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Sample records for multiquantum giant vortex

  1. Giant vortex state in mesoscopic superconductors

    NASA Astrophysics Data System (ADS)

    Cobacy García, Luis; Giraldo, Jairo

    2005-08-01

    Using the self-consistent solution of the nonlinear Ginzburg-Landau equations, the superconducting state of a type II mesoscopic cylinder and of an infinite thin sheet with a circular hole (antidot), in the presence of an homogeneous magnetic field is studied. Close to the third critical field, the magnetic field penetrates the sample in the form of a vortex around the axis of the cylinder or of the antidot. This result has been found previously by other authors. The vortex, called a giant vortex, can carry several flux quanta. The giant vortex is persistent when the state is metastable and evolves to the so called paramagnetic Meissner effect (PME) within the cylinder. The behaviour of this effect as a function of the Ginzburg-Landau (GL) parameter is studied and the results are discussed. Gibbs free energy, order parameter and magnetic induccion as a function of the applied field and of the GL parameter are also studied.

  2. Giant moving vortex mass in thick magnetic nanodots.

    PubMed

    Guslienko, K Y; Kakazei, G N; Ding, J; Liu, X M; Adeyeye, A O

    2015-09-10

    Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5-50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50-100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing.

  3. Giant moving vortex mass in thick magnetic nanodots

    PubMed Central

    Guslienko, K. Y.; Kakazei, G. N.; Ding, J.; Liu, X. M.; Adeyeye, A. O.

    2015-01-01

    Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5–50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50–100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing. PMID:26355430

  4. Self-consistent electronic structure of multiquantum vortices in superconductors at T ≪ Tc

    NASA Astrophysics Data System (ADS)

    Silaev, M. A.; Silaeva, V. A.

    2013-06-01

    We investigate the multiquantum vortex states in a type-II superconductor in both ‘clean’ and ‘dirty’ regimes defined by impurity scattering rate. Within a quasiclassical approach we calculate self-consistently the order parameter distributions and electronic local density of states (LDOS) profiles. In the clean case we find the low temperature vortex core anomaly predicted analytically by Volovik (1993 JETP Lett. 58 455) and obtain the patterns of LDOS distributions. In the dirty regime multiquantum vortices feature a peculiar plateau in the zero energy LDOS profile, which can be considered as an experimental hallmark of multiquantum vortex formation in mesoscopic superconductors.

  5. Stable giant vortex annuli in microwave-coupled atomic condensates

    NASA Astrophysics Data System (ADS)

    Qin, Jieli; Dong, Guangjiong; Malomed, Boris A.

    2016-11-01

    Stable self-trapped vortex annuli (VA) with large values of topological charge S (giant VA) not only are a subject of fundamental interest, but are also sought for various applications, such as quantum information processing and storage. However, in conventional atomic Bose-Einstein condensates (BECs) VA with S >1 are unstable. Here we demonstrate that robust self-trapped fundamental solitons (with S =0 ) and bright VA (with the stability checked up to S =5 ) can be created in the free space by means of the local-field effect (the feedback of the BEC on the propagation of electromagnetic waves) in a condensate of two-level atoms coupled by a microwave (MW) field, as well as in a gas of MW-coupled fermions with spin 1 /2 . The fundamental solitons and VA remain stable in the presence of an arbitrarily strong repulsive contact interaction (in that case, the solitons are constructed analytically by means of the Thomas-Fermi approximation). Under the action of the attractive contact interaction with strength β , which, by itself, would lead to collapse, the fundamental solitons and VA exist and are stable, respectively, at β <βmax(S ) and β <βst(S ) , with βst(S =0 ) =βmax(S =0 ) and βst(S ≥1 ) <βmax(S ≥1 ) . Accurate analytical approximations are found for both βst and βmax, with βst(S ) growing linearly with S . Thus, higher-order VA are more robust than their lower-order counterparts, in contrast to what is known in other systems that may support stable self-trapped vortices. Conditions for the experimental realizations of the VA are discussed.

  6. Solitons and Vortex Lattices in the Gross-Pitaevskii Equation with Spin-Orbit Coupling under Rotation

    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.

  7. Transition to the giant vortex state in a harmonic-plus-quartic trap

    SciTech Connect

    Fu, H.; Zaremba, E.

    2006-01-15

    We consider a rapidly rotating Bose-condensed gas in a harmonic-plus-quartic trap. At sufficiently high rotation rates, the condensate acquires an annular geometry with the superposition of a vortex lattice. With increasing rotation rate, the lattice evolves into a single ring of vortices. Of interest is the transition from this state to the giant vortex state in which the circulation is carried by only a central vortex. By analyzing the Gross-Pitaevskii energy functional variationally, we have been able to map out the phase boundary between these two states as a function of the rotation rate and the various trapped gas parameters. For strong interactions, the transition is first order. Our variational results are in good qualitative agreement with those obtained by means of a direct numerical solution of the Gross-Pitaevskii equation.

  8. Symmetry-induced giant vortex state in a superconducting Pb film with a fivefold Penrose array of magnetic pinning centers.

    PubMed

    Kramer, R B G; Silhanek, A V; Van de Vondel, J; Raes, B; Moshchalkov, V V

    2009-08-07

    A direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained by mapping the local field distribution with a scanning Hall probe microscope. We demonstrate that stable vortex configurations can be found for fields H approximately 0.8H_{1}, H_{1}, and 1.6H_{1}, where H_{1} corresponds to one flux quantum per pinning site. The vortex pattern at 0.8H_{1} corresponds to one vacancy in one of the vertices of the thin tiles, whereas at 1.6H_{1} the vortex structure can be associated with one interstitial vortex inside each thick tile. Strikingly, for H = 1.6H_{1}, interstitial and pinned vortices arrange themselves in ringlike structures ("vortex corrals") which favor the formation of a giant vortex state at their center.

  9. Rotating superfluids in anharmonic traps: From vortex lattices to giant vortices

    SciTech Connect

    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.

  10. Haze and clouds properties of Saturn's 2011 giant vortex retrieved from Cassini VIMS-V data.

    NASA Astrophysics Data System (ADS)

    Oliva, F.; Adriani, A.; Moriconi, M. L.; Liberti, G. L.; d'Aversa, E.

    2014-04-01

    This work is focused on the retrieval of the microphysical and geometrical properties of the clouds and hazes overlying the giant vortex observed in 2011 at Saturn, by the Visual and Infrared Mapping Spectrometer (VIMS) on board of Cassini. The retrieval algorithm is based on the optimal estimation technique [15] and takes advantage of a forward radiative transfer model developed by adapting the LibRadtran code [13] to the atmosphere of Saturn. For each of the retrieved parameters - that are effective radii, top pressures and total number densities for each considered deck - a 2D spatial map has been produced.

  11. Clouds and hazes vertical structure mapping of Saturn 2011 - 2012 giant vortex by means of Cassini VIMS data analysis.

    NASA Astrophysics Data System (ADS)

    Oliva, F.; Adriani, A.; Moriconi, M. L.; Liberti, G. L.; D'Aversa, E.

    On December 2010 a giant storm erupted in Saturn's North hemisphere. A giant vortex formed in the storm wake and persisted after the principal outburst exhausted on July 2011. The vortex had been imaged several times by the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini probe starting from May 2011 and it was still present in observations recorded on June 2013. In this work we have analyzed the vortex data recorded by the visual channel of the spectrometer (VIMS-V) in August 2011 and January 2012. An inverse model, based on the Bayesian approach and using the Gauss-Newton iterative method to minimize the cost function, has been developed to analyze those data. The model takes advantage of the results of a supporting forward radiative transfer model which relies on the assumptions of plane parallel atmosphere, multiple scattering, Mie theory to compute particles single scattering properties, and molecular scattering adapted to Saturn's atmosphere. Applying the inverse model we could retrieve the microphysical and geometrical properties of the clouds and hazes overlying the vortex and produce spatial maps for each retrieved parameter. Thanks to this study, the vertical structure of the hazes in this region has been quantitatively addressed for the first time. The comparative analysis of the results from the two observations seems to suggest that in 6 months the atmospheric dynamics, responsible for the formation and subsistence of the vortex, is weakening and the atmosphere is returning to a more stationary state. In addition, we suggest a correction for the imaginary part of the refractive index of the tropopause haze. This new value, that allows a better convergence between observed and simulated spectra, does not yet identify a composition of the haze and further investigation is needed to understand the real nature of the need for such a modification.

  12. Vertical structure mapping of Saturn's 2011 giant vortex by means of Cassini VIMS-V data analysis.

    NASA Astrophysics Data System (ADS)

    Oliva, Fabrizio; Adriani, Alberto; Moriconi, Maria Luisa; D'Aversa, Emiliano; Liberti, Gian Luigi

    On December 2010 a giant storm erupted in Saturn's North springtime hemisphere. A giant vortex formed in the storm wake and persisted after the principal outburst exhausted on July 2011. The vortex had been imaged several times by the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini probe, starting from May 2011, and it was still present in the December 2012 observations In this work we have analyzed the data recorded by the visual channel of the spectrometer (VIMS-V). VIMS-V operates in the spectral range 350 - 1050 nm with a nominal spectral resolution of 7.3 nm and a nominal angular resolution of 500 μrad. Spectral data have been first analyzed by a forward radiative transfer model based on the LibRadtran code, then an inverse model has used to retrieve microphysical and geometrical properties of the clouds overlying the vortex. The forward model relies on the assumptions of a plane parallel atmosphere, multiple scattering, the Mie theory to compute single scattering properties and the molecular scattering adapted to Saturn’s atmosphere. The inverse code is based on the optimal estimation technique, it is robust and capable to handle several free parameters at a time. The best fits to the observed radiance spectra are obtained by means of a least square analysis, in which the cost function is minimized taking advantage of the Gauss-Newton method. Applying this procedure, we produced spatial maps for each of the free parameters, including: effective radii for the particles size distributions of each cloud or aerosol deck; total number densities of the particles; and top pressures of each deck. In this work we focused on the data retrieved by VIMS on August 2011. We plan to extend the analysis on data retrieved months later, to map the evolution the parameters undergo in time. The analysis extension to the range 1.0-5.0 micron, covered by the infrared channel of VIMS (VIMS-IR) is also planned.

  13. Clouds and hazes vertical structure of a Saturn's giant vortex from Cassini/VIMS-V data analysis

    NASA Astrophysics Data System (ADS)

    Oliva, F.; Adriani, A.; Moriconi, M. L.; Liberti, G. L.; D'Aversa, E.; Filacchione, G.

    2016-11-01

    We studied the evolution of a giant tropospheric vortex formed in the wake of the storm that encircled Saturn from December 2010 to July 2011 (Fletcher et al. [2011a] Science, 332, 1413-1417; Fletcher et al. [2012] Icarus, 221, 560-586; Sánchez-Lavega et al. [2011] Nature, 475, 71-74; Sánchez-Lavega et al. [2012] Icarus, 220, 561-576; Sayanagi et al. [2013] Icarus, 223, 460-478; Fischer et al. [2011] Nature, 475, 75-77) taking advantage of the observations acquired by the instruments on board the Cassini spacecraft. In particular, the Visual and Infrared Mapping Spectrometer (VIMS) imaged the vortex several times. In this work we analyzed two observations registered by the visual channel of VIMS (VIMS-V) on 08/24/2011 and 01/04/2012, both after the active phase of the storm, and characterized quantitatively the vertical structure of the clouds and hazes above the vortex. Until now, VIMS-V dataset has been scarcely exploited to perform such an analysis. The IR channel of VIMS has always been preferred since it covers wavelengths containing spectral information on a wider range of altitudes in the atmosphere. Nevertheless, in our analysis we investigate the information content of VIMS-V observations and demonstrate that the covered spectral range contains valuable information that are helpful to improve our knowledge on the properties of Saturn's upper atmosphere. We developed a forward radiative transfer model to describe Saturn's atmosphere and simulate VIMS-V spectra in the 0.35-1.05 μm wavelength range. The analysis has then been performed by means of an inverse model that we built on the basis of the Bayesian approach. Spatial distributions of effective radii, column number densities and top pressures of the cloud decks have been mapped and as a by-product of our analysis we also suggest a modified spectral shape for the imaginary part of the refractive index of the tropospheric haze, with respect to the shape described in the study of Karkoschka and Tomasko

  14. Trapping of giant-planet cores - I. Vortex aided trapping at the outer dead zone edge

    NASA Astrophysics Data System (ADS)

    Regály, Zs.; Sándor, Zs.; Csomós, P.; Ataiee, S.

    2013-08-01

    In this paper the migration of a 10 M⊕ planetary core is investigated at the outer boundary of the `dead zone' of a protoplanetary disc by means of 2D hydrodynamic simulations done with the graphics processor unit version of the FARGO code. In the dead zone, the effective viscosity is greatly reduced due to the disc self-shielding against stellar UV radiation, X-rays from the stellar magnetosphere and interstellar cosmic rays. As a consequence, mass accumulation occurs near the outer dead zone edge, which is assumed to trap planetary cores enhancing the efficiency of the core-accretion scenario to form giant planets. Contrary to the perfect trapping of planetary cores in 1D models, our 2D numerical simulations show that the trapping effect is greatly dependent on the width of the region where viscosity reduction is taking place. Planet trapping happens exclusively if the viscosity reduction is sharp enough to allow the development of large-scale vortices due to the Rossby wave instability. The trapping is only temporarily, and its duration is inversely proportional to the width of the viscosity transition. However, if the Rossby wave instability is not excited, a ring-like axisymmetric density jump forms, which cannot trap the 10 M⊕ planetary cores. We revealed that the stellar torque exerted on the planet plays an important role in the migration history as the barycentre of the system significantly shifts away from the star due to highly non-axisymmetric density distribution of the disc. Our results still support the idea of planet formation at density/pressure maximum, since the migration of cores is considerably slowed down enabling them further growth and runaway gas accretion in the vicinity of an overdense region.

  15. Giant electromagnetic vortex and MeV monoenergetic electrons generated by short laser pulses in underdense plasma near quarter critical density region.

    PubMed

    Zhidkov, Alexei; Nemoto, Koshichi; Nayuki, Takuya; Oishi, Yuji; Fuji, Takashi

    2007-07-01

    Very efficient generation of monoenergetic, about 1MeV , electrons from underdense plasma with its electron density close to the critical, when irradiated by an intense femtosecond laser pulse, is found via two dimensional particle-in-cell simulation. The stimulated Raman scattering of a laser pulse with frequency omega< or =2omega(pl max) gives rise to a giant electromagnetic vortex. In contrast to electron acceleration by the well-known laser pulse wake, injected plasma electrons are accelerated up to vortex ponderomotive potential forming a quite monoenergetic distribution. A relatively high charge of such an electron source makes very efficient generation of soft gamma rays with homega>300 keV .

  16. Investigating aspects of dark spot structure and environment in relation to vortex drift on the Ice Giants

    NASA Astrophysics Data System (ADS)

    Le Beau, Raymond P.; Palotai, Csaba J.

    2016-10-01

    Geophysical vortices called Dark Spots, whether directly observed like the original Great Dark Spot (GDS-89) or inferred as with "The Berg" cloud feature, that drift meridionally are distinctive atmospheric features of Uranus and Neptune. Numerical simulations of GDS-89 suggest a possible link between the environmental gradient of potential vorticity and the vortex drift rate (starting with LeBeau and Dowling, 1998). This mechanism could be similar to the "beta gyre" concept proposed for hurricane drift (Fiorino and Elsberry, 1989) in which the advection of environmental potential vorticity by and about the vortex generates a residual vortex dipole, effectively propelling the original vortex away or towards the equator. In the case of hurricanes, this effect is considered one part of the overall environmental wind that forms the steering flow driving hurricane drift. For the dark spots, such a gyre might be the dominant mechanism for north-south motions.Similar numerical simulations of vortices on Uranus have not been fully consistent with the GDS-89 results. Some vortices like the original Uranus Dark Spot (UDS) do appear to favor regions of low environmental PV gradients, which in simulations suggest increased stability (Hammel et al., 2009). However, even near-zero PV gradients result in significant drift on Uranus in contrast to Neptune. The effect of companion clouds on vortex drift also requires greater understanding, particularly on Uranus.To better understand these vortex dynamics, a parametric approach is now being applied in which vortex characteristics such as size and wind strength as well as environmental conditions are varied through a range of possible values. While these simulations are not necessarily designed to capture a particular known dark spots, the goal of these simulations is to determine what conditions lead to what types of vortex behavior.References:M. Fiorino and R.L. Elsberry. Journal of the Atmospheric Sciences 46:975-990, 1989H

  17. Ramsey patterns for multiquantum transitions in fountain experiments

    SciTech Connect

    McColm, D. |

    1996-12-01

    Ramsey patterns for radio-frequency multiquantum transitions among Zeeman levels of the ground state of thallium, cesium, and francium have been calculated. The narrowing of these patterns observed earlier by Gould is predicted to occur only when both static electric and magnetic fields are present. {copyright} {ital 1996 The American Physical Society.}

  18. Analysis of energy states in modulation doped multiquantum well heterostructures

    NASA Technical Reports Server (NTRS)

    Ji, G.; Henderson, T.; Peng, C. K.; Huang, D.; Morkoc, H.

    1990-01-01

    A precise and effective numerical procedure to model the band diagram of modulation doped multiquantum well heterostructures is presented. This method is based on a self-consistent iterative solution of the Schroedinger equation and the Poisson equation. It can be used rather easily in any arbitrary modulation-doped structure. In addition to confined energy subbands, the unconfined states can be calculated as well. Examples on realistic device structures are given to demonstrate capabilities of this procedure. The numerical results are in good agreement with experiments. With the aid of this method the transitions involving both the confined and unconfined conduction subbands in a modulation doped AlGaAs/GaAs superlattice, and in a strained layer InGaAs/GaAs superlattice are identified. These results represent the first observation of unconfined transitions in modulation doped multiquantum well structures.

  19. Analysis of energy states in modulation doped multiquantum well heterostructures

    NASA Technical Reports Server (NTRS)

    Ji, G.; Henderson, T.; Peng, C. K.; Huang, D.; Morkoc, H.

    1990-01-01

    A precise and effective numerical procedure to model the band diagram of modulation doped multiquantum well heterostructures is presented. This method is based on a self-consistent iterative solution of the Schroedinger equation and the Poisson equation. It can be used rather easily in any arbitrary modulation-doped structure. In addition to confined energy subbands, the unconfined states can be calculated as well. Examples on realistic device structures are given to demonstrate capabilities of this procedure. The numerical results are in good agreement with experiments. With the aid of this method the transitions involving both the confined and unconfined conduction subbands in a modulation doped AlGaAs/GaAs superlattice, and in a strained layer InGaAs/GaAs superlattice are identified. These results represent the first observation of unconfined transitions in modulation doped multiquantum well structures.

  20. Hyperfine selectivity using multiquantum electron-nuclear-electron triple resonance

    NASA Astrophysics Data System (ADS)

    Christidis, T. C.; Mchaourab, Hassane S.; Hyde, James S.

    1996-06-01

    Hyperfine selectivity is demonstrated in a continuous wave electron-nuclear double resonance (ENDOR) experiment. A multiquantum electron-electron double resonance (ELDOR) signal is monitored as a function of the nuclear radio frequency. The signs and relative intensities of the ENDOR lines permit separating the case where both ELDOR and ENDOR frequencies match hyperfine couplings from the cases where this condition is not satisfied.

  1. Ferroelectric tunnel junctions with multi-quantum well structures

    SciTech Connect

    Ma, Zhijun; Zhang, Tianjin; Liang, Kun; Qi, Yajun; Wang, Duofa; Wang, Jinzhao; Jiang, Juan

    2014-06-02

    Ferroelectric tunnel junctions (FTJs) with multi-quantum well structures are proposed and the tunneling electroresistance (TER) effect is investigated theoretically. Compared with conventional FTJs with monolayer ferroelectric barriers, FTJs with single-well structures provide TER ratio improvements of one order of magnitude, while FTJs with optimized multi-well structures can enhance this improvement by another order of magnitude. It is believed that the increased resonant tunneling strength combined with appropriate asymmetry in these FTJs contributes to the improvement. These studies may help to fabricate FTJs with large TER ratio experimentally and put them into practice.

  2. Evidence for formation of multi-quantum dots in hydrogenated graphene

    PubMed Central

    2012-01-01

    We report the experimental evidence for the formation of multi-quantum dots in a hydrogenated single-layer graphene flake. The existence of multi-quantum dots is supported by the low-temperature measurements on a field effect transistor structure device. The resulting Coulomb blockade diamonds shown in the color scale plot together with the number of Coulomb peaks exhibit the characteristics of the so-called ‘stochastic Coulomb blockade’. A possible explanation for the formation of the multi-quantum dots, which is not observed in pristine graphene to date, was attributed to the impurities and defects unintentionally decorated on a single-layer graphene flake which was not treated with the thermal annealing process. Graphene multi-quantum dots developed around impurities and defect sites during the hydrogen plasma exposure process. PMID:22898058

  3. Ultrathin gradient nonlinear metasurfaces with giant nonlinear response (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Nookala, Nishant; Lee, Jongwon; Gomez-Diaz, Juan Sebastian; Tymchenko, Mykhailo; Demmerle, Frederic; Boehm, Gerhard; Amann, Markus-Christian; Alu, Andrea; Belkin, Mikhail A.

    2016-09-01

    Extending the `flat optics' paradigm to the nonlinear optics faces important challenges, since, for any practical situation, we are required to simultaneously achieve sub-diffraction phase control and efficient frequency conversion in metasurfaces of sub-wavelength thickness. Here, we experimentally demonstrate giant nonlinear response and continuous phase control of the giant nonlinear response in metasurfaces based on plasmonic nanoresonators coupled to intersubband transitions in semiconductor multi-quantum wells. Over 0.075% of second-harmonic power conversion efficiency is achieved experimentally in a 400-nm-thick metasurface using 10 microns wavelength pump with 20 kW/cm2 intensity.

  4. Vortex anomaly in low-dimensional fermionic condensates: Quantum confinement breaks chirality

    NASA Astrophysics Data System (ADS)

    Chen, Yajiang; Shanenko, A. A.; Peeters, F. M.

    2014-02-01

    Chiral fermions are responsible for low-temperature properties of vortices in fermionic condensates, both superconducting (charged) and superfluid (neutral). One of the most striking consequences of this fact is that the core of a single-quantum vortex collapses at low temperatures, T →0 (i.e., the Kramer-Pesch effect for superconductors), due to the presence of chiral quasiparticles in the vortex-core region. We show that the situation changes drastically for fermionic condensates confined in quasi-one-dimensional and quasi-two-dimensional geometries. Here quantum confinement breaks the chirality of in-core fermions. As a result, instead of the ultimate shrinking, the core of a single-quantum vortex extends at low temperatures, and the condensate profile surprisingly mimics the multiquantum vortex behavior. Our findings are relevant for nanoscale superconductors, such as recent metallic nanoislands on silicon, and also for ultracold superfluid Fermi gases in cigar-shaped and pancake-shaped atomic traps.

  5. Vortex rings

    NASA Technical Reports Server (NTRS)

    Shariff, Karim; Leonard, Anthony

    1992-01-01

    The vortex-ring problem in fluid mechanics is examined generally in terms of formation, the steady state, the duration of the rings, and vortex interactions. The formation is studied by examining the generation of laminar and turbulent vortex rings and their resulting structures with attention given to the three stages of laminar ring development. Inviscid dynamics is addressed to show how core dynamics affects overall ring motion, and laminar vortex structures are described in two dimensions. Viscous and inviscid structures are related in terms of 'leapfrogging', head-on collisions, and collisions with a no-slip wall. Linear instability theory is shown to successfully describe observational data, although late stages in the breakdown are not completely understood. This study of vortex rings has important implications for key aerodynamic issues including sound generation, transport and mixing, and vortex interactions.

  6. Vulcanized vortex

    SciTech Connect

    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.

  7. Standing on the shoulders of giants. Trojan Earths and vortex trapping in low mass self-gravitating protoplanetary disks of gas and solids

    NASA Astrophysics Data System (ADS)

    Lyra, W.; Johansen, A.; Klahr, H.; Piskunov, N.

    2009-01-01

    Context: Centimeter and meter-sized solid particles in protoplanetary disks are trapped within long-lived, high-pressure regions, creating opportunities for collapse into planetesimals and planetary embryos. Aims: We aim to study the effect of the high-pressure regions generated in the gaseous disks by a giant planet perturber. These regions consist of gas retained in tadpole orbits around the stable Lagrangian points as a gap is carved, and the Rossby vortices launched at the edges of the gap. Methods: We performed global simulations of the dynamics of gas and solids in a low mass non-magnetized self-gravitating thin protoplanetary disk. We employed the Pencil code to solve the Eulerian hydro equations, tracing the solids with a large number of Lagrangian particles, usually 100 000. To compute the gravitational potential of the swarm of solids, we solved the Poisson equation using particle-mesh methods with multiple fast Fourier transforms. Results: Huge particle concentrations are seen in the Lagrangian points of the giant planet, as well as in the vortices they induce at the edges of the carved gaps. For 1 cm to 10 cm radii, gravitational collapse occurs in the Lagrangian points in less than 200 orbits. For 5 cm particles, a 2M⊕ planet is formed. For 10 cm, the final maximum collapsed mass is around 3M⊕. The collapse of the 1 cm particles is indirect, following the timescale of gas depletion from the tadpole orbits. Vortices are excited at the edges of the gap, primarily trapping particles of 30 cm radii. The rocky planet that is formed is as massive as 17M⊕, constituting a Super-Earth. Collapse does not occur for 40 cm onwards. By using multiple particle species, we find that gas drag modifies the streamlines in the tadpole region around the classical L4 and L5 points. As a result, particles of different radii have their stable points shifted to different locations. Collapse therefore takes longer and produces planets of lower mass. Three super-Earths are

  8. Smell sensing and visualizing based on multi-quantum wells spatial light modulator

    NASA Astrophysics Data System (ADS)

    Tian, Fengchun; Zhao, Zhenzhen; Jia, Pengfei; Liao, Hailin; Chen, Danyu; Liu, Shouqiong

    2014-09-01

    For the existing drawbacks of traditional detecting methods which use gratings or prisms to detect light intensity distribution at each wavelength of polychromatic light, a novel method based on multi-quantum wells spatial light modulator (MQWs-SLM) has been proposed in this paper. In the proposed method, MQWs-SLM serves as a distribution features detector of the signal light. It is on the basis of quantum-confine Stark effect (QCSE) that the vertical applied voltage can change the absorption features of exciton in multi-quantum wells, and further change the distribution features of the readout polychromatic light of MQWs-SLM. It can be not only an universal detecting method, but also especially recommended to use in the Electronic nose system for features detecting of signal light so as to realize smell sensing and visualizing. The feasibility of the proposed method has been confirmed by mathematical modeling and analysis, simulation experiments and research status analysis.

  9. InGaAs/GaAs multiquantum-well electroabsorption modulator with integrated waveguide

    NASA Astrophysics Data System (ADS)

    Das, Utpal; Berger, Paul R.; Bhattacharya, Pallab K.

    1987-10-01

    A monolithically integrated guided-wave modulator has been realized by using molecular-beam epitaxial regrowth and ion-milling techniques. The guiding and modulating regions consist, respectively, of In-doped GaAs and GaAs/In(0.34)Ga(0.66)As strained-layer multiquantum wells. Modulation is achieved by field-enhanced electroabsorption in the multiquantum wells. The insertion loss of the modulator is 0.9 dB, and the transmission loss in the guides is less than or equal to 1 dB/cm. The temporal response of similar GaAs/InGaAs as-grown photodiodes to pulsed laser excitation is characterized by a rise time of 115 psec.

  10. Electrical tunability of infrared detectors using compositionally asymmetric GaAs/AlGaAs multiquantum wells

    NASA Astrophysics Data System (ADS)

    Martinet, E.; Luc, F.; Rosencher, E.; Bois, Ph.; Delaitre, S.

    1992-02-01

    For the first time, an electrically tunable infrared photoconductor is made with GaAs/AlGaAs asymmetric step multiquantum wells, using the linear Stark shift of the intersubband transition. An applied electric field excursion of +/- 40 kV/cm is sufficient to shift the peak responsivity wavelength from 8.5 to 13.5 micron. The photoresponse tunability is studied by comparing photocurrent and absorption spectra for different applied electric fields.

  11. Vortex methods and vortex statistics

    SciTech Connect

    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.

  12. Vortex methods

    SciTech Connect

    Chorin, A.J. |

    1993-06-01

    Vortex methods originated from the observation that in incompressible inviscid flow vorticity (or, more accurately, circulation) is a conserved quantity, as can be readily deduced from the absence of tangential stresses. Thus, if the vorticity is known at time t=0, one can find the flow at a later time by simply following the vorticity. In this narrow context, a vortex method is a numerical method that follows vorticity. The author restricts himself in these lectures to a special class of numerical vortex methods, those that are based on a Lagrangian transport of vorticity in hydrodynamics by smoothed particles (blobs) and those whose analysis contributes to the understanding of blob methods. Blob methods started in the 1930`s.

  13. Study of dual-valley transport across a multiquantum barrier to enhance carrier confinement

    NASA Astrophysics Data System (ADS)

    Brown, M. R.; Teng, K. S.; Kestle, A.; Smowton, P.; Blood, P.; Mawby, P. A.; Wilks, S. P.

    2004-07-01

    Red-emitting quantum well (QW) 630 nm laser diodes have many potential applications in industry and medicine. However, manufacture of such short wavelength lasers is impeded by severe electron leakage from the active region, which is predominantly attributed to loss of thermally activated electrons, via the inherently low conduction band offsets and possible inter-valley transfer to the lower energy X-band minima. To combat the high leakage current in such devices, we have implemented a multiquantum barrier (MQB) into the p-type cladding region of the device, and theoretically optimised the structure to reduce X-band transfer and predict effective enhancement to the intrinsic barrier height.

  14. Silicon-Germanium multi-quantum well photodetectors in the near infrared.

    PubMed

    Onaran, Efe; Onbasli, M Cengiz; Yesilyurt, Alper; Yu, Hyun Yong; Nayfeh, Ammar M; Okyay, Ali K

    2012-03-26

    Single crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ~10 mA/cm² and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage.

  15. Photoinduced field modulation in multiquantum well heterostructures: A new photocurrent gain mechanism

    NASA Astrophysics Data System (ADS)

    Ripamonti, Giancarlo; Capasso, Federico; Tsang, Won-Tien; Hutchinson, Albert L.

    A new photocurrent gain mechanism in multiquantum well structures has been observed. Unlike conventional photoconductors, the gain in these devices is caused not by a modulation of the conductivity, but by a modulation of the electric field. The physical basis of this phenomenon is the partial screening of the electric field in the wells due to the pile-up of photocarriers. At constant bias voltage this leads to an enhancement of the field in the barrier layers. In structures with injecting contacts this mechanism enhances electron injection and therefore gives rise to photocurrent gain.

  16. Brownian vortexes

    NASA Astrophysics Data System (ADS)

    Sun, Bo; Lin, Jiayi; Darby, Ellis; Grosberg, Alexander Y.; Grier, David G.

    2009-07-01

    Mechanical equilibrium at zero temperature does not necessarily imply thermodynamic equilibrium at finite temperature for a particle confined by a static but nonconservative force field. Instead, the diffusing particle can enter into a steady state characterized by toroidal circulation in the probability flux, which we call a Brownian vortex. The circulatory bias in the particle’s thermally driven trajectory is not simply a deterministic response to the solenoidal component of the force but rather reflects interplay between advection and diffusion in which thermal fluctuations extract work from the nonconservative force field. As an example of this previously unrecognized class of stochastic heat engines, we consider a colloidal sphere diffusing in a conventional optical tweezer. We demonstrate both theoretically and experimentally that nonconservative optical forces bias the particle’s fluctuations into toroidal vortexes whose circulation can reverse direction with temperature or laser power.

  17. Vortex transmutation.

    PubMed

    Ferrando, Albert; Zacarés, Mario; García-March, Miguel-Angel; Monsoriu, Juan A; de Córdoba, Pedro Fernández

    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" 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.

  18. Wavy growth onset in strain-balanced InGaAs multi-quantum wells

    NASA Astrophysics Data System (ADS)

    Nasi, L.; Ferrari, C.; Lanzi, A.; Lazzarini, L.; Balboni, R.; Clarke, G.; Mazzer, M.; Rohr, C.; Abbott, P.; Barnham, K. W. J.

    2005-01-01

    Different strain-balanced InGaAs/InGaAs multi-quantum wells (MQWs) were grown on (0 0 1) InP to be used as active layers of thermophotovoltaic devices. Transmission electron microscopy (TEM) and high-resolution X-ray diffraction (HRXRD) were performed to correlate the evolution of the layer interfaces from planar to wavy and the consequent nucleation of extended defects with the well and barrier compositions and thicknesses and the growth temperature. The existence of a critical elastic energy density for the wavy growth onset has been experimentally confirmed by changing both the well and barrier misfit and the multi-quantum well layer thickness. A decrease of the growth temperature shifts the critical energy to higher values. An empirical model to predict the maximum number of layers that can be grown without modulations as a function of the strain energy stored in the MQW period and the growth temperature is presented and successfully applied for the growth of high quality 40 repetitions MQWs with a well misfit of about 1.5%.

  19. Carrier localization in green emitting InGaN/GaN multiquantum well structure

    NASA Astrophysics Data System (ADS)

    Cheng, Chou-Jen; Mohanta, Antaryami; Jang, Der-Jun; Lee, Meng-En

    2015-03-01

    Green emitting InGaN/GaN multiquantum well sample is investigated using photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. Carrier localization of energy ~ 12 meV due to inhomogeneous distribution of In in the InGaN quantum well (QW) layer is observed. The temperature dependence of PL peak energy exhibits S-shape phenomenon and is comparatively discussed with the Varshni's empirical formula. The full width at half maximum (FWHM) of the PL emission band shows increasing-decreasing-increasing behavior with increase in temperature. The temperature dependence of radiative life time (τr) show τr ~ T 3 / 2 dependence with temperature above 200 K which confirms the insignificant effect of carrier localization at room temperature. Transmission electron microscopy (TEM) study reveals the absence of In-rich regions known for strong carrier localization in the InGaN QW layer which is consistent with the results of PL and TRPL.

  20. GaAlAs buried multiquantum well lasers fabricated by diffusion-induced disordering

    NASA Astrophysics Data System (ADS)

    Fukuzawa, Tadashi; Semura, Shigeru; Saito, Hiroshi; Ohta, Tsuneaki; Uchida, Yoko; Nakashima, Hisao

    1984-07-01

    A new transverse-mode-controlled laser called a buried multiquantum-well (BMQW) laser has been developed. In order to make it possible to bury the MQW laser active region utilizing the diffusion-induced disordering (DID) of GaAs-GaAlAs MQW, zinc was selectively diffused into the MQW structure, resulting in a 3-8-μm-wide stripe region. The threshold current is as low as 33 mA with a 300-μm cavity length and a fundamental transverse mode can be achieved. As a result of studying the relation of the waveguide geometry to the longitudinal and transverse modes it was concluded that this BMQW laser made by a simple DID process acts as an index-guided laser.

  1. Effects of multiquantum transitions on molecular populations in grain-forming circumstellar environments

    NASA Technical Reports Server (NTRS)

    Nuth, J. A.; Allen, J. E., Jr.; Wiant, M.

    1985-01-01

    Simplification of astrophysical calculations can be achieved by invoking the condition of local thermodynamic equilibrium; however, recent investigations suggest that this assumption may not be valid for certain astrophysical regions. To examine the effects of multiquantum translation to vibration transitions in expanding circumstellar envelopes, vibrational populations of the lowest 20 levels of CO have been calculated as a function of pressure and radiation density for H atom-CO collisions. Significant departure from local thermodynamic equilibrium is indicated, which implies lower dissociation rates for molecular components and a subsequent enhancement in the rate of grain formation by many orders of magnitude. Stabilization of intermediate species before they can dissociate may facilitate the formation of refractory grain cores in very hot, dilute outflows. As the present calculations indicate, laboratory measurements of state-to-state translation to vibration rates are needed for a more complete understanding of circumstellar chemistry.

  2. 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.

  3. Energy band design for p-type tensile strained Si/SiGe multi-quantum well infrared photodetector

    NASA Astrophysics Data System (ADS)

    Li, Jin-tao; Chen, Song-yan; Qi, Dong-feng; Huang, Wei; Li, Cheng; Lai, Hong-kai

    2011-05-01

    The band structure of the confined states is calculated for Si/SiGe multi-quantum well infrared photodetector (M-QWIP). The influence of the Ge component in pseudosubstrate on the energy band structure of Si/Si{in0.54}Ge{in0.46} multi-quantum wells (MQWs) is investigated. It is found that the high energy levels in the MQWs move up while the low energy levels move down as the Ge component in pseudosubstrate increases. The influence of the barrier width on the energy band structure of MQWs is also studied based on the 6 × 6 k·p method. The results show that the Si barrier between 5 nm and 10 nm is optimized to enhance the intersubband absorption in the MQWs.

  4. Switchable bicolor (5.5-9.0 microns) infrared detector using asymmetric GaAs/AlGaAs multiquantum well

    NASA Astrophysics Data System (ADS)

    Martinet, E.; Rosencher, E.; Luc, F.; Bois, Ph.; Costard, E.; Delaitre, S.

    1992-07-01

    Electrical switching of a bispectral infrared photoconductor is demonstrated with GaAs/AlGaAs asymmetric step multiquantum wells, presenting bound-to-bound (tunable 8.5-9.0 microns) and bound-to-extended (about 5.5 microns) intersubband transitions of similar oscillator strengths. The bound-to-bound photoresponse is switched on by applying an electric field of sufficient magnitude to permit the collection of the photoexcited bound electrons of tunneling.

  5. Sadovskii vortex in strain

    NASA Astrophysics Data System (ADS)

    Freilich, Daniel; Llewellyn Smith, Stefan

    2014-11-01

    A Sadovskii vortex is a patch of fluid with uniform vorticity surrounded by a vortex sheet. Using a boundary element type method, we investigate the steady states of this flow in an incompressible, inviscid straining flow. Outside the vortex, the fluid is irrotational. In the limiting case where the entire circulation is due to the vortex patch, this is a patch vortex (Moore & Saffman, Aircraft wake turbulence and its detection 1971). In the other limiting case, where all the circulation is due to the vortex sheet, this is a hollow vortex (Llewellyn Smith and Crowdy, J. Fluid Mech. 691, 2012). This flow has two governing nondimensional parameters, relating the strengths of the straining field, vortex sheet, and patch vorticity. We study the relationship between these two parameters, and examine the shape of the resulting vortices. We also work towards a bifurcation diagram of the steady states of the Sadovskii vortex in an attempt to understand the connection between vortex sheet and vortex patch desingularizations of the point vortex. Support from NSF-CMMI-0970113.

  6. Anisotropic and long-range vortex interactions in two-dimensional dipolar Bose gases.

    PubMed

    Mulkerin, B C; van Bijnen, R M W; O'Dell, D H J; Martin, A M; Parker, N G

    2013-10-25

    We perform a theoretical study into how dipole-dipole interactions modify the properties of superfluid vortices within the context of a two-dimensional atomic Bose gas of co-oriented dipoles. The reduced density at a vortex acts like a giant antidipole, changing the density profile and generating an effective dipolar potential centred at the vortex core whose most slowly decaying terms go as 1/ρ(2) and ln(ρ)/ρ(3). These effects modify the vortex-vortex interaction which, in particular, becomes anisotropic for dipoles polarized in the plane. Striking modifications to vortex-vortex dynamics are demonstrated, i.e., anisotropic corotation dynamics and the suppression of vortex annihilation.

  7. Anisotropic and Long-Range Vortex Interactions in Two-Dimensional Dipolar Bose Gases

    NASA Astrophysics Data System (ADS)

    Mulkerin, B. C.; van Bijnen, R. M. W.; O'Dell, D. H. J.; Martin, A. M.; Parker, N. G.

    2013-10-01

    We perform a theoretical study into how dipole-dipole interactions modify the properties of superfluid vortices within the context of a two-dimensional atomic Bose gas of co-oriented dipoles. The reduced density at a vortex acts like a giant antidipole, changing the density profile and generating an effective dipolar potential centred at the vortex core whose most slowly decaying terms go as 1/ρ2 and ln⁡(ρ)/ρ3. These effects modify the vortex-vortex interaction which, in particular, becomes anisotropic for dipoles polarized in the plane. Striking modifications to vortex-vortex dynamics are demonstrated, i.e., anisotropic corotation dynamics and the suppression of vortex annihilation.

  8. Multi-Quantum Well Structures to Improve the Performance of Multijunction Solar Cells

    NASA Astrophysics Data System (ADS)

    Samberg, Joshua Paul

    Current, lattice matched triple junction solar cell efficiency is approximately 44% at a solar concentration of 942x. Higher efficiency for such cells can be realized with the development of a 1eV bandgap material lattice matched to Ge. One of the more promising materials for this application is that of the InGaAs/GaAsP multi-quantum well (MQW) structure. By inserting a stress/strain-balanced InGaAs/GaAsP MQW structure into the iregion of a GaAs p-i-n diode, the absorption edge of the p-i-n diode can be red shifted with respect to that of a standard GaAs p-n diode. Compressive stress in the InGaAs wells are balanced via GaAsP barriers subjected to tensile stress. Individually, the InGaAs and GaAsP layers are grown below their critical layer thickness to prevent the formation of misfit and threading dislocations. Until recently InGaAs/GaAsP MQWs have been somewhat hindered by their usage of low phosphorus-GaAsP barriers. Presented within is the development of a high-P composition GaAsP and the merits for using such a high composition of phosphorus are discussed. It is believed that these barriers represent the highest phosphorus content to date in such a structure. By using high composition GaAsP the carriers are collected via tunneling (for barriers .30A) as opposed to thermionic emission. Thus, by utilizing thin, high content GaAsP barriers one can increase the percentage of the intrinsic region in a p-i-n structure that is comprised of the InGaAs well in addition to increasing the number of periods that can be grown for a given depletion width. However, standard MQWs of this type inherently possess undesirable compressive strain and quantum size effects (QSE) that cause the optical absorption of the InGaAs wells to blue shift. To circumvent these deleterious QSEs stress balanced, pseudomorphic InGaAs/GaAsP staggered MQWs were developed. Tunneling is still a viable mode for carrier transport in the staggered MQW structures. GaAs interfacial layers within the multi-quantum

  9. Investigation of temperature-dependent photoluminescence in multi-quantum wells

    PubMed Central

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-01-01

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells. PMID:26228734

  10. Investigation of temperature-dependent photoluminescence in multi-quantum wells.

    PubMed

    Fang, Yutao; Wang, Lu; Sun, Qingling; Lu, Taiping; Deng, Zhen; Ma, Ziguang; Jiang, Yang; Jia, Haiqiang; Wang, Wenxin; Zhou, Junming; Chen, Hong

    2015-07-31

    Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

  11. Investigation of carrier collection in multi-quantum well solar cells by luminescence spectra analysis

    NASA Astrophysics Data System (ADS)

    Delamarre, Amaury; Fujii, Hiromasa; Watanabe, Kentaroh; Guillemoles, Jean-François; Nakano, Yoshiaki; Sugiyama, Masakazu

    2015-03-01

    Multi-Quantum well solar cells (MQWSC) have been shown to present several advantages, among which are low dark currents and tunable bandgaps. They are especially suited for implementation in multi-junction cells, and are highly promising for absorbers in Hot Carrier Solar Cells (HCSC). Such applications require high concentration ratio, which arises the issue of collection efficiency. Whereas it is usually considered that collection in MQW is very close to unity at one sun, it has been shown to not be the case under high concentration at the maximum power point. We propose in this work to take advantage of the luminescence spectral variation to investigate the depth collection efficiency. In order to validate the model, a series of strain compensated InGaAs/GaAsP MQW solar cells with intentional variation of the MQW doping concentration are grown. This has the effect of switching the space charge region position and width as well as the electric field intensity. Recording the luminescence spectra at various illumination intensities and applied voltages, we show that the in-depth quasi-Fermi level splitting and thus collection properties can be probed. Other measurements (EQE, luminescence intensity variation) are shown to be consistent with these results. Regarding their use as HCSC, the luminescence of MQW solar cells has been mainly used so far for investigating the quasi-Fermi level splitting and the temperature. Our results improve our understanding by adding information on carrier transport.

  12. Radiation response of multi-quantum well solar cells: Electron-beam-induced current analysis

    NASA Astrophysics Data System (ADS)

    Maximenko, S. I.; Lumb, M. P.; Hoheisel, R.; Gonzalez, M.; Scheiman, D. A.; Messenger, S. R.; Tibbits, T. N. D.; Imaizumi, M.; Ohshima, T.; Sato, S. I.; Jenkins, P. P.; Walters, R. J.

    2015-12-01

    Solar cells utilizing multi-quantum well (MQW) structures are considered promising candidate materials for space applications. An open question is how well these structures can resist the impact of particle irradiation. The aim of this work is to provide feedback about the radiation response of In0.01Ga0.99As solar cells grown on Ge with MQWs incorporated within the i-region of the device. In particular, the local electronic transport properties of the MQW i-regions of solar cells subjected to electron and proton irradiation were evaluated experimentally using the electron beam induced current (EBIC) technique. The change in carrier collection distribution across the MQW i-region was analyzed using a 2D EBIC diffusion model in conjunction with numerical modeling of the electrical field distribution. Both experimental and simulated findings show carrier removal and type conversion from n- to p-type in MQW i-region at a displacement damage dose as low as ˜6.06-9.88 × 109 MeV/g. This leads to a redistribution of the electric field and significant degradation in charge carrier collection.

  13. Radiation response of multi-quantum well solar cells: Electron-beam-induced current analysis

    SciTech Connect

    Maximenko, S. I. Scheiman, D. A.; Jenkins, P. P.; Walters, R. J.; Lumb, M. P.; Hoheisel, R.; Gonzalez, M.; Messenger, S. R.; Tibbits, T. N. D.; Imaizumi, M.; Ohshima, T.; Sato, S. I.

    2015-12-28

    Solar cells utilizing multi-quantum well (MQW) structures are considered promising candidate materials for space applications. An open question is how well these structures can resist the impact of particle irradiation. The aim of this work is to provide feedback about the radiation response of In{sub 0.01}Ga{sub 0.99}As solar cells grown on Ge with MQWs incorporated within the i-region of the device. In particular, the local electronic transport properties of the MQW i-regions of solar cells subjected to electron and proton irradiation were evaluated experimentally using the electron beam induced current (EBIC) technique. The change in carrier collection distribution across the MQW i-region was analyzed using a 2D EBIC diffusion model in conjunction with numerical modeling of the electrical field distribution. Both experimental and simulated findings show carrier removal and type conversion from n- to p-type in MQW i-region at a displacement damage dose as low as ∼6.06–9.88 × 10{sup 9} MeV/g. This leads to a redistribution of the electric field and significant degradation in charge carrier collection.

  14. Sadovskii vortex in strain

    NASA Astrophysics Data System (ADS)

    Freilich, Daniel; Llewellyn Smith, Stefan

    2015-11-01

    Sadovskii vortices are patches of fluid with uniform vorticity surrounded by a vortex sheet. They were first constructed as models for wakes behind bluff objects. We investigate the Sadovskii vortex in a straining field and examine limiting cases to validate our computational method. One limit is the patch vortex in strain (Moore & Saffman, Aircraft wake turbulence and its detection 1971), where there is no vortex sheet. We solve this as a free-boundary problem, and show that a simple method using the Biot-Savart law quickly gives solutions for stable shapes. When used for the more elongated (stronger straining field) situations, the method also leads to new vortex shapes. In the hollow vortex case, where there is no vortex patch and the circulation is entirely due to the vortex sheet (Llewellyn Smith and Crowdy, J. Fluid Mech. 691 2012), we use the Birkhoff-Rott equation to calculate the velocity of the fluid on the vortex boundary. The combination of these two methods can then be used to calculate the shape and velocity field of the Sadovksii vortex in strain.

