New single vortex generation method for flame/vortex interaction using flow behind a rotating cylinder

This paper investigates a new experimental method to generate a single two-dimensional translated vortex for flame/vortex interaction studies. A rotating cylinder is immersed in a uniform flow and, its rotating speed is impulsively reduced. This sudden action triggers the generation of a single vortex when both the initial and the final rotation speeds are in the range of a steady-state regime. Flow visualization allows confirming the applicability of this method, while a complementary two-dimensional numerical simulation is conducted to understand the vortex formation process. A vorticity layer is detached from the cylinder, initiating a feeding process and gradual growth of a single leading vortex. The feeding process is saturated at a specific distance from the cylinder and, vortex separation from the vorticity layer is observed. At the final stage of the formation process, the generated vortex is advected away and, a steady-state regime is again established behind the cylinder. The vortex characteristics appear to be related to the normalized reduction in the rotation rate ∆α, defined as the initial and final rotation rates difference normalized by the initial rotation rate. Several combinations of initial and final rotation rates corresponding to different normalized reductions are investigated experimentally and numerically. The results allow understanding the effect of this parameter; a higher normalized reduction generates a stronger, more rapidly growing vortex. However, its trajectory is related to the wake deviation corresponding to the final rotation rate.

3D structure of single and multiple vortices in a flow under rotation

In this paper, we analyze the 3D structure of vortices developed in a rotating cylinder nonhomogeneously heated from below, when the rotation rate is increased. The analysis has been done by using nonlinear simulations. For a fixed Rayleigh number, the rotation rate is the bifurcation parameter. At low rotation rates, one single vortex is developed. When the rotation on the system is increased, another coexistent vortex appears at mid-levels in the cell. If the rotation is high enough, multiple-vortex structures with three or four vortices are developed at different heights. For larger rotation, complex multiple vortices appear with a chaotic behavior. A force balance analysis permits to study the role of the forces being determinant.

Spontaneous Self-propulsion and Nonequillibrium Shape Fluctuations of a Droplet Enclosing Active Particles

Active particles, such as swimming bacteria or self-propelled colloids, spontaneously assemble into large-scale dynamic structures. Geometric boundaries often enforce different spatio-temporal patterns compared to unconfined environment and thus provide a platform to control the behavior of active matter. Here, we report collective dynamics of active particles enclosed by soft, deformable boundaries, that is responsive to the particles' activity. We reveal that a fluid droplet enclosing motile colloids powered by the Quincke effect (Quincke rollers) exhibits strong shape fluctuations, and while the rollers do self-organize into a single vortex, it fills the droplet interior. We demonstrate that the shape fluctuations have a power spectrum consistent with active fluctuations driven by particle-interface collisions, and a broken detailed balance confirms the nonequilibrium nature of the shape dynamics. We further find that the rollers activity coupled to soft boundary fluctuations can result in a spontaneous symmetry breaking and vortex splitting. The droplet acquires motility while the vortex doublet exists. Our findings provide insights into the complex collective behavior of active colloidal suspensions in soft confinement.

Nano-photoluminescence of natural anyon molecules and topological quantum computation

The proposal of fault-tolerant quantum computations, which promise to dramatically improve the operation of quantum computers and to accelerate the development of the compact hardware for them, is based on topological quantum field theories, which rely on the existence in Nature of physical systems described by a Lagrangian containing a non-Abelian (NA) topological term. These are solid-state systems having two-dimensional electrons, which are coupled to magnetic-flux-quanta vortexes, forming complex particles, known as anyons. Topological quantum computing (TQC) operations thus represent a physical realization of the mathematical operations involving NA representations of a braid group Bn, generated by a set of n localized anyons, which can be braided and fused using a “tweezer” and controlled by a detector. For most of the potential TQC material systems known so far, which are 2D-electron–gas semiconductor structure at high magnetic field and a variety of hybrid superconductor/topological-material heterostructures, the realization of anyon localization versus tweezing and detecting meets serious obstacles, chief among which are the necessity of using current control, i.e., mobile particles, of the TQC operations and high density electron puddles (containing thousands of electrons) to generate a single vortex. Here we demonstrate a novel system, in which these obstacles can be overcome, and in which vortexes are generated by a single electron. This is a ~ 150 nm size many electron InP/GaInP2 self-organized quantum dot, in which molecules, consisting of a few localized anyons, are naturally formed and exist at zero external magnetic field. We used high-spatial-resolution scanning magneto-photoluminescence spectroscopy measurements of a set of the dots having five and six electrons, together with many-body quantum mechanical calculations to demonstrate spontaneous formation of the anyon magneto-electron particles (eν) having fractional charge ν = n/k, where n = 1–4 and k = 3–15 are the number of electrons and vortexes, respectively, arranged in molecular structures having a built-in (internal) magnetic field of 6–12 T. Using direct imaging of the molecular configurations we observed fusion and braiding of eν-anyons under photo-excitation and revealed the possibility of using charge sensing for their control. Our investigations show that InP/GaInP2 anyon-molecule QDs, which have intrinsic transformations of localized eν-anyons compatible with TQC operations and capable of being probed by charge sensing, are very promising for the realization of TQC.

