Granular} {Matter} - special edition}, volume = {14}, year = {2012} } @article{faucris.119753304, abstract = {The structural evolution of a nanopowder by repeated dispersion and settling can lead to characteristic fractal substructures. This is shown by numerical simulations of a two-dimensional model agglomerate of adhesive rigid particles. The agglomerate is cut into fragments of a characteristic size , which then are settling under gravity. Repeating this procedure converges to a loosely packed structure, the properties of which are investigated: (a)The final packing density is independent of the initialization, (b) the short-range correlation function is independent of the fragment size, (c) the structure is fractal up to the fragmentation scale with a fractal dimension close to 1.7, and (d) the relaxation time increases linearly with. © 2008 The American Physical Society.}, author = {Schwager, Thomas and Wolf, Dietrich E. and Pöschel, Thorsten}, doi = {10.1103/PhysRevLett.100.218002}, faupublication = {no}, journal = {Physical Review Letters}, peerreviewed = {Yes}, title = {{Fractal} substructure of a nanopowder}, volume = {100}, year = {2008} } @article{faucris.107702144, abstract = {When a thin tube is dipped into water, the water will ascend to a certain height, against the action of gravity. While this effect, termed capillarity, is well known, recent experiments have shown that agitated granular matter reveals a similar behavior. Namely, when a vertical tube is inserted into a container filled with granular material and is then set into vertical vibration, the particles rise up along the tube. In the present Letter, we investigate the effect of granular capillarity by means of numerical simulations and show that the effect is caused by convection of the granular material in the container. Moreover, we identify two regimes of behavior for the capillary height H

Analogies between fluid flows and granular flows are useful because they pave the way for continuum treatments of granular media. However, in practice it is impossible to predict under what experimental conditions the dynamics of fluids and granulates are qualitatively similar. In the case of unsteadily driven systems no such analogy is known. For example, in a partially filled container subject to horizontal oscillations liquids slosh, whereas granular media of complex particles exhibit large-scale convection rolls. We here show that smooth monodisperse steel spheres exhibit liquidlike sloshing dynamics. Our findings highlight the role of particle material and geometry for the dynamics and phase transitions of the system.

}, author = {Avila Canellas, Kerstin and Steub, Laura and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.96.040901}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {unknown}, title = {{Liquidlike} sloshing dynamics of monodisperse granulate}, volume = {96}, year = {2017} } @inproceedings{faucris.106410964, abstract = {

Part of the optimization steps for the additive manufacturing is related to the correct understanding of the mechanical behavior of the powder used in the process. Numerical simulations through the Discrete Element Method (DEM) provide a useful means to investigate additive manufacturing process thus assisting and complementing experimental investigations. In particular, with the help of DEM simulations, it is possible to study particle-scale processes that are difficult to access experimentally. We investigate the characteristics of the powder bed deposited onto the manufactured part using a roller as the coating system. Furthermore, the non-spherical shape of real particles is also taken explicitly into account in the numerical simulations. A combination of translational velocity and sinusoidal vibration is used in the roller. The effect of varying the translational velocity, vibration frequency and amplitude in the density and roughness of the formed bed is investigated.