  15. Hydrodynamic Vortex on Surfaces

    NASA Astrophysics Data System (ADS)

    Ragazzo, Clodoaldo Grotta; de Barros Viglioni, Humberto Henrique

    2017-04-01

    The equations of motion for a system of point vortices on an oriented Riemannian surface of finite topological type are presented. The equations are obtained from a Green's function on the surface. The uniqueness of the Green's function is established under hydrodynamic conditions at the surface's boundaries and ends. The hydrodynamic force on a point vortex is computed using a new weak formulation of Euler's equation adapted to the point vortex context. An analogy between the hydrodynamic force on a massive point vortex and the electromagnetic force on a massive electric charge is presented as well as the equations of motion for massive vortices. Any noncompact Riemann surface admits a unique Riemannian metric such that a single vortex in the surface does not move ("Steady Vortex Metric"). Some examples of surfaces with steady vortex metric isometrically embedded in R^3 are presented.

  16. 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.

  17. Strings, vortex rings, and modes of instability

    DOE PAGES

    Gubser, Steven S.; Nayar, Revant; Parikh, Sarthak

    2015-01-12

    We treat string propagation and interaction in the presence of a background Neveu–Schwarz three-form field strength, suitable for describing vortex rings in a superfluid or low-viscosity normal fluid. A circular vortex ring exhibits instabilities which have been recognized for many years, but whose precise boundaries we determine for the first time analytically in the small core limit. Two circular vortices colliding head-on exhibit stronger instabilities which cause splitting into many small vortices at late times. We provide an approximate analytic treatment of these instabilities and show that the most unstable wavelength is parametrically larger than a dynamically generated length scalemore » which in many hydrodynamic systems is close to the cutoff. We also summarize how the string construction we discuss can be derived from the Gross–Pitaevskii Lagrangian, and also how it compares to the action for giant gravitons.« less

  18. Anomalous diffusion of isoelectronic antimony implant induced defects in GaAs-AlGaAs multiquantum well structures

    NASA Astrophysics Data System (ADS)

    Rao, E. V. K.; Krauz, Ph.; Thibierge, H.; Azoulay, R.; Vieu, C.

    1994-03-01

    We present here evidence on the deep diffusion of isoelectronic Sb implant induced defects in thick GaAs-AlGaAs multiquantum well structures (MQW) to depths as far as ˜30 times the implant projected range (Rp). This observation has been confirmed by performing low temperature photoluminescence depth scanning measurements and cross-sectional transmission electron microscopy (XTEM) analysis on room temperature Sb implanted thick MQW samples. An explanation based on the isoelectronic nature of Sb and its substitution on As site (SbAs) has been proposed to understand the anomalous diffusion of defects during implant and their contribution to Al/Ga disordering during post-implant annealing.

  19. X-ray diffraction simulation of GeSn/Ge multi-quantum wells with kinematic approach

    NASA Astrophysics Data System (ADS)

    Li, Hui; Chang, Chiao; Cheng, Hung-Hsiang

    2017-06-01

    We report an investigation on X-ray diffraction simulation of GeSn/Ge Multi-quantum wells (MQWs) with kinematic approach. X-ray diffraction in (004) ω-2θ scan and (224) reciprocal space mapping are performed for characterization of the MQWs. However, simulation of the diffraction process is imperative for further structural analysis of the MQWs. The compressive strain not only affects the calculation of Sn composition in GeSn wells, but also dramatically affects the symmetry of satellite peaks.

  20. Design of monocrystalline Si/SiGe multi-quantum well microbolometer detector for infrared imaging systems

    NASA Astrophysics Data System (ADS)

    Shafique, Atia; Durmaz, Emre C.; Cetindogan, Barbaros; Yazici, Melik; Kaynak, Mehmet; Kaynak, Canan B.; Gurbuz, Yasar

    2016-05-01

    This paper presents the design, modelling and simulation results of silicon/silicon-germanium (Si/SiGe) multi-quantum well based bolometer detector for uncooled infrared imaging system. The microbolometer is designed to detect light in the long wave length infrared (LWIR) range from 8 to 14 μm with pixel size of 25 x 25 μm. The design optimization strategy leads to achieve the temperature coefficient of resistance (TCR) 4.5%/K with maximum germanium (Ge) concentration of 50%. The design of microbolometer entirely relies on standard CMOS and MEMS processes which makes it suitable candidate for commercial infrared imaging systems.

  1. Active Q switching in a GaAs/AlGaAs multiquantum well laser with an intracavity monolithic loss modulator

    NASA Technical Reports Server (NTRS)

    Arakawa, Y.; Larsson, A.; Paslaski, J.; Yariv, A.

    1986-01-01

    Active Q switching in a GaAs/AlGaAs multiquantum well laser with an intracavity electroabsorption monolithic loss modulator is demonstrated. In this device, an efficient loss modulation is achieved through the quantum confined Stark effect in a modulator section and the enhanced carrier induced band shrinkage effect in an optical amplifier section. It is found that a picosecond pulse as narrow as 18.6 ps full width at half-maximum is generated and a high repetition rate of more than 3 GHz is obtained.

  2. Analysis of the stability of InGaN/GaN multiquantum wells against ion beam intermixing.

    PubMed

    Redondo-Cubero, A; Lorenz, K; Wendler, E; Magalhães, S; Alves, E; Carvalho, D; Ben, T; Morales, F M; García, R; O'Donnell, K P; Wetzel, C

    2015-10-23

    Ion-induced damage and intermixing was evaluated in InGaN/GaN multi-quantum wells (MQWs) using 35 keV N(+) implantation at room temperature. In situ ion channeling measurements show that damage builds up with a similar trend for In and Ga atoms, with a high threshold for amorphization. The extended defects induced during the implantation, basal and prismatic stacking faults, are uniformly distributed across the quantum well structure. Despite the extremely high fluences used (up to 4 × 10(16) cm(-2)), the InGaN MQWs exhibit a high stability against ion beam mixing.

  3. Vortex cutting in superconductors

    NASA Astrophysics Data System (ADS)

    Vlasko-Vlasov, Vitalii K.; Koshelev, Alexei E.; Glatz, Andreas; Welp, Ulrich; Kwok, Wai-K.

    2015-03-01

    Unlike illusive magnetic field lines in vacuum, magnetic vortices in superconductors are real physical strings, which interact with the sample surface, crystal structure defects, and with each other. We address the complex and poorly understood process of vortex cutting via a comprehensive set of magneto-optic experiments which allow us to visualize vortex patterns at magnetization of a nearly twin-free YBCO crystal by crossing magnetic fields of different orientations. We observe a pronounced anisotropy in the flux dynamics under crossing fields and the filamentation of induced supercurrents associated with the staircase vortex structure expected in layered cuprates, flux cutting effects, and angular vortex instabilities predicted for anisotropic superconductors. At some field angles, we find formation of the vortex domains following a type-I phase transition in the vortex state accompanied by an abrupt change in the vortex orientation. To clarify the vortex cutting scenario we performed time-dependent Ginzburg-Landau simulations, which confirmed formation of sharp vortex fronts observed in the experiment and revealed a left-handed helical instability responsible for the rotation of vortices. This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.

  4. Giant Cell Arteritis

    MedlinePlus

    ... Patient / Caregiver Diseases & Conditions Giant Cell Arteritis Giant Cell Arteritis Fast Facts Giant cell arteritis (GCA) is ... polymyalgia rheumatica (also called PMR). What is giant cell arteritis? GCA is a type of vasculitis or ...

  5. Normal Shock Vortex Interaction

    DTIC Science & Technology

    2003-03-01

    Figure 9: Breakdown map for normal-shock vortex-interaction. References [1] O. Thomer, W. Schroder and M. Meinke , Numerical Simulation of Normal...and Oblique-Shock Vortex Interaction, ZAMM Band 80, Sub. 1, pp. 181-184, 2000. [2] O. Thomer, E. Krause, W. Schroder and M. Meinke , Computational

  6. Improved vortex reactor system

    DOEpatents

    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.

  7. Control of vortex dynamics

    NASA Astrophysics Data System (ADS)

    Chang, Hsiao-Lung

    Discrete vortex methods are used to provide computationally efficient simulations of vortex dynamics in fluid flows. An adaptive LQG controller is applied to reduce the oscillations in the wake caused by the vortex dynamics. The controller design is based on a discrete-time input/output model rather than the nonlinear differential equations of the discrete vortex model. The control philosophy is to identify time-varying parameters in the input/output model adaptively and use the identified parameters to update the control law. For numerically stable identification, an adaptive algorithm based on inverse QR decomposition is introduced. The derivation shows that this algorithm is a square-root implementation of recursive least squares estimation. For a preliminary test of the control strategy, the adaptive LQG controller is applied to a vortex street model simulated by discrete vortices. The identification shows that the stability of the identified zeros depends on whether the sensor is upstream or downstream of the actuator. Flow past a flat plate is another important application of the discrete vortex method. A control problem is studied and simulated in which suction at the back face of the plate is used to trap vortices behind the plate. Qualitatively, the results obtained with the discrete-vortex method used here agree with earlier results for a substantially different vortex method involving a small number of differential equations.

  8. Vortex diode jet

    DOEpatents

    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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Aerodynamics of vortex generators

    NASA Technical Reports Server (NTRS)

    Breidenthal, Robert E., Jr.; Russell, David A.

    1988-01-01

    An experimental and theoretical study was undertaken of the separation delay and dramatic boundary-layer thinning that can occur in vortex-generator installations. Wind tunnel measurements of the dynamic-pressure profile downstream of a vortex generator were found to compare under certain conditions with that downstream of a suction slit, while water-tunnel visualization studies of vortex-generator height and geometry suggested optimum configurations, and only a minor effect of base porosity. A series of progressively more complex inviscid flow models was developed to be applied to a 3-D integral boundary-layer code. This code predicted layer thinning downstream of the suction site of the vortex models, and other observed features. Thin-layer Navier-Stokes equations are now being used with the ultimate goal of clarifying the physical processes involved in vortex generator performance and developing calculational procedures capable of predicting it.

  14. Vortex cutting in superconductors

    SciTech Connect

    Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; Crabtree, G. W.

    2016-08-09

    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, in this paper, 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. Finally, our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.

  15. Vortex cutting in superconductors

    DOE PAGES

    Glatz, A.; Vlasko-Vlasov, V. K.; Kwok, W. K.; ...

    2016-08-09

    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, in this paper, 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 ofmore » the vortex-crossing scenario under practical situations with many interacting vortices in the presence of weak pinning. Finally, our simulations also reveal left-handed helical vortex instabilities that accompany the remagnetization process and participate in the vortex crossing events.« less

  16. Effect of potential barrier height on the carrier transport in InGaAs/GaAsP multi-quantum wells and photoelectric properties of laser diode.

    PubMed

    Dong, Hailiang; Sun, Jing; Ma, Shufang; Liang, Jian; Lu, Taiping; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

    2016-03-07

    The growth and strain-compensation behaviour of InGaAs/GaAsP multi-quantum wells, which were fabricated by metal-organic chemical vapor deposition, have been studied towards the application of these quantum wells in high-power laser diodes. The effect of the height of the potential barrier on the confined level of carrier transport was studied by incorporating different levels of phosphorus content into the GaAsP barrier. The crystal quality and interface roughness of the InGaAs/GaAsP multi-quantum wells with different phosphorus contents were evaluated by high resolution X-ray diffraction and in situ optical surface reflectivity measurements during the growth. The surface morphology and roughness were characterized by atomic force microscopy, which indicates the variation law of surface roughness, terrace width and uniformity with increasing phosphorus content, owing to strain accumulation. Moreover, the defect generation and structural disorder of the multi-quantum wells were investigated by Raman spectroscopy. The optical properties of the multi-quantum wells were characterized by photoluminescence, which shows that the spectral intensity increases as the phosphorus content increases. The results suggest that more electrons are well bound in InGaAs because of the high potential barrier. Finally, the mechanism of the effect of the height of the potential barrier on laser performance was proposed on the basis of simulation calculations and experimental results.

  17. High Speed Vortex Flows

    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.

  18. Vortex breakdown simulation

    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.

  19. Vortex crystals in fluids

    NASA Astrophysics Data System (ADS)

    Barry, Anna M.

    It is common in geophysical flows to observe localized regions of enhanced vorticity. This observation can be used to derive model equations to describe the motion and interaction of these localized regions, or vortices, and which are simpler than the original PDEs. The best known vortex model is derived from the incompressible Euler equations, and treats vortices as points in the plane. A large part of this dissertation utilizes this particular model, but we also survey other point vortex and weakly viscous models. The main focus of this thesis is an object known as the vortex crystal. These remarkable configurations of vortices maintain their basic shapes for long times, while perhaps rotating or translating rigidly in space. We study existence and stability of families of vortex crystals in the special case where N vortices have small and equal circulation and one vortex has large circulation. As the small circulation tends to zero, the weak vortices tend to a circle centered on the strong vortex. A special potential function of this limiting problem can be used to characterize orbits and stability. Whenever a critical point of this function is nondegenerate, we prove that the orbit can be continued via the Implicit Function Theorem, and its linear stability is determined by the eigenvalues of the Hessian matrix of the potential. For general N, we find at least three distinct families of critical points, one of which continues to a linearly stable class of vortex crystals. Because the stable family is most likely to be observed in nature, we study it extensively. Continuation methods allow us to follow these critical points to nonzero weak vortex strength and investigate stability and bifurcations. In the large N limit of this family, we prove that there is a unique one parameter family of distributions which minimize a "generalized" potential. Finally, we use point vortex and weakly viscous vortex models to analyze vortex crystal configurations observed in

  20. Wake Vortex Free Flight

    NASA Technical Reports Server (NTRS)

    1993-01-01

    A 10% scale B-737-100 model was tested in the vicinity of a vortex wake generated by a wing mounted on a support in the forward section of the NASA-Langley 30 x 60 ft. Wind Tunnel. The wing span, angle of attack, and generating wing location were varied to provide vortex strengths consistent with a large variety of combinations of leader-follower aircraft pairs during vortex encounters. The test, conducted as part of the AST Terminal Area Productivity Program, will provide data for validation of aerodynamic models which will be used for developing safe separate standards to apply to aircraft in terminal areas while increasing airport capacity.

  1. Vortex Lift Augmentation by Suction

    NASA Technical Reports Server (NTRS)

    Taylor, A. H.; Jackson, L. R.; Huffman, J. K.

    1983-01-01

    Lift performance is improved on a 60 degrees swept Gothic wing. Vortex lift at moderate to high angles of attack on highly swept wings used to improve takeoff performance and maneuverability. New design proposed in which suction of propulsion system augments vortex. Turbofan placed at down stream end of leading-edge vortex system induces vortex to flow into inlet which delays onset of vortex breakdown.

  2. Vortex Lift Augmentation by Suction

    NASA Technical Reports Server (NTRS)

    Taylor, A. H.; Jackson, L. R.; Huffman, J. K.

    1983-01-01

    Lift performance is improved on a 60 degrees swept Gothic wing. Vortex lift at moderate to high angles of attack on highly swept wings used to improve takeoff performance and maneuverability. New design proposed in which suction of propulsion system augments vortex. Turbofan placed at down stream end of leading-edge vortex system induces vortex to flow into inlet which delays onset of vortex breakdown.

  3. Magnetic vortex oscillators

    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.

  4. The singing vortex

    PubMed Central

    Arndt, R.; Pennings, P.; Bosschers, J.; van Terwisga, T.

    2015-01-01

    Marine propellers display several forms of cavitation. Of these, propeller-tip vortex cavitation is one of the important factors in propeller design. The dynamic behaviour of the tip vortex is responsible for hull vibration and noise. Thus, cavitation in the vortices trailing from tips of propeller blades has been studied extensively. Under certain circumstances cavitating vortices have been observed to have wave-like disturbances on the surfaces of vapour cores. Intense sound at discrete frequencies can result from a coupling between tip vortex disturbances and oscillating sheet cavitation on the surfaces of the propeller blades. This research article focuses on the dynamics of vortex cavitation and more in particular on the energy and frequency content of the radiated pressures. PMID:26442147

  5. Senkyo and Vortex

    NASA Image and Video Library

    2013-01-28

    NASA Cassini spacecraft simultaneously peers through the haze in Titan equatorial region down to its surface and captures the vortex of clouds hovering over its south pole just to the right of the terminator on the moon dark side.

  6. The singing vortex.

    PubMed

    Arndt, R; Pennings, P; Bosschers, J; van Terwisga, T

    2015-10-06

    Marine propellers display several forms of cavitation. Of these, propeller-tip vortex cavitation is one of the important factors in propeller design. The dynamic behaviour of the tip vortex is responsible for hull vibration and noise. Thus, cavitation in the vortices trailing from tips of propeller blades has been studied extensively. Under certain circumstances cavitating vortices have been observed to have wave-like disturbances on the surfaces of vapour cores. Intense sound at discrete frequencies can result from a coupling between tip vortex disturbances and oscillating sheet cavitation on the surfaces of the propeller blades. This research article focuses on the dynamics of vortex cavitation and more in particular on the energy and frequency content of the radiated pressures.

  7. Conformal Vortex Crystals.

    PubMed

    Menezes, Raí M; Silva, Clécio C de Souza

    2017-10-06

    We investigate theoretically globally nonuniform configurations of quantized-flux vortices in clean superconductors trapped by an external force field that induces a nonuniform vortex density profile. Using an extensive series of numerical simulations, we demonstrate that, for suitable choices of the force field, and bellow a certain transition temperature, the vortex system self-organizes into highly inhomogeneous conformal crystals in a way as to minimize the total energy. These nonuniform structures are topologically ordered and can be mathematically mapped into a triangular Abrikosov lattice via a conformal transformation. Above the crystallization temperature, the conformal vortex crystal becomes unstable and gives place to a nonuniform polycrystalline structure. We propose a simple method to engineer the potential energy profile necessary for the observation of conformal crystals of vortices, which can also be applied to other 2D particle systems, and suggest possible experiments in which conformal or quasi-conformal vortex crystals could be observed in bulk superconductors and in thin films.

  8. NASA wake vortex research

    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.

  9. Modeling gasodynamic vortex cooling

    NASA Astrophysics Data System (ADS)

    Allahverdyan, A. E.; Fauve, S.

    2017-08-01

    We aim at studying gasodynamic vortex cooling in an analytically solvable, thermodynamically consistent model that can explain limitations on the cooling efficiency. To this end, we study an angular plus radial flow between two (coaxial) rotating permeable cylinders. Full account is taken of compressibility, viscosity, and heat conductivity. For a weak inward radial flow the model qualitatively describes the vortex cooling effect, in terms of both temperature and the decrease of the stagnation enthalpy, seen in short uniflow vortex (Ranque) tubes. The cooling does not result from external work and its efficiency is defined as the ratio of the lowest temperature reached adiabatically (for the given pressure gradient) to the lowest temperature actually reached. We show that for the vortex cooling the efficiency is strictly smaller than 1, but in another configuration with an outward radial flow, we find that the efficiency can be larger than 1. This is related to both the geometry and the finite heat conductivity.

  10. Vortex flow hysteresis

    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.

  11. Improved vortex reactor system

    DOEpatents

    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.

  12. Wingtip vortex turbine

    NASA Technical Reports Server (NTRS)

    Patterson, James C., Jr. (Inventor)

    1990-01-01

    A means for extracting rotational energy from the vortex created at aircraft wing tips which consists of a turbine with blades located in the crossflow of the vortex and attached downstream of the wingtip. The turbine has blades attached to a core. When the aircraft is in motion, rotation of a core transmits energy to a centrally attached shaft. The rotational energy thus generated may be put to use within the airfoil or aircraft fuselage.

  13. 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.

  14. Dynamics of Giant Planet Polar Vortices

    NASA Astrophysics Data System (ADS)

    Brueshaber, Shawn R.; Sayanagi, Kunio M.

    2016-10-01

    The polar atmospheres of the giant planets have come under increasing interest since a compact, warm-core, stable, cyclonic polar vortex was discovered at each of Saturn's poles. In addition, the south pole of Neptune appears to have a similar feature, and Uranus' north pole is exhibiting activity that could indicate the formation of a polar vortex. We investigate the formation and maintenance of these giant planet polar vortices by varying several key atmospheric dynamics parameters in a forced-dissipative, 1.5-layer shallow water model. Our simulations are run using the EPIC (Explicit Planetary Isentropic Coordinate) global circulation model, to which we have added a gamma-plane rectangular grid option appropriate for simulating polar atmospheric dynamics.In our numerical simulations, we vary the atmospheric deformation radius, planetary rotation rate, storm forcing intensity, and storm vorticity (cyclone-to-anticyclone) ratio to determine what combination of values favors the formation of a polar vortex. We find that forcing the atmosphere by injecting small-scale mass perturbations ("storms") to form either all cyclones, all anticyclones, or equal numbers of both, may all result in a cyclonic polar vortex. Additionally, we examine the role of eddy momentum convergence in the intensification and maintenance of a polar cyclone.Our simulation results are applicable to understanding all four of the solar system giant planets. In the future, we plan to expand our modeling effort with a more realistic 3D primitive equations model, also with a gamma-plane rectangular grid using EPIC. With our 3D primitive equations model, we will study how various vertical atmospheric stratification structures influence the formation and maintenance of a polar cyclone. While our shallow-water model only involves storms of a single layer, a 3D primitive equations model allows us to study how storms of finite vertical extent and at differing levels in the atmosphere may further favor

  15. Atmospheric-wake vortex interactions

    NASA Technical Reports Server (NTRS)

    Bilanin, A. J.; Hirsh, J. E.; Teske, M. E.; Hecht, A. M.

    1978-01-01

    The interactions of a vortex wake with a turbulent stratified atmosphere are investigated with the computer code WAKE. It is shown that atmospheric shear, turbulence, and stratification can provide the dominant mechanisms by which vortex wakes decay. Computations included the interaction of a vortex wake with a viscous ground plane. The observed phenomenon of vortex bounce is explained in terms of secondary vorticity produced on the ground. This vorticity is swept off the ground and advected about the vortex pair, thereby altering the classic hyperbolic trajectory. The phenomenon of the solitary vortex is explained as an interaction of a vortex with crosswind shear. Here, the vortex having the sign opposite that of the sign of the vorticity in the shear is dispersed by a convective instability. This instability results in the rapid production of turbulence which in turn disperses the smoke marking the vortex.

  16. Carrier dynamics in Ga(NAsP)/Si multi-quantum well heterostructures with varying well thickness

    NASA Astrophysics Data System (ADS)

    Shakfa, M. K.; Woscholski, R.; Gies, S.; Wegele, T.; Wiemer, M.; Ludewig, P.; Jandieri, K.; Baranovskii, S. D.; Stolz, W.; Volz, K.; Heimbrodt, W.; Koch, M.

    2016-05-01

    Time-resolved photoluminescence (TR-PL) measurements have been performed in Ga(NAsP)/(BGa)(AsP) multi-quantum well heterostructures (MQWHs) with different well thicknesses. The studied structures have been pseudomorphically grown on Si substrates by metal organic vapor phase epitaxy (MOVPE) with an N content of about 7%. Experimental results reveal a shortening in the PL decay time with increasing QW thickness, meanwhile, accompanied by a decrease in the PL intensity. We attribute this behavior to an increasing non-radiative recombination rate for broader QWs which arises from an increasing number of defects in the QW material. The emission-energy distribution of the PL decay time is studied at various temperatures. The PL decay time strongly depends on the emission energy at low temperatures and becomes emission-energy-independent close to room temperature. This is discussed in terms of the carrier localization in the studied structures.

  17. Discrepancies between photocurrent and absorption spectroscopies in intersubband photoionization from GaAs/AlGaAs multiquantum wells

    NASA Astrophysics Data System (ADS)

    Rosencher, E.; Martinet, E.; Luc, F.; Bois, Ph.; Böckenhoff, E.

    1991-12-01

    Intersubband transitions between a bound state and extended states in GaAs/AlGaAs multiquantum wells are studied by simultaneous absorption and photocurrent spectroscopy under different electric field conditions. It is found that both types of spectra exhibit different line shapes, with the photocurrent maximum occurring at lower photon energy than in absorption spectra. Moreover, there is a blue shift of absorption peak and a red shift of photocurrent peak with increasing electric fields. These results suggest that a sequential mechanism is involved in the photocurrent collection from the quantum well. The blue shift is then well fitted by a quadratic Stark effect and the red shift by a barrier lowering mechanism.

  18. Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

    SciTech Connect

    Mohanta, Antaryami; Wang, Shiang-Fu; Jang, Der-Jun; Young, Tai-Fa; Yeh, Ping-Hung; Ling, Dah-Chin; Lee, Meng-En

    2015-04-14

    Green emitting InGaN/GaN multi-quantum well samples were investigated using transmission electron microscopy, photoluminescence (PL), and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ∼12 meV due to an inhomogeneous distribution of In in the InGaN quantum (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τ{sub r}, extracted from the TRPL profile shows ∼T{sup 3/2} dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.

  19. Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

    NASA Astrophysics Data System (ADS)

    Chao, Wen-Ching; Mohanta, Antaryami; Yen, Tsu-Chiang; Chen, Wei-Sheng; Jang, Der-Jun

    Green emitting InGaN/GaN multi-quantum well samples were investigated using photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ~12 meV due to an inhomogeneous distribution of In in the InGaN quantum well (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum (FWHM) of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τr, extracted from the TRPL profile shows ~T 3 / 2 dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.

  20. Observation of weak carrier localization in green emitting InGaN/GaN multi-quantum well structure

    NASA Astrophysics Data System (ADS)

    Mohanta, Antaryami; Wang, Shiang-Fu; Young, Tai-Fa; Yeh, Ping-Hung; Ling, Dah-Chin; Lee, Meng-En; Jang, Der-Jun

    2015-04-01

    Green emitting InGaN/GaN multi-quantum well samples were investigated using transmission electron microscopy, photoluminescence (PL), and time-resolved photoluminescence (TRPL) spectroscopy. Weak carrier localization with characteristic energy of ˜12 meV due to an inhomogeneous distribution of In in the InGaN quantum (QW) layer is observed. The temperature dependence of the PL peak energy exhibits S-shape phenomenon and is comparatively discussed within the framework of the Varshni's empirical formula. The full width at half maximum of the PL emission band shows an increasing-decreasing-increasing behavior with increasing temperature arising from the localized states caused by potential fluctuations. The radiative life time, τr, extracted from the TRPL profile shows ˜T3/2 dependence on temperature above 200 K, which confirms the absence of the effect of carrier localization at room temperature.

  1. Spectral linewidth and resonant frequency characteristics of InGaAsP/InP multiquantum well lasers

    SciTech Connect

    Sasai, Y.; Ohya, J.; Ogura, M.

    1989-04-01

    The spectral linewidth and resonant frequency characteristics of 1.3 ..mu..m InGaAsP/InP multiquantum well (MQW) lasers grown by liquid phase epitaxy (LPE) were investigated, compared to those of the conventional double heterostructure (DH) lasers. The result showed a decrease in spectral linewidth and an increase in resonant frequency f/sub r/ with decreasing well thickness. Moreover, it was recognized that the linewidth enhancement factor became smaller in well thicknesses of less than -- 200 A, namely, the factor ..cap alpha.. reduced to -- 2, while that of the DH laser was -- 6. The f/sub r/ of 9 GHz, which is about twice as large as that of conventional DH lasers, was achieved at an optical power of 5.3 mW/facet.

  2. Room temperature mid-infrared InAsSbN multi-quantum well photodiodes grown by MBE

    NASA Astrophysics Data System (ADS)

    Kesaria, M.; de la Mare, M.; Krier, A.

    2016-11-01

    Room temperature photoresponse in the mid-infrared spectral region is demonstrated from InAsSbN/InAs multi-quantum well photodiodes grown by nitrogen plasma assisted molecular beam epitaxy. The structural quality of the InAsSbN MQWs was ascertained in situ by reflection high energy electron diffraction and ex situ by high resolution x-ray diffraction and photoluminescence measurements. The extended long wavelength photoresponse is identified to originate from the electron-heavy hole (e1-hh1) and electron-light hole (e1-lh1) transitions in the InAsSbN MQW, with a cut off wavelength ~4.20 µm and peak detectivity D *  =  1.25  ×  109 cm Hz1/2 W-1.

  3. Dark current and optical properties in asymmetric GaAs/AlGaAs staircase-like multiquantum well structure

    NASA Astrophysics Data System (ADS)

    Altin, E.; Hostut, M.; Ergun, Y.

    2013-05-01

    In this study, we investigate dark current voltage characteristics of GaAs/AlGaAs staircase-like asymmetric multiquantum well structure at various temperatures experimentally. Measured dark current density-voltage (Jd-V) characteristics are compared with the Levine Model. It is seen that the model fits well with the experimental dark current density. Ground state energy of electrons, heavy holes and light holes are calculated by Kronig-Penney Model. Optical properties of sample are characterized by photoluminescence and photoconductivity measurements. The temperature-dependent photoluminescence (PL) spectra of the GaAs/GaAlAs QWIP show that the peaks corresponding interband transition from the ground heavy-hole subband to the ground electronic subband (Ehh1 - Ee1) are dominantly observed and the peak positions corresponding to the interband transitions of the PL spectrum are dependent on the temperature. Photoconductivity measurement is performed for different negative polarities at 37 K.

  4. Stress influenced trapping processes in Si based multi-quantum well structures and heavy ions implanted Si

    SciTech Connect

    Ciurea, Magdalena Lidia Lazanu, Sorina

    2014-10-06

    Multi-quantum well structures and Si wafers implanted with heavy iodine and bismuth ions are studied in order to evaluate the influence of stress on the parameters of trapping centers. The experimental method of thermostimullatedcurrents without applied bias is used, and the trapping centers are filled by illumination. By modeling the discharge curves, we found in multilayered structures the parameters of both 'normal' traps and 'stress-induced' ones, the last having a Gaussian-shaped temperature dependence of the cross section. The stress field due to the presence of stopped heavy ions implanted into Si was modeled by a permanent electric field. The increase of the strain from the neighborhood of I ions to the neighborhood of Bi ions produces the broadening of some energy levels and also a temperature dependence of the cross sections for all levels.

  5. Controlling vortex motion and vortex kinetic friction

    NASA Astrophysics Data System (ADS)

    Nori, Franco; Savel'ev, Sergey

    2006-05-01

    We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.

  6. Strained multiquantum-well corrugation-pitch-modulated distributed feedback laser with ultranarrow (3.6kHz) spectral linewidth

    NASA Astrophysics Data System (ADS)

    Okai, M.; Suzuki, M.; Taniwatari, T.

    1993-09-01

    Introducing a 1% compressive strained multiquantum-well (MQW) active layer into a corrugation-pitch-modulated distributed feedback (CPM-DFB) laser reduces the linewidth floor (residual linewidth for extrapolated infinite output power) to 2 kHz and results in a linewidth-power product of 140 kHz mW. Strained MQW CPM-DFB lasers produced a 55 mW output with a spectral linewidth of only 3.6 kHz.

  7. Vortex Characterization for Engineering Applications

    SciTech Connect

    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.

  8. 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.

  9. Vortex attenuation flight experiments

    NASA Technical Reports Server (NTRS)

    Barber, M. R.; Hastings, E. C., Jr.; Champine, R. A.; Tymczyszyn, J. J.

    1977-01-01

    Flight tests evaluating the effects of altered span loading, turbulence ingestion, combinations of mass and turbulence ingestion, and combinations of altered span loading turbulance ingestion on trailed wake vortex attenuation were conducted. Span loadings were altered in flight by varying the deflections of the inboard and outboard flaps on a B-747 aircraft. Turbulence ingestion was achieved in flight by mounting splines on a C-54G aircraft. Mass and turbulence ingestion was achieved in flight by varying the thrust on the B-747 aircraft. Combinations of altered span loading and turbulence ingestion were achieved in flight by installing a spoiler on a CV-990 aircraft and by deflecting the existing spoilers on a B-747 aircraft. The characteristics of the attenuated and unattenuated vortexes were determined by probing them with smaller aircraft. Acceptable separation distances for encounters with the attenuated and unattenuated vortexes are presented.

  10. Magnetic vortex racetrack memory

    NASA Astrophysics Data System (ADS)

    Geng, Liwei D.; Jin, Yongmei M.

    2017-02-01

    We report a new type of racetrack memory based on current-controlled movement of magnetic vortices in magnetic nanowires with rectangular cross-section and weak perpendicular anisotropy. Data are stored through the core polarity of vortices and each vortex carries a data bit. Besides high density, non-volatility, fast data access, and low power as offered by domain wall racetrack memory, magnetic vortex racetrack memory has additional advantages of no need for constrictions to define data bits, changeable information density, adjustable current magnitude for data propagation, and versatile means of ultrafast vortex core switching. By using micromagnetic simulations, current-controlled motion of magnetic vortices in cobalt nanowire is demonstrated for racetrack memory applications.

  11. The effects of noradrenaline on the amplitude-time characteristics of multiquantum endplate currents and the kinetics of induced secretion of transmitter quanta.

    PubMed

    Bukharaeva, E A; Gainulov, R Kh; Nikol'skii, E E

    2002-01-01

    Experiments on frog neuromuscular junctions using a two-electrode membrane potential clamping method were used to study the effects of noradrenaline on the amplitude-time characteristics of multiquantum endplate current (EPC) parameters and the time course of secretion of transmitter quanta during the process of EPC generation. Noradrenaline (10 microM) induced significant increases in EPC amplitude (by 16%), with a decrease in the ratio of the duration of the leading front of the EPC to the duration of the leading front of the miniature endplate current (mEPC). Analysis of the time course of induced secretion, based on sequential subtraction of signals with displacement on the time scale, showed that noradrenaline induced synchronization of the process of secretion of quanta involved in generating multiquantum EPC, resulting in a 25% decrease in parameter P90, which characterizes the extent of synchronization of quantum release. The quantum composition of EPC, measured by dividing the area of induced and spontaneous signals and by analysis of the time course of the secretion of quanta, showed no changes in response to noradrenaline. Thus, in conditions in which responses to single stimuli applied to the motor nerve results in the release of several tens of quanta, noradrenaline can lead to increases in the amplitude of multiquantum EPC by increasing the level of synchronization of secretion of the transmitter quanta forming this signal.

  12. Electric vortex in MHD flow

    SciTech Connect

    Garcia, M.

    1995-05-01

    An electric vortex is the circulation of electron space charge about a magnetic field line that is transported by ion momentum. In cold, or low {beta} flow the vortex diameter is the minimum length scale of charge neutrality. The distinctive feature of the vortex is its radial electric field which manifests the interplay of electrostatics, magnetism, and motion.

  13. Asymmetric Gaussian optical vortex.

    PubMed

    Kotlyar, Victor V; Kovalev, Alexey A; Porfirev, Alexey P

    2017-01-01

    We theoretically study a Gaussian optical beam with an embedded off-axis optical vortex. We also experimentally generate such an asymmetric Gaussian optical vortex by using an off-axis spiral phase plate. It is shown that depending on the shift distance the laser beam has the form of a crescent, which is rotated upon propagation. An analytical expression is obtained for the orbital angular momentum of such a beam, which appears to be fractional. When the shift increases, the greater the number of spirality of the phase plate or the "fork" hologram, the slower the momentum decreases. The experimental results are in qualitative agreement with the theory.

  14. Entangled transverse optical vortex.

    PubMed

    Chui, S T; Lin, Zhifang

    2014-10-01

    We discuss a new kind of optical vortex with the angular momentum perpendicular to the flow direction and entangled in that it is a coherent combination of different orbital angular momentum states of the same sign. This entangled state exhibits many unexpected physical properties. The transverse optical vortex can be generated from the reflection of an electromagnetic wave off an array of ferrite rods. Its vorticity can be reversed by switching the direction of the magnetization of the rods, which usually takes only a nanosecond.

  15. Vortex pairs on surfaces

    SciTech Connect

    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.

  16. Wake Vortex Minimization

    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.

  17. Quasi-steady vortices in protoplanetary disks. I. From dwarfs to giants

    NASA Astrophysics Data System (ADS)

    Surville, Clément; Barge, Pierre

    2015-07-01

    Aims: We determine the size, structure, and evolution of persistent vortices in 2D and inviscid Keplerian flows. Methods: A Gaussian model of the vortices is built and compared with numerical solutions issued from non-linear hydrodynamical simulations. Test vortices are also produced using a fiducial method based on the Rossby wave instability to help explore the vortex parameters. Numerical simulations are performed using a second order finite volume method. We assume a perfect-gas law and a non-homentropic adiabatic flow. Results: The new model nicely fits the numerical vortex solution. In the vortex centre it is consistent with existing models, whereas in the outer regions it enables the vortex to be connected with the background flow. Two families of vortices can be distinguished following the importance of the compressional effects. The model also permitted a new class of vortices to be discovered corresponding to huge perturbations of pressure and density and whose radial sizes are significantly larger than the disk scale height, in contrast with the standard way to define the maximum vortex size. Conclusions: Our Gaussian model of the vortex solutions of the 2D Euler's equations is a useful tool for studying vortex properties. Among the large number of vortex solutions, the possible existence of giant vortices could open interesting perspectives in planetary formation, particularly during the building stage of the giant gas planets.

  18. 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.

  19. Experimental study of vortex diffusers

    SciTech Connect

    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.

  20. Double-branched vortex generator

    NASA Technical Reports Server (NTRS)

    Cantwell, E. R.; Westphal, R. V.; Mehta, R. D.

    1985-01-01

    In order to assess the suitability of using a double branched vortex generator in parametric studies involving vortex interactions, an experimental study of the main vortex and secondary flows produced by a double branched vortex generator was conducted in a 20-by-40 cm indraft wind tunnel. Measurements of the cross flow velocities were made with a five hole pressure probe from which vorticity contours and vortex parameters were derived. The results showed that the optimum configuration consisted of chord extensions with the absence of a centerbody.

  1. Vortex breakdown theories

    NASA Astrophysics Data System (ADS)

    Escudier, M. P.

    Instability, stagnation, and wave phenomena in vortex breakdown are reviewed. Axisymmetric disturbances; spiral disturbances; nonlinear interactions; the separation analogy; failure of slender core/quasi-cylindrical approximation; numerical failure; solitary waves; inertia waves; transition between conjugate-flow states; and the shock/hydraulic-jump analogy are discussed.

  2. Micro Vortex Generators

    NASA Technical Reports Server (NTRS)

    2000-01-01

    An in house video made to show how NASA Langley scientists have found ways to improve airplane performance. Micro Vortex Generators placed on airplane wings can reduce drag, increase lift, and reduce fuel consumption. Nice animation and real footage of planes with this technology.

  3. Behavior of Vortex Systems

    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.

  4. Viscous vortex flows

    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.

  5. 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…

  6. 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…

  7. 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.

  8. Passive Wake Vortex Control

    SciTech Connect

    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

  9. Titan's Winter Polar Vortex

    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

  10. 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.

  11. Giant Magnons Meet Giant Gravitons

    SciTech Connect

    Hofman, Diego M.

    2008-07-28

    We study the worldsheet reflection matrix of a string attached to a D-brane in AdS{sub 5}xS{sup 5}. The D-brane corresponds to a maximal giant graviton that wraps an S{sup 3} inside S{sup 5}. In the gauge theory, the open string is described by a spin chain with boundaries. We focus on open strings with a large SO(6) charge and define an asymptotic boundary reflection matrix. Using the symmetries of the problem, we review the computation of the boundary reflection matrix, up to a phase. We also discuss weak and strong coupling computations where we obtain the overall phase factor and test our exact results.

  12. Enhanced giant magnetoimpedance in heterogeneous nanobrush

    PubMed Central

    2012-01-01

    A highly sensitive and large working range giant magnetoimpedance (GMI) effect is found in the novel nanostructure: nanobrush. The nanostructure is composed of a soft magnetic nanofilm and a nanowire array, respectively fabricated by RF magnetron sputtering and electrochemical deposition. The optimal GMI ratio of nanobrush is promoted to more than 250%, higher than the pure FeNi film and some sandwich structures at low frequency. The design of this structure is based on the vortex distribution of magnetic moments in thin film, and it can be induced by the exchange coupling effect between the interfaces of nanobrush. PMID:22963551

  13. Enhanced giant magnetoimpedance in heterogeneous nanobrush

    NASA Astrophysics Data System (ADS)

    Zhang, Yi; Mu, Congpu; Luo, Caiqin; Dong, Juan; Liu, Qingfang; Wang, Jianbo

    2012-09-01

    A highly sensitive and large working range giant magnetoimpedance (GMI) effect is found in the novel nanostructure: nanobrush. The nanostructure is composed of a soft magnetic nanofilm and a nanowire array, respectively fabricated by RF magnetron sputtering and electrochemical deposition. The optimal GMI ratio of nanobrush is promoted to more than 250%, higher than the pure FeNi film and some sandwich structures at low frequency. The design of this structure is based on the vortex distribution of magnetic moments in thin film, and it can be induced by the exchange coupling effect between the interfaces of nanobrush.

  14. Enhanced giant magnetoimpedance in heterogeneous nanobrush.

    PubMed

    Zhang, Yi; Mu, Congpu; Luo, Caiqin; Dong, Juan; Liu, Qingfang; Wang, Jianbo

    2012-09-10

    A highly sensitive and large working range giant magnetoimpedance (GMI) effect is found in the novel nanostructure: nanobrush. The nanostructure is composed of a soft magnetic nanofilm and a nanowire array, respectively fabricated by RF magnetron sputtering and electrochemical deposition. The optimal GMI ratio of nanobrush is promoted to more than 250%, higher than the pure FeNi film and some sandwich structures at low frequency. The design of this structure is based on the vortex distribution of magnetic moments in thin film, and it can be induced by the exchange coupling effect between the interfaces of nanobrush.

  15. The shock-vortex interaction patterns affected by vortex flow regime and vortex models

    NASA Astrophysics Data System (ADS)

    Chang, Keun-Shik; Barik, Hrushikesh; Chang, Se-Myong

    2009-08-01

    We have used a third-order essentially non-oscillatory method to obtain numerical shadowgraphs for investigation of shock-vortex interaction patterns. To search different interaction patterns, we have tested two vortex models (the composite vortex model and the Taylor vortex model) and as many as 47 parametric data sets. By shock-vortex interaction, the impinging shock is deformed to a S-shape with leading and lagging parts of the shock. The vortex flow is locally accelerated by the leading shock and locally decelerated by the lagging shock, having a severely elongated vortex core with two vertices. When the leading shock escapes the vortex, implosion effect creates a high pressure in the vertex area where the flow had been most expanded. This compressed region spreads in time with two frontal waves, an induced expansion wave and an induced compression wave. They are subsonic waves when the shock-vortex interaction is weak but become supersonic waves for strong interactions. Under a intermediate interaction, however, an induced shock wave is first developed where flow speed is supersonic but is dissipated where the incoming flow is subsonic. We have identified three different interaction patterns that depend on the vortex flow regime characterized by the shock-vortex interaction.

  16. Vortex lenses for optical micromanipulation

    NASA Astrophysics Data System (ADS)

    Skidanov, Roman V.; Ganchevskaya, Sofiya V.

    2017-04-01

    Vortex beams are currently used in areas such as optical communication, optical measurement optical micromanipulation and many other applications. There are several prospective ways to generate vortex beams such as: by using special gratings [1,2], spiral phase plates[3], vortex zone plate [4]. Bessel and Gauss-Laguerre beams [5,6] are also considered as Vortex beams. Generation of Bessel beams by vortex axicons were considered in [6]. Possibility of combining the structures and zones topological charge of axicon in the same element was shown. Desired order of Bessel beams can be generated by a large variability of phase diffractive optical elements. In [7] method of forming a simple vortex beams by using a new type of diffractive optical elements, was presented. Diffractive optical element is a lens vortex with a topological charge zones, like the vortex in axicon [8]. In this paper, we have generated vortex beams by the method described in [7], but in addition the lens partitioned into two areas. Each area has different focal length. The proposed element structure can significantly extend focal region with the generated vortex beam that allows rotating microscopic objects in the threedimensional layer.

  17. Vortex unwinding in a turbulent boundary layer

    NASA Technical Reports Server (NTRS)

    Mcginley, Catherine B.; Beeler, George B.

    1987-01-01

    The vortex unwinding method is used as a tool in performing vortex cancellation in a turbulent boundary layer. Sufficient reduction in the isotach variation was achieved to verify the usefulness of this technique, for the cases of both wall turbulence control and horseshoe vortex alleviation. More detailed measurements of vortex strength and position improve the optimization process and increase the amount of vortex unwinding.

  18. Enhanced Light Emission due to Formation of Semi-polar InGaN/GaN Multi-quantum Wells.

    PubMed

    Zhao, Wan-Ru; Weng, Guo-En; Wang, Jian-Yu; Zhang, Jiang-Yong; Liang, Hong-Wei; Sekiguchi, Takashi; Zhang, Bao-Ping

    2015-12-01

    InGaN/GaN multi-quantum wells (MQWs) are grown on (0001) sapphire substrates by metal organic chemical vapor deposition (MOCVD) with special growth parameters to form V-shaped pits simultaneously. Measurements by atomic force microscopy (AFM) and transmission electron microscopy (TEM) demonstrate the formation of MQWs on both (0001) and ([Formula: see text]) side surface of the V-shaped pits. The latter is known to be a semi-polar surface. Optical characterizations together with theoretical calculation enable us to identify the optical transitions from these MQWs. The layer thickness on ([Formula: see text]) surface is smaller than that on (0001) surface, and the energy level in the ([Formula: see text]) semi-polar quantum well (QW) is higher than in the (0001) QW. As the sample temperature is increased from 15 K, the integrated cathodoluminescence (CL) intensity of (0001) MQWs increases first and then decreases while that of the ([Formula: see text]) MQWs decreases monotonically. The integrated photoluminescence (PL) intensity of (0001) MQWs increases significantly from 15 to 70 K. These results are explained by carrier injection from ([Formula: see text]) to (0001) MQWs due to thermal excitation. It is therefore concluded that the emission efficiency of (0001) MQWs at high temperatures can be greatly improved due to the formation of semi-polar MQWs.

  19. Controlled manipulation of elastomers with radiation: Insights from multiquantum nuclear-magnetic-resonance data and mechanical measurements

    SciTech Connect

    Maiti, A.; Weisgraber, T.; Dinh, L. N.; Gee, R. H.; Wilson, T.; Chinn, S.; Maxwell, R. S.

    2011-03-15

    Filled and cross-linked elastomeric rubbers are versatile network materials with a multitude of applications ranging from artificial organs and biomedical devices to cushions, coatings, adhesives, interconnects, and seismic-isolation, thermal, and electrical barriers. External factors such as mechanical stress, temperature fluctuations, or radiation are known to create chemical changes in such materials that can directly affect the molecular weight distribution (MWD) of the polymer between cross-links and alter the structural and mechanical properties. From a materials science point of view it is highly desirable to understand, affect, and manipulate such property changes in a controlled manner. Unfortunately, that has not yet been possible due to the lack of experimental characterization of such networks under controlled environments. In this work we expose a known rubber material to controlled dosages of {gamma} radiation and utilize a newly developed multiquantum nuclear-magnetic-resonance technique to characterize the MWD as a function of radiation. We show that such data along with mechanical stress-strain measurements are amenable to accurate analysis by simple network models and yield important insights into radiation-induced molecular-level processes.

