bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-ergodicity of inviscid two-dimensional flow on a beta-plane and on the surface of a rotating sphere
Authors: Shepherd Theodore G.
Published: April 2006

It is shown that, for a sufficiently large value of β, two-dimensional flow on a doubly-periodic beta-plane cannot be ergodic (phase-space filling) on the phase-space surface of constant energy and enstrophy. A corresponding result holds for flow on the surface of a rotating sphere, for a sufficiently rapid rotation rate Ω. This implies that the higher-order, non-quadratic invariants are exerting a significant influence on the statistical evolution of the flow. The proof relies on the existence of a finite-amplitude Liapunov stability theorem for zonally symmetric basic states with a non-vanishing absolute-vorticity gradient. When the domain size is much larger than the size of a typical eddy, then a sufficient condition for non-ergodicity is that the wave steepness ε < 1, where ε = 2√2Z/βUin the planar case and$\epsilon = 2^{\frac{1}{4}} a^{\frac{5}{2}}Z^{\frac{7}{4}}/\Omega U^{\frac{5}{2}}$in the spherical case, and whereZis the enstrophy,Uthe r.m.s. velocity, andathe radius of the sphere. This result may help to explain why numerical simulations of unforced beta-plane turbulence (in which ε decreases in time) seem to evolve into a non-ergodic regime at large scales.
Heat transport by parallel-roll convection in a rectangular container
Authors: Walden R. W. , Kolodner Paul , Passner A. , Surko C. M.
Published: April 2006

Heat-transport measurements are reported for thermal convection in a rectangular box of aspect’ ratio 10 x 5. Results are presented for Rayleigh numbers up to 35Rc, Prandtl numbers between 2 and 20, and wavenumbers between 0.6 and 1.0kc, where Rc and kc are the critical Rayleigh number and wavenumber for the onset of convection in a layer of infinite lateral extent. The measurements are in good agreement with a phenomenological model which combines the calculations of Nusselt number, as a function of Rayleigh number and roll wavenumber for two-dimensional convection in an infinite layer, with a nonlinear amplitude-equation model developed to account for sidewell attenuation. The appearance of bimodal convection increases the heat transport above that expected for simple parallel-roll convection.
Throughflow effects in the Rayleigh-Bénard convective instability problem
Authors: Nield D. A.
Published: April 2006

The effect of vertical throughflow on the onset of convection in a fluid layer, between permeable horizontal boundaries, when heated uniformly from below, is re-examined analytically. It is shown that when the Péclet number Q is large in magnitude, the critical Rayleigh number Rc is proportional to Qn, where n = 0, 1, 2, 3 or 4, with a coefficient depending on the Prandtl number P, according to the types of boundaries. When the upper and lower boundaries are of different types, the effect of a small amount of throughflow in one direction is to decrease Rc. This is so when the throughflow is away from the more restrictive boundary. Contributions arise from the curvature of the basic temperature profile, and from the vertical transport of perturbation velocity and perturbation temperature. The decrease in Rc is small if P ∼ 1 but can be of significant size if P [Lt ] 1 or P [Gt ] 1.
On the performance of particle tracking
Authors: Agüí Juan C. , Jiménez J.
Published: April 2006

The sources of error associated with the use of particle-tracking techniques in the measurement of velocity and vorticity fields in moderately three-dimensional turbulent flows are analysed. The two dominant sources of error are the visualisation error, resulting from the limited resolution of the optical data acquisition system, and the sampling error, due to limited particle concentration. Their relative importance is discussed.

The performance of the interpolation methods used to translate the measurements from the positions of the particles to an arbitrary point is discussed, and a non-parametric algorithm is given to estimate the errors that arise, using only the available data. The smoothing of the results to produce flow maps of a given statistical significance is also discussed. Finally, the method is validated using simultaneous laser-Doppler velocity measurements.

The system is applied to measurements of the near wake of a circular cylinder. Velocity and vorticity maps are provided which throw light on the process by which the large eddies form and relax to their final equilibrium configurations.
On the Rallison and Acrivos solution for the deformation and burst of a viscous drop in an extensional flow
Authors: Power Henry
Published: April 2006

In this work we prove that the second-kind Fredholm's integral equations proposed by Rallison & Acrivos to solve the deformation and burst of a viscous drop in an extensional flow, with viscosity ratio λ, possess a unique continuous solution u(x) for any continuous datum F(x) when 0 < λ < ∞. In the original work they could only guarantee, analytically, the solvability of the integral equations in a small neighbourhood of λ = 1.
Parametrically excited, progressive cross-waves
Authors: Miles John , Becker Janet
Published: April 2006