}, address = {Ljubljana}, author = {Schiochet Nasato, Daniel and Pöschel, Thorsten and Ribeiro Parteli, Eric Josef}, booktitle = {6th International Conference on Additive Technologies iCAT}, date = {2016-11-29/2016-11-30}, editor = {Drstvenšek I, Drummer D, Schmidt M}, faupublication = {yes}, isbn = {978-961-285-537-6}, peerreviewed = {unknown}, publisher = {Interesansa - zavod}, title = {{Effect} of vibrations applied to the transport roller in the quality of the powder bed during additive manufacturing}, venue = {Nürnberg}, year = {2016} } @inproceedings{faucris.109844724, abstract = {In this paper an algorithm is described which combines the efficiency of event-driven Molecular-Dynamics (eMD) and the physical correctness of force-based Molecular-Dynamics (MD) for dilute granular systems of frictionless spheres. © 2013 AIP Publishing LL}, author = {Pöschel, Thorsten and Müller, Patric}, booktitle = {7th International Conference on Micromechanics of Granular Media: Powders and Grains 2013}, doi = {10.1063/1.4811889}, faupublication = {yes}, isbn = {9780735411661}, keywords = {event-driven Molecular-Dynamics; granular Gases; hard-sphere model; Molecular-Dynamics}, pages = {149-152}, title = {{Event}-driven {DEM} of soft spheres}, venue = {Sydney, NSW}, volume = {1542}, year = {2013} } @article{faucris.114386844, abstract = {Event-driven particle dynamics is a fast and precise method to simulate particulate systems of all scales. In this work it is demonstrated that, despite the high accuracy of the method, the finite machine precision leads to simulations entering invalid states where the dynamics are undefined. A general event-detection algorithm is proposed which handles these situations in a stable and efficient manner. This requires a definition of the dynamics of invalid states and leads to improved algorithms for event-detection in hard-sphere systems.}, author = {Bannerman, Marcus and Strobl, Severin and Formella, Arno and Pöschel, Thorsten}, doi = {10.1007/s40571-014-0021-8}, faupublication = {yes}, journal = {Computational Particle Mechanics}, pages = {191--198}, peerreviewed = {Yes}, title = {{Stable} algorithm for event detection in event-driven particle dynamics}, volume = {1}, year = {2014} } @article{faucris.110053724, abstract = {The onset of surface fluidization of granular material in a vertically vibrated container, z = A cos (ωt), is studied experimentally. Recently, for a column of spheres it has been theoretically found (see T. Pöschel, T. Schwager, C. Salueña, Phys. Rev. E 62, 1361 (2000)) that the particles lose contact if a certain condition for the acceleration amplitude z̈ ≡ Aω/g = f(ω) holds. This result is in disagreement with other findings where the criterion z̈ = z̈ = const was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not a proper criterion for fluidization and compare the results with theory.}, author = {Renard, S. and Schwager, Thomas and Pöschel, Thorsten and Salueña, Clara}, doi = {10.1007/s101890170133}, faupublication = {no}, journal = {European Physical Journal E}, pages = {233-239}, peerreviewed = {Yes}, title = {{Vertically} shaken column of spheres. {Onset} of fluidization}, volume = {4}, year = {2001} } @article{faucris.109955164, abstract = {About 20 years ago, Isaac Goldhirsch was one of the first to recognize that granular matter, behaving neither as a normal fluid nor as a normal solid, was not only an exotic terra incognita for basic science, but is paradigmatic for a whole class of complex systems with irreversible interactions. This field became his passion at a time when he was already a very successful, internationally renowned theoretical physicist. Certainly this helped to establish granular matter theory as a lively new branch of science. The very existence of a prominent new scientific journal ``Granular Matter'', entirely devoted to this field speaks for itself.}, author = {Pöschel, Thorsten and Wolf, Dietrich E.