Molten Steel Flow, Heat Transfer and Inclusion Distribution in a Single-Strand Continuous Casting Tundish with Induction Heating

The electrical magnetic field plays an important role in controlling the molten steel flow, heat transfer and migration of inclusions. However, industrial tests for inclusion distribution in a single-strand tundish under the electromagnetic field have never been reported before. The distribution of non-metallic inclusions in steel is still uncertain in an induction-heating (IH) tundish. In the present study, therefore, using numerical simulation methods, we simulate the flow and heat transfer characteristics of molten steel in the channel-type IH tundish, especially in the channel. At the same time, industrial trials were carried out on the channel-type IH tundish, and the temperature distribution of the tundish with or without IH under different pouring ladle furnace was analyzed. The method of scanning electron microscopy was employed to obtain the distribution of inclusions on different channel sections. The flow characteristics of molten steel in the channel change with flow time, and the single vortex and double vortex alternately occur under the electromagnetic field. The heat loss of molten steel can be compensated in a tundish with IH. As heating for 145 s, the temperature of the molten steel in the channel increases by 31.8 K. It demonstrates that the temperature of the molten steel in the tundish can be kept at the target value of around 1813 K, fluctuating up and down 3 K after using electromagnetic IH. In the IH channel, the large inclusions with diameters greater than 9 μm are more concentrated at the edge of the channel, and the effect of IH on the inclusion with diameters less than 9 μm has little effect.

The curl of angular velocity and its mechanical significance

The curl of the vector field is widely used in modern field theory, fluid mechanics, mathematics, electromagnetic field, and other fields. In this paper, by introducing an auxiliary vector parameter (We called 𝑷𝑼⃗⃗⃗⃗⃗⃗ ) whose direction satisfies the right-hand thread rule the mathematical expression of angular velocity vector curl (𝛁×𝝎⃗⃗⃗ ) was obtained by analogy with the method of defining velocity vector curl (𝛁×𝒗⃗⃗ ). We also pointed out that the laminar flow of viscous fluid in a circular pipe (Hogen-Poiseuille flow) in nature is a typical real example of angular velocity vector curl (𝛁×𝝎⃗⃗⃗ ). Moreover, a concise mathematical equation (Equation(11)) was given, which could be used to describe some motion characteristics of vortex ring theoretically; Therefore, the motion of a single vortex ring has the dual characteristics of the velocity curl(𝛁×𝒗⃗⃗ ) and the angular velocity curl(𝛁×𝝎⃗⃗⃗ ) at the same time.

Vortex precession and exchange in a Bose-Einstein condensate

Vortices in a Bose-Einstein condensate are modelled as spontaneously symmetry breaking minimum energy solutions of the time dependent Gross-Pitaevskii equation, using the method of constrained optimization. In a non-rotating axially symmetric trap, the core of a single vortex precesses around the trap center and, at the same time, the phase of its wave function shifts at a constant rate. The precession velocity, the speed of phase shift, and the distance between the vortex core and the trap center, depend continuously on the value of the conserved angular momentum that is carried by the entire condensate. In the case of a symmetric pair of identical vortices, the precession engages an emergent gauge field in their relative coordinate, with a flux that is equal to the ratio between the precession and shift velocities.

Nanoscale real-time detection of quantum vortices at millikelvin temperatures

Since we still lack a theory of classical turbulence, attention has focused on the conceptually simpler turbulence in quantum fluids. Reaching a better understanding of the quantum case may provide additional insight into the classical counterpart. That said, we have hitherto lacked detectors capable of the real-time, non-invasive probing of the wide range of length scales involved in quantum turbulence. Here we demonstrate the real-time detection of quantum vortices by a nanoscale resonant beam in superfluid 4He at 10 mK. Essentially, we trap a single vortex along the length of a nanobeam and observe the transitions as a vortex is either trapped or released, detected through the shift in the beam resonant frequency. By exciting a tuning fork, we control the ambient vortex density and follow its influence on the vortex capture and release rates demonstrating that these devices are capable of probing turbulence on the micron scale.