Nonequilibrium Dynamics in Astrophysics and Material Science
October 31–November 3, 2011, Yukawa Institute, Kyoto, Japan
University of Colorado
Invited, October 31, 11:00–12:10, Presentation File
Tightly collimated jets of plasma are formed under wide-ranging astrophysical conditions where a disc of rotating gas spirals into a gravitational potential well. They are believed to be propelled by large-scale electromagnetic fields and, when they form close to black holes, their speeds can approach to within a tiny fraction of the speed of light.
I will discuss the basic physical principles that regulate the acceleration of astrophysical jets, their collimation, and the processes by which they convert energy among different forms. Jets are subject to instabilities driven by electrical currents and shear, and to lateral expansion that can lead to loss of causal connection with their surroundings and strong recollimation shocks. The dissipation associated with these processes can make jets luminous objects that are readily studied observationally.
Sophia University
Invited, October 31, 13:30–14:40, Presentation File
Heavy ion collision experiments have been performed at Brookhaven National Laboratory and CERN towards understanding of the quark gluon plasma (QGP), namely the matter at extremely high-temperature (~1012 K). Contrary to experiments in condensed matter physics, one cannot control temperature and/or pressure of the QGP in heavy ion collisions as it dynamically evolves only for ~10−22 seconds. Thus, dynamical framework such as relativistic hydrodynamics has been used to describe space-time evolution of the QGP in heavy ion collisions. In this talk, after a brief introduction, I discuss relativistic hydrodynamic approach to the physics of the QGP and related topics from non-equilibrium dynamics point of view.
Kyoto University
Contributed, October 31, 14:40–15:05, Presentation File
We apply the so called renormalization-group method to derive the first and seconde order equations both for non-relativistic and relativistic systems. Our derivation in the first-order level naturally leads to Navier-Stokes and Landau-Lifshitz equations in the energy frame for the non-relativistic and relativistic cases, respectively; we obtain a relativistic equation that is stable in the particle frame, in contrast to the known equations in the literature. We also derive second-order equations both for non-relativistic and relativistic cases, which have new additional terms with a vorticity. On the basis of the results, we propose a proper ansatz to be taken in the Maxwell-Grad 14 (13) moment method in the (non-)relativistic case.
University of Chicago
Invited, October 31, 15:30–16:40, Presentation File
Children are taught that liquids are an intermediate state of matter: they flow easily, much as gases do, yet, like solids, hold themselves together in a condensed state due to inter-particle attractions. Later they may learn that liquids can be simulated without attractions if the density of the system is kept high by confinement. Unexpectedly, even with no attractions or confinement, a system of particles can collectively respond like a liquid — a high-density jet of non-cohesive granular particles hitting a target ejects particles in a thin sheet similar to water bells created when water jets hit a target. This similar outcome in two dissimilar systems raises the possibility that highly collimated ejecta is a generic outcome of dense particulate stream impact, one independent of precise microscopic interactions. Here I describe results on granular jets from experiment, simulation and continuum modeling that show collimated ejecta emerging regardless of whether the internal state is static or flowing.
Our result implies that characterization techniques based on scattering of dilute particulate streams cannot be extended to high density. This calls into question recent efforts to interpret collimation in the scattering pattern generated by gold-ion collisions at the Relativistic Heavy Ion Collider as evidence for a liquid phase in the quark-gluon plasma. Second, an interior dead zone with highly collimated ejecta have also been observed in impact experiments using cohesive silica aggregates. This regime of impact sheds light on the formation of planetesimals. Thus our results may provide a framework for thinking about impact in this, more complex circumstances as well.
This is a joint work with Herve Turlier, Nicholas Guttenberg, Jake Ellowitz and Sidney R. Nagel.
Cornell University
Invited, November 1, 9:15–10:25, Presentation File
According to ground-based and space-based observations (infrared spectroscopy and images, plus occultations at ultraviolet, infrared and radio wavelengths), planetary rings are highly flattened disks of innumerable particles that orbit the outer planets within a few planetary radii; particle sizes range in a power law from microns to tens of meters. Our understanding of planetary rings should improve through further theoretical scrutiny by specialists in granular dynamics.
