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  • 1. Ghosh, A.K.
    et al.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Physics.
    Teitel, S.
    Vortex Line Ordering in the Driven Three-Dimensional Vortex Glass2006In: Physical Review Letters, Vol. 97, no 26, p. 267002-Article in journal (Refereed)
  • 2.
    Keta, Yann-Edwin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Département de Physique, École Normale Supérieure de Lyon,France; Département de Physique, Université Claude Bernard Lyon 1, France.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Translational and rotational velocities in shear-driven jamming of ellipsoidal particles2020In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 102, no 5, article id 052905Article in journal (Refereed)
    Abstract [en]

    We study shear-driven jamming of ellipsoidal particles at zero temperature with a focus on the microscopic dynamics. We find that a change from spherical particles to ellipsoids with aspect ratio alpha = 1.02 gives dramatic changes of the microscopic dynamics with much lower translational velocities and a new role for the rotations. Whereas the velocity difference at contacts-and thereby the dissipation-in collections of spheres is dominated by the translational velocities and reduced by the rotations, the same quantity is in collections of ellipsoids instead totally dominated by the rotational velocities. By also examining the effect of different aspect ratios we find that the examined quantities show either a peak or a change in slope at alpha approximate to 1.2, which thus gives evidence for a crossover between different regions of low and high aspect ratio.

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  • 3. Marschall, Theodore
    et al.
    Keta, Yann-Edwin
    Umeå University, Faculty of Science and Technology, Department of Physics. Département de Physique, École Normale Supérieure de Lyon, Lyon, France; Déepartement de Physique, Université Claude Bernard Lyon 1, Villeurbanne, France.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S.
    Orientational Ordering in Athermally Sheared, Aspherical, Frictionless Particles2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 18, article id 188002Article in journal (Refereed)
    Abstract [en]

    We numerically simulate the uniform athermal shearing of bidisperse, frictionless, two-dimensional spherocylinders and three-dimensional prolate ellipsoids. We focus on the orientational ordering of particles as an asphericity parameter α → 0 and particles approach spherical. We find that the nematic order parameter S2 is nonmonotonic in the packing fraction ϕ and that, as α → 0, S2 stays finite at jamming and above. The approach to spherical particles thus appears to be singular. We also find that sheared particles continue to rotate above jamming and that particle contacts preferentially lie along the narrowest width of the particles, even as α → 0.

  • 4.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Asymmetric velocity correlations in shearing media2010In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 82, no 3, p. 031303-Article in journal (Refereed)
    Abstract [en]

    A model of soft frictionless disks in two dimensions at zero temperature is  simulated with a shearing dynamics to study various kinds of asymmetries in  sheared systems. We examine both single particle properties, the spatial  velocity correlation function, and a correlation function designed to  separate clockwise and counter-clockwise rotational fields from one  another. Among the rich and interesting behaviors we find that the velocity  correlation along the two different diagonals corresponding to compression and  dilation, respectively, are almost identical and, furthermore, that a feature  in one of the correlation functions is directly related to irreversible  plastic events.

  • 5.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Depinning of the Bragg glass in a point disordered model superconductor2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 9, article id 097001Article in journal (Refereed)
    Abstract [en]

    We perform simulations of the three-dimensional frustrated anisotropic XY model with point disorder as a model of a type-II superconductor with quenched point pinning in a magnetic field and a weak applied current. Using resistively shunted junction dynamics, we find a critical current Ic that separates a creep region with immeasurably low voltage from a region with a voltage V∝(I−Ic) and also identify the mechanism behind this behavior. It also turns out that data at fixed disorder strength may be collapsed by plotting V versus TI, where T is the temperature, though the reason for this behavior as yet not is fully understood.

