bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite-wavelength instability in a horizontal

liquid layer on an oscillating plane
Authors: OR A. C.
Published: July 2002

The linear stability of a thin liquid layer bounded from above
by a free

surface and from below by an oscillating plate is investigated for disturbances

of arbitrary wavenumbers, a range of imposed frequencies and selective
physical

parameters. The imposed motion of the lower wall occurs in its own plane
and is

unidirectional and time-periodic. Long-wave instabilities occur only over
certain

bandwidths of the imposed frequency, as determined by a long-wavelength
expansion.

A fully numerical method based on Floquet theory is used to investigate
solutions

with arbitrary wavenumbers, and a new free-surface instability is found
that has

a finite preferred wavelength. This instability occurs continuously once
the

imposed frequency exceeds a certain threshold. The neutral curves of this
new

finite-wavelength instability appear significantly more complex than those
for

long waves. In a certain parameter regime, folds occur in the finite-wavelength

stability limit, giving rise to isolated unstable regions. Only synchronous

solutions are found, i.e. subharmonic solutions have not been detected.
In

Appendix A, we provide an argument for the non-existence of subharmonic

solutions.
A global investigation of solitary-wave solutions

to a two-parameter model for water waves
Authors: CHAMPNEYS ALAN R. , GROVES MARK D.
Published: July 2002

The model equation

formula here

arises as the equation for solitary-wave solutions to a fifth-order

long-wave equation

for gravity–capillary water waves. Being Hamiltonian, reversible
and depending

upon two parameters, it shares the structure of the full steady water-wave
problem.

Moreover, all known analytical results for local bifurcations of

solitary-wave solutions

to the full water-wave problem have precise counterparts for the model
equation.

At the time of writing two major open problems for steady water waves
are

attracting particular attention. The first concerns the possible

existence of solitary

waves of elevation as local bifurcation phenomena in a particular parameter
regime;

the second, larger, issue is the determination of the global bifurcation
picture for

solitary waves. Given that the above equation is a good model for solitary
waves

of depression, it seems natural to study the above issues

for this equation; they are comprehensively treated in this article.

The equation is found to have branches of solitary waves of elevation
bifurcating

from the trivial solution in the appropriate parameter regime,

one of which is described

by an explicit solution. Numerical and analytical investigations

reveal a rich global

bifurcation picture including multi-modal solitary waves of elevation

and depression together with interactions between the two types of wave.
There

are also new orbit-flip

bifurcations and associated multi-crested solitary waves with non-oscillatory
tails.
On the extinction limit and flammability limit of
non-adiabatic stretched methane–air premixed flames
Authors: JU YIGUANG , GUO HONGSHENG , MARUTA KAORU , LIU FENGSHAN
Published: July 2002

Extinction limits and the lean flammability limit of
non-adiabatic stretched premixed
methane–air flames are investigated numerically with detailed chemistry and two
different Planck mean absorption coefficient models. Attention is paid to
the combined
effect of radiative heat loss and stretch at low stretch rate. It
is found that for a
mixture at an equivalence ratio lower than the standard lean flammability limit, a
moderate stretch can strengthen the combustion and allow burning. The flame is
extinguished at a high stretch rate due to stretch and is quenched at a
low stretch rate
due to radiation loss. A O-shaped curve of flame temperature versus stretch rate with
two distinct extinction limits, a radiation extinction limit and
a stretch extinction limit
respectively on the left- and right-hand sides, is obtained. A C-shaped curve showing
the flammability limit of the stretched methane–air flame
is obtained by plotting these
two extinction limits in the mixture strength coordinate. A good agreement is shown
on comparing the predicted results with the experimental data. For equivalence ratio
larger than a critical value, it is found that the O-shaped
temperature curve opens up
in the middle of the stable branch, so that the stable branch divides into two stable
flame branches; a weak flame branch and a normal flame branch. The weak flame
can survive between the radiation extinction limit and the opening point (jump limit)
while the normal flame branch can survive from its stretch extinction limit to zero
stretch rate. Finally, a G-shaped curve showing both extinction limits and jump limits
of stretched methane–air flames is presented. It is found
that the critical equivalence
ratio for opening up corresponds to the standard flammability limit measured in
microgravity. Furthermore, the results show that the flammability
limit (inferior limit)
of the stretched methane–air flame is lower than the standard
flammability limit
because flames are strengthened by a moderate stretch at Lewis number less than unity.
The vorticity jump across a shock in a non-uniform flow
Authors: KEVLAHAN N. K.-R.
Published: July 2002