After first describing the ongoing Cassini mission — circling Saturn since July 2004 — I review what its observations reveal about Saturn’s rings, emphasizing their granular nature and their dynamical interactions with neighboring moons. Mutual self-gravity attempts to aggregate this array of particles but planetary tides frustrate this attempt; instead “self-gravity wakes”, localized but temporary concentrations of particles, occur. In-plane density and vertical bending waves are found travelling through the rings after being initiated at resonant locations where particle orbit periods are fractional multiples of the orbital periods of a nearby satellite. The ring’s mechanical properties determine the waves’ propagation profile. These waves transfer angular momentum between the particulate disk and the satellites; in a few places, this transfer opens gaps, whose perimeters display complex undulations. Saturn’s remarkably thin rings thicken (“vertically splash”) at a few ring edges, near strong resonances and around embedded objects. Numerous “propellers”, features with characteristic shapes of two dashes, likely signal the presence of embedded masses that have sizes from tens of meters to about a kilometer. These bodies have a steeper size distribution and reside primarily in the outer ring regions. The largest of these objects moves along a non-Keplerian orbit perhaps driven by interactions with the surrounding disk. Vertical corrugations and “straw” are found in other ring locales. A handful of ring-moons that lie in, and just exterior to, the ring edge have very low densities and saucer-like shapes that suggest gravitational aggregation of granular materials. Some features in Saturn’s rings, as well as in Uranus’s rings, can be understood as ice-floe-like locking of granular solids.
This research derives from the efforts of many engineers and scientists on the Cassini mission. I especially thank my Cornell colleagues Matthew M. Hedman and Matthew S. Tiscareno for their assistance in the preparation of this presentation.
University of Potsdam
Invited, November 1, 10:50–12:00, Presentation File
Planetary rings are ensembles of particles that collectively evolve in a given circumplanetary environment. In the solar system a large variety of rings systems are found around all the giant planets, ranging from dusty rings formed by micron-sized grains to dense rings consisting of meter-sized bodies. For the dust rings physical collisions of particles generally play a minor role, if any, while non-gravitational forces like electromagnetic forces, solar radiation pressure, and possibly the interaction with ambient plasma can be important. In contrast, in dense rings physical collisions and the self-gravity of ring particles are key dynamical processes. In this talk I will briefly touch the physics of dust rings but will then focus mainly on dense rings. I will discuss general aspects like the energy and angular momentum budget of the collisional dynamics in the central gravity field and give a more focused overview on processes of structure formation in the rings.
Kobe University
Invited, November 1, 13:30–14:40, Presentation File
I will review dynamical studies on velocity dispersion and spins of ring particles, and viscosity in planetary rings. Ring particles orbit about the central planet, but they experience collision and gravitational interaction with other particles. As a result, their orbits become inclined and non-circular. Velocity dispersion of ring particles is determined by a balance between gravitational interaction and inelastic collisions. When the orbits of particles are close to the planet and/or their internal density is low, mutual gravity between particles can be neglected and the velocity dispersion is determined by inelastic collisions. When the effect of gravity becomes important, velocity dispersion is determined by gravitational two-body encounters between particles in dilute rings, while in dense rings so-called gravitational wakes are formed and the collective effect of the ring as a self-gravitating disk becomes important. In rings with a particle size distribution, the velocity dispersion of smaller particles generally exceeds that of larger particles, implying a larger vertical scale height for small particles. For dilute rings this was shown by solving the evolution equation for the velocity dispersion. On the other hand, actual ring particles should have rough and irregular surfaces, and an oblique impact between these particles lead to rotation. In the case with particles size distribution, the spin period was found to be roughly proportional to the particle size. Rapidly spinning small particles have larger orbital inclinations than slowly spinning large particles, thus the ring particles’ rotational states have vertical heterogeneity. The spin axes of slowly spinning large particles tend to be aligned normally to the ring plane, while the small particles’ spin axes are nearly randomly distributed. Finally, in planetary rings, angular momentum transport is caused by collisions and gravitational interactions between particles, and the rate of the transport is expressed in terms of viscosity. In dilute rings, viscosity can be expressed by particles’ velocity dispersion and is proportional to the surface density of the ring, while the dependence of the viscosity on surface density becomes stronger in dense self-gravitating rings, where angular momentum is transferred by interactions between gravitational wakes.
University of Oulu
Invited, November 1, 14:40–15:50, Presentation File
In local scale, the energy balance in planetary rings is governed by the collisional dissipation and the viscous gain of energy from the systematic orbital rotation. Details of the resulting balance (velocity dispersion, geometric thickness, viscosity) are determined by the frequency and degree of inelasticity of impacts, and the internal density and size distribution of particles. Depending on the implied viscosity-density relation, the ring can be either stable or unstable against the growth of local perturbations. For example, dense rings composed of quite inelastic particles can become viscously overstable, which is likely to relate to the strictly axisymmetric oscillations observed in certain regions of Saturn’s rings.
