bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of retinoids on proliferation and plasminogen activator expression in a bovine mammary epithelial cell line
Authors: Cheli Federica , Politis Ioannis , Rossi Luciana , Fusi Eleonora , Baldi Antonella
Published: October 2003

Effects of two natural (retinol and retinoic acid, RA) and one synthetic N-(4-hydroxyphenyl) retinamide (4-HPR) retinoids on proliferation and expression of urokinase-plasminogen activator (u-PA) by bovine mammary epithelial cells were examined. The BME-UV1 established bovine mammary epithelial cell line was used as a model system. All retinoids tested (retinol, RA and 4-HPR) were effective inhibitors of cell proliferation. When cells were cultured in the absence of fetal bovine calf serum (FBCS), inhibition occurred at concentrations as low as 1 nM for all retinoids tested. The effect of retinoids on cell proliferation was not dose-related when cells were cultured in the absence of FBCS. All retinoids (retinol, RA, 4-HPR), when used in the range 1 nM–10 μM (noncytotoxic concentrations), were equally effective and had identical inhibition patterns. Inhibition of cell proliferation by RA was apparent by 6 h and was higher after 24 h in culture. In contrast, when cells were cultured in the presence of FBCS, the effect of RA and retinol on cell proliferation was dose-related. RA and retinol inhibited cell proliferation (P<0·01) when added to the culture medium in concentrations as low as 10 nM and 100 nM, respectively. 4-HPR was inhibitory (P<0·01) in concentrations as low as 1 nM. Higher concentrations of 4-HPR in the range 1 nM–1 μM had no further effect on cell proliferation. None of the retinoids tested, when added to cultures in the presence or absence of FBCS, could completely arrest cell proliferation at noncytotoxic concentrations. RA at 1 μM inhibited (P<0·05) insulin or IGF-I-induced cell proliferation but had no effect (P>0·05) on u-PA mRNA levels or u-PA activity. Furthermore, RA inhibited cell proliferation in the presence of FBCS but had no effect (P>0·05) on u-PA mRNA levels. Thus, retinoids are effective inhibitors of bovine mammary epithelial cell proliferation and this growth inhibition does not seem to correlate with any changes in u-PA mRNA or u-PA activity.
DR Frank Dodd – Obituary.
Authors: Booth James
Published: October 2003

Dr Frank Dodd, formerly of the National Institute for Research in Dairying (NIRD) at Shinfield, Reading, has died aged 78. He had suffered ill health for the last few years but insisted on continuing his enthusiastic gardening and his voluntary work of chauffeuring the “old folk” to hospital and elsewhere.
Bishop Richard Fox's Manuscript Gifts to his Winchester Nuns: A Second Surviving Example
Authors: ERLER MARY C.
Published: October 2003

To regularise and strengthen female monastic life in his Winchester
diocese, in the early sixteenth century Bishop Richard Fox made
a new translation of the Rule of St Benedict explicitly for women. He
had it printed by Richard Pynson in 1517, thus taking advantage of the
ability of the printing press to provide multiple copies for all the members
of the four Hampshire womens' houses he addressed: St Mary Winchester
(Nunnaminster), Wherwell, Romsey and Wintney.

In addition to these printed copies Bishop Fox provided additional
manuscript books for each of the four houses, as his preface to the Rule tells
us: ‘And by cause we wolde not/that there shulde be any lacke amongis
them of the bokis of this sayd translation/we haue therfore/aboue and besyde
certayne bokes ther of/which we haue yeven to the sayde monasteris: caused it to be
emprinted’ [italics mine] (sig. Aiiv).
MODERN EUROPE Histoire agraire de la France au XVIIIe siècle. By Gérard Béaur. Paris: Éditions SEDES, 2000. Pp. 320. €21.13, paper.
Authors: Hoffman Philip T.
Published: October 2003

From the 1930s through the 1970s, French historians composed some of the greatest rural history—indeed, the greatest history—ever written. Scholars such as Marc Bloch, Pierre Goubert, and Emmanuel Le Roy Ladurie produced extraordinary works of social history, which pioneered in borrowing techniques from other fields such as geography, demography, and anthropology. Many of their best books—such as Ladurie's Peasants of Languedoc (Urbana: University of Illinois Press, 1974)—were local or regional studies; and although they were by and large uninformed by neoclassical economics, they created a consensus about the rural economy of Old Regime France. According to that consensus, French agriculture stagnated because rising population levels fragmented landholdings, and because the peasants' attitudes and village institutions blocked economic growth. The consensus endured for a number of years, but it has now begun to collapse under the weight of exciting new research conducted on both sides of the Atlantic. Some of this research is cliometric; some is innovative social history. Nearly all of it is fascinating, but it is proliferating at such a rate that it is hard to keep track of, even for the specialist. It is even harder to see whether a new consensus is beginning to form.
Did Takahashi Korekiyo Rescue Japan from the Great Depression?
Authors: Cha Myung Soo
Published: October 2003