The variational formulation of the nonlinear wavemaker problem, previously applied (Miles 1988) to cross-waves in a short tank, is extended to allow for slow spatial, as well as slow temporal, variation of cross-waves in a long tank. The resulting evolution equations for the envelope of the cross-waves are equivalent to those derived by Jones (1984) and may be combined to obtain a cubic Schrödinger equation in a semi-infinite domain. The corresponding criterion for the stability of plane waves (i.e. for the temporal decay of cross-waves) agrees with Jones but differs from Mahony (1972). Weak damping is incorporated, and those stationary envelopes that are evanescent at large distances from the wavemaker are determined through analytical approximations and numerical integration and compared with the experimental observations of Barnard & Pritchard (1972) and the numerical calculations of Lichter & Chen (1987). These comparisons suggest that stationary envelopes with either no or one maximum are stable for sufficiently small amplitudes (solutions with multiple maxima may be stable but more difficult to attain) and evolve into limit cycles for somewhat larger amplitudes, but the analytical question of stability remains open.
An experimental investigation of the flow of non-Newtonian fluids between rotating disks
Authors: Sirivat A. , Rajagopal K. R. , Szeri A. Z.
Published: April 2006

The results of an experimental investigation on the flow of a non-Newtonian fluid between rotating, parallel disks are described in this paper. These results are qualitatively different from those exhibited by linearly viscous fluids in that a narrow layer of exceedingly high velocity gradients appears in the non-Newtonian fluid.
On perturbations of Jeffery-Hamel flow
Authors: Banks W. H. H. , Drazin P. G. , Zaturska M. B.
Published: April 2006

We examine various perturbations of Jeffery-Hamel flows, the exact solutions of the Navier-Stokes equations governing the steady two-dimensional motions of an incompressible viscous fluid from a line source at the intersection of two rigid plane walls. First a pitchfork bifurcation of the Jeffery-Hamel flows themselves is described by perturbation theory. This description is then used as a basis to investigate the spatial development of arbitrary small steady two-dimensional perturbations of a Jeffery-Hamel flow; both linear and weakly nonlinear perturbations are treated for plane and nearly plane walls. It is found that there is strong interaction of the disturbances up- and downstream if the angle between the planes exceeds a critical value 2α2, which depends on the value of the Reynolds number. Finally, the problem of linear temporal stability of Jeffery-Hamel flows is broached and again the importance of specifying conditions up- and downstream is revealed. All these results are used to interpret the development of flow along a channel with walls of small curvature. Fraenkel's (1962) approximation of channel flow locally by Jeffery-Hamel flows is supported with the added proviso that the angle between the two walls at each station is less than 2α2.
Steady viscous flow near a stationary contact line
Authors: Proudman Ian , Asadullah Mir
Published: April 2006

The paper presents the asymptotic solution, near a stationary contact line at a plane boundary, for steady viscous incompressible flow of two immiscible liquids. The eigenvalues which determine this Stokes flow are determined by the contact angle α of the more viscous liquid and the ratio μ of the two viscosities. The dominant eigenvalues are found for all values of α and μ. As μ → 0 the results agree with those of Moffatt's (1964) one-phase theory for the case μ = 0 only when α > 81°. For α < 81° the two sets of results are qualitatively different. In particular, the eddy structure corresponding to complex eigenvalues occurs only in the α-range (34°, 81°). As μ increases from 0 to 1, this range steadily decreases to zero, which is located at 60°. The transport of energy across the liquid interface is almost always from the obtuse-angled sector to the acute-angled sector, irrespective of α, μ, and the location of the global power supply.
Large deformations and burst of a capsule freely suspended in an elongational flow
Authors: Li X. Z. , Barthes-Biesel D. , Helmy A.
Published: April 2006

An axisymmetric capsule, consisting of an incompressible liquid droplet, surrounded by an infinitely thin elastic membrane having a Mooney constitutive behaviour, is suspended into another incompressible Newtonian liquid subjected to an elongational shear flow. The motion and the deformation of the capsule are determined numerically by means of a boundary-integral technique. It is thus possible to reach large deformations, and to study the influence of the initial geometry of the particle, as well as that of the constitutive behaviour of the membrane. In all cases considered here, it appears that there exists a critical value of the non-dimensional shear rate (the capillary number) above which no steady solution can be obtained, and where the capsule continuously deforms. This phenomenon is interpreted as the outset of burst. The model shows also the importance of the sphericity index for the determination of the overall capsule deformability.
Three-dimensional Rayleigh-Taylor instability Part 2. Experiment
Authors: Jacobs J. W. , Catton I.
Published: April 2006

Three-dimensional Rayleigh-Taylor instability, induced by accelerating a small volume of water down a vertical tube using air pressure, is investigated. Two geometries are studied: a 15.875 cm circular tube and a 12.7 cm square tube. Runs were made with initial disturbances in the form of standing waves forced by shaking the test section in a lateral direction. Accelerations ranging from 5 to 10 times gravitational acceleration and wavenumbers from 1 cm−1to 8 cm−1are studied. The resulting instability was recorded and later analysed using high-speed motion picture photography. Measurements of the growth rate are found to agree well with linear theory. In addition, good qualitative agreement between photographs and three-dimensional surface plots of the weakly nonlinear solution of Part 1 of this series (Jacobs & Catton 1988) is obtained.
Free-surface effects on spin-up
Authors: CederlÖf Ulf
Published: April 2006