  20. Modeling of Metal-Insulator-Semiconductor Dualband Si/SiO2 Multi-Quantum Well UV Detectors

    NASA Astrophysics Data System (ADS)

    Rostami, A.; Leilaeioun, M.; Golmohammadi, S.; Rasooli Saghai, H.

    2012-11-01

    This article intends to propose a self-consistent theoretical model for Metal-Insulator-Semiconductor (MIS) dualband Si/SiO2 multi-quantum well (MQW) UV photodetector. Employing this model, general characteristics of MIS UV photodetectors such as dark and photocurrent density-voltage (J-V) curves are simulated. The results reveal that the proposed structure reduces dark current since first the resonant tunneling multi-barrier is designed such that the electron tunneling probability is unity at energies coincident with the peak detection wavelength, and secondly, tunneling significantly decreases at energies which are smaller than this optimum value and accordingly, transport of carriers contributing to the dark current, which have broad energy distribution at high temperatures, is inhibited. Moreover, the article demonstrates that the proposed structure can detect two individual x wavelengths in the UV range, simultaneously. The related absorption and responsivity curves are obtained and depicted. Defects in the SiO2 barriers are simulated indirectly by varying the electron effective tunneling mass in SiO2. Reductions in the SiO2 electron effective tunneling mass lead to an increase in dark current of the device.

  1. Dilute nitride multi-quantum well multi-junction design: a route to ultra-efficient photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Vijaya, Gopi Krishna; Alemu, Andenet; Freundlich, Alex

    2011-02-01

    The current high-efficiency triple junction (Al)InGaP (1.9eV)/GaAs(1.42eV)/ Ge(0.66eV) design for a solar cell can be improved upon by the use dilute nitrides to include a sub-cell in the 1eV range. Addition of a small percentage of nitrogen to III-V semiconductor alloys (such as GaAsN) enables us to achieve the required bandgap, however these bulk dilute nitride structures suffer from a reduced minority carrier lifetime, decreasing the overall current output. The route suggested herein is to include dilute nitride multi-quantum wells (with thicknesses much lesser than the minority carrier diffusion length) within the intrinsic region of a GaAs subcell. Modeling has been done for this structure to obtain the confined energies of the electrons and holes, as well as the absorption coefficient and thereby the spectral response of the 4-junction cell. The results show that it is possible to achieve with the appropriate current matching, a conversion efficiency of ~40% under AM0 (1 sun) with up to ~18 mAcm-2 short circuit current.

  2. 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.

  3. Slowing of Vortex Rings

    NASA Astrophysics Data System (ADS)

    Donnelly, Russell; Bolster, Diogo; Hershberger, Robert

    2008-11-01

    We have investigated the slowing of vortex rings in water which are created with very thin cores. We find that these rings propagate with no measurable change in diameter or core size. The drag appears to be the result of viscous forces on the core. A simple model for this drag describes experimental data in terms of a drag coefficient, which depends only on Reynolds number. Barenghi's group at Newcastle found that the translational velocity of a ring in an inviscid fluid perturbed by Kelvin waves decreases with increasing amplitude of Kelvin waves. This suggests that the velocity of vortex rings in a viscous fluid may well depend on the amplitude of Kelvin waves at the time of formation. Rings with substantial amplitude of Kelvin waves will be expected to move more slowly than rings with little or no Kelvin wave amplitude. We present experimental data confirming this suggestion.

  4. Vortex perturbation dynamics

    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.

  5. Two new vortex liquids

    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.

  6. Vortex flow aerodynamics

    NASA Technical Reports Server (NTRS)

    Smith, J. H. B.; Campbell, J. F.; Young, A. D. (Editor)

    1992-01-01

    The principal emphasis of the meeting was to be on the understanding and prediction of separation-induced vortex flows and their effects on vehicle performance, stability, control, and structural design loads. This report shows that a substantial amount of the papers covering this area were received from a wide range of countries, together with an attendance that was even more diverse. In itself, this testifies to the current interest in the subject and to the appropriateness of the Panel's choice of topic and approach. An attempt is made to summarize each paper delivered, and to relate the contributions made in the papers and in the discussions to some of the important aspects of vortex flow aerodynamics. This reveals significant progress and important clarifications, but also brings out remaining weaknesses in predictive capability and gaps in understanding. Where possible, conclusions are drawn and areas of continuing concern are identified.

  7. Polar vortex dynamics

    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.

  8. Vortex flow aerodynamics

    NASA Technical Reports Server (NTRS)

    Smith, J. H. B.; Campbell, J. F.; Young, A. D. (Editor)

    1992-01-01

    The principal emphasis of the meeting was to be on the understanding and prediction of separation-induced vortex flows and their effects on vehicle performance, stability, control, and structural design loads. This report shows that a substantial amount of the papers covering this area were received from a wide range of countries, together with an attendance that was even more diverse. In itself, this testifies to the current interest in the subject and to the appropriateness of the Panel's choice of topic and approach. An attempt is made to summarize each paper delivered, and to relate the contributions made in the papers and in the discussions to some of the important aspects of vortex flow aerodynamics. This reveals significant progress and important clarifications, but also brings out remaining weaknesses in predictive capability and gaps in understanding. Where possible, conclusions are drawn and areas of continuing concern are identified.

  9. Disrupted states of vortex flow and vortex breakdown

    NASA Technical Reports Server (NTRS)

    Faler, J. H.; Leibovich, S.

    1977-01-01

    Flow visualization studies and laser Doppler anemometer measurements on swirling water flows reveal six distinct types of very large amplitude disturbance modes of the vortex core. Three, 'axisymmetric' and spiral vortex breakdowns, and the 'double helix,' have been described by others. A definite order of evolution in parameter space (Reynolds number and circulations) occurs, and is described. Puzzling responses of the axisymmetric and spiral vortex breakdowns to imposed flow transients reported previously are confirmed here, and are traced to the shedding of starting and stopping vortices from swirl vanes. Conclusions bearing upon the validity of some theories of vortex breakdown are possible from the data.

  10. Transforming giants.

    PubMed

    Kanter, Rosabeth Moss

    2008-01-01

    Large corporations have long been seen as lumbering, inflexible, bureaucratic--and clueless about global developments. But recently some multinationals seem to be transforming themselves: They're engaging employees, moving quickly, and introducing innovations that show true connection with the world. Harvard Business School's Kanter ventured with a research team inside a dozen global giants--including IBM, Procter & Gamble, Omron, CEMEX, Cisco, and Banco Real--to discover what has been driving the change. After conducting more than 350 interviews on five continents, she and her colleagues came away with a strong sense that we are witnessing the dawn of a new model of corporate power: The coordination of actions and decisions on the front lines now appears to stem from widely shared values and a sturdy platform of common processes and technology, not from top-down decrees. In particular, the values that engage the passions of far-flung workforces stress openness, inclusion, and making the world a better place. Through this shift in what might be called their guidance systems, the companies have become as creative and nimble as much smaller ones, even while taking on social and environmental challenges of a scale that only large enterprises could attempt. IBM, for instance, has created a nonprofit partnership, World Community Grid, through which any organization or individual can donate unused computing power to research projects and see what is being done with the donation in real time. IBM has gained an inspiring showcase for its new technology, helped business partners connect with the company in a positive way, and offered individuals all over the globe the chance to contribute to something big.

  11. Trailing Vortex Attenuation Devices.

    DTIC Science & Technology

    1985-06-01

    hEEEE mhE|hElhEEEEEE EEEEEEEIIEIIEI Ell-EEllE.-lE .- EhEE//EEEEEE iEEEEEEEEEEEEE I. 1&0 Il 2-0N -v. ~MICROCOPY RESOLUTION TEST CHART NATIONAL OUREAU) OF... Panton , R.I., Cberkampf, W.L., and Soskic, N., "Flight Measurements of a Wingtip Vortex " Journal of Aircraft, vol. 17, pp. 250-259, April 1980.- 20

  12. Simulations of vortex generators

    NASA Technical Reports Server (NTRS)

    Koumoutsakos, P.

    1995-01-01

    We are interested in the study, via direct numerical simulations, of active vortex generators. Vortex generators may be used to modify the inner part of the boundary layer or to control separation thus enhancing the performance and maneuverability of aerodynamic configurations. We consider generators that consist of a surface cavity elongated in the stream direction and partially covered with a moving lid that at rest lies flush with the boundary. Streamwise vorticity is generated and ejected due to the oscillatory motion of the lid. The present simulations complement relevant experimental investigations of active vortex generators at NASA Ames and Stanford University (Saddoughi, 1994, and Jacobson and Reynolds, 1993). Jacobson and Reynolds (1993) used a piezoelectric device in water, allowing for small amplitude high frequency oscillations. They placed the lid asymmetrically on the cavity and observed a strong outward velocity at the small gap of the cavity. Saddoughi used a larger mechanically driven device in air to investigate this flow and he observed a jet emerging from the wide gap of the configuration, contrary to the findings of Jacobson and Reynolds. Our task is to simulate the flows generated by these devices and to conduct a parametric study that would help us elucidate the physical mechanisms present in the flow. Conventional computational schemes encounter difficulties when simulating flows around complex configurations undergoing arbitrary motions. Here we present a formulation that achieves this task on a purely Lagrangian frame by extending the formulation presented by Koumoutsakos, Leonard and Pepin (1994). The viscous effects are taken into account by modifying the strength of the particles, whereas fast multipole schemes employing hundreds of thousands of particles allow for high resolution simulations. The results of the present simulations would help us assess some of the effects of three-dimensionality in experiments and investigate the role

  13. Geostrophic Vortex Dynamics

    DTIC Science & Technology

    1988-10-01

    been made in the study of the two-dimensional incompressible vorticity fields. Not only have new and powerful techniques been developed, but a whole new...it deserves a thorough investigation by itself. More fundamentally, however, the techniques that we intend to use are not well suited to handle such...been exposed to a great wealth of techniques and results for the vortex dynamics of the Euler equations in two dimensions, we are now confronted with

  14. Formation of vortex dipoles

    NASA Astrophysics Data System (ADS)

    Afanasyev, Y. D.

    2006-03-01

    Evolution of a two-dimensional flow induced by a jet ejected from a nozzle of finite size is studied experimentally. Vortex dipole forms at the front of the developing flow while a trailing jet establishes behind the dipole. The dynamics of the flow is discussed on the basis of detailed measurements of vorticity and velocity fields which are obtained using particle image velocimetry. It is found that dipoles do not separate (pinch-off) from the trailing jet for values of the stroke ratio up to 15, which fact can be contrasted with the behavior of vortex rings reported previously by other authors. A characteristic time scale that is defined differently from the formation time of vortex rings can be introduced. This time scale (startup time) indicates the moment when the dipole starts translating after an initial period when it mainly grows absorbing the jet from the nozzle. A simple model that considers the competing effects of expansion and translation is developed to obtain an estimate of the dimensionless startup time. The dynamics of a dipole after the formation is characterized by a reduced flux of vorticity from the jet. The dipole moves forward with constant speed such that a value of the ratio of the speed of propagation of the dipole to the mean velocity of the jet is found to be 0.5. A universality of this ratio is explained in the framework of a model based on conservation of mass and momentum for the moving dipole.

  15. Control of vortex breakdown

    NASA Astrophysics Data System (ADS)

    Husain, H.; Shtern, F.; Hussain, V.

    1996-11-01

    The paper develops means of vortex breakdown (VB) control with the help of Controlling Vortex Generators (CVGs). Vortex breakdown plays the crucial role in many practical swirling flows, e.g. (a) leading-edge vortices above delta wings create a strong lift and (b) trailing vortices behind large aircraft disturbances are potentially dangerous to subsequent aircraft. It is useful to prevent VB in case (a) and to stimulate VB in case (b). We have recently obtained significant theoretical and experimental results related to swirling flow prediction and control. Firstly, a theory has been developed which models jump transitions in swirling flow (e.g. jumps in VB locations) and predicts ranges of control parameters where multiple stable states occur. Secondly, our experiments have revealed that effective control (enhancement and suppression) of VB can be achieved using CVGs. In our experiments we have used a thin rotaing rod as a CVG, placed along the axis of the basic swirling flow in a sealed cylinder driven by the rotating bottom disc. The effect of the rod depends on the direction of the rotation. With increasing rod co-rotational speed, the VB 'bubble' (VBB) becomes smaller and then disappear, and a cone-shaped wake forms. Counter-rotation of the rod causes increases VBBs' diameter and makes the flow unsteady. The VBBs begin to advect downstream, undergo tearing and pairing, and, hence, enhance mixing.

  16. Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Galvis, J. A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.

    2017-02-01

    Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

  17. Application of a discretized vortex impulse framework to fish maneuvering

    NASA Astrophysics Data System (ADS)

    Mendelson, Leah; Techet, Alexandra

    2015-11-01

    In studies of biological propulsion, metrics for quantitative analysis of the vortex wake, including circulation, impulse, and their time derivatives, are a valuable indicator of performance. To better utilize volumetric PIV data in this type of analysis, a discretized method of deriving vortex impulse relying only on velocity data is developed. The impulse formulation is based on the geometry and distribution of circulation along the vortex core line, which can be detected using critical points in the velocity field. This analysis method is then applied to time-resolved velocity data of a turning giant danio (Devario aequipinnatus) and a jumping archer fish (Toxotes microlepis) obtained using Synthetic Aperture PIV (SAPIV). In the case of the danio, the vortex force vector derived from the impulse derivative shows good agreement with the kinematics of the fish tail during the turning maneuver. With the archer fish, the model is used to explore the relationship between the number of tail beats prior to the jump and the jump height.

  18. Giant Cell Arteritis

    MedlinePlus

    Giant cell arteritis is a disorder that causes inflammation of your arteries, usually in the scalp, neck, and arms. ... arteries, which keeps blood from flowing well. Giant cell arteritis often occurs with another disorder called polymyalgia ...

  19. Interferometric optical vortex array generator

    SciTech Connect

    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.

  20. Interferometric optical vortex array generator.

    PubMed

    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.

  1. Giant impacts on giant planets

    NASA Astrophysics Data System (ADS)

    de Pater, Imke

    2013-10-01

    The 2009 impact and recent superbolides on Jupiter caught the world by surprise and cast doubt on impactor flux estimates for the outer solar system. Enhanced amateur planetary imaging techniques yield both high spatial resolution {enabling the 2009 impact debris field detection} and rapid frame rates {enabling the 2010/2012 impact flash detections and lightcurve measurements}.We propose a ToO program to image future impacts on Jupiter and Saturn. To remove the possibility of impact cloud non-detections, the program will be triggered only if an existing impact debris field is seen, an object on a collision course with Jupiter or Saturn is discovered, or an impact light curve is measured with an estimated total energy large enough to generate an impact cloud in a giant planet atmosphere {10^20 J}.HST provides the only way to image these events in the ultraviolet, providing information on aerosol altitudes and on smaller particles that are less visible to ground-based infrared observations. High-resolution imaging with proper timing {not achievable from the ground} is required to measure precisely both the velocity fields of impact sites and the optical spectrum of impact debris. HST observations of past impacts on Jupiter have also served both as cornerstones of science investigations at other wavelengths and as vehicles for effective public outreach.Large outer solar system impacts are governed by the same physics as in the terrestrial events that dominate the impact threat to humans. Studying the behavior of impactors of various sizes and compositions, as they enter the atmosphere at varying angles and speeds, will better quantify terrestrial impact hazards.

  2. Giant impacts on giant planets

    NASA Astrophysics Data System (ADS)

    de Pater, Imke

    2014-10-01

    The 2009 impact and recent superbolides on Jupiter caught the world by surprise and cast doubt on impactor flux estimates for the outer solar system. Enhanced amateur planetary imaging techniques yield both high spatial resolution (enabling the 2009 impact debris field detection) and rapid frame rates (enabling the 2010/2012 impact flash detections and lightcurve measurements).We propose a ToO program to image future impacts on Jupiter and Saturn. To remove the possibility of impact cloud non-detections, the program will be triggered only if an existing impact debris field is seen, an object on a collision course with Jupiter or Saturn is discovered, or an impact light curve is measured with an estimated total energy large enough to generate an impact cloud in a giant planet atmosphere (10^20 J).HST provides the only way to image these events in the ultraviolet, providing information on aerosol altitudes and on smaller particles that are less visible to ground-based infrared observations. High-resolution imaging with proper timing (not achievable from the ground) is required to measure precisely both the velocity fields of impact sites and the optical spectrum of impact debris. HST observations of past impacts on Jupiter have also served both as cornerstones of science investigations at other wavelengths and as vehicles for effective public outreach.Large outer solar system impacts are governed by the same physics as in the terrestrial events that dominate the impact threat to humans. Studying the behavior of impactors of various sizes and compositions, as they enter the atmosphere at varying angles and speeds, will better quantify terrestrial impact hazards.

  3. Giant impacts on giant planets

    NASA Astrophysics Data System (ADS)

    de Pater, Imke

    2012-10-01

    The 2009 impact on Jupiter caught the world by surprise and cast doubt on impactor flux estimates for the outer solar system. Enhanced amateur planetary imaging techniques yield both high spatial resolution {enabling the 2009 impact debris field detection} and rapid frame rates {enabling the 2010 impact flash detections and lightcurve measurements}.We propose a Target of Opportunity program to image future impacts on Jupiter and Saturn. To remove the possibility of impact cloud non-detections, the program will be triggered only if an existing impact debris field is seen, an object on a collision course with Jupiter or Saturn is discovered, or an impact light curve is measured with an estimated total energy large enough to generate an impact cloud in a giant planet atmosphere.HST provides the only way to image these events in the ultraviolet, providing information on aerosol altitudes and on smaller particles that are less visible to ground-based infrared observations. High-resolution imaging with proper timing {not achievable from the ground} is required to measure precisely both the velocity fields of impact sites and the optical spectrum of impact debris. HST observations of past impacts on Jupiter have also served both as cornerstones of science investigations at other wavelengths and as vehicles for effective public outreach.Large outer solar system impacts are governed by the same physics as in the terrestrial events that dominate the impact threat to humans. Studying the behavior of impactors of various sizes and compositions, as they enter the atmosphere at varying angles and speeds, will better quantify terrestrial impact hazards.

  4. Experimental Dynamics of a Vortex within a Vortex

    NASA Astrophysics Data System (ADS)

    Durkin, D.; Fajans, J.

    2000-11-01

    We report the experimental dynamics of a new two-dimensional (2D) fluid phenomenon that occurs when an intense, pointlike vortex is placed within a diffuse, circular vortex. Our observations, made using strongly magnetized electron columns to model the 2D fluid, support the analysis performed by Jin and Dubin.

  5. Design and experimental test of an optical vortex coronagraph

    NASA Astrophysics Data System (ADS)

    Liu, Cheng-Chao; Ren, De-Qing; Zhu, Yong-Tian; Dou, Jiang-Pei

    2017-05-01

    Using an optical vortex coronagraph (OVC) is one of the most promising techniques for directly imaging exoplanets because of its small inner working angle and high throughput. This paper presents the design and laboratory demonstration performance of an OVC based on liquid crystal polymers (LCPs) at 633 nm and 1520 nm. The OVC can deliver good performance in laboratory tests and achieve a contrast of 10-6 at an angular distance of 3λ/D, which can be implemented for imaging young giant exoplanets in combination with extreme adaptive optics.

  6. Room-temperature operation of MOCVD-grown GaInAs/InP strained-layer multiquantum well lasers in 1.8 micron range

    NASA Technical Reports Server (NTRS)

    Forouhar, S.; Larsson, A.; Ksendzov, A.; Lang, R. J.; Tothill, N.; Scott, M. D.

    1992-01-01

    The first successful room-temperature pulsed operation is reported of InGaAs strained layer multiquantum well injection lasers grown by MOVPE on InP substrates in the 1.8 micron range. The threshold current density and the external differential quantum efficiency of the 10 micron wide ridge waveguide lasers were 2.5 kA/sq cm (cavity length = 1 mm) and 5 percent (cavity length = 400 microns), respectively. Broad-area lasers, 100 microns wide and 1 mm long, had a reverse leakage current of less than 10 microamps at -1 V indicating high quality of the epitaxial layers.

  7. Electroluminescence emission from light-emitting diode of p-ZnO/(InGaN/GaN) multiquantum well/n-GaN

    NASA Astrophysics Data System (ADS)

    Park, Tae-Young; Choi, Yong-Seok; Kim, Sang-Mook; Jung, Gun-Young; Park, Seong-Ju; Kwon, Bong-Joon; Cho, Yong-Hoon

    2011-06-01

    We report on the fabrication and characteristics of light-emitting diodes (LEDs) which consist of antimony (Sb) doped p-ZnO, (InGaN/GaN) multiquantum well (MQW), and n-GaN. An electroluminescence (EL) emission at a wavelength of 468 nm is observed from the hybrid LEDs after thermal annealing at 750 °C, showing that Sb-doped p-ZnO can be used as a hole supplying layer in hybrid LEDs. Furthermore, the EL peaks are redshifted as the injection current is increased, indicating that the compressive strain in MQW layers is relaxed due to Sb-doped p-ZnO layer.

  8. Wingtip vortex turbine investigation for vortex energy recovery

    NASA Technical Reports Server (NTRS)

    Abeyounis, William K.; Patterson, James C., Jr.; Stough, H. P., III; Wunschel, Alfred J.; Curran, Patrick D.

    1990-01-01

    A flight test investigation has been conducted to determine the performance of wingtip vortex turbines and their effect on aircraft performance. The turbines were designed to recover part of the large energy loss (induced drag) caused by the wingtip vortex. The turbine, driven by the vortex flow, reduces the strength of the vortex, resulting in an associated induced drag reduction. A four-blade turbine was mounted on each wingtip of a single-engine, T-tail, general aviation airplane. Two sets of turbine blades were tested, one with a 15' twist (washin) and one with no twist. Th power recovered by the turbine and the installed drag increment were measured. A trade-off between turbine power and induced drag reduction was found to be a function of turbine blade incidence angle. This test has demonstrated that the wingtip vortex turbine is an attractive alternate, as well as an emergency, power source.

  9. On vortex bursting

    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.

  10. Vortex Flow Correlation

    DTIC Science & Technology

    1981-01-01

    j . 1978. 93. Grabowski , W.J.; "Solutions of the Navier-Stokes Equations for Vortex Breakdown," NASA CR...including foreign nations. This technical report has been reviewed and is approved for publication. LAWRENCE W. ROGERS Q LOWELL C. KEEL, Major, USAF Project...or’ a w U - a LU LU U- LU C - J ’di 2 2 C LU I- 4 S Ua * - w x 2 40 20 I- 2 LU W S ~ 00 * U. 4 I- 𔃾 LU a 4 U 4 2 C C LU 4 a 4a 2 I- 4 a 3 9

  11. Wingtip vortex dissipator for aircraft

    NASA Technical Reports Server (NTRS)

    Patterson, J. C., Jr. (Inventor)

    1976-01-01

    A means for attenuating the vortex created at aircraft wingtips which consists of a retractable planar surface transverse to the airstream and attached downstream of the wingtip which creates a positive pressure gradient just downstream from the wing is presented. The positive pressure forces a break up of the rotational air flow of the vortex.

  12. 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…

  13. 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…

  14. Spontaneous superfluid unpinning and the inhomogeneous distribution of vortex lines in neutron stars

    NASA Technical Reports Server (NTRS)

    Cheng, K. S.; Pines, D.; Alpar, M. A.; Shaham, J.

    1988-01-01

    The equation of motion of the pinned superfluid which couples to the crust of neutron stars via thermal vortex creep is studied. Spontaneous unpinning at locations characterized by a very inhomogeneous distribution of vortex lines is examined as a possible mechanism for the initiation of glitches. It is suggested that structural inhomogeneities in the crust of neutron stars may be responsible for frequent microglitches which lead to pulsar timing noise. A generalization of the model shows promise for explaining the origin of the giant glitches in pulsars.

  15. Vortex imaging of magnetic superconductor HoNi 2B 2C by scanning SQUID microscopy

    NASA Astrophysics Data System (ADS)

    Hata, Y.; Suzuki, J.; Kakeya, I.; Kadowaki, K.; Nakayama, S.; Nagata, A.; Odawara, A.; Chinone, K.

    2002-10-01

    We have observed vortex trapped images in the ab-plane of a HoNi 2B 2C single crystal in a magnetic field of 1.2 μT at 4 K using a scanning SQUID microscope. The vortex observed has a fine structure consisting of two regions with opposite signs of the magnetic field which is quantized with multiple flux quanta as a whole. The spatial size of the magnetic field distribution extends over 10 μm. Such giant vortices are also observed at TN< T< TC and disappear above TC where TN is the magnetic transition temperature and TC is the superconducting transition temperature.

  16. Electron-beam-induced current and cathodoluminescence characterization of InGaAs strain-balanced multiquantum well photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Tundo, Stefania; Mazzer, Massimo; Nasi, Lucia; Lazzarini, Laura; Salviati, Giancarlo; Rohr, Carsten; Abbott, Paul; Bushnell, David B.; Barnham, Keith W. J.; Clarke, Graham; Peng, Ruwen

    2003-11-01

    InxGa1-xAs/InyGa1-yAs strain-balanced quantum well cells (QWCs) have been shown to be beneficial for photovoltaic applications in particular to extend the light absorption edge of a single-junction cell toward the near infrared with a lower reduction of the open-circuit voltage compared to a single band-gap cell. The strain-balancing condition ensures that the multi-quantum well as a whole does not relax. However, if the mismatch between wells and barriers exceeds a critical limit, the structure becomes vulnerable to morphological or compositional fluctuations, which can lead to a local structural breakdown with the generation of extended defects of a completely different nature from misfit dislocations. In this work, we investigated a series of strain-balanced InGaAs QWCs grown on InP for thermophotovoltaic applications by means of electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements. Despite being electrically active, these defects appear to have a minor impact on the dark current of the cells but cause a drop of the photocurrent at relatively low forward bias voltage. The higher carrier collection efficiency revealed both by EBIC and CL at the boundaries of the defects suggests that a notch in the valence band edge limits the collection of holes generated in the MQW and the energy states, induced by the defects inside the energy gap, assist the tunneling of holes through the notch. At zero bias, the overall reduction of the collection efficiency is of the order of a few percent but the rate of recombination of photogenerated carriers increases dramatically with increasing forward-bias voltage as the junction built-in field drops more rapidly where the density of in-gap states is higher.

  17. Variable residence time vortex combustor

    DOEpatents

    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.

  18. 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.

  19. Vortex safety in aviation

    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.

  20. Vortex-vortex control in exciton-polariton condensates

    NASA Astrophysics Data System (ADS)

    Ma, Xuekai; Schumacher, Stefan

    2017-06-01

    Vortices are widely studied in fields ranging from nonlinear optics to magnetic systems and superconductors. A vortex carries binary information corresponding to its topological charge, "plus" or "minus", that can be used for information storage and processing. In spatially extended optical and condensed many-particle systems, achieving full control over vortex formation and its charge is particularly difficult and is not easily extended to systems of multiple vortices. Here we demonstrate the optical creation of multiplets of phase-locked vortices in polariton condensates using off-resonant excitation with ring-shaped pump beams. We find that the vorticity of one vortex can be controlled solely using the phase locking with other nearby vortices. Using this mechanism, we demonstrate how an existing vortex with a specific topological charge can be inverted to the oppositely charged state and how the charge state of one reference vortex can be copied to a neighboring vortex. This way we can optically encode any set of binary information onto a chain of vortices. We further show that this information can be modified later by using the possibility to address and manipulate each vortex in the chain individually.

  1. 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.

  2. The Electric Giant Resonances

    NASA Astrophysics Data System (ADS)

    van der Woude, A.

    The following sections are included: * Introduction * Experimental Methods to Study Giant Resonances * Introduction * The Tools * Introduction * Tools for Isoscalar Scattering * INELASTIC α-SCATTERING * INELASTIC PROTON SCATTERING * Tools for Isovector Excitations * γ-ABSORPTION AND PARTICLE CAPTURE REACTIONS * CHARGE EXCHANGE REACTIONS - THE (π+, π0) REACTION * Tools For Isoscalar And Isovector Excitations * INELASTIC ELECTRON SCATTERING * GIANT RESONANCE EXCITATION BY FAST HEAVY IONS * From Multipole Cross Section To Multipole Strength * The Electric Isoscalar Resonances * The Isoscalar Giant Monopole Resonance * Systematics on the GMR * Compressibility and the Giant Monopole Resonance * Introduction * The Compressibility of nuclear matter from the GMR energies * Discussion * The Isoscalar Giant Quadrupole Resonance * General Trends In Medium-Heavy and Heavy Nuclei * The GQR In Light Nuclei * The Isoscalar 3- Strength, LEOR and HEOR * Isoscalar 4+ Strength * Miscellaneous; Isoscalar 1- and L > 4-Strength * The Electric Isovector Giant Resonances * The Isovector Giant Dipole Resonance: GDR * The Isovector Giant Monopole Resonances: IVGMR * The Isovector Quadrupole Resonance: IVGQR * The Effect of Ground State Deformation on the Shape of Giant Resonance: Microscopic Picture * Giant Resonances Built on Excited States * Introduction * Capture Reactions on Light Nuclei * Statistical decay of GDR γ Emission in Heavy Compound Systems * Introduction * Theoretical Predictions * Some Experimental Results * Summary and Outlook * Acknowledgements * General References * References

  3. Sensory ecology: giant eyes for giant predators?

    PubMed

    Partridge, Julian C

    2012-04-24

    Mathematical models suggest the enormous eyes of giant and colossal squid evolved to see the bioluminescence induced by the approach of predatory whales. Copyright © 2012 Elsevier Ltd. All rights reserved.

  4. Comparison between an experimental turbulent vortex and the Lundgren vortex

    NASA Astrophysics Data System (ADS)

    Cuypers, Yannis; Maurel, Agnès; Petitjeans, Philippe

    2004-08-01

    In a recent letter (Cuypers Y et al 2003 Phys. ReV. Lett. 91 194502), the authors presented experimental results on a structure resulting from a vortex burst. The temporal evolution of this structure results in the k-5/3 Kolmogorov spectrum and some common features with the Lundgren theoretical vortex have been shown. The purpose of the present paper is to go further in the comparison with the Lundgren model by a parallel analysis of the experimental structure and of a Lundgren single spiral vortex, whose evolution is numerically obtained based on the calculations of Pullin et al (1993 Phys. Fluids A 5 126; 1994 Phys. Fluids 6 3010).

  5. All-optical discrete vortex switch

    SciTech Connect

    Desyatnikov, Anton S.; Dennis, Mark R.; Ferrando, Albert

    2011-06-15

    We introduce discrete vortex solitons and vortex breathers in circular arrays of nonlinear waveguides. The simplest vortex breather in a four-waveguide coupler is a nonlinear dynamic state changing its topological charge between +1 and -1 periodically during propagation. We find the stability domain for this solution and suggest an all-optical vortex switching scheme.

  6. Vortex states and spin textures of rotating spin-orbit-coupled Bose-Einstein condensates in a toroidal trap

    NASA Astrophysics Data System (ADS)

    Wang, Huan; Wen, Linghua; Yang, Hui; Shi, Chunxiao; Li, Jinghong

    2017-08-01

    We consider the ground-state properties of Rashba spin-orbit-coupled pseudo-spin-1/2 Bose-Einstein condensates (BECs) in a rotating two-dimensional (2D) toroidal trap. In the absence of spin-orbit coupling (SOC), the increasing rotation frequency enhances the creation of giant vortices for the initially miscible BECs, while it can lead to the formation of semiring density patterns with irregular hidden vortex structures for the initially immiscible BECs. Without rotation, strong 2D isotropic SOC yields a heliciform-stripe phase for the initially immiscible BECs. Combined effects of rotation, SOC, and interatomic interactions on the vortex structures and typical spin textures of the ground state of the system are discussed systematically. In particular, for a fixed rotation frequency above the critical value, the increasing isotropic SOC favors a visible vortex necklace in each component which is accompanied by a hidden giant vortex plus a (several) hidden vortex necklace(s) in the central region. In the case of one-dimensional anisotropic SOC, large SOC strength results in the generation of hidden linear vortex string and the transition from initial component separation (component mixing) to component mixing (component separation). Furthermore, the peculiar spin textures including skyrmion lattice, skyrmion pair and skyrmion string are revealed in this system.

  7. On the vortex ring state

    NASA Astrophysics Data System (ADS)

    Green, Richard; Gillies, E.; Giuni, M.; Hislop, J.; Savas, Omer

    2014-11-01

    The investigation considers the vortex ring state, a phenomenon normally associated with the collapse of a trailing, helical vortex wake into a unstable vortex ring, and is a problem encountered when a helicopter rotor descends into its own wake. A series of wind tunnel and towing tank experiments on rotor systems have been performed, and a comparison is then made with the behaviour of a specially designed open core, annular jet system that generates a mean flow velocity profile similar to that observed below a rotor. In experimentally simulated descents the jet system forms flow patterns that are topologically similar to the vortex ring state of a rotor system. Furthermore the dynamic behaviour of the flow shares many of the important characteristics of the rotor flow. This result suggests that the phenomenon of the vortex ring state of a rotor wake is decoupled from the detailed vortex dynamics of the helical vortex filaments themselves. The presentation will describe the principle behind the investigation, the details of the annular jet system and the results gained using PIV and flow visualisation of the wake and jet systems.

  8. Precise characterization of focused vortex beams

    NASA Astrophysics Data System (ADS)

    Saito, Takahiro; Takeo, Yoko; Mimura, Hidekazu

    2017-09-01

    Focused vortex beams are characterized in terms of their intensity and phase using an iterative phase retrieval method. The vortex beams generated by a vortex phase plate contain several phase singularities and vortex phase distributions. The wavefields were retrieved using many far-field diffraction profiles obtained by scanning a pinhole along the focal plane. The retrieved intensity and phase distributions agreed well with those predicted using the actual profiles of vortex phase plates, which indicates that the phase retrieval method can be used for the precise characterization of vortex beams. The information obtained is valuable for improving the performance of methods involving vortex beams, such as microscopy and laser processing.

  9. Josephson-vortex Cherenkov radiation

    SciTech Connect

    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.

  10. Rotating Vortex Dipoles in Ferromagnets

    SciTech Connect

    Komineas, S.

    2007-09-14

    Vortex-antivortex pairs are spontaneously created in magnetic elements. In the case of opposite vortex polarities the pair has a nonzero topological charge, and it behaves as a rotating vortex dipole. We find theoretically and confirm numerically its energy as a function of angular momentum and the associated rotation frequencies. The annihilation process of the pair changes the topological charge while the energy is monotonically decreasing. The change of topological charge affects the dynamics profoundly. We finally discuss the implications of our results for Bloch point dynamics.

  11. Rotating vortex dipoles in ferromagnets.

    PubMed

    Komineas, S

    2007-09-14

    Vortex-antivortex pairs are spontaneously created in magnetic elements. In the case of opposite vortex polarities the pair has a nonzero topological charge, and it behaves as a rotating vortex dipole. We find theoretically and confirm numerically its energy as a function of angular momentum and the associated rotation frequencies. The annihilation process of the pair changes the topological charge while the energy is monotonically decreasing. The change of topological charge affects the dynamics profoundly. We finally discuss the implications of our results for Bloch point dynamics.

  12. Dynamic signatures of driven vortex motion.

    SciTech Connect

    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.

  13. Polar Vortex [video

    NASA Image and Video Library

    2017-09-28

    1-9 January 2014. The full-disk images every 3 hours from GOES-WEST capture the sweep of a polar vortex that emerged from the arctic at the beginning of the new year, pushing a blizzard into the northeastern USA on January 3, followed by extensive bitter cold (-20 F, windchill -50 F) around the Great Lakes, and single digit temperatures as far south as Atlanta, Georgia. This western viewpoint displays the persistent flow of arctic air from northern Alaska and Yukon into North America. Credit: NOAA/NASA GOES Project NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  14. Vortex loops and Majoranas

    SciTech Connect

    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.

  15. 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.

  16. Entangled vector vortex beams

    NASA Astrophysics Data System (ADS)

    D'Ambrosio, Vincenzo; Carvacho, Gonzalo; Graffitti, Francesco; Vitelli, Chiara; Piccirillo, Bruno; Marrucci, Lorenzo; Sciarrino, Fabio

    2016-09-01

    Light beams having a vectorial field structure, or polarization, that varies over the transverse profile and a central optical singularity are called vector vortex (VV) beams and may exhibit specific properties such as focusing into "light needles" or rotation invariance. VV beams have already found applications in areas ranging from microscopy to metrology, optical trapping, nano-optics, and quantum communication. Individual photons in such beams exhibit a form of single-particle quantum entanglement between different degrees of freedom. On the other hand, the quantum states of two photons can be also entangled with each other. Here, we combine these two concepts and demonstrate the generation of quantum entanglement between two photons that are both in VV states: a form of entanglement between two complex vectorial fields. This result may lead to quantum-enhanced applications of VV beams as well as to quantum information protocols fully exploiting the vectorial features of light.

  17. Structure of leading-edge vortex flows including vortex breakdown

    SciTech Connect

    Payne, F.M.

    1987-01-01

    An experimental investigation of the structure of leading-edge vortex flows on thin sharp-edged delta wings was carried out at low Reynolds numbers. Flow-visualization techniques were used to study the topology of the vortex and the phenomenon of vortex breakdown. Seven-hole probe-wake surveys and laser-doppler-anemometer measurements were obtained and compared. Delta wings with sweep angles of 70, 75, 80, and 85/sup 0/ were tested at angles of attack of 10, 20, 30, and 40/sup 0/. The test were conducted in a Reynolds number range of 8.5 x 10/sup 4/ to 6.4 x 10/sup 5/. Smoke-flow visualization revealed the presence of small Kelvin-Helmholtz type vortical structures in the shear layer of a leading-edge vortex. These shear-layer vortices follow a helical path and grow in the streamwise direction as they wind into the vortex core where the individual shear layers merge. The phenomenon of vortex breakdown was studied using high-speed cinema photography. The bubble and spiral types of breakdown were observed and appear to represent the extremes in a continuum of breakdown forms.

  18. Noise Properties of Indium Gallium Arsenide/indium Aluminum Arsenide Multiquantum-Well Heterostructure P-I -n Photodiodes

    NASA Astrophysics Data System (ADS)

    Yu, Young-June

    The charge transport process in InGaAs/InAlAs multiquantum-well (MQw) heterostructure p-i-n photodiodes is studied experimentally and theoretically. Current-voltage (I-V), capacitance-voltage (C-V), S-parameter, and noise measurements are performed at room temperature over a wide range of reverse bias. The devices under study consist of alternating, undoped, lattice matched InGaAs and InAlAs layers sandwiched between a heavily doped n and p layer of InGaAs. To determine the dependence of charge transport phenomena on quantum-well width, a set of three different quantum-well layers of, respectively, 30, 90, and 500 Angstrom wide were used. Upon illumination by a light-emitting-diode (1350 nm), measurements of the noise spectra were performed at frequencies ranging from 100 Hz to 1 GHz. In the frequency range of 200 MHz and 1 GHz, the 90-90 and 500-500 Angstrom devices which have nontransparent barriers between neighboring quantum-wells, show distinctive sub-shot noise level at low bias. This sub-shot noise phenomenon is interpreted in terms of the trapping and detrapping of electrons in undepleted quantum-wells. The magnitude of the noise is proportional to 1/N, where N is the number of undepleted quantum-wells. The dependence of noise levels on bias indicates that quantum-wells located in the i-region are successively and gradually depleted with increasing reverse bias. C-V measurements support this finding. To explain the sub-shot noise levels, a MQW trapping noise model was developed employing the Transfer Impedance method. The excess noise observed at frequencies below 200 MHz is caused by the trapping and detrapping of electrons in heterojunction interface states. Current-voltage measurements performed under illumination indicated that the quantum efficiency of the photodiode is bias dependent. We established that the photocurrent is controlled by field assisted injection of optically generated electrons from the low bandgap absorption region into the intrinsic

  19. Vortex dynamics in anisotropic traps

    SciTech Connect

    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.

  20. Wake Vortex Sensors Requirements Overview

    NASA Technical Reports Server (NTRS)

    Hinton, David A.

    1997-01-01

    The presentation includes discussions of primary wake vortex system requirements, evolution models, sensor evolution, site specific sensor tradeoffs, wake sensor functions, deployment considerations, the operational test bed system and additional sensor requirements.

  1. Vortex rings in Bose gas

    SciTech Connect

    Belyaev, S. T.

    2016-06-15

    We consider excitations that exist, in addition to phonons, in the ideal Bose gas at zero temperature. These excitations are vortex rings whose energy spectrum is similar to the roton one in liquid helium.

  2. Instability of cyclonic convective vortex

    NASA Astrophysics Data System (ADS)

    Sukhanovskii, A.; Evgrafova, A.; Popova, E.

    2017-06-01

    Localized heating in the rotating layer of fluid leads to the formation of intensive cyclonic vortex. Cyclonic vortex becomes unstable at low values of viscosity and fast rotation of the experimental model. The instability of the vortex is tightly connected with a structure of the radial inflow. For moderate values of rotational Reynolds number Re the radial flows consist of several branches which transport angular momentum to the center of the model. When Re exceeds critical value (about 23) radial inflow changes its structure and appears as one wide branch which does not reach the center. As a result of strong anisotropy of radial inflow the cyclonic vortex is formed at some distance from the center. Further increase of Re leads to chaotic state with several vortices which appears at different locations near the periphery of the heating area. The map of regimes with stable and unstable vortices is presented.

  3. Vortex-based all-optical manipulation of stored light at low light levels.

    PubMed

    Zhao, Lu

    2015-11-16

    We exploit the giant cross-Kerr nonlinearity of electromagnetically induced transparency (EIT) system in ultracold atoms to implement vortex-based multimode manipulation of stored light at low light levels. Using image-bearing signal light fields with angular intensity profiles, sinusoidal grating structures with phase-only modulation can be azimuthally imprinted on the stored probe light field, where the nonlinear absorption loss can be ignored. Upon retrieval of the probe light, collinearly superimposed vortex modes can be generated in the far field. Considering the finite size of atomic gas, the Fraunhofer diffraction patterns of the retrieved probe fields and their spiral spectra are numerically investigated, where the diffracted vortex modes can be efficiently controlled by tuning the weak signal fields. Our studies not only exhibit a fundamental diffraction phenomenon with angular grating structures in EIT system, but also provide a fascinating opportunity to realize multidimensional quantum information processing for stored light in an all-optical manner.

  4. Vortex Imaging of REB2Ni2C (RE=Ho,Er) Using Scanning SQUID Microscopy

    NASA Astrophysics Data System (ADS)

    Hata, Yoshiaki; Suzuki, Jun-Ichi; Kakeya, Itsuhiro; Kadowaki, Kazuo; Nakayama, Satoshi; Nagata, Atsushi; Chinone, Kazuo

    2001-03-01

    Scanning SQUID microscopy studies have been carried out on the [001] surface of a REB_2Ni_2C (RE = Ho, Er) single crystal at 2.8 K in weak magnetic field. This SQUID microscopy enables us to observe high resolution image of individual vortices at low temperature. In most of cases this giant vortex accompanies a few small antivortices as satellites. The distance of each vortex is about 10 μm apart and the size of the vortex is about 40 μm in diameter. The total flux of most paired vortices are estimated a few integer multiple of quantum flux. This interesting phenomenon is interpreted by a model proposed by Tachiki & Maekawa that the quantization of magnetic flux may occur in total flux including both supercurrent and spin magnetic moment.

  5. Mathematical analysis of vortex dynamics

    NASA Astrophysics Data System (ADS)

    Caflisch, Russel E.

    This review paper discusses the mathematical theory of vortex dynamics for incompressible, inviscid flow in two and three dimensions. The surveyed results include existence and uniqueness of time-dependent solutions, instability and singularity formation, convergence of numerical methods, and existence and stability of steady states. A simple integral formulation for the evolution of a three dimensional vortex sheet and a variational principle for the Batchelor flow problem are presented.

  6. Formation number for vortex dipoles

    NASA Astrophysics Data System (ADS)

    Sadri, Vahid; Krueger, Paul S.

    2016-11-01

    This investigation considers the axisymmetric formation of two opposite sign concentric vortex rings from jet ejection between concentric cylinders. This arrangement is similar to planar flow in that the vortex rings will travel together when the gap between the cylinders is small, similar to a vortex dipole, but it has the advantage that the vortex motion is less constrained than the planar case (vortex stretching and vortex line curvature is allowed). The flow was simulated numerically at a jet Reynolds number of 1,000 (based on ΔR and the jet velocity), jet pulse length-to-gap ratio (L / ΔR) in the range 10-20, and gap-to-outer radius ratio (ΔR /Ro) in the range 0.01-0.1. Small gap ratios were chosen for comparison with 2D results. In contrast with 2D results, the closely paired vortices in this study exhibited pinch-off from the generating flow and finite formation numbers. The more complex flow evolution afforded by the axisymmetric model and its influence on the pinch-off process will be discussed. This material is based on work supported by the National Science Foundation under Grant No. 1133876 and SMU. This supports are gratefully acknowledged.

  7. 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.

  8. Vortex and Rings

    NASA Image and Video Library

    2014-07-07

    NASA Cassini spacecraft captures three magnificent sights at once: Saturn north polar vortex and hexagon along with its expansive rings. The hexagon, which is wider than two Earths, owes its appearance to the jet stream that forms its perimeter. The jet stream forms a six-lobed, stationary wave which wraps around the north polar regions at a latitude of roughly 77 degrees North. This view looks toward the sunlit side of the rings from about 37 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 2, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 1.4 million miles (2.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 43 degrees. Image scale is 81 miles (131 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18274

  9. Mid-infrared electro-luminescence and absorption from AlGaN/GaN-based multi-quantum well inter-subband structures

    SciTech Connect

    Hofstetter, Daniel; Bour, David P.; Kirste, Lutz

    2014-06-16

    We present electro-modulated absorption and electro-luminescence measurements on chirped AlGaN/GaN-based multi-quantum well inter-subband structures grown by metal-organic vapour phase epitaxy. The absorption signal is a TM-polarized, 70 meV wide feature centred at 230 meV. At medium injection current, a 58 meV wide luminescence peak corresponding to an inter-subband transition at 1450 cm{sup −1} (180 meV) is observed. Under high injection current, we measured a 4 meV wide structure peaking at 92.5 meV in the luminescence spectrum. The energy location of this peak is exactly at the longitudinal optical phonon of GaN.

  10. Composition and Interface Analysis of InGaN/GaN Multiquantum-Wells on GaN Substrates Using Atom Probe Tomography

    SciTech Connect

    Liu, Fang; Huang, Li; Davis, Robert F.; Porter, Lisa M.; Schreiber, Daniel K.; Kuchibhatla, S. V. N. T.; Shutthanandan, V.; Thevuthasan, Suntharampillai; Preble, Edward; Paskova, Tanya; Evans, K. R.

    2014-09-04

    In0.20Ga0.80N/GaN multi-quantum wells grown on [0001]-oriented GaN substrates with and without an InGaN buffer layer were characterized using three-dimensional atom probe tomography. In all samples, the upper interfaces of the QWs were slightly more diffuse than the lower interfaces. The buffer layers did not affect the roughness of the interfaces within the quantum well structure, a result attributed to planarization of the surface of the 1st GaN barrier layer which had an average root-mean-square roughness of 0.177 nm. The In and Ga distributions within the MQWs followed the expected distributions for a random alloy with no indications of In clustering.

