The structure of a moving vortex lattice
Braun, D.W.; Crabtree, G.W.; Kaper, H.G.; Leaf, G.K.; Levine, D.M.; Vinokur, V.M.; Koshelev, A.E.
1995-11-01
Numerical solutions of the time-dependent Ginzburg-Landau equations show a new mechanism for plastic motion of a driven vortex lattice in a clean superconductor. The mechanism, which involves the creation of a defect superstructure, is intrinsic to the moving vortex lattice and is independent of bulk pinning. Other structural features found in the solutions include a reorientation of the vortex lattice and a gradual healing of lattice defects under the influence of a transport current.
Dynamic signatures of driven vortex motion.
Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M.; Safar, H.
1999-09-16
We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.
Phase-locking of driven vortex lattices with transverse ac force and periodic pinning
Reichhardt, Charles; Kolton, Alejandro B.; Dominguez, Daniel; Gronbech-Jensen, Niels
2001-10-01
For a vortex lattice moving in a periodic array we show analytically and numerically that a new type of phase locking occurs in the presence of a longitudinal dc driving force and a transverse ac driving force. This phase locking is distinct from the Shapiro step phase locking found with longitudinal ac drives. We show that an increase in critical current and a fundamental phase-locked step width scale with the square of the driving ac amplitude. Our results should carry over to other systems such as vortex motion in Josephson-junction arrays.
Vortex lattice of surface plasmon polaritons
NASA Astrophysics Data System (ADS)
Dzedolik, Igor V.; Lapayeva, Svetlana; Pereskokov, Vladislav
2016-07-01
We theoretically investigate the formation of a plasmon polariton vortex lattice on a metal surface following the interference of surface plasmon polaritons (SPPs). The plasmon polariton vortex lattice is formed by the interference of the SPP transverse-magnetic mode (TM-mode) and electric mode (E-mode) in the presence of the inhomogeneity with a curvilinear boundary on the surface of the metal layer. The SPP vortex lattice can be controlled by changing the configuration of the boundary. Weak nonlinearity of the metal permittivity does not change the interference pattern, but it increases the propagation length of the SPPs and, therefore, the area of the vortex lattice too.
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.
The nature of long range order in the vortex lattice of high {Tc} superconductors
Ryu, S.; Doniach, S.; Kapitulnik, A.
1994-12-31
Recent neutron data on the disappearance of long-range order in the vortex lattice of BSCCO at fields of order 1 kGauss is interpreted in terms of the results of a Monte Carlo simulation of the thermodynamics of the vortex lattice in a pure system. The authors show that the neutron data is consistent with a disorder-driven phase transition from a vortex crystal at low fields to a vortex glass at higher fields.
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.
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.
Inverse Melting of Vortex Lattice in Layered Superconductors
NASA Astrophysics Data System (ADS)
Wu, W. J.; He, Y. W.; Zhao, Z. G.; Liu, M.; Yang, Y. H.
Using molecular dynamic simulations for the melting transition of a flux line lattice(FLL) with point disordered pinnings, thermal fluctuations and magnetic interactions between pancake vortices, we study the disorder-driven melting transition from a disentangled and ordered Bragg glass (BG) to an entangled amorphous vortex glass (VG) or a vortex liquid (VL) in the pinning strength-temperature phase diagram. A portion of the BG region is found to be sandwiched in between the VG phase at lower temperatures and VL phase at higher temperatures, exhibiting inverse melting behavior observed recently on BSCCO crystals.
NASA Astrophysics Data System (ADS)
Shaidiuk, V.; Ammor, L.; Ruyter, A.
From the I-V characteristics for as-grown and irradiated Bi2Sr2CaCu2O8+δ single crystals at T=5K (i.e. T → 0) in a magnetic field applied parallel to c axis, we have seen two types of vortex dynamics above the depinning threshold, depending on the vortex-vortex interaction strength (λab/a0). For the as-grown sample, at a low field, the I-V curves show steps that clearly indicate a "fingerprint phenomenon" since they reflex the current dependence of the differential resistance rd(I). This can be ascribed to vortices flowing through uncorrelated channels for the highly defective lattice. As field sufficiently increase, these peaks merge to become broader ones indicating a crossover from filament type to braid river type. In contrast, in the irradiated sample, the pinning is found to be individual at low fields and collective when the vortex-vortex interactions are involved.
Energy of infinite vortex lattices
Campbell, L.J.; Doria, M.M.; Kadtke, J.B.
1989-05-15
An expression is derived for the energy density of a lattice of point vortices (or other logarithmic objects) having an arbitrary number of vortices of arbitrary strengths in an arbitrary unit cell. The result is expressed in the form of a rapidly convergent series well suited for numerical evaluation. The effects of separately changing the shape and dimensions of the unit cell are shown for simple cases, and the energy of the triangular lattice is calculated as a function of slip displacement.
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…
Reconstruction of vortex lattices at low inductions
Sudbro, A.; Brandt, E.H. Max-Planck-Institut fuer Metallforschung, Institut fuer Physik, Heisenbergstrasse 1, D-7000 Stuttgart 80 )
1992-03-16
The nonlocal elasticity and the normal modes of an unpinned flux-line lattice (FLL) in a uniaxially anisotropic supeconductor are considered in the low-induction regime {ital b}={ital B}/{ital B}{sub {ital c}2}{much lt}1 at oblique angles {theta} between {bold B} and the {bold {cflx c}} axis. A novel feature of anisotropic superconductors is {ital strongly} {ital dispersive} {ital shear} {ital moduli} when {theta}{gt}0. Thus, the normal modes of the FLL may become soft away from the zone center, signaling a {bold k}{ne}{bold 0} {ital structural} instability of the distorted hexagonal FLL. Vortex structures of a novel type are thus possible in anisotropic superconductors.
Simulating infinite vortex lattices in superfluids.
Mingarelli, Luca; Keaveny, Eric E; Barnett, Ryan
2016-07-20
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. PMID:27219843
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.
Quasi-Long-Range Order and Vortex Lattice in the Three-State Potts Model
NASA Astrophysics Data System (ADS)
Bhattacharya, Soumyadeep; Ray, Purusattam
2016-03-01
We show that the order-disorder phase transition in the three-state Potts ferromagnet on a square lattice is driven by a coupled proliferation of domain walls and vortices. Raising the vortex core energy above a threshold value decouples the proliferation and splits the transition into two. The phase between the two transitions exhibits an emergent U(1) symmetry and quasi-long-range order. Lowering the core energy below a threshold value also splits the order-disorder transition but the system forms a vortex lattice in the intermediate phase.
Dynamic Reorganization of Vortex Matter into Partially Disordered Lattices.
Marziali Bermúdez, M; Eskildsen, M R; Bartkowiak, M; Nagy, G; Bekeris, V; Pasquini, G
2015-08-01
We report structural evidence of dynamic reorganization in vortex matter in clean NbSe(2) by joint small-angle neutron scattering and ac susceptibility measurements. The application of oscillatory forces in a transitional region near the order-disorder transition results in robust bulk vortex lattice configurations with an intermediate degree of disorder. These dynamically originated configurations correlate with intermediate pinning responses previously observed, resolving a long-standing debate regarding the origin of such responses. PMID:26296127
Vortex configurations of bosons in an optical lattice
Wu Congjun; Zhang Shoucheng; Chen Handong; Hu Jiangpiang
2004-04-01
The single-vortex problem in a strongly correlated bosonic system is investigated self-consistently within the mean-field theory of the Bose-Hubbard model. Near the superfluid-Mott-insulator transition, the vortex core has a tendency toward the Mott-insulating phase, with the core particle density approaching the nearest commensurate value. If the nearest-neighbor repulsion exists, the charge-density wave order may develop locally in the core. The evolution of the vortex configuration from the strong- to weak-coupling regions is studied. This phenomenon can be observed in systems of rotating ultracold atoms in optical lattices and Josephson-junction arrays.
Vortex-Antivortex Lattice in Ultracold Fermionic Gases
Botelho, S.S.; Melo, C.A.R. sa de
2006-02-03
We discuss ultracold Fermi gases in two dimensions, which could be realized in a strongly confining one-dimensional optical lattice. We obtain the temperature versus effective interaction phase diagram for an s-wave superfluid and show that, below a certain critical temperature T{sub c}, spontaneous vortex-antivortex pairs appear for all coupling strengths. In addition, we show that the evolution from weak-to-strong coupling is smooth, and that the system forms a square vortex-antivortex lattice at a lower critical temperature T{sub M}.
Quantum fluctuations of vortex lattices in ultracold gases
NASA Astrophysics Data System (ADS)
Kwasigroch, M. P.; Cooper, N. R.
2012-12-01
We discuss the effects of quantum fluctuations on the properties of vortex lattices in rapidly rotating ultracold atomic gases. We develop a variational method that goes beyond the Bogoliubov theory by including the effects of interactions between the quasiparticle excitations. These interactions are found to have significant quantitative effects on physical properties even at relatively large filling factors. We use our theory to predict the expected experimental signatures of quantum fluctuations of vortices and to assess the competition of the triangular vortex lattice phase with other phases in finite-sized systems.
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.
Imaging superconducting vortex cores and lattices with a scanning tunneling microscope
NASA Astrophysics Data System (ADS)
Suderow, H.; Guillamón, I.; Rodrigo, J. G.; Vieira, S.
2014-06-01
The observation of vortices in superconductors was a major breakthrough in developing the conceptual background for superconducting applications. Each vortex carries a flux quantum, and the magnetic field decreases radially from the center. Techniques used to make magnetic field maps, such as magnetic decoration, give vortex lattice images in a variety of systems. However, strong type II superconductors allow penetration of the magnetic field over large distances, of the order of the magnetic penetration depth λ. Superconductivity survives up to magnetic fields where, for imaging purposes, there is no magnetic contrast at all. Static and dynamic properties of vortices are largely unknown at such high magnetic fields. Reciprocal space studies using neutron scattering have been employed to obtain insight into the collective behavior. But the microscopic details of vortex arrangements and their motion remain difficult to obtain. Direct real-space visualization can be made using scanning tunneling microscopy and spectroscopy (STM/S). Instead of using magnetic contrast, the electronic density of states describes spatial variations of the quasiparticle and pair wavefunction properties. These are of the order of the superconducting coherence length ξ, which is much smaller than λ. In principle, individual vortices can be imaged using STM up to the upper critical field where vortex cores, of size ξ, overlap. In this review, we describe recent advances in vortex imaging made with scanning tunneling microscopy and spectroscopy. We introduce the technique and discuss vortex images that reveal the influence of the Fermi surface distribution of the superconducting gap on the internal structure of vortices, the collective behavior of the lattice in different materials and conditions, and the observation of vortex lattice melting. We consider challenging lines of work, which include imaging vortices in nanostructures, multiband and heavy fermion superconductors, single layers
Beyond the simple hexagonal Abrikosov vortex lattice in layered superconductors
NASA Astrophysics Data System (ADS)
Feinberg, D.; Ettouhami, A. M.
1993-01-01
In layered superconductors as high-Tc materials but also organic superconductors, chalcogenides and superlattices, the simple concept of an distorted hexagonal lattice of straight vortices becomes unsufficient. Due to anisotropy and short coherence lengths, quite new vortex structures may arise. Some of them, as staircase vortices, simply add a modulation in the direction of vortex lines. This phenomenon is reviewed, together with the resulting lock-in transition, especially when the effects of the layered structure are weak. More exotic structures like a decomposed vortex lattice can also occur in specific situations: they involve two perpendicular sublattices, one parallel and one normal to the layers. We propose that extended defects as twin boundaries or irradiation tracks can trigger such a structure even in moderately anisotropic compounds as Y:123.
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.
Dynamic Melting of Driven Abrikosov Lattices in an Amorphous MoxGe1-x Film in Tilted Field
NASA Astrophysics Data System (ADS)
Ochi, Aguri; Kawamura, Yasuki; Inoue, Toshiki; Kaji, Tetsuya; Mihaly, Dobroka; Kaneko, Shin-ichi; Kokubo, Nobuhito; Okuma, Satoshi
2016-03-01
We report a comparative study of the dynamic melting of driven vortex lattices in magnetic field tilted (by θ = 36°) from the normal to the film surface and that of a driven Abrikosov lattice in untilted field (θ = 0). From the mode-locking (ML) resonance, we confirm that vortex lattices in tilted field are stretched in the tilt direction and that, with increasing dc velocity at ML, the shape and orientation of the driven lattice change. Associated with this structural change, the dynamic melting field at which the driven lattice melts also changes. Our results show that, regardless of the lattice shape and orientation, dynamic melting occurs as the shorter side of the distorted lattices reaches close to the side at which the isotropic lattice melts dynamically.
The Vortex Lattice Method for the Rotor-Vortex Interaction Problem
NASA Technical Reports Server (NTRS)
Padakannaya, R.
1974-01-01
The rotor blade-vortex interaction problem and the resulting impulsive airloads which generate undesirable noise levels are discussed. A numerical lifting surface method to predict unsteady aerodynamic forces induced on a finite aspect ratio rectangular wing by a straight, free vortex placed at an arbitrary angle in a subsonic incompressible free stream is developed first. Using a rigid wake assumption, the wake vortices are assumed to move downsteam with the free steam velocity. Unsteady load distributions are obtained which compare favorably with the results of planar lifting surface theory. The vortex lattice method has been extended to a single bladed rotor operating at high advance ratios and encountering a free vortex from a fixed wing upstream of the rotor. The predicted unsteady load distributions on the model rotor blade are generally in agreement with the experimental results. This method has also been extended to full scale rotor flight cases in which vortex induced loads near the tip of a rotor blade were indicated. In both the model and the full scale rotor blade airload calculations a flat planar wake was assumed which is a good approximation at large advance ratios because the downwash is small in comparison to the free stream at large advance ratios. The large fluctuations in the measured airloads near the tip of the rotor blade on the advance side is predicted closely by the vortex lattice method.
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.
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
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
Quasiclassical analysis of vortex lattice states in Rashba noncentrosymmetric superconductors
NASA Astrophysics Data System (ADS)
Dan, Yuichiro; Ikeda, Ryusuke
2015-10-01
Vortex lattice states occurring in noncentrosymmetric superconductors with a spin-orbit coupling of Rashba type under a magnetic field parallel to the symmetry plane are examined by assuming the s -wave pairing case and in an approach combining the quasiclassical theory with the Landau level expansion of the superconducting order parameter. The resulting field-temperature phase diagrams include not only a discontinuous transition but a continuous crossover between different vortex lattice structures, and, further, a critical end point of a structural transition line is found at an intermediate field and a low temperature in the present approach. It is pointed out that the strange field dependence of the vortex lattice structure is a consequence of that of its anisotropy stemming from the Rashba spin-orbit coupling, and that the critical end point is related to the helical phase modulation peculiar to these materials in the ideal Pauli-limited case. Furthermore, calculation results on the local density of states detectable in STM experiments are also presented.
Statistical Transmutation in Floquet Driven Optical Lattices
NASA Astrophysics Data System (ADS)
Sedrakyan, Tigran A.; Galitski, Victor M.; Kamenev, Alex
2015-11-01
We show that interacting bosons in a periodically driven two dimensional (2D) optical lattice may effectively exhibit fermionic statistics. The phenomenon is similar to the celebrated Tonks-Girardeau regime in 1D. The Floquet band of a driven lattice develops the moat shape, i.e., a minimum along a closed contour in the Brillouin zone. Such degeneracy of the kinetic energy favors fermionic quasiparticles. The statistical transmutation is achieved by the Chern-Simons flux attachment similar to the fractional quantum Hall case. We show that the velocity distribution of the released bosons is a sensitive probe of the fermionic nature of their stationary Floquet state.
Statistical Transmutation in Floquet Driven Optical Lattices.
Sedrakyan, Tigran A; Galitski, Victor M; Kamenev, Alex
2015-11-01
We show that interacting bosons in a periodically driven two dimensional (2D) optical lattice may effectively exhibit fermionic statistics. The phenomenon is similar to the celebrated Tonks-Girardeau regime in 1D. The Floquet band of a driven lattice develops the moat shape, i.e., a minimum along a closed contour in the Brillouin zone. Such degeneracy of the kinetic energy favors fermionic quasiparticles. The statistical transmutation is achieved by the Chern-Simons flux attachment similar to the fractional quantum Hall case. We show that the velocity distribution of the released bosons is a sensitive probe of the fermionic nature of their stationary Floquet state. PMID:26588392
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.
Perturbed vortex lattices and the stability of nucleated topological phases
NASA Astrophysics Data System (ADS)
Lahtinen, Ville; Ludwig, Andreas W. W.; Trebst, Simon
2014-02-01
We study the stability of nucleated topological phases that can emerge when interacting non-Abelian anyons form a regular array. The studies are carried out in the context of Kitaev's honeycomb model, where we consider three distinct types of perturbations in the presence of a lattice of Majorana mode binding vortices—spatial anisotropy of the vortices, dimerization of the vortex lattice, and local random disorder. While all the nucleated phases are stable with respect to weak perturbations of each kind, strong perturbations are found to result in very different behavior. Anisotropy of the vortices stabilizes the strong-pairing-like phases, while dimerization can recover the underlying non-Abelian phase. Local random disorder, on the other hand, can drive all the nucleated phases into a gapless thermal metal state. We show that all these distinct behaviors can be captured by an effective staggered tight-binding model for the Majorana modes. By studying the pairwise interactions between the vortices, i.e., the amplitudes for the Majorana modes to tunnel between vortex cores, the locations of phase transitions and the nature of the resulting states can be predicted. We also find that, due to oscillations in the Majorana tunneling amplitude, lattices of Majorana modes may exhibit a Peierls-like instability, where a dimerized configuration is favored over a uniform lattice. As the nature of the nucleated phases depends only on the Majorana tunneling, our results are expected to apply also to other system supporting localized Majorana mode arrays, such as Abrikosov lattices in p-wave superconductors, Wigner crystals in Moore-Read fractional quantum Hall states, or arrays of topological nanowires.
Convectively Driven Vortex Flows in the Sun
NASA Astrophysics Data System (ADS)
Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello, I.; Domingo, V.
2008-11-01
We have discovered small whirlpools in the Sun, with a size similar to terrestrial hurricanes (lesssim0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral on their way to being engulfed by a downdraft. Our disk-center observations show 0.9 × 10-2 vortexes per Mm2, with a lifetime of the order of 5 minutes, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs.
Vortex core-driven magnetization dynamics.
Choe, S B; Acremann, Y; Scholl, A; Bauer, A; Doran, A; Stöhr, J; Padmore, H A
2004-04-16
Time-resolved x-ray imaging shows that the magnetization dynamics of a micron-sized pattern containing a ferromagnetic vortex is determined by its handedness, or chirality. The out-of-plane magnetization in the nanometer-scale vortex core induces a three-dimensional handedness in the planar magnetic structure, leading to a precessional motion of the core parallel to a subnanosecond field pulse. The core velocity was an order of magnitude higher than expected from the static susceptibility. These results demonstrate that handedness, already well known to be important in biological systems, plays an important role in the dynamics of microscopic magnets. PMID:15087545
Dynamics of polarized vortex solitons in nonlocal media with Bessel optical lattices.
Zhang, Bingzhi; Chen, Zhifeng
2015-09-21
We investigate the formation of polarized vortex solitons in nonlocal media with Bessel optical lattices and show the various dynamics of these solitons. Particularly, the stable high-order polarized vortex solitons, which are not found in local media with Bessel optical lattices, are found in nonlocal media. It is found that the nonlocal nonlinearity plays an important role in the stability of these solitons which is similar to that of phase vortex solitons. However, we show that the dynamics of these polarized vortex solitons are quite different from the phase vortex solitons. PMID:26406632
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.
Melting of Vortex Lattice in Bose-Einstein Condensate in Presence of Disorder
NASA Astrophysics Data System (ADS)
Dey, Bishwajyoti
We study the vortex lattice dynamics in Bose-Einstein condensate (BEC) in presence of single impurity as well as random impurities or disorder. The single impurity is modeled by a Gaussian function while disorder is introduced in the system by a uniform random potential. Such potentials can be created experimentally by lasers. We solve the time-dependent Gross-Pitaevskii equation in two-dimensions using split-step Crank-Nicolson method. We first show that a single vortex can be pinned by an impurity. We then show that even a single impurity can distort the vortex lattice. For sufficiently strong impurity potential, the vortex lattice gets pinned to the impurity. We also show that a new type of giant hole with hidden vortices inside it can be created in the vortex lattice by a cluster of impurities. In presence of random impurity potential or disorder, the vortices get pinned at random positions leading to melting of the vortex lattice. We further show that the vortex lattice melting can also be induced by the pseudorandom potential generated by the superposition of two optical lattices. The absence of long-range order in the melted vortex lattice is demonstrated from the structure factor profile and the histogram of the distance between each pair of vortices. I would like to thank DST, India and BCUD SPPU, for financial assisance through research grants.
Statistical Transmutation in Periodically Driven Optical Lattices
NASA Astrophysics Data System (ADS)
Sedrakyan, Tigran; Galitski, Victor; Kamenev, Alex
We show that interacting bosons in a periodically driven two dimensional (2D) optical lattice may effectively exhibit fermionic statistics. The phenomenon is similar to the celebrated Tonks-Girardeau regime in 1D. The Floquet band of a driven lattice develops the moat shape, i.e., a minimum along a closed contour in the Brillouin zone. Such degeneracy of the kinetic energy favors fermionic quasiparticles. The statistical transmutation is achieved by the Chern-Simons flux attachment similar to the fractional quantum Hall case. We show that the velocity distribution of the released bosons is a sensitive probe of the fermionic nature of their stationary Floquet state. This work was supported by the PFC-JQI (T.S.), USARO and Simons Foundation (V.G.), and DOE Contract DE-FG02-08ER46482 (A.K.).
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.
Vortex lattice phases in bosonic ladders in the presence of gauge field
NASA Astrophysics Data System (ADS)
Piraud, Marie; Greschner, Sebastian; Kolley, Fabian; McCulloch, Ian P.; Schollwoeck, Ulrich; Heidrich-Meisner, Fabian; Vekua, Temo
2016-05-01
We study vortex lattices in the interacting Bose-Hubbard model defined on two- and three-leg ladder geometries in the presence of a homogeneous flux. Our work is motivated by recent experiments using laser assisted-tunneling in optical lattices and lattices in synthetic dimensions, which studied the regime of weak interactions. We focus on the effects arising from stronger interactions, in both the real space optical lattice and the synthetic dimension schemes. Based on extensive density matrix renormalization group simulations and a bosonization analysis, we show that vortex lattices form at certain commensurate vortex densities. We identify the parameter space in which they emerge, and study their properties. Very interestingly, an enlarged unit cell forms in the vortex lattice phases, which can lead to the reversal of the current circulation-direction in both geometries. We demonstrate this effect in weak coupling and at sufficiently low temperature, and show that it is significant for intermediate interactions.
Current-driven vortex formation in a magnetic multilayer ring
NASA Astrophysics Data System (ADS)
Nam, Chunghee; Ng, B. G.; Castaño, F. J.; Mascaro, M. D.; Ross, C. A.
2009-02-01
Current-driven domain wall (DW) motion has been studied in the NiFe layer of a Co/Cu/NiFe thin film ring using giant-magnetoresistance measurements in a four-point contact geometry. The NiFe layer is initially in an onion state configuration with two 180° DWs. An electric current drives the walls around the ring so that they annihilate and the NiFe layer forms a DW-free vortex state. The direction of motion of the two DWs is determined by the current polarity, enabling the vortex chirality to be selected.
Tornadolike gravity-driven vortex model
NASA Technical Reports Server (NTRS)
Deissler, R. G.; Boldman, D. R.
1974-01-01
The buoyancy-induced vorticity concentration produced as the fluid in a vortex accelerates vertically was studied. The boiloff from liquid nitrogen, to which a small amount of initial vorticity was added, provided a source of cool, heavy gas in which a concentration of vorticity took place. Condensation streamers made the flow visible. It is shown that the presence of a surface boundary layer is not necessary for the effective concentration of vorticity. A simple theoretical analysis of the phenomenon was also made. A radial contraction of the flow with vertical position and a characteristic hook shape in the top view of the streamlines were observed in both theory and experiment. The vorticity concentration observed may be similar to that which occurs in tornadoes.
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.
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.
Ferromagnetic and antiferromagnetic order in bacterial vortex lattices
Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Goldstein, Raymond E.
2016-01-01
Despite their inherent non-equilibrium nature1, living systems can self-organize in highly ordered collective states2,3 that share striking similarities with the thermodynamic equilibrium phases4,5 of conventional condensed matter and fluid systems. Examples range from the liquid-crystal-like arrangements of bacterial colonies6,7, microbial suspensions8,9 and tissues10 to the coherent macro-scale dynamics in schools of fish11 and flocks of birds12. Yet, the generic mathematical principles that govern the emergence of structure in such artificial13 and biological6–9,14 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 phases of ferro- and antiferromagnetic order. The preferred phase can be controlled by tuning the vortex coupling through changes of the inter-cavity gap widths. The emergence of opposing order regimes is tightly linked to the existence of geometry-induced edge currents15,16, reminiscent of those in quantum systems17–19. 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. PMID:27213004
Entanglement of Vortex Lattices for Ultracold Bose Gases in a Non-Abelian Gauge Potential
NASA Astrophysics Data System (ADS)
Cheng, Szu-Cheng; Jiang, T. F.; Jheng, Shih-Da; Atomic; Molecular Physics Team; Atomic; Molecular Physics Team
We develop a theory, referred to as the von Neumann lattice in a higher Landau level, for vortex lattices labelled by an integral number of flux quantums per unit cell in a higher Landau level. Using this lattice theory, we study the vortex lattice states of a pseudospin-1/2 ultracold Bose gas with contact interactions in a non-Abelian gauge potential. In addition to a uniform magnetic field, the Bose gas is also subjected to a non-Abelian gauge field, which creates an effect of the spin-orbit coupling to lift the spin degeneracy of the Landau levels. Because of interactions from the spin-orbit coupling, there are new degenerate points of the single particle spectrum due to the crossings of two Landau levels at certain coupling strengths. We show that interactions from the spin-orbit coupling force the nature and structure of the vortex lattice changing dramatically if the strength of the non-Abelian gauge field is increasing. We also find that the ground state of the vortex lattice at a degenerate point exhibits strong correlation and entanglement involving vortex lattices from different Landau levels. This entangled state builds the connection between two phases of vortex lattices during the first order phase transition of the adiabatic evolution.
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.
Ubiquitous Solar Eruptions Driven by Magnetized Vortex Tubes
NASA Astrophysics Data System (ADS)
Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour, N. N.; Wray, A. A.
2013-06-01
The solar surface is covered by high-speed jets transporting mass and energy into the solar corona and feeding the solar wind. The most prominent of these jets have been known as spicules. However, the mechanism initiating these eruption events is still unknown. Using realistic numerical simulations we find that small-scale eruptions are produced by ubiquitous magnetized vortex tubes generated by the Sun's turbulent convection in subsurface layers. The swirling vortex tubes (resembling tornadoes) penetrate into the solar atmosphere, capture and stretch background magnetic field, and push the surrounding material up, generating shocks. Our simulations reveal complicated high-speed flow patterns and thermodynamic and magnetic structure in the erupting vortex tubes. The main new results are: (1) the eruptions are initiated in the subsurface layers and are driven by high-pressure gradients in the subphotosphere and photosphere and by the Lorentz force in the higher atmosphere layers; (2) the fluctuations in the vortex tubes penetrating into the chromosphere are quasi-periodic with a characteristic period of 2-5 minutes; and (3) the eruptions are highly non-uniform: the flows are predominantly downward in the vortex tube cores and upward in their surroundings; the plasma density and temperature vary significantly across the eruptions.
UBIQUITOUS SOLAR ERUPTIONS DRIVEN BY MAGNETIZED VORTEX TUBES
Kitiashvili, I. N.; Kosovichev, A. G.; Lele, S. K.; Mansour, N. N.; Wray, A. A.
2013-06-10
The solar surface is covered by high-speed jets transporting mass and energy into the solar corona and feeding the solar wind. The most prominent of these jets have been known as spicules. However, the mechanism initiating these eruption events is still unknown. Using realistic numerical simulations we find that small-scale eruptions are produced by ubiquitous magnetized vortex tubes generated by the Sun's turbulent convection in subsurface layers. The swirling vortex tubes (resembling tornadoes) penetrate into the solar atmosphere, capture and stretch background magnetic field, and push the surrounding material up, generating shocks. Our simulations reveal complicated high-speed flow patterns and thermodynamic and magnetic structure in the erupting vortex tubes. The main new results are: (1) the eruptions are initiated in the subsurface layers and are driven by high-pressure gradients in the subphotosphere and photosphere and by the Lorentz force in the higher atmosphere layers; (2) the fluctuations in the vortex tubes penetrating into the chromosphere are quasi-periodic with a characteristic period of 2-5 minutes; and (3) the eruptions are highly non-uniform: the flows are predominantly downward in the vortex tube cores and upward in their surroundings; the plasma density and temperature vary significantly across the eruptions.
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.
An interferometric patchwork to generate high-order quasi-nondiffracting vortex lattices
NASA Astrophysics Data System (ADS)
Li, Zhenhua; Liu, Hanping; Liu, Huilan; Xu, Shicai; Ma, Li; Cheng, Chuanfu; Wang, Li; Mingzhen, Li
2016-06-01
We propose an novel kind of interferometer to generate various quasinondiffracting vortex lattices with high topological charges. The wave vectors of the interfering beams distribute spatial-symmetrically on the surface patchwork of two concentric cones of different opening angles, and their transverse components site at the vertices of two mutual-inscribed common regular polygons. With certain beam number and particular initial phase distribution at the beams, novel vortex lattices such as Kagome type lattice with unusual vortex distribution are obtained. We further extend such interferometric scheme to multipoint interferometers for easier experimental realization, where the generated vortex lattices lose nondiffracting property. Such interferometric method have potential applications in fields such as direct nanostructure writings and multichannel optical manipulations.
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.
Formation flying benefits based on vortex lattice calculations
NASA Technical Reports Server (NTRS)
Maskew, B.
1977-01-01
A quadrilateral vortex-lattice method was applied to a formation of three wings to calculate force and moment data for use in estimating potential benefits of flying aircraft in formation on extended range missions, and of anticipating the control problems which may exist. The investigation led to two types of formation having virtually the same overall benefits for the formation as a whole, i.e., a V or echelon formation and a double row formation (with two staggered rows of aircraft). These formations have unequal savings on aircraft within the formation, but this allows large longitudinal spacings between aircraft which is preferable to the small spacing required in formations having equal benefits for all aircraft. A reasonable trade-off between a practical formation size and range benefit seems to lie at about three to five aircraft with corresponding maximum potential range increases of about 46 percent to 67 percent. At this time it is not known what fraction of this potential range increase is achievable in practice.
Vortex-lattice melting in magnesium diboride in terms of the elastic theory
NASA Astrophysics Data System (ADS)
Nie, Qing-Miao; Lv, Jian-Ping; Chen, Qing-Hu
2010-01-01
In the framework of elastic theory, we study the vortex-lattice melting transitions in magnesium diboride for magnetic fields both parallel and perpendicular to the anisotropy axis. Using the parameters from experiments, the vortex-lattice melting lines in the H- T diagram are located systematically by various groups of Lindemann numbers. It is observed that the theoretical result for the vortex melting with parallel and perpendicular fields agrees well with the experimental data. Therefore, it is suggested that the phenomenological elastic theory is universal to various type-II superconductors, including two- and multi-band superconductors.
Arnold diffusion in a driven optical lattice
NASA Astrophysics Data System (ADS)
Boretz, Yingyue; Reichl, L. E.
2016-03-01
The effect of time-periodic forces on matter has been a topic of growing interest since the advent of lasers. It is known that dynamical systems with 2.5 or more degrees of freedom are intrinsically unstable. As a consequence, time-periodic driven systems can experience large excursions in energy. We analyze the classical and quantum dynamics of rubidium atoms confined to a time-periodic optical lattice with 2.5 degrees of freedom. When the laser polarizations are orthogonal, the system consists of two 1.5 uncoupled dynamical systems. When laser polarizations are turned away from orthogonal, an Arnold web forms and the dynamics undergoes a fundamental change. For parallel polarizations, we find huge random excursions in the rubidium atom energies and significant entanglement of energies in the quantum dynamics.
Arnold diffusion in a driven optical lattice.
Boretz, Yingyue; Reichl, L E
2016-03-01
The effect of time-periodic forces on matter has been a topic of growing interest since the advent of lasers. It is known that dynamical systems with 2.5 or more degrees of freedom are intrinsically unstable. As a consequence, time-periodic driven systems can experience large excursions in energy. We analyze the classical and quantum dynamics of rubidium atoms confined to a time-periodic optical lattice with 2.5 degrees of freedom. When the laser polarizations are orthogonal, the system consists of two 1.5 uncoupled dynamical systems. When laser polarizations are turned away from orthogonal, an Arnold web forms and the dynamics undergoes a fundamental change. For parallel polarizations, we find huge random excursions in the rubidium atom energies and significant entanglement of energies in the quantum dynamics. PMID:27078351
Application of lattice Boltzmann method for analysis of underwater vortex dynamics
NASA Astrophysics Data System (ADS)
Nuraiman, Dian; Viridi, Sparisoma; Purqon, Acep
2015-09-01
Vortex dynamics is one of problems arising in fluid dynamics. Vortices are a major characteristic of turbulent flow. We perform the Lattice Boltzmann Method (LBM) with Bhatnagar-Gross-Krook (BGK) approximation to analyze the underwater vortex dynamics close to the shoreline. Additionally, the Smagorinsky tubulence model is applied to treat turbulent flow and a special method for free surface treatment is applied to overcome free surface. Furthermore, we investigate the effect of the turbulence factor and the seabed profile to vortex dynamics. The results show a smaller turbulence factor affected to more turbulent flow and coral reefs reduced movement of vortex towards the shoreline.
