Speed limit to the Abrikosov lattice in mesoscopic superconductors
NASA Astrophysics Data System (ADS)
Grimaldi, G.; Leo, A.; Sabatino, P.; Carapella, G.; Nigro, A.; Pace, S.; Moshchalkov, V. V.; Silhanek, A. V.
2015-07-01
We study the instability of the superconducting state in a mesoscopic geometry for the low pinning material Mo3Ge characterized by a large Ginzburg-Landau parameter. We observe that in the current-driven switching to the normal state from a nonlinear region of the Abrikosov flux flow, the mean critical vortex velocity reaches a limiting maximum velocity as a function of the applied magnetic field. Based on time-dependent Ginzburg-Landau simulations, we argue that the observed behavior is due to the high-velocity vortex dynamics confined on a mesoscopic scale. We build up a general phase diagram which includes all possible dynamic configurations of the Abrikosov lattice in a mesoscopic superconductor.
Numerical calculations of the driving force on an Abrikosov vortex
NASA Astrophysics Data System (ADS)
Chen, D.-X.; Pardo, E.; Sanchez, A.
2010-05-01
The driving force on an Abrikosov vortex is calculated numerically from the London equation and involved energies for a vortex perpendicular to the screening current near the surface of a superconductor. Compared with previous analytical derivation of the total force, the partial magnetic, kinematic, and external forces are also obtained so that the nature of the driving force may be deeply discussed. It is shown that the force is neither a Lorentz force nor a Magnus force as often believed and that in order to get a correct result, the image effects and the work done by the applied field must be taken into account. A name of London force is suggested for the driving force. A deep understanding of the nature of the driving force on Abrikosov vortices may also be important in the study of vortex pinning and dynamics in type-II superconductors.
Magnetic translation group on Abrikosov lattice
NASA Astrophysics Data System (ADS)
Goto, Akira
1996-02-01
We investigate the magnetic translational symmetry of the Bogoliubov-de Gennes equation describing quasiparticles in the vortex lattice state. Magnetic translation group is formulated for the quasiparticles and the generalized Bloch theorem is established. Projection operators are obtained and used to construct the symmetry adopted basis functions. Careful treatment of the phase of the pair potential and its quasiperiodicity enable us to get the magnetic Wannier functions, which are utilized to justify a part of Canel's assertion about the effective Hamiltonian theory.
Detection of the phase shift from a single Abrikosov vortex.
Golod, T; Rydh, A; Krasnov, V M
2010-06-01
We probe a quantum mechanical phase rotation induced by a single Abrikosov vortex in a superconducting lead, using a Josephson junction, made at the edge of the lead, as a phase-sensitive detector. We observe that the vortex induces a Josephson phase shift equal to the polar angle of the vortex within the junction length. When the vortex is close to the junction it induces a π step in the Josephson phase difference, leading to a controllable and reversible switching of the junction into the 0-π state. This in turn results in an unusual Φ(0)/2 quantization of the flux in the junction. The vortex may hence act as a tunable "phase battery" for quantum electronics.
Melting of the Abrikosov flux lattice in anisotropic superconductors
NASA Technical Reports Server (NTRS)
Beck, R. G.; Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.; Kogan, V. G.
1992-01-01
It has been proposed that the Abrikosov flux lattice in high-Tc superconductors is melted over a significant fraction of the phase diagram. A thermodynamic argument is provided which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal YBa2Cu3O(7-delta). The results offer decisive support for the melting proposal.
Macroscopic evidence for Abrikosov-type magnetic vortexes in MnSi A-phase.
Lobanova, I I; Glushkov, V V; Sluchanko, N E; Demishev, S V
2016-01-01
Intrinsic phase coherence between individual topologically stable knots in spin arrangement - skyrmions - is known to induce the crystalline-like structure in the A-phase of non-centrosymmetric MnSi with chiral spin-orbit interaction. Here we report the experimental evidence for two types of the skyrmion lattice (SL) inside the A-phase of MnSi, which are distinguished by different coupling to the anisotropic magnetic interactions. The transition between these SLs is shown to induce a change in magnetic scattering between isotropic MR discovered in the area inside the A-phase (the A-phase core) and anisotropic MR found on the border of the A-phase. We argue that the SL in the A-phase core corresponds to the dense skyrmion state built from individual skyrmions in a way similar to Abrikosov-type magnetic vortexes. PMID:26915818
Macroscopic evidence for Abrikosov-type magnetic vortexes in MnSi A-phase
Lobanova, I. I.; Glushkov, V. V.; Sluchanko, N. E.; Demishev, S. V.
2016-01-01
Intrinsic phase coherence between individual topologically stable knots in spin arrangement – skyrmions – is known to induce the crystalline-like structure in the A-phase of non-centrosymmetric MnSi with chiral spin-orbit interaction. Here we report the experimental evidence for two types of the skyrmion lattice (SL) inside the A-phase of MnSi, which are distinguished by different coupling to the anisotropic magnetic interactions. The transition between these SLs is shown to induce a change in magnetic scattering between isotropic MR discovered in the area inside the A-phase (the A-phase core) and anisotropic MR found on the border of the A-phase. We argue that the SL in the A-phase core corresponds to the dense skyrmion state built from individual skyrmions in a way similar to Abrikosov-type magnetic vortexes. PMID:26915818
A single Abrikosov vortex trapped in a mesoscopic superconducting cylindrical surface.
Carapella, G; Sabatino, P; Costabile, G
2011-11-01
We investigate the behaviour of a single Abrikosov vortex trapped in a mesoscopic superconducting cylindrical surface with a magnetic field applied transverse to its axis. In the framework of the time-dependent Ginzburg-Landau formalism we show that, provided the transport current and the magnetic field are not large, the vortex behaves as an overdamped quasi-particle in a tilted washboard potential. The cylindrical thin strip with the trapped vortex exhibits E(J) curves and time-dependent electric fields very similar to the ones exhibited by a resistively shunted Josephson weak link.
Hall Effect in the Abrikosov Lattice of Type-II Superconductors
NASA Astrophysics Data System (ADS)
Kohno, Wataru; Ueki, Hikaru; Kita, Takafumi
2016-08-01
We study vortex charging caused by the Lorentz force on supercurrent based on the augmented quasiclassical equations of superconductivity. Our numerical study on an s-wave vortex lattice in the range Hc1 < H < Hc2 reveals that each vortex core with a single flux quantum also accumulates charge due to the circulating supercurrent and has a Hall voltage across the core. The field dependence of the charge density at the core center is well described by ρ(0) ∝ H(Hc2 - H) with a peak near Hc2/2 originating from competition between the increasing magnetic field and the decreasing pair potential. The peak value of the accumulated charge in a core region of radius 0.5ξ0 is estimated to be about ηΔ0/(kFξ0) × |e| C per Δz = 10 Å along the flux line at low temperatures, where η ≡ πɛ0Δz/|e|2 = 1.09 × 1018 J-1 with e < 0 the charge of an electron, Δ0 the energy gap at T = 0, kF the Fermi wave number, and ξ0 the coherence length at T = 0.
Carapella, G.; Sabatino, P.; Barone, C.; Pagano, S.; Gombos, M.
2016-01-01
Vortices are topological defects accounting for many important effects in superconductivity, superfluidity, and magnetism. Here we address the stability of a small number of such excitations driven by strong external forces. We focus on Abrikosov-Josephson vortex that appears in lateral superconducting S/S’/S weak links with suppressed superconductivity in S’. In such a system the vortex is nucleated and confined in the narrow S’ region by means of a small magnetic field and moves under the effect of a force proportional to an applied electrical current with a velocity proportional to the measured voltage. Our numerical simulations show that when a slow moving Abrikosov-Josephson vortex is driven by a strong constant current it becomes unstable with respect to a faster moving excitation: the Josephon-like vortex. Such a current-driven transition explains the structured dissipative branches that we observe in the voltage-current curve of the weak link. When vortex matter is strongly confined phenomena as magnetoresistance oscillations and reentrance of superconductivity can possibly occur. We experimentally observe these phenomena in our weak links. PMID:27752137
Vortex lattice inhomogeneity in spatially inhomogeneous superfluids
NASA Astrophysics Data System (ADS)
Sheehy, Daniel E.; Radzihovsky, Leo
2004-11-01
A trapped degenerate Bose gas exhibits superfluidity with spatially nonuniform superfluid density. We show that the vortex distribution in such a highly inhomogeneous rotating superfluid is nevertheless nearly uniform. The inhomogeneity in vortex density, which diminishes in the rapid-rotation limit, is driven by the discrete way vortices impart angular momentum to the superfluid. This effect favors the highest vortex density in regions where the superfluid density is most uniform (e.g., the center of a harmonically trapped gas). A striking consequence of this is that the boson velocity deviates from a rigid-body form exhibiting a radial-shear flow past the vortex lattice.
Josephson vortex lattice in layered superconductors
Koshelev, A. E.; Dodgson, M. J. W.
2013-09-15
Many superconducting materials are composed of weakly coupled conducting layers. Such a layered structure has a very strong influence on the properties of vortex matter in a magnetic field. This review focuses on the properties of the Josephson vortex lattice generated by the magnetic field applied in the direction of the layers. The theoretical description is based on the Lawrence-Doniach model in the London limit, which takes only the phase degree of freedom of the superconducting order parameter into account. In spite of its simplicity, this model leads to an amazingly rich set of phenomena. We review in detail the structure of an isolated vortex line and various properties of the vortex lattice, in both dilute and dense limits. In particular, we extensively discuss the influence of the layered structure and thermal fluctuations on the selection of lattice configurations at different magnetic fields.
Vortex lattices in theory and practice
Capmbell, Laurence J.
1988-01-01
The formal simplicity of ideal point vortex systems in two dimensions has long attracted interest in both their exact solutions and in their capacity to simulate physical processes. Attention here is focused on infinite, two-fold periodic vortex arrays, including an expression for the energy density of an arbitrary vortex lattice (i.e., an arbitrary number of vortices with arbitrary strengths in a unit cell parallelogram of arbitrary shape). For the case of two vortices per unit cell, the morphology of stable lattices can be described completely. A non-trivial physical realization of such lattices is a rotating mixture of /sup 3/He and /sup 4/He at temperatures so low that both isotopic components are superfluid. The structure of the expected lattices is quite different from the usual triangular structure. Magnetic flux lines in high-temperature superconductors show a one-parameter family of degenerate ground state of the lattice due to the anisotropy of the vortex--vortex interaction. A final topic, closely related to Josephson-junction arrays, is the case of vortices confined to a grid. That is, the vortices interact pair-wise in the usual manner but are constrained to occupy only locations on an independent periodic grid. By using vortex relaxation methods in the continuum and then imposing the grid it is possible to find low-lying states extremely rapidly compared to previous Monte Carlo calculations. 11 refs., 8 figs.
Single vortex core recording in a magnetic vortex lattice
NASA Astrophysics Data System (ADS)
Mitin, D.; Nissen, D.; Schädlich, P.; Arekapudi, S. S. P. K.; Albrecht, M.
2014-02-01
We investigated the reversal characteristics of magnetic vortex cores in a two dimensional assembly of magnetic vortices. The vortex lattice was created by film deposition of 30-nm-thick permalloy onto large arrays of self-assembled spherical SiO2-particles with a diameter of 330 nm. The vortex core reversal was investigated by employing a write/read tester. This device uses a state-of-the-art magnetic recording head of a hard disc drive, which allows imaging as well as applying a local magnetic field pulse to individual vortices. The successful writing and reading of individual vortex cores is demonstrated, including a switching map, which indicates the switching behavior dependent on the relative position of the field pulse with respect to the vortex core.
Optical vortex array in spatially varying lattice
NASA Astrophysics Data System (ADS)
Kapoor, Amit; Kumar, Manish; Senthilkumaran, P.; Joseph, Joby
2016-04-01
We present an experimental method based on a modified multiple beam interference approach to generate an optical vortex array arranged in a spatially varying lattice. This method involves two steps which are: numerical synthesis of a consistent phase mask by using two-dimensional integrated phase gradient calculations and experimental implementation of produced phase mask by utilizing a phase only spatial light modulator in an optical 4f Fourier filtering setup. This method enables an independent variation of the orientation and period of the vortex lattice. As working examples, we provide the experimental demonstration of various spatially variant optical vortex lattices. We further confirm the existence of optical vortices by formation of fork fringes. Such lattices may find applications in size dependent trapping, sorting, manipulation and photonic crystals.
Ooi, S; Mochiku, T; Tachiki, M; Hirata, K
2015-02-27
The vortex-lattice melting transition of a limited number of vortices confined in mesoscopic square superconductors was studied by c-axis resistance measurements using stacks of intrinsic Josephson junctions in Bi_{2}Sr_{2}CaCu_{2}O_{8+y}. In contrast to the melting transition in bulk crystals, we have first found a clear oscillatory behavior in the field dependence of the melting temperature in small samples of 5-10 μm square. The periods of the oscillations roughly obey the regularity of the matching conditions of square vortex lattices surrounded by a square boundary and the melting temperatures are enhanced around the vortex number of i^{2} (where i is an integer). The results suggest that a confinement effect by the square boundary stabilizes square lattice structures which are realized around i^{2} vortex number even in competition with the favorable Abrikosov triangular lattice in the bulk. PMID:25768774
Vortex lattice theory: A linear algebra approach
NASA Astrophysics Data System (ADS)
Chamoun, George C.
Vortex lattices are prevalent in a large class of physical settings that are characterized by different mathematical models. We present a coherent and generalized Hamiltonian fluid mechanics-based formulation that reduces all vortex lattices into a classic problem in linear algebra for a non-normal matrix A. Via Singular Value Decomposition (SVD), the solution lies in the null space of the matrix (i.e., we require nullity( A) > 0) as well as the distribution of its singular values. We demonstrate that this approach provides a good model for various types of vortex lattices, and makes it possible to extract a rich amount of information on them. The contributions of this thesis can be classified into four main points. The first is asymmetric equilibria. A 'Brownian ratchet' construct was used which converged to asymmetric equilibria via a random walk scheme that utilized the smallest singular value of A. Distances between configurations and equilibria were measured using the Frobenius norm ||·||F and 2-norm ||·||2, and conclusions were made on the density of equilibria within the general configuration space. The second contribution used Shannon Entropy, which we interpret as a scalar measure of the robustness, or likelihood of lattices to occur in a physical setting. Third, an analytic model was produced for vortex street patterns on the sphere by using SVD in conjunction with expressions for the center of vorticity vector and angular velocity. Equilibrium curves within the configuration space were presented as a function of the geometry, and pole vortices were shown to have a critical role in the formation and destruction of vortex streets. The fourth contribution entailed a more complete perspective of the streamline topology of vortex streets, linking the bifurcations to critical points on the equilibrium curves.
Historical evolution of vortex-lattice methods
NASA Technical Reports Server (NTRS)
Deyoung, J.
1976-01-01
A review of the beginning and some orientation of the vortex-lattice method were given. The historical course of this method was followed in conjunction with its field of computational fluid dynamics, spanning the period from L.F. Richardson's paper in 1910 to 1975. The following landmarks were pointed out: numerical analysis of partial differential equations, lifting-line theory, finite-difference method, 1/4-3/4 rule, block relaxation technique, application of electronic computers, and advanced panel methods.
Simulating infinite vortex lattices in superfluids
NASA Astrophysics Data System (ADS)
Mingarelli, Luca; Keaveny, Eric E.; Barnett, Ryan
2016-07-01
We present an efficient framework to numerically treat infinite periodic vortex lattices in rotating superfluids described by the Gross-Pitaevskii theory. The commonly used split-step Fourier (SSF) spectral methods are inapplicable to such systems as the standard Fourier transform does not respect the boundary conditions mandated by the magnetic translation group. We present a generalisation of the SSF method which incorporates the correct boundary conditions by employing the so-called magnetic Fourier transform. We test the method and show that it reduces to known results in the lowest-Landau-level regime. While we focus on rotating scalar superfluids for simplicity, the framework can be naturally extended to treat multicomponent systems and systems under more general ‘synthetic’ gauge fields.
Single Abrikosov vortices as quantized information bits.
Golod, T; Iovan, A; Krasnov, V M
2015-10-12
Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex.
Single Abrikosov vortices as quantized information bits
NASA Astrophysics Data System (ADS)
Golod, T.; Iovan, A.; Krasnov, V. M.
2015-10-01
Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex.
Onset of motion and dynamic reordering of a vortex lattice.
Li, Guohong; Andrei, Eva Y; Xiao, Z L; Shuk, P; Greenblatt, M
2006-01-13
Time resolved transport measurements on a driven vortex lattice in an undoped 2H-NbSe2 crystal show that the response to a current pulse is governed by healing of defects as the lattice evolves from a stationary to a moving steady state and that the response time reflects the degree of order in the initial vortex state. We find that stationary field cooled vortex lattices become more ordered with decreasing temperature and identify a temperature below which a qualitative change in the response signals the disappearance of topological defects.
Fluctuating pancake vortices revealed by dissipation of Josephson vortex lattice.
Koshelev, A. E.; Buzdin, A. I.; Kakeya, I.; Yamamoto, T.; Kadowaki, K.
2011-06-01
In strongly anisotropic layered superconductors in tilted magnetic fields, the Josephson vortex lattice coexists with the lattice of pancake vortices. Due to the interaction between them, the dissipation of the Josephson vortex lattice is very sensitive to the presence of the pancake vortices. If the c-axis magnetic field is smaller than the corresponding lower critical field, the pancake stacks are not formed but the individual pancakes may exist in the fluctuational regime either near the surface in large-size samples or in the central region for small-size mesas. We calculate the contribution of such fluctuating pancake vortices to the c-axis conductivity of the Josephson vortex lattice and compare the theoretical results with measurements on small mesas fabricated out of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} crystals. A fingerprint of fluctuating pancakes is a characteristic exponential dependence of the c-axis conductivity observed experimentally. Our results provide strong evidence of the existence of the fluctuating pancakes and their influence on the Josephson vortex lattice dissipation.
Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.
Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R
2013-09-01
Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.
Persistence of Metastable Vortex Lattice Domains in MgB2 in the Presence of Vortex Motion
Rastovski, Catherine; Schlesinger, Kimberly; Gannon, William J; Dewhurst, Charles; Debeer-Schmitt, Lisa M; Zhigadlo, Nikolai; Karpinski, Janusz; Eskildsen, Morten
2013-01-01
Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.
Vortex lattice disorder in pseudorandom potential in rotating Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Mithun, T.; Porsezian, K.; Dey, Bishwajyoti
2016-05-01
We numerically study the vortex lattice dynamics in presence of pseudorandom potential in rotating Bose-Einstein condensate. The rotating condensate displays highly ordered triangular vortex lattice. In presence of pseudorandom potential the vortex lattice gets distorted. The histogram of the distances between each pair of the vortices shows how the long-range order of the triangular vortex lattice is destroyed in presence of pseudorandom potential.
Creation of vortex lattices by a wavefront division.
Masajada, J; Popiolek-Masajada, A; Leniec, M
2007-04-16
The Young's double-slit experiment is one of the most popular stories in the history of physics. This paper, like many others, has emerged from the Young's idea. It investigates the diffraction of the plane or spherical wave produced by three or four small holes in an opaque screen. It was noticed that the interference field contained a lattice of optical vortices which were equivalent to those produced in optical vortex interferometer. The vortex lattice generated by the three holes possessed some unique properties from which the analytical formulae for vortex points position were derived. We also pointed out the differences between our case and the double-slit experiment. Finally, some remarks on possible applications of our arrangement are discussed briefly. These theoretical considerations are illustrated with the use of experimental results.
Vortex-Lattice Utilization. [in aeronautical engineering and aircraft design
NASA Technical Reports Server (NTRS)
1976-01-01
The many novel, innovative, and unique implementations and applications of the vortex-lattice method to aerodynamic design and analysis which have been performed by Industry, Government, and Universities were presented. Although this analytical tool is not new, it continues to be utilized and refined in the aeronautical community.
Vortex penetration depth of organic superconductors: Evidence for vortex lattice melting
Tea, N.H.; Giannetta, R.W.; Salamon, M.B.; Williams, J.M.; Wang, H.H.; Geiser, U.
1997-07-01
The authors observe a crossover field H* in the temperature and magnetic field dependence of the rf vortex penetration depth in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br for {rvec H}{sub dc}{parallel}{cflx b}-axis. They find that H* can be described quantitatively by the 3D Lindemann melting theory; thus, it corresponds to the melting of the vortex lattice in {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br and lies very close to the irreversibility line. In the vortex-liquid state, they argue that the saturation of the vortex penetration depth in a magnetic field results from the finite size of the sample. The results do not have the scaling form predicted by the Coffey-Clem model in contrast to previous findings.
Single Abrikosov vortices as quantized information bits.
Golod, T; Iovan, A; Krasnov, V M
2015-01-01
Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex. PMID:26456592
Single Abrikosov vortices as quantized information bits
Golod, T.; Iovan, A.; Krasnov, V. M.
2015-01-01
Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex. PMID:26456592
Vortex Lattices in Rotating Atomic Bose Gases with Dipolar Interactions
Cooper, N.R.; Rezayi, E.H.; Simon, S.H.
2005-11-11
We show that dipolar interactions have dramatic effects on the ground states of rotating atomic Bose gases in the weak-interaction limit. With increasing dipolar interaction (relative to the net contact interaction), the mean field, or high filling factor, ground state undergoes a series of transitions between vortex lattices of different symmetries: triangular, square, 'stripe', and 'bubble' phases. We also study the effects of dipolar interactions on the quantum fluids at low filling factors. We show that the incompressible Laughlin state at filling factor {nu}=1/2 is replaced by compressible stripe and bubble phases.
Elastic Moduli of Vortex Lattices within Nonlocal London Model
NASA Astrophysics Data System (ADS)
Miranović, P.; Kogan, V. G.
2001-09-01
Vortex lattice (VL) elastic response is analyzed within the nonlocal London model which holds for high- κ clean superconductors. The squash modulus vanishes at the field H□ where VL undergoes a square-to-rhombus transition. For H>H□, where the square VL is stable, the rotation modulus turns zero at H = Hr, indicating VL instability to rotations. The shear modulus depends on the shear direction; the dependence is strong in the vicinity of H□ where the square VL is soft with respect to the shear along [110]. The H dependences of the moduli are evaluated for LuNi2B2C.
Vortex formation of a Bose-Einstein condensate in a rotating deep optical lattice
Kato, Akira; Nakano, Yuki; Kasamatsu, Kenichi; Matsui, Tetsuo
2011-11-15
We study the dynamics of vortex nucleation and lattice formation in a Bose-Einstein condensate in a rotating square optical lattice by numerical simulations of the Gross-Pitaevskii equation. Different dynamical regimes of vortex nucleation are found, depending on the depth and period of the optical lattice. We make an extensive comparison with the experiments by R. A. Williams et al.[Phys. Rev. Lett. 104, 050404 (2010)], especially focusing on the issues of the critical rotation frequency for the first vortex nucleation and the vortex number as a function of rotation frequency.
Transverse forces on a vortex in lattice models of superfluids
NASA Astrophysics Data System (ADS)
Sonin, E. B.
2013-12-01
The paper derives the transverse forces (the Magnus and the Lorentz forces) in the lattice models of superfluids in the continuous approximation. The continuous approximation restores translational invariance absent in the original lattice model, but the theory is not Galilean invariant. As a result, calculation of the two transverse forces on the vortex, Magnus force and Lorentz force, requires the analysis of two balances, for the true momentum of particles in the lattice (Magnus force) and for the quasimomentum (Lorentz force) known from the Bloch theory of particles in the periodic potential. While the developed theory yields the same Lorentz force, which was well known before, a new general expression for the Magnus force was obtained. The theory demonstrates how a small Magnus force emerges in the Josephson-junction array if the particle-hole symmetry is broken. The continuous approximation for the Bose-Hubbard model close to the superfluid-insulator transition was developed, which was used for calculation of the Magnus force. The theory shows that there is an area in the phase diagram for the Bose-Hubbard model, where the Magnus force has an inverse sign with respect to that which is expected from the sign of velocity circulation.
Anisotropic Peak Effect due to Structural Phase Transition in the Vortex Lattice
NASA Astrophysics Data System (ADS)
Rosenstein, Baruch; Knigavko, Anton
1999-07-01
It is shown that the recently observed new peak effect in YBCO could be explained by the softening of the vortex lattice due to a structural phase transition in the vortex lattice. At this transition square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with the softening of shear modes (elastic modulus c66 vanishes) at melting, in this case the relevant mode is ``squash'' mode ( c11+c22-2c12 vanishes).
Elastic Moduli of Vortex Lattices within Nonlocal London Model
Miranovic, P.; Kogan, V. G.
2001-09-24
Vortex lattice (VL) elastic response is analyzed within the nonlocal London model which holds for high-{kappa} clean superconductors. The squash modulus vanishes at the field H{sub (open square)} where VL undergoes a square-to-rhombus transition. For H>H{sub (open square)}, where the square VL is stable, the rotation modulus turns zero at H=H{sub r} , indicating VL instability to rotations. The shear modulus depends on the shear direction; the dependence is strong in the vicinity of H{sub (open square)} where the square VL is soft with respect to the shear along [110] . The H dependences of the moduli are evaluated for LuNi{sub 2}B {sub 2}C .
Vortex lattices in strongly interacting Fermi gas with crossed-beam dipole trap
NASA Astrophysics Data System (ADS)
Wu, Yuping; Yao, Xingcan; Chen, Haoze; Liu, Xiangpei; Wang, Xiaoqiong
2016-05-01
We have built an experiment system to explore the dynamic and vortex in quantum degenerate Li6 gas. By using UV MOT and crossed-beam dipole trap, we obtained BEC of 2* 105 molecules. With a tightly focused 532nm laser beam as rotating bucket wall, We observed vortex formation in strongly interacting fermi superfluid. At suitable stirring frequency we produced the condensate of fermi pairs for which up to 10 vortices were simultaneously present. We produced vortex lattices in different magnetic fields (from BEC side to BCS side). Also we measured the lifetime of vortex lattices in different interaction region. This work was funded by CAS and USTC.
Observation of Vortex Nucleation in a Rotating Two-Dimensional Lattice of Bose-Einstein Condensates
Williams, R. A.; Al-Assam, S.; Foot, C. J.
2010-02-05
We report the observation of vortex nucleation in a rotating optical lattice. A {sup 87}Rb Bose-Einstein condensate was loaded into a static two-dimensional lattice and the rotation frequency of the lattice was then increased from zero. We studied how vortex nucleation depended on optical lattice depth and rotation frequency. For deep lattices above the chemical potential of the condensate we observed a linear dependence of the number of vortices created with the rotation frequency, even below the thermodynamic critical frequency required for vortex nucleation. At these lattice depths the system formed an array of Josephson-coupled condensates. The effective magnetic field produced by rotation introduced characteristic relative phases between neighboring condensates, such that vortices were observed upon ramping down the lattice depth and recombining the condensates.
Tailored complex 3D vortex lattice structures by perturbed multiples of three-plane waves.
Xavier, Jolly; Vyas, Sunil; Senthilkumaran, Paramasivam; Joseph, Joby
2012-04-20
As three-plane waves are the minimum number required for the formation of vortex-embedded lattice structures by plane wave interference, we present our experimental investigation on the formation of complex 3D photonic vortex lattice structures by a designed superposition of multiples of phase-engineered three-plane waves. The unfolding of the generated complex photonic lattice structures with higher order helical phase is realized by perturbing the superposition of a relatively phase-encoded, axially equidistant multiple of three noncoplanar plane waves. Through a programmable spatial light modulator assisted single step fabrication approach, the unfolded 3D vortex lattice structures are experimentally realized, well matched to our computer simulations. The formation of higher order intertwined helices embedded in these 3D spiraling vortex lattice structures by the superposition of the multiples of phase-engineered three-plane waves interference is also studied.
Observation of the vortex lattice melting by NMR spin-lattice relaxation in the mixed state
Bulaevskii, L.N.; Hammel, P.C.; Vinokur, V.M.
1994-01-01
For anisotropic layered superconductors the effect of moving vortices on the nuclear spin magnetization is calculated. Current is supposed to flow along layers, and applied magnetic field is tilted with respect to c-axis. In the solid phase the motion of the vortex lattice produces an alternating magnetic field perpendicular to the applied field which causes the decay of the spin-echo amplitude. This decay rate will display an array of peaks as a function of frequency. In the liquid phase this alternating field contribute to the longitudinal relaxation rate W{sub 1} which has a single peak.
Vortex lattices generated by the Kelvin-Helmholtz instability in the Gross-Pitaevskii equation
Ohta, A.; Kashiwa, R.; Sakaguchi, H.
2010-11-15
Vortex streets are formed from sheared initial conditions in classical fluids even without viscosity, which is called the Kelvin-Helmholtz instability. We demonstrate that similar vortex streets are generated from sheared initial conditions by the direct numerical simulation of the Gross-Pitaevskii (GP) equation which describes the dynamics of the Bose-Einstein condensates. Furthermore, we show the vortex-lattice formation from sheared initial conditions analogous to the rigid-body rotation in the GP equation under a rotating harmonic potential. The vortex-lattice formation by the dynamical instability in the system without energy dissipation differs from the vortex-lattice formation process by the imaginary time evolution of the GP equation where the lowest energy state is obtained.
NASA Astrophysics Data System (ADS)
Ganguli, Somesh Chandra; Singh, Harkirat; Ganguly, Rini; Bagwe, Vivas; Thamizhavel, Arumugam; Raychaudhuri, Pratap
2016-04-01
We report experimental evidence of strong orientational coupling between the crystal lattice and the vortex lattice in a weakly pinned Co-doped NbSe2 single crystal through direct imaging using low temperature scanning tunneling microscopy/spectroscopy. When the magnetic field is applied along the six-fold symmetric c-axis of the NbSe2 crystal, the basis vectors of the vortex lattice are preferentially aligned along the basis vectors of the crystal lattice. The orientational coupling between the vortex lattice and crystal lattice becomes more pronounced as the magnetic field is increased. This orientational coupling enhances the stability of the orientational order of the vortex lattice, which persists even in the disordered state at high fields where dislocations and disclinations have destroyed the topological order. Our results underpin the importance of crystal lattice symmetry on the vortex state phase diagram of weakly pinned type II superconductors.
Vortex lattice disorder in YBa2Cu3O studied with β-NMR
NASA Astrophysics Data System (ADS)
Saadaoui, H.; MacFarlane, W. A.; Morris, G. D.; Salman, Z.; Chow, K. H.; Fan, I.; Hossain, M. D.; Liang, R.; Mansour, A. I.; Parolin, T. J.; Smadella, M.; Song, Q.; Wang, D.; Kiefl, R. F.
2009-04-01
In this paper, we report Li+8β-NMR measurements in thin Ag films deposited on the surface of YBa2Cu3O (YBCO) in the vortex state. The resonance in the Ag overlayer broadens dramatically below the superconducting transition temperature Tc, as expected from the underlying vortex lattice in the YBCO. However, the lineshape is much broader and more symmetric than expected for an ideal vortex lattice. These results indicate the observed field distribution in the Ag overlayer is dominated by extrinsic, long length scale disorder.
NASA Astrophysics Data System (ADS)
Sakaguchi, Hidetsugu; Umeda, Kanji
2016-06-01
The Gross-Pitaevskii equation for two-component rotating Bose-Einstein condensates with the Rashba-type spin-orbit (SO) coupling is studied with numerical simulations and variational analyses. A multiquantum vortex state becomes a ground state in a harmonic potential when mutual interaction is absent. When the attractive interaction is strong, the multiquantum vortex state exhibits modulational instability in the azimuthal direction, and a soliton-like state appears. When the repulsive interaction is strong, a vortex lattice state with a multiquantum vortex at the center is created. We find that the vortex lattice state is approximated at a linear combination of multiquantum vortex states.
NASA Astrophysics Data System (ADS)
Sakaguchi, Hidetsugu; Umeda, Kanji
2016-06-01
The Gross-Pitaevskii equation for two-component rotating Bose-Einstein condensates with the Rashba-type spin-orbit (SO) coupling is studied with numerical simulations and variational analyses. A multiquantum vortex state becomes a ground state in a harmonic potential when mutual interaction is absent. When the attractive interaction is strong, the multiquantum vortex state exhibits modulational instability in the azimuthal direction, and a soliton-like state appears. When the repulsive interaction is strong, a vortex lattice state with a multiquantum vortex at the center is created. We find that the vortex lattice state is approximated at a linear combination of multiquantum vortex states.
NASA Technical Reports Server (NTRS)
Lamar, J. E.
1976-01-01
A new subsonic method has been developed by which the mean camber surface can be determined for trimmed noncoplanar planforms with minimum vortex drag. This method uses a vortex lattice and overcomes previous difficulties with chord loading specification. A Trefftz plane analysis is utilized to determine the optimum span loading for minimum drag, then solved for the mean camber surface of the wing, which provides the required loading. Sensitivity studies, comparisons with other theories, and applications to configurations which include a tandem wing and a wing winglet combination have been made and are presented.
A generalized vortex lattice method for subsonic and supersonic flow applications
NASA Technical Reports Server (NTRS)
Miranda, L. R.; Elliot, R. D.; Baker, W. M.
1977-01-01
If the discrete vortex lattice is considered as an approximation to the surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vorticity-induced velocity field. The proper incorporation of this term to the velocity field generated by the discrete vortex lines renders the present vortex lattice method valid for supersonic flow. Special techniques for simulating nonzero thickness lifting surfaces and fusiform bodies with vortex lattice elements are included. Thickness effects of wing-like components are simulated by a double (biplanar) vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentrical cylindrical surfaces. The analysis of sideslip effects by the subject method is described. Numerical considerations peculiar to the application of these techniques are also discussed. The method has been implemented in a digital computer code. A users manual is included along with a complete FORTRAN compilation, an executed case, and conversion programs for transforming input for the NASA wave drag program.
System Identification of a Vortex Lattice Aerodynamic Model
NASA Technical Reports Server (NTRS)
Juang, Jer-Nan; Kholodar, Denis; Dowell, Earl H.
2001-01-01
The state-space presentation of an aerodynamic vortex model is considered from a classical and system identification perspective. Using an aerodynamic vortex model as a numerical simulator of a wing tunnel experiment, both full state and limited state data or measurements are considered. Two possible approaches for system identification are presented and modal controllability and observability are also considered. The theory then is applied to the system identification of a flow over an aerodynamic delta wing and typical results are presented.
Vortex states and quantum magnetic oscillations in conventional type-II superconductors
NASA Astrophysics Data System (ADS)
Maniv, Tsofar; Zhuravlev, Vladimir; Vagner, Israel; Wyder, Peter
2001-10-01
The theory of pure type-II superconductors at high magnetic fields and low temperatures has recently attracted much attention due to the discovery of de Haas-van Alphen oscillations deep in the vortex state. In this article the authors review the state of the art in this rapidly growing new field of research. The very existence of quantum magnetic oscillations deep in the vortex state poses challenging questions to the theorists working in this field. For a conventional extreme type-II superconductor in magnetic fields just below the upper critical field Hc2, the quasiparticle spectrum is gapless and the de Haas-van Alphen effect is suppressed with respect to the corresponding normal-state signal due to superconducting induced currents near the vortex cores, which are of paramagnetic nature. Numerical simulations of the quasiparticle band structure in the Abrikosov vortex lattice show the existence of well-separated Landau bands below Hc2. An analytical perturbative approach, which emphasizes the importance of phase coherence in quasiparticle scattering by the pair potential in the Abrikosov lattice, predicts a relatively weak magnetic breakdown of the corresponding cyclotron orbits. In contrast to the situation in the Abrikosov lattice state, a theory based on a random vortex lattice model yields large exponential decay of the de Haas-van Alphen oscillations with the superconducting order parameter below Hc2. The disordered nature of the vortex state near Hc2 in real superconductors, where long-range phase coherence in the superconducting order parameter is destroyed, could explain the success of this model in interpreting experimental data below Hc2. In the Abrikosov vortex lattice state, which usually stabilizes well below Hc2, the residual damping of the de Haas-van Alphen amplitude is significantly reduced. In quasi-two-dimensional superconductors, phase fluctuations associated with sliding Bragg chains along principal axes in the vortex lattice lead to a weak
Formation of Vortex Lattices in Superfluid Bose Gases at Finite Temperatures
NASA Astrophysics Data System (ADS)
Arahata, E.; Nikuni, T.
2016-05-01
We study the dynamics of a rotating trapped Bose-Einstein condensate (BEC) at finite temperatures. Using the Zaremba-Nikuni-Griffin formalism, based on a generalized Gross-Pitaevskii equation for the condensate coupled to a semiclassical kinetic equation for a thermal cloud, we numerically simulate vortex lattice formation in the presence of a time-dependent rotating trap potential. At low rotation frequency, the thermal cloud undergoes rigid body rotation, while the condensate exhibits irrotational flow. Above a certain threshold rotation frequency, vortices penetrate into the condensate and form a vortex lattice. Our simulation result clearly indicates a crucial role for the thermal cloud, which triggers vortex lattice formation in the rotating BEC.
Photonic Band Gap via Quantum Coherence in Vortex Lattices of Bose-Einstein Condensates
Muestecaplioglu, Oe.E.; Oktel, M.Oe.
2005-06-10
We investigate the optical response of an atomic Bose-Einstein condensate with a vortex lattice. We find that it is possible for the vortex lattice to act as a photonic crystal and create photonic band gaps, by enhancing the refractive index of the condensate via a quantum coherent scheme. If high enough index contrast between the vortex core and the atomic sample is achieved, a photonic band gap arises depending on the healing length and the lattice spacing. A wide range of experimentally accessible parameters are examined and band gaps in the visible region of the electromagnetic spectrum are found. We also show how directional band gaps can be used to directly measure the rotation frequency of the condensate.
Measuring the disorder of vortex lattices in a Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Rakonjac, A.; Marchant, A. L.; Billam, T. P.; Helm, J. L.; Yu, M. M. H.; Gardiner, S. A.; Cornish, S. L.
2016-01-01
We report observations of the formation and subsequent decay of a vortex lattice in a Bose-Einstein condensate confined in a hybrid optical-magnetic trap. Vortices are induced by rotating the anharmonic magnetic potential that provides confinement in the horizontal plane. We present simple numerical techniques based on image analysis to detect vortices and analyze their distributions. We use these methods to quantify the amount of order present in the vortex distribution as it transitions from a disordered array to the energetically favorable ordered lattice.
Model for nodal quasiparticle scattering in a disordered vortex lattice
NASA Astrophysics Data System (ADS)
Maltseva, Marianna; Coleman, P.
2009-10-01
Recent scanning-tunneling experiments on Ca2-xNaxCuO2Cl2 by Hanaguri [Science 323, 923 (2009)] observe field-dependent quasiparticle interference effects which are sensitive to the sign of the d -wave order parameter. Their analysis of spatial fluctuations in the local density of states shows that there is a selective enhancement of quasiparticle scattering events that preserve the gap sign and a selective depression of the quasiparticle scattering events that reverse the gap sign. We introduce a model which accounts for this phenomenon as a consequence of vortex pinning to impurities. Each pinned vortex embeds several impurities in its core. The observations of recent experiments can be accounted for by assuming that the scattering potentials of the impurities inside the vortex cores acquire an additional resonant or Andreev scattering component, both of which induce gap sign preserving scattering events.
Anisotropic peak effect due to structural phase transition in the vortex lattice
NASA Astrophysics Data System (ADS)
Rosenstein, Baruch; Knigavko, Anton
2000-05-01
The recently observed new peak effect in YBCO is explained by softening of the vortex lattice (VL) due to a structural phase transition in the VL. At this transition, square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with softening of shear modes at melting, in this case the relevant mode is the point. The squash mode is highly anisotropic and we point out some peculiar effects associated with this feature.
Electronic structure of topological superconductors in the presence of a vortex lattice
NASA Astrophysics Data System (ADS)
Liu, Tianyu; Franz, M.
2015-10-01
Certain types of topological superconductors and superfluids are known to host protected Majorana zero modes in cores of Abrikosov vortices. When such vortices are arranged in a dense periodic lattice one expects zero modes from neighboring vortices to hybridize and form dispersing bands. Understanding the structure of these bands is essential for the schemes that aim to employ the zero modes in quantum computation applications and in studies of their strongly interacting phases. We investigate here the band formation phenomenon in two concrete models, describing a two-dimensional px+i py superconductor and a superconducting surface of a three-dimensional strong topological insulator (Fu-Kane model), using a combination of analytical and numerical techniques. We find that the physics of the Majorana bands is well described by tight-binding models of Majorana fermions coupled to a static Z2 gauge field with a nontrivial gauge flux through each plaquette, in accord with expectations based on very general arguments. In the case of the Fu-Kane model we also find that, irrespective of the lattice geometry, the Majorana band becomes completely flat at the so-called neutrality point (chemical potential coincident with the Dirac point) where the model exhibits an extra chiral symmetry. In this limit the low-energy physics will be dominated by four-fermion interaction terms which are permitted by symmetries and may arise from the Coulomb interaction between the constituent electron degrees of freedom.
Visualizing the morphology of vortex lattice domains in a bulk type-II superconductor
Reimann, T.; Mühlbauer, S.; Schulz, M.; Betz, B.; Kaestner, A.; Pipich, V.; Böni, P.; Grünzweig, C.
2015-01-01
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice. PMID:26522610
Visualizing the morphology of vortex lattice domains in a bulk type-II superconductor.
Reimann, T; Mühlbauer, S; Schulz, M; Betz, B; Kaestner, A; Pipich, V; Böni, P; Grünzweig, C
2015-01-01
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice. PMID:26522610
Visualizing the morphology of vortex lattice domains in a bulk type-II superconductor
NASA Astrophysics Data System (ADS)
Reimann, T.; Mühlbauer, S.; Schulz, M.; Betz, B.; Kaestner, A.; Pipich, V.; Böni, P.; Grünzweig, C.
2015-11-01
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice.
Visualizing the morphology of vortex lattice domains in a bulk type-II superconductor.
Reimann, T; Mühlbauer, S; Schulz, M; Betz, B; Kaestner, A; Pipich, V; Böni, P; Grünzweig, C
2015-01-01
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice.
Validation of Vortex-Lattice Method for Loads on Wings in Lift-Generated Wakes
NASA Technical Reports Server (NTRS)
Rossow, Vernon J.
1995-01-01
A study is described that evaluates the accuracy of vortex-lattice methods when they are used to compute the loads induced on aircraft as they encounter lift-generated wakes. The evaluation is accomplished by the use of measurements made in the 80 by 120 ft Wind Tunnel of the lift, rolling moment, and downwash in the wake of three configurations of a model of a subsonic transport aircraft. The downwash measurements are used as input for a vortex-lattice code in order to compute the lift and rolling moment induced on wings that have a span of 0.186, 0.510, or 1.022 times the span of the wake-generating model. Comparison of the computed results with the measured lift and rolling-moment distributions the vortex-lattice method is very reliable as long as the span of the encountering or following wing is less than about 0.2 of the generator span. As the span of the following wing increases above 0.2, the vortex-lattice method continues to correctly predict the trends and nature of the induced loads, but it overpredicts the magnitude of the loads by increasing amounts.
Some applications of the quasi vortex-lattice method in steady and unsteady aerodynamics
NASA Technical Reports Server (NTRS)
Lan, C. E.
1976-01-01
The quasi vortex-lattice method is reviewed and applied to the evaluation of backwash, with applications to ground effect analysis. It is also extended to unsteady aerodynamics, with particular interest in the calculation of unsteady leading-edge suction. Some applications in ornithopter aerodynamics are given.
Manifestation of chirality in the vortex lattice in a two-dimensional topological superconductor
NASA Astrophysics Data System (ADS)
Smith, Evan D. B.; Tanaka, K.; Nagai, Yuki
2016-08-01
We study the vortex lattice in a two-dimensional s -wave topological superconductor with Rashba spin-orbit coupling and Zeeman field by solving the Bogoliubov-de Gennes equations self-consistently for the superconducting order parameter. We find that when spin-orbit coupling is relatively weak, one of the two underlying chiralities in the topological superconducting state can be strongly manifest in the vortex core structure and govern the response of the system to vorticity and a nonmagnetic impurity where the vortex is pinned. The Majorana zero mode in the vortex core is found to be robust against the nonmagnetic impurity in that it remains effectively a zero-energy bound state regardless of the impurity potential strength and the major chirality. The spin polarization of the Majorana bound state depends on the major chirality for weak spin-orbit coupling, while it is determined simply by the vorticity when spin-orbit coupling is relatively strong.
Yao, Xiaoyan; Dong, Shuai
2016-01-01
The expanded classical Kitaev-Heisenberg model on a honeycomb lattice is investigated with the next-nearest-neighboring Heisenberg interaction considered. The simulation shows a rich phase diagram with periodic behavior in a wide parameter range. Beside the double 120° ordered phase, an inhomogeneous phase is uncovered to exhibit a topological triple-vortex lattice, corresponding to the hexagonal domain structure of vector chirality, which is stabilized by the mixed frustration of two sources: the geometrical frustration arising from the lattice structure as well as the frustration from the Kitaev couplings. PMID:27229486
Yao, Xiaoyan; Dong, Shuai
2016-01-01
The expanded classical Kitaev-Heisenberg model on a honeycomb lattice is investigated with the next-nearest-neighboring Heisenberg interaction considered. The simulation shows a rich phase diagram with periodic behavior in a wide parameter range. Beside the double 120° ordered phase, an inhomogeneous phase is uncovered to exhibit a topological triple-vortex lattice, corresponding to the hexagonal domain structure of vector chirality, which is stabilized by the mixed frustration of two sources: the geometrical frustration arising from the lattice structure as well as the frustration from the Kitaev couplings. PMID:27229486
NASA Astrophysics Data System (ADS)
Zhao, Qiang
2016-02-01
Motivated by recent experiments carried out by Spielman's group at NIST, we study the vortex formation in a rotating Bose-Einstein condensate in synthetic magnetic field confined in a harmonic potential combined with an optical lattice. We obtain numerical solutions of the two-dimensional Gross-Pitaevskii equation and compare the vortex formation by synthetic magnetic field method with those by rotating frame method. We conclude that a large angular momentum indeed can be created in the presence of the optical lattice. However, it is still more difficult to rotate the condensate by the synthetic magnetic field than by the rotating frame even if the optical lattice is added, and the chemical potential and energy remain almost unchanged by increasing rotational frequency.
Applications of the unsteady vortex-lattice method in aircraft aeroelasticity and flight dynamics
NASA Astrophysics Data System (ADS)
Murua, Joseba; Palacios, Rafael; Graham, J. Michael R.
2012-11-01
The unsteady vortex-lattice method provides a medium-fidelity tool for the prediction of non-stationary aerodynamic loads in low-speed, but high-Reynolds-number, attached flow conditions. Despite a proven track record in applications where free-wake modelling is critical, other less-computationally expensive potential-flow models, such as the doublet-lattice method and strip theory, have long been favoured in fixed-wing aircraft aeroelasticity and flight dynamics. This paper presents how the unsteady vortex-lattice method can be implemented as an enhanced alternative to those techniques for diverse situations that arise in flexible-aircraft dynamics. A historical review of the methodology is included, with latest developments and practical applications. Different formulations of the aerodynamic equations are outlined, and they are integrated with a nonlinear beam model for the full description of the dynamics of a free-flying flexible vehicle. Nonlinear time-marching solutions capture large wing excursions and wake roll-up, and the linearisation of the equations lends itself to a seamless, monolithic state-space assembly, particularly convenient for stability analysis and flight control system design. The numerical studies emphasise scenarios where the unsteady vortex-lattice method can provide an advantage over other state-of-the-art approaches. Examples of this include unsteady aerodynamics in vehicles with coupled aeroelasticity and flight dynamics, and in lifting surfaces undergoing complex kinematics, large deformations, or in-plane motions. Geometric nonlinearities are shown to play an instrumental, and often counter-intuitive, role in the aircraft dynamics. The unsteady vortex-lattice method is unveiled as a remarkable tool that can successfully incorporate all those effects in the unsteady aerodynamics modelling.
NASA Astrophysics Data System (ADS)
Cheng, Szu-Cheng; Jheng, Shih-Da
2016-08-01
This paper reports a novel type of vortex lattice, referred to as a bubble crystal, which was discovered in rapidly rotating Bose gases with long-range interactions. Bubble crystals differ from vortex lattices which possess a single quantum flux per unit cell, while atoms in bubble crystals are clustered periodically and surrounded by vortices. No existing model is able to describe the vortex structure of bubble crystals; however, we identified a mathematical lattice, which is a subset of coherent states and exists periodically in the physical space. This lattice is called a von Neumann lattice, and when it possesses a single vortex per unit cell, it presents the same geometrical structure as an Abrikosov lattice. In this report, we extend the von Neumann lattice to one with an integral number of flux quanta per unit cell and demonstrate that von Neumann lattices well reproduce the translational properties of bubble crystals. Numerical simulations confirm that, as a generalized vortex, a von Neumann lattice can be physically realized using vortex lattices in rapidly rotating Bose gases with dipole interatomic interactions.
Cheng, Szu-Cheng; Jheng, Shih-Da
2016-01-01
This paper reports a novel type of vortex lattice, referred to as a bubble crystal, which was discovered in rapidly rotating Bose gases with long-range interactions. Bubble crystals differ from vortex lattices which possess a single quantum flux per unit cell, while atoms in bubble crystals are clustered periodically and surrounded by vortices. No existing model is able to describe the vortex structure of bubble crystals; however, we identified a mathematical lattice, which is a subset of coherent states and exists periodically in the physical space. This lattice is called a von Neumann lattice, and when it possesses a single vortex per unit cell, it presents the same geometrical structure as an Abrikosov lattice. In this report, we extend the von Neumann lattice to one with an integral number of flux quanta per unit cell and demonstrate that von Neumann lattices well reproduce the translational properties of bubble crystals. Numerical simulations confirm that, as a generalized vortex, a von Neumann lattice can be physically realized using vortex lattices in rapidly rotating Bose gases with dipole interatomic interactions. PMID:27545446
Cheng, Szu-Cheng; Jheng, Shih-Da
2016-01-01
This paper reports a novel type of vortex lattice, referred to as a bubble crystal, which was discovered in rapidly rotating Bose gases with long-range interactions. Bubble crystals differ from vortex lattices which possess a single quantum flux per unit cell, while atoms in bubble crystals are clustered periodically and surrounded by vortices. No existing model is able to describe the vortex structure of bubble crystals; however, we identified a mathematical lattice, which is a subset of coherent states and exists periodically in the physical space. This lattice is called a von Neumann lattice, and when it possesses a single vortex per unit cell, it presents the same geometrical structure as an Abrikosov lattice. In this report, we extend the von Neumann lattice to one with an integral number of flux quanta per unit cell and demonstrate that von Neumann lattices well reproduce the translational properties of bubble crystals. Numerical simulations confirm that, as a generalized vortex, a von Neumann lattice can be physically realized using vortex lattices in rapidly rotating Bose gases with dipole interatomic interactions. PMID:27545446
Transition from slow Abrikosov to fast moving Josephson vortices in iron pnictide superconductors.
Moll, Philip J W; Balicas, Luis; Geshkenbein, Vadim; Blatter, Gianni; Karpinski, Janusz; Zhigadlo, Nikolai D; Batlogg, Bertram
2013-02-01
Iron pnictides are layered high T(c) superconductors with moderate material anisotropy and thus Abrikosov vortices are expected in the mixed state. Yet, we have discovered a distinct change in the nature of the vortices from Abrikosov-like to Josephson-like in the pnictide superconductor SmFeAs(O,F) with T(c)~48-50 K on cooling below a temperature T*~41-42 K, despite its moderate electronic anisotropy γ~4-6. This transition is hallmarked by a sharp drop in the critical current and accordingly a jump in the flux-flow voltage in a magnetic field precisely aligned along the FeAs layers, indicative of highly mobile vortices. T* coincides well with the temperature where the coherence length ξ(c) perpendicular to the layers matches half of the FeAs-layer spacing. For fields slightly out-of-plane (> 0.1°- 0.15°) the vortices are completely immobilized as well-pinned Abrikosov segments are introduced when the vortex crosses the FeAs layers. We interpret these findings as a transition from well-pinned, slow moving Abrikosov vortices at high temperatures to weakly pinned, fast flowing Josephson vortices at low temperatures. This vortex dynamics could become technologically relevant as superconducting applications will always operate deep in the Josephson regime.
Stabilization of active matter by flow-vortex lattices and defect ordering
Doostmohammadi, Amin; Adamer, Michael F.; Thampi, Sumesh P.; Yeomans, Julia M.