Takahashi Korekiyo is remembered as a wise finance minister saving Japan from the Great Depression. The contribution of his policy measures however remains to be rigorously measured, with proper control of other forces also driving the recovery. Structural vector autoregression analysis of previously unexploited monthly data confirms the pivotal role of Takahashi's debt-financed fiscal expansion. Monetizing the public debts, the Bank of Japan maintained a neutral stance. The recovery was aided by exchange-rate shocks generated during the transition from the gold standard to the floating-exchange-rate regime and, to a smaller extent, by the world recovery.
Jewish Immigrant Entrepreneurship in New York and London, 1880–1914: Enterprise and Culture. By Andrew Godley. Basingstoke, England, and New York: Palgrave, 2001. Pp. xii, 187. $60.00.
Authors: Soyer Daniel
Published: October 2003

In this imaginative and readable book, Andrew Godley argues that culture matters in economics, and that some cultural traits encourage entrepreneurship, and therefore material prosperity, more than others. More specifically, he joins debates among British historians over the causes for Britain's relative economic decline around the turn of the twentieth century. He argues that British culture was in fact anti-entrepreneurial and concludes that this was likely to have had a negative impact on the country's economic fortunes. This is, therefore, really a book about Britain and its economic culture. Though it certainly has interesting insights into Jewish history as well; the author uses the Jews primarily as a “control group” in his historical “experiment.”
The supercritical bore produced by a high-speed ship in a channel
Authors: GOURLAY T. P.
Published: October 2003

An experimental investigation is made into the various flow regimes accompanying
a ship travelling in a channel at supercritical speeds. The phenomena of smooth
solitons, broken solitons, bores, and steady supercritical flow are observed. We look
at the conditions under which each phenomenon exists, and the depth-based Froude
numbers at which the transitions occur. Special emphasis is placed on ship bores, and
we put forward a simple theoretical model for predicting the form of the bores as
well as the transition to steady supercritical flow.
Downstream and upstream influence in river meandering. Part 2. Planimetric development
Authors: ZOLEZZI G. , SEMINARA G.
Published: October 2003

Perturbations of channel geometry (like variations of channel curvature or channel
width) in meandering rivers give rise to morphodynamic effects which display themselves
through the development of large-scale perturbations of bottom topography in
the form of stationary bars developing in the longitudinal direction. The latter may
then drive the lateral migration of the channel by enhancing bank erosion at bar
pools: through this mechanism local perturbations of channel geometry may affect
the planimetric development of meandering rivers on large timescales. The problem
tackled herein is whether such morphodynamic influence is invariably felt downstream
as the commonly employed model of river meandering would suggest.

In order to solve this problem, we derive the exact solution of the linearized form of
the mathematical problem of river morphodynamics. Linear analysis had pointed out
the existence of a resonance phenomenon: in a linear (hence ideal) context, resonance
occurs when the meander wavenumber and the width ratio of the channel take values
(λR and βR, respectively) such as
to force free spatial modes of the system consisting
of free bars which neither grow nor decay either in time or in space. Channels
characterized by values of the width ratio β larger (smaller) than βR are called
super- (sub-)resonant. The present solution, which applies to channels with constant
width and arbitrary curvature distribution, shows that two distinct scenarios may
occur: downstream influence is associated with sub-resonant channels and vice versa
dominant upstream influence occurs in super-resonant channels. Small-amplitude
waves of bottom topography are shown to migrate downstream in the former case
and may migrate upstream in the latter, as resonance also defines the threshold
conditions below (above) which small-amplitude alternate bar perturbations (may)
migrate downstream (upstream).

These results have several implications. In the present paper we examine the
overdeepening phenomenon whereby abrupt variations of channel curvature, as in
sequences of straight and constant curvature reaches, lead to sequences of stationary
alternate bars with amplitude decaying in the longitudinal direction. We show
that, along with downstream overdeepening, an upstream overdeepening scenario is
predicted in the super-resonant regime.

Implications of the upstream influence on planimetric development of meandering
rivers are investigated in Part 2.
DAVID CRIGHTON
1942–2000
Authors: FFOWCS WILLIAMS JOHN E.
Published: October 2003

David Crighton was struck down by cancer in his fifty-eighth year. He was then
at the height of his career and was one of the most admired personalities in fluid
mechanics. He had specialized in wave theory, helping to understand and solve
problems of practical importance using the full power of mathematical method. Efforts
to control the sound and vibration caused by unsteady flow were never far from his
thinking, and Crighton's contribution to those efforts has changed significantly the
way the subject is viewed. Having first attracted him into the field and never losing
my interest in the way he was influencing it, it is natural that I should comment on
the technical developments while looking back on Crighton's professional life. The
subject has changed a great deal and there are now many more researchers involved in
its study, many of whom rely on techniques that Crighton pioneered – really powerful
mathematical methods. But the basic problems remain: powerful flows are noisy.
Motion of a triple junction
Authors: MIKSIS MICHAEL J. , VANDEN-BROECK JEAN-MARC
Published: October 2003

The motion of a triple junction is investigated. We consider only the two-dimensional
case and assume that initially the fluid is in the form of three inviscid wedges. A
similarity solution is determined which accounts for a balance of force at the triple
junction. This similarity solution is computed numerically using boundary integral
methods. Results are presented for different initial wedge angles and surface tension
ratios. In particular the location of the triple junction and the resulting capillary
waves along the interfaces are discussed.
Three-dimensional theory of water impact. Part 1. Inverse Wagner problem
Authors: SCOLAN Y.-M. , KOROBKIN A. A.
Published: October 2003

