Search results for "Vortex"
showing 10 items of 244 documents
Vortex diffusion and vortex-line hysteresis in radial quantum turbulence
2014
Abstract We study the influence of vortex diffusion on the evolution of inhomogeneous quantized vortex tangles. A simple hydrodynamical model to describe inhomogeneous counterflow superfluid turbulence is used. As an illustration, we obtain solutions for these effects in radial counterflow of helium II between two concentric cylinders at different temperatures. The vortex diffusion from the inner hotter cylinder to the outer colder cylinder increases the vortex length density everywhere as compared with the non-diffusive situation. The possibility of hysteresis in the vortex line density under cyclical variations of the heat flow is explored.
Vortex solitons in photonic crystal fibers
2003
We demonstrate the existence of vortex soliton solutions in photonic crystal fibers. We analyze the role played by the photonic crystal fiber defect in the generation of optical vortices. An analytical prediction for the angular dependence of the amplitude and phase of the vortex solution based on group theory is also provided. Furthermore, all the analysis is performed in the non-paraxial regime.
Vortex mutual friction in rotating superfluid 3He
1996
The Manchester rotating cryostat has been used to measure the longitudinal and transverse coefficients of vortex mutual friction in the A and B phases of superfluid 3He. In the B phase the dominant contribution to the mutual friction is scattering of excitations off occupied bound states in the vortex core. The A phase results are explained quantitatively by assuming that doubly quantised continuous vortices are created with a dynamics determined by the equation of motion of the orbital vector I; the measurements enable us to put an upper limit on the orbital inertia of less than 0.01h{stroke} per Cooper pair. History-dependent textural effects which had to be overcome in order to make mean…
Spatial distribution and statistical properties of small-scale convective vortex-like motions in a quiet-Sun region
2011
High-resolution observations of a quiet Sun internetwork region taken with the Solar 1-m Swedish Telescope in La Palma are analyzed. We determine the location of small-scale vortex motions in the solar photospheric region by computing the horizontal proper motions of small-scale structures on time series of images. These plasma convectively-driven swirl motions are associated to: (1) downdrafts (that have been commonly explained as corresponding to sites where the plasma is cooled down and hence returned to the interior below the visible photospheric level), and (2) horizontal velocity vectors converging into a central point. The sink cores are proved to be the final destination of passive …
Troubled cosmic flows: turbulence, enstrophy and helicity from the assembly history of the intracluster medium
2021
Both simulations and observations have shown that turbulence is a pervasive phenomenon in cosmic scenarios, yet it is particularly difficult to model numerically due to its intrinsically multiscale character which demands high resolutions. Additionally, turbulence is tightly connected to the dynamical state and the formation history of galaxies and galaxy clusters, producing a diverse phenomenlogy which requires large samples of such structures to attain robust conclusions. In this work, we use an adaptive mesh refinement (AMR) cosmological simulation to explore the generation and dissipation of turbulence in galaxy clusters, in connection to its assembly history. We find that major mergers…
Cosmic magnetic fields with masclet: an application to galaxy clusters
2020
We describe and test a new version of the adaptive mesh refinement (AMR) cosmological code MASCLET. The new version of the code includes all the ingredients of its previous version plus a description of the evolution of the magnetic field under the approximation of the ideal magneto-hydrodynamics (MHD). To preserve the divergence-free condition of MHD, the original divergence cleaning algorithm of Dedner et al. (2002) is implemented. We present a set of well-known 1D and 2D tests, such as several shock-tube problems, the fast rotor and the Orszag-Tang vortex. The performance of the code in all the tests is excellent with estimated median relative errors of $\nabla \cdot {\bf B}$ in the 2D t…
Second sound near lambda transition in presence of quantum vortices
2018
In this paper, temperature waves (also known as second sound) are consid- ered, with their respective coupling with waves in the order parameter describing the transition from normal phase to superfluid phase, and with waves in the vortex length density. We analyze the coupling between these three kinds of waves and explore its relevance in situations not far from the lambda transition. In particular, the expres- sions for the second sound speed and second sound attenuation are explicitly obtained within some approximations, showing the influence of the order parameter and the vortex length density, which is decisive close to the transition.
Differential operator formalism for axial optical vortex beam and the double-phase-ramp converter
2019
A systematic study of the properties of the output dark rays or singular skeleton for the Laguerre-Gaussian beam LG 01 passed through double-phase-ramp converter is presented. When the DOE is discontinuous at the origin, as is the case here, the transfer function is not analytical, so that a special theoretical approach is needed. The previously reported formalism of scattering modes, which permitted the analytical calculation of arbitrary multisingular Gaussian beams, requires analyticity everywhere. We present here an adaption of this formalism that overcomes this limitation. The procedure is based on the differential operator algebra used in the previous construction. We give an example …
Local control of domain wall dynamics in ferromagnetic rings
2015
Ferromagnetic nanorings are of great interest due to prospective applications in memory and logic devices based on domain wall (DW) motion.1-3A key-prerequisite for their realization is a reproducible domain wall spin structure with a well-controllable wall velocity. We have found that DW propagation in magnetic ring is characterized by non-constant vortex DW velocity even below Walker breakdown4 (as opposed to straight wires). Several studies have been devoted to the optimization of ring reversal on a global scale using out-of plane field5 or flux charges emanating from neighboring rings if placed in close proximity6. However, these methods involve DW pinning and vortex nucleation processe…
Dynamic domain wall chirality rectification by rotating magnetic fields
2015
We report on the observation of magnetic vortex domain wall chirality reversal in ferromagnetic rings that is controlled by the sense of rotation of a magnetic field. We use time-resolved X-ray microscopy to dynamically image the chirality-switching process and perform micromagnetic simulations to deduce the switching details from time-resolved snapshots. We find experimentally that the switching occurs within less than 4 ns and is observed in all samples with ring widths ranging from 0.5 μm to 2 μm, ring diameters between 2 μm and 5 μm, and a thickness of 30 nm, where a vortex domain wall is present in the magnetic onion state of the ring. From the magnetic contrast in the time-resolved im…