2016-01-01
Active systems, from bacterial suspensions to cellular monolayers, are continuously driven out of equilibrium by local injection of energy from their constituent elements and exhibit turbulent-like and chaotic patterns. Here we demonstrate both theoretically and through numerical simulations, that the crossover between wet active systems, whose behaviour is dominated by hydrodynamics, and dry active matter where any flow is screened, can be achieved by using friction as a control parameter. Moreover, we discover unexpected vortex ordering at this wet–dry crossover. We show that the self organization of vortices into lattices is accompanied by the spatial ordering of topological defects leading to active crystal-like structures. The emergence of vortex lattices, which leads to the positional ordering of topological defects, suggests potential applications in the design and control of active materials. PMID:26837846
Mobile impurities and orthogonality catastrophe in two-dimensional vortex lattices
NASA Astrophysics Data System (ADS)
Caracanhas, M. A.; Pereira, R. G.
2015-01-01
We investigate the properties of a neutral impurity atom coupled with the Tkachenko modes of a two-dimensional vortex lattice in a Bose-Einstein condensate. In contrast with polarons in homogeneous condensates, the marginal impurity-boson interaction in the vortex lattice leads to infrared singularities in perturbation theory and to the breakdown of the quasiparticle picture in the low-energy limit. These infrared singularities are interpreted in terms of a renormalization of the coupling constant, quasiparticle weight, and effective impurity mass. The divergence of the effective mass in the low-energy limit gives rise to a power-law singularity in the impurity spectral function and provides an example of an emergent orthogonality catastrophe in a bosonic system.
Stabilization of active matter by flow-vortex lattices and defect ordering
NASA Astrophysics Data System (ADS)
Doostmohammadi, Amin; Adamer, Michael F.; Thampi, Sumesh P.; Yeomans, Julia M.
2016-02-01
Active systems, from bacterial suspensions to cellular monolayers, are continuously driven out of equilibrium by local injection of energy from their constituent elements and exhibit turbulent-like and chaotic patterns. Here we demonstrate both theoretically and through numerical simulations, that the crossover between wet active systems, whose behaviour is dominated by hydrodynamics, and dry active matter where any flow is screened, can be achieved by using friction as a control parameter. Moreover, we discover unexpected vortex ordering at this wet-dry crossover. We show that the self organization of vortices into lattices is accompanied by the spatial ordering of topological defects leading to active crystal-like structures. The emergence of vortex lattices, which leads to the positional ordering of topological defects, suggests potential applications in the design and control of active materials.
Stabilization of active matter by flow-vortex lattices and defect ordering.
Doostmohammadi, Amin; Adamer, Michael F; Thampi, Sumesh P; Yeomans, Julia M
2016-01-01
Active systems, from bacterial suspensions to cellular monolayers, are continuously driven out of equilibrium by local injection of energy from their constituent elements and exhibit turbulent-like and chaotic patterns. Here we demonstrate both theoretically and through numerical simulations, that the crossover between wet active systems, whose behaviour is dominated by hydrodynamics, and dry active matter where any flow is screened, can be achieved by using friction as a control parameter. Moreover, we discover unexpected vortex ordering at this wet-dry crossover. We show that the self organization of vortices into lattices is accompanied by the spatial ordering of topological defects leading to active crystal-like structures. The emergence of vortex lattices, which leads to the positional ordering of topological defects, suggests potential applications in the design and control of active materials. PMID:26837846
Observation of Coupled Vortex Lattices in a Mass-Imbalance Bose and Fermi Superfluid Mixture
NASA Astrophysics Data System (ADS)
Yao, Xing-Can; Chen, Hao-Ze; Wu, Yu-Ping; Liu, Xiang-Pei; Wang, Xiao-Qiong; Jiang, Xiao; Deng, Youjin; Chen, Yu-Ao; Pan, Jian-Wei
2016-09-01
Quantized vortices play an essential role in diverse superfluid phenomena. In a Bose-Fermi superfluid mixture, especially of two mass-imbalance species, such macroscopic quantum phenomena are particularly rich due to the interplay between the Bose and Fermi superfluidity. However, generating a Bose-Fermi two-species superfluid, producing coupled vortex lattices within, and further probing interspecies interaction effects remain challenging. Here, we experimentally realize a two-species superfluid with dilute gases of lithium-6 and potassium-41, having a mass ratio of about seven. By rotating the superfluid mixture, we simultaneously produce coupled vortex lattices of the two species and thus present a definitive visual evidence for the double superfluidity. Moreover, we report several unconventional behaviors, due to the Bose-Fermi interaction, on the formation and decay of two-species vortices.
Zehetmayer, M
2015-01-01
Order-disorder transitions take place in many physical systems, but observing them in detail in real materials is difficult. In two- or quasi-two-dimensional systems, the transition has been studied by computer simulations and experimentally in electron sheets, dusty plasmas, colloidal and other systems. Here I show the different stages of defect formation in the vortex lattice of a superconductor while it undergoes an order-disorder transition by presenting real-space images of the lattice from scanning tunneling spectroscopy. When the system evolves from the ordered to the disordered state, the predominant kind of defect changes from dislocation pairs to single dislocations, and finally to defect clusters forming grain boundaries. Correlation functions indicate a hexatic-like state preceding the disordered state. The transition in the microscopic vortex distribution is mirrored by the well-known spectacular second peak effect observed in the macroscopic current density of the superconductor.
Rotating superfluids in anharmonic traps: From vortex lattices to giant vortices
Correggi, Michele; Pinsker, Florian; Rougerie, Nicolas; Yngvason, Jakob
2011-11-15
We study a superfluid in a rotating anharmonic trap and explicate a rigorous proof of a transition from a vortex lattice to a giant vortex state as the rotation is increased beyond a limiting speed determined by the interaction strength. The transition is characterized by the disappearance of the vortices from the annulus where the bulk of the superfluid is concentrated due to centrifugal forces while a macroscopic phase circulation remains. The analysis is carried out within two-dimensional Gross-Pitaevskii theory at large coupling constant and reveals significant differences between ''soft'' anharmonic traps (like a quartic plus quadratic trapping potential) and traps with a fixed boundary: in the latter case the transition takes place in a parameter regime where the size of vortices is very small relative to the width of the annulus, whereas in soft traps the vortex lattice persists until the width of the annulus becomes comparable to the vortex cores. Moreover, the density profile in the annulus where the bulk is concentrated is, in the soft case, approximately Gaussian with long tails and not of the Thomas-Fermi type like in a trap with a fixed boundary.
Ferromagnetic and antiferromagnetic order in bacterial vortex lattices
NASA Astrophysics Data System (ADS)
Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Goldstein, Raymond E.
2016-04-01
Despite their inherently non-equilibrium nature, living systems can self-organize in highly ordered collective states that share striking similarities with the thermodynamic equilibrium phases of conventional condensed-matter and fluid systems. Examples range from the liquid-crystal-like arrangements of bacterial colonies, microbial suspensions and tissues to the coherent macro-scale dynamics in schools of fish and flocks of birds. Yet, the generic mathematical principles that govern the emergence of structure in such artificial and biological systems are elusive. It is not clear when, or even whether, well-established theoretical concepts describing universal thermostatistics of equilibrium systems can capture and classify ordered states of living matter. Here, we connect these two previously disparate regimes: through microfluidic experiments and mathematical modelling, we demonstrate that lattices of hydrodynamically coupled bacterial vortices can spontaneously organize into distinct patterns characterized by ferro- and antiferromagnetic order. The coupling between adjacent vortices can be controlled by tuning the inter-cavity gap widths. The emergence of opposing order regimes is tightly linked to the existence of geometry-induced edge currents, reminiscent of those in quantum systems. Our experimental observations can be rationalized in terms of a generic lattice field theory, suggesting that bacterial spin networks belong to the same universality class as a wide range of equilibrium systems.
Skyrmionic vortex lattices in coherently coupled three-component Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Orlova, Natalia V.; Kuopanportti, Pekko; Milošević, Milorad V.
2016-08-01
We show numerically that a harmonically trapped and coherently Rabi-coupled three-component Bose-Einstein condensate can host unconventional vortex lattices in its rotating ground state. The discovered lattices incorporate square and zig-zag patterns, vortex dimers and chains, and doubly quantized vortices, and they can be quantitatively classified in terms of a skyrmionic topological index, which takes into account the multicomponent nature of the system. The exotic ground-state lattices arise due to the intricate interplay of the repulsive density-density interactions and the Rabi couplings as well as the ubiquitous phase frustration between the components. In the frustrated state, domain walls in the relative phases can persist between some components even at strong Rabi coupling, while vanishing between others. Consequently, in this limit the three-component condensate effectively approaches a two-component condensate with only density-density interactions. At intermediate Rabi coupling strengths, however, we face unique vortex physics that occurs neither in the two-component counterpart nor in the purely density-density-coupled three-component system.
NASA Astrophysics Data System (ADS)
Lee, Jeongseop; Xin, Yizhou; Halperin, W. P.; Reyes, A. P.; Kuhns, P. L.
The vortex lattice in HgBa2CuO4+δ forms at a vortex melting temperature, Tv, typically ~40K for underdoped crystals with a hole doping ~ 0.11. We present our results from 17O NMR for investigation of the vortex lattice as a function of external magnetic field up to 30 T and temperature as low as 5 K. The vortex contribution to the NMR linewidth can be separated from inhomogeneous broadening by deconvolution of the normal state spectra which was measured separately above, Tv. The vortex melting temperature was measured for two underdoped samples marked by the onset of extra linewidth broadening due to the inhomogeneous magnetic field distribution from the solid vortex lattice consistent with transverse relaxation measurements. We have found evidence for a change in the vortex lattice symmetry as a function of external fields. This work was supported by the DOE BES under Grant No. DE-FG02-05ER46248 and the NHMFL through the NSF and State of Florida.
Magnetic vortex lattice in HgBa2CuO4+δ observed by small-angle neutron scattering
NASA Astrophysics Data System (ADS)
Li, Yuan; Egetenmeyer, N.; Gavilano, J. L.; Barišić, N.; Greven, M.
2011-02-01
We report the direct observation of the magnetic vortex lattice in the model high-temperature superconductor HgBa2CuO4+δ. Using small-angle neutron scattering on high-quality crystals, we observe two equal domains of undistorted triangular vortex lattices well aligned with the tetragonal crystallographic axes. The signal decreases rapidly with increasing magnetic field and vanishes above 0.4 T, which we attribute to a crossover from a three-dimensional to a two-dimensional vortex system, similar to previous results for the more anisotropic compound Bi2.15Sr1.95CaCu2O8+δ. Our result indicates that a triangular vortex lattice (with or without distortion) at low magnetic fields is a generic property of cuprates with critical temperatures above 80 K.
Large-scale vortex lattice emerging from collectively moving microtubules.
Sumino, Yutaka; Nagai, Ken H; Shitaka, Yuji; Tanaka, Dan; Yoshikawa, Kenichi; Chaté, Hugues; Oiwa, Kazuhiro
2012-03-21
Spontaneous collective motion, as in some flocks of bird and schools of fish, is an example of an emergent phenomenon. Such phenomena are at present of great interest and physicists have put forward a number of theoretical results that so far lack experimental verification. In animal behaviour studies, large-scale data collection is now technologically possible, but data are still scarce and arise from observations rather than controlled experiments. Multicellular biological systems, such as bacterial colonies or tissues, allow more control, but may have many hidden variables and interactions, hindering proper tests of theoretical ideas. However, in systems on the subcellular scale such tests may be possible, particularly in in vitro experiments with only few purified components. Motility assays, in which protein filaments are driven by molecular motors grafted to a substrate in the presence of ATP, can show collective motion for high densities of motors and attached filaments. This was demonstrated recently for the actomyosin system, but a complete understanding of the mechanisms at work is still lacking. Here we report experiments in which microtubules are propelled by surface-bound dyneins. In this system it is possible to study the local interaction: we find that colliding microtubules align with each other with high probability. At high densities, this alignment results in self-organization of the microtubules, which are on average 15 µm long, into vortices with diameters of around 400 µm. Inside the vortices, the microtubules circulate both clockwise and anticlockwise. On longer timescales, the vortices form a lattice structure. The emergence of these structures, as verified by a mathematical model, is the result of the smooth, reptation-like motion of single microtubules in combination with local interactions (the nematic alignment due to collisions)--there is no need for long-range interactions. Apart from its potential relevance to cortical arrays in
Gamma-ray superconducting detector based on Abrikosov vortices: Principle of operation
Lisitskiy, M. P.
2009-11-15
The high atomic number of some superconducting elements such as niobium (Z=41) and tantalum (Z=73) and a high material thickness (e.g., t=300 mum) are emphasized as essential properties for development of a gamma-ray solid state detector with high intrinsic detection efficiency in the energy range up to 100 keV. To exploit these properties, a new detection principle based on the interaction of a single gamma-ray photon with Abrikosov vortex is proposed. The interaction of gamma-ray photon with a superconductor is discussed in terms of the photoelectric absorption and a hot-spot formation, the last acts as a short-time pinning center on an Abrikosov vortex and activates its motion, namely, a jump or damped vibration. Both types of vortex motion lead to variation (either static or dynamic) in the magnetic field on the absorber surface. The high sensitivity of the Josephson tunneling to weak magnetic field can be exploited for revealing the magnetic field variation and to make the readout of the detector. Main intrinsic properties of a gamma-ray detector based on Abrikosov vortices are evaluated, including the possibility to measure the energy deposited in the detector. A single Josephson tunnel junction configuration or a superconducting quantum interference device (SQUID) configuration is proposed and discussed as possible realization of working gamma-ray detector both in the counter operation mode and in the radiation spectroscopy operation mode.
Vortex lattice structures in YNi{sub 2}B{sub 2}C
Yethiraj, M.; Paul, D.M.; Tomy, C.V.; Forgan, E.M.
1997-12-01
The authors observe a flux lattice with square symmetry in the superconductor YNi{sub 2}B{sub 2}C when the applied field is parallel to the c-axis of the crystal. A square lattice observed previously in the isostructural magnetic analog ErNi{sub 2}B{sub 2}C was attributed to the interaction between magnetic order in that system and the flux lattice. Since the Y-based compound does not order magnetically, it is clear that the structure of the flux lattice is unrelated to magnetic order. In fact, they show that the flux lines have a square cross-section when the applied field is parallel to the c-axis of the crystal, since the measured penetration depth along the 100 crystal direction is larger than the penetration depth along the 110 by approximately 60%. This is the likely reason for the square symmetry of the lattice. Although they find considerable disorder in the arrangement of the flux lines at 2.5T, no melting of the vortex lattice was observed.
Vortex Confinement in Superconducting/Ferromagnet Hybrid Structures
NASA Astrophysics Data System (ADS)
Iavarone, M.; Scarfato, A.; Bobba, F.; Longobardi, M.; Giubileo, F.; Karapetrov, G.; Novosad, V.; Yefremenko, V. G.; Cucolo, A.
2011-03-01
Magnetically coupled superconductor-ferromagnet hybrids offer advanced routes for nanoscale control of superconductivity. Scanning tunneling microscopy (STM) and scanning magnetic force microscopy (MFM) coupled to magneto-transport measurements reveal rich vortex phase diagram. The magnetic stripe domain of the ferromagnet induces periodic local magnetic induction in the superconductor, creating a series of pinning and anti-pinning channels for vortices observed with low temperature STM and MFM. Such laterally confined Abrikosov vortices form chains. We also found general equilibrium condition for which vortex-antivortex pairs are spontaneously formed during zero-field cooling. In the non-equilibrium state the strong magnetic pinning of the vortex lattice results in avalanches of antivortices when changing the polarity of the applied magnetic field.
Convergence characteristics of nonlinear vortex-lattice methods for configuration aerodynamics
NASA Technical Reports Server (NTRS)
Seginer, A.; Rusak, Z.; Wasserstrom, E.
1983-01-01
Nonlinear panel methods have no proof for the existence and uniqueness of their solutions. The convergence characteristics of an iterative, nonlinear vortex-lattice method are, therefore, carefully investigated. The effects of several parameters, including (1) the surface-paneling method, (2) an integration method of the trajectories of the wake vortices, (3) vortex-grid refinement, and (4) the initial conditions for the first iteration on the computed aerodynamic coefficients and on the flow-field details are presented. The convergence of the iterative-solution procedure is usually rapid. The solution converges with grid refinement to a constant value, but the final value is not unique and varies with the wing surface-paneling and wake-discretization methods within some range in the vicinity of the experimental result.
Interaction of vortex lattice with ultrasound and the acoustic Faraday effect
Dominguez, D.; Bulaevskii, L.; Ivlev, B.; Maley, M.; Bishop, A.R. |
1995-03-27
The interaction of sound with the vortex lattice is considered for high-{ital T}{sub {ital c}} superconductors, taking into account pinning and electrodynamic forces between vortices and crystal displacements. At low temperatures the Magnus force results in the acoustic Faraday effect; the velocity of sound propagating along the magnetic field depends on the polarization. This effect is linear in the Magnus force and magnetic field in crystals with equivalent {ital a} and {ital b} axes for a field parallel to the {ital c} axis. In the thermally activated flux flow regime, the Faraday effect is caused by electric and magnetic fields induced by vortices and acting on ions.
Cooperative ring exchange and quantum melting of vortex lattices in atomic Bose-Einstein condensates
Ghosh, Tarun Kanti; Baskaran, G.
2004-02-01
Cooperative ring exchange is suggested as a mechanism of quantum melting of vortex lattices in a rapidly rotating quasi-two-dimensional atomic Bose-Einstein condensate (BEC). Using an approach pioneered by Kivelson et al. [Phys. Rev. Lett. 56, 873 (1986)] for the fractional quantized Hall effect, we calculate the condition for quantum melting instability by considering large-correlated ring exchanges in a two-dimensional Wigner crystal of vortices in a strong 'pseudomagnetic field' generated by the background superfluid Bose particles. BEC may be profitably used to address issues of quantum melting of a pristine Wigner solid devoid of complications of real solids.
Rossby vortex simulation on a paraboloidal coordinate system using the lattice Boltzmann method
NASA Astrophysics Data System (ADS)
Yu, Huidan; Zhao, Kaihua
2001-11-01
In this paper, we apply our compressible lattice Boltzmann model to a rotating parabolic coordinate system to simulate Rossby vortices emerging in a layer of shallow water flowing zonally in a rotating paraboloidal vessel. By introducing a scaling factor, nonuniform curvilinear mesh can be mapped to a flat uniform mesh and then normal lattice Boltzmann method works. Since the mass per unit area on the two-dimensional (2D) surface varies with the thickness of the water layer, the 2D flow seems to be ``compressible'' and our compressible model is applied. Simulation solutions meet with the experimental observations qualitatively. Based on this research, quantitative solutions and many natural phenomena simulations in planetary atmospheres, oceans, and magnetized plasma, such as the famous Jovian Giant Red Spot, the Galactic Spiral-vortex, the Gulf Stream, and the Kuroshio Current, etc., can be expected.
Rossby vortex simulation on a paraboloidal coordinate system using the lattice Boltzmann method.
Yu, H; Zhao, K
2001-11-01
In this paper, we apply our compressible lattice Boltzmann model to a rotating parabolic coordinate system to simulate Rossby vortices emerging in a layer of shallow water flowing zonally in a rotating paraboloidal vessel. By introducing a scaling factor, nonuniform curvilinear mesh can be mapped to a flat uniform mesh and then normal lattice Boltzmann method works. Since the mass per unit area on the two-dimensional (2D) surface varies with the thickness of the water layer, the 2D flow seems to be "compressible" and our compressible model is applied. Simulation solutions meet with the experimental observations qualitatively. Based on this research, quantitative solutions and many natural phenomena simulations in planetary atmospheres, oceans, and magnetized plasma, such as the famous Jovian Giant Red Spot, the Galactic Spiral-vortex, the Gulf Stream, and the Kuroshio Current, etc., can be expected. PMID:11736137
NASA Technical Reports Server (NTRS)
Herbert, H. E.; Lamar, J. E.
1982-01-01
The source code for the latest production version, MARK IV, of the NASA-Langley Vortex Lattice Computer Program is presented. All viable subcritical aerodynamic features of previous versions were retained. This version extends the previously documented program capabilities to four planforms, 400 panels, and enables the user to obtain vortex-flow aerodynamics on cambered planforms, flowfield properties off the configuration in attached flow, and planform longitudinal load distributions.
NASA Technical Reports Server (NTRS)
Lamar, J. E.; Herbert, H. E.
1982-01-01
The latest production version, MARK IV, of the NASA-Langley vortex lattice computer program is summarized. All viable subcritical aerodynamic features of previous versions were retained. This version extends the previously documented program capabilities to four planforms, 400 panels, and enables the user to obtain vortex-flow aerodynamics on cambered planforms, flowfield properties off the configuration in attached flow, and planform longitudinal load distributions.
NASA Astrophysics Data System (ADS)
Guillamon, I.; Vieira, S.; Suderow, H.; Cordoba, R.; Sese, J.; de Teresa, J. M.; Ibarra, R.
In two dimensional (2D) systems, theory has proposed that random disorder destroys long range correlations driving a transition to a glassy state. Here, I will discuss new insights into this issue obtained through the direct visualization of the critical behaviour of a 2D superconducting vortex lattice formed in a thin film with a smooth 1D thickness modulation. Using scanning tunneling microscopy at 0.1K, we have tracked the modification in the 2D vortex arrangements induced by the 1D thickness modulation while increasing the vortex density by three orders of magnitude. Upon increasing the field, we observed a two-step order-disorder transition in the 2D vortex lattice mediated by the appearance of dislocations and disclinations and accompanied by an increase in the local vortex density fluctuations. Through a detailed analysis of correlation functions, we find that the transition is driven by the incommensurate 1D thickness modulation. We calculate the critical points and exponents and find that they are well above theoretical expectation for random disorder. Our results show that long range 1D correlations in random potentials enhance the stability range of the ordered phase in a 2D vortex lattice. Work supported by Spanish MINECO, CIG Marie Curie Grant, Axa Research Fund and FBBVA.
Knotted Vortices: Entropic Lattice Boltzmann Method for Simulation of Vortex dynamics
NASA Astrophysics Data System (ADS)
Boesch, Fabian; Chikatamarla, Shyam; Karlin, Ilya
2013-11-01
Knotted and interlinked vortex structures in real fluids are conjectured to play a major role in hydrodynamic flow dissipation. Much interest lies in determining their temporal stability and the mechanism through which knots dissolve. Kleckner and Irvine recently have shown the existence of such knotted vortices experimentally by accelerating hydrofoils in water. In the present work we employ the entropic lattice Boltzmann method (ELBM) to perform DNS simulations of the creation and dynamics of knotted vortex rings inspired by the experimental setup in. ELBM renders LBM scheme unconditionally stable by restoring the second law of thermodynamics (the Boltzmann H-theorem), and thus enables simulations of large domains and high Reynolds numbers with DNS quality. The results presented in this talk provide an in-depth study of the dynamics of knotted vortices and vortex reconnection events and confirm the existence of trefoil knots in silicio for the first time. This work was supported by a grant from the Swiss National Supercomputing Centre (CSCS) under project ID s347.
Dynamic and Structural Studies of Metastable Vortex Lattice Domains in MgB2
NASA Astrophysics Data System (ADS)
de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.
Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. The VL can be driven to the GS through successive application of an AC magnetic field. Here we report on detailed studies of the transition kinetics and structure of the VL domains. Stroboscopic studies of the transition revealed a stretched exponential decrease of the metastable volume fraction as a function of the number of applied AC cycles, with subtle differences depending on whether the AC field is oriented parallel or perpendicular to the DC field used to create the VL. We speculate the slower transition kinetics for the transverse AC field may be due to vortex cutting. Spatial studies include scanning SANS measurements showing the VL domain distribution within the MgB2 single crystal as well as measurements of VL correlation lengths. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.
Liu Zhao; Guo Hongli; Fan Heng; Vedral, Vlatko
2011-01-15
We use entanglement to investigate the transition from vortex-liquid phase to vortex-lattice phase in a weakly interacting rotating Bose-Einstein condensate. For the torus geometry, the ground-state entanglement spectrum is analyzed to distinguish these two phases. The low-lying part of the ground-state entanglement spectrum, as well as the behavior of its lowest level, changes clearly when the transition occurs. For the sphere geometry, the entanglement gap in the conformal limit is also studied. We also show that the decrease in entanglement between particles can be regarded as a signal of the transition.
NASA Astrophysics Data System (ADS)
Zhou, Xiang-Fa; Zhou, Zheng-Wei; Wu, Congjun; Guo, Guang-Can
2015-03-01
We consider the ground-state properties of the two-component spin-orbit-coupled ultracold bosons subject to a rotationally symmetric in-plane gradient magnetic field. In the noninteracting case, the ground state supports giant vortices carrying large angular momenta without rotating the trap. The vorticity is highly tunable by varying the amplitudes and orientations of the magnetic field. Interactions drive the system from a giant-vortex state to various configurations of vortex lattice states along a ring. Vortices exhibit ellipse-shaped envelopes with the major and minor axes determined by the spin-orbit coupling and healing lengths, respectively. Phase diagrams of vortex lattice configurations are constructed and their stabilities are analyzed.
Vortex Lattice Studies in CeCoIn₅ with H⊥c
Das, P.; White, J. S.; Holmes, A. T.; Gerber, S.; Forgan, E. M.; Bianchi, A. D.; Kenzelmann, M.; Zolliker, M.; Gavilano, J. L.; Bauer, E. D.; Sarrao, J. L.; Petrovic, C.; Eskildsen, M. R.
2012-02-23
We present small angle neutron scattering studies of the vortex lattice (VL) in CeCoIn₅ with magnetic fields applied parallel (H) to the antinodal [100] and nodal [110] directions. For H II 100], a single VL orientation is observed, while a 90° reorientation transition is found for H II [110]. For both field orientations and VL configurations we find a distorted hexagonal VL with an anisotropy, Γ=2.0±0.05. The VL form factor shows strong Pauli paramagnetic effects similar to what have previously been reported for H II [001]. At high fields, above which the upper critical field (H_{c2}) becomes a first-order transition, an increased disordering of the VL is observed.
Vortex Lattice Studies in CeCoIn₅ with H⊥c
Das, P.; White, J. S.; Holmes, A. T.; Gerber, S.; Forgan, E. M.; Bianchi, A. D.; Kenzelmann, M.; Zolliker, M.; Gavilano, J. L.; Bauer, E. D.; et al
2012-02-23
We present small angle neutron scattering studies of the vortex lattice (VL) in CeCoIn₅ with magnetic fields applied parallel (H) to the antinodal [100] and nodal [110] directions. For H II 100], a single VL orientation is observed, while a 90° reorientation transition is found for H II [110]. For both field orientations and VL configurations we find a distorted hexagonal VL with an anisotropy, Γ=2.0±0.05. The VL form factor shows strong Pauli paramagnetic effects similar to what have previously been reported for H II [001]. At high fields, above which the upper critical field (Hc2) becomes a first-order transition,more » an increased disordering of the VL is observed.« less
Quantum melting of a two-dimensional vortex lattice at zero temperature
Rozhkov, A.; Stroud, D.
1996-11-01
We consider the quantum melting of a two-dimensional flux lattice at temperature {ital T} = 0 in the {open_quote}{open_quote}superclean limit.{close_quote}{close_quote} In this regime, we find that vortex motion is dominated by the Magnus force. A Lindemann criterion predicts melting when {ital n}{sub {ital v}}/{ital n}{sub {ital p}}{ge}{beta}, where {ital n}{sub {ital v}} and {ital n}{sub {ital p}} are the areal number densities of vortex pancakes and Cooper pairs, and {beta}{approx_equal}0.1. A second criterion is derived by using Wigner-crystal and Laughlin wave functions for the solid and liquid phases respectively, and setting the two energies equal. This gives a melting value similar to the Lindemann result. We discuss the numerical value of the {ital T}=0 melting field for thin layers of a low-{ital T}{sub {ital c}} superconductor, such as {ital a}-MoGe, and single layers of high-{ital T}{sub {ital c}} materials. {copyright} {ital 1996 The American Physical Society.}
Structural Studies of Metastable and Ground State Vortex Lattice Domains in MgB2
NASA Astrophysics Data System (ADS)
de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.
2015-03-01
Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. Application of an AC magnetic field to drive the VL to the ground state revealed a two-step power law behavior, indicating a slow nucleation of ground state domains followed by a faster growth. The dependence on the number of applied AC cycles is reminiscent of jamming of soft, frictionless spheres. Here, we report on detailed structural studies of both metastable and ground state VL domains. These include measurements of VL correlation lengths as well as spatially resolved SANS measurements showing the VL domain distribution within the MgB2 single crystal. We discuss these results and how they may help to resolve the mechanism responsible for stabilizing the metastable VL phases. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.
NASA Astrophysics Data System (ADS)
Moreno, A. J.; Chiliotte, C. E.; Pasquini, G.; Bekeris, V.; Gomez, A.; del Valle, J.; Gonzalez, E. M.; Prieto, J. L.; Vicent, J. L.
2015-01-01
We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T > 0.70 TC. The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the JC(T) behavior. Moreover, the temperature dependence of the pinning force FP(T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex-vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena.
Superconducting gap and vortex lattice of the heavy-fermion compound CeCu2Si2
NASA Astrophysics Data System (ADS)
Enayat, Mostafa; Sun, Zhixiang; Maldonado, Ana; Suderow, Hermann; Seiro, Silvia; Geibel, Christoph; Wirth, Steffen; Steglich, Frank; Wahl, Peter
2016-01-01
The order parameter and pairing mechanism for superconductivity in heavy-fermion compounds are still poorly understood. Scanning tunneling microscopy and spectroscopy at ultralow temperatures can yield important information about the superconducting order parameter and the gap structure. Here, we study the first heavy-fermion superconductor, CeCu2Si2 . Our data show the superconducting gap which is not fully formed and exhibits features that point to a multigap order parameter. Spatial mapping of the zero-bias conductance in magnetic field reveals the vortex lattice, which allows us to unequivocally link the observed conductance gap to superconductivity in CeCu2Si2 . The vortex lattice is found to be predominantly triangular with distortions at fields close to ˜0.7 Hc 2 .
NASA Technical Reports Server (NTRS)
Hall, G. F.
1975-01-01
The application is considered of vortex lattice techniques to the problem of describing the aerodynamics and performance of statically thrusting propellers. A numerical lifting surface theory to predict the aerodynamic forces and power is performed. The chordwise and spanwise loading is modelled by bound vortices fixed to a twisted flat plate surface. In order to eliminate any apriori assumptions regarding the wake shape, it is assumed the propeller starts from rest. The wake is generated in time and allowed to deform under its own self-induced velocity field as the motion of the propeller progresses. The bound circulation distribution is then determined with time by applying the flow tangency boundary condition at certain selected control points on the blades. The aerodynamics of the infinite wing and finite wing are also considered. The details of wake formation and roll-up are investigated, particularly the localized induction effect. It is concluded that proper wake roll-up and roll-up rates can be established by considering the details of motion at the instant of start.
Localization of a Bose-Einstein-condensate vortex in a bichromatic optical lattice
Adhikari, S. K.
2010-04-15
By numerical simulation of the time-dependent Gross-Pitaevskii equation we show that a weakly interacting or noninteracting Bose-Einstein condensate (BEC) vortex can be localized in a three-dimensional bichromatic quasiperiodic optical-lattice (OL) potential generated by the superposition of two standing-wave polarized laser beams with incommensurate wavelengths. We also study the localization of a (nonrotating) BEC in two and three dimensions by bichromatic OL potentials along orthogonal directions. This is a generalization of the localization of a BEC in a one-dimensional bichromatic OL as studied in a recent experiment [Roati et al., Nature 453, 895 (2008)]. We demonstrate the stability of the localized state by considering its time evolution in the form of a stable breathing oscillation in a slightly altered potential for a large period of time. Finally, we consider the localization of a BEC in a random one-dimensional potential in the form of several identical repulsive spikes arbitrarily distributed in space.
NASA Technical Reports Server (NTRS)
Chaparro, Daniel; Fujiwara, Gustavo E. C.; Ting, Eric; Nguyen, Nhan
2016-01-01
The need to rapidly scan large design spaces during conceptual design calls for computationally inexpensive tools such as the vortex lattice method (VLM). Although some VLM tools, such as Vorview have been extended to model fully-supersonic flow, VLM solutions are typically limited to inviscid, subcritical flow regimes. Many transport aircraft operate at transonic speeds, which limits the applicability of VLM for such applications. This paper presents a novel approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft. The approach is extended to predict flow separation and capture the attenuation of aerodynamic forces due to boundary layer viscosity by coupling the TSD solver with an integral boundary layer (IBL) model. The modeling framework is applied to the NASA General Transport Model (GTM) integrated with a novel control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF).
Description, Usage, and Validation of the MVL-15 Modified Vortex Lattice Analysis Capability
NASA Technical Reports Server (NTRS)
Ozoroski, Thomas A.
2015-01-01
MVL-15 is the most recent version of the Modified Vortex-Lattice (MVL) code developed within the Aerodynamics Systems Analysis Branch (ASAB) at NASA LaRC. The term "modified" refers to the primary modification of the core vortex-lattice methodology: inclusion of viscous aerodynamics tables that are linked to the linear solution via iterative processes. The inclusion of the viscous aerodynamics inherently converts the MVL-15 from a purely analytic linearized method to a semi-empirical blend which retains the rapid execution speed of the linearized method while empirically characterizing the section aerodynamics at all spanwise lattice points. The modification provides a means to assess non-linear effects on lift that occur at angles of attack near stall, and provides a means to determine the drag associated with the application of design strategies for lift augmentation such as the use of flaps or blowing. The MVL-15 code is applicable to the analyses of aircraft aerodynamics during cruise, but it is most advantageously applied to the analysis of aircraft operating in various high-lift configurations. The MVL methodology has been previously conceived and implemented; the initial concept version was delivered to the ASAB in 2001 (van Dam, C.), subsequently revised (Gelhausen, P. and Ozoroski, T. 2002 / AVID Inc., Gelhausen, P., and Roberts, M. 2004), and then overhauled (Ozoroski, T., Hahn, A. 2008). The latest version, MVL-15 has been refined to provide analysis transparency and enhanced to meet the analysis requirements of the Environmentally Responsible Aviation (ERA) Project. Each revision has been implemented with reasonable success. Separate applications of the methodology are in use, including a similar in-house capability, developed by Olson, E. that is tailored for structural and acoustics analyses. A central premise of the methodology is that viscous aerodynamic data can be associated with analytic inviscid aerodynamic results at each spanwise wing section
Peak effect and square-to-rhombic vortex lattice transition in La2-xSrxCuO4
NASA Astrophysics Data System (ADS)
Rosenstein, B.; Shapiro, B. Ya.; Shapiro, I.; Bruckental, Y.; Shaulov, A.; Yeshurun, Y.
2005-10-01
A theory of structural phase transition of the vortex lattice in tetragonal superconductors is constructed based on the self consistent harmonic approximation for lattice anharmonicities, within the fourfold-symmetric generalization of the London model. Thermal fluctuations on the mesoscopic scale are strong enough to affect the location of the square to rhomb transition line in the T-H plane. We find that the slope of the transition line is generally negative: thermal fluctuations favor the more symmetric square lattice. The calculated transition line is concave, and fits the experimental line deduced in LaSCO crystals from the onset of the second magnetization peak. Near the transition line the “squash” modulus Csq=2(C11+C12)-C66 is softened leading to enhancement of the critical current, born out in the experiment as a second magnetization peak.
NASA Astrophysics Data System (ADS)
Ge, Jun-Yi; Gutierrez, Joffre; Lyashchenko, A.; Filipov, V.; Li, Jun; Moshchalkov, Victor V.
2014-11-01
In nature, many systems exhibit modulated phases with periodic macroscopic patterns and textures mainly due to the competitive interactions of different phases. Vortex systems in superconductors, which are easy to access, offer the possibility of tuning the ratio between the competitive interactions, providing a unique tool to study the evolution and equilibrium of similar patterns. The κ -T phase diagram of clean superconductors shows the transition from type-I to type-II superconductivity via a narrow κ range near the dual point κ =1 /√{2 } where the vortices attract each other at long distances and repel each other at short distances. This κ range, which is termed the type-II/1 phase, becomes larger with decreasing temperature. The direct imaging at the scale of individual vortices of the vortex pattern transition would provide valuable information. Therefore, by using scanning Hall probe microscopy, we have performed direct visualization of the vortex pattern transition in a ZrB12 single crystal across the type-II and type-II/1 phases. By gradually lowering the temperature, and thereby tuning vortex interactions, a transition is observed from the ordered Abrikosov vortex lattice to a disordered vortex pattern with large areas of Meissner phase, vortex chains, and vortex clusters. The formation of vortex chains and clusters has been found to arise from the combined effect of quenched disorder and the attractive vortex-vortex interaction in the type-II/1 phase. The clusters and chains serve as the vortex reservoir to enable the formation of a triangular vortex lattice of the type-II phase at high temperatures.
Johnson, T H; Yuan, Y; Bao, W; Clark, S R; Foot, C; Jaksch, D
2016-06-17
We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes. PMID:27367366
Quantum melting of the quasi-two-dimensional vortex lattice in kappa- (ET)2Cu(NCS)(2).
Mola, M M; Hill, S; Brooks, J S; Qualls, J S
2001-03-01
We report torque magnetization measurements in regions of the mixed state phase diagram ( B approximately mu(o)H(c2) and T(c)/10(3)) of the organic superconductor kappa-(ET)2Cu(NCS)(2), where quantum fluctuations are expected to dominate thermal effects. Over most of the field range below the irreversibility line ( B(irr)), magnetothermal instabilities are observed in the form of flux jumps. The abrupt cessation of these instabilities just below B(irr) indicates a quantum melting transition from a quasi-two-dimensional vortex lattice phase to a quantum liquid phase.
Johnson, T H; Yuan, Y; Bao, W; Clark, S R; Foot, C; Jaksch, D
2016-06-17
We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes.
Aerodynamic Analysis of the Truss-Braced Wing Aircraft Using Vortex-Lattice Superposition Approach
NASA Technical Reports Server (NTRS)
Ting, Eric Bi-Wen; Reynolds, Kevin Wayne; Nguyen, Nhan T.; Totah, Joseph J.
2014-01-01
The SUGAR Truss-BracedWing (TBW) aircraft concept is a Boeing-developed N+3 aircraft configuration funded by NASA ARMD FixedWing Project. This future generation transport aircraft concept is designed to be aerodynamically efficient by employing a high aspect ratio wing design. The aspect ratio of the TBW is on the order of 14 which is significantly greater than those of current generation transport aircraft. This paper presents a recent aerodynamic analysis of the TBW aircraft using a conceptual vortex-lattice aerodynamic tool VORLAX and an aerodynamic superposition approach. Based on the underlying linear potential flow theory, the principle of aerodynamic superposition is leveraged to deal with the complex aerodynamic configuration of the TBW. By decomposing the full configuration of the TBW into individual aerodynamic lifting components, the total aerodynamic characteristics of the full configuration can be estimated from the contributions of the individual components. The aerodynamic superposition approach shows excellent agreement with CFD results computed by FUN3D, USM3D, and STAR-CCM+. XXXXX Demand for green aviation is expected to increase with the need for reduced environmental impact. Most large transports today operate within the best cruise L/D range of 18-20 using the conventional tube-and-wing design. This configuration has led to marginal improvements in aerodynamic efficiency over this past century, as aerodynamic improvements tend to be incremental. A big opportunity has been shown in recent years to significantly reduce structural weight or trim drag, hence improved energy efficiency, with the use of lightweight materials such as composites. The Boeing 787 transport is an example of a modern airframe design that employs lightweight structures. High aspect ratio wing design can provide another opportunity for further improvements in energy efficiency. Historically, the study of high aspect ratio wings has been intimately tied to the study of
DC to AC converter on Abrikosov vortices in a washboard pinning potential
NASA Astrophysics Data System (ADS)
Shklovskij, Valerij A.; Dobrovolskiy, Oleksandr V.
2014-05-01
The nonlinear dynamics of Abrikosov vortices in a cosine dc-biased washboard pinning potential at nonzero temperature is theoretically investigated. The problem is treated relying upon the exact solution of the Langevin equation for non-interacting vortices by using the Fokker-Planck method combined with the scalar continued fractions technique. The time variation of the local mean vortex velocity v(t) is calculated. The time voltage E(t) ~ v(t) is predicted to oscillate with a dc current-dependent frequency and a tunable pulse shape. Formulas for v(t) are discussed as functions of dc transport current and temperature, in a wide range of the corresponding dimensionless parameters. The derived expressions can be adapted for a number of physical applications utilizing the overdamped motion of a Brownian particle in a tilted cosine potential, e.g., the resistively shunted Josephson junction model.
Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate
Zhang, Xiao-Fei; Wen, Lin; Dai, Cai-Qing; Dong, Rui-Fang; Jiang, Hai-Feng; Chang, Hong; Zhang, Shou-Gang
2016-01-01
In the last decade, considerable advances have been made in the investigation of dipolar quantum gases. Previous theoretical investigations of a rotating binary dipolar Bose-Einstein condensate, where only one component possesses dipole moment, were mainly focused on two special orientations of the dipoles: perpendicular or parallel to the plane of motion. Here we study the ground-state and rotational properties of such a system for an arbitrary orientation of the dipoles. We demonstrate the ground-state vortex structures depend strongly on the relative strength between dipolar and contact interactions and the rotation frequency, as well as on the orientation of the dipoles. In the absence of rotation, the tunable dipolar interaction can be used to induce the squeezing or expansion of the cloud, and to derive the phase transition between phase coexistence and separation. Under finite rotation, the system is found to exhibit exotic ground-state vortex configurations, such as kernel-shell, vortex necklace, and compensating stripe vortex structures. We also check the validity of the Feynman relation, and find no significant deviations from it. The obtained results open up alternate ways for the quantum control of dipolar quantum gases. PMID:26778736
Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate.
Zhang, Xiao-Fei; Wen, Lin; Dai, Cai-Qing; Dong, Rui-Fang; Jiang, Hai-Feng; Chang, Hong; Zhang, Shou-Gang
2016-01-01
In the last decade, considerable advances have been made in the investigation of dipolar quantum gases. Previous theoretical investigations of a rotating binary dipolar Bose-Einstein condensate, where only one component possesses dipole moment, were mainly focused on two special orientations of the dipoles: perpendicular or parallel to the plane of motion. Here we study the ground-state and rotational properties of such a system for an arbitrary orientation of the dipoles. We demonstrate the ground-state vortex structures depend strongly on the relative strength between dipolar and contact interactions and the rotation frequency, as well as on the orientation of the dipoles. In the absence of rotation, the tunable dipolar interaction can be used to induce the squeezing or expansion of the cloud, and to derive the phase transition between phase coexistence and separation. Under finite rotation, the system is found to exhibit exotic ground-state vortex configurations, such as kernel-shell, vortex necklace, and compensating stripe vortex structures. We also check the validity of the Feynman relation, and find no significant deviations from it. The obtained results open up alternate ways for the quantum control of dipolar quantum gases. PMID:26778736
Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Zhang, Xiao-Fei; Wen, Lin; Dai, Cai-Qing; Dong, Rui-Fang; Jiang, Hai-Feng; Chang, Hong; Zhang, Shou-Gang
2016-01-01
In the last decade, considerable advances have been made in the investigation of dipolar quantum gases. Previous theoretical investigations of a rotating binary dipolar Bose-Einstein condensate, where only one component possesses dipole moment, were mainly focused on two special orientations of the dipoles: perpendicular or parallel to the plane of motion. Here we study the ground-state and rotational properties of such a system for an arbitrary orientation of the dipoles. We demonstrate the ground-state vortex structures depend strongly on the relative strength between dipolar and contact interactions and the rotation frequency, as well as on the orientation of the dipoles. In the absence of rotation, the tunable dipolar interaction can be used to induce the squeezing or expansion of the cloud, and to derive the phase transition between phase coexistence and separation. Under finite rotation, the system is found to exhibit exotic ground-state vortex configurations, such as kernel-shell, vortex necklace, and compensating stripe vortex structures. We also check the validity of the Feynman relation, and find no significant deviations from it. The obtained results open up alternate ways for the quantum control of dipolar quantum gases.
Exotic vortex lattices in a rotating binary dipolar Bose-Einstein condensate.
Zhang, Xiao-Fei; Wen, Lin; Dai, Cai-Qing; Dong, Rui-Fang; Jiang, Hai-Feng; Chang, Hong; Zhang, Shou-Gang
2016-01-18
In the last decade, considerable advances have been made in the investigation of dipolar quantum gases. Previous theoretical investigations of a rotating binary dipolar Bose-Einstein condensate, where only one component possesses dipole moment, were mainly focused on two special orientations of the dipoles: perpendicular or parallel to the plane of motion. Here we study the ground-state and rotational properties of such a system for an arbitrary orientation of the dipoles. We demonstrate the ground-state vortex structures depend strongly on the relative strength between dipolar and contact interactions and the rotation frequency, as well as on the orientation of the dipoles. In the absence of rotation, the tunable dipolar interaction can be used to induce the squeezing or expansion of the cloud, and to derive the phase transition between phase coexistence and separation. Under finite rotation, the system is found to exhibit exotic ground-state vortex configurations, such as kernel-shell, vortex necklace, and compensating stripe vortex structures. We also check the validity of the Feynman relation, and find no significant deviations from it. The obtained results open up alternate ways for the quantum control of dipolar quantum gases.
NASA Astrophysics Data System (ADS)
Kuhn, S. J.; Kawano-Furukawa, H.; Jellyman, E.; Riyat, R.; Forgan, E. M.; Ono, M.; Kihou, K.; Lee, C. H.; Hardy, F.; Adelmann, P.; Wolf, Th.; Meingast, C.; Gavilano, J.; Eskildsen, M. R.
2016-03-01
We study the intrinsic anisotropy of the superconducting state in KFe2As2 by using small-angle neutron scattering to image the vortex lattice as the applied magnetic field is rotated towards the FeAs crystalline planes. The anisotropy is found to be strongly field dependent, indicating multiband superconductivity. Furthermore, the high-field anisotropy significantly exceeds that of the upper critical field, providing further support for Pauli limiting in KFe2As2 for fields applied in the basal plane. The effect of Pauli paramagnetism on the unpaired quasiparticles in the vortex cores is directly evident from the ratio of scattered intensities due to the longitudinal and transverse vortex lattice field modulation.
Chandra Ganguli, Somesh; Singh, Harkirat; Saraswat, Garima; Ganguly, Rini; Bagwe, Vivas; Shirage, Parasharam; Thamizhavel, Arumugam; Raychaudhuri, Pratap
2015-01-01
The vortex lattice in a Type II superconductor provides a versatile model system to investigate the order-disorder transition in a periodic medium in the presence of random pinning. Here, using scanning tunnelling spectroscopy in a weakly pinned Co0.0075NbSe2 single crystal, we show that the vortex lattice in a 3-dimensional superconductor disorders through successive destruction of positional and orientational order, as the magnetic field is increased across the peak effect. At the onset of the peak effect, the equilibrium quasi-long range ordered state transforms into an orientational glass through the proliferation of dislocations. At a higher field, the dislocations dissociate into isolated disclination giving rise to an amorphous vortex glass. We also show the existence of a variety of additional non-equilibrium metastable states, which can be accessed through different thermomagnetic cycling. PMID:26039699
Das, P; Rastovski, C; O'Brien, T R; Schlesinger, K J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R
2012-04-20
The vortex lattice (VL) symmetry and orientation in clean type-II superconductors depends sensitively on the host material anisotropy, vortex density and temperature, frequently leading to rich phase diagrams. Typically, a well-ordered VL is taken to imply a ground-state configuration for the vortex-vortex interaction. Using neutron scattering we studied the VL in MgB(2) for a number of field-temperature histories, discovering an unprecedented degree of metastability in connection with a known, second-order rotation transition. This allows, for the first time, structural studies of a well-ordered, nonequilibrium VL. While the mechanism responsible for the longevity of the metastable states is not resolved, we speculate it is due to a jamming of VL domains, preventing a rotation to the ground-state orientation.
Das, Pinaki; Rastovski, Catherine; O'Brien, Timothy; Schlesinger, Kimberly; Dewhurst, Charles; Debeer-Schmitt, Lisa M; Zhigadlo, Nikolai; Karpinski, Janusz; Eskildsen, Morten
2012-01-01
The vortex lattice (VL) symmetry and orientation in clean type-II superconductors depends sensitively on the host material anisotropy, vortex density and temperature, frequently leading to rich phase diagrams. Typically, a well-ordered VL is taken to imply a ground-state configuration for the vortex-vortex interaction. Using neutron scattering we studied the VL in MgB2 for a number of field-temperature histories, discovering an unprecedented degree of metastability in connection with a known, second-order rotation transition. This allows, for the first time, structural studies of a well-ordered, nonequilibrium VL. While the mechanism responsible for the longevity of the metastable states is not resolved, we speculate it is due to a jamming of VL domains, preventing a rotation to the ground-state orientation.
White, J S; Hinkov, V; Heslop, R W; Lycett, R J; Forgan, E M; Bowell, C; Strässle, S; Abrahamsen, A B; Laver, M; Dewhurst, C D; Kohlbrecher, J; Gavilano, J L; Mesot, J; Keimer, B; Erb, A
2009-03-01
We report on small-angle neutron scattering studies of the intrinsic vortex lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8 T. Because of the suppressed pinning to twin-domain boundaries, a new distorted hexagonal VL structure phase is stabilized at intermediate fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy. PMID:19392554
Vortex states in a non-Abelian magnetic field
NASA Astrophysics Data System (ADS)
Nikolić, Predrag
2016-08-01
A type-II superconductor survives in an external magnetic field by admitting an Abrikosov lattice of quantized vortices. This is an imprint of the Aharonov-Bohm effect created by the Abelian U(1) gauge field. The simplest non-Abelian analog of such a gauge field, which belongs to the SU(2) symmetry group, can be found in topological insulators. Here we discover a superconducting ground state with a lattice of SU(2) vortices in a simple two-dimensional model that presents an SU(2) "magnetic" field (invariant under time reversal) to attractively interacting fermions. The model directly captures the correlated topological insulator quantum well, and approximates one channel for instabilities on the Kondo topological insulator surface. Due to its simplicity, the model might become amenable to cold atom simulations in the foreseeable future. The vitality of low-energy vortex states born out of SU(2) magnetic fields is promising for the creation of incompressible vortex liquids with non-Abelian fractional excitations.
NASA Astrophysics Data System (ADS)
Dong, Biao; Wang, Lin-Xue; Chen, Guang-Ping; Han, Wei; Zhang, Shou-Gang; Zhang, Xiao-Fei
2016-10-01
We perform a detailed numerical study of the equilibrium ground-state structures of a binary rotating Bose-Einstein condensate with unequal atomic masses. Our results show that the ground-state distribution and its related vortex configurations are complex events that differ markedly depending strongly on the strength of rotation frequency, as well as on the ratio of atomic masses. We also discuss the structures and radii of the clouds, the number and the size of the core region of the vortices, as a function of the rotation frequency, and of the ratio of atomic masses, and the analytical results agree well with our numerical simulations. This work may open an alternate way in the quantum control of the binary rotating quantum gases with unequal atomic masses.
Vortex-lattice pinning and critical current density in anisotropic high-temperature superconductors
NASA Astrophysics Data System (ADS)
Li, Yingxu; Li, Xiangyu; Kang, Guozheng; Gao, Yuanwen
2016-10-01
The anisotropy of critical current density is an impressive manifestation in the physics of high-temperature superconductors. We develop an analytical characterization of anisotropic flux-lattice pinning and critical current density in a system of random point defects. The effect of superconducting anisotropy on the pinning force and critical current density is formulated. The in-plane/out-of-plane anisotropy and microscopic characteristic lengths are incorporated in the field and angular dependence of the critical current density. This is helpful in understanding the physical essence of the scaling behavior in the experiments for critical current anisotropy. We discuss the role of strong and weak point defects in the anisotropic flux-lattice pinning. Relevance of the theory to the critical-state model is dictated as well.
NASA Technical Reports Server (NTRS)
Nguyen, Nhan; Ting, Eric; Nguyen, Daniel; Dao, Tung; Trinh, Khanh
2013-01-01
This paper presents a coupled vortex-lattice flight dynamic model with an aeroelastic finite-element model to predict dynamic characteristics of a flexible wing transport aircraft. The aircraft model is based on NASA Generic Transport Model (GTM) with representative mass and stiffness properties to achieve a wing tip deflection about twice that of a conventional transport aircraft (10% versus 5%). This flexible wing transport aircraft is referred to as an Elastically Shaped Aircraft Concept (ESAC) which is equipped with a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for active wing shaping control for drag reduction. A vortex-lattice aerodynamic model of the ESAC is developed and is coupled with an aeroelastic finite-element model via an automated geometry modeler. This coupled model is used to compute static and dynamic aeroelastic solutions. The deflection information from the finite-element model and the vortex-lattice model is used to compute unsteady contributions to the aerodynamic force and moment coefficients. A coupled aeroelastic-longitudinal flight dynamic model is developed by coupling the finite-element model with the rigid-body flight dynamic model of the GTM.