The vorticity jump across an unsteady curved shock propagating
into a

two-dimensional non-uniform flow is considered in detail. The exact

general expression for the

vorticity jump across a shock is derived from the gasdynamics equations.
This general

expression is then simplified by writing it entirely in terms of the Mach
number of

the shock MS and the local Mach number of
the

flow ahead of the shock MU.

The vorticity jump is very large at places where the curvature of the
shock is

very large, even in the case of weak shocks. Vortex sheets form behind
shock-shocks

(associated with kinks in the shock front).

The ratio of vorticity production by shock curvature to vorticity production
by

baroclinic effects is

O(½(γ−1)M2U),

where γ is ratio of specific heats, which is very small if the flow
ahead of

the shock is only weakly compressible. If, however, the

tangential gradient along the shock of M2U

is large then baroclinic production is

significant; this is the case in turbulent flows with large gradients of

turbulent kinetic energy ½M2U.

The vorticity jump across a weak shock decreases in proportion to shock

intensity if the flow ahead of the shock is rotational, rather than in
proportion to

the cube of shock intensity as is often assumed, and thus is not negligible.

It is also

shown that vorticity may be generated across a straight shock even if the
flow ahead

of the shock is irrotational. The importance of the

contribution to the vorticity jump

by non-uniformities in the flow ahead of the shock has not been recognized
in the

past.

Examples are given of the vorticity jump across strong and weak

shocks in a variety of flows exhibiting some properties of turbulence.
Numerical modelling of Coulomb-driven convection in insulating liquids
Authors: CHICÓN R. , CASTELLANOS A. , MARTIN E.
Published: July 2002

Electroconvection in a layer of liquid subjected to unipolar

injection is characterized

by two stability criteria, a linear and a nonlinear one, with an

associated hysteresis

loop. Experimentally it is found that the velocity field fluctuates

around its mean value.

A temporal analysis of the measured current, which is directly related

to the velocity,

revealed the existence of a well-defined frequency correlated to the

mean rotation time

of a fluid particle in the convective cell, thus indicating

that these fluctuations are not

stochastic but related to the intrinsic dynamics of the system. Here a
method of

superparticles is used to solve the problem of the non-stationary

electroconvection of

the liquid. A good agreement between theoretical and experimental

results is obtained.
Centreline velocity decay measurements in

low-velocity axisymmetric jets
Authors: MALMSTRÖM TOR G. , KIRKPATRICK ALLAN T. , CHRISTENSEN BRIAN , KNAPPMILLER KEVIN D.
Published: July 2002

The streamwise velocity profiles of low-velocity isothermal

axisymmetric jets from

nozzles of different diameters were measured and compared with previous
experimental

data. The objective of the measurements was to examine the dependence of
the

diffusion of the jet on the outlet conditions. As the outlet velocity was

decreased, the

centreline velocity decay coefficient began to decrease at an outlet

velocity of about 6 m s−1.
Self-diffusion in granular shear flows
Authors: CAMPBELL CHARLES S.
Published: July 2002

The collisionally induced random particle velocities in
a rapid granular shear flow drive
the diffusion of particles in manner directly analogous to the thermal
diffusion of
molecules or the eddy-induced diffusion in a turbulent flow. This paper
reports
measurements, via computer simulation, of the anisotropic diffusion tensor
for a
granular shear flow. The components are determined both by particle tracking
and
through velocity correlations, which are found to agree with reasonable
accuracy. As
might be expected from symmetry arguments, there are four non-zero components
generated in a simple shear flow: the three diagonal components and one
off-diagonal
component.
The spin-up of liquid metal driven by a rotating magnetic field
Authors: UNGARISH MARIUS
Published: July 2002

The paper considers the flow field during spin-up from

rest of liquid metal in

a cylindrical stationary cavity due to a rotating transverse uniform low-frequency

magnetic field. It is assumed that the Ekman and the magnetic Reynolds
numbers are

small. An approximate model, based on matching of Bödewadt-type layers
with an

inviscid core, with possible influence from the sidewall,

for laminar flow is developed.