  • 6.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Diffusion and velocity auto-correlation at the jamming transition2010In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 81, no 4, p. 040301-Article in journal (Refereed)
    Abstract [en]

    We perform numerical simulations to examine particle diffusion at steady shear  in a soft-disk model in two dimensions and zero temperature around the jamming  density. We find that the diffusion constant depends on shear rate as  D\sim\dot\gamma below jamming and as D\sim\dot\gamma^{q_D} with q_D<1 at the  transition, and set out to relate this to properties of the velocity  auto-correlation function. It is found that this correlation function is  governed by two processes with different time scales. The first time scale,  the inverse of the externally applied shear rate, controls an exponential  decay of the correlations whereas the second time scale, equal to the inverse  shear stress, governs an algebraic decay with time. The obtained value of  q_D is related to these properties of the correlation function.

  • 7.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dimensionality and Viscosity Exponent in Shear-driven Jamming2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 10, article id 108003Article in journal (Refereed)
    Abstract [en]

    Collections of bidisperse frictionless particles at zero temperature in three dimensions are simulated with a shear-driven dynamics with the aim to compare with the behavior in two dimensions. Contrary to the prevailing picture, and in contrast to results from isotropic jamming from compression or quench, we find that the critical exponents in three dimensions are different from those in two dimensions and conclude that shear-driven jamming in two and three dimensions belong to different universality classes.

  • 8.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dissipation and velocity distribution at the shear-driven jamming transition2016In: Physical Review E, ISSN 2470-0045, Vol. 93, no 4, article id 042614Article in journal (Refereed)
    Abstract [en]

    We investigate energy dissipation and the distribution of particle velocities at the jamming transition for overdamped shear-driven frictionless disks in two dimensions at zero temperature. We find that the dissipation is caused by the fastest particles and that the fraction of particles responsible for the dissipation decreases towards zero as jamming is approached. These particles belong to an algebraic tail of the velocity distribution that approaches similar to v(-3) as jamming is approached. We further find that different measures of the velocity diverge differently, which means that concepts such as typical velocity may no longer be used, a finding that should have implications for analytical approaches to shear-driven jamming.

  • 9.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Relaxation times and rheology in dense athermal suspensions2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 91, no 6, article id 062209Article in journal (Refereed)
    Abstract [en]

    We study the jamming transition in a model of elastic particles under shear at zero temperature. The key quantity is the relaxation time tau which is obtained by stopping the shearing and letting energy and pressure decay to zero. At many different densities and initial shear rates we do several such relaxations to determine the average tau. We establish that tau diverges with the same exponent as the viscosity and determine another exponent from the relation between tau and the coordination number. Though most of the simulations are done for the model with dissipation due to the motion of particles relative to an affinely shearing substrate, we also examine a model, where the dissipation is instead due to velocity differences of disks in contact, and confirm that the above-mentioned exponent is the same for these two models. We also consider finite size effects on both tau and the coordination number.

  • 10.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Relaxation times, rheology, and finite size effects for non-Brownian disks in two dimensions2022In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 105, no 3, article id 034902Article in journal (Refereed)
    Abstract [en]

    We carry out overdamped simulations in a simple model of jamming - a collection of bidisperse soft core frictionless disks in two dimensions - with the aim to explore the finite size dependence of different quantities, both the relaxation time obtained from the relaxation of the energy and the pressure equivalent of the shear viscosity. The motivation for the paper is the observation [Nishikawa, J. Stat. Phys. 182, 37 (2021) 10.1007/s10955-021-02710-8] that there are finite size effects in the relaxation time, τ, that give problems in the determination of the critical divergence, and the claim that this is due to a finite size dependence, τ∼lnN, which makes τ an ill-defined quantity. Beside analyses to determine the relaxation time for the whole system we determine particle relaxation times which allow us to determine both histograms of particle relaxation times and the average particle relaxation times - two quantities that are very useful for the analyses. The starting configurations for the relaxation simulations are of two different kinds - completely random or taken from steady shearing simulations - and we find that the difference between these two cases are bigger than previously noted and that the observed problems in the determination of the critical divergence obtained when starting from random configurations are not present when instead starting the relaxations from shearing configurations. We also argue that the the effect that causes the lnN dependence is not as problematic as asserted. When it comes to the finite size dependence of the pressure equivalent of the shear viscosity we find that our data don't give support for the claimed strong finite size dependence, but also that the finite size dependence is at odds with what one would normally expect for a system with a diverging correlation length, and that this calls for an alternative understanding of the phenomenon of shear-driven jamming.