The importance of ring self-gravity for shaping the local structure of Saturn’s rings has been strikingly demonstrated by the Cassini stellar and radio occultation measurements, which indicate the presence of unresolved trailing structures (‘self-gravity wakes’) throughout the A and B rings. These structures arise as a superposition of tiny perturbations excited around each individual ring particle, amplified by the swing-amplification mechanism. Such structures were envisioned by Alar Toomre already decades ago, though in a very different context (and scale - kpc’s rather than meters), as a suggestion of how to create spiral structure in galactic disks. The crucial ingredient in planetary rings is the mutual dissipative impacts between particles, which keep the ring cool and thus reactive to gravitational disturbances. Self-gravity wakes are just one example: similarly the resonance excitation of spiral density waves has the clearest manifestation in Saturn’s rings; Saturn’s rings also provide the most extreme examples of disk warping, and the effect of embedded mass concentrations on the surrounding particles (‘propellers’).
In this talk I will discuss simulations of self-gravitating, mutually colliding particles, using a local method where the evolution of a small co-moving ring patch is followed. Simulation examples of self-gravity wakes and nonlinear structures resulting from viscous instability and overstability are presented, including the interplay of inclined self-gravity wakes with axisymmetric overstable oscillations. I will also highlight the similarities and differences of planetary rings with respect to galactic disks.
Cornell University
Invited, November 1, 16:10–17:20, Presentation File, Addition
We discuss the application of continuum equations that result from kinetic theory for inelastic grains to the prediction of the features of dilute and dense planetary rings. In a dilute ring, we focus on the structure normal to its mid-plane and its lateral extent and thickness. In a dense ring, we describe the development of inhomogeneities in concentration around an embedded moonlet. We concentrate on the role played by the collisional transfer of momentum and energy between grains, rather than on their gravitational interaction.
This is joint work with Volker Simon, Brian Lawney, and Joe Burns
Jawaharlal Nehru Centre for Advanced Scientific Research
Invited, November 1, 17:20–18:30, Presentation File
In the first part, I will briefly review the dense gas kinetic theory of granular fluids. This will be followed by linear and nonlinear stability analyses of the underlying constitutive model for a plane shear flow. Various types of shear-flow Instabilities and their subsequent bifurcations into nonlinear patterns will be discussed from the viewpoint of Landau and Ginzburg-Landau equations. Possible connections of a certain shear-flow instability with Staurn’s ring will also be discussed.
Hokkaido University
Invited, November 2, 9:15–10:25
Adhesion and inelastic interaction between nano- or submicron-sized solid particles are an important subject in many areas of technology and applied science including astrophysics. However, detail of the particle interaction in such a size range has not been studied yet even for simple and homogeneous molecular systems. We examined interactions between small particles which consist of up to 100 millions of Lennard-Jones molecules, by performing molecular dynamics simulation. With molecular dynamics simulation, we can see clearly how the energy dissipation proceeds at collisions or rolling motions of particles. In my talk, I will first introduce recent studies on inelastic collisions and aggregation of cosmic particles and show some results of our molecular dynamics simulations and show new empirical laws on the energy dissipation derived from our numerical experiments.
Tokyo University of Science
Contributed, November 2, 10:50–11:15, Presentation File
In 1976, the author developed the scaling theory of order formation from unstable states by extending Einstein’s linear theory of Brownian motion[1] to nonlinear unstable cases[2]. At the first stage, an exponential growing has been shown to be dominant, namely the initial microscopic fluctuation grows rapidly upto the microscopic order around the onset time in the scaling regime[2], where the nonlinearity of the relevant system plays an essential role to stabilize the system. The author found the synergetic effect (or synergism)of the initial fluctuation, random noise and nonlinearity to the formation of macroscopic order. This scaling theory of a single macrovariable or order parameter has been extended to an infinite number of order parameters[3]. This kind of exponential growing played later an essential role in the inflation model of an early universe[4,5]. The entropy change or entropy production will be also discussed from a new point of view, namely from the symmetry of the non-equilibrium density-matrix[6], using the von Neumann equation. The above scaling theory of order formation has been performed using the nonlinear Langevin equation with Gaussian noise. However, the main idea can be extended to the case of non-Gaussian noise[7], for example, using the Hamilton-Jacobi equation[8]. There are many other related problems to be discussed in the conference[2,6,9,10].