NASA Technical Reports Server (NTRS)
Ting, Eric; Nguyen, Nhan; Trinh, Khanh
2014-01-01
This paper presents a static aeroelastic model and longitudinal trim model for the analysis of a flexible wing transport aircraft. The static aeroelastic model is built using a structural model based on finite-element modeling and coupled to an aerodynamic model that uses vortex-lattice solution. An automatic geometry generation tool is used to close the loop between the structural and aerodynamic models. The aeroelastic model is extended for the development of a three degree-of-freedom longitudinal trim model for an aircraft with flexible wings. The resulting flexible aircraft longitudinal trim model is used to simultaneously compute the static aeroelastic shape for the aircraft model and the longitudinal state inputs to maintain an aircraft trim state. The framework is applied to an aircraft model based on the NASA Generic Transport Model (GTM) with wing structures allowed to flexibly deformed referred to as the Elastically Shaped Aircraft Concept (ESAC). The ESAC wing mass and stiffness properties are based on a baseline "stiff" values representative of current generation transport aircraft.
SANS study of vortex lattice structural transition in optimally doped (Ba1-x K x )Fe2As2
NASA Astrophysics Data System (ADS)
Demirdiş, S.; van der Beek, C. J.; Mühlbauer, S.; Su, Y.; Wolf, Th
2016-10-01
Small-angle neutron scattering on high quality single crystalline Ba1-x K x Fe2As2 reveals the transition from a low-field vortex solid phase with orientational order to a vortex polycrystal at high magnetic field. The vortex order-disorder transition is correlated with the second-peak feature in isothermal hysteresis loops, and is interpreted in terms of the generation of supplementary vortex solid dislocations. The sharp drop of the structure factor above the second peak field is explained by the dynamics of freezing of the vortex ensemble in the high field phase.
SANS study of vortex lattice structural transition in optimally doped (Ba1-x K x )Fe2As2.
Demirdiş, S; van der Beek, C J; Mühlbauer, S; Su, Y; Wolf, Th
2016-10-26
Small-angle neutron scattering on high quality single crystalline Ba1-x K x Fe2As2 reveals the transition from a low-field vortex solid phase with orientational order to a vortex polycrystal at high magnetic field. The vortex order-disorder transition is correlated with the second-peak feature in isothermal hysteresis loops, and is interpreted in terms of the generation of supplementary vortex solid dislocations. The sharp drop of the structure factor above the second peak field is explained by the dynamics of freezing of the vortex ensemble in the high field phase. PMID:27541966
NASA Astrophysics Data System (ADS)
Hankin, D.; Graham, J. M. R.
2014-12-01
An unsteady formulation of the vortex lattice method, VLM, is presented that uses a force- free representation of the wake behind a horizontal axis wind turbine, HAWT, to calculate the aerodynamic loading on a turbine operating in the wake of an upstream rotor. A Cartesian velocity grid is superimposed over the computational domain to facilitate the representation of the atmospheric turbulence surrounding the turbine and wind shear. The wake of an upstream rotor is modelled using two methods: a mean velocity deficit with superimposed turbulence, based on experimental observations, and a purely numeric periodic boundary condition. Both methods are treated as frozen and propagated with the velocity grid. Measurements of the mean thrust and blade root bending moment on a three bladed horizontal axis rotor modelling a 5 MW HAWT at 1:250 scale were carried out in a wind tunnel. Comparisons are made between operation in uniform flow and in the wake of a similarly loaded rotor approximately 6.5 diameters upstream. The measurements were used to validate the output from the VLM simulations, assuming a completely rigid rotor. The trends in the simulation thrust predictions are found to compare well with the uniform flow case, except at low tip speed ratios where there are losses due to stall which are yet to be included in the model. The simple wake model predicts the mean deficit, whilst the periodic boundary condition captures more of the frequency content of the loading in an upstream wake. However, all the thrust loads are over-predicted. The simulation results severely overestimate the bending moment, which needs addressing. However, the reduction in bending due to the simple wake model is found to reflect the experimental data reasonably well.
Kitaev anisotropy induces mesoscopic Z2 vortex crystals in frustrated hexagonal antiferromagnets
NASA Astrophysics Data System (ADS)
Rousochatzakis, Ioannis; Rössler, Ulrich K.; van den Brink, Jeroen; Daghofer, Maria
2016-03-01
The triangular-lattice Heisenberg antiferromagnet (HAF) is known to carry topological Z2 vortex excitations which form a gas at finite temperatures. Here we show that the spin-orbit interaction, introduced via a Kitaev term in the exchange Hamiltonian, condenses these vortices into a triangular Z2 vortex crystal at zero temperature. The cores of the Z2 vortices show abrupt, soliton-like magnetization modulations and arise by a special intertwining of three honeycomb superstructures of ferromagnetic domains, one for each of the three sublattices of the 120∘ state of the pure HAF. This is an example of a nucleation transition, analogous to the spontaneous formation of magnetic domains, Abrikosov vortices in type-II superconductors, blue phases in cholesteric liquid crystals, and skyrmions in chiral helimagnets. As the mechanism relies on the interplay of geometric frustration and spin-orbital anisotropies, such vortex mesophases can materialize as a ground state property in spin-orbit coupled correlated systems with nearly hexagonal topology, as in triangular or strongly frustrated honeycomb iridates.
Paramagnetic excited vortex states in superconductors
NASA Astrophysics Data System (ADS)
Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.
2016-06-01
We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.
Dynamic instabilities in the vortex lattice of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}
Kwok, W.K.; Crabtree, G.W.; Fendrich, J.A.; Paulius, L.M.
1997-07-01
A dynamic instability in the ac response of the vortex solid phase just below the melting/freezing line is reported. The instability takes the form of a voltage oscillation whose frequency is much lower than the driving frequency. The dependence of the voltage oscillation on experimental parameters is described.
Ishida, Takekazu; Okuda, Kiichi; Asaoka, Hidehito
1999-12-01
Vortex lattice melting in the H{perpendicular}c configuration of an YBa{sub 2}Cu{sub 3}O{sub 6.94} single crystal has been investigated by means of the ac susceptibility {chi}{prime}-i{chi}{double{underscore}prime} and the magnetic torque {tau}. The melting transition of vortex lattice occurs in H{perpendicular}c, too. Since the torque curve shows a sharp peak in the irreversible torque at {theta}{sub c} {approx{underscore}equal} 90{degree} due to intrinsic pinning at lower temperatures, the authors can determine the irreversibility line for the intrinsic pinning. The melting transition in the H{perpendicular}c configuration appears at temperatures where the intrinsic-pinning peak is absent. They consider that the intrinsic pinning does not affect the nature of the vortex melting transition in the H{perpendicular}c configuration.
Critical current oscillations in the intrinsic hybrid vortex state of SmFeAs(O,F).
Moll, Philip J W; Balicas, Luis; Zhu, Xiyu; Wen, Hai-Hu; Zhigadlo, Nikolai D; Karpinski, Janusz; Batlogg, Bertram
2014-10-31
In layered superconductors the order parameter may be modulated within the unit cell, leading to nontrivial modifications of the vortex core if the interlayer coherence length ξ(c)(T) is comparable to the interlayer spacing. In the iron pnictide SmFeAs(O,F) (T(c)≈50 K) this occurs below a crossover temperature T(⋆)≈41 K, which separates two regimes of vortices: anisotropic Abrikosov-like at high and Josephson-like at low temperatures. Yet in the transition region around T(⋆), hybrid vortices between these two characteristics appear. Only in this region around T(⋆) and for magnetic fields well aligned with the FeAs layers, we observe oscillations of the c-axis critical current j(c)(H) periodic in 1/sqrt[H] due to a delicate balance of intervortex forces and interaction with the layered potential. j(c)(H) shows pronounced maxima when a hexagonal vortex lattice is commensurate with the underlying crystal structure. The narrow temperature window in which oscillations are observed suggests a significant suppression of the order parameter between the superconducting layers in SmFeAs(O,F), despite its low coherence length anisotropy (γ(ξ)≈3-5).
Critical Current Oscillations in the Intrinsic Hybrid Vortex State of SmFeAs(O,F)
NASA Astrophysics Data System (ADS)
Moll, Philip J. W.; Balicas, Luis; Zhu, Xiyu; Wen, Hai-Hu; Zhigadlo, Nikolai D.; Karpinski, Janusz; Batlogg, Bertram
2014-10-01
In layered superconductors the order parameter may be modulated within the unit cell, leading to nontrivial modifications of the vortex core if the interlayer coherence length ξc(T ) is comparable to the interlayer spacing. In the iron pnictide SmFeAs(O,F) (Tc≈50 K ) this occurs below a crossover temperature T⋆≈41 K , which separates two regimes of vortices: anisotropic Abrikosov-like at high and Josephson-like at low temperatures. Yet in the transition region around T⋆ , hybrid vortices between these two characteristics appear. Only in this region around T⋆ and for magnetic fields well aligned with the FeAs layers, we observe oscillations of the c -axis critical current jc(H ) periodic in 1 /√{H } due to a delicate balance of intervortex forces and interaction with the layered potential. jc(H ) shows pronounced maxima when a hexagonal vortex lattice is commensurate with the underlying crystal structure. The narrow temperature window in which oscillations are observed suggests a significant suppression of the order parameter between the superconducting layers in SmFeAs(O,F), despite its low coherence length anisotropy (γξ≈3 - 5 ).
NASA Astrophysics Data System (ADS)
Kajzer, A.; Pozorski, J.; Szewc, K.
2014-08-01
In the paper we present Large-eddy simulation (LES) results of 3D Taylor- Green vortex obtained by the three different computational approaches: Smoothed Particle Hydrodynamics (SPH), Lattice Boltzmann Method (LBM) and Finite Volume Method (FVM). The Smagorinsky model was chosen as a subgrid-scale closure in LES for all considered methods and a selection of spatial resolutions have been investigated. The SPH and LBM computations have been carried out with the use of the in-house codes executed on GPU and compared, for validation purposes, with the FVM results obtained using the open-source CFD software OpenFOAM. A comparative study in terms of one-point statistics and turbulent energy spectra shows a good agreement of LES results for all methods. An analysis of the GPU code efficiency and implementation difficulties has been made. It is shown that both SPH and LBM may offer a significant advantage over mesh-based CFD methods.
NASA Astrophysics Data System (ADS)
Ohlin, Kjell; Berggren, Karl Fredrik
2016-07-01
Faraday first characterised the behaviour of a fluid in a container subjected to vertical periodic oscillations. His study pertaining to hydrodynamic instability, the ‘Faraday instability’, has catalysed a myriad of experimental, theoretical, and numerical studies shedding light on the mechanisms responsible for the transition of a system at rest to a new state of well-ordered vibrational patterns at fixed frequencies. Here we study dual strata in a shallow vessel containing distilled water and high-viscosity lubrication oil on top of it. At elevated driving power, beyond the Faraday instability, the top stratum is found to ‘freeze’ into a rigid pattern with maxima and minima. At the same time there is a dynamic crossover into a new state in the form of a lattice of recirculating vortices in the lower layer containing the water. Instrumentation and the physics behind are analysed in a phenomenological way together with a basic heuristic modelling of the wave field. The study, which is based on relatively low-budget equipment, stems from related art projects that have evolved over the years. The study is of value within basic research as well as in education, especially as more advanced collective project work in e.g. engineering physics, where it invites further studies of pattern formation, the emergence of vortex lattices and complexity.
Dynamics of the Abrikosov Vortices on Cylindrical Microtubes
NASA Astrophysics Data System (ADS)
Rezaev, R. O.; Levchenko, E. A.; Schmidt, O. G.; Fomin, V. M.
2015-09-01
We consider the special features at nano- and microscales of the vortex dynamics on superconducting cylindrical Nb tubes produced by the roll-up (self-rolling) technique. A transport current enters the tube through electrodes placed on both sides of a cut (in the paraxial direction) of the tube. The system is in the magnetic field perpendicular to the tube axis. The vortex dynamics is described by means of characteristic times: time (Δt1) needed for a vortex to move from one edge of the tube to another and time (Δt2) between two consecutive vortex nucleation events at one edge of the tube. A range of magnetic field values is analyzed where Δt1 as a function of the magnetic field has a highly nonlinear and non-monotonic behavior. For certain values of the magnetic field, two different trajectories are possible for a moving vortex, i.e., a bifurcation phenomenon occurs. We explain the reason of this bifurcation.
Induced vacuum current and magnetic field in the background of a vortex
NASA Astrophysics Data System (ADS)
Gorkavenko, Volodymyr M.; Ivanchenko, Iryna V.; Sitenko, Yurii A.
2016-02-01
A topological defect in the form of the Abrikosov-Nielsen-Olesen vortex is considered as a gauge-flux-carrying tube that is impenetrable for quantum matter. Charged scalar matter field is quantized in the vortex background with the perfectly reflecting (Dirichlet) boundary condition imposed at the side surface of the vortex. We show that a current circulating around the vortex and a magnetic field directed along the vortex are induced in the vacuum, if the Compton wavelength of the matter field exceeds considerably the transverse size of the vortex. The vacuum current and magnetic field are periodic in the value of the gauge flux of the vortex, providing a quantum-field-theoretical manifestation of the Aharonov-Bohm effect. The total flux of the induced vacuum magnetic field attains notable finite values even for the Compton wavelength of the matter field exceeding the transverse size of the vortex by just three orders of magnitude.
Neutron Scattering Studies of Vortex Matter in Type-II Superconductors
Xinsheng Ling
2012-02-02
The proposed program is an experimental study of the fundamental properties of Abrikosov vortex matter in type-II superconductors. Most superconducting materials used in applications such as MRI are type II and their transport properties are determined by the interplay between random pinning, interaction and thermal fluctuation effects in the vortex state. Given the technological importance of these materials, a fundamental understanding of the vortex matter is necessary. The vortex lines in type-II superconductors also form a useful model system for fundamental studies of a number of important issues in condensed matter physics, such as the presence of a symmetry-breaking phase transition in the presence of random pinning. Recent advances in neutron scattering facilities such as the major upgrade of the NIST cold source and the Spallation Neutron Source are providing unprecedented opportunities in addressing some of the longstanding issues in vortex physics. The core component of the proposed program is to use small angle neutron scattering and Bitter decoration experiments to provide the most stringent test of the Bragg glass theory by measuring the structure factor in both the real and reciprocal spaces. The proposed experiments include a neutron reflectometry experiment to measure the precise Q-dependence of the structure factor of the vortex lattice in the Bragg glass state. A second set of SANS experiments will be on a shear-strained Nb single crystal for testing a recently proposed theory of the stability of Bragg glass. The objective is to artificially create a set of parallel grain boundaries into a Nb single crystal and use SANS to measure the vortex matter diffraction pattern as a function of the changing angle between the applied magnetic field to the grain boundaries. The intrinsic merits of the proposed work are a new fundamental understanding of type-II superconductors on which superconducting technology is based, and a firm understanding of phases
Vortex Patterns in Ginzburg-Landau Minimizers
NASA Astrophysics Data System (ADS)
Serfaty, Sylvia; Sandier, Etienne
2010-03-01
We present a survey of results obtained with Etienne Sandier on vortices in the minimizers of the 2D Ginzburg-Landau energy of superconductivity with an applied magnetic field, in the asymptotic regime of large kappa where vortices become point-like. We describe results which characterize the critical values of the applied field for which vortices appear, their numbers and locations. If the applied field is large enough, it is observed in experiments that vortices are densely packed and form triangular (hexagonal) lattices named Abrikosov lattices. Part of our results is the rigorous derivation of a mean field model describing the optimal density of vortices at leading order in the energy, and then the derivation of a next order limiting energy which governs the positions of the vortices after blow-up at their inter-distance scale. This limiting energy is a logarithmic-type interaction between points in the plane. Among lattice configurations it is uniquely minimized by the hexagonal lattice, thus providing a first justification of the Abrikosov lattice in this regime.
Vortex dynamics in anisotropic traps
McEndoo, S.; Busch, Th.
2010-07-15
We investigate the dynamics of linear vortex lattices in anisotropic traps in two dimensions and show that the interplay between the rotation and the anisotropy leads to a rich but highly regular dynamics.
User's manual for interfacing a leading edge, vortex rollup program with two linear panel methods
NASA Technical Reports Server (NTRS)
Desilva, B. M. E.; Medan, R. T.
1979-01-01
Sufficient instructions are provided for interfacing the Mangler-Smith, leading edge vortex rollup program with a vortex lattice (POTFAN) method and an advanced higher order, singularity linear analysis for computing the vortex effects for simple canard wing combinations.
Van de Vondel, J; Gladilin, V N; Silhanek, A V; Gillijns, W; Tempere, J; Devreese, J T; Moshchalkov, V V
2011-04-01
We investigated experimentally the frequency dependence of a superconducting vortex ratchet effect by means of electrical transport measurements and modeled it theoretically using the time-dependent Ginzburg-Landau formalism. We demonstrate that the high frequency vortex behavior can be described as a discrete motion of a particle in a periodic potential, i.e., the so-called stepper-motor behavior. Strikingly, in the more conventional low frequency response a transition takes place from an Abrikosov vortex rectifier to a phase slip line rectifier. This transition is characterized by a strong increase in the rectified voltage and the appearance of a pronounced hysteretic behavior.
NASA Astrophysics Data System (ADS)
Chigvinadze, Jaba G.; Mamniashvilli, Gogi I.; Acrivos, Juana V.
2004-03-01
The increased flux expulsion as T->Tc (observed as the external magnetic field, Bz = +/- 0.75 oe. goes through zero [1]) is related to the increased transmission as T->Tc (observed in all cuprate superconductors in the EXFAS region of X-ray absorption [2]). The expulsion of Abrikosov vortices as T->Tc is a cooperative dynamic phenomenon that affects only the EXAFS region of the spectrum. When the flux expulsion diverges beyond a critical value, we propose the EXAFS transmission increases because photoelectrons are involved in the Abrikosov Vortex. The phenomenon is similar to the increased transmission observed in He 4 by the formation of supercritical vortices [3]. [1] J.V. Acrivos, Lei Chen, C.M. Burch, P. Metcalf, J.M.Honig, R.S.Liu and K.K.Singh, Phys. Rev. B 50, 13710 (1994), [2] J.V. Acrivos, L.Nguyen, T.Norman, C.T. Lin, W.Y.Liang, J.M Honig and P.Somasundaram, Microchemical Journal, 71, 117 (2002), [3] E.J.Yarmchuk, M.J.V.Gordon, R.E.Packard, Phys.Rev.Lett. 43, 214 (1979)
Experimental evidence for flux-lattice melting. [in high-Tc superconductors
NASA Technical Reports Server (NTRS)
Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.
1991-01-01
A low-frequency torsional oscillator has been used to search for flux-lattice melting in an untwinned single crystal of YBa2Cu3O(7-delta). The damping of the oscillator was measured as a function of temperature, for applied magnetic fields in the range H = 0.1-2.3 T. A remarkably sharp damping peak has been located. It is suggested that the temperature of the peak corresponds to the melting point of the Abrikosov flux lattice.
Willemin, M.; Schilling, A.; Keller, H.; Hofer, J.; Rossel, C.; Welp, U.; Kwok, W.K.; Olsson, R.J.; Crabtree, G.W.
1998-11-01
High-resolution magnetic-torque studies on an untwinned YBa{sub 2}Cu {sub 3}O{sub 7{minus}{delta}} single crystal near its critical temperature T{sub c} reveal that the first-order vortex-lattice melting transition (VLMT) persists at least up to 0.5thinspthinspK below T{sub c} . The associated sharp discontinuity in magnetization is detectable even at temperatures where the torque signal deviates from mean-field behavior due to fluctuations. The magnetic irreversibility at the VLMT can be suppressed by applying a weak transverse ac magnetic field. This offers the possibility of separating the irreversibility line from the melting line near T{sub c} . {copyright} {ital 1998} {ital The American Physical Society }
Rayleigh instability of confined vortex droplets in critical superconductors
NASA Astrophysics Data System (ADS)
Lukyanchuk, I.; Vinokur, V. M.; Rydh, A.; Xie, R.; Milošević, M. V.; Welp, U.; Zach, M.; Xiao, Z. L.; Crabtree, G. W.; Bending, S. J.; Peeters, F. M.; Kwok, W. K.
2015-01-01
Depending on the Ginzburg-Landau parameter κ, superconductors can either be fully diamagnetic if (type I superconductors) or allow magnetic flux to penetrate through Abrikosov vortices if (type II superconductors; refs , ). At the Bogomolny critical point, , a state that is infinitely degenerate with respect to vortex spatial configurations arises. Despite in-depth investigations of conventional type I and type II superconductors, a thorough understanding of the magnetic behaviour in the near-Bogomolny critical regime at κ ~ κc remains lacking. Here we report that in confined systems the critical regime expands over a finite interval of κ forming a critical superconducting state. We show that in this state, in a sample with dimensions comparable to the vortex core size, vortices merge into a multi-quanta droplet, which undergoes Rayleigh instability on increasing κ and decays by emitting single vortices. Superconducting vortices realize Nielsen-Olesen singular solutions of the Abelian Higgs model, which is pervasive in phenomena ranging from quantum electrodynamics to cosmology. Our study of the transient dynamics of Abrikosov-Nielsen-Olesen vortices in systems with boundaries promises access to non-trivial effects in quantum field theory by means of bench-top laboratory experiments.
Cho, Inyong; Lee, Youngone
2009-01-15
We investigate vortex configurations with the 'vulcanization' term inspired by the renormalization of {phi}{sub *}{sup 4} theory in the canonical {theta}-deformed noncommutativity. We focus on the classical limit of the theory described by a single parameter which is the ratio of the vulcanization and the noncommutativity parameters. We perform numerical calculations and find that nontopological vortex solutions exist as well as Q-ball type solutions, but topological vortex solutions are not admitted.
NASA Astrophysics Data System (ADS)
Cho, Inyong; Lee, Youngone
2009-01-01
We investigate vortex configurations with the “vulcanization” term inspired by the renormalization of ϕ⋆4 theory in the canonical θ-deformed noncommutativity. We focus on the classical limit of the theory described by a single parameter which is the ratio of the vulcanization and the noncommutativity parameters. We perform numerical calculations and find that nontopological vortex solutions exist as well as Q-ball type solutions, but topological vortex solutions are not admitted.
Dynamic visualization of nanoscale vortex orbits.
Timmermans, Matias; Samuely, Tomas; Raes, Bart; Van de Vondel, Joris; Moshchalkov, Victor V
2014-03-25
Due to the atomic-scale resolution, scanning tunneling microscopy is an ideal technique to observe the smallest objects. Nevertheless, it suffers from very long capturing times in order to investigate dynamic processes at the nanoscale. We address this issue, for vortex matter in NbSe2, by driving the vortices using an ac magnetic field and probing the induced periodic tunnel current modulations. Our results reveal different dynamical modes of the driven vortex lattices. In addition, by recording and synchronizing the time evolution of the tunneling current at each pixel, we visualize the overall dynamics of the vortex lattice with submillisecond time resolution and subnanometer spatial resolution.
Critical depinning current of elastic vortex strings in superconductors with extended linear defects
NASA Astrophysics Data System (ADS)
Fedirko, V. A.; Kasatkin, A. L.; Polyakov, S. V.
2016-09-01
The problem of the depinning of an Abrikosov elastic vortex string from an extended linear defect in the plate of a 3 D anisotropic superconductor of thickness d > 2λ (where λ is the London penetration depth) under the action of an inhomogeneously distributed transport current that flows in the surface shielding layer has been solved using classical mechanics approach. Conditions for the appearance of the instability of the pinned state of a vortex have been investigated and calculations of the corresponding critical current density on the surface at which the depinning of the vortex string occurs have been carried out. The dependence of the average of the critical current density on the thickness of the plate has been determined.
Electromagnetic response of a static vortex line in a type-II superconductor: A microscopic study
Janko, B.; Shore, J.D. )
1992-10-01
The electromagnetic response of a pinned Abrikosov fluxoid is examined in the framework of the Bogoliubov--de Gennes formalism. The matrix elements and the section rules for both the single photon (emission-absorption) and two photon (Raman scattering) processes are obtained. The results reveal striking asymmetries: light absorption by quasiparticle pair creation or single quasiparticle scattering can occur only if the handedness of the incident radiation is opposite to that of the vortex core states. We show how these effects will lead to nonreciprocal circular birefringence, and also predict structure in the frequency dependence of conductivity and in the differential cross section of the Raman scattering.
Vortex dynamics during blade-vortex interactions
NASA Astrophysics Data System (ADS)
Peng, Di; Gregory, James W.
2015-05-01
Vortex dynamics during parallel blade-vortex interactions (BVIs) were investigated in a subsonic wind tunnel using particle image velocimetry (PIV). Vortices were generated by applying a rapid pitch-up motion to an airfoil through a pneumatic system, and the subsequent interactions with a downstream, unloaded target airfoil were studied. The blade-vortex interactions may be classified into three categories in terms of vortex behavior: close interaction, very close interaction, and collision. For each type of interaction, the vortex trajectory and strength variation were obtained from phase-averaged PIV data. The PIV results revealed the mechanisms of vortex decay and the effects of several key parameters on vortex dynamics, including separation distance (h/c), Reynolds number, and vortex sense. Generally, BVI has two main stages: interaction between vortex and leading edge (vortex-LE interaction) and interaction between vortex and boundary layer (vortex-BL interaction). Vortex-LE interaction, with its small separation distance, is dominated by inviscid decay of vortex strength due to pressure gradients near the leading edge. Therefore, the decay rate is determined by separation distance and vortex strength, but it is relatively insensitive to Reynolds number. Vortex-LE interaction will become a viscous-type interaction if there is enough separation distance. Vortex-BL interaction is inherently dominated by viscous effects, so the decay rate is dependent on Reynolds number. Vortex sense also has great impact on vortex-BL interaction because it changes the velocity field and shear stress near the surface.
NASA Astrophysics Data System (ADS)
Flis, V. S.; Kalenyuk, A. A.; Kasatkin, A. L.; Moskalyuk, V. O.; Rebikov, A. I.; Svechnikov, V. L.; Tret'yachenko, K. G.; Pan, V. M.
2010-01-01
This paper presents the results of a comprehensive study of the relationship of the structural and electrodynamic characteristics of quasi-single-crystal films of the HTSC cuprate YBa2Cu3O7-δ (YBCO) with various concentrations (several mass percent) of nanosize inclusions of the perovskitelike phase of BaZrO3 (BZO). High-resolution electron microscopy is used to investigate the nanostructure of the fabricated films and to determine the main types of defects that cause strong pinning of Abrikosov vortices and, accordingly, large critical current densities. The results of theoretically modelling the genesis of the defect nanostructure that appears in such films and its influence on the critical current are presented. The magnetic and transport properties of HTSC films made from YBCO(BZO) have been experimentally studied. The temperature, magnetic-field, and magnetic-orientation dependences of the critical current density of the test films are found. The results of an experimental investigation of the high-frequency properties of YBZO(BZO) films—the surface microwave impedance of the films in the linear and nonlinear regimes—are also given. The experimental results are discussed, and the influence of the nanostructure of the impurity phase on the electrodynamic characteristics of the HTSC films is analyzed.
Chorin, A.J. |
1993-06-01
Vortex methods originated from the observation that in incompressible inviscid flow vorticity (or, more accurately, circulation) is a conserved quantity, as can be readily deduced from the absence of tangential stresses. Thus, if the vorticity is known at time t=0, one can find the flow at a later time by simply following the vorticity. In this narrow context, a vortex method is a numerical method that follows vorticity. The author restricts himself in these lectures to a special class of numerical vortex methods, those that are based on a Lagrangian transport of vorticity in hydrodynamics by smoothed particles (blobs) and those whose analysis contributes to the understanding of blob methods. Blob methods started in the 1930`s.
Spectroscopy of magnetic excitations in magnetic superconductors using vortex motion.
Bulaevskii, L N; Hruska, M; Maley, M P
2005-11-11
In magnetic superconductors a moving vortex lattice is accompanied by an ac magnetic field which leads to the generation of spin waves. At resonance conditions the dynamics of vortices in magnetic superconductors changes drastically, resulting in strong peaks in the dc I-V characteristics at voltages at which the washboard frequency of the vortex lattice matches the spin wave frequency omegaS(g), where g are the reciprocal vortex lattice vectors. We show that if the washboard frequency lies above the magnetic gap, measurement of the I-V characteristics provides a new method to obtain information on the spectrum of magnetic excitations in borocarbides and cuprate layered magnetic superconductors.
Leapfrogging of multiple coaxial viscous vortex rings
Cheng, M. Lou, J.; Lim, T. T.
2015-03-15
A recent theoretical study [Borisov, Kilin, and Mamaev, “The dynamics of vortex rings: Leapfrogging, choreographies and the stability problem,” Regular Chaotic Dyn. 18, 33 (2013); Borisov et al., “The dynamics of vortex rings: Leapfrogging in an ideal and viscous fluid,” Fluid Dyn. Res. 46, 031415 (2014)] shows that when three coaxial vortex rings travel in the same direction in an incompressible ideal fluid, each of the vortex rings alternately slips through (or leapfrogs) the other two ahead. Here, we use a lattice Boltzmann method to simulate viscous vortex rings with an identical initial circulation, radius, and separation distance with the aim of studying how viscous effect influences the outcomes of the leapfrogging process. For the case of two identical vortex rings, our computation shows that leapfrogging can be achieved only under certain favorable conditions, which depend on Reynolds number, vortex core size, and initial separation distance between the two rings. For the case of three coaxial vortex rings, the result differs from the inviscid model and shows that the second vortex ring always slips through the leading ring first, followed by the third ring slipping through the other two ahead. A simple physical model is proposed to explain the observed behavior.
Atmospheric Science Data Center
2013-06-26
... within the cloud layer downwind of the obstacle. These turbulence patterns are known as von Karman vortex streets. In these images ... was the first to derive the conditions under which these turbulence patterns occur. von Karman was a professor of aeronautics at the ...
Nonlinear electrodynamics of vortex matter in hard superconductors (Review)
NASA Astrophysics Data System (ADS)
Voloshin, I. F.; Fisher, L. M.; Yampol'Skiĭ, V. A.
2010-01-01
Nontrivial electrodynamic properties of vortex matter, which are due to a specific nonlinearity of the material equations, in hard superconductors are discussed: collapse of the transport current and the static magnetization of superconductors by an external orthogonal ac magnetic field; appearance of jumps in the time dependence of the electric field at the boundary of a sample as a result of nonlinear interaction of waves having different frequencies; specific staged penetration of an electromagnetic field into anisotropic superconductors. Nonlocal effects resulting in a large modification of nonlinear phenomena are also examined. Special attention is given to a discussion of the unique phenomenon of macroturbulent instability, associated with the flow of Abrikosov vortices, in hard superconductors. Most results presented are based on original experimental and theoretical investigations performed with the participation of the present authors.
Optimum lattice arrangement developed from a rigorous analytical basis
NASA Technical Reports Server (NTRS)
Deyoung, J.
1976-01-01
The spanwise vortex-lattice arrangement is mathematically established by lattice solutions of the slender wing which are shown to be analogous to the chordwise vortex-lattice thin wing solution. Solutions for any number N of panels wing theory lift and induced drag and thin wing theory lift and moment are predicted exactly. As N approaches infinity, the slender wing elliptic spanwise loading and thin wing cotangent chordwise loading are predicted, which proves there is mathematical convergence of the vortex-lattice method to the exact answer. Based on this planform spanwise lattice arrangement, an A-vortex-lattice spanwise system is developed for an arbitrary aspect ratio A. This A-lattice has the optimum characteristic of predicting lift accurately for any value of N.
NASA Astrophysics Data System (ADS)
Mills, Shaun A.; Wisser, Jacob J.; Shen, Chenyi; Xu, Zhuan; Liu, Ying
2016-06-01
Nanowires of two-dimensional (2D) crystals of type-II superconductor NbSe2 prepared by electron-beam lithography were studied, focusing on the effect of the motion of Abrikosov vortices. We present magnetoresistance measurements on these nanowires and show features related to vortex crossing, trapping, and pinning. The vortex crossing rate was found to vary nonmonotonically with the applied field, which results in nonmonotonic magnetoresistance variations in agreement with theoretical calculations in the London approximation. Above the lower critical field Hc 1 the crossing rate is also influenced by vortices trapped by sample boundaries or pinning centers, leading to sample-specific magnetoresistance patterns. We show that the local pinning potential can be modified by intentionally introducing surface adsorbates, making the magnetoresistance pattern a "magnetofingerprint" of the sample-specific configuration of vortex pinning centers in a 2D crystal superconducting nanowire.
Sun, Bo; Lin, Jiayi; Darby, Ellis; Grosberg, Alexander Y; Grier, David G
2009-07-01
Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static but nonconservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle's thermally driven trajectory is not simply a deterministic response to the solenoidal component of the force but rather reflects interplay between advection and diffusion in which thermal fluctuations extract work from the nonconservative force field. As an example of this previously unrecognized class of stochastic heat engines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that nonconservative optical forces bias the particle's fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power. PMID:19658638
Vortex dynamics in cubic-quintic Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Mithun, T.; Porsezian, K.; Dey, Bishwajyoti
2013-07-01
We study vortex dynamics in a trapped Bose-Einstein condensate with tunable two- and three-body interactions. The dynamics is governed by two-dimensional cubic-quintic Gross-Pitaevskii equation. A time-dependent variational method has been used to obtain critical rotational frequency and surface mode frequency analytically and are compared with numerical simulation results. An imaginary time propagation method and Crank-Nicolson scheme for discretization have been used for numerical simulation. The numerically calculated average value of the angular momentum per particle shows very clearly its dynamical relation with the time development of the vortex formation. The rotational frequency dependence of the variation of average value of the angular momentum per particle with time shows that vortices form much faster in time for higher rotational frequency. Similarly, the vortex forms much faster in time with an increase of the strength of the repulsive three-body interaction. The simulation of the vortex lattice formation in the condensate shows that the presence of the three-body interactions does not alter the vortex lattice pattern but it helps in the shape deformations of the condensate thereby leading to vortex lattice formation. Likewise, the three-body interactions enable the vortex lattice formation in Bose-Einstein condensates even with attractive two-body interactions and in purely quintic BEC.
Revisiting the vortex-core tunnelling spectroscopy in YBa2Cu3O7−δ
Bruér, Jens; Maggio-Aprile, Ivan; Jenkins, Nathan; Ristić, Zoran; Erb, Andreas; Berthod, Christophe; Fischer, Øystein; Renner, Christoph
2016-01-01
The observation by scanning tunnelling spectroscopy of Abrikosov vortex cores in the high-temperature superconductor YBa2Cu3O7−δ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterized by a strong zero-bias conductance peak. Here, we present scanning tunnelling spectroscopy data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel, which contributes to the tunnelling signal in parallel with the superconducting density of states. PMID:27030516
Vortex Flow Aerodynamics, volume 1
NASA Technical Reports Server (NTRS)
Campbell, J. F. (Editor); Osborn, R. F. (Editor); Foughner, J. T., Jr. (Editor)
1986-01-01
Vortex modeling techniques and experimental studies of research configurations utilizing vortex flows are discussed. Also discussed are vortex flap investigations using generic and airplane research models and vortex flap theoretical analysis and design studies.
NASA Astrophysics Data System (ADS)
Song, T. L.; Ma, Y. L.
2011-08-01
The ground state of a three-dimensional (3D) rotating trapped superfluid Fermi gas in the BCS-BEC crossover is mapped to finite N v -body vortex states by a simple ansatz. The total vortex energy is measured from the ground-state energy of the system in the absence of the vortices. The vortex state is stable since the vortex potential and rotation energies are attractive while the vortex kinetic energy and interaction between vortices are repulsive. By combining the analytical and numerical works for the minimal vortex energy, the 2D configurations of N v vortices are studied by taking into account of the finite size effects both on xy-plane and on z-direction. The calculated vortex numbers as a function of the interaction strength are appropriate to the renew experimental results by Zwierlein in [ High-temperature superfluidity in a ultracold Fermi gas, Ph.D. thesis, Massachusetts Institute of Technology, 2006]. The numerical results show that there exist two types of vortex structures: the trap center is occupied and unoccupied by a vortex, even in the case of N v < 10 with regular polygon and in the case of N v ≥ 10 with finite triangle lattice. The rotation frequency dependent vortex numbers with different interaction strengths are also discussed.
Schwinger boson spin-liquid states on square lattice
NASA Astrophysics Data System (ADS)
Yang, Xu; Wang, Fa
2016-07-01
We study possible spin liquids on square lattice that respect all lattice symmetries and time-reversal symmetry within the framework of Schwinger boson (mean-field) theory. Such spin liquids have spin gap and emergent Z2 gauge field excitations. We classify them by the projective symmetry group method, and find six spin-liquid states that are potentially relevant to the J1-J2 Heisenberg model. The properties of these states are studied under mean-field approximation. Interestingly we find a spin-liquid state that can go through continuous phase transitions to either the Néel magnetic order or magnetic orders of the wave vector at the Brillouin zone edge center. We also discuss the connection between our results and the Abrikosov fermion spin liquids.
NASA Astrophysics Data System (ADS)
Freilich, Daniel; Llewellyn Smith, Stefan
2014-11-01
A Sadovskii vortex is a patch of fluid with uniform vorticity surrounded by a vortex sheet. Using a boundary element type method, we investigate the steady states of this flow in an incompressible, inviscid straining flow. Outside the vortex, the fluid is irrotational. In the limiting case where the entire circulation is due to the vortex patch, this is a patch vortex (Moore & Saffman, Aircraft wake turbulence and its detection 1971). In the other limiting case, where all the circulation is due to the vortex sheet, this is a hollow vortex (Llewellyn Smith and Crowdy, J. Fluid Mech. 691, 2012). This flow has two governing nondimensional parameters, relating the strengths of the straining field, vortex sheet, and patch vorticity. We study the relationship between these two parameters, and examine the shape of the resulting vortices. We also work towards a bifurcation diagram of the steady states of the Sadovskii vortex in an attempt to understand the connection between vortex sheet and vortex patch desingularizations of the point vortex. Support from NSF-CMMI-0970113.
Quantum vortex dynamics in two-dimensional neutral superfluids
Wang, C.-C. Joseph; Duine, R. A.; MacDonald, A. H.
2010-01-15
We derive an effective action for the vortex-position degree of freedom in a superfluid by integrating out condensate phase- and density-fluctuation environmental modes. When the quantum dynamics of environmental fluctuations is neglected, we confirm the occurrence of the vortex Magnus force and obtain an expression for the vortex mass. We find that this adiabatic approximation is valid only when the superfluid droplet radius R, or the typical distance between vortices, is very much larger than the coherence length xi. We go beyond the adiabatic approximation numerically, accounting for the quantum dynamics of environmental modes and capturing their dissipative coupling to condensate dynamics. For the case of an optical-lattice superfluid, we demonstrate that vortex motion damping can be adjusted by tuning the ratio between the tunneling energy J and the on-site interaction energy U. We comment on the possibility of realizing vortex-Landau-level physics.
Superconducting vortex pinning with artificial magnetic nanostructures.
Velez, M.; Martin, J. I.; Villegas, J. E.; Hoffmann, A.; Gonzalez, E. M.; Vicent, J. L.; Schuller, I. K.; Univ. de Oviedo-CINN; Unite Mixte de Physique CNRS Univ. Paris-Sud; Univ.Complutense de Madrid; Univ. California at San Diego
2008-11-01
This review is dedicated to summarizing the recent research on vortex dynamics and pinning effects in superconducting films with artificial magnetic structures. The fabrication of hybrid superconducting/magnetic systems is presented together with the wide variety of properties that arise from the interaction between the superconducting vortex lattice and the artificial magnetic nanostructures. Specifically, we review the role that the most important parameters in the vortex dynamics of films with regular array of dots play. In particular, we discuss the phenomena that appear when the symmetry of a regular dot array is distorted from regularity towards complete disorder including rectangular, asymmetric, and aperiodic arrays. The interesting phenomena that appear include vortex-lattice reconfigurations, anisotropic dynamics, channeling, and guided motion as well as ratchet effects. The different regimes are summarized in a phase diagram indicating the transitions that take place as the characteristic distances of the array are modified respect to the superconducting coherence length. Future directions are sketched out indicating the vast open area of research in this field.
Three-dimensional vortex structures in a rotating dipolar Bose–Einstein condensate
NASA Astrophysics Data System (ADS)
Kishor Kumar, Ramavarmaraja; Sriraman, Thangarasu; Fabrelli, Henrique; Muruganandam, Paulsamy; Gammal, Arnaldo
2016-08-01
We study three-dimensional vortex lattice structures in purely dipolar Bose–Einstein condensate (BEC). By using the mean-field approximation, we obtain a stability diagram for the vortex states in purely dipolar BECs as a function of harmonic trap aspect ratio (λ) and dipole–dipole interaction strength (D) under rotation. Rotating the condensate within the unstable region leads to collapse while in the stable region furnishes stable vortex lattices of dipolar BECs. We analyse stable vortex lattice structures by solving the three-dimensional time-dependent Gross–Pitaevskii equation in imaginary time. Further, the stability of vortex states is examined by evolution in real-time. We also investigate the distribution of vortices in a fully anisotropic trap by increasing eccentricity of the external trapping potential. We observe the breaking up of the condensate in two parts with an equal number of vortices on each when the trap is sufficiently weak, and the rotation frequency is high.
NASA Astrophysics Data System (ADS)
Freilich, Daniel; Llewellyn Smith, Stefan
2015-11-01
Sadovskii vortices are patches of fluid with uniform vorticity surrounded by a vortex sheet. They were first constructed as models for wakes behind bluff objects. We investigate the Sadovskii vortex in a straining field and examine limiting cases to validate our computational method. One limit is the patch vortex in strain (Moore & Saffman, Aircraft wake turbulence and its detection 1971), where there is no vortex sheet. We solve this as a free-boundary problem, and show that a simple method using the Biot-Savart law quickly gives solutions for stable shapes. When used for the more elongated (stronger straining field) situations, the method also leads to new vortex shapes. In the hollow vortex case, where there is no vortex patch and the circulation is entirely due to the vortex sheet (Llewellyn Smith and Crowdy, J. Fluid Mech. 691 2012), we use the Birkhoff-Rott equation to calculate the velocity of the fluid on the vortex boundary. The combination of these two methods can then be used to calculate the shape and velocity field of the Sadovksii vortex in strain.
Transfer and storage of vortex states in light and matter waves.
Dutton, Zachary; Ruostekoski, Janne
2004-11-01
We theoretically explore the transfer of vortex states between atomic Bose-Einstein condensates and optical pulses using ultraslow and stopped light techniques. We find shining a coupling laser on a rotating two-component ground state condensate with a vortex lattice generates a probe laser field with optical vortices. We also find that optical vortex states can be robustly stored in the atomic superfluids for times, in Rb-87 condensates, limited only by the ground state coherence time.
NASA Astrophysics Data System (ADS)
Hayward, A. L. C.; Martin, A. M.
2016-02-01
We investigate the ground-state behavior of Jaynes-Cummings-Hubbard lattices in the presence of a synthetic magnetic field, via a Gutzwiller ansatz. Specifically, we study the superfluid-Mott transition and the formation of vortex lattices in the superfluid regime. We find a suppression of the superfluid fraction due to the frustration induced by the incommensurate magnetic and spacial lattice lengths. We also predict the formation of triangular vortex lattices inside the superfluid regime.
Phase transition in the vortex liquid and the critical endpoint in YBa2Cu3Oy
NASA Astrophysics Data System (ADS)
Shibata, Kenji; Nishizaki, Terukazu; Sasaki, Takahiko; Kobayashi, Norio
2002-12-01
The vortex phase diagram of optimally doped untwinned YBa2Cu3Oy is studied. We find a first-order transition TL(H) in the vortex liquid above the terminal point Hmcp (≃7 T) of both the vortex glass line Tg(H) and the field-driven disordering transition line H*(T). The obtained small entropy change (˜0.02 kB/vortex/layer) and the critical endpoint Hcep (≃11 T) of the TL(H) line indicate that the vortex liquid undergoes the vortex slush regime before the solidification into the vortex glass phase. Below Hmcp, the vortex liquid phase shows the first-order melting transition into the Bragg glass phase. We also study the oxygen content y dependence of the vortex phase diagram and find that the vortex slush regime is located in the borderline (i.e., 6.90⩽y⩽6.92) below which the vortex lattice melting transition disappears. The result indicates that the point disorder with the intermediate strength plays an important role in the vortex slush regime.
Vortex dynamics and Hall conductivity of hard-core bosons
Lindner, Netanel; Auerbach, Assa; Arovas, Daniel P.
2010-10-01
Magnetotransport of hard-core bosons is studied using an XXZ quantum spin model representation, appropriately gauged on the torus to allow for an external magnetic field. We find strong lattice effects near half filling. An effective quantum mechanical description of the vortex degrees of freedom is derived. Using semiclassical and numerical analysis we compute the vortex-hopping energy t{sub V}, which at half filling is close to magnitude of the boson hopping energy. The critical quantum melting density of the vortex lattice is estimated at 6.5x10{sup -3} vortices per unit cell. The Hall conductance is computed from the Chern numbers of the low-energy eigenstates. At zero temperature, it reverses sign abruptly at half filling. At precisely half filling, all eigenstates are doubly degenerate for any odd number of flux quanta. We prove the exact degeneracies on the torus by constructing an SU(2) algebra of point-group symmetries, associated with the center of vorticity. This result is interpreted as if each vortex carries an internal spin-half degree of freedom, which can manifest itself as a charge density modulation in its core. Our findings suggest interesting experimental implications for vortex motion of cold atoms in optical lattices and magnet transport of short coherence length superconductors.
Houck, Edward D.
1994-01-01
A fluid transfer system that combines a vortex diode with a jet ejector to transfer liquid from one tank to a second tank by a gas pressurization method having no moving mechanical parts in the fluid system. The vortex diode is a device that has a high resistance to flow in one direction and a low resistance to flow in the other.
Scientist Examines Tornado Vortex
NASA Technical Reports Server (NTRS)
1999-01-01
In this Quick Time movie, a scientist examines what appears to be a tornado vortex (blue) coming out of a thunderstorm. The scientist uses 3D glasses to be able to see in 3 dimensions the different flows going out into the vortex. Earth science and weather studies are an important ongoing function of NASA and its affiliates.
Improved vortex reactor system
Diebold, James P.; Scahill, John W.
1995-01-01
An improved vortex reactor system for affecting fast pyrolysis of biomass and Refuse Derived Fuel (RDF) feed materials comprising: a vortex reactor having its axis vertically disposed in relation to a jet of a horizontally disposed steam ejector that impels feed materials from a feeder and solids from a recycle loop along with a motive gas into a top part of said reactor.
Vortex shedding by matched asymptotic vortex method
NASA Astrophysics Data System (ADS)
Guo, Xinjun; Mandre, Shreyas
2014-11-01
An extension of the Kutta condition, using matched asymptotic expansion applied to the Navier-Stokes equations, is presented for flow past a smooth body at high Reynolds number. The goal is to study the influence of unsteady fluid dynamical effects like leading edge vortex, unsteady boundary layer separation, etc. In order to capture accurately the location and strength of vortex shedding, the simplified Navier-Stokes equations in the form of boundary layer approximation are solved in the thin inner region close to the solid body. In the outer region far from the structure, the vortex methods are applied, which significantly reduces the computational cost compared to CFD in the whole domain. With this method, the flow past an airfoil with two degrees of freedom, pitching and heaving, is investigated.
Disordered vortex phases in YBa{sub 2}Cu{sub 3}O{sub x}
Crabtree, G. W.; Kwok, W. K.; Olsson, R. J.; Karapetrov, G.; Paulius, L. M.; Petrean, A.; Tobos, V.; Moulton, W. G.
2000-05-22
The disordered vortex phases induced by line and point pinning in YBa{sub 2}Cu{sub 3}O{sub x} are explored. At high defect densities there is a single disordered solid separated from the liquid phase by a melting line. At low defect densities the topology of the phase diagram changes dramatically, with a vortex lattice phase adjoining disordered phases at high or low field. Critical points at the termination of first order melting separate the lattice and disordered phases. The line defect disordered phases follow the expected Bose glass behavior, while the point defect disordered phases do not exhibit the expected vortex glass behavior.
Pinning-modulated non-collective Josephson-vortex motion in stacked Josephson junctions.
Jin, Y.-D.; Lee, G.-H.; Lee, H.-J.; Bae, M.-H.; Koshelev, A. E.; Pohang Univ. of Science and Technology; Univ. of Illinois
2009-01-01
Josephson vortices in naturally stacked Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} tunneling junctions display rich dynamic behavior that derives from the coexistence of three basic states: static Josephson vortex lattice, coherently moving lattice, and incoherent quasiparticle tunneling state. The rich structure of hysteretic branches observed in the current-voltage characteristics can be understood as combinatorial combinations of these three states which are realized in different junctions and evolve separately with magnetic field and bias current. In particular, the multiple Josephson vortex flow branches at low-bias currents arise from the individual depinning of Josephson vortex rows in each junction.
Vortex cutting in superconductors
NASA Astrophysics Data System (ADS)
Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.
2016-08-01
Vortex cutting and reconnection is an intriguing and still-unsolved problem central to many areas of classical and quantum physics, including hydrodynamics, astrophysics, and superconductivity. Here, we describe a comprehensive investigation of the crossing of magnetic vortices in superconductors using time dependent Ginsburg-Landau modeling. Within a macroscopic volume, we simulate initial magnetization of an anisotropic high temperature superconductor followed by subsequent remagnetization with perpendicular magnetic fields, creating the crossing of the initial and newly generated vortices. The time resolved evolution of vortex lines as they approach each other, contort, locally conjoin, and detach, elucidates the fine details of the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.
NASA Technical Reports Server (NTRS)
Wood, Richard M.; Wilcox, Floyd J., Jr.; Bauer, Steven X. S.; Allen, Jerry M.
2000-01-01
A review of the research conducted at the National Aeronautics and Space Administration (NASA), Langley Research Center (LaRC) into high-speed vortex flows during the 1970s, 1980s, and 1990s is presented. The data reviewed is for flat plates, cavities, bodies, missiles, wings, and aircraft. These data are presented and discussed relative to the design of future vehicles. Also presented is a brief historical review of the extensive body of high-speed vortex flow research from the 1940s to the present in order to provide perspective of the NASA LaRC's high-speed research results. Data are presented which show the types of vortex structures which occur at supersonic speeds and the impact of these flow structures to vehicle performance and control is discussed. The data presented shows the presence of both small- and large scale vortex structures for a variety of vehicles, from missiles to transports. For cavities, the data show very complex multiple vortex structures exist at all combinations of cavity depth to length ratios and Mach number. The data for missiles show the existence of very strong interference effects between body and/or fin vortices and the downstream fins. It was shown that these vortex flow interference effects could be both positive and negative. Data are shown which highlights the effect that leading-edge sweep, leading-edge bluntness, wing thickness, location of maximum thickness, and camber has on the aerodynamics of and flow over delta wings. The observed flow fields for delta wings (i.e. separation bubble, classical vortex, vortex with shock, etc.) are discussed in the context of' aircraft design. And data have been shown that indicate that aerodynamic performance improvements are available by considering vortex flows as a primary design feature. Finally a discussing of a design approach for wings which utilize vortex flows for improved aerodynamic performance at supersonic speed is presented.
Method and apparatus for enhancing vortex pinning by conformal crystal arrays
Janko, Boldizsar; Reichhardt, Cynthia; Reichhardt, Charles; Ray, Dipanjan
2015-07-14
Disclosed is a method and apparatus for strongly enhancing vortex pinning by conformal crystal arrays. The conformal crystal array is constructed by a conformal transformation of a hexagonal lattice, producing a non-uniform structure with a gradient where the local six-fold coordination of the pinning sites is preserved, and with an arching effect. The conformal pinning arrays produce significantly enhanced vortex pinning over a much wider range of field than that found for other vortex pinning geometries with an equivalent number of vortex pinning sites, such as random, square, and triangular.
NASA Technical Reports Server (NTRS)
Lan, C. Edward
1985-01-01
A computer program based on the Quasi-Vortex-Lattice Method of Lan is presented for calculating longitudinal and lateral-directional aerodynamic characteristics of nonplanar wing-body combination. The method is based on the assumption of inviscid subsonic flow. Both attached and vortex-separated flows are treated. For the vortex-separated flow, the calculation is based on the method of suction analogy. The effect of vortex breakdown is accounted for by an empirical method. A summary of the theoretical method, program capabilities, input format, output variables and program job control set-up are described. Three test cases are presented as guides for potential users of the code.