  11. Characterization of cromolyn sodium hydrates and its formulation by (23) Na-multiquantum and magic-angle spinning nuclear magnetic resonance spectroscopy.

    PubMed

    Umino, Makoto; Higashi, Kenjirou; Masu, Hyuma; Limwikrant, Waree; Yamamoto, Keiji; Moribe, Kunikazu

    2013-08-01

    We characterized cromolyn sodium (CS) hydrates and evaluated their molecular states in low-dose formulations using Na-multiquantum magic-angle spinning (MQMAS) nuclear magnetic resonance (NMR) analysis. Two CS hydrates, low-water-content hydrated form and high-water-content hydrated form containing 2-3 and 5-6 hydrates, respectively, were prepared by humidification. Single-crystal X-ray diffraction and powder X-ray diffraction analysis revealed that these CS hydrates contained sodium channel structures and that water molecules were adsorbed on the sodium nucleus. (13) C-cross-polarization/MAS NMR spectra of these hydrates revealed similar results, confirming that the water molecules were adsorbed not on the cromolyn skeletons but mainly on the sodium nucleus. In contrast, (23) Na-MQMAS NMR analysis allowed us to clearly distinguish these hydrates without discernible effects from quadrupolar interaction. Thus, MQMAS NMR analysis is a valuable tool for evaluating salt drugs and their formulations.

  12. Optical properties of InGaN/GaN multiquantum wells light-emitting diode with one-dimensional Au nanoparticle grating

    NASA Astrophysics Data System (ADS)

    Tu, Sheng-Han; Ruan, Da-Ge; Tzeng, Shien-Der; Ni, I.-Chi; Wang, Chih-Ming

    2014-01-01

    The polarization-dependent optical properties of InGaN/GaN multiquantum wells blue light-emitting diode with one-dimensional (1-D) plasmonic nanoparticles grating are investigated using an angle-resolved photoluminescence spectrometer. The light extraction efficiencies of the 1-D GaN grating coated with an Au layer and 1-D GaN grating coated with an Au nanoparticle monolayer are measured. It is shown that the light extraction efficiency of plasmonic nanoparticle grating coated with an Au nanoparticle monolayer is 1.4-fold higher than that of a 1-D GaN grating coated with Au film because the surface plasmon losses are conquered. In addition, the experimental dispersion of the surface plasmon (SP)-assisted light enhancement shows a good agreement with the dispersion of SP at the Au/GaN interface.

  13. Piezo-Phototronic Effect Controlled Dual-Channel Visible light Communication (PVLC) Using InGaN/GaN Multiquantum Well Nanopillars.

    PubMed

    Du, Chunhua; Jiang, Chunyan; Zuo, Peng; Huang, Xin; Pu, Xiong; Zhao, Zhenfu; Zhou, Yongli; Li, Linxuan; Chen, Hong; Hu, Weiguo; Wang, Zhong Lin

    2015-12-02

    Visible light communication (VLC) simultaneously provides illumination and communication via light emitting diodes (LEDs). Keeping a low bit error rate is essential to communication quality, and holding a stable brightness level is pivotal for illumination function. For the first time, a piezo-phototronic effect controlled visible light communication (PVLC) system based on InGaN/GaN multiquantum wells nanopillars is demonstrated, in which the information is coded by mechanical straining. This approach of force coding is also instrumental to avoid LED blinks, which has less impact on illumination and is much safer to eyes than electrical on/off VLC. The two-channel transmission mode of the system here shows great superiority in error self-validation and error self-elimination in comparison to VLC. This two-channel PVLC system provides a suitable way to carry out noncontact, reliable communication under complex circumstances.

  14. Effect of strain relaxation on forward bias dark currents in GaAs/InGaAs multiquantum well p-i-n diodes

    NASA Astrophysics Data System (ADS)

    Griffin, P. R.; Barnes, J.; Barnham, K. W. J.; Haarpaintner, G.; Mazzer, M.; Zanotti-Fregonara, C.; Grünbaum, E.; Olson, C.; Rohr, C.; David, J. P. R.; Roberts, J. S.; Grey, R.; Pate, M. A.

    1996-11-01

    The effect of the dislocation line density produced by the relaxation of strain in GaAs/InxGa1-xAs multiquantum wells where x=0.155-0.23 has been studied. There is a strong correlation between the dark line density, observed by cathodoluminescence, before processing of the wafers into photodiode devices, and the subsequent low forward bias (<1.5 V) dark current densities of the devices. A comparison is made of the correlation between the reverse bias current density and dark line density and it is found that, in this range of strain, the forward bias current density varies more. Two growth methods, molecular beam epitaxy and metal organic vapor phase epitaxy, have been used to produce the wafers and no difference between the growth methods has been found in dark line or current density variations with strain.

  15. Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

    SciTech Connect

    Yang, J.; Zhao, D. G. Jiang, D. S.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Le, L. C.; Li, X. J.; He, X. G.; Liu, J. P.; Yang, H.; Zhang, Y. T.; Du, G. T.

    2015-02-07

    The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, and therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.

  16. Optical and structural properties of GaN nanopillar and nanostripe arrays with embedded InGaN /GaN multi-quantum wells

    NASA Astrophysics Data System (ADS)

    Keller, S.; Schaake, C.; Fichtenbaum, N. A.; Neufeld, C. J.; Wu, Y.; McGroddy, K.; David, A.; DenBaars, S. P.; Weisbuch, C.; Speck, J. S.; Mishra, U. K.

    2006-09-01

    GaN nanopillar and nanostripe arrays with embedded InGaN /GaN multi-quantum wells (MQWs) were fabricated by holographic lithography and subsequent reactive ion etching. Etch related damage of the nanostructures was successfully healed through annealing in NH3/N2 mixtures under optimized conditions. The nanopatterned samples exhibited enhanced luminescence in comparison to the planar wafers. X-ray reciprocal space maps recorded around the asymmetric (101¯5) reflection revealed that the MQWs in both nanopillars and nanostripes relaxed after nanopatterning and adopted a larger in-plane lattice constant than the underlying GaN layer. The pillar relaxation process had no measurable effect on the Stokes shift typically observed in MQWs on c-plane GaN, as evaluated by excitation power dependent photoluminescence (PL) measurements. Angular-resolved PL measurements revealed the extraction of guided modes from the nanopillar arrays.

  17. Investigating the origin of efficiency droop by profiling the voltage across the multi-quantum well of an operating light-emitting diode

    SciTech Connect

    Kim, Taewoong; Seong, Tae-Yeon; Kwon, Ohmyoung

    2016-06-06

    Efficiency droop is a phenomenon in which the efficiency of a light-emitting diode (LED) decreases with the increase in current density. To analyze efficiency droop, direct experimental observations on the energy conversion occurring inside the LED is required. Here, we present the measured voltage profiles on the cross section of an operating LED and analyze them with the cross-sectional temperature profiles obtained in a previous study under the same operation conditions. The measured voltage profiles suggest that with increases in the injection current density, electron depletion shifts from the multi-quantum well through an electron blocking layer to the p-GaN region. This is because electron leakage increases with increases in current density.

  18. Numerical simulation of vortex-wedge interaction

    NASA Astrophysics Data System (ADS)

    Park, Jin-Ho; Lee, Duck-Joo

    1994-06-01

    Interactions between vortical flows and a solid surface cause one of the primary sources of noise and unsteady loading. The mechanism of the interaction is studied numerically for a single Rankine vortex impinging upon a wedge. An Euler-Lagrangian method is employed to calculate the unsteady, viscous, incompressible flows in two dimensions. A random vortex method is used to describe the vorticity dominant field. A fast vortex method is used to reduce the computational time in the calculation of the convection velocity of each vortex particle. A Schwarz-Christoffel transformation is used to map the numerical domain onto the physical domain. Vortex partical plots, velocity vectors, and streamlines are presented at selected times for both inviscid and viscous interactions. It is observed that the incident rankine vortex distorts and is split by the wedge as it nears and passes the wedge, and the vortices generated from the leading edge toward the underside of the wedge form into a single vortex. The vorticity orientation of the shed vortex is opposite to that of the incident vortex. It is found that the convection velocity of the shed vortex is changed wheen it comes off the leading edge of the wedge, and the strength of the shed vortex varies with the time during the vortex-wedge interaction. This strength variation is presumed to influence the shed vortex convection velocity. The overall features for the interaction agree well with the experimental results of Ziada and Rockwell.

  19. 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.

  20. 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.

  1. Green functions of vortex operators

    SciTech Connect

    Polchinski, Joseph

    1981-03-16

    In this paper, we study the euclidean Green 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 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 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 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 functions of the Wilson and vortex operators, for a general gauge theory. Finally, the surface-like cluster property of the vortex operator in an abelian Higgs theory is explored in more detail.

  2. The structure of vortex breakdown

    NASA Technical Reports Server (NTRS)

    Leibovich, S.

    1978-01-01

    The term 'vortex breakdown', as used in the reported investigation, refers to a disturbance characterized by the formation of an internal stagnation point on the vortex axis, followed by reversed flow in a region of limited axial extent. Two forms of vortex breakdown, which predominate, are shown in photographs. One form is called 'near-axisymmetric' (sometimes 'axisymmetric'), and the other is called 'spiral'. A survey is presented of work published since the 1972 review by Hall. Most experimental data taken since Hall's review have been in tubes, and the survey deals primarily with such cases. It is found that the assumption of axial-symmetry has produced useful results. The classification of flows as supercritical or subcritical, a step that assumes symmetry, has proved universally useful. Experiments show that vortex breakdown is always preceded by an upstream supercritical flow and followed by a subcritical wake. However, a comparison between experiments and attempts at prediction is less than encouraging. For a satisfactory understanding of the structure of vortex breakdown it is apparently necessary to take into account also aspects of asymmetry.

  3. Quantitative vortex models of turbulence

    NASA Astrophysics Data System (ADS)

    Pullin, D. I.

    2001-11-01

    This presentation will review attempts to develop models of turbulence, based on compact vortex elements, that can be used both to obtain quantitative estimates of various statistical properties of turbulent fine scales and also to formulate subgrid-transport models for large-eddy simulation (LES). Attention will be focused on a class of stretched-vortex models. Following a brief review of prior work, recent studies of vortex-based modeling of the small-scale behavior of a passive scalar will be discussed. The large-wavenumber spectrum of a passive scalar undergoing mixing by the velocity field of a stretched-spiral vortex will be shown to consist of the sum of two classical power laws, a k-1 Batchelor spectrum for wavenumbers up to the inverse Batchelor scale, and a k-5/3 Obukov-Corrsin spectrum for wavenumbers less than the inverse Kolmogorov scale (joint work with T.S. Lundgren). We will then focus on the use of stretched vortices as the basic subgrid structure in subgrid-scale (SGS) modeling for LES of turbulent flows. An SGS stress model and a vortex-based scalar-flux model for the LES of flows with turbulent mixing will be outlined. Application of these models to the LES of decaying turbulence, channel flow, the mixing of a passive scalar by homogeneous turbulence in the presence of a mean scalar gradient, and to the LES of compressible turbulence will be described.

  4. 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.

  5. Recent progress in vortex coronagraphy

    NASA Astrophysics Data System (ADS)

    Serabyn, G.; Mawet, D.

    The Optical Vortex Coronagraph (OVC) is a phase-based coronagraph that can enable high-contrast imaging observations very near bright stars and can make use of smaller telescope diameters than most alternative techniques. This paper first briefly describes the basic principles of operation of the vortex coronagraph, which applies an azimuthal phase spiral to the focal plane point spread function, and then turns to recent advances, both in understanding and in the needed technology development. In particular, vortex phase masks based on circularly-symmetric half-wave plates made of both liquid-crystal polymers and photonic crystals have now achieved very good contrast. Moreover, a dual-stage vortex coronagraph configuration can be used to achieve high contrast in the case of an on-axis telescope, i.e., in the presence of obscuration due to a secondary mirror and a secondary support structure. Further development of the relevant vortex techniques could potentially enable a range of high-contrast coronagraphic space missions, from an initial explorer class mission to a large flagship class exoplanet imaging mission. Of particular interest in this regard is the use of one of the two former 2.4 m National Reconnaissance Office telescopes for coronagraphic observations.

  6. Giant prostatic calculi

    PubMed Central

    Najoui, Mohammed; Qarro, Abdelmounaim; Ammani, Abdelghani; Alami, Mohammed

    2013-01-01

    Prostatic parenchymal calculi are common, usually incidental, findings on morphological examinations. They are typically asymptomatic and may be present in association with normal glands, benign prostatic hyperplasia, and prostate cancer. However giant prostatic calculi are rare. Less than 20 cases have been reported in the literature. We present the case of a 35-year-old man with two giant prostatic calculi that replaced the entire gland. He underwent an open cystolithotomy, two giant stones were removed from the prostate, and we used a lithotripsy in situ for extraction of stone fragments. PMID:23565316

  7. Unstable giant gravitons

    SciTech Connect

    Mello Koch, Robert de; Ives, Norman; Smolic, Jelena; Smolic, Milena

    2006-03-15

    We find giant graviton solutions in Frolov's three parameter generalization of the Lunin-Maldacena background. The background we study has {gamma}-tilde{sub 1}=0 and {gamma}-tilde{sub 2}={gamma}-tilde{sub 3}={gamma}-tilde. This class of backgrounds provides a nonsupersymmetric example of the gauge theory/gravity correspondence that can be tested quantitatively, as recently shown by Frolov, Roiban, and Tseytlin. The giant graviton solutions we find have a greater energy than the point gravitons, making them unstable states. Despite this, we find striking quantitative agreement between the gauge theory and gravity descriptions of open strings attached to the giant.

  8. Giant vortices in combined harmonic and quartic traps

    SciTech Connect

    Aftalion, Amandine; Danaila, Ionut

    2004-03-01

    We consider a rotating Bose-Einstein condensate confined in combined harmonic and quartic traps, following recent experiments [V. Bretin, S. Stock, Y. Seurin, and J. Dalibard, Phys. Rev. Lett. 92, 050403 (2004)]. We investigate numerically the behavior of the wave function which solves the three-dimensional Gross Pitaevskii equation and analyze in detail the structure of vortices. For a quartic-plus-harmonic potential, as the angular velocity increases, the vortex lattice evolves into a vortex array with hole. The merging of vortices into the hole is highly three dimensional, starting from the top and bottom of the condensate to reach the center. We also investigate the case of a quartic-minus-harmonic potential, not covered by experiments or previous numerical works. For intermediate repulsive potentials, we show that the transition to a vortex array with hole takes place for lower angular velocities, when the lattice is made up of a small number of vortices. For the strong repulsive case, a transition from a giant vortex to a hole with a circle of vortices around is observed.

  9. 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.

  10. Vortex chains travelling with discrete velocities

    NASA Astrophysics Data System (ADS)

    Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.

    2008-05-01

    It has been shown that Swihart waves slowing down caused by Josephson junction spatial dispersion leads to the new field periodic nonlinear vortex states moving with discrete velocities. Swihart waves trapping by periodic vortex structures is discovered.

  11. Titan South Polar Vortex in Motion

    NASA Image and Video Library

    2012-07-10

    This image from a movie captured by NASAS Cassini spacecraft shows a south polar vortex, or shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere, at Saturn moon Titan.

  12. Vortex waves in sunspots

    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.

  13. Generation of vortex circular Airy beam through binary amplitude digital hologram

    NASA Astrophysics Data System (ADS)

    Fang, Zhao-Xiang; Ren, Yu-Xuan; Lu, Rong-De

    2016-02-01

    Airy beam is a kind of wavepacket existing in the form of photons, electrons, and plasmonics. Well known as diffraction-free beam, optical Airy beam tends to accelerate in transverse space with a parabolic trajectory, and exhibits self-healing property when partially blocked. Those properties have attracted a great deal of research interests and applications. Circular Airy beam, exhibiting cylindrically symmetric intensity pattern and abruptly autofocusing characteristics in the linear media, is a variant of Airy-like wave. Optical vortex, on the other hand, is a kind of phase singularity. We present to shape the autofocusing Airy beam with a vortex phase structure, which was realized through the binary amplitude modulation with a digital micromirror device (DMD). Each mirror on the DMD could be electronically addressed to situate at either of the two solid positional states corresponding to on and off. Shaping the light into a specific mode requires the calculation of the amplitude pattern for display on the DMD. By reshaping individual DMD pixels into giant pixels, the complex field of the vortex Airy beam could be encoded with a super-pixel method. The propagation property of the vortex Airy beam was investigated through numerical simulation for different topological charges. Furthermore, the propagation characteristics of this beam in free space were verified and discussed through the experiments. We anticipate that the proposed vortex Airy beam in particle trapping, biological field and optical communications. This method with DMD can also be used to generate other beams with different characteristics.

  14. 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.

  15. Magnetic vortex based transistor operations.

    PubMed

    Kumar, D; Barman, S; Barman, A

    2014-02-17

    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).

  16. 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.

  17. Magnetic Vortex Based Transistor Operations

    PubMed Central

    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

  18. 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.

  19. The free compressible viscous vortex

    NASA Technical Reports Server (NTRS)

    Colonius, Tim; Lele, Sanjiva K.; Moin, Parviz

    1991-01-01

    The present study investigates the effects of compressibility on free (unsteady) viscous heat-conducting vortices. Analytical solutions are found in the limit of large but finite Reynolds number and small but finite Mach number. It is shown that the spreading of the vortex causes a radial flow. This flow is given by the solution of an ordinary differential equation, which gives the dependence of the radial velocity on the tangential velocity, density, and temperature profiles of the vortex. Estimates of the radial velocity found by solving this equation are found to be in good agreement with numerical solutions of the full equations. The equations for the viscous evolution are expanded in powers of Mach number to obtain detailed analytical solutions. It is shown that swirling axisymmetric compressible flows generate negative radial velocities far from the vortex core owing to viscous effects, regardless of the initial distributions of vorticity, density, and entropy.

  20. Three-dimensional vortex methods

    NASA Astrophysics Data System (ADS)

    Greengard, C. A.

    1984-08-01

    Reformulations of the filament method and of the method of Beale and Majda show them to be very similar algorithms. The method of Anderson in which vorticity is evaluated by the exact differentiation of the approximate velocity field is discussed. It is shown that, in the inviscid version of this algorithm, each approximate vector of vorticity remains tangent to a material curve moving with the computed flow, with magnitude proportional to the stretching of this vortex line. It is explained that the expanding core vortex method converges to a system of equations different from the Navier-Stokes equations. Computations with the filament method of the inviscid interaction of two vortex rings are reported, both with single filaments in each ring and with a fully three-dimensional discretization of vorticity. The dependence on parameters is discussed, and convergence of the computed solutions is observed.

  1. Tracks of a Giant

    NASA Image and Video Library

    2010-08-25

    The giant, 70-meter-wide antenna at NASA Deep Space Network complex in Goldstone, Calif., tracks a spacecraft on Nov. 17, 2009. This antenna, officially known as Deep Space Station 14, is also nicknamed the Mars antenna.

  2. The Next Giant Step

    NASA Image and Video Library

    Artist Robert McCall painted "The Next Giant Step" in 1979 to commemorate the heroism and courage of spaceflight pioneers. Located in the lobby of Johnson's building 2, the mural depicts America's ...

  3. Silvics of Giant Sequoia

    Treesearch

    C. Phillip Weatherspoon

    1986-01-01

    Ecological relationships-including habitat and life history---of giant sequoia (Sequoiadendron giganteum [Lindl.] Buchholz) in natural stands are summarized. Such silvical information provides an important foundation for sound management of the species.

  4. The Giant Cell.

    ERIC Educational Resources Information Center

    Stockdale, Dennis

    1998-01-01

    Provides directions for the construction of giant plastic cells, including details for building and installing the organelles. Also contains instructions for preparing the ribosomes, nucleolus, nucleus, and mitochondria. (DDR)

  5. Giant Earlobe Epidermoid Cyst

    PubMed Central

    Pérez-Guisado, Joaquín; Scilletta, Alessandra; Cabrera-Sánchez, Emilio; Rioja, Luis F; Perrotta, Rosario

    2012-01-01

    Epidermoid cysts represent the most common cutaneous cysts. They are usually small and benign; however, sometimes they can grow to giant epidermoid cists, and occasionally malignancies develop. Giant epidermoid cysts at the earlobe have never been described but in other locations. We describe a case of a giant epidermoid cyst at the earlobe, a location where such a large cyst has never been reported before. The mass was completely resected and the wound of the pedunculated base was sutured with four stitches of nylon 5/0. Histopathology confirmed the presumptive diagnosis of an epidermoid cyst. Six months after the resection, the patient did not have any relapse of the epidermoid cyst. The earlobe is a potential location for giant epidermoid cysts. Although the clinical diagnosis could be enough, due to the possibility of malignancy and to ensure appropriate diagnosis, we consider that all cysts should be sent to the anatomic pathology laboratory for histological evaluation. PMID:22557855

  6. The Giant Cell.

    ERIC Educational Resources Information Center

    Stockdale, Dennis

    1998-01-01

    Provides directions for the construction of giant plastic cells, including details for building and installing the organelles. Also contains instructions for preparing the ribosomes, nucleolus, nucleus, and mitochondria. (DDR)

  7. Cutting of bent vortex lines

    SciTech Connect

    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.

  8. A Closer Examination of the Joint Behavior of Dark Spots and their Companion Clouds on the Ice Giants

    NASA Astrophysics Data System (ADS)

    Le Beau, Raymond P.; Warning, S. W.; Palotai, C.; Deng, X.

    2012-10-01

    Starting with the Voyager observations of the Great Dark Spot-Bright Companion duo on Neptune, discrete cloud features have been linked to vortices on the Ice Giants. Building on these observations, numerical simulations of these features have begun to reveal a complex physical interaction in which the vortex can generate clouds which in turn influence the behavior of the vortex. For example, simulations in the EPIC general circulation model of a vortex similar to the Uranian Dark Spot can generate companion clouds from a cloud-free initial condition. These clouds are generated orographically, with a region of upwelling on the leading edge of vortex lifting methane from the warmer lower atmosphere to cooler conditions above the vortex. This increases the local humidity to the point where condensation can occur. The upwelling is perceptible in some simulations a scale height above the vortex with vertical velocities on the order of 0.01-0.1 m/s. The strength of this upwelling is dependent on the local humidity as well as the vortex characteristics; likewise, the meridional drift rate of these vortices is affected by the changes in methane distribution. While the described UDS simulation provides an illustration of the interactive physics underlying vortex-cloud phenomena, there are other, more perplexing observations that require further explanation. These range from the changing shape of the original bright companion cloud above and about the drifting, oscillating Great Dark Spot to the meridional drift and time-varying cloud structure of the “Berg” on Uranus. Ongoing numerical examination of these vortex-cloud pairings will provide further insight into these features and the overall atmospheric physics of the Ice Giants. This research is supported by NASA Planetary Atmospheres grant NNX11AC01G.

  9. Coulombic contribution and fat center vortex model

    SciTech Connect

    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.

  10. Giant Cell Arteritis and Polymyalgia Rheumatica

    MedlinePlus

    ... Controlfamilydoctor.org editorial staff Home Diseases and Conditions Giant Cell Arteritis and Polymyalgia Rheumatica Condition Giant Cell Arteritis and Polymyalgia Rheumatica Share Print Giant ...

  11. Capella: Separating the Giants

    NASA Astrophysics Data System (ADS)

    Young, P. R.; Dupree, A. K.

    2002-01-01

    Images from the Faint Object Camera (FOC) on the Hubble Space Telescope (HST) are used to spatially separate the two giants of Capella (α Aurigae; HD 34029) for the first time at ultraviolet wavelengths. The images were obtained with broadband filters that isolate the wavelength regions 2500-3000 Å and 1300-1500 Å. The cool G8 giant is found to be weaker than the hot G1 giant by factors of around 4 and 17, respectively, in these bands. The latter factor is largely due to the much stronger G1 continuum at short wavelengths. No evidence is found for material lying between the two stars in the images. In addition, the objective prisms of the FOC were used to obtain low-resolution spectra from 1200 to 3000 Å, allowing individual emission lines from each star to be spatially separated. Cool-to-hot star ratios for the emission lines H I Lyα, O I λ1305, Si II λ1816, C II λ1335, He II λ1640, and Si IV λ1393 are presented, showing that the cool giant is weaker than the hot giant by factors of 5-10 in these lines. The O I emission is only a factor of 2.5 weaker in the cool giant, most probably resulting from fluorescence in the extended atmosphere of the cool giant. The line ratios are compared with values derived from International Ultraviolet Explorer and HST/Goddard High Resolution Spectrograph spectra, which could separate the stars spectrally but not spatially. Reasonable agreement is found although the FOC ratios generally imply lower contributions from the cool giant. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  12. Vortex ice in nanostructured superconductors

    SciTech Connect

    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.

  13. 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.

  14. Vortex 'puddles' and magic vortex numbers in mesoscopic superconducting disks

    SciTech Connect

    Connolly, M. R.; Milosevic, M. V.; Bending, S. J.; Clem, J. R.; Tamegai, T.

    2009-01-01

    The magnetic properties of a superconducting disk change dramatically when its dimensions become mesoscopic. Unlike large disks, where the screening currents induced by an applied magnetic field are strong enough to force vortices to accumulate in a 'puddle' at the centre, in a mesoscopic disk the interaction between one of these vortices and the edge currents can be comparable to the intervortex repulsion, resulting in a destruction of the ordered triangular vortex lattice structure at the centre. Vortices instead form clusters which adopt polygonal and shell-like structures which exhibit magic number states similar to those of charged particles in a confining potential, and electrons in artificial atoms. We have fabricated mesoscopic high temperature superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} disks and investigated their magnetic properties using magneto-optical imaging (MOI) and high resolution scanning Hall probe microscopy (SHPM). The temperature dependence of the vortex penetration field measured using MOI is in excellent agreement with models of the thermal excitation of pancake vortices over edge barriers. The growth of the central vortex puddle has been directly imaged using SHPM and magic vortex numbers showing higher stability have been correlated with abrupt jumps in the measured local magnetisation curves.

  15. Chirality induced tilted-hill giant Nernst signal.

    PubMed

    Kotetes, P; Varelogiannis, G

    2010-03-12

    We reveal a novel source of a giant Nernst response exhibiting strong nonlinear temperature and magnetic field dependence, including the mysterious tilted-hill temperature profile observed in a pleiad of materials. The phenomenon results directly from the formation of a chiral ground state, e.g., a chiral d-density wave, which is compatible with the eventual observation of diamagnetism and is distinctly different from the usual quasiparticle and vortex Nernst mechanisms. Our picture provides a unified understanding of the anomalous thermoelectricity observed in materials as diverse as the hole-doped cuprates and heavy-fermion compounds like URu(2)Si(2).

  16. Evolution of a plasma vortex in air.

    PubMed

    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.

  17. Scattering of electromagnetic wave by vortex flow

    NASA Astrophysics Data System (ADS)

    Wei, Jian-Ye; Liu, Jing-Yu; Mahmood, Waqas; Zhao, Qing

    2017-04-01

    In this paper, the scattering behaviour of an electromagnetic wave by vortex flow is studied in detail by solving the first-order (in v / c) Maxwell's equation in the cylindrical coordinate system (r, φ, z) and the general solutions are obtained. From these solutions, the differential cross-section of the vortex flow is calculated and the electromagnetic scattering characteristics of the vortex flow are discussed. The dependence of differential cross-section on the velocity profile and the radius of the vortex flow is investigated independently. Besides, by considering the dependence of scattering characteristics on the frequency of an incident wave we conclude that the vortex flow has frequency selectivity.

  18. Particle-vortex symmetric liquid

    NASA Astrophysics Data System (ADS)

    Mulligan, Michael

    2017-01-01

    We introduce an effective theory with manifest particle-vortex symmetry for disordered thin films undergoing a magnetic field-tuned superconductor-insulator transition. The theory may enable one to access both the critical properties of the strong-disorder limit, which has recently been confirmed by Breznay et al. [Proc. Natl. Acad. Sci. USA 113, 280 (2016), 10.1073/pnas.1522435113] to exhibit particle-vortex symmetric electrical response, and the nearby metallic phase discovered earlier by Mason and Kapitulnik [Phys. Rev. Lett. 82, 5341 (1999), 10.1103/PhysRevLett.82.5341] in less disordered samples. Within the effective theory, the Cooper-pair and field-induced vortex degrees of freedom are simultaneously incorporated into an electrically neutral Dirac fermion minimally coupled to a (emergent) Chern-Simons gauge field. A derivation of the theory follows upon mapping the superconductor-insulator transition to the integer quantum Hall plateau transition and the subsequent use of Son's particle-hole symmetric composite Fermi liquid. Remarkably, particle-vortex symmetric response does not require the introduction of disorder; rather, it results when the Dirac fermions exhibit vanishing Hall effect. The theory predicts approximately equal (diagonal) thermopower and Nernst signal with a deviation parameterized by the measured electrical Hall response at the symmetric point.

  19. Titan Colorful South Polar Vortex

    NASA Image and Video Library

    2012-07-10

    This true color image captured by NASAS Cassini spacecraft before a distant flyby of Saturn moon Titan on June 27, 2012, shows a south polar vortex, or a mass of fluid-like clouds and haze swirling around the pole in the atmosphere of the moon.

  20. Integrated optical vortex beam receivers.

    PubMed

    Cicek, Kenan; Hu, Ziyang; Zhu, Jiangbo; Meriggi, Laura; Li, Shimao; Nong, Zhichao; Gao, Shengqian; Zhang, Ning; Wang, Xuyang; Cai, Xinlun; Sorel, Marc; Yu, Siyuan

    2016-12-12

    A simple and ultra-compact integrated optical vortex beam receiver device is presented. The device is based on the coupling between the optical vortex modes and whispering gallery modes in a micro-ring resonator via embedded angular gratings, which provides the selective reception of optical vortex modes with definitive total angular momentum (summation of spin and orbital angular momentum) through the phase matching condition in the coupling process. Experimental characterization confirms the correct detection of the total angular momentum carried by the vortex beams incident on the device. In addition, photonic spin-controlled unidirectional excitation of whispering-gallery modes in the ring receiver is also observed, and utilized to differentiate between left- and right-circular polarizations and therefore unambiguously identify the orbital angular momentum of incident light. Such characteristics provide an effective mode-selective receiver for the eigen-modes in orbital angular momentum fiber transmission where the circularly polarized OAM modes can be used as data communications channels in multiplexed communications or as photonic states in quantum information applications.

  1. 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.

  2. Three-dimensional vortex methods

    SciTech Connect

    Greengard, C.A.

    1984-08-01

    Three-dimensional vortex methods for the computation of incompressible fluid flow are presented from a unified point of view. Reformulations of the filament method and of the method of Beale and Majda show them to be very similar algorithms; in both of them, the vorticity is evaluated by a discretization of the spatial derivative of the flow map. The fact that the filament method, the one which is most often used in practice, can be formulated as a version of the Beale and Majda algorithm in a curved coordinate system is used to give a convergence theorem for the filament method. The method of Anderson is also discussed, in which vorticity is evaluated by the exact differentiation of the approximate velocity field. It is shown that, in the inviscid version of this algorithm, each approximate vector of vorticity remains tangent to a material curve moving with the computed flow, with magnitude proportional to the stretching of this vortex line. This remains true even when time discretization is taken into account. It is explained that the expanding core vortex method converges to a system of equations different from the Navier-Stokes equations. Computations with the filament method of the inviscid interaction of two vortex rings are reported, both with single filaments in each ring and with a fully three-dimensional discretization of vorticity. The dependence on parameters is discussed, and convergence of the computed solutions is observed. 36 references, 4 figures.

  3. Perturbative theory for Brownian vortexes.

    PubMed

    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.

  4. 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.

  5. Vortex cavitation: A progress report

    SciTech Connect

    Arndt, R.E.A.; Maines, B.H.

    1994-12-31

    Cavitation in vortical flows is a significant problem. An important aspect is the need for a better understanding of the physics of cavitation in the vortices tailing from lifting surfaces such as propellers and hydrofoils. This is a review of experimental and numerical research that has been recently carried out with a series of hydrofoils. This is a review of experimental and numerical research that has been recently carried out with a series of hydrofoils. This research was aimed at investigating the interrelated effects of vortex structure, including the details of the vortex roll-up process close to the tip, dissolved gas content, and water quality as it related to the amount of tension that can be sustained in the vortex before cavitation occurs. The experimental phase includes lift and drag measurements, oil flow visualization of the boundary layer flow on the lifting surfaces, and observation of both cavitation inception and desinence in strong and weak water. An improved photographic technique has been developed to study the complex bubble dynamics inherent in the inception process. Preliminary results indicate that the bubble growth process is strongly dependent on the size and number of nuclei in the free stream. Numerical simulations indicate that the minimum pressure in the vortex is very close to the tip of the lifting surface, in agreement with the observation that the inception process also occurs very close to the tip under most conditions.

  6. Extended applications of the vortex lattice method

    NASA Technical Reports Server (NTRS)

    Miranda, L. R.

    1976-01-01

    The application of the vortex lattice method to problems not usually dealt with by this technique is considered. It is shown that if the discrete vortex lattice is considered as an approximation to surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vortex-induced velocity that renders the vortex lattice method valid for supersonic flow. Special schemes for simulating non-zero thickness lifting surfaces and fusiform bodies with vortex lattice elements are presented. Thickness effects of wing-like components are simulated by a double vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentric cylindrical surfaces. Numerical considerations peculiar to the application of these techniques are briefly discussed.

  7. Three-dimensional stability of vortex arrays

    NASA Astrophysics Data System (ADS)

    Robinson, A. C.; Saffman, P. G.

    1982-12-01

    The stability to three-dimensional disturbances of three classical steady vortex configurations in an incompressible inviscid fluid is studied in the limit of small vortex cross-sectional area and long axial disturbance wavelength. The configurations examined are the single infinite vortex row, the Karman vortex street of staggered vortices and the symmetric vortex street. It is shown that the single row is most unstable to a two-dimensional disturbance, while the Karman vortex street is most unstable to a three-dimensional disturbance over a significant range of street spacing ratios. The symmetric vortex street is found to be most unstable to three-dimensional or two-dimensional symmetric disturbances depending on the spacing ratio of the street. Short remarks are made concerning the relevance of the calculations to the observed instabilities in free shear layer, wake and boundary-layer type flows.

  8. Vortex spin-torque oscillator using Co2FexMn1 -xSi Heusler alloys

    NASA Astrophysics Data System (ADS)

    Yamamoto, Tatsuya; Seki, Takeshi; Takanashi, Koki

    2016-09-01

    We show spin-transfer-torque-driven vortex oscillations in current-perpendicular-to-plane giant magnetoresistance junctions using epitaxially grown Co2FexMn1 -xSi (CFMS) Heusler alloy thin films. The soft magnetic property and high spin polarization of CFMS enable us to realize vortex oscillation emitting large microwave power with a low threshold current. The output power is maximized for a certain Fe-Mn composition ratio associated with a reduction of the threshold current for the oscillation, which is in agreement with a general model for spin-torque oscillation. Through comparison with an analytical theory that describes the translational motion of a vortex core, we show that the vortex core motion excited in the present device is inhomogeneous along the thickness direction. In spite of the inhomogeneity, the gyration radius at the CFMS/spacer interface region was estimated to be ˜75 % of the actual ferromagnetic layer radius, which indicates that the CFMS-based all-metallic junction is useful for achieving large-amplitude vortex core motion. This comprehensive investigation would also be useful for designing high-performance all-metallic nano-oscillators based on magnetic vortex dynamics.

  9. 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.

  10. Rossby solitary vortices, on giant planets and in the laboratory.

    PubMed

    Nezlin, Mikhail V.

    1994-06-01

    This is a review of laboratory experiments with a layer of shallow water having a free surface and rotating together with a vessel of parabolic form. Such a (rather original) setup has allowed one to create Rossby solitary vortex for the first time. The latter is an anticyclonic Rossby vortex not subjected to dispersive spread owing to its compensation by the nonlinearity of KdV type. By its structural, collisional, and other properties, including clear-cut cyclonic-anticyclonic asymmetry, it may be considered as a physical prototype of the large-scale long-lived anticyclonic Rossby vortices like the Great Red Spot of Jupiter or the Great Dark Spot of Neptune (this remarkable vortex was discovered by the spacecraft Voyager-2 during its farewell to the Solar System) and other vortices dominating in the atmospheres of giant planets and created by the unstable zonal flows. It has been shown that the vortex under study is a long-lived entity provided it satisfies "antitwisting condition," i.e., it has rather large amplitude (at which it rotates more quickly than it propagates and thereby carries the trapped fluid). In this case, it is not subjected to the "twisting" deformation and may be ascribed by the generalized Charney-Obukhov equation for Rossby vortices on shallow water with a free surface. The results of creating the vortex under consideration by the different methods have been compared with the results obtained by other authors in the experiments on shear-flow generation of Rossby vortices.

  11. Giant congenital melanocytic nevus.

    PubMed

    Viana, Ana Carolina Leite; Gontijo, Bernardo; Bittencourt, Flávia Vasques

    2013-01-01

    Giant congenital melanocytic nevus is usually defined as a melanocytic lesion present at birth that will reach a diameter ≥ 20 cm in adulthood. Its incidence is estimated in <1:20,000 newborns. Despite its rarity, this lesion is important because it may associate with severe complications such as malignant melanoma, affect the central nervous system (neurocutaneous melanosis), and have major psychosocial impact on the patient and his family due to its unsightly appearance. Giant congenital melanocytic nevus generally presents as a brown lesion, with flat or mammilated surface, well-demarcated borders and hypertrichosis. Congenital melanocytic nevus is primarily a clinical diagnosis. However, congenital nevi are histologically distinguished from acquired nevi mainly by their larger size, the spread of the nevus cells to the deep layers of the skin and by their more varied architecture and morphology. Although giant congenital melanocytic nevus is recognized as a risk factor for the development of melanoma, the precise magnitude of this risk is still controversial. The estimated lifetime risk of developing melanoma varies from 5 to 10%. On account of these uncertainties and the size of the lesions, the management of giant congenital melanocytic nevus needs individualization. Treatment may include surgical and non-surgical procedures, psychological intervention and/or clinical follow-up, with special attention to changes in color, texture or on the surface of the lesion. The only absolute indication for surgery in giant congenital melanocytic nevus is the development of a malignant neoplasm on the lesion.

  12. Giant congenital melanocytic nevus*

    PubMed Central

    Viana, Ana Carolina Leite; Gontijo, Bernardo; Bittencourt, Flávia Vasques

    2013-01-01

    Giant congenital melanocytic nevus is usually defined as a melanocytic lesion present at birth that will reach a diameter ≥ 20 cm in adulthood. Its incidence is estimated in <1:20,000 newborns. Despite its rarity, this lesion is important because it may associate with severe complications such as malignant melanoma, affect the central nervous system (neurocutaneous melanosis), and have major psychosocial impact on the patient and his family due to its unsightly appearance. Giant congenital melanocytic nevus generally presents as a brown lesion, with flat or mammilated surface, well-demarcated borders and hypertrichosis. Congenital melanocytic nevus is primarily a clinical diagnosis. However, congenital nevi are histologically distinguished from acquired nevi mainly by their larger size, the spread of the nevus cells to the deep layers of the skin and by their more varied architecture and morphology. Although giant congenital melanocytic nevus is recognized as a risk factor for the development of melanoma, the precise magnitude of this risk is still controversial. The estimated lifetime risk of developing melanoma varies from 5 to 10%. On account of these uncertainties and the size of the lesions, the management of giant congenital melanocytic nevus needs individualization. Treatment may include surgical and non-surgical procedures, psychological intervention and/or clinical follow-up, with special attention to changes in color, texture or on the surface of the lesion. The only absolute indication for surgery in giant congenital melanocytic nevus is the development of a malignant neoplasm on the lesion. PMID:24474093

  13. Front propagation in a vortex lattice: dependence on boundary conditions and vortex depth.

    PubMed

    Beauvier, E; Bodea, S; Pocheau, A

    2016-11-04

    We experimentally address the propagation of reaction-diffusion fronts in vortex lattices by combining, in a Hele-Shaw cell and at low Reynolds number, forced electroconvective flows and an autocatalytic reaction in solution. We consider both vortex chains and vortex arrays, the former referring to mixed free/rigid boundary conditions for vortices and the latter to free boundary conditions. Varying the depth of the fluid layer, we observe no variation of the mean front velocities for vortex arrays and a noticeable variation for vortex chains. This questions the two-dimensional character of front propagation in low Reynolds number vortex lattices, as well as the mechanisms of this dependence.

  14. 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.

  15. Giant star seismology

    NASA Astrophysics Data System (ADS)

    Hekker, S.; Christensen-Dalsgaard, J.

    2017-06-01

    The internal properties of stars in the red-giant phase undergo significant changes on relatively short timescales. Long near-uninterrupted high-precision photometric timeseries observations from dedicated space missions such as CoRoT and Kepler have provided seismic inferences of the global and internal properties of a large number of evolved stars, including red giants. These inferences are confronted with predictions from theoretical models to improve our understanding of stellar structure and evolution. Our knowledge and understanding of red giants have indeed increased tremendously using these seismic inferences, and we anticipate that more information is still hidden in the data. Unraveling this will further improve our understanding of stellar evolution. This will also have significant impact on our knowledge of the Milky Way Galaxy as well as on exo-planet host stars. The latter is important for our understanding of the formation and structure of planetary systems.

  16. 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.

  17. Two vortex-blob regularization models for vortex sheet motion

    NASA Astrophysics Data System (ADS)

    Sohn, Sung-Ik

    2014-04-01

    Evolving vortex sheets generally form singularities in finite time. The vortex blob model is an approach to regularize the vortex sheet motion and evolve past singularity formation. In this paper, we thoroughly compare two such regularizations: the Krasny-type model and the Beale-Majda model. It is found from a linear stability analysis that both models have exponentially decaying growth rates for high wavenumbers, but the Beale-Majda model has a faster decaying rate than the Krasny model. The Beale-Majda model thus gives a stronger regularization to the solution. We apply the blob models to the two example problems: a periodic vortex sheet and an elliptically loaded wing. The numerical results show that the solutions of the two models are similar in large and small scales, but are fairly different in intermediate scales. The sheet of the Beale-Majda model has more spiral turns than the Krasny-type model for the same value of the regularization parameter δ. We give numerical evidences that the solutions of the two models agree for an increasing amount of spiral turns and tend to converge to the same limit as δ is decreased. The inner spiral turns of the blob models behave differently with the outer turns and satisfy a self-similar form. We also examine irregular motions of the sheet at late times and find that the irregular motions shrink as δ is decreased. This fact suggests a convergence of the blob solution to the weak solution of infinite regular spiral turns.

  18. Interaction of Vortex Ring with Cutting Plate

    NASA Astrophysics Data System (ADS)

    Musta, Mustafa

    2015-11-01

    The interaction of a vortex ring impinging on a thin cutting plate was made experimentally using Volumetric 3-component Velocitmetry (v3v) technique. The vortex rings were generated with piston-cylinder vortex ring generator using piston stroke-to-diameter ratios and Re at 2-3 and 1500 - 3000, respectively. The cutting of vortex rings below center line leads to the formation of secondary vortices on each side of the plate which is look like two vortex rings, and a third vortex ring propagates further downstream in the direction of the initial vortex ring, which is previously showed by flow visualization study of Weigand (1993) and called ``trifurcation''. Trifurcation is very sensitive to the initial Reynolds number and the position of the plate with respect to the vortex ring generator pipe. The present work seeks more detailed investigation on the trifurcation using V3V technique. Conditions for the formation of trifurcation is analyzed and compared with Weigand (1993). The formed secondary vortex rings and the propagation of initial vortex ring in the downstream of the plate are analyzed by calculating their circulation, energy and trajectories.

  19. Vortex tube reconnection at Re = 104

    NASA Astrophysics Data System (ADS)

    van Rees, Wim M.; Hussain, Fazle; Koumoutsakos, Petros

    2012-07-01

    We present simulations of the long-time dynamics of two anti-parallel vortex tubes with and without initial axial flow, at Reynolds number Re = Γ/ν = 104. Simulations were performed in a periodic domain with a remeshed vortex method using 785 × 106 particles. We quantify the vortex dynamics of the primary vortex reconnection that leads to the formation of elliptical rings with axial flow and report for the first time a subsequent collision of these rings. In the absence of initial axial flow, a -5/3 slope of the energy spectrum is observed during the first reconnection of the tubes. The resulting elliptical vortex rings experience a coiling of their vortex lines imparting an axial flow inside their cores. These rings eventually collide, exhibiting a -7/3 slope of the energy spectrum. Studies of vortex reconnection with an initial axial flow exhibit also the -7/3 slope during the initial collision as well as in the subsequent collision of the ensuing elliptical vortex rings. We quantify the detailed vortex dynamics of these collisions and examine the role of axial flow in the breakup of vortex structures.

  20. An Innocent Giant

    PubMed Central

    Solanki, Lakhan Singh; Dhingra, Mandeep; Raghubanshi, Gunjan; Thami, Gurvinder Pal

    2014-01-01

    A cutaneous horn (cornu cutaneum) is a protrusion from the skin composed of a cornified material. It may be associated with a benign, premalignant, or malignant lesion at the base, masking numerous dermatoses. In a 24-year-old female, a giant cutaneous horn arising from a seborrheic keratosis located on the leg is presented. This case has been reported to emphasize that a giant cutaneous horn may also occur in young patients, even in photoprotected areas, and are not always associated with malignancy. PMID:25484426

  1. Unconventional vortex states in nanoscale superconductors due to shape-induced resonances in the inhomogeneous cooper-pair condensate.

    PubMed

    Zhang, L-F; Covaci, L; Milošević, M V; Berdiyorov, G R; Peeters, F M

    2012-09-07

    Vortex matter in mesoscopic superconductors is known to be strongly affected by the geometry of the sample. Here we show that in nanoscale superconductors with coherence length comparable to the Fermi wavelength the shape resonances of the order parameter results in an additional contribution to the quantum topological confinement-leading to unconventional vortex configurations. Our Bogoliubov-de Gennes calculations in a square geometry reveal a plethora of asymmetric, giant multivortex, and vortex-antivortex structures, stable over a wide range of parameters and which are very different from those predicted by the Ginzburg-Landau theory. These unconventional states are relevant for high-T(c) nanograins, confined Bose-Einstein condensates, and graphene flakes with proximity-induced superconductivity.

  2. Optical Rankine Vortex and Anomalous Circulation of Light

    SciTech Connect

    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.

  3. Divergence of optical vortex beams.

    PubMed

    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.

  4. Collisions of Vortex Filament Pairs

    NASA Astrophysics Data System (ADS)

    Banica, Valeria; Faou, Erwan; Miot, Evelyne

    2014-12-01

    We consider the problem of collisions of vortex filaments for a model introduced by Klein et al. (J Fluid Mech 288:201-248, 1995) and Zakharov (Sov Phys Usp 31(7):672-674, 1988, Lect. Notes Phys 536:369-385, 1999) to describe the interaction of almost parallel vortex filaments in three-dimensional fluids. Since the results of Crow (AIAA J 8:2172-2179, 1970) examples of collisions are searched as perturbations of antiparallel translating pairs of filaments, with initial perturbations related to the unstable mode of the linearized problem; most results are numerical calculations. In this article, we first consider a related model for the evolution of pairs of filaments, and we display another type of initial perturbation leading to collision in finite time. Moreover, we give numerical evidence that it also leads to collision through the initial model. We finally study the self-similar solutions of the model.

  5. Drag of buoyant vortex rings

    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.

  6. 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.

