Peltier-effect in the mixed state of (Bi,Pb)2Sr2Ca2Cu3Oδ

We present measurements of the Peltier-effect in the mixed state of Bi_1.76Pb_0.24Sr₂Ca₂Cu₃O_δ. The Peltier-coefficient broadens in a magnetic field quite similar to the resistivity and the thermopower. Comparison with the thermopower shows that Onsagers relation holds well. The occurrence of the Peltier-heat in the mixed state well below T_c implies that the electric current is accompanied by a large heat current. We show that the vortex contribution to the Peltier-heat is negligibly small. Therefore the heat current has to be attributed to normal quasiparticle excitations. Our results indicate that this quasiparticle contribution to the heat current remains large even at temperatures far below T_c.     

Thermocapillary Vortices Induced by a Light Beam near a Bubble Surface in a Hele-Shaw Cell

This paper studies thermocapillary vortices induced by local heating of a bubble surface in a Hele-Shaw cell by a light beam. It is found that the vortex rotation frequency and its depth depend on the distance from the light-beam projection onto the layer to the bubble boundary. The surface velocity of the thermocapillary flow is calculated using the balance of the near-surface and return flows of the thermocapillary vortex and the equality of capillary and dynamic pressures. It is shown that a decrease in the surface velocity and the vortex rotation frequency with increase in the distance from the light beam to the bubble surface is due to a decrease in the temperature gradient between the illuminated and cold poles of the bubble.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 93–99, September–October, 2005.     

Effect of rotation on Goertler vortices in the boundary layer flow on a curved surface

This paper presents a numerical prediction of the formation of Goertler vortices on a curved surface with effect of rotation. The criterion of flow visualization marking the onset position of Goertler vortices is employed in the present paper. For facilitating the numerical study, the computation is carried out in the transformed x and ηplane. The results show that the onset position characterized by the Goertler number, depends on the rotation number Ro, the Prandtl number and the wave number. The value of critical Goertler number increases with the increase in negative rotation, while the value of Goertler number decreases with the increase in positive rotation on a concave surface. On the contrary, the value of critical Goertler number decreases with the increase in negative rotation on a convex surface. The obtained critical Goertler number and wave number are compared with the previous theoretical and experimental data. Copyright © 2002 John Wiley & Sons, Ltd.     

Corner flow of a suspension of rigid rods

Stress singularities in the neighbourhood of sharp corners can be a source of severe problems in the numerical simulation of non-Newtonian flows leading to loss of convergence with grid refinement (G.G. Lipscombe, R. Kennings and M.M. Denn, J. Non-Newtonian Fluid Mech., 24 (1987) 85 [1]). For Newtonian flows the nature of this singularity is given by the analysis of Dean and Montagnon (W.R. Dean and P.E. Montagnon, Phil. Trans. R. Soc. London, Ser. A., 308 (1949) 199 [2]) in terms of similarity solutions. In this paper we extend this similarity analysis to a suspension of rigid rods. In the limit of nearly full extension the FENE constitutive model has the same behaviour as such a suspension. Our analysis predicts the possibility of lip vortices but their behaviour is somewhat inconsistent with those observed experimentally.     

Dynamics of Ultracold Bosons in Artificial Gauge Fields—Angular Momentum,Fragmentation, and the Variance of Entropy

We consider the dynamics of two-dimensional interacting ultracold bosons triggered by suddenly switching on an artificial gauge field. The system is initialized in the ground state of a harmonic trapping potential. As a function of the strength of the applied artificial gauge field, we analyze the emergent dynamics by monitoring the angular momentum, the fragmentation as well as the entropy and variance of the entropy of absorption or single-shot images. We solve the underlying time-dependent many-boson Schrödinger equation using the multiconfigurational time-dependent Hartree method for indistinguishable particles (MCTDH-X). We find that the artificial gauge field implants angular momentum in the system. Fragmentation—multiple macroscopic eigenvalues of the reduced one-body density matrix—emerges in sync with the dynamics of angular momentum: the bosons in the many-body state develop non-trivial correlations. Fragmentation and angular momentum are experimentally difficult to assess; here, we demonstrate that they can be probed by statistically analyzing the variance of the image entropy of single-shot images that are the standard projective measurement of the state of ultracold atomic systems.     