References
[1] A. Einstein, Ann. Phys. 17 (1905) 549, 19 (1906) 371.
[2] M. Suzuki, Prog. Theor. Phys. 56 (1976) 77, 477; ibid 57 (1977) 380; ibid Suppl. 64 (1978) 402; Adv. Chem. Phys. 46 (1981) 195; Int. J. Mod. Phys. B (2011) in press.
[3] K. Kawasaki, M. C. Yalabik and J. D. Gunton, Phys. Rev. 17 (1978) 455.
[4] K. Sato, Month. Not. Roy. Astron. Soc. 195 (1981) 467 and Phys. Lett. B 99 (1981) 66.
[5] A. H. Guth, Phys. Rev. D 23 (1981) 347.
[6] M. Suzuki, Physica A 390 (2011) 1904, Paper II (2011) in press, and Paper III (in preparation).
[7] K. Kanazawa and H. Hayakawa, to be published.
[8] R. Kubo, K. Matsuo and K. Kitahara, J. Stat. Phys. 9 (1973) 51.
[9] T. Nakata and S. Miyashita, to be published.
[10] T. Imamura and T. Sasamoto, to be published.
Kyoto University
Contributed, November 2, 11:15–11:40, Presentation File
We consider a strongly-interacting gauge-theory plasma with a constant flow of quark charge. The system is a non-equilibrium steady state (NESS) under which the dissipation and the work of the driving force are balanced. The conductivity, the ratio of the quark-charge current to the external force, can be computed purely from the microscopic theory even in the non-linear region if the AdS/CFT correspondence is applicable. We show how the AdS/CFT correspondence works in the study of NESS, and we report novel (first and second order) phase transitions that appear only outside the linear-response regime at finite current.
Aoyama Gakuin University
Contributed, November 2, 11:40–12:05, Presentation File
Let us consider mechanical properties of the assemblies of grains. When the density is low enough, they behave as liquids. However, when the density exceeds a critical value, they obtain rigidity. Such kind of transition for the rigidity is known as the jamming transition. The jamming transition of granular materials has attracted the attentions of a large number of physicists.
Recently, some scaling laws for the jamming transition have been propose. These scaling laws are analogous to those in conventional critical phenomena. However, we still do not know the details of the scaling laws whether the analogy from the critical phenomena is useful.
In this talk, to clarify the properties of the jamming transition, we demonstrate that the scaling exponents do not depend on the dimension of the system, but depend on the particle interaction based on our extensive numerical simulation. We also present that all the numerical values of the exponents are consistent with the prediction of our phenomenological theory.
Okayama University
Invited, November 2, 13:45–14:55, Presentation File
It is believed that small-scale statistics of turbulent flows are universal irrespective of the boundary condition. This remarkable property is due to the so-called Richardson cascade; the information of boundary condition may be lost through the cascade process.
On the other hand, turbulence is not a random motion but consists of coherent structures. More concretely, there exist multi-scale self-similar tubular vortices in turbulence at high Reynolds numbers. Since these multi-scale structures are created by the Richardson cascade, it is essential to understand their creation mechanism in order to understand the origin of the small-scale universality of turbulence.
For this purpose, we define the energy at each scale as a function of time and position, and investigate its transfer between scales. Then, it is numerically shown that the energy cascade is caused by the vortex stretching of smaller-scale vortices in straining regions around larger-scale ones.
However, another problem arises. Namely, this scenario implies that tiny structures as small as the Taylor micro-scale can be created directly by the largest scale structures in turbulence, and that the small-scale universality of turbulence might be questionable.
Kyoto University
Contributed, November 2, 13:55–15:20, Presentation File
A correlation function is proportional to a response function if fluctuations obey Gaussian statistics. Hence, deviation from being Gaussian is manifested in discrepancy between the two functions. We study this discrepancy in a dynamical system model of fluid turbulence, which is known as the Gledzer-Ohkitani-Yamada shell model. We here add small Gaussian white noise for each shell variable to facilitate application of the path integral formalism. Our numerical result shows that the discrepancy is described with a certain 3-point correlation function. We discuss its implications in this presentation.