The effects of a free surface on the spin-up of a homogeneous fluid are studied, both analytically and experimentally. The analysis is carried out in cylindrical geometry and shows that the spin-up process is strongly modified as the rotational Froude number F = 4ω2L2/gH becomes large. The dynamic effect of the free surface causes delayed response outside a sidewall boundary layer of thickness LF−½. The timescale in the slowly decaying core is larger than the usual spin-up time by a factor of order F. A set of laboratory experiments using a cylinder with a parabolic bottom were carried out in order to test the theory. Reasonable agreement is found in all the experiments except close to the centre where an interesting deviation was observed, especially in cases corresponding to smaller Froude numbers. The deviation consisted of an anticyclonic vortex at the centre. It is shown that this phenomenon might be explained by Lagrangian mean motion resulting from inertial oscillations. In fact, the analysis shows that this motion produces a singular vortex at the centre.
Variational determination of the coefficient of sound dispersion in binary gas mixtures
Authors: Riesco-Chueca P. , De La Mora J. Fernandez
Published: April 2006

The propagation of plane linear acoustic wave in a mixture of inert gases is considered by means of a variational formulation of the Boltzmann equations, through which the sound speed c is expressed with errors of order ε2 in terms of trial functions determined with errors of order ε. This feature allows the exact determination of the coefficient of sound dispersion d2 ≡ [dc/dω2] at zero frequency (ω = 0), in terms of trial functions known from the Chapman—Enskog theory. Explicit results for d2 are given for all combinations of noble gases from He to Xe, assumed to interact through the Lennard—Jones potential. Comparison with previous approximate descriptions and with experiments is made.
The flow of a liquid film along a periodic wall
Authors: Pozrikidis C.
Published: April 2006

The creeping flow of a liquid film along an inclined periodic wall of arbitrary geometry is considered. The problem is formulated using the boundary-integral method for Stokes flow. This method is extended to two-dimensional flows involving free surfaces, and is implemented in an iterative numerical procedure. Detailed calculations for flow along a sinusoidal wall are perfomed. The free-surface profile is studied as a function of flow rate, inclination angle, wave amplitude, and surface tension, and is compared with previous asymptotic solutions. The results include streamline patterns, velocity profiles and wall-shear-stress distributions, and establish criteria for flow reversal. For specified wall geometry, the asymptotic behaviour for very small flow rates is shown to be a strong function of surface tension. It is demonstrated that these results are valid in a qualitative sense for general wall geometries. The analogy between gravity-driven flow and the flow of a liquid layer on a rotating disk (spin coating) is also discussed.
Turbulence structure near a sharp density interface
Authors: Hannoun Imad A. , Fernando Harindra J. S. , List E. John
Published: April 2006

The effects of a sharp density interface and a rigid flat plate on oscillating-grid induced shear-free turbulence were investigated experimentally. A two-component laser-Doppler velocimeter was used to measure turbulence intensities in and above the density interface (with matched refractive indices) and near the rigid flat plate. Energy spectra, velocity correlations, and kinetic energy fluxes were also measured. Amplification of the horizontal turbulent velocity, coupled with a sharp reduction in the vertical turbulent velocity, was observed near both the density interface and the flat plate. These findings are in agreement with some previous results pertaining to shear-free turbulence near rigid walls (Hunt & Graham 1978) and near density interfaces (Long 1978). The results imply that, near the density interface, the turbulent kinetic energy in the vertical velocity component is only a small fraction of the total turbulent kinetic energy and indicate that the effects of the anisotropy created by the density interface or the flat plate are confined to the large turbulence scales.
Effect of vortex shedding on the coupled roll response of bodies in waves
Authors: Downie M. J. , Bearman P. W. , Graham J. M. R.
Published: April 2006

Hydrodynamic damping of floating bodies is due mainly to wave radiation and viscous damping. The latter is particularly important in controlling those responses of the body for which the wave damping is small. The roll response of ship hulls near resonance in beam seas is an example of this. The present paper applies a discrete vortex method as a local solution to model vortex shedding from the bilges of a barge hull of rectangular cross-section and hence provides an analytic method for predicting its coupled motions in three degrees of freedom, including the effects of the main component of viscous damping. The method provides a frequency-domain solution satisfying the full linearized boundary conditions on the free surface.
The unsteady force on a body at low Reynolds number; the axisymmetric motion of a spheroid
Authors: Lawrence C. J. , Weinbaum S.
Published: April 2006