}, doi = {10.1007/s10035-012-0345-0}, faupublication = {yes}, journal = {Granular Matter}, peerreviewed = {Yes}, title = {{Isaac} {Goldhirsch}: a pioneer of granular matter theory}, year = {2012} } @article{faucris.122146024, author = {Masel, Joanna and Jansen, Vincent A. A. and Pöschel, Thorsten and Brilliantov, Nikolai V. and Frömmel, Cornelius}, doi = {10.1529/biophysj.104.039867}, faupublication = {no}, journal = {Biophysical Journal}, pages = {728-729}, peerreviewed = {Yes}, title = {{Prion} {Kinetics} (multiple letters)}, volume = {87}, year = {2004} } @article{faucris.123556444, abstract = {Convection, surface fluidization, spontaneous heap formation, and other effects are analyzed when a granular material is shaken vertically. The existence of a threshold for the Froude number Γ = Aω-0$//g is investigated, below which these effects cannot be observed. It is proved that there is no such threshold using computer simulation.}, author = {Pöschel, Thorsten and Schwager, Thomas and Salueña, Clara}, doi = {10.1103/PhysRevE.62.1361}, faupublication = {no}, journal = {Physical Review E}, pages = {1361-1367}, peerreviewed = {Yes}, title = {{Onset} of fluidization in vertically shaken granular material}, volume = {62}, year = {2000} } @article{faucris.109987504, abstract = {We study the mechanism leading to the formation of stripe-like patterns in a rectangular container filled with a sub-monolayer of frictional spherical particles when it is subjected to horizontal oscillations. By means of Molecular Dynamics simulations we could reproduce the experimental results. Systematic simulations allow to identify friction to be responsible for the pattern formation, that is, the tangential interaction between contacting particles and between the particles and the floor of the container. When particles are in contact with the floor and other adjacent particles simultaneously, there emerges a frustrated situation in which the particles are prevented from rolling on the floor. This effect leads to local jamming and eventually to stripe-like pattern formation. In the long time evolution, the stripes are unstable. Stripes may merge as well as disintegrate. © 2013 Springer-Verlag Berlin Heidelberg.}, author = {Krengel, Dominik and Strobl, Severin and Sack, Achim and Heckel, Michael and Pöschel, Thorsten}, doi = {10.1007/s10035-013-0411-2}, faupublication = {yes}, journal = {Granular Matter}, keywords = {Frustration effects; Horizontal shaking; Pattern formation}, pages = {377-387}, peerreviewed = {Yes}, title = {{Pattern} formation in a horizontally shaken granular submonolayer}, volume = {15}, year = {2013} } @article{faucris.110054824, abstract = {Numerical simulations of a dissipative hard sphere gas reveal a dependence of the cooling rate on correlation of the particle velocities due to inelastic collisions. We propose a coefficient which characterizes the velocity correlations in the two-particle velocity distribution function and express the temperature decay rate in terms of this coefficient. The analytical results are compared with numerics.}, author = {Pöschel, Thorsten and Brilliantov, Nikolai and Schwager, Thomas}, doi = {10.1142/S012918310200411X}, faupublication = {no}, journal = {International Journal of Modern Physics C}, keywords = {Dissipative gases; Granular gases; Kinetic gas theory; Many-particle systems; Velocity correlations}, pages = {1263-1272}, peerreviewed = {Yes}, title = {{Violation} of molecular chaos in dissipative gases}, volume = {13}, year = {2002} } @article{faucris.119197584, abstract = {The velocity distribution function of granular gases in the homogeneous cooling state as well as some heated granular gases decays for large velocities as fexp(-const×v). That is, its high-energy tail is overpopulated as compared with the Maxwell distribution. At the present time, there is no theory to describe the influence of the tail on the kinetic characteristics of granular gases. We develop an approach to quantify the overpopulated tail and analyze its impact on granular gas properties, in particular on the cooling coefficient. We observe and explain anomalously slow relaxation of the velocity distribution function to its steady state. © 2006 The American Physical Society.}, author = {Pöschel, Thorsten and Brilliantov, Nikolai V. and Formella, Arno}, doi = {10.1103/PhysRevE.74.041302}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Impact} of high-energy tails on granular gas properties}, volume = {74}, year = {2006} } @article{faucris.110308924, abstract = {We investigate jammed granular matter in a slowly rotating drum partially filled with granular material and find a state of polydirectional stability. In this state, the material responds elastically to small stresses in a wide angular interval while it responds by plastic deformation when subjected to small stresses outside this interval of directions. We describe the evolution of the granulate by means of a rate equation and find quantitative agreement with the experiment. The state of polydirectional stability complements the fragile state, where the material responds elastically to small applied stresses only in a certain direction but even very small stresses in any other direction would lead to plastic deformations. Similar to fragile matter, polydirectionally stable matter is created in a dynamic process by self-organization. © 2013 American Physical Society.