Aspect ratio effects in turbulent duct flows studied through direct numerical simulation

Three-dimensional effects in turbulent duct flows, i.e., sidewall boundary layers and secondary motions, are studied by means of direct numerical simulation (DNS). The spectral element code Nek5000 is used to compute turbulent duct flows with aspect ratios 1–7 (at Re_{b, c} = 2800, Re_{τ, c} ? 180) and aspect ratio 1 (at Re_{b, c} = 5600, Re_{τ, c} ? 330), in streamwise-periodic boxes of length 25h. The total number of grid points ranges from 28 to 145 million, and the pressure gradient is adjusted iteratively in order to keep the same bulk Reynolds number in the centreplane with changing aspect ratio. Turbulence is initiated via a trip forcing active during the initial stages of the simulation, and the statistical convergence of the data is discussed both in terms of transient approach and averaging period. Spanwise variations in wall shear, mean-flow profiles, and turbulence statistics are analysed as a function of aspect ratio, and also compared with the spanwise-periodic channel (as idealisation of an infinite aspect ratio duct). The computations show good agreement with experimental measurements carried out in parallel at the Illinois Institute of Technology (IIT) in Chicago, and highlight the relevance of sidewall boundary layers and secondary vortices in the physics of the duct flow. The rich array of secondary vortices extending throughout the upper and lower walls of the duct, and their dependence on Reynolds number and aspect ratio, had not been reported in the literature before.     

Experimental investigation on tip vortices and aerodynamics

The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel. The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance, respectively. The evolution of the flow structures and aerodynamics with a ground height were analyzed. The vorticity of tip vortices was found to reduce with the decreasing of the ground height, and the position of vortex-core moved gradually to the outboard of the wing tip. Therefore, the down-wash flow induced by the tip vortices was weakened. However, vortex breakdown occurred as the wing lowered to the ground. From the experimental results of aerodynamics, the maximum lift-to-drag ratio was observed when the angle of attack was 2.5° and the ground clearance was 0.2.     

Stability of polarization vortices within two interacting ferroelectric nanoparticles

The state of polarization vortices within a ferroelectric nanoparticle could be affected by the long-range electrostatic and elastic interactions from the neighboring particles. Phase field simulations were conducted to investigate the stability of polarization vortices within two interacting ferroelectric nanodots embedded in a non-ferroelectric medium. The interaction between these two nanodots can be neglected if the intermediate distance is larger than a critical distance, whereas the interaction becomes visible once the distance is smaller than that. Two separate vortices were observed to merge into one single vortex once an extreme state of perfect contact condition has been virtually achieved.     

Half-quantum vortices in exciton–polariton condensates in applied magnetic field

We study the behavior of half-quantum vortices (HQVs) in exciton–polariton condensates in planar semiconductor microcavities in applied magnetic field. Below the critical magnetic field, that is defined by the polariton–polariton interaction constant, the condensate is elliptically polarized and there are two types of HQVs, deep and shallow. They correspond to singularities in majority and minority circular components of the condensate wave function, respectively. The core radius (healing length) of the deep HQVs decreases and the core radius of the shallow HQVs increases with increase of magnetic field. The shallow HQVs disappear and the deep HQVs transform into the integer vortices in the circularly polarized condensate when the applied magnetic field exceeds the critical one.     

Vortex structure in superconductors with a many-component order parameter

Abstract

The phenomenological theory of superconductors with a many-component order parameter (OP) is developed. On the basis of a generalized Ginzburg-Landau functional, equations for a two-component-OP superconductor are derived. It is shown that such a superconductor is specified by three length dimensionality parameters—penetration depth λ, correlation length ζ, and width d of the boundary between two superconducting-phase domains. With λ ? d ? ζ, the equations for the OP of a superconductor in a magnetic field can be explored analytically. The transition from the superconducting to the mixed phase may occur not only by the formation of ordinary Abrikosov vortices, but also owing to vortices that have two cores, each transferring a half-integral flux quantum. The total flux transferred by a vortex certainly constitutes an integral quantum. The cores of such a dimer are interconnected by two domain walls, which exercise confinement within the dimer. The distance between the cores in the dimer is of the order of d. Within a domain wall that separates two superconducting-phase domains, a dimer may fall apart into two vortices with a half-integral flux quantum.

For many-component-OP superconductors in a magnetic field, vortex structures of a more complicated nature than a dimer may occur. An individual core may transfer a fractional flux quantum, but the structure as a whole transfers an integral flux quantum. Confinement of individual cores occurs owing to a complicated system of domain walls determined by the topological charges of these vortices.

Under certain conditions, on attaining field H _c1, vortices may arise first in the domain walls, carrying a fractional flux quantum, and then within the superconducting domains.