bluuebunny/crossref_metadata_2025 huggingface dataset:
Interleukin‐6 induces both cell growth and VEGF production in malignant mesotheliomas
Authors: Adachi Yasuo , Aoki Chieko , Yoshio‐Hoshino Naoko , Takayama Koichi , Curiel David T. , Nishimoto Norihiro
Published: April 2006

Malignant mesothelioma (MM), an incurable tumor, is reportedly an interleukin‐6 (IL‐6) secreting tumor. The pathological significance of IL‐6 overexpression in this tumor, however, has remained unclear. We investigated the biological functions of IL‐6 in mesotheliomas. Five mesothelioma cell lines were analyzed for IL‐6 production and IL‐6 receptor (IL‐6R) expression. Of them, 2 produced high levels of IL‐6, 2 produced intermediate levels and 1 cell line showed no secretion. All mesothelioma cell lines used in this study expressed very small amounts of IL‐6R mRNA. We compensated for this low level of IL‐6R expression in mesotheliomas by adding recombinant soluble IL‐6R (sIL‐6R) to mediate the IL‐6 signal. IL‐6 together with sIL‐6R was found to promote cell growth of H2052 and H226 MMs classified as high‐level IL‐6 producers in a dose‐dependent manner. Moreover, a humanized anti‐IL‐6R antibody (MRA) capable of blocking IL‐6 signaling suppressed the cell growth of mesotheliomas induced by IL‐6/sIL‐6R. These findings demonstrate that IL‐6 serves as an autocrine growth factor in the development of mesothelioma. In addition, IL‐6/sIL‐6R stimulation increased the expression of vascular endothelial growth factor (VEGF) in 4 out of 5 cell lines, and this induction was inhibited by MRA treatment. The involvement of the signal transducer and activator of transcription 3 (STAT3) pathway in both cell growth and VEGF induction by IL‐6/sIL‐6R was verified by dominant negative STAT3 transduction combined with adenovirus gene‐delivery methods. Although IL‐6 induces VEGF through the JAK2/STAT3 pathway, anti‐VEGF antibody could not inhibit the IL‐6‐induced cell growth observed in H2052 and H226. We concluded that IL‐6‐dependent growth does not occur via VEGF induction. These results suggest that treatment with anti‐IL‐6R antibody may constitute a potential molecular targeting therapy for MMs. © 2006 Wiley‐Liss, Inc.
Volatility dynamics and heterogeneous markets
Authors: McMillan David G. , Speight Alan E. H.
Published: April 2006

Recent research has suggested that intra‐day volatility may possess a component structure, resulting either from the arrival of heterogeneous information or the actions of heterogeneous market agents. This paper reports direct evidence for the existence of such components in S&P500 index and DM/$ exchange rate data. Estimation of a FIGARCH model supports the contention that volatility dynamics result from multiple sources. Using a HARCH conditional variance model which defines volatility components over differing time horizons, confirmatory evidence of heterogeneous components is reported, in which context the impact of high‐frequency speculation and noise‐trading are particularly apparent. Copyright © 2006 John Wiley & Sons, Ltd.
The real exchange rate–real interest rate relation: evidence from tests for symmetric and asymmetric threshold cointegration
Authors: Sollis Robert , Wohar Mark E.
Published: April 2006

This paper investigates the existence of threshold cointegration between real exchange rates and real interest rate differentials. Unlike previous work, which generally fails to find evidence of a long‐run relationship employing linear models, we employ tests of the null hypothesis of no cointegration derived from nonlinear bivariate models that allow for threshold cointegration under the alternative hypothesis. For six of the countries in our sample our analysis reveals some evidence of a nonlinear long‐run relationship between real exchange rates and real interest rate differentials. Asymmetric mean reversion of the equilibrium error is found to be driven by the asymmetric short‐run adjustment of the real exchange rate to dis‐equilibrium. When threshold cointegration is found to exist, we find stronger mean reversion when the equilibrium error is negative relative to when it is positive. Copyright © 2006 John Wiley & Sons, Ltd.
Concentric‐needle single‐fiber electromyography for the diagnosis of myasthenia gravis
Authors: Benatar Michael , Hammad Mustafa , Doss‐Riney Heidi
Published: April 2006

The goal of this study was to estimate the accuracy of concentric‐needle single‐fiber electromyography (CN‐SFEMG) for the diagnosis of myasthenia gravis (MG). A consecutive series of patients referred for CN‐SFEMG was evaluated by an investigator blinded to the results of CN‐SFEMG in order to determine the presence or absence of MG using an independent reference standard. Sensitivity, specificity, predictive values, and likelihood ratios were calculated. The study population included 51 patients (21 with MG). CN‐SFEMG was normal in 34 patients (67%) and abnormal in 17 (33%). The sensitivity of CN‐SFEMG for the diagnosis of MG was 0.67 and the specificity was 0.96. The positive likelihood ratio was 16.8 and the negative likelihood ratio was 0.34. The positive and negative predictive values were 0.93 and 0.76, respectively. These results indicate that CN‐SFEMG showing abnormal jiggle is extremely useful for confirming the diagnosis of MG, but that CN‐SFEMG showing normal jiggle has limited utility in excluding the diagnosis. Muscle Nerve, 2006
Anionic grafting polymerization of propylene sulfide onto human hair in water
Authors: Morinaga Hisatoyo , Ochiai Bungo , Mori Hideharu , Endo Takeshi
Published: April 2006