  7. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1986-01-01

    Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.

  8. Giant optical manipulation.

    PubMed

    Shvedov, Vladlen G; Rode, Andrei V; Izdebskaya, Yana V; Desyatnikov, Anton S; Krolikowski, Wieslaw; Kivshar, Yuri S

    2010-09-10

    We demonstrate a new principle of optical trapping and manipulation increasing more than 1000 times the manipulation distance by harnessing strong thermal forces while suppressing their stochastic nature with optical vortex beams. Our approach expands optical manipulation of particles into a gas media and provides a full control over trapped particles, including the optical transport and pinpoint positioning of ∼100  μm objects over a meter-scale distance with ±10  μm accuracy.

  9. On Vortex Breakdown and Instability.

    DTIC Science & Technology

    1981-03-01

    Hydrodynamic and Hydromagnetic Stability of Swirling flows," J. Fluid Mech., Vol. 14, 463-76, 1962. 23. Hummel, D., "Untersuchtingen uber das Aufplatzen...initiated the study of linear hydrodynamic stability concerning 30,31, an ebvc 41swirling flows. Then Leibovich Randall and Leibovich4 , Uberoi, Chow...Vortex Breakdown, Delta Wing, Richardson Number, Stability 20. RACT (Continue on reveso side If necessary end identify by block number) A literature

  10. The Helicity of Vortex Filaments.

    NASA Astrophysics Data System (ADS)

    Petrich, Dean; Tao, Louis

    1996-03-01

    The helicity, defined by H = int dV v \\cdot nabla × v, is a conserved quantity of the three-dimensional Euler equations. Traditionally the helicity has been viewed as a measure of the topology of vortex lines, but it is shown that the helicity measures their geometry as well as their topology (J.D. Bekenstein, Physics Letters B), 282 (1992) 44-49.. The existence of helicity-preserving reconnection events is discussed.

  11. 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.

  12. Numerical simulation of vortex breakdown by the vortex-filament method

    NASA Technical Reports Server (NTRS)

    Nakamura, Y.; Leonard, A.; Spalart, P. R.

    1983-01-01

    The vortex filament method was applied to the simulation of vortex breakdown. The principal vortex region was represented by multiple filaments, and an axial velocity component was induced by a spiral winding of the filaments. First, an accuracy check was performed for a cylindrical swirling flow with simple analytical expressions for the axial and theta velocities. The result suggests that the flow field is simulated to any accuracy by increasing the number of filaments. Second, an axisymmetric type vortex breakdown was simulated, with experimental data serving as upstream conditions. The calculated axial and theta velocity contours show the breakdown of the vortex, including a rapid change in the vortex core, followed axially by a recovery zone and then a second breakdown. When three dimensional initial data are used the second breakdown appears to be of the spiral type in correspondence with experimental observations. The present method is easily used to simulate other types of vortex breakdown or other vortex flows with axial velocity.

  13. 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.

  14. Birth and evolution of an optical vortex.

    PubMed

    Vallone, Giuseppe; Sponselli, Anna; D'Ambrosio, Vincenzo; Marrucci, Lorenzo; Sciarrino, Fabio; Villoresi, Paolo

    2016-07-25

    When a phase singularity is suddenly imprinted on the axis of an ordinary Gaussian beam, an optical vortex appears and starts to grow radially, by effect of diffraction. This radial growth and the subsequent evolution of the optical vortex under focusing or imaging can be well described in general within the recently introduced theory of circular beams, which generalize the hypergeometric-Gaussian beams and which obey novel kinds of ABCD rules. Here, we investigate experimentally these vortex propagation phenomena and test the validity of circular-beam theory. Moreover, we analyze the difference in radial structure between the newly generated optical vortex and the vortex obtained in the image plane, where perfect imaging would lead to complete closure of the vortex core.

  15. Analytical model of the optical vortex microscope.

    PubMed

    Płocinniczak, Łukasz; Popiołek-Masajada, Agnieszka; Masajada, Jan; Szatkowski, Mateusz

    2016-04-20

    This paper presents an analytical model of the optical vortex scanning microscope. In this microscope the Gaussian beam with an embedded optical vortex is focused into the sample plane. Additionally, the optical vortex can be moved inside the beam, which allows fine scanning of the sample. We provide an analytical solution of the whole path of the beam in the system (within paraxial approximation)-from the vortex lens to the observation plane situated on the CCD camera. The calculations are performed step by step from one optical element to the next. We show that at each step, the expression for light complex amplitude has the same form with only four coefficients modified. We also derive a simple expression for the vortex trajectory of small vortex displacements.

  16. 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.

  17. Topology of Vortex-Wing Interaction

    NASA Astrophysics Data System (ADS)

    McKenna, Chris; Rockwell, Donald

    2016-11-01

    Aircraft flying together in an echelon or V formation experience aerodynamic advantages. Impingement of the tip vortex from the leader (upstream) wing on the follower wing can yield an increase of lift to drag ratio. This enhancement is known to depend on the location of vortex impingement on the follower wing. Particle image velocimetry is employed to determine streamline topology in successive crossflow planes, which characterize the streamwise evolution of the vortex structure along the chord of the follower wing and into its wake. Different modes of vortex-follower wing interaction are created by varying both the spanwise and vertical locations of the leader wing. These modes are defined by differences in the number and locations of critical points of the flow topology, and involve bifurcation, attenuation, and mutual induction. The bifurcation and attenuation modes decrease the strength of the tip vortex from the follower wing. In contrast, the mutual induction mode increases the strength of the follower tip vortex. AFOSR.

  18. Vortex dynamics in nonrelativistic Abelian Higgs model

    NASA Astrophysics Data System (ADS)

    Kozhevnikov, A. A.

    2015-11-01

    The dynamics of the gauge vortex with arbitrary form of a contour is considered in the framework of the nonrelativistic Abelian Higgs model, including the possibility of the gauge field interaction with the fermion asymmetric background. The equations for the time derivatives of the curvature and the torsion of the vortex contour generalizing the Betchov-Da Rios equations in hydrodynamics, are obtained. They are applied to study the conservation of helicity of the gauge field forming the vortex, twist, and writhe numbers of the vortex contour. It is shown that the conservation of helicity is broken when both terms in the equation of the vortex motion are present, the first due to the exchange of excitations of the phase and modulus of the scalar field and the second one due to the coupling of the gauge field forming the vortex, with the fermion asymmetric background.

  19. Vortex diode jet performance and theory

    SciTech Connect

    Houck, E.D.

    1993-12-01

    Fluidics is the technology dealing with the use of a flowing liquid or gas in various devices for controls and fluid transfers. Existing fluidic technology transfers fluid at approximately the same rate as air lifts and jets. A vortex diode combined in parallel with a jet (vortex diode jet) produces significantly higher transfer rates` and retains the fluidic system advantages. This paper presents the proof of concept research and gives design parameters for the vortex diode jet. The goal of this research was to develop a vortex diode jet that would improve fluidic system transfer rates, and to develop and verify the,design equations. Proven design equations could then be used to design, and model vortex diode jet systems. This research has shown that vortex diode jets improve fluidic system transfer rate by up to 60 percent and can be modelled with the design equations.

  20. 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.

  1. Modeling vortex swarming in Daphnia.

    PubMed

    Mach, Robert; Schweitzer, Frank

    2007-02-01

    Based on experimental observations in Daphnia, we introduce an agent-based model for the motion of single and swarms of animals. Each agent is described by a stochastic equation that also considers the conditions for active biological motion. An environmental potential further reflects local conditions for Daphnia, such as attraction to light sources. This model is sufficient to describe the observed cycling behavior of single Daphnia. To simulate vortex swarming of many Daphnia, i.e. the collective rotation of the swarm in one direction, we extend the model by considering avoidance of collisions. Two different ansatzes to model such a behavior are developed and compared. By means of computer simulations of a multi-agent system we show that local avoidance - as a special form of asymmetric repulsion between animals - leads to the emergence of a vortex swarm. The transition from uncorrelated rotation of single agents to the vortex swarming as a function of the swarm size is investigated. Eventually, some evidence of avoidance behavior in Daphnia is provided by comparing experimental and simulation results for two animals.

  2. Shadows on a Giant

    NASA Image and Video Library

    2012-07-02

    Saturn rings cast wide shadows on the planet, and the shadow of a moon also graces the gas giant in this scene from NASA Cassini spacecraft. The moon Enceladus is not shown in this view, but it does cast a small, elongated shadow.

  3. Giant scrotal elephantiasis.

    PubMed

    Kuepper, Daniel

    2005-02-01

    How much can a man carry? Penoscrotal elephantiasis is a debilitating syndrome. This is a case report of a patient with giant genital elephantiasis secondary to long-standing lymphogranuloma venereum infection in Ethiopia. Complete surgical resection of the pathologic tissue and penile reconstruction was undertaken with good cosmetic and functional results.

  4. [Giant retroperitoneal liposarcoma].

    PubMed

    Mezzour, Mohamed Hicham; El Messaoudi, Yasser Arafat; Fekak, Hamid; Rabii, Redouane; Marnissi, Farida; Karkouri, Mehdi; Salam, Siham; Iraki, Moulay Ahmed; Joual, Abdenbi; Meziane, Fathi

    2006-02-01

    The authors report a case of giant retroperitoneal liposarcoma. The diagnosis was suspected after scanography and magnetic resonance imaging and confirmed by the histological analysis of the extracted piece after surgical treatment. Postoperative evolution was favourable after one year without recurrence or distant metastasis. The authors discuss the pathologic and therapeutic aspects and the prognosis of retroperitoneal liposarcoma.

  5. Electroluminescence of Giant Stretchability.

    PubMed

    Yang, Can Hui; Chen, Baohong; Zhou, Jinxiong; Chen, Yong Mei; Suo, Zhigang

    2016-06-01

    A new type of electroluminescent device achieves giant stretchability by integrating electronic and ionic components. The device uses phosphor powders as electroluminescent materials, and hydrogels as stretchable and transparent ionic conductors. Subject to cyclic voltage, the phosphor powders luminesce, but the ionic conductors do not electrolyze. The device produces constant luminance when stretched up to an area strain of 1500%.

  6. ProFile Vortex and Vortex Blue Nickel-Titanium Rotary Instruments after Clinical Use.

    PubMed

    Shen, Ya; Zhou, Huimin; Coil, Jeffrey M; Aljazaeri, Bassim; Buttar, Rene; Wang, Zhejun; Zheng, Yu-feng; Haapasalo, Markus

    2015-06-01

    The aim of this study was to analyze the incidence and mode of ProFile Vortex and Vortex Blue instrument defects after clinical use in a graduate endodontic program and to examine the impact of clinical use on the instruments' metallurgical properties. A total of 330 ProFile Vortex and 1136 Vortex Blue instruments from the graduate program were collected after each had been used in 3 teeth. The incidence and type of instrument defects were analyzed. The lateral surfaces and fracture surfaces of the fractured files were examined by using scanning electron microscopy. Unused and used instruments were examined by full and partial differential scanning calorimetry. No fractures were observed in the 330 ProFile Vortex instruments, whereas 20 (6.1%) revealed bent or blunt defects. Only 2 of the 1136 Vortex Blue files fractured during clinical use. The cause of fracture was shear stress. The fractures occurred at the tip end of the spirals. Only 1.8% (21 of 1136) of the Vortex Blue files had blunt tips. Austenite-finish temperatures were very similar for unused and used ProFile Vortex files and were all greater than 50°C. The austenite-finish temperatures of used and unused Vortex Blue files (38.5°C) were lower than those in ProFile Vortex instruments (P < .001). However, the transformation behavior of Vortex Blue files had an obvious 2-stage transformation, martensite-to-R phase and R-to-austenite phase. The trends of differential scanning calorimetry plots of unused Vortex Blue instruments and clinically used instruments were very similar. The risk of ProFile Vortex and Vortex Blue instrument fracture is very low when instruments are discarded after clinical use in the graduate endodontic program. The Vortex Blue files have metallurgical behavior different from ProFile Vortex instruments. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  7. Optical vortex arrays from smectic liquid crystals.

    PubMed

    Son, Baeksik; Kim, Sejeong; Kim, Yun Ho; Käläntär, K; Kim, Hwi-Min; Jeong, Hyeon-Su; Choi, Siyoung Q; Shin, Jonghwa; Jung, Hee-Tae; Lee, Yong-Hee

    2014-02-24

    We demonstrate large-area, closely-packed optical vortex arrays using self-assembled defects in smectic liquid crystals. Self-assembled smectic liquid crystals in a three-dimensional torus structure are called focal conic domains. Each FCD, having a micro-scale feature size, produces an optical vortex with consistent topological charge of 2. The spiral profile in the interferometry confirms the formation of an optical vortex, which is predicted by Jones matrix calculations.

  8. Two-color interface vortex solitons

    SciTech Connect

    Xu Zhiyong

    2010-02-15

    We study the existence and properties of vortex solitons supported by an interface between two distinct optical lattices imprinted in nonlinear quadratic media. We analyze the impact of guiding parameters of lattices and phase mismatching conditions on the existence and stability of two-color interface vortex solitons. The salient point is that interface vortex solitons feature highly asymmetric profiles, and are stable throughout almost the entire existence domain.

  9. On the structure of the turbulent vortex

    NASA Technical Reports Server (NTRS)

    Roberts, L.

    1985-01-01

    The trailing vortex generated by a lifting surface, the structure of its turbulent core and the influence of axial flow within the vortex on its initial persistence and on its subsequent decay are described. Similarity solutions of the turbulent diffusion equation are given in closed form and results are expressed in sufficiently simple terms that the influence of the lifting surface parameters on the length of persistence and the rate of decay of the vortex can be evaluated.

  10. Quantum Kinematics of Bosonic Vortex Loops

    SciTech Connect

    Goldin, G.A.; Owczarek, R.; Sharp, D.H.

    1999-05-06

    Poisson structure for vortex filaments (loops and arcs) in 2D ideal incompressible fluid is analyzed in detail. Canonical coordinates and momenta on coadjoint orbits of the area-preserving diffeomorphism group, associated with such vortices, are found. The quantum space of states in the simplest case of ''bosonic'' vortex loops is built within a geometric quantization approach to the description of a quantum fluid. Fock-like structure and non-local creation and annihilation operators of quantum vortex filaments are introduced.

  11. Vortex Beams for Atomic Resolution Dichroism

    SciTech Connect

    Idrobo Tapia, Juan C; Pennycook, Stephen J

    2011-01-01

    Vortex beams carrying orbital angular momentum have been produced recently with electron microscopy by interfering an incident electron beam with a grid containing dislocations. Here, we present an analytical derivation of vortex wave functions in reciprocal and real space. We outline their mathematical and physical properties and describe the conditions under which vortex beams can be used in scanning transmission microscopy to measure magnetic properties of materials at the atomic scale.

  12. An investigation of counterrotating tip vortex interaction

    NASA Technical Reports Server (NTRS)

    Majjigi, R. K.; Uenishi, K.; Gliebe, P. R.

    1989-01-01

    A tip vortex interaction model originally developed for compressors has been extended and adapted for use with counterrotating open rotors. Comparison of available acoustic data with predictions (made with and without the tip vortex model included) illustrate the importance of this interaction effect. This report documents the analytical modeling, a limited experimental verification, and certain key parametric studies pertaining to the tip vortex as a noise source mechanism for the unsteady loading noise of counterrotating properllers.

  13. Combined electrical and resonant optical excitation characterization of multi-quantum well InGaN-based light-emitting diodes

    SciTech Connect

    Presa, S.; Maaskant, P. P.; Corbett, B.; Kappers, M. J.; Humphreys, C. J.

    2016-07-15

    We present a comprehensive study of the emission spectra and electrical characteristics of InGaN/GaN multi-quantum well light-emitting diode (LED) structures under resonant optical pumping and varying electrical bias. A 5 quantum well LED with a thin well (1.5 nm) and a relatively thick barrier (6.6 nm) shows strong bias-dependent properties in the emission spectra, poor photovoltaic carrier escape under forward bias and an increase in effective resistance when compared with a 10 quantum well LED with a thin (4 nm) barrier. These properties are due to a strong piezoelectric field in the well and associated reduced field in the thicker barrier. We compare the voltage ideality factors for the LEDs under electrical injection, light emission with current, photovoltaic mode (PV) and photoluminescence (PL) emission. The PV and PL methods provide similar values for the ideality which are lower than for the resistance-limited electrical method. Under optical pumping the presence of an n-type InGaN underlayer in a commercial LED sample is shown to act as a second photovoltaic source reducing the photovoltage and the extracted ideality factor to less than 1. The use of photovoltaic measurements together with bias-dependent spectrally resolved luminescence is a powerful method to provide valuable insights into the dynamics of GaN LEDs.

  14. Improved light extraction efficiency of InGaN-based multi-quantum well light emitting diodes by using a single die growth.

    PubMed

    Park, Min Joo; Kwon, K W; Kim, Y H; Park, S H; Kwak, Joon Seop

    2011-05-01

    We have demonstrated that the light extraction efficiency of the InGaN based multi-quantum well light-emitting diodes (LEDs) can be improved by using a single die growth (SDG) method. The SDG was performed by patterning the n-GaN and sapphire substrate with a size of single chip (600 x 250 microm2) by using a laser scriber, followed by the regrowth of the n-GaN and LED structures on the laser patterned n-GaN. We fabricated lateral LED chips having the SDG structures (SDG-LEDs), in which the thickness of the regrown n-GaN was varied from 2 to 6 microm. For comparison, we also fabricated conventional LED chips without the SDG structures. The SDG-LEDs showed lower operating voltage when compared to the conventional LEDs. In addition, the output power of the SDG-LEDs was significantly higher than that of the conventional LEDs. From optical ray tracing simulations, the increase in the thickness and sidewall angle of the regrown n-GaN and LED structures may enhance photon escapes from the tilted facets of the regrown n-GaN, followed by the increase in light output power and extraction efficiency of the SDG-LEDs.

  15. Combined electrical and resonant optical excitation characterization of multi-quantum well InGaN-based light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Presa, S.; Maaskant, P. P.; Kappers, M. J.; Humphreys, C. J.; Corbett, B.

    2016-07-01

    We present a comprehensive study of the emission spectra and electrical characteristics of InGaN/GaN multi-quantum well light-emitting diode (LED) structures under resonant optical pumping and varying electrical bias. A 5 quantum well LED with a thin well (1.5 nm) and a relatively thick barrier (6.6 nm) shows strong bias-dependent properties in the emission spectra, poor photovoltaic carrier escape under forward bias and an increase in effective resistance when compared with a 10 quantum well LED with a thin (4 nm) barrier. These properties are due to a strong piezoelectric field in the well and associated reduced field in the thicker barrier. We compare the voltage ideality factors for the LEDs under electrical injection, light emission with current, photovoltaic mode (PV) and photoluminescence (PL) emission. The PV and PL methods provide similar values for the ideality which are lower than for the resistance-limited electrical method. Under optical pumping the presence of an n-type InGaN underlayer in a commercial LED sample is shown to act as a second photovoltaic source reducing the photovoltage and the extracted ideality factor to less than 1. The use of photovoltaic measurements together with bias-dependent spectrally resolved luminescence is a powerful method to provide valuable insights into the dynamics of GaN LEDs.

  16. Effect of Sapphire Substrate Thickness on the Characteristics of 450 nm InGaN/GaN Multi-Quantum Well Light-Emitting Diodes.

    PubMed

    Tawfik, Wael Z; Bea, Seo-Jung; Yang, Seung Bea; Ryu, Sang-Wan; Lee, June Key

    2015-07-01

    450 nm InGaN/GaN multi-quantum well (MQW) ligth-emitting diodes (LEDs) prepared on sapphire substrate with different thicknesses were fabricated and characterized. By thinning the sapphire substrate to 50 µm, it was found that the LED exhibited the highest light output power of ~48 mW under high injection current of 50 mA, improved by about 35% compared to that with 200 µm-thick sapphire without increasing the operating voltage. The electroluminescence intensity was increased and the spectral peak wavelength was blue-shifted, because the wafer bowing-induced mechanical stress alters the piezoelectric field in the InGaN/GaN MQW active region of the LED. The internal quantum efficiency was also improved by about 10% at an injection current of 50 mA. Moreover, the external quantum efficiency and light extraction efficiency were optimized because of enhanced light output intensity. The results confirmed that sapphire substrate thinning effectively alters the piezoelectric field in the InGaN/GaN active region, and hence increases both of the effective band gap and the probability of radiative recombination.

  17. Effect of surface tension on electrocaloric effects in the ferroelectric nanomaterial with vortex domain structures

    NASA Astrophysics Data System (ADS)

    Li, B.; Wang, J. B.; Zhong, X. L.; Wang, F.; Wang, L. J.; Zhou, Y. C.

    2013-07-01

    The influence of intrinsic surface tension on the electrocaloric effect (ECE) in the ferroelectric nanomaterial with vortex domain structures is studied by using the phase field method. The calculation results show that a giant adiabatic temperature change (ΔT = 5.8 K) related to the toroidal moment change appears in the PbTiO3 (PTO) ferroelectric nanoparticle with the surface tension coefficient μ = 5 N/m under the vorticity vector of curled electric field (Q1 = 0 mV/Å2, ΔQ1 = 0.9 mV/Å2) at room temperature. The magnitude of the adiabatic temperature change decreases with the increase in surface tension. The decrease in size is found to enhance the ECE of PTO nanoparticle with vortex domain structures when the surface tension is not considered.

  18. The quasi-vortex-lattice method for wings with edge vortex separation

    NASA Technical Reports Server (NTRS)

    Pao, J. L.; Lan, E.

    1980-01-01

    The aerodynamic characteristics of wings with leading-edge vortex separation were predicted using a method based on a flow model with free vortex elements which are allowed to merge into a concentrated core. The calculated pressure distribution is more accurate than that predicted by methods with discrete vortex filaments alone. In addition, the computer time is reduced approximately by half.

  19. Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays

    NASA Astrophysics Data System (ADS)

    Baldacchino, D.; Ferreira, C.; Ragni, D.; van Bussel, G. J. W.

    2016-09-01

    In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the infinite vortex cascade, a numerical model of four base-vortices is chosen to represent two primary counter-rotating vortex pairs and their mirror plane images, introducing the vortex strength ratio as a free parameter. The resulting system of equations is also defined in terms of the vortex row separation and the qualitative features of the ensuing motion are mapped. A translating and orbiting regime are identified for different cascade separations. The latter occurs for all unequal strength vortex pairs. Thus, the motion is further classified by studying the cyclic behaviour of the orbiting regime and it is shown that for small mismatches in vortex strength, the orbiting length and time scales are sufficiently large as to appear, in the near wake, as translational (non-orbiting). However, for larger mismatches in vortex strength, the orbiting motion approaches the order of the starting height of the vortex. Comparisons between experimental data and the potential flow model show qualitative agreement whilst viscous effects account for the major discrepancies. Despite this, the model captures the orbital mode observed in the measurements and provides an impetus for considering the impact of these complex interactions on vortex generator designs.

  20. Leapfrogging of multiple coaxial viscous vortex rings

    SciTech Connect

    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.

  1. Spin transport in tilted electron vortex beams

    SciTech Connect

    Basu, Banasri; Chowdhury, Debashree

    2014-12-10

    In this paper we have enlightened the spin related issues of tilted Electron vortex beams. We have shown that in the skyrmionic model of electron we can have the spin Hall current considering the tilted type of electron vortex beam. We have considered the monopole charge of the tilted vortex as time dependent and through the time variation of the monopole charge we can explain the spin Hall effect of electron vortex beams. Besides, with an external magnetic field we can have a spin filter configuration.

  2. ASRS Reports on Wake Vortex Encounters

    NASA Technical Reports Server (NTRS)

    Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

    2010-01-01

    ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

  3. Motion of a linear vortex singularity

    SciTech Connect

    Kiknadze, L.V.; Mamaladze, Y.G.

    1980-10-01

    A formula is obtained for the velocity of a certain element of a linear vortex in a Bose gas and in helium II in terms of the contribution made to the wave function by the remaining elements of the same wave vortex and of other perturbations of the ground state of the medium. It is shown that, besides the Magnus force, the vortex is acted upon by a force proportional to the condensate-density gradient and directed opposite to the gradient. A generalization is possible to linear vortex singularities of relativistic fields that do not describe any condensed medium at all.

  4. Leapfrogging of multiple coaxial viscous vortex rings

    NASA Astrophysics Data System (ADS)

    Cheng, M.; Lou, J.; Lim, T. T.

    2015-03-01

    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.

  5. The Vortex of Burgers in Protoplanetary Disc

    NASA Astrophysics Data System (ADS)

    Abrahamyan, M. G.

    2017-07-01

    The effect of a Burgers vortex on formation of planetesimals in a protoplanetary disc in local approach is considered. It is shown that there is not any circular orbit for rigid particles in centrifugal balance; only stable position in Burgers vortex under the influence of centrifugal, Coriolis, pressure gradient and Stokes drag forces is the center of vortex. The two-dimensional anticyclonic Burgers vortex with homogeneously rotating kernel and a converging radial stream of substance can effectively accumulate in its nuclear area the meter- sized rigid particles of total mass ˜1028g for characteristic time ˜106yr.

  6. Optical vortex phase-shifting digital holography.

    PubMed

    Guo, Cheng-Shan; Cheng, Xin; Ren, Xiu-Yun; Ding, Jian-Ping; Wang, Hui-Tian

    2004-10-18

    We report a new optical vortex phase-shifting method for digital holography, in which an optical vortex mode is taken as the reference beam for holographic recording, and the required phase shifts are directly generated by rotating the vortex mode. In digital reconstruction, the complex amplitude of the object wave can be retrieved by use of the conventional phase shifting algorithm on condition that the digital illumination beam is replaced by an vortex beam with the same topological charge as the reference used. Both the theoretical analysis and experimental results demonstrate the feasibility of this approach.

  7. Vortex dynamics investigation using an acoustic technique

    NASA Astrophysics Data System (ADS)

    Manneville, S.; Robres, J. H.; Maurel, A.; Petitjeans, P.; Fink, M.

    1999-11-01

    A new acoustic technique using the double time-reversal mirrors system and based on geometrical acoustics, is used to study a vortical flow. The interaction between the sound and a vortex is described in details. This technique has been applied to the study of a stretched vortex. This vortex is generated by stretching the vorticity of a boundary layer in a low velocity water channel. It is shown that the velocity field can be reconstructed from the phase distortion of an ultrasonic wave. The technique gives access to a complete characterization of the vortex dynamics, such as the temporal evolution of its size, its circulation and its position.

  8. The vortex structure of magnetic solitons

    NASA Astrophysics Data System (ADS)

    Kovalev, A. S.

    2017-02-01

    Soliton excitations in the general form are considered using the classical model, in a two-dimensional easy-plane ferromagnet. Equations are derived and solved for small-amplitude two-parameter dynamic solitons. It is demonstrated that they have a vortex structure and that as their amplitude increases, the excitations turn into coupled quadrupole vortex states that are characterized by two dynamic parameters: the soliton velocity and its internal precession frequency. The limit transitions of vortex solitons in the general form into vortex dipoles, magnetic lamps, and magnon droplets, are analyzed. The obtained results are compared against the corresponding information about solitons in one-dimensional magnetic systems.

  9. Measurements of a supersonic turbulent vortex

    NASA Technical Reports Server (NTRS)

    Metwally, O. M.; Settles, G. S.

    1988-01-01

    Mean-flow measurements of a supersonic turbulent streamwise vortex are presented. This vortex was produced by the injection of a swirling flow along the centerline of a supersonic airstream at Mach 3. Directional Mach number distributions, obtained via a five-hole flow-angularity probe, reveal vortex characteristics similar to those of the incompressible case, even though rotational Mach numbers up to 0.8 were obtained. This work is the first step of a study of the supersonic vortex breakdown phenomenon.

  10. Vectorial complex-source vortex beams

    NASA Astrophysics Data System (ADS)

    Orlov, S.; Banzer, P.

    2014-08-01

    The scalar complex source vortex model is an accurate description of highly focused scalar vortices. We use it to construct a variety of vectorial solutions of Maxwell's equations describing highly focused and variously polarized vector vortex beams accurately. Three different families of optical vector vortex beams are presented and studied in detail. In this model, optical vortices derived within Cartesian symmetry correspond to circularly and linearly polarized highly focused vortex beams in the focus of a high numerical aperture focusing system. In addition, we report on vortical complex-source beams derived within cylindrical and spherical symmetries which exhibit very special and intriguing properties.

  11. Measuring vortex charge with a triangular aperture.

    PubMed

    de Araujo, Luís E E; Anderson, Matthew E

    2011-03-15

    A triangular aperture illuminated with a vortex beam creates a truncated lattice diffraction pattern that identifies the charge of the vortex. In this Letter, we demonstrate the measurement of vortex charge via this approach for vortex beams up to charge ±7. We also demonstrate the use of this technique for measuring femtosecond vortices and noninteger vortices, comparing these results with numerical modeling. It is shown that this technique is simple and reliable, but care must be taken when interpreting the results for the noninteger case.

  12. Investigation of the Vortex Tab. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Hoffler, K. D.

    1985-01-01

    An investigation was made into the drag reduction capability of vortex tabs on delta wing vortex flaps. The vortex tab is an up-deflected leading edge portion of the vortex flap. Tab deflection augments vortex suction on the flap, thus improving its thrust, but the tab itself is drag producing. Whether a net improvement in the drag reduction can be obtained with vortex tabs, in comparison with plane vortex flaps of the same total area, was the objective of this investigation. Wind tunnel tests were conducted on two models, and analytical studies were performed on one of them using a free vortex sheet theory.

  13. Recent Laboratory and Numerical Trailing Vortex Studies

    NASA Technical Reports Server (NTRS)

    Delisi, Donald P.; Greene, George C.; Robins, Robert E.; Singh, Raminder

    1996-01-01

    Results from two laboratory studies and two numerical studies are presented. In the first laboratory study, measurements of the strength of vortices from a three-dimensional (3-D) model wing are presented. The measurements follow the vortices as they evolve in time from a two-dimensional (2-D) line vortex pair to the development and migration of 3-D vortex rings. It is shown that the resulting vortex rings can contain up to 40 percent of the initial vortex circulation. Thus, the formation of vortex rings may not necessarily signal the end of the wake hazard to following aircraft. In the second laboratory study, we present the results of an experiment which shows how the spanwise drag distribution affects wake-vortex evolution. In this experiment, we modified the spanwise drag distribution on a model wing while keeping the total lift and drag constant. The results show that adding drag on or near the centerline of the wing has a larger effect than adding drag at or near the wingtips. These measurements complement the results of NASA studies in the 1970s. In the first numerical study, results of 3-D numerical calculations are presented which show that the vortex Reynolds number has a significant influence on the evolution and migration of wake vortices. When the Reynolds number is large, 3-D vortex rings evolve from the initially 2-D line vortex pairs. These vortex rings then migrate vertically. When the Reynolds number is lower, the transition of vorticity from 2-D to 3-D is delayed. When the Reynolds number is very low, the vortices never transition to 3-D, and the vertical migration is significantly reduced. It is suggested that this effect may have been important in previous laboratory wake-evolution studies. A second numerical study shows the influence that vertical wind shear can have on trailing vortex evolution.

  14. Rotating hot-wire investigation of the vortex responsible for blade-vortex interaction noise

    NASA Technical Reports Server (NTRS)

    Fontana, Richard Remo

    1988-01-01

    This distribution of the circumferential velocity of the vortex responsible for blade-vortex interaction noise was measured using a rotating hot-wire rake synchronously meshed with a model helicopter rotor at the blade passage frequency. Simultaneous far-field acoustic data and blade differential pressure measurements were obtained. Results show that the shape of the measured far-field acoustic blade-vortex interaction signature depends on the blade-vortex interaction geometry. The experimental results are compared with the Widnall-Wolf model for blade-vortex interaction noise.

  15. Experimental study of surface waves scattering by a single vortex and a vortex dipole.

    PubMed

    Vivanco, Francisco; Melo, Francisco

    2004-02-01

    Surface waves interacting with filamentary vortex offer an interesting tool to characterize static and dynamics of surface vorticity. An experimental study of the scattered wave by a single vortex as well as by a vortex dipole is reported. On a plane wave front, the vortex circulation introduces a spatial phase shift that gives rise to dislocated waves. Dislocations can be explained by the effect of the differential advection due to the vortex flow, on the propagating wave front. Both the Burgers vector of dislocations and the scattering cross section are measured in the deep water regime. The analogy between the wave-vortex interaction and the Aharonov-Bohm effect in quantum mechanics is explored by contrasting the Burgers vectors of dislocations as well as the form of the scattered wave in both cases. For the case of the hard core vortex, spiral waves are observed in agreement with theoretical works on both the Aharanov-Bohm effect and classical surface wave mechanics.

  16. The effect of tip vortex structure on helicopter noise due to blade/vortex interaction

    NASA Technical Reports Server (NTRS)

    Wolf, T. L.; Widnall, S. E.

    1978-01-01

    A potential cause of helicopter impulsive noise, commonly called blade slap, is the unsteady lift fluctuation on a rotor blade due to interaction with the vortex trailed from another blade. The relationship between vortex structure and the intensity of the acoustic signal is investigated. The analysis is based on a theoretical model for blade/vortex interaction. Unsteady lift on the blades due to blade/vortex interaction is calculated using linear unsteady aerodynamic theory, and expressions are derived for the directivity, frequency spectrum, and transient signal of the radiated noise. An inviscid rollup model is used to calculate the velocity profile in the trailing vortex from the spanwise distribution of blade tip loading. A few cases of tip loading are investigated, and numerical results are presented for the unsteady lift and acoustic signal due to blade/vortex interaction. The intensity of the acoustic signal is shown to be quite sensitive to changes in tip vortex structure.

  17. Pinch-off of axisymmetric vortex pairs in the limit of vanishing vortex line curvature

    NASA Astrophysics Data System (ADS)

    Sadri, V.; Krueger, P. S.

    2016-07-01

    Pinch-off of axisymmetric vortex pairs generated by flow between concentric cylinders with radial separation ΔR was studied numerically and compared with planar vortex dipole behavior. The axisymmetric case approaches planar vortex dipole behavior in the limit of vanishing ΔR. The flow was simulated at a jet Reynolds number of 1000 (based on ΔR and the jet velocity), jet pulse length-to-gap ratio ( /L Δ R ) in the range 10-20, and gap-to-outer radius ratio ( /Δ R R o ) in the range 0.01-0.1. Contrary to investigations of strictly planar flows, vortex pinch-off was observed for all gap sizes investigated. This difference was attributed to the less constrained geometry considered, suggesting that even very small amounts of vortex line curvature and/or vortex stretching may disrupt the absence of pinch-off observed in strictly planar vortex dipoles.

  18. Intelligent and mass vortex flowmeters

    SciTech Connect

    Ribolini, E.

    1996-02-01

    In nature, Karman vortices are quite common. For instance, they happen when an airstream flows past a mountain, house, pole, tower, or skyscraper, or, more simply, when it blows among branches of a tree. The typical spiral shape of these swirls is invisible because there is no tracing element, such as the clouds in the satellite photo. Also, the observation point is rarely above or below the plane of these classic spiral shapes. Or you can watch the alternating whirlpool train that a river or stream makes behind bridge piers. Regular Karman vortices form downstream of a bluff body along two distinct wakes: the vortices of one wake rotate clockwise, those of the other rotate counterclockwise. Close to the bluff body, the wake distance is always constant and depends on bluff body shape and dimensions. The distance between two adjacent vortices is also constant and independent of fluid parameters such as velocity, pressure, density, and temperature. Vortices interact with their surrounding space by stimulating or choking every other nearby swirl on the verge of birth and development. Two Karman vortices cannot be generated simultaneously, but only one at a time, alternately on the left and right side of the bluff body. The process works just like a fluidic flip-flop. This natural phenomenon can be created artificially by placing a trapezoidal, or similarly symmetrical, bar across the diameter of a pipe section. Parallelism of the internal walls of the pipe and the corners of the trapezoidal bar ensure stability of the separation point of the boundary layer. Consequently, the separation point of each vortex with respect to the bar remains stable and the vortex train is regular. If the fluid speed doubles, creation of swirls doubles while the small volume encompassed by each vortex remains constant. So, by counting the number of swirls passing a fixed point during a defined time interval, one can compute the total passed fluid volume. 3 figs.

  19. Simulations of Active Vortex Generators

    NASA Technical Reports Server (NTRS)

    Mansour, N. N.; Koumoutsakos, P.; Merriam, Marshal (Technical Monitor)

    1996-01-01

    We are interested in the study, via numerical simulations, of active vortex generators. Vortex generators may be used to modify the inner part of the boundary layer or to control separation thus enhancing the performance and maneuverability of aerodynamic configurations. we consider generators that consist of a surface cavity elongated in the streamwise direction and partially covered with a moving lid that at rest lies flush with the boundary. Streamwise vorticity is generated and ejected due to the oscillatory motion of the lid. The present simulations complement relevant experimental investigations of active vortex generators that have been conducted at NASA Ames Research Center and Stanford University used a piezoelectric device in water, allowing for small amplitude high frequency oscillations. They placed the lid asymmetrically on the cavity and observed a strong outward velocity at the small gap of the cavity. Saddoughi used a larger mechanically driven device in air to investigate this flow and observed a jet emerging from the wide gap of the configuration, contrary to the findings of Jacobson and Reynolds We are simulating the flows generated by these devices and we are conducting a parametric study that would help us elucidate the physical mechanisms present in the flow. Conventional computational schemes encounter difficulties when simulating flows around complex configurations undergoing arbitrary motions. Here we present a formulation that achieves this task on a purely Lagrangian frame by extending the formulation presented by Koumoutsakos, Leonard and Pepin (1994). The viscous effects are taken into account by modifying the strength Of the particles, whereas fast multipole schemes employing hundreds of thousands of particles allow for high resolution simulations. We shall present simulation results of an oscillating plate at various Reynolds numbers and Strouhal frequencies.

  20. Simulations of Active Vortex Generators

    NASA Technical Reports Server (NTRS)

    Mansour, N. N.; Koumoutsakos, P.; Merriam, Marshal (Technical Monitor)

    1996-01-01

    We are interested in the study, via numerical simulations, of active vortex generators. Vortex generators may be used to modify the inner part of the boundary layer or to control separation thus enhancing the performance and maneuverability of aerodynamic configurations. We consider generators that consist of a surface cavity elongated in the streamwise direction and partially covered with a moving lid that at rest lies flush with the boundary. Streamwise voracity is generated and ejected due to the oscillatory motion of the lid. The present simulations c Implement relevant experimental investigations of active vortex generators that have been conducted at NASA Ames Research Center and Stanford University. Jacobson and Reynolds used a piezoelectric device in water, allowing for small amplitude high frequency oscillations. They placed the lid asymmetrically on the cavity and observed a strong outward velocity at the small gap of the cavity. Saddoughi used a larger mechanically driven device in air to investigate this flow and observed a jet emerging from the wide gap of the configuration, contrary to the findings of Jacobson and Reynolds. More recently, Lachowiez and Wlezien are investigating the flow generated by an electro-mechanically driven lid to be used for assertion control in aerodynamic applications. We are simulating the flows generated by these devices and we are conducting a parametric study that would help us elucidate the physical mechanisms present in the flow. Conventional computational schemes encounter difficulties when simulating flows around complex configurations undergoing arbitrary motions. Here we present a formulation that achieves this task on a purely Lagrangian frame by extending the formulation presented by Koumoutsakos, Leonard and Pepin. The viscous effects are taken into account by modifying the strength of the particles, whereas fast multipole schemes employing hundreds of thousands ol'particle's allow for high resolution simulations

  1. Simulations of Active Vortex Generators

    NASA Technical Reports Server (NTRS)

    Mansour, N. N.; Koumoutsakos, P.; Merriam, Marshal (Technical Monitor)

    1996-01-01

    We are interested in the study, via numerical simulations, of active vortex generators. Vortex generators may be used to modify the inner part of the boundary layer or to control separation thus enhancing the performance and maneuverability of aerodynamic configurations. We consider generators that consist of a surface cavity elongated in the streamwise direction and partially covered with a moving lid that at rest lies flush with the boundary. Streamwise voracity is generated and ejected due to the oscillatory motion of the lid. The present simulations c Implement relevant experimental investigations of active vortex generators that have been conducted at NASA Ames Research Center and Stanford University. Jacobson and Reynolds used a piezoelectric device in water, allowing for small amplitude high frequency oscillations. They placed the lid asymmetrically on the cavity and observed a strong outward velocity at the small gap of the cavity. Saddoughi used a larger mechanically driven device in air to investigate this flow and observed a jet emerging from the wide gap of the configuration, contrary to the findings of Jacobson and Reynolds. More recently, Lachowiez and Wlezien are investigating the flow generated by an electro-mechanically driven lid to be used for assertion control in aerodynamic applications. We are simulating the flows generated by these devices and we are conducting a parametric study that would help us elucidate the physical mechanisms present in the flow. Conventional computational schemes encounter difficulties when simulating flows around complex configurations undergoing arbitrary motions. Here we present a formulation that achieves this task on a purely Lagrangian frame by extending the formulation presented by Koumoutsakos, Leonard and Pepin. The viscous effects are taken into account by modifying the strength of the particles, whereas fast multipole schemes employing hundreds of thousands ol'particle's allow for high resolution simulations

  2. Ice Giant Exploration

    NASA Astrophysics Data System (ADS)

    Rymer, A. M.; Arridge, C. S.; Masters, A.; Turtle, E. P.; Simon, A. A.; Hofstadter, M. D.; Turrini, D.; Politi, R.

    2015-12-01

    The Ice Giants in our solar system, Uranus and Neptune, are fundamentally different from their Gas Giant siblings Jupiter and Saturn, from the different proportions of rock and ice to the configuration of their planetary magnetic fields. Kepler space telescope discoveries of exo-planets indicate that planets of this type are among the most ubiquitous universally and therefore a future mission to explore the nature of the Ice Giants in our own solar system will provide insights into the nature of extra-solar system objects in general. Uranus has the smallest self- luminosity of all the planets, potentially related to catastrophic events early in the planet's history, which also may explain Uranus' large obliquity. Uranus' atmosphere is subject to extreme seasonal forcing making it unique in the Solar System. Neptune is also unique in a number of ways, notably its large moon Triton which is likely a captured Kuiper Belt Object and one of only two moons in the solar system with a robustly collisional atmosphere. Similar to Uranus, the angle between the solar wind and the magnetic dipole axis is subject to large-amplitude variations on both diurnal and seasonal timescales, but peculiarly it has one of the quietest magnetospheres of the solar system, at least according to Voyager 2, the only spacecraft to encounter Neptune to date. A comprehensive mission, as advocated in the Decadal Survey, would provide enormous science return but is also challenging and expensive. In this presentation we will discuss mission scenarios and suggest how collaboration between disciplines and internationally can help us to pursue a mission that includes Ice Giant exploration.

  3. Giant cell arteritis

    PubMed Central

    Calvo-Romero, J

    2003-01-01

    Giant cell arteritis (GCA), temporal arteritis or Horton's arteritis, is a systemic vasculitis which involves large and medium sized vessels, especially the extracranial branches of the carotid arteries, in persons usually older than 50 years. Permanent visual loss, ischaemic strokes, and thoracic and abdominal aortic aneurysms are feared complications of GCA. The treatment consists of high dose steroids. Mortality, with a correct treatment, in patients with GCA seems to be similar that of controls. PMID:13679546

  4. Giant Cell Arteritis.

    PubMed

    Hoffman, Gary S

    2016-11-01

    This issue provides a clinical overview of giant cell arteritis, focusing on diagnosis, treatment, and practice improvement. The content of In the Clinic is drawn from the clinical information and education resources of the American College of Physicians (ACP), including MKSAP (Medical Knowledge and Self-Assessment Program). Annals of Internal Medicine editors develop In the Clinic in collaboration with the ACP's Medical Education and Publishing divisions and with the assistance of additional science writers and physician writers.

  5. Vortex metrology using Fourier analysis techniques: vortex networks correlation fringes.

    PubMed

    Angel-Toro, Luciano; Sierra-Sosa, Daniel; Tebaldi, Myrian; Bolognini, Néstor

    2012-10-20

    In this work, we introduce an alternative method of analysis in vortex metrology based on the application of the Fourier optics techniques. The first part of the procedure is conducted as is usual in vortex metrology for uniform in-plane displacement determination. On the basis of two recorded intensity speckled distributions, corresponding to two states of a diffuser coherently illuminated, we numerically generate an analytical signal from each recorded intensity pattern by using a version of the Riesz integral transform. Then, from each analytical signal, a two-dimensional pseudophase map is generated in which the vortices are located and characterized in terms of their topological charges and their core's structural properties. The second part of the procedure allows obtaining Young's interference fringes when Fourier transforming the light passing through a diffracting mask with multiple apertures at the locations of the homologous vortices. In fact, we use the Fourier transform as a mathematical operation to compute the far-field diffraction intensity pattern corresponding to the multiaperture set. Each aperture from the set is associated with a rectangular hole that coincides both in shape and size with a pixel from recorded images. We show that the fringe analysis can be conducted as in speckle photography in an extended range of displacement measurements. Effects related with speckled decorrelation are also considered. Our experimental results agree with those of speckle photography in the range in which both techniques are applicable.

  6. Low flow vortex shedding flowmeter

    NASA Technical Reports Server (NTRS)

    Waugaman, Charles J.

    1989-01-01

    The purpose was to continue a development project on a no moving parts vortex shedding flowmeter used for flow measurement of hypergols. The project involved the design and construction of a test loop to evaluate the meter for flow of Freon which simulates the hypergol fluids. Results were obtained on the output frequency characteristics of the flow meter as a function of flow rate. A family of flow meters for larger size lines and ranges of flow was sized based on the results of the tested meter.

  7. Investigation of Wake-Vortex Aircraft Encounters

    NASA Technical Reports Server (NTRS)

    Smith, Sonya T.

    1999-01-01

    The National Aeronautics and Space Administration is addressing airport capacity enhancements during instrument meteorological conditions though the Terminal Area Productivity (TAP) program. The major goal of the TAP program is to develop the technology that will allow air traffic levels during instrument meteorological condition to approach those achieved during visual operations. The Reduced Spacing Operations (RSO) subelement of TAP at the NASA Langley Research Center (LaRC) will develop the Aircraft Vortex Spacing System (AVOSS). The purpose of the AVOSS is to integrate current and predicted weather conditions, wake vortex transport and decay knowledge, wake vortex sensor data, and operational definitions of acceptable strengths for vortex encounters to produce dynamic wake vortex separation criteria. The proposed research is in support of the wake vortex hazard definition component of the LaRC AVOSS development research. The research program described in the next section provided an analysis of the static test data and uses this data to evaluate the accuracy vortex/wake-encounter models. The accuracy of these models has not before been evaluated using experimental data. The research results also presented the first analysis of the forces and moments imparted on an airplane during a wake vortex encounter using actual flight test data.

  8. Photographic System Makes Path Of Vortex Visible

    NASA Technical Reports Server (NTRS)

    Jones, Stephen B.; Szczepkowsky, Greg

    1993-01-01

    System making rapid flows visible developed to record track followed by ring vortex when encountering object near its path. Schlieren optical setup includes standard Z-configuration mirror arrangement and pulsed, synchronized source of light. System proves valuable in determining position, velocity, and acceleration of vortex as it passes over and interacts with object in its path.

  9. Vortex avalanches in a type II superconductor

    SciTech Connect

    Behnia, K.; Capan, C.; Mailly, D.; Etienne, B.