In a recent paper by Lawrence & Weinbaum (1986) an unexpected new behaviour was discovered for a nearly spherical body executing harmonic oscillations in unsteady Stokes flow. The force was not a simple quadratic function in half-integer powers of the frequency parameter λ2 = −ia2ω/ν, as in the classical solution of Stokes (1851) for a sphere, and the force for an arbitrary velocity U(t) contained a new memory integral whose kernel differed from the classical t−½ behaviour derived by Basset (1888) for a sphere. A more general analysis of the unsteady Stokes equations is presented herein for the axisymmetric flow past a spheroidal body to elucidate the behaviour of the force at arbitrary aspect ratio. Perturbation solutions in the frequency parameter λ are first obtained for a spheroid in the limit of low- and high-frequency oscillations. These solutions show that in contrast to a sphere the first order corrections for the component of the drag force that is proportional to the first power of λ exhibit a different behaviour in the extreme cases of the steady Stokes flow and inviscid limits. Exact solutions are presented for the middle frequency range in terms of spheroidal wave functions and these results are interpreted in terms of the analytic solutions for the asymptotic behaviour. It is shown that the force on a body can be represented in terms of four contributions; the classical Stokes and virtual mass forces; a newly defined generalized Basset force proportional to λ whose coefficient is a function of body geometry derived from the perturbation solution for high frequency; and a fourth term which combines frequency and geometry in a more general way. In view of the complexity of this fourth term, a relatively simple correlation is proposed which provides good accuracy for all aspect ratios in the range 0.1 < b/a < 10 where exact solutions were calculated and for all values of λ. Furthermore, the correlation has a simple inverse Laplace transform, so that the force may be found for an arbitrary velocity U(t) of the spheroid. The new fourth term transforms to a memory integral whose kernel is either bounded or has a weaker singularity than the t−½ behaviour of the Basset memory integral. These results are used to propose an approximate functional form for the force on an arbitrary body in unsteady motion at low Reynolds number.
Nonlinear spiral waves in rotating pipe flow
Authors: Toplosky N. , Akylas T. R.
Published: April 2006

A numerical investigation of finite-amplitude, non-axisymmetric disturbances, in the form of travelling spiral waves, is made in pipe flow with superimposed solid-body rotation. Rotating pipe flow is found to be supercritically unstable both in the rapid and slow-rotation regimes. Earlier weakly nonlinear calculations, suggesting subcritical instability in the slow-rotation limit, are shown to be in error. Bifurcating neutral waves are calculated for various axial and azimuthal Reynolds numbers and wavenumbers. For fixed axial mean pressure gradient, the axial mean flow induced by these waves gives rise to a significant flux defect, in certain cases as large as 40-50% of the undisturbed mass flux; the possible relevance of this finding to the phenomenon of vortex breakdown is pointed out. In non-rotating pipe flow, no neutral disturbances in the assumed form of spiral waves are found for moderate Reynolds numbers; this indicates that previous conjectures, regarding a possible connection between nonlinear spiral waves in slowly rotating pipe flow and the asymptotic neutral states of Smith & Bodonyi (1982) in non-rotating pipe flow, are not valid.
Resonant wave interactions in a stratified shear flow
Authors: Grimshaw R.
Published: April 2006

Resonant interactions between triads of internal gravity waves propagating in a shear flow are considered for the case when the stratification and the background shear flow vary slowly with respect to typical wavelengths. If ωn, kn(n = 1, 2, 3) are the local frequencies and wavenumbers respectively then the resonance conditions are that ω1 + ω2 + ω3 = 0 and k1 + k2 + k3 = 0. If the medium is only weakly inhomogeneous, then there is a strong resonance and to leading order the resonance conditions are satisfied globally. The equations governing the wave amplitudes are then well known, and have been extensively discussed in the literature. However, if the medium is strongly inhomogeneous, then there is a weak resonance and the resonance conditions can only be satisfied locally on certain space-time resonance surfaces. The equations governing the wave amplitudes in this case are derived, and discussed briefly. Then the results are applied to a study of the hierarchy of wave interactions which can occur near a critical level, with the aim of determining to what extent a critical layer can reflect wave energy.
Radiation and diffraction of second-order surface waves by floating bodies
Authors: Sclavounos P. D.
Published: April 2006

The paper studies the radiation and diffraction by floating bodies of deep-water bichromatic and bidirectional surface waves subject to the second-order free-surface condition. A theory is developed for the evaluation of the second-order velocity potential and wave forces valid for bodies of arbitrary geometry, which does not involve the evaluation of integrals over the free surface or require an increased accuracy in the solution of the linear problem. Explicit sum- and difference-frequency ‘Green functions’ are derived for the radiation and diffraction problems, obtained from the solution of initial-value problems that ensure they satisfy the proper radiation condition at infinity. The second-order velocity potential is expressed as the sum of a particular and a homogeneous component. The former satisfies the non-homogeneous free-surface condition and is expressed explicitly in terms of the second-order Green functions. The latter is subject to the homogeneous free-surface condition and enforces the body boundary condition by the solution of a linear problem. An analysis is carried out of the singular behaviour of the second-order potential near the intersection of the body boundary with the free surface.
On the wind force needed to dislodge a drop adhered to a surface
Authors: Durbin Paul A.
Published: April 2006

The dislodging by dynamic pressure forces of a drop adhered by surface tension to a plane is analysed. An integro-differential equation describing the drop shape is solved numerically and the critical Weber number as a function of contact angle hysteresis is found.
Instabilities caused by oscillating accelerations normal to a viscous fluid-fluid interface
Authors: Jacqmin David , Duval Walter M. B.
Published: April 2006