Natural human hair was modified by the graft polymerization of propylene sulfide in an aqueous medium. The amount of the polymer grafted onto the reduced hair was 0.15–0.19 g on 1.0 g of hair. The grafted polymer was isolated by the hydrolysis of the hair in the polymer‐grafted hair under basic conditions and was confirmed to be poly(propylene sulfide) by 1H NMR, 13C NMR, and Fourier transform infrared spectra. The number‐average molecular weights of the isolated polymers from the grafted products were 10,000–12,000. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3778–3786, 2006
Fertility of internal migrants: comparison between Austria and Poland
Authors: Kulu Hill
Published: April 2006

Previous research has proposed four competing views on an individual's fertility following a move from one social context to another. Each view has received support but has also been challenged in the literature. This study contributes to the existing discussion on fertility by providing an analysis of the effects of internal migration on the fertility of post‐war Austrian and Polish female cohorts. The study is based on retrospective event‐history data and applies intensity regression to both single and simultaneous equations. The analysis shows, firstly, that natives in urban areas in general and in large cities in particular have lower fertility compared with non‐migrants in rural areas, both in Austria and Poland. Secondly, it reveals that people who move from one place to another adopt the fertility behaviour that dominates at the destination. Thirdly, we observe an elevated first‐birth risk for women who move because of union formation, and a short‐term postponement of childbearing for those who settle in a large city. The country comparison shows some differences in fertility variation across settlements, but overall the results are quite similar, despite the different post‐war societal contexts of the two countries. Copyright © 2006 John Wiley & Sons, Ltd.
The effects of boundary imperfections on convection in a saturated porous layer: near-resonant wavelength excitation
Authors: Rees D. A. S. , Riley D. S.
Published: April 2006

Weakly nonlinear theory is used to study the porous-medium analogue of the classical Rayleigh-Bénard problem, i.e. Lapwood convection in a saturated porous layer heated from below. Two particular aspects of the problem are focused upon: (i) the effect of thermal imperfections on the stability characteristics of steady rolls near onset; and (ii) the evolution of unstable rolls.

For Rayleigh-Bénard convection it is well known (see Busse and co-workers 1974, 1979, 1986) that the stability of steady two-dimensional rolls near onset is limited by the presence of cross-roll, zigzag and sideband disturbances; this is shown to be true also in Lapwood convection. We further determine the modifications to the stability boundaries when small-amplitude imperfections in the boundary temperatures are present. In practice imperfections would usually consist of broadband thermal noise, but it is the Fourier component with wavenumber close to the critical wavenumber for the perfect problem (i.e. in the absence of imperfections) which, when present, has the greatest effect due to resonant forcing. This particular case is the sole concern of the present paper; other resonances are considered in a complementary study (Rees & Riley 1989).

For the case when the modulations on the upper and lower boundaries are in phase, asymptotic analysis and a spectral method are used to determine the stability of roll solutions and to calculate the evolution of the unstable flows. It is shown that steady rolls with spatially deformed axes or spatially varying wavenumbers evolve. The evolution of the flow that is unstable to sideband disturbances is also calculated when the modulations are π out of phase. Again rolls with a spatially varying wavenumber result.
Effects of heat release in a turbulent, reacting shear layer
Authors: Hermanson J. C. , Dimotakis P. E.
Published: April 2006

Experiments were conducted to study the effects of heat release in a planar, gas-phase, reacting mixing layer formed between two free streams, one containing hydrogen in an inert diluent, the other, fluorine in an inert diluent. Sufficiently high concentrations of reactants were utilized to produce adiabatic flame temperature rises of up to 940 K (corresponding to 1240 K absolute). The temperature field was measured at eight fixed points across the layer. Flow visualization was accomplished by schlieren spark and motion picture photography. Mean velocity information was extracted from Pitot-probe dynamic pressure measurements. The results showed that the growth rate of the layer, for conditions of zero streamwise pressure gradient, decreased slightly with increasing heat release. The overall entrainment into the layer was substantially reduced as a consequence of heat release. A posteriori calculations suggest that the decrease in layer growth rate is consistent with a corresponding reduction in turbulent shear stress. Large-scale coherent structures were observed at all levels of heat release in this investigation. The mean structure spacing decreased with increasing temperature. This decrease was more than the corresponding decrease in shear-layer growth rate, and suggests that the mechanisms of vortex amalgamation are, in some manner, inhibited by heat release. The mean temperature rise profiles, normalized by the adiabatic flame temperature rise, were not greatly changed in shape over the range of heat release of this investigation. A small decrease in normalized mean temperature rise with heat release was however observed. Imposition of a favourable pressure gradient in a mixing layer with heat release resulted in an additional decrease in layer growth rate, and caused only a very slight increase in the mixing and amount of chemical product formation. The additional decrease in layer growth rate is shown to be accounted for in terms of the change in free-stream velocity ratio induced by the pressure gradient.
Numerical simulation of boundary-layer transition and transition control
Authors: Laurien E. , Kleiser L.
Published: April 2006