PPPL, Princeton University, Princeton NJ, USA
Invited, November 2, 15:50–17:00, Presentation File
Magnetic reconnection is a phenomenon of nature in which magnetic field lines change their topology and convey magnetic energy to plasma particles by acceleration and heating. The process can stretch out over time or occur quite suddenly. It is one of the most fundamental processes at work in laboratory and astrophysical plasmas. Magnetic reconnection occurs everywhere: In solar flares; coronal mass ejections; the earth’s magnetosphere; in the star forming galaxies; and in plasma fusion devices. Solar flares may be the best known example of magnetic reconnection. As shown by a soft-X ray satellite picture, rapidly evolving solar flares produce vivid examples of the global magnetic topology changes that occur during magnetic reconnection. This talk reviews the most recent progress in the research of magnetic reconnection (1).
A sudden topology change of solar flare structure leads to a coronal mass ejection (CME). During the interaction of solar winds with the earth dipole field, the magnetosphere creates a substorm, one type of magnetic self-organization phenomena. Significant progress has been recently made in understanding the magnetic self-organization through collaboration between numerical simulations, space observations, and lab experiments. Particularly the physics of the reconnection layer has moved forward through a new understanding of the local physics of magnetic reconnection. Two-fluid dynamics have been verified through experimental identification of both the ion and electron diffusion layers. The reconnection rate increases significantly when the ratio of the electron mean free path to the scale length approaches unity. A new scaling of reconnection resistivity with respect to this ratio has been obtained from the laboratory results. Comparison of these lab results with the recent space satellite observations will be made.
(1) M. Yamada, R. Kulsrud, H. Ji, Rev. Mod. Phys. v.82, 602 (2010)
Max Planck Institute for Astrophysics
Invited, November 3, 9:15–10:25, Presentation File, Movies
The Sun’s magnetic field is generated in its convective envelope; it is often considered a consequence of ‘the interaction between magnetic fields and turbulence’. In the first part of the talk I’ll review some observational properties, both old and new, showing that such a turbulent interaction picture fits the observations very poorly. The observations, complemented with numerical work, lead to a considerably different conceptual picture. The second part is a brief review of spectacular recent successes in realistic numerical simulations of magnetic structures at the solar surface. In the third I discuss the (controversial) possibility that variations of the Sun’s magnetic field might have an influence on climate.
Nagoya University
Invited, November 3, 10:50–12:00, Presentation File (ISM), Presentation File (MRI)
In this talk I will explain two kinds of self-sustained turbulence without external driving force. The first one is the turbulent motion of multi-phase interstellar medium internally driven by thermal instability. The analysis of turbulent multi-phase interstellar medium is required to understand the formation of interstellar clouds and stars. We can find many interesting behavior of transition layers that play critical roles in sustaining turbulent motions. The second is the magnetohydrodynamical turbulence in the accretion disks driven by magneto-rotational instability. Understanding of the time-averaged saturation of this turbulence is required to estimate the mass accretion rate of matter in the disk onto the gravitating central objects via the fluctuation-dissipation.
Osaka University
Contributed, November 3, 13:30–13:55, Presentation File
Recent discovery of the year-scale variability in the syncrtron X-ray emission of supernova remnants (SNRs) suggests that the magnetic field should be amplified in the SNR up to the level of milligauss (Uchiyama et al 2007). Since the typical magnetic field in the interstellar medium (ISM) is on the order of microgauss, amplification beyond the simple shock compression is necessary to achieve a milligauss of a magnetic field. Turbulence and magnetic field amplification has been studied for shock wave propagation through two-phase ISM composed of small-scale cloudlets (Inoue et al 2009). We here present some MHD simulation results of the Magnetic field amplification by the Richtmyer-Meshkov instability for a sinusoidal interface corrugation. The field amplification observed is found to be more than a factor of 100, which is consistent with the observation (Uchiyama et al 2007). Physical mechanism of the amplification will be discussed in detail.
Osaka City University
Invited, November 3, 13:55–15:05, Presentation File
We discuss recent important topics in quantum fluid dynamics and quantum turbulence. Quantum turbulence (QT) was discovered in superfluid 4He in the 1950s, but this is still one of the most important topics in low temperature physics. The realization of atomic Bose-Einstein condensation in 1995 has proposed another important stage for this issue. A general introduction to this issue and a brief review of the basic concepts are followed by the recent developments of the studies of QT. I will discuss some of the interesting topics. (1) Vortex lattice formation in a rotating Bose-Einstein condensate. (2) Energy spectra of QT. (3) Vortex states in rotating two-component Bose-Einstein condensates. (4) Binary QT in two-component BECs.