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  • 11.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Slow and fast particles in shear-driven jamming: critical behavior2023In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 108, no 2, article id 024904Article in journal (Refereed)
    Abstract [en]

    We do extensive simulations of a simple model of shear-driven jamming in two dimensions to determine and analyze the velocity distribution at different densities φ around the jamming density φJ and at different low shear strain rates, γ˙. We then find that the velocity distribution is made up of two parts which are related to two different physical processes which we call the slow process and the fast process as they are dominated by the slower and the faster particles, respectively. Earlier scaling analyses have shown that the shear viscosity η, which diverges as the jamming density is approached from below, consists of two different terms, and we present strong evidence that these terms are related to the two different processes: the leading divergence is due to the fast process, whereas the correction-to-scaling term is due to the slow process. The analysis of the slow process is possible thanks to the observation that the velocity distribution for different γ˙ and φ at and around the shear-driven jamming transition has a peak at low velocities and that the distribution has a constant shape up to and slightly above this peak. We then find that it is possible to express the contribution to the shear viscosity due to the slow process in terms of height and position of the peak in the velocity distribution and find that this contribution matches the correction-to-scaling term, determined through a standard critical scaling analysis. A further observation is that the collective particle motion is dominated by the slow process. In contrast to the usual picture in critical phenomena with a direct link between the diverging correlation length and a diverging order parameter, we find that correlations and shear viscosity decouple since they are controlled by different sets of particles and that shear-driven jamming is thus an unusual kind of critical phenomenon.

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  • 12.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vortex fluctuations in superconductors1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The vortex fluctuations have proved to be responsible for the onset of dissipation in thin type-II superconducting Aims. There is also growing evidence that dissipation in high- temperature superconductors exhibits the same kind of two-dimensional (2D) behavior. However, a proper analysis of these materials requires a thorough understanding of the two-dimensional fluctuations.

    This thesis may be considered to consist of two parts. The first is concerned with two models that have often been used as models for 2D superconductors, the 2D Coulomb gas and the 2D XY model. The second part contains analyses related to high-temperature sup er conductivity.

    Through analysis of some renormalization equations for the Kosterlitz-Thouless (KT) transition, it is shown that the region governed by the KT critical behavior is very small and only applies at very low values for the flux-flow resistance. It is concluded that this critical behavior not is observable in superconductors, and, furthermore, that the only available method to test for 2D fluctuations at the onset of resistance, is through comparison with the 2D resistance scaling function.

    The critical temperature for the 2D XY model is determined by means of a finite- size scaling relation for the helicity modulus. The linearly screened potential in the XY model is written in terms of a correlation function. The analogy to the 2D Coulomb gas is found to be exact with a temperature-dependent bare interaction and a new expression for vorticity. It is also demonstrated that the Coulomb gas scaling concept may be applied to XY-type models.

    An analysis of resistance data for YBCO/PBCO superlattices in terms of the 2D resistance scaling function gives evidence for 2D behavior in the cases with large separation of the superconducting layers. In the superlattices with stronger interlayer coupling, the crossover to three-dimensional behavior is seen as a deviation from the scaling function as Tc is approached from above.

    The anisotropic three-dimensional (3D) XY model is examined as a model for high- temperature superconductors. It is shown that the density of vortices above Tc are closely equal in the anisotropic 3D model and the 2D model. This is taken as evidence that the 3D to 2D crossover found in the superlattices also is present in the anisotropic 3D XY model.

