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When a nano-drop comprising a single spherical central ion and dielectric solvent is charged above a well-defined threshold, it acquires a stable star morphology. In contrast, conducting droplets, will undergo fission. Here we report combined atomistic molecular dynamics and continuum modelling study of star formation of droplets that contain a highly charged ion. We assume that in the continuum model the dielectric response is linear. In this linear continuum model, which is an extension of Rayleigh model, the energy of the drop is comprised of terms analogous to those in Rayleigh model, which are surface energy and electrostatic energy of dielectric droplet charged by a central point charge. We present the stability analysis of the continuum model to determine the threshold of instability. Indeed we find that the model accounts well for the onset of the instabilities. Molecular dynamics show that the number of points of the star-shaped nano-drops depends only on the surface tension, dielectric constant and size of the droplet, and on the magnitude of the charge of the central ion, but not on its sign. Intuitively, it is expected that when a spherical dielectric drop becomes unstable it would transform into a non-spherical finite shape of the same volume as the initial spherical shape with the point charge located in the drop interior. To test whether the extended Rayleigh model can account for the observed droplet shapes, we performed numerical simulations of the linear continuum model. Contrary to the expectations, the simulations of the extended Rayleigh model does not reproduce the stable star shapes found in the atomistic simulations, not even when we account for the bending rigidity and spontaneous curvature of the surface. We argue that the assumption that the dielectric response is linear breaks down if the droplet surface approaches the central macro-ion, where the electric field strength is such that dielectric saturation sets in. We envisage that for certain solvents, these stars could be made permanent by cross-linking, opening the way to the production of a novel class of highly-non-convex colloids.

We consider the propagation of 2D solitary electromagnetic waves and their scattering on a lattice of metallic inhomogeneities in the system of carbon nanotubes (CNTs). The electromagnetic field is considered on the basis of Maxwell equations, and the electronic system of carbon nanotubes is treated by the Boltzmann equation in relaxation time approximation. We numerically analyze the derived effective equation and reveal an increase of spectral composition of the last electromagnetic wave. Some possible practical applications of the discovered effect are discussed.

We consider Maxwell equations for an electromagnetic field propagating in carbon nanotubes (CNTs) placed on a dispersive nonmagnetic dielectric medium. We obtain the effective equation analogous to the classical sine-Gordon equation. Then it has been analyzed numerically. We have revealed the dependence of the pulse on the type of CNT and on the initial pulse amplitude, as well as on the medium dispersion constants.

Starting with the Dirac equation in a curved space–time, applied for the description of the long-wave electrons in curved graphene nanoribbons, we calculated the electronic spectrum and the density of states. Based on the derived density of states we were able to compute the I V -characteristics of a nanoribbon–metal tunnel junction. The dependence on the geometric characteristics of a nanoribbon is revealed.

The exotic quantum phenomenon of Bose–Einstein condensation (BEC) is the key ingredient in a new type of laser that emits atoms rather than photons, and that promises to revolutionize atom optics. In this paper, we consider the possibility of stable angular momentum transfer by an atom laser beam which should be more useful in various applications than a circularly polarized photon laser. The most promising way to assign the initial angular momentum is the outcoupling from the BEC cloud in a vortex state. However, the question of the vortex stability (metastability) arises as well as stability of the beam angular momentum. Here we propose a method for the solution of this problem by developing a quasi-hydrodynamic approach to the condensate with account of its interaction with the non-condensed atoms. Using the concept of local hydrodynamical invariants, we further derive the necessary conditions for the beam, such that the initial angular momentum is transferred conservatively. Both continuous and pulsed schemes are considered.