Azimuthal-spin-wave-mode-driven vortex-core reversals
Yoo, Myoung-Woo; Kim, Sang-Koog
2015-01-14
We studied, by micromagnetic numerical calculations, asymmetric vortex-core reversals driven by the m = −1 and m = +1 azimuthal spin-wave modes' excitations in soft magnetic circular nano-disks. We addressed the similarities and differences between the asymmetric core reversals in terms of the temporal evolutions of the correlated core-motion speed, locally concentrated perpendicular gyrofield, and magnetization dip near the original vortex core. The criterion for the core reversals was found to be the magnetization dip that must reach the out-of-plane magnetization component, m{sub z} = −p, with the initial polarization p, where p = +1 (−1) for the upward (downward) core magnetization. The core-motion speed and the associated perpendicular gyrofield, variable and controllable with static perpendicular field, H{sub z}, applied perpendicularly to the disk plane, must reach their threshold values to meet the ultimate core-reversal criterion. Also, we determined the H{sub z} strength and direction dependence of the core-switching time and threshold exciting field strength required for the core reversals, whose parameters are essential in the application aspect. This work offers deeper insights into the azimuthal spin-wave-driven core-reversal dynamics as well as an efficient means of controlling the azimuthal-modes-driven core reversals.
Critical frequency for vortex nucleation in Bose-Fermi mixtures in optical lattices
NASA Astrophysics Data System (ADS)
Guilleumas, M.; Centelles, M.; Barranco, M.; Mayol, R.; Pi, M.
2005-11-01
We investigate within mean-field theory the influence of a one-dimensional optical lattice and of trapped degenerate fermions on the critical rotational frequency for vortex line creation in a Bose-Einstein condensate. We consider laser intensities of the lattice such that quantum coherence across the condensate is ensured. We find a sizable decrease of the thermodynamic critical frequency for vortex nucleation with increasing applied laser strength and suggest suitable parameters for experimental observation. Since Rb87-K40 mixtures may undergo collapse, we analyze the related question of how the optical lattice affects the mechanical stability of the system.
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.
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.
Chaotic and ballistic dynamics in time-driven quasiperiodic lattices
NASA Astrophysics Data System (ADS)
Wulf, Thomas; Schmelcher, Peter
2016-04-01
We investigate the nonequilibrium dynamics of classical particles in a driven quasiperiodic lattice based on the Fibonacci sequence. An intricate transient dynamics of extraordinarily long ballistic flights at distinct velocities is found. We argue how these transients are caused and can be understood by a hierarchy of block decompositions of the quasiperiodic lattice. A comparison to the cases of periodic and fully randomized lattices is performed.
Chaotic and ballistic dynamics in time-driven quasiperiodic lattices.
Wulf, Thomas; Schmelcher, Peter
2016-04-01
We investigate the nonequilibrium dynamics of classical particles in a driven quasiperiodic lattice based on the Fibonacci sequence. An intricate transient dynamics of extraordinarily long ballistic flights at distinct velocities is found. We argue how these transients are caused and can be understood by a hierarchy of block decompositions of the quasiperiodic lattice. A comparison to the cases of periodic and fully randomized lattices is performed. PMID:27176301
Validation of Vortex-Lattice Method for loads on wings in lift-generated wakes
NASA Technical Reports Server (NTRS)
Rossow, J.
1994-01-01
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 use of measurements made in the 80- by 120-foot 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 are used to determine the accuracy of the vortex-lattice code. It was found that the vortex-lattice method is very reliable as long as the span of the encountering of 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. The increase in deviation of the computed from the measured loads with size of the following wing is attributed to the increase in distortion of the structure of the vortex wake as it approaches and passes the larger following wings.
Vortex lattices in a rotating Fermi superfluid in the BCS-BEC crossover with many Landau levels
Song, Tie-ling; Ma, C.R.; Ma, Yong-li
2012-08-15
We present an explicit analytical analysis of the ground state of vortex lattice structure, based on a minimization of the generalized Gross-Pitaevskii energy functional in a trapped rotating Fermi superfluid gas. By a Bogoliubov-like transformation we find that the coarse-grained average of the atomic density varies as inverted parabola in three dimensional cases; the Fermi superfluid in the BEC regime enters into the lowest Landau level at fast rotation, in which the vortices form an almost regular triangular lattice over a central region and the vortex lattice is expanded along the radial direction in the outer region; the fluid in the unitarity and BCS regimes occupies many low-lying Landau levels, in which a trapped gas with a triangular vortex lattice has a superfluid core surrounded by a normal gas. The calculation is qualitatively consistent with recent numerical and experimental data both in the vortex lattice structure and vortex numbers and in the density profiles versus the stirring frequency in the whole BCS-BEC crossover. - Highlights: Black-Right-Pointing-Pointer We present an analysis of vortex lattice in an interacting trapped rotating Fermi superfluid gas. Black-Right-Pointing-Pointer Decomposing the vortex from the condensate, we can explain the vortex lattice. Black-Right-Pointing-Pointer The calculation is consistent with numerical and experimental data. Black-Right-Pointing-Pointer It can characterize experimentally properties in different regimes of the BCS-BEC crossover.
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
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.
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)
Yao, Xiaoyan; Dong, Shuai
2016-05-01
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.
Z2-vortex lattice in the ground state of the triangular Kitaev-Heisenberg model
NASA Astrophysics Data System (ADS)
Daghofer, Maria; Rousochatzakis, Ioannis; Roessler, Ulrich K.; van den Brink, Jeroen
2013-03-01
Investigating the classical Kitaev-Heisenberg Hamiltonian on a triangular lattice, we establish the presence of an incommensurate non-coplanar magnetic phase, which is identified as a lattice of Z2 vortices. The vortices, topological point defects in the SO(3) order parameter of the nearby Heisenberg antiferromagnet, are not thermally excited but due to the spin-orbit coupling and arise at temperature T --> 0 . This Z2-vortex lattice is stable in a parameter regime relevant to iridates. We show that in the other, strongly anisotropic, limit a robust nematic phase emerges. Sponsored by the DFG (Emmy-Noether program).
Han, Qiang
2010-01-27
In this paper, we present a method to construct the eigenspace of the tight-binding electrons moving on a 2D square lattice with nearest-neighbor hopping in the presence of a perpendicular uniform magnetic field which imposes (quasi-)periodic boundary conditions for the wavefunctions in the magnetic unit cell. Exact unitary transformations are put forward to correlate the discrete eigenvectors of the 2D electrons with those of the Harper equation. The cyclic tridiagonal matrix associated with the Harper equation is then tridiagonalized by another unitary transformation. The obtained truncated eigenbasis is utilized to expand the Bogoliubov-de Gennes equations for the superconducting vortex lattice state, which shows the merit of our method in studying large-sized systems. To test our method, we have applied our results to study the vortex lattice state of an s-wave superconductor. PMID:21386295
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.
Thorsmølle, V. K.; Averitt, R. D.; Aranson, I. S.; Maley, M. P.; Bulaevskiĭ, L. N.; Taylor, Antoinette J.,
2004-01-01
Employing terahertz time-domain spectroscopy in transmission, they have measured the Josephson plasma resonance in Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} high-T{sub c} thin films, and studied the current-driven coupling-decoupling crossover in the driven vortex lattice.
Fractionalizing the vortex lattice in multiband superconductors in the flux flow region
NASA Astrophysics Data System (ADS)
Lin, Shi-Zeng
2014-03-01
Because of the discovery of MgB2 and iron-based superconductors, multiband superconductors have attracted considerable attention recently. Multiband superconductors are not always straightforward extensions of the single-band counterpart, and novel features may arise. In multiband superconductors, electrons in different bands form distinct superfluid condensates, which are coupled to the same gauge field. Each condensate thus supports vortex excitation with fractional flux quantum. However the energy of a fractional vortex diverges logarithmically in the thermodynamic limit. In the ground state vortices in different bands are bounded and their normal cores are locked together to form a composite vortex with the standard integer quantum flux. It is interesting to ask whether the vortices in different condensates can decouple under certain conditions. In this talk, I will discuss the dissociation of the composite vortex lattice in the flux flow region when the disparity of superfluid density and coherence length between different bands is large. The fractional vortex lattice in different bands move with different velocities after the dissociation transition, and the dissociation transition shows up as an increase of flux flow resistivity. In the dissociated phase, the Shapiro steps are developed when an ac current is superimposed with a dc current. We also propose to stabilize the fractional vortices by periodic pinning arrays. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.
Temperature effects in excitonic condensation driven by the lattice distortion
NASA Astrophysics Data System (ADS)
Do, Thi-Hong-Hai; Nguyen, Huu-Nha; Nguyen, Thi-Giang; Phan, Van-Nham
2016-06-01
The stability of the excitonic condensation at low temperature driven by a coupling of electrons to vibrational degrees of freedom in semimetal two-dimensional electronic system is discussed. In the framework of the unrestricted Hartree-Fock approximation, we derive a set of equations to determine both the excitonic condensate order parameter and lattice displacement self-consistently. By lowering temperature we find out a semimetal-insulator transition in the system if the coupling is large enough. The insulating state typifies an excitonic condensation accompanied by a finite lattice distortion. Increasing temperature, both excitonic condensate order parameter and the lattice distortion decrease and then disappear in the same manner. Microscopic analysis in momentum space strongly specifies that the excitonic condensate driven by the lattice distortion favours the BCS type.
NASA Technical Reports Server (NTRS)
Lamar, J. E.
1994-01-01
This program represents a subsonic aerodynamic method for determining the mean camber surface of trimmed noncoplaner planforms with minimum vortex drag. With this program, multiple surfaces can be designed together to yield a trimmed configuration with minimum induced drag at some specified lift coefficient. The method uses a vortex-lattice and overcomes previous difficulties with chord loading specification. A Trefftz plane analysis is used to determine the optimum span loading for minimum drag. The program then solves for the mean camber surface of the wing associated with this loading. Pitching-moment or root-bending-moment constraints can be employed at the design lift coefficient. Sensitivity studies of vortex-lattice arrangements have been made with this program and comparisons with other theories show generally good agreement. The program is very versatile and has been applied to isolated wings, wing-canard configurations, a tandem wing, and a wing-winglet configuration. The design problem solved with this code is essentially an optimization one. A subsonic vortex-lattice is used to determine the span load distribution(s) on bent lifting line(s) in the Trefftz plane. A Lagrange multiplier technique determines the required loading which is used to calculate the mean camber slopes, which are then integrated to yield the local elevation surface. The problem of determining the necessary circulation matrix is simplified by having the chordwise shape of the bound circulation remain unchanged across each span, though the chordwise shape may vary from one planform to another. The circulation matrix is obtained by calculating the spanwise scaling of the chordwise shapes. A chordwise summation of the lift and pitching-moment is utilized in the Trefftz plane solution on the assumption that the trailing wake does not roll up and that the general configuration has specifiable chord loading shapes. VLMD is written in FORTRAN for IBM PC series and compatible computers
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.
Quantum fluctuations of the vortex-lattice state in an ultrafast rotating Bose gas
Li Qiong; Feng Bo; Li Dingping
2011-04-15
Quantum fluctuations in an ultrafast rotating Bose gas at zero temperature are investigated. We calculate the condensate density perturbatively to show that no condensate is present in the thermodynamic limit. The excitation from Gaussian fluctuations around the mean-field solution causes infrared divergences in loop diagrams, nevertheless, in calculating the atom number density, the correlation functions and the free energy, we find that the sum of the divergences in the same loop order vanishes and we obtain finite physical quantities. The long-range correlation is explored and the algebraic decay exponent for the single-particle correlation function is obtained. The atom number density distribution is obtained at the one-loop level, which illustrates the quantum fluctuation effects to melt the mean-field vortex lattice. By the nonperturbative Gaussian variational method, we locate the spinodal point of the vortex-lattice state.
Quantum fluctuations of the vortex-lattice state in an ultrafast rotating Bose gas
NASA Astrophysics Data System (ADS)
Li, Qiong; Feng, Bo; Li, Dingping
2011-04-01
Quantum fluctuations in an ultrafast rotating Bose gas at zero temperature are investigated. We calculate the condensate density perturbatively to show that no condensate is present in the thermodynamic limit. The excitation from Gaussian fluctuations around the mean-field solution causes infrared divergences in loop diagrams, nevertheless, in calculating the atom number density, the correlation functions and the free energy, we find that the sum of the divergences in the same loop order vanishes and we obtain finite physical quantities. The long-range correlation is explored and the algebraic decay exponent for the single-particle correlation function is obtained. The atom number density distribution is obtained at the one-loop level, which illustrates the quantum fluctuation effects to melt the mean-field vortex lattice. By the nonperturbative Gaussian variational method, we locate the spinodal point of the vortex-lattice state.
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. PMID:25784605
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.
Morphology of the Superconducting Vortex Lattice in Ultrapure Niobium
NASA Astrophysics Data System (ADS)
Mühlbauer, S.; Pfleiderer, C.; Böni, P.; Laver, M.; Forgan, E. M.; Fort, D.; Keiderling, U.; Behr, G.
2009-04-01
The morphology of the superconducting flux line lattice (FLL) of Nb comprises gradual variations with various lock-in transitions and symmetry breaking rotations. We report a comprehensive small-angle neutron scattering study of the FLL in an ultrapure single crystal of Nb as a function of the orientation of the applied magnetic field. We attribute the general morphology of the FLL and its orientation to three dominant mechanisms; first, nonlocal contributions, second, the transition between open and closed Fermi surface sheets and, third, the intermediate mixed state between the Meissner and the Shubnikov phase.
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.
Dissipation-Induced Symmetry Breaking in a Driven Optical Lattice
Gommers, R.; Bergamini, S.; Renzoni, F.
2005-08-12
We analyze the atomic dynamics in an ac driven periodic optical potential which is symmetric in both time and space. We experimentally demonstrate that in the presence of dissipation the symmetry is broken, and a current of atoms through the optical lattice is generated as a result.
Vortex lattices in the superconducting phases of doped topological insulators and heterostructures
NASA Astrophysics Data System (ADS)
Hung, Hsiang-Hsuan; Ghaemi, Pouyan; Hughes, Taylor L.; Gilbert, Matthew J.
2013-01-01
Majorana fermions are predicted to play a crucial role in condensed matter realizations of topological quantum computation. These heretofore undiscovered quasiparticles have been predicted to exist at the cores of vortex excitations in topological superconductors and in heterostructures of superconductors and materials with strong spin-orbit coupling. In this work, we examine topological insulators with bulk s-wave superconductivity in the presence of a vortex lattice generated by a perpendicular magnetic field. Using self-consistent Bogoliubov-de Gennes calculations, we confirm that beyond the semiclassical, weak-pairing limit the Majorana vortex states appear as the chemical potential is tuned from either side of the band edge so long as the density of states is sufficient for superconductivity to form. Further, we demonstrate that the previously predicted vortex phase transition survives beyond the semiclassical limit. At chemical potential values smaller than the critical chemical potential, the vortex lattice modes hybridize within the top and bottom surfaces, giving rise to a dispersive low-energy mid-gap band. As the chemical potential is increased, the Majorana states become more localized within a single surface but spread into the bulk toward the opposite surface. Eventually, when the chemical potential is sufficiently high in the bulk bands, the Majorana modes can tunnel between surfaces and eventually a critical point is reached at which modes on opposite surfaces can freely tunnel and annihilate leading to the topological phase transition previously studied in the work of Hosur [Phys. Rev. Lett.10.1103/PhysRevLett.107.097001 107, 097001 (2011)].
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.
Lennard-Jones and lattice models of driven fluids.
Díez-Minguito, M; Garrido, P L; Marro, J
2005-08-01
We introduce a nonequilibrium off-lattice model for anisotropic phenomena in fluids. This is a Lennard-Jones generalization of the driven lattice-gas model in which the particles' spatial coordinates vary continuously. A comparison between the two models allows us to discuss some exceptional, hardly realistic features of the original discrete system--which has been considered a prototype for nonequilibrium anisotropic phase transitions. We thus help to clarify open issues, and discuss on the implications of our observations for future investigation of anisotropic phase transitions. PMID:16196640
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-Loop Unbinding and Flux-Line Lattice Melting in Superconductors
Nguyen, A.K.; Sudbo Hetzel, R. |
1996-08-01
We study the interplay between a novel vortex-loop unbinding in finite magnetic field at {ital T}={ital T}{sub {ital V}} and flux-line-lattice (FLL) melting at {ital T}={ital T}{sub {ital M}} in type-II superconductors. The FLL melts due to nucleation of vortex loops parallel to the {ital {cflx c}} axis, connected to flux lines. For moderate anisotropy, phase coherence parallel to {ital {cflx c}} is lost at {ital T}{sub {ital V}}{approx_gt}{ital T}{sub {ital M}} due to an {ital ab}-plane vortex-loop unbinding with loops located close to thermal FLL fluctuations. For large anisotropy, phase coherence parallel to {ital {cflx c}} is lost at {ital T}{sub {ital V}}{lt}{ital T}{sub {ital M}} due to nucleation of vortex loops uncorrelated to flux lines, predominantly in the {ital ab} plane. {copyright} {ital 1996 The American Physical Society.}
Vortex-Driven Sound in a Cylindrical Cavity.
NASA Astrophysics Data System (ADS)
Flatau, Alison
1990-08-01
An experimental investigation of the flow induced acoustic response of a cylindrical cavity to variations in the stiffness of baffles that cause flow separation and vortex shedding is presented. Vortex shedding in the Space Shuttle solid rocket motors (SRMs) contributes to undesirable combustion instabilities or oscillations in the propellant burn rate that can introduce detrimental vibratory loads to the shuttle and its cargo, including astronauts who complain of a "rough ride." This study presents a cold flow simulation of the conditions that produce vortex shedding in the SRMs using a cylindrical cavity with annular protrusions or baffles extending from the cavity walls into the flow path. This work provides quantification of the frequency and relative amplitude of this flow induced acoustic response, called a hole tone response. Specifically investigated are the effects of variable baffle stiffness and of baffle resonance excitation on the acoustic frequency and amplitude of the cavity response.
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.
Effect of Rolling Massage on the Vortex Flow in Blood Vessels with Lattice Boltzmann Simulation
NASA Astrophysics Data System (ADS)
Yi, Hou Hui
The rolling massage manipulation is a classic Chinese Medical Massage, which is a nature therapy in eliminating many diseases. Here, the effect of the rolling massage on the cavity flows in blood vessel under the rolling manipulation is studied by the lattice Boltzmann simulation. The simulation results show that the vortex flows are fully disturbed by the rolling massage. The flow behavior depends on the rolling velocity and the rolling depth. Rolling massage has a better effect on the flows in the cavity than that of the flows in a planar blood vessel. The result is helpful to understand the mechanism of the massage and develop the rolling techniques.
A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly
NASA Astrophysics Data System (ADS)
Krishnaraj, K. P.; Nott, Prabhu R.
2016-02-01
Granular flows occur widely in nature and industry, yet a continuum description that captures their important features is yet not at hand. Recent experiments on granular materials sheared in a cylindrical Couette device revealed a puzzling anomaly, wherein all components of the stress rise nearly exponentially with depth. Here we show, using particle dynamics simulations and imaging experiments, that the stress anomaly arises from a remarkable vortex flow. For the entire range of fill heights explored, we observe a single toroidal vortex that spans the entire Couette cell and whose sense is opposite to the uppermost Taylor vortex in a fluid. We show that the vortex is driven by a combination of shear-induced dilation, a phenomenon that has no analogue in fluids, and gravity flow. Dilatancy is an important feature of granular mechanics, but not adequately incorporated in existing models.
A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly
Krishnaraj, K. P.; Nott, Prabhu R.
2016-01-01
Granular flows occur widely in nature and industry, yet a continuum description that captures their important features is yet not at hand. Recent experiments on granular materials sheared in a cylindrical Couette device revealed a puzzling anomaly, wherein all components of the stress rise nearly exponentially with depth. Here we show, using particle dynamics simulations and imaging experiments, that the stress anomaly arises from a remarkable vortex flow. For the entire range of fill heights explored, we observe a single toroidal vortex that spans the entire Couette cell and whose sense is opposite to the uppermost Taylor vortex in a fluid. We show that the vortex is driven by a combination of shear-induced dilation, a phenomenon that has no analogue in fluids, and gravity flow. Dilatancy is an important feature of granular mechanics, but not adequately incorporated in existing models. PMID:26864086
A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly.
Krishnaraj, K P; Nott, Prabhu R
2016-01-01
Granular flows occur widely in nature and industry, yet a continuum description that captures their important features is yet not at hand. Recent experiments on granular materials sheared in a cylindrical Couette device revealed a puzzling anomaly, wherein all components of the stress rise nearly exponentially with depth. Here we show, using particle dynamics simulations and imaging experiments, that the stress anomaly arises from a remarkable vortex flow. For the entire range of fill heights explored, we observe a single toroidal vortex that spans the entire Couette cell and whose sense is opposite to the uppermost Taylor vortex in a fluid. We show that the vortex is driven by a combination of shear-induced dilation, a phenomenon that has no analogue in fluids, and gravity flow. Dilatancy is an important feature of granular mechanics, but not adequately incorporated in existing models. PMID:26864086
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
Driven cavity simulation of turbomachine blade flows with vortex control
NASA Technical Reports Server (NTRS)
Athavale, M. M.; Przekwas, A. J.; Hendricks, R. C.
1993-01-01
This paper presents a computational study of the three-dimensional flows in a rotating cavity with clearance between cavity walls and lid wall. The objectives of this study is to understand the interaction mechanism between tip leakage and blade passage flows and to assess the means to control the flow pattern and pressure losses. The classes of problems addressed include: passage geometry, passage loading including lid velocity and anti-vortex strength, and placement necessary to provide flow control. The computational model is first validated on generic flow problems and then applied to a specific blade passage configuration. Results of parametric studies for secondary flow pattern control are analyzed, and practical means of vortex control are discussed.
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 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.
Exploratory experiments on acoustic oscillations driven by periodic vortex shedding
NASA Astrophysics Data System (ADS)
Dunlap, R.; Brown, R. S.
1981-03-01
Periodic vortex shedding is investigated as a mechanism by which low-amplitude pressure oscillations can be generated in segmented solid propellant rocket engines. Acoustic responses were monitored in an acoustically isolated flow chamber with two flow restrictors in the flow path as a function of resistor spacing and flow Mach number. At Mach 0.042, the maximum acoustic response is observed with a marked increase in the amplitude of the wave corresponding to the third acoustic mode of the chamber. Reduction of the Mach number by a factor of three is found to excite the first longitudinal mode of the chamber at the same restrictor spacing. Attempts to produce the second axial mode are unsuccessful when the restrictors were kept at the center of the chamber, indicating the importance of restrictor position relative to the acoustic mode structure. The restrictor spacing at which maximum response is obtained indicates a Strouhal number of 0.8 characterizing the vortex shedding frequency, in agreement with calculations. The results thus demonstrate that a significant (5-10%) pressure oscillation can be generated by coupling from periodic vortex shedding
Lee, J. ); Teitel, S. )
1994-08-01
We carry out driven-diffusion Monte Carlo simulations of the two-dimensional classical lattice Coulomb gas in an applied uniform electric field, as a model for vortex motion due to an applied dc current in a periodic superconducting network. A finite-size version of dynamic scaling is used to extract the dynamic critical exponent [ital z], and infer the nonlinear response at the transition temperature. We consider the Coulomb gases [ital f]=0 and [ital f]=1/2, corresponding to a superconducting network with an applied transverse magnetic field of zero, and one-half flux quantum per unit cell, respectively.
Floquet engineering with quasienergy bands of periodically driven optical lattices
NASA Astrophysics Data System (ADS)
Holthaus, Martin
2016-01-01
A primer on the Floquet theory of periodically time-dependent quantum systems is provided, and it is shown how to apply this framework for computing the quasienergy band structure governing the dynamics of ultracold atoms in driven optical cosine lattices. Such systems are viewed here as spatially and temporally periodic structures living in an extended Hilbert space, giving rise to spatio-temporal Bloch waves whose dispersion relations can be manipulated at will by exploiting ac-Stark shifts and multiphoton resonances. The elements required for numerical calculations are introduced in a tutorial manner, and some example calculations are discussed in detail, thereby illustrating future prospects of Floquet engineering.
Photonic currents in driven and dissipative resonator lattices
NASA Astrophysics Data System (ADS)
Mertz, Thomas; Vasić, Ivana; Hartmann, Michael J.; Hofstetter, Walter
2016-07-01
Arrays of coupled photonic cavities driven by external lasers represent a highly controllable setup to explore photonic transport. In this paper we address (quasi)-steady states of this system that exhibit photonic currents introduced by engineering driving and dissipation. We investigate two approaches: in the first one, photonic currents arise as a consequence of a phase difference of applied lasers and, in the second one, photons are injected locally and currents develop as they redistribute over the lattice. Effects of interactions are taken into account within a mean-field framework. In the first approach, we find that the current exhibits a resonant behavior with respect to the driving frequency. Weak interactions shift the resonant frequency toward higher values, while in the strongly interacting regime in our mean-field treatment the effect stems from multiphotonic resonances of a single driven cavity. For the second approach, we show that the overall lattice current can be controlled by incorporating few cavities with stronger dissipation rates into the system. These cavities serve as sinks for photonic currents and their effect is maximal at the onset of quantum Zeno dynamics.
Lattice-Polarity-Driven Epitaxy of Hexagonal Semiconductor Nanowires.
Wang, Ping; Yuan, Ying; Zhao, Chao; Wang, Xinqiang; Zheng, Xiantong; Rong, Xin; Wang, Tao; Sheng, Bowen; Wang, Qingxiao; Zhang, Yongqiang; Bian, Lifeng; Yang, Xuelin; Xu, Fujun; Qin, Zhixin; Li, Xinzheng; Zhang, Xixiang; Shen, Bo
2016-02-10
Lattice-polarity-driven epitaxy of hexagonal semiconductor nanowires (NWs) is demonstrated on InN NWs. In-polarity InN NWs form typical hexagonal structure with pyramidal growth front, whereas N-polarity InN NWs slowly turn to the shape of hexagonal pyramid and then convert to an inverted pyramid growth, forming diagonal pyramids with flat surfaces and finally coalescence with each other. This contrary growth behavior driven by lattice-polarity is most likely due to the relatively lower growth rate of the (0001̅) plane, which results from the fact that the diffusion barriers of In and N adatoms on the (0001) plane (0.18 and 1.0 eV, respectively) are about 2-fold larger in magnitude than those on the (0001̅) plane (0.07 and 0.52 eV), as calculated by first-principles density functional theory (DFT). The formation of diagonal pyramids for the N-polarity hexagonal NWs affords a novel way to locate quantum dot in the kink position, suggesting a new recipe for the fabrication of dot-based devices. PMID:26694227
Evolution of a superfluid vortex filament tangle driven by the Gross-Pitaevskii equation
NASA Astrophysics Data System (ADS)
Villois, Alberto; Proment, Davide; Krstulovic, Giorgio
2016-06-01
The development and decay of a turbulent vortex tangle driven by the Gross-Pitaevskii equation is studied. Using a recently developed accurate and robust tracking algorithm, all quantized vortices are extracted from the fields. The Vinen's decay law for the total vortex length with a coefficient that is in quantitative agreement with the values measured in helium II is observed. The topology of the tangle is then investigated showing that linked rings may appear during the evolution. The tracking also allows for determining the statistics of small-scale quantities of vortex lines, exhibiting large fluctuations of curvature and torsion. Finally, the temporal evolution of the Kelvin wave spectrum is obtained providing evidence of the development of a weak-wave turbulence cascade.
Evolution of a superfluid vortex filament tangle driven by the Gross-Pitaevskii equation.
Villois, Alberto; Proment, Davide; Krstulovic, Giorgio
2016-06-01
The development and decay of a turbulent vortex tangle driven by the Gross-Pitaevskii equation is studied. Using a recently developed accurate and robust tracking algorithm, all quantized vortices are extracted from the fields. The Vinen's decay law for the total vortex length with a coefficient that is in quantitative agreement with the values measured in helium II is observed. The topology of the tangle is then investigated showing that linked rings may appear during the evolution. The tracking also allows for determining the statistics of small-scale quantities of vortex lines, exhibiting large fluctuations of curvature and torsion. Finally, the temporal evolution of the Kelvin wave spectrum is obtained providing evidence of the development of a weak-wave turbulence cascade. PMID:27415198
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
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.
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.}
NASA Astrophysics Data System (ADS)
Dean, C. L.; Kunchur, M. N.; He, Q. L.; Liu, H.; Wang, J.; Lortz, R.; Sou, I. K.
2016-08-01
We investigated the dissipative regime of the Bi2Te3/FeTe topological insulator-chalcogenide interface superconductor at temperatures well below the Berezinski-Kosterlitz-Thouless transition. We observe a transition in the current-resistance and temperature-resistance curves that quantitatively agrees with the Likharev vortex-explosion phenomenon. In the limit of low temperatures and high current densities, we were able to demonstrate the regime of complete vortex-antivortex dissociation arising from current driven vortex-antivortex pair breaking.
Effects of parallel dynamics on vortex structures in electron temperature gradient driven turbulence
Nakata, M.; Watanabe, T.-H.; Sugama, H.; Horton, W.
2011-01-15
Vortex structures and related heat transport properties in slab electron temperature gradient (ETG) driven turbulence are comprehensively investigated by means of nonlinear gyrokinetic Vlasov simulations, with the aim of elucidating the underlying physical mechanisms of the transition from turbulent to coherent states. Numerical results show three different types of vortex structures, i.e., coherent vortex streets accompanied with the transport reduction, turbulent vortices with steady transport, and a zonal-flow-dominated state, depending on the relative magnitude of the parallel compression to the diamagnetic drift. In particular, the formation of coherent vortex streets is correlated with the strong generation of zonal flows for the cases with weak parallel compression, even though the maximum growth rate of linear ETG modes is relatively large. The zonal flow generation in the ETG turbulence is investigated by the modulational instability analysis with a truncated fluid model, where the parallel dynamics such as acoustic modes for electrons is incorporated. The modulational instability for zonal flows is found to be stabilized by the effect of the finite parallel compression. The theoretical analysis qualitatively agrees with secondary growth of zonal flows found in the slab ETG turbulence simulations, where the transition of vortex structures is observed.
Explosive-driven shock wave and vortex ring interaction with a propane flame
NASA Astrophysics Data System (ADS)
Giannuzzi, P. M.; Hargather, M. J.; Doig, G. C.
2016-02-01
Experiments were performed to analyze the interaction of an explosively driven shock wave and a propane flame. A 30 g explosive charge was detonated at one end of a 3-m-long, 0.6-m-diameter shock tube to produce a shock wave which propagated into the atmosphere. A propane flame source was positioned at various locations outside of the shock tube to investigate the effect of different strength shock waves. High-speed retroreflective shadowgraph imaging visualized the shock wave motion and flame response, while a synchronized color camera imaged the flame directly. The explosively driven shock tube was shown to produce a repeatable shock wave and vortex ring. Digital streak images show the shock wave and vortex ring propagation and expansion. The shadowgrams show that the shock wave extinguishes the propane flame by pushing it off of the fuel source. Even a weak shock wave was found to be capable of extinguishing the flame.
Gradient-Driven Vortex Motion in Nonneutral Plasmas and Ideal 2D Fluids
NASA Astrophysics Data System (ADS)
Schecter, David A.
2000-10-01
gradient exceeds a critical level, gradient-driven vortex motion is suppressed. An estimate of this critical shear compares favorably to vortex-in-cell simulations.
NASA Technical Reports Server (NTRS)
Lan, C. E.
1981-01-01
The nonplanar quasi-vortex-lattice method is applied to the calculation of lateral-directional stability derivatives of wings with and without vortex-lift effect. Results for conventional configurations and those with winglets, V-tail, etc. are compared with available data. All rolling moment derivatives are found to be accurately predicted. The prediction of side force and yawing moment derivatives for some configurations is not as accurate. Causes of the discrepancy are discussed. A user's manual for the program and the program listing are also included.
NASA Technical Reports Server (NTRS)
Lamar, J. E.; Gloss, B. B.
1975-01-01
Because the potential flow suction along the leading and side edges of a planform can be used to determine both leading- and side-edge vortex lift, the present investigation was undertaken to apply the vortex-lattice method to computing side-edge suction force for isolated or interacting planforms. Although there is a small effect of bound vortex sweep on the computation of the side-edge suction force, the results obtained for a number of different isolated planforms produced acceptable agreement with results obtained from a method employing continuous induced-velocity distributions. By using the method outlined, better agreement between theory and experiment was noted for a wing in the presence of a canard than was previously obtained.
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).
Chen, Shujun; Zhang, Senfu; Zhu, Qiyuan; Liu, Xianyin; Jin, Chendong; Wang, Jianbo; Liu, Qingfang
2015-05-07
By micromagnetic simulation, we investigated the dynamic of magnetic vortex driven by spin-polarized current in Permalloy nanodisks in the presence of interfacial/superficial Dzyaloshinskii-Moriya interactions (DMI). It is found that spin-polarized current can drive the vortex precession. In the presence of DMI, the oscillation frequency of the vortex is about 3 times higher than that of without DMI for the same nanodisk. Moreover, the linewidth is more narrow than that of without DMI when the radius of nanodisk is 50 nm. In addition, the vortex can support a higher current density than that of without DMI. Introduction of DMI in this system can provide a new way to design magnetic vortex oscillator.