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  • 13.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Physics.
    Vortex glass transitions in disordered three-dimensional XY models: Simulations for several different sets of parameters2005In: Physical Review B, Vol. 72, no 14, p. 144525-Article in journal (Refereed)
  • 14.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S
    Athermal jamming versus thermalized glassiness in sheared frictionless particles2013In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 88, no 1, p. 010301-Article in journal (Refereed)
    Abstract [en]

    Numerical simulations of soft-core frictionless disks in two dimensions are carried out to study the behavior of a simple liquid as a function of temperature T, packing fraction phi, and uniform applied shear strain rate (gamma) over dot. Inferring the hard-core limit from our soft-core results, we find that it depends on the two parameters phi and T/(gamma) over dot. Here T/(gamma) over dot -> 0 defines the athermal limit in which a shear-driven jamming transition occurs at a well defined phi(J) and T/(gamma) over dot -> infinity defines the thermalized limit where an equilibrium glass transition may take place at phi(G). This conclusion argues that athermal jamming and equilibrium glassy behavior are not controlled by the same critical point. Preliminary results suggest phi(G) < phi(J).

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  • 15.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Teitel, S.
    Comment on "effects of point defects on the phase diagram of vortex states in high-Tc superconductors in the Bc axis"2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Physical Review Letters, Vol. 94, no 21, p. 219703-Article in journal (Refereed)
  • 16.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S
    Critical Scaling of Shearing Rheology at the Jamming Transition of Soft-Core Frictionless Disks2011In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 83, p. 030302-Article in journal (Refereed)
    Abstract [en]

    We perform numerical simulations to determine the shear stress and pressure of steady-state shear flow in a soft-disk model in two dimensions at zero temperature in the vicinity of the jamming transition ϕJ. We use critical point scaling analyses to determine the critical behavior at jamming, and we find that it is crucial to include corrections to scaling for a reliable analysis. We find that the relative size of these corrections are much smaller for pressure than for shear stress. We furthermore find a superlinear behavior for pressure and shear stress above ϕJ, both from the scaling analysis and from a direct analysis of pressure data extrapolated to the limit of vanishing shear rate.

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  • 17.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S.
    Dynamic length scales in athermal, shear-driven jamming of frictionless disks in two dimensions2020In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 102, no 4, article id 042906Article in journal (Refereed)
    Abstract [en]

    We carry out numerical simulations of athermally sheared, bidisperse, frictionless disks in two dimensions. From an appropriately defined velocity correlation function, we determine that there are two diverging length scales, xi and l, as the jamming transition is approached. We analyze our results using a critical scaling ansatz for the correlation function and argue that the more divergent length l is a consequence of a dangerous irrelevant scaling variable and that it is xi, which is the correlation length that determines the divergence of the system viscosity as jamming is approached from below in the liquid phase. We find that xi similar to (phi(J) - phi)(-v) diverges with the critical exponent v = 1. We provide evidence that xi measures the length scale of fluctuations in the rotation of the particle velocity field, while l measures the length scale of fluctuations in the divergence of the velocity field.

  • 18.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S.
    Herschel-bulkley shearing rheology near the athermal jamming transition2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 10, p. 108001-Article in journal (Refereed)
    Abstract [en]

    We consider the rheology of soft-core frictionless disks in two dimensions in the neighborhood of the athermal jamming transition. From numerical simulations of bidisperse, overdamped particles, we argue that the divergence of the viscosity below jamming is characteristic of the hard-core limit, independent of the particular soft-core interaction. We develop a mapping from soft-core to hard-core particles that recovers all the critical behavior found in earlier scaling analyses. Using this mapping we derive a relation that gives the exponent of the nonlinear Herschel-Bulkley rheology above jamming in terms of the exponent of the diverging viscosity below jamming.

  • 19.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Teitel, S.
    Kink-antikink unbinding transition in the two-dimensional fully frustrated XY model2005In: Physical Review B, Vol. 71, no 10, p. 104423-Article in journal (Refereed)
  • 20.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, Stephen
    Critical scaling of shear viscosity at the jamming transition2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 17, article id 178001Article in journal (Refereed)
    Abstract [en]

    We carry out numerical simulations to study transport behavior about the jamming transition of a model granular material in two dimensions at zero temperature. Shear viscosity η is computed as a function of particle volume density ρ and applied shear stress σ, for diffusively moving particles with a soft core interaction. We find an excellent scaling collapse of our data as a function of the scaling variable σ/|ρc−ρ|Δ, where ρc is the critical density at σ=0 ("point J"), and Δ is the crossover scaling critical exponent. We define a correlation length ξ from velocity correlations in the driven steady state and show that it diverges at point J. Our results support the assertion that jamming is a true second-order critical phenomenon.