The laminar-turbulent transition process in a parallel boundary-layer with Blasius profile is simulated by numerical integration of the three-dimensional incompressible Navier-Stokes equations using a spectral method. The model of spatially periodic disturbances developing in time is used. Both the classical Klebanoff-type and the subharmonic type of transition are simulated. Maps of the three-dimensional velocity and vorticity fields and visualizations by integrated fluid markers are obtained. The numerical results are compared with experimental measurements and flow visualizations by other authors. Good qualitative and quantitative agreement is found at corresponding stages of development up to the one-spike stage. After the appearance of two-dimensional Tollmien-Schlichting waves of sufficiently large amplitude an increasing three-dimensionality is observed. In particular, a peak-valley structure of the velocity fluctuations, mean longitudinal vortices and sharp spike-like instantaneous velocity signals are formed. The flow field is dominated by a three-dimensional horseshoe vortex system connected with free high-shear layers. Visualizations by time-lines show the formation of A-structures. Our numerical results connect various observations obtained with different experimental techniques. The initial three-dimensional steps of the transition process are consistent with the linear theory of secondary instability. In the later stages nonlinear interactions of the disturbance modes and the production of higher harmonics are essential.

We also study the control of transition by local two-dimensional suction and blowing at the wall. It is shown that transition can be delayed or accelerated by superposing disturbances which are out of phase or in phase with oncoming Tollmien-Schlichting instability waves, respectively. Control is only effective if applied at an early, two-dimensional stage of transition. Mean longitudinal vortices remain even after successful control of the fluctuations.
Choking of liquid flows
Authors: Richardson S. M.
Published: April 2006

It is well-known that laminar flow of a liquid in a duct is predicted to choke if the viscosity of the liquid increases exponentially with increasing pressure. In other words, the pressure drop in the duct is predicted to become unbounded when the volumetric flow rate reaches a critical finite value. Choking is not observed in practice, however: the reason why is investigated here. It is shown that choking is always predicted to occur if the viscosity is independent of temperature or heat generation by viscous dissipation is neglected. If the viscosity decreases exponentially with increasing temperature and heat generation is not neglected, however, and if the temperature field is fully developed or if the flow is adiabatic, it is shown that choking is predicted not to occur.
An iterative method for high-Reynolds-number flows with closed streamlines
Authors: Mestel A. J.
Published: April 2006

In steady, two-dimensional, inviscid flows it is well-known that, in the absence of rotational forcing, the vorticity is constant along streamlines. In a bounded domain the streamlines are necessarily closed. In some circumstances, investigated in this paper, this behaviour is exhbited also by forced viscous flows, when the variation of vorticity across the streamlines is determined by a balance between viscous diffusion and the forcing. Similar results hold in axisymmetry. For such flows, an iterative process for finding the vorticity as a function of the stream function is described. The method applies whenever the viscous boundary condition can be expressed in terms of the vorticity or tangential stress rather then the tangential velocity. When it is applicable, the iterative method is faster than direct solution of the Navier-Stokes equations at high Reynolds numbers. As an example, the method is used to calculate the flow in a model of the electromagnetic stirring process. In this model, a conducting fluid in an elliptical region is driven by a rotating magnetic field and resisted by a surface stress. The functional dependence of the vorticity on the stream function is found for various values of the magnetic skin depth, surface stress and eccentricity of the ellipse. The form of the flow is discussed with particular reference to whether it consists of a single circulatory region or separates into two or more such regions.
On the stability of high-Reynolds-number flows with closed streamlines
Authors: Mestel A. J.
Published: April 2006

In steady, two-dimensional, inertia-dominated flows it is well known that the vorticity is constant along the streamlines, which, in a bounded domain, are necessarily closed. For inviscid flows, the variation of vorticity across the streamlines is arbitrary, while for forced, weakly dissipitative flows, it is determined by the balance between viscous diffusion and the forcing. This paper discusses the linear stability of flows of this type to two-dimensional disturbances. Arnol'd's stability theorems are discussed. An alternative functional to Arnol'd's is found, which gives the same stability criteria and which permits a representation of the problem in terms of a Schrödinger equation. Conditions for stability are derived from this functional. In particular it is shown that total flow reversals are potentially unstable. The results are illustrated with respect to the geometrically simple case when the streamlines are circular and the forcing is due to a rotating magnetic field, for which case the stability regions are calculated as a function of two parameters. It is shown that the entire theory, including Arnol'd's theorems, applies also to poloidal axisymmetric flows.
A study of linearized oscillatory flow past particles by the boundary-integral method
Authors: Pozrikidis C.
Published: April 2006