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
NASA Astrophysics Data System (ADS)
Herrera-Vasco, Edwin; Guillamon, Isabel; Fente, Anton; Galvis, Jose; Correa, Alexandre; Luccas, Roberto; Mompean, Federico; Garcia Hernandez, Mar; Brison, Jean P.; Vieira, Sebastian; Suderow, Hermann
We present very low-temperature scanning tunneling microscopy (STM) experiments on the superconductor β-Bi2 Pd. We find a single superconducting gap from the zero-field tunneling conductance. We also find that the hexagonal vortex lattice is locked to the square atomic lattice. The magnetic field dependence of the intervortex tunneling conductance is higher than the one expected in a single-gap superconductor. Such an increase in the intervortex tunneling conductance has been found in superconductors with multiple superconducting gaps. We fit the upper critical field Hc2(T) and show that multiband Fermi surface is needed to explain the observed behavior. We propose that β-Bi2Pd is a single-gap multiband superconductor. We have measured the tilted vortex lattice (TVL) using a three axis superconducting magnet. Our results give first real space imaging of the TVL in a nearly isotropic s-wave BCS superconductor. From a detailed study of the TVL varying polar and azimuthal angles, we find correlations between the square atomic lattice and the TVL.
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. PMID:24460428
Mode-locking transitions and vortex flows in current-driven Josephson-junction arrays
NASA Astrophysics Data System (ADS)
Das, Shantilal; Sahdev, Deshdeep; Mehrotra, Ravi
1997-03-01
The dynamical behavior of overdamped dc-driven Josephson-junction arrays is studied numerically in two dimensions. Currents varying linearly along an edge are injected into the array and drawn out at the opposite edge either uniformly or through a busbar. The system is found to undergo a series of dynamical transitions as the gradient of the current drive is increased. We show that, for ladder arrays, these transitions mark the loss of mode locking across specific bonds. The transitions can, alternatively, be associated with the onset of well-defined vortex flows. Spatial localization of vortices in individual plaquettes of a ladder, driven in the direction of its length, is seen to stablize quasiperiodicity of order N>3 in a certain region of the underlying parameter space. We also discuss the extension of each of these features to full-fledged rectangular arrays.
Active suppression of vortex-driven combustion instability using controlled liquid-fuel injection
NASA Astrophysics Data System (ADS)
Pang, Bin
Combustion instabilities remain one of the most challenging problems encountered in developing propulsion and power systems. Large amplitude pressure oscillations, driven by unsteady heat release, can produce numerous detrimental effects. Most previous active control studies utilized gaseous fuels to suppress combustion instabilities. However, using liquid fuel to suppress combustion instabilities is more realistic for propulsion applications. Active instability suppression in vortex-driven combustors using a direct liquid fuel injection strategy was theoretically established and experimentally demonstrated in this dissertation work. Droplet size measurements revealed that with pulsed fuel injection management, fuel droplet size could be modulated periodically. Consequently, desired heat release fluctuation could be created. If this oscillatory heat release is coupled with the natural pressure oscillation in an out of phase manner, combustion instabilities can be suppressed. To identify proper locations of supplying additional liquid fuel for the purpose of achieving control, the natural heat release pattern in a vortex-driven combustor was characterized in this study. It was found that at high Damkohler number oscillatory heat release pattern closely followed the evolving vortex front. However, when Damkohler number became close to unity, heat release fluctuation wave no longer coincided with the coherent structures. A heat release deficit area was found near the dump plane when combustor was operated in lean premixed conditions. Active combustion instability suppression experiments were performed in a dump combustor using a controlled liquid fuel injection strategy. High-speed Schlieren results illustrated that vortex shedding plays an important role in maintaining self-sustained combustion instabilities. Complete combustion instability control requires total suppression of these large-scale coherent structures. The sound pressure level at the excited dominant
NASA Astrophysics Data System (ADS)
Zhang, Jianying; Yan, Guangwu; Wang, Moran
2016-02-01
A lattice Boltzmann model for solving the three-dimensional cubic-quintic complex Ginzburg-Landau equation (CQCGLE) is proposed. Differently from the classic lattice Boltzmann models, this lattice Boltzmann model is based on uniformly distributed lattice points in a three-dimensional space, and the evolution of the model is about a spatial axis rather than time. The algorithm provides advantages similar to the lattice Boltzmann method in that it is easily adapted to complex Ginzburg-Landau equations. Examples show that the model accurately reproduces the vortex tori pattern in the CQCGLE.
NASA Astrophysics Data System (ADS)
Wolf, Michael; Badea, Robert; Berezovsky, Jesse
The core of a ferromagnetic (FM) vortex domain creates a strong, localized magnetic field which can be manipulated on nanosecond timescales using small magnetic fields, or electrical currents. These capabilities present opportunities for nanoscale spin-based devices. Here, we demonstrate how these FM vortex properties can be used in a room temperature, integrated device by coupling a FM vortex to nitrogen-vacancy (NV) center spins in diamond. Measurements are carried out using a combined magneto-optical microscopy and optically-detected spin resonance technique. We show that the FM vortex can be driven into proximity with an NV, inducing significant NV spin splitting and sufficiently large magnetic field gradient to address spins separated by nanometer length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the NV spins, resulting in enhanced coherent rotation of the spin state. Finally we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on 100 ns timescales, while driving on faster timescales results in non-trivial coherent dynamics of the coupled vortex/NV system. We acknowledge the DOE Award #DE-SC008148.
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
NASA Astrophysics Data System (ADS)
Johnson, T. H.; Yuan, Y.; Bao, W.; Clark, S. R.; Foot, C.; Jaksch, D.
2016-06-01
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.
Haymaker, Richard W.; Matsuki, Takayuki
2007-01-01
We address the problem of determining the type I, type II or borderline dual superconductor behavior in maximal Abelian gauge SU(2) through the study of the dual Abrikosov vortex. We find that significant electric currents in the simulation data call into question the use of the dual Ginzburg-Landau Higgs model in interpreting the data. Further, two definitions of the penetration depth parameter take two different values. The splitting of this parameter into two is intricately connected to the existence of electric currents. It is important in our approach that we employ definitions of flux and electric and magnetic currents that respect Maxwell equations exactly for lattice averages independent of lattice spacings. Applied to specific Wilson loop sizes, our conclusions differ from those that use the dual GLH model.
NASA Astrophysics Data System (ADS)
Jiang, Xiaohai; Lee, Taehun; Andreopoulos, Yiannis; Wang, Zhexuan
2013-11-01
Vortex-induced vibrations (VIV) phenomena related to self-excited energy harvesters consisting of circular or square cylinders have been investigated numerically by using the BGK or MRT Lattice Boltzmann Method. In the present work such a harvester is placed inside a channel flow and is allowed to oscillate without a structural restoring force in a direction normal to the flow. Currently the half-way bounce-back boundary scheme and interpolations are being used to model the moving boundary. The numerical results were compared to the ones by classical CFD methods and experiments. A good agreement was obtained. The vortex dynamics and the development of the flow patterns for different flow parameters such as Reynolds number, blockage and aspect ratios will be presented. Particular emphasis is given to the dynamics of vortex pairing observed in several of the simulations. The present approach will be extended to simulate the flexible beam with the Immersed Boundary Method. Sponsored by the National Science Foundation (CBET #1033117) and a fellowship support from China Scholarship Council.
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
Lattice-Boltzmann simulation of coalescence-driven island coarsening
Basagaoglu, H.; Green, C.T.; Meakin, P.; McCoy, B.J.
2004-01-01
The first-order phase separation in a thin fluid film was simulated using a two-dimensional lattice-Boltzman model (LBM) with fluid-fluid interactions. The effects of the domain size on the intermediate asymptotic island size distribution were also discussed. It was observed that the overall process is dominated by coalescence which is independent of island mass. The results show that the combined effects of growth, coalescence, and Ostwald ripening control the phase transition process in the LBM simulations.
NASA Astrophysics Data System (ADS)
Vahala, George; Yepez, Jeffrey; Vahala, Linda
2008-04-01
The ground state wave function for a Bose Einstein condensate is well described by the Gross-Pitaevskii equation. A Type-II quantum algorithm is devised that is ideally parallelized even on a classical computer. Only 2 qubits are required per spatial node. With unitary local collisions, streaming of entangled states and a spatially inhomogeneous unitary gauge rotation one recovers the Gross-Pitaevskii equation. Quantum vortex reconnection is simulated - even without any viscosity or resistivity (which are needed in classical vortex reconnection).
Freezing, accelerating, and slowing directed currents in real time with superimposed driven lattices
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Aritra K.; Liebchen, Benno; Wulf, Thomas; Schmelcher, Peter
2016-05-01
We provide a generic scheme offering real-time control of directed particle transport using superimposed driven lattices. This scheme allows one to accelerate, slow, and freeze the transport on demand by switching one of the lattices subsequently on and off. The underlying physical mechanism hinges on a systematic opening and closing of channels between transporting and nontransporting phase space structures upon switching and exploits cantori structures which generate memory effects in the population of these structures. Our results should allow for real-time control of cold thermal atomic ensembles in optical lattices but might also be useful as a design principle for targeted delivery of molecules or colloids in optical devices.
Producing directed migration with correlated atoms in a tilted ac-driven lattice
NASA Astrophysics Data System (ADS)
Zheng, Yi; Yang, Shi-Jie
2016-06-01
The correlated atoms in a tilted optical lattice driven by an ac field are studied within the Hubbard model. By making use of both photon-assisted tunneling and coherent destructive tunneling effects, we can move a pair of strongly correlated atoms in the lattice via manipulating the global amplitude of the driving field. We propose a scheme for creating entanglement between the particle pair and a single particle through interacting oscillations. Our model may provide a new building block for investigating quantum computing and quantum information processing with ultracold atoms in optical lattices.
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
2016-01-01
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
Multiphoton interband excitations of quantum gases in driven optical lattices
NASA Astrophysics Data System (ADS)
Weinberg, M.; Ölschläger, C.; Sträter, C.; Prelle, S.; Eckardt, A.; Sengstock, K.; Simonet, J.
2015-10-01
We report on the observation of multiphoton interband absorption processes for quantum gases in shaken light crystals. Periodic inertial forcing, induced by a spatial motion of the lattice potential, drives multiphoton interband excitations of up to the ninth order. The occurrence of such excitation features is systematically investigated with respect to the potential depth and the driving amplitude. Ab initio calculations of resonance positions as well as numerical evaluation of their strengths exhibit good agreement with experimental data. In addition our findings could make it possible to reach novel phases of quantum matter by tailoring appropriate driving schemes.
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
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.
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.
Origin of Spontaneous Broken Mirror Symmetry of Vortex Lattices in Nb
NASA Astrophysics Data System (ADS)
Adachi, Hiroki M.; Ishikawa, Masaki; Hirano, Tomoya; Ichioka, Masanori; Machida, Kazushige
2011-11-01
Combining the microscopic Eilenberger theory with the first-principles band calculation, we investigate the stable flux line lattice (FLL) for a field applied to the fourfold axis, i.e., H\\parallel [001] in cubic Nb. The observed FLL transformation along Hc2 is almost perfectly explained without using adjustable parameter, including the tilted square, scalene triangle with broken mirror symmetry, and isosceles triangle lattices upon increasing T. We construct a minimum Fermi surface model to understand such morphologies, particularly the stability of the scalene triangle lattice attributed to the lack of mirror symmetry about the Fermi velocity maximum direction in k-space.
Lattice-Boltzmann Simulation of Coalescence-Driven Island Coarsening
Hakan Basagaoglu; Christopher T. Green; Paul Meakin; Benjamin J. McCoy
2004-10-01
A two-dimensional lattice-Boltzmann model (LBM) with fluid-fluid interactions was used to simulate first-order phase separation in a thin fluid film. The intermediate asymptotic time dependence of the mean island size, island number concentration, and polydispersity were determined and compared with the predictions of the distribution-kinetics model. The comparison revealed that the combined effects of growth, coalescence, and Ostwald ripening control the phase transition process in the LBM simulations. However, the overall process is dominated by coalescence, which is independent of island mass. As the phase transition advances, the mean island size increases, the number of islands decrease, and the polydispersity approaches unity, which conforms to the predictions of the distribution-kinetics model. The effects of the domain size on the intermediate asymptotic island size distribution, scaling form of the island size distribution, and the crossover to the long-term asymptotic behavior were elucidated. (C) 2004 American Institute of Physics.
Current-driven vortex domain wall motion in wire-tube nanostructures
NASA Astrophysics Data System (ADS)
Espejo, A. P.; Vidal-Silva, N.; López-López, J. A.; Goerlitz, D.; Nielsch, K.; Escrig, J.
2015-03-01
We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.
SUNRISE/IMaX Observations of Convectively Driven Vortex Flows in the Sun
NASA Astrophysics Data System (ADS)
Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios, J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.; Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
2010-11-01
We characterize the observational properties of the convectively driven vortex flows recently discovered on the quiet Sun, using magnetograms, Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE telescope. By visual inspection of time series, we find some 3.1 × 10-3 vortices Mm-2 minute-1, which is a factor of ~1.7 larger than previous estimates. The mean duration of the individual events turns out to be 7.9 minutes, with a standard deviation of 3.2 minutes. In addition, we find several events appearing at the same locations along the duration of the time series (31.6 minutes). Such recurrent vortices show up in the proper motion flow field map averaged over the time series. The typical vertical vorticities are lsim6 × 10-3 s-1, which corresponds to a period of rotation of some 35 minutes. The vortices show a preferred counterclockwise sense of rotation, which we conjecture may have to do with the preferred vorticity impinged by the solar differential rotation.
SUNRISE/IMaX OBSERVATIONS OF CONVECTIVELY DRIVEN VORTEX FLOWS IN THE SUN
Bonet, J. A.; Marquez, I.; Almeida, J. Sanchez; Pillet, V. MartInez; Palacios, J.; Domingo, V.; Solanki, S. K.; Gandorfer, A.; Barthol, P.; Del Toro Iniesta, J. C.; Berkefeld, T.; Schmidt, W.; Knoelker, M.
2010-11-10
We characterize the observational properties of the convectively driven vortex flows recently discovered on the quiet Sun, using magnetograms, Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE telescope. By visual inspection of time series, we find some 3.1 x 10{sup -3} vortices Mm{sup -2} minute{sup -1}, which is a factor of {approx}1.7 larger than previous estimates. The mean duration of the individual events turns out to be 7.9 minutes, with a standard deviation of 3.2 minutes. In addition, we find several events appearing at the same locations along the duration of the time series (31.6 minutes). Such recurrent vortices show up in the proper motion flow field map averaged over the time series. The typical vertical vorticities are {approx_lt}6 x 10{sup -3} s{sup -1}, which corresponds to a period of rotation of some 35 minutes. The vortices show a preferred counterclockwise sense of rotation, which we conjecture may have to do with the preferred vorticity impinged by the solar differential rotation.
Current-driven vortex domain wall motion in wire-tube nanostructures
Espejo, A. P.; Vidal-Silva, N.; López-López, J. A.; Goerlitz, D.; Nielsch, K.; Escrig, J.
2015-03-30
We have investigated the current-driven domain wall motion in nanostructures comprised of a pair of nanotube and nanowire segments. Under certain values of external magnetic fields, it is possible to pin a vortex domain wall in the transition zone between the wire and tube segments. We explored the behavior of this domain wall under the action of an electron flow applied in the opposite direction to the magnetic field. Thus, for a fixed magnetic field, it is possible to release a domain wall pinned simply by increasing the intensity of the current density, or conversely, for a fixed current density, it is possible to release the domain wall simply decreasing the magnetic external field. When the domain wall remains pinned due to the competition between the current density and the magnetic external field, it exhibits a oscillation frequency close to 8 GHz. The amplitude of the oscillations increases with the current density and decreases over time. On the other hand, when the domain wall is released and propagated through the tube segment, this shows the standard separation between a steady and a precessional regime. The ability to pin and release a domain wall by varying the geometric parameters, the current density, or the magnetic field transforms these wire-tube nanostructures in an interesting alternative as an on/off switch nano-transistor.
Anomalous magnetization due to the vortex lattice melting transition in YBa{sub 2}Cu{sub 3}O{sub y}
Nishizaki, Terukazu; Onodera, Yasuaki; Naito, Tomoyuki; Kobayashi, Norio
1996-12-01
Magnetization measurements in YBa{sub 2}Cu{sub 3}O{sub y} single crystals are performed as a function of the temperature T and the magnetic field H. It is found that an anomalous magnetization step which provides the thermodynamic evidence of the first-order vortex lattice melting transition and the resistive kink with the hysteresis are observed in the same phase boundary in H-T plane. For samples with a small value of the irreversibility field H{sub irr}(T) as compared with the vortex lattice melting line H{sub m}(T), the vortex lattice melting is observed in the reversible magnetization region and the entropy change per vortex per CuO{sub 2} layer at the transition is estimated to be {Delta}s {approx_equal} 0.5 - 1.0 k{sub B}. For samples with a slightly larger value of H{sub irr}(T) comparable to H{sub m}(T), on the other hand, the jump height and the value of {Delta}s is enhanced. Thus, the value of {Delta}s is affected significantly by the relation between H{sub irr}(T) which varies from sample to sample and H{sub m}(T) which is an universal line.
Anisotropic vortex lattice in YBa[sub 2]Cu[sub 3]O[sub 7
Yethiraj, M.; Mook, H.A.; Wignall, G.D.; Cubitt, R.; Forgan, E.M.; Lee, S.L.; Paul, D.M.; Armstrong, T. Superconductivity Research Group, University of Birmingham, Birmingham B15 2TT Physik-Institut der Universitaet Zuerich, Schoenberggasse 9, CH 8001, Zuerich Department of Physics, University of Warwick, Coventry CV4 7AL Allied Signal Research Laboratories, Torrance, California 90509 )
1993-11-01
We report on small angle neutron scattering observations of the flux line lattice (FLL) in a single crystal of YBa[sub 2]Cu[sub 3]O[sub 7]. To probe the mass anisotropy ratio, [ital m][sub 3]/[ital m][sub 1], measurements were made as a function of angle, [Theta], between the 8 kOe applied field and the crystallographic (001) axis for 0[degree][le][Theta][le]80[degree]. With the rotation about an [ital a]/[ital b] (or [ital y]) axis, two symmetry-related distorted hexagonal FLL domains formed. Contrary to theoretical prediction, the lattices formed are consistent with a rotation of the short basis vector, [bold a][sub 1], from the [ital x] axis by 15[degree], after the effects of anisotropy are removed. The mass ratio is 20[plus minus]2, which is slightly lower than published values. The temperature dependence of the intensity is not conventional.
Singularimetry of local phase gradients using vortex lattices and in-line holography.
Petersen, Timothy C; Bishop, Alexis I; Eastwood, Samuel A; Paganin, David M; Morgan, Kaye S; Morgan, Michael J
2016-02-01
We have developed a differential form of singularimetry, which utilizes phase vortices or intensity gradient singularities as topological fiducial markers in a structured illumination context. This approach analytically measures phase gradients imparted by refracting specimens, yielding quantitative information that is both local and deterministic. We have quantified our phase gradient experiments to demonstrate that lattices of wave field singularities can be used to detect subtle phase gradients imparted by a spherical specimen and fiber optic cylinders. PMID:26906802
Existence and non-existence of breather solutions in damped and driven nonlinear lattices
NASA Astrophysics Data System (ADS)
Hennig, D.
2013-10-01
We investigate the existence of spatially localised solutions, in the form of discrete breathers, in general damped and driven nonlinear lattice systems of coupled oscillators. Conditions for the exponential decay of the difference between the maximal and minimal amplitudes of the oscillators are provided which proves that initial non-uniform spatial patterns representing breathers attain exponentially fast a spatially uniform state preventing the formation and/or preservation of any breather solution at all. Strikingly our results are generic in the sense that they hold for arbitrary dimension of the system, any attractive interaction, coupling strength and on-site potential and general driving fields. Furthermore, our rigorous quantitative results establish conditions under which discrete breathers in general damped and driven nonlinear lattices can exist at all and open the way for further research on the emergent dynamical scenarios, in particular features of pattern formation, localisation and synchronisation, in coupled cell networks.
NASA Technical Reports Server (NTRS)
Gross, L. W.
1976-01-01
The F-4E (CCV) wind tunnel model with closely coupled canard control surfaces was analyzed by means of a version of a vortex lattice program that included the effects of nonlinear leading edge or side edge vortex lift on as many as four individual planforms. The results were compared with experimental data from wind tunnel tests of a 5% scale model tested at a Mach number M = 0.6. They indicated that a nonlinear vortex lift developed on the side edges due to tip vortices, but did not appear to develop on the leading edges within the range of angles of attack that were studied. Instead, substantial leading edge thrust was developed on the lifting surfaces. A configuration buildup illustrated the mutual interference between the wing and control surfaces. On the configuration studied, addition of the wing increased the loading on the canard, but the additional load on the canard due to adding the stabilator was small.
Hierarchy of gaps and magnetic minibands in graphene in the presence of the Abrikosov vortex lattice
NASA Astrophysics Data System (ADS)
Chen, Xi; Fal'ko, Vladimir I.
2016-01-01
We determine the bands and gaps in graphene subjected to the magnetic field of an Abrikosov lattice of vortices in the underlying superconducting film. The spectrum features one nondispersive magnetic miniband at zero energy, separated by the largest gaps in the miniband spectrum from a pair of minibands resembling a slightly broadened first Landau level in graphene, suggesting the persistence of ν =±2 and ±6 quantum Hall effect states. Also, we identify an occasional merging point of magnetic minibands with a Dirac-type dispersion at the miniband edges.
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.
Effect of magnetic impurities on the vortex lattice properties in NbSe{sub 2} single crystals.
Iavarone, M.; Di Capua, R.; Karapetrov, G.; Koshelev, A. E.; Rosenmann, D.; Claus, H.; Malliakas, C. D.; Kanatzidis, M. G.; Nishizaki, T.; Kobayashi, N.; Materials Science Division; Univ. degli Studi del Molise; CNR-INFM Coherentia; Northwestern Univ.; Tohoku Univ.
2008-11-01
We report a pronounced peak effect in the magnetization of Co{sub x}NbSe{sub 2} single crystals with critical temperatures T{sub c} ranging between 7.1 and 5.0 K, and Mn{sub x}NbSe{sub 2} single crystals with critical temperatures down to 3.4 K. We correlate the peak effect in magnetization with the structure of the vortex lattice across the peak-effect region using scanning-tunneling microscopy. Magnetization measurements show that the amplitude of the peak effect in the case of Co{sub x}NbSe{sub 2} exhibits a nonmonotonic behavior as a function of the Co content, reaching a maximum for concentration of Co of about 0.4 at. % (corresponding to a T{sub c} of 5.7 K) and after that gradually decreasing in amplitude with the increase in the Co content. The normalized value of the peak position H{sub p}/H{sub c2} has weak dependence on Co concentration. In the case of Mn{sub x}NbSe{sub 2} the features of the peak effect as a function of the Mn content are different and they can be understood in terms of strong pinning.
History Dependence of the Vortex Lattice Rotation in the B-phase of UPt3 with H ∥ c
NASA Astrophysics Data System (ADS)
Avers, K. E.; Eskildsen, M. R.; Halperin, W. P.; Gannon, W. J.; Gavilano, J. L.; Nagy, G.; Gasser, U.
The unconventional superconductor UPt3 is widely believed to be a triplet superconductor, where the low temperature superconducting B-phase is a chiral state. We have performed small angle neutron scattering (SANS) from the vortex lattice (VL) in UPt3 at the Paul Scherrer Institute with the magnetic field parallel to the hexagonal c-axis in the 0.5 T to 0.9 T range. The diffraction pattern of the VL rotates away from a high symmetry direction producing two domains of different orientation. Our field dependent measurements show a subtle magnetic field history dependence of this orientation; VLs prepared with the magnetic field parallel or anti-parallel with respect to the angular momentum from the circulating screening currents show different field-history dependence. These results suggest a coupling of a chiral superconducting order parameter with the applied magnetic field. US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Awards DE-FG02-10ER46783 (University of Notre Dame; neutron scattering) and DE-FG02-05ER46248 (Northwestern University; crystal growth, characterization, neutron.
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.
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
Interaction-Driven Spontaneous Quantum Hall Effect on a Kagome Lattice.
Zhu, W; Gong, Shou-Shu; Zeng, Tian-Sheng; Fu, Liang; Sheng, D N
2016-08-26
Topological states of matter have been widely studied as being driven by an external magnetic field, intrinsic spin-orbital coupling, or magnetic doping. Here, we unveil an interaction-driven spontaneous quantum Hall effect (a Chern insulator) emerging in an extended fermion-Hubbard model on a kagome lattice, based on a state-of-the-art density-matrix renormalization group on cylinder geometry and an exact diagonalization in torus geometry. We first demonstrate that the proposed model exhibits an incompressible liquid phase with doublet degenerate ground states as time-reversal partners. The explicit spontaneous time-reversal symmetry breaking is determined by emergent uniform circulating loop currents between nearest neighbors. Importantly, the fingerprint topological nature of the ground state is characterized by quantized Hall conductance. Thus, we identify the liquid phase as a quantum Hall phase, which provides a "proof-of-principle" demonstration of the interaction-driven topological phase in a topologically trivial noninteracting band. PMID:27610866
Tseng, W.S.; Lin, W.L.; Yin, C.P.; Lin, C.L.; Lin, T.F.
2000-02-01
At high buoyancy-to-inertia ratio frequently encountered in various heat transfer equipment, the buoyancy-driven secondary vortex flow in a forced laminar flow through a bottom heated rectangular duct is rather unstable. Heat transfer augmentation associated with the buoyancy-driven vortex flow is desirable and welcome in many technological applications in which the efficient energy transport is of major concern. Here, stabilization of the buoyancy-driven unstable mixed convective vortex air flow in a bottom heated rectangular duct by tapering its top plate is investigated experimentally. Specifically, the duct is tapered so that its aspect ratio at the duct inlet is 4 and gradually raised to 12 at the exit of the duct. In the study the secondary flow in the duct is visualized and the steady and transient thermal characteristics of the flow are examined by measuring the spanwise distributions of the time-average temperature. The effects of the Reynolds and Grashof numbers on the vortex flow structure are studied in detail. Moreover, the spanwise-averaged Nusselt numbers for the horizontal rectangular and tapering ducts are also measured and compared. Furthermore, the time records of the air temperature are obtained to further detect the temporal stability of the flow. Over the ranges of the Re and Gr investigated for 5 {le} Re {le} 102 and 1.0 x 10{sup 4} {le} Gr {le} 1.7 x 10{sup 5}, the vortex flow induced in the rectangular duct exhibits temporal transition from a steady laminar to time periodic and then to chaotic state at increasing buoyancy-to-inertia ratio. Substantial change in the spatial structure of the vortex flow is also noted to accompany this temporal transition. The results for the tapering duct indicate that more vortex rolls can be induced due to the increase in the aspect ratio of the duct with the axial distance. But the vortex rolls are weaker and are completely stabilized by the tapering of the top plate.
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.
NASA Astrophysics Data System (ADS)
Yu, Huidan; Zhang, Jinsuo; Li, Ning
2006-03-01
We investigate the enhancement of mass transfer in 2D thermally driven cavities using lattice Boltzmann equation (LBE) method. The computational technique integrates three coupled LBEs for solving velocity, temperature, and concentration fields simultaneously. Simulation is performed for oxygen transfer in lead/lead-bismuth eutectic with variations of temperature boundary, Schmidt number, and field aspect ratio to investigate the effects on enhancement of oxygen transfer. Interested characteristics include oxygen concentration, Sherwood number, and velocity profiles, etc. Our results clearly indicate that oxygen transfer is dominated by convection while diffusion also plays a role on it. Comparative studies demonstrate that side heating and top cooling device is more efficient to transfer oxygen than side heating and cooling device and oxygen transfers more rapidly in square cavity than in rectangular cavity. This work establishes a reliable thermal LBE model for thermally driven heat and mass transfer.
Driven dynamic mode-splitting of the magnetic vortex translational resonance.
Buchanan, K. S.; Grimsditch, M.; Fradin, F. Y.; Bader, S. D.; Novosad, V.
2007-12-31
A magnetic vortex in a restricted geometry possesses a nondegenerate translational excitation that corresponds to circular motion of its core at a characteristic frequency. For 40-nm thick, micron-sized permalloy elements, we find that the translational-mode microwave absorption peak splits into two peaks that differ in frequency by up to 25% as the driving field is increased. An analysis of micromagnetic equations shows that for large driving fields two stable solutions emerge.
Competition of coarsening and shredding of clusters in a driven diffusive lattice gas
NASA Astrophysics Data System (ADS)
Kunwar, Ambarish; Chowdhury, Debashish; Schadschneider, Andreas; Nishinari, Katsuhiro
2006-06-01
We investigate a driven diffusive lattice gas model with two oppositely moving species of particle. The model is motivated by bidirectional traffic of ants on a pre-existing trail. A third species, corresponding to pheromones used by the ants for communication, is not conserved and mediates interactions between the particles. Here we study the spatio-temporal organization of the particles. In the unidirectional variant of this model it is known to be determined by the formation and coarsening of 'loose clusters'. For our bidirectional model, we show that the interaction of oppositely moving clusters is essential. In the late stages of evolution the cluster size oscillates because of a competition between their 'shredding' during encounters with oppositely moving counterparts and subsequent 'coarsening' during collision-free evolution. We also establish a nontrivial dependence of the spatio-temporal organization on the system size.
Observing artificial-field-driven vortex nucleation in a BEC via bulk response
NASA Astrophysics Data System (ADS)
Leblanc, L. J.; Jiménez-García, K.; Williams, R. A.; Beeler, M. C.; Perry, A. R.; Spielman, I. B.
2014-05-01
By exploiting the quantum mechanical phase's relationship to velocity, we extracted information about a Bose-Einstein condensate's (BEC's) order parameter through time-of-flight (TOF) imaging. In these experiments, trapped BECs were equilibrated in Raman-induced artificial gauge fields, then released and imaged. The removal of the artificial field at the moment of release caused a shearing of the atomic distribution as the BEC evolved in field-free TOF. The quantitative measure of the cloud's shear increased suddenly at magnetic fields sufficient to nucleate vortices. Using superfluid hydrodynamics and Gross-Pitaevskii equation calculations, we confirmed the critical field for this structural phase transition from the vortex-free state. We discuss the relationship between the apparatus and the vector potential's ``natural gauge'' in quantum gas experiments with artificial magnetic fields. Current address: University of Alberta.
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.
Anupindi, Kameswararao; Lai, Weichen; Frankel, Steven
2014-01-01
In the present work, lattice Boltzmann method (LBM) is applied for simulating flow in a three-dimensional lid driven cubic and deep cavities. The developed code is first validated by simulating flow in a cubic lid driven cavity at 1000 and 12000 Reynolds numbers following which we study the effect of cavity depth on the steady-oscillatory transition Reynolds number in cavities with depth aspect ratio equal to 1, 2 and 3. Turbulence modeling is performed through large eddy simulation (LES) using the classical Smagorinsky sub-grid scale model to arrive at an optimum mesh size for all the simulations. The simulation results indicate that the first Hopf bifurcation Reynolds number correlates negatively with the cavity depth which is consistent with the observations from two-dimensional deep cavity flow data available in the literature. Cubic cavity displays a steady flow field up to a Reynolds number of 2100, a delayed anti-symmetry breaking oscillatory field at a Reynolds number of 2300, which further gets restored to a symmetry preserving oscillatory flow field at 2350. Deep cavities on the other hand only attain an anti-symmetry breaking flow field from a steady flow field upon increase of the Reynolds number in the range explored. As the present work involved performing a set of time-dependent calculations for several Reynolds numbers and cavity depths, the parallel performance of the code is evaluated a priori by running the code on up to 4096 cores. The computational time required for these runs shows a close to linear speed up over a wide range of processor counts depending on the problem size, which establishes the feasibility of performing a thorough search process such as the one presently undertaken. PMID:24587561
Anupindi, Kameswararao; Lai, Weichen; Frankel, Steven
2014-03-20
In the present work, lattice Boltzmann method (LBM) is applied for simulating flow in a three-dimensional lid driven cubic and deep cavities. The developed code is first validated by simulating flow in a cubic lid driven cavity at 1000 and 12000 Reynolds numbers following which we study the effect of cavity depth on the steady-oscillatory transition Reynolds number in cavities with depth aspect ratio equal to 1, 2 and 3. Turbulence modeling is performed through large eddy simulation (LES) using the classical Smagorinsky sub-grid scale model to arrive at an optimum mesh size for all the simulations. The simulation results indicate that the first Hopf bifurcation Reynolds number correlates negatively with the cavity depth which is consistent with the observations from two-dimensional deep cavity flow data available in the literature. Cubic cavity displays a steady flow field up to a Reynolds number of 2100, a delayed anti-symmetry breaking oscillatory field at a Reynolds number of 2300, which further gets restored to a symmetry preserving oscillatory flow field at 2350. Deep cavities on the other hand only attain an anti-symmetry breaking flow field from a steady flow field upon increase of the Reynolds number in the range explored. As the present work involved performing a set of time-dependent calculations for several Reynolds numbers and cavity depths, the parallel performance of the code is evaluated a priori by running the code on up to 4096 cores. The computational time required for these runs shows a close to linear speed up over a wide range of processor counts depending on the problem size, which establishes the feasibility of performing a thorough search process such as the one presently undertaken. PMID:24587561
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.
Aegerter, C.M.; Hofer, J.; Savic, I.M.; Keller, H.; Lee, S.L.; Ager, C.; Lloyd, S.H.; Forgan, E.M.
1998-01-01
Using the techniques of muon spin rotation and torque magnetometry, we investigate the crossover field B{sub cr} in Bi{sub 2.15}Sr{sub 1.85}Ca{sub 1}Cu{sub 2}O{sub 8+{delta}} at which the vortex lattice becomes disordered along the field direction. It is found that B{sub cr} scales as the projection of the applied field along the perpendicular to the superconducting planes. This has the implication that a field large enough to give a disordered lattice when applied perpendicular to the planes, can give a well-ordered vortex-line lattice for angles of the field to the c axis greater than a critical value. {copyright} {ital 1998} {ital The American Physical Society}
Mathematical aspects of vortex dynamics; Proceedings of the Workshop, Leesburg, VA, Apr. 25-27, 1988
Caflisch, R.E.
