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Shielded vortices consist of a core of potential vorticity (PV) of a given sign surrounded (or shielded) by a layer of opposite-signed PV. Such vortices have specific properties and have been the focus of numerous studies, first i...
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Shielded vortices consist of a core of potential vorticity (PV) of a given sign surrounded (or shielded) by a layer of opposite-signed PV. Such vortices have specific properties and have been the focus of numerous studies, first in two dimensional geometries (where PV is just the vertical component of the vorticity vector) and in geophysical applications (mostly in layered models). The present paper focuses on three-dimensional, spheroidal shielded vortices. In particular, we focus on vortical structures whose overall volume-integrated PV is zero. We restrict attention to vortices of piecewise uniform PV in the present research. We first revisit the problem within the quasi-geostrophic model, then we extend the results to the non-hydrostatic regime. We show that the stability of the structure depends on the ratio of PV between the inner core and the outer shield. In particular it depends on the polarity of the core and of the wavenumber of the azimuthal mode perturbed.
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The manipulation of collective states and switching processes is of paramount importance for the development of advanced computing technologies based on unconventional multifunctional materials, including multiferroics with strong...
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The manipulation of collective states and switching processes is of paramount importance for the development of advanced computing technologies based on unconventional multifunctional materials, including multiferroics with strong spin-orbit coupling. In this article, we explore the manifestation of Dzyaloshinskii-Moriya interaction (DMI) in the reversal magnetization processes in magnetoelectric nanomagnet. We focus on the situations realized in DMI - systems that we consider interesting for practical implementations: magnetization switching with minimum energy consumption and magnetic topological states emerging during magnetization reversal processes. In magnetoelectric materials, magnetic topological states exhibit ferroelectric properties and can be classified as polar states. We show that a square nanoelement allows the formation of several polar states (single, double and quadrupole), the number of which depends on the combination of system parameters, and explore their effect on polarization that accompanies magnetization reversal processes.
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We study numerically the excitations of off-centered vortices in a Bose-Einstein condensate. The displacement of a single vortex and the separation of a doubly quantized vortex are considered. We find that the core-localized excit...
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We study numerically the excitations of off-centered vortices in a Bose-Einstein condensate. The displacement of a single vortex and the separation of a doubly quantized vortex are considered. We find that the core-localized excitations of the precessing vortices continue to feature the property which implies that the vortices are unstable. The core-localized, dipolar, and quadrupolar excitations are found to deform continuously as functions of vortex displacements and intervortex separation. [References: 26]
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The relative stability of various axisymmetric vortices in a spinor Bose-Einstein condensate with F=1 is examined within extended Bogoliubov theory. This yields the phase diagram in the plane of external rotation frequency vs magn...
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The relative stability of various axisymmetric vortices in a spinor Bose-Einstein condensate with F=1 is examined within extended Bogoliubov theory. This yields the phase diagram in the plane of external rotation frequency vs magnetization. We compare antiferromagnetic, nonmagnetic, and ferromagnetic cases. The excitation spectrum is evaluated under rotation to investigate the local stability of the possible vortices and the vortex nucleation frequency. [References: 40]
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This work investigates interactions of vortices in superconducting materials between standard types I and II, in the domain of the so-called intertype (IT) superconductivity. Contrary to common expectations, the many-body (many-vo...
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This work investigates interactions of vortices in superconducting materials between standard types I and II, in the domain of the so-called intertype (IT) superconductivity. Contrary to common expectations, the many-body (many-vortex) contribution is not a correction to the pair-vortex interaction here but plays a crucial role in the formation of the IT vortex matter. In particular, the many-body interactions stabilize vortex clusters that otherwise could not exist. Furthermore, clusters with large numbers of vortices become more stable when approaching the boundary between the intertype domain and type I. This indicates that IT superconductors develop a peculiar unconventional type of the vortex matter governed by the many-body interactions of vortices.
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Steady uniform vortices are widely used to represent high Reynolds number flows, yet their efficient computation still presents some challenges. Existing Newton iteration methods become inefficient as the vortices develop fine-sca...