}, author = {Zimber, Fabian and Kollmer, Jonathan and Pöschel, Thorsten}, doi = {10.1103/PhysRevLett.111.168003}, faupublication = {yes}, journal = {Physical Review Letters}, peerreviewed = {Yes}, title = {{Polydirectional} stability of granular matter}, volume = {111}, year = {2013} } @inproceedings{faucris.122137884, abstract = {We investigate the collective dissipative behavior of a model granular material (steel beads) when subjected to vibration. To this end, we study the attenuation of the amplitude of an oscillating leaf spring whose free end carries a rectangular box partly filled with granulate. To eliminate the perturbing influence of gravity, the experiment was performed under conditions of microgravity during parabolic flights. Different regimes of excitation could be distinguished, namely, a gas-like state of disordered particle motion and a state where the particles slosh back and forth between the container walls in a collective way, referred to as collect-and-collide regime. For the latter regime, we provide an expression for the container size leading to maximal dissipation of energy, that also marks the transition to the gas like regime. Also for systems driven at fixed amplitude and frequency, we find both the gas regime and the collect-and-collide regime resulting in similar dissipative behavior as in the case of the attenuating vibration. © 2013 AIP Publishing LL}, author = {Kollmer, Jonathan and Sack, Achim and Heckel, Michael and Zimber, Fabian and Müller, Patric and Bannerman, Marcus and Pöschel, Thorsten}, booktitle = {7th International Conference on Micromechanics of Granular Media: Powders and Grains 2013}, doi = {10.1063/1.4812055}, faupublication = {yes}, isbn = {9780735411661}, keywords = {damping; Granular material}, pages = {811-814}, peerreviewed = {Yes}, title = {{Collective} granular dynamics in a shaken container at low gravity conditions}, venue = {Sydney, NSW}, volume = {1542}, year = {2013} } @article{faucris.213926450, abstract = {The intensity of a monochromatic X-ray beam decreases exponentially with the distance it has traveled inside a material; this behavior is commonly referred to as Beer-Lambert's law. Knowledge of the material-specific attenuation coefficient mu allows us to determine the thickness of a sample from the intensity decrease the beam has experienced. However, classical X-ray tubes emit a polychromatic bremsstrahlung-spectrum. And the attenuation coefficients of all materials depend on the photon energy: photons with high energy are attenuated less than photons with low energy. In consequence, the X-ray spectrum changes while traveling through the medium; due to the relative increase in high energy photons, this effect is called beam hardening. For this varying spectrum, the Beer-Lambert law only remains valid if mu is replaced by an effective attenuation coefficient mu(eff) which depends not only on the material but also on its thickness x and the details of the X-ray setup used. We present here a way to deduce mu(eff)(x) from a small number of auxiliary measurements using a phenomenological model. This model can then be used to determine an unknown material thickness or in the case of a granular media its volume fraction. Published under license by AIP Publishing.}, author = {Baur, Manuel and Uhlmann, Norman and Pöschel, Thorsten and Schröter, Matthias}, doi = {10.1063/1.5080540}, faupublication = {yes}, journal = {Review of Scientific Instruments}, note = {CRIS-Team WoS Importer:2019-03-20}, peerreviewed = {Yes}, title = {{Correction} of beam hardening in {X}-ray radiograms}, volume = {90}, year = {2019} } @article{faucris.107686304, abstract = {We create nearly perfect centimetric spheres of water by splitting a cavity consisting of two metal hemispheres coated with a hydrophobic paint and under-filled with liquid, while releasing the apparatus in free-fall. A high-speed camera captures how water spread on hydrophobic aluminum and polycarbonate plates perforated with cylindrical capillaries. We compare observations at the ZARM drop tower in Bremen with Lattice-Boltzmann numerical simulations of Frank, Perré and Li for the inertial phase of imbibition.