Viscous oscillatory flow past particles, governed by the unsteady Stokes equation, is considered. The problem is addressed in its general form for arbitrary flows and particle shapes using the boundary-integral method. It is shown that the leading-order correction to the force exerted on a particle in unsteady flow may be inferred directly from the drag in steady translational motion. For axisymmetric flow, a numerical procedure for solving the boundary-integral equation is developed, and is applied to study streaming oscillatory flow past spheroids, dumbbells, and biconcave disks. The effect of the particle geometry on the structure of the flow is studied by comparing the streamline pattern associated with these particles to that for the sphere. The results reveal the existence of travelling stagnation points on the surface of non-spherical particles, and the formation of unsteady viscous eddies in the interior of the flow. These eddies grow during the decelerating flow period, and shrink during the accelerating flow period. For particles with concave boundaries, unsteady free eddies may originate from an expansion of wall eddies that reside within the concave regions.
The instability and acoustic wave modes of supersonic mixing layers inside a rectangular channel
Authors: Tam Christopher K. W. , Hu Fang Q.
Published: April 2006

At high supersonic convective Mach numbers the familiar Kelvin-Helmholtz instability of a thin unconfined two-dimensional shear layer becomes neutrally stable. In this paper, it is shown that when the same shear layer is put inside a rectangular channel the coupling between the motion of the shear layer and the acoustic modes of the channel produces new two-dimensional instability waves. The instability mechanism of these waves is examined. Extensive numerical computation of the properties of these new instability waves has been carried out. Based on these results two classes of these waves are identified. Some of the important characteristic features of these waves are reported in this paper. In addition to the unstable waves, a thorough analysis of the normal modes of a supersonic shear layer inside a rectangular channel reveals that there are basically two other families of neutral acoustic waves. Examples of some of the prominent characteristics of these neutral acoustic waves are also provided in this paper. The new instability waves are the dominant instabilities of a confined mixing layer at high supersonic convective Mach number. As such they are very relevant to the supersonic mixing and combustion processes inside a ramjet engine combustion chamber.
Pulsatile flow through constricted tubes: an experimental investigation using photochromic tracer methods
Authors: Ojha Matadial , Cobbold Richard S. C. , Johnston K. Wayne , Hummel Richard L.
Published: April 2006

A photochromic tracer method has been used to record pulsatile flow velocity profiles simultaneously at three axial locations along a flow channel. Two major advantages of this multiple-trace method are that it enables velocity data to be acquired in an efficient non-invasive manner and that it provides a detailed description of the spatial relationship of the flow field. The latter is found to be particularly useful in the investigation of transitional type flows; for example, in describing coherent flow structures. Studies of the flow patterns in tubes with mild to moderate degrees of vessel constriction were performed using a 2.9 Hz sinusoidal flow superimposed on a steady flow (frequency parameter of 7.5; mean and modulation Reynolds numbers of 575 and 360, respectively). With mild constrictions (< 50% area reduction), isolated regions of vortical and helical structures were observed primarily during the deceleration phase of the flow cycle and in the vicinity of the reattachment point. As expected, these effects were accentuated when the constriction was asymmetric. For moderate constrictions (50%–80%), transition to turbulence was triggered just before peak flow through the breakdown of waves and streamwise vortices that were shed in the high-shear layer. During this vortex generation phase of the flow cycle, the wall shear stress fluctuated quite intensely, especially in the vicinity of the reattachment point, and its instantaneous value increased by at least a factor of eight. Such detailed descriptions of the transition to turbulence and of the spatial and temporal variation of the wall shear stress, particularly near the reattachment point, have not been previously reported for pulsatile flow through constricted tubes. The observed wall shear stress variations support a proposal by Mao & Hanratty (1986) of an interaction of the imposed flow oscillation with the turbulent fluctuations within the viscous sublayer.
The interference of two passive scalars in a homogeneous isotropic turbulent field
Authors: Kaplan H. , Dinar N.
Published: April 2006

In this work, we study the interference of two scalars diffusing in homogeneous isotropic turbulence. We use the method described by Kaplan & Dinar (1988b) to calculate the cross-correlation coefficient ρ between the concentration fluctuations of two sources. The dependence of ρ on the source separation, shapes and sizes, and its time evolution is calculated for different points in space. Results for the case of two line sources are compared with data from wind tunnel experiments (Warhaft 1984), and seen to be in good agreement. At the centreline ρ is shown to increase as overlap of the two plumes increases. ρ may be either negative or positive depending on the separation between the two sources.
The generation and collapse of a foam layer at the roof of a basaltic magma chamber
Authors: Jaupart Claude , Vergniolle Sylvie
Published: April 2006

