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Vortex structure in rotating Rayleigh-Benard convection

Description: The authors investigate the flow patterns in a cylindrical rotating Rayleigh-Benard convection cell with radius-to-height ratio {Gamma} = 0.5. The Rayleigh number R is 2 x 10{sup 8}, the dimensionless rotation rate {Omega} varies from 10{sup 4} to 5 x 10{sup 4}, and the convective Rossby number Ro is between 2 and 0.4. Measurements of the velocity field in the volume adjacent to the top of the cell are acquired with a scanning particle image velocimetry (PIV) system. The authors present quantitative results for velocity and vorticity of the cyclonic and anticyclonic vortices characterizing the convection, as well as for the dependence of the vortex size on the rotation rate and variation of vorticity with depth.
Date: July 15, 1997
Creator: Vorobieff, P. & Ecke, R.E.

Vortex unbinding in superconducting thin films

Description: The study of the origin of broad resistive transitions in 2D superconducting films requires extremely homogeneous samples. Granular aluminum evaporated onto freshly eleaved mica substrates are shown to satisfy this criterion. Values of T/sub c/, as a function of resistance per square, are in agreement with a one parameter model of independent grains coupled by the Josephson effect, and not the predictions of the Kosterlitz-Thouless vortex unbinding model.
Date: January 1, 1980
Creator: Bancel, P.A. & Gray, K.E.

Vortical structures in pool fires: Observation, speculation, and simulation

Description: While all fires are complex and involve many phenomena, this report is limited to large, turbulent liquid-hydrocarbon pool fires. Large, liquid-hydrocarbon pool fires present a risk in petrochemical storage and processing facilities and transportation systems that contain large amounts of liquid hydrocarbons. This report describes observations, speculations, and numerical simulations of vortical structures in pool fires. Vortical structures are observed in fires with length scales ranging from those that bend millimeter-thick flame zones to those that entrain air many meters from the edge of the fire to its centerline. The authors propose that baroclinic vorticity generation is primarily responsible for production of rotational motion at small scale and that amalgamation is responsible for the production of large-scale rotational structures from the myriad of small-scale structures. Numerical simulations show that vortical structures having time-mean definitions can be resolved with a Reynolds-Average Navier-Stokes (RANS) approach. However, for vortical structures without time-mean definition, RANS is inappropriate, and another technique, such as Large Eddy Simulation (LES), should be employed. 39 refs., 52 figs., 3 tabs.
Date: November 1, 1996
Creator: Tieszen, S. R.; Nicolette, V. F.; Gritzo, L. A.; Moya, J. L.; Holen, J. K. & Murray, D.

Vortices and the Related Principles of Hydrodynamics

Description: Here, conceptions concerning vortices are illustrated by the simplest possible examples. Mathematical formulas and similar means of presentation, which, for the most part, do not help the understanding of persons not versed therein, have been avoided as much as possible. Instead, the author has endeavored to demonstrate the phenomena by means of simple geometrical and mechanical illustrations. For the sake of clarity, the author chiefly considers currents in one plane only, a situation that can be readily represented by diagrams. Some of the peculiarities of vortices in three dimensional flow are briefly discussed.
Date: November 1921
Creator: Betz, A.

Vortices associated with toroidal ion temperature gradient driven fluctuations

Description: The three nonlinear hydrodynamic equations for potential, parallel ion velocity and ion pressure used in simulations of the toroidal ion temperature gradient driven fluctuations and transport in a shear magnetic field are analyzed for coherent vortex structures. Two types of vortex structures are found: one type for weak shear that is a generalization of the usual modon vortex construction and the second type of solution for strong magnetic shear where the convective nonlinearity in the parallel velocity field generates a cubic trapping nonlinearity in the vorticity equation. These vortex structures show the possibility of explaining the saturated states observed in the numerical simulations as self-organized nonlinear states in contrast to wave turbulence.
Date: May 1, 1992
Creator: Horton, W. (Texas Univ., Austin, TX (United States). Inst. for Fusion Studies); Jovanovic, D. (Belgrade Univ. (Yugoslavia). Inst. za Fiziku) & Rasmussen, J.J. (Association Euratom-Risoe National Lab., Roskilde (Denmark))

Vortices associated with toroidal ion temperature gradient driven fluctuations

Description: The three nonlinear hydrodynamic equations for potential, parallel ion velocity and ion pressure used in simulations of the toroidal ion temperature gradient driven fluctuations and transport in a shear magnetic field are analyzed for coherent vortex structures. Two types of vortex structures are found: one type for weak shear that is a generalization of the usual modon vortex construction and the second type of solution for strong magnetic shear where the convective nonlinearity in the parallel velocity field generates a cubic trapping nonlinearity in the vorticity equation. These vortex structures show the possibility of explaining the saturated states observed in the numerical simulations as self-organized nonlinear states in contrast to wave turbulence.
Date: May 1, 1992
Creator: Horton, W.; Jovanovic, D. & Rasmussen, J. J.

Vortices in dense self-assembled hole arrays.

Description: We present a study of the upper critical field and pinning strength from the resistivity and magnetization of a Nb film containing a dense array of 45 nm diameter holes on a hexagonal lattice with a spacing of 101 nm. The holes were formed by self-assembly in anodic aluminum oxide (AAO) using an electrochemical procedure. Confinement effects and Little-Parks oscillations are seen above 6 K, and strong pinning with matching field effects is seen below 6 K. Above the first matching field interstitial vortices coexist with vortices trapped in the hole array. Pinning in the Nb films with hole arrays is enhanced by two orders of magnitude over that in continuous Nb films. At low temperature, flux avalanches are observed and imaged using the magneto-optical Faraday effect.
Date: October 9, 2002
Creator: Crabtree, G. W.; Welp, U.; Xiao, Z. L.; Jiang, J. S.; Vlasko-Vlasov, V. K.; Bader, S. D. et al.