The three-dimensional problem of blunt-body impact onto the free surface of an ideal
incompressible liquid is considered within the Wagner theory. The theory is formally
valid during an initial stage of the impact. The problem has been extensively studied
in both two-dimensional and axisymmetric cases. However, there are no exact truly
three-dimensional solutions of the problem even within the Wagner theory. At present,
three-dimensional effects in impact problems are mainly handled approximately by
using a sequence of two-dimensional solutions and/or aspect-ratio correction factor.
In this paper we present exact analytical rather than approximate solutions to the
three-dimensional Wagner problem. The solutions are obtained by the inverse method.
In this method the body velocity and the projection on the horizontal plane of the
contact line between the liquid free surface and the surface of the entering body
are assumed to be given at any time instant. The shape of the impacting body
is determined from the Wagner condition. It is proved that an elliptic paraboloid
entering calm water at a constant velocity has an elliptic contact line with the
free surface. Most of the results are presented for elliptic contact lines, for which
analytical solutions of the inverse Wagner problem are available. The results obtained
can be helpful in testing other numerical approaches and studying the influence of
three-dimensional effects on the liquid flow and the hydrodynamic loads.
The erosion of a distributed two-dimensional vortex in a background straining flow
Authors: LEGRAS BERNARD , DRITSCHEL DAVID G. , CAILLOL PHILIPPE
Published: October 2003

Herein we present a simplified theory for the behaviour of a vortex embedded in
a growing external straining flow. Such a flow arises naturally as a vortex moves
relative to other vortices. While the strain may generally exhibit a complex time
dependence, the salient features of the vortex evolution can be understood in the
simpler context, studied here, of a linearly growing strain. Then, all of the typical
stages of evolution can be seen, from linear deformation, to the stripping or erosion
of low-lying peripheral vorticity, and finally to the breaking or rapid elongation of
the vortex into a thin filament.

When, as is often the case in practice, the strain growth is slow, the vortex adjusts
itself to be in approximate equilibrium with the background flow. Then, the vortex
passes through, or near, a sequence of equilibrium states until, at a critical value of
the strain, it suddenly breaks. In the intermediate period before breaking, the vortex
continuously sheds peripheral vorticity, thereby steepening its edge gradients. This
stripping is required to keep the vortex in a near equilibrium configuration.

We show that this behaviour can be captured, quantitatively, by a reduced model,
the elliptical model, which represents the vortex by a nested set of elliptical vorticity
contours, each having a (slightly) different aspect ratio and orientation. Here, we have
extended the original elliptical model by allowing for edge vorticity levels to be shed
when appropriate (to represent stripping) and by incorporating the flow induced by
the vorticity being stripped away. The success of this model proves that the essential
characteristics of vortex erosion are captured simply by the leading-order, elliptical
shape deformations of vorticity contours.

Finally, we discuss the role of viscosity. Then, there is a competition between
gradient steepening by stripping and smoothing by viscosity. If the strain grows too
slowly, the vortex is dominated by viscous decay, and the edge gradients become
very smooth. On the other hand, for sufficiently rapid strain growth (which can still
be slow, depending on the viscosity), the vortex edge remains steep until the final
breaking.
Nonlinear theory of geostrophic adjustment. Part 1. Rotating shallow-water model
Authors: REZNIK G. M. , ZEITLIN V. , BEN JELLOUL M.
Published: October 2003

We develop a theory of nonlinear geostrophic adjustment of arbitrary localized (i.e.
finite-energy) disturbances in the framework of the non-dissipative rotating shallow-water
dynamics. The only assumptions made are the well-defined scale of disturbance
and the smallness of the Rossby number Ro. By systematically using the multi-time-scale
perturbation expansions in Rossby number it is shown that the resulting field is
split in a unique way into slow and fast components evolving with characteristic time
scales f−10 and (f0Ro)−1
respectively, where f0 is the Coriolis parameter. The slow
component is not influenced by the fast one and remains close to the geostrophic
balance. The algorithm of its initialization readily follows by construction.

The scenario of adjustment depends on the characteristic scale and/or initial relative
elevation of the free surface ΔH/H0, where
ΔH and H0 are typical values of the initial
elevation and the mean depth, respectively. For small relative elevations
(ΔH/H0 = O(Ro))
the evolution of the slow motion is governed by the well-known quasi-geostrophic potential
vorticity equation for times t [les ] (f0Ro)−1.
We find modifications to this equation for longer times
t [les ] (f0Ro2)−1. The fast component consists mainly
of linear inertia–gravity waves rapidly propagating outward from the initial disturbance.