Nagoya University
Poster #1
The fate of the heavy-quark bound states, such as J/Psi, in the hot quark-gluon plasma has been discussed by various approaches. I will specifically discuss the potential model, which is recently found to have complex potential by lattice QCD simulation. I will construct a stochastic model and show how the fate of the heavy-quark bound states can be discussed on the basis of the master equation.
The University of Electro-Communications
Poster #2
Previous time-of-flight studies of our group with two-dimensional polygonal simulations and one- and three-dimensional experiments showed that the sound-velocity in granular materials in one and two dimensions is of the order of ten percent of that of the bulk material, while in three dimensions it is of the order of one percent. The conclusion was that the force network in granular particles plays a crucial role for the magnitude of the sound velocity. With our newly completed fully three dimensional discrete element method with polyhedral particles, we investigate the relation between force network, packing density and sound velocity.
National Astronomical Observatory of Japan
Poster #3
The spatial structure of planetary rings has been numerically studied by local N-body simulations in a local shearing box. The self-gravity wakes are believed to dominate in most parts of dense rings such as Saturn’s B ring. The spatial structure in dense rings is an important key to ring mass estimation, and thus to the origin of Saturnian ring system. The characteristic spatial scale of the wakes is given by the critical wavelength of gravitational instability. In order to properly resolve the wake structure, the size of a shearing box needs to be larger than several times the critical wavelength, which means that we need more than one million ring particles for ring regions whose optical depth exceeds unity. We have developed a local N-body code to simulate dense rings. With the aid of a special-purpose computer GRAPE-DR, our code may be applicable to regions with greater optical depth than those investigated in former studies.
Kyoto University
Poster #4
We derive a time-dependent Ginzburg=Landau equation as an amplitude equation in terms of weakly nonlinear analysis for a sheared granular flow. This equation has been derived from a set of granular hydrodynamic equations whose validity has been verified through the comparison between the hydrodynamic equations and the molecular dynamic simulation. See the reference for details.[1]
[1] K. Saitoh and H. Hayakawa, DOI: 10.1007/s10035-011-0283-2
Kyoto University
Poster #5
Observations of quiescent prominences by the Solar Optical Telescope (SOT) on board the Hinode satellite show plumes of hot, underdense material rising through the prominence. These plumes form at the boundary between the prominence and low density bubbles, approximately 10 Mm in size, that appear beneath the prominence, and then rise through the prominence material at speeds of approximately 20 km/s and widths of approximately 1.5 Mm. The plume profile ranges from highly turbulent to smooth, suggesting that the prominence conditions, as well as those of the bubble, are important in determining the dynamics. To investigate this phenomenon, we perform simulations of the magnetic Rayleigh-Taylor instability in a local prominence model. The instability creates rising plumes of hot, underdense material that propagate through the prominence material at a velocity of approximately 6–7 km/s and widths of approximately 1.5 Mm, in rough agreement with the Hinode observations. Nonlinear effects, in which the interaction between plumes drives an inverse cascade process creating large plumes from smaller plumes, are found to be important. Increasing the magnetic field strength creates smoother plume structures. The addition of a strong guide field, which is suggested in some prominence models, does not hinder plume formation but does change the dynamic scaling. The Rayleigh-Taylor instability drives an upward flow of magnetic energy and a downward flow of mass. The results from the simulations well match the characteristics of the observed plumes, suggesting that the magnetic Rayleigh-Taylor instability could be important in determining prominence structure as well as changing the magnetic energy distribution in overlying coronal cavities which ultimately erupt as coronal mass ejections.
Kyoto University
Poster #6
The formation of lanes is a well known phenomenon when two species of particles are driven against each other. This phenomenon can be observed in pedestrian motion and the dynamics of charged colloidal mixtures. However when particles have smaller dissipation vertical to the driven force than parallel to the driven force or higher driven force applied to the particles in our model, particles exhibits active motion in which lane formation is no longer stable and particles behave turbulence-like flow. In this poster, we discuss this instability to use the least dissipation principle and influence of oblong periodic boundary condition.