The vortices in the latticed model of the planar nematic

Description: The vortices in the planar nematic are considered using the field-theoretical description in terms of the Rp{sup 2} {sigma}-model. In the strong-coupling expansion the vortices interactions are considered and the new type of phase transition is obtained in the mean-field approximation.
Date: June 1, 1990
Creator: Khvechshenko, D.V.; Kogan, Y.I. & Nechaev, S.K.

Vortices, Reconnection and Turbulence in High Electron-Beta Plasmas

Description: Plasmas in which the kinetic energy exceeds the magnetic energy by a significant factor are common in space and in the laboratory. Such plasmas can convect magnetic fields and create null points in whose vicinity first the ions become unmagnetized, then the electrons. This project focuses on the detailed study of the transition regime of these plasmas.
Date: August 31, 2004
Creator: Stenzel, R. L.

Vortices wiggled and dragged

Description: When a sufficiently strong magnetic field is applied to a superconductor, some of the field can pierce it through the generation of magnetic vortices, each of which contains a quantized amount of magnetic flux. Although the superconducting state of the material outside each vortex is maintained (and destroyed within each vortex), the interaction of vortices with a current passing through the material can cause them to move, dissipating energy and thereby generating a source of electrical resistance. The ability to manipulate an individual superconducting vortex represents a powerful tool for studying the dynamics of vortices and the superconductors that support them. It could also lead to the development of a new class of fluxon-based electronics.
Date: January 1, 2008
Creator: Reichhardt, Charles

Vorticism in Aeronautics

Description: Since the war there has been a considerable advance in knowledge on the subject of the airfoil and its behavior. The theory is now sufficiently advanced to make it possible to predict and to calculate certain results which previously could only be attained by direct experiment. The vortex theory receives special attention.
Date: August 1923
Creator: Sayers, W. H.

A Vorticity-Divergence Global Semi-Lagrangian Spectral Model for the Shallow Water Equations

Description: The shallow water equations modeling flow on a sphere are useful for the development and testing of numerical algorithms for atmospheric climate and weather models. A new formulation of the shallow water equations is derived which exhibits an advective form for the vorticity and divergence. This form is particularly well suited for numerical computations using a semi-Lagrangian spectral discretization. A set of test problems, standard for the shallow water equations on a sphere, are solved and results compared with an Eulerian spectral model. The semi-Lagrangian transport method was introduced into atmospheric modeling by Robert, Henderson, and Turnbull. A formulation based on a three time level integration scheme in conjunction with a finite difference spatial discretization was studied by Ritchie. Two time level grid point schemes were derived by Bates et al. Staniforth and Cote survey developments of the application of semi-Lagrangian transport (SLT) methods for shallow water models and for numerical weather prediction. The spectral (or spherical harmonic transform) method when combined with a SLT method is particularly effective because it allows for long time steps avoiding the Courant-Friedrichs-Lewy (CFL) restriction of Eulerian methods, while retaining accurate (spectral) treatment of the spatial derivatives. A semi-implicit, semi-Lagrangian formulation with spectral spatial discretization is very effective because the Helmholz problem arising from the semi-implicit time integration can be solved cheaply in the course of the spherical harmonic transform. The combination of spectral, semi-Lagrangian transport with a semi-implicit time integration schemes was first proposed by Ritchie. A advective formulation using vorticity and divergence was introduced by Williamson and Olson. They introduce the vorticity and divergence after the application of the semi-Lagrangian discretization. The semi-Lagrangian formulation of Williamson and Olson and Bates et al. has the property that the metric terms of the advective form are treated discretely requiring a delicate spherical vector addition ...
Date: November 30, 2001
Creator: Drake, J. B.

Voter Identification Requirements: Background and Legal Issues

Description: Since 2008, more than 30 states have enacted laws relating to voter identification, with several containing photo ID requirements. Several states enacted voter identification laws that have either been struck down by courts or are not yet in effect. A number of bills with voter identification provisions have been introduced in the 113th Congress and one (S. 1945) has received committee consideration. This report examines this type of legislation and the legal issues regarding it.
Date: November 10, 2014
Creator: Coleman, Kevin J.; Fischer, Eric A. & Whitaker, L. Paige

Voters With Disabilities: Access to Polling Places and Alternative Voting Methods

Description: A letter report issued by the General Accounting Office with an abstract that begins "Federal law requires that disabled persons have access to polling places on election day. State political subdivisions must ensure that polling places used in federal elections are accessible. Exceptions are allowed if all potential polling places have been surveyed, no accessible place is available, and the political subdivision cannot make one temporarily accessible. In these cases, disabled voters must either be reassigned to an accessible polling place or provided another means for voting on election day. All states have provisions that address voting by people with disabilities, but these provisions vary greatly. All states provide for one or more alternative voting methods or accommodations that may facilitate voting by people with disabilities. States and localities have made several efforts to improve voting accessibility for the disabled, such as modifying poling places, acquiring new voting equipment, and expanding voting options. Nevertheless, state and county election officials GAO surveyed cited various challenges to improving access."
Date: October 15, 2001
Creator: United States. General Accounting Office.