Two incompressible viscous fluids with different densities meet at a planar interface. The fluids are subject to an externally imposed oscillating acceleration directed normal to the interface. The resulting basic-state flow is motionless with an internal pressure oscillation. We discuss the linear evolution of perturbations to this basic state. General viscosities and densities for the two fluids are considered but a Boussinesq equal-viscosity approximation is discussed in particular detail. For this case we show that the linear evolution of a perturbation to the interface subject to an arbitrary oscillating acceleration is governed by a single integro-differential equation. We apply a Floquet analysis to the fluid system for the case of sinusoidal forcing. Parameter regions of subharmonic, harmonic, and untuned modes are delineated. The critical Stokes-Reynolds number is found as a function of the surface tension and the difference in density and viscosity between the two fluids. The most unstable perturbation wavelengths are determined. For zero surface tension these are found to be short, on the order of a small multiple of the Stokes viscous lengthscale. The critical Stokes-Reynolds number and the most unstable perturbation wavelengths are found to be insensitive to the degree of density and viscosity differences between the two fluids.
Propagation of weak shocks through a random medium
Authors: Hesselink Lambertus , Sturtevant Bradford
Published: April 2006

The propagation of weak shock waves (Ms = 1.007, 1.03 and 1.1) through a statistically uniform random medium has been investigated experimentally in a shock tube. The wave-from geometry, rise time and amplitude of initially plane shocks which have propagated through a random mixture of helium and refrigerant 12 are measured. The effect of shock propagation on the properties of the random medium is visualized with schlieren and shadow photography. The pressure histories of the distorted shock waves reflecting from a normal end wall are observed to be both peaked and rounded. In the rounded case the perturbed shock is found to be made up of a succession of weak, slightly curved fronts with a total effective rise time orders of magnitude greater than the classical Taylor thickness. The radius of curvature of the weakest shocks after propagating through the random medium is inferred from observations at two downstream stations to be about 7 times the integral scale of the gas inhomogeneities. It is concluded that the observed distortions of the wave fronts can best be explained in terms of random focusing and defocusing of the front by the inhomogeneities in the medium. A ray-tracing calculation has been used to interpret the experimental observations. It is found that geometrical considerations are sufficient to account for many of the effects observed on the shocks.
Hydromagnetic screw dynamo
Authors: Ruzmaikin Alexander , Sokoloff Dmitry , Shukurov Anvar
Published: April 2006

We solve the problem of magnetic field generation by a laminar flow of conducting fluid with helical (screw-like) streamlines for large magnetic Reynolds numbers, Rm. Asymptotic solutions are obtained with help of the singular perturbation theory. The generated field concentrates within cylindrical layers whose position, the magnetic field configuration and the growth rate are determined by the distribution of the angular, Ω, and longitudinal, Vz, velocities along the radius. The growth rate is proportional to Rm−½. When Ω and Vz are identically distributed along the radius, the asymptotic forms are of the WKB type; for different distributions, singular-layer asymptotics of the Prandtl type arise. The solutions are qualitatively different from those obtained for solid-body screw motion. The generation threshold strongly depends on the velocity profiles.
Numerical calculations of the primary-flow exchange process in the Taylor problem
Authors: Cliffe K. A.
Published: April 2006

Numerical methods are used to study the way in which the number of cells present in the Taylor experiment changes as the length of the comparatively short annulus varies. The structure of the solution surface is determined by following paths of singular points in a finite-element discretization of the axisymmetric Navier–Stokes equations. The numerical results are compared with the experiments of Benjamin (1978b), Mullin (1982) and Mullin et al. (1982). The calculations are in agreement with the qualitative theory of Benjamin (1978a) and Schaeffer (1980) except that in the interaction involving four- and six-cell flows, the numerical calculations indicate that the six-cell flow can become unstable owing to perturbations that are antisymmetric about the midplane.
Nonlinear spatial evolution of an externally excited instability wave in a free shear layer
Authors: Goldstein M. E. , Hultgren Lennart S.
Published: April 2006

We consider a disturbance that evolves from a strictly linear finite-growth-rate instability wave, with nonlinear effects first becoming important in the critical layer. The local Reynolds number is assumed to be just small enough so that the spatial-evolution, nonlinear-convection, and viscous-diffusion terms are of the same order of magnitude in the interactive critical-layer vorticity equation. The numerical results show that viscous effects eventually become important even when the viscosity is very small due to continually decreasing scales generated by the nonlinear effects. The vorticity distribution diffuses into a more regular pattern vis-a-vis the inviscid case, and the instability-wave growth ultimately becomes algebraic. This leads to a new dominant balance between linear- and nonlinear-convection terms and an equilibrium critical layer of the Benney & Bergeron (1969) type begins to emerge, but the detailed flow field, which has variable vorticity within the cat's-eye boundary, turns out to be somewhat different from theirs. The solution to this rescaled problem is compared with the numerical results and is then used to infer the scaling for the next stage of evolution of the flow. The instability-wave growth is simultaneously affected by mean-flow divergence and nonlinear critical-layer effects in this latter stage of development and is eventually converted to decay. The neutral stability point is the same as in the corresponding linear case, however.
The stability of the Couette flow of helium II
Authors: Barenghi C. F. , Jones C. A.
Published: April 2006

The stability of Couette flow in HeII is considered by an analysis of the HVBK equations. These equations are based on the Landau two-fluid model of HeII and include mutual friction between the normal and superfluid components, and the vortex tension due to the presence of superfluid vortices. We find that the vortex tension strongly affects the nature of the Taylor instability at temperatures below ≈ 2.05 K. The effect of the vortex tension is to make non-axisymmetric modes the most unstable, and to make the critical axial wavelength very long.