    1999-12-01

    The authors report on a study of the spatiotemporal variation of magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. A sizable fraction of the increase in the local vortex population occurs in abrupt jumps. They compare the size distribution of these avalanches with the predictions of self-organized-criticality models for vortex dynamics.

  10. Obstacle-induced spiral vortex breakdown

    NASA Astrophysics Data System (ADS)

    Pasche, Simon; Gallaire, François; Dreyer, Matthieu; Farhat, Mohamed

    2014-08-01

    An experimental investigation on vortex breakdown dynamics is performed. An adverse pressure gradient is created along the axis of a wing-tip vortex by introducing a sphere downstream of an elliptical hydrofoil. The instrumentation involves high-speed visualizations with air bubbles used as tracers and 2D Laser Doppler Velocimeter (LDV). Two key parameters are identified and varied to control the onset of vortex breakdown: the swirl number, defined as the maximum azimuthal velocity divided by the free-stream velocity, and the adverse pressure gradient. They were controlled through the incidence angle of the elliptical hydrofoil, the free-stream velocity and the sphere diameter. A single helical breakdown of the vortex was systematically observed over a wide range of experimental parameters. The helical breakdown coiled around the sphere in the direction opposite to the vortex but rotated along the vortex direction. We have observed that the location of vortex breakdown moved upstream as the swirl number or the sphere diameter was increased. LDV measurements were corrected using a reconstruction procedure taking into account the so-called vortex wandering and the size of the LDV measurement volume. This allows us to investigate the spatio-temporal linear stability properties of the flow and demonstrate that the flow transition from columnar to single helical shape is due to a transition from convective to absolute instability.

  11. An investigation of the vortex method

    SciTech Connect

    Pryor, Jr., Duaine Wright

    1994-05-01

    The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of three dimensional slightly viscous flow with boundaries. This section gives an introduction to the fundamentals of the vortex method. This is done in order to give a basic impression of the previous work and its line of development, as well as develop some notation and concepts which will be used later. The purpose here is not to give a full review of vortex methods or the contributions made by all the researchers in the field. Please refer to the excellent review papers in Sethian and Gustafson, chapters 1 Sethian, 2 Hald, 3 Sethian, 8 Chorin provide a solid introduction to vortex methods, including convergence theory, application in two dimensions and connection to statistical mechanics and polymers. Much of the information in this review is taken from those chapters, Chorin and Marsden and Batchelor, the chapters are also useful for their extensive bibliographies.

  12. Spectral stability of Taylor's vortex array

    NASA Technical Reports Server (NTRS)

    Lin, S. P.; Tobak, M.

    1986-01-01

    In a global sense it is shown that the two-dimensional Taylor vortex array, an exact solution of the Navier-Stokes equation, is absolutely and monotonically stable with respect to infinitesimal disturbances of all discrete frequencies as long as the viscosity is positive. It is suggested that the Taylor vortex array may also be stable with respect to finite amplitude disturbances.

  13. Vortex motion on surfaces of small curvature

    SciTech Connect

    Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.

    2013-12-15

    We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.

  14. The modelling of symmetric airfoil vortex generators

    NASA Technical Reports Server (NTRS)

    Reichert, B. A.; Wendt, B. J.

    1996-01-01

    An experimental study is conducted to determine the dependence of vortex generator geometry and impinging flow conditions on shed vortex circulation and crossplane peak vorticity for one type of vortex generator. The vortex generator is a symmetric airfoil having a NACA 0012 cross-sectional profile. The geometry and flow parameters varied include angle-of-attack alfa, chordlength c, span h, and Mach number M. The vortex generators are mounted either in isolation or in a symmetric counter-rotating array configuration on the inside surface of a straight pipe. The turbulent boundary layer thickness to pipe radius ratio is delta/R = 0. 17. Circulation and peak vorticity data are derived from crossplane velocity measurements conducted at or about 1 chord downstream of the vortex generator trailing edge. Shed vortex circulation is observed to be proportional to M, alfa, and h/delta. With these parameters held constant, circulation is observed to fall off in monotonic fashion with increasing airfoil aspect ratio AR. Shed vortex peak vorticity is also observed to be proportional to M, alfa, and h/delta. Unlike circulation, however, peak vorticity is observed to increase with increasing aspect ratio, reaching a peak value at AR approx. 2.0 before falling off.

  15. Spectral stability of Taylor's vortex array

    NASA Technical Reports Server (NTRS)

    Lin, S. P.; Tobak, M.

    1986-01-01

    In a global sense it is shown that the two-dimensional Taylor vortex array, an exact solution of the Navier-Stokes equation, is absolutely and monotonically stable with respect to infinitesimal disturbances of all discrete frequencies as long as the viscosity is positive. It is suggested that the Taylor vortex array may also be stable with respect to finite amplitude disturbances.

  16. Vortex attraction and the formation of sunspots

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1992-01-01

    A downdraft vortex ring in a stratified atmosphere exhibits universal attraction for nearby vertical magnetic flux bundles. It is speculated that the magnetic fields emerging through the surface of the sun are individually encircled by one or more subsurface vortex rings, providing an important part of the observed clustering of magnetic fibrils to form pores and sunspots.

  17. Some aspects of streamwise vortex behavior during oblique shock wave/vortex interaction

    NASA Astrophysics Data System (ADS)

    Smart, M. K.; Kalkhoran, I. M.; Popovic, S.

    An experimental study of the flowfield generated by the interaction of a streamwise vortex having a strong wake-type axial Mach number profile and a two-dimensional oblique shock wave was conducted in a Mach 2.49 flow. The experiments were aimed at investigating the dynamics of supersonic vortex distortion and to study downstream behavior of a streamwise vortex during a strong shock wave/vortex encounter. The experiments involved positioning an oblique shock generator in the form of a two-dimensional wedge downstream of a semi-span, vortex generator wing section so that the wing-tip vortex interacted with the otherwise planar oblique shock wave. Planar laser sheet visualizations of the flowfield indicated an expansion of the vortex core in crossing a spherically blunt-nose shock front. The maximum vortex core diameter occurred at a distance of 12.7 mm downstream of the wedge leading edge where the vortex had a core diameter of more than double its undisturbed value. At distances further downstream the vortex core diameter remained nearly constant, while it appeared to become more diffused at distances far from the wedge leading edge. Measurements of vortex trajectory revealed that the vortex convected in the freestream direction immediately downstream of the bulged-forward shock structure, while it traveled parallel to the wedge surface at distances further downstream. The turbulent distorted vortex structure which formed as a result of the interaction, was found to be sensitive to downstream disturbances in a manner consistent with incompressible vortex breakdown. Physical arguments are presented to relate behavior of streamwise vortices during oblique and normal shock wave interactions.

  18. Supersonic shock wave/vortex interaction

    NASA Technical Reports Server (NTRS)

    Settles, G. S.; Cattafesta, L.

    1993-01-01

    Although shock wave/vortex interaction is a basic and important fluid dynamics problem, very little research has been conducted on this topic. Therefore, a detailed experimental study of the interaction between a supersonic streamwise turbulent vortex and a shock wave was carried out at the Penn State Gas Dynamics Laboratory. A vortex is produced by replaceable swirl vanes located upstream of the throat of various converging-diverging nozzles. The supersonic vortex is then injected into either a coflowing supersonic stream or ambient air. The structure of the isolated vortex is investigated in a supersonic wind tunnel using miniature, fast-response, five-hole and total temperature probes and in a free jet using laser Doppler velocimetry. The cases tested have unit Reynolds numbers in excess of 25 million per meter, axial Mach numbers ranging from 2.5 to 4.0, and peak tangential Mach numbers from 0 (i.e., a pure jet) to about 0.7. The results show that the typical supersonic wake-like vortex consists of a non-isentropic, rotational core, where the reduced circulation distribution is self similar, and an outer isentropic, irrotational region. The vortex core is also a region of significant turbulent fluctuations. Radial profiles of turbulent kinetic energy and axial-tangential Reynolds stress are presented. The interactions between the vortex and both oblique and normal shock waves are investigated using nonintrusive optical diagnostics (i.e. schlieren, planar laser scattering, and laser Doppler velocimetry). Of the various types, two Mach 2.5 overexpanded-nozzle Mach disc interactions are examined in detail. Below a certain vortex strength, a 'weak' interaction exists in which the normal shock is perturbed locally into an unsteady 'bubble' shock near the vortex axis, but vortex breakdown (i.e., a stagnation point) does not occur. For stronger vortices, a random unsteady 'strong' interaction results that causes vortex breakdown. The vortex core reforms downstream of

  19. Origin of reversed vortex ratchet motion.

    PubMed

    Gillijns, W; Silhanek, A V; Moshchalkov, V V; Reichhardt, C J Olson; Reichhardt, C

    2007-12-14

    We experimentally demonstrate that the origin of multiply reversed rectified vortex motion in an asymmetric pinning landscape not only is a consequence of the vortex-vortex interactions but also essentially depends on the ratio between the characteristic interaction distance and the period of the asymmetric pinning potential. We study four samples with different periods d of the asymmetric potential. For large d the dc voltage V(dc) recorded under a ac excitation indicates that the average vortex drift is from bigger to smaller dots for all explored positive fields. As d is reduced, a series of sign reversals in the dc response are observed as a function of field. We show that the number of sign reversals increases as d decreases. These findings are in agreement with recent computer simulations and illustrate the relevance of the different characteristic lengths for the vortex rectification effects.

  20. Internal structure of a vortex breakdown

    NASA Technical Reports Server (NTRS)

    Nakamura, Y.; Leonard, A.; Spalart, P. R.

    1986-01-01

    An axisymmetric vortex breakdown was well simulated by the vortex filament method. The agreement with the experiment was qualitatively good. In particular, the structure in the interior of the vortex breakdown was ensured to a great degree by the present simulation. The second breakdown, or spiral type, which occurs downstream of the first axisymmetric breakdown, was simulated more similarly to the experiment than before. It shows a kink of the vortex filaments and strong three-dimensionality. Furthermore, a relatively low velocity region was observed near the second breakdown. It was also found that it takes some time for this physical phenomenon to attain its final stage. The comparison with the experiment is getting better as time goes on. In this paper, emphasis is placed on the comparison of the simulated results with the experiment. The present results help to make clear the mechanism of a vortex breakdown.

  1. Vortex ratchet induced by controlled edge roughness

    NASA Astrophysics Data System (ADS)

    Cerbu, D.; Gladilin, V. N.; Cuppens, J.; Fritzsche, J.; Tempere, J.; Devreese, J. T.; Moshchalkov, V. V.; Silhanek, A. V.; Van de Vondel, J.

    2013-06-01

    We demonstrate theoretically and experimentally the generation of rectified mean vortex displacement resulting from a controlled difference between the surface barriers at the opposite borders of a superconducting strip. Our investigation focuses on Al superconducting strips where, in one of the two sample borders, a saw tooth-like array of micro-indentations has been imprinted. The origin of the vortex ratchet effect is based on the fact that (i) the onset of vortex motion is mainly governed by the entrance/nucleation of vortices and (ii) the current lines bunching produced by the indentations facilitates the entrance/nucleation of vortices. Only for one current direction the indentations are positioned at the side of vortex entry and the onset of the resistive regime is lowered compared to the opposite current direction. This investigation points to the relevance of ubiquitous border effects typically neglected when interpreting vortex ratchet measurements on samples with arrays of local asymmetric pinning sites.

  2. Unusual Giant Prostatic Urethral Calculus

    PubMed Central

    Bello, A.; Maitama, H. Y.; Mbibu, N. H.; Kalayi, G. D.; Ahmed, A.

    2010-01-01

    Giant vesico-prostatic urethral calculus is uncommon. Urethral stones rarely form primarily in the urethra, and they are usually associated with urethral strictures, posterior urethral valve or diverticula. We report a case of a 32-year-old man with giant vesico-prostatic (collar-stud) urethral stone presenting with sepsis and bladder outlet obstruction. The clinical presentation, management, and outcome of the giant prostatic urethral calculus are reviewed. PMID:22091328

  3. Barotropic Vortex Evolution on a Beta Plane.

    NASA Astrophysics Data System (ADS)

    Shapiro, Lloyd J.; Ooyama, Katsuyuki V.

    1990-01-01

    A barotropic, primitive equation (shallow water) model is used on the beta plane to investigate the influence of divergence, total relative angular momentum (RAM) and advective nonlinearities on the evolution of a hurricane-like vortex. The multinested numerical model is based on the spectral application of a finite element representation. The undisturbed fluid depth is taken to be 1 km. Scaling of the vorticity equation, in conjunction with a Bessel function spectral decomposition, indicates that divergence should have a very small effect on the hurricane motion. Simulations with an initially symmetric cyclonic vortex in a resting environment confirm this analysis, and contradict previous published studies on the effect of divergence in a barotropic model.During a 120 h simulation the cyclonic vortex develops asymmetries that have an influence far from the initial circulation. The total RAM within a large circle centered on the vortex decreases with time, and then oscillates about zero. For circles with radii 1000 km, the total RAM approaches, but does not reach, zero. An angular momentum budget indicates that the horizontal angular momentum flux tends to counteract the net Coriolis torque on the vortex. If the total RAM of the initial symmetric vortex is zero, the weak far-field asymmetries are essentially eliminated. The motion of the vortex is not, however, related to the RAM in any simple way.Within a few days the near-vortex asymmetries reach a near-steady state. The Asymmetric Absolute vorticity (AAV) is nearly uniform within 350 km of the vortex center. The homogenization of AAV, which occurs within the closed vortex gyre, is likely due to shearing by the symmetric wind, combined with removal of energy at the smallest scales. The homogenization effectively neutralizes the planetary beta effect, as well as the vorticity associated with an environmental wind.

  4. Giant bulla mimicking tension pneumothorax.

    PubMed

    Gökçe, Mertol; Saydam, Ozkan; Altin, Remzi; Kart, Levent

    2009-01-01

    In the chest X-ray, we observe tension pneumothorax (TPX) as wide radiolucent view in a hemithorax and pushing the mediastinal structures contralateral. Giant bulla may mimic TPX with wide radiolucent view and mediastinal shift. The present report includes giant pulmonary bulla in 35-year-old woman. The giant bulla was diagnosed as a TPX in emergency, and chest tube was performed. The differentiation between TPX and a giant bulla may be very difficult. The therapies of these two similar entities are completely different. So that, we must be careful about anamnesis, physical examination and radiology for true diagnosis.

  5. Stirring properties of vortex rings

    NASA Astrophysics Data System (ADS)

    Auerbach, David

    1991-05-01

    Ring vortex evolution, from the initial roll-up phase through to the final turbulent phase, was experimentally studied to see the dependence of its stirring properties on both the initial (accelerating, constant, decelerating, slow, fast) piston motion as well as on the boundary (tube/hole geometry) conditions. Stirring between fluid initially upstream and that initially downstream of the nozzle plane is done more by convective entrainment at the beginning (roll-up and contraction phases), by diffusive entrainment during the laminar and wavy phases, and by mixed entrainment and ejection during the transition to turbulence and the turbulent phase itself. During vortex roll-up, it was found that tubes eject shorter streaklines than do holes, and that there is less Re dependence for this for tubes than for holes. During the contraction phase, entrainment ends, save for minimal entrainment due to axial inflow into the ring from along the cores of Goertler-type vortices. Generally, the rate of fluid ejected is largest during the transition from the wavy to the turbulent state. As far as the stability of the vortices is concerned, rings generated at holes are less stable than those generated at tubes. During the final turbulent phase, rings not only entrain fluid but eject it periodically into the wake: Between two and four hairpin vortices are generated and laid off in the wake during each ejection. The frequency at which such ejections takes place scales as a Strouhal number that takes on values of between 2 and 4.

  6. Terahertz circular Airy vortex beams.

    PubMed

    Liu, Changming; Liu, Jinsong; Niu, Liting; Wei, Xuli; Wang, Kejia; Yang, Zhengang

    2017-06-20

    Vortex beams have received considerable research interests both in optical and millimeter-wave domain since its potential to be utilized in the wireless communications and novel imaging systems. Many well-known optical beams have been demonstrated to carry orbital angular momentum (OAM), such as Laguerre-Gaussian beams and high-order Bessel beams. Recently, the radially symmetric Airy beams that exhibit an abruptly autofocusing feature are also demonstrated to be capable of carrying OAM in the optical domain. However, due to the lack of efficient devices to manipulate terahertz (THz) beams, it could be a challenge to demonstrate the radially symmetric Airy beams in the THz domain. Here we demonstrate the THz circular Airy vortex beams (CAVBs) with a 0.3-THz continuous wave through 3D printing technology. Assisted by the rapidly 3D-printed phase plates, individual OAM states with topological charge l ranging from l = 0 to l = 3 and a multiplexed OAM state are successfully imposed into the radially symmetric Airy beams. We both numerically and experimentally investigate the propagation dynamics of the generated THz CAVBs, and the simulations agree well with the observations.

  7. Majorana Fermions in Vortex Lattices

    NASA Astrophysics Data System (ADS)

    Biswas, Rudro R.

    2013-09-01

    We consider Majorana fermions tunneling among an array of vortices in a 2D chiral p-wave superconductor or equivalent material. The amplitude for Majorana fermions to tunnel between a pair of vortices is found to necessarily depend on the background superconducting phase profile; it is found to be proportional to the sine of half the difference between the phases at the two vortices. Using this result we study tight-binding models of Majorana fermions in vortices arranged in triangular or square lattices. In both cases we find that the aforementioned phase-tunneling relationship leads to the creation of superlattices where the Majorana fermions form macroscopically degenerate localizable flat bands at zero energy, in addition to other dispersive bands. This finding suggests that tunneling processes in these vortex arrays do not change the energies of a finite fraction of Majorana fermions, contrary to previous expectation. The presence of flat Majorana bands, and hence less-than-expected decoherence in these vortex arrays, bodes well for the prospects of topological quantum computation with large numbers of Majorana states.

  8. Majorana fermions in vortex lattices.

    PubMed

    Biswas, Rudro R

    2013-09-27

    We consider Majorana fermions tunneling among an array of vortices in a 2D chiral p-wave superconductor or equivalent material. The amplitude for Majorana fermions to tunnel between a pair of vortices is found to necessarily depend on the background superconducting phase profile; it is found to be proportional to the sine of half the difference between the phases at the two vortices. Using this result we study tight-binding models of Majorana fermions in vortices arranged in triangular or square lattices. In both cases we find that the aforementioned phase-tunneling relationship leads to the creation of superlattices where the Majorana fermions form macroscopically degenerate localizable flat bands at zero energy, in addition to other dispersive bands. This finding suggests that tunneling processes in these vortex arrays do not change the energies of a finite fraction of Majorana fermions, contrary to previous expectation. The presence of flat Majorana bands, and hence less-than-expected decoherence in these vortex arrays, bodes well for the prospects of topological quantum computation with large numbers of Majorana states.

  9. Vortex dynamics in R4

    NASA Astrophysics Data System (ADS)

    Shashikanth, Banavara N.

    2012-01-01

    The vortex dynamics of Euler's equations for a constant density fluid flow in {R}^4 is studied. Most of the paper focuses on singular Dirac delta distributions of the vorticity two-form ω in {R}^4. These distributions are supported on two-dimensional surfaces termed membranes and are the analogs of vortex filaments in {R}^3 and point vortices in {R}^2. The self-induced velocity field of a membrane is shown to be unbounded and is regularized using a local induction approximation. The regularized self-induced velocity field is then shown to be proportional to the mean curvature vector field of the membrane but rotated by 90° in the plane of normals. Next, the Hamiltonian membrane model is presented. The symplectic structure for this model is derived from a general formula for vorticity distributions due to Marsden and Weinstein ["Coadjoint orbits, vortices and Clebsch variables for incompressible fluids," Physica D 7, 305-323 (1983), 10.1016/0167-2789(83)90134-3]. Finally, the dynamics of the four-form ω ∧ ω is examined. It is shown that Ertel's vorticity theorem in {R}^3, for the constant density case, can be viewed as a special case of the dynamics of this four-form.

  10. Generalized formulation of Brownian Vortexes

    NASA Astrophysics Data System (ADS)

    Moyses, Henrique; Bauer, Ross; Grier, David

    2013-03-01

    Brownian vortexes are stochastic noise driven machines that arise from the motion of particles subjected to static non conservative force fields. This motion is characterized by a toroidal circulation in the probability flux whose direction can be tuned by changing the temperature of the system. A discrete minimal model for Brownian Vortexes were described by previous work done by B.Sun, D.G.Grier and A.Y.Grosberg. Here we theoretically look for a continuous model in the form of a generalization of the equilibrium Boltzmann relation for the probability density in the case where the driven forces have a non conservative solenoidal component. This generalized relation features the temperature induced probability flux reversal. We further extend our theory to time dependent force fields and study the possibility of stochastic resonance in the characteristic frequency of circulation of the driven particle. This model is experimentally applied to investigate the motion of colloidal spheres in an optical trap whose intensity is oscillatory in time.

  11. The VORTEX coronagraphic test bench

    NASA Astrophysics Data System (ADS)

    Jolivet, A.; Piron, P.; Huby, E.; Absil, O.; Delacroix, C.; Mawet, D.; Surdej, J.; Habraken, S.

    2014-07-01

    In this paper, we present the infrared coronagraphic test bench of the University of Liège named VODCA (Vortex Optical Demonstrator for Coronagraphic Applications). The goal of the bench is to assess the performances of the Annular Groove Phase Masks (AGPMs) at near- to mid-infrared wavelengths. The AGPM is a subwavelength grating vortex coronagraph of charge two (SGVC2) made out of diamond. The bench is designed to be completely achromatic and will be composed of a super continuum laser source emitting in the near to mid-infrared, several parabolas, diaphragms and an infrared camera. This way, we will be able to test the different AGPMs in the M, L, K and H bands. Eventually, the bench will also allow the computation of the incident wavefront aberrations on the coronagraph. A reflective Lyot stop will send most of the stellar light to a second camera to perform low-order wavefront sensing. This second system coupled with a deformable mirror will allow the correction of the wavefront aberrations. We also aim to test other pre- and/or post-coronagraphic concepts such as optimal apodization.

  12. PREFACE: Special section on vortex rings Special section on vortex rings

    NASA Astrophysics Data System (ADS)

    Fukumoto, Yasuhide

    2009-10-01

    This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill

  13. InGaAs/GaAsP strain balanced multi-quantum wires grown on misoriented GaAs substrates for high efficiency solar cells

    NASA Astrophysics Data System (ADS)

    Alonso-Álvarez, D.; Thomas, T.; Führer, M.; Hylton, N. P.; Ekins-Daukes, N. J.; Lackner, D.; Philipps, S. P.; Bett, A. W.; Sodabanlu, H.; Fujii, H.; Watanabe, K.; Sugiyama, M.; Nasi, L.; Campanini, M.

    2014-08-01

    Quantum wires (QWRs) form naturally when growing strain balanced InGaAs/GaAsP multi-quantum wells (MQW) on GaAs [100] 6° misoriented substrates under the usual growth conditions. The presence of wires instead of wells could have several unexpected consequences for the performance of the MQW solar cells, both positive and negative, that need to be assessed to achieve high conversion efficiencies. In this letter, we study QWR properties from the point of view of their performance as solar cells by means of transmission electron microscopy, time resolved photoluminescence and external quantum efficiency (EQE) using polarised light. We find that these QWRs have longer lifetimes than nominally identical QWs grown on exact [100] GaAs substrates, of up to 1 μs, at any level of illumination. We attribute this effect to an asymmetric carrier escape from the nanostructures leading to a strong 1D-photo-charging, keeping electrons confined along the wire and holes in the barriers. In principle, these extended lifetimes could be exploited to enhance carrier collection and reduce dark current losses. Light absorption by these QWRs is 1.6 times weaker than QWs, as revealed by EQE measurements, which emphasises the need for more layers of nanostructures or the use light trapping techniques. Contrary to what we expected, QWR show very low absorption anisotropy, only 3.5%, which was the main drawback a priori of this nanostructure. We attribute this to a reduced lateral confinement inside the wires. These results encourage further study and optimization of QWRs for high efficiency solar cells.

  14. Correlation of optical and structural properties of GaN/AlN multi-quantum wells—Ab initio and experimental study

    SciTech Connect

    Kaminska, A.; Strak, P.; Sakowski, K.; Sobczak, K.; Domagala, J. Z.; Grzanka, E.

    2016-01-07

    The results of comprehensive theoretical and experimental study of binary GaN/AlN multi-quantum well (MQW) systems oriented along polar c-direction of their wurtzite structure are presented. A series of structures with quantum wells and barriers of various thicknesses were grown by plasma-assisted molecular-beam epitaxy and characterized by x-ray diffraction and transmission electron microscopy. It was shown that in general the structures of good quality were obtained, with the defect density decreasing with increasing quantum well thickness. The optical transition energies in these structures were investigated comparing experimental measurements with ab initio calculations of the entire GaN/AlN MQW structure depending on the QW widths and strains, allowing for direct determination of the energies of optical transitions and the electric fields in wells/barriers by electric potential double averaging procedure. Photoluminescence (PL) measurements revealed that the emission efficiency as well as the shape of luminescence spectra correlated well with their structural quality. Additionally, due to the Quantum-Confined Stark Effect, the emission energy decreased by over 1 eV for quantum well thicknesses increasing from 1 nm up to 6 nm, and this effect was accompanied by the drastic drop of the PL efficiency. The experimental results are consistent with theoretical models. Comparison of experimental data obtained by a number of different characterization techniques with the density functional theory results received on the same geometry structure allowed to prove directly the theoretical models and to determine the polarization and the oscillator strengths in the AlN/GaN nitride systems for the first time.

  15. Vortex bursting and tracer transport of a counter-rotating vortex pair

    NASA Astrophysics Data System (ADS)

    Misaka, T.; Holzäpfel, F.; Hennemann, I.; Gerz, T.; Manhart, M.; Schwertfirm, F.

    2012-02-01

    Large-eddy simulations of a coherent counter-rotating vortex pair in different environments are performed. The environmental background is characterized by varying turbulence intensities and stable temperature stratifications. Turbulent exchange processes between the vortices, the vortex oval, and the environment, as well as the material redistribution processes along the vortex tubes are investigated employing passive tracers that are superimposed to the initial vortex flow field. It is revealed that the vortex bursting phenomenon, known from photos of aircraft contrails or smoke visualization, is caused by collisions of secondary vortical structures traveling along the vortex tube which expel material from the vortex but do not result in a sudden decay of circulation or an abrupt change of vortex core structure. In neutrally stratified and weakly turbulent conditions, vortex reconnection triggers traveling helical vorticity structures which is followed by their collision. A long-lived vortex ring links once again establishing stable double rings. Key phenomena observed in the simulations are supported by photographs of contrails. The vertical and lateral extents of the detrained passive tracer strongly depend on environmental conditions where the sensitivity of detrainment rates on initial tracer distributions appears to be low.

  16. Rotor Wake Vortex Definition Using 3C-PIV Measurements: Corrected for Vortex Orientation

    NASA Technical Reports Server (NTRS)

    Burley, Casey L.; Brooks, Thomas F.; vanderWall, Berend; Richard, Hughues Richard; Raffel, Markus; Beaumier, Philippe; Delrieux, Yves; Lim, Joon W.; Yu, Yung H.; Tung, Chee

    2003-01-01

    Three-component (3-C) particle image velocimetry (PIV) measurements, within the wake across a rotor disk plane, are used to determine wake vortex definitions important for BVI (Blade Vortex Interaction) and broadband noise prediction. This study is part of the HART II test program conducted using a 40 percent scale BO-105 helicopter main rotor in the German-Dutch Wind Tunnel (DNW). In this paper, measurements are presented of the wake vortex field over the advancing side of the rotor operating at a typical descent landing condition. The orientations of the vortex (tube) axes are found to have non-zero tilt angles with respect to the chosen PIV measurement cut planes, often on the order of 45 degrees. Methods for determining the orientation of the vortex axis and reorienting the measured PIV velocity maps (by rotation/projection) are presented. One method utilizes the vortex core axial velocity component, the other utilizes the swirl velocity components. Key vortex parameters such as vortex core size, strength, and core velocity distribution characteristics are determined from the reoriented PIV velocity maps. The results are compared with those determined from velocity maps that are not corrected for orientation. Knowledge of magnitudes and directions of the vortex axial and swirl velocity components as a function of streamwise location provide a basis for insight into the vortex evolution.

  17. Fluid entrainment by isolated vortex rings

    NASA Astrophysics Data System (ADS)

    Dabiri, John O.; Gharib, Morteza

    2004-07-01

    Of particular importance to the development of models for isolated vortex ring dynamics in a real fluid is knowledge of ambient fluid entrainment by the ring. This time-dependent process dictates changes in the volume of fluid that must share impulse delivered by the vortex ring generator. Therefore fluid entrainment is also of immediate significance to the unsteady forces that arise due to the presence of vortex rings in starting flows. Applications ranging from industrial and transportation, to animal locomotion and cardiac flows, are currently being investigated to understand the dynamical role of the observed vortex ring structures. Despite this growing interest, fully empirical measurements of fluid entrainment by isolated vortex rings have remained elusive. The primary difficulties arise in defining the unsteady boundary of the ring, as well as an inability to maintain the vortex ring in the test section sufficiently long to facilitate measurements. We present a new technique for entrainment measurement that utilizes a coaxial counter-flow to retard translation of vortex rings generated from a piston cylinder apparatus, so that their growth due to fluid entrainment can be observed. Instantaneous streamlines of the flow are used to determine the unsteady vortex ring boundary and compute ambient fluid entrainment. Measurements indicate that the entrainment process does not promote self-similar vortex ring growth, but instead consists of a rapid convection-based entrainment phase during ring formation, followed by a slower diffusive mechanism that entrains ambient fluid into the isolated vortex ring. Entrained fluid typically constitutes 30% to 40% of the total volume of fluid carried with the vortex ring. Various counter-flow protocols were used to substantially manipulate the diffusive entrainment process, producing rings with entrained fluid fractions up to 65%. Measurements of vortex ring growth rate and vorticity distribution during diffusive entrainment

  18. Vortex-induced vibrations of a sphere

    NASA Astrophysics Data System (ADS)

    Govardhan, R. N.; Williamson, C. H. K.

    2005-05-01

    There are many studies on the vortex-induced vibrations of a cylindrical body, but almost none concerned with such vibrations for a sphere, despite the fact that tethered bodies are a common configuration. In this paper, we study the dynamics of an elastically mounted or tethered sphere in a steady flow, employing displacement, force and vorticity measurements. Within a particular range of flow speeds, where the oscillation frequency (f) is of the order of the static-body vortex shedding frequency (f_{vo}), there exist two modes of periodic large-amplitude oscillation, defined as modes I and II, separated by a transition regime exhibiting non-periodic vibration. The dominant wake structure for both modes is a chain of streamwise vortex loops on alternating sides of the wake. Further downstream, the heads of the vortex loops pinch off to form a sequence of vortex rings. We employ an analogy with the lift on an aircraft that is associated with its trailing vortex pair (of strength Gamma(*) and spacing b(*) ), and thereby compute the rate of change of impulse for the streamwise vortex pair, yielding the vortex force coefficient (cvortex): [ cvortex = {8}/{pi} {U^*_{v}}b^*( - Gamma^*). ] This calculation yields predicted forces in reasonable agreement with direct measurements on the sphere. This is significant because it indicates that the principal vorticity dynamics giving rise to vortex-induced vibration for a sphere are the motions of these streamwise vortex pairs. The Griffin plot, showing peak amplitudes as a function of the mass damping (m(*zeta) ), exhibits a good collapse of data, indicating a maximum response of around 0.9 diameters. Following recent studies of cylinder vortex-induced vibration, we deduce the existence of a critical mass ratio, m(*_{crit}) {≈} 0.6, below which large-amplitude vibrations are predicted to persist to infinite normalized velocities. An unexpected large-amplitude and highly periodic mode (mode III) is found at distinctly higher

  19. Vortex-Vortex Interactions for the Maintenance of Blocking

    NASA Astrophysics Data System (ADS)

    Yamazaki, A.; Itoh, H.

    2012-12-01

    A new eddy-feedback mechanism, the Selective Absorption Mechanism (SAM), is proposed to explain block maintenance. According to this mechanism, which is based on vortex-vortex interactions (i.e., the interactions between a blocking anticyclone and synoptic eddies with the same polarity), a blocking anticyclone actively and selectively absorbs synoptic anticyclones (strictly, air parcels with low potential vorticity). The blocking anticyclone, which is thus supplied with low potential vorticity of the synoptic anticyclones, can subsist for a prolonged period, withstanding dissipation. The SAM was verified in a case study through trajectory analysis. Ten actual cases of blocking were examined. Trajectories were calculated by tracing parcels originating from synoptic anticyclones and cyclones located upstream of the blocking. Parcels starting from anticyclones were attracted to and absorbed by the blocking anticyclone, whereas parcels from cyclones were repelled by the blocking anticyclone and attracted to the blocking cyclone, if one was present. Numerical experiments are also performed. The experiments were based on the nonlinear equivalent-barotropic potential vorticity equation, with varying conditions with respect to the shape and amplitude of blocking, the characteristics of stormtracks (displacement and strength), and the characteristics of background zonal flow, to investigate whether the SAM is adoptable to real situations. The experiments indicate that the SAM effectively maintains blocking, independently of the above conditions. By applying a channel model on a beta-plane, numerical experiments were conducted using a uniform background westerly with a jet. Results show that the presence of a jet promotes the effectiveness of the SAM. Two spherical model experiments were also performed. In an idealized model, the SAM was as effective as the beta-plane model in explaining the maintenance of blocking. Moreover, a quantitative experiment showed that the SAM

  20. Helicity within the vortex filament model.

    PubMed

    Hänninen, R; Hietala, N; Salman, H

    2016-11-24

    Kinetic helicity is one of the invariants of the Euler equations that is associated with the topology of vortex lines within the fluid. In superfluids, the vorticity is concentrated along vortex filaments. In this setting, helicity would be expected to acquire its simplest form. However, the lack of a core structure for vortex filaments appears to result in a helicity that does not retain its key attribute as a quadratic invariant. By defining a spanwise vector to the vortex through the use of a Seifert framing, we are able to introduce twist and henceforth recover the key properties of helicity. We present several examples for calculating internal twist to illustrate why the centreline helicity alone will lead to ambiguous results if a twist contribution is not introduced. Our choice of the spanwise vector can be expressed in terms of the tangential component of velocity along the filament. Since the tangential velocity does not alter the configuration of the vortex at later times, we are able to recover a similar equation for the internal twist angle to that of classical vortex tubes. Our results allow us to explain how a quasi-classical limit of helicity emerges from helicity considerations for individual superfluid vortex filaments.

  1. Nonlinear ion acoustic waves scattered by vortexes

    NASA Astrophysics Data System (ADS)

    Ohno, Yuji; Yoshida, Zensho

    2016-09-01

    The Kadomtsev-Petviashvili (KP) hierarchy is the archetype of infinite-dimensional integrable systems, which describes nonlinear ion acoustic waves in two-dimensional space. This remarkably ordered system resides on a singular submanifold (leaf) embedded in a larger phase space of more general ion acoustic waves (low-frequency electrostatic perturbations). The KP hierarchy is characterized not only by small amplitudes but also by irrotational (zero-vorticity) velocity fields. In fact, the KP equation is derived by eliminating vorticity at every order of the reductive perturbation. Here, we modify the scaling of the velocity field so as to introduce a vortex term. The newly derived system of equations consists of a generalized three-dimensional KP equation and a two-dimensional vortex equation. The former describes 'scattering' of vortex-free waves by ambient vortexes that are determined by the latter. We say that the vortexes are 'ambient' because they do not receive reciprocal reactions from the waves (i.e., the vortex equation is independent of the wave fields). This model describes a minimal departure from the integrable KP system. By the Painlevé test, we delineate how the vorticity term violates integrability, bringing about an essential three-dimensionality to the solutions. By numerical simulation, we show how the solitons are scattered by vortexes and become chaotic.

  2. Phenomena, dynamics and instabilities of vortex pairs

    NASA Astrophysics Data System (ADS)

    Williamson, C. H. K.; Leweke, T.; Asselin, D. J.; Harris, D. M.

    2014-12-01

    Our motivation for studying the dynamics of vortex pairs stems initially from an interest in the trailing wake vortices from aircraft and the dynamics of longitudinal vortices close to a vehicle surface. However, our motivation also comes from the fact that vortex-vortex interactions and vortex-wall interactions are fundamental to many turbulent flows. The intent of the paper is to present an overview of some of our recent work concerning the formation and structure of counter-rotating vortex pairs. We are interested in the long-wave and short-wave three-dimensional instabilities that evolve for an isolated vortex pair, but also we would like to know how vortex pairs interact with a wall, including both two-dimensional interactions, and also the influence of the surface on the three-dimensional instabilities. The emphasis of this presentation is on physical mechanisms by which vortices interact with each other and with surfaces, principally from an experimental approach, but also coupled with analytical studies.

  3. Vortex Ring Interaction with a Heated Screen

    NASA Astrophysics Data System (ADS)

    Smith, Jason; Krueger, Paul S.

    2008-11-01

    Previous examinations of vortex rings impinging on porous screens has shown the reformation of the vortex ring with a lower velocity after passing through the screen, the creation of secondary vortices, and mixing. A heated screen could, in principle, alter the vortex-screen interaction by changing the local liquid viscosity and density. In the present investigation, a mechanical piston-cylinder vortex ring generator was used to create vortex rings in an aqueous sucrose solution. The rings impinged on a screen of horizontal wires that were heated using electrical current. The flow was visualized with food color and video imaging. Tests with and without heat were conducted at a piston stroke-to-jet diameter ratio of 4 and a jet Reynolds number (Re) of 1000. The vortex rings slowed after passing through the screen, but in tests with heat, they maintained a higher fraction of their before-screen velocity due to reduction in fluid viscosity near the wires. In addition, small ``fingers'' that developed on the front of the vortex rings as they passed through the screen exhibited positive buoyancy effects in the heated case.

  4. Helicity within the vortex filament model

    NASA Astrophysics Data System (ADS)

    Hänninen, R.; Hietala, N.; Salman, H.

    2016-11-01

    Kinetic helicity is one of the invariants of the Euler equations that is associated with the topology of vortex lines within the fluid. In superfluids, the vorticity is concentrated along vortex filaments. In this setting, helicity would be expected to acquire its simplest form. However, the lack of a core structure for vortex filaments appears to result in a helicity that does not retain its key attribute as a quadratic invariant. By defining a spanwise vector to the vortex through the use of a Seifert framing, we are able to introduce twist and henceforth recover the key properties of helicity. We present several examples for calculating internal twist to illustrate why the centreline helicity alone will lead to ambiguous results if a twist contribution is not introduced. Our choice of the spanwise vector can be expressed in terms of the tangential component of velocity along the filament. Since the tangential velocity does not alter the configuration of the vortex at later times, we are able to recover a similar equation for the internal twist angle to that of classical vortex tubes. Our results allow us to explain how a quasi-classical limit of helicity emerges from helicity considerations for individual superfluid vortex filaments.

  5. Topology of vortex-wing interaction

    NASA Astrophysics Data System (ADS)

    McKenna, C.; Rockwell, D.

    2016-10-01

    A trailing vortex incident upon a wing can generate different modes of vortex-wing interaction. These modes, which may involve either enhancement or suppression of the vortex generated at the tip of the wing, are classified on the basis of the present experiments together with computations at the Air Force Research Laboratory. Occurrence of a given mode of interaction is predominantly determined by the dimensionless location of the incident vortex relative to the tip of the wing and is relatively insensitive to the Reynolds number and dimensionless circulation of the incident vortex. The genesis of the basic interaction modes is clarified using streamline topology with associated critical points that show compatibility between complex streamline patterns in the vicinity of the tip of the wing. Whereas formation of an enhanced tip vortex involves a region of large upwash in conjunction with localized flow separation, complete suppression of the tip vortex is associated with a small-scale separation-reattachment bubble bounded by downwash at the wing tip.

  6. On cooperative instabilities of parallel vortex pairs

    NASA Astrophysics Data System (ADS)

    Bristol, R. L.; Ortega, J. M.; Marcus, P. S.; Savas, Ö.

    2004-10-01

    We present a combined analytical and numerical study of the instabilities of a pair of parallel unequal-strength vortices. We extend the analyses of a vortex in an external strain field (Crow, AIAA J. vol. 8, 1970, p. 2172; Widnall et al., J. Fluid Mech. vol. 66, 1974, p. 35) to include the orbital motion of the vortex pair. For counter-rotating pairs, the classic Crow-type periodic displacement perturbations are unstable for all vortex strength ratios, with fastest-growing wavelengths several times the vortex spacing. For co-rotating pairs, the orbital motion acts to suppress instability due to displacement perturbations. Instabilities in this case arise for elliptic perturbations at wavelengths that scale with the vortex core size. We also examine the influence of a second vortex pair by extending Crouch's (J. Fluid Mech. vol. 350, 1997, p. 311) analysis. Numerical results from a spectral initial-value code with subgrid-scale modelling agree with the growth rates from the theoretical models. Computations reveal the nonlinear evolution at late times, including wrapping and ring-rejection behaviour observed in experiments. A pair of co-rotating Gaussian vortices perturbed by noise develops elliptic instabilities, leading to the formation of vorticity bridges between the two vortices. The bridging is a prelude to vortex merger. Analytic, computational and experimental results agree well at circulation Reynolds numbers of order 10(5) .

  7. Dynamics of Isolated Tip Vortex Cavitation

    NASA Astrophysics Data System (ADS)

    Pennings, Pepijn; Bosschers, Johan; van Terwisga, Tom

    2014-11-01

    Performance of ship propellers and comfort levels in the surroundings are limited by various forms of cavitation. Amongst these forms tip vortex cavitation is one of the first appearing forms and is expected to be mainly responsible for the emission of broadband pressure fluctuations typically occurring between the 4th to the 7th blade passing frequency (approx. 40--70 Hz). These radiated pressure pulses are likely to excite parts of the hull structure resulting in a design compromise between efficiency and comfort. Insight is needed in the mechanism of acoustic emission from the oscillations by a tip vortex cavity. In the current experimental study the tip vortex cavity from a blade with an elliptic planform and sections based on NACA 662 - 415 with meanline a = 0 . 8 is observed using high speed shadowgraphy in combination with blade force and acoustic measurements. An analytic model describing three main cavity deformation modes is verified and used to explain the origin of a cavity eigenfrequency or ``vortex singing'' phenomenon observed by Maines and Arndt (1997) on the tip vortex cavity originating from the same blade. As no hydrodynamic sound originating from the tip vortex cavity was observed it is posed that a tip flow instability is essential for ``vortex singing.'' This research was funded by the Lloyd's Register Foundation as part of the International Institute for Cavitation Research.

  8. Helicity within the vortex filament model

    PubMed Central

    Hänninen, R.; Hietala, N.; Salman, H.

    2016-01-01

    Kinetic helicity is one of the invariants of the Euler equations that is associated with the topology of vortex lines within the fluid. In superfluids, the vorticity is concentrated along vortex filaments. In this setting, helicity would be expected to acquire its simplest form. However, the lack of a core structure for vortex filaments appears to result in a helicity that does not retain its key attribute as a quadratic invariant. By defining a spanwise vector to the vortex through the use of a Seifert framing, we are able to introduce twist and henceforth recover the key properties of helicity. We present several examples for calculating internal twist to illustrate why the centreline helicity alone will lead to ambiguous results if a twist contribution is not introduced. Our choice of the spanwise vector can be expressed in terms of the tangential component of velocity along the filament. Since the tangential velocity does not alter the configuration of the vortex at later times, we are able to recover a similar equation for the internal twist angle to that of classical vortex tubes. Our results allow us to explain how a quasi-classical limit of helicity emerges from helicity considerations for individual superfluid vortex filaments. PMID:27883029

  9. Microscale vortex laser with controlled topological charge

    NASA Astrophysics Data System (ADS)

    Wang, Xing-Yuan; Chen, Hua-Zhou; Li, Ying; Li, Bo; Ma, Ren-Min

    2016-12-01

    A microscale vortex laser is a new type of coherent light source with small footprint that can directly generate vector vortex beams. However, a microscale laser with controlled topological charge, which is crucial for virtually any of its application, is still unrevealed. Here we present a microscale vortex laser with controlled topological charge. The vortex laser eigenmode was synthesized in a metamaterial engineered non-Hermitian micro-ring cavity system at exceptional point. We also show that the vortex laser cavity can operate at exceptional point stably to lase under optical pumping. The microscale vortex laser with controlled topological charge can serve as a unique and general building block for next-generation photonic integrated circuits and coherent vortex beam sources. The method we used here can be employed to generate lasing eigenmode with other complex functionalities. Project supported by the “Youth 1000 Talent Plan” Fund, Ministry of Education of China (Grant No. 201421) and the National Natural Science Foundation of China (Grant Nos. 11574012 and 61521004).

  10. Phase diagram of a lattice of pancake vortex molecules

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Crisan, A.; Shivagan, D. D.; Iyo, A.; Shirage, P. M.; Tokiwa, K.; Watanabe, T.; Terada, N.

    2009-10-01

    On a superconducting bi-layer with thickness much smaller than the penetration depth, λ, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom.

  11. New scanning technique for the optical vortex microscope.

    PubMed

    Augustyniak, Ireneusz; Popiołek-Masajada, Agnieszka; Masajada, Jan; Drobczyński, Sławomir

    2012-04-01

    In the optical vortex microscopy the focused Gaussian beam with optical vortex scans a sample. An optical vortex can be introduced into a laser beam with the use of a special optical element--a vortex lens. When moving the vortex lens, the optical vortex changes its position inside the spot formed by a focused laser beam. This effect can be used as a new precise scanning technique. In this paper, we study the optical vortex behavior at the sample plane. We also estimate if the new scanning technique results in observable effects that could be used for a phase object detection.

  12. Imaging Extrasolar Giant Planets

    NASA Astrophysics Data System (ADS)

    Bowler, Brendan P.

    2016-10-01

    High-contrast adaptive optics (AO) imaging is a powerful technique to probe the architectures of planetary systems from the outside-in and survey the atmospheres of self-luminous giant planets. Direct imaging has rapidly matured over the past decade and especially the last few years with the advent of high-order AO systems, dedicated planet-finding instruments with specialized coronagraphs, and innovative observing and post-processing strategies to suppress speckle noise. This review summarizes recent progress in high-contrast imaging with particular emphasis on observational results, discoveries near and below the deuterium-burning limit, and a practical overview of large-scale surveys and dedicated instruments. I conclude with a statistical meta-analysis of deep imaging surveys in the literature. Based on observations of 384 unique and single young (≈5-300 Myr) stars spanning stellar masses between 0.1 and 3.0 M ⊙, the overall occurrence rate of 5-13 M Jup companions at orbital distances of 30-300 au is {0.6}-0.5+0.7 % assuming hot-start evolutionary models. The most massive giant planets regularly accessible to direct imaging are about as rare as hot Jupiters are around Sun-like stars. Dividing this sample into individual stellar mass bins does not reveal any statistically significant trend in planet frequency with host mass: giant planets are found around {2.8}-2.3+3.7 % of BA stars, <4.1% of FGK stars, and <3.9% of M dwarfs. Looking forward, extreme AO systems and the next generation of ground- and space-based telescopes with smaller inner working angles and deeper detection limits will increase the pace of discovery to ultimately map the demographics, composition, evolution, and origin of planets spanning a broad range of masses and ages.