For large relative elevations (ΔH/H0 [Gt ] Ro)
the slow field is governed by the frontal geostrophic dynamics equation. The fast component in this case is a spatially
localized packet of inertial oscillations coupled to the slow component of the flow.
Its envelope experiences slow modulation and obeys a Schrödinger-type modulation
equation describing advection and dispersion of the packet. A case of intermediate
elevation is also considered.
Fluid instabilities in precessing spheroidal cavities
Authors: LORENZANI S. , TILGNER A.
Published: October 2003

We study by direct numerical simulation the motion of incompressible fluid contained
in an ellipsoid of revolution with ellipticity 0.1 or less which rotates about its axis
of symmetry and whose rotation axis is executing precessional motion. A solution
to this problem for an inviscid fluid given by Poincaré (1910) predicts motion of
uniform vorticity. The simulations show how the orientation of the average vorticity
of a real fluid is influenced by both pressure and viscous torques exerted by the
boundaries. Axisymmetric shear layers appear which agree well with those observed
experimentally by Malkus (1968). Shear caused by deviations from a velocity field
with uniform vorticity triggers an instability consisting of waves propagating around
the average rotation axis of the fluid. The Ekman layers at the boundaries may also
become unstable.
Extensions to the theory of selective withdrawal
Authors: WOOD IAN R.
Published: October 2003

Most reservoirs contain stratified fluid and selective withdrawal is used to obtain
water with the desired properties. We initially deal with a layered density distribution.
The theory for the critical discharge for a single layer and a point sink is reviewed
and extended to cover the case where there is gate discharge (a line sink). The theory
for the case when the upper layer depth is large and the flow is coming from both
layers is reviewed and it is shown that the valve controls the discharge and a virtual
control determines the ratio of the discharge in each layer. This virtual control moves
further from the valve as the total discharge increases. We determine the position
of the virtual control and the criteria for the maximum for two layers when the
upper layer is finite and below a stationary layer. Before this maximum, we show
that when the discharge is increased above the critical discharge for the single layer,
the finite upper layer does not affect the ratio of the flows from each layer until the
virtual control reaches that for the maximum discharge. At this stage, the upper layer
becomes tangential to the dam face and this condition and the smoothness of the
lower interface determine both the total discharge and the ratio of the flow from each
layer. Indeed, at this stage, virtual control and the control of the discharge are at the
same section.

In a similar way, with a stationary layer above and below two flowing layers,
we derive the maximum discharge from the two flowing layers. For this case, the
solution is self-similar. This is then extended to a stable stratified continuous density
distribution. The experiments of Gariel (1949) and Lawrence & Imberger (1979)
suggest that the predictions of the theory are within the experimental errors.
A numerical investigation of solitary internal waves with trapped cores formed via shoaling
Authors: LAMB KEVIN G.
Published: October 2003

The formation of solitary internal waves with trapped cores via shoaling is investigated numerically.
For density fields for which the buoyancy frequency increases
monotonically towards the surface, sufficiently large solitary waves break as they shoal
and form solitary-like waves with trapped fluid cores. Properties of large-amplitude
waves are shown to be sensitive to the near-surface stratification. For the monotonic
stratifications considered, waves with open streamlines are limited in amplitude by the
breaking limit (maximum horizontal velocity equals wave propagation speed). When
an exponential density stratification is modified to include a thin surface mixed layer,
wave amplitudes are limited by the conjugate flow limit, in which case waves become
long and horizontally uniform in the centre. The maximum horizontal velocity in the
limiting wave is much less than the wave's propagation speed and as a consequence,
waves with trapped cores are not formed in the presence of the surface mixed layer.
Coherent structure generation in near-wall turbulence
Authors: SCHOPPA W. , HUSSAIN F.
Published: October 2003

We present a new mechanism for generation of near-wall streamwise vortices – which
dominate turbulence phenomena in boundary layers – using linear perturbation analysis
and direct numerical simulations of turbulent channel flow. The base flow, consisting
of the mean velocity profile and low-speed streaks (free from any initial vortices),
is shown to be linearly unstable to sinuous normal modes only for relatively strong
streaks, i.e. for wall inclination angles of streak vortex lines exceeding 50°. Analysis
of streaks extracted from fully developed near-wall turbulence indicates that about
20% of streak regions in the buffer layer exceed the strength threshold for instability.
More importantly, these unstable streaks exhibit only moderate (twofold) normal-mode
amplification, the growth being arrested by self-annihilation of streak-flank
normal vorticity due to viscous cross-diffusion. We present here an alternative, streak
transient growth (STG) mechanism, capable of producing much larger (tenfold) linear
ampliflcation of x-dependent disturbances. Note the distinction of STG – responsible
for perturbation growth on a streak velocity distribution U(y, z) – from prior transient
growth analyses of the (streakless) mean velocity U(y). We reveal that streamwise
vortices are generated from the more numerous normal-mode-stable streaks, via a new
STG-based scenario: (i) transient growth of perturbations leading to formation of a
sheet of streamwise vorticity ωx (by a ‘shearing’ mechanism of vorticity generation),
(ii) growth of sinuous streak waviness and hence ∂u/∂x as STG reaches nonlinear
amplitude, and (iii) the ωx sheet’s collapse via stretching by ∂u/∂x (rather than rollup)
into streamwise vortices. Significantly, the three-dimensional features of the (instantaneous)
streamwise vortices of x-alternating sign generated by STG agree well with the
(ensemble-averaged) coherent structures educed from fully turbulent flow. The STG-induced
formation of internal shear layers, along with quadrant Reynolds stresses and
other turbulence measures, also agree well with fully developed turbulence. Results
indicate the prominent – possibly dominant – role of this new, transient-growth-based
vortex generation scenario, and suggest interesting possibilities for robust control of
drag and heat transfer.
Stability of steep gravity–capillary solitary waves
in deep water
Authors: CALVO DAVID C. , AKYLAS T. R.
Published: October 2003