  • 21.
    Olsson, Peter
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Teitel, Stephen
    University of Rochester, Rochester, NY.
    Unified Phase Diagram for the Three-Dimensional XY Model of a Point    Disordered Type-II Superconductor2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 21, p. 214503-Article in journal (Refereed)
    Abstract [en]

    We carry out extensive Monte Carlo simulations of the three-dimensional uniformly frustrated XY model with uncorrelated randomly perturbed couplings, as a model for the equilibrium behavior of an extreme type-II superconductor with quenched uncorrelated random point vortex pinning, in the presence of a uniform applied magnetic field. We map out the resulting phase diagram as a function of temperature T and pinning strength p for a fixed value of the vortex line density. At low p we find a sharp first-order vortex lattice melting phase boundary separating a vortex lattice from a vortex liquid. As p increases, it appears that this first-order transition smears out over a finite temperature interval due to the effects of the random pinning, in agreement with several recent experiments. At large p we find a second-order transition from vortex liquid to vortex glass.

  • 22. Vagberg, Daniel
    et al.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S.
    Shear banding, discontinuous shear thickening, and rheological phase transitions in athermally sheared frictionless disks2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 95, no 5, article id 052903Article in journal (Refereed)
    Abstract [en]

    We report on numerical simulations of simple models of athermal, bidisperse, soft-core, massive disks in two dimensions, as a function of packing fraction phi, inelasticity of collisions as measured by a parameter Q, and applied uniform shear strain rate (gamma) over dot. Our particles have contact interactions consisting of normally directed elastic repulsion and viscous dissipation, as well as tangentially directed viscous dissipation, but no interparticle Coulombic friction. Mapping the phase diagram in the (phi, Q) plane for small (gamma) over dot, we find a sharp first-order rheological phase transition from a region with Bagnoldian rheology to a region with Newtonian rheology, and show that the system is always Newtonian at jamming. We consider the rotational motion of particles and demonstrate the crucial importance that the coupling between rotational and translational degrees of freedom has on the phase structure at small Q (strongly inelastic collisions). At small Q, we show that, upon increasing (gamma) over dot, the sharp Bagnoldian-to-Newtonian transition becomes a coexistence region of finite width in the (phi,(gamma) over dot) plane, with coexisting Bagnoldian and Newtonian shear bands. Crossing this coexistence region by increasing (gamma) over dot at fixed phi, we find that discontinuous shear thickening can result if (gamma) over dot is varied too rapidly for the system to relax to the shear-banded steady state corresponding to the instantaneous value of (gamma) over dot.

  • 23. Varnik, Fathollah
    et al.
    Mandal, Suvendu
    Chikkadi, Vijaykumar
    Denisov, Dmitry
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Vågberg, Daniel
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Raabe, Dierk
    Schall, Peter
    Correlations of plasticity in sheared glasses2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 89, no 4, p. 040301-Article in journal (Refereed)
    Abstract [en]

    In a recent paper [Mandal et al., Phys. Rev. E 88, 022129 (2013)], the nature of spatial correlations of plasticity in hard-sphere glasses was addressed both via computer simulations and in experiments. It was found that the experimentally obtained correlations obey a power law, whereas the correlations from simulations are better fitted by an exponential decay. We here provide direct evidence-via simulations of a hard-sphere glass in two dimensions (2D)-that this discrepancy is a consequence of the finite system size in the 3D simulations. By extending the study to a 2D soft disk model at zero temperature [Durian, Phys. Rev. Lett. 75, 4780 (1995)], the robustness of the power-law decay in sheared amorphous solids is underlined. Deviations from a power law occur when either reducing the packing fraction towards the supercooled regime in the case of hard spheres or changing the dissipation mechanism from contact dissipation to a mean-field-type drag in the case of soft disks.