It is shown that the angular velocity in the core is a function

of time only. Analytical

solutions for the angular velocity and the meridional flow in the core
are presented,

and supplemented by finite-difference results to show the sidewall

effects. The spin-down following the switch-off of the magnetic

forcing, the influence of the axial

variations of the magnetic field, and the relevance to turbulent flows
are discussed.
Subgrid-scale stresses and their modelling in a

turbulent plane wake
Authors: O'NEIL JOHN , MENEVEAU CHARLES
Published: July 2002

Velocity measurements using hot wires are performed across a

high-Reynolds-number

turbulent plane wake, with the aim of studying the subgrid-scale (SGS)
stress and

its modelling. This quantity is needed to close the filtered

Navier–Stokes equations

used for large-eddy simulation (LES) of turbulent flows. Comparisons of
various

globally time-averaged quantities involving the measured and modelled SGS
stress

are made, with special emphasis on the SGS energy dissipation rate. Experimental

constraints require the analysis of a one-dimensional surrogate

of the SGS dissipation.

Broadly, the globally averaged results show that all models considered,
namely the

Smagorinsky and similarity models, as well as the dynamic Smagorinsky model,

approximately reproduce profiles of the surrogate SGS

dissipation. Some discrepancies

near the outer edge of the wake are observed, where the Smagorinsky model
slightly

overpredicts, and the similarity model underpredicts, energy dissipation
unless the

filtering scale is about two orders of magnitude smaller than the integral

length scale.

A more detailed comparison between real and modelled SGS stresses is
achieved

by conditional averaging based on particular physical phenomena: (i) the
outer

intermittency of the wake, and (ii) large-scale coherent structures of
the turbulent

wake. Thus, the interaction of the subgrid scales with the resolved flow
and model

viability can be individually tested in regions where isolated mechanisms

such as outer

intermittency, vortex stretching, rotation, etc., are dominant. Conditioning
on outer

intermittency did not help to clarify observed features of the measurements.
On the

other hand, the large-scale organized structures are found to have a strong
impact

upon the distribution of surrogate SGS energy dissipation, even at filter
scales well

inside the inertial range. The similarity model is able to capture this

result, while the

Smagorinsky model gives a more uniform (i.e. unrealistic) distribution.
Both dynamic

Smagorinsky and similarity models reproduce realistic distributions, but
only if all

filter levels are contained well inside the inertial range.
Observations of shock waves in cloud cavitation
Authors: REISMAN G. E. , WANG Y.-C. , BRENNEN C. E.
Published: July 2002

This paper describes an investigation of the dynamics
and acoustics of cloud cavitation, the structures which are
often formed by the periodic breakup and collapse of a
sheet or vortex cavity. This form of cavitation frequently
causes severe noise and damage, though the precise mechanism
responsible for the enhancement of these adverse
effects is not fully understood. In this paper, we investigate
the large impulsive surface
pressures generated by this type of cavitation and correlate
these with the images
from high-speed motion pictures. This reveals that several
types of propagating structures (shock waves) are formed in
a collapsing cloud and dictate the dynamics and
acoustics of collapse. One type of shock wave structure is
associated with the coherent
collapse of a well-defined and separate cloud when it is
convected into a region of
higher pressure. This type of global structure causes the
largest impulsive pressures
and radiated noise. But two other types of structure,
termed ‘crescent-shaped regions’
and ‘leading-edge structures’ occur during
the less-coherent collapse of clouds. These
local events are smaller and therefore produce less
radiated noise but the interior
pressure pulse magnitudes are almost as large as those
produced by the global events.