The stability of steep gravity–capillary solitary waves in deep water is numerically
investigated using the full nonlinear water-wave equations with surface tension. Out
of the two solution branches that bifurcate at the minimum gravity–capillary phase
speed, solitary waves of depression are found to be stable both in the small-amplitude
limit when they are in the form of wavepackets and at finite steepness when they
consist of a single trough, consistent with observations. The elevation-wave solution
branch, on the other hand, is unstable close to the bifurcation point but becomes
stable at finite steepness as a limit point is passed and the wave profile features two
well-separated troughs. Motivated by the experiments of Longuet-Higgins & Zhang
(1997), we also consider the forced problem of a localized pressure distribution applied
to the free surface of a stream with speed below the minimum gravity–capillary
phase speed. We find that the finite-amplitude forced solitary-wave solution branch
computed by Vanden-Broeck & Dias (1992) is unstable but the branch corresponding
to Rayleigh’s linearized solution is stable, in agreement also with a weakly nonlinear
analysis based on a forced nonlinear Schrödinger equation. The significance of viscous
effects is assessed using the approach proposed by Longuet-Higgins (1997): while for
free elevation waves the instability predicted on the basis of potential-flow theory is
relatively weak compared with viscous damping, the opposite turns out to be the case
in the forced problem when the forcing is strong. In this régime, which is relevant
to the experiments of Longuet-Higgins & Zhang (1997), the effects of instability can
easily dominate viscous effects, and the results of the stability analysis are used to
propose a theoretical explanation for the persistent unsteadiness of the forced wave
profiles observed in the experiments.
Uniform steady free-surface flow in
heterogeneous porous formations
Authors: AMIR ORNA , DAGAN GEDEON
Published: October 2003

The effect of spatial variability of the hydraulic conductivity upon free-surface flow
is investigated in a stochastic framework. We examine the three-dimensional free-surface
gravitational flow problem for a sloped mean uniform flow in a randomly
heterogeneous porous medium. The model also describes the interface between two
fluids of differing densities, e.g. freshwater/saltwater and water/oil with the denser
fluid at rest. We develop analytic solutions for the variance and integral scale of
free-surface fluctuations and of specific discharge on the free surface. Additionally,
we obtain semi-analytic solutions for the statistical moments of the head and the
specific discharge beneath the free surface. Statistical moments are derived using a
first-order approximation and then compared with their counterpart in an unbounded
medium. The effect of anisotropy and angle of mean uniform flow on the statistical
moments is analysed. The solutions can be used for solving more complex flows,
slowly varying in the mean.
Particle pressures generated around bubbles in
gas-fluidized beds
Authors: RAHMAN KHURRAM , CAMPBELL CHARLES S.
Published: October 2003

The particle pressure is the surface force in a particle/fluid mixture that is exerted
solely by the particle phase. This paper presents measurements of the particle
pressure on the faces of a two-dimensional gas-fluidized bed and gives insight into the
mechanisms by which bubbles generate particle pressure. The particle pressure is
measured by a specially designed ‘particle pressure transducer’. The results show that,
around single bubbles, the most significant particle pressures are generated below
and to the sides of the bubble and that these particle pressures steadily increase and
reach a maximum value at bubble eruption. The dominant mechanism appears to be
defluidization of material in the particle phase that results from the bubble attracting
fluidizing gas away from the surrounding material; the surrounding material is no
longer supported by the gas flow and can only be supported across interparticle
contacts which results in the observed particle pressures. The contribution of particle
motion to particle pressure generation is insignificant.

The magnitude of the particle pressure below a single bubble in a gas-fluidized
bed depends on the bubble size and the density of the solid particles, as might be
expected as the amount of gas attracted by the bubble should increase with bubble
size and because the weight of defluidized material depends on the density of the
solid material. A simple scaling of these quantities is suggested that is otherwise
independent of the bed material.

In freely bubbling gas-fluidized beds the particle pressures generated behave
differently. Overall they are smaller in magnitude and reach their maximum value soon
after the bubble passes instead of at eruption. In this situation, it appears that the
bubbles interact with one another in such a way that the de uidization effect below a
leading bubble is largely counteracted by refluidizing gas exiting the roof of trailing
bubbles.
The formation of shear and density layers
in stably stratified turbulent flows:
linear processes
Authors: GALMICHE M. , HUNT J. C. R.
Published: October 2003

The initial evolution of the momentum and buoyancy fluxes in a freely decaying,
stably stratified homogeneous turbulent flow with r.m.s. velocity u′0 and integral
lengthscale l0 is calculated using a weakly inhomogeneous and unsteady form of the
rapid distortion theory (RDT) in order to study the growth of small temporal and
spatial perturbations in the large-scale mean stratification N(z, t) and mean velocity
profile ū(z, t) (here N is the local Brunt–Väisälä frequency and ū is the local velocity
of the horizontal mean flow) when the ratio of buoyancy forces to inertial forces is
large, i.e. Nl0/u′0[Gt ]1. The lengthscale L of the perturbations in the mean profiles of
stratification and shear is assumed to be large compared to l0 and the presence of a
uniform background mean shear can be taken into account in the model provided
that the inertial shear forces are still weaker than the buoyancy forces, i.e. when the
Richardson number Ri = (N/∂zū)2[Gt ]1 at each height.