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  • 24.
    Vågberg, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    S., Teitel
    University of Rochester, Rochester NY 14627 USA.
    Dissipation and Rheology of Sheared Soft-Core Frictionless Disks Below Jamming2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 112, no 20, article id 208303Article in journal (Refereed)
    Abstract [en]

    We use numerical simulations to investigate the effect that different models of energy dissipation have on the rheology of soft-core frictionless disks, below jamming in two dimensions. We find that it is not necessarily the mass of the particles that determines whether a system has Bagnoldian or Newtonian rheology, but rather the presence or absence of large connected clusters of particles. We demonstrate the key role that tangential dissipation plays in the formation of such clusters and in several models find a transition from Bagnoldian to Newtonian rheology as the packing fraction. is varied. For each model, we show that appropriately scaled rheology curves approach a well defined limit as the mass of the particles decreases and collisions become strongly inelastic.

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  • 25.
    Vågberg, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    S., Teitel
    University of Rochester, Rochester NY 14627 USA.
    Universality of Jamming Criticality in Overdamped Shear-Driven Frictionless Disks2014In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 113, no 14, article id 148002Article in journal (Refereed)
    Abstract [en]

    We investigate the criticality of the jamming transition for overdamped shear-driven frictionless disks in two dimensions for two different models of energy dissipation: (i) Durian’s bubble model with dissipation proportional to the velocity difference of particles in contact, and (ii) Durian’s “mean-field” approximation to (i), with dissipation due to the velocity difference between the particle and the average uniform shear flow velocity. By considering the finite-size behavior of pressure, the pressure analog of viscosity, and the macroscopic friction σ/p  , we argue that these two models share the same critical behavior.

  • 26. Vågberg, Daniel
    et al.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S.
    Critical scaling of Bagnold rheology at the jamming transition of frictionless two-dimensional disks2016In: Physical Review E, ISSN 2470-0045, Vol. 93, no 5, article id 052902Article in journal (Refereed)
    Abstract [en]

    We carry out constant volume simulations of steady-state shear-driven rheology in a simple model of bidisperse soft-core frictionless disks in two dimensions, using a dissipation law that gives rise to Bagnoldian rheology. We discuss in detail the critical scaling ansatz for the shear-driven jamming transition and carry out a detailed scaling analysis of our resulting data for pressure p and shear stress sigma. Our analysis determines the critical exponent beta that describes the algebraic divergence of the Bagnold transport coefficients lim((gamma) over dot -> 0) p/(gamma) over dot(2), sigma/(gamma) over dot(2) similar to (phi(J) -phi)(-beta) as the jamming transition phi(J) is approached from below. For the low strain rates considered in this work, we show that it is still necessary to consider the leading correction-to-scaling term in order to achieve a self-consistent analysis of our data, in which the critical parameters become independent of the size of the window of data used in the analysis. We compare our resulting value beta approximate to 5.0 +/- 0.4 against previous numerical results and competing theoretical models. Our results confirm that the shear-driven jamming transition in Bagnoldian systems is well described by a critical scaling theory and we relate this scaling theory to the phenomenological constituent laws for dilatancy and friction.

  • 27. Vågberg, Daniel
    et al.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S.
    Effect of collisional elasticity on the Bagnold rheology of sheared frictionless two-dimensional disks2017In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 95, no 1, article id 012902Article in journal (Refereed)
    Abstract [en]

    We carry out constant volume simulations of steady-state, shear-driven flow in a simple model of athermal, bidisperse, soft-core, frictionless disks in two dimensions, using a dissipation law that gives rise to Bagnoldian rheology. Focusing on the small strain rate limit, we map out the rheological behavior as a function of particle packing fraction phi and a parameter Q that measures the elasticity of binary particle collisions. We find a Q*(phi) that marks the clear crossover from a region characteristic of strongly inelastic collisions, Q < Q*, to a region characteristic of weakly inelastic collisions, Q > Q*, and give evidence that Q*(phi) diverges as phi -> phi(J), the shear-driven jamming transition. We thus conclude that the jamming transition at any value of Q behaves the same as the strongly inelastic case, provided one is sufficiently close to fJ. We further characterize the differing nature of collisions in the strongly inelastic vs weakly inelastic regions, and recast our results into the constitutive equation form commonly used in discussions of hard granular matter.