The ubiquity and severity of these propagating shock
wave structures provides a
new perspective on the mechanisms reponsible for noise
and damage in cavitating
flows involving clouds of bubbles. It would appear that
shock wave dynamics rather
than the collapse dynamics of single bubbles determine the
damage and noise in many cavitating flows.
Particle motion in resonance tubes
Authors: GOLDSHTEIN A. , SHUSTER K. , VAINSHTEIN P. , FICHMAN M. , GUTFINGER C.
Published: July 2002

Small particle motions in standing or travelling acoustic waves
are well known and
extensively studied. Particle motion in weak shock waves has been studied
much less,
especially particle motion in periodic weak shock waves which as yet has
not been dealt
with.

The present study considers small particle motions caused by weak periodic
shock
waves in resonance tubes filled with air. A simple mathematical model is
developed for
resonance gas oscillations under the influence of a vibrating piston with
a finite
amplitude at the first acoustic resonance frequency. It is shown that a
symmetrical
sinusoidal piston motion generates non-symmetric periodic shock waves.
A model of
particle motion in such a flow field is suggested. It is found that non-symmetric
shock
waves cause particle drift from the middle cross-section toward the ends
of the
resonance tube. The velocity of particle drift is found to be of the order
of
Dpρp/
Trρg,
where Dp is the particle diameter,
Tr the period of
the resonance oscillation, ρp and
ρg are the particle and gas density, respectively.

At the same time, the velocity drift
strongly depends on the ratio τ/Tr,
where
τ is the particle relaxation time. Particle drift
is vigorous when τ/Tr∼1 and
insignificant when τ/Tr 1. Theoretical
predictions of
particle drift in resonance tubes are verified numerically as well as experimentally.

When the particle relaxation time is much smaller than period of the
resonance
oscillations particles perform oscillations around their equilibrium positions
with
amplitude of the order of
Dpρp/ρg.

It is shown that the difference in oscillation
amplitude of particle of difference sizes explains coalescence of aerosol
droplets
observed in experiments of Temkin (1970).

The importance of the phenomena for particle separation, coagulation
and transport
processes is discussed.
Laminar–turbulent transition in pipe flow for
Newtonian and non-Newtonian fluids
Authors: DRAAD A. A. , KUIKEN G. D. C. , NIEUWSTADT F. T. M.
Published: July 2002

A cylindrical pipe facility with a length of 32 m and a diameter
of 40 mm has been designed. The natural transition Reynolds number, i.e. the Reynolds number at which transition occurs as a result of non-forced, natural disturbances, is approximately

60 000. In this facility we have studied the stability of cylindrical pipe
flow to imposed disturbances. The disturbance consists of periodic suction and injection of fluid from a slit over the whole circumference in the pipe wall. The injection and suction are equal in magnitude and each distributed over half the circumference so
that the disturbance is divergence free. The amplitude and frequency can be varied
over a wide range.

First, we consider a Newtonian fluid, water in our case. From the observations we compute the critical disturbance velocity, which is the smallest disturbance
at a given Reynolds number for which transition occurs. For large wavenumbers, i.e.
large frequencies, the dimensionless critical disturbance velocity scales according to
Re−1, while for small wavenumbers, i.e. small frequencies, it scales as Re−2/3. The latter is in agreement with weak nonlinear stability theory. For Reynolds numbers
above 30 000 multiple transition points are found which means that increasing the
disturbance velocity at constant dimensionless wavenumber leads to the following
course of events. First, the flow changes from laminar to turbulent at the critical
disturbance velocity; subsequently at a higher value of the disturbance it returns back
to laminar and at still larger disturbance velocities the flow again becomes turbulent.