When a mean shear perturbation is introduced initially with no uniform background
mean shear and uniform stratification, the analysis shows that the perturbations in the
mean flow profile grow on a timescale of order N-1. When the mean density profile is
perturbed initially in the absence of a background mean shear, layers with significant
density gradient fluctuations grow on a timescale of order N−10 (where N0 is the order
of magnitude of the initial Brunt–Väisälä frequency) without any associated mean
velocity gradients in the layers. These results are in good agreement with the direct
numerical simulations performed by Galmiche et al. (2002) and are consistent with the
earlier physically based conjectures made by Phillips (1972) and Posmentier (1977).
The model also shows that when there is a background mean shear in combination
with perturbations in the mean stratification, negative shear stresses develop which
cause the mean velocity gradient to grow in the density layers. The linear analysis for
short times indicates that the scale on which the mean perturbations grow fastest is
of order u′0/N0, which is consistent with the experiments of Park et al. (1994).

We conclude that linear mechanisms are widely involved in the formation of shear
and density layers in stratified flows as is observed in some laboratory experiments
and geophysical flows, but note that the layers are also significantly influenced by
nonlinear and dissipative processes at large times.
Three-dimensional flow structures and vorticity
control in fish-like swimming
Authors: ZHU Q. , WOLFGANG M. J. , YUE D. K. P. , TRIANTAFYLLOU M. S.
Published: October 2003

We employ a three-dimensional, nonlinear inviscid numerical method, in conjunction
with experimental data from live fish and from a fish-like robotic mechanism, to
establish the three-dimensional features of the flow around a fish-like body swimming
in a straight line, and to identify the principal mechanisms of vorticity control
employed in fish-like swimming. The computations contain no structural model for
the fish and hence no recoil correction. First, we show the near-body flow structure
produced by the travelling-wave undulations of the bodies of a tuna and a giant
danio. As revealed in cross-sectional planes, for tuna the flow contains dominant
features resembling the flow around a two-dimensional oscillating plate over most
of the length of the fish body. For the giant danio, on the other hand, a mixed
longitudinal–transverse structure appears along the hind part of the body. We also
investigate the interaction of the body-generated vortices with the oscillating caudal
fin and with tail-generated vorticity. Two distinct vorticity interaction modes are
identified: the first mode results in high thrust and is generated by constructive
pairing of body-generated vorticity with same-sign tail-generated vorticity, resulting
in the formation of a strong thrust wake; the second corresponds to high propulsive
efficiency and is generated by destructive pairing of body-generated vorticity with
opposite-sign tail-generated vorticity, resulting in the formation of a weak thrust
wake.
Particle image velocimetry investigation of a turbulent boundary layer manipulated by spanwise wall oscillations
Authors: DI CICCA GAETANO MARIA , IUSO GAETANO , SPAZZINI PIER GIORGIO , ONORATO MICHELE
Published: October 2003

Particle image velocimetry has been applied to the study of a canonical turbulent
boundary layer and to a turbulent boundary layer forced by transversal wall oscillations.
This work is part of the research programme at the Politecnico di Torino
aerodynamic laboratory with the objective of investigating the response of near-wall
turbulence to external perturbations. Results are presented for the optimum oscillation
period of 100 viscous time units and for an oscillation amplitude of 320 viscous
units. As expected, turbulent velocity fluctuations are considerably reduced by the
wall oscillations. Particle image velocimetry has allowed comparisons between the
canonical and forced flows in an attempt to find the physical mechanisms by which
the wall oscillation influences the near-wall organized motions.
High-Rayleigh-number convection of pressurized
gases in a horizontal enclosure
Authors: FLEISCHER A. S. , GOLDSTEIN R. J.
Published: October 2003

High-pressure gases are used to study high-Rayleigh-number Rayleigh–Bénard
convection in cylindrical horizontal enclosures. The Nusselt–Rayleigh heat transfer
relationship is investigated for 1×109 < Ra < 1.7×1012. Schlieren video images of
the flow field are recorded through optical viewports in the pressure vessel. The data
set is well correlated by Nu = 0.071Ra0.328. The schlieren results confirm the existence
of a large-scale flow that periodically interrupts the ascending and descending plumes.
The intensity of both the plumes and the large-scale flow increases with Rayleigh
number.
Axisymmetric acoustic scattering by vortices
Authors: HATTORI Y. , LLEWELLYN SMITH STEFAN G.
Published: October 2003

The scattering of acoustic waves by compact three-dimensional axisymmetric vortices
is studied using direct numerical simulation in the case where the incoming wave is
aligned with the symmetry axis and the direction of propagation of the vortices. The
cases of scattering by Hill’s spherical vortex and Gaussian vortex rings are examined,
and results are compared with predictions obtained by matched asymptotic expansions
and the Born approximation. Good agreement is obtained for long waves, with the
Born approximation usually giving better predictions, especially as the difference in
scale between vortex and incoming waves decreases and as the Mach number of the
flow increases. An improved version of the Born approximation which takes into
account higher-order effects in Mach number gives the best agreement.
Sound radiation in turbulent channel flows
Authors: HU ZHIWEI , MORFEY CHRISTOPHER L. , SANDHAM NEIL D.
Published: October 2003