Vortex Phase Diagram as a Function of Oxygen Deficiency in Untwinned YBa_2Cu_3O_y
NASA Astrophysics Data System (ADS)
Nishizaki, Terukazu
2000-03-01
This talk will present recent results of the vortex phase diagram of untwinned YBa2Cu3Oy (YBCO) single crystals with a different oxygen content under high magnetic fields up to 30T. We show that the first-order vortex lattice melting line T_m(H) and the second-order vortex glass transition line T_g(H) terminate at the critical point H_cp and the field-driven disordering transition line separates the vortex solid phase into the Bragg glass and the vortex glass phases(T. Nishizaki et al., Phys. Rev. B 58, 11169 (1998).). The value of H_cp strongly depends on the oxygen content and the vortex lattice melting transition is observed up to 30 T for fully oxidized YBCO (y~=7, T_c~=87.5 K). For optimally doped YBCO (T_c~= 93 K), on the other hand, T_g(H) decreases with increasing temperature and approaches to the vortex lattice melting line well below the critical point of T_m(H), indicating the existence of the new vortex state such as a vortex slush regime between T_g(H) and T_m(H). Thermodynamic properties are also examined above and below the terminal point of T_g(H). We find that the entropy change at the first-order melting transition becomes considerably small above the terminal field of T_g(H). The novel vortex phase diagram is discussed.
Vortex matter driven through mesoscopic channels
NASA Astrophysics Data System (ADS)
Kes, P. H.; Kokubo, N.; Besseling, R.
2004-08-01
The dynamics of vortex matter confined to mesoscopic channels has been investigated by means of mode locking experiments. When vortices are coherently driven through the potential provided by static vortices pinned in the channel edges, interference between the washboard frequency of the moving vortex lattice and the frequency of the superimposed rf-drive causes (Shapiro-like) steps in the dc- I- V curves. The position of the voltage steps uniquely determines the number of moving rows in each channel. It also shows how the frustration between row spacing and channel width behaves as a function of magnetic field. Maxima in flow stress (∼ Ic) occur at mismatch conditions. They are related to the traffic-jam-like flow impedance caused by the disorder in the edges. At higher fields, near the 2D-melting line Bm( T), the mode-locking interference characteristic for crystalline motion, strongly depends on the velocity, i.e. the applied frequency at which the vortex motion is probed. The minimum velocity at which coherent motion could be observed, diverges when the melting line is approached from below. Above the melting line interference is absent for any frequency. These observations give the first direct evidence for a dynamic phase transition of vortex matter driven through a disorder potential as predicted by Koshelev and Vinokur.
Phase transitions and connectivity in three-dimensional vortex equilibria
Akao, J.H.
1994-05-01
The statistical mechanics of collections of closed self avoiding vortex loops on a lattice are studied. The system is related to the vortex form of the three dimensional XY model and to lattice vortex equilibrium models of turbulence. The system exhibits vortex connectivity and screening effects, and models in vorticity variables the superfluid transition. The equilibrium states of the system are simulated by a grand canonical Monte Carlo method. A set of geometric transformations for self-avoiding loops is developed. The numerical method employs histogram sampling techniques and utilizes a modification to the Metropolis flow which enhances efficiency. Results are given for a region in the temperature-chemical potential plane, where the chemical potential is related to the vortex fugacity. A line of second order transitions is identified at low temperature. The transition is shown to be a percolation threshold at which connected vortex loops of infinite size appear in the system. The nature of the transition supports the assumption that the lambda transition in bulk superfluid helium is driven by vortices. An asymptotic analysis is performed for the energy and entropy scaling of the system as functions of the system size and the lattice spacing. These estimates indicate that the infinite temperature line is a phase boundary between small scale fractal vortices and large scale smooth vortices. A suggestion is made that quantum vortices have uniform structure on the scale of the lattice spacing and lie in the positive temperature regime, while classical vortices have uniform structure on the scale of the domain and lie in the negative temperature regime.
Composite vortex beams by coaxial superposition of Laguerre-Gaussian beams
NASA Astrophysics Data System (ADS)
Huang, Sujuan; Miao, Zhuang; He, Chao; Pang, Fufei; Li, Yingchun; Wang, Tingyun
2016-03-01
We propose the generation of novel composite vortex beams by coaxial superposition of Laguerre-Gaussian (LG) beams with common waist position and waist parameter. Computer-generated holography by conjugate-symmetric extension is applied to produce the holograms of several composite vortex beams. Utilizing the holograms, fantastic light modes including optical ring lattice, double dark-ring and double bright-ring composite vortex beams etc. are numerically reconstructed. The generated composite vortex beams show diffraction broadening with some of them showing dynamic rotation around beam centers while propagating. Optical experiments based on a computer-controlled spatial light modulator (SLM) verify the numerical results. These novel composite vortex beams possess more complicated distribution and more controllable parameters for their potential application in comparison to conventional optical ring lattice.
Vortex Rings in Superfluid Helium
NASA Astrophysics Data System (ADS)
Alamri, Sultan Z.; Barenghi, Carlo F.
2008-11-01
We present results of numerical simulations of large-scale vortex rings in superfluid helium. These large-scale vortex rings consists of many discrete (quantized) vortex filaments which interact with each other moving according to the Biot-Savart law. Lifetime, structural stability and speed of large-scale vortex rings will be discussed and compared to experimental results.
NASA Technical Reports Server (NTRS)
Nakamura, Y.; Leonard, A.; Spalart, P. R.
1985-01-01
A vortex breakdown was simulated by the vortex filament method, and detailed figures are presented based on the results. Deformations of the vortex filaments showed clear and large swelling at a particular axial station which implied the presence of a recirculation bubble at that station. The tendency for two breakdowns to occur experimentally was confirmed by the simulation, and the jet flow inside the bubble was well simulated. The particle paths spiralled with expansion, and the streamlines took spiral forms at the breakdown with expansion.
Universal statistics of vortex lines.
Nahum, Adam; Chalker, J T
2012-03-01
We study the vortex lines that are a feature of many random or disordered three-dimensional systems. These show universal statistical properties on long length scales, and geometrical phase transitions analogous to percolation transitions but in distinct universality classes. The field theories for these problems have not previously been identified, so that while many numerical studies have been performed, a framework for interpreting the results has been lacking. We provide such a framework with mappings to simple supersymmetric models. Our main focus is on vortices in short-range-correlated complex fields, which show a geometrical phase transition that we argue is described by the CP(k|k) model (essentially the CP(n-1) model in the replica limit n→1). This can be seen by mapping a lattice version of the problem to a lattice gauge theory. A related field theory with a noncompact gauge field, the 'NCCP(k|k) model', is a supersymmetric extension of the standard dual theory for the XY transition, and we show that XY duality gives another way to understand the appearance of field theories of this type. The supersymmetric descriptions yield results relevant, for example, to vortices in the XY model and in superfluids, to optical vortices, and to certain models of cosmic strings. A distinct but related field theory, the RP(2l|2l) model (or the RP(n-1) model in the limit n→1) describes the unoriented vortices that occur, for instance, in nematic liquid crystals. Finally, we show that in two dimensions, a lattice gauge theory analogous to that discussed in three dimensions gives a simple way to see the known relation between two-dimensional percolation and the CP(k|k) σ model with a θ term.
Universal statistics of vortex lines.
Nahum, Adam; Chalker, J T
2012-03-01
We study the vortex lines that are a feature of many random or disordered three-dimensional systems. These show universal statistical properties on long length scales, and geometrical phase transitions analogous to percolation transitions but in distinct universality classes. The field theories for these problems have not previously been identified, so that while many numerical studies have been performed, a framework for interpreting the results has been lacking. We provide such a framework with mappings to simple supersymmetric models. Our main focus is on vortices in short-range-correlated complex fields, which show a geometrical phase transition that we argue is described by the CP(k|k) model (essentially the CP(n-1) model in the replica limit n→1). This can be seen by mapping a lattice version of the problem to a lattice gauge theory. A related field theory with a noncompact gauge field, the 'NCCP(k|k) model', is a supersymmetric extension of the standard dual theory for the XY transition, and we show that XY duality gives another way to understand the appearance of field theories of this type. The supersymmetric descriptions yield results relevant, for example, to vortices in the XY model and in superfluids, to optical vortices, and to certain models of cosmic strings. A distinct but related field theory, the RP(2l|2l) model (or the RP(n-1) model in the limit n→1) describes the unoriented vortices that occur, for instance, in nematic liquid crystals. Finally, we show that in two dimensions, a lattice gauge theory analogous to that discussed in three dimensions gives a simple way to see the known relation between two-dimensional percolation and the CP(k|k) σ model with a θ term. PMID:22587072
NASA Technical Reports Server (NTRS)
Stough, H. P., III; Greene, George C.; Stewart, Eric C.; Stuever, Robert A.; Jordan, Frank L., Jr.; Rivers, Robert A.; Vicroy, Dan D.
1993-01-01
NASA is conducting research that will enable safe improvements in the capacity of the nation's air transportation system. The wake-vortex hazard is a factor in establishing the minimum safe spacing between aircraft during landing and takeoff operations and, thus, impacts airport capacity. The ability to accurately model the wake hazard and determine safe separation distances for a wide range of aircraft and operational scenarios may provide the basis for significant increases in airport capacity. Current and planned NASA research is described which is focused on increasing airport capacity by safely reducing wake-hazard-imposed aircraft separations through advances in a number of technologies including vortex motion and decay prediction, vortex encounter modeling, wake-vortex hazard characterization, and in situ flow sensing.
NASA Technical Reports Server (NTRS)
Bodstein, G. C. R.; George, A. R.; Hui, C. Y.
1993-01-01
This paper considers the interaction of a vortex generated upstream in a flow field with a downstream aerodynamic surface that possesses a large chord. The flow is assumed to be steady, incompressible, inviscid and irrotational, and the surface to be semiinfinite. The vortex is considered to be a straight vortex filament. To lowest order the problem is modeled using potential theory, where the 3D Laplace's equation for the velocity potential on the surface is solved exactly. The closed-form equation for pressure distribution obtained from this theory is found to have a square root singularity at the leading-edge. It also converges, as x goes to infinity, to the solution of the 2D point-vortex/infinite plane problem. The pressure coefficient presents an anti-symmetric behavior, near the leading-edge and a symmetric behavior as x goes to infinity.
NASA Technical Reports Server (NTRS)
Cunningham, A. M., Jr.
1986-01-01
An experimental study was conducted to quantify the hysteresis associated with various vortex flow transition points and to determine the effect of planform geometry. The transition points observed consisted of the appearance (or disappearance) of trailing edge vortex burst and the transition to (or from) flat plate or totally separated flows. Flow visualization with smoke injected into the vortices was used to identify the transitions on a series of semi-span models tested in a low speed tunnel. The planforms tested included simple deltas (55 deg to 80 deg sweep), cranked wings with varying tip panel sweep and dihedral, and a straked wing. High speed movies at 1000 frames per second were made of the vortex flow visualization in order to better understand the dynamics of vortex flow, burst and transition.
Arndt, R.; Pennings, P.; Bosschers, J.; van Terwisga, T.
2015-01-01
Marine propellers display several forms of cavitation. Of these, propeller-tip vortex cavitation is one of the important factors in propeller design. The dynamic behaviour of the tip vortex is responsible for hull vibration and noise. Thus, cavitation in the vortices trailing from tips of propeller blades has been studied extensively. Under certain circumstances cavitating vortices have been observed to have wave-like disturbances on the surfaces of vapour cores. Intense sound at discrete frequencies can result from a coupling between tip vortex disturbances and oscillating sheet cavitation on the surfaces of the propeller blades. This research article focuses on the dynamics of vortex cavitation and more in particular on the energy and frequency content of the radiated pressures. PMID:26442147
Improved vortex reactor system
Diebold, J.P.; Scahill, J.W.
1995-05-09
An improved vortex reactor system is described for affecting fast pyrolysis of biomass and Refuse Derived Fuel (RDF) feed materials comprising: a vortex reactor having its axis vertically disposed in relation to a jet of a horizontally disposed steam ejector that impels feed materials from a feeder and solids from a recycle loop along with a motive gas into a top part of said reactor. 12 figs.
Bornyakov, V.G.
2005-06-01
Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.
Glory, Vortex Street off Baja California
NASA Technical Reports Server (NTRS)
2007-01-01
On June 19, 2007, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured both a vortex street and a glory visible amid the lattice of clouds over the Pacific Ocean off Baja California. In this image, the swirling clouds known as vortex streets appear along the left edge of the image, stretching southward from Isla Guadalupe. Another NASA satellite captured an earlier example of vortex streets in June 2000. These atmospheric vortices, known as Von Karman vortex streets, often occur in the wake of an obstacle to air flow, such as an island. Stratocumulus clouds--low-lying, sheets of puffy clouds-- over the ocean show the impact of the island on air flow visible though their alternating pattern of clockwise and counter-clockwise swirls. Southeast of the vortex street, a glory, which resembles a rainbow, hovers above the cloud cover. The glory is faint but large, 200 to 300 kilometers long, along a north-south orientation. This phenomenon can occur when the satellite passes directly between the Sun and a bank of clouds below. (People also observe them while looking down on clouds from airplanes.) Not just any kind of cloud can produce a glory; only clouds composed entirely of water droplets (as opposed to ice crystals) can make them. The droplets that form glories generally have diameters of less than 50 micrometers (a micrometers is a millionth of a meter). The water droplets bend the light, showing its different wavelengths, or colors. In this glory, reds and oranges are most visible. NASA image by Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center.
NASA Astrophysics Data System (ADS)
Wang, Da-Wei; Liu, Ren-Bao; Zhu, Shi-Yao; Scully, Marlan O.
2015-01-01
We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on electromagnetically induced transparency (EIT). For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective uniform force in momentum space. The quantum lattice dynamics, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing, and dynamic localization can be observed in the SL. The two-dimensional SL provides a flexible platform for Dirac physics in graphene. The SL can be extended to three and higher dimensions where no analogous real space lattices exist with new physics waiting to be explored.
Defect pair in the elastic lattice of pancake vortices
Slutzky, M.; Mints, R.G.; Brandt, E.H.
1997-07-01
An additional pancake-antipancake vortex pair is considered in the vortex lattice of layered superconductors. Within linear elastic continuum theory, the relaxation of the background lattice screens the long-range logarithmic interaction of the defect pair, reducing the factor ln(r{sub 0}/{xi}) to ln(a/{xi}) where r{sub 0} is the pair spacing, {xi} the in-plane coherence length, and a the vortex spacing. The finite tilt modulus does not destroy this ideal two-dimensional screening, yielding a small correction {approximately}(a{sup 2}/8{pi}{lambda}{sup 2})ln(r{sub 0}/a), which in principle is of long range, but has a very small prefactor when the vortex spacing a is smaller than the in-plane penetration depth {lambda}. {copyright} {ital 1997} {ital The American Physical Society}
Magnetic Vortex Induced by Nonmagnetic Impurity in Frustrated Magnets
NASA Astrophysics Data System (ADS)
Lin, Shi-Zeng; Hayami, Satoru; Batista, Cristian D.
2016-05-01
We study the effect of a nonmagnetic impurity inserted in a two-dimensional frustrated ferromagnet above its saturation magnetic field Hsat for arbitrary spin S . We demonstrate that the ground state includes a magnetic vortex that is nucleated around the impurity over a finite range of magnetic field Hsat≤H ≤HsatI. Upon approaching the quantum critical point at H =Hsat, the radius of the magnetic vortex diverges as the magnetic correlation length: ξ ∝1 /√{H -Hsat }. These results are derived both for the lattice and in the continuum limit.
Magnetic Vortex Induced by Nonmagnetic Impurity in Frustrated Magnets.
Lin, Shi-Zeng; Hayami, Satoru; Batista, Cristian D
2016-05-01
We study the effect of a nonmagnetic impurity inserted in a two-dimensional frustrated ferromagnet above its saturation magnetic field H_{sat} for arbitrary spin S. We demonstrate that the ground state includes a magnetic vortex that is nucleated around the impurity over a finite range of magnetic field H_{sat}≤H≤H_{sat}^{I}. Upon approaching the quantum critical point at H=H_{sat}, the radius of the magnetic vortex diverges as the magnetic correlation length: ξ∝1/sqrt[H-H_{sat}]. These results are derived both for the lattice and in the continuum limit. PMID:27203342
Vortex Solutions of the Defocusing Discrete Nonlinear Schroedinger Equation
Cuevas, J.; Kevrekidis, P. G.; Law, K. J. H.
2009-09-09
We consider the existence, stability and dynamical evolution of dark vortex states in the two-dimensional defocusing DNLS equation, a model of interest both to atomic physics and to nonlinear optics. Our considerations are chiefly based on initializing such vortex configurations at the anti-continuum limit of zero coupling between adjacent sites, and continuing them to finite values of the coupling. Discrete defocusing vortices become unstable past a critical coupling strength and, subsequently feature a cascade of alternating stabilization-destabilization windows for any finite lattice.
Dual vortex theory of doped Mott insulators
Balents, Leon; Sachdev, Subir
2007-11-15
We present a general framework for describing the quantum phases obtained by doping paramagnetic Mott insulators on the square lattice. The undoped insulators are efficiently characterized by the projective transformations of various fields under the square lattice space group (the PSG). We show that the PSG also imposes powerful constraints on the doped system, and on the effective action for the vortex and Bogoliubov quasiparticle excitations of superconducting states. This action can also be extended across transitions to supersolid or insulating states at non-zero doping. For the case of a valence bond solid (VBS) insulator, we show that the doped system has the same PSG as that of elementary bosons with density equal to the density of electron Cooper pairs. We also discuss aspects of the action for a d-wave superconductor obtained by doping a 'staggered-flux' spin liquid state.
Point-vortex approach in two-dimensional turbulence
NASA Astrophysics Data System (ADS)
Kuvshinov, B. N.; Schep, T. J.
2016-05-01
The properties of two-dimensional turbulence in a circular domain are investigated within the framework of the punctuated point-vortex model. Vortex dynamics is governed by Hamiltonian equations, and it is interrupted by instantaneous events resulting in vortex merging. Motion of about 100 point vortices is simulated using an accurate, symplectic integration method. Ensembles of like-sign vortices relax to a quasi-lattice state. Vortices with zero total vorticity tend to be randomized. Their motion still does not become fully chaotic. We observe emergence of long lived large dipoles (co-propagating pairs of vortices with opposite signs), which affect the evolution of the whole vortex ensemble. The presence of such dipoles accelerate the vortex decay rate. The decay exponent has been estimated as ξ ≃ 1.7, which is much larger than ξ ≃ 0.7, reported in previous studies of decaying turbulence. Since dipole dynamics depends on specific properties of the point vortex system, our findings suggest that a universal decay exponent in such systems does not exist.
Vortex Apparatus and Demonstrations
NASA Astrophysics Data System (ADS)
Shakerin, Said
2010-05-01
Vortex flow, from millimeter to kilometer in scale, is important in many scientific and technological areas. Examples are seen in water strider locomotion, from industrial pipe flow (wastewater treatment) to air traffic control (safe distance between aircrafts on a runway ready for takeoff) to atmospheric studies.2-5 In this paper, we focus on a particular vortex known as bathtub vortex (BTV). It occurs when water is drained from a hole at the bottom of a container such as a bathtub or a sink under the action of gravity. The vortex has a funnel shape with a central air core, resembling a tornado. We have designed a portable apparatus to demonstrate bathtub vortex on a continual basis. The apparatus consists of a clear cylinder supported by a frame over a water reservoir and a submersible pump. Young and old have been equally amazed by watching the demonstrations at various public presentations held at the University of the Pacific recently. With material cost of less than 100, the apparatus can be easily fabricated and used at other universities. With a short set-up time, it is an ideal device for promoting science to the general public, and it can be used to enhance lectures in physics courses as well.
NASA Astrophysics Data System (ADS)
Arnoldus, Henk F.; Li, Xin; Xu, Zhangjin
2016-06-01
The field lines of energy flow of radiation emitted by an oscillating electric dipole in free space are either straight lines (linear dipole) or they form a vortex (rotating dipole). When the dipole is embedded in a material, the properties of the medium affect the direction of energy flow. Damping due to the imaginary part of the relative permittivity ? makes the field lines curve for the case of a linear dipole, and for a rotating dipole, the shape of the vortex is altered. In addition, a negative value of the real part of ? has the effect that the rotation direction of the vortex reverses for the case of a rotating dipole. The value of the relative permeability ? has in general not much effect on the redistribution of the direction of energy propagation. We show that a dramatic effect occurs when the embedding material is near-single-negative (both ? and ? approximately real, and the real parts of opposite sign). The curving of field lines is in general a sub-wavelength phenomenon. For near-single-negative materials, however, this curving extends over large distances from the dipole. In particular, the small free-space vortex of a rotating dipole becomes a vortex of enormous dimensions when the radiation is emitted into a near-single-negative material.
Vortex attenuation flight experiments
NASA Technical Reports Server (NTRS)
Barber, M. R.; Hastings, E. C., Jr.; Champine, R. A.; Tymczyszyn, J. J.
1977-01-01
Flight tests evaluating the effects of altered span loading, turbulence ingestion, combinations of mass and turbulence ingestion, and combinations of altered span loading turbulance ingestion on trailed wake vortex attenuation were conducted. Span loadings were altered in flight by varying the deflections of the inboard and outboard flaps on a B-747 aircraft. Turbulence ingestion was achieved in flight by mounting splines on a C-54G aircraft. Mass and turbulence ingestion was achieved in flight by varying the thrust on the B-747 aircraft. Combinations of altered span loading and turbulence ingestion were achieved in flight by installing a spoiler on a CV-990 aircraft and by deflecting the existing spoilers on a B-747 aircraft. The characteristics of the attenuated and unattenuated vortexes were determined by probing them with smaller aircraft. Acceptable separation distances for encounters with the attenuated and unattenuated vortexes are presented.
Aircraft vortex marking program
NASA Technical Reports Server (NTRS)
Pompa, M. F.
1979-01-01
A simple, reliable device for identifying atmospheric vortices, principally as generated by in-flight aircraft and with emphasis on the use of nonpolluting aerosols for marking by injection into such vortex (-ices) is presented. The refractive index and droplet size were determined from an analysis of aerosol optical and transport properties as the most significant parameters in effecting vortex optimum light scattering (for visual sighting) and visual persistency of at least 300 sec. The analysis also showed that a steam-ejected tetraethylene glycol aerosol with droplet size near 1 micron and refractive index of approximately 1.45 could be a promising candidate for vortex marking. A marking aerosol was successfully generated with the steam-tetraethylene glycol mixture from breadboard system hardware. A compact 25 lb/f thrust (nominal) H2O2 rocket chamber was the key component of the system which produced the required steam by catalytic decomposition of the supplied H2O2.
NASA Astrophysics Data System (ADS)
Zuccher, S.; Caliari, M.; Baggaley, A. W.; Barenghi, C. F.
2012-12-01
We study reconnections of quantum vortices by numerically solving the governing Gross-Pitaevskii equation. We find that the minimum distance between vortices scales differently with time before and after the vortex reconnection. We also compute vortex reconnections using the Biot-Savart law for vortex filaments of infinitesimal thickness, and find that, in this model, reconnections are time symmetric. We argue that the likely cause of the difference between the Gross-Pitaevskii model and the Biot-Savart model is the intense rarefaction wave which is radiated away from a Gross-Pitaeveskii reconnection. Finally we compare our results to experimental observations in superfluid helium and discuss the different length scales probed by the two models and by experiments.
The Acoustically Driven Vortex Cannon
NASA Astrophysics Data System (ADS)
Perry, Spencer B.; Gee, Kent L.
2014-03-01
Vortex cannons have been used by physics teachers for years, mostly to teach the continuity principle. In its simplest form, a vortex cannon is an empty coffee can with a hole cut in the bottom and the lid replaced. More elaborate models can be purchased through various scientific suppliers under names such as "Air Cannon"2 and "Airzooka."3 We will briefly discuss the uses of a vortex cannon in teaching and a new type of vortex cannon for teaching.
Vortex Characterization for Engineering Applications
Jankun-Kelly, M; Thompson, D S; Jiang, M; Shannahan, B; Machiraju, R
2008-01-30
Realistic engineering simulation data often have features that are not optimally resolved due to practical limitations on mesh resolution. To be useful to application engineers, vortex characterization techniques must be sufficiently robust to handle realistic data with complex vortex topologies. In this paper, we present enhancements to the vortex topology identification component of an existing vortex characterization algorithm. The modified techniques are demonstrated by application to three realistic data sets that illustrate the strengths and weaknesses of our approach.
Evolution of an elliptic vortex ring in a viscous fluid
NASA Astrophysics Data System (ADS)
Cheng, M.; Lou, J.; Lim, T. T.
2016-03-01
The evolution of a viscous elliptic vortex ring in an initially quiescent fluid or a linear shear flow is numerically simulated using a lattice Boltzmann method. A wide range of parameters are considered, namely, aspect ratios (AR) (1 ≤ AR ≤ 8), core radius to ring radius ratios (σ0) (0.1 ≤ σ0 ≤ 0.3), Reynolds number (Re) (500 ≤ Re ≤ 3000), and shear rate (K) (0 ≤ K ≤ 0.12). The study aims to fill the gap in the current knowledge of the dynamics of an elliptic vortex ring in a viscous fluid and also to address the issue of whether an elliptic ring undergoes vortex stretching and compression during axis-switching. In a quiescent fluid, results show that for fixed Re and σ0, there exists a critical aspect ratio (ARc), below which an elliptic ring undergoes oscillatory deformation with the period that increases with increasing AR. Above ARc, the vortex ring breaks up into two or three sub-rings after the first half-cycle of oscillation. While higher Reynolds number enhances vortex ring breakup, larger core size has the opposite effect. Contrary to an inviscid theory, an elliptic ring does undergo vortex stretching and compression during oscillatory deformation. In the presence of a linear shear flow, the vortex ring undergoes not only oscillatory deformation and stretching but also tilting as it propagates downstream. The tilting angle increases with the shear rate K and is responsible for inducing a "tail" that consists of a counter-rotating vortex pair (CVP) near the upstream end of the initial major axis after the first half-cycle of oscillation. For a high shear rate, the CVP wraps around the ring and transforms its topological structure from a simple elliptic geometry to a complicated structure that eventually leads to the generation of turbulence.
Koiller, Jair
2009-05-06
A pair of infinitesimally close opposite vortices moving on a curved surface moves along a geodesic, according to a conjecture by Kimura. We outline a proof. Numerical simulations are presented for a pair of opposite vortices at a close but nonzero distance on a surface of revolution, the catenoid. We conjecture that the vortex pair system on a triaxial ellipsoid is a KAM perturbation of Jacobi's geodesic problem. We outline some preliminary calculations required for this study. Finding the surfaces for which the vortex pair system is integrable is in order.
Consider vortex shedding flowmeters
Wilbeck, K.
1988-08-01
Precise flow control is becoming a critical concern in the hydrocarbon processing industry. The old practice of ''one flowmeter fits all services'' is no longer possible with the different service conditions and measurement requirements of refineries and petrochemical plants in the late 1980s. Proper selection of a flowmeter for a given service requires consideration of all flowmeter types and a detailed examination of the application's measurement requirements. This article discusses the vortex shedding flowmeter, an instrument that can be used in a wide variety of applications in the hydrocarbon processing industry. This article will discuss the theory of operation and offer guidelines for the application, installation and maintenance of vortex meters.
Lattice Kinetic Theory in a Comoving Galilean Reference Frame.
Frapolli, N; Chikatamarla, S S; Karlin, I V
2016-07-01
We prove that the fully discrete lattice Boltzmann method is invariant with respect to Galilean transformation. Based on this finding, a novel class of shifted lattices is proposed which dramatically increases the operating range of lattice Boltzmann simulations, in particular, for gas dynamics applications. A simulation of vortex-shock interaction is used to demonstrate the accuracy and efficiency of the proposed lattices. With one single algorithm it is now possible to simulate a broad range of applications, from low Mach number flows to transonic and supersonic flow regimes. PMID:27419555
Lattice Kinetic Theory in a Comoving Galilean Reference Frame.
Frapolli, N; Chikatamarla, S S; Karlin, I V
2016-07-01
We prove that the fully discrete lattice Boltzmann method is invariant with respect to Galilean transformation. Based on this finding, a novel class of shifted lattices is proposed which dramatically increases the operating range of lattice Boltzmann simulations, in particular, for gas dynamics applications. A simulation of vortex-shock interaction is used to demonstrate the accuracy and efficiency of the proposed lattices. With one single algorithm it is now possible to simulate a broad range of applications, from low Mach number flows to transonic and supersonic flow regimes.
Lattice Kinetic Theory in a Comoving Galilean Reference Frame
NASA Astrophysics Data System (ADS)
Frapolli, N.; Chikatamarla, S. S.; Karlin, I. V.
2016-07-01
We prove that the fully discrete lattice Boltzmann method is invariant with respect to Galilean transformation. Based on this finding, a novel class of shifted lattices is proposed which dramatically increases the operating range of lattice Boltzmann simulations, in particular, for gas dynamics applications. A simulation of vortex-shock interaction is used to demonstrate the accuracy and efficiency of the proposed lattices. With one single algorithm it is now possible to simulate a broad range of applications, from low Mach number flows to transonic and supersonic flow regimes.
Picosecond optical vortex pulse illumination forms a monocrystalline silicon needle
NASA Astrophysics Data System (ADS)
Takahashi, Fuyuto; Miyamoto, Katsuhiko; Hidai, Hirofumi; Yamane, Keisaku; Morita, Ryuji; Omatsu, Takashige
2016-02-01
The formation of a monocrystalline silicon needle by picosecond optical vortex pulse illumination was demonstrated for the first time in this study. The dynamics of this silicon needle formation was further revealed by employing an ultrahigh-speed camera. The melted silicon was collected through picosecond pulse deposition to the dark core of the optical vortex, forming the silicon needle on a submicrosecond time scale. The needle was composed of monocrystalline silicon with the same lattice index (100) as that of the silicon substrate, and had a height of approximately 14 μm and a thickness of approximately 3 μm. Overlaid vortex pulses allowed the needle to be shaped with a height of approximately 40 μm without any changes to the crystalline properties. Such a monocrystalline silicon needle can be applied to devices in many fields, such as core-shell structures for silicon photonics and photovoltaic devices as well as nano- or microelectromechanical systems.
Unsteady Free-Wake Vortex Particle Model for HAWT
NASA Astrophysics Data System (ADS)
Bogateanu, R.; Frunzulicǎ, F.; Cardos, V.
2010-09-01
In the design of horizontal axis wind turbines (HAWT) one problem is to determine the aeroelastic behaviour of the rotor blades for the various wind inflow conditions. A step in this process is to predict with accuracy the aerodynamic loads on the blades. The Vortex Lattice Method (VLM) provides a transparent investigation concerning the role of various physical parameters which influence the aerodynamic problem. In this paper we present a method for the calculation of the non-uniform induced downwash of a HAWT rotor using the vortex ring model for the lifting surface coupled with an unsteady free-wake vortex particle model. Comparative studies between results obtained with different models of wake for a generic HAWT are presented.
Calculation of wing response to gusts and blast waves with vortex lift effect
NASA Technical Reports Server (NTRS)
Chao, D. C.; Lan, C. E.
1983-01-01
A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex-lattice method, unsteady suction analogy, and Pade approximate. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.
Calculation of wing response to gusts and blast waves with vortex lift effect
NASA Technical Reports Server (NTRS)
Chao, D. C.; Lan, C. E.
1983-01-01
A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex lattice method, unsteady suction analogy and Pade approximant. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.
Calculation of wing response to gusts and blast waves with vortex lift effect
Chao, D.C.; Lan, C.E.
1983-04-01
A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex lattice method, unsteady suction analogy and Pade approximant. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.
Experimental study of vortex diffusers
Shakerin, S.; Miller, P.L.
1995-11-01
This report documents experimental research performed on vortex diffusers used in ventilation and air-conditioning systems. The main objectives of the research were (1) to study the flow characteristics of isothermal jets issuing from vortex diffusers, (2) to compare the vortex diffuser`s performance with that of a conventional diffuser, and (3) to prepare a report that disseminates the results to the designers of ventilation and air-conditioning systems. The researchers considered three diffusers: a conventional round ceiling diffuser and two different styles of vortex diffusers. Overall, the vortex diffusers create slightly more induction of ambient air in comparison to the conventional diffuser.
Vortex Apparatus and Demonstrations
ERIC Educational Resources Information Center
Shakerin, Said
2010-01-01
Vortex flow, from millimeter to kilometer in scale, is important in many scientific and technological areas. Examples are seen in water strider locomotion, from industrial pipe flow (wastewater treatment) to air traffic control (safe distance between aircrafts on a runway ready for takeoff) to atmospheric studies. In this paper, we focus on a…
NASA Technical Reports Server (NTRS)
Flasar, F.M.; Achterberg, R.K.; Schinder, P.J.
2008-01-01
Titan's atmosphere has provided an interesting study in contrasts and similarities with Earth's. While both have N$_2$ as the dominant constituent and comparable surface pressures $\\sim1$ bar, Titan's next most abundant molecule is CH$_4$, not O$_2$, and the dissociative breakup of CH$_4$ and N$_2$ by sunlight and electron impact leads to a suite of hydrocarbons and nitriles, and ultimately the photochemical smog that enshrouds the moon. In addition, with a 15.95-day period, Titan is a slow rotator compared to Earth. While the mean zonal terrestrial winds are geostrophic, Titan's are mostly cyclostrophic, whipping around the moon in as little as 1 day. Despite the different dynamical regime, Titan's winter stratosphere exhibits several characteristics that should be familiar to terrestrial meteorologists. The cold winter pole near the 1 -mbar level is circumscribed by strong winds (up to 190 m/s) that act as a barrier to mixing with airmasses at lower latitudes. There is evidence of enhancement of several organic species over the winter pole, indicating subsidence. The adiabatic heating associated with this subsidence gives rise to a warm anomaly at the 0.01-mbar level, raising the stratopause two scale heights above its location at equatorial latitudes. Condensate ices have been detected in Titan's lower stratosphere within the winter polar vortex from infrared spectra. Although not always unambiguously identified, their spatial distribution exhibits a sharp gradient, decreasing precipitously across the vortex away from the winter pole. The interesting question of whether there is important heterogeneous chemistry occurring within the polar vortex, analogous to that occurring in the terrestrial polar stratospheric clouds in the ozone holes, has not been addressed. The breakup of Titan's winter polar vortex has not yet been observed. On Earth, the polar vortex is nonlinearly disrupted by interaction with large-amplitude planetary waves. Large-scale waves have not
Ortega, J M
2001-10-18
The collapse of the Soviet Union and ending of the Cold War brought about many significant changes in military submarine operations. The enemies that the US Navy faces today and in the future will not likely be superpowers armed with nuclear submarines, but rather smaller, rogue nations employing cheaper diesel/electric submarines with advanced air-independent propulsion systems. Unlike Cold War submarine operations, which occurred in deep-water environments, future submarine conflicts are anticipated to occur in shallow, littoral regions that are complex and noisy. Consequently, non-acoustic signatures will become increasingly important and the submarine stealth technology designed for deep-water operations may not be effective in these environments. One such non-acoustic signature is the surface detection of a submarine's trailing vortex wake. If a submarine runs in a slightly buoyant condition, its diving planes must be inclined at a negative angle of attack to generate sufficient downforce, which keeps the submarine from rising to the surface. As a result, the diving planes produce a pair of counter-rotating trailing vortices that propagate to the water surface. In previous deep-water operations, this was not an issue since the submarines could dive deep enough so that the vortex pair became incoherent before it reached the water surface. However, in shallow, littoral environments, submarines do not have the option of diving deep and, hence, the vortex pair can rise to the surface and leave a distinct signature that might be detectable by synthetic aperture radar. Such detection would jeopardize not only the mission of the submarine, but also the lives of military personnel on board. There has been another attempt to solve this problem and reduce the intensity of trailing vortices in the wakes of military submarines. The research of Quackenbush et al. over the past few years has been directed towards an idea called ''vortex leveraging.'' This active concept
Control of submersible vortex flows
NASA Technical Reports Server (NTRS)
Bushnell, D. M.; Donaldson, C. D.
1990-01-01
Vortex flows produced by submersibles typically unfavorably influence key figures of merit such as acoustic and nonacoustic stealth, control effectiveness/maneuverability, and propulsor efficiency/body drag. Sources of such organized, primarily longitudinal, vorticity include the basic body (nose and sides) and appendages (both base/intersection and tip regions) such as the fairwater, dive planes, rear control surfaces, and propulsor stators/tips. Two fundamentally different vortex control approaches are available: (1) deintensification of the amplitude and/or organization of the vortex during its initiation process; and (2) downstream vortex disablement. Vortex control techniques applicable to the initiation region (deintensification approach) include transverse pressure gradient minimization via altered body cross section, appendage dillets, fillets, and sweep, and various appendage tip and spanload treatment along with the use of active controls to minimize control surface size and motions. Vortex disablement can be accomplished either via use of control vortices (which can also be used to steer the vortices off-board), direct unwinding, inducement of vortex bursting, or segmentation/tailoring for enhanced dissipation. Submersible-applicable vortex control technology is also included derived from various aeronautical applications such as mitigation of the wing wake vortex hazard and flight aircraft maneuverability at high angle of attack as well as the status of vortex effects upon, and mitigation of, nonlinear control forces on submersibles. Specific suggestions for submersible-applicable vortex control techniques are presented.
Lattices of quantized vortices in polariton superfluids
NASA Astrophysics Data System (ADS)
Boulier, Thomas; Cancellieri, Emiliano; Sangouard, Nicolas D.; Hivet, Romain; Glorieux, Quentin; Giacobino, Élisabeth; Bramati, Alberto
2016-10-01
In this review, we will focus on the description of the recent studies conducted in the quest for the observation of lattices of quantized vortices in resonantly injected polariton superfluids. In particular, we will show how the implementation of optical traps for polaritons allows for the realization of vortex-antivortex lattices in confined geometries and how the development of a flexible method to inject a controlled orbital angular momentum (OAM) in such systems results in the observation of patterns of same-sign vortices.
Rotor-vortex interaction noise
NASA Technical Reports Server (NTRS)
Schlinker, R. H.; Amiet, R. K.
1983-01-01
A theoretical and experimental study was conducted to develop a validated first principles analysis for predicting noise generated by helicopter main-rotor shed vortices interacting with the tail rotor. The generalized prediction procedure requires a knowledge of the incident vortex velocity field, rotor geometry, and rotor operating conditions. The analysis includes compressibility effects, chordwise and spanwise noncompactness, and treats oblique intersections with the blade planform. Assessment of the theory involved conducting a model rotor experiment which isolated the blade-vortex interaction noise from other rotor noise mechanisms. An isolated tip vortex, generated by an upstream semispan airfoil, was convected into the model tail rotor. Acoustic spectra, pressure signatures, and directivity were measured. Since assessment of the acoustic prediction required a knowledge of the vortex properties, blade-vortes intersection angle, intersection station, vortex stength, and vortex core radius were documented. Ingestion of the vortex by the rotor was experimentally observed to generate harmonic noise and impulsive waveforms.
Thermally assisted vortex motion in intrinsic Josephson junctions
NASA Astrophysics Data System (ADS)
Irie, A.; Oya, G.
2008-02-01
The vortex dynamics in intrinsic Josephson junctions (IJJs) at finite temperatures has been investigated numerically by taking into account the thermal fluctuations. Our simulations based on the perturbed, coupled sine-Gordon model successfully reproduce the experimental results associated with the Josephson-vortex flow resistance (JVFR) at low bias currents. Depending on the junction length, bias current, and temperature, the JVFR oscillation is changed from the period of half flux quantum per junction to the period of one flux quantum per junction. It is shown that the oscillation is essentially due to the field dependence of the critical current. At currents slightly exceeding the critical current the stationary vortex lattice structure becomes unstable and an irregular vortex flow can be induced by thermal fluctuations in different junctions. Our simulation results strongly suggest that the triangular lattice of vorticies in the dynamical state is more stable rather than the rectangular one even in a submicrometer IJJ stack when IJJs are biased at a low current.
Vortex Crystals with Chiral Stripes in Itinerant Magnets
NASA Astrophysics Data System (ADS)
Ozawa, Ryo; Hayami, Satoru; Barros, Kipton; Chern, Gia-Wei; Motome, Yukitoshi; Batista, Cristian D.
2016-10-01
We study noncoplanar magnetic ordering in frustrated itinerant magnets. For a family of Kondo square lattice models with classical local moments, we find that a double-Q noncoplanar vortex crystal has lower energy than the single-Q helical order expected from the Ruderman-Kittel-Kasuya-Yosida interaction when the lattice symmetry dictates four global maxima in the bare magnetic susceptibility. By expanding in the small Kondo exchange and the degree of noncoplanarity, we demonstrate that this noncoplanar state arises from a Fermi surface instability occurring in independent sections connected by two ordering wave vectors.
A subvortex technique for the close approach to a discretized vortex sheet
NASA Technical Reports Server (NTRS)
Maskew, B.
1976-01-01
The close-approach problem associated with vortex-lattice methods was examined numerically with the objective of calculating velocities at arbitrary points, not just at midpoints, between the vortices. The objective was achieved using a subvortex technique in which a vortex splits into an increasing number of subvortices as it is approached. The technique, incorporated in a two-dimensional potential flow method using "submerged" vortices and sources, was evaluated for a cambered Joukowski airfoil. The method could be extended to three dimensions, and should improve non-linear methods, which calculate interference effects between multiple wings and vortex wakes, and which include procedures for force-free wakes.
Generic Weyl phase in the vortex state of quasi-two-dimensional chiral superconductors
NASA Astrophysics Data System (ADS)
Yoshida, Tomohiro; Udagawa, Masafumi
2016-08-01
We study the collective behavior of Majorana modes in the vortex state of chiral p -wave superconductors. Away from the isolated vortex limit, the zero-energy Majorana states communicate with each other on a vortex lattice, and form a coherent band structure with a nontrivial topological character. We reveal that the topological nature of Majorana bands changes sensitively via quantum phase transitions in two-dimensional (2D) systems, by sweeping magnetic field or Fermi energy. Through the idea of dimensional reduction, we show the existence of a generic superconducting Weyl phase in a low magnetic field region of quasi-2D chiral superconductors.
Anisotropic superconductivity and vortex dynamics in magnetially coupled F/S and F/S/F hybrids.
Karapetrov, G.; Belkin, A.; Iavarone, M.; Fedor, J.; Novosad, V.; Milosevic, M. V.; Peeters, F. M.
2011-01-01
Magnetically coupled superconductor-ferromagnet hybrids offer advanced routes for nanoscale control of superconductivity. Magnetotransport characteristics and scanning tunneling microscopy images of vortex structures in superconductor-ferromagnet hybrids reveal rich superconducting phase diagrams. Focusing on a particular combination of a ferromagnet with a well-ordered periodic magnetic domain structure with alternating out-of-plane component of magnetization, and a small coherence length superconductor, we find directed nucleation of superconductivity above the domain wall boundaries. We show that near the superconductor-normal state phase boundary the superconductivity is localized in narrow mesoscopic channels. In order to explore the Abrikosov flux line ordering in F/S hybrids, we use a combination of scanning tunneling microscopy and Ginzburg-Landau simulations. The magnetic stripe domain structure induces periodic local magnetic induction in the superconductor, creating a series of pinning-anti-pinning channels for externally added magnetic flux quanta. Such laterally confined Abrikosov vortices form quasi-1D arrays (chains). The transitions between multichain states occur through propagation of kinks at the intermediate fields. At high fields we show that the system becomes nonlinear due to a change in both the number of vortices and the confining potential. In F/S/F hybrids we demonstrate the evolution of the anisotropic conductivity in the superconductor that is magnetically coupled with two adjacent ferromagnetic layers. Stripe magnetic domain structures in both F-layers are aligned under each other, resulting in a directional superconducting order parameter in the superconducting layer. The conductance anisotropy strongly depends on the period of the magnetic domains and the strength of the local magnetization. The anisotropic conductivity of up to three orders of magnitude can be achieved with a spatial critical temperature modulation of 5% of T{sub c
Consider vortex flowmeters for gas custody transfer
Ostling, H.
1995-07-01
Much natural gas measurement falls under the category of custody transfer, where inaccurate metering could mean financial disaster (or windfall) for one of the parties. Modern vortex flowmeters eliminate the inaccuracies of DP/orifice plate installations and provide the added security of reduced fugitive emissions. What follows are seven reasons why you should consider vortex flow measurement technology for custody transfer or any other measurement of natural gas. Vortex flowmeters offer higher accuracy; vortex flowmeters have no density/viscosity distortion; vortex flowmeters feature low installation costs; vortex flowmeters mean low cost of ownership; vortex flowmeters reduce pressure drop; vortex flowmeters allow accurate billing; nd vortex flowmeters have fewer fugitive emission sources.
Vortex equations: Singularities, numerical solution, and axisymmetric vortex breakdown
NASA Technical Reports Server (NTRS)
Bossel, H. H.
1972-01-01
A method of weighted residuals for the computation of rotationally symmetric quasi-cylindrical viscous incompressible vortex flow is presented and used to compute a wide variety of vortex flows. The method approximates the axial velocity and circulation profiles by series of exponentials having (N + 1) and N free parameters, respectively. Formal integration results in a set of (2N + 1) ordinary differential equations for the free parameters. The governing equations are shown to have an infinite number of discrete singularities corresponding to critical values of the swirl parameters. The computations point to the controlling influence of the inner core flow on vortex behavior. They also confirm the existence of two particular critical swirl parameter values: one separates vortex flow which decays smoothly from vortex flow which eventually breaks down, and the second is the first singularity of the quasi-cylindrical system, at which point physical vortex breakdown is thought to occur.
Olson, C.J.; Reichhardt, C.; Nori, F.
1997-09-01
Using large-scale simulations on parallel processors, we analyze in detail the dynamical behavior of superconducting vortices undergoing avalanches. In particular, we quantify the effect of the pinning landscape on the macroscopic properties of vortex avalanches and vortex plastic flow. These dynamical instabilities are triggered when the external magnetic field is increased slightly, and are thus driven by a flux gradient rather than by thermal effects. The flux profiles, composed of rigid flux lines that interact with 100 or more vortices, are maintained in the Bean critical state and do not decay away from it. By directly determining vortex positions during avalanches in the plastically moving lattice, we find that experimentally observable voltage bursts correspond to the pulsing movement of vortices along branched channels or winding chains in a manner reminiscent of lightning strikes. This kind of motion cannot be described by elastic theories. We relate the velocity field and cumulative patterns of vortex flow channels with statistical quantities, such as distributions of avalanche sizes. Samples with a high density of strong pinning sites produce very broad avalanche distributions. Easy-flow vortex channels appear in samples with a low pinning density, and typical avalanche sizes emerge in an otherwise broad distribution of sizes. We observe a crossover from interstitial motion in narrow channels to pin-to-pin motion in broad channels as pin density is increased. {copyright} {ital 1997} {ital The American Physical Society}
NASA Technical Reports Server (NTRS)
Smith, J. H. B.; Campbell, J. F.; Young, A. D. (Editor)
1992-01-01
The principal emphasis of the meeting was to be on the understanding and prediction of separation-induced vortex flows and their effects on vehicle performance, stability, control, and structural design loads. This report shows that a substantial amount of the papers covering this area were received from a wide range of countries, together with an attendance that was even more diverse. In itself, this testifies to the current interest in the subject and to the appropriateness of the Panel's choice of topic and approach. An attempt is made to summarize each paper delivered, and to relate the contributions made in the papers and in the discussions to some of the important aspects of vortex flow aerodynamics. This reveals significant progress and important clarifications, but also brings out remaining weaknesses in predictive capability and gaps in understanding. Where possible, conclusions are drawn and areas of continuing concern are identified.
NASA Technical Reports Server (NTRS)
Criminale, W. O.; Lasseigne, D. G.; Jackson, T. L.
1995-01-01
An initial value approach is used to examine the dynamics of perturbations introduced into a vortex under strain. Both the basic vortex considered and the perturbations are taken as fully three-dimensional. An explicit solution for the time evolution of the vorticity perturbations is given for arbitrary initial vorticity. Analytical solutions for the resulting velocity components are found when the initial vorticity is assumed to be localized. For more general initial vorticity distributions, the velocity components are determined numerically. It is found that the variation in the radial direction of the initial vorticity disturbance is the most important factor influencing the qualitative behavior of the solutions. Transient growth in the magnitude of the velocity components is found to be directly attributable to the compactness of the initial vorticity.
Delta Wing Vortex Breakdown Suppression by Vortex Core Oscillation
NASA Astrophysics Data System (ADS)
Cain, Charles
2000-11-01
The flow over a delta wing is characterized by two counter-rotating vortices that can undergo a sudden radial expansion at high angles of attack known as vortex breakdown. Downstream of this breakdown is a region of organized unsteady flow that can cause tail buffeting and structural fatigue, especially on twin-tailed aircraft. The recent self-induction theory of vortex breakdown points to the "pile-up" of vorticity due to the linear addition of vorticity in the spiraling shear layer that surrounds the vortex core as a principal cause of vortex breakdown (Kurosaka 1998). Based on that theory, this research attempts to relieve vorticity pile-up by altering the straight-line path of the vortex core and preventing the linear addition of vorticity. This is accomplished by applying a combination of periodic blowing and suction with low mass and momentum flux. The blowing and suction are directed normal to the low-pressure surface and supplied from ports under the vortex core which are near the forward tip of the delta wing. This oscillating input causes the vortex core to transition into a spiral formation downstream of the input ports. Initial results indicate that this change in the vortex core path may prevent vortex breakdown over the surface of the delta wing.
Not Available
1990-07-01
The program objective is to demonstrate efficient removal of fine particulates to sufficiently low levels to meet proposed small scale coal combustor emission standards using a cleanup technology appropriate to small scale coal combustors. This to be accomplished using a novel particulate removal device, the Confined Vortex Scrubber (CVS), which consists of a cylindrical vortex chamber with tangential flue gas inlets. The clean gas exit is via vortex finder outlets, one at either end of the tube. Liquid is introduced into the chamber and is confined within the vortex chamber by the centrifugal force generated by the gas flow itself. This confined liquid forms a layer through which the flue gas is then forced to bubble, producing a strong gas/liquid interaction, high inertial separation forces and efficient particulate cleanup. During this quarter a comprehensive series of cleanup experiments have been made for three CVS configurations. The first CVS configuration tested gave very efficient fine particulate removal at the design air mass flow rate (1 MM BUT/hr combustor exhaust flow), but had over 20{double prime}WC pressure drop. The first CVS configuration was then re-designed to produce the same very efficient particulate collection performance at a lower pressure drop. The current CVS configuration produces 99.4 percent cleanup of ultra-fine fly ash at the design air mass flow at a pressure drop of 12 {double prime}WC with a liquid/air flow ratio of 0.31/m{sup 3}. Unlike venturi scrubbers, the collection performance of the CVS is insensitive to dust loading and to liquid/air flow ratio.
Experimental Study of Vortex Dynamics during Blade-Vortex Interactions
NASA Astrophysics Data System (ADS)
Peng, Di; Gregory, James
2013-11-01
Vortices incident upon bodies, such as cylinders, airfoils, and rotor blades, can give rise to substantial unsteady loading, sound generation, and vibration in a variety of engineering applications. A comprehensive study on vortex dynamics during blade-vortex interaction (BVI) is performed in this work. Evidence has been found in previous studies that the vortex behavior during BVI varies with Reynolds number, but the effects are not clear. In the current study, the experiments are performed in a 3' × 5' low speed wind tunnel where the Reynolds number can be varied from 6 × 104 to 8 × 105 by adjusting freestream speed and airfoil size. The vortex is generated by the pitching motion of a wing, which is driven by an air cylinder. Another wing is placed downstream to initiate parallel interactions with the generated vortices. Smoke visualization is used originally to characterize the vortex. Then the BVI problem is studied in detail using time-resolved PIV and unsteady pressure measurements on the downstream target airfoil. The vortex behaviors at selected Reynolds numbers are investigated. The influence of other factors on vortex behavior, such as vortex strength and core size, is also discussed.
Control of diffusion of nanoparticles in an optical vortex lattice.
Zapata, Ivar; Delgado-Buscalioni, Rafael; Sáenz, Juan José
2016-06-01
A two-dimensional periodic optical force field, which combines conservative dipolar forces with vortices from radiation pressure, is proposed in order to influence the diffusion properties of optically susceptible nanoparticles. The different deterministic flow patterns are identified. In the low-noise limit, the diffusion coefficient is computed from a mean first passage time and the most probable escape paths are identified for those flow patterns which possess a stable stationary point. Numerical simulations of the associated Langevin equations show remarkable agreement with the analytically deduced expressions. Modifications of the force field are proposed so that a wider range of phenomena could be tested. PMID:27415231
Discrete breathers in hexagonal dusty plasma lattices.