  13. Giant left ventricular pseudoaneurysm.

    PubMed

    Prakash, Sumi; Garg, Nadish; Xie, Gong-Yuan; Dellsperger, Kevin C

    2010-01-01

    Left ventricular (LV) pseudoaneurysm (PS) is an uncommon, often fatal complication associated with myocardial infarction, cardiothoracic surgery, trauma, and, rarely, infective endocarditis. A 28-year-old man with prior history of bioprosthetic mitral valve replacement presented with congestive heart failure and bacteremia with Abiotrophia granulitica. Transesophageal echocardiogram showed bioprosthesis dysfunction, large vegetations, mitral regurgitation, and probable PS. Cardiac and chest CT confirmed a PS communicating with the left ventricle Patient had pulseless electrical activity and died. Autopsy showed a giant PS with layered thrombus and pseudo-endothelialized cavity. Our case highlights the importance of multimodality imaging as an important tool in management of PS.

  14. Giant mesenteric cyst

    PubMed Central

    Guraya, Salman Yousuf; Salman, Shaista; Almaramhy, Hamdi H.

    2011-01-01

    Mesenteric cysts are uncommon benign abdominal lesions with no classical clinical features. The preoperative diagnosis requires the common imaging modalities but the final diagnosis is established only during surgery or histological analysis. The treatment of choice is complete surgical excision. We report an 18-year-old female with a non-specific abdominal pain and discomfort since 3 weeks. Her CT scan showed a huge cystic swelling, which necessitated surgical exploration. Preoperatively, a giant cyst was encountered with displacement of bowel loops. The cyst was completely removed and histology report confirmed mesenteric cyst without evidence of malignancy. PMID:24765349

  15. Giant mesenteric cyst.

    PubMed

    Guraya, Salman Yousuf; Salman, Shaista; Almaramhy, Hamdi H

    2011-09-28

    Mesenteric cysts are uncommon benign abdominal lesions with no classical clinical features. The preoperative diagnosis requires the common imaging modalities but the final diagnosis is established only during surgery or histological analysis. The treatment of choice is complete surgical excision. We report an 18-year-old female with a non-specific abdominal pain and discomfort since 3 weeks. Her CT scan showed a huge cystic swelling, which necessitated surgical exploration. Preoperatively, a giant cyst was encountered with displacement of bowel loops. The cyst was completely removed and histology report confirmed mesenteric cyst without evidence of malignancy.

  16. A Giant Urethral Calculus.

    PubMed

    Sigdel, G; Agarwal, A; Keshaw, B W

    2014-01-01

    Urethral calculi are rare forms of urolithiasis. Majority of the calculi are migratory from urinary bladder or upper urinary tract. Primary urethral calculi usually occur in presence of urethral stricture or diverticulum. In this article we report a case of a giant posterior urethral calculus measuring 7x3x2 cm in a 47 years old male. Patient presented with acute retention of urine which was preceded by burning micturition and dribbling of urine for one week. The calculus was pushed in to the bladder through the cystoscope and was removed by suprapubic cystolithotomy.

  17. A vortex-filament and core model for wings with edge vortex separation

    NASA Technical Reports Server (NTRS)

    Pao, J. L.; Lan, C. E.

    1982-01-01

    A vortex filament-vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separation was developed. Semi-empirical but simple methods were used to determine the initial positions of the free sheet and vortex core. Comparison with available data indicates that: (1) the present method is generally accurate in predicting the lift and induced drag coefficients but the predicted pitching moment is too positive; (2) the spanwise lifting pressure distributions estimated by the one vortex core solution of the present method are significantly better than the results of Mehrotra's method relative to the pressure peak values for the flat delta; (3) the two vortex core system applied to the double delta and strake wings produce overall aerodynamic characteristics which have good agreement with data except for the pitching moment; and (4) the computer time for the present method is about two thirds of that of Mehrotra's method.

  18. Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors.

    PubMed

    Meng, Qingyou; Varney, Christopher N; Fangohr, Hans; Babaev, Egor

    2017-01-25

    It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.

  19. On the Use of Vortex-Fitting in the Numerical Simulation of Blade-Vortex Interaction

    NASA Technical Reports Server (NTRS)

    Srinivasan, G. R.; VanDalsem, William (Technical Monitor)

    1997-01-01

    The usefulness of vortex-fitting in the computational fluid dynamics (CFD) methods to preserve the vortex strength and structure while convecting in a uniform free stream is demonstrated through the numerical simulations of two- and three-dimensional blade-vortex interactions. The fundamental premise of the formulation is the velocity and pressure field of the interacting vortex are unaltered either in the presence of an airfoil or a rotor blade or by the resulting nonlinear interactional flowfield. Although, the governing Euler and Navier-Stokes equations are nonlinear and independent solutions cannot be superposed, the interactional flowfield can be accurately captured by adding and subtracting the flowfield of the convecting vortex at each instant. The aerodynamics and aeroacoustics of two- and three-dimensional blade-vortex interactions have been calculated in Refs. 1-6 using this concept. Some of the results from these publications and similar other published material will be summarized in this paper.

  20. Contrasting vortex-gyration dispersions for different lattice bases in one-dimensional magnetic vortex arrays

    NASA Astrophysics Data System (ADS)

    Han, Dong-Soo; Jeong, Han-Byeol; Kim, Sang-Koog

    2013-09-01

    We performed micromagnetic numerical and analytical calculations in studying the effects of change in the primitive unit cells of one-dimensional (1D) vortex arrays on collective vortex-gyration dispersion. As the primitive basis, we consider alternating constituent materials (NiMnSb vs. Permalloy) and alternating dimensions including constituent disk diameter and thickness. In the simplest case, that of one vortex-state disk of given dimensions and single material in the primitive cell, only a single branch of collective vortex-gyration dispersion appears. By contrast, two constituent disks' different alternating materials, thicknesses, and diameters yield characteristic two-branch dispersions, the band widths and gaps of which differ in each case. This work offers not only an efficient means of manipulating collective vortex-gyration band structures but also a foundation for the development of a rich variety of 1D or 2D magnonic crystals and their band structures based on dipolar-coupled-vortex arrays.

  1. Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors

    NASA Astrophysics Data System (ADS)

    Meng, Qingyou; Varney, Christopher N.; Fangohr, Hans; Babaev, Egor

    2017-01-01

    It was recently proposed to use the stray magnetic fields of superconducting vortex lattices to trap ultracold atoms for building quantum emulators. This calls for new methods for engineering and manipulating of the vortex states. One of the possible routes utilizes type-1.5 superconducting layered systems with multi-scale inter-vortex interactions. In order to explore the possible vortex states that can be engineered, we present two phase diagrams of phenomenological vortex matter models with multi-scale inter-vortex interactions featuring several attractive and repulsive length scales. The phase diagrams exhibit a plethora of phases, including conventional 2D lattice phases, five stripe phases, dimer, trimer, and tetramer phases, void phases, and stable low-temperature disordered phases. The transitions between these states can be controlled by the value of an applied external field.

  2. Evaluation of travelling vortex speed by means of vortex tracking and dynamic mode decomposition

    NASA Astrophysics Data System (ADS)

    Hyhlík, Tomáš

    2016-06-01

    The article deals with the analysis of unsteady periodic flow field related to synthetic jet creation. The analyses are based on the data obtained using ANSYS Fluent solver. Numerical results are validated by hot wire anemometry data measured along the jet centerline. The speed of travelling vortex ring is evaluated by using vortex tracking method and by using dynamic mode decomposition method. Vortex identification is based on residual vorticity which allows identifying regions in the flow field where fluid particles perform the rotational motion. The regime of the synthetic jet with Re = 329 and S = 19.7 is chosen. Both the vortex tracking and the dynamic mode decomposition based vortex speed evaluation indicate an increase in the vortex speed close to the orifice and then decrease with maximum reaching almost one and half of orifice centerline velocity. The article contains extended version the article presented at the conference AEaNMiFMaE 2016.

  3. Comparison of two vortex models of wind turbines using a free vortex wake scheme

    NASA Astrophysics Data System (ADS)

    Xu, B. F.; Yuan, Y.; Wang, T. G.; Zhao, Z. Z.

    2016-09-01

    Developing suitably generalized models for rotor blade vortices that accurately predict their evolution continues to be a challenge for wind turbine analysts. During the past few decades, several vortex models have been developed according to the theoretical analysis and the experimental research. A comparison of two different vortex models is made for predicting wind turbine aerodynamic performance using a free vortex wake (FVW) model. The two models are the Lamb-Oseen vortex model for laminar vortices and the β-Vatistas model for turbulent vortices. A new formula that approximates parameter β, which represents the degree of turbulence in the β-Vatistas model, is proposed. The formula of parameter β is validated by comparison of simulated and measured aerodynamic performances of wind turbines of different blade tip vortex Reynolds numbers. Then, the induced velocity streamlines and the distribution of the axial velocity in the rotational plane are simulated. Also, the differences due to the vortex models are discussed.

  4. Stable optical vortex solitons in pair plasmas

    SciTech Connect

    Berezhiani, V. I.; Shatashvili, N. L.; Mahajan, S. M.

    2010-05-15

    It is shown that the pair plasmas with small temperature asymmetry can support existence of localized as well as delocalized optical vortex solitons. Coexistence of such solitons is possible due to peculiar form of saturating nonlinearity which has a focusing-defocusing nature--for weak amplitudes being focusing becoming defocusing for higher amplitudes. It is shown that delocalized vortex soliton is stable in entire region of its existence while single- and multicharged localized vortex solitons are unstable for low amplitudes and become stable for relativistic amplitudes.

  5. RANS computations of tip vortex cavitation

    NASA Astrophysics Data System (ADS)

    Decaix, Jean; Balarac, Guillaume; Dreyer, Matthieu; Farhat, Mohamed; Münch, Cécile

    2015-12-01

    The present study is related to the development of the tip vortex cavitation in Kaplan turbines. The investigation is carried out on a simplified test case consisting of a NACA0009 blade with a gap between the blade tip and the side wall. Computations with and without cavitation are performed using a R ANS modelling and a transport equation for the liquid volume fraction. Compared with experimental data, the R ANS computations turn out to be able to capture accurately the development of the tip vortex. The simulations have also highlighted the influence of cavitation on the tip vortex trajectory.

  6. Vortex motion behind a circular cylinder

    NASA Technical Reports Server (NTRS)

    Foeppl, L.

    1983-01-01

    Vortex motion behind a circular cylinder moving through water is discussed. It is shown that a pair of vortices form behind a moving cylinder and that their centers will move along a predictable curve. This curve represents an equilibrium condition which, however, is subject to perturbation. The stability of the vortex pair is investigated. Movement of the vortex pair away from the cylinder is calculated as an explanation of the resistance of the cylinder. Finally, the principles elaborated are applied to the flow around a flat plate.

  7. Improved Flow-Controlling Vortex Generator

    NASA Technical Reports Server (NTRS)

    Collins, Earl R., Jr.; Marner, Wilbur J.; Rohatgi, Naresh K.

    1989-01-01

    Symmetrical tangential streams control flow of radial primary streams. Vortex generator uses small secondary stream of fluid to control normally-larger primary stream. Improved version of vortex generator described in "Variable Control Port for Fluidic Control Device," (NPO-16603). Secondary, or control, flows entering tangentially through diametrically opposite ports set up swirling motion restraining primary flow. Pressure of secondary fluid in relation to primary fluid controlling factor. Like valve, vortex generator varies rate of flow of primary fluid from maximum value down to zero. When properly designed, requires low pressure differential between primary and secondary streams and expends relatively small amount of secondary fluid.

  8. All-electrical magnetic vortex array sensing

    NASA Astrophysics Data System (ADS)

    Tannous, C.; Gieraltowski, J.

    2016-08-01

    Vortex sensing magnetometers based on arrays of soft magnetic dots are good candidates for high-resolution and accurate spatial magnetic-field estimation. When the arrays are laid out along different spatial directions they can perform tensor gradiometry allowing the measurement of field components and their spatial derivatives as a function of orientation. Detection is based on using spin-polarized currents to counteract vortex displacements or to excite vortex oscillation modes triggered by magnetic-field application. Sensor linearization, field detection range and conditions to obtain large sensitivity electronic compatibility and scalability are discussed.

  9. Vortex line in the unitary Fermi gas

    SciTech Connect

    Madeira, Lucas; Vitiello, Silvio A.; Gandolfi, Stefano; Schmidt, Kevin E.

    2016-04-06

    Here, we report diffusion Monte Carlo results for the ground state of unpolarized spin-1/2 fermions in a cylindrical container and properties of the system with a vortex-line excitation. The density profile of the system with a vortex line presents a nonzero density at the core. We also calculate the ground-state energy per particle, the superfluid pairing gap, and the excitation energy per particle. Finally, these simulations can be extended to calculate the properties of vortex excitations in other strongly interacting systems such as superfluid neutron matter using realistic nuclear Hamiltonians.

  10. Effects of disorder on the vortex charge

    NASA Astrophysics Data System (ADS)

    Lages, J.; Sacramento, P. D.

    2006-04-01

    We study the influence of disorder on the vortex charge, both due to random pinning of the vortices and due to scattering off nonmagnetic impurities. In the case when there are no impurities present, but the vortices are randomly distributed, the effect is very small, except when two or more vortices are close by. When impurities are present, they have a noticeable effect on the vortex charge. This, together with the effect of temperature, changes appreciably the vortex charge. In the case of an attractive impurity potential the sign of the charge naturally changes.

  11. Optical vortex converter with helical-periodically poled ferroelectric crystal.

    PubMed

    Tian, Linghao; Ye, Fangwei; Chen, Xianfeng

    2011-06-06

    A kind of optical vortex converter is proposed in helical-periodically poled ferroelectric crystal based on transverse electro-optics effect. It can be used to generate optical vortex from non-vortex beam and transform the topological charge of optical vortex. An optical vortex adder or substrator is proposed under the control of electric filed. This device will find its applications in high dimensional communication system for signal processing and optical manipulation in micro and mesoscopic scale.

  12. Interaction of a turbulent vortex with a lifting surface

    NASA Technical Reports Server (NTRS)

    Lee, D. J.; Roberts, L.

    1985-01-01

    The impulsive noise due to blade-vortex-interaction is analyzing in the time domain for the extreme case when the blade cuts through the center of the vortex core with the assumptions of no distortion of the vortex path or of the vortex core. An analytical turbulent vortex core model, described in terms of the tip aerodynamic parameters, is used and its effects on the unsteady loading and maximum acoustic pressure during the interaction are determined.

  13. Vortex Structures of Whistler Waves

    NASA Astrophysics Data System (ADS)

    Zaliznyak, Yu.; Davydova, T.; Yakimenko, A.

    Starting with two-dimensional nonlinear Scroedinger equation for a parallel electric field of spatially localized beam of whistler waves we investigate formation, evolu- tion and stability of nonlinear whistler waveguides (or ducts) which are frequently observed during heating active experiments in the ionosphere. When the generator frequency is close to the half of electron cyclotron frequency, one have take into ac- count the additional terms of the next order in the equation for the interpretation of existing experimental data. It is needed to use a full Maxwell's equation set to describe the propagation of whistlers and to account for the nonlinearity saturation at high val- ues of pump power. Nonlinear waveguides of vortex type (with topological charge 1, 2 and 3) are found and their stability properties are investigated by means of numerical simulations.

  14. Vortex generator for flow control

    NASA Technical Reports Server (NTRS)

    Collins, Jr., Earl R. (Inventor); Marner, Wilbur J. (Inventor); Rohatgi, Naresh K. (Inventor)

    1989-01-01

    Fluidics flow control of a multiphase supply using a cylindrical chamber is achieved by introducing the supply flow radially into the chamber. The supply flow exits through a port in the center at the chamber. A control fluid is then introduced tangentially about 90.degree. upstream from the supply port. A second control fluid port may be added about 90.degree. upstream from the first control fluid port, but preferably two sets of supply and control ports are added with like ports diametrically opposite each other. The control fluid flows against the circular wall of the control chamber, which introduces a vortex in the flow of the supply flow that decays into a spiral path to the exit port in the center of the chamber. The control flow rate may thus be used to control the spiral path, and therefore the supply flow rate through the exit port.

  15. Optimal response of Batchelor vortex

    NASA Astrophysics Data System (ADS)

    Blanco-Rodríguez, Francisco J.; Rodríguez-García, Jesús O.; Parras, Luis; del Pino, Carlos

    2017-06-01

    The optimal response of the Batchelor vortex is studied by considering the time-harmonically forced problem with frequency ω . High variance levels are sustained in this system under periodic forcing. The optimal response is largest when the input frequency is null in the axisymmetric case (m = 0). In addition, the axial flow does not play a relevant part in determining the optimal response. When considering helical modes |m | = 1 , perturbations are excited through a resonance mechanism at moderate and large wavelengths. At smaller wavelengths, a large response is excited by steady forcing. Regarding the axial flow, the response is largest when the axial velocity intensity is near to zero. For perturbations with larger azimuthal wavenumbers |m | > 1 , the magnitude of the response is smaller than those for helical modes. Therefore, studying the response for |m | > 1 is of no interest.

  16. Majorana fermions in vortex lattices

    NASA Astrophysics Data System (ADS)

    Biswas, Rudro

    2013-03-01

    We consider Majorana fermions tunneling between vortices, within an array of such vortices in a 2D chiral p-wave superconductor. We calculate that the tunneling amplitude for Majorana fermions in a pair of vortices is proportional to the sine of half the difference between the global order parameter phases at the two vortices. Using this result we study tight-binding models of Majorana fermions in vortices arranged in a triangular or square lattice. In both cases we find that this phase-tunneling relationship leads to the creation of superlattices where the Majorana fermions form macroscopically degenerate `flat' bands at zero energy, in addition to other dispersive bands. This finding suggests that in vortex arrays tunneling processes do not change the energies of a finite fraction of Majorana fermions and hence brighten the prospects of topological quantum computing with a large number of Majorana states.

  17. Vortex Dynamics in Anisotropic Superconductors

    NASA Astrophysics Data System (ADS)

    Steel, David Gordon

    Measurements of the ac screening response and resistance of superconducting Bi_2Sr _2CaCu_2O _8 (BSCCO) crystals have been used to probe the dynamics of the magnetic flux lines within the mixed state as a function of frequency, temperature, and applied dc field. For the particular range of temperature and magnetic field in which measurements were made, the systematic behavior of the observed dissipation peak in the screening response is consistent with electromagnetic skin size effects rather than a phase transition. According to microscopic theories of the interaction between the flux lines and a driving ac field, such a skin size effect is expected for the case when the vortex motion is diffusive in nature. However, diffusive motion is inconsistent with simple activation models that use a single value for the pinning energy (derived from direct measurement of the dc resistance). This contradiction suggests a distribution of pinning energies within the sample. Interlayer vortex decoupling has been directly observed as a function of temperature and applied magnetic field using electronic transport perpendicular to the layers in synthetic amorphous MoGe/Ge multilayer samples. Perpendicular transport has been shown to be a far more sensitive measure of the phase coupling between layers than in-plane properties. Below the decoupling temperature T_{D} the resistivity anisotropy collapses and striking nonlinearities appear in the perpendicular current-voltage behavior, which are not observed in parallel transport. A crossover in behavior is also observed at a field H _{x}, in accordance with theory. The data suggest the presence of a phase transition into a state with finite in-plane resistivity. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

  18. Giant extragenital Bowen's disease.

    PubMed

    Bakardzhiev, Ilko; Chokoeva, Anastasiya Atanasova; Tchernev, Georgi

    2015-12-01

    Giant extragenital forms of Morbus Bowen are extremely rare. The already described cases in the word literature are most commonly with periungual localization, as well as located on the foot and neck area. The clinical manifestation is presented most commonly by non-specific erythematous to erythematous-squamous plaques or papules, which is confusing to the clinician. From the pathogenic point of view, it is important to be confirmed or rejected the presence of human papilloma viruses (HPVs) in each case of affected patient, as this information is mandatory in respect to the adequate selection of the subsequent regimen. If HPVs are detected, systemic antiviral therapy could be initiated to reduce the size of the lesions before subsequent surgical eradication. A postoperative prevention through vaccination could be also considered additionally. In cases of HPV-negative giant extragenital forms of Morbus Bowen (as in the described patient), the focus should be on local immunomodulation by substances such as imiquimod, which reduce the size of the lesions, thereby creating optimal opportunities for their future surgical eradication. Other possible options described in the literature include topical application of 5-fluorouracil, photodynamic therapy, cryotherapy, and laser therapy (carbon dioxide laser). The choice of the most appropriate regimen should have been an individual decision of the clinician, considering also the location and the extent of the lesion.

  19. Gas Giants Form Quickly

    NASA Technical Reports Server (NTRS)

    2007-01-01

    This is an artist's concept of a hypothetical 10-million-year-old star system. The bright blur at the center is a star much like our sun. The other orb in the image is a gas-giant planet like Jupiter. Wisps of white throughout the image represent traces of gas.

    Astronomers using NASA's Spitzer Space Telescope have found evidence showing that gas-giant planets either form within the first 10 million years of a sun-like star's life, or not at all. The lifespan for sun-like stars is about 10 billion years.

    The scientists came to this conclusion after searching for traces of gas around 15 different sun-like stars, most with ages ranging from 3 million to 30 million years. With the help of Spitzer's Infrared Spectrometer instrument, they were able to search for relatively warm gas in the inner regions of these star systems, an area comparable to the zone between Earth and Jupiter in our own solar system. They also used ground-based radio telescopes to search for cooler gas in the outer regions of these systems, an area comparable to the zone around Saturn and beyond.

  20. Giant papillary conjunctivitis.

    PubMed Central

    Donshik, P C

    1994-01-01

    Giant papillary conjunctivitis is a syndrome found frequently as a complication of contact lenses. Many variables can affect the onset and severity of the presenting signs and symptoms. Rigid gas permeable contact lenses appear to result in less severe signs and symptoms, with a longer time before the development of giant papillary conjunctivitis. Nonionic, low-water-content soft contact lenses tend to produce less severe signs and symptoms than ionic, low-water-content soft contact lenses. Enzymatic treatment appears to lessen the severity of signs and symptoms. The association of an allergy appears to play a role in the onset of the severity of the signs and symptoms but does not appear to affect the final ability of the individual to wear contact lenses. Using multiple treatment options, such as changing the polymer to a glyceryl methyl methacrylate or a rigid lens, or utilizing a soft lens on a frequent-replacement basis, can result in a success rate of over 90%. In individuals who still have a return of symptoms, the use of topical mast cell stabilizers or a nonsteroidal anti-inflammatory drug as an adjunctive therapy offers the added possibility of keeping these patients in contact lenses. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 11 A FIGURE 11 B FIGURE 11 C FIGURE 11 D PMID:7886881

  1. Gas Giants Form Quickly

    NASA Technical Reports Server (NTRS)

    2007-01-01

    This is an artist's concept of a hypothetical 10-million-year-old star system. The bright blur at the center is a star much like our sun. The other orb in the image is a gas-giant planet like Jupiter. Wisps of white throughout the image represent traces of gas.

    Astronomers using NASA's Spitzer Space Telescope have found evidence showing that gas-giant planets either form within the first 10 million years of a sun-like star's life, or not at all. The lifespan for sun-like stars is about 10 billion years.

    The scientists came to this conclusion after searching for traces of gas around 15 different sun-like stars, most with ages ranging from 3 million to 30 million years. With the help of Spitzer's Infrared Spectrometer instrument, they were able to search for relatively warm gas in the inner regions of these star systems, an area comparable to the zone between Earth and Jupiter in our own solar system. They also used ground-based radio telescopes to search for cooler gas in the outer regions of these systems, an area comparable to the zone around Saturn and beyond.

  2. Giant Intradiverticular Bladder Tumor

    PubMed Central

    Noh, Mohamad Syafeeq Faeez Md; Aziz, Ahmad Fuad Abdul; Ghani, Khairul Asri Mohd; Siang, Christopher Lee Kheng; Yunus, Rosna; Yusof, Mubarak Mohd

    2017-01-01

    Patient: Male, 74 Final Diagnosis: Giant intradiverticular bladder tumor with metastasis Symptoms: Hematuria Medication:— Clinical Procedure: — Specialty: Urology Objective: Rare disease Background: Intradiverticular bladder tumors are rare. This renders diagnosis of an intradiverticular bladder tumor difficult. Imaging plays a vital role in achieving the diagnosis, and subsequently staging of the disease. Case Report: A 74-year-old male presented to our center with a few months history of constitutional symptoms. Upon further history, he reported hematuria two months prior to presentation, which stopped temporarily, only to recur a few days prior to coming to the hospital. The patient admitted to having lower urinary tract symptoms. However, there was no dysuria, no sandy urine, and no fever. Palpation of his abdomen revealed a vague mass at the suprapubic region, which was non tender. In view of his history and the clinical examination findings, an ultrasound of the abdomen and computed tomography (CT) was arranged. These investigations revealed a giant tumor that seemed to be arising from a bladder diverticulum, with a mass effect and hydronephrosis. He later underwent operative intervention. Conclusions: Intradiverticular bladder tumors may present a challenge to the treating physician in an atypical presentation; thus requiring a high index of suspicion and knowledge of tumor pathophysiology. As illustrated in our case, CT with its wide availability and multiplanar imaging capabilities offers a useful means for diagnosis, disease staging, operative planning, and follow-up. PMID:28246375

  3. Scattering of a vortex pair by a single quantum vortex in a Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Smirnov, L. A.; Smirnov, A. I.; Mironov, V. A.

    2016-01-01

    We analyze the scattering of vortex pairs (the particular case of 2D dark solitons) by a single quantum vortex in a Bose-Einstein condensate with repulsive interaction between atoms. For this purpose, an asymptotic theory describing the dynamics of such 2D soliton-like formations in an arbitrary smoothly nonuniform flow of a ultracold Bose gas is developed. Disregarding the radiation loss associated with acoustic wave emission, we demonstrate that vortex-antivortex pairs can be put in correspondence with quasiparticles, and their behavior can be described by canonical Hamilton equations. For these equations, we determine the integrals of motion that can be used to classify various regimes of scattering of vortex pairs by a single quantum vortex. Theoretical constructions are confirmed by numerical calculations performed directly in terms of the Gross-Pitaevskii equation. We propose a method for estimating the radiation loss in a collision of a soliton-like formation with a phase singularity. It is shown by direct numerical simulation that under certain conditions, the interaction of vortex pairs with a core of a single quantum vortex is accompanied by quite intense acoustic wave emission; as a result, the conditions for applicability of the asymptotic theory developed here are violated. In particular, it is visually demonstrated by a specific example how radiation losses lead to a transformation of a vortex-antivortex pair into a vortex-free 2D dark soliton (i.e., to the annihilation of phase singularities).

  4. Nested contour-dynamic models for axisymmetric vortex rings and vortex wakes

    NASA Astrophysics Data System (ADS)

    O'Farrell, Clara; Dabiri, John O.

    2013-11-01

    Jetting swimmers, such as squid and jellyfish, propel themselves by forming vortex rings. It is known that vortex rings cannot grow indefinitely, but rather ``pinch off'' once they reach their physical limit, and that a decrease in efficiency of fluid transport is associated with pinch-off. Previously, the Norbury family of vortices has been used as a model for axisymmetric vortex rings, and the response of this family to shape perturbations has been characterized. We improve upon the Norbury models, using nested patches of vorticity to construct a family of models for vortex rings generated by a piston-cylinder apparatus at different stroke ratios. The perturbation response of this family is considered by the introduction of a small region of vorticity at the rear of the vortex, which mimics the addition of circulation to a growing vortex ring by a feeding shear layer. Model vortex rings are found to either accept the additional circulation or shed it into a tail, depending on the perturbation size. A change in the behavior of the model vortex rings is identified at a stroke ratio of three. We hypothesize that this change in response is analogous to pinch-off, and that pinch-off might be understood and predicted based on the perturbation responses of model vortex rings.

  5. Prediction and control of vortex-dominated and vortex-wake flows

    NASA Technical Reports Server (NTRS)

    Kandil, Osama

    1993-01-01

    This progress report documents the accomplishments achieved in the period from December 1, 1992 until November 30, 1993. These accomplishments include publications, national and international presentations, NASA presentations, and the research group supported under this grant. Topics covered by documents incorporated into this progress report include: active control of asymmetric conical flow using spinning and rotary oscillation; supersonic vortex breakdown over a delta wing in transonic flow; shock-vortex interaction over a 65-degree delta wing in transonic flow; three dimensional supersonic vortex breakdown; numerical simulation and physical aspects of supersonic vortex breakdown; and prediction of asymmetric vortical flows around slender bodies using Navier-Stokes equations.

  6. Vortex formation and instability in the left ventricle

    NASA Astrophysics Data System (ADS)

    Le, Trung Bao; Sotiropoulos, Fotis; Coffey, Dane; Keefe, Daniel

    2012-09-01

    We study the formation of the mitral vortex ring during early diastolic filling in a patient-specific left ventricle (LV) using direct numerical simulation. The geometry of the left ventricle is reconstructed from Magnetic Resonance Imaging (MRI) data of a healthy human subject. The left ventricular kinematics is modeled via a cell-based activation methodology, which is inspired by cardiac electro-physiology and yields physiologic LV wall motion. In the fluid dynamics videos, we describe in detail the three-dimensional structure of the mitral vortex ring, which is formed during early diastolic filling. The ring starts to deform as it propagates toward the apex of the heart and becomes inclined. The trailing secondary vortex tubes are formed as the result of interaction between the vortex ring and the LV wall. These vortex tubes wrap around the circumference and begin to interact with and destabilize the mitral vortex ring. At the end of diastole, the vortex ring impinges on the LV wall and the large-scale intraventricular flow rotates in clockwise direction. We show for the first time that the mitral vortex ring evolution is dominated by a number of vortex-vortex and vortex-wall interactions, including lateral straining and deformation of vortex ring, the interaction of two vortex tubes with unequal strengths, helicity polarization of vortex tubes and twisting instabilities of the vortex cores.

  7. Reinflating Giant Planets

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-01-01

    Two new, large gas-giant exoplanets have been discovered orbiting close to their host stars. A recent study examining these planets and others like them may help us to better understand what happens to close-in hot Jupiters as their host stars reach the end of their main-sequence lives.OversizedGiantsUnbinned transit light curves for HAT-P-65b. [Adapted from Hartman et al. 2016]The discovery of HAT-P-65b and HAT-P-66b, two new transiting hot Jupiters, is intriguing. These planets have periods of just under 3 days and masses of roughly 0.5 and 0.8 times that of Jupiter, but their sizes are whats really interesting: they have inflated radii of 1.89 and 1.59 times that of Jupiter.These two planets, discovered using the Hungarian-made Automated Telescope Network (HATNet) in Arizona and Hawaii, mark the latest in an ever-growing sample of gas-giant exoplanets with radii larger than expected based on theoretical planetary structure models.What causes this discrepancy? Did the planets just fail to contract to the expected size when they were initially formed, or were they reinflated later in their lifetimes? If the latter, how? These are questions that scientists are only now starting to be able to address using statistics of the sample of close-in, transiting planets.Unbinned transit light curves for HAT-P-66b. [Hartman et al. 2016]Exploring Other PlanetsLed by Joel Hartman (Princeton University), the team that discovered HAT-P-65b and HAT-P-66b has examined these planets observed parameters and those of dozens of other known close-in, transiting exoplanets discovered with a variety of transiting exoplanet missions: HAT, WASP, Kepler, TrES, and KELT. Hartman and collaborators used this sample to draw conclusions about what causes some of these planets to have such large radii.The team found that there is a statistically significant correlation between the radii of close-in giant planets and the fractional ages of their host stars (i.e., the stars age divided by its full

  8. Allometry indicates giant eyes of giant squid are not exceptional.

    PubMed

    Schmitz, Lars; Motani, Ryosuke; Oufiero, Christopher E; Martin, Christopher H; McGee, Matthew D; Gamarra, Ashlee R; Lee, Johanna J; Wainwright, Peter C

    2013-02-18

    The eyes of giant and colossal squid are among the largest eyes in the history of life. It was recently proposed that sperm whale predation is the main driver of eye size evolution in giant squid, on the basis of an optical model that suggested optimal performance in detecting large luminous visual targets such as whales in the deep sea. However, it is poorly understood how the eye size of giant and colossal squid compares to that of other aquatic organisms when scaling effects are considered. We performed a large-scale comparative study that included 87 squid species and 237 species of acanthomorph fish. While squid have larger eyes than most acanthomorphs, a comparison of relative eye size among squid suggests that giant and colossal squid do not have unusually large eyes. After revising constants used in a previous model we found that large eyes perform equally well in detecting point targets and large luminous targets in the deep sea. The eyes of giant and colossal squid do not appear exceptionally large when allometric effects are considered. It is probable that the giant eyes of giant squid result from a phylogenetically conserved developmental pattern manifested in very large animals. Whatever the cause of large eyes, they appear to have several advantages for vision in the reduced light of the deep mesopelagic zone.

  9. Allometry indicates giant eyes of giant squid are not exceptional

    PubMed Central

    2013-01-01

    Background The eyes of giant and colossal squid are among the largest eyes in the history of life. It was recently proposed that sperm whale predation is the main driver of eye size evolution in giant squid, on the basis of an optical model that suggested optimal performance in detecting large luminous visual targets such as whales in the deep sea. However, it is poorly understood how the eye size of giant and colossal squid compares to that of other aquatic organisms when scaling effects are considered. Results We performed a large-scale comparative study that included 87 squid species and 237 species of acanthomorph fish. While squid have larger eyes than most acanthomorphs, a comparison of relative eye size among squid suggests that giant and colossal squid do not have unusually large eyes. After revising constants used in a previous model we found that large eyes perform equally well in detecting point targets and large luminous targets in the deep sea. Conclusions The eyes of giant and colossal squid do not appear exceptionally large when allometric effects are considered. It is probable that the giant eyes of giant squid result from a phylogenetically conserved developmental pattern manifested in very large animals. Whatever the cause of large eyes, they appear to have several advantages for vision in the reduced light of the deep mesopelagic zone. PMID:23418818

  10. Laboratory Applications of the Vortex Tube.

    ERIC Educational Resources Information Center

    Bruno, Thomas J.

    1987-01-01

    Discussed are a brief explanation of the function of the vortex tube and some applications for the chemistry laboratory. It is a useful and inexpensive solution to many small-scale laboratory heating and cooling applications. (RH)

  11. Cavitating vortex generation by a submerged jet

    SciTech Connect

    Belyakov, G. V.; Filippov, A. N.

    2006-05-15

    The surface geometry of a cavitating vortex is determined in the limit of inviscid incompressible flow. The limit surface is an ovaloid of revolution with an axis ratio of 5: 3. It is shown that a cavitating vortex ring cannot develop if the cavitation number is lower than a certain critical value. Experiments conducted at various liquid pressures and several jet exit velocities confirm the existence of a critical cavitation number close to 3. At cavitation numbers higher than the critical one, the cavitating vortex ring does not develop. At substantially lower cavitation numbers (k {<=} 0.1), an elongated asymmetric cavitation bubble is generated, with an axial reentrant jet whose length can exceed the initial jet length by several times. This flow structure is called an asymmetric cavitating vortex, even though steady motion of this structure has not been observed.

  12. Drift due to viscous vortex rings

    NASA Astrophysics Data System (ADS)

    Morrell, Thomas; Spagnolie, Saverio; Thiffeault, Jean-Luc

    2016-11-01

    Biomixing is the study of fluid mixing due to swimming organisms. While large organisms typically produce turbulent flows in their wake, small organisms produce less turbulent wakes; the main mechanism of mixing is the induced net particle displacement (drift). Several experiments have examined this drift for small jellyfish, which produce vortex rings that trap and transport a fair amount of fluid. Inviscid theory implies infinite particle displacements for the trapped fluid, so the effect of viscosity must be included to understand the damping of real vortex motion. We use a model viscous vortex ring to compute particle displacements and other relevant quantities, such as the integrated moments of the displacement. Fluid entrainment at the tail end of a growing vortex 'envelope' is found to play an important role in the total fluid transport and drift. Partially supported by NSF Grant DMS-1109315.

  13. NASA Wake Vortex Research for Aircraft Spacing

    NASA Technical Reports Server (NTRS)

    Perry, R. Brad; Hinton, David A.; Stuever, Robert A.

    1996-01-01

    The National Aeronautics and Space Administration (NASA) is addressing airport capacity enhancements during instrument meteorological conditions through the Terminal Area Productivity (TAP) program. Within TAP, the Reduced Spacing Operations (RSO) subelement at the NASA Langley Research Center is developing an Aircraft Vortex Spacing System (AVOSS). AVOSS will integrate the output of several inter-related areas to produce weather dependent, dynamic wake vortex spacing criteria. These areas include current and predicted weather conditions, models of wake vortex transport and decay in these weather conditions, real-time feedback of wake vortex behavior from sensors, and operationally acceptable aircraft/wake interaction criteria. In today's ATC system, the AVOSS could inform ATC controllers when a fixed reduced separation becomes safe to apply to large and heavy aircraft categories. With appropriate integration into the Center/TRACON Automation System (CTAS), AVOSS dynamic spacing could be tailored to actual generator/follower aircraft pairs rather than a few broad aircraft categories.

  14. Josephson vortex lattice in layered superconductors

    SciTech Connect

    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.

  15. Titan's South Polar Vortex in Motion

    NASA Image and Video Library

    This movie captured by NASA'S Cassini spacecraft shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere, at Saturn’s moon Titan. The swirling mass appears to exec...

  16. Optical Scully vortex and its spatial evolution.

    PubMed

    Aksenov, Valerii P; Pogutsa, Cheslav E

    2012-04-01

    The structure of an optical vortex formed in a partially coherent Laguerre-Gauss laser beam was considered. The main object of study was the recorded vector field of wavefront tilts that consisted of the vortical and potential components. It was found that the vortical motion weakened as the coherence decreased. Main regularities in the behavior of the vortical component can be described by the Scully vortex model of vortical liquid flow. In the spatial evolution, the potential component of tilts may alternate the sign, thus determining the direction of energy flow to the center or to the periphery of the vortex. Energy flow lines in the beam demonstrate the pattern of decay of an optical vortex similar to the pattern of decaying vortical motion in viscous liquid.

  17. Vortex phase separation in mesoscopic superconductors

    PubMed Central

    Iaroshenko, O.; Rybalko, V.; Vinokur, V. M.; Berlyand, L.

    2013-01-01

    We demonstrate that in mesoscopic type II superconductors with the lateral size commensurate with London penetration depth, the ground state of vortices pinned by homogeneously distributed columnar defects can form a hierarchical nested domain structure. Each domain is characterized by an average number of vortices trapped at a single pinning site within a given domain. Our study marks a radical departure from the current understanding of the ground state in disordered macroscopic systems and provides an insight into the interplay between disorder, vortex-vortex interaction, and confinement within finite system size. The observed vortex phase segregation implies the existence of the soliton solution for the vortex density in the finite superconductors and establishes a new class of nonlinear systems that exhibit the soliton phenomenon.

  18. Vortex Dynamics and its Characterization using Ultrasound

    NASA Astrophysics Data System (ADS)

    Manneville, Sébastien; Robres, Jean-Henry; Maurel, Agnès; Petitjeans, Philippe

    1998-11-01

    We present a new method of vortex characterization using the interaction between flow and ultrasound: the Time Reversal Mirrors, developped in the Lab. Ondes et Acoustique (see Roux & Fink, Europhys. Lett., 32:25, 1997). The study concerns a stretched vortex generated in a long duct (see Petitjeans & al. Experiments in Fluids, 22:351, 1997) where we have performed static (for a stationary vortex) as well dynamic (for a vortex advected by the mean flow before breaking) measurements. The advantage of this method is to be non intrusive (the ultrasounds do not perturb the flow) and global (we obtaine the whole velocity field and can describe a 2D motion) with an acquisition frequency of 15 Hz.

  19. Vortex simulation of reacting shear flow

    NASA Astrophysics Data System (ADS)

    Ghoniem, Ahmed F.

    Issues involved in the vortex simulation of reacting shear flow are discussed. It is shown that maintaining accuracy in the vortex methods requires the application of elaborate vorticity-updating schemes as vortex elements are moved along particle trajectories when shear or a strong strain field is represented. Solutions using 2D and 3D methods are discussed to illustrate some of the most common instabilities encountered in nonreacting and reacting shear flows and to reveal the mechanisms by which the maturation of these instabilities enhance mixing and hence burning in a reacting flow. The transport element method is developed and its application to compute scalar mixing in a shear layer is reviewed. The method is then combined with the vortex method to solve the problem of nonuniform-density shear flow. The results of incompressible reacting flow models are used to examine reaction extinction due to the formation of localized regions of strong strains as instabilities grow into their nonlinear range.

  20. Guiding principles for vortex flow controls

    NASA Technical Reports Server (NTRS)

    Wu, J. Z.; Wu, J. M.

    1991-01-01

    In the practice of vortex flow controls, the most important factor is that the persistency and obstinacy of a concentrated vortex depend on its stability and dissipation. In this paper, the modern nonlinear stability theory for circulation-preserving flows is summarized, and the dissipation for general viscous flows is analyzed in terms of the evolution of total enstrophy. These analyses provide a theoretical base for understanding relevant physics of vortex flows, and lead to some guiding principles and methods for their controls. Case studies taken from various theoretical and/or experimental works of vortex controls, due to the present authors as well as others, confirm the feasibility of the recommended principles and methods.

  1. Direct numerical simulations of vortex ring collisions

    NASA Astrophysics Data System (ADS)

    Ostilla Monico, Rodolfo; Pumir, Alain; Brenner, Michael

    2016-11-01

    We numerically simulate the ring vortex collision experiment of Lim and Nickels in an attempt to understand the rapid formation of very fine scale turbulence (or 'smoke') from relatively smooth initial conditions. Reynolds numbers of up to Re = Γ / ν = 7500 , where Γ is the vortex ring circulation and ν the kinematic viscosity of the fluid are reached, which coincide with the highest Reynolds number case of the experiments. Different perturbations to the ring vortex are added, and their effect on the generation and amplification of turbulence is quantified. The underlying dynamics of the vortex core is analyzed, and compared to the dynamics arising from a simple Biot-Savart filament model for the core.

  2. Development of gas pressure vortex regulator

    NASA Astrophysics Data System (ADS)

    Uss, A. Yu.; Chernyshyov, A. V.; Krylov, V. I.

    2017-08-01

    The present paper describes the applications of vortex regulators and the current state of the issue on the use and development of such devices. A patent review has been carried out. Automatic control systems using a vortex regulator are considered. Based on the analysis and preliminary numerical calculation of gas flow in the working cavity of the regulator, a new design of a vortex gas pressure regulator has been developed. An experimental sample of the device was made using additive technologies and a number of tests were carried out. The results of experimental studies confirmed the adequacy of the created mathematical model. Based on further numerical studies a new design of a vortex regulator with a distributed feed of the process control flow as well as with the regulated swirl of the supply and control process flows has been developed.

  3. THz Cherenkov radiation of Josephson vortex

    NASA Astrophysics Data System (ADS)

    Malishevskii, A. S.; Silin, V. P.; Uryupin, S. A.; Uspenskii, S. G.

    2008-01-01

    It is shown that Josephson vortices travelling in sandwich embedded in dielectric media radiate electromagnetic waves with THz frequencies. This phenomenon is caused by the Cherenkov effect and takes place if vortex velocity exceeds the speed of light in dielectric.

  4. 'Optimal' vortex rings and aquatic propulsion mechanisms.

    PubMed Central

    Linden, P. F.; Turner, J. S.

    2004-01-01

    Fishes swim by flapping their tail and other fins. Other sea creatures, such as squid and salps, eject fluid intermittently as a jet. We discuss the fluid mechanics behind these propulsion mechanisms and show that these animals produce optimal vortex rings, which give the maximum thrust for a given energy input. We show that fishes optimize both their steady swimming efficiency and their ability to accelerate and turn by producing an individual optimal ring with each flap of the tail or fin. Salps produce vortex rings directly by ejecting a volume of fluid through a rear orifice, and these are also optimal. An important implication of this paper is that the repetition of vortex production is not necessary for an individual vortex to have the 'optimal' characteristics. PMID:15156924

  5. Analysis of vortex wake encounter upsets

    NASA Technical Reports Server (NTRS)

    Johnson, W. A.; Teper, G. L.

    1974-01-01

    The problem of an airplane being upset by encountering the vortex wake of a large transport on takeoff or landing is currently receiving considerable attention. This report describes the technique and results of a study to assess the effectiveness of automatic control systems in alleviating vortex wake upsets. A six-degree-of-freedom nonlinear digital simulation was used for this purpose. The analysis included establishing the disturbance input due to penetrating a vortex wake from an arbitrary position and angle. Simulations were computed for both a general aviation airplane and a commercial jet transport. Dynamic responses were obtained for the penetrating aircraft with no augmentation, and with various command augmentation systems, as well as with human pilot control. The results of this preliminary study indicate that attitude command augmentation systems can provide significant alleviation of vortex wake upsets; and can do it better than a human pilot.

  6. Laboratory Applications of the Vortex Tube.

    ERIC Educational Resources Information Center

    Bruno, Thomas J.

    1987-01-01

    Discussed are a brief explanation of the function of the vortex tube and some applications for the chemistry laboratory. It is a useful and inexpensive solution to many small-scale laboratory heating and cooling applications. (RH)

  7. Shallow flow vortex formation and control

    NASA Astrophysics Data System (ADS)

    Fu, Haojun

    Vortical structures in shallow flow past a vertical cylinder are addressed in this investigation. A cinema technique of digital particle image velocimetry (DPIV) provided quantitative representations of the wholefield flow patterns in both instantaneous and averaged forms. Techniques for passive and active control of these vortices, and their influence on the loading of the bed, were explored. In a fully-developed, laminar shallow flow, the unstable structure in the near-wake of the cylinder correlates with the horseshoe (necklace) vortex system about the upstream surface of the cylinder. A coherent varicose mode of vortex formation is observed in the near-wake, even though the classical large-scale vortex shedding is suppressed due to bed friction effects. It is also demonstrated that when the near-wake is stable at a sufficiently low value of Reynolds number, applications of external perturbations lead to destabilization of the wake. Classes of small-scale three-dimensional structures arise in a fully-turbulent shallow flow past a surface-piercing cylinder. A prevalent feature is an upward moving jet-like flow from the bed surface, through the center of the developing quasi-two-dimensional primary vortex, at a location in the very near-wake of the cylinder. Passive control via base-bleed through a narrow streamwise slot leads to substantially delay/attenuation of vortex formation in the near-wake. The large-scale near-wake structure is recoverable through combined positive-active control, in the form of rotational perturbations in the presence of small magnitude base bleed. These alterations of the near-wake structure occur in conjunction with modifications of the streamline topology and Reynolds stress at the bed, as well as the shallow approach flow. Active control via rotational perturbations of the cylinder at the most unstable shear-layer frequency promotes well-defined vortical structures in the separating shearlayer, which contribute to the earlier

  8. Vortex core identification in viscous hydrodynamics.

    PubMed

    Finn, Lucas I; Boghosian, Bruce M; Kottke, Christopher N

    2005-08-15

    We describe a software package designed for the investigation of topological fluid dynamics with a novel algorithm for locating and tracking vortex cores. The package is equipped with modules for generating desired vortex knots and links and evolving them according to the Navier-Stokes equations, while tracking and visualizing them. The package is parallelized using a message passing interface for a multiprocessor environment and makes use of a computational steering library for dynamic user intervention.

  9. Imaging magnetic vortex configurations in ferromagnetic nanotubes

    NASA Astrophysics Data System (ADS)

    Wyss, M.; Mehlin, A.; Gross, B.; Buchter, A.; Farhan, A.; Buzzi, M.; Kleibert, A.; Tütüncüoglu, G.; Heimbach, F.; Fontcuberta i Morral, A.; Grundler, D.; Poggio, M.