}, author = {Steub, Laura and Kollmer, Jonathan and Paxson, Derek and Sack, Achim and Pöschel, Thorsten and Bartlett, John and Berman, Douglas and Richardson, Yaateh and Louge, Michel Y.}, doi = {10.1051/epjconf/201714016001}, faupublication = {yes}, journal = {EPJ Web of Conferences}, peerreviewed = {unknown}, title = {{Microgravity} spreading of water spheres on {Hydrophobic} capillary plates}, volume = {140}, year = {2017} } @article{faucris.110047124, abstract = {The main precondition of simulating systems of hard particles by means of event-driven modeling is the assumption of instantaneous collisions. The aim of this paper is to quantify the deviation of event-driven modeling from the solution of Newton's equation of motion using a paradigmatic example: If a tennis ball is held above a basketball with their centers vertically aligned, and the balls are released to collide with the floor, the tennis ball may rebound at a surprisingly high speed. We show in this article that the simple textbook explanation of this effect is an oversimplification, even for the limit of perfectly elastic particles. Instead, there may occur a rather complex scenario including multiple collisions which may lead to a very different final velocity as compared with the velocity resulting from the oversimplified model. © 2011 American Physical Society.}, author = {Müller, Patric and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.83.041304}, faupublication = {yes}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Two}-ball problem revisited: {Limitations} of event-driven modeling}, volume = {83}, year = {2011} } @article{faucris.111557204, abstract = {We study actively rotating granular particles manufactured by rapid prototyping. Such particles, as introduced in Ref. [1], convert vibrational motion into rotational motion via tilted elastic legs in a circular arrangement at the bottom of the particle. We extend the original design of the particles to make them suitable for mass-fabrication via rapid prototyping. The rotational velocity is measured in dependence of the driving frequency and amplitude. We find two different regimes of motion. For small amplitudes the particle performs a slow and stable rotation, while above a certain threshold the particle starts to perform a precission and consequently rotates significantly faster.}, author = {Scholz, Christian and Pöschel, Thorsten}, faupublication = {yes}, journal = {Revista Cubana de Fisica }, pages = {37-38}, peerreviewed = {unknown}, title = {{Actively} rotating granular particles manufactured by rapid prototyping}, url = {http://www.mss.cbi.fau.de/content/uploads/granular_particles_revcubfis_2016.pdf}, volume = {33}, year = {2016} } @article{faucris.110045584, abstract = {A force-free granular gas was considered with an impact-velocity-dependent coefficient of restitution as it followed from the model of viscoelastic particles. Structural formation in this system was studied by means of three independent methods: event-driven molecular dynamics (MD), numerical solution of the hydrodynamic (HD) equations, and linear stability analysis of the HD equations. It was observed that cluster growth resulted in the decrease in gas density with time. It was found that structural formulation occurred in force-free granular gases only as a transient process.}, author = {Brilliantov, Nikolai V. and Salueña, Clara and Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1103/PhysRevLett.93.134301}, faupublication = {no}, journal = {Physical Review Letters}, peerreviewed = {Yes}, title = {{Transient} structures in a granular gas}, volume = {93}, year = {2004} } @incollection{faucris.218986811, abstract = {With increasing density of plasmas, non-ideality effects become more and more apparent. This is of particular importance for plasmas with deep bound states, that is, when the thermal energy is smaller than or of the same order as the ground state energies of the atoms in the plasma. For hydrogen this is the case already for T < 10