1989-01-01
Various papers on the mathematical aspects of vortex dynamics are presented. Individual topics addressed include: mathematical analysis of vortex dynamics, improved vortex methods for three-dimensional flows, the relation between thin vortex layer and vortex sheets, computations of broadband instabilities in a class of closed-streamline flows, vortex-sheet dynamics and hyperfunction theory, free surface vortex method with weak viscous effects, iterative method for computing steady vortex flow systems, invariant measures for the two-dimensional Euler flow, similarity flows containing two-branched vortex sheets, strain-induced vortex stripping, convergence of the vortex method for vortex sheets, boundary conditions and deterministic vortex methods for the Navier-Stokes equations, vorticity creation boundary conditions, vortex dynamics of stratified flows, vortex breakdown, numerical studies of vortex reconnection, vortex lattices in theory and practice, dynamics of vortex structures in the wall region of a turbulent boundary layer, and energy of a vortex lattice configuration.
NASA Astrophysics Data System (ADS)
Wu, Ya-Jie; Li, Ning; He, Jing; Kou, Su-Peng
2016-03-01
In this paper, based on mean-field approach and random-phase-approximation, we study the magnetic properties of the repulsive Haldane-Hubbard model on a square lattice. We find antiferromagnetic order driven topological spin density waves beyond Landau’s symmetry-breaking paradigm, for which the effective low energy physics is determined by Chern-Simons-Hopf gauge field theories with different K matrices.
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.
Ferrando, Albert; Garcia-March, Miguel-Angel
2005-09-16
Using group theory arguments and numerical simulations, we demonstrate the possibility of changing the vorticity or topological charge of an individual vortex by means of the action of a system possessing a discrete rotational symmetry of finite order. We establish on theoretical grounds a 'transmutation pass rule' determining the conditions for this phenomenon to occur and numerically analyze it in the context of two-dimensional optical lattices. An analogous approach is applicable to the problems of Bose-Einstein condensates in periodic potentials.
Siracusano, G; Tomasello, R; Giordano, A; Puliafito, V; Azzerboni, B; Ozatay, O; Carpentieri, M; Finocchio, G
2016-08-19
Solitons are very promising for the design of the next generation of ultralow power devices for storage and computation. The key ingredient to achieving this goal is the fundamental understanding of their stabilization and manipulation. Here, we show how the interfacial Dzyaloshinskii-Moriya Interaction (IDMI) is able to lift the energy degeneracy of a magnetic vortex state by stabilizing a topological soliton with radial chirality, hereafter called radial vortex. It has a noninteger Skyrmion number S (0.5<|S|<1) due to both the vortex core polarity and the magnetization tilting induced by the IDMI boundary conditions. Micromagnetic simulations predict that a magnetoresistive memory based on the radial vortex state in both free and polarizer layers can be efficiently switched by a threshold current density smaller than 10^{6} A/cm^{2}. The switching processes occur via the nucleation of topologically connected vortices and vortex-antivortex pairs, followed by spin-wave emissions due to vortex-antivortex annihilations. PMID:27588879
THz-Driven Ultrafast Spin-Lattice Scattering in Amorphous Metallic Ferromagnets.
Bonetti, S; Hoffmann, M C; Sher, M-J; Chen, Z; Yang, S-H; Samant, M G; Parkin, S S P; Dürr, H A
2016-08-19
We use single-cycle THz fields and the femtosecond magneto-optical Kerr effect to, respectively, excite and probe the magnetization dynamics in two thin-film ferromagnets with different lattice structures: crystalline Fe and amorphous CoFeB. We observe Landau-Lifshitz-torque magnetization dynamics of comparable magnitude in both systems, but only the amorphous sample shows ultrafast demagnetization caused by the spin-lattice depolarization of the THz-induced ultrafast spin current. Quantitative modeling shows that such spin-lattice scattering events occur on similar time scales than the conventional spin conserving electronic scattering (∼30 fs). This is significantly faster than optical laser-induced demagnetization. THz conductivity measurements point towards the influence of lattice disorder in amorphous CoFeB as the driving force for enhanced spin-lattice scattering. PMID:27588880
NASA Astrophysics Data System (ADS)
Yepez, J.; Vahala, G.; Vahala, L.
2009-04-01
Presented is a type-II quantum algorithm for superfluid dynamics, used to numerically predict solutions of the GP equation for a complex scalar field (spinless bosons) in φ4 theory. The GP equation is a long wavelength effective field theory of a microscopic quantum lattice gas with nonlinear state reduction. The quantum lattice gas algorithm for modeling the dynamics of the one-body BEC state in 3+1 dimensions is presented. To demonstrate the method's strength as a computational physics tool, a difficult situation of filamentary singularities is simulated, the dynamics of solitary vortex-antivortex pairs, which are a basic building block of morphologies of quantum turbulence.
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.
Tilt-modulus enhancement of the vortex lattice in the layered superconductor 2 H -NbSe sub 2
Koorevaar, P.; Aarts, J.; Berghuis, P.; Kes, P.H. )
1990-07-01
The field dependence of the pinning force has been studied in thin single crystals of the layered superconductor 2{ital H}-NbSe{sub 2} in fields directed perpendicular to the layers. At high fields a peak effect is observed which sets in at about {ital B}{sub co}{approx}0.8{ital B}{sub {ital c}2}. Below this field the pinning force agrees well with the theory of two-dimensional collective pinning. The onset of the peak is triggered by the transition to three-dimensional flux-line lattice (FLL) disorder at the field {ital B}{sub co}. Comparison of the crossover field with the criterion set by the collective-pinning theory reveals that the tilt modulus of the FLL in a layered superconductor is considerably reduced. The reduction factor corresponds very well to recent theoretical predictions. These results are of importance for the prediction of depinning and flux-line lattice melting in all kinds of anisotropic superconductors.
NASA Astrophysics Data System (ADS)
Cuadra-Solís, P.-de-J.; Hernandez, J. M.; García-Santiago, A.; Tejada, J.; Vanacken, J.; Moshchalkov, V. V.
2013-12-01
Different vortex penetration regimes have been registered in the output voltage signal of a magnetometer when single microwave pulses are applied to an epitaxial overdoped La2-xSrxCuO4 thin film in a perpendicular dc magnetic field. The onset of a significant variation in the sample magnetization which exists below threshold values of temperature, dc magnetic field, and pulse duration is interpreted as an avalanche-type flux penetration. The microwave contribution to the background electric field suggests that the nucleation of this fast vortex motion is of electric origin, which also guarantees the occurrence of vortex instabilities under adiabatic conditions via the enhancement of the flux flow resistivity. Flux creep phenomena and heat transfer effects act as stabilizing factors against the microwave-pulse-induced fast flux diffusion.
NASA Technical Reports Server (NTRS)
Berry, John D.
1988-01-01
A method is described for the analysis of the unsteady, incompressible potential flow associated with a helicopter rotor and it's wake in forward flight. This method is particularly useful in low advance ratio flight due to the major contribution, in the near field, of the deformed wake. The rotor geometry is prescribed and the unsteady wake geometry is computed from the local flow perturbation velocities. The wake is modeled as a full vortex lattice. The rotor geometry is arbitrary and several rotor blades can be represented. The unsteady airloads on the rotor blades are computed in the presence of the deformed rotor wake by a time-stepping technique. Solution for the load distribution on the blade surfaces is found by prescribing boundary conditions in a reference system which rotates with the blade tips. Transformation tensors are used to describe the contribution of the wake in the inertial system to the rotor in the rotating reference system. The effects of blade cyclic pitch variation are computed using a rotation tensor. The deformation of the wake is computed in the inertial frame. The wake is started impulsively from rest, allowing a natural convection of the wake with time.
Self-similar roll-up of a vortex sheet driven by a shear flow: Hyperbolic double spiral
NASA Astrophysics Data System (ADS)
Sohn, Sung-Ik
2016-06-01
In this paper, we consider the roll-up of an infinite vortex sheet and investigate its self-similar behavior. We address the question of whether the unsteady double spiral produced by the curvature singularity in finite time exhibits self-similar behavior. We find a self-similar solution of the double-spiral vortex sheet, which in fact, is a hyperbolic spiral. The radius of the spiral asymptotically grows with time and is proportional to the inverse of the angle from the spiral center. The curvature singularity plays the role of triggering spiral formation, but the source of vorticity for forming the spiral is the initial vorticity of the sheet. We show analytically that the self-similar solution satisfies the Birkhoff-Rott equation asymptotically. Numerical validation is also given by applying the blob-regularization model to the vortex sheet with a periodic perturbation. We examine various asymptotic relations among primitive variables for the spiral turns and find agreement of numerical results of the inner turns of the vortex sheet with the analytic solution. Our study clarifies contrasting results on the existence of the self-similar double-spiral of a large structure in the previous studies. Our solution also suggests the possibility of bifurcation of the self-similar solution of the double-spiral as the sheet strength varies.
Fulde-Ferrell Superfluids without Spin Imbalance in Driven Optical Lattices.
Zheng, Zhen; Qu, Chunlei; Zou, Xubo; Zhang, Chuanwei
2016-03-25
Spin-imbalanced ultracold Fermi gases have been widely studied recently as a platform for exploring the long-sought Fulde-Ferrell-Larkin-Ovchinnikov superfluid phases, but so far conclusive evidence has not been found. Here we propose to realize an Fulde-Ferrell (FF) superfluid without spin imbalance in a three-dimensional fermionic cold atom optical lattice, where s- and p-orbital bands of the lattice are coupled by another weak moving optical lattice. Such coupling leads to a spin-independent asymmetric Fermi surface, which, together with the s-wave scattering interaction between two spins, yields an FF type of superfluid pairing. Unlike traditional schemes, our proposal does not rely on the spin imbalance (or an equivalent Zeeman field) to induce the Fermi surface mismatch and provides a completely new route for realizing FF superfluids. PMID:27058062
Lattice Boltzmann model for Coulomb-driven flows in dielectric liquids
NASA Astrophysics Data System (ADS)
Luo, Kang; Wu, Jian; Yi, Hong-Liang; Tan, He-Ping
2016-02-01
In this paper, we developed a unified lattice Boltzmann model (LBM) to simulate electroconvection in a dielectric liquid induced by unipolar charge injection. Instead of solving the complex set of coupled Navier-Stokes equations, the charge conservation equation, and the Poisson equation of electric potential, three consistent lattice Boltzmann equations are formulated. Numerical results are presented for both strong and weak injection regimes, and different scenarios for the onset and evolution of instability, bifurcation, and chaos are tracked. All LBM results are found to be highly consistent with the analytical solutions and other numerical work.
Lattice Boltzmann model for Coulomb-driven flows in dielectric liquids.
Luo, Kang; Wu, Jian; Yi, Hong-Liang; Tan, He-Ping
2016-02-01
In this paper, we developed a unified lattice Boltzmann model (LBM) to simulate electroconvection in a dielectric liquid induced by unipolar charge injection. Instead of solving the complex set of coupled Navier-Stokes equations, the charge conservation equation, and the Poisson equation of electric potential, three consistent lattice Boltzmann equations are formulated. Numerical results are presented for both strong and weak injection regimes, and different scenarios for the onset and evolution of instability, bifurcation, and chaos are tracked. All LBM results are found to be highly consistent with the analytical solutions and other numerical work. PMID:26986441
Equilibrium and Dynamic Vortex States near Absolute Zero in a Weak Pinning Amorphous Film
NASA Astrophysics Data System (ADS)
Ochi, Aguri; Sohara, Naoya; Kaneko, Shin-ichi; Kokubo, Nobuhito; Okuma, Satoshi
2016-04-01
By developing and employing a mode-locking measurement with pulsed currents, we successfully determine the dynamic melting field B{c,dyn}∞ (T) for a driven vortex lattice of an amorphous MoxGe1-x film in the limit of zero temperature (T → 0) and complete a dynamic as well as a static vortex phase diagram. At T = 0, the mixed state in the absence of pinning comprises vortex-lattice and quantum-vortex-liquid (QVL) phases, and the melting field separating the two phases is identified as B{c,dyn}∞ (0). Comparison of the dynamic and static phase diagrams reveals that, when the weak pinning is introduced into the pin-free system, a disordered phase emerges just above the vortex-lattice phase and a threshold field separating the two phases is slightly suppressed from B{c,dyn}∞ (0), indicative of defect-induced disordering of the lattice. By contrast, a melting field into QVL is much enhanced from B{c,dyn}∞ (0) up to a point near the upper critical field, resulting in a significant suppression of the QVL phase. This is attributed to the stronger effective pinning at lower T, which survives quantum fluctuations.
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.
Boundary-field-driven control of discontinuous phase transitions on hyperbolic lattices.
Lee, Yoju; Verstraete, Frank; Gendiar, Andrej
2016-08-01
The multistate Potts models on two-dimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the so-called bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the second-order phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the first-order (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field. PMID:27627272
NASA Astrophysics Data System (ADS)
Masters, A.; Achilleos, N. A.; Sergis, N.; Dougherty, M. K.; Kivelson, M. G.; Arridge, C. S.; Krimigis, S. M.; McAndrews, H. J.; Thomsen, M. F.; Kanani, S. J.; Krupp, N.; Coates, A. J.
2009-12-01
We present the first observations of a vortex structure in Saturn’s dayside, outer magnetosphere. The identification of the structure provides conclusive evidence of the operation of the Kelvin-Helmholtz (K-H) instability at Saturn’s magnetospheric boundaries. Cassini observations taken during the inbound pass of the spacecraft’s Revolution B orbit in Decmber 2004 are analysed. Magnetic field conditions during the magnetopause crossings that occurred on this orbital pass suggest that the boundary was highly K-H unstable. Following multiple magnetopause crossings the spacecraft encountered the low-latitude boundary layer. Magnetic field, thermal plasma, and superthermal plasma observations made by Cassini during the spacecraft transition between the boundary layer and magnetosphere proper are consistent with an encounter with a vortex structure on the edge of the boundary layer - this interface is also anticipated to be K-H unstable. High-energy (>20 keV) electrons observed while the spacecraft was within the vortex suggest that the structure was associated with auroral emissions. A model of the coupling between an outer magnetospheric vortex and Saturn’s ionsphere via field-aligned currents is proposed. Estimates based on Knight’s theory imply that field-aligned potentials of a few kV were associated with the region of upward-directed field-aligned current in the northern ionosphere, and that the resulting precipitation of accelerated electrons produced UV auroral emissions with an intensity of a few kR. We propose that K-H vortices in Saturn’s outer magnetosphere produce bright spots of UV aurora. This discovery has implications for our understanding of the interaction between the solar wind and Saturn’s magnetosphere.
Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet
Mitamura, H.; Watanuki, R.; Kaneko, Koji; Onozaki, N.; Amou, Y.; Kittaka, S.; Kobayashi, Riki; Shimura, Y.; Yamamoto, I.; Suzuki, K.; Chi, Songxue; Sakakibara, T.
2014-10-01
Magnetic field (B) variation of the electrical polarization P_{c} ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO_{4})_{2} is examined up to the saturation point of the magnetization for B⊥c. P_{c} is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in P_{c} at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation of which would require a new mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.
Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet
Mitamura, H.; Watanuki, R.; Kaneko, Koji; Onozaki, N.; Amou, Y.; Kittaka, S.; Kobayashi, Riki; Shimura, Y.; Yamamoto, I.; Suzuki, K.; et al
2014-10-01
Magnetic field (B) variation of the electrical polarization Pc ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO4)2 is examined up to the saturation point of the magnetization for B⊥c. Pc is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in Pc at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation of which would require a newmore » mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.« less
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.
Kolovsky, Andrey R.
2010-07-15
We discuss a method for creating bright matter solitons by loading a Bose-Einstein condensate of atoms in a driven tilted optical lattice. It is shown that one can realize the self-focusing regime for the wave-packet dynamics by properly adjusting the phase of the driving field with respect to the phase of Bloch oscillations. If atom-atom interactions are larger than some critical value g{sub min}, this self-focusing regime is followed by the formation of bright solitons. Increasing the interactions above another critical value g{sub max} makes this process unstable. Instead of soliton formation one now meets the phenomenon of incoherent self-trapping. In this regime a fraction of atoms is trapped in incoherent localized wave packets, while the remaining atoms spread ballistically.
NASA Astrophysics Data System (ADS)
Chen, Rou; Diao, Wei; Cheng, Yongguang; Zhu, Likun; Yu, Huidan (Whitney)
2014-11-01
An innovative self-circulation, self-regulation mechanism has recently been proposed to experimentally generate gaseous species from liquid reactants with little or zero parasitic power consumption. When a bubble grows at a location close to a virtual check valve, expansion of the left meniscus of the bubble is hindered due to its capability to provide a higher capillary pressure than the right meniscus does. We perform numerical simulation of bubble transport in a channel with a virtual check valve using lattice Boltzmann method to provide benchmarks for the experiments. A stable discretized lattice Boltzmann equation is employed to simulate incompressible bubble-liquid flows with density ratio above 1000. Polynomial wall free energy boundary condition is introduced and examined for static cases with a bubble sitting on solid surfaces for a triple contact among bubble, liquid, and solid surface. In this work, we focus on the effects of channel ratio between with and without check valve on the dynamics of bubble-driven liquid circulation. This work is supported by NSF Collabrotive Research (1264739).
Driven-dissipative many-body pairing states for cold fermionic atoms in an optical lattice
NASA Astrophysics Data System (ADS)
Yi, W.; Diehl, S.; Daley, A. J.; Zoller, P.
2012-05-01
We discuss the preparation of many-body states of cold fermionic atoms in an optical lattice via controlled dissipative processes induced by coupling the system to a reservoir. Based on a mechanism combining Pauli blocking and phase locking between adjacent sites, we construct complete sets of jump operators describing coupling to a reservoir that leads to dissipative preparation of pairing states for fermions with various symmetries in the absence of direct inter-particle interactions. We discuss the uniqueness of these states, and demonstrate it with small-scale numerical simulations. In the late-time dissipative dynamics, we identify a ‘dissipative gap’ that persists in the thermodynamic limit. This gap implies exponential convergence of all many-body observables to their steady-state values. We then investigate how these pairing states can be used as a starting point for the preparation of the ground state of the Fermi-Hubbard Hamiltonian via an adiabatic state preparation process also involving the parent Hamiltonian of the pairing state. We also provide a proof-of-principle example for implementing these dissipative processes and the parent Hamiltonians of the pairing states, based on 171Yb atoms in optical lattice potentials.
Lattice-Boltzmann simulation for pressure driven microscale gas flows in transition regime
NASA Astrophysics Data System (ADS)
Yue, Xiang-Ji; Wu, Ze-Huan; Ba, Yao-Shuai; Lu, Yan-Jun; Zhu, Zhi-Peng; Ba, De-Chun
2015-09-01
This paper carries out numerical simulation for pressure driven microscale gas flows in transition flow regime. The relaxation time of LBM model was modified with the application of near wall effective mean free path combined with a combination of Bounce-back and Specular Reflection (BSR) boundary condition. The results in this paper are more close to those of DSCM and IP-DSCM compared with the results obtained by other LBM models. The calculation results show that in transition regime, with the increase of Knudsen number, the dimensionless slip velocity at the wall significantly increases, but the maximum linear deviation of nonlinear pressure distribution gradually decreases.
Hierarchy of Floquet gaps and edge states for driven honeycomb lattices
NASA Astrophysics Data System (ADS)
Perez-Piskunow, P. M.; Foa Torres, L. E. F.; Usaj, Gonzalo
2015-04-01
Electromagnetic driving in a honeycomb lattice can induce gaps and topological edge states with a structure of increasing complexity as the frequency of the driving lowers. While the high-frequency case is the most simple to analyze we focus on the multiple photon processes allowed in the low-frequency regime to unveil the hierarchy of Floquet edge states. In the case of low intensities an analytical approach allows us to derive effective Hamiltonians and address the topological character of each gap in a constructive manner. At high intensities we obtain the net number of edge states, given by the winding number, with a numerical calculation of the Chern numbers of each Floquet band. Using these methods, we find a hierarchy that resembles that of a Russian nesting doll. This hierarchy classifies the gaps and the associated edge states in different orders according to the electron-photon coupling strength. For large driving intensities, we rely on the numerical calculation of the winding number, illustrated in a map of topological phase transitions. The hierarchy unveiled with the low-energy effective Hamiltonians, along with the map of topological phase transitions, discloses the complexity of the Floquet band structure in the low-frequency regime. The proposed method for obtaining the effective Hamiltonian can be easily adapted to other Dirac Hamiltonians of two-dimensional materials and even the surface of a three-dimensional topological insulator.
NASA Astrophysics Data System (ADS)
Hrkac, Gino; Keatley, Paul S.; Bryan, Matthew T.; Butler, Keith
2015-11-01
The magnetic vortex has sparked the interest of the academic and industrial communities over the last few decades. From their discovery in the 1970s for bubble memory devices to their modern application as radio frequency oscillators, magnetic vortices have been adopted to modern telecommunication and sensor applications. Basic properties of vortex structures in the static and dynamic regime, from a theoretical and experimental point of view, are presented as well as their application in spin torque driven nano-pillar and magnetic tunnel junction devices. Single vortex excitations and phase locking phenomena of coupled oscillators are discussed with an outlook of vortex oscillators in magnetic hybrid structures with imprinted domain confinement and dynamic encryption devices.
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}
The physicist's companion to current fluctuations: one-dimensional bulk-driven lattice gases
NASA Astrophysics Data System (ADS)
Lazarescu, Alexandre
2015-12-01
One of the main features of statistical systems out of equilibrium is the currents they exhibit in their stationary state: microscopic currents of probability between configurations, which translate into macroscopic currents of mass, charge, etc. Understanding the general behaviour of these currents is an important step towards building a universal framework for non-equilibrium steady states akin to the Gibbs-Boltzmann distribution for equilibrium systems. In this review, we consider one-dimensional bulk-driven particle gases, and in particular the asymmetric simple exclusion process (ASEP) with open boundaries, which is one of the most popular models of one-dimensional transport. We focus, in particular, on the current of particles flowing through the system in its steady state, and on its fluctuations. We show how one can obtain the complete statistics of that current, through its large deviation function, by combining results from various methods: exact calculation of the cumulants of the current, using the integrability of the model; direct diagonalization of a biased process in the limits of very high or low current; hydrodynamic description of the model in the continuous limit using the macroscopic fluctuation theory. We give a pedagogical account of these techniques, starting with a quick introduction to the necessary mathematical tools, as well as a short overview of the existing works relating to the ASEP. We conclude by drawing the complete dynamical phase diagram of the current. We also remark on a few possible generalizations of these results.
NASA Astrophysics Data System (ADS)
Zhu, W.; Gong, S. S.; Sheng, D. N.
2016-07-01
There has been a growing interest in realizing topologically nontrivial states of matter in band insulators, where a quantum Hall effect can appear as an intrinsic property of the band structure. While ongoing progress is under way with a number of directions, the possibility of realizing novel interaction-generated topological phases, without the requirement of a nontrivial invariant encoded in single-particle wave function or band structure, can significantly extend the class of topological materials and is thus of great importance. Here, we show an interaction-driven topological phase emerging in an extended Bose-Hubbard model on a kagome lattice, where the noninteracting band structure is topological trivial with zero Berry curvature in the Brillouin zone. By means of an unbiased state-of-the-art density-matrix renormalization group technique, we identify that the ground state in a broad parameter region is equivalent to a bosonic fractional quantum Hall Laughlin state, based on the characterization of universal properties including ground-state degeneracy, edge excitations, and anyonic quasiparticle statistics. Our work paves a way to finding an interaction-induced topological phase at the phase boundary of conventionally ordered solid phases.
NASA Astrophysics Data System (ADS)
Redapangu, Prasanna; Vanka, Pratap; Sahu, Kirti
2012-11-01
The pressure-driven displacement of two immiscible fluids in an inclined channel in the presence of viscosity and density gradients is investigated using a multiphase lattice Boltzmann approach. The effects of viscosity ratio, Atwood number, Froude number, capillary number and channel inclination are investigated through flow structures, front velocities and fluid displacement rates. Our results indicate that increasing viscosity ratio between the fluids decreases the displacement rate. We observe that increasing the viscosity ratio has a non-monotonic effect on the velocity of the leading front; however, the velocity of the trailing edge decreases with increasing the viscosity ratio. The displacement rate of the thin-layers formed at the later times of the displacement process increases with increasing the angle of inclination because of the increase in the intensity of the interfacial instabilities. Our results also predict the front velocity of the lock-exchange flow of two immiscible fluids in the exchange flow dominated regime. Department of Science and Technology, India.
NASA Astrophysics Data System (ADS)
Wu, Hao; Sun, Hong; Chen, Changfeng
2015-02-01
Manganese-substitution-doped iron nitride MnFe3N holds great promise for applications in high-density magnetic recording and spintronic devices. However, existing theory contradicts experimental results on the structural and magnetic stability of MnFe3N , and the underlying mechanisms remain elusive. Here we demonstrate by first-principles calculations that the ferromagnetic state with enhanced magnetization in MnFe3N is driven by the electron correlation effect not previously considered. We further reveal a large nonlinear shear plasticity, which produces an unexpectedly high shear strength in MnFe3N despite its initial ductile nature near the equilibrium structure. Moreover, we identify strong lattice anharmonicity that plays a pivotal role in stabilizing MnFe3N under high pressures at room temperature. These remarkable properties stem from the intriguing bonding nature of the parent compound Fe4N . Our results explain experimental results and offer insights into the fundamental mechanisms for the superior magnetic and mechanical properties of MnFe3N .
NASA Astrophysics Data System (ADS)
Poussou, Stephane B.; Plesniak, Michael W.
2012-09-01
The air ventilation system in wide-body aircraft cabins provides passengers with a healthy breathing environment. In recent years, the increase in global air traffic has amplified contamination risks by airborne flu-like diseases and terrorist threats involving the onboard release of noxious materials. In particular, passengers moving through a ventilated cabin may transport infectious pathogens in their wake. This paper presents an experimental investigation of the wake produced by a bluff body driven through a steady recirculating flow. Data were obtained in a water facility using particle image velocimetry and planar laser induced fluorescence. Ventilation attenuated the downward convection of counter-rotating vortices produced near the free-end corners of the body and decoupled the downwash mechanism from forward entrainment, creating stagnant contaminant regions.
Quantum vortices in optical lattices
Vignolo, P.; Fazio, R.; Tosi, M. P.
2007-08-15
A vortex in a superfluid gas inside an optical lattice can behave as a massive particle moving in a periodic potential and exhibiting quantum properties. In this paper we discuss these properties and show that the excitation of vortex dynamics in a two-dimensional lattice can lead to striking measurable changes in its dynamic response. It would be possible by means of Bragg spectroscopy to carry out the first direct measurement of the effective vortex mass. In addition, the experiments proposed here provide an alternative way to study the pinning to the underlying lattice and the dissipative damping.
Liu, Xianyin; Zhu, Qiyuan; Zhang, Senfu; Liu, Qingfang E-mail: wangjb@lzu.edu.cn; Wang, Jianbo E-mail: wangjb@lzu.edu.cn
2015-08-15
An interesting type of skyrmion-like spin texture, 2π-vortex, is obtained in a thin nano-disk with Dzyaloshinskii-Moriya interaction. We have simulated the existence of 2π-vortex by micromagnetic method. Furthermore, the spin polarized current is introduced in order to drive the motion of 2π-vortex in a nano-disk with diameter 2 R = 140 nm. When the current density matches with the current injection area, 2π-vortex soon reaches a stable precession (3∼4 ns). The relationship between the precession frequency of 2π-vortex and the current density is almost linear. It may have potential use in spin torque nano-oscillators.
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.
Vortex induced strain effects in anisotropic superconductors
Miranovic, P.; Dobrosavljevic-Grujic, L.; Kogan, V.G.
1996-12-31
Strain in a superconductor, produced by the normal vortex core, can affect both static and dynamic properties of vortices. It causes an additional vortex-vortex interaction which is long-ranged ({approximately} 1/r{sup 2}) as compared with finite but much stronger London interaction in the fields far below H{sub c2}. The energy of this magneto-elastic interaction is calculated within London model. The role of strain effects in forming vortex lattice structure is demonstrated for YBa{sub 2}Cu{sub 3}O{sub 7}.
NASA Astrophysics Data System (ADS)
Soufiene, Bettaibi; Ezeddine, Sediki; Frédéric, Kuznik; Sauro, Succi
2015-01-01
The goal of this article is to study numerically the mixed convection in a differentially heated lid-driven cavity with non-uniform heating of the bottom wall. The velocity field is solved by a hybrid scheme with multiple relaxation time Lattice Boltzmann (MRT-LBM) model, while the temperature field is obtained by resolution of the energy balance equation using the finite difference method (FDM). First, the model is checked and validated using data from the literature. Validation of the present results with those available in the literature shows a good agreement. A good efficiency in time simulation is confirmed. Thereafter, the model has been applied to mixed convection in a driven cavity with non-uniform heating wall at the fixed Grashof number Gr = 106. It is found that, the heat transfer is weakened as the Richardson number is augmented. For Gr = 106, we note the appearance of secondary vortices at different positions of the cavity corners.
Programmable lattices of optical vortices in nematic liquid crystal
NASA Astrophysics Data System (ADS)
Barboza, R.; Assanto, G.; Bortolozzo, U.; Clerc, M. G.; Residori, S.; Vidal-Henriquez, E.
2015-09-01
Using self-induced vortex-like defects in the nematic liquid crystal layer of a light valve with photo-sensible wall, we demonstrate the realization of programable optical vortices lattices with arbitrary configuration in space. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler and an array of circularly polarized input beams is converted into an output array of vortex beams with topological charges consistent with the vortex matter lattice. The vortex arrangements are explained the basis of light-induced matter defects and topological rules.
Vortex methods and vortex statistics
Chorin, A.J.
1993-05-01
Vortex methods originated from the observation that in incompressible, inviscid, isentropic 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 deduce the flow at a later time by simply following it around. In this narrow context, a vortex method is a numerical method that makes use of this observation. Even more generally, the analysis of vortex methods leads, to problems that are closely related to problems in quantum physics and field theory, as well as in harmonic analysis. A broad enough definition of vortex methods ends up by encompassing much of science. Even the purely computational aspects of vortex methods encompass a range of ideas for which vorticity may not be the best unifying theme. 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 understanding contributes to the understanding of blob methods. Vortex methods for inviscid flow lead to systems of ordinary differential equations that can be readily clothed in Hamiltonian form, both in three and two space dimensions, and they can preserve exactly a number of invariants of the Euler equations, including topological invariants. Their viscous versions resemble Langevin equations. As a result, they provide a very useful cartoon of statistical hydrodynamics, i.e., of turbulence, one that can to some extent be analyzed analytically and more importantly, explored numerically, with important implications also for superfluids, superconductors, and even polymers. In the authors view, vortex ``blob`` methods provide the most promising path to the understanding of these phenomena.
Electromagnetic Radiation from Vortex Flow in Type-II Superconductors
Bulaevskii, L. N.; Chudnovsky, E. M.
2006-11-10
We show that a moving vortex lattice, as it comes to a crystal edge, radiates into a free space the harmonics of the washboard frequency, {omega}{sub 0}=2{pi}v/a, up to a superconducting gap, {delta}/({Dirac_h}/2{pi}). Here v is the velocity of the vortex lattice and a is the intervortex spacing. We compute radiation power and show that this effect can be used for the generation of terahertz radiation and for characterization of moving vortex lattices.
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 ...
NASA Astrophysics Data System (ADS)
Itin, A. P.; Katsnelson, M. I.
2015-08-01
We consider 1D lattices described by Hubbard or Bose-Hubbard models, in the presence of periodic high-frequency perturbations, such as uniform ac force or modulation of hopping coefficients. Effective Hamiltonians for interacting particles are derived using an averaging method resembling classical canonical perturbation theory. As is known, a high-frequency force may renormalize hopping coefficients, causing interesting phenomena such as coherent destruction of tunneling and creation of artificial gauge fields. We find explicitly additional corrections to the effective Hamiltonians due to interactions, corresponding to nontrivial processes such as single-particle density-dependent tunneling, correlated pair hoppings, nearest neighbor interactions, etc. Some of these processes arise also in multiband lattice models, and are capable of giving rise to a rich variety of quantum phases. The apparent contradiction with other methods, e.g., Floquet-Magnus expansion, is explained. The results may be useful for designing effective Hamiltonian models in experiments with ultracold atoms, as well as in the field of ultrafast nonequilibrium magnetism. An example of manipulating exchange interaction in a Mott-Hubbard insulator is considered, where our corrections play an essential role.
NASA Astrophysics Data System (ADS)
Hu, W.; Catalano, S.; Gibert, M.; Triscone, J.-M.; Cavalleri, A.
2016-04-01
We investigate the nonequilibrium insulator-metal transition driven in a SmNi O3 thin film by coherent optical excitation of the LaAl O3 substrate lattice. By probing the transient optical properties over a broad frequency range (100 -800 c m-1 ), we analyze both the time-dependent metallic plasma and the infrared optical phonon line shapes. We show that the light-induced metallic phase in SmNi O3 has the same carrier density as the equilibrium metallic phase. We also report that the LaAl O3 substrate acts as a transducer only at the earlier time delays, as the vibrations are driven coherently. No long-lived structural rearrangement takes place in the substrate. Finally, we show that the transient insulator-metal transition occurs both below and above the Néel temperature. We conclude that the supersonic melting of magnetic order measured with ultrafast x rays is not the driving force of the formation of the metallic phase. We posit that the insulator-metal transition may origin from the rearrangement of ordered charges at the interface propagating into the film.
NASA Astrophysics Data System (ADS)
Buerge, Brandon T.