Secondly, we have carried out stability measurements for (non-Newtonian)
dilute polymer solutions. The results show that the polymers reduce in general the natural transition Reynolds number. The cause of this reduction remains unclear, but a possible explanation may be related to a destabilizing effect of the elasticity on the
developing boundary layers in the entry region of the flow. At the same time the
polymers have a stabilizing effect with respect to the forced disturbances, namely
the critical disturbance velocity for the polymer solutions is larger than for water. The stabilization is stronger for fresh polymer solutions and it is also larger when the polymers adopt a more extended conformation. A delay in transition has been only found for extended fresh polymers where delay means an increase of the critical Reynolds number, i.e. the number below which the flow remains laminar at any imposed disturbance.
On a turbulent wall jet flowing over a circular cylinder
Authors: NEUENDORF R. , WYGNANSKI I.
Published: July 2002

The effect of surface curvature on the development of a two-dimensional
wall jet
was investigated experimentally. A comparison was made between a wall jet
flowing
around a circular cylinder and its plane equivalent. Velocity surveys and
surface
pressure measurements in the curved wall jet suggest the existence of two
primary
regions of interest. The first region, ranging from the end of the potential
core to
an approximate angular position of θ=120°, is characterized by
a constant surface
pressure and a self similarity of the mean flow. The second region is marked
by an
adverse pressure gradient leading to separation around θ=230°.
The rate of spread
of this flow, even in the initial region, is much higher than in the plane
wall jet and
so are the levels of turbulence and Reynolds stress. The dominant lengthscale
in this
flow is the radius of curvature R and the dominant velocity scale
is the square root
of the kinematic jet momentum divided by the radius of curvature. Entrainment
of
ambient fluid which causes the jet to adhere to the curved surface is also
the main
reason for its separation which is preceded by a rapid rate of spread of
the flow
leading to the failure of the boundary-layer approximation.
Experiments on a barotropic rotating shear
layer. Part 1. Instability and steady vortices
Authors: FRÜH WOLF-GERRIT , READ PETER L.
Published: July 2002

The barotropic shear layer in a rotating fluid is studied in a
laboratory experiment.
Through the rotation of circular sections in the base and lid of a circular
tank relative
to a background rotation of the entire system, a vertical layer of strong
horizontal
shear develops, the Stewartson layer. Above a critical shear, the shear
layer breaks up
through barotropic instability, which is an inertial instability. The flow
then develops
a string of vortices along the shear zone. It will be shown that the transition
from an
axisymmetric flow to regular vortices occurs through a Hopf bifurcation.
Subsequent
transitions to more complex flows, such as modulated vortices, chaos and
highly
irregular flow, will be presented briefly, while the main points of this
paper are the
primary instability, steady vortices and their nonlinear dynamics. Among
the issues
discussed is the sensitivity of the flow to the direction of the differential
shear. The
experimental data will be used to test the ability of boundary layer theory
and
quasi-geostrophic theory to predict the onset of instability and the range
of unstable
wavenumbers.
Richtmyer–Meshkov instability growth:
experiment, simulation and theory
Authors: HOLMES RICHARD L. , DIMONTE GUY , FRYXELL BRUCE , GITTINGS MICHAEL L. , GROVE JOHN W. , SCHNEIDER MARILYN , SHARP DAVID H. , VELIKOVICH ALEXANDER L. , WEAVER ROBERT P. , ZHANG QIANG
Published: July 2002

Richtmyer–Meshkov instability is investigated for negative Atwood number and
two-dimensional sinusoidal perturbations by comparing experiments, numerical simulations
and analytic theories. The experiments were conducted on the NOVA laser
with strong radiatively driven shocks with Mach numbers greater than 10. Three
different hydrodynamics codes (RAGE, PROMETHEUS and FronTier) reproduce
the amplitude evolution and the gross features in the experiment while the fine-scale
features differ in the different numerical techniques. Linearized theories correctly calculate
the growth rates at small amplitude and early time, but fail at large amplitude
and late time. A nonlinear theory using asymptotic matching between the linear theory
and a potential flow model shows much better agreement with the late-time and
large-amplitude growth rates found in the experiments and simulations. We vary the
incident shock strength and initial perturbation amplitude to study the behaviour of
the simulations and theory and to study the effects of compression and nonlinearity.
G. K. Batchelor. Founding editor of the Journal of Fluid Mechanics
Authors: Crighton D. G.
Published: July 2002