vibrational motion into rotation by frictional impact, are of scientific interest

since they could reveal various types of collective behavior. Looking at an

isolated Vibrot, we note at least two dierent dynamical modes, depending on the

parameters of the vibrational driving. By means of Finite Element simulations,

we reveal the driving mechanism for both cases which may be correspondingly

identified as ratcheting and tumbling. The transition between both modes

resembles period doubling in certain bouncing ball problems leading eventually

to chaotic motion in such systems.}, author = {Scholz, Christian and Dsilva, Sean and Pöschel, Thorsten}, doi = {10.1088/1367-2630/18/12/123001}, faupublication = {yes}, journal = {New Journal of Physics}, peerreviewed = {Yes}, title = {{Ratcheting} and tumbling motion of {Vibrots}}, volume = {18}, year = {2016} } @article{faucris.119643744, abstract = {Dense granular clusters often behave like macro-particles. We address this interesting phenomenon in a model system of inelastically colliding hard disks inside a circular box, driven by a thermal wall at zero gravity. Molecular dynamics simulations show a close-packed cluster of almost circular shape, weakly fluctuating in space and isolated from the driving wall by a low-density gas. The density profile of the system agrees very well with the azimuthally symmetric solution of granular hydrostatic equations employing constitutive relations by Grossman et al., whereas the widely used Enskog-type constitutive relations show poor accuracy. We find that fluctuations of the center of mass of the system are Gaussian. This suggests an effective Langevin description in terms of a macro-particle, confined by a harmonic potential and driven by delta-correlated noise. Surprisingly, the fluctuations persist when increasing the number of particles in the system. © 2007 Springer-Verlag.}, author = {Meerson, Baruch and Díez-Minguito, Manuel and Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1007/s10035-007-0055-1}, faupublication = {no}, journal = {Granular Matter}, keywords = {Granular cluster; Granular hydrodynamics; Strong fluctuations}, pages = {21-27}, peerreviewed = {Yes}, title = {{Close}-packed granular clusters: {Hydrostatics} and persistent {Gaussian} fluctuations}, volume = {10}, year = {2007} } @article{faucris.109923924, abstract = {The transmission of kinetic energy through chains of inelastically colliding spheres is investigated for the case of constant coefficient of restitution ε=const and impact-velocity-dependent coefficient ε(υ) for viscoelastic particles. We derive a theory for the optimal distribution of particle masses which maximize the energy transfer along the chain and check it numerically. We found that for ε=const, the mass distribution is a monotonous function which does not depend on the value of ε. In contrast, for ε(υ) the mass distribution reveals a pronounced maximum, depending on the particle properties and on the chain length. The system investigated demonstrates that even for small and simple systems, the velocity dependence of the coefficient of restitution may lead to new effects with respect to the same systems under the simplifying approximation ε=const. ©2001 The American Physical Society.}, author = {Pöschel, Thorsten and Brilliantov, Nikolai}, doi = {10.1103/PhysRevE.63.021505}, faupublication = {no}, journal = {Physical Review E}, pages = {1-9}, peerreviewed = {Yes}, title = {{Extremal} collision sequences of particles on a line: {Optimal} transmission of kinetic energy}, volume = {63}, year = {2001} } @article{faucris.109027644, abstract = {In [1] the rotational frequency of a single Vibrot was incorrectly plotted as a function