Basaltic volcanoes erupt in several different regimes which have not been explained. At Kilauea (Hawaii), eruption can take the form of either fire fountaining, where gas-rich jets propel lava clots to great heights in the atmosphere, or quiet effusive outflow of vesicular lava. Another regime is commonly observed at Stromboli, where large gas slugs burst intermittently at the vent. In an attempt to provide a unifying framework for these regimes, we investigate phenomena induced by degassing in a reservoir which empties into a small conduit. Laboratory experiments are done in a cylindrical tank topped by a thin vertical tube. Working liquids are silicone oils and glycerol solutions to investigate a range of viscosity and surface tension. Gas bubbles are generated at the tank bottom with known bubble diameter and total gas flux. The bubbles rise through the tank and accumulate in a foam layer at the roof. Depending on the behaviour of this foam layer, three different regimes can be distinguished: (i) steady horizontal flow of the foam leading to bubbly flow in the conduit; (ii) alternating regimes of foam build-up and collapse leading to the eruption of a single, large gas pocket; (iii) flow of the foam partially coalesced into larger gas pockets leading to intermittent slug flow in the conduit. These regimes have natural counterparts in basaltic volcanoes.

A simple theory is proposed to explain regimes (i) and (ii). The bubbles in contact with the roof deform under the action of buoyancy forces, developing flat contact areas whose size increases as a function of foam thickness. Maximum deformation corresponds to a critical thickness hc = 2σ/ερlgR, where σ is the coefficient of surface tension, ρl the liquid density, g the acceleration due to gravity, R the bubble radius and ε the gas volume fraction in the foam. The foam thickness is determined by a balance between the input of bubbles from below and the output into the conduit, and is proportional to (μlQ/ε2 ρlg)¼, where μl is the liquid viscosity and Q the gas flux. A necessary and sufficient condition for collapse is that it exceeds the critical value hc. In a liquid of given physical properties, this occurs when the gas flux exceeds a critical value which depends on viscosity, surface tension and bubble size. Experimental determinations of the critical gas flux and of the time between two events of foam collapse are in agreement with this simple theory.
The stress tensor for simple shear flows of a granular material
Authors: Campbell Charles S.
Published: April 2006

The complete stress tensor has been measured using a computer simulation of an assemblage of rough, inelastic spheres in an imposed simple shear flow. Only five components of the stress tensor were found to be significantly different from zero. These represent the disperssive normal stresses τxx, τyyand τzzand the in-the-shear-plane shear stresses τxyand τyx; furthermore, the two off-diagonal stresses, τxyand τyx, were found to be equal so that the resultant stress tensor is symmetric. Two modes of microscopic momentum transport produce the final macroscopic stress tensor: the streaming or kinetic mode by which particles carry the momentum of their motion as they move through the bulk material, and the collisional mode by which momentum is transported by interparticle collisions. The contribution of each to the final result is examined separately. The friction coefficient, the ratio of shear to normal force, is shown to decrease at dense packings for both the collisional and streaming modes. Also observed were normal stress differences, both in and out of the shear plane, reflecting anisotropies in the granular temperature.
Reynolds-number effects on the structure of a turbulent channel flow
Authors: Wei T. , Willmarth W. W.
Published: April 2006

A high resolution, two component laser-Doppler anemometer has been used for turbulence measurements at a high data rate in a channel flow of water. Measurements of the velocity components in the stream direction and in a direction normal to the wall are reported over the Reynolds number range of 3000–40000. The combination of high spatial resolution and high data rates enabled accurate reconstruction of time dependent velocity traces. Long-time statistical averages of these signals clearly show that profiles of the dimensionless turbulence quantities such as turbulence intensities and Reynolds stress are strongly Reynolds-number dependent over a large part of the channel flow. For instance, in the Reynolds-number range of this investigation, it is shown that the fluctuating turbulence quantities do not scale with wall variables even as close as 15 viscous lengths from the wall. The velocity traces and associated power spectra exposed two phenomena which may explain the Reynolds number dependencies.
Image processing of the near wakes of stationary and rotating cylinders
Authors: Massons J. , Ruiz X. , Díaz F.
Published: April 2006

Statistical properties of the position of the turbulent/non-turbulent interface in the near wake of stationary and spinning cylinders have been measured for Re = 2000, using image processing techniques. The results include the first statistical moments, intermittency and burst-rate profiles, auto- and cross-correlation functions, auto- and cross-spectra and phase spectra. They indicate that the rotation of the cylinder causes substantial changes in the structure of the flow.
Structure of the turbulent flow field under breaking waves in the surf zone
Authors: Nadaoka Kazuo , Hino Mikio , Koyano Yoshiji
Published: April 2006