We compare our results with experiments.
The Frankish Annals of Lindisfarne and Kent
Authors: Story Joanna
Published: April 2006

The Frankish Annals of Lindisfarne and Kent lie at the root of the ‘making of history’ in Anglo-Saxon England. They are brief ‘paschal annals’, recording mainly the accession or burials of Kentish and Northumbrian kings between 616 and 704, and are found in the margins of Easter tables in one Anglo-Saxon and six Frankish manuscripts dating from c. 740-c. 830. These annals are not well known, but they deserve close attention since they provide factual details not just of ‘what happened’ in early Anglo-Saxon England, but also how such historical data was collected, copied, and transmitted across generations. Crucially, the annals contain chronological details that are not found in any other source, not even in Bede's Historia Ecclesiastica Gentis Anglorum, and they are a unique source for those details. The evidence points to the variety of formats and contexts in which precise chronological details were first recorded in Anglo-Saxon England, and shows that these annals are a very rare piece of independent evidence not just for the history of the seventh century, but also for the type of ‘raw material’ that was available to Bede at Jarrow in the early decades of the eighth.
Scanning ultrafast Sagnac interferometry for imaging two-dimensional surface wave propagation
Authors: Tachizaki Takehiro , Muroya Toshihiro , Matsuda Osamu , Sugawara Yoshihiro , Hurley David H. , Wright Oliver B.
Published: April 2006

We describe an improved two-dimensional optical scanning technique combined with an ultrafast Sagnac interferometer for delayed-probe imaging of surface wave propagation. We demonstrate the operation of this system, which involves the use of a single focusing objective, by monitoring surface acoustic wave propagation on opaque substrates with picosecond temporal and micron lateral resolutions. An improvement in the lateral resolution by a factor of 3 is achieved in comparison with previous setups for similar samples.
Four phases of amorphous water: Simulations versus experiment
Authors: Brovchenko Ivan , Oleinikova Alla
Published: April 2006

Multiplicity of the liquid-liquid phase transitions in supercooled water, first obtained in computer simulations [Brovchenko et al., J. Chem. Phys. 118, 9473 (2003)], has got strong support from the recent experimental observation of the two phase transitions between amorphous ices [Loerting et al., Phys. Rev. Lett. 96, 025702 (2006)]. These experimental results allow assignment of the four amorphous water phases (I–IV) obtained in simulations to the three kinds of amorphous ices. Water phase I (ρ≈0.90g∕cm3) corresponds to the low-density amorphous ice, phase III (ρ≈1.10g∕cm3) to the high-density amorphous ice, and phase IV (ρ≈1.20g∕cm3) to the very-high-density amorphous ice. Phase II of model water with density ρ≈1.00g∕cm3 corresponds to the normal-density water. Such assignment is confirmed by the comparison of the structural functions of the amorphous phases of model water and real water. In phases I and II the first and second coordination shells are clearly divided. Phase I consists mainly of the four coordinated tetrahedrally ordered water molecules. Phase II is enriched with molecules, which have tetrahedrally ordered four nearest neighbors and up six molecules in the first coordination shell. Majority of the molecules in phase III still have tetrahedrally ordered four nearest neighbors. Transition from phase III to phase IV is characterized by a noticeable drop of tetrahedral order, and phase IV consists mainly of molecules with highly isotropic angular distribution of the nearest neighbors. Relation between the structures of amorphous water phases, crystalline ices, and liquid water is discussed.
Charge storage model for hysteretic negative-differential resistance in metal-molecule-metal junctions
Authors: Kiehl Richard A. , Le John D. , Candra Panglijen , Hoye Rebecca C. , Hoye Thomas R.
Published: April 2006

Experimental results on the electrical characteristics of Hg-alkanethiol∕arenethiol-Au molecular junctions are used to develop a physical model for the hysteretic negative-differential resistance (NDR) for these, and possibly other, metal-molecule-metal junctions. The dependence of the room-temperature current-voltage characteristic on sweep direction and sweep rate is examined. Based on several specific electronic behaviors, it is concluded that the NDR is caused by slow charge capture (reduction or oxidation) during the forward sweep and the resultant effect on tunneling. The implications of this model on potential electronic applications are discussed.
Electrorheological fluid-actuated flexible platform
Authors: Liu Liyu , Niu Xize , Wen Weijia , Sheng Ping
Published: April 2006

The design, fabrication, and performance of an electrorheological (ER) fluid-actuated flexible platform integrated on a microfluidic chip are reported in this letter. The digitally regulated ER microvalves control the four diaphragms on which a platform is sustained. With electrical input signals, the platform can perform vibrations at tunable frequencies as well as generate complex leveling modes. The flexible platform can potentially act as a microdamper when its inputs are generated from a sensor, in combination with a feedback control system.
Pressure induced phase transition in periodic microtwinned thin film of La0.88Sr0.1MnO3
Authors: Razavi F. S. , Sudhakar Rao G. V. , Jalili H. , Habermeier H.-U.
Published: April 2006