of the excitation amplitude A. Instead the figure shows the data in dependence of the

dimensionless acceleration Γ= A(2πƒD)2/g, where g is the gravitational acceleration.

Only in the case of ƒD = 50 Hz A = 0.13 mm corresponds to Γ = 1.3 g and vice versa.

The corresponding paragraph of the original manuscript must then be replaced by the

following: „Figure 4 shows ϖ vs. ƒD for two different values of the dimensionless

acceleration Γ = A(2πƒD)2/g. For a low Γ the particle performs slow rotation where

ƒD depends non-monotonously on the frequency characterized by a minimum at ƒD = 50

Hz. For large Γ, we observe slow rotation at low frequency and tumbling motion for

ƒD ≥ 30 Hz, where the rotational velocity decreases with increasing ƒD.“ The

corrected version of the plot is shown in Fig. 4.}, author = {Scholz, Christian and Pöschel, Thorsten}, faupublication = {yes}, journal = {Revista Cubana de Fisica }, peerreviewed = {unknown}, title = {{Erratum} to: {Actively} {Rotating} {Granular} {Particles} {Manufactured} by {Rapid} {Prototyping}}, volume = {33}, year = {2016} } @inproceedings{faucris.122077164, abstract = {We investigate collective dissipative properties of vibrated granular materials by means of molecular dynamics simulations. The rate of energy loss indicates three different phases in the amplitude-frequency plane of the external forcing, namely solid, convective and gas-like regimes. The behavior of the effective damping decrement is consistent with the glassy nature of granular solids. The gas-like regime is most promising for practical applications.}, author = {Salueña, Clara and Esipov, Sergei E. and Pöschel, Thorsten and Simonian, Stephan S.}, booktitle = {Smart Structures and Materials 2002: Damping and Isolation}, doi = {10.1117/12.310696}, editor = {Agnes G.S.}, faupublication = {no}, keywords = {Damping regimes; Molecular Dynamics simulations}, pages = {23-29}, title = {{Dissipative} properties of granular ensembles}, venue = {San Diego, CA}, volume = {3327}, year = {1998} } @article{faucris.109879044, abstract = {We consider the collision of a rough sphere with a plane by detailed analysis of the collision geometry. Using stochastic methods, the effective coefficient of restitution may be described as a fluctuating quantity whose probability density follows an asymmetric Laplace distribution. This result agrees with recent experiments by Montaine [Phys. Rev. E 84, 041306 (2011)]PLEEE81539-375510.1103/PhysRevE.84.041306. © 2014 American Physical Society.}, author = {Gunkelmann, Nina and Montaine, Marina and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.89.022205}, faupublication = {yes}, journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics}, peerreviewed = {Yes}, title = {{Stochastic} behavior of the coefficient of normal restitution}, volume = {89}, year = {2014} } @article{faucris.119744284, abstract = {In a granular gas of rough particles the axis of rotation is shown to be correlated with the translational velocity of the particles. The average relative orientation of angular and linear velocities depends on the parameters which characterize the dissipative nature of the collision. We derive a simple theory for these correlations and validate it with numerical simulations for a wide range of coefficients of normal and tangential restitution. The limit of smooth spheres is shown to be singular: even an arbitrarily small roughness of the particles gives rise to orientational correlations. © 2007 The American Physical Society.}, author = {Brilliantov, Nikolai V. and Pöschel, Thorsten and Kranz, W. T. and Zippelius, A.}, doi = {10.1103/PhysRevLett.98.128001}, faupublication = {no}, journal = {Physical Review Letters}, peerreviewed = {Yes}, title = {{Translations} and rotations are correlated in granular gases}, volume = {98}, year = {2007} } @article{faucris.109971664, abstract = {We report the first three-dimensional molecular dynamics simulation of particle segregation by shaking. Two different containers are considered: one cylindrical and another with periodic boundary conditions. The dependence of the time evolution of a test particle inside the material is studied as a function of the shaking frequency and amplitude, damping coefficients, and dispersivity.}, author = {Gallas, Jason A. and Herrmann, Hans J. and Pöschel, Thorsten and Sokolowski, Stefan}, doi = {10.1007/BF02189239}, faupublication = {no}, journal = {Journal of Statistical Physics}, keywords = {Granular dynamics; Granular materials; Molecular dynamics; Size segregation; Whale effect}, pages = {443-450}, peerreviewed = {Yes}, title = {{Molecular} dynamics simulation of size segregation in three dimensions}, volume = {82}, year = {1996} } @inproceedings{faucris.109930524, abstract = {Cohesive powders form agglomerates that can be very porous. Hence they are also very fragile. Consider a process of complete fragmentation on a characteristic length scale I, where the fragments are subsequently allowed to settle under gravity. If this fragmentation-reagglomeration cycle is repeated sufficiently often, the powder develops a fractal substructure with robust statistical properties. The structural evolution is discussed for two different models: The first one is an off-lattice model, in which a fragment does not stick to the surface of other fragments that have already settled, but rolls down until it finds a locally stable position. The second one is a simpler lattice model, in which a fragment sticks at first contact with the agglomerate of fragments that have already settled. Results for the fragment size distribution are shown as well. One can distinguish scale invariant dust and fragments of a characteristic size. Their role in the process of structure formation will be addressed. © 2009 American Institute of Physic}, author = {Wolf, D. E. and Pöschel, Thorsten and Schwager, T. and Weuster, A. and Brendel, L.