Lighthill’s acoustic analogy is formulated for turbulent channel flow with pressure
as the acoustic variable, and integrated over the channel width to produce a two-dimensional
inhomogeneous wave equation. The equivalent sources consist of a
dipole distribution related to the sum of the viscous shear stresses on the two
walls, together with monopole and quadrupole distributions related to the unsteady
turbulent dissipation and Reynolds stresses respectively. Using a rigid-boundary Green
function, an expression is found for the power spectrum of the far-field pressure
radiated per unit channel area. Direct numerical simulations (DNS) of turbulent plane
Poiseuille and Couette flow have been performed in large computational domains in
order to obtain good resolution of the low-wavenumber source behaviour. Analysis
of the DNS databases for all sound radiation sources shows that their wavenumber–frequency
spectra have non-zero limits at low wavenumber. The sound power per
unit channel area radiated by the dipole distribution is proportional to Mach number
squared, while the monopole and quadrupole contributions are proportional to the
fourth power of Mach number. Below a particular Mach number determined by the
frequency and radiation direction, the dipole radiation due to the wall shear stress
dominates the far field. The quadrupole takes over at Mach numbers above about
0.1, while the monopole is always the smallest term. The resultant acoustic field at
any point in the channel consists of a statistically diffuse assembly of plane waves,
with spectrum limited by damping to a value that is independent of Mach number
in the low-M limit.
Spatio-temporal dynamics of a periodically driven cavity flow
Authors: VOGEL M. J. , HIRSA A. H. , LOPEZ J. M.
Published: October 2003

The flow in a rectangular cavity driven by the sinusoidal motion of the floor in its own plane has been studied both experimentally and computationally over a broad range of parameters. The stability limits of the time-periodic two-dimensional base state are of primary interest in the present study, as it is within these limits that the flow can be used as a viable surface viscometer (as outlined theoretically in Lopez & Hirsa 2001). Three flow regimes have been found experimentally in the parameter space considered: an essentially two-dimensional time-periodic flow, a time-periodic three-dimensional flow with a cellular structure in the spanwise direction, and a three-dimensional irregular (in both space and time) flow. The system poses a space–time symmetry that consists of a reflection about the vertical mid-plane together with a half-period translation in time (RT symmetry); the two-dimensional base state is invariant to this symmetry. Computations of the two-dimensional Navier–Stokes equations agree with experimentally measured velocity and vorticity to within experimental uncertainty in parameter regimes where the flow is essentially uniform in the spanwise direction, indicating that in this cavity with large spanwise aspect ratio, endwall effects are small and localized for these cases. Two classes of flows have been investigated, one with a rigid no-slip top and the other with a free surface. The basic states of these two cases are quite similar, but the free-surface case breaks RT symmetry at lower forcing amplitudes, and the structure of the three-dimensional states also differs significantly between the two classes.
On the streamwise evolution of turbulent
boundary layers in arbitrary pressure gradients
Authors: PERRY A. E. , MARUSIC IVAN , JONES M. B.
Published: October 2003

A new approach to the classic closure problem for turbulent boundary layers is
presented. This involves, first, using the well-known mean-flow scaling laws such as
the log law of the wall and the law of the wake of Coles (1956) together with the
mean continuity and the mean momentum differential and integral equations. The
important parameters governing the flow in the general non-equilibrium case are
identified and are used for establishing a framework for closure. Initially closure
is achieved here empirically and the potential for achieving closure in the future
using the wall-wake attached eddy model of Perry & Marusic (1995) is outlined.
Comparisons are made with experiments covering adverse-pressure-gradient flows in
relaxing and developing states and flows approaching equilibrium sink flow. Mean
velocity profiles, total shear stress and Reynolds stress profiles can be computed for
different streamwise stations, given an initial upstream mean velocity profile and the
streamwise variation of free-stream velocity. The attached eddy model of Perry &
Marusic (1995) can then be utilized, with some refinement, to compute the remaining
unknown quantities such as Reynolds normal stresses and associated spectra and
cross-power spectra in the fully turbulent part of the flow.
Scattering of oblique waves in a two-layer fluid
Authors: LINTON C. M. , CADBY J. R.
Published: October 2003

We consider problems based on linear water wave theory concerning the interaction
of oblique waves with horizontal cylinders in a fluid consisting of a layer of finite
depth bounded above by a free surface and below by an infinite layer of fluid of
greater density. For such a situation time-harmonic waves can propagate with two
different wavenumbers K and k. The particular problems of wave scattering by
a horizontal circular cylinder in either the upper or lower layer are solved using
multipole expansions.
Multiple-arrayed pressure measurement for
investigation of the unsteady flow structure of a
reattaching shear layer
Authors: LEE INWON , SUNG HYUNG JIN
Published: October 2003