We have studied the resistivity of a hole-doped 95nm thin film of La0.88Sr0.1MnO3 sample as a function of pressure up to 2.0GPa. For pressures below 0.81GPa, the sample showed that the resistivity decreased at all temperatures and the metal insulator transition temperature TMI increased to higher temperatures similar to the pressure results observed previously in bulk samples and thin films of manganites. However, for pressures above 0.81GPa, we observed a rapid increase in resistivity and a rapid decrease of TMI as a function of pressure. The rate of change of TMI with pressure is −133.5K∕GPa which is an order of magnitude larger than that of bulk samples and thin films of manganite with an opposite sign. We interpreted our results as a consequence of a phase change in the film by pressure from having strain induced periodic microtwinned regions below 0.81GPa to a strained free region and formation of coherent twins above this pressure in 95nm thin film of La0.88Sr0.1MnO3.
Population‐based study of the relationship between hospital surgical volume and 10‐year survival of breast cancer patients in Osaka, Japan
Authors: Nomura Etsuko , Tsukuma Hideaki , Ajiki Wakiko , Ishikawa Osamu , Oshima Akira
Published: April 2006

Breast cancer is the most prevalent cancer among Japanese women; however, its outcome has never been analyzed in relation to hospital volume in Japan. We utilized data from the Osaka Cancer Registry for investigating correlations between hospital volume and 10‐year survival of breast cancer patients. According to the total number of surgical procedures of breast cancer in each hospital during the period 1985–1991, we classified reporting hospitals in Osaka into four categories (high, medium, low, very low). The survival analysis was restricted to the 4333 female patients reported who were 30–64 years old, living in Osaka Prefecture (except for Osaka City), and for whom active follow up was available more than 10 years after diagnosis. In total, the relative 10‐year survival was 79.7% in the high‐volume, 80.3% in the medium‐volume, 78.2% in the low‐volume, and 68.2% in the very low‐volume hospitals. After adjustment for age at diagnosis, clinical stage and clues for detection with the Cox regression model, the patients who received care in the very low‐volume hospitals had a significantly higher risk of death than those in the high‐volume hospitals. Meanwhile, no significant differences in risk were observed for the other two categories. These findings led us to conclude that the surgical volume of the hospitals did not affect the 10‐year survival rate significantly, except for the very low‐volume hospitals in Osaka, Japan. However, the study of these relationships should be continued and expanded in future to include quality of life. (Cancer Sci 2006; 97: 618–622)
Cell surface proteoglycan expression during maturation of human monocytes-derived dendritic cells and macrophages
Authors: Wegrowski Y , Milard A-L , Kotlarz G , Toulmonde E , Maquart F-X , Bernard J
Published: April 2006

Cell surface proteoglycans play an important part in the functional and metabolic behaviour of leucocytes. We studied the expression of cell surface proteoglycans in human monocytes, in monocyte-derived immature and mature dendritic cells and in macrophages by metabolic labelling with [35S]-sulphate, reverse transcriptase–polymerase chain reaction (RT–PCR) and Western blotting. Immature dendritic cells had the highest metabolic activity for the synthesis of cell surface proteoglycans. The major part of these proteoglycans was in phosphatidylinositol-anchored form and was released after treatment with phospholipase C. A minor part was released by trypsin. Digestion with chondroitinase ABC and mild HNO2 treatment showed that cell surface proteoglycans had a higher proportion of chondroitin sulphate, both in the phospholipase C and trypsin fractions, suggesting that at least some glypicans contained chondroitin sulphate chains. RT–PCR detected the transcripts of glypicans 1, 3, 4 and 5 and all syndecans. Immature dendritic cells expressed a most complex spectrum of glypicans and syndecans, glypican-1 and syndecan-1 being expressed preferentially by this type of cells. Mature dendritic cells expressed glypican-3, which was not present in other lineages. These results suggest that different mononuclear cells synthesize cell surface proteoglycans actively with characteristic expression of different syndecans and glypicans genes, depending on the degree of cell differentiation and/or maturation.
Relationship between maternal and child cytokine responses to allergen and phytohaemagglutinin 2 years after delivery
Authors: Larsson A-K , Nilsson C , Höglind A , Sverremark-Ekström E , Lilja G , Troye-Blomberg M
Published: April 2006