The structure of turbulence and its role in the breaking wave dynamics within the surf zone have been investigated through laboratory experiments using several flow visualization techniques and a fibre-optic LDV system. The results indicate that there exists a characteristic structure of large-scale eddies referred to here as ‘horizontal eddies’ and ‘obliquely descending eddies’, which has a significant role in the generation of Reynolds stress and thus affects the deformation of the mean flow field. The experiments also reveal that these eddies caused by the wave breaking bring a large amount of vorticity (with non-zero average) into otherwise almost irrotational velocity fields, resulting in the generation of vorticity-related mean flow fields as well as turbulence (vorticity-containing velocity fluctuation). This means that the breaking waves in the surf zone can be regarded as pseudowaves which consist of irrotational velocity components as ‘wave motion’ and appreciable amounts of rotational mean velocity components as ‘eddying motion’ (with non-zero mean vorticity) together with turbulence. It is found that the generation of the mean rotational velocity component due to wave breaking causes considerable increase in mass and momentum transport, as compared with ordinary non-breaking waves, and thus a decrease in wave height.
Evolution and decay of cylindrical and spherical nonlinear acoustic waves generated by a sinusoidal source
Authors: Sachdev P. L. , Nair K. R. C.
Published: April 2006

The present work gives a comprehensive numerical study of the evolution and decay of cylindrical and spherical nonlinear acoustic waves generated by a sinusoidal source. Using pseudospectral and predictor–corrector implicit finite difference methods, we first reproduced the known analytic results of the plane harmonic problem to a high degree of accuracy. The non-planar harmonic problems, for which the amplitude decay is faster than that for the planar case, are then treated. The results are correlated with the known asymptotic results of Scott (1981) and Enflo (1985). The constant in the old-age formula for the cylindrical canonical problem is found to be 1.85 which is rather close to 2, ‘estimated’ analytically by Enflo. The old-age solutions exhibiting strict symmetry about the maximum are recovered; these provide an excellent analytic check on the numerical solutions. The evolution of the waves for different source geometries is depicted graphically.
A numerical method for treating time-periodic boundary layers
Authors: Duck P. W.
Published: April 2006

The development of an incompressible, laminar, pulsatile boundary layer over a semi-infinite flat plate is studied. Although the undisturbed free stream flow is taken to be non-reversing (following previous studies), sufficiently far downstream, the flow in part of the boundary layer must ultimately reverse direction during part of the cycle.

A novel numerical (finite-difference) scheme is described, which builds in the time periodicity of the flow, and also takes into account the direction of the flow in deciding the form of the differencing in the streamwise direction. The effect of variations in numerical grid is investigated, and comparison is made with asymptotic formulae applicable close to and far from the leading edge of the plate, together with linearized (small oscillation) results obtained using the analysis of Ackerberg & Phillips (1972), which is shown to yield remarkably accurate results when compared with the solution for the full problem, even for quite large oscillation amplitudes.
Three-dimensionality of organized structures in a plane turbulent wake
Authors: Hayakawa Michio , Hussain Fazle
Published: April 2006

This paper describes a quantitative study of the three-dimensional nature of organized motions in a turbulent plane wake. Coherent structures are detected from the instantaneous, spatially phase-correlated vorticity field using certain criteria based on size, strength and geometry of vortical structures. With several combinations of X-wire rakes, vorticity distributions in the spanwise and transverse planes are measured in the intermediate region (10d [les ] x [les ] 40d) of the plane turbulent wake of a circular cylinder at a Reynolds number of 13000 based on the cylinder diameter d. Spatial correlations of smoothed vorticity signals as well as phase-aligned ensemble-averaged vorticity maps over structure cross-sections yield a quantitative measure of the spatial coherence and geometry of organized structures in the fully turbulent field. The data demonstrate that the organized structures in the nominally two-dimensional wake exhibit significant three-dimensionality even in the near field. Using instantaneous velocity and vorticity maps as well as correlations of vorticity distributions in different planes, some topological features of the dominant coherent structures in a plane wake are inferred.
Aerodynamic characteristics of a two-dimensional porous sail
Authors: Murata S. , Tanaka S.
Published: April 2006

A method is presented for the numerical analysis of the aerodynamic characteristics of a two-dimensional single-surface porous sail. In this analysis the authors apply a series of Jacobi polynomials to express the pressure distribution and chordwise shape, considering carefully leading-edge conditions. It is found that the aero-dynamic stability of a sail increases with increasing porosity. The effects of porosity on the value of the life coefficient and the position of the centre of pressure are shown in diagrams as functions of angle of attack and of excess length of membrane over the chord length.
Stabilization of dielectric liquid bridges by electric fields in the absence of gravity
Authors: González H. , Mccluskey F. M. J. , Castellanos A. , Barrero A.
Published: April 2006