Koukouloyannis, V; Kourakis, I
2009-08-01
The occurrence of single-site or multisite localized vibrational modes, also called discrete breathers, in two-dimensional hexagonal dusty plasma lattices is investigated. The system is described by a Klein-Gordon hexagonal lattice characterized by a negative coupling parameter epsilon in account of its inverse dispersive behavior. A theoretical analysis is performed in order to establish the possibility of existence of single as well as three-site discrete breathers in such systems. The study is complemented by a numerical investigation based on experimentally provided potential forms. This investigation shows that a dusty plasma lattice can support single-site discrete breathers, while three-site in phase breathers could exist if specific conditions, about the intergrain interaction strength, would hold. On the other hand, out of phase and vortex three-site breathers cannot be supported since they are highly unstable.
Discrete breathers in hexagonal dusty plasma lattices
Koukouloyannis, V.; Kourakis, I.
2009-08-15
The occurrence of single-site or multisite localized vibrational modes, also called discrete breathers, in two-dimensional hexagonal dusty plasma lattices is investigated. The system is described by a Klein-Gordon hexagonal lattice characterized by a negative coupling parameter epsilon in account of its inverse dispersive behavior. A theoretical analysis is performed in order to establish the possibility of existence of single as well as three-site discrete breathers in such systems. The study is complemented by a numerical investigation based on experimentally provided potential forms. This investigation shows that a dusty plasma lattice can support single-site discrete breathers, while three-site in phase breathers could exist if specific conditions, about the intergrain interaction strength, would hold. On the other hand, out of phase and vortex three-site breathers cannot be supported since they are highly unstable.
Research of the high performance low temperature vortex street flowmeter
NASA Astrophysics Data System (ADS)
Gao, Feng; Chen, Yang; Zhang, Zhen-peng; Geng, Wei-guo
2007-07-01
Flow measurement is the key method for R&D and operation monitoring of liquid rocket engine. Therefore, it is important to measure flux of low temperature liquid propellants for the liquid hydrogen/liquid oxygen or the liquid oxygen/kerosene rocket engine. Presently in China, the level meter and the turbine flowmeter are usually used in the experimentation of the liquid hydrogen/liquid oxygen rocket engine. The level meter can only scale average flux and the precision of the turbine flowmeter (the measuring wild point is 1.5%) can not be ensured due to the reason which there is not devices of low temperature real-time demarcation in China. Therefore, it is required to research the high performance low temperature flow measurement equipment and the vortex street flowmeter is selected because of its advantages. In the paper, some key techniques of low temperature vortex street flowmeter are researched from the design aspect. Firstly, the basic theoretical research of vortex street flowmeter includes signal detection method, shape of vortex producer and effects of dimension of vertex producer to vortex quality. Secondly, low temperature vortex street flowmeter adopts the method of piezoelectric components stress mode. As for the weakness of phase-change, lattice change and fragility for many piezoelectric materials in low temperature, it can not be fulfilled piezoelectric signal and mechanism performance under this condition. Some piezoelectric materials which can be used in low temperature are illustrated in the paper by lots of research in order for the farther research. The article places emphasis upon low temperature trait of piezoelectric materials, and the structure designs of signal detector and calculation of stress, electric charge quantity and heat transfer.
The Acoustically Driven Vortex Cannon
ERIC Educational Resources Information Center
Perry, Spencer B.; Gee, Kent L.
2014-01-01
Vortex cannons have been used by physics teachers for years, mostly to teach the continuity principle. In its simplest form, a vortex cannon is an empty coffee can with a hole cut in the bottom and the lid replaced. More elaborate models can be purchased through various scientific suppliers under names such as "Air Cannon" and…
Wingtip vortex dissipator for aircraft
NASA Technical Reports Server (NTRS)
Patterson, J. C., Jr. (Inventor)
1976-01-01
A means for attenuating the vortex created at aircraft wingtips which consists of a retractable planar surface transverse to the airstream and attached downstream of the wingtip which creates a positive pressure gradient just downstream from the wing is presented. The positive pressure forces a break up of the rotational air flow of the vortex.
Robustness of a coherence vortex.
Alves, Cleberson R; Jesus-Silva, Alcenisio J; Fonseca, Eduardo J S
2016-09-20
We study, experimentally and theoretically, the behavior of a coherence vortex after its transmission through obstacles. Notably, we find that such a vortex survives and preserves its effective topological charge. Despite suffering changes on the modulus of the coherence function, these changes disappear during propagation.
Variable residence time vortex combustor
Melconian, Jerry O.
1987-01-01
A variable residence time vortex combustor including a primary combustion chamber for containing a combustion vortex, and a plurality of louvres peripherally disposed about the primary combustion chamber and longitudinally distributed along its primary axis. The louvres are inclined to impel air about the primary combustion chamber to cool its interior surfaces and to impel air inwardly to assist in driving the combustion vortex in a first rotational direction and to feed combustion in the primary combustion chamber. The vortex combustor also includes a second combustion chamber having a secondary zone and a narrowed waist region in the primary combustion chamber interconnecting the output of the primary combustion chamber with the secondary zone for passing only lower density particles and trapping higher density particles in the combustion vortex in the primary combustion chamber for substantial combustion.
Vortex structures of a two-component Bose-Einstein condensate for large anisotropies
Wei Ran; Mueller, Erich
2011-12-15
We calculate the vortex structures of an elongated two-component Bose-Einstein condensate. We study how these structures depend on the intracomponent and intercomponent interaction strengths. We present analytical and numerical results respectively at weak and strong interactions; finding lattices with different interlocking geometries: triangular, square, rectangular, and double core.
NASA Astrophysics Data System (ADS)
Tanaeva, I. A.; Lindemann, U.; Jiang, N.; de Waele, A. T. A. M.; Thummes, G.
2004-06-01
A superfluid vortex cooler (SVC) is a combination of a fountain pump and a vortex cooler. The working fluid in the SVC is 4He at a temperature below the lambda line. The cooler has no moving parts, is gravity independent, and hardly requires any additional infrastructure. At saturated vapour pressure the SVC is capable of reaching a temperature as low as 0.75 K. At pressures close to the melting pressure the temperature can be brought down to 0.65 K. As the SVC operates only below the lambda line, it has to be precooled e.g. by a liquid-helium bath or a cryocooler. As a first step of our research we have carried out a number of experiments, using a liquid-helium bath as a precooler for the SVC. In this arrangement we have reached temperatures below 1 K with 3.5 mW heating power supplied to the fountain part of the SVC at 1.4 K. The next step was combining the SVC with a pulse tube refrigerator (PTR), developed at the University of Giessen. It is a two-stage G-M type refrigerator with 3He as a working fluid that reached a lowest temperature of 1.27 K. In this contribution we report on the results of the SVC tests in liquid helium and the progress in the integration of the SVC with the PTR.
The VOrtex Ring Transit EXperiment (VORTEX) GAS project
NASA Technical Reports Server (NTRS)
Bilen, Sven G.; Langenderfer, Lynn S.; Jardon, Rebecca D.; Cutlip, Hansford H.; Kazerooni, Alexander C.; Thweatt, Amber L.; Lester, Joseph L.; Bernal, Luis P.
1995-01-01
Get Away Special (GAS) payload G-093, also called VORTEX (VOrtex Ring Transit EXperiment), is an investigation of the propagation of a vortex ring through a liquid-gas interface in microgravity. This process results in the formation of one or more liquid droplets similar to earth based liquid atomization systems. In the absence of gravity, surface tension effects dominate the drop formation process. The Shuttle's microgravity environment allows the study of the same fluid atomization processes as using a larger drop size than is possible on Earth. This enables detailed experimental studies of the complex flow processes encountered in liquid atomization systems. With VORTEX, deformations in both the vortex ring and the fluid surface will be measured closely for the first time in a parameters range that accurately resembles liquid atomization. The experimental apparatus will record images of the interactions for analysis after the payload has been returned to earth. The current design of the VORTEX payload consists of a fluid test cell with a vortex ring generator, digital imaging system, laser illumination system, computer based controller, batteries for payload power, and an array of housekeeping and payload monitoring sensors. It is a self-contained experiment and will be flown on board the Space Shuttle in a 5 cubic feet GAS canister. The VORTEX Project is entirely run by students at the University of Michigan but is overseen by a faculty advisor acting as the payload customer and the contact person with NASA. This paper summarizes both the technical and programmatic aspects of the VORTEX Project.
Wingtip-Vortex Turbine Lowers Aircraft Drag
NASA Technical Reports Server (NTRS)
Patterson, J. C. J.
1982-01-01
Turbine captures some of energy lost in aircraft wingtip vortexes. Wing-tip vortex turbine operates in crossflow of the lift-induced vortex; i.e., flow not parallel to the flightpath. Each turbine blade generates a force as a result of angle of attack between blade and nonstreamwise local flow. Turbine converts lost vortex energy to rotational energy and reduces induced drag.
Vortex Matter in Highly Strained Nb_{75} Zr_{25} : Analogy with Viscous Flow of Disordered Solids
NASA Astrophysics Data System (ADS)
Chandra, Jagdish; Manekar, Meghmalhar; Sharma, V. K.; Mondal, Puspen; Tiwari, Pragya; Roy, S. B.
2016-06-01
We present the results of magnetization and magneto-transport measurements in the superconducting state of an as-cast Nb_{75} Zr_{25} alloy. We also report the microstructure of our sample at various length scales by using optical, scanning electron and transmission electron microscopies. The information of microstructure is used to understand the flux pinning properties in the superconducting state within the framework of collective pinning. The magneto-transport measurements show a non-Arrhenius behaviour of the temperature- and field-dependent resistivity across the resistive transition and is understood in terms of a model for viscous flow of disordered solids which is popularly known as the `shoving model'. The activation energy for flux flow is assumed to be mainly the elastic energy stored in the flux-line lattice. The scaling of pinning force density indicates the presence of two pinning mechanisms of different origins. The elastic constants of the flux-line lattice are used to estimate the length scale of vortex lattice movement, or the volume displaced by the flux-line lattice. It appears that the vortex lattice displacement estimated from elastic energy considerations is of the same order of magnitude as that of the flux bundle hopping length during flux flow. Our results could provide possible directions for establishing a framework where vortex matter and glass-forming liquids or amorphous solids can be treated in a similar manner for understanding the phenomenon of viscous flow in disordered solids or more generally the pinning and depinning properties of elastic manifolds in random media. It is likely that the vortex molasses scenario is more suited to explain the vortex dynamics in conventional low-T_C superconductors.
New vortex-matter size effect observed in Bi(2)Sr(2)CaCu(2)O(8 + delta).
Wang, Y M; Fuhrer, M S; Zettl, A; Ooi, S; Tamegai, T
2001-04-16
The vortex-matter 3D to 2D phase transition is studied in micron-sized Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals using local Hall magnetization measurements. At a given temperature, the second magnetization peak, the signature of a possible 3D--2D vortex phase transition, disappears for samples smaller than a critical length. We suggest that this critical length should be equated with the 2D vortex lattice ab-plane correlation length R(2D)(c). The magnitude and temperature dependence of R(2D)(c) agree well with Larkin-Ovchinnikov collective pinning theory.
Vortex operator and BKT transition in Abelian duality
NASA Astrophysics Data System (ADS)
Chern, Tong
2016-04-01
We give a new simple derivation for the sine-Gordon description of Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Our derivation is simpler than traditional derivations. Besides, our derivation is a continuous field theoretic derivation by using path integration, different from the traditional derivations which are based on lattice theory or based on Coulomb gas model. Our new derivation relies on Abelian duality of two dimensional quantum field theory. By utilizing this duality in path integration, we find that the vortex configurations are naturally mapped to exponential operators in dual description. Since these operators are the vortex operators that can create vortices, the sine-Gordon description then naturally follows. Our method may be useful for the investigation to the BKT physics of superconductors.
Vortex creep in TFA-YBCO nanocomposite films
NASA Astrophysics Data System (ADS)
Rouco, V.; Bartolomé, E.; Maiorov, B.; Palau, A.; Civale, L.; Obradors, X.; Puig, T.
2014-11-01
Vortex creep in YBa2Cu3O7 - x (YBCO) films grown from the trifluoracetate (TFA) chemical route with BaZrO3 and Ba2YTaO6 second-phase nanoparticles (NPs) has been investigated by magnetic relaxation measurements. We observe that in YBCO nanocomposites the phenomenological crossover line from the elastic to the plastic creep regime is shifted to higher magnetic fields and temperatures. The origin of this shift lies on the new isotropic-strong vortex pinning contribution appearing in these nanocomposites, induced by local lattice distortions. As a consequence, we demonstrate that the addition of non-coherent NPs produces a decrease in the creep rate S in most of the phase diagram, particularly, in the range of fields and temperatures (T\\gt 60 K, {{μ }0}H\\gt 0.5 T) relevant for large scale applications.
Minimal model for Brownian vortexes.
Sun, Bo; Grier, David G; Grosberg, Alexander Y
2010-08-01
A Brownian vortex is a noise-driven machine that uses thermal fluctuations to extract a steady-state flow of work from a static force field. Its operation is characterized by loops in a probability current whose topology and direction can change with changes in temperature. We present discrete three- and four-state minimal models for Brownian vortexes that can be solved exactly with a master-equation formalism. These models elucidate conditions required for flux reversal in Brownian vortexes and provide insights into their thermodynamic efficiency through the rate of entropy production. PMID:20866791
Josephson-vortex Cherenkov radiation
Mints, R.G.; Snapiro, I.B.
1995-10-01
We predict the Josephson-vortex Cherenkov radiation of an electromagnetic wave. We treat a long one-dimensional Josephson junction. We consider the wavelength of the radiated electromagnetic wave to be much less than the Josephson penetration depth. We use for calculations the nonlocal Josephson electrodynamics. We find the expression for the radiated power and for the radiation friction force acting on a Josephson vortex and arising due to the Cherenkov radiation. We calculate the relation between the density of the bias current and the Josephson vortex velocity.
Chesi, Stefano; Jaffe, Arthur; Loss, Daniel; Pedrocchi, Fabio L.
2013-11-15
We investigate the role that vortex loops play in characterizing eigenstates of interacting Majoranas. We give some general results and then focus on ladder Hamiltonian examples as a test of further ideas. Two methods yield exact results: (i) A mapping of certain spin Hamiltonians to quartic interactions of Majoranas shows that the spectra of these two examples coincide. (ii) In cases with reflection-symmetric Hamiltonians, we use reflection positivity for Majoranas to characterize vortices in the ground states. Two additional methods suggest wider applicability of these results: (iii) Numerical evidence suggests similar behavior for certain systems without reflection symmetry. (iv) A perturbative analysis also suggests similar behavior without the assumption of reflection symmetry.
NASA Astrophysics Data System (ADS)
Chen, Z. Z.; Ma, Y. L.
2007-01-01
The minimal energy configurations of finite Nv-body vortices in a rotating trapped Bose-Einstein condensate is studied analytically by extending the previous work [Y. Castin, R. Dum, Eur. Phys. J. D 7, 399 (1999)], and taking into account the finite size effects on z-direction and the bending of finite vortex lines. The calculation of the energy of the vortices as a function of the rotation frequency of the trap gives number, curvature, configuration of vortices and width of vortex cores self-consistently. The numerical results show that (1) the simplest regular polynomial of the several vortex configurations is energetically favored; while the hexagonal vortex lattice is more stable than square lattice; (2) bending is more stable then straight vortex line along the z-axis for λ<1; (3) the boundary effect is obvious: compared with the estimation made under infinite boundary, the finite size effect leads to a lower vortex density, while the adding vortex bending results in a less higher density because of the expansion. The results are in well agreement with the other authors' ones.
Structure of leading-edge vortex flows including vortex breakdown
Payne, F.M.
1987-01-01
An experimental investigation of the structure of leading-edge vortex flows on thin sharp-edged delta wings was carried out at low Reynolds numbers. Flow-visualization techniques were used to study the topology of the vortex and the phenomenon of vortex breakdown. Seven-hole probe-wake surveys and laser-doppler-anemometer measurements were obtained and compared. Delta wings with sweep angles of 70, 75, 80, and 85/sup 0/ were tested at angles of attack of 10, 20, 30, and 40/sup 0/. The test were conducted in a Reynolds number range of 8.5 x 10/sup 4/ to 6.4 x 10/sup 5/. Smoke-flow visualization revealed the presence of small Kelvin-Helmholtz type vortical structures in the shear layer of a leading-edge vortex. These shear-layer vortices follow a helical path and grow in the streamwise direction as they wind into the vortex core where the individual shear layers merge. The phenomenon of vortex breakdown was studied using high-speed cinema photography. The bubble and spiral types of breakdown were observed and appear to represent the extremes in a continuum of breakdown forms.
Numerical simulation of vortex breakdown
NASA Technical Reports Server (NTRS)
Shi, X.
1985-01-01
The breakdown of an isolated axisymmetric vortex embedded in an unbounded uniform flow is examined by numerical integration of the complete Navier-Stokes equations for unsteady axisymmetric flow. Results show that if the vortex strength is small, the solution approaches a steady flow and the vortex is stable. If the strength is large enough, the solution remains unsteady and a recirculating zone will appear near the axis, its form and internal structure resembling those of the axisymmetric breakdown bubbles with multi-cells observed by Faler and Leibovich (1978). For apppropriate combinations of flow parameters, the flow reveals quasi-periodicity. Parallel calculations with the quasi-cylindrical approximation indicate that so far as predicting of breakdown is concerned, its results coincide quite well with the results mentioned above. Both show that the vortex breakdown has little concern with the Reynolds number or with the critical classification of the upstream flow, at least for the lower range of Reynolds numbers.
Vortex state in ferromagnetic nanoparticles
NASA Astrophysics Data System (ADS)
Betto, Davide; Coey, J. M. D.
2014-05-01
The evolution of the magnetic state of a soft ferromagnetic nanoparticle with its size is usually thought to be from superparamagnetic single domain to blocked single domain to a blocked multidomain structure. Néel pointed out that a vortex configuration produces practically no stray field at the cost of an increase in the exchange energy, of the order of RJS2lnR /c, where JS2 is the bond energy, R is the particle radius, and c is of the order of the exchange length. A vortex structure is energetically cheaper than single domain when the radius is greater than a certain value. The correct sequence should include a vortex configuration between the single domain and the multidomain states. The critical size is calculated for spherical particles of four important materials (nickel, magnetite, permalloy, and iron) both numerically and analytically. A vortex state is favored in materials with high magnetisation.
New omega vortex identification method
NASA Astrophysics Data System (ADS)
Liu, ChaoQun; Wang, YiQian; Yang, Yong; Duan, ZhiWei
2016-08-01
A new vortex identification criterion called Ω-method is proposed based on the ideas that vorticity overtakes deformation in vortex. The comparison with other vortex identification methods like Q-criterion and λ 2-method is conducted and the advantages of the new method can be summarized as follows: (1) the method is able to capture vortex well and very easy to perform; (2) the physical meaning of Ω is clear while the interpretations of iso-surface values of Q and λ 2 chosen to visualize vortices are obscure; (3) being different from Q and λ 2 iso-surface visualization which requires wildly various thresholds to capture the vortex structure properly, Ω is pretty universal and does not need much adjustment in different cases and the iso-surfaces of Ω=0.52 can always capture the vortices properly in all the cases at different time steps, which we investigated; (4) both strong and weak vortices can be captured well simultaneously while improper Q and λ 2 threshold may lead to strong vortex capture while weak vortices are lost or weak vortices are captured but strong vortices are smeared; (5) Ω=0.52 is a quantity to approximately define the vortex boundary. Note that, to calculate Ω, the length and velocity must be used in the non-dimensional form. From our direct numerical simulation, it is found that the vorticity direction is very different from the vortex rotation direction in general 3-D vortical flow, the Helmholtz velocity decomposition is reviewed and vorticity is proposed to be further decomposed to vortical vorticity and non-vortical vorticity.
Inverse Problem of Vortex Reconstruction
NASA Astrophysics Data System (ADS)
Protas, Bartosz; Danaila, Ionut
2014-11-01
This study addresses the following question: given incomplete measurements of the velocity field induced by a vortex, can one determine the structure of the vortex? Assuming that the flow is incompressible, inviscid and stationary in the frame of reference moving with the vortex, the ``structure'' of the vortex is uniquely characterized by the functional relation between the streamfunction and vorticity. To focus attention, 3D axisymmetric vortex rings are considered. We show how this inverse problem can be framed as an optimization problem which can then be efficiently solved using variational techniques. More precisely, we use measurements of the tangential velocity on some contour to reconstruct the function defining the streamfunction-vorticity relation in a continuous setting. Two test cases are presented, involving Hill's and Norbury vortices, in which very good reconstructions are obtained. A key result of this study is the application of our approach to obtain an optimal inviscid vortex model in an actual viscous flow problem based on DNS data which leads to a number of nonintuitive findings.
Intrinsic and extrinsic pinning in NdFeAs(O,F): vortex trapping and lock-in by the layered structure
Tarantini, C.; Iida, K.; Hänisch, J.; Kurth, F.; Jaroszynski, J.; Sumiya, N.; Chihara, M.; Hatano, T.; Ikuta, H.; Schmidt, S.; Seidel, P.; Holzapfel, B.; Larbalestier, D. C.
2016-01-01
Fe-based superconductors (FBS) present a large variety of compounds whose properties are affected to different extents by their crystal structures. Amongst them, the REFeAs(O,F) (RE1111, RE being a rare-earth element) is the family with the highest critical temperature Tc but also with a large anisotropy and Josephson vortices as demonstrated in the flux-flow regime in Sm1111 (Tc ∼ 55 K). Here we focus on the pinning properties of the lower-Tc Nd1111 in the flux-creep regime. We demonstrate that for H//c critical current density Jc at high temperatures is dominated by point-defect pinning centres, whereas at low temperatures surface pinning by planar defects parallel to the c-axis and vortex shearing prevail. When the field approaches the ab-planes, two different regimes are observed at low temperatures as a consequence of the transition between 3D Abrikosov and 2D Josephson vortices: one is determined by the formation of a vortex-staircase structure and one by lock-in of vortices parallel to the layers. This is the first study on FBS showing this behaviour in the full temperature, field, and angular range and demonstrating that, despite the lower Tc and anisotropy of Nd1111 with respect to Sm1111, this compound is substantially affected by intrinsic pinning generating a strong ab-peak in Jc. PMID:27782196
NASA Astrophysics Data System (ADS)
Malcolm, Gerald N.
Because conventional fighter aircraft control surfaces (e.g. rudder) become ineffective at high angles of attack, alternate means of providing aerodynamic control are being explored. A prime potential source for improved control power is the vortex flowfield existing on typical fighter aircraft forebodies. Several techniques to manipulate the forebody vortices to produce controlled forces and moments at high angles of attack have been investigated by a number of researchers in the past few years. This paper reviews some of the reported research results and discusses the merits of several methods applied directly to the forebody, including: (1) movable strakes, (2) blowing surface jets, (3) blowing and suction through surface slots, (4) suction through surface holes, and (5) miniaturized rotatable tip strakes. All of these were found to be effective over a varying range of angles of attack and sideslip. Most of the methods work on the basis of boundary layer separation control. The presence of closely spaced forebody vortices enhances the effectiveness since controlling the separation controls the vortices which, in turn, creates large changes in the forebody forces. Regardless of which method is employed, the maximum effectiveness is realized if it is applied near the forebody tip. The advantage of one method over another will depend on the configuration and specific performance requirements.
VORTEX CREEP AGAINST TOROIDAL FLUX LINES, CRUSTAL ENTRAINMENT, AND PULSAR GLITCHES
Gügercinoğlu, Erbil; Alpar, M. Ali E-mail: alpar@sabanciuniv.edu
2014-06-10
A region of toroidally oriented quantized flux lines must exist in the proton superconductor in the core of the neutron star. This region will be a site of vortex pinning and creep. Entrainment of the neutron superfluid with the crustal lattice leads to a requirement of superfluid moment of inertia associated with vortex creep in excess of the available crustal moment of inertia. This will bring about constraints on the equation of state. The toroidal flux region provides the moment of inertia necessary to complement the crust superfluid with postglitch relaxation behavior fitting the observations.
Arrays of Gaussian vortex, Bessel and Airy beams by computer-generated hologram
NASA Astrophysics Data System (ADS)
Lu, Yang; Jiang, Bo; Lü, Shuchao; Liu, Yongqi; Li, Shasha; Cao, Zheng; Qi, Xinyuan
2016-03-01
We generate various kinds of arrays of Gaussian vortex, Bessel and Airy beams, respectively, with digital phase holograms (DPH) based on the fractional-Talbot effect by using the phase-only spatial light modulator (SLM). The linear and nonlinear transmissions of these beam arrays in strontium barium niobate (SBN) crystal are investigated numerically and experimentally. Compared with Gaussian vortex arrays, Bessel and Airy beam arrays can keep their patterns unchanged in over 20 mm, realizing non-diffracting transmission. The Fourier spectra (far-field diffraction patterns) of the lattices are also studied. The experimental results are in good agreement with the numerical simulations.
Probing commensurate ground states of Josephson vortex in layered superconductors.
Takahashi, Y; Luo, M-B; Nishizaki, T; Kobayashi, N; Hu, X
2014-04-01
Because of the commensurability condition between the vortex lattice constant determined by external magnetic field and the nano-scale layered structure, interlayer Josephson vortices (JVs) in high-Tc cuprate superconductors can take various configurations. We have simulated with Langevin scheme the in-plane flux-flow dynamics of JVs subject to point-like pinning centers. Oscillation in resistivity is found with the applied magnetic field, where the resistivity peaks occur around commensurate JV configurations. We have also measured the resistivity experimentally using single crystals of underdoped YBa2Cu3Oy with the anisotropy parameter gamma approximately equal to 50. A unique JV lattice has been detected for the first time.
The vortex interaction in a propeller/stator flow field
NASA Technical Reports Server (NTRS)
Johnston, R. T.; Sullivan, J. P.
1991-01-01
The vortex interaction encounered in the flow field of a propeller and a stator has been investigated using smoke flow visualization. A stator at angle of attack was used to generate a line vortex which interacted with the helical vortex filaments generated by a propeller. Changes in the relative vortex strengths and vortex rotational directions yielded several distinct vortex structures. Axial flow in the vortex cores is determined to influence the development of the vortex interaction.
Entrainment in interacting vortex rings
NASA Astrophysics Data System (ADS)
Shami, Rammah; Ganapathisubramani, Bharathram
2014-11-01
The efficiency of entrainment in single vortex rings has been examined by various studies in the literature. These studies have shown that this efficiency is greatly increased for smaller stroke-time to nozzle-diameter ratios, L/D. However, no clear consensus exists regarding the effect on the entrainment process for the sectioned delivery of the vortex forming impulse. In the present work the entrainment mechanism associated with the interaction between two co-axially separated vortex rings is explored. Planar, time-resolved particle image velocimetry (PIV) measurements are taken of a interacting vortex flow field. Lagrangian coherent structures (LCS) extracted from the finite-time Lyapunov exponent (FTLE) fields are employed to determine the vortex boundaries of the interacting rings and is then used to measure entrainment. Preliminary results indicate that whilst the most efficient entrainment of ambient fluid by the ring pairs occurs at larger separations, the rate and overall mass transport increase can be controlled by altering the spatial/temporal separation between successive rings and is higher at smaller ring spacing. Variation in mass transport behaviour for different ring strengths (L/D) and Reynolds numbers will also be discussed.
The Onset of Vortex Turbulence.
NASA Astrophysics Data System (ADS)
Huber, Greg
The onset of turbulence in two-dimensional, excitable media close to a global Hopf bifurcation is investigated. There one finds that the turbulence is associated with the appearance of topological point defects (vortices). A discrete form of the complex Ginzburg-Landau equation is used to explore this dynamics. Linear stability analysis of the complex Ginzburg -Landau equation indicates in what regions of parameter space the global, homogeneous solution is stable. However, in general the system does not asymptotically settle into this homogeneous state, rather it finds a many-vortex state. This can be either a 'frozen' state of stationary vortices, or a highly turbulent state with vortex-antivortex creation and annihilation. These states are related to the dynamics of the vortex statistics, as computed numerically. A phase diagram, based on the numerical simulations, is presented. Transient turbulence, near the transition line that separates the frozen states and the turbulent states, is discovered. These transients are identified as metastable states having a well-defined vortex density. Just below the transition to turbulence, the metastable states break down through the nucleation and growth of single-vortex droplets, leading to a finite-density frozen state. The lifetime of the metastable state is found to depend on the distance to the transition line. A relation between the nucleation time and droplet radius is derived, and their dependence on the distance to the turbulence transition is found.
The onset of vortex turbulence
Huber, G.
1993-01-01
The onset of turbulence in two-dimensional, excitable media close to a global Hopf bifurcation is investigated. There one finds that the turbulence is associated with the appearance of topological point defects (vortices). A discrete form of the complex Ginzburg-Landau equation is used to explore this dynamics. Linear stability analysis of the complex Ginzburg-Landau equation indicates in what regions of parameter space the global, homogeneous solution is stable. However, in general the system does not asymptotically settle into this homogeneous state, rather it finds a many-vortex state. This can be either a [open quotes]frozen[close quotes] state of stationary vortices, or a highly turbulent state with vortex-antivortex creation and annihilation. These states are related to the dynamics of the vortex statistics, as computed numerically. A phase diagram, based on the numerical simulations, is presented. Transient turbulence, near the transition line that separates the frozen states and the turbulent states, is discovered. These transients are identified a metastable states having a well-defined vortex density. Just below the transition to turbulence, the metastable states break down through the nucleation and growth of single-vortex droplets, leading to a finite-density frozen state. The lifetime of the metastable state is found to depend on the distance to the transition line. A relation between the nucleation time and droplet radius is derived, and their dependence on the distance to the turbulence transition is found.
The structure of vortex breakdown
NASA Technical Reports Server (NTRS)
Leibovich, S.
1978-01-01
The term 'vortex breakdown', as used in the reported investigation, refers to a disturbance characterized by the formation of an internal stagnation point on the vortex axis, followed by reversed flow in a region of limited axial extent. Two forms of vortex breakdown, which predominate, are shown in photographs. One form is called 'near-axisymmetric' (sometimes 'axisymmetric'), and the other is called 'spiral'. A survey is presented of work published since the 1972 review by Hall. Most experimental data taken since Hall's review have been in tubes, and the survey deals primarily with such cases. It is found that the assumption of axial-symmetry has produced useful results. The classification of flows as supercritical or subcritical, a step that assumes symmetry, has proved universally useful. Experiments show that vortex breakdown is always preceded by an upstream supercritical flow and followed by a subcritical wake. However, a comparison between experiments and attempts at prediction is less than encouraging. For a satisfactory understanding of the structure of vortex breakdown it is apparently necessary to take into account also aspects of asymmetry.
Geometries of Karman Vortex Street
NASA Astrophysics Data System (ADS)
Roushan, Pedram; Wu, X. L.
2004-03-01
The Bénard-von Kármán vortex street is studied in a flowing soap film channel. The two-dimensional fluid flow in the film allows stable vortex streets to be generated and investigated over a broad range of Reynolds numbers, 10
Vortex Formation in Shallow Flows
NASA Astrophysics Data System (ADS)
Rockwell, Donald
2006-11-01
Vortical structures having a scale much larger than the depth of the flow, which arise in bluff body wakes, jets, and mixing layers generated in shallow layers, show distinctive features due to the influence of bed friction. Cinema techniques of high-image-density particle image velocimetry are employed to characterize quasi-two-dimensional and three-dimensional aspects of the vortex development in terms of: patterns of vorticity; flow topology involving definition of critical points; and global spectral and cross-spectral analyses, based on simultaneous time records at thousands of grid points of the cinema imaging. Taken together, these representations lead to an understanding of the relationship between coherent vortex development and unsteadiness along the bed and, furthermore, provide a basis for exploration of concepts generic to separated shear layers in shallow flows. These concepts include: suppression of a primary mode of vortex formation due to bed friction and emergence of another mode; resonant coupling between a gravity wave of the shallow layer and vortex formation, leading to large-scale vortices; and passive and active (open loop) control, which can either retard or enhance the onset of vortex formation. These studies suggest opportunities for further investigation on both experimental and numerical fronts. Collaboration with Haojun Fu, Alis Ekmekci, Jung-Chang Lin, and Muammer Ozgoren is gratefully acknowledged.
Vortex Flows at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Wood, Richard M.; Wilcox, Floyd J., Jr.; Bauer, Steven X. S.; Allen, Jerry M.
2003-01-01
A review of research conducted at the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) into high-speed vortex flows during the 1970s, 1980s, and 1990s is presented. The data are for flat plates, cavities, bodies, missiles, wings, and aircraft with Mach numbers of 1.5 to 4.6. Data are presented to show the types of vortex structures that occur at supersonic speeds and the impact of these flow structures on vehicle performance and control. The data show the presence of both small- and large-scale vortex structures for a variety of vehicles, from missiles to transports. For cavities, the data show very complex multiple vortex structures exist at all combinations of cavity depth to length ratios and Mach number. The data for missiles show the existence of very strong interference effects between body and/or fin vortices. Data are shown that highlight the effect of leading-edge sweep, leading-edge bluntness, wing thickness, location of maximum thickness, and camber on the aerodynamics of and flow over delta wings. Finally, a discussion of a design approach for wings that use vortex flows for improved aerodynamic performance at supersonic speeds is presented.
NASA Astrophysics Data System (ADS)
López Ariste, A.; Centeno, R.; Khomenko, E.
2016-06-01
Context. Waves in the magnetized solar atmosphere are one of the favourite means of transferring and depositing energy into the solar corona. The study of waves brings information not just on the dynamics of the magnetized plasma, but also on the possible ways in which the corona is heated. Aims: The identification and analysis of the phase singularities or dislocations provide us with a complementary approach to the magnetoacoustic and Aflvén waves propagating in the solar atmosphere. They allow us to identify individual wave modes, shedding light on the probability of excitation or the nature of the triggering mechanism. Methods: We use a time series of Doppler shifts measured in two spectral lines, filtered around the three-minute period region. The data show a propagating magnetoacoustic slow mode with several dislocations and, in particular, a vortex line. We study under what conditions the different wave modes propagating in the umbra can generate the observed dislocations. Results: The observed dislocations can be fully interpreted as a sequence of sausage and kink modes excited sequentially on average during 15 min. Kink and sausage modes appear to be excited independently and sequentially. The transition from one to the other lasts less than three minutes. During the transition we observe and model the appearance of superoscillations inducing large phase gradients and phase mixing. Conclusions: The analysis of the observed wave dislocations leads us to the identification of the propagating wave modes in umbrae. The identification in the data of superoscillatory regions during the transition from one mode to the other may be an important indicator of the location of wave dissipation.
Analysis and control of asymmetric vortex flows and supersonic vortex breakdown
NASA Technical Reports Server (NTRS)
Kandil, Osama A.
1991-01-01
Topics relative to the analysis and control of asymmetric vortex flow and supersonic vortex breakdown are discussed. Specific topics include the computation of compressible, quasi-axisymmetric slender vortex flow and breakdown; supersonic quasi-axisymmetric vortex breakdown; and three-dimensional Navier-Stokes asymmetric solutions for cones and cone-cylinder configurations.
Picosecond optical vortex pulse illumination forms a monocrystalline silicon needle.
Takahashi, Fuyuto; Miyamoto, Katsuhiko; Hidai, Hirofumi; Yamane, Keisaku; Morita, Ryuji; Omatsu, Takashige
2016-01-01
The formation of a monocrystalline silicon needle by picosecond optical vortex pulse illumination was demonstrated for the first time in this study. The dynamics of this silicon needle formation was further revealed by employing an ultrahigh-speed camera. The melted silicon was collected through picosecond pulse deposition to the dark core of the optical vortex, forming the silicon needle on a submicrosecond time scale. The needle was composed of monocrystalline silicon with the same lattice index (100) as that of the silicon substrate, and had a height of approximately 14 μm and a thickness of approximately 3 μm. Overlaid vortex pulses allowed the needle to be shaped with a height of approximately 40 μm without any changes to the crystalline properties. Such a monocrystalline silicon needle can be applied to devices in many fields, such as core-shell structures for silicon photonics and photovoltaic devices as well as nano- or microelectromechanical systems. PMID:26907639
Picosecond optical vortex pulse illumination forms a monocrystalline silicon needle
Takahashi, Fuyuto; Miyamoto, Katsuhiko; Hidai, Hirofumi; Yamane, Keisaku; Morita, Ryuji; Omatsu, Takashige
2016-01-01
The formation of a monocrystalline silicon needle by picosecond optical vortex pulse illumination was demonstrated for the first time in this study. The dynamics of this silicon needle formation was further revealed by employing an ultrahigh-speed camera. The melted silicon was collected through picosecond pulse deposition to the dark core of the optical vortex, forming the silicon needle on a submicrosecond time scale. The needle was composed of monocrystalline silicon with the same lattice index (100) as that of the silicon substrate, and had a height of approximately 14 μm and a thickness of approximately 3 μm. Overlaid vortex pulses allowed the needle to be shaped with a height of approximately 40 μm without any changes to the crystalline properties. Such a monocrystalline silicon needle can be applied to devices in many fields, such as core–shell structures for silicon photonics and photovoltaic devices as well as nano- or microelectromechanical systems. PMID:26907639
Vortex structure and dynamics in kagome and triangular pinning potentials
Laguna, M. F.; Balseiro, C. A.; Dominguez, D.; Nori, Franco
2001-09-01
We study the dynamics of thermally driven superconducting vortices in two types of periodic pinning potentials: kagome and triangular. For the first, second, and third matching fields, we obtain the corresponding ground-state vortex configurations and their phase diagrams. We analyze the system properties by looking at the vortex trajectories and the structure factor, as well as the linear and angular diffusion. The temperature versus pinning force phase diagram is analyzed in detail for each matching field. When the temperature is varied, we observe several stages of lattice pinning and melting. In most of the cases we find, for decreasing temperature, first a pinning of vortices and afterwards a freezing transition of the interstitial vortices. The intermediate regime corresponds to interstitial vortices in a confined liquidlike state and pinned vortices. The kagome pinning potential shows interesting behavior at low temperatures: there is a phase with rotating vortex triangles caged by kagome hexagons (''cooperative ring elementary excitations''), and there is geometric frustration for T{yields}0 with a nearly degenerate ground state.
Vortex trails in stratified fluids
NASA Astrophysics Data System (ADS)
Pao, H.-P.; Lai, R. Y.; Schemm, C. E.
1982-03-01
A framework is proposed which accounts for the properties of atmospheric vortex trails used by wind flow. Similarities between atmospheric vortex patterns and those in stratified fluids are observed noting that the generation of vortex trails is primarily due to density stratification. Horizontal vortices form for values of Froude numbers between 2-505, and for Reynolds numbers between 600-100,000. The cause of late-wake vortices and the reason for their great regularity is the presence of a large-scale coherent structure in the early wake. A critical Froude number exists above which no horizontal vortices form and its value for a bluff body is about 160. Finally, it is also noted that ambient shear can prevent or destroy late-wake horizontal vortices.
Magnetic Vortex Based Transistor Operations
Kumar, D.; Barman, S.; Barman, A.
2014-01-01
Transistors constitute the backbone of modern day electronics. Since their advent, researchers have been seeking ways to make smaller and more efficient transistors. Here, we demonstrate a sustained amplification of magnetic vortex core gyration in coupled two and three vortices by controlling their relative core polarities. This amplification is mediated by a cascade of antivortex solitons travelling through the dynamic stray field. We further demonstrated that the amplification can be controlled by switching the polarity of the middle vortex in a three vortex sequence and the gain can be controlled by the input signal amplitude. An attempt to show fan–out operation yielded gain for one of the symmetrically placed branches which can be reversed by switching the core polarity of all the vortices in the network. The above observations promote the magnetic vortices as suitable candidates to work as stable bipolar junction transistors (BJT). PMID:24531235
Vortex methods for separated flows
NASA Technical Reports Server (NTRS)
Spalart, Philippe R.
1988-01-01
The numerical solution of the Euler or Navier-Stokes equations by Lagrangian vortex methods is discussed. The mathematical background is presented and includes the relationship with traditional point-vortex studies, convergence to smooth solutions of the Euler equations, and the essential differences between two and three-dimensional cases. The difficulties in extending the method to viscous or compressible flows are explained. Two-dimensional flows around bluff bodies are emphasized. Robustness of the method and the assessment of accuracy, vortex-core profiles, time-marching schemes, numerical dissipation, and efficient programming are treated. Operation counts for unbounded and periodic flows are given, and two algorithms designed to speed up the calculations are described.
Unsuccessful Concepts for Aircraft Wake Vortex Minimization
NASA Technical Reports Server (NTRS)
Dunham, R. E., Jr.
1977-01-01
Exploratory concepts are described which were investigated to achieve a reduction in the vortex induced rolling upsets produced by heavy aircraft trailing vortexes. The initial tests included the use of mass injection, oscillating devices, wingtip shape design, interacting multiple vortexes, and end plates. Although later refinements of some of these concepts were successful, initial test results did not indicate a capability of these concepts to significantly alter the vortex induced rolling upset on a following aircraft.
Wagenleithner, P.
1982-07-01
One of the major problems in the application of type II superconductors is the appearance of resistivity in case where a current-carrying specimen is in a longitudinal magnetic field. This is explained by the onset of flux-line cutting events, followed by cross-joining of the line parts. The calculation given here shows the amount of repulsive force and energy between two curved vortex lines and examines the general stability of the vortex-vortex system. First, the actual interaction potential between curved vortices is computed. It includes all electromagnetic and core overlap terms of interactions and self-interaction, and allows computation of the system energy under all curved vortex-line configurations. A computer program is used to find the form of lowest free energy. To do this, special trial functions are established to describe the three-dimensional form of the vortex-vortex system. In these functions parameters determine the qualitative and quantitative form. The asymptotic boundary conditions are built into the nature of the trial functions. The computer program now minimizes the free energy with respect to these parameters. The resulting repulsive energy and force are more than ten times less than the known results for straight flux lines, especially for small asymptotic cutting angles. There is no sharp maximum in the plot of repulsive force versus flux-line separation. A remarkable results is the loss of general stability below a separation distance of several London penetration depths, depending on the cutting angle and the Ginzburg-Landau parameter. The explanation lies in the local attraction of central sections of the vortices as a result of configurational adaption. This explains the onset of resistance at small currents and small magnetic fields.
Coulombic contribution and fat center vortex model
Rafibakhsh, Shahnoosh; Deldar, Sedigheh
2007-02-27
The fat (thick) center vortex model is one of the phenomenological models which is fairly successful to interpret the linear potential between static sources. However, the Coulombic part of the potential has not been investigated by the model yet. In an attempt to get the Coulombic contribution and to remove the concavity of the potentials, we are studying different vortex profiles and vortex sizes.
A Experimental Study of Viscous Vortex Rings.
NASA Astrophysics Data System (ADS)
Dziedzic, Mauricio
Motivated by the role played by vortex rings in the process of turbulent mixing, the work is focused on the problem of stability and viscous decay of a single vortex ring. A new classification is proposed for vortex rings which is based on extensive hot-wire measurements of velocity in the ring core and wake and flow visualization. Vortex rings can be classified as laminar, wavy, turbulence-producing, and turbulent. Prediction of vortex ring type is shown to be possible based on the vortex ring Reynolds number. Linear growth rates of ring diameter with time are observed for all types of vortex rings, with different growth rates occurring for laminar and turbulent vortex rings. Data on the viscous decay of vortex rings are used to provide experimental confirmation of the accuracy of Saffman's equation for the velocity of propagation of a vortex ring. Experimental data indicate that instability of the vortex ring strongly depends on the mode of generation and can be delayed by properly adjusting the generation parameters. A systematic review of the literature on vortex-ring interactions is presented in the form of an appendix, which helps identify areas in which further research may be fruitful.
Generation of Nonlinear Vortex Precursors.
Chen, Yue-Yue; Feng, Xun-Li; Liu, Chengpu
2016-07-01
We numerically study the propagation of a few-cycle pulse carrying orbital angular momentum (OAM) through a dense atomic system. Nonlinear precursors consisting of high-order vortex harmonics are generated in the transmitted field due to carrier effects associated with ultrafast Bloch oscillation. The nonlinear precursors survive to propagation effects and are well separated with the main pulse, which provides a straightforward way to measure precursors. By virtue of carrying high-order OAM, the obtained vortex precursors as information carriers have potential applications in optical information and communication fields where controllable loss, large information-carrying capacity, and high speed communication are required.
Vortex ice in nanostructured superconductors
Reichhardt, Charles; Reichhardt, Cynthia J; Libal, Andras J
2008-01-01
We demonstrate using numerical simulations of nanostructured superconductors that it is possible to realize vortex ice states that are analogous to square and kagome ice. The system can be brought into a state that obeys either global or local ice rules by applying an external current according to an annealing protocol. We explore the breakdown of the ice rules due to disorder in the nanostructure array and show that in square ice, topological defects appear along grain boundaries, while in kagome ice, individual defects appear. We argue that the vortex system offers significant advantages over other artificial ice systems.
Generation of Nonlinear Vortex Precursors.
Chen, Yue-Yue; Feng, Xun-Li; Liu, Chengpu
2016-07-01
We numerically study the propagation of a few-cycle pulse carrying orbital angular momentum (OAM) through a dense atomic system. Nonlinear precursors consisting of high-order vortex harmonics are generated in the transmitted field due to carrier effects associated with ultrafast Bloch oscillation. The nonlinear precursors survive to propagation effects and are well separated with the main pulse, which provides a straightforward way to measure precursors. By virtue of carrying high-order OAM, the obtained vortex precursors as information carriers have potential applications in optical information and communication fields where controllable loss, large information-carrying capacity, and high speed communication are required. PMID:27447507
Realization of Ground State Artificial Skyrmion Lattices at Room Temperature
NASA Astrophysics Data System (ADS)
Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew J.; Kirby, Brian J.; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Fischer, Peter; Liu, Kai
Artificial skyrmion lattices stable at ambient conditions offer a convenient and powerful platform to explore skyrmion physics and topological phenomena and motivates their inclusion in next-generation data and logic devices. In this work we present direct experimental evidence of artificial skyrmion lattices with a stable ground state at room temperature. Our approach is to pattern vortex-state Co nanodots (560 nm diameter) in hexagonal arrays on top of a Co/Pd multilayer with perpendicular magnetic anisotropy; the skyrmion state is prepared using a specific magnetic field sequence. Ion irradiation has been employed to suppress PMA in the underlayer and allow imprinting of the vortex structure from the nanodots to form skyrmion lattices, as revealed by polarized neutron reflectometry. Circularity control is realized through Co dot shape asymmetry, and confirmed by microscopy and FORC magnetometry. The vortex polarity is set during the field sequence and confirmed by magnetometry. Spin-transport studies further demonstrate a sensitivity to the skyrmion spin texture.Work supported by NSF (DMR-1008791, ECCS-1232275 and DMR-1543582)
Magnetic coupling of vortices in a two dimensional lattice.
Nissen, D; Mitin, D; Klein, O; Arekapudi, S S P K; Thomas, S; Im, M-Y; Fischer, P; Albrecht, M
2015-11-20
We investigated the magnetization reversal of magnetic vortex structures in a two-dimensional lattice. The structures were formed by permalloy (Py) film deposition onto large arrays of self assembled spherical SiO(2)-particles with a diameter of 330 nm. We present the dependence of the nucleation and annihilation field of the vortex structures as a function of the Py layer thickness(aspect ratio) and temperature. By increasing the Py thickness up to 90 nm or alternatively by lowering the temperature the vortex structure becomes more stable as expected. However, the increase of the Py thickness results in the onset of strong exchange coupling between neighboring Py caps due to the emergence of Py bridges connecting them. In particular, we studied the influence of magnetic coupling locally by in-field scanning magne to-resistive microscopy and full-field magnetic soft x-ray microscopy, revealing a domain-like nucleation process of vortex states, which arises via domain wall propagation due to exchange coupling of the closely packed structures. By analyzing the rotation sense of the reversed areas, large connected domains are present with the same circulation sense. Furthermore, the lateral core displacements when an in-plane field is applied were investigated, revealing spatially enlarged vortex cores and a broader distribution with increasing Py layer thickness. In addition, the presence of some mixed states, vortices and c-states, is indicated for the array with the thickest Py layer. PMID:26511585
Quantum Phase Transitions of Hard-Core Bosons on the Kagome Lattice
NASA Astrophysics Data System (ADS)
Isakov, S. V.; Melko, R. G.; Sengupta, K.; Wessel, S.; Kim, Yong Baek
2006-03-01
We study hard-core bosons with nearest-neighbor repulsion on the kagome lattice at different filling factors using quantum Monte Carlo simulations and a dual vortex theory. At half-filling, the ground state of the system is always a uniform superfluid in contrast to the case of the triangular lattice. There exists a quantum phase transition from a superfluid to a valence bond solid phase away from half-filling. The possibility of unusual quantum criticality is investigated.
Vortex structures of rotating Bose-Einstein condensates in an anisotropic harmonic potential
Matveenko, S. I.
2010-09-15
We found an analytical solution for the vortex structure in a rapidly rotating trapped Bose-Einstein condensate in the lowest Landau level approximation. This solution is exact in the limit of a large number of vortices and is obtained for the case of a condensate in a anisotropic harmonic potential. The solution describes as limiting cases both a triangle vortex lattice in the symmetric potential trap and a quasi-one-dimensional structure of vortex rows in an asymmetric case, when the rotation frequency is very close to the lower trapping potential frequency. The shape of the density profile is found to be close to the Thomas-Fermi inverted paraboloid form, except in the vicinity of edges of a condensate cloud.
Vortex fluctuation in HgBa 2Ca 3Cu 4O 10+δ
NASA Astrophysics Data System (ADS)
Kim, Mun-Seog; Kim, Wan-Seon; Lee, Sung-Ik; Yu, Seong-Cho; Itskevich, E. S.; Kuzemskaya, I.
1997-08-01
Reversible magnetization with the external magnetic fields of 1 T ≤ H ≤ 5 T parallel to the c-axis has been measured for the grain aligned HgBa2Ca3Cu4O10+δ. A strong vortex fluctuation effect was clearly observed and the magnetization is well described by the vortex fluctuation model. From this analysis, the penetration depth λab(0) = 1583 Å and the effective interlayer spacing s = 44.6 Å were estimated. However, the value of s is significantly larger than the lattice parameter c = 19 Å, which is different from the prediction of the vortex fluctuation model. From the model on superconducting fluctuations proposed by Koshelev, in which not only the critical fluctuations at the lowest Landau level but also the Gaussian fluctuations at higher Landau levels were considered, the different value of s = 15.4 Å was obtained.
Quantized Vortex State in hcp Solid 4He
NASA Astrophysics Data System (ADS)
Kubota, Minoru
2012-11-01
The quantized vortex state appearing in the recently discovered new states in hcp 4He since their discovery (Kim and Chan, Nature, 427:225-227, 2004; Science, 305:1941, 2004) is discussed. Special attention is given to evidence for the vortex state as the vortex fluid (VF) state (Anderson, Nat. Phys., 3:160-162, 2007; Phys. Rev. Lett., 100:215301, 2008; Penzev et al., Phys. Rev. Lett., 101:065301, 2008; Nemirovskii et al., arXiv:0907.0330, 2009) and its transition into the supersolid (SS) state (Shimizu et al., arXiv:0903.1326, 2009; Kubota et al., J. Low Temp. Phys., 158:572-577, 2010; J. Low Temp. Phys., 162:483-491, 2011). Its features are described. The historical explanations (Reatto and Chester, Phys. Rev., 155(1):88-100, 1967; Chester, Phys. Rev. A, 2(1):256-258, 1970; Andreev and Lifshitz, JETP Lett., 29:1107-1113, 1969; Leggett, Phys. Rev. Lett., 25(22), 1543-1546, 1970; Matsuda and Tsuneto, Prog. Theor. Phys., 46:411-436, 1970) for the SS state in quantum solids such as solid 4He were based on the idea of Bose Einstein Condensation (BEC) of the imperfections such as vacancies, interstitials and other possible excitations in the quantum solids which are expected because of the large zero-point motions. The SS state was proposed as a new state of matter in which real space ordering of the lattice structure of the solid coexists with the momentum space ordering of superfluidity. A new type of superconductors, since the discovery of the cuprate high T c superconductors, HTSCs (Bednorz and Mueller, Z. Phys., 64:189, 1986), has been shown to share a feature with the vortex state, involving the VF and vortex solid states. The high T c s of these materials are being discussed in connection to the large fluctuations associated with some other phase transitions like the antiferromagnetic transition in addition to that of the low dimensionality. The supersolidity in the hcp solid 4He, in contrast to the new superconductors which have multiple degrees of freedom of
Bouquet, F.; Calemczuk, R.; Crabtree, G. W.; Erb, A.; Fisher, R. A.; Junod, A.; Kwok, W. K.; Marcenat, C.; Phillips, N. E.; Roulin, M.; Schilling, A.; Welp, U.