Little is known at present about the relation between parental and child cytokine profiles. In this study we aimed to investigate the cytokine profile of 2-year-old children and their corresponding mothers, 2 years after delivery. Peripheral blood mononuclear cells (PBMC) were isolated from IgE-sensitized (n = 15) and non-sensitized (n = 58) 2-year-old children and their mothers. The responses to ovalbumin, cat and phytohaemagglutinin (PHA) were investigated using the enzyme-linked immunospot (ELISpot) technique. Interferon (IFN)-γ-, interleukin (IL)-4-, IL-10- and IL-12-producing cells were enumerated. At 2 years of age, IgE-sensitized children exhibited increased numbers of IL-4-producing cells in response to PHA and also showed an increase in IL-10- and IL-12-producing cells to allergen that was more pronounced in response to ovalbumin than to cat. A statistically significant increase in the numbers of IFN-γ-, IL-10- and IL-12-producing cells to the allergens, but not to PHA, was found in the mothers of IgE-sensitized children irrespective of their own atopic status. IgE levels and cytokine responses were correlated between the mothers and their children, indicating that cytokine responses to both allergen and PHA might be governed by genetic factors. We speculate that the increased cytokine response to allergen, as opposed to the allergic status of the mother, might be a better predictor and/or a risk factor for the child to develop IgE-sensitization in early life.
Immunogenetic association and thyroid autoantibodies in juvenile autoimmune thyroiditis in North India
Authors: Kanga U. , Tandon N. , Marwaha R. K. , Khanna R. , Bhattacharya B. , Singh S. , Kumar N. , Mehra N. K.
Published: April 2006

Objectives  Autoimmune thyroid diseases (AITD) encompass a number of conditions that have in common cellular and humoral responses targeting the thyroid gland. Interactions between susceptibility genes and environmental triggers are thought to initiate an autoimmune response to thyroid antigens leading to disease manifestation. Commencement of the disease in childhood leads to the presumption that genetics may have an important role in the causation of the disease.

Design  The present study was aimed at evaluating the human leucocyte antigen (HLA) encoded susceptibility to develop juvenile autoimmune thyroiditis (JAT) in patients from North India.

Patients  We studied 48 consecutive patients of JAT along with 176 first‐degree relatives for their thyroid function (FT4, TSH) and anti‐thyroid peroxidase antibody status (AbTPO).

Measurements  HLA studies were carried out using serology for HLA‐class I antigens and DNA analysis of HLA‐class II alleles. The data were compared with a cohort of 308 ethnically matched healthy individuals.

Results  We observed overt hypothyroidism in 50% and AbTPO positivity in 70·8% of the index cases. Among the first‐degree relatives, goitre was observed in 51·7%, thyroid dysfunction in 28·4% and AbTPO in 29·5% of individuals. Of the 37 relatives who underwent fine‐needle aspiration cytology (FNAC), 60% had evidence of chronic lymphocytic thyroiditis (CLT). A strong positive association of HLA‐DRB1*1404 was observed with the JAT (35·4%vs. 10·4%, χ2 = 19·8, Pc = 0·0001). We also observed a higher (72%, P = 0·03) paternal transmission of HLA‐DRB1*1404 to affected offspring in comparison to unaffected offspring. HLA‐DRB1*03 was also increased among JAT patients but did not reach statistical significance.

Conclusion  These studies point towards an important role of immune modifying genes, such as HLA, in influencing susceptibility to juvenile‐onset AITD.
Anterior pituitary dysfunction following traumatic brain injury (TBI)
Authors: Agha Amar , Thompson Christopher J.
Published: April 2006

Traumatic brain injury (TBI) is the commonest cause of death and disability in young adults living in industrialized countries. Several recent studies have convincingly shown that anterior hypopituitarism is a common complication of head trauma with a prevalence of at least 25% among long‐term survivors. This is a much higher frequency than previously thought and suggests that most cases of post‐traumatic hypopituitarism (PTHP) remain undiagnosed and untreated. These findings raise important questions about the potential contribution of PTHP to the high physical and neuropsychiatric morbidity seen in this group of patients. In this review, we examine the published reports on the neuroendocrine abnormalities in TBI patients and highlight new data that give novel insights into the natural history of this disorder. We discuss the potential contribution of PTHP to recovery and rehabilitation after injury and the need for the identification and the appropriate and timely management of hormone deficiencies to optimize patient recovery from head trauma, improve quality of life and avoid the long‐term adverse consequences of untreated hypopituitarism.
Dimensional analysis of the concept of obesity
Authors: Davidson Maryanne , Knafl Kathleen A.
Published: April 2006

Aim.  The aim of this paper is to explore the evolution of the concept of obesity and to identify variations in its meaning and use from the perspectives of healthcare professionals and Black Americans, Caucasian Americans, and Latino Americans.

Background.  Obesity constitutes an emerging global healthcare epidemic. Little convergence is found between the meaning and use of the concept of obesity by healthcare professionals and those they are trying to serve. This lack of convergence points to the need for exploration of the assumptions, use and various meanings associated with this important concept.

Method.  The analysis included 20 papers from 18 research studies from the fields of nursing, psychology, epidemiology, medicine, and sociology. Caron and Bowers’ dimensional analysis method guided the analysis.

Results.  Eight dimensions were identified: objective measure, attractiveness, sexual desirability, health, body image, strength or goodness, self‐esteem, and social acceptability. Substantial differences in assumptions, use, and meanings of this concept were found within and between the perspectives studied. However, there were insufficient data to fully assess use and meaning of the concept of obesity from the Latino American perspective.

Conclusion.  This analysis contributes to the development of an understanding of the meaning and use of the concept of obesity within varied socio‐cultural contexts as well as from a healthcare perspective. Culture was found to play a significant role in how obesity is understood by the individual.