Kyoto University
Poster #8
Nonlinear evolution of interacting rarefaction waves excited at two-sides of jet-ambient interfaces are studied through one-dimensional relativistic hydrodynamic simulation. A strong pressure gradient formed behind the interface is a consequence of the relativistic rarefaction wave, and has a crucial role in self-collimating jets. The excited rarefaction waves are confined by the pressure gradient force and are interacted repeatedly in tangentially moving plasma. We find that the interaction of rarefaction waves causes a decrease of relativistic pressure and yields more powerful boost of the bulk jet transiently than that expected from a single rarefaction wave. The seesaw cycle of energy transport between thermal and bulk kinetic energies is a natural relativistic outcome of the repeated excited rarefaction waves. This might be a possible origin of multiple shocks accounting for variable properties of Gamma-Ray Bursts and Active Galactic Nuclei.
National Astronomical Observatory of Japan
Poster #9
The Cassini spacecraft discovered a propeller-shaped structure in Saturn’s A ring. This propeller structure is thought to be formed by gravitational scattering of ring particles by an unseen embedded moonlet. Self-gravity wakes are prevalent in dense rings due to gravitational instability, which are non-uniform and non-stationary structures. Strong gravitational wakes affect and destroy the propeller structure. Here, we derive the condition for formation of a propeller structure by a moonlet embedded in a dense ring with gravitational wakes. We find that a propeller structure is formed when the moonlet is sufficiently large. We confirm the formation condition by performing numerical simulations.
Ochanomizu University
Poster #10
Intermittent Geomagnetic reversal is one of the fundamental problems in geophysics. Quasi-regular Solar-magnetic reversal is also the same in stellar physics. We propose a coupled macro-spin model to describe them in a unified form. This simple model successfully describes several observed features of the above dynamics including the time series of polarity reversals and its power spectrum, interval distribution function, etc. The basic idea of the model is that the whole dynamo mechanism of geomagnetism and the solar magnetism can be decomposed into almost independent multiple elements — dynamo elements — whose non-local coupling yields variety of dynamics in wide range time scales. Actually the spin-model, similar to the Hamiltonian Mean Field model, has coexisting two phases, core and halo, which respectively describe the steady dipole and perpetually varying magnetic components for geomagnetism. Furthermore the spin model, similar to the Kuramoto model, can describe synchronization dynamics which is essential for the solar magnetic reversals. This spin model also reproduces the 1/f-like fluctuation observed in the solar magnetism power spectrum. Furthermore, we derive the magnetic field scaling for many planets and satellites based on the basic MHD equations. This scaling result is used to estimate the size and the number of spin element of our model.
Ref. http://arxiv.org/abs/1104.5093
Waseda University
Poster #11
A quasi-stability principle applied to stochastic differential equation of momentum conservation (Naitoh, 2001–2011) has revealed the magic numbers including the silver ratio appearing in various systems. This model explains the reason why particles such as biological cells, nitrogenous bases, and liquid droplets have bimodal size ratios of about 2:3 and 1:1. This paper shows that the same theory holds true for several levels of parcels from baryons to stars in the cosmos: specifically, at the levels of nuclear force, van der Waals force, surface tension, and the force of gravity. A higher order of analysis also clarifies other asymmetric ratios over 2:3, i.e., the super-magic number of about 1:3.5, 1:2.5, 1:2.1, and 1:1.78 in various systems related to the amino acids, halo structure in atoms, and cold fusion.
Nihon University
Poster #12
A densely packed colloidal suspension, called paste, has a memory of external mechanical fields, such as vibration and flow. These memories in pastes can be visualized by the morphology of crack patterns which appear when pastes are dried. By mixing two kinds of pastes, we observe corporative phenomenon of memory effect induced by interactions among colloidal particles of two kinds.
The University of Electro-Communications
Poster #13
We introduce a novel simulation method of granular particles in fluids, where the particles are modeled with a discrete element method for polygons, while the (incompressible) fluid is modeled with a finite element method. The fluid boundaries are modeled as the particle boundaries without any additional data structures. We obtain stable simulation results for sedimentation for particles of an area of ten triangles of the fluid mesh. The implicit time integration allows to select the time-step according to the rate of the physical processes, so there is no limitation due to the area of the small mesh in the pore space between the particles. In the next step, we want to introduce a current in the fluid to see how far we can come with a microscopic simulation of the two-dimensional experiment of a Barchan in water by Groh et al.