Spatio-temporal characteristics of wall pressure fluctuations in separated and
reattaching flows over a backward-facing step were investigated through an extensive
pressure-velocity joint measurement with an array of microphones. The experiment
was performed in a wind tunnel with a Reynolds number of 33 000 based on the step
height and the free-stream velocity. Synchronized wavelet maps showed the evolutionary
behaviour of pressure fluctuations and gave further insight into the modulated
nature of large-scale vortical structures. To see the relationship between the flow field
and the relevant spatial mode of the pressure field, a new kind of wavenumber filtering,
termed ‘spatial box filtering’ (SBF), was introduced and examined. The vortical
flow field was reconstructed using every single-point velocity measurement by means
of the conditional average based on the SBF second mode of pressure fluctuations.
The flow field showed a well-organized spanwise vortical structure convected with
a speed of 0.6U0 and a characteristic ‘sawtooth’ pattern of the unsteady trace of
reattachment length. In addition to the coherent vortical structures, the periodic
enlargement/shrinkage process of the recirculation region owing to apping motion was
analysed. The recirculation region was found to undergo an enlargement/shrinkage
cycle in accordance with the lowpass-filtered component of pressure fluctuations. In
addition, such modulatory behaviour of the vortical structure as the global oscillation
phase was discussed in connection with the conditionally averaged flow field.
Solution for jump conditions at fast shocks in an anisotropic magnetized plasma
Authors: ERKAEV N. V. , VOGL D. F. , BIERNAT H. K.
Published: October 2003

We study the magnetic field and plasma parameters downstream of a
fast shock as functions of normalized upstream parameters and the rate of pressure
anisotropy (defined as the ratio of perpendicular to parallel pressure). We analyse
two cases: with the shock (i) perpendicular and (ii) inclined with respect to the
magnetic field. The relations on the fast shock in a magnetized anisotropic plasma
are solved taking into account the criteria for the mirror instability and firehose
instability bounding the pressure anisotropy downstream of the shock. Our analysis
shows that the parallel pressure and the parallel temperature as well as the
tangential component of the velocity are the parameters that are most sensitive to the
rate of pressure anisotropy. The variations of the other parameters, namely density,
normal velocity, tangential component of the magnetic field, perpendicular
pressure, and perpendicular temperature are much less pronounced, in particular when
the perpendicular pressure exceeds the parallel pressure. The variations of all
parameters increase substantially for a very low rate of anisotropy, which is bounded
by the firehose instability in the case of inclined shocks. Using the criterion for
mirror instability as a closure relation for the jump conditions at the fast shock, we
obtain the plasma parameters and the magnetic field downstream of the shock as
functions of the Alfvén Mach number. For each Alfvén Mach number, the criterion
for mirror instability determines the minimum jumps in such parameters as
density, tangential magnetic field component, parallel pressure, and temperature, and
determines the maximum values of the velocity components and the perpendicular
temperature. Ideal anisotropic magnetohydrodynamics (MHD) has wide
applications for space plasma physics. Observations of the field and plasma behaviour in
the solar wind as well as in the Earth's magnetosheath have highlighted the need
for an MHD model where the plasma pressure is treated as a tensor.
DNLS equation for large-amplitude solitons
propagating in an arbitrary direction in a
high-β Hall plasma
Authors: RUDERMAN MICHAEL S.
Published: October 2003

The one-dimensional oblique propagation of magnetohydrodynamic
waves with arbitrary amplitudes in a Hall plasma with isotropic pressure is studied
under assumption that the plasma β is large. It is shown that the wave evolution
is described by the derivative nonlinear Schrödinger equation (DNLS).
Stimulated scattering of electromagnetic waves in a two-electron plasma
Authors: SHUKLA P. K. , HELLBERG M. A.
Published: October 2003

The nonlinear interaction between large-amplitude electromagnetic
waves and electron-acoustic (EA) waves in a two-electron-temperature plasma is
considered, taking into account the combined effects of the radiation pressure and
the thermal force involving the differential Joule heating of the electrons caused
by the electromagnetic waves. By employing a fluid approach, we derive a system
of coupled equations for the electromagnetic waves and the EA waves; the latter
are nonlinearly driven by the radiation and thermal forces. We have carried out
a normal mode analysis of our nonlinearly coupled equations, and have derived a
general dispersion relation that is useful for studying different types of parametric
instabilities. A new class of modulational instability in the collision-dominated
regime is identified. The implications for space and laboratory plasmas are pointed
out.
Higher-order growth rate of instability of obliquely propagating kinetic Alfvén and ion-acoustic solitons in a magnetized non-thermal plasma
Authors: BANDYOPADHYAY ANUP , DAS K. P.
Published: October 2003

The higher-order growth rate of instability for obliquely propagating kinetic Alfvén and ion-acoustic solitons in a magnetized non-thermal plasma have been obtained by the multiple-scale perturbation expansion method developed by Allen and Rowlands (1993). The growth rate of instability is obtained correct to order k2, where k is the wave number of a long-wavelength plane-wave perturbation. The corresponding lowest-order stability analysis has been considered recently by Bandyopadhyay and Das (2000b). It has been found that the kinetic Alfvén solitary waves are stable at the order of k but are unstable at the order of k2. It has also been found that the growth rate of instability at the order of k for ion-acoustic solitary waves is free from the parameters of the non-thermal plasma but at the order of k2 depends on the parameters of the non-thermal plasma.