}, booktitle = {6th International Conference on Micromechanics of Granular Media, Powders and Grains 2009}, doi = {10.1063/1.3180065}, faupublication = {yes}, isbn = {9780735406827}, keywords = {Fractals macroscopic aggregates; Granular systems; Pattern formation; Porous materials; Powders}, pages = {859-862}, title = {{Fractal} substructures due to fragmentation and reagglomeration}, venue = {Golden, CO}, volume = {1145}, year = {2009} } @article{faucris.122587124, abstract = {In a granular gas of rough particles the spin of a grain is correlated with its linear velocity. We develop an analytical theory to account for these correlations and compare its predictions to numerical simulations, using Direct Simulation Monte Carlo as well as Molecular Dynamics. The system is shown to relax from an arbitrary initial state to a steady-state, which is characterized by time-independent, finite correlations of spin and linear velocity. The latter are analyzed systematically for a wide range of system parameters, including the coefficients of tangential and normal restitution as well as the moment of inertia of the particles. For most parameter values the axis of rotation and the direction of linear momentum are perpendicular like in a sliced tennis ball, while parallel orientation, like in a rifled bullet, occurs only for a small range of parameters. The limit of smooth spheres is singular: any arbitrarily small roughness unavoidably causes significant translation-rotation correlations, whereas for perfectly smooth spheres the rotational degrees of freedom are completely decoupled from the dynamic evolution of the gas. © 2009 EDP Sciences and Springer.}, author = {Kranz, W. T. and Brilliantov, Nikolai V. and Pöschel, Thorsten and Zippelius, A.}, doi = {10.1140/epjst/e2010-01196-0}, faupublication = {yes}, journal = {European Physical Journal-Special Topics}, pages = {91-111}, peerreviewed = {Yes}, title = {{Correlation} of spin and velocity in the homogeneous cooling state of a granular gas of rough particles}, volume = {179}, year = {2009} } @article{faucris.107382044, abstract = {Biological organisms and artificial active particles self-organize into swarms and patterns. Open questions concern the design of emergent phenomena by choosing appropriate forms of activity and particle interactions. A particularly simple and versatile system are 3D-printed robots on a vibrating table that can perform self-propelled and self-spinning motion. Here we study a mixture of minimalistic clockwise and counter-clockwise rotating robots, called rotors. Our experiments show that rotors move collectively and exhibit super-diffusive interfacial motion and phase separate via spinodal decomposition. On long time scales, confinement favors symmetric demixing patterns. By mapping rotor motion on a Langevin equation with a constant driving torque and by comparison with computer simulations, we demonstrate that our macroscopic system is a form of active soft matter.}, author = {Scholz, Christian and Engel, Michael and Pöschel, Thorsten}, doi = {10.1038/s41467-018-03154-7}, faupublication = {yes}, journal = {Nature Communications}, pages = {931}, peerreviewed = {Yes}, title = {{Rotating} robots move collectively and self-organize.}, volume = {9}, year = {2018} } @article{faucris.109817224, abstract = {We report the experimental discovery of a remarkable organization of the set of self-generated periodic oscillations in the parameter space of a nonlinear electronic circuit. When control parameters are suitably tuned, the wave pattern complexity of the periodic oscillations is found to increase orderly without bound. Such complex patterns emerge forming self-similar discontinuous phases that combine in an artful way to produce large discontinuous spirals of stability. This unanticipated discrete accumulation of stability phases was detected experimentally and numerically in a Duffing-like proxy specially designed to bypass noisy spectra conspicuously present in driven oscillators. Discontinuous spirals organize the dynamics over extended parameter intervals around a focal point. They are useful to optimize locking into desired oscillatory modes and to control complex systems. The organization of oscillations into discontinuous spirals is expected to be generic for a class of nonlinear oscillators.}, author = {Sack, Achim and Freire, J. G. and Lindberg, Erik and Pöschel, Thorsten and Gallas, Jason}, doi = {10.1038/srep03350}, faupublication = {yes}, journal = {Scientific Reports}, peerreviewed = {Yes}, title = {{Discontinuous} spirals of stable periodic oscillations}, volume = {3}, year = {2013} } @article{faucris.118403604, abstract = {The velocity distribution in a homogeneously cooling granular gas has been studied in the viscoelastic regime, when the restitution coefficient of colliding particles depends on the impact velocity. We show that for viscoelastic particles a simple scaling hypothesis is violated, i.e., that the time dependence of the velocity distribution does not scale with the mean square velocity as in the case of particles interacting via a constant restitution coefficient. The deviation from the Maxwellian distribution does not depend on time monotonically. For the case of small dissipation we detected two regimes of evolution of the velocity distribution function: Starting from the initial Maxwellian distribution, the deviation first increases with time on a collision time scale saturating at some maximal value; then it decays to zero on a much larger time scale which corresponds to the temperature relaxation. For larger values of the dissipation parameter there appears an additional intermediate relaxation regime. Analytical calculations for small dissipation agree well with the results of a numerical analysis.}, author = {Brilliantov, Nikolai and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.61.5573}, faupublication = {no}, journal = {Physical Review E}, pages = {5573-5587}, peerreviewed = {Yes}, title = {{Velocity} distribution in granular gases of viscoelastic particles}, volume = {61}, year = {2000} } @article{faucris.122894684, abstract = {The coefficient of normal restitution of colliding viscoelastic spheres is computed as a function of the material properties and the impact velocity. From simple arguments it becomes clear that, in a collision of purely repulsively interacting particles, the particles lose contact slightly before the distance of the centers of the spheres reaches the sum of the radii, that is, the particles recover their shape only after they lose contact with their collision partner. This effect was neglected in earlier calculations, which leads erroneously to attractive forces and thus to an underestimation of the coefficient of restitution. As a result we find a different dependence of the coefficient of restitution on the impact rate. © 2008 The American Physical Society.}, author = {Schwager, Thomas and Pöschel, Thorsten}, doi = {10.1103/PhysRevE.78.051304}, faupublication = {no}, journal = {Physical Review E}, peerreviewed = {Yes}, title = {{Coefficient} of restitution for viscoelastic spheres: {The} effect of delayed recovery}, volume = {78}, year = {2008} }