The Vortex Flap is a new type of mechanically driven high-lift device consisting of a rotating cylinder placed underneath and near the trailing edge of an airfoil. Wind tunnel tests were designed and conducted in the Washington University Low-Speed Wind Tunnel. Wind tunnel tests indicate that the Vortex Flap produces notable lift coefficient increments and increases maximum lift coefficients, particularly for the low Reynolds number range tested. The best configurations of the configurations investigated (not necessarily optimal) produce lift increments of 300-900% at low-to-moderate angles of attack, and increase the maximum lift coefficient on the order of 200%. The large lift increments found, particularly at low angles of attack, underscore the ability to drive the airfoil to high lift coefficients even at low angles of attack, a potentially useful characteristic for certain flight maneuvers. Regions of fairly high L/D (on the order of 10) as well as low L/D performance were identified. The nondimensional cylinder rotation speed was found to be the most important experimental parameter. Methods for correcting wind tunnel data were developed and outlined, and a Response Surface Method was applied to the corrected data for ease of interpretation. Performance comparisons between the Vortex Flap and other trailing-edge high-lift devices are included. To demonstrate the potential of the device, a Navy mission specification for a VTOL ship-borne UAV, currently filled by a rotary-wing aircraft, is analyzed using a hypothetical fixed wing aircraft and the Vortex Flap. It is demonstrated that, under certain reasonable wind-over-deck conditions, such an aircraft could hypothetically fill a VTOL mission.
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.
Vortex phase diagram as a function of oxygen deficiency in untwinned YBa{sub 2}Cu{sub 3}O{sub y}
Nishizaki, Terukazu; Shibata, Kenji; Naito, Tomoyuki; Maki, Makoto; Kobayashi, Norio
1999-12-01
Magnetization and resistivity measurements were performed in untwinned YBa{sub 2}Cu{sub 3}O{sub y} (YBCO) single crystals with different oxygen content. The authors find that the vortex phase diagram is a strong function of the oxygen deficiency: (1) For fully oxidized YBCO (y {approx{underscore}equal} 7, {Tc} {approx{underscore}equal} 87.5 K), the first-order vortex lattice melting line T{sub m}(H) is observed up to 30 T. (2) For slightly overdoped YBCO ({Tc} {approx{underscore}equal} 92 K), T{sub m}(H) and the vortex glass transition line T{sub g}(H) terminate at the multicritical point and the field-driven disordering transition line separates the vortex solid phase into the Bragg glass and the vortex glass phases. (3) For slightly underdoped YBCO ({Tc} {approx{underscore}equal} 92.3 K), T{sub g}(H) terminates well below the critical point of T{sub m}(H), indicating the existence of the vortex slush regime by the introduced oxygen deficiency.
Hexatic vortex glass in disordered superconductors
Chudnovsky, E.M. )
1989-12-01
It is shown that interaction of the flux-line lattice with randomly arranged pinning centers should destroy the long-range positional order in the lattice, but not the long-range orientational order. A new phase: hexatic vortex glass, is suggested for the mixed state of disordered, type-II superconductors. Relevance to amorphous and high-{ital T}{sub {ital c}} superconductors is discussed.
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.
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.
Shizawa, T.; Eaton, J.K.
1990-12-31
The interaction of a longitudinal vortex with a pressure-driven, three dimensional turbulent boundary layer was investigated experimentally. The vortex was attenuated much more rapidly in the three dimensional layer than in a two-dimensional boundary layer. The persistence for the vortex-induced perturbation was strongly dependent on the sign of the vortex.
Confining bond rearrangement in the random center vortex model
NASA Astrophysics Data System (ADS)
Altarawneh, Derar; Höllwieser, Roman; Engelhardt, Michael
2016-03-01
We present static meson-meson and baryon-antibaryon potentials in Z (2 ) and Z (3 ) random center vortex models for the infrared sector of Yang-Mills theory, i.e., hypercubic lattice models of random vortex world surfaces. In particular, we calculate multiple Polyakov loop correlators corresponding to static meson-meson or baryon-antibaryon configurations in a center vortex background and observe that their expectation values follow the minimal area law, displaying bond rearrangement behavior, a characteristic expected for the confining dynamics of the strong interaction. The static meson-meson and baryon-antibaryon potentials are compared with theoretical predictions and lattice QCD simulations.
Fractionalized gapless quantum vortex liquids
NASA Astrophysics Data System (ADS)
Wang, Chong; Senthil, T.
2015-05-01
The standard theoretical approach to gapless spin liquid phases of two-dimensional frustrated quantum antiferromagnets invokes the concept of fermionic slave particles into which the spin fractionalizes. As an alternate we explore different kinds of gapless spin liquid phases in frustrated quantum magnets with X Y anisotropy where the vortex of the spin fractionalizes into gapless itinerant fermions. The resulting gapless fractionalized vortex liquid phases are studied within a slave particle framework that is dual to the usual one. We demonstrate the stability of some such phases and describe their properties. We give an explicit construction in an X Y -spin-1 system on triangular lattice, and interpret it as a critical phase in the vicinity of spin-nematic states.
NASA Astrophysics Data System (ADS)
Eder, R.; Wróbel, P.
2011-07-01
We study the two-dimensional Kondo lattice model with an additional Heisenberg exchange between localized spins. In a first step, we use mean-field theory with two order parameters. The first order parameter is a complex pairing amplitude between conduction electrons and localized spins that describes condensation of Kondo (or Zhang-Rice) singlets. A nonvanishing value implies that the localized spins contribute to the Fermi surface volume. The second-order parameter describes singlet pairing between the localized spins and competes with the Kondo-pairing order parameter. Reduction of the carrier density in the conduction band reduces the energy gain due to the formation of the large Fermi surface and induces a phase transition to a state with strong singlet correlations between the localized spins and a Fermi surface that comprises only the conduction electrons. The model thus shows a doping driven change of its Fermi surface volume. At intermediate doping and low temperature, there is a phase where both order parameters coexist, which has a gapped large Fermi surface and dx2-y2 superconductivity. The theory thus qualitatively reproduces the phase diagram of cuprate superconductors. In the second part of this paper, we show how the two phases with different Fermi surface volume emerge in a strong-coupling theory applicable in the limit of large Kondo exchange. The large Fermi surface phase corresponds to a “vacuum” of localized Kondo singlets with uniform phase, and the quasiparticles are spin-1/2 charge fluctuations around this fully paired state. In the small Fermi surface phase, the quasiparticles correspond to propagating Kondo singlets or triplets whereby the phase of a given Kondo singlet corresponds to its momentum. In this picture, a phase transition occurs for low filling of the conduction band as well.
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.
Vortex Flow Aerodynamics, volume 1
Campbell, J.F.; Osborn, R.F.; Foughner, J.T. Jr.
1986-07-01
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.
Sayko, G.V.; Bugaev, A.S.; Popkov, A.F.
1994-12-31
The authors consider vortex lattice interaction with transverse surface magnetoacoustic wave in high-{Tc} superconductor-ferrite structure. It has been found that the magnetoacoustic waves excited in the ferrite can be efficiently coupled with vortex structure in superconducting film. The nonlinear effect of vortex drift as well as the possibility of the wave amplification are discussed.
Critical Capacitance and Charge-Vortex Duality Near the Superfluid-to-Insulator Transition
NASA Astrophysics Data System (ADS)
Gazit, Snir; Podolsky, Daniel; Auerbach, Assa
2014-12-01
Using a generalized reciprocity relation between charge and vortex conductivities at complex frequencies in two space dimensions, we identify the capacitance in the insulating phase as a measure of vortex condensate stiffness. We compute the ratio of boson superfluid stiffness to vortex condensate stiffness at mirror points to be 0.21(1) for the relativistic O(2) model. The product of dynamical conductivities at mirror points is used as a quantitative measure of deviations from self-duality between charge and vortex theories. We propose the finite wave vector compressibility as an experimental measure of the vortex condensate stiffness for neutral lattice bosons.
Eskildsen, M.; Andersen, N.; Mortensen, K.; Bolle, C.; Lieber, C.; Oxx, S.; Sridhar, S.; Canfield, P.
1997-03-01
Small-angle neutron scattering and magnetic decoration both demonstrate a topological transition in the flux line lattice (FLL) in ErNi{sub 2}B{sub 2}C. The high-field square lattice slowly transforms into a hexagonal lattice via an area preserving [100] rhombohedral distortion below roughly 500Oe. The square FLL is aligned with the [110] direction of the tetragonal crystal, while the two domains of the hexagonal FLL are aligned with [100] and [010]. The differences in pinning for the two FLL topologies are reflected in the rf kinetic inductance. {copyright} {ital 1997} {ital The American Physical Society}
Crossover from crossing to tilted vortex phase in Bi2Sr2CaCu2O8+δ single crystals near ab-plane
NASA Astrophysics Data System (ADS)
Mirkovic, Jovan; Buzdin, Alexandre; Kashiwagi, Takanari; Yamamoto, Takashi; Kadowaki, Kazuo
2013-01-01
In extremely anisotropic layered superconductors of Bi2Sr2CaCu2O8+δ the stacks of vortex pancakes (PV) and the Josephson vortex (JV) interpenetrate, and due to PV-JV mutual pinning energy, weakly interact and form various tilted and crossing lattice structures including vortex chains, stripes, mixed chain + lattice phases, etc. In order to study these phenomena, it is decisive to have excellent quality of samples and the ideal experimental techniques. The vortex phases in high-quality Bi2Sr2CaCu2O8+δ single crystals were studied by in-plane resistivity measurement and local ac magnetic permeability. The sharp crossover was shown by both techniques, deep in the vortex solid state separating the Abrikosov dominant ‘strong pinning’ phase from the Josephson dominant ‘weak pinning’ phase. Those two vortex states were recognized as the mixed chain + lattice vortex phase and chains (tilted) vortex phase, respectively.
Reconfigurable large-area magnetic vortex circulation patterns
NASA Astrophysics Data System (ADS)
Streubel, Robert; Kronast, Florian; Rößler, Ulrich K.; Schmidt, Oliver G.; Makarov, Denys
2015-09-01
Magnetic vortices in nanodots own a switchable circulation sense. These nontrivial magnetization configurations can be arranged into extended and interacting patterns. We have experimentally created large arrays of magnetically reconfigurable vortex patterns in nonplanar honeycomb lattices using particle lithography. Optimizing height asymmetry of the vertices and applying an in-plane magnetic field provide means to switch between homocircular and staggered vortex patterns with a potentially high impact on magnonics and spintronics relying on chiral noncollinear spin textures. To this end, exchange coupling of extended vortex lattices with an out-of-plane magnetized layer allows one to realize artificial skyrmionic core textures with controllable circulation and topological properties in extended exchange coupled honeycomb lattices that may pave the way towards magnetic memory and logic devices based on artificial skyrmions.
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.
Some observations on vortex-ring collisions upon inclined surfaces
NASA Astrophysics Data System (ADS)
New, T. H.; Shi, Shengxian; Zang, B.
2016-06-01
This paper reports upon a laser-induced fluorescence visualization and time-resolved particle image velocimetry study to resolve the detailed dynamics associated with Re = 2000 and 4000 circular vortex rings colliding with 30°-75° inclined surfaces. Two-dimensional visualization results show that larger inclination angles lead to increasingly rapid size reduction in the primary vortex-ring core closer to the surface, faster formation of the secondary vortex-ring core, and subsequent ingestion by the former. In contrast, primary vortex-ring core further away from the surface becomes physically larger and incoherent more rapidly, with slower formation and entrainment of the secondary vortex-ring core. Interestingly, a vortex dipole and small vortex-ring-like structure are produced for the largest inclination angle of 75°, possibly due to vortex disconnection and reconnection processes. Results taken along the non-inclined plane show significant bulging of the primary vortex-ring cores when the inclination angle increases from 30° onwards. More importantly, additional vortex cores are observed to entwine with the primary vortex-ring core and provide strong direct evidence for the bi-helical vortex line flow mechanism put forward by Lim (Exp Fluids 7:453-463, 1989). Lastly, the behaviour of the primary and secondary vortex-ring cores further away from the surface is highly sensitive towards the state of the bi-helical lines compressed at that region. Strong compression driven by circumferential flows due to large inclination angles may explain the unique flow structures and behaviour observed for 75° inclination angle here.
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.
Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals
Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog
2013-01-01
Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices. PMID:23877284
Wave modes of collective vortex gyration in dipolar-coupled-dot-array magnonic crystals.
Han, Dong-Soo; Vogel, Andreas; Jung, Hyunsung; Lee, Ki-Suk; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Fischer, Peter; Meier, Guido; Kim, Sang-Koog
2013-01-01
Lattice vibration modes are collective excitations in periodic arrays of atoms or molecules. These modes determine novel transport properties in solid crystals. Analogously, in periodical arrangements of magnetic vortex-state disks, collective vortex motions have been predicted. Here, we experimentally observe wave modes of collective vortex gyration in one-dimensional (1D) periodic arrays of magnetic disks using time-resolved scanning transmission x-ray microscopy. The observed modes are interpreted based on micromagnetic simulation and numerical calculation of coupled Thiele equations. Dispersion of the modes is found to be strongly affected by both vortex polarization and chirality ordering, as revealed by the explicit analytical form of 1D infinite arrays. A thorough understanding thereof is fundamental both for lattice vibrations and vortex dynamics, which we demonstrate for 1D magnonic crystals. Such magnetic disk arrays with vortex-state ordering, referred to as magnetic metastructure, offer potential implementation into information processing devices. PMID:23877284
Vortex gyroscope imaging of planar superfluids.
Powis, A T; Sammut, S J; Simula, T P
2014-10-17
We propose a robust imaging technique that makes it possible to distinguish vortices from antivortices in quasi-two-dimensional Bose-Einstein condensates from a single image of the density of the atoms. Tilting the planar condensate prior to standard absorption imaging excites a generalized gyroscopic mode of the condensate, revealing the sign and location of each vortex. This technique is anticipated to enable experimental measurement of the incompressible kinetic energy spectrum of the condensate and the observation of a negative-temperature phase transition of the vortex gas, driven by two-dimensional superfluid turbulence. PMID:25361263
Propeller tip vortex interactions
NASA Technical Reports Server (NTRS)
Johnston, Robert T.; Sullivan, John P.
1990-01-01
Propeller wakes interacting with aircraft aerodynamic surfaces are a source of noise and vibration. For this reason, flow visualization work on the motion of the helical tip vortex over a wing and through the second stage of a counterrotation propeller (CRP) has been pursued. Initially, work was done on the motion of a propeller helix as it passes over the center of a 9.0 aspect ratio wing. The propeller tip vortex experiences significant spanwise displacements when passing across a lifting wing. A stationary propeller blade or stator was installed behind the rotating propeller to model the blade vortex interaction in a CRP. The resulting vortex interaction was found to depend on the relative vortex strengths and vortex sign.
Kim, P.; Yao, Z.; Lieber, C.M.
1996-12-01
The microscopic structure of the magnetic flux-line lattice (FLL) in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} superconductors was studied at temperatures up to 77K by decoration. Comparison of FLLs obtained at 55 and 4.2K shows that twisted bond defects are a manifestation of thermal fluctuations at elevated temperature. Analyses of the orientational and translational correlation functions for field and zero-field cooled lattices obtained at 55K suggest that the observed FLL is an equilibrium hexatic. These data were also used to estimate the FLL freezing temperature. {copyright} {ital 1996 The American Physical Society.}
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
Vortex structures of rotating spin-orbit-coupled Bose-Einstein condensates
Zhou Xiangfa; Zhou Jing; Wu Congjun
2011-12-15
We consider the quasi-two-dimensional two-component Bose-Einstein condensates with Rashba spin-orbit (SO) coupling in a rotating trap. The rotation angular velocity couples to the mechanical angular momentum, which contains a noncanonical part arising from SO coupling. The effects of an external Zeeman term favoring spin polarization along the radial direction is also considered, which has the same form as the noncanonical part of the mechanical angular momentum. The rotating condensate exhibits a variety of rich structures by varying the strengths of the trapping potential and interaction. With a strong trapping potential, the condensate exhibits a half-quantum vortex-lattice configuration. Such a configuration is driven to the normal one by introducing the external radial Zeeman field. In the case of a weak trap potential, the condensate exhibits a multidomain pattern of plane-wave states under the external radial Zeeman field.
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.
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.
Formation of Small-Scale Vortex Rings from Vortex Pairs Close to the Ground
NASA Astrophysics Data System (ADS)
Asselin, Daniel; Williamson, Charles
2013-11-01
In this research, we examine the effect of a solid boundary on the dynamics and instabilities of a pair of counter-rotating vortices. An isolated vortex pair is subject to a short-wave elliptic instability and a long-wave Crow (1970) instability. Near a wall, the boundary layer between the primary vortices and the wall can separate, leading to the generation of secondary vorticity. These secondary vortices can be subject to small-scale instabilities (Harris & Williamson, 2012) as they come under the influence of the primary vortices. In contrast, in the present study we are interested in the long-wave Crow instability interrupted by interaction with a wall. This can cause significant axial flow, resulting in a periodic concentration of fluid containing vorticity at the peaks of each wavy vortex tube and a corresponding evacuation of fluid containing vorticity from the troughs. It appears that this axial flow is driven at least in part by the formation of vortex ring-like structures in the secondary vortex as it is deformed by the primary vortex. Furthermore, additional small scale-vortex rings evolve from the secondary vorticity and from the concentrated vortical regions in the primary vorticity. In both cases, these rings cause vorticity to rebound away from the ground.
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.
Electrostatically Enhanced Vortex Separator
NASA Technical Reports Server (NTRS)
Collins, Earl R.
1993-01-01
Proposed device removes fine particles from high-pressure exhaust gas of chemical reactor. Negatively charged sectors on rotating disks in vortex generator attracts positively charged particles from main stream of exhaust gas. Electrostatic charge enhances particle-separating action of vortex. Gas without particles released to atmosphere.
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.
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.
Vortex distribution in the lowest Landau level
NASA Astrophysics Data System (ADS)
Aftalion, Amandine; Blanc, Xavier; Nier, Francis
2006-01-01
We study the vortex distribution of the wave functions minimizing the Gross-Pitaevskii energy for a fast rotating condensate in the lowest Landau level (LLL): we prove that the minimizer cannot have a finite number of zeroes, thus the lattice is infinite, but not uniform. This uses the explicit expression of the projector onto the LLL. We also show that any slow varying envelope function can be approximated in the LLL by distorting the lattice. This is used in particular to approximate the inverted parabola and understand the role of “invisible” vortices: the distortion of the lattice is very small in the Thomas-Fermi region but quite large outside, where the “invisible” vortices lie.
Strain Induced Vortex Core Switching in Planar Magnetostrictive Nanostructures
NASA Astrophysics Data System (ADS)
Ostler, T. A.; Cuadrado, R.; Chantrell, R. W.; Rushforth, A. W.; Cavill, S. A.
2015-08-01
The dynamics of magnetic vortex cores is of great interest because the gyrotropic mode has applications in spin torque driven magnetic microwave oscillators, and also provides a means to flip the direction of the core for use in magnetic storage devices. Here, we propose a new means of stimulating magnetization reversal of the vortex core by applying a time-varying strain gradient to planar structures of the magnetostrictive material Fe8 1Ga1 9 (Galfenol), coupled to an underlying piezoelectric layer. Using micromagnetic simulations we have shown that the vortex core state can be deterministically reversed by electric field control of the time-dependent strain-induced anisotropy.
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.
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.
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 formation during rf heating of plasma
Motley, R.W.
1980-05-01
Experiments on a test plasma show that the linear theory of waveguide coupling to slow plasma waves begins to break down if the rf power flux exceeds approx. 30 W/cm/sup 2/. Probe measurements reveal that within 30 ..mu..s an undulation appears in the surface plasma near the mouth of the twin waveguide. This surface readjustment is part of a vortex, or off-center convective cell, driven by asymmetric rf heating of the plasma column.
Center vortex model for Sp(2) Yang-Mills theory
Engelhardt, M.; Sperisen, B.
2006-12-15
The question whether the center vortex picture of the strongly interacting vacuum can encompass the infrared dynamics of both SU(2) as well as Sp(2) Yang-Mills theory is addressed. These two theories contain the same center vortex degrees of freedom, and yet exhibit deconfinement phase transitions of different order. This is argued to be caused by the effective action governing the vortices being different in the two cases. To buttress this argument, a random vortex world-surface model is constructed which reproduces available lattice data characterizing Sp(2) Yang-Mills confinement properties. A new effective action term which can be interpreted in terms of a vortex stickiness serves to realize a first-order deconfinement phase transition, as found in Sp(2) Yang-Mills theory. Predictions are given for the behavior of the spatial string tension at finite temperatures.
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.
Motion of a vortex ring in a simple shear flow
NASA Astrophysics Data System (ADS)
Cheng, M.; Lou, J.; Lim, T. T.
2009-08-01
The motion and deformation of a vortex ring in a linear or simple shear flow have been simulated numerically by using the lattice Boltzmann method with multiple relaxation times. The study is motivated by a recent experiment [T. T. Lim, K. B. Lua, and K. Thet, Phys. Fluids 20, 051701 (2008)], which shows that a vortex ring propagating in a uniform cross flow does not experience Kutta lift and undergo tilting and deformation. The focus of the present study is to examine the effect of a simple shear in a cross flow on the motion of a vortex ring. Numerical approach is adopted here because a truly simple shear flow is difficult to generate experimentally. Our computation shows that a vortex ring tilts and deforms in a simple shear flow, and the tilting can be attributed to the modification of the vorticity distribution of the vortex ring as a result of the entrainment of background vorticity by the vortex core. It is further shown that although the shear in the flow has the tendency to elongate the vortex ring, the tilting angle of the ring increases with the shear ratio.
Driving an individual vortex in the presence of a periodic pinning array
Reichhardt, Charles; Reichhardt, Cynthia
2009-01-01
Recently it has been demonstrated experimentally that it is possible to manipulate an individual vortex in a type-II superconductor using a magnetic force microscope tip. Using numerical simulations, we investigate the dynamics of a single driven individual vortex in the presence of a periodic pinning array and other vortices. Remarkably, we find that the effective drag on the driven vortex is reduced at the matching fields, which is opposite from the behavior of the critical current when all the vortices are driven. We discuss this effect in the context of the type of dynamics that occur at matching and nonmatching fields.
NASA Astrophysics Data System (ADS)
Crowdy, Darren; Marshall, Jonathan
2004-08-01
This paper demonstrates that two well-known equilibrium solutions of the Euler equations—the corotating point vortex pair and the Rankine vortex—are connected by a continuous branch of exact solutions. The central idea is to "grow" new vortex patches at two stagnation points that exist in the frame of reference of the corotating point vortex pair. This is done by generalizing a mathematical technique for constructing vortex equilibria first presented by Crowdy [D. G. Crowdy, "A class of exact multipolar vortices," Phys. Fluids 11, 2556 (1999)]. The solutions exhibit several interesting features, including the merging of two separate vortex patches via the development of touching cusps. Numerical contour dynamics methods are used to verify the mathematical solutions and reveal them to be robust structures. The general issue of how simple vortex equilibria can be continued continuously to more complicated ones with very different vortical topologies is discussed. The solutions are examples of exact solutions of the Euler equations involving multiple interacting vortex patches.
Hairpin Vortex Regeneration Threshold
NASA Astrophysics Data System (ADS)
Sabatino, Daniel; Maharjan, Rijan
2015-11-01
A free surface water channel is used to study hairpin vortex formation created by fluid injection through a narrow slot into a laminar boundary layer. Particle image velocimetry is used to calculate the circulation of the primary hairpin vortex head which is found to monotonically decrease in strength with downstream distance. When a secondary hairpin vortex is formed upstream of the primary vortex, the circulation strength of the head is comparable to the strength of the primary head at the time of regeneration. However, the legs of the primary vortex strengthen up to the moment the secondary hairpin is generated. Although the peak circulation in the legs is not directly correlated to the strength of the original elongated ring vortex, when the circulation is scaled with the injection momentum ratio it is linearly related to scaled injection time. It is proposed that the injection momentum ratio and nondimensionalized injection time based on the wall normal penetration time can be used to identify threshold conditions which produce a secondary vortex. Supported by the National Science Foundation under Grant CBET- 1040236.
Influence of Initial Vorticity Distribution on Axisymmetric Vortex Breakdown and Reconnection
NASA Technical Reports Server (NTRS)
Young, Larry A.
2007-01-01
An analytical treatment has been developed to study some of the axisymmetric vortex breakdown and reconnection fluid dynamic processes underlying body-vortex interactions that are frequently manifested in rotorcraft and propeller-driven fixed-wing aircraft wakes. In particular, the presence of negative vorticity in the inner core of a vortex filament (one example of which is examined in this paper) subsequent to "cutting" by a solid body has a profound influence on the vortex reconnection, leading to analog flow behavior similar to vortex breakdown phenomena described in the literature. Initial vorticity distributions (three specific examples which are examined) without an inner core of negative vorticity do not exhibit vortex breakdown and instead manifest diffusion-like properties while undergoing vortex reconnection. Though this work focuses on laminar vortical flow, this work is anticipated to provide valuable insight into rotary-wing aerodynamics as well as other types of vortical flow phenomena.
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.
Skyrmion Flux Lattices and their μSR signature
NASA Astrophysics Data System (ADS)
Li, Qi; Toner, John; Belitz, Dietrich
2008-03-01
Recently, topological excitations known as skyrmions were predicted to exist in p-wave superconductors [1]. The elastic theory of an induced skyrmion lattice was developed in [2], and its melting curve was found to be qualitatively different from that for vortex lattices. Here we show that the muon spin resonance (μSR) signatures of the two types of lattices are also very different. μSR has been applied extensively to study the magnetic properties of vortex flux lattices [3]. The observable in this technique is the μSR line shape n(B), which is the probability density that a muon experiences a local magnetic induction B. In a vortex lattice, for small B, n(B) (1/B)/B. By contrast, for a skyrmion lattice we predict n(B) B^ (-3/2). This difference provides another way to easily distinguish between vortex and skyrmion flux lattices, and can thus help to identify p-wave superconductors. [1] A. Knigavko, B. Rosenstein, and Y.F. Chen, Phys. Rev. B 60, 550 (1999). [2] Qi Li, John Toner, and D. Belitz, Phys.Rev. Lett. 98, 187002 (2007). [3] J. E. Sonier, J.H. Brewer, and R. F. Kiefl, Rev. Mod. Phys. 72, 769 (2000).
Macroscopic Artificial Magnetic Honeycomb Lattice of Thermally Controlled Ultra-Small Bonds
NASA Astrophysics Data System (ADS)
Summers, Brock; Dahal, Ashutosh; Debeer-Schitt, Lisa; Gunasekera, Jagath; Singh, Deepak
The two-dimensional artificial magnetic honeycomb lattice system is evolving into a new research arena to explore a plethora of novel magnetism that are predicted to occur as functions of temperature and magnetic field: a long-range spin ice, spin liquid, an entropy-driven magnetic charge-ordered state involving topological vortex pairs and a spin-order due to the spin chirality. We have created macroscopic samples of artificial magnetic honeycomb lattices of Cobalt and Permalloy having connected ultra-small elements (bonds), with length scales of sub-10 nm to 30 nm, which have never before been possible. The equivalent energy of the resulting systems is 10-100 K and is thus amenable to both temperature- and field-dependent exploration of novel magnetic phenomena. We have performed detailed magnetic and small angle neutron scattering measurements (SANS) on the newly fabricated honeycomb lattice of Permalloy that show the thermal character of the system. Furthermore, the experimental data reveals the onset of magnetic ordered regimes in temperature that are consistent with the predicted novel phase diagram in artificial honeycomb lattice. Research is supported by U.S. Department of Energy, Office of Basic Energy Sciences under Grant No. DE-SC0014461.
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 Astrophysics Data System (ADS)
Conlisk, A. T.
1998-11-01
The interaction of vortices with solid surfaces occurs in many different situations including, but not limited to tornadoes, propeller wakes, flows over swept wings and missile forebodies, turbomachinery flows, blade-vortex interactions and tip vortex-surface interactions on helicopters. Often, parts of a system must operate within such flows and thus encounter these vortices. In the present paper we discuss the nature of a particular subset of interactions called ``collisions''. A ``collision'' is characterized by the fact that the core of the vortex is permanently altered; usually the core is locally destroyed. The focus is on fully three-dimensional collisions although two-dimensional collisions are discussed as well. Examples of collisions in helicopter aerodynamics and turbomachinery flows are discussed and the dynamics of the vortex core during a collision process are illustrated for a 90^o collision. ^Supported by the US Army Research Office
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)
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.
NASA Technical Reports Server (NTRS)
Rao, D. M.
1983-01-01
Segmented vortex flaps were suggested as a means of delaying the vortex spill-over causing thrust loss over the outboard region of single-panel flaps. Also proposed was hinge-line setback for exploiting leading-edge suction in conjunction with vortex flaps to improve the overall thrust per unit flap area. These two concepts in combination were tested on a 60-deg cropped delta wing model. Significant improvement in flap efficiency was indicated by a reduction of the flap/wing area from 11.4% of single-panel flap to 6.3% of a two segment delta flap design, with no lift/drag penalty at lift coefficients between 0.5 and 0.7. The more efficient vortex flap arrangement of this study should benefit the performance attainable with flaps of given area on wings of moderate leading-edge sweep.
NASA Astrophysics Data System (ADS)
Saul, Andres; Radtke, Guillaume; Jaime, Marcelo; Salamon, Myron; Dabkowska, Hanna
2015-03-01
Recent magnetostriction experiments have shown that the macroscopic physical dimensions of the Shastry-Sutherland compound SrCu2(BO3)2 change with the applied magnetic field mimicking the same complex behavior observed in the magnetization. Using Density Functional based methods we find that the driving force behind the magnetoelastic coupling is the Cu-O-Cu superexchange angle which, thanks to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44%) with minute (0.01%) variations in the lattice parameters. The consequence is a reduction of the order of ~10% in the antiferromagnetic intra-dimer exchange integral J, sufficient to compensate the elastic energy loss in the deformation.
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.
NASA Technical Reports Server (NTRS)
Betz, A
1933-01-01
Progressive application of the Kutta-Joukowsky theorem to the relationship between airfoil lift and circulation affords a number of formulas concerning the conduct of vortex systems. The application of this line of reasoning to several problems of airfoil theory yields an insight into many hitherto little observed relations. This report is confined to plane flow, hence all vortex filaments are straight and mutually parallel (perpendicular to the plane of flow).
Houck, E.D.
1994-05-17
A fluid transfer system is described 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. 10 figures.
Buoyant Norbury's vortex rings
NASA Astrophysics Data System (ADS)
Blyth, Mark; Rodriguez-Rodriguez, Javier; Salman, Hayder
2014-11-01
Norbury's vortices are a one-parameter family of axisymmetric vortex rings that are exact solutions to the Euler equations. Due to their relative simplicity, they are extensively used to model the behavior of real vortex rings found in experiments and in Nature. In this work, we extend the original formulation of the problem to include buoyancy effects for the case where the fluid that lies within the vortex has a different density to that of the ambient. In this modified formulation, buoyancy effects enter the problem through the baroclinic term of the vorticity equation. This permits an efficient numerical solution of the governing equation of motion in terms of a vortex contour method that tracks the evolution of the boundary of the vortex. Finally, we compare our numerical results with the theoretical analysis of the short-time evolution of a buoyant vortex. Funded by the Spanish Ministry of Economy and Competitiveness through grant DPI2011-28356-C03-02 and by the London Mathematical Society.
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.
Yaron, U.; Gammel, P.; Boebinger, G.; Aeppli, G.; Schiffer, P.; Bucher, E.; Bishop, D.; Broholm, C.; Mortensen, K.
1997-04-01
Small angle neutron scattering studies of the flux line lattice (FLL) in UPt{sub 3} for fields {bold H}{perpendicular}{bold c} provide direct microscopic evidence for the 5kOe B{r_arrow}C transition. We find a pronounced maximum in the longitudinal correlation length of the FLL at the transition and an abrupt change in the field dependence of the scattered intensity which can be interpreted as a 15{percent} decrease in the coherence length and a 9{percent} increase in the penetration depth, consistent with discontinuities in the critical fields. Finally, in the low field phase, the FLL distortion evolves roughly linearly with field, while in the high field phase it appears to be less field dependent. {copyright} {ital 1997} {ital The American Physical Society}
On variational features of vortex flows
NASA Astrophysics Data System (ADS)
Berdichevsky, V. L.
2008-09-01
Ideal incompressible fluid is a Hamiltonian system which possesses an infinite number of integrals, the circulations of velocity over closed fluid contours. This allows one to split all the degrees of freedom into the driving ones and the “slave” ones, the latter to be determined by the integrals of motions. The “slave” degrees of freedom correspond to “potential part” of motion, which is driven by vorticity. Elimination of the “slave” degrees of freedom from equations of ideal incompressible fluid yields a closed system of equations for dynamics of vortex lines. This system is also Hamiltonian. The variational principle for this system was found recently (Berdichevsky in Thermodynamics of chaos and order, Addison-Wesly-Longman, Reading, 1997; Kuznetsov and Ruban in JETP Lett 67, 1076 1081, 1998). It looks striking, however. In particular, the fluid motion is set to be compressible, while in the least action principle of fluid mechanics the incompressibility of motion is a built-in property. This striking feature is explained in the paper, and a link between the variational principle of vortex line dynamics and the least action principle is established. Other points made in this paper are concerned with steady motions. Two new variational principles are proposed for steady vortex flows. Their relation to Arnold’s variational principle of steady vortex motion is discussed.
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.
Analysis of collective pinning and depinning of the flux line lattice in pristine 2H-NbSe2
NASA Astrophysics Data System (ADS)
Lee, Jonghee; Wang, Hui; Dreyer, Michael; Barker, Barry I.
2007-03-01
Larkin and Ovchinnikov predicted collective pinning of the flux line lattice (FLL) in type II superconductors several decades ago. The collective pinning results from the interplay between strong vortex-vortex interaction and randomly distributed weak pinning centers in a media. The evidence of collective pinning was previously observed at a magnetic field, H, close to Hc2 in current-driven transport experiments on the macroscopic scale. But there still exists a lack of understanding of collective pinning on the microscopic level. In this talk, we show collective pinning and depinning of the FLL in pristine 2H-NbSe2 in a long time series (15 days), measured by a low temperature scanning tunneling microscope. We observed the motion of the FLL within an area of 400 nm x 400 nm, with an initial magnetic field of 0.5 T. The motion was caused by the very slow decay of magnetic field (˜ 5 nT/s) in a defective superconducting magnet. The average speed of FLL was ˜ 2.5 pm/s, lower than previously reported. Using highly time resolved data, we will further discuss the average direction of motion, the strength of pinning centers in pristine 2H-NbSe2, flux line mass, and the difference between current-driven and field-driven FLL motions.