The stability of liquid bridges in zero gravity conditions under the influence of an a.c. electric field tangential to the interface is examined in this paper. For the theoretical study, a static analysis was carried out to find the bifurcation surfaces as a function of the three relevant non-dimensional parameters: Λ, the slenderness or ratio of height to diameter of the cylindrical bridge; β0, the ratio of dielectric constants of the two fluids used and Ξ, a non-dimensional quantity proportional to the applied voltage. Stable and unstable regions of Λ−βo−Ξ space were distinguished. Results indicate a strong stabilizing effect for higher values of β0. The experimental study, using silicone and ricinus oil to approximate zero gravity conditions fully confirmed quantitatively the theoretical results.
Experimental study of bore run-up
Authors: Yeh Harry H. , Ghazali Abdulhamid , Marton Ingunn
Published: April 2006

Bore propagation near the shoreline, the transition from bore to wave run-up, and the ensuing run-up motion on a uniformly sloping beach are investigated experimentally. As a bore approaches the shoreline, the propagation speed first decelerates by compressing its wave form and then suddenly accelerates at the shoreline. Although this behaviour is qualitatively in agreement with the inviscid shallow-water wave prediction (often called the ‘bore collapse’ phenomenon), unlike the genuine bore-collapse phenomenon, the acceleration is caused by the ‘momentum exchange’ process, i.e. collision of the bore against the initially quiescent water along the shoreline. Owing to this momentum exchange, a single bore motion degenerates into two successive run-up water masses; one involves a turbulent run-up water motion followed by the original incident wave motion. The transition process from undular bore to wave run-up appears to be different from that of a fully developed bore. The bore front overturns directly onto the dry beach surface, and the run-up is characterized by a thin splashed-up flow layer.
Time-dependent convection in a fluid-saturated porous cube heated from below
Authors: Kimura S. , Schubert G. , Straus J. M.
Published: April 2006

A numerical scheme based on the pseudospectral method has been implemented in order to study three-dimensional convection in a fluid-saturated cube of porous material. With increasing Rayleigh number R, convection first evolves from a symmetric steady state (S) to a partially non-symmetric steady state (S’, physical symmetry in the vertical direction is preserved). The transition Rayleigh number is about 550. At a Rayleigh number of 575 the flow becomes oscillatory P(1) with a single frequency that increases with R. At a value of R between 650 and 680 the oscillation becomes quasi-periodic with at least two fundamental frequencies. It returns to a simply periodic state in a narrow range about R = 725. A further increase of R transforms the simply periodic state again to a quasi-periodic state. The sequence of three-dimensional time-dependent states resembles previously studied two-dimensional cases in that evolution from more complex states to less complex states occurs with increasing R. The partial symmetry breaking prior to the onset of time dependence is unique to the three-dimensional flows, but a dependence of the S → S’ transition on the step size in R suggests the possibility that S → S’ might not occur prior to S → P(1) for sufficiently small steps in R. The quasi-periodic flows sometimes exhibit intermittency, causing difficulty in exactly defining their spectral characteristics.
The shearless turbulence mixing layer
Authors: Veeravalli S. , Warhaft Z.
Published: April 2006

The interaction of two energy-containing turbulence scales is studied in the absence of mean shear. The flow, a turbulence mixing layer, is formed in decaying grid turbulence in which there are two distinct scales, one on either side of the stream. This is achieved using a composite grid with a larger mesh spacing on one side of the grid than the other. The solidity of the grid, and thus the mean velocity, is kept constant across the entire flow. Since there is no mean shear there is no turbulence production and thus spreading is caused solely by the fluctuating pressure and velocity fields. Two different types of grids were used: a parallel bar grid and a perforated plate. The mesh spacing ratio was varied from 3.3:1 to 8.9:1 for the bar grid, producing a turbulence lengthscale ratio of 2.4:1 and 4.3:1 for two different experiments. For the perforated plate the mesh ratio was 3:1 producing a turbulence lengthscale ratio of 2.2:1. Cross-stream profiles of the velocity variance and spectra indicate that for the large lengthscale ratio (4.3:1) experiment, a single scale dominates the flow while for the smaller lengthscale ratio experiments, the energetics are controlled by both lengthscales on either side of the flow. In all cases the mixing layer is strongly intermittent and the transverse velocity fluctuations have large skewness. The downstream data of the second, third and fourth moments for all experiments collapse well using a single composite lengthscale. The component turbulent energy budgets show the importance of the triple moment transport and pressure terms within the layer and the dominance of advection and dissipation on the outer edge. It is also shown that the bar grids tend toward self-similarity with downstream distance. The perforated plate could not be measured to the same downstream extent and did not reach self-similarity within its measurement range. In other respects the two types of grids yielded qualitatively similar results. Finally, we emphasize the distinction between intermittent turbulent penetration and turbulent diffusion and show that both play an important role in the spreading of the mixing layer.
Selection of convective planform orientation by boundary anisotropy
Authors: Pearlstein Arne J. , Oztekin Alparslan
Published: April 2006