  • 28.
    Vågberg, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, Stephen
    Dept of Phys and Astr, Univ of Rochester, Rochester, NY14627.
    Glassiness, Rigidity, and Jamming of Frictionless Soft Core Disks2011In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 83, no 3, p. 031307-Article in journal (Refereed)
    Abstract [en]

    The jamming of bidisperse soft core disks is considered, using a variety of different protocols to produce the jammed state. In agreement with other works, we find that cooling and compression can lead to a broad range of jamming packing fractions ϕJ, depending on cooling rate and initial configuration; the larger the degree of big particle clustering in the initial configuration, the larger will be the value of ϕJ. In contrast, we find that shearing disrupts particle clustering, leading to a much narrower range of ϕJ as the shear strain rate varies. In the limit of vanishingly small shear strain rate, we find a unique nontrivial value for the jamming density that is independent of the initial system configuration. We conclude that shear driven jamming is a unique and well-defined critical point in the space of shear driven steady states. We clarify the relation between glassy behavior, rigidity, and jamming in such systems and relate our results to recent experiments.

    Download full text (pdf)
    PhysRevE.83.031307
  • 29.
    Vågberg, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Valdez-Balderas, Daniel
    Dept of Phys and Astr, Univ of Rochester, Rochester, NY14627.
    Moore, M. A.
    School of Phys and Astr, The Univ of Manchester, Manchester M13 9PL, UK.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, Stephen
    Dept of Phys and Astr, Univ of Rochester, Rochester, NY14627.
    Finite-Size Scaling at the Jamming Transition: Corrections to Scaling and the Correlation-Length Critical Exponent2011In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 83, no 3, p. 030303-Article in journal (Refereed)
    Abstract [en]

    We carry out a finite-size scaling analysis of the jamming transition in frictionless bidisperse soft core disks in two dimensions. We consider two different jamming protocols: (i) quench from random initial positions and (ii) quasistatic shearing. By considering the fraction of jammed states as a function of packing fraction for systems with different numbers of particles, we determine the spatial correlation length critical exponent ν≈1 and show that corrections to scaling are crucial for analyzing the data. We show that earlier numerical results yielding ν<1 are due to the improper neglect of these corrections.

    Download full text (pdf)
    fulltext
  • 30.
    Vågberg, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wu, Yegang
    University of Rochester, USA.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, Stephen
    University of Rochester, USA.
    Pressure distribution and critical exponent in statically jammed and shear-driven frictionless disks2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 89, no 2, p. 022201-Article in journal (Refereed)
    Abstract [en]

    We numerically study the distributions of global pressure that are found in ensembles of statically jammed and quasistatically sheared systems of bidisperse, frictionless disks at fixed packing fraction phi in two dimensions. We use these distributions to address the question of how pressure increases as phi increases above the jamming point phi(J), p similar to |phi - phi(J) |(y). For statically jammed ensembles, our results are consistent with the exponent y being simply related to the power law of the interparticle soft-core interaction. For sheared systems, however, the value of y is consistent with a nontrivial value, as found previously in rheological simulations.

    Download full text (pdf)
    fulltext
  • 31. Wu, Yegang
    et al.
    Olsson, Peter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Teitel, S
    Search for hyperuniformity in mechanically stable packings of frictionless disks above jamming2015In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, no 5, article id 052206Article in journal (Refereed)
    Abstract [en]

    We numerically simulate mechanically stable packings of soft-core, frictionless, bidisperse disks in two dimensions, above the jamming packing fraction phi(J). For configurations with a fixed isotropic global stress tensor, we investigate the fluctuations of the local packing fraction phi(r) to test whether such configurations display the hyperuniformity that has been claimed to exist exactly at phi(J). For our configurations, generated by a rapid quench protocol, we find that hyperuniformity persists only out to a finite length scale and that this length scale appears to remain finite as the system stress decreases towards zero, i.e., towards the jamming transition. Our result suggests that the presence of hyperuniformity at jamming may be sensitive to the specific protocol used to construct the jammed configurations.

1 - 31 of 31
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