Related papers: Interaction of multi-armed spirals in bistable med…

We present high-resolution (30 mas or 130 au at 4.2 kpc) Atacama Large Millimeter/submillimeter Array observations at 1.2 mm of the disc around the forming O-type star AFGL 4176 mm1. The disc (AFGL 4176 mm1-main) has a radius of ~1000 au…

The coupling between the dark matter (DM) halo and the stellar disc is a key factor in galactic evolution. While the interaction between structures like the Galactic bar and DM halos has been explored (e.g. slowing down of the bar due to…

Explicit formulas for the rotation frequency and the long-wavenumber diffusion coefficients of global spirals with $m$ arms in Rayleigh-Benard convection are obtained. Global spirals and parallel rolls share exactly the same Eckhaus, zigzag…

We study transient spiral structures in an isothermal, thin, galactic disc. We find no instability that can grow everywhere from infinitesimal disturbances, but spiral structure does grow in the disc due to an arbitrarily strong,…

Trapping and un-trapping of spiral tips in a two-dimensional homogeneous excitable medium with local small-world connections is studied by numerical simulation. In a homogeneous medium which can be simulated with a lattice of regular…

Spiral patterns in some disc galaxies have two arms in the centre, and three or more arms on the periphery. The same result is also obtained in numerical simulations of stellar and gaseous discs. We argue that such patterns may occur due to…

The causes of spiral structure in galaxies remain uncertain. Leaving aside the grand bisymmetric spirals with their own well-known complications, here we consider the possibility that multi-armed spiral features originate from density…

Spiral waves are observed in many natural phenomena. They have been extensively represented by the mathematical FitzHugh-Nagumo (FHN) model [Barkley et al., Phys. Rev. A 42, 2489 (1990)] of excitable media. In incompressible fluid…

Rings and spiral arms are distinctive features of many galaxies, and their properties are closely related to the disk dynamics. They are often associated to stellar bars, but the details of this connection are far from clear. We study the…

An overwhelming majority of galactic spiral arms trail with respect to the rotation of the galaxy, though a small sample of leading spiral arms has been observed. The formation of these leading spirals is not well understood. Here we show,…

We begin by recalling the isothermal, collisionless, disc-halo. The disc component is the Mestel disc. Subsequently we introduce spiral arms to such an isothermal disc-halo system that are co-moving in the mean with an axi-symmetric…

Rotating spiral waves are a form of self-organization observed in spatially extended systems of physical, chemical, and biological nature. A small perturbation causes gradual change in spatial location of spiral's rotation center and…

We study the dynamics of tidally induced spiral arms in our Galaxy in the context of its encounters with Sagittarius. We built toy models of the interaction between a host and a satellite galaxy using orbital integrations after a tidal…

The PERLAS potential has been successfully used in many studies related with the dynamics of the spiral arms \textit{on} the equatorial plane of normal (non-barred) spiral galaxies. In the present work we extend these studies by…

We study two delay-coupled FitzHugh-Nagumo systems, introducing a mismatch between the delay times, as the simplest representation of interacting neurons. We demonstrate that the presence of delays can cause periodic oscillations which…

We study the dynamics and interaction of coaxial vortex rings in the FitzHugh-Nagumo excitable medium. We find that threading vortex rings with a vortex string results in significant qualitative differences in their evolution and…

Many multicellular communities propagate signals in a directed manner via excitable waves. Cell-to-cell heterogeneity is a ubiquitous feature of multicellular communities, but the effects of heterogeneity on wave propagation are still…

We study analytically and numerically the stability of the pressure-less, viscously spreading accretion ring. We show that the ring is unstable to small non-axisymmetric perturbations. To perform the perturbation analysis of the ring we use…

Pattern formation of a thin layer of vertically agitated wet granular matter is investigated experimentally. Rotating spirals with three arms, which correspond to the kinks between regions with different colliding phases, are the dominating…

High resolution N-body simulations using different codes and initial condition techniques reveal two different behaviours for the rotation frequency of transient spiral arms like structures. Whereas unbarred disks present spiral arms nearly…