ISAS/JAXA
Poster #14
Intermittent and recurrent chromospheric plasma ejections were discovered in the sunspot light bridge (LB) by the Solar Optical Telescope of the Hinode satellite. Strong current was observed under the jet, suggesting existence of twisted flux tube in the vertical background field. The magnetic reconnection between the flux tube and the vertical field is considered to cause the plasma ejection. It is left unsolved why the intermittent reconnection continuing more than one day. Note that the magnetic configuration of LB is similar to the spheromak plasma maintained by vertical field in the laboratory. We formed spheromak in the TS-4 device and drove magnetic reconnection with center solenoid coil. We measured 2D magnetic profile of the reconnecting field lines between the spheromak and the solenoid coil by the magnetic probe array and local temperature, density and plasma flow at the reconnection point by the Langmuir probes and ion Doppler spectroscopy. We will discuss the LB reconnection by comparing the laboratory experiment with Hinode observations.
Tottori University
Poster #15
The problem of one-dimensional diffusion for Brownian particles with short-range repulsive interaction, referred to as single-file diffusion, is studied as a simple example of slow dynamics. We show that the adoption of the continuous label variable, corresponding to the Lagrangian description in fluid mechanics, can be a powerful tool in this problem: the label variable method allows us correct calculation of some quantities characterizing the slow dynamics, in which the standard “Eulerian” theory fails.
Kyoto University
Poster #16
The granular jet scattering experiment provides us many interesting questions. Not only granular physicists but also nuclear physicists are interested in this experiment. We believe that the inelastic scatterings cause scattering pattern to be firework-like pattern or sheet-like one, changing the ratio of the particle size and the jet diameter. We performed numerical simulation of the granular jet scattering experiment using Discrete Element Method and found that firework-like pattern or sheet-like one may emerge even in the elastic limit. Our results suggest that dissipation dosen’t play a major role in “firework-sheet transition.” We also analyzed the differential cross section based on scattering theory.
Kyoto university
Poster #17
There are many cases that attractive force between grains plays an important role. Indeed, such a force is not negligible for fine powders or molecules. In this poster, we consider a system of Lennard-Jones molecules under a plane shear, and clarify the role of the cohesive force among molecules in macroscopic behavior such as the rheological properties. Through our molecular dynamics simulation, we have confirmed that the molecules form clusters according to the cohesive force, and the rheological properties have been changed due to the attractive force.
Kyoto University
Poster #18
The cool jets are the collimated plasma flows whose temperature and the velocity are 10,000 K and ~100 km/s, respectively. This temperature is cool compared to the coronal temperature (~1000,000 K). They are often observed in the emerging flux regions, where the magnetic flux is provided above the solar surface from the convective zone. Although such cool jets have been observed for a long time, the triggering mechanism is still unknown. The triggering force may not be the gas pressure gradient, because the sound speed corresponding to 10,000 K is ~10 km/s. Therefore we consider the magnetically driving mechanism, especially magnetic reconnection between the emerging flux and the coronal field, where magnetic reconnection is a physical process in which a magnetic field in a highly conducting plasma changes its connectivity due to finite resistivity. The whip-like motion of the magnetic field due to the change of the topology is a candidate of the acceleration mechanisms. We investigate this effect by using two dimensional MHD simulation and report the results.
Kobe University
Poster #19
Saturn’s rings are composed of many icy particles, and angular momentum is transported due to collision and gravitational interaction between these particles. Viscosity in the rings arising from such interactions between particles governs the rate of dynamical evolution and structure formation in the rings. We examine viscosity in self-gravitating planetary rings using local N-body simulation. We investigate dependence of viscosity on various parameters in detail, including effects of particles’ surface friction. In the case of self-gravitating rings with low optical depth, we find that viscosity is determined by particle’s random velocity. When particles’ random velocity is determined by inelastic collisions, inclusion of surface friction slightly reduces both random velocity and viscosity. On the other hand, when gravitational encounters play a major role in particle velocity evolution, surface friction slightly increases viscosity, since the viscous heating increases to balance with increased energy dissipation at collisions due to surface friction. In the case of self-gravitating dense rings, however, we find that effects of varying restitution coefficients on ring viscosity are not significant, as compared to significant increase due to the effect of gravitational wakes. We confirm that our numerical results for viscosity in dense rings with gravitational wakes can be well approximated by a semi-analytic expression that is consistent with a previously obtained formula. However, this formula overestimates viscosity in the case of outer rings where temporary aggregates are formed due to self-gravity, thus we derive a set of semi-analytic expressions that well reproduce our numerical results for the entire range of parameters examined.