1999-08-17
We have studied the vortex phase diagram of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) in very strong magnetic field (0-26 Tesla) by a.c. calorimetry. We describe the anomalies associated with the transitions between the different vortex states (solid, liquid, and glass), with special emphasis on the first order flux lattice melting.
Evolution of a plasma vortex in air.
Tsai, Cheng-Mu; Chu, Hong-Yu
2016-01-01
We report the generation of a vortex-shaped plasma in air by using a capacitively coupled dielectric barrier discharge system. We show that a vortex-shaped plasma can be produced inside a helium gas vortex and is capable of propagating for 3 cm. The fluctuation of the plasma ring shows a scaling relation with the Reynolds number of the vortex. The transient discharge reveals the property of corona discharge, where the conducting channel within the gas vortex and the blur plasma emission are observed at each half voltage cycle. PMID:26871181
Evolution of a plasma vortex in air.
Tsai, Cheng-Mu; Chu, Hong-Yu
2016-01-01
We report the generation of a vortex-shaped plasma in air by using a capacitively coupled dielectric barrier discharge system. We show that a vortex-shaped plasma can be produced inside a helium gas vortex and is capable of propagating for 3 cm. The fluctuation of the plasma ring shows a scaling relation with the Reynolds number of the vortex. The transient discharge reveals the property of corona discharge, where the conducting channel within the gas vortex and the blur plasma emission are observed at each half voltage cycle.
Vortex telegraph noise in high magnetic fields
Shung, E.; Rosenbaum, T.F.; Coppersmith, S.N.; Crabtree, G.W.; Kwok, W.
1997-11-01
We cool untwinned single crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} with columnar defects down to liquid-He temperatures and study the development of pinning in the strongly interacting Bose glass with local Hall-probe magnetometry. We are able to resolve discrete fluctuations in the local vortex density resulting from reconfigurations of the vortex assembly between metastable states nearby in energy. By varying the applied magnetic field, and therefore the mean vortex density, we gain microscopic information about vortex-vortex interactions. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Kuramashi, Yoshinobu
2007-12-01
Preface -- Fixed point actions, symmetries and symmetry transformations on the lattice / P. Hasenfratz -- Algorithms for dynamical fennions / A. D. Kennedy -- Applications of chiral perturbation theory to lattice QCD / Stephen R. Sharpe -- Lattice QCD with a chiral twist / S. Sint -- Non-perturbative QCD: renormalization, O(A) - Improvement and matching to Heavy Quark effective theory / Rainer Sommer.
Disorder-induced two-step melting of vortex matter in Co-intercalated NbS e2 single crystals
NASA Astrophysics Data System (ADS)
Ganguli, Somesh Chandra; Singh, Harkirat; Roy, Indranil; Bagwe, Vivas; Bala, Dibyendu; Thamizhavel, Arumugam; Raychaudhuri, Pratap
2016-04-01
Disorder-induced melting where the increase in positional entropy created by random pinning sites drives the order-disorder transition in a periodic solid provides an alternate route to the more conventional thermal melting. Here, using real-space imaging of the vortex lattice through scanning tunneling spectroscopy, we show that, in the presence of weak pinning, the vortex lattice in a type-II superconductor disorders through two distinct topological transitions. Across each transition, we separately identify metastable states formed through superheating of the low-temperature state or supercooling of the high-temperature state. Comparing crystals with different levels of pinning we conclude that the two-step melting is fundamentally associated with the presence of random pinning which generates topological defects in the ordered vortex lattice.
Perturbative theory for Brownian vortexes.
Moyses, Henrique W; Bauer, Ross O; Grosberg, Alexander Y; Grier, David G
2015-06-01
Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers. PMID:26172698
Perturbative theory for Brownian vortexes
NASA Astrophysics Data System (ADS)
Moyses, Henrique W.; Bauer, Ross O.; Grosberg, Alexander Y.; Grier, David G.
2015-06-01
Brownian vortexes are stochastic machines that use static nonconservative force fields to bias random thermal fluctuations into steadily circulating currents. The archetype for this class of systems is a colloidal sphere in an optical tweezer. Trapped near the focus of a strongly converging beam of light, the particle is displaced by random thermal kicks into the nonconservative part of the optical force field arising from radiation pressure, which then biases its diffusion. Assuming the particle remains localized within the trap, its time-averaged trajectory traces out a toroidal vortex. Unlike trivial Brownian vortexes, such as the biased Brownian pendulum, which circulate preferentially in the direction of the bias, the general Brownian vortex can change direction and even topology in response to temperature changes. Here we introduce a theory based on a perturbative expansion of the Fokker-Planck equation for weak nonconservative driving. The first-order solution takes the form of a modified Boltzmann relation and accounts for the rich phenomenology observed in experiments on micrometer-scale colloidal spheres in optical tweezers.
Wulferding, Dirk; Yang, Ilkyu; Yang, Jinho; Lee, Minkyung; Choi, Hee Cheul; Bud'ko, Sergey L.; Canfield, Paul C.; Yeom, Han Woong; Kim, Jeehoon
2015-07-31
We present a local probe study of the magnetic superconductor ErNi_{2}B_{2}C, using magnetic force microscopy at sub-Kelvin temperatures. ErNi_{2}B_{2}C is an ideal system to explore the effects of concomitant superconductivity and ferromagnetism. At 500 mK, far below the transition to a weakly ferromagnetic state, we directly observe a structured magnetic background on the micrometer scale. We determine spatially resolved absolute values of the magnetic penetration depth λ and study its temperature dependence as the system undergoes magnetic phase transitions from paramagnetic to antiferromagnetic, and to weak ferromagnetic, all within the superconducting regime. We estimate the absolute pinning force of Abrikosov vortices, which shows a position dependence and temperature dependence as well, and discuss the possibility of the purported spontaneous vortex formation.
Vortex lines in layered superconductors. I. From 3D to 2D behaviour
NASA Astrophysics Data System (ADS)
Feinberg, D.
1994-02-01
The fundamental aspects of vortices in layered superconductors (natural or artificial multilayered materials) are reviewed, focusing on the role of anisotropy and very short coherence lengths. These materials divide into three classes, with increasing T_c's : chalcogenides, organic superconductors and high-T_c copper oxides. The first part of the paper summarizes the quantitative features of the vortex lattice, due to the incorporation of anisotropy in the 3D Ginzburg-Landau or London descriptions : anisotropy of critical fields and vortex lattice, elastic coefficients and melting. This kind of model describes most of the properties of moderately anisotropic compounds as Y : 123. The second part concerns the Josephson-coupled layered systems and identifies in which regimes vortices exhibit a quasi-2D character. Qualitatively new features as Josephson vortices, 2D vortices, Kosterlitz-Thouless transition and lock-in of vortices are reviewed. This analysis is adapted to compounds as Bi : 2212 or multilayers, but also to Y : 123 for some aspects. On passe en revue les aspects fondamentaux des vortex dans les supraconducteurs lamellaires (naturels ou superréseaux artificiels), en mettant l'accent sur le rôle de l'anisotropie et des très courtes longueurs de cohérence. Ces composés se divisent en trois classes, de T_c croissants : chalcogénures, supraconducteurs organiques et oxydes de cuivre à haut T_c. La première partie de l'article résume les aspects quantitatifs dus à l'incorporation de l'anisotropie dans les descriptions 3D Ginzburg-Landau ou London du réseau de vortex.: anisotropie des champs critiques et du réseau de vortex, coefficients élastiques et fusion. Ce type de modèle décrit une grande partie des propriétés des composés modérément anisotropes tels que Y : 123. La seconde partie concerne les systèmes lamellaires à couplage Josephson et identifie dans quels régimes les vortex présentent un caractère quasi-2D. Des effets
Vortex pinning vs. superconducting wire network in nanostructured superconductors
NASA Astrophysics Data System (ADS)
Vicent, Jose L.
2014-03-01
Superconducting films with array of ordered defects allow studying effects which are governed by the interplay between lengths of the nanostructured sample and lengths related to physical parameters, as for example coherence length. When the coherence length and the separation between the defects are similar, the sample can mimic a superconducting wire network. In this situation, applied magnetic fields induce Little-Parks oscillations due to fluxoid quantization constraint. These L-P oscillations vanish when the coherence length is smaller than the ``stripe'' superconducting region between the defects. In superconducting films with array of nanodefects periodic oscillations can also be detected in resistance R(H), critical current Ic(H), magnetization M(H) and ac-susceptibility χac(H) in a broader temperature range than the temperature interval where L-P oscillations are present. Vortex pinning mechanisms are the origin of these oscillations. These oscillations emerge due to matching effects between two lattices: the vortex lattice and the lattice of defects. These oscillations are detected in a broader temperature interval than the temperature interval where L-P oscillations are present. Worth to note that, due to the coherence length divergence at Tc, a crossover to wire network behavior is experimentally found always. Interestingly, both mechanisms coexist close to superconducting critical temperatures; i. e. in the temperature region where the sample mimics superconducting wire network. These overlapping effects can be experimentally separated and both origins can be discriminated. We have analyzed and single out, with magnetotransport measurements, both mechanisms: pinning and fluxoid quantization constraint in superconducting films with arrays of non-magnetic and magnetic dots. Work supported by Spanish MINECO and CAM.
NASA Astrophysics Data System (ADS)
Iskin, M.; de Melo, C. A. R. Sá
2009-10-01
We analyze the finite temperature phase diagram of fermion mixtures in one-dimensional optical lattices as a function of interaction strength. At low temperatures, the system evolves from an anisotropic three-dimensional Bardeen-Cooper-Schrieffer (BCS) superfluid to an effectively two-dimensional Berezinskii-Kosterlitz-Thouless (BKT) superfluid as the interaction strength increases. We calculate the critical temperature as a function of interaction strength, and identify the region where the dimensional crossover occurs for a specified optical lattice potential. Finally, we show that the dominant vortex excitations near the critical temperature evolve from multiplane elliptical vortex loops in the three-dimensional regime to planar vortex-antivortex pairs in the two-dimensional regime, and we propose a detection scheme for these excitations.
Preliminary study of the three-dimensional deformation of the vortex in Karman vortex street
NASA Astrophysics Data System (ADS)
Ling, Guocan; Guo, Liang; Wu, Zuobin; Ma, Huiyang
1992-03-01
The mechanism for 3D evolution of the isolated Karman vortex and the thin-vortex filament in a circular cylinder wake is studied numerically using the LIA method. The results show that the vortex motion is unstable for small 3D disturbances in the separated wake of a circular cylinder. Karman vortex in the time-averaged wake flowfield wolves into a horseshoe-spoon-like 3D structure. The thin vortex filament deforms three-dimensionally in the braid and generates streamwise vortex structures which incline to the region maximum-deformation direction of the flowfield.
A lattice-Boltzmann scheme of the Navier-Stokes equations on a 3D cuboid lattice
NASA Astrophysics Data System (ADS)
Min, Haoda; Peng, Cheng; Wang, Lian-Ping
2015-11-01
The standard lattice-Boltzmann method (LBM) for fluid flow simulation is based on a square (in 2D) or cubic (in 3D) lattice grids. Recently, two new lattice Boltzmann schemes have been developed on a 2D rectangular grid using the MRT (multiple-relaxation-time) collision model, by adding a free parameter in the definition of moments or by extending the equilibrium moments. Here we developed a lattice Boltzmann model on 3D cuboid lattice, namely, a lattice grid with different grid lengths in different spatial directions. We designed our MRT-LBM model by matching the moment equations from the Chapman-Enskog expansion with the Navier-Stokes equations. The model guarantees correct hydrodynamics. A second-order term is added to the equilibrium moments in order to restore the isotropy of viscosity on a cuboid lattice. The form and the coefficients of the extended equilibrium moments are determined through an inverse design process. An additional benefit of the model is that the viscosity can be adjusted independent of the stress-moment relaxation parameter, thus improving the numerical stability of the model. The resulting cuboid MRT-LBM model is then validated through benchmark simulations using laminar channel flow, turbulent channel flow, and the 3D Taylor-Green vortex flow.
Shock/vortex interaction and vortex-breakdown modes
NASA Technical Reports Server (NTRS)
Kandil, Osama A.; Kandil, H. A.; Liu, C. H.
1992-01-01
Computational simulation and study of shock/vortex interaction and vortex-breakdown modes are considered for bound (internal) and unbound (external) flow domains. The problem is formulated using the unsteady, compressible, full Navier-Stokes (NS) equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. For the bound flow domain, a supersonic swirling flow is considered in a configured circular duct and the problem is solved for quasi-axisymmetric and three-dimensional flows. For the unbound domain, a supersonic swirling flow issued from a nozzle into a uniform supersonic flow of lower Mach number is considered for quasi-axisymmetric and three-dimensional flows. The results show several modes of breakdown; e.g., no-breakdown, transient single-bubble breakdown, transient multi-bubble breakdown, periodic multi-bubble multi-frequency breakdown and helical breakdown.
Vortex phase transitions in monolayer FeSe film on SrTiO3
NASA Astrophysics Data System (ADS)
Zhao, Weiwei; Chang, Cui-Zu; Xi, Xiaoxiang; Mak, Kin Fai; Moodera, Jagadeesh S.
2016-06-01
The voltage–current (V–I) characteristics in superconducting monolayer FeSe film on SrTiO3 (100) under different magnetic fields are investigated. The zero-field V–I result exhibits signatures of a Berezinski–Kosterlitz–Thouless transition, a characteristic of two-dimensional (2D) superconductors. Under an applied magnetic field, with current density lower than the critical current density, the sheet resistance versus current density (R sq–J) dependence changes from ohmic (R sq independent of J) to non-ohmic (a nonlinear dependence of R sq on J) as the temperature decreases, indicative of a vortex phase transition/crossover. We interpret the high-temperature phase as the vortex liquid phase and the low-temperature phase as the vortex slush phase, which has short-ranged vortex lattice correlation, while long-range correlation (i.e. true superconductivity) is absent. No transition into a vortex glass phase is seen, illustrating the importance of thermal fluctuations in a perfect 2D superconductor under a magnetic field.
Vortex-Core Reversal Dynamics: Towards Vortex Random Access Memory
NASA Astrophysics Data System (ADS)
Kim, Sang-Koog
2011-03-01
An energy-efficient, ultrahigh-density, ultrafast, and nonvolatile solid-state universal memory is a long-held dream in the field of information-storage technology. The magnetic random access memory (MRAM) along with a spin-transfer-torque switching mechanism is a strong candidate-means of realizing that dream, given its nonvolatility, infinite endurance, and fast random access. Magnetic vortices in patterned soft magnetic dots promise ground-breaking applications in information-storage devices, owing to the very stable twofold ground states of either their upward or downward core magnetization orientation and plausible core switching by in-plane alternating magnetic fields or spin-polarized currents. However, two technologically most important but very challenging issues --- low-power recording and reliable selection of each memory cell with already existing cross-point architectures --- have not yet been resolved for the basic operations in information storage, that is, writing (recording) and readout. Here, we experimentally demonstrate a magnetic vortex random access memory (VRAM) in the basic cross-point architecture. This unique VRAM offers reliable cell selection and low-power-consumption control of switching of out-of-plane core magnetizations using specially designed rotating magnetic fields generated by two orthogonal and unipolar Gaussian-pulse currents along with optimized pulse width and time delay. Our achievement of a new device based on a new material, that is, a medium composed of patterned vortex-state disks, together with the new physics on ultrafast vortex-core switching dynamics, can stimulate further fruitful research on MRAMs that are based on vortex-state dot arrays.
Interaction of Vortex Ring with Cutting Plate
NASA Astrophysics Data System (ADS)
Musta, Mustafa
2015-11-01
The interaction of a vortex ring impinging on a thin cutting plate was made experimentally using Volumetric 3-component Velocitmetry (v3v) technique. The vortex rings were generated with piston-cylinder vortex ring generator using piston stroke-to-diameter ratios and Re at 2-3 and 1500 - 3000, respectively. The cutting of vortex rings below center line leads to the formation of secondary vortices on each side of the plate which is look like two vortex rings, and a third vortex ring propagates further downstream in the direction of the initial vortex ring, which is previously showed by flow visualization study of Weigand (1993) and called ``trifurcation''. Trifurcation is very sensitive to the initial Reynolds number and the position of the plate with respect to the vortex ring generator pipe. The present work seeks more detailed investigation on the trifurcation using V3V technique. Conditions for the formation of trifurcation is analyzed and compared with Weigand (1993). The formed secondary vortex rings and the propagation of initial vortex ring in the downstream of the plate are analyzed by calculating their circulation, energy and trajectories.
Lattice Boltzmann method and channel flow
NASA Astrophysics Data System (ADS)
Stensholt, Sigvat; Mongstad Hope, Sigmund
2016-07-01
Lattice Boltzmann methods are presented at an introductory level with a focus on fairly simple simulations that can be used to test and illustrate the model’s capabilities. Two scenarios are presented. The first is a simple laminar flow in a straight channel driven by a pressure gradient (Poiseuille flow). The second is a more complex, including a wedge where Moffatt vortices may be induced if the wedge is deep enough. Simulations of the Poiseuille flow scenario accurately capture the theoretical velocity profile. The experiment shows the location of the fluid-wall boundary and the effects viscosity has on the velocity and convergence time. The numerical capabilities of the lattice Boltzmann model are tested further by simulating the more complex Moffatt vortex scenario. The method reproduces with high accuracy the theoretical predction that Moffat vortices will not form in a wedge if the vertex angle exceeds 146°. Practical issues limitations of the lattice Boltzmann method are discussed. In particular the accuracy of the bounce-back boundary condition is first order dependent on the grid resolution.
Wake Vortex Algorithm Scoring Results
NASA Technical Reports Server (NTRS)
Robins, R. E.; Delisi, D. P.; Hinton, David (Technical Monitor)
2002-01-01
This report compares the performance of two models of trailing vortex evolution for which interaction with the ground is not a significant factor. One model uses eddy dissipation rate (EDR) and the other uses the kinetic energy of turbulence fluctuations (TKE) to represent the effect of turbulence. In other respects, the models are nearly identical. The models are evaluated by comparing their predictions of circulation decay, vertical descent, and lateral transport to observations for over four hundred cases from Memphis and Dallas/Fort Worth International Airports. These observations were obtained during deployments in support of NASA's Aircraft Vortex Spacing System (AVOSS). The results of the comparisons show that the EDR model usually performs slightly better than the TKE model.
Vortex boundary-layer interactions
NASA Technical Reports Server (NTRS)
Bradshaw, P.
1986-01-01
Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.
NASA Astrophysics Data System (ADS)
Vasel-Be-Hagh, Ahmadreza; Carriveau, Rupp; Ting, David S.-K.; Turner, John Stewart
2015-10-01
Extending from the model proposed by Vasel-Be-Hagh et al. [J. Fluid Mech. 769, 522 (2015), 10.1017/jfm.2015.126], a perturbation analysis is performed to modify Turner's radius by taking into account the viscous effect. The modified radius includes two terms; the zeroth-order solution representing the effect of buoyancy, and the first-order perturbation correction describing the influence of viscosity. The zeroth-order solution is explicit Turner's radius; the first-order perturbation modification, however, includes the drag coefficient, which is unknown and of interest. Fitting the photographically measured radius into the modified equation yields the time history of the drag coefficient of the corresponding buoyant vortex ring. To give further clarification, the proposed model is applied to calculate the drag coefficient of a buoyant vortex ring at a Bond number of approximately 85; a similar procedure can be applied at other Bond numbers.
Perturbations of vortex ring pairs
NASA Astrophysics Data System (ADS)
Gubser, Steven S.; Horn, Bart; Parikh, Sarthak
2016-02-01
We study pairs of coaxial vortex rings starting from the action for a classical bosonic string in a three-form background. We complete earlier work on the phase diagram of classical orbits by explicitly considering the case where the circulations of the two vortex rings are equal and opposite. We then go on to study perturbations, focusing on cases where the relevant four-dimensional transfer matrix splits into two-dimensional blocks. When the circulations of the rings have the same sign, instabilities are mostly limited to wavelengths smaller than a dynamically generated length scale at which single-ring instabilities occur. When the circulations have the opposite sign, larger wavelength instabilities can occur.
Vasel-Be-Hagh, Ahmadreza; Carriveau, Rupp; Ting, David S-K; Turner, John Stewart
2015-10-01
Extending from the model proposed by Vasel-Be-Hagh et al. [J. Fluid Mech. 769, 522 (2015)], a perturbation analysis is performed to modify Turner's radius by taking into account the viscous effect. The modified radius includes two terms; the zeroth-order solution representing the effect of buoyancy, and the first-order perturbation correction describing the influence of viscosity. The zeroth-order solution is explicit Turner's radius; the first-order perturbation modification, however, includes the drag coefficient, which is unknown and of interest. Fitting the photographically measured radius into the modified equation yields the time history of the drag coefficient of the corresponding buoyant vortex ring. To give further clarification, the proposed model is applied to calculate the drag coefficient of a buoyant vortex ring at a Bond number of approximately 85; a similar procedure can be applied at other Bond numbers.
Lattice Boltzmann Equation On a 2D Rectangular Grid
NASA Technical Reports Server (NTRS)
Bouzidi, MHamed; DHumieres, Dominique; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
We construct a multi-relaxation lattice Boltzmann model on a two-dimensional rectangular grid. The model is partly inspired by a previous work of Koelman to construct a lattice BGK model on a two-dimensional rectangular grid. The linearized dispersion equation is analyzed to obtain the constraints on the isotropy of the transport coefficients and Galilean invariance for various wave propagations in the model. The linear stability of the model is also studied. The model is numerically tested for three cases: (a) a vortex moving with a constant velocity on a mesh periodic boundary conditions; (b) Poiseuille flow with an arbitrasy inclined angle with respect to the lattice orientation: and (c) a cylinder &symmetrically placed in a channel. The numerical results of these tests are compared with either analytic solutions or the results obtained by other methods. Satisfactory results are obtained for the numerical simulations.
Vortex methods for separated flows
NASA Technical Reports Server (NTRS)
Spalart, Philippe R.
1988-01-01
The numerical solution of the Euler or Navier-Stokes equations by Lagrangian vortex methods is discussed. The mathematical background is presented in an elementary fashion and includes the relationship with traditional point-vortex studies, the convergence to smooth solutions of the Euler equations, and the essential differences between two- and three-dimensional cases. The difficulties in extending the method to viscous or compressible flows are explained. The overlap with the excellent review articles available is kept to a minimum and more emphasis is placed on the area of expertise, namely two-dimensional flows around bluff bodies. When solid walls are present, complete mathematical models are not available and a more heuristic attitude must be adopted. The imposition of inviscid and viscous boundary conditions without conformal mappings or image vortices and the creation of vorticity along solid walls are examined in detail. Methods for boundary-layer treatment and the question of the Kutta condition are discussed. Practical aspects and tips helpful in creating a method that really works are explained. The topics include the robustness of the method and the assessment of accuracy, vortex-core profiles, timemarching schemes, numerical dissipation, and efficient programming. Calculations of flows past streamlined or bluff bodies are used as examples when appropriate.
Review of Idealized Aircraft Wake Vortex Models
NASA Technical Reports Server (NTRS)
Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don
2014-01-01
Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.
Birth and evolution of an optical vortex
NASA Astrophysics Data System (ADS)
Vallone, Giuseppe; Sponselli, Anna; D'Ambrosio, Vincenzo; Marrucci, Lorenzo; Sciarrino, Fabio; Villoresi, Paolo
2016-07-01
When a phase singularity is suddenly imprinted on the axis of an ordinary Gaussian beam, an optical vortex appears and starts to grow radially, by effect of diffraction. This radial growth and the subsequent evolution of the optical vortex under focusing or imaging can be well described in general within the recently introduced theory of circular beams, which generalize the hypergeometric-Gaussian beams and which obey novel kinds of ABCD rules. Here, we investigate experimentally these vortex propagation phenomena and test the validity of circular-beam theory. Moreover, we analyze the difference in radial structure between the newly generated optical vortex and the vortex obtained in the image plane, where perfect imaging would lead to complete closure of the vortex core.
Vortex Breakdown-Aircraft Tail Interaction
NASA Astrophysics Data System (ADS)
Kim, Younjong; Rockwell, Donald
2003-11-01
The interaction of vortex breakdown with the tail of an aircraft can lead to severe unsteady loading and vibration. A technique of high-image-density particle image velocimetry is employed to characterize the instantaneous and averaged structure of a broken-down vortex with a generic tail configuration. Interaction of the primary (incident) vortex with the tail results in formation of a relatively large-scale cluster of secondary vorticity. The coexistence of these primary and secondary vortical structures is intimately associated with the unsteadiness of the vortex system, and thereby the near-surface fluctuations associated with buffet loading. Instantaneous and averaged representations of the vortex-tail interaction provide insight into the complex physics. Furthermore, a low order POD model is employed to characterize the most energetic modes of the vortex-tail interaction.
On Traveling Waves in Lattices: The Case of Riccati Lattices
NASA Astrophysics Data System (ADS)
Dimitrova, Zlatinka
2012-09-01
The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.
Contributions to theory of vortex breakdown
NASA Astrophysics Data System (ADS)
Shivamoggi, B. K.; Uberoi, M. S.
A study is made of vortex breakdown in stratified flows, and it is found that a positive stratification in the vortex where the density is increasing away from the axis, postpones the vortex breakdown and vice versa. This is apparent due to the density increasing in a direction opposite to that of an effective gravity which would correspond to a topheavy arrangement under gravity. It is also shown that a wavemotion promotes the possibility of axisymmetric flow downstream of the transaction.
An investigation of counterrotating tip vortex interaction
NASA Technical Reports Server (NTRS)
Majjigi, R. K.; Uenishi, K.; Gliebe, P. R.
1989-01-01
A tip vortex interaction model originally developed for compressors has been extended and adapted for use with counterrotating open rotors. Comparison of available acoustic data with predictions (made with and without the tip vortex model included) illustrate the importance of this interaction effect. This report documents the analytical modeling, a limited experimental verification, and certain key parametric studies pertaining to the tip vortex as a noise source mechanism for the unsteady loading noise of counterrotating properllers.
Vortex knot cascade in polynomial skein relations
NASA Astrophysics Data System (ADS)
Ricca, Renzo L.
2016-06-01
The process of vortex cascade through continuous reduction of topological complexity by stepwise unlinking, that has been observed experimentally in the production of vortex knots (Kleckner & Irvine, 2013), is shown to be reproduced in the branching of the skein relations of knot polynomials (Liu & Ricca, 2015) used to identify topological complexity of vortex systems. This observation can be usefully exploited for predictions of energy-complexity estimates for fluid flows.
On the structure of the turbulent vortex
NASA Technical Reports Server (NTRS)
Roberts, L.
1985-01-01
The trailing vortex generated by a lifting surface, the structure of its turbulent core and the influence of axial flow within the vortex on its initial persistence and on its subsequent decay are described. Similarity solutions of the turbulent diffusion equation are given in closed form and results are expressed in sufficiently simple terms that the influence of the lifting surface parameters on the length of persistence and the rate of decay of the vortex can be evaluated.
Facts and fallacies of vortex flowmeters
DeVries, E.A.
1982-08-01
Vortex flowmeters have been popular since the late 1960s. They have been sold as everything from a panacea for severe service flow applications to a direct replacement for orifice meters. In many ways, vortex flowmeters have not lived up to industry expectations and therefore, have obtained a bad reputation. However, vortex flowmeters can be good flow measurement devices if applied properly, and they do have a place in the processing industries for certain flow applications.
Engineering novel optical lattices.
Windpassinger, Patrick; Sengstock, Klaus
2013-08-01
Optical lattices have developed into a widely used and highly recognized tool to study many-body quantum physics with special relevance for solid state type systems. One of the most prominent reasons for this success is the high degree of tunability in the experimental setups. While at the beginning quasi-static, cubic geometries were mainly explored, the focus of the field has now shifted toward new lattice topologies and the dynamical control of lattice structures. In this review we intend to give an overview of the progress recently achieved in this field on the experimental side. In addition, we discuss theoretical proposals exploiting specifically these novel lattice geometries. PMID:23828639
Mechanics of viscous vortex reconnection
NASA Astrophysics Data System (ADS)
Hussain, Fazle; Duraisamy, Karthik
2011-02-01
This work is motivated by our long-standing claim that reconnection of coherent structures is the dominant mechanism of jet noise generation and plays a key role in both energy cascade and fine-scale mixing in fluid turbulence [F. Hussain, Phys. Fluids 26, 2816 (1983); J. Fluid Mech. 173, 303 (1986)]. To shed further light on the mechanism involved and quantify its features, the reconnection of two antiparallel vortex tubes is studied by direct numerical simulation of the incompressible Navier-Stokes equations over a wide range (250-9000) of the vortex Reynolds number, Re (=circulation/viscosity) at much higher resolutions than have been attempted. Unlike magnetic or superfluid reconnections, viscous reconnection is never complete, leaving behind a part of the initial tubes as threads, which then undergo successive reconnections (our cascade and mixing scenarios) as the newly formed bridges recoil from each other by self-advection. We find that the time tR for orthogonal transfer of circulation scales as tR≈Re-3/4. The shortest distance d between the tube centroids scales as d ≈a[Re(t0-t)]3/4 before reconnection (collision) and as d ≈b[Re(t -t0)]2 after reconnection (repulsion), where t0 is the instant of smallest separation between vortex centroids. We find that b is a constant, thus suggesting self-similarity, but a is dependent on Re. Bridge repulsion is faster than collision and is more autonomous as local induction predominates, and, given the associated acceleration of vorticity, is potentially a source of intense sound generation. At the higher Re studied, the tails of the colliding threads are compressed into a planar jet with multiple vortex pairs. For Re>6000, there is an avalanche of smaller scales during the reconnection, the rate of small scale generation and the spectral content (in vorticity, transfer function and dissipation spectra) being quite consistent with the structures visualized by the λ2 criterion. The maximum rate of vortex
Phases of d-orbital bosons in optical lattices
NASA Astrophysics Data System (ADS)
Pinheiro, Fernanda; Matrikainen, Jani-Petri; Larson, Jonas
2015-05-01
We explore the properties of bosonic atoms loaded into the d bands of an isotropic square optical lattice. Following the recent experimental success reported in Zhai et al (2013 Phys. Rev. A 87 063638), in which populating d bands with a 99 % fidelity was demonstrated, we present a theoretical study of the possible phases that can appear in this system. Using the Gutzwiller ansatz for the three d band orbitals we map the boundaries of the Mott insulating phases. For not too large occupation, two of the orbitals are predominantly occupied, while the third, of a slightly higher energy, remains almost unpopulated. In this regime, in the superfluid phase we find the formation of a vortex lattice, where the vortices come in vortex/anti-vortex pairs with two pairs locked to every site. Due to the orientation of the vortices time-reversal symmetry is spontaneously broken. This state also breaks a discrete {{{Z}}2}-symmetry. We further derive an effective spin-1/2 model that describe the relevant physics of the lowest Mott-phase with unit filling. We argue that the corresponding two dimensional phase diagram should be rich with several different phases. We also explain how to generate anti-symmetric spin interactions that can give rise to novel effects like spin canting.
Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays
NASA Astrophysics Data System (ADS)
Baldacchino, D.; Ferreira, C.; Ragni, D.; van Bussel, G. J. W.
2016-09-01
In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the infinite vortex cascade, a numerical model of four base-vortices is chosen to represent two primary counter-rotating vortex pairs and their mirror plane images, introducing the vortex strength ratio as a free parameter. The resulting system of equations is also defined in terms of the vortex row separation and the qualitative features of the ensuing motion are mapped. A translating and orbiting regime are identified for different cascade separations. The latter occurs for all unequal strength vortex pairs. Thus, the motion is further classified by studying the cyclic behaviour of the orbiting regime and it is shown that for small mismatches in vortex strength, the orbiting length and time scales are sufficiently large as to appear, in the near wake, as translational (non-orbiting). However, for larger mismatches in vortex strength, the orbiting motion approaches the order of the starting height of the vortex. Comparisons between experimental data and the potential flow model show qualitative agreement whilst viscous effects account for the major discrepancies. Despite this, the model captures the orbital mode observed in the measurements and provides an impetus for considering the impact of these complex interactions on vortex generator designs.
Spin transport in tilted electron vortex beams
NASA Astrophysics Data System (ADS)
Basu, Banasri; Chowdhury, Debashree
2014-12-01
In this paper we have enlightened the spin related issues of tilted Electron vortex beams. We have shown that in the skyrmionic model of electron we can have the spin Hall current considering the tilted type of electron vortex beam. We have considered the monopole charge of the tilted vortex as time dependent and through the time variation of the monopole charge we can explain the spin Hall effect of electron vortex beams. Besides, with an external magnetic field we can have a spin filter configuration.
ASRS Reports on Wake Vortex Encounters
NASA Technical Reports Server (NTRS)
Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl
2010-01-01
ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.
The permeability of the Antarctic vortex edge
NASA Technical Reports Server (NTRS)
Chen, Ping
1994-01-01
Mixing and cross-vortex mass transport along isentropic surfaces in the lower stratosphere are investigated with a 'contour advection' technique and a semi-Lagrangian transport model for the Antarctic winter of 1993 using analyzed winds from the United Kingdom Meteorological Office data assimilation system. Results from the 'contour advection' technique show that at the vortex edge there exists a potential vorticity (PV) contour that has the smallest lengthening rate. This PV contour is referred to as the 'line of separation' because it essentially separates the inner and outer vortex. The average e-folding time for the lengthening of the 'line of separation' increases monotonically with altitude, ranging from about 7 days on the 350 K isentropic surface to about 105 days on the 500 K isentropic surface. The results also suggest the existence of a transition layer around the 400 K isentropic surface, above which the vortex is nearly completely isolated from the midlatitudes and below which the vortex is less isolated. Results from a semi-Lagrangian transport model with an idealized tracer initially inside the inner vortex show that at 425 K and above virtually no tracer is transported out of the vortex during a 40-day integration starting from July 21, 1993. At 400 K and below a small amount of the tracer is transported out of the vortex while the bulk of the tracer remains confined within the inner vortex.
Spin transport in tilted electron vortex beams
Basu, Banasri; Chowdhury, Debashree
2014-12-10
In this paper we have enlightened the spin related issues of tilted Electron vortex beams. We have shown that in the skyrmionic model of electron we can have the spin Hall current considering the tilted type of electron vortex beam. We have considered the monopole charge of the tilted vortex as time dependent and through the time variation of the monopole charge we can explain the spin Hall effect of electron vortex beams. Besides, with an external magnetic field we can have a spin filter configuration.
Tree Method for Quantum Vortex Dynamics
NASA Astrophysics Data System (ADS)
Baggaley, A. W.; Barenghi, C. F.
2012-01-01
We present a numerical method to compute the evolution of vortex filaments in superfluid helium. The method is based on a tree algorithm which considerably speeds up the calculation of Biot-Savart integrals. We show that the computational cost scales as Nlog( N) rather than N 2, where N is the number of discretization points. We test the method and its properties for a variety of vortex configurations, ranging from simple vortex rings to a counterflow vortex tangle, and compare results against the Local Induction Approximation and the exact Biot-Savart law.
Vortex Line Density Fluctuations of Quantum Turbulence
NASA Astrophysics Data System (ADS)
Fujiyama, Shoji; Tsubota, Makoto
2010-02-01
We investigate vortex line density fluctuations of quantum turbulence generated by an oscillating grid in superfluid 3He- B. The scenario of quantum turbulence experimentally suggested by the Lancaster group is confirmed in the numerical simulation. The spectrum of the vortex line density fluctuations with respect to frequency obeyed a -5/3 power law, which is consistent with the experiment of the Lancaster group. Based on the argument of time scales experienced by vortex rings with different sizes and on the power spectrum, the connection between the self-similar structure of the vortex tangle and the power spectrum is discussed.
Measurements of a supersonic turbulent vortex
NASA Technical Reports Server (NTRS)
Metwally, O. M.; Settles, G. S.
1988-01-01
Mean-flow measurements of a supersonic turbulent streamwise vortex are presented. This vortex was produced by the injection of a swirling flow along the centerline of a supersonic airstream at Mach 3. Directional Mach number distributions, obtained via a five-hole flow-angularity probe, reveal vortex characteristics similar to those of the incompressible case, even though rotational Mach numbers up to 0.8 were obtained. This work is the first step of a study of the supersonic vortex breakdown phenomenon.
Flow visualizations of perpendicular blade vortex interactions
NASA Technical Reports Server (NTRS)
Rife, Michael C.; Davenport, William J.
1992-01-01
Helium bubble flow visualizations have been performed to study perpendicular interaction of a turbulent trailing vortex and a rectangular wing in the Virginia Tech Stability Tunnel. Many combinations of vortex strength, vortex-blade separation (Z(sub s)) and blade angle of attack were studied. Photographs of representative cases are presented. A range of phenomena were observed. For Z(sub s) greater than a few percent chord the vortex is deflected as it passes the blade under the influence of the local streamline curvature and its image in the blade. Initially the interaction appears to have no influence on the core. Downstream, however, the vortex core begins to diffuse and grow, presumably as a consequence of its interaction with the blade wake. The magnitude of these effects increases with reduction in Z(sub s). For Z(sub s) near zero the form of the interaction changes and becomes dependent on the vortex strength. For lower strengths the vortex appears to split into two filaments on the leading edge of the blade, one passing on the pressure and one passing on the suction side. At higher strengths the vortex bursts in the vicinity of the leading edge. In either case the core of its remnants then rapidly diffuse with distance downstream. Increase in Reynolds number did not qualitatively affect the flow apart from decreasing the amplitude of the small low-frequency wandering motions of the vortex. Changes in wing tip geometry and boundary layer trip had very little effect.
Dynamics of non Newtonian vortex rings
NASA Astrophysics Data System (ADS)
Palacios-Morales, C. A.; Barbosa, C.; Zenit, R.
2012-11-01
The dynamics of formation and evolution of non-Newtonian vortex rings generated in a piston-cylinder arrangement are studied. The ratio of the piston displacement Lm to the internal cylinder diameter D0, the piston velocity Up and fluid properties determine the vortex properties and evolution. Measurements of the 2D velocity field were obtained with a PIV technique. The vortex circulation Γ was computed considering a vortex identification scheme (Q criterion). Experiments with fluids with different rheological properties (shear thinning and viscoelastic) are presented. Our Newtonian experiments agree with previous investigations. For shear-thinning liquids, we observed that the final vortex circulation decreases with the fluid power index, n. We show that the total circulation ejected from the cylinder is reduced when the thinning property of the liquid increases; thus, the circulation confined inside the vortex ring, is reduced too. For vortex rings in a viscoelastic liquid, the formation of a `negative wake' (returning flow) and a second vortex ring with opposite whirl are observed. We show that the negative wake results from the high extension rates produced during the vortex formation.
Vortex Crystals with Chiral Stripes in Itinerant Magnets
NASA Astrophysics Data System (ADS)
Ozawa, Ryo; Hayami, Satoru; Barros, Kipton; Chern, Gia-Wei; Motome, Yukitoshi; Batista, Cristian D.
Noncoplanar spin textures in itinerant magnets are generating increasing interest because of the associated spin Berry phase, which induces a tremendous effective magnetic field on the itinerant electrons. Such noncoplanar spin textures appear frequently in itinerant magnets, even with vanishingly small spin-orbit coupling. We explore a generic condition for noncoplanar spin ordering, with a focus on ``frustration'' in itinerant magnets, that is characterized by multiple global maxima in the magnetic susceptibility. In a simple square Kondo lattice model, we find that a noncoplanar vortex-antivortex crystal with a one-dimensional modulation of spin scalar chirality becomes stable in a wide range of electron filling fraction. The unexpected result is obtained by careful analyses of higher-order terms in the perturbative expansion in terms of the Kondo exchange coupling and the degree of noncoplanarity, as well as numerical simulation based on the Langevin and stochastic Landau-Lifshitz-Gilbert dynamics with the kernel polynomial method.
NASA Astrophysics Data System (ADS)
Bergner, Georg; Catterall, Simon
2016-08-01
We discuss the motivations, difficulties and progress in the study of supersymmetric lattice gauge theories focusing in particular on 𝒩 = 1 and 𝒩 = 4 super-Yang-Mills in four dimensions. Brief reviews of the corresponding lattice formalisms are given and current results are presented and discussed. We conclude with a summary of the main aspects of current work and prospects for the future.
Laterally closed lattice homomorphisms
NASA Astrophysics Data System (ADS)
Toumi, Mohamed Ali; Toumi, Nedra
2006-12-01
Let A and B be two Archimedean vector lattices and let be a lattice homomorphism. We call that T is laterally closed if T(D) is a maximal orthogonal system in the band generated by T(A) in B, for each maximal orthogonal system D of A. In this paper we prove that any laterally closed lattice homomorphism T of an Archimedean vector lattice A with universal completion Au into a universally complete vector lattice B can be extended to a lattice homomorphism of Au into B, which is an improvement of a result of M. Duhoux and M. Meyer [M. Duhoux and M. Meyer, Extended orthomorphisms and lateral completion of Archimedean Riesz spaces, Ann. Soc. Sci. Bruxelles 98 (1984) 3-18], who established it for the order continuous lattice homomorphism case. Moreover, if in addition Au and B are with point separating order duals (Au)' and B' respectively, then the laterally closedness property becomes a necessary and sufficient condition for any lattice homomorphism to have a similar extension to the whole Au. As an application, we give a new representation theorem for laterally closed d-algebras from which we infer the existence of d-algebra multiplications on the universal completions of d-algebras.
Investigation of the Vortex Tab. M.S. Thesis
NASA Technical Reports Server (NTRS)
Hoffler, K. D.
1985-01-01
An investigation was made into the drag reduction capability of vortex tabs on delta wing vortex flaps. The vortex tab is an up-deflected leading edge portion of the vortex flap. Tab deflection augments vortex suction on the flap, thus improving its thrust, but the tab itself is drag producing. Whether a net improvement in the drag reduction can be obtained with vortex tabs, in comparison with plane vortex flaps of the same total area, was the objective of this investigation. Wind tunnel tests were conducted on two models, and analytical studies were performed on one of them using a free vortex sheet theory.
Recent Laboratory and Numerical Trailing Vortex Studies
NASA Technical Reports Server (NTRS)
Delisi, Donald P.; Greene, George C.; Robins, Robert E.; Singh, Raminder
1996-01-01
Results from two laboratory studies and two numerical studies are presented. In the first laboratory study, measurements of the strength of vortices from a three-dimensional (3-D) model wing are presented. The measurements follow the vortices as they evolve in time from a two-dimensional (2-D) line vortex pair to the development and migration of 3-D vortex rings. It is shown that the resulting vortex rings can contain up to 40 percent of the initial vortex circulation. Thus, the formation of vortex rings may not necessarily signal the end of the wake hazard to following aircraft. In the second laboratory study, we present the results of an experiment which shows how the spanwise drag distribution affects wake-vortex evolution. In this experiment, we modified the spanwise drag distribution on a model wing while keeping the total lift and drag constant. The results show that adding drag on or near the centerline of the wing has a larger effect than adding drag at or near the wingtips. These measurements complement the results of NASA studies in the 1970s. In the first numerical study, results of 3-D numerical calculations are presented which show that the vortex Reynolds number has a significant influence on the evolution and migration of wake vortices. When the Reynolds number is large, 3-D vortex rings evolve from the initially 2-D line vortex pairs. These vortex rings then migrate vertically. When the Reynolds number is lower, the transition of vorticity from 2-D to 3-D is delayed. When the Reynolds number is very low, the vortices never transition to 3-D, and the vertical migration is significantly reduced. It is suggested that this effect may have been important in previous laboratory wake-evolution studies. A second numerical study shows the influence that vertical wind shear can have on trailing vortex evolution.
Rotating hot-wire investigation of the vortex responsible for blade-vortex interaction noise
NASA Technical Reports Server (NTRS)
Fontana, Richard Remo
1988-01-01
This distribution of the circumferential velocity of the vortex responsible for blade-vortex interaction noise was measured using a rotating hot-wire rake synchronously meshed with a model helicopter rotor at the blade passage frequency. Simultaneous far-field acoustic data and blade differential pressure measurements were obtained. Results show that the shape of the measured far-field acoustic blade-vortex interaction signature depends on the blade-vortex interaction geometry. The experimental results are compared with the Widnall-Wolf model for blade-vortex interaction noise.
BERG,J.S.; RUGGIERO, A.; MACHIDA, S.; KOSCIELNIAK, S.
2007-06-25
EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non-scaling fixed field alternating gradient accelerator (FFAG). This paper describes the design of the EMMA lattice. We begin with a summary of the experimental goals that impact the lattice design, and then outline what motivated the choice for the basic lattice parameters, such as the type of cells, the number of cells, and the RF frequency. We next list the different configurations that we wish to operate the machine in so as to accomplish our experimental goals. Finally, we enumerate the detailed lattice parameters, showing how these parameters result from the various lattice configurations.
Measurement-based quantum lattice gas model of fluid dynamics in 2+1 dimensions.
Micci, Michael M; Yepez, Jeffrey
2015-09-01
Presented are quantum simulation results using a measurement-based quantum lattice gas algorithm for Navier-Stokes fluid dynamics in 2+1 dimensions. Numerical prediction of the kinematic viscosity was measured by the decay rate of an initial sinusoidal flow profile. Due to local quantum entanglement in the quantum lattice gas, the minimum kinematic viscosity in the measurement-based quantum lattice gas is lower than achievable in a classical lattice gas. The numerically predicted viscosities precisely match the theoretical predictions obtained with a mean field approximation. Uniform flow profile with double shear layers, on a 16K×8K lattice, leads to the Kelvin-Helmholtz instability, breaking up the shear layer into pairs of counter-rotating vortices that eventually merge via vortex fusion and dissipate because of the nonzero shear viscosity.
Vortex metrology using Fourier analysis techniques: vortex networks correlation fringes.
Angel-Toro, Luciano; Sierra-Sosa, Daniel; Tebaldi, Myrian; Bolognini, Néstor
2012-10-20
In this work, we introduce an alternative method of analysis in vortex metrology based on the application of the Fourier optics techniques. The first part of the procedure is conducted as is usual in vortex metrology for uniform in-plane displacement determination. On the basis of two recorded intensity speckled distributions, corresponding to two states of a diffuser coherently illuminated, we numerically generate an analytical signal from each recorded intensity pattern by using a version of the Riesz integral transform. Then, from each analytical signal, a two-dimensional pseudophase map is generated in which the vortices are located and characterized in terms of their topological charges and their core's structural properties. The second part of the procedure allows obtaining Young's interference fringes when Fourier transforming the light passing through a diffracting mask with multiple apertures at the locations of the homologous vortices. In fact, we use the Fourier transform as a mathematical operation to compute the far-field diffraction intensity pattern corresponding to the multiaperture set. Each aperture from the set is associated with a rectangular hole that coincides both in shape and size with a pixel from recorded images. We show that the fringe analysis can be conducted as in speckle photography in an extended range of displacement measurements. Effects related with speckled decorrelation are also considered. Our experimental results agree with those of speckle photography in the range in which both techniques are applicable.
The effect of tip vortex structure on helicopter noise due to blade/vortex interaction
NASA Technical Reports Server (NTRS)
Wolf, T. L.; Widnall, S. E.
1978-01-01
A potential cause of helicopter impulsive noise, commonly called blade slap, is the unsteady lift fluctuation on a rotor blade due to interaction with the vortex trailed from another blade. The relationship between vortex structure and the intensity of the acoustic signal is investigated. The analysis is based on a theoretical model for blade/vortex interaction. Unsteady lift on the blades due to blade/vortex interaction is calculated using linear unsteady aerodynamic theory, and expressions are derived for the directivity, frequency spectrum, and transient signal of the radiated noise. An inviscid rollup model is used to calculate the velocity profile in the trailing vortex from the spanwise distribution of blade tip loading. A few cases of tip loading are investigated, and numerical results are presented for the unsteady lift and acoustic signal due to blade/vortex interaction. The intensity of the acoustic signal is shown to be quite sensitive to changes in tip vortex structure.
Delaying vortex breakdown by waves
NASA Astrophysics Data System (ADS)
Yao, M. F.; Jiang, L. B.; Wu, J. Z.; Ma, H. Y.; Pan, J. Y.
1989-03-01
The effect of spiral waves on delaying vortex breakdown in a tube is studied experimentally and theoretically. When a harmonic oscillation was imposed on one of guiding vanes in the tube, the breakdown was observed to be postponed appreciately. According to the generalized Lagrangian mean theory, proper forcing spiral waves may produce an additional streaming momentum, of which the effect is favorable and similar to an axial suction at downstream end. The delayed breakdown position is further predicted by using nonlinear wave theory. Qualitative agreement between theory and experiment is obtained, and experimental comparison of the effects due to forcing spiral wave and axial suction is made.
Ergoregion instability: The hydrodynamic vortex
NASA Astrophysics Data System (ADS)
Oliveira, Leandro A.; Cardoso, Vitor; Crispino, Luís C. B.
2014-06-01
Four-dimensional, asymptotically flat spacetimes with an ergoregion but no horizon have been shown to be linearly unstable against a superradiant-triggered mechanism. This result has wide implications in the search for astrophysically viable alternatives to black holes, but also in the understanding of black holes and Hawking evaporation. Here we investigate this instability in detail for a particular setup that can be realized in the laboratory: the hydrodynamic vortex, an effective geometry for sound waves, with ergoregion and without an event horizon.
Spectral stability of Taylor's vortex array
NASA Technical Reports Server (NTRS)
Lin, S. P.; Tobak, M.
1986-01-01
In a global sense it is shown that the two-dimensional Taylor vortex array, an exact solution of the Navier-Stokes equation, is absolutely and monotonically stable with respect to infinitesimal disturbances of all discrete frequencies as long as the viscosity is positive. It is suggested that the Taylor vortex array may also be stable with respect to finite amplitude disturbances.
Shadowgraphs Of Helicopter-Rotor-Tip Vortexes
NASA Technical Reports Server (NTRS)
Parthasarathy, Shakkottai P.; Cho, Young I.; Back, Lloyd H.
1988-01-01
Optical apparatus produces full-scale or larger shadowgraph of tip vortexes of helicopter rotor. Stroboscope projects shadow image of helicopter rotor on large, square screen. Commercial, highly reflecting projection screen used; simply projecting image on white wall does not yield enough light for photographing vortexes with standard 35-mm camera. Apparatus adapts to use in large wind tunnels.
The modelling of symmetric airfoil vortex generators
NASA Technical Reports Server (NTRS)
Reichert, B. A.; Wendt, B. J.
1996-01-01
An experimental study is conducted to determine the dependence of vortex generator geometry and impinging flow conditions on shed vortex circulation and crossplane peak vorticity for one type of vortex generator. The vortex generator is a symmetric airfoil having a NACA 0012 cross-sectional profile. The geometry and flow parameters varied include angle-of-attack alfa, chordlength c, span h, and Mach number M. The vortex generators are mounted either in isolation or in a symmetric counter-rotating array configuration on the inside surface of a straight pipe. The turbulent boundary layer thickness to pipe radius ratio is delta/R = 0. 17. Circulation and peak vorticity data are derived from crossplane velocity measurements conducted at or about 1 chord downstream of the vortex generator trailing edge. Shed vortex circulation is observed to be proportional to M, alfa, and h/delta. With these parameters held constant, circulation is observed to fall off in monotonic fashion with increasing airfoil aspect ratio AR. Shed vortex peak vorticity is also observed to be proportional to M, alfa, and h/delta. Unlike circulation, however, peak vorticity is observed to increase with increasing aspect ratio, reaching a peak value at AR approx. 2.0 before falling off.
Obstacle-induced spiral vortex breakdown
NASA Astrophysics Data System (ADS)
Pasche, Simon; Gallaire, François; Dreyer, Matthieu; Farhat, Mohamed
2014-08-01
An experimental investigation on vortex breakdown dynamics is performed. An adverse pressure gradient is created along the axis of a wing-tip vortex by introducing a sphere downstream of an elliptical hydrofoil. The instrumentation involves high-speed visualizations with air bubbles used as tracers and 2D Laser Doppler Velocimeter (LDV). Two key parameters are identified and varied to control the onset of vortex breakdown: the swirl number, defined as the maximum azimuthal velocity divided by the free-stream velocity, and the adverse pressure gradient. They were controlled through the incidence angle of the elliptical hydrofoil, the free-stream velocity and the sphere diameter. A single helical breakdown of the vortex was systematically observed over a wide range of experimental parameters. The helical breakdown coiled around the sphere in the direction opposite to the vortex but rotated along the vortex direction. We have observed that the location of vortex breakdown moved upstream as the swirl number or the sphere diameter was increased. LDV measurements were corrected using a reconstruction procedure taking into account the so-called vortex wandering and the size of the LDV measurement volume. This allows us to investigate the spatio-temporal linear stability properties of the flow and demonstrate that the flow transition from columnar to single helical shape is due to a transition from convective to absolute instability.