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}
Vortex states in superconductors with strong Pauli-paramagnetic effect
NASA Astrophysics Data System (ADS)
Ichioka, Masanori; Machida, Kazushige
2007-08-01
Using quasiclassical theory, we analyze the vortex structure of strong-paramagnetic superconductors. There, induced paramagnetic moments are accumulated exclusively around the vortex core. We quantitatively evaluate the significant paramagnetic effect in the H dependence of various quantities, such as low temperature specific heat, Knight shift, magnetization, and the flux line lattice (FLL) form factor. The anomalous H dependence of the FLL form factor observed by the small angle neutron scattering in CeCoIn5 is attributable to the large paramagnetic contribution.
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.
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
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.
Critical behavior at a dynamic vortex insulator-to-metal transition.
Poccia, Nicola; Baturina, Tatyana I; Coneri, Francesco; Molenaar, Cor G; Wang, X Renshaw; Bianconi, Ginestra; Brinkman, Alexander; Hilgenkamp, Hans; Golubov, Alexander A; Vinokur, Valerii M
2015-09-11
An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables investigation of the nature of competing vortex states and phase transitions between them. A square array creates the eggcrate potential in which magnetic field-induced vortices are frozen into a vortex insulator. We observed a vortex insulator-vortex metal transition driven by the applied electric current and determined critical exponents that coincided with those for thermodynamic liquid-gas transition. Our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibrium phase transitions. PMID:26359398
Critical behavior at a dynamic vortex insulator-to-metal transition
NASA Astrophysics Data System (ADS)
Poccia, Nicola; Baturina, Tatyana I.; Coneri, Francesco; Molenaar, Cor G.; Wang, X. Renshaw; Bianconi, Ginestra; Brinkman, Alexander; Hilgenkamp, Hans; Golubov, Alexander A.; Vinokur, Valerii M.
2015-09-01
An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables investigation of the nature of competing vortex states and phase transitions between them. A square array creates the eggcrate potential in which magnetic field-induced vortices are frozen into a vortex insulator. We observed a vortex insulator-vortex metal transition driven by the applied electric current and determined critical exponents that coincided with those for thermodynamic liquid-gas transition. Our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibrium phase transitions.
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 confinement by magnetic domains in superconductor-ferromagnet bilayers
NASA Astrophysics Data System (ADS)
Cieplak, Marta Z.; Adamus, Z.; Konczykowski, M.; Zhu, L. Y.; Chien, C. L.; Cheng, X. M.
2013-03-01
We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in between to avoid proximity effect. The magnetic domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature the magnetic pinning increases but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth. Supported by Polish NCS grant 2011/01/B/ST3/00462, by the French-Polish Program PICS 2012, by EU grant POIG.01.01.02-00-108/09, and by NSF grants DMR05-20491 and DMR-1053854.
A relativistic spherical vortex
Pekeris, C. L.
1976-01-01
This investigation is concerned with stationary relativistic flows of an inviscid and incompressible fluid. In choosing a density-pressure relation to represent relativistic “incompressibility,” it is found that a fluid in which the velocity of sound equals the velocity of light is to be preferred for reasons of mathematical simplicity. In the case of axially symmetric flows, the velocity field can be derived from a stream function obeying a partial differential equation which is nonlinear. A transformation of variables is found which makes the relativistic differential equation linear. An exact solution is obtained for the case of a vortex confined to a stationary sphere. One can make all three of the components of velocity vanish on the surface of the sphere, as in the nonrelativistic Hicks spherical vortex. In the case of an isolated vortex on whose surface the pressure is made to vanish, it is found that the pressure at the center of the sphere becomes negative, as in the nonrelativistic case. A solution is also obtained for a relativistic vortex advancing in a fluid. The sphere is distorted into an oblate spheroid. The maximum possible velocity of advance of the vortex is (2/3) c. PMID:16578745
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.
Force Evaluation in the Lattice Boltzmann Method Involving Curved Geometry
NASA Technical Reports Server (NTRS)
Mei, Renwei; Yu, Dazhi; Shyy, Wei; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
The present work investigates two approaches for force evaluation in the lattice Boltzmann equation: the momentum- exchange method and the stress-integration method on the surface of a body. The boundary condition for the particle distribution functions on curved geometries is handled with second order accuracy based on our recent works. The stress-integration method is computationally laborious for two-dimensional flows and in general difficult to implement for three-dimensional flows, while the momentum-exchange method is reliable, accurate, and easy to implement for both two-dimensional and three-dimensional flows. Several test cases are selected to evaluate the present methods, including: (i) two-dimensional pressure-driven channel flow; (ii) two-dimensional uniform flow past a column of cylinders; (iii) two-dimensional flow past a cylinder asymmetrically placed in a channel (with vortex shedding); (iv) three-dimensional pressure-driven flow in a circular pipe; and (v) three-dimensional flow past a sphere. The drag evaluated by using the momentum-exchange method agrees well with the exact or other published results.
Force evaluation in the lattice Boltzmann method involving curved geometry
NASA Astrophysics Data System (ADS)
Mei, Renwei; Yu, Dazhi; Shyy, Wei; Luo, Li-Shi
2002-04-01
The present work investigates two approaches for force evaluation in the lattice Boltzmann equation: the momentum-exchange method and the stress-integration method on the surface of a body. The boundary condition for the particle distribution functions on curved geometries is handled with second-order accuracy based on our recent works [Mei et al., J. Comput. Phys. 155, 307 (1999); ibid. 161, 680 (2000)]. The stress-integration method is computationally laborious for two-dimensional flows and in general difficult to implement for three-dimensional flows, while the momentum-exchange method is reliable, accurate, and easy to implement for both two-dimensional and three-dimensional flows. Several test cases are selected to evaluate the present methods, including: (i) two-dimensional pressure-driven channel flow; (ii) two-dimensional uniform flow past a column of cylinders; (iii) two-dimensional flow past a cylinder asymmetrically placed in a channel (with vortex shedding); (iv) three-dimensional pressure-driven flow in a circular pipe; and (v) three-dimensional flow past a sphere. The drag evaluated by using the momentum-exchange method agrees well with the exact or other published results.
A one-dimensional chain state of vortex matter.
Grigorenko, A; Bending, S; Tamegai, T; Ooi, S; Henini, M
2001-12-13
Magnetic flux penetrates isotropic type II superconductors in flux-quantized vortices, which arrange themselves into a lattice structure that is independent of the direction of the applied field. In extremely anisotropic high-transition-temperature (high-Tc) superconductors, a lattice of stacks of circular 'pancake' vortices forms when a magnetic field is applied perpendicular to the copper oxide layers, while an orthogonal elongated lattice of elliptical Josephson vortices forms when the applied field is parallel to the layers. Here we report that when a tilted magnetic field is applied to single crystals of Bi2Sr2CaCu2O8+delta, these lattices can interact to form a new state of vortex matter in which all stacks of pancake vortices intersect the Josephson vortices. The sublattice of Josephson vortices can therefore be used to manipulate the sublattice of pancake vortices. This result explains the suppression of irreversible magnetization by in-plane fields as seen in Bi2Sr2CaCu2O8+delta crystals, a hitherto mysterious observation. The ability to manipulate sublattices could be important for flux-logic devices, where a 'bit' might be represented by a pancake vortex stack, and the problem of vortex positioning is overcome through sublattice interactions. This also enables the development of flux transducers and amplifiers, considerably broadening the scope for applications of anisotropic high-Tc superconductors. PMID:11742393
Vortex soliton motion and steering
NASA Astrophysics Data System (ADS)
Christou, Jason; Tikhonenko, Vladimir; Kivshar, Yuri S.; Luther-Davies, Barry
1996-10-01
Experimental demonstration of the steering of an optical vortex soliton by the superposition of a weak coherent background field is presented. A model to account for vortex motion is derived, and its validity is verified experimentally and numerically.
A mesoscale vortex over Halley Station, Antarctica
Turner, J.; Lachlan-Cope, T.A.; Warren, D.E. ); Duncan, C.N. )
1993-05-01
A detailed analysis of the evolution and structure of a mesoscale vortex and associated cloud comma that developed at the eastern edge of the Weddell Sea, Antarctica, during the early part of January 1986 is presented. The system remained quasi-stationary for over three days close to the British research station Halley (75[degrees]36'S, 26'42[degrees]W) and gave severe weather with gale-force winds and prolonged snow. The formation and development of the system were investigated using conventional surface and upper-air meteorological observations taken at Halley, analyses from the U.K. Meteorological Office 15-level model, and satellite imagery and sounder data from the TIROS-N-NOAA series of polar orbiting satellites. The thermal structure of the vortex was examined using atmospheric profiles derived from radiance measurements from the TIROS Operational Vertical Sounder. Details of the wind field were examined using cloud motion vectors derived from a sequence of Advanced Very High Resolution Radiometer images. The vortex developed inland of the Brunt Ice Shelf in a strong baroclinic zone separating warm air, which had been advected polewards down the eastern Weddell Sea, and cold air descending from the Antarctic Plateau. The system intensified when cold, continental air associated with an upper-level short-wave trough was advected into the vortex. A frontal cloud band developed when slantwise ascent of warm air took place at the leading edge of the cold-air outbreak. Most of the precipitation associated with the low occurred on this cloud band. The small sea surface-atmospheric temperature differences gave only limited heat fluxes and there was no indication of deep convection associated with the system. The vortex was driven by baroclinic forcing and had some features in common with the baroclinic type of polar lows that occur in the Northern Hemisphere. 25 refs., 14 figs.
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.
Reconnection of superfluid vortex bundles.
Alamri, Sultan Z; Youd, Anthony J; Barenghi, Carlo F
2008-11-21
Using the vortex filament model and the Gross-Pitaevskii nonlinear Schroedinger equation, we show that bundles of quantized vortex lines in He II are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence and show that, during the bundle reconnection process, kelvin waves of large amplitude are generated, in agreement with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows. PMID:19113421
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.
ERIC Educational Resources Information Center
Parris, Richard
2011-01-01
Given a segment that joins two lattice points in R[superscript 3], when is it possible to form a lattice cube that uses this segment as one of its twelve edges? A necessary and sufficient condition is that the length of the segment be an integer. This paper presents an algorithm for finding such a cube when the prime factors of the length are…
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.
NASA Technical Reports Server (NTRS)
1977-01-01
A status report is presented on research directed at reducing the vortex disturbances of aircraft wakes. The objective of such a reduction is to minimize the hazard to smaller aircraft that might encounter these wakes. Inviscid modeling was used to study trailing vortices and viscous effects were investigated. Laser velocimeters were utilized in the measurement of aircraft wakes. Flight and wind tunnel tests were performed on scale and full model scale aircraft of various design. Parameters investigated included the effect of wing span, wing flaps, spoilers, splines and engine thrust on vortex attenuation. Results indicate that vortives may be alleviated through aerodynamic means.
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.
Nanostructure of vortex during explosion welding.
Rybin, V V; Greenberg, B A; Ivanov, M A; Patselov, A M; Antonova, O V; Elkina, O A; Inozemtsev, A V; Salishchev, G A
2011-10-01
The microstructure of a bimetallic joint made by explosion welding of orthorhombic titanium aluminide (Ti-30Al-16Nb-1Zr-1Mo) with commercially pure titanium is studied. It is found that the welded joint has a multilayered structure including a severely deformed zone observed in both materials, a recrystallized zone of titanium, and a transition zone near the interface. Typical elements of the transition zone-a wavy interface, macrorotations of the lattice, vortices and tracks of fragments of the initial materials-are determined. It is shown that the observed vortices are formed most probably due to local melting of the material near the contact surface. Evidence for this assumption is deduced from the presence of dipoles, which consist of two vortices of different helicity and an ultrafine duplex structure of the vortex. Also, high mixing of the material near the vortex is only possible by the turbulent transport whose coefficient is several orders of magnitude larger than the coefficient of atomic diffusion in liquids. The role played by fragmentation in both the formation of lattice macrorotations and the passage of coarse particles of one material through the bulk of the other is determined. PMID:22400276
NASA Technical Reports Server (NTRS)
Maskew, B.
1975-01-01
The close-approach problem associated with flow calculation methods based on vortex-lattice theory was examined numerically using two-dimensional discretized vortex sheets. The analysis first yields a near-field radius of approximately the distance apart of the vortices in the lattice; only within this distance from the sheet are the errors arising from the discretization significant. Various modifications to the discrete vortices are then considered with the objective of reducing the errors. This leads to a near-field model in which a vortex splits into an increasing number of subvortices as it is approached. The subvortices, whose strengths vary linearly from the vortex position, are evenly distributed along an interpolated curve passing through the basic vortices. This subvortex technique can be extended to the three-dimensional case and is efficient because the number of vortices is effectively increased, but only where and when needed.
Theoretical study of aerodynamic characteristics of wings having vortex flow
NASA Technical Reports Server (NTRS)
Reddy, C. S.
1979-01-01
The aerodynamic characteristics of slender wings having separation induced vortex flows are investigated by employing three different computer codes--free vortex sheet, quasi vortex lattice, and suction analogy methods. Their capabilities and limitations are examined, and modifications are discussed. Flat wings of different configurations: arrow, delta, and diamond shapes, as well as cambered delta wings, are studied. The effect of notch ratio on the load distributions and the longitudinal characteristics of a family of arrow and diamond wings is explored. The sectional lift coefficients and the accumulated span loadings are determined for an arrow wing and are seen to be unusual in comparison with the attached flow results. The theoretically predicted results are compared with the existing experimental values.
Rolling moments in a trailing vortex flow field
NASA Technical Reports Server (NTRS)
Mcmillan, O. J.; Schwind, R. G.; Nielsen, J. N.; Dillenius, M. F. E.
1977-01-01
Pressure distributions are presented which were measured on a wing in close proximity to a tip vortex of known structure generated by a larger, upstream semispan wing. Overall loads calculated by integration of these pressures are checked by independent measurements made with an identical model mounted on a force balance. Several conventional methods of wing analysis are used to predict the loads on the following wing. Strip theory is shown to give uniformly poor results for loading distribution, although predictions of overall lift and rolling moment are sometimes acceptable. Good results are obtained for overall coefficients and loading distribution by using linearized pressures in vortex-lattice theory in conjunction with a rectilinear vortex. The equivalent relation from reverse-flow theory that can be used to give economic predictions for overall loads is presented.
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.
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.
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.
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.
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
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.
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)
Betz, A.
1979-01-01
Application of the Kutta-Joukowski theorem to the relationship between airfoil lift and circulation is described. A number of formulas concerning the conduct of vortex systems derived from the theorem are presented. The application of this line of reasoning to several problems of airfoil theory and the observed relations are discussed.
NASA Technical Reports Server (NTRS)
Weston, R. P.; Chamberlain, J. P.; Liu, C. H.; Hartwich, Peter-Michael
1986-01-01
Several computational studies are currently being pursued that focus on various aspects of representing the entire lifetime of the viscous trailing vortex wakes generated by an aircraft. The formulation and subsequent near-wing development of the leading-edge vortices formed by a delta wing are being calculated at modest Reynolds numbers using a three-dimensional, time-dependent Navier-Stokes code. Another computational code was developed to focus on the roll-up, trajectory, and mutual interaction of trailing vortices further downstream from the wing using a two-dimensional, time-dependent, Navier-Stokes algorithm. To investigate the effect of a cross-wind ground shear flow on the drift and decay of the far-field trailing vortices, a code was developed that employs Euler equations along with matched asymptotic solutions for the decaying vortex filaments. And finally, to simulate the conditions far down stream after the onset of the Crow instability in the vortex wake, a full three-dimensional, time-dependent Navier-Stokes code was developed to study the behavior of interacting vortex rings.
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.
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.
Probing the charge-vortex duality near the superfluid-to-insulator transition
NASA Astrophysics Data System (ADS)
Gazit, Snir; Podolsky, Daniel; Auerbach, Assa
2015-03-01
We study the charge vortex duality near the superfluid-to-insulator quantum phase transition in d=2+1 dimensions. We use a generalized reciprocity relation between charge and vortex conductivities at complex frequencies to identify the capacitance in the insulating phase as a measure of vortex condensate stiffness. We then compute the ratio of boson superfluid stiffness to vortex condensate stiffness at mirror points to be 0.21(1). This corroborates and provides a quantitative measure to the non self-dual nature of the charge-vortex duality. We further study deviations from self-duality at finite frequency by computing the product of Matsubara frequency conductivities at mirror points across the phase transition. Finally, we propose experimental realizations that test our predictions in THz spectroscopy of disordered superconductors and cold atomic systems trapped in an optical lattice.
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.
Bulk vortices and half-vortex surface modes in parity-time-symmetric media
NASA Astrophysics Data System (ADS)
Li, Huagang; Zhu, Xing; Shi, Zhiwei; Malomed, Boris A.; Lai, Tianshu; Lee, Chaohong
2014-05-01
We demonstrate that in-bulk vortex localized modes and their surface half-vortex ("horseshoe") counterparts self-trap in two-dimensional nonlinear optical systems with PT-symmetric photonic lattices (PLs). The respective stability regions are identified in the underlying parameter space. The in-bulk states are related to truncated nonlinear Bloch waves in gaps of the PL-induced spectrum. The basic vortex and horseshoe modes are built, severally, of four and three beams with appropriate phase shifts between them. Their stable complex counterparts, built of up to 12 beams, are also reported.
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.
Wake-vortex structure from lift and torque induced on a following wing
NASA Technical Reports Server (NTRS)
Rossow, Vernon J.
1993-01-01
A procedure based on vortex lattice theory to interpret the lift and torque measured on a following model in a wind tunnel is developed to retrieve the velocity distribution in the vortex wake that caused the induced forces. It is concluded that the retrieval procedure has a potential for reliably determining the structure of vortex wakes that trail from the wings of subsonic transport aircraft. Tests using idealized theoretical models show that the procedure is highly reliable and accurate. However, certain difficulties are found in the retrieval procedure when applied to actual data measured with following wings of various sizes in a wind tunnel.
Instabilities and nonlinearities in the elastic vortex solid
NASA Astrophysics Data System (ADS)
Banerjee, Satyajit; Mohan, Shyam; Sinha, Jaivardhan; Ramakrishnan, S.; Grover, A. K.; Sood, Ajay
2009-03-01
In recent times the influence of microscopic disorder has been viewed to play a crucial role in determining the configuration of vortices inside superconductors. Our recent investigations into the dissipation properties of the driven vortices [1], have found the existence of possible symmetry changes deep within the well ordered elastic vortex solid [1]. The result is significant, as it requires a deeper revision of understanding the properties of the so called `benign' elastic vortex solid. We have also studied the nonlinear properties of the driven elastic vortex solid [2] through a random pinning environment and have found interesting highly nonlinear fluctuation in the time domain. We believe our results indicate the presence of process deep within the elastic driven phase which is a precursor to the plastic transformation in the vortex matter. [1] Shyam Mohan, Jaivardhan Sinha, S. S. Banerjee*, and Yuri Myasoedov, Phys. Rev. Lett. 98,027003 (2007). [2] Shyam Mohan, Jaivardhan Sinha, S. S. Banerjee* A. K. Sood, S. Ramakrishna, A. K. Grover (submitted, 2008) *satyajit@iitk.ac.in
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.
Evolution of a curved vortex filament into a vortex ring
NASA Technical Reports Server (NTRS)
Moin, P.; Leonard, A.; Kim, J.
1985-01-01
The deformation of a hairpin-shaped vortex filament under self-induction and in the presence of shear is studied numerically using the Biot-Savart law. It is shown that the tip region of an elongated hairpin vortex evolves into a vortex ring and that the presence of mean shear impedes the process. Evolution of a finite-thickness vortex sheet under self-induction is also investigated using the Navier-Stokes equations. The layer evolves into a hairpin vortex which in turn produces a vortex ring of high Reynolds stress content. These results indicate a mechanism for the generation of ring vortices in turbulent shear flows, and a link between the experimental and numerical observation of hairpin vortices and the observation of ring vortices in the outer regions of turbulent boundary layers.
Evolution of a curved vortex filament into a vortex ring
NASA Technical Reports Server (NTRS)
Moin, P.; Leonard, A.; Kim, J.
1986-01-01
The deformation of a hairpin-shaped vortex filament under self-induction and in the presence of shear is studied numerically using the Biot-Savart law. It is shown that the tip region of an elongated hairpin vortex evolves into a vortex ring and that the presence of mean shear impedes the process. Evolution of a finite-thickness vortex sheet under self-induction is also investigated using the Navier-Stokes equations. The layer evolves into a hairpin vortex which in turn produces a vortex ring of high Reynolds stress content. These results indicate a mechanism for the generation of ring vortices in turbulent shear flows, and a link between the experimental and numerical observation of hairpin vortices and the observation of ring vortices in the outer regions of turbulent boundary layers.
Segmented trapped vortex cavity
NASA Technical Reports Server (NTRS)
Grammel, Jr., Leonard Paul (Inventor); Pennekamp, David Lance (Inventor); Winslow, Jr., Ralph Henry (Inventor)
2010-01-01
An annular trapped vortex cavity assembly segment comprising includes a cavity forward wall, a cavity aft wall, and a cavity radially outer wall there between defining a cavity segment therein. A cavity opening extends between the forward and aft walls at a radially inner end of the assembly segment. Radially spaced apart pluralities of air injection first and second holes extend through the forward and aft walls respectively. The segment may include first and second expansion joint features at distal first and second ends respectively of the segment. The segment may include a forward subcomponent including the cavity forward wall attached to an aft subcomponent including the cavity aft wall. The forward and aft subcomponents include forward and aft portions of the cavity radially outer wall respectively. A ring of the segments may be circumferentially disposed about an axis to form an annular segmented vortex cavity assembly.
NASA Astrophysics Data System (ADS)
Anderson, Philip W.
2007-03-01
In 1967, Reatto and Chester proposed that solid helium-4 might exhibit superfluidity, and in 1970, Leggett suggested what was thought to be a definitive experimental test: to find non-classical rotational inertia in a toroidal sample. More than three decades later, the observation by Kim and Chan of exactly that effect generated great interest and has been repeated and confirmed by a number of groups. However, many attempts to find actual superflow in truly solid samples have failed. Here, I draw an analogy with a second example of anomalous response to vorticity in a dissipative fluid, the vortex liquid phase in the pseudogap region of high-temperature superconductors, and propose that the solid helium experiments have been mischaracterized: what is observed is not supersolidity but an incompressible vortex liquid. This state is distinct from a conventional liquid in that its properties are dominated by conserved supercurrents flowing around a thermally fluctuating tangle of vortices.
NASA Technical Reports Server (NTRS)
Mcintyre, Michael
1988-01-01
Recent work with high resolution, one-layer numerical models of fluid flows resembling those in the real stratosphere has suggested that: (1) the interiors of strong cyclonic vortices like the Antarctic polar vortex may be almost completely isolated laterally from their surroundings - perhaps even completely isolated, under some circumstances; (2) by contrast, material near the edge of such and isolated region can easily be eroded (or mixed one-sidedly) into the surrounding region; and (3) the erosion characteristically produces extremely steep gradients in isentropic distributions of potential vorticity (PV) and of other tracers, possibly down to horizontal length scales of a few kilometers only. Such length scales may occur both at the edge of the main polar vortex and in smaller features outside it, such as thin filamentary structures, produced by the erosion process.
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.
Correcting vortex splitting in higher order vortex beams.
Neo, Richard; Tan, Shiaw Juen; Zambrana-Puyalto, Xavier; Leon-Saval, Sergio; Bland-Hawthorn, Joss; Molina-Terriza, Gabriel
2014-04-21
We demonstrate a general method for the first order compensation of singularity splitting in a vortex beam at a single plane. By superimposing multiple forked holograms on the SLM used to generate the vortex beam, we are able to compensate vortex splitting and generate beams with desired phase singularities of order ℓ = 0, 1, 2, and 3 in one plane. We then extend this method by application of a radial phase, in order to simultaneously compensate the observed vortex splitting at two planes (near and far field) for an ℓ = 2 beam. PMID:24787874
Not Available
1990-02-01
The program objective is to demonstrate efficient removal of fine particulates to sufficiently low levels to meet proposed small scale coal combustor emission standards. This is to be accomplished using a novel particulate removal device, the Confined Vortex Scrubber. This is the first quarterly technical progress report under this contract. Accordingly, a summary of the cleanup concept and the structure of the program is given here.
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.
High sensitivity vortex shedding flowmeter
Lew, H.S.
1989-12-05
This patent describes an apparatus for measuring fluid flows. It comprises: a flowmeter body including a flow passage; a vortex generator of an elongated cylindrical shape disposed across a cross section of the flow passage, wherein at lest one extremity of the vortex generator is secured to the flowmeter body; a transducer contained in a container vessel secured to the flowmeter body, wherein the transducer is pressed onto a thin wall of the container vessel; and a flexible coupling connecting the thin wall of the container vessel to a deflective portion of the vortex generating, wherein the flexible coupling enhances relative deflection between the vortex generator and the container vessel. Wherein fluctuating fluid dynamic forces resulting from vortices shed from the vortex generator and experienced by vortex generator generate fluctuating electrical signals from the transducer as a measure of fluid flow through the flow passage.
Aeroacoustics of viscous vortex reconnection
NASA Astrophysics Data System (ADS)
Paredes, Pedro; Nichols, Joseph W.; Duraisamy, Karthik; Hussain, Fazle
2011-11-01
Reconnection of two anti-parallel vortex tubes is studied by direct numerical simulations and large-eddy simulations of the incompressible Navier-Stokes equations over a wide range (2000-50,000) of the vortex Reynolds number (Re). A detailed investigation of the flow dynamics is performed and at high Re, multiple reconnections are observed as the newly formed ``bridges'' interact by self and mutual induction. To investigate acoustics produced by the recoil action of the vortex threads, Möhring's theory of vortex sound is applied to the flow field and evaluated at varying far-field locations. The acoustic solver is verified against calculations of laminar vortex ring collision. For anti-parallel vortex reconnection, the resulting far-field spectra are shown to be grid converged at low-to-mid frequencies. To assess the relevance to fully turbulent jet noise, the dependence of reconnection upon Reynolds number is investigated.
Skyrmion Flux Lattices in p,-wave Superconductors
NASA Astrophysics Data System (ADS)
Li, Qi; Toner, John; Belitz, Dietrich
2007-03-01
In p,-wave superconductors, topological excitations known as skyrmions are allowed, in addition to the usual vortices. In strongly type-II materials in an external magnetic field, a skyrmion flux lattice is expected to be energetically favored compared to a vortex flux lattice [1]. We analytically calculate the energy, magnetization curves (B(H)), and elasticity of skyrmion flux lattices in p,-wave superconductors near the lower critical field Hc1, and use these results with the Lindemann criterion to predict their melting curve [2]. In striking contrast to vortex flux lattices, which always melt at an external field H > Hc1, skyrmion flux lattices never melt near Hc1. This provides a simple and unambiguous test for the presence of skyrmions. In addition, the internal magnetic field distributions (which are measurable by muon spin rotation techniques [3]) of skyrmion and vortex lattices are very different. [1] A. Knigavko, B. Rosenstein, and Y.F. Chen, Phys. Rev. B 60, 550 (1999). [2] Qi Li, John Toner, and D. Belitz, cond-mat/0607391 [3] J.E. Sonier, J. Phys. Cond. Matt. 16, S4499 (2004)
Vortex reconnection in superfluid helium
Koplik, J. ); Levine, H. )
1993-08-30
A useful physical model for superfluid turbulence considers the flow to consist of a dense tangle of vortex lines which evolve and interact. It has been suggested that these vortex lines can dynamically reconnect upon close approach. Here, we consider the nonlinear Schroedinger equation model of superfluid quantum mechanics, and use numerical simulation to study this topology changing core-scale process. Our results support the idea that vortex reconnection will occur whenever filaments come within a few core lengths of one another.
Design and evaluation of a Dean vortex-based micromixer.
Howell, Peter B; Mott, David R; Golden, Joel P; Ligler, Frances S
2004-12-01
A mixer, based on the Dean vortex, is fabricated and tested in an on-chip format. When fluid is directed around a curve under pressure driven flow, the high velocity streams in the center of the channel experience a greater centripetal force and so are deflected outward. This creates a pair of counter-rotating vortices moving fluid toward the inner wall at the top and bottom of the channel and toward the outer wall in the center. For the geometries studied, the vortices were first seen at Reynolds numbers between 1 and 10 and became stronger as the flow velocity is increased. Vortex formation was monitored in channels with depth/width ratios of 0.5, 1.0, and 2.0. The lowest aspect ratio strongly suppressed vortex formation. Increasing the aspect ratio above 1 appeared to provide improved mixing. This design has the advantages of easy fabrication and low surface area. PMID:15570382
Accumulation of heavy particles around a helical vortex filament
NASA Astrophysics Data System (ADS)
IJzermans, Rutger H. A.; Hagmeijer, Rob; van Langen, Pieter J.
2007-10-01
The motion of small heavy particles near a helical vortex filament in incompressible flow is investigated. Both the configurations of a helical vortex filament in free space and a helical vortex filament in a concentric pipe are considered, and the corresponding helically symmetric velocity fields are expressed in terms of a stream function. Particle motion is assumed to be driven by Stokes drag, and the flow fields are assumed to be independent from the motion of particles. Numerical results show that heavy particles may be attracted to helical trajectories. The stability of these attraction trajectories is demonstrated by linear stability analysis. In addition, the correlation between the attraction trajectories and the streamline topologies is investigated.
Interferometric optical vortex array generator.
Vyas, Sunil; Senthilkumaran, P
2007-05-20
Two new interferometric configurations for optical vortex array generation are presented. These interferometers are different from the conventional interferometers in that they are capable of producing a large number of isolated zeros of intensity, and all of them contain optical vortices. Simulation and theory for optical vortex array generation using three-plane-wave interference is presented. The vortex dipole array produced this way is noninteracting, as there are no attraction or repulsion forces between them, leading to annihilation or creation of vortex pairs. PMID:17514234
Interferometric optical vortex array generator
Vyas, Sunil; Senthilkumaran, P
2007-05-20
Two new interferometric configurations for optical vortex array generation are presented.These interferometers are different from the conventional interferometers in that they are capable of producing a large number of isolated zeros of intensity, and all of them contain optical vortices. Simulation and theory for optical vortex array generation using three-plane-wave interference is presented. The vortex dipole array produced this way is noninteracting, as there are no attraction or repulsion forces between them, leading to annihilation or creation of vortex pairs.
Vortex reconnection in a swirling flow
NASA Astrophysics Data System (ADS)
Alekseenko, S. V.; Kuibin, P. A.; Shtork, S. I.; Skripkin, S. G.; Tsoy, M. A.
2016-04-01
Processes of vortex reconnection on a helical vortex, which is formed in a swirling flow in a conical diffuser, have been studied experimentally. It has been shown that reconnection can result in the formation of both an isolated vortex ring and a vortex ring linked with the main helical vortex. A number of features of vortex reconnection, including the effects of asymmetry, generation of Kelvin waves, and formation of various bridges, have been described.
NASA Astrophysics Data System (ADS)
Straser, Valentino
2014-05-01
The relationship between the convection currents of the mantle-lithosphere system with terrestrial dynamics has represented one of the main themes of tectonophysics for over a century, in addition to the relationships interwoven with crust dynamics. Likewise, the relevant debate has animated the scientific community for more than a century, as recalled by the work of Kreighauger (1902), Ampferer (1906), Schwinner (1919), Holmes (1928), Griggs (1932), Pekeris (1935), Kraus (1951), Hess (1962). Though never directly observed, the convection currents in the mantle manifest their effects in the Earth's crust in various ways, such as the flow of heat in the oceans and continents, and magnetic anomalies. These are the result of effects caused by ferromagnetic materials dragged upwards by convection movements, as demonstrated by the laboratory simulations carried out by Glatzmaier and Olson (2005). With respect to the initial simplified and theoretical modelling of the first authors of the last century, the studies by Bercovici, Schubert and Glatzmaier (1989) and those of Glatzmaier and Olson (2005) revealed a complex three-dimensional model of the dynamics of convection processes in the mantle, even if it is not yet clear to what extent this mechanism actually reflects reality. The differences in temperature in the Earth's inner shells causes convection movements that can manifest both on a large scale with laminar flows and plumes, and on a small scale with turbulent flows concentrated in limited areas of the globe. The trajectories in a vortex, also proposed by Gurevich (2012), generated by complex motions in the mantle-lithosphere system, are driven by the Coriolis Effect. The combination of these mechanisms together with the Coriolis force creates, on the whole, ascending helical motions with a similar effect to that of an atmospheric cyclone interacting with the lithospheric shell. In this study it is believed that the ascending whirling movements (Vortex Theory
Vortex nozzle for segmenting and transporting metal chips from turning operations
Bieg, L.F.
1993-04-20
Apparatus for collecting, segmenting and conveying metal chips from machining operations utilizes a compressed gas driven vortex nozzle for receiving the chip and twisting it to cause the chip to segment through the application of torsional forces to the chip. The vortex nozzle is open ended and generally tubular in shape with a converging inlet end, a constant diameter throat section and a diverging exhaust end. Compressed gas is discharged through angled vortex ports in the nozzle throat section to create vortex flow in the nozzle and through an annular inlet at the entrance to the converging inlet end to create suction at the nozzle inlet and cause ambient air to enter the nozzle. The vortex flow in the nozzle causes the metal chip to segment and the segments thus formed to pass out of the discharge end of the nozzle where they are collected, cleaned and compacted as needed.
NASA Astrophysics Data System (ADS)
Wolf, M. S.; Badea, R.; Berezovsky, J.