Thermal instability of a fluid layer confined between isotropic horizontal solid walls leads to convection cells having no preferred horizontal direction. For thermally anisotropic walls, we find that certain planform orientations are preferred, in that convection sets in at a smaller Rayleigh number (Ra) for some orientations than for others, thus providing a means by which a regular planform may be established in a large-aspect-ratio layer. We consider horizontal layers of two Boussinesq, Newtonian fluids separated by a rigid, thermally anisotropic plate of constant thickness. The upper and lower fluid layers are bounded above and below, respectively, by rigid, thermally anisotropic plates of arbitrary thickness. When the bounding surfaces are thermally anisotropic, the horizontal wavevector (a) of the resulting convective flow has two distinct components. Thus, instead of a neutral curve in the (Ra, a)-plane, there is a neutral surface, and Ra depends on both components of a, or alternatively, on |a| and the planform orientation angle Φrε[0, 2π]. In the isotropic case, the neutral surface is axisymmetric (i.e. invariant with respect to Φr consistent with the known dependence on |a| only.

For anisotropic walls, axisymmetry is replaced by π- periodicity in the Φr direction, corresponding to invariance with respect to a 180° rotation, and the neutral surface has an even number of local minima. We study the dependence of Φr on the middle plate orientation (Φp) Several different Φr−Φp topologies are found. When the number of local minima exceeds two, discontinuous Φr−Φp plots may occur. The dependence of Φr on the thicknesses and conductivities of the plates and fluids and on the orientation of the plates is discussed, with special reference to the transitions between different Φr−Φp topologies.
Elliptic jets. Part 1. Characteristics of unexcited and excited jets
Authors: Hussain Fazle , Husain Hyder S.
Published: April 2006

This paper summarizes experimental studies of incompressible elliptic jets of different aspect ratios and initial conditions, and effects of excitations at selected frequencies and amplitudes. Elliptic jets are quite different from the extensively studied plane and circular jets - owing mainly to the fact that the azimuthal curvature variation of a vortical structure causes its non-uniform self-induction and hence complex three-dimensional deformation. Such deformation, combined with properly selected excitation can substantially alter entrainment and other turbulence phenomena, thus suggesting preference for the elliptic shape in many jet applications. The dominance of coherent structures in the jet far field is evident from the finding that switching over of the cross-section shape continues at least up to 100 equivalent diameters De. The locations and the number of switchovers are strongly dependent on the initial condition, on the aspect ratio, and, when excited, on the Strouhal number and the excitation level. We studied jets with constant exit momentum thickness θe, all around the perimeter, thus separating the effects of azimuthal variations of θe, (typical of elliptic jets) and of the shear-layer curvature. Also investigated are the instability characteristics, and enhanced entrainment caused by bifurcation as well as pairing of vortical structures. We discuss shear-layer and jet- column domains, and find the latter to be characterized by two modes : the preferred mode and the stable pairing mode - similar to those found in circular jets -both modes scaling on the newly-defined lengthscale De. The paper documents some time- average measurements and their comparison with those in circular and plane jets.
The distortion of short internal waves produced by a long wave, with application to ocean boundary mixing
Authors: Thorpe S. A.
Published: April 2006

The propagation of a train of short, small-amplitude, internal waves through a long, finite-amplitude, two-dimensional, internal wave is studied. An exact solution of the equations of motion for a Boussinesq fluid of constant density gradient is used to describe the long wave, and its distortion of the density gradient as well as its velocity field are accounted for in determining the propagation characteristics of the short waves. To illustrate the magnitude of the effects on the short waves, particular numerical solutions are found for short waves generated by an idealized flow induced by a long wave adjacent to sloping, sinusoidal topography in the ocean, and the results are compared with a laboratory experiment. The theory predicts that the long wave produces considerably distortion of the short waves, changing their amplitudes, wavenumbers and propagation directions by large factors, and in a way which is generally consistent with, but not fully tested by, the observations. It is suggested that short internal waves generated by the interaction of relatively long waves with a rough sloping topography may contribute to the mixing observed near continental slopes.
Axisymmetric convection at large Rayleigh and infinite Prandtl number
Authors: Umemura Akira , Busse F. H.
Published: April 2006

A matched-asymptotic analysis has been carried out for an axisymmetric convection cell in the case of stress-free boundaries. This problem differs from that of two-dimensional convection rolls mainly through the special role played by the central plume. The radius, of order ε, of the latter depends on the Rayleigh number R through the relationship $\epsilon^4(-\ln \epsilon) = R^{\frac{2}{3}}$. The plume velocity is independent of height at lowest order and its magnitude exceeds by a factor (− ln ε)½ the strength, of order $R^{\frac{2}{3}}$, of the core flow. As a result of these properties the central plume is governed by advection, in contrast to the perimeter plume which is affected by conduction as well. This asymmetry is reflected in the different thickness of the horizontal thermal boundary layers and gives rise to the deviation of the core temperature from the mean value of the top and bottom temperatures. This deviation is positive (negative) for the case of a falling (rising) central plume. While the core flow is driven mainly by the perimeter plume the fraction of the heat flux carried by the central plume is always above three-quarters and increases as the radius-to-height-ratio λ decreases.