Vortex dynamics in thin elliptic ferromagnetic nanodisks
NASA Astrophysics Data System (ADS)
Wysin, G. M.
2015-10-01
Vortex gyrotropic motion in thin ferromagnetic nanodisks of elliptical shape is described here for a pure vortex state and for a situation with thermal fluctuations. The system is analyzed using numerical simulations of the Landau-Lifshitz-Gilbert (LLG) equations, including the demagnetization field calculated with a Green's function approach for thin film problems. At finite temperature the thermalized dynamics is found using a second order Heun algorithm for a magnetic Langevin equation based on the LLG equations. The vortex state is stable only within a limited range of ellipticity, outside of which a quasi-single-domain becomes the preferred minimum energy state. A vortex is found to move in an elliptical potential, whose force constants along the principal axes are determined numerically. The eccentricity of vortex motion is directly related to the force constants. Elliptical vortex motion is produced spontaneously by thermal fluctuations. The vortex position and velocity distributions in thermal equilibrium are Boltzmann distributions. The results show that vortex motion in elliptical disks can be described by a Thiele equation.
Flight tests of vortex-attenuating splines
NASA Technical Reports Server (NTRS)
Patterson, J. C., Jr.
1974-01-01
Visual data on formation and motion of lift-induced wingtip vortex were obtained by stationary, airflow visualization method. Visual data indicated that vortex cannot be eliminated by merely reshaping wingtip. Configuration change will likely have only small effect on far-field flow.
Vortex avalanches in a type II superconductor
Behnia, K.; Capan, C.; Mailly, D.; Etienne, B.
1999-12-01
The authors report on a study of the spatiotemporal variation of magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. A sizable fraction of the increase in the local vortex population occurs in abrupt jumps. They compare the size distribution of these avalanches with the predictions of self-organized-criticality models for vortex dynamics.
An investigation of the vortex method
Pryor, D.W. Jr.
1994-05-01
The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of three dimensional slightly viscous flow with boundaries. This section gives an introduction to the fundamentals of the vortex method. This is done in order to give a basic impression of the previous work and its line of development, as well as develop some notation and concepts which will be used later. The purpose here is not to give a full review of vortex methods or the contributions made by all the researchers in the field. Please refer to the excellent review papers in Sethian and Gustafson, chapters 1 Sethian, 2 Hald, 3 Sethian, 8 Chorin provide a solid introduction to vortex methods, including convergence theory, application in two dimensions and connection to statistical mechanics and polymers. Much of the information in this review is taken from those chapters, Chorin and Marsden and Batchelor, the chapters are also useful for their extensive bibliographies.
Vortex motion on surfaces of small curvature
Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.
2013-12-15
We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.
Supersonic shock wave/vortex interaction
NASA Technical Reports Server (NTRS)
Settles, G. S.; Cattafesta, L.
1993-01-01
Although shock wave/vortex interaction is a basic and important fluid dynamics problem, very little research has been conducted on this topic. Therefore, a detailed experimental study of the interaction between a supersonic streamwise turbulent vortex and a shock wave was carried out at the Penn State Gas Dynamics Laboratory. A vortex is produced by replaceable swirl vanes located upstream of the throat of various converging-diverging nozzles. The supersonic vortex is then injected into either a coflowing supersonic stream or ambient air. The structure of the isolated vortex is investigated in a supersonic wind tunnel using miniature, fast-response, five-hole and total temperature probes and in a free jet using laser Doppler velocimetry. The cases tested have unit Reynolds numbers in excess of 25 million per meter, axial Mach numbers ranging from 2.5 to 4.0, and peak tangential Mach numbers from 0 (i.e., a pure jet) to about 0.7. The results show that the typical supersonic wake-like vortex consists of a non-isentropic, rotational core, where the reduced circulation distribution is self similar, and an outer isentropic, irrotational region. The vortex core is also a region of significant turbulent fluctuations. Radial profiles of turbulent kinetic energy and axial-tangential Reynolds stress are presented. The interactions between the vortex and both oblique and normal shock waves are investigated using nonintrusive optical diagnostics (i.e. schlieren, planar laser scattering, and laser Doppler velocimetry). Of the various types, two Mach 2.5 overexpanded-nozzle Mach disc interactions are examined in detail. Below a certain vortex strength, a 'weak' interaction exists in which the normal shock is perturbed locally into an unsteady 'bubble' shock near the vortex axis, but vortex breakdown (i.e., a stagnation point) does not occur. For stronger vortices, a random unsteady 'strong' interaction results that causes vortex breakdown. The vortex core reforms downstream of
Origin of reversed vortex ratchet motion.
Gillijns, W; Silhanek, A V; Moshchalkov, V V; Reichhardt, C J Olson; Reichhardt, C
2007-12-14
We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also essentially depends on the ratio between the characteristic interaction distance and the period of the asymmetric pinning potential. We study four samples with different periods d of the asymmetric potential. For large d the dc voltage V(dc) recorded under a ac excitation indicates that the average vortex drift is from bigger to smaller dots for all explored positive fields. As d is reduced, a series of sign reversals in the dc response are observed as a function of field. We show that the number of sign reversals increases as d decreases. These findings are in agreement with recent computer simulations and illustrate the relevance of the different characteristic lengths for the vortex rectification effects.
Calculation of vortex flows on complex configurations
NASA Technical Reports Server (NTRS)
Maskew, B.; Rao, B. M.
1982-01-01
The calculation of aerodynamic characteristics of complex configurations having strongly coupled vortex flows is a non-linear problem requiring iterative solution techniques. This paper discusses the use of a low-order panel method as a means of obtaining practical solutions to such problems. The panel method is based on piecewise constant source and doublet quadrilateral panels and uses the internal Dirichlet boundary condition of zero perturbation potential. The problems of predicting vortex/surface interaction and vortex separation are discussed. Some example calculations are included but further test cases have yet to be carried out, in particular for comparisons with experimental data. The problem of convergence on the iterative calculation for the shape of the free vortex sheet is addressed and a preprocessor routine, based on an unsteady, two-dimensional version of the panel method, is put forward as a cost-effective way of generating an initial vortex structure for use as a starting solution for general configurations.
Phase structure, magnetic monopoles, and vortices in the lattice Abelian Higgs model
Ranft, J.; Kripfganz, J.; Ranft, G.
1983-07-15
We present Monte Carlo calculations of lattice Abelian Higgs models in four dimensions and with charges of the Higgs particles equal to q = 1, 2, and 6. The phase transitions are studied in the plane of the two coupling constants considering separately average plaquette and average link expectation values. The density of topological excitations is studied. In the confinement phase we find finite densities of magnetic-monopole currents, electric currents, and vortex currents. The magnetic-monopole currents vanish exponentially in the Coulomb phase. The density of electric currents and vortex currents is finite in the Coulomb phase and vanishes exponentially in the Higgs phase.
Effect of point-like disorder on the vortex phase diagram in Bi2Sr2CaCu2O8-δ in oblique field
NASA Astrophysics Data System (ADS)
Konczykowski, M.; van der Beek, C. J.; Mosser, V.; Koshelev, A. E.; Li, M.; Kes, P. H.
2010-12-01
The phase diagram of vortex matter in the layered superconductor Bi2Sr2CaCu2O8-δ exposed to a magnetic field oblique to the crystalline c-axis contains two first order transition (FOT) lines [1]. The first, HFOTm, separates the vortex solid from the vortex liquid, the second, HFOTct, separates the combined lattice state in the vortex solid from a tilted lattice state. The angular dependence of HFOTm in the tilted lattice region follows the anisotropic Ginzburg-Landau model [2], allowing for the determination of the anisotropy factor γeff and the contribution of magnetic coupling to the mutual interaction of “pancake” vortices in the crossed lattice limit. The later parameter is directly related to the in-plane penetration depth λab. We investigate the evolution of the phase diagram of Bi2Sr2CaCu2O8-δ in oblique fields with point-like disorder, introduced by irradiation with 2.3 MeV electrons. Apart from the depression of Tc, point-like disorder induces an increase of γeff and a depression of the superfluid density.
Chemical doping effect in the LaRu3Si2 superconductor with a kagome lattice
NASA Astrophysics Data System (ADS)
Li, Baoxuan; Li, Sheng; Wen, Hai-Hu
2016-09-01
LaRu3Si2 is a superconductor with a kagome lattice and transition temperature of 7 K. By doping different rare-earth and transition-metal elements on the La and Ru sites, the evolution of superconductivity has been extensively investigated. It is found that, except for doping Fe to Ru sites, all other dopants with rare-earth (Y, Lu, and Ce) or transition metals (Ni, Cr, and Cu) seem to suppress superconducting transition temperature in LaRu3Si2 very slowly. The quick suppression of superconductivity by Fe doping can be described by the Abrikosov-Gorkov relation. By fitting and analyzing the magnetic susceptibility data under a high magnetic field with the Curie-Weiss law, we find that the effective magnetic moments for Ni and Cr doped samples are very small, indicating that these ions actually do not behave like strong magnetic scattering centers as Fe ions do in the present environment. Our experiments on systematically doped samples and related analysis indicate that the superconducting gap in LaRu3Si2 has no sign change.
Courant, E.D.; Garren, A.A.
1985-10-01
A realistic, distributed interaction region (IR) lattice has been designed that includes new components discussed in the June 1985 lattice workshop. Unlike the test lattices, the lattice presented here includes utility straights and the mechanism for crossing the beams in the experimental straights. Moreover, both the phase trombones and the dispersion suppressors contain the same bending as the normal cells. Vertically separated beams and 6 Tesla, 1-in-1 magnets are assumed. Since the cells are 200 meters long, and have 60 degree phase advance, this lattice has been named RLD1, in analogy with the corresponding test lattice, TLD1. The quadrupole gradient is 136 tesla/meter in the cells, and has similar values in other quadrupoles except in those in the IR`s, where the maximum gradient is 245 tesla/meter. RLD1 has distributed IR`s; however, clustered realistic lattices can easily be assembled from the same components, as was recently done in a version that utilizes the same type of experimental and utility straights as those of RLD1.
Superalloy Lattice Block Structures
NASA Technical Reports Server (NTRS)
Whittenberger, J. D.; Nathal, M. V.; Hebsur, M. G.; Kraus, D. L.
2003-01-01
In their simplest form, lattice block panels are produced by direct casting and result in lightweight, fully triangulated truss-like configurations which provide strength and stiffness [2]. The earliest realizations of lattice block were made from A1 and steels, primarily under funding from the US Navy [3]. This work also showed that the mechanical efficiency (eg., specific stiffness) of lattice block structures approached that of honeycomb structures [2]. The lattice architectures are also less anisotropic, and the investment casting route should provide a large advantage in cost and temperature capability over honeycombs which are limited to alloys that can be processed into foils. Based on this early work, a program was initiated to determine the feasibility of extending the high temperature superalloy lattice block [3]. The objective of this effort was to provide an alternative to intermetallics and composites in achieving a lightweight high temperature structure without sacrificing the damage tolerance and moderate cost inherent in superalloys. To establish the feasibility of the superalloy lattice block concept, work was performed in conjunction with JAMCORP, Inc. Billerica, MA, to produce a number of lattice block panels from both IN71 8 and Mar-M247.
Closer look at the low-frequency dynamics of vortex matter using scanning susceptibility microscopy
NASA Astrophysics Data System (ADS)
Raes, B.; de Souza Silva, C. C.; Silhanek, A. V.; Cabral, L. R. E.; Moshchalkov, V. V.; Van de Vondel, J.
2014-10-01
Using scanning susceptibility microscopy, we shed light on the dynamics of individual superconducting vortices and examine the hypotheses of the phenomenological models traditionally used to explain the macroscopic ac electromagnetic properties of superconductors. The measurements, carried out on a 2H-NbSe2 single crystal at relatively high temperature (T =6.8 K), show a linear amplitude dependence of the global ac susceptibility for excitation amplitudes between 0.3 and 2.6 Oe. We observe that the low amplitude response, typically attributed to the oscillation of vortices in a potential well defined by a single, relaxing, Labusch constant, actually corresponds to strongly nonuniform vortex shaking. This is particularly pronounced in the field-cooled disordered phase, which undergoes a dynamic reorganization above 0.8 Oe as evidenced by the healing of lattice defects and a more uniform oscillation of vortices. These observations are corroborated by molecular dynamics simulations when choosing the microscopic input parameters from the experiments. The theoretical simulations allow us to reconstruct the vortex trajectories, providing deeper insight into the thermally induced hopping dynamics and the vortex lattice reordering.
NASA Astrophysics Data System (ADS)
Radzihovsky, Leo
2006-03-01
I will discuss results on a thermal and a transverse magnetic field response of a vortex line array confined to a plane with a dilute concentration of columnar pins. As a function of temperature, for a magnetic field aligned with defects this system exhibits a one-dimensional analog of a roughening transition, with a low-temperature ``smooth'' phase corresponding to a vortex array pinned by the defects, and a high-temperature ``rough'' phase in which at long scales thermal fluctuations effectively average away pinning by the defects. In the low-T pinned phase, the vortex lattice tilt response to a transverse magnetic field proceeds via a soliton proliferation ``transition'', governed by an integrable sine-Hilbert equation. Combining the aforementioned roughenning transitition with this commensurate-incommensurate transition, I map out the transverse-field---temperature phase diagram for this system.
PREFACE: Special section on vortex rings Special section on vortex rings
NASA Astrophysics Data System (ADS)
Fukumoto, Yasuhide
2009-10-01
This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill
NASA Technical Reports Server (NTRS)
Grantz, A. C.
1984-01-01
The low speed lateral/directional characteristics of a generic 74 degree delta wing body configuration employing the latest generation, gothic planform vortex flaps was determined. Longitudinal effects are also presented. The data are compared with theoretical estimates from VORSTAB, an extension of the Quasi vortex lattice Method of Lan which empirically accounts for vortex breakdown effects in the calculation of longitudinal and lateral/directional aerodynamic characteristics. It is indicated that leading edge deflections of 30 and 40 degrees reduce the magnitude of the wing effective dihedral relative to the baseline for a specified angle of attack or lift coefficient. For angles of attack greater than 15 degrees, these flap deflections reduce the configuration directional stability despite improved vertical tail effectiveness. It is shown that asymmetric leading edge deflections are inferior to conventional ailerons in generating rolling moments. VORSTAB calculations provide coarse lateral/directional estimates at low to moderate angles of attack. The theory does not account for vortex flow induced, vertical tail effects.
Modeling of Wake-vortex Aircraft Encounters. Appendix B
NASA Technical Reports Server (NTRS)
Smith, Sonya T.
1999-01-01
There are more people passing through the world's airports today than at any other time in history. With this increase in civil transport, airports are becoming capacity limited. In order to increase capacity and thus meet the demands of the flying public, the number of runways and number of flights per runway must be increased. In response to the demand, the National Aeronautics and Space Administration (NASA), in conjunction with the Federal Aviation Administration (FAA), airport operators, and the airline industry are taking steps to increase airport capacity without jeopardizing safety. Increasing the production per runway increases the likelihood that an aircraft will encounter the trailing wake-vortex of another aircraft. The hazard of a wake-vortex encounter is that heavy load aircraft can produce high intensity wake turbulence, through the development of its wing-tip vortices. A smaller aircraft following in the wake of the heavy load aircraft will experience redistribution of its aerodynamic load. This creates a safety hazard for the smaller aircraft. Understanding this load redistribution is of great importance, particularly during landing and take-off. In this research wake-vortex effects on an encountering 10% scale model of the B737-100 aircraft are modeled using both strip theory and vortex-lattice modeling methods. The models are then compared to wind tunnel data that was taken in the 30ft x 60ft wind tunnel at NASA Langley Research Center (LaRC). Comparisons are made to determine if the models will have acceptable accuracy when parts of the geometry are removed, such as the horizontal stabilizer and the vertical tail. A sensitivity analysis was also performed to observe how accurately the models could match the experimental data if there was a 10% error in the circulation strength. It was determined that both models show accurate results when the wing, horizontal stabilizer, and vertical tail were a part of the geometry. When the horizontal
Vortex bursting and tracer transport of a counter-rotating vortex pair
NASA Astrophysics Data System (ADS)
Misaka, T.; Holzäpfel, F.; Hennemann, I.; Gerz, T.; Manhart, M.; Schwertfirm, F.
2012-02-01
Large-eddy simulations of a coherent counter-rotating vortex pair in different environments are performed. The environmental background is characterized by varying turbulence intensities and stable temperature stratifications. Turbulent exchange processes between the vortices, the vortex oval, and the environment, as well as the material redistribution processes along the vortex tubes are investigated employing passive tracers that are superimposed to the initial vortex flow field. It is revealed that the vortex bursting phenomenon, known from photos of aircraft contrails or smoke visualization, is caused by collisions of secondary vortical structures traveling along the vortex tube which expel material from the vortex but do not result in a sudden decay of circulation or an abrupt change of vortex core structure. In neutrally stratified and weakly turbulent conditions, vortex reconnection triggers traveling helical vorticity structures which is followed by their collision. A long-lived vortex ring links once again establishing stable double rings. Key phenomena observed in the simulations are supported by photographs of contrails. The vertical and lateral extents of the detrained passive tracer strongly depend on environmental conditions where the sensitivity of detrainment rates on initial tracer distributions appears to be low.
Rotor Wake Vortex Definition Using 3C-PIV Measurements: Corrected for Vortex Orientation
NASA Technical Reports Server (NTRS)
Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughues Richard; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee
2003-01-01
Three-component (3-C) particle image velocimetry (PIV) measurements, within the wake across a rotor disk plane, are used to determine wake vortex definitions important for BVI (Blade Vortex Interaction) and broadband noise prediction. This study is part of the HART II test program conducted using a 40 percent scale BO-105 helicopter main rotor in the German-Dutch Wind Tunnel (DNW). In this paper, measurements are presented of the wake vortex field over the advancing side of the rotor operating at a typical descent landing condition. The orientations of the vortex (tube) axes are found to have non-zero tilt angles with respect to the chosen PIV measurement cut planes, often on the order of 45 degrees. Methods for determining the orientation of the vortex axis and reorienting the measured PIV velocity maps (by rotation/projection) are presented. One method utilizes the vortex core axial velocity component, the other utilizes the swirl velocity components. Key vortex parameters such as vortex core size, strength, and core velocity distribution characteristics are determined from the reoriented PIV velocity maps. The results are compared with those determined from velocity maps that are not corrected for orientation. Knowledge of magnitudes and directions of the vortex axial and swirl velocity components as a function of streamwise location provide a basis for insight into the vortex evolution.
Superalloy Lattice Block Structures
NASA Technical Reports Server (NTRS)
Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.
2004-01-01
Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.
NASA Astrophysics Data System (ADS)
Weidner, Carrie; Yu, Hoon; Anderson, Dana
2016-05-01
In this work, we report on progress towards performing interferometry using atoms trapped in an optical lattice. That is, we start with atoms in the ground state of an optical lattice potential V(x) =V0cos [ 2 kx + ϕ(t) ] , and by a prescribed phase function ϕ(t) , transform from one atomic wavefunction to another. In this way, we implement the standard interferometric sequence of beam splitting, propagation, reflection, reverse propagation, and recombination. Through the use of optimal control techniques, we have computationally demonstrated a scalable accelerometer that provides information on the sign of the applied acceleration. Extension of this idea to a two-dimensional shaken-lattice-based gyroscope is discussed. In addition, we report on the experimental implementation of the shaken lattice system.
ORGINOS,K.
2003-01-07
I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.
NASA Astrophysics Data System (ADS)
Yan, Weigen; Zhang, Zuhe
2009-04-01
The energy of a simple graph G arising in chemical physics, denoted by E(G), is defined as the sum of the absolute values of eigenvalues of G. As the dimer problem and spanning trees problem in statistical physics, in this paper we propose the energy per vertex problem for lattice systems. In general for a type of lattice in statistical physics, to compute the entropy constant with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are different tasks with different hardness and may have different solutions. We show that the energy per vertex of plane lattices is independent of the toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions. In particular, the asymptotic formulae of energies of the triangular, 33.42, and hexagonal lattices with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are obtained explicitly.
Composite Fermion Theory for Bosonic Quantum Hall States on Lattices
NASA Astrophysics Data System (ADS)
Möller, G.; Cooper, N. R.
2009-09-01
We study the ground states of the Bose-Hubbard model in a uniform magnetic field, motivated by the physics of cold atomic gases on lattices at high vortex density. Mapping the bosons to composite fermions (CF) leads to the prediction of quantum Hall fluids that have no counterpart in the continuum. We construct trial states for these phases and test numerically the predictions of the CF model. We establish the existence of strongly correlated phases beyond those in the continuum limit and provide evidence for a wider scope of the composite fermion approach beyond its application to the lowest Landau level.
Automated Lattice Perturbation Theory
Monahan, Christopher
2014-11-01
I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.
Nonlinear ion acoustic waves scattered by vortexes
NASA Astrophysics Data System (ADS)
Ohno, Yuji; Yoshida, Zensho
2016-09-01
The Kadomtsev-Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here, we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes 'scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are 'ambient' because they do not receive reciprocal reactions from the waves (i.e., the vortex equation is independent of the wave fields). This model describes a minimal departure from the integrable KP system. By the Painlevé test, we delineate how the vorticity term violates integrability, bringing about an essential three-dimensionality to the solutions. By numerical simulation, we show how the solitons are scattered by vortexes and become chaotic.
Phenomena, dynamics and instabilities of vortex pairs
NASA Astrophysics Data System (ADS)
Williamson, C. H. K.; Leweke, T.; Asselin, D. J.; Harris, D. M.
2014-12-01
Our motivation for studying the dynamics of vortex pairs stems initially from an interest in the trailing wake vortices from aircraft and the dynamics of longitudinal vortices close to a vehicle surface. However, our motivation also comes from the fact that vortex-vortex interactions and vortex-wall interactions are fundamental to many turbulent flows. The intent of the paper is to present an overview of some of our recent work concerning the formation and structure of counter-rotating vortex pairs. We are interested in the long-wave and short-wave three-dimensional instabilities that evolve for an isolated vortex pair, but also we would like to know how vortex pairs interact with a wall, including both two-dimensional interactions, and also the influence of the surface on the three-dimensional instabilities. The emphasis of this presentation is on physical mechanisms by which vortices interact with each other and with surfaces, principally from an experimental approach, but also coupled with analytical studies.
Dynamics of Isolated Tip Vortex Cavitation
NASA Astrophysics Data System (ADS)
Pennings, Pepijn; Bosschers, Johan; van Terwisga, Tom
2014-11-01
Performance of ship propellers and comfort levels in the surroundings are limited by various forms of cavitation. Amongst these forms tip vortex cavitation is one of the first appearing forms and is expected to be mainly responsible for the emission of broadband pressure fluctuations typically occurring between the 4th to the 7th blade passing frequency (approx. 40--70 Hz). These radiated pressure pulses are likely to excite parts of the hull structure resulting in a design compromise between efficiency and comfort. Insight is needed in the mechanism of acoustic emission from the oscillations by a tip vortex cavity. In the current experimental study the tip vortex cavity from a blade with an elliptic planform and sections based on NACA 662 - 415 with meanline a = 0 . 8 is observed using high speed shadowgraphy in combination with blade force and acoustic measurements. An analytic model describing three main cavity deformation modes is verified and used to explain the origin of a cavity eigenfrequency or ``vortex singing'' phenomenon observed by Maines and Arndt (1997) on the tip vortex cavity originating from the same blade. As no hydrodynamic sound originating from the tip vortex cavity was observed it is posed that a tip flow instability is essential for ``vortex singing.'' This research was funded by the Lloyd's Register Foundation as part of the International Institute for Cavitation Research.
Topology of vortex-wing interaction
NASA Astrophysics Data System (ADS)
McKenna, C.; Rockwell, D.
2016-10-01
A trailing vortex incident upon a wing can generate different modes of vortex-wing interaction. These modes, which may involve either enhancement or suppression of the vortex generated at the tip of the wing, are classified on the basis of the present experiments together with computations at the Air Force Research Laboratory. Occurrence of a given mode of interaction is predominantly determined by the dimensionless location of the incident vortex relative to the tip of the wing and is relatively insensitive to the Reynolds number and dimensionless circulation of the incident vortex. The genesis of the basic interaction modes is clarified using streamline topology with associated critical points that show compatibility between complex streamline patterns in the vicinity of the tip of the wing. Whereas formation of an enhanced tip vortex involves a region of large upwash in conjunction with localized flow separation, complete suppression of the tip vortex is associated with a small-scale separation-reattachment bubble bounded by downwash at the wing tip.
Vortex Ring Interaction with a Heated Screen
NASA Astrophysics Data System (ADS)
Smith, Jason; Krueger, Paul S.
2008-11-01
Previous examinations of vortex rings impinging on porous screens has shown the reformation of the vortex ring with a lower velocity after passing through the screen, the creation of secondary vortices, and mixing. A heated screen could, in principle, alter the vortex-screen interaction by changing the local liquid viscosity and density. In the present investigation, a mechanical piston-cylinder vortex ring generator was used to create vortex rings in an aqueous sucrose solution. The rings impinged on a screen of horizontal wires that were heated using electrical current. The flow was visualized with food color and video imaging. Tests with and without heat were conducted at a piston stroke-to-jet diameter ratio of 4 and a jet Reynolds number (Re) of 1000. The vortex rings slowed after passing through the screen, but in tests with heat, they maintained a higher fraction of their before-screen velocity due to reduction in fluid viscosity near the wires. In addition, small ``fingers'' that developed on the front of the vortex rings as they passed through the screen exhibited positive buoyancy effects in the heated case.
Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.
2016-01-01
Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes. PMID:27679822
Legless locomotion in lattices
NASA Astrophysics Data System (ADS)
Schiebel, Perrin; Dai, Jin; Gong, Chaohui; Serrano, Miguel M.; Mendelson, Joseph R., III; Choset, Howie; Goldman, Daniel I.
2015-03-01
By propagating waves from head to tail, limbless organisms like snakes can traverse terrain composed of rocks, foliage, soil and sand. Previous research elucidated how rigid obstacles influence snake locomotion by studying a model terrain-symmetric lattices of pegs placed in hard ground. We want to understand how different substrate-body interaction modes affect performance in desert-adapted snakes during transit of substrates composed of both rigid obstacles and granular media (GM). We tested Chionactis occipitalis, the Mojave shovel-nosed snake, in two laboratory treatments: lattices of 0 . 64 cm diameter obstacles arrayed on both a hard, slick substrate and in a GM of ~ 0 . 3 mm diameter glass particles. For all lattice spacings, d, speed through the hard ground lattices was less than that in GM lattices. However, maximal undulation efficiencies ηu (number of body lengths advanced per undulation cycle) in both treatments were comparable when d was intermediate. For other d, ηu was lower than this maximum in hard ground lattices, while on GM, ηu was insensitive to d. To systematically explore such locomotion, we tested a physical robot model of the snake; performance depended sensitively on base substrate, d and body wave parameters.
Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.
2016-01-01
Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes.
Pautrat, A; Brûlet, A
2014-06-11
We investigated the intermediate mixed state of a superconducting niobium sample using very small angle neutron scattering. We show that this state is stabilized through a sequence where a regular vortex lattice appears, which then coexists with vortex clusters before vanishing at low temperature. Vortices in clusters have a constant periodicity regardless of the applied field and exhibit a temperature dependence close to the one of the penetration depth. The clusters disappear in the high temperature limit. All the results agree with an explanation in terms of vortex attraction due to non-local effects and indicate a negligible role for pinning. Phase coexistence between the Abrikosov vortex lattice and vortex clusters is reported, showing the first-order nature of the boundary line.
Chemical definition of the mesospheric polar vortex
NASA Astrophysics Data System (ADS)
Harvey, V. L.; Randall, C. E.; Collins, R. L.
2015-10-01
We present a simple chemical definition to demark the edge of the mesospheric polar vortices. Because this vortex definition does not rely on the wind field, it is useful in the mesosphere where wind observations are sparse and reanalysis winds are unreliable. The chemical definition is also insensitive to double jets that complicate vortex identification in the mesosphere. The algorithm is based on horizontal gradients of carbon monoxide (CO) and mirrors the widely used vortex edge definition in the stratosphere based on potential vorticity (PV) gradients. Here the approach is used to identify the Arctic vortex in the mesosphere during a 10 year (2004-2014) record of Microwave Limb Sounder data. Vortex size and shape comparisons are made where the CO and PV methods overlap in the upper stratosphere. A case study is presented during the NH 2008-2009 winter that demonstrates the fidelity of the CO gradient method on individual days and emphasizes the impact of double jets on methods to identify the polar vortex. We recommend transitioning from a PV or stream function-based vortex definition in the stratosphere to using a CO gradient definition above 0.1 hPa (~60 km). The CO gradient method identifies a coherent region of high CO at 80 km that is confined to mid-to-high latitudes 99.8% of the time during Arctic winter. Taking advantage of the CO gradient method to identify the polar vortex adds ~20 km of reliable vortex information (from 60 to 80 km) in a region of the atmosphere where reanalyses are most suspect.
Lobanov, Valery E; Kartashov, Yaroslav V; Konotop, Vladimir V
2014-05-01
Using the parity and time reversal symmetries of a two-dimensional spin-orbit coupled Bose-Einstein condensate in a lattice created by the Zeeman field, we identify and find numerically various families of localized solutions, including multipole and half-vortex solitons. The obtained solutions may exist at any direction of the gauge field with respect to the lattice and can be found either in finite gaps (for repulsive interatomic interactions) or in a semi-infinite gap (for attractive interactions). The existence of half-vortices requires higher symmetry (the reflection with respect to the field direction). Stability of these modes makes them feasible for experimental observation.
Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets.
Wang, Zhentao; Kamiya, Yoshitomo; Nevidomskyy, Andriy H; Batista, Cristian D
2015-09-01
We demonstrate that frustrated exchange interactions can produce exotic 3D crystals of vortex strings near the saturation field (H=H(sat)) of body- and face-centered cubic Mott insulators. The combination of cubic symmetry and frustration leads to a magnon spectrum of the fully polarized spin state (H>H(sat)) with degenerate minima at multiple noncoplanar Q vectors. This spectrum becomes gapless at the quantum critical point H=H(sat) and the magnetic ordering below H(sat) can be formally described as a condensate of a dilute gas of bosons. By expanding in the lattice gas parameter, we find that different vortex crystals span sizable regions of the phase diagrams for isotropic exchange and are further stabilized by symmetric exchange anisotropy. PMID:26382699
Three-Dimensional Crystallization of Vortex Strings in Frustrated Quantum Magnets.
Wang, Zhentao; Kamiya, Yoshitomo; Nevidomskyy, Andriy H; Batista, Cristian D
2015-09-01
We demonstrate that frustrated exchange interactions can produce exotic 3D crystals of vortex strings near the saturation field (H=H(sat)) of body- and face-centered cubic Mott insulators. The combination of cubic symmetry and frustration leads to a magnon spectrum of the fully polarized spin state (H>H(sat)) with degenerate minima at multiple noncoplanar Q vectors. This spectrum becomes gapless at the quantum critical point H=H(sat) and the magnetic ordering below H(sat) can be formally described as a condensate of a dilute gas of bosons. By expanding in the lattice gas parameter, we find that different vortex crystals span sizable regions of the phase diagrams for isotropic exchange and are further stabilized by symmetric exchange anisotropy.
Evaluation of travelling vortex speed by means of vortex tracking and dynamic mode decomposition
NASA Astrophysics Data System (ADS)
Hyhlík, Tomáš
2016-06-01
The article deals with the analysis of unsteady periodic flow field related to synthetic jet creation. The analyses are based on the data obtained using ANSYS Fluent solver. Numerical results are validated by hot wire anemometry data measured along the jet centerline. The speed of travelling vortex ring is evaluated by using vortex tracking method and by using dynamic mode decomposition method. Vortex identification is based on residual vorticity which allows identifying regions in the flow field where fluid particles perform the rotational motion. The regime of the synthetic jet with Re = 329 and S = 19.7 is chosen. Both the vortex tracking and the dynamic mode decomposition based vortex speed evaluation indicate an increase in the vortex speed close to the orifice and then decrease with maximum reaching almost one and half of orifice centerline velocity. The article contains extended version the article presented at the conference AEaNMiFMaE 2016.
Simulation of vortex-dominated aerodynamic flows by a point-vortex method
Jia, Z.
1988-01-01
A numerical study was made to simulate vortex-dominated aerodynamic flows by the point-vortex method. Attention was divided into three different aspects: a nascent vortex-shedding algorithm, numerical demonstration of the point-vortex method, and the calculation of some example of aerodynamic interesting flows, which include two major categories: unsteady flow about a flat plate at a fixed angle of attack with and without a leading edge flap, and the transient, vortical cross flow produced by a slender delta wing. Evolution of the vortex traces, streamlines, surface pressure, and forces are studied. Flow features based on data obtained by different point-vortex shedding rates and different integration time steps and schemes are found to be consistent with each other on length and time scales comparable to as well as considerably smaller than those of the global flow.
Multi-vortex states in magnetic nanoparticles
NASA Astrophysics Data System (ADS)
Gan, W. L.; Chandra Sekhar, M.; Wong, D. W.; Purnama, I.; Chiam, S. Y.; Wong, L. M.; Lew, W. S.
2014-10-01
We demonstrate a fabrication technique to create cylindrical NiFe magnetic nanoparticles (MNPs) with controlled dimensions and composition. MNPs thicker than 200 nm can form a double vortex configuration, which consists of a pair of vortices with opposite chirality. When MNPs thicker than 300 nm are relaxed after saturation, it forms a frustrated triple vortex state which produces a higher net magnetization as verified by light transmissivity measurements. Therefore, a greater magnetic torque can be actuated on a MNP in the triple vortex state.
Vortex dynamics in oscillatory chemical systems.
Wu, Xiao-Guang; Chee, Merk-Na; Kapral, Raymond
1991-12-01
Vortex core dynamics is studied in the Brusselator both near to and far from the Hopf bifurcation line for random and pair initial conditions. Extensive simulations are carried out for a pair of counter-rotating vortices close to the Hopf bifurcation line. Provided the vortices are not so far apart that wave-front annihilation produces strong gradients between their centers, the simulation results compare favorably with theories based on the complex Ginzburg-Landau equation. Far from the Hopf line the vortex core dynamics changes character and phenomena such as periodic motion of the vortex centers arise. PMID:12779938
Observations of the Mars Polar Vortex
NASA Technical Reports Server (NTRS)
McConnochie, T. H.; Conrath, B. J.; Gierasch, P. J.; Banfield, D.; Smith, M. D.
2003-01-01
The winter season, westerly circumpolar flow of the Martian atmosphere, and of the terrestrial stratosphere, is concentrated into a jet whose latitude falls between 60 and 80 degrees. This jet is known as the polar vortex. The terrestrial polar vortex has been understood to be the dynamical controlling mechanism for ozone depletion in the polar stratosphere for more than a decade. More recently, the earth's stratospheric annular modes, which are essentially a weakening/strengthening oscillation of the polar vortex jet, have been shown to be coupled to and possibly even a driving mechanism for, the tropospheric Arctic Oscillation (AO) / North Atlantic Oscillation (NAO) phenomenon.
Vortex motion behind a circular cylinder
NASA Technical Reports Server (NTRS)
Foeppl, L.
1983-01-01
Vortex motion behind a circular cylinder moving through water is discussed. It is shown that a pair of vortices form behind a moving cylinder and that their centers will move along a predictable curve. This curve represents an equilibrium condition which, however, is subject to perturbation. The stability of the vortex pair is investigated. Movement of the vortex pair away from the cylinder is calculated as an explanation of the resistance of the cylinder. Finally, the principles elaborated are applied to the flow around a flat plate.
RANS computations of tip vortex cavitation
NASA Astrophysics Data System (ADS)
Decaix, Jean; Balarac, Guillaume; Dreyer, Matthieu; Farhat, Mohamed; Münch, Cécile
2015-12-01
The present study is related to the development of the tip vortex cavitation in Kaplan turbines. The investigation is carried out on a simplified test case consisting of a NACA0009 blade with a gap between the blade tip and the side wall. Computations with and without cavitation are performed using a R ANS modelling and a transport equation for the liquid volume fraction. Compared with experimental data, the R ANS computations turn out to be able to capture accurately the development of the tip vortex. The simulations have also highlighted the influence of cavitation on the tip vortex trajectory.
Observation of an x-ray vortex
NASA Astrophysics Data System (ADS)
Peele, Andrew G.; McMahon, Philip J.; Paterson, David; Tran, Chanh Q.; Mancuso, Adrian P.; Nugent, Keith A.; Hayes, Jason P.; Harvey, Erol; Lai, Barry; McNulty, Ian
2002-10-01
Phase singularities are a ubiquitous feature of waves of all forms and represent a fundamental aspect of wave topology. An optical vortex phase singularity occurs when there is a spiral phase ramp about a point phase singularity. We report an experimental observation of an optical vortex in a field consisting of 9-keV x-ray photons. The vortex is created with an x-ray optical structure that imparts a spiral phase distribution to the incident wave field and is observed by use of diffraction about a wire to create a division-of-wave-front interferometer.
NASA Astrophysics Data System (ADS)
Andersen, A.; Bohr, T.; Stenum, B.; Rasmussen, J. Juul; Lautrup, B.
2003-09-01
We present experiments and theory for the “bathtub vortex,” which forms when a fluid drains out of a rotating cylindrical container through a small drain hole. The fast down-flow is found to be confined to a narrow and rapidly rotating “drainpipe” from the free surface down to the drain hole. Surrounding this drainpipe is a region with slow upward flow generated by the Ekman layer at the bottom of the container. This flow structure leads us to a theoretical model similar to one obtained earlier by Lundgren [
Vortex Structures of Whistler Waves
NASA Astrophysics Data System (ADS)
Zaliznyak, Yu.; Davydova, T.; Yakimenko, A.
Starting with two-dimensional nonlinear Scroedinger equation for a parallel electric field of spatially localized beam of whistler waves we investigate formation, evolu- tion and stability of nonlinear whistler waveguides (or ducts) which are frequently observed during heating active experiments in the ionosphere. When the generator frequency is close to the half of electron cyclotron frequency, one have take into ac- count the additional terms of the next order in the equation for the interpretation of existing experimental data. It is needed to use a full Maxwell's equation set to describe the propagation of whistlers and to account for the nonlinearity saturation at high val- ues of pump power. Nonlinear waveguides of vortex type (with topological charge 1, 2 and 3) are found and their stability properties are investigated by means of numerical simulations.
Vortex generator for flow control
NASA Technical Reports Server (NTRS)
Collins, Jr., Earl R. (Inventor); Marner, Wilbur J. (Inventor); Rohatgi, Naresh K. (Inventor)
1989-01-01
Fluidics flow control of a multiphase supply using a cylindrical chamber is achieved by introducing the supply flow radially into the chamber. The supply flow exits through a port in the center at the chamber. A control fluid is then introduced tangentially about 90.degree. upstream from the supply port. A second control fluid port may be added about 90.degree. upstream from the first control fluid port, but preferably two sets of supply and control ports are added with like ports diametrically opposite each other. The control fluid flows against the circular wall of the control chamber, which introduces a vortex in the flow of the supply flow that decays into a spiral path to the exit port in the center of the chamber. The control flow rate may thus be used to control the spiral path, and therefore the supply flow rate through the exit port.
Interaction of a turbulent vortex with a lifting surface
NASA Technical Reports Server (NTRS)
Lee, D. J.; Roberts, L.
1985-01-01
The impulsive noise due to blade-vortex-interaction is analyzing in the time domain for the extreme case when the blade cuts through the center of the vortex core with the assumptions of no distortion of the vortex path or of the vortex core. An analytical turbulent vortex core model, described in terms of the tip aerodynamic parameters, is used and its effects on the unsteady loading and maximum acoustic pressure during the interaction are determined.
Prediction and control of vortex-dominated and vortex-wake flows
NASA Technical Reports Server (NTRS)
Kandil, Osama
1993-01-01
This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.
The transition from vortex liquid to vortex slush in YB2Cu3Oy superconductors
NASA Astrophysics Data System (ADS)
Liu, S. L.; Wu, G. J.; Tan, H. J.; Xu, X. B.; Shao, H. M.
2006-06-01
The phase transition from vortex liquid to vortex slush has been confirmed in resistance measurements for YBCO crystal superconductors, on the basis of scaling analysis. The temperature dependence of the resistivity under various magnetic fields collapses onto two branches in the scaling behaviour, associated with the vortex slush and the vortex liquid states. The lower branch, for temperatures below the transition point, has a negative curvature, while the upper one shows a plateau above the transition point. The critical exponents are estimated from the scaling result. The phase diagram in the H-T plane is presented and compared with previous reports.
Nested contour-dynamic models for axisymmetric vortex rings and vortex wakes
NASA Astrophysics Data System (ADS)
O'Farrell, Clara; Dabiri, John O.
2013-11-01
Jetting swimmers, such as squid and jellyfish, propel themselves by forming vortex rings. It is known that vortex rings cannot grow indefinitely, but rather ``pinch off'' once they reach their physical limit, and that a decrease in efficiency of fluid transport is associated with pinch-off. Previously, the Norbury family of vortices has been used as a model for axisymmetric vortex rings, and the response of this family to shape perturbations has been characterized. We improve upon the Norbury models, using nested patches of vorticity to construct a family of models for vortex rings generated by a piston-cylinder apparatus at different stroke ratios. The perturbation response of this family is considered by the introduction of a small region of vorticity at the rear of the vortex, which mimics the addition of circulation to a growing vortex ring by a feeding shear layer. Model vortex rings are found to either accept the additional circulation or shed it into a tail, depending on the perturbation size. A change in the behavior of the model vortex rings is identified at a stroke ratio of three. We hypothesize that this change in response is analogous to pinch-off, and that pinch-off might be understood and predicted based on the perturbation responses of model vortex rings.
Vortex formation and instability in the left ventricle
NASA Astrophysics Data System (ADS)
Le, Trung Bao; Sotiropoulos, Fotis; Coffey, Dane; Keefe, Daniel
2012-09-01
We study the formation of the mitral vortex ring during early diastolic filling in a patient-specific left ventricle (LV) using direct numerical simulation. The geometry of the left ventricle is reconstructed from Magnetic Resonance Imaging (MRI) data of a healthy human subject. The left ventricular kinematics is modeled via a cell-based activation methodology, which is inspired by cardiac electro-physiology and yields physiologic LV wall motion. In the fluid dynamics videos, we describe in detail the three-dimensional structure of the mitral vortex ring, which is formed during early diastolic filling. The ring starts to deform as it propagates toward the apex of the heart and becomes inclined. The trailing secondary vortex tubes are formed as the result of interaction between the vortex ring and the LV wall. These vortex tubes wrap around the circumference and begin to interact with and destabilize the mitral vortex ring. At the end of diastole, the vortex ring impinges on the LV wall and the large-scale intraventricular flow rotates in clockwise direction. We show for the first time that the mitral vortex ring evolution is dominated by a number of vortex-vortex and vortex-wall interactions, including lateral straining and deformation of vortex ring, the interaction of two vortex tubes with unequal strengths, helicity polarization of vortex tubes and twisting instabilities of the vortex cores.
'Optimal' vortex rings and aquatic propulsion mechanisms
NASA Astrophysics Data System (ADS)
Linden, Paul; Turner, Stewart
2004-11-01
Fish swim by flapping their tail and other fins. Other sea creatures, such as squid and salps, eject fluid intermittently as a jet. We discuss the fluid mechanics behind these propulsion mechanisms, and show that these animals produce optimal vortex rings, which give the maximum thrust for a given energy input. We show fish optimise both their steady swimming and their ability to accelerate and turn by producing an individual optimal ring with each flap of the tail or fin. Salps produce vortex rings directly by ejecting a volume of fluid through a rear orifice, and these are also optimal. An important implication of this paper is that the repetition of vortex production is not necessary for an individual vortex to have the `optimal' characteristics.
Titan's South Polar Vortex in Motion
This movie captured by NASA'S Cassini spacecraft shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere, at Saturnâs moon Titan. The swirling mass appears to exec...
Analysis of vortex wake encounter upsets
NASA Technical Reports Server (NTRS)
Johnson, W. A.; Teper, G. L.
1974-01-01
The problem of an airplane being upset by encountering the vortex wake of a large transport on takeoff or landing is currently receiving considerable attention. This report describes the technique and results of a study to assess the effectiveness of automatic control systems in alleviating vortex wake upsets. A six-degree-of-freedom nonlinear digital simulation was used for this purpose. The analysis included establishing the disturbance input due to penetrating a vortex wake from an arbitrary position and angle. Simulations were computed for both a general aviation airplane and a commercial jet transport. Dynamic responses were obtained for the penetrating aircraft with no augmentation, and with various command augmentation systems, as well as with human pilot control. The results of this preliminary study indicate that attitude command augmentation systems can provide significant alleviation of vortex wake upsets; and can do it better than a human pilot.
Investigation of aircraft vortex wake structure
NASA Astrophysics Data System (ADS)
Baranov, N. A.; Turchak, L. I.
2014-11-01
In this work we analyze the mechanisms of formation of the vortex wake structure of aircraft with different wing shape in the plan flying close to or away from the underlying surface cleaned or released mechanization wing.
Vortex phase separation in mesoscopic superconductors
Iaroshenko, O.; Rybalko, V.; Vinokur, V. M.; Berlyand, L.
2013-01-01
We demonstrate that in mesoscopic type II superconductors with the lateral size commensurate with London penetration depth, the ground state of vortices pinned by homogeneously distributed columnar defects can form a hierarchical nested domain structure. Each domain is characterized by an average number of vortices trapped at a single pinning site within a given domain. Our study marks a radical departure from the current understanding of the ground state in disordered macroscopic systems and provides an insight into the interplay between disorder, vortex-vortex interaction, and confinement within finite system size. The observed vortex phase segregation implies the existence of the soliton solution for the vortex density in the finite superconductors and establishes a new class of nonlinear systems that exhibit the soliton phenomenon.
Experimental studies on coaxial vortex loops
NASA Astrophysics Data System (ADS)
Mariani, R.; Kontis, K.
2010-12-01
An experimental study has been conducted on the formation and propagation of coaxial vortex loops using a shock tube facility. The study aimed at evaluating the flow characteristics of pairs of corotating vortex rings that generate the leapfrogging phenomenon. The driver and driven gas of the shock tube were air. Three driver pressures were used (4, 8, and 12 bars) with the driven gas being at ambient conditions. The Mach numbers of the shock wave generated inside the shock tube were 1.34, 1.54, and 1.66, respectively. The sudden expansion present at the diaphragm location effectively decreased the Mach number value of the traveling shock wave. Results showed that a pair of vortex rings staggered with respect to time and with the same direction rotation lead to leapfrogging. Results also indicated that the number of leapfrogging occurrences is related to the Reynolds number of the vortex ring pairs with a decrease in leapfrogs at higher Reynolds numbers.
Cavitating vortex generation by a submerged jet
Belyakov, G. V.; Filippov, A. N.
2006-05-15
The surface geometry of a cavitating vortex is determined in the limit of inviscid incompressible flow. The limit surface is an ovaloid of revolution with an axis ratio of 5: 3. It is shown that a cavitating vortex ring cannot develop if the cavitation number is lower than a certain critical value. Experiments conducted at various liquid pressures and several jet exit velocities confirm the existence of a critical cavitation number close to 3. At cavitation numbers higher than the critical one, the cavitating vortex ring does not develop. At substantially lower cavitation numbers (k {<=} 0.1), an elongated asymmetric cavitation bubble is generated, with an axial reentrant jet whose length can exceed the initial jet length by several times. This flow structure is called an asymmetric cavitating vortex, even though steady motion of this structure has not been observed.
Valley Vortex States in Sonic Crystals
NASA Astrophysics Data System (ADS)
Lu, Jiuyang; Qiu, Chunyin; Ke, Manzhu; Liu, Zhengyou
2016-03-01
Valleytronics is quickly emerging as an exciting field in fundamental and applied research. In this Letter, we study the acoustic version of valley states in sonic crystals and reveal a vortex nature of such states. In addition to the selection rules established for exciting valley polarized states, a mimicked valley Hall effect of sound is proposed further. The extraordinary chirality of valley vortex states, detectable in experiments, may open a new possibility in sound manipulations. This is appealing to scalar acoustics that lacks a spin degree of freedom inherently. In addition, the valley selection enables a handy way to create vortex matter in acoustics, in which the vortex chirality can be controlled flexibly. Potential applications can be anticipated with the exotic interaction of acoustic vortices with matter, such as to trigger the rotation of the trapped microparticles without contact.
The dynamics of barotropic vortex merging
NASA Astrophysics Data System (ADS)
Kieu, Chanh
2016-08-01
The merging of multiple vortices is a fundamental process of the dynamics of Earth's atmosphere and oceans. In this study, the interaction of like-signed vortices is analytically and numerically examined in a framework of two-dimensional inviscid barotropic flows. It is shown that barotropic vortex interaction turns out to be more intricate than simple merging scenarios often assumed in previous studies. Some particular configurations exist in which the vortex merging process is never complete despite strong interaction of like-signed vortices, regardless of the strengths or distances between the vortices. While the conditions for a complete vortex merging process introduced in this study appear to be too strict for most practical applications, this study suggests that careful criteria for vortex mergers should be properly defined when simulating the interaction of vortices, because the merging may not always result in a final enhanced circulation at the end of the interaction, as usually assumed in the literature.
Laboratory Applications of the Vortex Tube.
ERIC Educational Resources Information Center
Bruno, Thomas J.
1987-01-01
Discussed are a brief explanation of the function of the vortex tube and some applications for the chemistry laboratory. It is a useful and inexpensive solution to many small-scale laboratory heating and cooling applications. (RH)
Optical Scully vortex and its spatial evolution.
Aksenov, Valerii P; Pogutsa, Cheslav E
2012-04-01
The structure of an optical vortex formed in a partially coherent Laguerre-Gauss laser beam was considered. The main object of study was the recorded vector field of wavefront tilts that consisted of the vortical and potential components. It was found that the vortical motion weakened as the coherence decreased. Main regularities in the behavior of the vortical component can be described by the Scully vortex model of vortical liquid flow. In the spatial evolution, the potential component of tilts may alternate the sign, thus determining the direction of energy flow to the center or to the periphery of the vortex. Energy flow lines in the beam demonstrate the pattern of decay of an optical vortex similar to the pattern of decaying vortical motion in viscous liquid.
Vortex ring impingement and particle suspension
NASA Astrophysics Data System (ADS)
Staymates, Matthew
2005-11-01
Previous research has shown that the impact of a vortex ring with a solid surface can dislodge particles attached to that surface and suspend them in the surrounding fluid. A possible use for this phenomenon arises in the detection of trace explosives on clothing and belongings: Once liberated from the surface, suspended particles can be collected and interrogated. The current technology successfully uses round turbulent jets for this purpose, but also generates a large concomitant airflow due to entrainment. Here we present the results of initial experiments to construct vortex-ring generators producing a similar particle release from surfaces with much less entrainment than jets. A discussion of vortex-ring-generator design issues and semi-quantitative flow visualization results will be presented. Both normal and oblique vortex-ring impacts are considered.