2016-06-01
The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defect using small applied magnetic fields, inducing significant nitrogen-vacancy spin splitting. We also find that the magnetic field gradient produced by the vortex is sufficient to address spins separated by nanometre-length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced coherent rotation of the spin state. Finally, we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ~100 ns timescales.
Wolf, M. S.; Badea, R.; Berezovsky, J.
2016-01-01
The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defect using small applied magnetic fields, inducing significant nitrogen-vacancy spin splitting. We also find that the magnetic field gradient produced by the vortex is sufficient to address spins separated by nanometre-length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced coherent rotation of the spin state. Finally, we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ∼100 ns timescales. PMID:27296550
Wolf, M. S.; Badea, R.; Berezovsky, J.
2016-06-14
The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defect using small applied magnetic fields, inducing significant nitrogen-vacancy spin splitting. We also find that the magnetic field gradient produced by the vortex is sufficient to address spins separated by nanometre-length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the nitrogen-vacancymore » spins, resulting in enhanced coherent rotation of the spin state. Lastly, we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ~ 100 ns timescales.« less
Wolf, M S; Badea, R; Berezovsky, J
2016-01-01
The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defect using small applied magnetic fields, inducing significant nitrogen-vacancy spin splitting. We also find that the magnetic field gradient produced by the vortex is sufficient to address spins separated by nanometre-length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced coherent rotation of the spin state. Finally, we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ∼100 ns timescales. PMID:27296550
Magnetic vortex crystal formation in the antidot complement of square artificial spin ice
Araujo, C. I. L. de Silva, R. C.; Ribeiro, I. R. B.; Nascimento, F. S.; Felix, J. F.; Ferreira, S. O.; Moura-Melo, W. A.; Pereira, A. R.; Mól, L. A. S.
2014-03-03
We have studied ferromagnetic nickel thin films patterned with square lattices of elongated antidots that are negative analogues of square artificial spin ice. Micromagnetic simulations and direct current magnetic moment measurements reveal in-plane anisotropy of the magnetic hysteresis loops, and the formation of a dense array of magnetic vortices with random polarization and chirality. These multiply-connected antidot arrays could be superior to lattices of disconnected nanodisks for investigations of vortex switching by applied electric current.
Magnetic vortex crystal formation in the antidot complement of square artificial spin ice
NASA Astrophysics Data System (ADS)
de Araujo, C. I. L.; Silva, R. C.; Ribeiro, I. R. B.; Nascimento, F. S.; Felix, J. F.; Ferreira, S. O.; Mól, L. A. S.; Moura-Melo, W. A.; Pereira, A. R.
2014-03-01
We have studied ferromagnetic nickel thin films patterned with square lattices of elongated antidots that are negative analogues of square artificial spin ice. Micromagnetic simulations and direct current magnetic moment measurements reveal in-plane anisotropy of the magnetic hysteresis loops, and the formation of a dense array of magnetic vortices with random polarization and chirality. These multiply-connected antidot arrays could be superior to lattices of disconnected nanodisks for investigations of vortex switching by applied electric current.
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
Fermion zero modes in a chromomagnetic vortex lattice
NASA Astrophysics Data System (ADS)
Chernodub, M. N.; Kalaydzhyan, Tigran; Van Doorsselaere, Jos; Verschelde, Henri
2014-03-01
We prove the existence of zero modes of massless quarks in a background of spaghetti vacuum of chromomagnetic vortices in QCD. We find a general solution for the zero modes and show that the modes can be localized at pairs of vortices.
Vortex-Vortex Interactions Behind an Oscillating Plate
NASA Astrophysics Data System (ADS)
Unal, M. F.; Rockwell, D.
1996-11-01
A blunt-based flat plate in a uniform stream is subjected to periodic pitching oscillations at multiples of the natural shedding frequency over a range of dime nsionless amplitudes. The near wake is characterized by dye and hydrogen bubble visualization. At low amplitudes of oscillation, the nature of the vortex-vortex interaction in the near-wake is such that, irrespective of oscillation frequency , the downstream wake remarkably recovers to the classical vortex street. For hi gh amplitudes, at frequencies higher than the natural shedding frequency, the vo rtex street gives way to complex vortex configurations. These features are relat ed to several interesting phenomena in the base region, including pronounced she dding of vorticity from the base and existence of a very small-scale vortex stre et along the plane of symmetry.
Vortex Flipping in Superconductor-Ferromagnet Spin Valve Structures
NASA Astrophysics Data System (ADS)
Patino, Edgar J.; Aprili, Marco; Blamire, Mark; Maeno, Yoshiteru
2014-03-01
We report in plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni, below the superconducting transition Tc, our results show strong evidence of vortex flipping driven by the ferromagnets magnetization. This is a direct consequence of proximity effect that leads to vortex supercurrents leakage into the ferromagnets. Here the polarized electron spins are subject to vortices magnetic field occasioning vortex flipping. Such novel mechanism has been made possible for the first time by fabrication of the F/S/F/AF multilayered spin valves with a thin-enough S layer to barely confine vortices inside as well as thin-enough F layers to align and control the magnetization within the plane. When Co is used there is no observation of vortex flipping effect. This is attributed to Co shorter coherence length. Interestingly instead a reduction in pinning field of about 400 Oe is observed when the Nb layer is in superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts any explanation must be directly related to proximity effect and thus a remarkable phenomenon that deserves further investigation. Programa Nacional de Ciencias Basicas COLCIENCIAS (No. 120452128168).
Hoyatdavoudi, A.; Adams, L. M.
1985-04-23
A drilling sub is provided in a drill string above a drill bit. The drilling sub includes a nozzle oriented to eject drilling fluid from said drill string into an annulus between the drill string and a well bore hole at an elevation above the drill bit with a horizontal velocity component tangential to said annulus to thereby impart a swirling motion to drilling fluid in the annulus. This creates a vortex extending down to the drill bit to enhance the cleaning of cuttings from the bore hole and to reduce a pressure differential thereby increasing a penetration rate of the drill bit.
Magnetic vortex filament flows
Barros, Manuel; Cabrerizo, Jose L.; Fernandez, Manuel; Romero, Alfonso
2007-08-15
We exhibit a variational approach to study the magnetic flow associated with a Killing magnetic field in dimension 3. In this context, the solutions of the Lorentz force equation are viewed as Kirchhoff elastic rods and conversely. This provides an amazing connection between two apparently unrelated physical models and, in particular, it ties the classical elastic theory with the Hall effect. Then, these magnetic flows can be regarded as vortex filament flows within the localized induction approximation. The Hasimoto transformation can be used to see the magnetic trajectories as solutions of the cubic nonlinear Schroedinger equation showing the solitonic nature of those.
NASA Technical Reports Server (NTRS)
Werle, H.
1984-01-01
Vortex bursting is studied by means of visualization. The physical behavior of the phenomenon is emphasized, and its similarity with boundary layer separation or wake bursting becomes apparent. The essential influence of an increasing pressure gradient on the initiation, the position and the type of bursting is clearly confirmed. The evolution of the phenomena as a function of several parameters is analyzed in the case of delta wings, alone or installed on aircraft models, and compared with the results of similar wind tunnel or flight tests.
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.
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.
Optical vortex generation with wavelength tunability based on an acoustically-induced fiber grating.
Zhang, Wending; Wei, Keyan; Huang, Ligang; Mao, Dong; Jiang, Biqiang; Gao, Feng; Zhang, Guoquan; Mei, Ting; Zhao, Jianlin
2016-08-22
We presented a method to actualize the optical vortex generation with wavelength tunability via an acoustically-induced fiber grating (AIFG) driven by a radio frequency source. The circular polarization fundamental mode could be converted to the first-order optical vortex through the AIFG, and its topological charges were verified by the spiral pattern of coaxial interference between the first-order optical vortex and a Gaussian-reference beam. A spectral tuning range from 1540 nm to 1560 nm was demonstrated with a wavelength tunability slope of 4.65 nm/kHz. The mode conversion efficiency was 95% within the whole tuning spectral range. PMID:27557207
Underwing compression vortex attenuation device
NASA Technical Reports Server (NTRS)
Patterson, James C., Jr. (Inventor)
1993-01-01
A vortex attenuation device is presented which dissipates a lift-induced vortex generated by a lifting aircraft wing. The device consists of a positive pressure gradient producing means in the form of a compression panel attached to the lower surface of the wing and facing perpendicular to the airflow across the wing. The panel is located between the midpoint of the local wing cord and the trailing edge in the chord-wise direction and at a point which is approximately 55 percent of the wing span as measured from the fuselage center line in the spanwise direction. When deployed in flight, this panel produces a positive pressure gradient aligned with the final roll-up of the total vortex system which interrupts the axial flow in the vortex core and causes the vortex to collapse.
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.
Lift enhancement by trapped vortex
NASA Technical Reports Server (NTRS)
Rossow, Vernon J.
1992-01-01
The viewgraphs and discussion of lift enhancement by trapped vortex are provided. Efforts are continuously being made to find simple ways to convert wings of aircraft from an efficient cruise configuration to one that develops the high lift needed during landing and takeoff. The high-lift configurations studied here consist of conventional airfoils with a trapped vortex over the upper surface. The vortex is trapped by one or two vertical fences that serve as barriers to the oncoming stream and as reflection planes for the vortex and the sink that form a separation bubble on top of the airfoil. Since the full three-dimensional unsteady flow problem over the wing of an aircraft is so complicated that it is hard to get an understanding of the principles that govern the vortex trapping process, the analysis is restricted here to the flow field illustrated in the first slide. It is assumed that the flow field between the two end plates approximates a streamwise strip of the flow over a wing. The flow between the endplates and about the airfoil consists of a spanwise vortex located between the suction orifices in the endplates. The spanwise fence or spoiler located near the nose of the airfoil serves to form a separated flow region and a shear layer. The vorticity in the shear layer is concentrated into the vortex by withdrawal of fluid at the suction orifices. As the strength of the vortex increases with time, it eventually dominates the flow in the separated region so that a shear or vertical layer is no longer shed from the tip of the fence. At that point, the vortex strength is fixed and its location is such that all of the velocity contributions at its center sum to zero thereby making it an equilibrium point for the vortex. The results of a theoretical analysis of such an idealized flow field are described.
NASA Astrophysics Data System (ADS)
Turchak, L. I.
2012-10-01
The objective is the general review of impact of aircraft wake vortices on the follower aircraft encountering the wake. Currently, the presence of wake vortices past aircraft limits the airspace capacity and flight safety level for aircraft of different purposes. However, wake vortex nature and evolution have not been studied in full measure. A mathematical model simulating the process of near wake generation past bodies of different shapes, as well as the wake evolution after rolling-up into wake vortices (far wake) is developed. The processes are suggested to be modeled by means of the Method of Discrete Vortices. Far wake evolution is determined by its complex interaction with the atmosphere and ground boundary layer. The main factors that are supposed to take into account are: wind and ambient turbulence 3Ddistributions, temperature stratification of the atmosphere, wind shear, as well as some others which effects will be manifested as considerable during the investigation. The ground boundary layer effects on wake vortex evolution are substantial at low flight altitudes and are determined through the boundary layer separation.
NASA Astrophysics Data System (ADS)
Maines, Brant H.; Arndt, Roger E. A.
2000-11-01
Cavitation in vortical flows is a problem of practical importance, that is relatively unexplored. Vortical structures of importance range from the eddies occurring randomly in space and time in turbulent flows to the developed vortices that occur at the tips of lifting surfaces and at the hubs of propellers and hydraulic turbines. A variety of secondary flow phenomena such as the horse shoe vortices that form around bridge piers, chute blocks and struts, and the secondary vortices found in the clearance passages of turbomachinery are also important cavitation sites. Tip vortex cavitation can be viewed as a canonical problem that captures many of the essential physics associated with vortex cavitation in general. This paper describes the inception process and focuses on the high levels of tension that can be sustained in the flow, which appears to scale with the blade loading. High speed video visualization indicates that the details of how free stream nuclei are ingested plays a major role in the nucleation and inception process. A new photographic technique was used to obtain high quality images of the bubble growth process at framing rates as high as 40,000 fps. Sponsored by the Office of Naval Research
Analytical solutions for rotating vortex arrays involving multiple vortex patches
NASA Astrophysics Data System (ADS)
Crowdy, Darren; Marshall, Jonathan
2005-01-01
A continous two-parameter family of analytical solutions to the Euler equations are presented representing a class of steadily rotating vortex arrays involving N+1 interacting vortex patches where N ≥ 3 is an integer. The solutions consist of a central vortex patch surrounded by an N-fold symmetric alternating array of satellite point vortices and vortex patches. One of the parameters governs the size of the central patch, the other governs the size of the N satellite patches. In the limit where the areas of the satellite vortex patches tend to zero, the solutions degenerate to the exact solutions of Crowdy (J. Fluid Mech. vol. 469, 2002, p. 209). Limiting states are found in which cusps form only on the central patch, only on the satellite patches, or simultaneously on both central and satellite patches. Contour dynamics simulations are used to check the mathematical solutions and test their robustness. The linear stability of a class of "point-vortex models" (in which the patches are replaced by point vortices) are also studied in order to examine the stability of the distributed-vorticity configurations to pure-displacement modes. On the other hand, a desingularization of all point vortices to Rankine vortices leads to a class of "quasi-equilibria" consisting purely of interacting vortex patches close to hydrodynamic equilibrium.
Leading-edge vortex burst on a low-aspect-ratio rotating flat plate
NASA Astrophysics Data System (ADS)
Medina, Albert; Jones, Anya R.
2016-08-01
This study experimentally investigates the phenomenon of leading-edge-vortex burst on rotating flat plate wings. An aspect-ratio-2 wing was driven in pure rotation at a Reynolds number of Re=2500 . Of primary interest is the evolution of the leading-edge vortex along the wing span over a single-revolution wing stroke. Direct force measurements of the lift produced by the wing revealed a single global lift maximum relatively early in the wing stroke. Stereoscopic particle image velocimetry was applied to several chordwise planes to quantify the structure and strength of the leading-edge vortex and its effect on lift production. This analysis revealed opposite-sign vorticity entrainment into the core of the leading-edge vortex, originating from a layer of secondary vorticity along the wing surface. Coincident with the lift peak, there emerged both a concentration of opposite vorticity in the leading-edge-vortex core, as well as axial flow stagnation within the leading-edge-vortex core. Planar control volume analysis was performed at the midspan to quantify the contributions of vorticity transport mechanisms to the leading-edge-vortex circulation. The rate of circulation annihilation by opposite-signed vorticity entrainment was found to be minimal during peak lift production, where convection balanced the flux of vorticity resulting in stagnation and eventually reversal of axial flow. Finally, vortex burst was found to be correlated with swirl number, where bursting occurs at a swirl threshold of Sw<0.6 .
Evolution and Control of the Leading Edge Vortex on an Unsteady Wing
NASA Astrophysics Data System (ADS)
Akkala, James; Buchholz, James
2015-11-01
The development of the leading-edge vortex is investigated on a periodically plunging plate within a uniform free stream. Vortex circulation is governed primarily by the strength of the leading edge shear layer, which provides the primary source of circulation, and a substantial opposite-sign contribution due to the pressure-gradient-driven diffusive flux of vorticity from the suction surface of the plate. The latter has been shown to produce a substantial reduction in leading-edge vortex strength, and leads to the development of a secondary vortex whose evolution influences the interaction between the leading edge vortex and the surface, and thus alters the surface pressure gradients. Suction is applied in the vicinity of the secondary vortex in an attempt to regulate the aerodynamic loads in the presence of the leading-edge vortex. The effect on vorticity transport, leading-edge vortex dynamics, and the resulting aerodynamic loads is discussed. This work was supported, in part, by the Air Force Office of Scientific Research under Grant number FA9550-11-1-0019 and the National Science Foundation under EPSCoR grant EPS1101284.
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.
Vortex wall dynamics and pinning in helical magnets
NASA Astrophysics Data System (ADS)
Roostaei, Bahman
2014-06-01
Domain walls formed by one dimensional array of vortex lines have been recently predicted to exist in disordered helical magnets and multiferroics. These systems are on one hand analogues to the vortex line lattices in type-II superconductors while on the other hand they propagate in the magnetic medium as a domain boundary. Using a long wavelength approach supported by numerical optimization we lay out detailed theory for dynamics and structure of such topological fluctuations at zero temperature in presence of weak disorder. We show the interaction between vortex lines is weak. This is the direct consequence of the screening of the vorticity by helical background in the system. We explain how one can use this result to understand the elasticity of the wall with a vicinal surface approach. Also we show the internal degree of freedom of this array leads to the enhancement of its mobility. We present estimates for the interaction and mobility enhancements using the microscopic parameters of the system. Finally we determine the range of velocities/force densities in which the internal movement of the vortex wall can be effective in its dynamics.
Reichhardt, Charles; Reichhardt, Cynthia
2008-01-01
We show using numerical simulations that vortices in honeycomb pinning arrays can exhibit a remarkable variety of dynamical phases that are distinct from those found for triangular and square pinning arrays. In the honeycomb arrays, it is possible for the interstitial vortices to form dimer or higher n-mer states which have an additional orientational degree of freedom that can lead to the formation of vortex molecular crystals. For filling fractions where dimer states appear, a dynamical symmetry breaking can occur when the dimers flow in one of two possible alignment directions. This leads to transport in the direction transverse to the applied drive. We show that dimerization produces distinct types of moving phases which depend on the direction of the driving force with respect to the pinning lattice symmetry. When the dimers are driven along certain directions, a reorientation of the dimers can produce a jamming phenomenon which results in a strong enhancement in the critical depinning force. The jamming can also cause unusual effects such as an increase in the critical depinning force when the size of the pinning sites is reduced.
NASA Astrophysics Data System (ADS)
Garaud, Julien; Babaev, Egor
2015-01-01
We study superconductors with two order components and phase separation driven by intercomponent density-density interaction, focusing on the phase where only one condensate has nonzero ground-state density and a competing order parameter exists only in vortex cores. We demonstrate there that multibody intervortex interactions can be strongly nonpairwise, leading to some unusual vortex patterns in an external field, such as vortex pairs and vortex chains. We demonstrate that in an external magnetic field such a system undergoes a field-driven phase transition from (broken) U (1 ) to (broken) U (1 )×U (1 ) symmetries when a subdominant order parameter in the vortex cores acquires global coherence. Observation of these characteristic ordering patterns in surface probes may signal the presence of a subdominant condensate in the vortex core.
Lattice gas and lattice Boltzmann computational physics
Chen, S.
1993-05-01
Recent developments of the lattice gas automata method and its extension to the lattice Boltzmann method have provided new computational schemes for solving a variety of partial differential equations and modeling different physics systems. The lattice gas method, regarded as the simplest microscopic and kinetic approach which generates meaningful macroscopic dynamics, is fully parallel and can be easily programmed on parallel machines. In this talk, the author will review basic principles of the lattice gas and lattice Boltzmann method, its mathematical foundation and its numerical implementation. A detailed comparison of the lattice Boltzmann method with the lattice gas technique and other traditional numerical schemes, including the finite-difference scheme and the pseudo-spectral method, for solving the Navier-Stokes hydrodynamic fluid flows, will be discussed. Recent achievements of the lattice gas and the the lattice Boltzmann method and their applications in surface phenomena, spinodal decomposition and pattern formation in chemical reaction-diffusion systems will be presented.
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.
ERIC Educational Resources Information Center
Scott, Paul
2006-01-01
A lattice is a (rectangular) grid of points, usually pictured as occurring at the intersections of two orthogonal sets of parallel, equally spaced lines. Polygons that have lattice points as vertices are called lattice polygons. It is clear that lattice polygons come in various shapes and sizes. A very small lattice triangle may cover just 3…
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.
Numerical study of vortex reconnection
Ashurst, W.T.; Meiron, D.I.
1987-04-20
With a Biot-Savart model of vortex filaments to provide initial conditions, a finite difference scheme for the incompressible Navier-Stokes equation is used in the region of closest approach of two vortex rings. In the Navier-Stokes solution, we see that the low pressure which develops between the interacting vorticity regions causes the distortion of the initially circular vortex cross section and forces the rearrangement of vorticity on a convective time scale which is much faster than that estimated from viscous transport.
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.
NASA Astrophysics Data System (ADS)
Faller, Alan J.
2001-05-01
It has been found that the generation of swirl by a continuous rotary oscillation of a right-circular cylinder partially filled with water can leave a vortex with a radially constant tangential velocity, V, i.e. [partial partial differential]V/[partial partial differential]r = 0, excepting a small central core and the sidewall boundary layer. This vortex maintains [partial partial differential]V/[partial partial differential]r = 0 during viscous decay by the turbulent bottom boundary layer, a fact that suggests that [partial partial differential]V/[partial partial differential]r = 0 is a stable condition for a decaying vortex.
Bathtub vortex induced by instability.
Mizushima, Jiro; Abe, Kazuki; Yokoyama, Naoto
2014-10-01
The driving mechanism and the swirl direction of the bathtub vortex are investigated by the linear stability analysis of the no-vortex flow as well as numerical simulations. We find that only systems having plane symmetries with respect to vertical planes deserve research for the swirl direction. The bathtub vortex appearing in a vessel with a rectangular cross section having a drain hole at the center of the bottom is proved to be induced by instability when the flow rate exceeds a threshold. The Coriolis force is capable of determining the swirl direction to be cyclonic. PMID:25375427
Holographic Vortex Coronagraph
NASA Technical Reports Server (NTRS)
Palacios, David
2010-01-01
A holographic vortex coronagraph (HVC) has been proposed as an improvement over conventional coronagraphs for use in high-contrast astronomical imaging for detecting planets, dust disks, and other broadband light scatterers in the vicinities of stars other than the Sun. Because such light scatterers are so faint relative to their parent stars, in order to be able to detect them, it is necessary to effect ultra-high-contrast (typically by a factor of the order of 1010) suppression of broadband light from the stars. Unfortunately, the performances of conventional coronagraphs are limited by low throughput, dispersion, and difficulty of satisfying challenging manufacturing requirements. The HVC concept offers the potential to overcome these limitations.
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.
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.
Helimagnons in the skyrmion lattice of MnSi
NASA Astrophysics Data System (ADS)
Janoschek, M.; Jonietz, F.; Link, P.; Pfleiderer, C.; Böni, P.
2010-01-01
In MnSi the application of a small magnetic field destabilizes the helimagnetic order in a narrow temperature interval just below the helimagnetic ordering temperature and stabilizes the formation of a hexagonal lattice of skyrmions, i.e., a lattice composed of a type of magnetic vortex lines. We have studied the skyrmion lattice in MnSi using a cold triple-axis spectrometer. Our data suggests that the skyrmion lattice represents a three-dimensional spin structure. The collective spin excitations of the skyrmion lattice are strongly reminiscent of the rich spectrum of helimagnon bands, recently shown to be a universal property of the helimagnetic state of MnSi in zero magnetic field.
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.
Vortex breakdown in a truncated conical bioreactor
NASA Astrophysics Data System (ADS)
Balci, Adnan; Brøns, Morten; Herrada, Miguel A.; Shtern, Vladimir N.
2015-12-01
This numerical study explains the eddy formation and disappearance in a slow steady axisymmetric air-water flow in a vertical truncated conical container, driven by the rotating top disk. Numerous topological metamorphoses occur as the water height, Hw, and the bottom-sidewall angle, α, vary. It is found that the sidewall convergence (divergence) from the top to the bottom stimulates (suppresses) the development of vortex breakdown (VB) in both water and air. At α = 60°, the flow topology changes eighteen times as Hw varies. The changes are due to (a) competing effects of AMF (the air meridional flow) and swirl, which drive meridional motions of opposite directions in water, and (b) feedback of water flow on AMF. For small Hw, the AMF effect dominates. As Hw increases, the swirl effect dominates and causes VB. The water flow feedback produces and modifies air eddies. The results are of fundamental interest and can be relevant for aerial bioreactors.
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.
Discrete vortex representation of magnetohydrodynamics
Kinney, R.; Tajima, T.; Petviashvili, N.; McWilliams, J.C.
1993-02-01
We present an alternative approach to statistical analysis of an intermittent ideal MHD fluid in two dimensions, based on the hydrodynamical discrete vortex model applied to the Elsasser variables. The model contains negative temperature states which predict the formation of magnetic islands, but also includes a natural limit under which the equilibrium states revert to the familiar twin-vortex states predicted by hydrodynamical turbulence theories. Numerical dynamical calculations yield equilibrium spectra in agreement with the theoretical predictions.
Collapsing lattice animals and lattice trees in two dimensions
NASA Astrophysics Data System (ADS)
Hsu, Hsiao-Ping; Grassberger, Peter
2005-06-01
We present high statistics simulations of weighted lattice bond animals and lattice trees on the square lattice, with fugacities for each non-bonded contact and for each bond between two neighbouring monomers. The simulations are performed using a newly developed sequential sampling method with resampling, very similar to the pruned-enriched Rosenbluth method (PERM) used for linear chain polymers. We determine with high precision the line of second-order transitions from an extended to a collapsed phase in the resulting two-dimensional phase diagram. This line includes critical bond percolation as a multicritical point, and we verify that this point divides the line into different universality classes. One of them corresponds to the collapse driven by contacts and includes the collapse of (weakly embeddable) trees. There is some evidence that the other is subdivided again into two parts with different universality classes. One of these (at the far side from collapsing trees) is bond driven and is represented by the Derrida-Herrmann model of animals having bonds only (no contacts). Between the critical percolation point and this bond-driven collapse seems to be an intermediate regime, whose other end point is a multicritical point P* where a transition line between two collapsed phases (one bond driven and the other contact driven) sparks off. This point P* seems to be attractive (in the renormalization group sense) from the side of the intermediate regime, so there are four universality classes on the transition line (collapsing trees, critical percolation, intermediate regime, and Derrida-Herrmann). We obtain very precise estimates for all critical exponents for collapsing trees. It is already harder to estimate the critical exponents for the intermediate regime. Finally, it is very difficult to obtain with our method good estimates of the critical parameters of the Derrida-Herrmann universality class. As regards the bond-driven to contact-driven transition in the
Instability of spiral convective vortex
NASA Astrophysics Data System (ADS)
Evgrafova, Anna; Andrey, Sukhanovsky; Elena, Popova
2014-05-01
Formation of large-scale vortices in atmosphere is one of the interesting problems of geophysical fluid dynamics. Tropical cyclones are examples of atmospheric spiral vortices for which convection plays an important role in their formation and evolution. Our study is focused on intensive cyclonic vortex produced by heating in the central part of the rotating layer. The previous studies made by Bogatyrev et al, showed that structure of such vortex is very similar to the structure of tropical cyclones. Qualitative observations described in (Bogatyrev, 2009) showed that the evolution of large-scale vortex in extreme regimes can be very complicated. Our main goal is the study of evolution of convective cyclonic vortex at high values of Grasshof number by PIV system. Experimental setup is a rotating cylindrical tank of fluid (radius 150 mm, depth 30 mm, free upper surface). Velocity fields for different values of heat flux were obtained and temporal and spatial structure of intensive convective vortex were studied in details. With the use of PIV data vorticity fields were reconstructed in different horizontal cross-sections. Physical interpretation of mechanisms that lead to the crucial change in the vortex structure with the growth of heat rate is described. Financial support from program of UD RAS, the International Research Group Program supported by Perm region Government is gratefully acknowledged.
VORTEX MIGRATION IN PROTOPLANETARY DISKS
Paardekooper, Sijme-Jan; Lesur, Geoffroy; Papaloizou, John C. B.
2010-12-10
We consider the radial migration of vortices in two-dimensional isothermal gaseous disks. We find that a vortex core, orbiting at the local gas velocity, induces velocity perturbations that propagate away from the vortex as density waves. The resulting spiral wave pattern is reminiscent of an embedded planet. There are two main causes for asymmetries in these wakes: geometrical effects tend to favor the outer wave, while a radial vortensity gradient leads to an asymmetric vortex core, which favors the wave at the side that has the lowest density. In the case of asymmetric waves, which we always find except for a disk of constant pressure, there is a net exchange of angular momentum between the vortex and the surrounding disk, which leads to orbital migration of the vortex. Numerical hydrodynamical simulations show that this migration can be very rapid, on a timescale of a few thousand orbits, for vortices with a size comparable to the scale height of the disk. We discuss the possible effects of vortex migration on planet formation scenarios.
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.
Regimes of flow past a vortex generator
NASA Astrophysics Data System (ADS)
Velte, C. M.; Okulov, V. L.; Naumov, I. V.
2012-04-01
A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator.
Ultracold quantum gases in triangular optical lattices
NASA Astrophysics Data System (ADS)
Becker, C.; Soltan-Panahi, P.; Kronjäger, J.; Dörscher, S.; Bongs, K.; Sengstock, K.
2010-06-01
Over recent years, exciting developments in the field of ultracold atoms confined in optical lattices have led to numerous theoretical proposals devoted to the quantum simulation of problems e.g. known from condensed matter physics. Many of those ideas demand experimental environments with non-cubic lattice geometries. In this paper, we report on the implementation of a versatile three-beam lattice allowing for the generation of triangular as well as hexagonal optical lattices. As an important step, the superfluid-Mott insulator (SF-MI) quantum phase transition has been observed and investigated in detail in this lattice geometry for the first time. In addition to this, we study the physics of spinor Bose-Einstein condensates (BEC) in the presence of the triangular optical lattice potential, especially spin changing dynamics across the SF-MI transition. Our results suggest that, below the SF-MI phase transition, a well-established mean-field model describes the observed data when renormalizing the spin-dependent interaction. Interestingly, this opens up new perspectives for a lattice-driven tuning of a spin dynamics resonance occurring through the interplay of the quadratic Zeeman effect and spin-dependent interaction. Finally, we discuss further lattice configurations that can be realized with our setup.
Transverse ac-driven and geometric ratchet effects for vortices in conformal crystal pinning arrays
NASA Astrophysics Data System (ADS)
Reichhardt, C.; Reichhardt, C. J. Olson
2016-02-01
A conformal pinning array is created by taking a conformal transformation of a uniform hexagonal lattice to create a structure in which the sixfold ordering of the original lattice is preserved but which has a spatial gradient in the pinning site density. With a series of conformal arrays it is possible to create asymmetric substrates, and it was previously shown that when an ac drive is applied parallel to the asymmetry direction, a pronounced ratchet effect occurs with a net dc flow of vortices in the same direction as the ac drive. Here we show that when the ac drive is applied perpendicular to the substrate asymmetry direction, it is possible to realize a transverse ratchet effect where a net dc flow of vortices is generated perpendicular to the ac drive. The conformal transverse ratchet effect is distinct from previous versions of transverse ratchets in that it occurs due to the generation of non-Gaussian transverse vortex velocity fluctuations by the plastic motion of vortices, so that the system behaves as a noise correlation ratchet. The transverse ratchet effect is much more pronounced in the conformal arrays than in random gradient arrays and is absent in square gradient arrays due the different nature of the vortex flow in each geometry. We show that a series of reversals can occur in the transverse ratchet effect due to changes in the vortex flow across the pinning gradient as a function of vortex filling, pinning strength, and ac amplitude. We also consider the case where a dc drive applied perpendicular to the substrate asymmetry direction generates a net flow of vortices perpendicular to the dc drive, producing what is known as a geometric or drift ratchet that again arises due to non-Gaussian dynamically generated fluctuations. The drift ratchet is more efficient than the ac driven ratchet and also exhibits a series of reversals for varied parameters. Our results should be general to a wide class of systems undergoing nonequilibrium dynamics on
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.
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.
Multiple-Relaxation-Time Lattice Boltzmann Models in 3D
NASA Technical Reports Server (NTRS)
dHumieres, Dominique; Ginzburg, Irina; Krafczyk, Manfred; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
This article provides a concise exposition of the multiple-relaxation-time lattice Boltzmann equation, with examples of fifteen-velocity and nineteen-velocity models in three dimensions. Simulation of a diagonally lid-driven cavity flow in three dimensions at Re=500 and 2000 is performed. The results clearly demonstrate the superior numerical stability of the multiple-relaxation-time lattice Boltzmann equation over the popular lattice Bhatnagar-Gross-Krook equation.
Tuning vortex confinement by magnetic domains in a superconductor/ferromagnet bilayer
NASA Astrophysics Data System (ADS)
Cieplak, Marta Z.; Adamus, Z.; Kończykowski, M.; Zhu, L. Y.; Cheng, X. M.; Chien, C. L.
2013-01-01
We use a line of miniature Hall sensors to study the effect of magnetic-domain-induced vortex confinement on the flux dynamics in a superconductor/ferromagnet bilayer. A single tunable bilayer is built of a ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy and a superconducting Nb layer, with the insulating layer in-between to avoid the proximity effect. The magnetic-domain patterns of various geometries are reversibly predefined in the Co/Pt multilayer using the appropriate magnetization procedure. The magnetic-domain geometry strongly affects vortex dynamics, leading to geometry-dependent trapping of vortices at the sample edge, nonuniform flux penetration, and strongly nonuniform critical current density. With the decreasing temperature, the magnetic pinning increases, but this increase is substantially weaker than that of the intrinsic pinning. The analysis of the initial flux penetration suggests that vortices may form various vortex structures, including disordered Abrikosov lattice or single and double vortex chains, in which minimal vortex-vortex distance is comparable to the magnetic penetration depth.