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Steady uniform vortices are widely used to represent high Reynolds number flows, yet their efficient computation still presents some challenges. Existing Newton iteration methods become inefficient as the vortices develop fine-scale features; in addition, these methods cannot, in general, find solutions with specified Casimir invariants. On the other hand, available relaxation approaches are computationally inexpensive, but can fail to converge to a solution. In this paper, we overcome these limitations by introducing a new discretization, based on an inverse-velocity map, which radically increases the efficiency of Newton iteration methods. In addition, we introduce a procedure to prescribe Casimirs and remove the degeneracies in the steady vorticity equation, thus ensuring convergence for general vortex configurations. We illustrate our methodology by considering several unbounded flows involving one or two vortices. Our method enables the computation, for the first time, of steady vortices that do not exhibit any geometric symmetry. In addition, we discover that, as the limiting vortex state for each flow is approached, each family of solutions traces a clockwise spiral in a bifurcation plot consisting of a velocity-impulse diagram. By the recently introduced "IVI diagram" stability approach [Phys. Rev. Lett. 104 (2010) 044504], each turn of this spiral is associated with a loss of stability for the steady flows. Such spiral structure is suggested to be a universal feature of steady, uniform-vorticity flows.
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The problem of the evolution of a single vortex in a nonequilibrium medium with a temperature-or density-dependent energy release was solved. In a medium that is stable against small perturbations, the vortex passes to a new stati...
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The problem of the evolution of a single vortex in a nonequilibrium medium with a temperature-or density-dependent energy release was solved. In a medium that is stable against small perturbations, the vortex passes to a new stationary state, and no vortex breakdown occurs. For a temperature-dependent energy release, analytical solutions that define changes in the characteristics of the vortex were obtained for high and low relaxation times. The solutions were compared with the results of numerical simulation by the Godunov method.
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The interactions between flame and vortex in a 2-D Trapped Vortex Combustor are investigated by simulating the Reynolds Averaged Navier Stokes (RANS) equations, for the following five cases namely (i) non-reacting (base) case, ...
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The interactions between flame and vortex in a 2-D Trapped Vortex Combustor are investigated by simulating the Reynolds Averaged Navier Stokes (RANS) equations, for the following five cases namely (i) non-reacting (base) case, (ii) post-vortex ignition without premixing, (iii) post-vortex ignition with premixing, (iv) pre-vortex ignition without premixing and (v) pre-vortex ignition with premixing. For the post-vortex ignition without premixing case, the reactants are mixed well in the cavity resulting in a stable ‘C’ shaped flame along the vortex edge. Further, there is insignificant change in the vorticity due to chemical reactions. In contrast, for the pre-vortex ignition case (no premixing); the flame gets stabilized at the interface of two counter rotating vortices resulting in reduced reaction rates. There is a noticeable change in the location and size of the primary vortex as compared to case (ii). When the mainstream air is premixed with fuel, there is a further reduction in the reaction rates and thus structure of cavity flame gets altered significantly for case (v). Pilot flame established for cases (ii) and (iii) are well shielded from main flow and hence the flame structure and reaction rates do not change appreciably. Hence, it is expected that cases (ii) and (iii) can perform well over a wide range of operating conditions.
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In this paper we address the question of the singular vortex dynamics exhibited in [15], which generates a corner in finite time. The purpose is to prove that under some appropriate small regular perturbation the corner still rema...
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In this paper we address the question of the singular vortex dynamics exhibited in [15], which generates a corner in finite time. The purpose is to prove that under some appropriate small regular perturbation the corner still remains. Our approach uses the Hasimoto transform and deals with the long range scattering properties of a Gross-Pitaevski equation with time-variable coefficients.
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摘要 :
In this paper we address the question of the singular vortex dynamics exhibited in [15], which generates a corner in finite time. The purpose is to prove that under some appropriate small regular perturbation the corner still rema...
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In this paper we address the question of the singular vortex dynamics exhibited in [15], which generates a corner in finite time. The purpose is to prove that under some appropriate small regular perturbation the corner still remains. Our approach uses the Hasimoto transform and deals with the long range scattering properties of a Gross-Pitaevski equation with time-variable coefficients.
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