    2017-07-01

    We image the remnant magnetization configurations of CoFeB and permalloy nanotubes (NTs) using x-ray magnetic circular dichroism photoemission electron microscopy. The images provide direct evidence for flux-closure configurations, including a global vortex state, in which magnetization points circumferentially around the NT axis. Furthermore, micromagnetic simulations predict and measurements confirm that vortex states can be programmed as the equilibrium remnant magnetization configurations by reducing the ratio of the NT's length and diameter.

  10. Vortex interactions and decay in aircraft wakes

    NASA Technical Reports Server (NTRS)

    Bilanin, A. J.; Teske, M. E.; Dupdonaldson, C.; Williamson, G. G.

    1977-01-01

    The dynamic interaction of aircraft wake vortices was investigated using both inviscid and viscous models. For the viscous model, a computer code was developed using a second-order closure model of turbulent transport. The phenomenon of vortex merging which results in the rapid aging of a vortex wake was examined in detail. It was shown that the redistribution of vorticity during merging results from both convective and diffusive mechanisms.

  11. Towards a string formulation of vortex dynamics

    SciTech Connect

    Elsebeth Schroeder; Ola Toernkvist

    1998-01-01

    We derive an exact equation of motion for a non-relativistic vortex in two- and three-dimensional models with a complex field. The velocity is given in terms of gradients of the complex field at the vortex position. We discuss the problem of reducing the field dynamics to a closed dynamical system with non-locally interacting strings as the fundamental degrees of freedom.

  12. [Development of a "vortex bed" drying apparatus].

    PubMed

    Bibileishvili, V I; Setti, D; Peri, C

    1976-01-01

    Fundamental parameters in dimensioning a "vortex bed" drying apparatus are the pressure drop across the bed and the higher and lower limit of fluidization velocity. The analysis of the Navier-Stokes equations brings to the following functional relations between dimensionless groups: (see journal). These relations define the fluidization conditions in a "vortex bed" apparatus. Experimental tests carried out on a laboratory scale apparatus will provide us with the unknown constants for industrial scale extrapolation.

  13. Giant magnetostrictive composites

    NASA Astrophysics Data System (ADS)

    Duenas, Terrisa Ann

    The limitation of magnetostrictive composites has been in their low magnetostrictive response when compared to their monolithic counterparts. In this dissertation research is presented describing the methods and analysis used to create a giant magnetostrictive composite (GMC) producing giant strains at low fields, exhibiting magnetization ``jumping'' and the ΔE effect. This composite combines the giant magnetostrictive material, Terfenol-D (Tb0.3Dy0.7Fe2) in particle form, with a nonmetallic binder and is capable of producing strains (at room temperature) exceeding 1000 ppm at a nominal field of 1.5 kOe mechanically unloaded and 1200 ppm at 8 MPa preload (2.5 kOe). Several studies leading to the high response of this composite are presented. A connectivity study shows that a [1-3] connected composite produces 50% more strain than a [0-3] composite. A resin study indicates that the lower the viscosity of the resin, the greater the magnetostrictive response; this is attributed to the removal of voids during degassing. A void study correlates the increase in voids to the decrease in strain response. A model is used to correlate analysis with experimental results within 10% accuracy and shows that an optimal volume fraction exists based on the properties of the binder. Using a Polyscience Spurr low- viscosity (60 cps) binder this volume fraction is nominally 20%; this optimum is attributed to the balance of epoxy contracting on the particle (built-in preload) and the actuation delivered by the magnetostrictive material. In addition to the connectivity, resin, void, and volume-fraction study, particle size and gradation studies are presented. Widely dispersed (<106, <212, <300 μm), narrowly dispersed (<45, (90-106), (275-300) μm), and an optimized bimodal (18.7% of (45-90) μm with 81.3% of (250-300) μm) particle distributions are studied. Results show that the larger the particle size, the higher the magnetostrictive response; this is attributed to the reduction of

  14. Counterexamples to Moffatt's statements on vortex knots.

    PubMed

    Bogoyavlenskij, Oleg

    2017-04-01

    One of the well-known problems of hydrodynamics is studied: the problem of classification of vortex knots for ideal fluid flows. In the literature there are known Moffatt statements that all torus knots K_{m,n} for all rational numbers m/n (0vortex knots for each one of the considered axisymmetric fluid flows. We prove that actually such a uniformity does not exist because it does not correspond to the facts. Namely, we derive a complete classification of all vortex knots realized for the fluid flows studied by Moffatt and demonstrate that the real structure of vortex knots is much more rich because the sets of mutually nonisotopic vortex knots realized for different axisymmetric fluid flows are all different. An exact formula for the limit of the hydrodynamic safety factor q_{h} at a vortex axis is derived for arbitrary axisymmetric fluid equilibria. Another exact formula is obtained for the limit of the magnetohydrodynamics safety factor q at a magnetic axis for the general axisymmetric plasma equilibria.

  15. Aperiodicity Correction for Rotor Tip Vortex Measurements

    NASA Technical Reports Server (NTRS)

    Ramasamy, Manikandan; Paetzel, Ryan; Bhagwat, Mahendra J.

    2011-01-01

    The initial roll-up of a tip vortex trailing from a model-scale, hovering rotor was measured using particle image velocimetry. The unique feature of the measurements was that a microscope was attached to the camera to allow much higher spatial resolution than hitherto possible. This also posed some unique challenges. In particular, the existing methodologies to correct for aperiodicity in the tip vortex locations could not be easily extended to the present measurements. The difficulty stemmed from the inability to accurately determine the vortex center, which is a prerequisite for the correction procedure. A new method is proposed for determining the vortex center, as well as the vortex core properties, using a least-squares fit approach. This approach has the obvious advantage that the properties are derived from not just a few points near the vortex core, but from a much larger area of flow measurements. Results clearly demonstrate the advantage in the form of reduced variation in the estimated core properties, and also the self-consistent results obtained using three different aperiodicity correction methods.

  16. Counterexamples to Moffatt's statements on vortex knots

    NASA Astrophysics Data System (ADS)

    Bogoyavlenskij, Oleg

    2017-04-01

    One of the well-known problems of hydrodynamics is studied: the problem of classification of vortex knots for ideal fluid flows. In the literature there are known Moffatt statements that all torus knots Km ,n for all rational numbers m /n (0 vortex knots for each one of the considered axisymmetric fluid flows. We prove that actually such a uniformity does not exist because it does not correspond to the facts. Namely, we derive a complete classification of all vortex knots realized for the fluid flows studied by Moffatt and demonstrate that the real structure of vortex knots is much more rich because the sets of mutually nonisotopic vortex knots realized for different axisymmetric fluid flows are all different. An exact formula for the limit of the hydrodynamic safety factor qh at a vortex axis is derived for arbitrary axisymmetric fluid equilibria. Another exact formula is obtained for the limit of the magnetohydrodynamics safety factor q at a magnetic axis for the general axisymmetric plasma equilibria.

  17. Multiple breathers on a vortex filament

    NASA Astrophysics Data System (ADS)

    Salman, H.

    2014-10-01

    In this paper we investigate the correspondence between the Da Rios-Betchov equation, which appears in the three-dimensional motion of a vortex filament, and the nonlinear Schrödinger equation. Using this correspondence we map a set of solutions corresponding to breathers in the nonlinear Schrödinger equation to waves propagating along a vortex filament. The work presented generalizes the recently derived family of vortex configurations associated with these breather solutions to a wider class of configurations that are associated with combination homoclinic/heteroclinic orbits of the 1D self-focussing nonlinear Schrödinger equation. We show that by considering these solutions of the governing nonlinear Schrödinger equation, highly nontrivial vortex filament configurations can be obtained that are associated with a pair of breather excitations. These configurations can lead to loop-like excitations emerging from an otherwise weakly perturbed helical vortex. The results presented further demonstrate the rich class of solutions that are supported by the Da Rios-Betchov equation that is recovered within the local induction approximation for the motion of a vortex filament.

  18. Ambient Fluid Entrainment by Vortex Ring Formation

    NASA Astrophysics Data System (ADS)

    Olcay, Ali B.; Krueger, Paul S.

    2004-11-01

    During the formation of a vortex ring from a piston-cylinder mechanism, the roll-up of the ejected shear layer entrains ambient fluid. The resulting vortex ring convects both ejected and ambient fluid downstream. Ambient fluid entrained during the formation phase must be accelerated with the forming ring and can contribute to elevated propulsive effectiveness for pulsed-jet propulsion. In this regard it is of interest to know how much ambient fluid is entrained during vortex ring formation and if the entrainment occurs primarily during jet ejection or afterward. The present investigation evaluates ambient fluid entrainment experimentally using laser induced fluorescence of vortex ring formation from a piston-cylinder vortex ring generator. The fraction of ambient fluid in fully-developed vortex rings is evaluated directly for piston stroke-to-diameter (L/D) ratios in the range 0.25 to 4 for jet Reynolds number in the range 500 to 2000. The results indicate that the ambient fluid fraction is greater than 50% for L/D < 2.0, and the fraction tends to decrease as L/D increases. Time evolution of the entrainment during ring formation will also be presented.

  19. Asymmetric Vortex Merger in an Electron Plasma

    NASA Astrophysics Data System (ADS)

    Amoretti, M.; Durkin, D.; Fajans, J.; Pozzoli, R.; Rome, M.; Siegel, J.

    2000-10-01

    We investigate the merging of an intense, localized vortex with an extended vortex through the analysis of the hamiltonian flow associated to the electric potential, and numerical simulation with 2D contour dynamics and PIC [1] codes. The study is restricted to highly nonlinear conditions, where the perturbative approach [2] does not hold, in principle. We perform the experimental analysis of this process on a Malmberg-Penning trap with photocatode [3], already used to study the dynamics of intense vortices inside an extended vortex [4]. An excellent agreement between experimental results and simulations is obtained, showing that the dynamics is 2D inviscid. It is found that the localized vortex is wrapped around by the extended vortex, then moves towards the center (while the extended vortex ejects filaments, owing to canonical momentum conservation), eventually approaching an almost stationary state of rotation. An interpretation of the different phases of the process is given. [1] J.P. Varboncoeur, A.B.Langdon and N.T.Gladd, Comp. Phys. Comm. 87, 199 (1995) [2] I.M.Lansky, T.M.O'Neil, D.A.Schecter, Phys. Rev. Lett. 79, 1479 (1997) [3] D. Durkin and J. Fajans, Rev. Sci. Instrum. 70, 4539 (1999) [4] D. Durkin and J. Fajans, submitted to Phys. Rev. Lett. (2000)

  20. Magnetism near Vortex Cores of Cuprate Superconductors

    NASA Astrophysics Data System (ADS)

    Lee, J. C.; Prudchenko, K.; Launspach, B.; Ruiz, E. J.; Boekema, C.

    2005-03-01

    We examined muon-spin-resonance (μSR) vortex data of Bi2212, Tl2223, and YBCO to search for antiferromagnetism (AF) near the vortex cores. [1] Field distributions were obtained from μSR data using Maximum-Entropy analysis. The grainboundary and vortex signals were fitted by Gaussian and Lorentzian curves, the latter suggestive of extra AF ordering. Narrow Gaussians fit the grainboundary signals well, independent of temperature. For T < 0.4Tc, Lorentzians fit much better than Gaussians on the high-field side associated with the vortex core. Such results suggest that magnetism exists near the vortex cores. [1,2] The field dependence of the YBCO AF Lorentzian width is discussed. An AF presence near vortex cores supports theories that predict spin ordering for cuprate superconductivity. Research supported by REU-NSF, WiSE@SJSU & SJSU College of Science. [1] J. Lee et al, J Appl Phys 95 (2004) 6906, and Virtual J Appl of Superconductivity, June 2004 V6 Issue11; K Prudchenko et al, www.jyi.org/volumes/volume10/issue6/articles/prudchenko.html [2] C. Boekema et al, Int J Modern Phys B17 (2003) 3436.

  1. On to the Ice Giants

    NASA Astrophysics Data System (ADS)

    Reh, Kim; Hofstdater, Mark; Simon, Amy; Elliott, John

    2017-04-01

    Voyager 2 mission flew by Uranus in 1986 and Neptune in 1989 resulting in stunning remote observations not previously accessible from the ground. There have been no follow-up space flight missions to examine ice giants and, as a result there are significant gaps in our understanding of planetary formation and evolution. This gap not only affects our understanding of our own solar system but also our understanding of exoplanets; the majority of planets discovered around other stars are thought to be ice giants. Ice Giants are likely to be far more abundant in our galaxy than previously thought. The U.S. 2011 Planetary Science Decadal Survey committee recognized the importance of Uranus and Neptune, and prioritized the exploration of the Ice Giants. Following from this, NASA and ESA have recently completed a study of candidate missions to Uranus and Neptune, the so-called ice giant planets. The intent was to examine what could be accomplished within the budget realities of the predictable future. This "Pre-Decadal Study," focused on opportunities for missions launching in the 2020's and early 2030's. This paper presents results from the Ice Giants study (science, architectures and technologies) and concludes that compelling and affordable missions to the Ice Giants are within our reach.

  2. 2P Vortex Wake Pattern in Vortex-Induced Vibration

    NASA Astrophysics Data System (ADS)

    Govardhan, R.; Williamson, C. H. K.

    1999-11-01

    Flow-visualization in the free vibration experiments of Khalak & Williamson (1997,1999) indicated the existence of the 2P wake vortex pattern (2 pairs of vortices per cycle; as defined in the forced vibration experiments of Williamson & Roshko, 1988), in support of Brika & Laneville (1993), although these visualization techniques are distinctly unclear at high Reynolds numbers (Re ~10^3-10^4 ). Forced vibrations [Sheridan et al. (1998), Techet et al. (1998)] show the 2P mode under some conditions. However, a large number of accurate numerical simulations, at low Re ~200, as well as 2D simulations at higher Re ~500 (Blackburn & Henderson 1999), clearly do not find the 2P mode. There has thus been some debate as to the existence of the 2P mode as a steady state pattern. Hence, DPIV measurements in the wake of the elastically-mounted cylinder have been performed to finally resolve this question. The present results show that the 2P mode is remarkably repeatable and continues indefinitely. The reason for this apparent disparity between experiments and DNS therefore seems to be either a Reynolds number effect or the fact that the computed flow is constrained to be 2D. Further, it is shown that this pattern corresponds with the splitting of a region of vorticity due to the strain rate field of neighbouring vortices. wake patterns show interesting differences. Supported by ONR Contracts N00014-94-1-1197 & N00014-95-1-0332.

  3. Giant magnetofossils and hyperthermal events

    NASA Astrophysics Data System (ADS)

    Chang, Liao; Roberts, Andrew P.; Williams, Wyn; Fitz Gerald, John D.; Larrasoaña, Juan C.; Jovane, Luigi; Muxworthy, Adrian R.

    2012-10-01

    Magnetotactic bacteria biomineralize magnetic minerals with precisely controlled size, morphology, and stoichiometry. These cosmopolitan bacteria are widely observed in aquatic environments. If preserved after burial, the inorganic remains of magnetotactic bacteria act as magnetofossils that record ancient geomagnetic field variations. They also have potential to provide paleoenvironmental information. In contrast to conventional magnetofossils, giant magnetofossils (most likely produced by eukaryotic organisms) have only been reported once before from Paleocene-Eocene Thermal Maximum (PETM; 55.8 Ma) sediments on the New Jersey coastal plain. Here, using transmission electron microscopic observations, we present evidence for abundant giant magnetofossils, including previously reported elongated prisms and spindles, and new giant bullet-shaped magnetite crystals, in the Southern Ocean near Antarctica, not only during the PETM, but also shortly before and after the PETM. Moreover, we have discovered giant bullet-shaped magnetite crystals from the equatorial Indian Ocean during the Mid-Eocene Climatic Optimum (˜40 Ma). Our results indicate a more widespread geographic, environmental, and temporal distribution of giant magnetofossils in the geological record with a link to "hyperthermal" events. Enhanced global weathering during hyperthermals, and expanded suboxic diagenetic environments, probably provided more bioavailable iron that enabled biomineralization of giant magnetofossils. Our micromagnetic modelling indicates the presence of magnetic multi-domain (i.e., not ideal for navigation) and single domain (i.e., ideal for navigation) structures in the giant magnetite particles depending on their size, morphology and spatial arrangement. Different giant magnetite crystal morphologies appear to have had different biological functions, including magnetotaxis and other non-navigational purposes. Our observations suggest that hyperthermals provided ideal conditions for

  4. Formation and evolution of concentric vortex rings

    NASA Astrophysics Data System (ADS)

    Sadri, Vahid

    The formation and interactions of concentric vortex rings are studied experimentally and computationally using a concentric piston-cylinder geometry to generate concentric vortex rings in water at a maximum jet Reynolds number of 2000. The effects of cylinder gap ratio, DeltaR/R, and jet stroke length-to-gap ratio, L/DeltaR, on the evolution of the flow were investigated. For the experimental study, the jet pulses were generated using piston stroke to gap size ratios (?R/R) in the range 0.2 to 0.05, and L/DeltaR in the range 1-20, for a trapezoidal piston velocity program. Digital Particle Image Velocimetry (DPIV) was used to measure concentric vortex ring position, vorticity, and velocity. Additional experiments were conducted using dye visualizations to reveal the spatial structure of the instability for concentric vortex rings. For the computational study, the flow was simulated at a jet Reynolds number of 1,000 (based on DeltaR and the jet velocity), L/DeltaR in the range 1-20, and DeltaR/R in the range 0.01-0.25. The large L/DeltaR and small DeltaR/R cases were included, in part, to investigate the pinch-off of axisymmetric vortex pairs generated by flow between concentric cylinders with radial separation DeltaR for comparison with planar vortex dipole behavior. Five characteristic flow evolution patterns were observed and classified based on L/DeltaR and DeltaR/R for concentric vortex ring behavior. The results showed that the relative position, relative strength, and radii of the vortex rings during and soon after formation played a prominent role in the evolution of the trajectories of their vorticity centroids at the later time. The conditions on relative strength of the vortices necessary for them to travel together as a pair following formation were studied and factors affecting differences in vortex circulation following formation were investigated. In addition to the characteristics of the primary vortices, the stopping vortices had a strong influence

  5. [Giant esophageal fibrovascular polyp].

    PubMed

    Palacios, Fernando; Contardo, Carlos; Guevara, Jorge; Vera, Augusto; Aguilar, Luis; Huamán, Manuel; Palomino, Américo; Yabar, Alejandro

    2003-01-01

    Fibrovascular polyps are extremely rare benign neoplasias of the esophagus, which usually originate in the lower cricoid area. They do not produce any discomfort in the patient for a long time, however it may make itself evident by the patient's regurgitation of the polyp, producing asphyxia or, more frequently, dysphagia. The case of a 58 year old male patient is presented herein, with a 9 month record of dysphagia, weight loss and intermittent melena. The barium x-ray showed a distended esophagus, with a tumor running from the upper esophageal sphincter to the cardia. The endoscopy confirmed the presence of a pediculated tumor, implanted in the cervical esophagus. Surgeons suspected the potential malignancy of the tumor and performed a transhiatal esophagectomy. The final pathologic diagnosis was giant fibrovascular esophageal polyp.

  6. A giant Ordovician anomalocaridid.

    PubMed

    Van Roy, Peter; Briggs, Derek E G

    2011-05-26

    Anomalocaridids, giant lightly sclerotized invertebrate predators, occur in a number of exceptionally preserved early and middle Cambrian (542-501 million years ago) biotas and have come to symbolize the unfamiliar morphologies displayed by stem organisms in faunas of the Burgess Shale type. They are characterized by a pair of anterior, segmented appendages, a circlet of plates around the mouth, and an elongate segmented trunk lacking true tergites with a pair of flexible lateral lobes per segment. Disarticulated body parts, such as the anterior appendages and oral circlet, had been assigned to a range of taxonomic groups--but the discovery of complete specimens from the middle Cambrian Burgess Shale showed that these disparate elements all belong to a single kind of animal. Phylogenetic analyses support a position of anomalocaridids in the arthropod stem, as a sister group to the euarthropods. The anomalocaridids were the largest animals in Cambrian communities. The youngest unequivocal examples occur in the middle Cambrian Marjum Formation of Utah but an arthropod retaining some anomalocaridid characteristics is present in the Devonian of Germany. Here we report the post-Cambrian occurrence of anomalocaridids, from the Early Ordovician (488-472 million years ago) Fezouata Biota in southeastern Morocco, including specimens larger than any in Cambrian biotas. These giant animals were an important element of some marine communities for about 30 million years longer than previously realized. The Moroccan specimens confirm the presence of a dorsal array of flexible blades attached to a transverse rachis on the trunk segments; these blades probably functioned as gills.

  7. Giant Hedge-Hogs: Spikes on Giant Gravitons

    SciTech Connect

    Sadri, D

    2004-01-28

    We consider giant gravitons on the maximally supersymmetric plane-wave background of type IIB string theory. Fixing the light-cone gauge, we work out the low energy effective light-cone Hamiltonian of the three-sphere giant graviton. At first order, this is a U(1) gauge theory on R x S{sup 3}. We place sources in this effective gauge theory. Although non-vanishing net electric charge configurations are disallowed by Gauss' law, electric dipoles can be formed. From the string theory point of view these dipoles can be understood as open strings piercing the three-sphere, generalizing the usual BIons to the giant gravitons, BIGGons. Our results can be used to give a two dimensional (worldsheet) description of giant gravitons, similar to Polchinski's description for the usual D-branes, in agreement with the discussions of hep-th/0204196.

  8. Giant resonances: Progress, new directions, new challenges

    SciTech Connect

    Bertrand, J.R.; Beene, J.R.

    1989-01-01

    A review of some recent developments in the field of giant multipole resonances is presented. Particular emphasis is placed on directions that the authors feel will be followed in this field during the next several years. In particular, the use of high-energy heavy ions to excite the giant resonances is shown to provide exciting new capabilities for giant resonance studies. Among subjects covered are: Coulomb excitation of giant resonances, photon decay of giant resonances, the recent controversy over the identity of the giant monopole resonance, the most recent value for incompressibility of nuclear matter from analysis of giant monopole data, the isospin character of the 63 A/sup /minus/1/3/ GQR, agreement between (e,e/prime/) and (hadron, hadron/prime/) excitation of the giant quadrupole resonance, prospects for multiphonon giant resonance observation, and isolation of the isovector giant quadrupole resonance. 55 refs., 23 figs., 4 tabs.

  9. Geo Spots and Vortex Theory

    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

  10. Flow-Driven Rapid Vesicle Fusion via Vortex Trapping.

    PubMed

    Shin, Sangwoo; Ault, Jesse T; Stone, Howard A

    2015-07-07

    Fusion between suspended lipid vesicles is difficult to achieve without membrane proteins or ions because the vesicles have extremely low equilibrium membrane tension and high poration energy. Nonetheless, vesicle fusion in the absence of mediators can also be achieved by mechanical forcing that is strong enough to induce membrane poration. Here, we employ a strong fluid shear stress to achieve vesicle fusion. By utilizing a unique vortex formation phenomenon in branched channels as a platform for capturing, stressing, and fusing the lipid vesicles, we directly visualize using high-speed imaging the vesicle fusion events, induced solely by shear, on the time scale of submilliseconds. We show that a large vesicle with a size of up to ∼10 μm can be achieved by the fusion of nanoscale vesicles. This technique has the potential to be utilized as a fast and simple way to produce giant unilamellar vesicles and to serve as a platform for visualizing vesicle interactions and fusions in the presence of shear.

  11. Thermal study of vortex states in mesoscopic superconducting disks

    NASA Astrophysics Data System (ADS)

    Ong, Florian; Bourgeois, Olivier; Skipetrov, Sergey; Chaussy, Jacques

    2007-03-01

    We present low temperature highly sensitive heat capacity C measurements [1,2] of aluminum disks with diameters close to ξ(T), the superconducting coherence length. C(T) scans under fixed perpendicular magnetic fields H reveal a quasiperiodic modulation of the height δC of the C jump at the superconducting to normal phase transition. This behavior is due to transitions between several arrangements of vortices in the disks. Indeed giant vortex states or multivortex states can be observed, with a vorticity (an integer equal to the number of vortices threading a single disk) depending on H, T, and on the size of the disks. Heat capacity measurements enable to study phase transitions between such states, without contacting or biasing them. Thus phase boudaries in the H-T plane can be drawn in all the superconducting region. [1] O. Bourgeois, F. Ong, S.E. Skipetrov, and J. Chaussy, Phys. Rev. Lett. 94, 057007 (2005) [2] F.R. Ong, O. Bourgeois, S.E. Skipetrov, and J. Chaussy, Phys. Rev. B 74, 140503(R) (2006)

  12. A distributed vortex method for computing the vortex field of a missile

    NASA Technical Reports Server (NTRS)

    Barger, R. L.

    1978-01-01

    Vortex sheet development in the flow field of a missile was investigated by approximating the sheets in the cross-flow plane with short straight-line segments having distributed vorticity. In contrast with the method that represents the sheets as lines of discrete vortices, this distributed vortex method produced calculations with a high degree of computational stability.

  13. An experimental investigation of the parallel blade-vortex interaction

    NASA Technical Reports Server (NTRS)

    Caradonna, F. X.; Laub, G. H.; Tung, C.

    1984-01-01

    A scheme for investigating the parallel blade vortex interaction (BVI) has been designed and tested. The scheme involves setting a vortex generator upstream of a nonlifting rotor so that the vortex interacts with the blade at the forward azimuth. The method has revealed two propagation mechanisms: a type C shock propagation from the leading edge induced by the vortex at high tip speeds, and a rapid but continuous pressure pulse associated with the proximity of the vortex to the leading edge. The latter is thought to be the more important source. The effects of Mach number and vortex proximity are discussed.

  14. Devices that Alter the Tip Vortex of a Rotor

    NASA Technical Reports Server (NTRS)

    McAlister, Kenneth W.; Tung, Chee; Heineck, James T.

    2001-01-01

    Small devices were attached near the tip of a hovering rotor blade 'in order to alter the structure and trajectory of the trailing vortex. Stereo particle image velocimetry (PIV) images were used to quantify the wake behind the rotor blade during the first revolution. A procedure for analyzing the 3D-velocity field is presented that includes a method for accounting for vortex wander. The results show that a vortex generator can alter the trajectory of the trailing vortex and that a major change in the size and intensity of the trailing vortex can be achieved by introducing a high level of turbulence into the core of the vortex.

  15. Low NOx Advanced Vortex Combustor

    SciTech Connect

    Edmonds, Ryan G; Williams, Joseph T; Steele, Robert C; Straub, Douglas L; Casleton, Kent H; Bining, Avtar

    2008-05-01

    A lean-premixed advanced vortex combustor (AVC) has been developed and tested. The natural gas fueled AVC was tested at the U.S. Department of Energy’s National Energy Technology Laboratory in Morgantown, WV. All testing was performed at elevated pressures and inlet temperatures and at lean fuel-air ratios representative of industrial gas turbines. The improved AVC design exhibited simultaneous NOx /CO/unburned hydrocarbon (UHC) emissions of 4/4/0 ppmv (all emissions corrected to 15% O2 dry). The design also achieved less than 3 ppmv NOx with combustion efficiencies in excess of 99.5%. The design demonstrated marked acoustic dynamic stability over a wide range of operating conditions, which potentially makes this approach significantly more attractive than other lean-premixed combustion approaches. In addition, the measured 1.75% pressure drop is significantly lower than conventional gas turbine combustors, which could translate into an overall gas turbine cycle efficiency improvement. The relatively high velocities and low pressure drop achievable with this technology make the AVC approach an attractive alternative for syngas fuel applications.

  16. Vortex Cores of Inertial Particles.

    PubMed

    Günther, Tobias; Theisel, Holger

    2014-12-01

    The cores of massless, swirling particle motion are an indicator for vortex-like behavior in vector fields and to this end, a number of coreline extractors have been proposed in the literature. Though, many practical applications go beyond the study of the vector field. Instead, engineers seek to understand the behavior of inertial particles moving therein, for instance in sediment transport, helicopter brownout and pulverized coal combustion. In this paper, we present two strategies for the extraction of the corelines that inertial particles swirl around, which depend on particle density, particle diameter, fluid viscosity and gravity. The first is to deduce the local swirling behavior from the autonomous inertial motion ODE, which eventually reduces to a parallel vectors operation. For the second strategy, we use a particle density estimation to locate inertial attractors. With this, we are able to extract the cores of swirling inertial particle motion for both steady and unsteady 3D vector fields. We demonstrate our techniques in a number of benchmark data sets, and elaborate on the relation to traditional massless corelines.

  17. Low NOx Advanced Vortex Combustor

    SciTech Connect

    Edmonds, R.G.; Williams, J.T.; Steele, R.C.; Straub, D.L.; Casleton, K.H.; Bining, Avtar

    2008-05-01

    A lean-premixed advanced vortex combustor (AVC) has been developed and tested. The natural gas fueled AVC was tested at the U.S. Department of Energy’s National Energy Technology Laboratory in Morgantown, WV. All testing was performed at elevated pressures and inlet temperatures and at lean fuel-air ratios representative of industrial gas turbines. The improved AVC design exhibited simultaneous NOx /CO/unburned hydrocarbon (UHC) emissions of 4/4/0 ppmv (all emissions corrected to 15% O2 dry). The design also achieved less than 3 ppmv NOx with combustion efficiencies in excess of 99.5%. The design demonstrated marked acoustic dynamic stability over a wide range of operating conditions, which potentially makes this approach significantly more attractive than other lean-premixed combustion approaches. In addition, the measured 1.75% pressure drop is significantly lower than conventional gas turbine combustors, which could translate into an overall gas turbine cycle efficiency improvement. The relatively high velocities and low pressure drop achievable with this technology make the AVC approach an attractive alternative for syngas fuel applications.

  18. Phenomenon of Alfvenic Vortex Shedding

    SciTech Connect

    Gruszecki, M.; Nakariakov, V. M.; Van Doorsselaere, T.; Arber, T. D.

    2010-07-30

    Generation of Alfvenic (magnetohydrodynamic) vortices by the interaction of compressible plasma flows with magnetic-field-aligned blunt obstacles is modeled in terms of magnetohydrodynamics. It is found that periodic shedding of vortices with opposite vorticity is a robust feature of the interaction in a broad range of plasma parameters: for plasma beta from 0.025 to 0.5, and for the flow speeds from 0.1 to 0.99 of the fast magnetoacoustic speed. The Strouhal number is the dimensionless ratio of the blunt body diameter to the product of the period of vortex shedding and the inflow speed. It is found to be consistently in the range 0.15-0.25 in the whole range of parameters. The induced Alfvenic vortices are compressible and contain spiral-armed perturbations of the magnetic field strength and plasma mass density up to 50%-60% of the background values. The generated electric current also has the spiral-armed structuring.

  19. Theories of Giant Planet Formation

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

    1998-01-01

    An overview of current theories of planetary formation, with emphasis on giant planets, is presented. The most detailed models are based upon observations of our own Solar System and of young stars and their environments. While these models predict that rocky planets should form around most single stars, the frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Most models for extrasolar giant planets suggest that they formed as did Jupiter and Saturn (in nearly circular orbits, far enough from the star that ice could), and subsequently migrated to their current positions, although some models suggest in situ formation.

  20. Lichens On Galapagos Giant Tortoises.

    PubMed

    Hendrickson, J R; Weber, W A

    1964-06-19

    The association of Physcia picta with the giant Galdpagos tortoise is believed to be the first reported occurrence of lichens on land animals. The habitat is restricted to specific sites on the carapace of male tortoises.

  1. Landscape of the lost giants

    NASA Astrophysics Data System (ADS)

    2013-09-01

    The Pleistocene megafauna extinction erased a group of remarkable animals. Whether humans had a prominent role in the extinction remains controversial, but it is emerging that the disappearance of the giants has markedly affected the environment.

  2. What Is Giant Cell Arteritis?

    MedlinePlus

    ... 01, 2017 Giant cell arteritis (GCA) is an inflammation (swelling) of the arteries, which are the blood ... help nourish your eyes, reduced blood flow can cause sudden, painless vision loss. This condition is called ...

  3. Pharma giants swap research programs.

    PubMed

    2014-07-01

    Pharmaceutical giants Novartis and GlaxoSmithKline (GSK) agreed in late April to swap some assets, with Novartis handing off its vaccine business to GSK and getting most of the British company's cancer portfolio in return.

  4. Giant sacrolumbar meningioma. Case report.

    PubMed

    Feldenzer, J A; McGillicuddy, J E; Hopkins, J W

    1990-06-01

    A case of giant sacral meningioma with presacral and lumbar extension is presented. The difficulties in diagnosis and management are emphasized including the staged multidisciplinary surgical approaches and preoperative tumor embolization.

  5. Atmospheres of Extrasolar Giant Planets

    NASA Technical Reports Server (NTRS)

    Marley, Mark

    2006-01-01

    The next decade will almost certainly see the direct imaging of extrasolar giant planets around nearby stars. Unlike purely radial velocity detections, direct imaging will open the door to characterizing the atmosphere and interiors of extrasola planets and ultimately provide clues on their formation and evolution through time. This process has already begun for the transiting planets, placing new constraints on their atmospheric structure, composition, and evolution. Indeed the key to understanding giant planet detectability, interpreting spectra, and constraining effective temperature and hence evolution-is the atmosphere. I will review the universe of extrasolar giant planet models, focusing on what we have already learned from modeling and what we will likely be able to learn from the first generation of direct detection data. In addition to these theoretical considerations, I will review the observations and interpretation of the - transiting hot Jupiters. These objects provide a test of our ability to model exotic atmospheres and challenge our current understanding of giant planet evolution.

  6. Theories of Giant Planet Formation

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Young, Richard E. (Technical Monitor)

    1998-01-01

    An overview of current theories of planetary formation, with emphasis on giant planets, is presented. The most detailed models are based upon observations of our own Solar System and of young stars and their environments. While these models predict that rocky planets should form around most single stars, the frequency of formation of gas giant planets is more difficult to predict theoretically. Terrestrial planets are believed to grow via pairwise accretion until the spacing of planetary orbits becomes large enough that the configuration is stable for the age of the system. Giant planets begin their growth as do terrestrial planets, but they become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. Most models for extrasolar giant planets suggest that they formed as did Jupiter and Saturn (in nearly circular orbits, far enough from the star that ice could), and subsequently migrated to their current positions, although some models suggest in situ formation.

  7. Intraventricular vortex properties in nonischemic dilated cardiomyopathy.

    PubMed

    Bermejo, Javier; Benito, Yolanda; Alhama, Marta; Yotti, Raquel; Martínez-Legazpi, Pablo; Del Villar, Candelas Pérez; Pérez-David, Esther; González-Mansilla, Ana; Santa-Marta, Cristina; Barrio, Alicia; Fernández-Avilés, Francisco; Del Álamo, Juan C

    2014-03-01

    Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1-74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m(2)/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound.

  8. Intraventricular vortex properties in nonischemic dilated cardiomyopathy

    PubMed Central

    Benito, Yolanda; Alhama, Marta; Yotti, Raquel; Martínez-Legazpi, Pablo; del Villar, Candelas Pérez; Pérez-David, Esther; González-Mansilla, Ana; Santa-Marta, Cristina; Barrio, Alicia; Fernández-Avilés, Francisco; del Álamo, Juan C.

    2014-01-01

    Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1–74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m2/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound. PMID:24414062

  9. Giant cell arteritis: a review

    PubMed Central

    Patil, Pravin; Karia, Niral; Jain, Shaifali; Dasgupta, Bhaskar

    2013-01-01

    Giant cell arteritis is the most common vasculitis in Caucasians. Acute visual loss in one or both eyes is by far the most feared and irreversible complication of giant cell arteritis. This article reviews recent guidelines on early recognition of systemic, cranial, and ophthalmic manifestations, and current management and diagnostic strategies and advances in imaging. We share our experience of the fast track pathway and imaging in associated disorders, such as large-vessel vasculitis. PMID:28539785

  10. Low-amplitude magnetic vortex core reversal by non-linear interaction between azimuthal spin waves and the vortex gyromode

    SciTech Connect

    Sproll, Markus; Noske, Matthias; Kammerer, Matthias; Dieterle, Georg; Weigand, Markus; Stoll, Hermann; Schütz, Gisela; Bauer, Hans; Gangwar, Ajay; Woltersdorf, Georg; Back, Christian H.

    2014-01-06

    We show, by experiments and micromagnetic simulations in vortex structures, that an active “dual frequency” excitation of both the sub-GHz vortex gyromode and multi-GHz spin waves considerably changes the frequency response of spin wave mediated vortex core reversal. Besides additional minima in the switching threshold, a significant broadband reduction of the switching amplitudes is observed, which can be explained by non-linear interaction between the vortex gyromode and the spin waves. We conclude that the well known frequency spectra of azimuthal spin waves in vortex structures are altered substantially, when the vortex gyromode is actively excited simultaneously.

  11. On the swelling of rolled up vortex surfaces and the breakdown of the vortex core for slender wings

    NASA Technical Reports Server (NTRS)

    Das, A.

    1980-01-01

    Simplified models of the vortex distribution over cylindrical surfaces are developed. The effect of a change of vortex strength was analyzed quantitatively by menas of potential theory. The considerable bulging of the cylindrical vortex sheet as a consequence of the change of the vortex strength is discussed. The coiling-up of the vortices rotation in opposite directions over the cylindrical surface renders the condition for instability and the subsequent large spreading of the vortex core. These processes occur without a positive pressure gradient being necessary in the field of flow surrounding the coiled up vortex sheet.

  12. Analysis of Vortex Line Cutting and Reconnection by a Blade

    NASA Astrophysics Data System (ADS)

    Saunders, Curtis; Marshall, Jeffrey

    2015-11-01

    The essence of vortex reconnection involves the cutting of vortex lines originating from one region and reconnecting to vortex lines originating from another region via the diffusion-regulated annihilation of vorticity. Vortex cutting by a blade is a special case of the more general class of vortex reconnection problems, with an important difference being that vorticity is generated at the reconnection site. In this study, a series of Navier-Stokes simulations of orthogonal vortex cutting by a blade with different values of vortex strength are reported. The three phases of vortex reconnection identified in the literature are found to have counterparts for the vortex cutting problem. However numerous differences between the mechanics of vortex cutting and reconnection within each phase are discussed. In addition, comparisons are made between the temporal changes of the maximum and minimum components of vorticity for vortices of differing strength but still within the vortex cutting regime. The vortex cutting results are also compared with predictions of a simple analytical model that incorporates the key elements of a stretched vorticity field interacting with a solid surface, which is representative of the vortex cutting mechanism near the blade leading edge. Funded by National Science Foundation project DGE-1144388.

  13. Giants in the Local Region

    NASA Astrophysics Data System (ADS)

    Luck, R. Earle; Heiter, Ulrike

    2007-06-01

    We present parameter and abundance data for a sample of 298 nearby giants. The spectroscopic data for this work have a resolution of R~60,000, S/N>150, and spectral coverage from 475 to 685 nm. Overall trends in the Z>10 abundances are dominated by Galactic chemical evolution, while the light-element abundances are influenced by stellar evolution, as well as Galactic evolution. We find several super-Li stars in our sample and confirm that Li abundances in the first giant branch are related to mixing depths. Once astration of lithium on the main sequence along with the overall range of main-sequence lithium abundances are taken into account, the lithium abundances of the giants are not dramatically at odds with the predictions of standard stellar evolution. We find the giants to be carbon-diluted in accord with standard stellar evolution and that the carbon and oxygen abundances determined for the local giants are consistent with those found in local field dwarfs. We find that there is evidence for systematic carbon variations in the red giant clump in the sense that the blue side of the clump is carbon-poor (more diluted) than the red side.

  14. Kuiper Prize: Giant Planet Atmospheres

    NASA Astrophysics Data System (ADS)

    Ingersoll, Andrew P.

    2007-10-01

    The study of giant planet atmospheres is near and dear to me, for several reasons. First, the giant planets are photogenic; the colored clouds are great tracers, and one can make fantastic movies of the atmosphere in motion. Second, the giant planets challenge us with storms that last for hundreds of years and winds that blow faster the farther you go from the sun. Third, they remind us of Earth with their hurricanes, auroras, and lightning, but they also are the link to the 200 giant planets that have been discovered around other stars. This talk will cover the past, present, and future (one hopes) of giant planet research. I will review the surprises of the Voyager and Galileo eras, and will discuss what we are learning now from the Cassini orbiter. I will review the prospects for answering the outstanding questions like: Where's the water? What is providing the colors of the clouds? How deep do the features extend? Where do the winds get their energy? What is the role of the magnetic field? Finally, I will briefly discuss how extrasolar giant planets compare with objects in our own solar system.

  15. The Changing Face of the Extrasolar Giant Planet HD 209458b

    NASA Astrophysics Data System (ADS)

    Cho, James Y.-K.; Menou, Kristen; Hansen, Bradley M. S.; Seager, Sara

    2003-04-01

    High-resolution atmospheric flow simulations of the tidally locked extrasolar giant planet HD 209458b show large-scale spatio-temporal variability. This is in contrast to the simple, permanent day/night (i.e., hot/cold) picture. The planet's global circulation is characterized by a polar vortex in motion around each pole and a banded structure corresponding to approximately three broad zonal (east-west) jets. For very strong jets, the circulation-induced temperature difference between moving hot and cold regions can reach up to ~1000 K, suggesting that atmospheric variability could be observed in the planet's spectral and photometric signatures.

  16. Vortex-Based Aero- and Hydrodynamic Estimation

    NASA Astrophysics Data System (ADS)

    Hemati, Maziar Sam

    Flow control strategies often require knowledge of unmeasurable quantities, thus presenting a need to reconstruct flow states from measurable ones. In this thesis, the modeling, simulation, and estimator design aspects of flow reconstruction are considered. First, a vortex-based aero- and hydrodynamic estimation paradigm is developed to design a wake sensing algorithm for aircraft formation flight missions. The method assimilates wing distributed pressure measurements with a vortex-based wake model to better predict the state of the flow. The study compares Kalman-type algorithms with particle filtering algorithms, demonstrating that the vortex nonlinearities require particle filters to yield adequate performance. Furthermore, the observability structure of the wake is shown to have a negative impact on filter performance regardless of the algorithm applied. It is demonstrated that relative motions can alleviate the filter divergence issues associated with this observability structure. In addition to estimator development, the dissertation addresses the need for an efficient unsteady multi-body aerodynamics testbed for estimator and controller validation studies. A pure vortex particle implementation of a vortex panel-particle method is developed to satisfy this need. The numerical method is demonstrated on the impulsive startup of a flat plate as well as the impulsive startup of a multi-wing formation. It is clear, from these validation studies, that the method is able to accommodate the unsteady wake effects that arise in formation flight missions. Lastly, successful vortex-based estimation is highly dependent on the reliability of the low-order vortex model used in representing the flow of interest. The present treatise establishes a systematic framework for vortex model improvement, grounded in optimal control theory and the calculus of variations. By minimizing model predicted errors with respect to empirical data, the shortcomings of the baseline vortex model

  17. The Giant Magnetocaloric Effect

    NASA Astrophysics Data System (ADS)

    Pecharsky, Vitalij K.

    1998-03-01

    Since the discovery of the magnetocaloric effect in pure iron by E.Warburg in 1881, it has been measured experimentally on many magnetic metals and compounds. The majority of the materials studied order magnetically undergoing a second order phase transformation. The magnetocaloric effect, typically peaking near the Curie or the Néel temperature, generally ranges from 0.5 to 2 K (in terms of adiabatic temperature change) or at 1 to 4 J/kg K (in terms of isothermal magnetic entropy change) per 1 T magnetic field change. The giant magnetocaloric effect recently discovered in Gd_5(Si_xGe_1-x)4 alloys, where x <= 0.5, is associated with a first order magnetic phase transition and it reaches values of 3 to 4 K and 6 to 10 J/kg K per 1 T field change, respectively. The refrigerant capacity, which is the measure of how much heat can be transferred from a cold to a hot reservoir in one ideal thermodynamic cycle, is larger than that of the best second order phase transition materials by 25 to 100%. When the Gd_5(Si_xGe_1-x)4 alloys are compared with other known materials, which show first order magnetic phase transition, such as Dy, Ho, Er, HoCo_2, NdMn_2Si_2, Fe_0.49Rh_0.51, and (Hf_0.83Ta_0.17)Fe_2+x, only Fe_0.49Rh_0.51 has comparable magnetocaloric properties. However, the first order magnetic phase transition in Fe_0.49Rh_0.51 is irreversible, and the magnetocaloric effect disappears after one magnetizing/demagnetizing cycle. A study of the crystal structure, thermodynamics, and magnetism of the Gd_5(Si_xGe_1-x)4 alloys, where 0 <= x <= 1 allowed us to obtain a qualitative understanding of the basic relations between the composition, the crystal structure, and the change in thermodynamics and magnetocaloric properties, which occur in the Gd_5(Si_xGe_1-x)4 system, and which brings about the giant magnetocaloric effect when x <= 0.5.

  18. The calculation of some Batchelor flows - The Sadovskii vortex and rotational corner flow

    NASA Astrophysics Data System (ADS)

    Moore, D. W.; Saffman, P. G.; Tanveer, S.

    1988-05-01

    Steady inviscid incompressible two-dimensional flows with vortex patches bounded by vortex sheets (Batchelor flows) are calculated with attention given to the vortex on a plane wall (Sadovskii vortex) and the vortex in a right-angled corner. Nonlinear integral equations derived for the shape of the bounding vortex sheet are solved numerically. Only symmetrical solutions are shown to exist.

  19. Vortices and vortex lattices in quantum ferrofluids.

    PubMed

    Martin, A M; Marchant, N G; O'Dell, D H J; Parker, N G

    2017-03-15

    The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices. Here we give a review of the theory of vortices in dipolar Bose-Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. We cover single vortex solutions, including structure, energy and stability, vortex pairs, including interactions and dynamics, and also vortex lattices. Our discussion is founded on the mean-field theory provided by the dipolar Gross-Pitaevskii equation, ranging from analytic treatments based on the Thomas-Fermi (hydrodynamic) and variational approaches to full numerical simulations. Routes for generating vortices in dipolar condensates are discussed, with particular attention paid to rotating condensates, where surface instabilities drive the nucleation of vortices, and lead to the emergence of rich and varied vortex lattice structures. We also present an outlook, including potential extensions to degenerate Fermi gases, quantum Hall physics, toroidal systems and the Berezinskii-Kosterlitz-Thouless transition.

  20. Majorana Kramers pair in a nematic vortex

    DOE PAGES

    Wu, Fengcheng; Martin, Ivar

    2017-06-05

    A time-reversal (TR) invariant topological superconductor is characterized by a Kramers pair of Majorana zero-energy modes on boundaries and in a core of a TR invariant vortex. A vortex defect that preserves TR symmetry has remained primarily of theoretical interest, since typically a magnetic field, which explicitly breaks TR, needs to be applied to create vortices in superconductors. In this paper, we show that an odd-parity topological superconductor with a nematic pairing order parameter can host a nematic vortex that preserves TR symmetry and binds a Majorana Kramers pair. Such a nematic superconductor could be realized in metal-doped Bi2Se3, asmore » suggested by recent experiments. We provide an analytic solution for the zero modes in a continuous nematic vortex. In lattice, crystalline anisotropy can pin the two-component order parameter along high-symmetry directions. We show that a discrete nematic vortex, which forms when three nematic domains meet, also supports a TR pair of Majorana modes. Lastly, we discuss possible experiments to probe the zero modes.« less