The Solar Vortex: Electric Power Generation using Anchored, Buoyancy-Induced Columnar Vortices
NASA Astrophysics Data System (ADS)
Glezer, Ari
2015-04-01
Naturally-occurring, buoyancy-driven columnar vortices (``dust devils'') that are driven by the instability of thermally stratified air layers and sustained by the entrainment of ground- heated air, occur spontaneously in the natural environment with core diameters of 1-50 m and heights up to 1 km. These vortices convert low-grade waste heat in the air layer overlying the warm surface into a solar-induced wind with significant kinetic energy. Unlike dust devil vortices that are typically free to wander laterally, the Solar Vortex (SoV) is deliberately triggered and anchored within a cylindrical domain bounded by an azimuthal array of stationary ground-mounted vertical vanes and sustained by continuous entrainment of the ground-heated air through these vanes. The mechanical energy of the anchored vortex is exploited for power generation by coupling the vortex to a vertical-axis turbine. This simple, low-cost electric power generating unit is competitive in cost, intermittency, and capacity factor with traditional solar power technologies. The considerable kinetic energy of the vortex column cannot be explained by buoyancy alone, and the fundamental mechanisms associated with the formation, evolution, and dynamics of an anchored, buoyancy-driven columnar vortex were investigated experimentally and numerically with specific emphasis on flow manipulation for increasing the available kinetic energy and therefore the generated power. These investigations have also considered the dependence of the vortex scaling and strength on the thermal resources and on the flow enclosure in the laboratory and in the natural environment. Preliminary outdoor tests of a two-meter scale prototype successfully demonstrated the ability to engender and anchor a columnar vortex using only solar radiation and couple the flow to a vertical axis wind turbine. A kilowatt-scale outer door prototype will be tested during the summer of 2015.
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.
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.
NASA aircraft trailing vortex research
NASA Technical Reports Server (NTRS)
Mcgowan, W. A.
1971-01-01
A brief description is given of NASA's comprehensive program to study the aircraft trailing vortex problem. Wind tunnel experiments are used to develop the detailed processes of wing tip vortex formation and explore different means to either prevent trailing vortices from forming or induce early break-up. Flight tests provide information on trailing vortex system behavior behind large transport aircraft, both near the ground, as in the vicinity of the airport, and at cruise/holding pattern altitudes. Results from some flight tests are used to show how pilots might avoid the dangerous areas when flying in the vicinity of large transport aircraft. Other flight tests will be made to verify and evaluate trailing vortex elimination schemes developed in the model tests. Laser Doppler velocimeters being developed for use in the research program and to locate and measure vortex winds in the airport area are discussed. Field tests have shown that the laser Doppler velocimeter measurements compare well with those from cup anemometers.
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
GREEN'S FUNCTIONS OF VORTEX OPERATORS
Polchinski, Joseph
1980-08-01
We study the Euclidean Green's functions of the 't Hooft vortex operator, primarily for Abelian gauge theories. The operator is written in terms of elementary fields, with emphasis on a form in which it appears as the exponential of a surface integral, We explore the requirement that the Green's functions depend only on the boundary of this surface, The Dirac veto problem appears in a new guise, We present a two dimensional ''solvable model" of a Dirac string, which suggests a new solution of the veto problem. The renormalization of the Green's functions of the Abelian Wilson loop and Abelian vortex operator is studied with the aid of the operator product expansion. In each case. an overall multiplication of the operator makes all Green's functions finite; a surprising cancellation of divergences occurs with the vortex operator. We present a brief discussion of the relation between the nature of the vacuum and the cluster properties of the Green's functions of the Wilson and vortex operators. for a general gauge theory. The surface-like cluster property of the vortex operator in an Abelian Higgs theory is explored in more detail.
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.
NASA Technical Reports Server (NTRS)
Chin, Suei; Lan, C. Edward; Gainer, Thomas G.
1989-01-01
The boundary value problem for vortex separation at zero sideslip on cones and tangent ogives is set up by means of a discrete vortex model. The nonlinear algebraic equations for the boundary value problem admit multiple, physically feasible solutions, including the symmetric and asymmetric vortex solutions. Multiple solutions are proposed as an alternative explanation of the existence of asymmetric vortex separation at zero sideslip.
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
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 breakdown incipience: Theoretical considerations
NASA Technical Reports Server (NTRS)
Berger, Stanley A.; Erlebacher, Gordon
1992-01-01
The sensitivity of the onset and the location of vortex breakdowns in concentrated vortex cores, and the pronounced tendency of the breakdowns to migrate upstream have been characteristic observations of experimental investigations; they have also been features of numerical simulations and led to questions about the validity of these simulations. This behavior seems to be inconsistent with the strong time-like axial evolution of the flow, as expressed explicitly, for example, by the quasi-cylindrical approximate equations for this flow. An order-of-magnitude analysis of the equations of motion near breakdown leads to a modified set of governing equations, analysis of which demonstrates that the interplay between radial inertial, pressure, and viscous forces gives an elliptic character to these concentrated swirling flows. Analytical, asymptotic, and numerical solutions of a simplified non-linear equation are presented; these qualitatively exhibit the features of vortex onset and location noted above.
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.
Ground vortex flow field investigation
NASA Technical Reports Server (NTRS)
Kuhn, Richard E.; Delfrate, John H.; Eshleman, James E.
1988-01-01
Flow field investigations were conducted at the NASA Ames-Dryden Flow Visualization Facility (water tunnel) to investigate the ground effect produced by the impingement of jets from aircraft nozzles on a ground board in a STOL operation. Effects on the overall flow field with both a stationary and a moving ground board were photographed and compared with similar data found in other references. Nozzle jet impingement angles, nozzle and inlet interaction, side-by-side nozzles, nozzles in tandem, and nozzles and inlets mounted on a flat plate model were investigated. Results show that the wall jet that generates the ground effect is unsteady and the boundary between the ground vortex flow field and the free-stream flow is unsteady. Additionally, the forward projection of the ground vortex flow field with a moving ground board is one-third less than that measured over a fixed ground board. Results also showed that inlets did not alter the ground vortex flow field.
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.
Iengo, R. |; Jug, G. |
1995-09-01
We investigate the phenomenon of the decay of a supercurrent through homogeneous nucleation of vortex-antivortex pairs in a two-dimensional (2D) like superconductor or superfluid by means of a quantum electrodynamic formulation for the decay of the 2D vacuum. The case in which both externally driven current and Magnus force are present is treated exactly, taking the vortex activation energy and its inertial mass as independent parameters. Quantum dissipation is included through the formulation introduced by Caldeira and Leggett. The most relevant consequence of quantum dissipation is the elimination of the threshold for vortex production due to the Magnus force. In the dissipation-dominated case, corresponding formally to the limit of zero intertial mass, an exact formula for the pair production rate is given. If however the inertial mass is strictly zero we find that vortex production is inhibited by a quantum effect related to the Magnus force. The possibility of including vortex pinning is investigated by means of an effective harmonic potential. While an additional term in the vortex activation energy can account for the effect of a finite barrier in the direction perpendicular to the current, pinning along the current depresses the role of the Magnus force in the dissipation-dominated dynamics, except for the above-mentioned quantum effect. A possible description of vortex nucleation due to the combined effects of temperature and externally driven currents is also presented along with an evaluation of the resulting voltage drop.
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.
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
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
NASA Astrophysics Data System (ADS)
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.
Quenching of vortex breakdown oscillations via harmonic modulation
NASA Astrophysics Data System (ADS)
Lopez, J. M.; Cui, Y. D.; Marques, F.; Lim, T. T.
Vortex breakdown is a phenomenon inherent to many practical problems, such as leading-edge vortices on aircraft, atmospheric tornadoes, and flame-holders in combustion devices. The breakdown of these vortices is associated with the stagnation of the axial velocity on the vortex axis and the development of a near-axis recirculation zone. For large enough Reynolds number, the breakdown can be time-dependent. The unsteadiness can have serious consequences in some applications, such as tail-buffeting in aircraft flying at high angles of attack. There has been much interest in controlling the vortex breakdown phenomenon, but most efforts have focused on either shifting the threshold for the onset of steady breakdown or altering the spatial location of the recirculation zone. There has been much less attention paid to the problem of controlling unsteady vortex breakdown. Here we present results from a combined experimental and numerical investigation of vortex breakdown in an enclosed cylinder in which low-amplitude modulations of the rotating endwall that sets up the vortex are used as an open-loop control. As expected, for very low amplitudes of the modulation, variation of the modulation frequency reveals typical resonance tongues and frequency locking, so that the open-loop control allows us to drive the unsteady vortex breakdown to a prescribed periodicity within the resonance regions. For modulation amplitudes above a critical level that depends on the modulation frequency (but still very low), the result is a periodic state synchronous with the forcing frequency over an extensive range of forcing frequencies. Of particular interest is the spatial form of this forced periodic state: for modulation frequencies less than about twice the natural frequency of the unsteady breakdown, the oscillations of the near-axis recirculation zone are amplified, whereas for modulation frequencies larger than about twice the natural frequency the oscillations of the recirculation
Experimental Realization of Artificial Skyrmion Lattices
NASA Astrophysics Data System (ADS)
Gilbert, Dustin; Maranville, Brian; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai
2015-03-01
Magnetic skyrmions exhibit topologically protected states, offering new mechanisms for high density/low dissipation information storage, and also exhibiting a host of unique topological phenomena. In bulk crystals, chiral spin textures are only found in certain systems and in limited regions in the temperature-magnetic field parameter space. We present experimental evidence of room-temperature artificially structured skyrmion lattices fabricated by carefully controlling the three dimensional anisotropy of a Co on Co/Pd hybrid structure. The hybrid structures were fabricated by patterning chirality controlled vortex-state Co nanodot arrays on top of a Co/Pd multilayer with perpendicular anisotropy; chirality control was confirmed by microscopy and magnetometry. The vortex polarity is set by an external magnetic field to manifest the skyrmion state, and confirmed by magnetometry measurements. The chiral structure of the nanodots is imprinted into the Co/Pd underlayer, as revealed by polarized neutron reflectometry and spin-transport studies. These artificial skyrmion lattices offer a convenient platform to explore skyrmion physics. This work has been supported by the NSF (DMR-1008791 and ECCS-1232275).
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
NASA Astrophysics Data System (ADS)
Nissen, D.; Mitin, D.; Klein, O.; Arekapudi, S. S. P. K.; Thomas, S.; Im, M.-Y.; Fischer, P.; Albrecht, M.
2015-11-01
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 SiO2-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 magneto-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.
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
Soft vortex matter in a type-I/type-II superconducting bilayer
NASA Astrophysics Data System (ADS)
Komendová, L.; Milošević, M. V.; Peeters, F. M.
2013-09-01
Magnetic flux patterns are known to strongly differ in the intermediate state of type-I and type-II superconductors. Using a type-I/type-II bilayer we demonstrate hybridization of these flux phases into a plethora of unique new ones. Owing to a complicated multibody interaction between individual fluxoids, many different intriguing patterns are possible under applied magnetic field, such as few-vortex clusters, vortex chains, mazes, or labyrinthal structures resembling the phenomena readily encountered in soft-matter physics. However, in our system the patterns are tunable by sample parameters, magnetic field, current, and temperature, which reveals transitions from short-range clustering to long-range ordered phases such as parallel chains, gels, glasses, and crystalline vortex lattices, or phases where lamellar type-I flux domains in one layer serve as a bedding potential for type-II vortices in the other, configurations clearly beyond the soft-matter analogy.
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
NASA Astrophysics Data System (ADS)
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.
NASA Technical Reports Server (NTRS)
Morris, B. G.
1986-01-01
Liquid/gas separator vents gas from tank of liquid that contains gas randomly distributed in bubbles. Centrifugal force separates liquid and gas, forcing liquid out of vortex tube through venturi tube. Gas vented through exhaust port. When liquid detected in vent tube, exhaust port closed, and liquid/gas mixture in vent tube drawn back into tank through venturi.
The 1987 Ground Vortex Workshop
NASA Technical Reports Server (NTRS)
Margason, Richard J. (Editor)
1988-01-01
The purpose of this workshop was to discuss the current understanding of the ground vortex phenomena and their effects on aircraft, and to establish directions for further research on advanced, high-performance aircraft designs, particularly those concepts utilizing powered-lift systems; e.g., V/STOL. ASTOVL, and STOL aircraft.
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.
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
Kagome lattices for ultracold atoms induced by additional lightfields
NASA Astrophysics Data System (ADS)
Zhang, Huirong; Chen, Xuzong; Ma, Zhaoyuan; Zhou, Yuqing
2016-06-01
We propose a novel method for the realization of an optical Kagome lattice due to the Raman processes driven by additional light fields applied to the ultracold atoms of two hyperfine internal states trapped in a planar optical triangular lattice. The tunneling between the different internal states of the nearest-neighbor atoms in Kagome lattices can be adjusted by the additional light fields independently of the on-site interaction. This optical lattice protocol can be used to investigate the magnetic quantum phenomena and the nearest-neighbor magnetic coupling becomes strong enough by increasing the intensities of the additional light fields.
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.
The dynamics of vortex streets in channels
NASA Astrophysics Data System (ADS)
Wang, Xiaolin; Alben, Silas
2015-07-01
We develop a model to numerically study the dynamics of vortex streets in channel flows. Previous work has studied the vortex wakes of specific vortex generators. Here, we study a wide range of vortex wakes including regular and reverse von Kármán streets with various strengths, geometries, and Reynolds numbers (Re) by applying a smoothed von Kármán street as an inflow condition. We find that the spatial structure of the inflow vortex street is maintained for the reverse von Kármán street and altered for the regular street. For regular streets, we identify a transition to asymmetric dynamics which happens when Re increases, or vortices are stronger, or vortex streets are compressed horizontally or extended vertically. We also determine the effects of these parameters on vortex street inversion.
Burning invariant manifolds in time-periodic and time-aperiodic vortex flows
NASA Astrophysics Data System (ADS)
Gowen, Savannah; Solomon, Tom
2014-11-01
We present experiments that study reaction fronts in a flow composed of a single, translating vortex. The fronts are produced by the excitable Belousov-Zhabotinsky (BZ) chemical reaction, and the vortex flow is driven magnetohydrodynamically by a radial current in a thin fluid layer above a Nd-Fe-Bo magnet. The magnet is mounted on a pair of perpendicular translation stages, allowing for controlled, two-dimensional movement of the magnet and the resulting vortex. We study reaction fronts that pin to the vortex for time-independent flows (produced by moving the vortex with a constant velocity) and for time-periodic and time-aperiodic flows produced by oscillating the vortex laterally. The steady-state front shape is analyzed in terms of burning invariant manifolds (BIMs) that act as one-way barriers against any propagating reaction fronts. For time independent and time-periodic flows, the location of the BIMs are calculated numerically and are compared with experimental images of the pinned reaction fronts. We investigate extensions of this BIM approach for analyzing fronts in time-aperiodic flows. Supported by NSF Grants DMR-1004744, DMR-1361881 and PHY-1156964.
Rotor blade vortex interaction noise
NASA Astrophysics Data System (ADS)
Yu, Yung H.
2000-02-01
Blade-vortex interaction noise-generated by helicopter main rotor blades is one of the most severe noise problems and is very important both in military applications and community acceptance of rotorcraft. Research over the decades has substantially improved physical understanding of noise-generating mechanisms, and various design concepts have been investigated to control noise radiation using advanced blade planform shapes and active blade control techniques. The important parameters to control rotor blade-vortex interaction noise and vibration have been identified: blade tip vortex structures and its trajectory, blade aeroelastic deformation, and airloads. Several blade tip design concepts have been investigated for diffusing tip vortices and also for reducing noise. However, these tip shapes have not been able to substantially reduce blade-vortex interaction noise without degradation of rotor performance. Meanwhile, blade root control techniques, such as higher-harmonic pitch control (HHC) and individual blade control (IBC) concepts, have been extensively investigated for noise and vibration reduction. The HHC technique has proved the substantial blade-vortex interaction noise reduction, up to 6 dB, while vibration and low-frequency noise have been increased. Tests with IBC techniques have shown the simultaneous reduction of rotor noise and vibratory loads with 2/rev pitch control inputs. Recently, active blade control concepts with smart structures have been investigated with the emphasis on active blade twist and trailing edge flap. Smart structures technologies are very promising, but further advancements are needed to meet all the requirements of rotorcraft applications in frequency, force, and displacement.
Palmer, R.B.
1987-05-01
This paper looks at, and compares three types of damping ring lattices: conventional, wiggler lattice with finite ..cap alpha.., wiggler lattice with ..cap alpha.. = 0, and observes the attainable equilibrium emittances for the three cases assuming a constraint on the attainable longitudinal impedance of 0.2 ohms. The emittance obtained are roughly in the ratio 4:2:1 for these cases.
NASA Astrophysics Data System (ADS)
Gezo, Joseph Christopher
The two-dimensional superconductors based on the organic molecule "ET" have been an active area of research since their discovery over two decades ago. The member of this family with the highest critical temperature, kappa-(ET)2Cu[N(CN)2]Br ( Tc=11.7 K), has seen renewed interest since the observation of an anomalous Nernst signal by Nam et al in 2007 [51]. A similar effect was seen earlier by Ong's group in some of the high-temperature cuprate superconductors by [78,84]. This is interpreted to be evidence of a picture of superconductivity in which the resistive transition is driven by thermal fluctuations in the phase of the superconducting order parameter. Below Tc, these fluctuations take the form of bound vortex-antivortex pairs that have no long-range effect on the phase. At Tc, they undergo a Kosterlitz-Thouless unbinding transition; the unbound vortices destroy long-range phase coherence. Previously reported proton NMR measurements on this material have shown a high sensitivity to vortex motion, but reported no interesting behavior above the phase transition [15,25,42]. In this thesis, we revisit the 1H NMR properties of kappa-(ET)2Cu[N(CN)2]Br, paying specific attention to the spin-lattice relaxation, to look for some fingerprint of the phenomenon observed by Nam et al.
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.
Transformation of the vortex beam in the optical vortex scanning microscope
NASA Astrophysics Data System (ADS)
Płociniczak, Łukasz; Popiołek-Masajada, Agnieszka; Szatkowski, Mateusz; Wojnowski, Dariusz
2016-07-01
We investigate the microscopic system in which the Gaussian beam with embedded optical vortex is used. The optical vortex is introduced by vortex lens. The vortex lens shift induces a precise nanometer shift of the embedded vortices inside the focused spot. The analytical formula for the complex amplitude of the focused spot with off-axis vortex was calculated, to our knowledge, for the first time. This solution is an important step in the development of the optical vortex scanning microscope. Experimental results are also presented that demonstrate the behavior of such a beam in an experimental setup.
Vortex transport in a channel with periodic constrictions
NASA Astrophysics Data System (ADS)
Kapra, A. V.; Y Vodolazov, D.; Misko, V. R.
2013-09-01
By numerically solving the time-dependent Ginzburg-Landau equations in a type-II superconductor, characterized by a critical temperature Tc1, and the coherence length ξ1, with a channel formed by overlapping rhombuses (diamond-like channel) made of another type-II superconductor, characterized, in general, by different Tc2 and ξ2, we investigate the dynamics of driven vortex matter for varying parameters of the channel: the width of the neck connecting the diamond cells, the cell geometry, and the ratio between the coherence lengths in the bank and the channel. We analyzed samples with periodic boundary conditions (which we call ‘infinite’ samples) and finite-size samples (with boundaries for vortex entry/exit), and we found that by tuning the channel parameters, one can manipulate the vortex dynamics, e.g., change the transition from flux-pinned to flux-flow regime and tune the slope of the IV-curves. In addition, we analyzed the effect of interstitial vortices on these characteristics. The critical current of this device was studied as a function of the applied magnetic field, jc(H). The function jc(H) reveals a striking commensurability peak, in agreement with recent experimental observations. The obtained results suggest that the diamond channel, which combines the properties of pinning arrays and flux-guiding channels, can be a promising candidate for potential use in devices controlling magnetic flux motion.
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.
Shetty, Dinesh A; Frankel, Steven H
2013-09-20
The physical space version of the stretched vortex subgrid scale model [Phys. Fluids 12, 1810 (2000)] is tested in large eddy simulations (LES) of the turbulent lid driven cubic cavity flow. LES is carried out using a higher order finite-difference method [J. Comput. Phys. 229, 8802 (2010)]. The effects of different vortex orientation models and subgrid turbulence spectrums are assessed through comparisons of the LES predictions against direct numerical simulations (DNS) [Phys. Fluids 12, 1363 (2000)]. Three Reynolds numbers 12000, 18000, and 22000 are studied. Good agreement with the DNS data for the mean and fluctuating quantities is observed. PMID:24187423
Two-body problem of core-region coupled magnetic vortex stacks
NASA Astrophysics Data System (ADS)
Hänze, Max; Adolff, Christian F.; Velten, Sven; Weigand, Markus; Meier, Guido
2016-02-01
The dynamics of all four combinations of possible polarity and circularity states in a stack of two vortices is investigated by time-resolved scanning transmission x-ray microscopy. The vortex stacks are excited by unidirectional magnetic fields leading to a collective oscillation. Four different modes are observed that depend on the relative polarizations and circularities of the stacks. They are excited to a driven oscillation. We observe a repulsive and attractive interaction of the vortex cores depending on their relative polarizations. The nonlinearity of this core interaction results in different trajectories that describe a two-body problem.
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.
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.
Simulation of Rotary-Wing Near-Wake Vortex Structures Using Navier-Stokes CFD Methods
NASA Technical Reports Server (NTRS)
Kenwright, David; Strawn, Roger; Ahmad, Jasim; Duque, Earl; Warmbrodt, William (Technical Monitor)
1997-01-01
This paper will use high-resolution Navier-Stokes computational fluid dynamics (CFD) simulations to model the near-wake vortex roll-up behind rotor blades. The locations and strengths of the trailing vortices will be determined from newly-developed visualization and analysis software tools applied to the CFD solutions. Computational results for rotor nearwake vortices will be used to study the near-wake vortex roll up for highly-twisted tiltrotor blades. These rotor blades typically have combinations of positive and negative spanwise loading and complex vortex wake interactions. Results of the computational studies will be compared to vortex-lattice wake models that are frequently used in rotorcraft comprehensive codes. Information from these comparisons will be used to improve the rotor wake models in the Tilt-Rotor Acoustic Code (TRAC) portion of NASA's Short Haul Civil Transport program (SHCT). Accurate modeling of the rotor wake is an important part of this program and crucial to the successful design of future civil tiltrotor aircraft. The rotor wake system plays an important role in blade-vortex interaction noise, a major problem for all rotorcraft including tiltrotors.
Widnall instabilities in vortex pairs
NASA Astrophysics Data System (ADS)
Sipp, Denis; Jacquin, Laurent
2003-07-01
In this article we analyze the cooperative three-dimensional short-wave instabilities developing on concentrated vortex dipoles that have been obtained by means of two-dimensional direct numerical simulations. These dipoles are characterized by their aspect ratio a/b where a is the radius of the vortices based on the polar moments of vorticity and b is the separation between the vortex centroids. In the inviscid case, we show that the selection of the antisymmetric eigenmode smoothly increases with a/b: for a/b=0.208, the amplification rate of the antisymmetric eigenmode is only 1.4% larger than the amplification rate of the symmetric eigenmode. When a/b=0.288, this difference increases up to 7%. The results of the normal mode analysis may be compared to those of an asymptotic stability analysis of a Lamb-Oseen vortex subjected to a weak straining field, following Moore and Saffman [Proc. R. Soc. London, Ser. A 346, 413 (1975)]. This theory shows that the instability may occur whenever two Kelvin waves exist with the same frequency ω, the same axial wavenumber k and with azimuthal wavenumbers m and m+2. Contrary to the case of a Rankine vortex [Tsai and Widnall, J. Fluid Mech. 73, 721 (1976)], the presence of critical layers in a Lamb-Oseen vortex prevents a large number of possible resonances. For example, resonances between m=-2 and m=0 modes lead to damped modes. The only resonances that occur are related to the stationary (ω=0) bending waves (m=±1) obtained for specific values of the axial wavenumber. All these predictions are found to be in good agreement with the results obtained by the stability analysis of the considered vortex pairs. At last, we present a nonautonomous amplitude equation which takes into account all effects of viscosity, i.e., the viscous damping of the amplification rate of the perturbation but also the increase of the dipole aspect ratio a/b due to the viscous diffusion of the basic flowfield. The low-Reynolds number experiment of
Vortex depinning in Josephson-junction arrays
NASA Astrophysics Data System (ADS)
Dang, E. K. F.; Györffy, B. L.
1993-02-01
On the basis of a simple model we study the supercurrent-carrying capacity of a planar array of Josephson junctions. In particular we investigate the zero-temperature vortex-depinning current iBc, which is the largest supercurrent in an array containing one extra vortex on top of the ground-state vortex superlattice induced by an external magnetic field f. In the zero-field, f=0, case our results support the tilted-sinusoidal vortex-potential description of previous workers. However, in the fully frustrated, f=1/2 case, a more careful interpretation is required. We find that on the application of a transport current, the resulting vortex motion is not that of the extra vortex moving over a rigid field-induced vortex background. Rather, a vortex belonging to the checkerboard ground-state pattern first crosses over a junction into a neighboring ``empty'' plaquette. Then, the ``extra'' vortex moves to take its place. Our interpretation is based on a linear stability analysis, with the onset of vortex motion being associated with the vanishing of one eigenvalue of the stability matrix. Further applications of the method are suggested.
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.
Optical rankine vortex and anomalous circulation of light.
Swartzlander, Grover A; Hernandez-Aranda, Raul I
2007-10-19
Rankine vortex characteristics of a partially coherent optical vortex are explored using classical and physical optics. Unlike a perfectly coherent vortex mode, the circulation is not quantized. Excess circulation is predicted owing to the wave nature of composite vortex fields. Based on these findings, we propose a vortex stellar interferometer. PMID:17995253
Optical Rankine Vortex and Anomalous Circulation of Light
Swartzlander, Grover A. Jr.; Hernandez-Aranda, Raul I.
2007-10-19
Rankine vortex characteristics of a partially coherent optical vortex are explored using classical and physical optics. Unlike a perfectly coherent vortex mode, the circulation is not quantized. Excess circulation is predicted owing to the wave nature of composite vortex fields. Based on these findings, we propose a vortex stellar interferometer.
Optical Rankine Vortex and Anomalous Circulation of Light
NASA Astrophysics Data System (ADS)
Swartzlander, Grover A., Jr.; Hernandez-Aranda, Raul I.
2007-10-01
Rankine vortex characteristics of a partially coherent optical vortex are explored using classical and physical optics. Unlike a perfectly coherent vortex mode, the circulation is not quantized. Excess circulation is predicted owing to the wave nature of composite vortex fields. Based on these findings, we propose a vortex stellar interferometer.
Dielectric-barrier discharges in two-dimensional lattice potentials.
Sinclair, J; Walhout, M
2012-01-20
We use a pin-grid electrode to introduce a corrugated electrical potential into a planar dielectric-barrier discharge (DBD) system, so that the amplitude of the applied electric field has the profile of a two-dimensional square lattice. The lattice potential provides a template for the spatial distribution of plasma filaments in the system and has pronounced effects on the patterns that can form. The positions at which filaments become localized within the lattice unit cell vary with the width of the discharge gap. The patterns that appear when filaments either overfill or underfill the lattice are reminiscent of those observed in other physical systems involving 2D lattices. We suggest that the connection between lattice-driven DBDs and other areas of physics may benefit from the further development of models that treat plasma filaments as interacting particles. PMID:22400753
A spectral-element discontinuous Galerkin lattice Boltzmann method for incompressible flows.
Min, M.; Lee, T.; Mathematics and Computer Science; City Univ. of New York
2011-01-01
We present a spectral-element discontinuous Galerkin lattice Boltzmann method for solving nearly incompressible flows. Decoupling the collision step from the streaming step offers numerical stability at high Reynolds numbers. In the streaming step, we employ high-order spectral-element discontinuous Galerkin discretizations using a tensor product basis of one-dimensional Lagrange interpolation polynomials based on Gauss-Lobatto-Legendre grids. Our scheme is cost-effective with a fully diagonal mass matrix, advancing time integration with the fourth-order Runge-Kutta method. We present a consistent treatment for imposing boundary conditions with a numerical flux in the discontinuous Galerkin approach. We show convergence studies for Couette flows and demonstrate two benchmark cases with lid-driven cavity flows for Re = 400-5000 and flows around an impulsively started cylinder for Re = 550-9500. Computational results are compared with those of other theoretical and computational work that used a multigrid method, a vortex method, and a spectral element model.
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.
Divergence of optical vortex beams.
Reddy, Salla Gangi; Permangatt, Chithrabhanu; Prabhakar, Shashi; Anwar, Ali; Banerji, J; Singh, R P
2015-08-01
We show, both theoretically and experimentally, that the propagation of optical vortices in free space can be analyzed by using the width [w(z)] of the host Gaussian beam and the inner and outer radii of the vortex beam at the source plane (z=0) as defined in [Opt. Lett.39, 4364 (2014)10.1364/OL.39.004364OPLEDP0146-9592]. We also studied the divergence of vortex beams, considered as the rate of change of inner or outer radius with the propagation distance (z), and found that it varies with the order in the same way as that of the inner and outer radii at z=0. These results may be useful in designing optical fibers for orbital angular momentum modes that play a crucial role in quantum communication. PMID:26368081
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. PMID:26565349
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.
NASA Astrophysics Data System (ADS)
Först, M.; Tobey, R. I.; Bromberger, H.; Wilkins, S. B.; Khanna, V.; Caviglia, A. D.; Chuang, Y.-D.; Lee, W. S.; Schlotter, W. F.; Turner, J. J.; Minitti, M. P.; Krupin, O.; Xu, Z. J.; Wen, J. S.; Gu, G. D.; Dhesi, S. S.; Cavalleri, A.; Hill, J. P.
2014-04-01
We report femtosecond resonant soft x-ray diffraction measurements of the dynamics of the charge order and of the crystal lattice in nonsuperconducting, stripe-ordered La1.875Ba0.125CuO4. Excitation of the in-plane Cu-O stretching phonon with a midinfrared pulse has been previously shown to induce a transient superconducting state in the closely related compound La1.675Eu0.2Sr0.125CuO4. In La1.875Ba0.125CuO4, we find that the charge stripe order melts promptly on a subpicosecond time scale. Surprisingly, the low temperature tetragonal (LTT) distortion is only weakly reduced, reacting on significantly longer time scales that do not correlate with light-induced superconductivity. This experiment suggests that charge modulations alone, and not the LTT distortion, prevent superconductivity in equilibrium.
Först, M; Tobey, R I; Bromberger, H; Wilkins, S B; Khanna, V; Caviglia, A D; Chuang, Y-D; Lee, W S; Schlotter, W F; Turner, J J; Minitti, M P; Krupin, O; Xu, Z J; Wen, J S; Gu, G D; Dhesi, S S; Cavalleri, A; Hill, J P
2014-04-18
We report femtosecond resonant soft x-ray diffraction measurements of the dynamics of the charge order and of the crystal lattice in nonsuperconducting, stripe-ordered La1.875Ba0.125CuO4. Excitation of the in-plane Cu-O stretching phonon with a midinfrared pulse has been previously shown to induce a transient superconducting state in the closely related compound La1.675Eu0.2Sr0.125CuO4. In La1.875Ba0.125CuO4, we find that the charge stripe order melts promptly on a subpicosecond time scale. Surprisingly, the low temperature tetragonal (LTT) distortion is only weakly reduced, reacting on significantly longer time scales that do not correlate with light-induced superconductivity. This experiment suggests that charge modulations alone, and not the LTT distortion, prevent superconductivity in equilibrium. PMID:24785066
NASA Astrophysics Data System (ADS)
Yabunaka, Shunsuke
2014-10-01
We study interface and vortex motion in the two-component dissipative Ginzburg-Landau equation in two-dimensional space. We consider cases where the whole system is divided into several domains, and we assume that these domains are separated by interfaces and each domain contains quantized vortices. The equations for interface and vortex motion will be derived by means of a variational approach by Kawasaki. These equations indicate that, along an interface, the phase gradient fields of the complex order parameters is parallel to the interface. They also indicate that the interface motion is driven by the curvature and the phase gradient fields along the interface, and vortex motion is driven by the phase gradient field around the vortex. With respect to the static interactions between defects, we find an analogy between quantized vortices in a domain and electric charges in a vacuum domain surrounded by a metallic object in electrostatic. This analogy indicates that there is an attractive interaction between an interface and a quantized vortex with any charge. We also discuss several examples of interface and vortex motion.
Prediction and Control of Vortex Dominated and Vortex-wake Flows
NASA Technical Reports Server (NTRS)
Kandil, Osama
1996-01-01
This report describes the activities and accomplishments under this research grant, including a list of publications and dissertations, produced in the field of prediction and control of vortex dominated and vortex wake flows.
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.
Linear stability of a vortex ring revisited
NASA Astrophysics Data System (ADS)
Fukumoto, Yasuhide; Hattori, Yuji
We revisit the stability of an elliptically strained vortex and a thin axisymmetric vortex ring, embedded in an inviscid incompressible fluid, to three-dimensional disturbances of infinitesimal amplitude. The results of Tsai & Widnall (1976) for an elliptically strained vortex are simplified by providing an explicit expression for the disturbance flow field. A direct relation is established with the elliptical instability. For Kelvin's vortex ring, the primary perturbation to the Rankine vortex is a dipole field. We show that the dipole field causes a parametric resonance instability between axisymmetric and bending waves at intersection points of the dispersion curves. It is found that the dipole effect predominates over the straining effect for a very thin core. The mechanism is attributable to stretching of the disturbance vortex lines in the toroidal direction.
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.
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.
Vortex rings impinging on permeable boundaries
NASA Astrophysics Data System (ADS)
Mujal-Colilles, Anna; Dalziel, Stuart B.; Bateman, Allen
2015-01-01
Experiments with vortex rings impinging permeable and solid boundaries are presented in order to investigate the influence of permeability. Utilizing Particle Image Velocimetry, we compared the behaviour of a vortex ring impinging four different reticulated foams (with permeability k ˜ 26 - 85 × 10-8 m2) and a solid boundary. Results show how permeability affects the stretching phenomena of the vortex ring and the formation and evolution of the secondary vortex ring with opposite sign. Moreover, permeability also affects the macroscopic no-slip boundary condition found on the solid boundary, turning it into an apparent slip boundary condition for the most permeable boundary. The apparent slip-boundary condition and the flux exchange between the ambient fluid and the foam are jointly responsible for both the modified formation of the secondary vortex and changes on the vortex ring diameter increase.