Shallow flow vortex formation and control
NASA Astrophysics Data System (ADS)
Fu, Haojun
Vortical structures in shallow flow past a vertical cylinder are addressed in this investigation. A cinema technique of digital particle image velocimetry (DPIV) provided quantitative representations of the wholefield flow patterns in both instantaneous and averaged forms. Techniques for passive and active control of these vortices, and their influence on the loading of the bed, were explored. In a fully-developed, laminar shallow flow, the unstable structure in the near-wake of the cylinder correlates with the horseshoe (necklace) vortex system about the upstream surface of the cylinder. A coherent varicose mode of vortex formation is observed in the near-wake, even though the classical large-scale vortex shedding is suppressed due to bed friction effects. It is also demonstrated that when the near-wake is stable at a sufficiently low value of Reynolds number, applications of external perturbations lead to destabilization of the wake. Classes of small-scale three-dimensional structures arise in a fully-turbulent shallow flow past a surface-piercing cylinder. A prevalent feature is an upward moving jet-like flow from the bed surface, through the center of the developing quasi-two-dimensional primary vortex, at a location in the very near-wake of the cylinder. Passive control via base-bleed through a narrow streamwise slot leads to substantially delay/attenuation of vortex formation in the near-wake. The large-scale near-wake structure is recoverable through combined positive-active control, in the form of rotational perturbations in the presence of small magnitude base bleed. These alterations of the near-wake structure occur in conjunction with modifications of the streamline topology and Reynolds stress at the bed, as well as the shallow approach flow. Active control via rotational perturbations of the cylinder at the most unstable shear-layer frequency promotes well-defined vortical structures in the separating shearlayer, which contribute to the earlier
Spatiotemporal complexity of the aortic sinus vortex
NASA Astrophysics Data System (ADS)
Moore, Brandon; Dasi, Lakshmi Prasad
2014-07-01
The aortic sinus vortex is a classical flow structure of significant importance to aortic valve dynamics and the initiation and progression of calcific aortic valve disease. We characterize the spatiotemporal characteristics of aortic sinus vortex dynamics in relation to the viscosity of blood analog solution as well as heart rate. High-resolution time-resolved (2 kHz) particle image velocimetry was conducted to capture 2D particle streak videos and 2D instantaneous velocity and streamlines along the sinus midplane using a physiological but rigid aorta model fitted with a porcine bioprosthetic heart valve. Blood analog fluids used include a water-glycerin mixture and saline to elucidate the sensitivity of vortex dynamics to viscosity. Experiments were conducted to record 10 heart beats for each combination of blood analog and heart rate condition. Results show that the topological characteristics of the velocity field vary in timescales as revealed using time bin-averaged vectors and corresponding instantaneous streamlines. There exist small timescale vortices and a large timescale main vortex. A key flow structure observed is the counter vortex at the upstream end of the sinus adjacent to the base (lower half) of the leaflet. The spatiotemporal complexity of vortex dynamics is shown to be profoundly influenced by strong leaflet flutter during systole with a peak frequency of 200 Hz and peak amplitude of 4 mm observed in the saline case. While fluid viscosity influences the length and timescales as well as the introduction of leaflet flutter, heart rate influences the formation of counter vortex at the upstream end of the sinus. Higher heart rates are shown to reduce the strength of the counter vortex that can greatly influence the directionality and strength of shear stresses along the base of the leaflet. This study demonstrates the impact of heart rate and blood analog viscosity on aortic sinus hemodynamics.
Towards a string formulation of vortex dynamics
Elsebeth Schroeder; Ola Toernkvist
1998-01-01
We derive an exact equation of motion for a non-relativistic vortex in two- and three-dimensional models with a complex field. The velocity is given in terms of gradients of the complex field at the vortex position. We discuss the problem of reducing the field dynamics to a closed dynamical system with non-locally interacting strings as the fundamental degrees of freedom.
Spontaneous splitting of a quadruply charged vortex.
Isoshima, T; Okano, M; Yasuda, H; Kasa, K; Huhtamäki, J A M; Kumakura, M; Takahashi, Y
2007-11-16
We studied the splitting instability of a quadruply charged vortex both experimentally and theoretically. The density defect, which is a signature of the vortex core, is experimentally observed to deform into a linear shape. The deformed defect is theoretically confirmed to be an array of four linearly aligned singly charged vortices. The array of vortices rotates and precesses simultaneously with different angular velocities. The initial state of the system is not rotationally symmetric, which enables spontaneous splitting without external perturbations. PMID:18233124
Spontaneous Splitting of a Quadruply Charged Vortex
Isoshima, T.; Okano, M.; Yasuda, H.; Kasa, K.; Huhtamaeki, J. A. M.; Kumakura, M.; Takahashi, Y.
2007-11-16
We studied the splitting instability of a quadruply charged vortex both experimentally and theoretically. The density defect, which is a signature of the vortex core, is experimentally observed to deform into a linear shape. The deformed defect is theoretically confirmed to be an array of four linearly aligned singly charged vortices. The array of vortices rotates and precesses simultaneously with different angular velocities. The initial state of the system is not rotationally symmetric, which enables spontaneous splitting without external perturbations.
White-light optical vortex coronagraph
NASA Astrophysics Data System (ADS)
Kanburapa, Prachyathit
An optical vortex is characterized by a dark core of destructive interference in a light beam. One of the methods commonly employed to create an optical vortex is by using a computer-generated hologram. A vortex hologram pattern is computed from the interference pattern between a reference plane wave and a vortex wave, resulting in a forked grating pattern. In astronomy, an optical vortex coronagraph is one of the most promising high contrast imaging techniques for the direct imaging of extra-solar planets. Direct imaging of extra-solar planets is a challenging task since the brightness of the parent star is extremely high compared to its orbiting planets. The on-axis light from the parent star gets diffracted in the coronagraph, forming a "ring of fire" pattern, whereas the slightly off-axis light from the planet remains intact. Lyot stop can then be used to block the ring of fire pattern, thus allowing only the planetary light to get through to the imaging camera. Contrast enhancements of 106 or more are possible, provided the vortex lens (spiral phase plate) has exceptional optical quality. By using a vortex hologram with a 4 microm pitch, and an f/300 focusing lens, we were able to demonstrate the creation of a "ring of fire" using a white light emitting diode as a source. A dispersion compensating linear diffraction grating of 4 microm pitch was used to bring the rings together to form a single white light ring of fire. To our knowledge, this is the first time a vortex hologram based OVC has been demonstrated, resulting in a well-formed white light ring of fire. Experimental results show measured power contrast of 1/515 when HeNe laser source was used as a light source and 1/77 when using a white light emitting diode.
Field dependence of the vortex core size probed by scanning tunneling microscopy
NASA Astrophysics Data System (ADS)
Fente, A.; Herrera, E.; Guillamón, I.; Suderow, H.; Mañas-Valero, S.; Galbiati, M.; Coronado, E.; Kogan, V. G.
2016-07-01
We study the spatial distribution of the density of states (DOS) at zero bias N (r ) in the mixed state of single and multigap superconductors. We provide an analytic expression for N (r ) based on deGennes' relationship between DOS and the order parameter that reproduces well scanning tunneling microscopy (STM) data in several superconducting materials. In the single gap superconductor β -Bi2Pd , we find that N (r ) is governed by a length scale ξH=√{ϕ0/2 π H } , which decreases in rising fields. The vortex core size C , defined via the slope of the order parameter at the vortex center, C ∝(dΔ /d r |r→0) -1 , differs from ξH by a material dependent numerical factor. The new data on the tunneling conductance and vortex lattice of the 2 H -NbSe1.8S0.2 show the in-plane isotropic vortices, suggesting that substitutional scattering removes the in-plane anisotropy found in the two-gap superconductor 2 H -NbSe2. We fit the tunneling conductance of 2 H -NbSe1.8S0.2 to a two gap model and calculate the vortex core size C for each band. We find that C is field independent and has the same value for both bands. We also analyze the two-band superconductor 2 H -NbS2 and find the same result. We conclude that, independently of the magnetic field induced variation of the order parameter values in both bands, the spatial variation of the order parameter close to the vortex core is the same for all bands.
Boundary Layers in Laminar Vortex Flows.
NASA Astrophysics Data System (ADS)
Baker, Glenn Leslie
A detailed experimental study of the flow in an intense, laminar, axisymmetric vortex has been conducted in the Purdue Tornado Vortex Simulator. The complicated nature of the flow in the boundary layer of laboratory vortices and presumably on that encountered in full-scale tornadoes has been examined. After completing a number of modifications to the existing facility to improve the quality of the flow in the simulator, hot-film anemometry was employed for making velocity-component and turbulence-intensity measurements of both the free-stream and boundary layer portions of the flow. The measurements represent the first experimental boundary layer investigation of a well-defined vortex flow to appear in the literature. These results were compared with recent theoretical work by Burggraf, Stewartson and Belcher (1971) and with an exact similarity solution for line-sink boundary layers developed by the author. A comparison is also made with the numerical simulation of Wilson (1981) in which the boundary conditions were matched to those of the present experimental investigation. Expressions for the vortex core radius, the maximum tangential velocity and the maximum pressure drop are given in terms of dimensionless modeling parameters. References. Burggraf, O. R., K. Stewartson and R. Belcher, Boundary layer. induced by a potential vortex. Phys. Fluids 14, 1821-1833 (1971). Wilson, T., M. S. thesis, Vortex Boundary Layer Dynamics, Univ. Calif. Davis (1981).
Magnetism near Vortex Cores of Cuprate Superconductors
NASA Astrophysics Data System (ADS)
Lee, J. C.; Prudchenko, K.; Launspach, B.; Ruiz, E. J.; Boekema, C.
2005-03-01
We examined muon-spin-resonance (μSR) vortex data of Bi2212, Tl2223, and YBCO to search for antiferromagnetism (AF) near the vortex cores. [1] Field distributions were obtained from μSR data using Maximum-Entropy analysis. The grainboundary and vortex signals were fitted by Gaussian and Lorentzian curves, the latter suggestive of extra AF ordering. Narrow Gaussians fit the grainboundary signals well, independent of temperature. For T < 0.4Tc, Lorentzians fit much better than Gaussians on the high-field side associated with the vortex core. Such results suggest that magnetism exists near the vortex cores. [1,2] The field dependence of the YBCO AF Lorentzian width is discussed. An AF presence near vortex cores supports theories that predict spin ordering for cuprate superconductivity. Research supported by REU-NSF, WiSE@SJSU & SJSU College of Science. [1] J. Lee et al, J Appl Phys 95 (2004) 6906, and Virtual J Appl of Superconductivity, June 2004 V6 Issue11; K Prudchenko et al, www.jyi.org/volumes/volume10/issue6/articles/prudchenko.html [2] C. Boekema et al, Int J Modern Phys B17 (2003) 3436.
Realization of ground-state artificial skyrmion lattices at room temperature
Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai
2015-10-08
We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.
Realization of ground-state artificial skyrmion lattices at room temperature
Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai
2015-10-08
We report that the topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. We demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from themore » dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. In conclusion, the imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices.« less
Realization of ground-state artificial skyrmion lattices at room temperature
Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai
2015-01-01
The topological nature of magnetic skyrmions leads to extraordinary properties that provide new insights into fundamental problems of magnetism and exciting potentials for novel magnetic technologies. Prerequisite are systems exhibiting skyrmion lattices at ambient conditions, which have been elusive so far. Here, we demonstrate the realization of artificial Bloch skyrmion lattices over extended areas in their ground state at room temperature by patterning asymmetric magnetic nanodots with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted from the dots into the interfacial region of the underlayer via suppression of the PMA by a critical ion-irradiation step. The imprinted skyrmion lattices are identified directly with polarized neutron reflectometry and confirmed by magnetoresistance measurements. Our results demonstrate an exciting platform to explore room-temperature ground-state skyrmion lattices. PMID:26446515
David Richards
2004-10-01
This talk describes progress at understanding the properties of the nucleon and its excitations from lattice QCD. I begin with a review of recent lattice results for the lowest-lying states of the excited baryon spectrum. The need to approach physical values of the light quark masses is emphasized, enabling the effects of the pion cloud to be revealed. I then outline the development of techniques that will enable the extraction of the masses of the higher resonances, and describe how such calculations provide insight into the structure of the hadrons. Finally, I discuss direct probes of the quark and gluon structure of baryons through the lattice measurement of the moments of quark distributions and of Generalized Parton Distributions.
Latticed pentamode acoustic cloak.
Chen, Yi; Liu, Xiaoning; Hu, Gengkai
2015-01-01
We report in this work a practical design of pentamode acoustic cloak with microstructure. The proposed cloak is assembled by pentamode lattice made of a single-phase solid material. The function of rerouting acoustic wave round an obstacle has been demonstrated numerically. It is also revealed that shear related resonance due to weak shear resistance in practical pentamode lattices punctures broadband feature predicted based on ideal pentamode cloak. As a consequence, the latticed pentamode cloak can only conceal the obstacle in segmented frequency ranges. We have also shown that the shear resonance can be largely reduced by introducing material damping, and an improved broadband performance can be achieved. These works pave the way for experimental demonstration of pentamode acoustic cloak. PMID:26503821
Latticed pentamode acoustic cloak
Chen, Yi; Liu, Xiaoning; Hu, Gengkai
2015-01-01
We report in this work a practical design of pentamode acoustic cloak with microstructure. The proposed cloak is assembled by pentamode lattice made of a single-phase solid material. The function of rerouting acoustic wave round an obstacle has been demonstrated numerically. It is also revealed that shear related resonance due to weak shear resistance in practical pentamode lattices punctures broadband feature predicted based on ideal pentamode cloak. As a consequence, the latticed pentamode cloak can only conceal the obstacle in segmented frequency ranges. We have also shown that the shear resonance can be largely reduced by introducing material damping, and an improved broadband performance can be achieved. These works pave the way for experimental demonstration of pentamode acoustic cloak. PMID:26503821
Vortex sound in confined flows
NASA Astrophysics Data System (ADS)
Hofmans, Gerardus Carolus Johannus
The interaction of vortex structures with the acoustic velocity field is prerequisite for the production or absorption of acoustic energy. When the source region in which this interaction occurs is much smaller than the wavelength of the acoustic wave, it is possible to neglect wave propagation in the source region itself. Such a source region is called 'compact' and it results in a simplified description of the acoustic source. We have restricted ourselves to compact source regions. Three relevant applications have been studied: speech modelling, damping of acoustic waves by means of diaphragms, and the prediction of flow-induced resonances in bifurcated pipe systems with T-shaped junctions. Experimental as well as numerical work has been carried out for rigid in vitro models of the vocal folds. It was found that it is possible to use a simplified quasi- steady model, which describes the boundary-layer flow in the glottis, to reasonably predict the separation point during a part of one cycle of the vocal-fold movement. This results in a reasonable prediction of the source of sound in voiced speech. Furthermore, it was found that the instability of the jet, that is formed downstream of the glottis, can be a significant source of broad-band sound. A diaphragm used as a constriction in a pipe is a common element in mufflers. This configuration is investigated theoretically, numerically, and experimentally. Results of the quasi-steady flow model and of the numerical calculations are in good agreement with results of experiments. Theory also correctly describes the limit of high frequencies. For the intermediate frequencies we found some deviation between theory and experiments, which is not yet fully understood. The flow through T-joints, with sharp edges, has been numerically investigated as a function of the acoustic amplitude, the Strouhal number, and the flow configuration. In the limit of low frequencies the acoustic source in a T-joint can be described by means
Lattice Boltzmann simulation of a fluid flow around a triangular unit of three isothermal cylinders
NASA Astrophysics Data System (ADS)
Alinejad, J.
2016-01-01
The lattice Boltzmann method is employed to simulate heat transfer in the flow past three arrangements of elliptical and circular cylinders under an isothermal boundary condition. The lattice Boltzmann equations and the Bhatnagar-Gross-Krook model are used to simulate two-dimensional forced convection at 30 ≤ Re ≤ 100 and Pr = 0.71. Pressure distributions, isotherms, and streamlines are obtained. Vortex shedding maps are observed in detail for several cases. The present results are in good agreement with available experimental and numerical data.
Catterall, Simon; Kaplan, David B.; Unsal, Mithat
2009-03-31
We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.
NASA Astrophysics Data System (ADS)
Xia, J. W.; Yuan, Y. J.; Song, M. T.; Zhang, W. Z.; Yang, X. D.; He, Y.; Mao, L. Z.; Xia, G. X.; Yang, J. C.; Wu, J. X.; Liu, W.
2001-12-01
CSR, a new Cooler-Storage-Ring project, is the post-acceleration system of the Heavy Ion Research Facility in Lanzhou (HIRFL). It consists of a main ring (CSRm) and an experimental ring (CSRe). From the HIRFL cyclotron system the heavy ions will be accumulated, cooled and accelerated in the CSRm, then extracted fast and injected into the CSRe for many internal-target experiments with electron cooling. The experimental ring (CSRe) will be operated with three lattice modes for different experiments. The details of the lattice for the two rings will be described in this paper.
Numerical simulation of vortex breakdown by the vortex-filament method
NASA Technical Reports Server (NTRS)
Nakamura, Y.; Leonard, A.; Spalart, P. R.
1983-01-01
The vortex-filament method was applied to the simulation of vortex breakdown. The principal vortex region was represented by multiple filaments, and an axial velocity component was induced by a spiral winding of the filaments. An accuracy check was performed for a cylindrical swirling flow with simple analytical expressions for the axial and theta velocities. The result suggests that the flow field can be simulated to any accuracy by increasing the number of filaments. An axisymmetric-type vortex breakdown was simulated, with experimental data serving as upstream conditions. The calculated axial- and theta-velocity contours show the breakdown of the vortex, including a rapid change in the vortex core, followed axially by a recovery zone and then a second breakdown. When three dimensional initial data are used the second breakdown appears to be of the spiral type in correspondence with experimental observations. The present method can easily be used to simulate other types of vortex breakdown or other vortex flows with axial velocity.
Entropic multirelaxation lattice Boltzmann models for turbulent flows
NASA Astrophysics Data System (ADS)
Bösch, Fabian; Chikatamarla, Shyam S.; Karlin, Ilya V.
2015-10-01
We present three-dimensional realizations of a class of lattice Boltzmann models introduced recently by the authors [I. V. Karlin, F. Bösch, and S. S. Chikatamarla, Phys. Rev. E 90, 031302(R) (2014), 10.1103/PhysRevE.90.031302] and review the role of the entropic stabilizer. Both coarse- and fine-grid simulations are addressed for the Kida vortex flow benchmark. We show that the outstanding numerical stability and performance is independent of a particular choice of the moment representation for high-Reynolds-number flows. We report accurate results for low-order moments for homogeneous isotropic decaying turbulence and second-order grid convergence for most assessed statistical quantities. It is demonstrated that all the three-dimensional lattice Boltzmann realizations considered herein converge to the familiar lattice Bhatnagar-Gross-Krook model when the resolution is increased. Moreover, thanks to the dynamic nature of the entropic stabilizer, the present model features less compressibility effects and maintains correct energy and enstrophy dissipation. The explicit and efficient nature of the present lattice Boltzmann method renders it a promising candidate for both engineering and scientific purposes for highly turbulent flows.
Entropic multirelaxation lattice Boltzmann models for turbulent flows.
Bösch, Fabian; Chikatamarla, Shyam S; Karlin, Ilya V
2015-10-01
We present three-dimensional realizations of a class of lattice Boltzmann models introduced recently by the authors [I. V. Karlin, F. Bösch, and S. S. Chikatamarla, Phys. Rev. E 90, 031302(R) (2014)] and review the role of the entropic stabilizer. Both coarse- and fine-grid simulations are addressed for the Kida vortex flow benchmark. We show that the outstanding numerical stability and performance is independent of a particular choice of the moment representation for high-Reynolds-number flows. We report accurate results for low-order moments for homogeneous isotropic decaying turbulence and second-order grid convergence for most assessed statistical quantities. It is demonstrated that all the three-dimensional lattice Boltzmann realizations considered herein converge to the familiar lattice Bhatnagar-Gross-Krook model when the resolution is increased. Moreover, thanks to the dynamic nature of the entropic stabilizer, the present model features less compressibility effects and maintains correct energy and enstrophy dissipation. The explicit and efficient nature of the present lattice Boltzmann method renders it a promising candidate for both engineering and scientific purposes for highly turbulent flows. PMID:26565366
Artificial Staggered Magnetic Field for Ultracold Atoms in Optical Lattices
NASA Astrophysics Data System (ADS)
Morais Smith, Cristiane
2011-03-01
Uniform magnetic fields are ubiquitous in nature, but this is not the case for staggered magnetic fields. In this talk, I will discuss an experimental set-up for cold atoms recently proposed by us, which allows for the realization of a ``staggered gauge field'' in a 2D square optical lattice. If the lattice is loaded with bosons, it may be described by an effective Bose-Hubbard Hamiltonian, with complex and anisotropic hopping coefficients. A very rich phase diagram emerges: besides the usual Mott-insulator and zero-momentum condensate, a new phase with a finite momentum condensate becomes the ground-state at strong gauge fields. By using the technique of Feshbach resonance, the dynamics of a coherent superposition of a vortex-carrying atomic condensate and a conventional zero-momentum molecular condensate can also be studied within the same scheme. On the other hand, if the lattice is loaded with fermions, a highly tunable, graphene-like band structure can be realized, without requiring the honeycomb lattice symmetry. When the system is loaded with a mixture of bosons and two-species fermions, several features of the high-Tc phase diagram can be reproduced. A dome-shaped unconventional superconducting region arises, surrounded by a non-Fermi liquid and a Fermi liquid at low and high doping, respectively. We acknowledge financial support from the Netherlands Organization for Scientific Research (NWO).
Vortex Cores of Inertial Particles.
Günther, Tobias; Theisel, Holger
2014-12-01
The cores of massless, swirling particle motion are an indicator for vortex-like behavior in vector fields and to this end, a number of coreline extractors have been proposed in the literature. Though, many practical applications go beyond the study of the vector field. Instead, engineers seek to understand the behavior of inertial particles moving therein, for instance in sediment transport, helicopter brownout and pulverized coal combustion. In this paper, we present two strategies for the extraction of the corelines that inertial particles swirl around, which depend on particle density, particle diameter, fluid viscosity and gravity. The first is to deduce the local swirling behavior from the autonomous inertial motion ODE, which eventually reduces to a parallel vectors operation. For the second strategy, we use a particle density estimation to locate inertial attractors. With this, we are able to extract the cores of swirling inertial particle motion for both steady and unsteady 3D vector fields. We demonstrate our techniques in a number of benchmark data sets, and elaborate on the relation to traditional massless corelines. PMID:26356967
Vortex Cores of Inertial Particles.
Günther, Tobias; Theisel, Holger
2014-12-01
The cores of massless, swirling particle motion are an indicator for vortex-like behavior in vector fields and to this end, a number of coreline extractors have been proposed in the literature. Though, many practical applications go beyond the study of the vector field. Instead, engineers seek to understand the behavior of inertial particles moving therein, for instance in sediment transport, helicopter brownout and pulverized coal combustion. In this paper, we present two strategies for the extraction of the corelines that inertial particles swirl around, which depend on particle density, particle diameter, fluid viscosity and gravity. The first is to deduce the local swirling behavior from the autonomous inertial motion ODE, which eventually reduces to a parallel vectors operation. For the second strategy, we use a particle density estimation to locate inertial attractors. With this, we are able to extract the cores of swirling inertial particle motion for both steady and unsteady 3D vector fields. We demonstrate our techniques in a number of benchmark data sets, and elaborate on the relation to traditional massless corelines.
Three-vortex configurations in trapped Bose-Einstein condensates
Seman, J. A.; Henn, E. A. L.; Shiozaki, R. F.; Ramos, E. R. F.; Caracanhas, M.; Castilho, P.; Castelo Branco, C.; Tavares, P. E. S.; Poveda-Cuevas, F. J.; Magalhaes, K. M. F.; Bagnato, V. S.; Haque, M.; Roati, G.
2010-09-15
We report on the creation of three-vortex clusters in a {sup 87}Rb Bose-Einstein condensate by oscillatory excitation of the condensate. This procedure can create vortices of both circulations, so that we are able to create several types of vortex clusters using the same mechanism. The three-vortex configurations are dominated by two types, namely, an equilateral-triangle arrangement and a linear arrangement. We interpret these most stable configurations respectively as three vortices with the same circulation and as a vortex-antivortex-vortex cluster. The linear configurations are very likely experimental signatures of predicted stationary vortex clusters.
Spur-type instability observed on numerically simulated vortex filaments
NASA Technical Reports Server (NTRS)
Rossow, Vernon J.
1988-01-01
An instability observed on vortex filaments during numerical simulations of the three-dimensional, time-dependent dynamics of vortex wakes is studied to determine when and why it occurs. It is concluded that the observed instability is a consequence of the use of straight-line vortex segments of finite length to model continuously curving vortex filaments. The instability appears to occur only when the link length is a sizable fraction of the vortex span and, therefore, is not expected in an experiment. Guidelines are then given that help avoid numerical instabilities when vortex filaments are used in flow simulations.
Devices that Alter the Tip Vortex of a Rotor
NASA Technical Reports Server (NTRS)
McAlister, Kenneth W.; Tung, Chee; Heineck, James T.
2001-01-01
Small devices were attached near the tip of a hovering rotor blade 'in order to alter the structure and trajectory of the trailing vortex. Stereo particle image velocimetry (PIV) images were used to quantify the wake behind the rotor blade during the first revolution. A procedure for analyzing the 3D-velocity field is presented that includes a method for accounting for vortex wander. The results show that a vortex generator can alter the trajectory of the trailing vortex and that a major change in the size and intensity of the trailing vortex can be achieved by introducing a high level of turbulence into the core of the vortex.
NASA Technical Reports Server (NTRS)
Savelyev, V. A.
1979-01-01
The means of ensuring total rigidity of lattice domes, using comparison with solid shells of 1-3 layers are discussed. Irregularities of manufacture, processing, and other factors are considered, as they relate to diminution of rigidity. The discussion uses the concepts of upper and lower critical loads on the structure in question.
NASA Astrophysics Data System (ADS)
Schaich, David
2016-03-01
Lattice field theory provides a non-perturbative regularization of strongly interacting systems, which has proven crucial to the study of quantum chromodynamics among many other theories. Supersymmetry plays prominent roles in the study of physics beyond the standard model, both as an ingredient in model building and as a tool to improve our understanding of quantum field theory. Attempts to apply lattice techniques to supersymmetric field theories have a long history, but until recently these efforts have generally encountered insurmountable difficulties related to the interplay of supersymmetry with the lattice discretization of spacetime. In recent years these difficulties have been overcome for a class of theories that includes the particularly interesting case of maximally supersymmetric Yang-Mills (N = 4 SYM) in four dimensions, which is a cornerstone of AdS/CFT duality. In combination with computational advances this progress enables practical numerical investigations of N = 4 SYM on the lattice, which can address questions that are difficult or impossible to handle through perturbation theory, AdS/CFT duality, or the conformal bootstrap program. I will briefly review some of the new ideas underlying this recent progress, and present some results from ongoing large-scale numerical calculations, including comparisons with analytic predictions.
Andreas S. Kronfeld
2002-09-30
After reviewing some of the mathematical foundations and numerical difficulties facing lattice QCD, I review the status of several calculations relevant to experimental high-energy physics. The topics considered are moments of structure functions, which may prove relevant to search for new phenomena at the LHC, and several aspects of flavor physics, which are relevant to understanding CP and flavor violation.
NASA Astrophysics Data System (ADS)
Shigaki, Kenta; Noda, Fumiaki; Yamamoto, Kazami; Machida, Shinji; Molodojentsev, Alexander; Ishi, Yoshihiro
2002-12-01
The JKJ high-intensity proton accelerator facility consists of a 400-MeV linac, a 3-GeV 1-MW rapid-cycling synchrotron and a 50-GeV 0.75-MW synchrotron. The lattice and beam dynamics design of the two synchrotrons are reported.
NASA Astrophysics Data System (ADS)
Singh, Kevin; Geiger, Zachary; Senaratne, Ruwan; Rajagopal, Shankari; Fujiwara, Kurt; Weld, David; Weld Group Team
2015-05-01
Quasiperiodicity is intimately involved in quantum phenomena from localization to the quantum Hall effect. Recent experimental investigation of quasiperiodic quantum effects in photonic and electronic systems have revealed intriguing connections to topological phenomena. However, such experiments have been limited by the absence of techniques for creating tunable quasiperiodic structures. We propose a new type of quasiperiodic optical lattice, constructed by intersecting a Gaussian beam with a 2D square lattice at an angle with an irrational tangent. The resulting potential, a generalization of the Fibonacci lattice, is a physical realization of the mathematical ``cut-and-project'' construction which underlies all quasiperiodic structures. Calculation of the energies and wavefunctions of atoms loaded into the proposed quasiperiodic lattice demonstrate a fractal energy spectrum and the existence of edge states. We acknowledge support from the ONR (award N00014-14-1-0805), the ARO and the PECASE program (award W911NF-14-1-0154), the AFOSR (award FA9550-12-1-0305), and the Alfred P. Sloan foundation (grant BR2013-110).
NASA Astrophysics Data System (ADS)
Weidner, Carrie; Yu, Hoon; Anderson, Dana
2015-05-01
This work introduces a method to perform interferometry using atoms trapped in an optical lattice. Starting at t = 0 with atoms in the ground state of a lattice potential V(x) =V0cos [ 2 kx + ϕ(t) ] , we show that it is possible to transform from one atomic wavefunction to another by a prescribed shaking of the lattice, i.e., by an appropriately tailored time-dependent phase shift ϕ(t) . In particular, the standard interferometer sequence of beam splitting, propagation, reflection, reverse propagation, and recombination can be achieved via a set of phase modulation operations {ϕj(t) } . Each ϕj(t) is determined using a learning algorithm, and the split-step method calculates the wavefunction dynamics. We have numerically demonstrated an interferometer in which the shaken wavefunctions match the target states to better than 1 % . We carried out learning using a genetic algorithm and optimal control techniques. The atoms remain trapped in the lattice throughout the full interferometer sequence. Thus, the approach may be suitable for use in an dynamic environment. In addition to the general principles, we discuss aspects of the experimental implementation. Supported by the Office of Naval Research (ONR) and Northrop Grumman.
Intraventricular vortex properties in nonischemic dilated cardiomyopathy
Benito, Yolanda; Alhama, Marta; Yotti, Raquel; Martínez-Legazpi, Pablo; del Villar, Candelas Pérez; Pérez-David, Esther; González-Mansilla, Ana; Santa-Marta, Cristina; Barrio, Alicia; Fernández-Avilés, Francisco; del Álamo, Juan C.
2014-01-01
Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1–74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m2/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound. PMID:24414062
The evolution of swirling axisymmetric vortex rings
NASA Astrophysics Data System (ADS)
Gargan-Shingles, C.; Rudman, M.; Ryan, K.
2015-08-01
Swirling vortex rings form in any turbulent flow where a swirling component is present, such as in combustion chambers or the downwash of helicopter blades. Instabilities on initially non-swirling vortex rings result in a localized swirl velocity being generated within the core. The presence of a swirl component of velocity in a vortex ring modifies the relaxation and evolution of numerical Gaussian cores in a manner that is currently unknown. The evolution of Gaussian axisymmetric vortex rings of size 0.2 < Λ < 0.5, with Gaussian swirls of magnitude 0.0 < W < 0.5, is analyzed with reference to the governing equations. A relaxation time, at which the initial Gaussian approximation has minimal influence on the subsequent evolution, has been estimated for each case. An axial vortex forms along the axis of the ring and is responsible for the growth of a shear layer that is found to form at the leading edge. The circulation based Reynolds number is set at 10 000 to encourage the growth of shear layer instabilities from within this region. Secondary vortex rings are subsequently shown to evolve from the Kelvin-Helmholtz instability for shear layers of sufficient strength and are convected around the original ring and shed from the system. It is shown that complete settling of the strain rate within the core does not occur until all sheddings have ceased. Increasing the swirl magnitude past that considered in this paper is expected to result in the original ring losing its structure before the instability can occur. The evolution is found to be qualitatively similar to that of a piston generated axisymmetric vortex ring with swirl, with both cases eventually reaching a similar quasi-steady state.
Flux noise resulting from vortex avalanches using a simple kinetic model
Mohler, G.; Stroud, D.
1999-10-01
We have carried out a model calculation of the flux noise produced by vortex avalanches in a type-II superconductor, using a simple kinetic model proposed by Bassler and Paczuski. Over a broad range of frequencies, we find that the flux noise S{sub {Phi}}({omega}) has a power-law dependence on frequency, S{sub {Phi}}({omega}){approximately}{omega}{sup {minus}s}, with s{approximately}1.4 in reasonable agreement with experiment. In addition, for small lattices, the calculated S{sub {Phi}}({omega}) has a high-frequency knee, which is seen in some experiments, and which is due to the finite lattice size. Deviations between calculation and experiment are attributed mostly to uncertainties in the measured critical current densities and pinning strengths of the experimental samples. {copyright} {ital 1999} {ital The American Physical Society}
Flux noise resulting from vortex avalanches using a simple kinetic model
NASA Astrophysics Data System (ADS)
Mohler, G.; Stroud, D.
1999-10-01
We have carried out a model calculation of the flux noise produced by vortex avalanches in a type-II superconductor, using a simple kinetic model proposed by Bassler and Paczuski. Over a broad range of frequencies, we find that the flux noise SΦ(ω) has a power-law dependence on frequency, SΦ(ω)~ω-s, with s~1.4 in reasonable agreement with experiment. In addition, for small lattices, the calculated SΦ(ω) has a high-frequency knee, which is seen in some experiments, and which is due to the finite lattice size. Deviations between calculation and experiment are attributed mostly to uncertainties in the measured critical current densities and pinning strengths of the experimental samples.
Sproll, Markus; Noske, Matthias; Kammerer, Matthias; Dieterle, Georg; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Bauer, Hans; Gangwar, Ajay; Woltersdorf, Georg; Back, Christian H.
2014-01-06
We show, by experiments and micromagnetic simulations in vortex structures, that an active “dual frequency” excitation of both the sub-GHz vortex gyromode and multi-GHz spin waves considerably changes the frequency response of spin wave mediated vortex core reversal. Besides additional minima in the switching threshold, a significant broadband reduction of the switching amplitudes is observed, which can be explained by non-linear interaction between the vortex gyromode and the spin waves. We conclude that the well known frequency spectra of azimuthal spin waves in vortex structures are altered substantially, when the vortex gyromode is actively excited simultaneously.
NASA Aircraft Vortex Spacing System Development Status
NASA Technical Reports Server (NTRS)
Hinton, David A.; Charnock, James K.; Bagwell, Donald R.; Grigsby, Donner
1999-01-01
The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft VOrtex Spacing System (AVOSS). AVOSS will integrate the output of several systems to produce weather dependent, dynamic wake vortex spacing criteria. These systems provide current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, and real-time feedback of wake vortex behavior from sensors. The goal of the NASA program is to provide the research and development to demonstrate an engineering model AVOSS in real-time operation at a major airport. The demonstration is only of concept feasibility, and additional effort is required to deploy an operational system for actual aircraft spacing reduction. This paper describes the AVOSS system architecture, a wake vortex facility established at the Dallas-Fort Worth International Airport (DFW), initial operational experience with the AVOSS system, and emerging considerations for subsystem requirements. Results of the initial system operation suggest a significant potential for reduced spacing.
Vortex-based line beam optical tweezers
NASA Astrophysics Data System (ADS)
Cheng, Shubo; Tao, Shaohua
2016-10-01
A vortex-based line beam, which has a straight-line shape of intensity and possesses phase gradient along the line trajectory is developed and applied for optical manipulation in this paper. The intensity and phase distributions of the beam in the imaging plane of the Fourier transform are analytically studied. Simulation results show that the length of the line and phase gradient possessed by a vortex-based line beam are dependent on the topological charge and the azimuthal proportional constant. A superposition of multiple phase-only holograms with elliptical azimuthal phases can be used to generate an array of vortex-based line beams. Optical trapping with the vortex-based line beams has been implemented. Furthermore, the automatic transportation of microparticles along the line trajectory perpendicular to the optical axis is realized with an array of the beams. The generation method for the vortex-based line beam is simple. The beam would have potential applications in fields such as optical trapping, laser machining, and so on.
Nonlinear Binormal Flow of Vortex Filaments
NASA Astrophysics Data System (ADS)
Strong, Scott; Carr, Lincoln
2015-11-01
With the current advances in vortex imaging of Bose-Einstein condensates occurring at the Universities of Arizona, São Paulo and Cambridge, interest in vortex filament dynamics is experiencing a resurgence. Recent simulations, Salman (2013), depict dissipative mechanisms resulting from vortex ring emissions and Kelvin wave generation associated with vortex self-intersections. As the local induction approximation fails to capture reconnection events, it lacks a similar dissipative mechanism. On the other hand, Strong&Carr (2012) showed that the exact representation of the velocity field induced by a curved segment of vortex contains higher-order corrections expressed in powers of curvature. This nonlinear binormal flow can be transformed, Hasimoto (1972), into a fully nonlinear equation of Schrödinger type. Continued transformation, Madelung (1926), reveals that the filament's square curvature obeys a quasilinear scalar conservation law with source term. This implies a broader range of filament dynamics than is possible with the integrable linear binormal flow. In this talk we show the affect higher-order corrections have on filament dynamics and discuss physical scales for which they may be witnessed in future experiments. Partially supported by NSF.
Wake Vortex Study at Wallops Island
NASA Technical Reports Server (NTRS)
1990-01-01
The air flow from the wing of this agricultural plane is made by a technique that uses colored smoke rising from the ground. The swirl at the wingtip traces the aircraft's wake vortex, which exerts a powerful influence on the flow field behind the plane. Because of wake vortex, the Federal Aviation Administration (FAA) requires aircraft to maintain set distances behind each other when they land. A joint NASA-FAA program aimed at boosting airport capacity, however, is aimed at determining conditions under which planes may fly closer together. NASA researchers are studying wake vortex with a variety of tools, from supercomputers to wind tunnels to actual flight tests in research aircraft. Their goal is to fully understand the phenomenon, then use that knowledge to create an automated system that could predict changing wake vortex conditions at airports. Pilots already know, for example, that they have to worry less about wake vortex in rough weather because windy conditions cause them to dissipate more rapidly.
Point vortex interactions on a toroidal surface
NASA Astrophysics Data System (ADS)
Sakajo, Takashi; Shimizu, Yuuki
2016-07-01
Owing to non-constant curvature and a handle structure, it is not easy to imagine intuitively how flows with vortex structures evolve on a toroidal surface compared with those in a plane, on a sphere and a flat torus. In order to cultivate an insight into vortex interactions on this manifold, we derive the evolution equation for N-point vortices from Green's function associated with the Laplace-Beltrami operator there, and we then formulate it as a Hamiltonian dynamical system with the help of the symplectic geometry and the uniformization theorem. Based on this Hamiltonian formulation, we show that the 2-vortex problem is integrable. We also investigate the point vortex equilibria and the motion of two-point vortices with the strengths of the same magnitude as one of the fundamental vortex interactions. As a result, we find some characteristic interactions between point vortices on the torus. In particular, two identical point vortices can be locally repulsive under a certain circumstance.
Numerical analysis of slender vortex motion
Zhou, H.
1996-02-01
Several numerical methods for slender vortex motion (the local induction equation, the Klein-Majda equation, and the Klein-Knio equation) are compared on the specific example of sideband instability of Kelvin waves on a vortex. Numerical experiments on this model problem indicate that all these methods yield qualitatively similar behavior, and this behavior is different from the behavior of a non-slender vortex with variable cross-section. It is found that the boundaries between stable, recurrent, and chaotic regimes in the parameter space of the model problem depend on the method used. The boundaries of these domains in the parameter space for the Klein-Majda equation and for the Klein-Knio equation are closely related to the core size. When the core size is large enough, the Klein-Majda equation always exhibits stable solutions for our model problem. Various conclusions are drawn; in particular, the behavior of turbulent vortices cannot be captured by these local approximations, and probably cannot be captured by any slender vortex model with constant vortex cross-section. Speculations about the differences between classical and superfluid hydrodynamics are also offered.
NASA Astrophysics Data System (ADS)
Xu, Si-Liu; Belić, Milivoj R.
2014-11-01
We investigate the existence of spatiotemporal necklace vortex solitons or light bullets in the complex Ginzburg-Landau equation with the modulated Kummer-Gauss (KG) external lattice potential and the spiraling phase of vorticities S=0,1 , and 2. We find localized vortex necklaces in a three-dimensional nonlinear medium, trapped by the KG external potential with different orders of vorticity. Stable and quasi-stable solitons form from input pulses with embedded vorticity. The stability is established by calculating growth rates of the perturbed eigenmodes. We establish that spatiotemporal necklace solitons may coexist in a large domain of the parameter space.
Interaction of a line vortex with a round parachute canopy
NASA Astrophysics Data System (ADS)
Johari, H.; Levshin, A.
2009-11-01
The interaction of a rectilinear vortex with an inflated round parachute canopy model was studied experimentally in a water tunnel where the vortex core was aligned with the axis of the canopy. Three different canopy diameters were used, and the canopy model was attached to a streamlined forebody. Dye flow visualization indicated that vortex breakdown was present when the core trajectory was within the canopy opening. Vortex breakdown occurred about one to two canopy diameters upstream of the canopy opening. The vortex core completely disintegrated when it interacted with the forebody near the canopy centerline. The vortex breakdown and disintegration caused unsteady, asymmetric deformations on the canopy surface. A reduction in the time-averaged drag and an increase in the fluctuating drag was observed when the vortex core was within the canopy opening. The disintegration of the vortex core near the canopy centerline lessened the drag reduction brought on by the presence of the core.
Vortex Filaments in Grids for Scalable, Fine Smoke Simulation.
Meng, Zhang; Weixin, Si; Yinling, Qian; Hanqiu, Sun; Jing, Qin; Heng, Pheng-Ann
2015-01-01
Vortex modeling can produce attractive visual effects of dynamic fluids, which are widely applicable for dynamic media, computer games, special effects, and virtual reality systems. However, it is challenging to effectively simulate intensive and fine detailed fluids such as smoke with fast increasing vortex filaments and smoke particles. The authors propose a novel vortex filaments in grids scheme in which the uniform grids dynamically bridge the vortex filaments and smoke particles for scalable, fine smoke simulation with macroscopic vortex structures. Using the vortex model, their approach supports the trade-off between simulation speed and scale of details. After computing the whole velocity, external control can be easily exerted on the embedded grid to guide the vortex-based smoke motion. The experimental results demonstrate the efficiency of using the proposed scheme for a visually plausible smoke simulation with macroscopic vortex structures. PMID:25594961
Vortex Filaments in Grids for Scalable, Fine Smoke Simulation.
Meng, Zhang; Weixin, Si; Yinling, Qian; Hanqiu, Sun; Jing, Qin; Heng, Pheng-Ann
2015-01-01
Vortex modeling can produce attractive visual effects of dynamic fluids, which are widely applicable for dynamic media, computer games, special effects, and virtual reality systems. However, it is challenging to effectively simulate intensive and fine detailed fluids such as smoke with fast increasing vortex filaments and smoke particles. The authors propose a novel vortex filaments in grids scheme in which the uniform grids dynamically bridge the vortex filaments and smoke particles for scalable, fine smoke simulation with macroscopic vortex structures. Using the vortex model, their approach supports the trade-off between simulation speed and scale of details. After computing the whole velocity, external control can be easily exerted on the embedded grid to guide the vortex-based smoke motion. The experimental results demonstrate the efficiency of using the proposed scheme for a visually plausible smoke simulation with macroscopic vortex structures.
Sagnac interferometry with coherent vortex superposition states in exciton-polariton condensates
NASA Astrophysics Data System (ADS)
Moxley, Frederick Ira; Dowling, Jonathan P.; Dai, Weizhong; Byrnes, Tim
2016-05-01
We investigate prospects of using counter-rotating vortex superposition states in nonequilibrium exciton-polariton Bose-Einstein condensates for the purposes of Sagnac interferometry. We first investigate the stability of vortex-antivortex superposition states, and show that they survive at steady state in a variety of configurations. Counter-rotating vortex superpositions are of potential interest to gyroscope and seismometer applications for detecting rotations. Methods of improving the sensitivity are investigated by targeting high momentum states via metastable condensation, and the application of periodic lattices. The sensitivity of the polariton gyroscope is compared to its optical and atomic counterparts. Due to the large interferometer areas in optical systems and small de Broglie wavelengths for atomic BECs, the sensitivity per detected photon is found to be considerably less for the polariton gyroscope than with competing methods. However, polariton gyroscopes have an advantage over atomic BECs in a high signal-to-noise ratio, and have other practical advantages such as room-temperature operation, area independence, and robust design. We estimate that the final sensitivities including signal-to-noise aspects are competitive with existing methods.
Reichhardt, Charles; Reichhardt, Cynthia
2008-01-01
We show using simulations that when interstitial vortices are present in superconductors with periodic pinning arrays, the transport in two perpendicular directions can be anisotropic. The degree of the anisotropy varies as a function of field due to the fact that the interstitial vortex lattice has distinct orderings at different matching fields. The anisotropy is most pronounced at the matching fields but persists at incommensurate fields, and it is most prominent for triangular, honeycomb, and kagome pinning arrays. Square pinning arrays can also show anisotropic transport at certain fields in spite of the fact that the perpendicular directions of the square pinning array are identical. We show that the anisotropy results from distinct vortex dynamical states and that although the critical depinning force may be lower in one direction, the vortex velocity above depinning may also be lower in the same direction for ranges of external drives where both directions are depinned. For honeycomb and kagome pinning arrays, the anisotropy can show multiple reversals as a function of field. We argue that when the pinning sites can be multiply occupied such that no interstitial vortices are present, the anisotropy is strongly reduced or absent.
The use of linearized-aerodynamics and vortex-flow methods in aircraft design /invited paper/
NASA Technical Reports Server (NTRS)
Lamar, J. E.
1982-01-01
This paper deals with selected linearized-aerodynamic and vortex-flow methods as applied to aircraft design problems at high subsonic speeds. In particular, the NASA Vortex Lattice and Modified Multhopp methods are the linearized techniques employed, and the suction analogy is used to provide estimates associated with vortex-flow aerodynamics. Many examples are given as to how researchers at Langley have used these methods to design the high subsonic, wing-mean-camber shapes for various configurations such as a supersonic transport, high-aspect-ratio transport, trapezoidal fighter wing, strake wing, tandem wing, joined wing, delta wing, and slender cranked wing. Many of these have been built, tested, and have had their data compared with theory. In addition, a technique for defining efficiently performing strake planforms for use in strake-wing combinations is discussed, and further improvements in wing design are outlined. The latter may be obtained by using higher-ordered linear panel methods as well as nonlinear-transonic methods.
Anisotropy of the Vortex Magnetic Field Distribution in LuNi2B2
NASA Astrophysics Data System (ADS)
Eskildsen, M. R.; Debeer-Schmitt, L.; Rovira, K.; Jenkins, N.; Dewhurst, C. D.; Bud'Ko, S. L.; Canfield, P. C.
2008-03-01
It is well known that the vortex lattice (VL) symmetry and orientation in type-II superconductors is very sensitive to any anisotropy within the screening current plane. A classic example is the sequence of transitions from hexagonal to rhombic to square symmetry, which was first observed in the borocarbide superconductors and explained by a Fermi surface anisotropy coupled with the non-local electrodynamics responsible for vortex-vortex interactions. Recently, however, this is mounting experimental evidence for a strong gap anisotropy and possible point nodes in the basal plane of these materials. Here we report on small-angle neutron scattering studies of the VL in a carefully annealed, high quality LuNi2B2C single crystal, which permitted us to measure the VL form factor for a large number of reflections. These measurements allow a reconstruction of the real space profile of the magnetic field around the vortices, reflecting the basal plane anisotropy of the screening currents in LuNi2B2C. The results will be compared to predictions for both Fermi surface and gap anisotropies, and will serve as a valuable reference for more complicated compounds as e.g. Sr2RuO4, heavy fermions and high-Tc's.
Development of a nonlinear vortex method
NASA Technical Reports Server (NTRS)
Kandil, O. A.
1982-01-01
Steady and unsteady Nonliner Hybrid Vortex (NHV) method, for low aspect ratio wings at large angles of attack, is developed. The method uses vortex panels with first-order vorticity distribution (equivalent to second-order doublet distribution) to calculate the induced velocity in the near field using closed form expressions. In the far field, the distributed vorticity is reduced to concentrated vortex lines and the simpler Biot-Savart's law is employed. The method is applied to rectangular wings in steady and unsteady flows without any restriction on the order of magnitude of the disturbances in the flow field. The numerical results show that the method accurately predicts the distributed aerodynamic loads and that it is of acceptable computational efficiency.
Vortex knots in tangled quantum eigenfunctions
NASA Astrophysics Data System (ADS)
Taylor, Alexander J.; Dennis, Mark R.
2016-07-01
Tangles of string typically become knotted, from macroscopic twine down to long-chain macromolecules such as DNA. Here, we demonstrate that knotting also occurs in quantum wavefunctions, where the tangled filaments are vortices (nodal lines/phase singularities). The probability that a vortex loop is knotted is found to increase with its length, and a wide gamut of knots from standard tabulations occur. The results follow from computer simulations of random superpositions of degenerate eigenstates of three simple quantum systems: a cube with periodic boundaries, the isotropic three-dimensional harmonic oscillator and the 3-sphere. In the latter two cases, vortex knots occur frequently, even in random eigenfunctions at relatively low energy, and are constrained by the spatial symmetries of the modes. The results suggest that knotted vortex structures are generic in complex three-dimensional wave systems, establishing a topological commonality between wave chaos, polymers and turbulent Bose-Einstein condensates.
Quasinormal modes of the polytropic hydrodynamic vortex
NASA Astrophysics Data System (ADS)
Oliveira, Leandro A.; Cardoso, Vitor; Crispino, Luís C. B.
2015-07-01
Analogue systems are a powerful instrument to investigate and understand in a controlled setting many general-relativistic effects. Here, we focus on superradiant-triggered instabilities and quasinormal modes. We consider a compressible hydrodynamic vortex characterized by a polytropic equation of state, the polytropic hydrodynamic vortex, a purely circulating system with an ergoregion but no event horizon. We compute the quasinormal modes of this system numerically with different methods, finding excellent agreement between them. When the fluid velocity is larger than the speed of sound, an ergoregion appears in the effective spacetime, triggering an "ergoregion instability." We study the details of the instability for the polytropic vortex, and in particular find analytic expressions for the marginally stable configuration.
Optical vortex beam generator at nanoscale level
NASA Astrophysics Data System (ADS)
Garoli, Denis; Zilio, Pierfrancesco; Gorodetski, Yuri; Tantussi, Francesco; de Angelis, Francesco
2016-07-01
Optical beams carrying orbital angular momentum (OAM) can find tremendous applications in several fields. In order to apply these particular beams in photonic integrated devices innovative optical elements have been proposed. Here we are interested in the generation of OAM-carrying beams at the nanoscale level. We design and experimentally demonstrate a plasmonic optical vortex emitter, based on a metal-insulator-metal holey plasmonic vortex lens. Our plasmonic element is shown to convert impinging circularly polarized light to an orbital angular momentum state capable of propagating to the far-field. Moreover, the emerging OAM can be externally adjusted by switching the handedness of the incident light polarization. The device has a radius of few micrometers and the OAM beam is generated from subwavelength aperture. The fabrication of integrated arrays of PVLs and the possible simultaneous emission of multiple optical vortices provide an easy way to the large-scale integration of optical vortex emitters for wide-ranging applications.
Sphagnum moss disperses spores with vortex rings.
Whitaker, Dwight L; Edwards, Joan
2010-07-23
Sphagnum spores, which have low terminal velocities, are carried by turbulent wind currents to establish colonies many kilometers away. However, spores that are easily kept aloft are also rapidly decelerated in still air; thus, dispersal range depends strongly on release height. Vascular plants grow tall to lift spores into sufficient wind currents for dispersal, but nonvascular plants such as Sphagnum cannot grow sufficiently high. High-speed videos show that exploding capsules of Sphagnum generate vortex rings to efficiently carry spores high enough to be dispersed by turbulent air currents. Spores launched ballistically at similar speeds through still air would travel a few millimeters and not easily reach turbulent air. Vortex rings are used by animals; here, we report vortex rings generated by plants.
Vortex knots in tangled quantum eigenfunctions
Taylor, Alexander J.; Dennis, Mark R.
2016-01-01
Tangles of string typically become knotted, from macroscopic twine down to long-chain macromolecules such as DNA. Here, we demonstrate that knotting also occurs in quantum wavefunctions, where the tangled filaments are vortices (nodal lines/phase singularities). The probability that a vortex loop is knotted is found to increase with its length, and a wide gamut of knots from standard tabulations occur. The results follow from computer simulations of random superpositions of degenerate eigenstates of three simple quantum systems: a cube with periodic boundaries, the isotropic three-dimensional harmonic oscillator and the 3-sphere. In the latter two cases, vortex knots occur frequently, even in random eigenfunctions at relatively low energy, and are constrained by the spatial symmetries of the modes. The results suggest that knotted vortex structures are generic in complex three-dimensional wave systems, establishing a topological commonality between wave chaos, polymers and turbulent Bose–Einstein condensates. PMID:27468801
Vortex generation in oscillatory canopy flow
NASA Astrophysics Data System (ADS)
Ghisalberti, Marco; Schlosser, Tamara
2013-03-01
In this paper, we demonstrate for the first time the generation of coherent vortices at the top of a canopy in oscillatory (i.e., wave-dominated) flow. Through a series of flow visualization experiments, vortex formation is shown to occur when two conditions described by the Keulegan-Carpenter (KC) and Reynolds (Re) numbers are met. First, the wave period must be sufficiently long to allow the generation of the shear-driven instability at the top of the canopy; this occurs when KC ≳ 5. Second, the vortex instability must be able to overcome the stabilizing effects of viscosity; this occurs when Re ≳ 1000. The vortices greatly increase the rate of vertical mixing within the canopy, such that any prediction of residence time in a coastal canopy requires an understanding of whether vortex generation is occurring.