Although developments in fluid mechanics continue at a heady pace, and are reported
in JFM at about 800 pages per month, things in the editorial management of JFM
change only slowly. There is a continuity among the JFM Editorial Team and among
the policies they espouse and implement that appears to be appreciated by the fluid
mechanics community. A major change has, however, occurred from January 1999, in
that George Batchelor has, after 43 years as Editor, stepped down from the day-to-day
handling of papers and from the formulation of policies and practices, and allowed
himself to be named on our masthead as Founding Editor. I say ‘allowed’ because
George's initial wish was not to be so named, feeling that this might be seen as an
immodest and presumptuous title. But Founding Editor is exactly what George was
and is. He launched JFM in May 1956, having persuaded Taylor & Francis to be the
publisher and printer, and having enlisted the help of G. F. Carrier, W. C. Griffith
and M. J. Lighthill as Associate Editors, and T. Brooke Benjamin and I. Proudman
as Assistant Editors. Then, as now, all members of the JFM Editorial Team were to
work autonomously in the handling of papers, with complete delegated authority and
similar workloads, but all following similar procedures and with similar philosophies,
and all under the watchful eye of G. K. B.
Kinetic theory of simple granular shear flows of
smooth hard spheres
Authors: MONTANERO J. M. , GARZÓ V. , SANTOS A. , BREY J. J.
Published: July 2002

Steady simple shear flows of smooth inelastic spheres are studied by means of a
model kinetic equation and also of a direct Monte Carlo simulation method. Both
approaches are based on the Enskog equation and provide for each other a test of
consistency. The dependence of the granular temperature and of the shear and normal
stresses on both the solid fraction and the coefficient of restitution is analysed. Quite a
good agreement is found between theory and simulations in all cases. Also, simplified
expressions based on the analytical solution of the model for small dissipation are
shown to describe fairly well the simulation results even for not small inelasticity. A
critical comparison with previous theories is carried out.
Second-order water wave diffraction by
an array of vertical cylinders
Authors: MALENICA š. , TAYLOR R. EATOCK , HUANG J. B.
Published: July 2002

The problem of second-order water wave diffraction of an incident monochromatic
wave field by an array of bottom-mounted circular cylinders is solved by a semi-analytical approach. The solution for the second-order potential is obtained by
combining eigenfunction expansions with an integral representation. Unlike the indirect
approach for second-order forces (Lighthill 1979; Molin 1979), this approach
gives complete information about local flow characteristics (pressure, velocities, wave
elevation, etc.) thus providing a basis for solving the third-order problem. The results
obtained are compared with other published data, and new detailed results, useful for
benchmarking purposes, are given. Finally the influences of wave incidence, cylinder
radius and cylinder configuration are considered. This leads to the suggestion that
there exists a near-trapping phenomenon for the second-order wave in an array of
cylinders, at half the wave frequency at which the corresponding linear near-trapped
mode occurs.
Buoyancy-driven convection with a uniform magnetic field.
Part 2. Experimental investigation
Authors: DAVOUST L. , COWLEY M. D. , MOREAU R. , BOLCATO R.
Published: July 2002

In this paper, an experimental study of laminar magnetohydrodynamic (MHD)
buoyancy-driven flow in a cylindrical cell with axis horizontal is described. A steady
uniform magnetic field is applied vertically to the mercury-filled cell, which is also
subjected to a horizontal temperature gradient. The main features of this internal
MHD thermogravitational flow are made experimentally evident from temperature
and electric potential measurements. Whatever the level of convection, raising the
Hartmann number Ha to a value of the order of 10 is sufficient to stabilize an
initially turbulent flow. At much higher values of the Hartmann number (Ha∼100)
the MHD effects cause a change of regime from boundary-layer driven to core
driven. In this latter regime an inviscid inertialess MHD core flow is bounded by a
Hartmann layer on the horizontal cylindrical wall and viscous layers on the endwalls.
Since the Hartmann layer is found to stay electrically inactive along the cell, the
relevant asymptotic (Ha[Gt ]1) laws for velocity and heat transfer are found from the
balance between the curl of buoyancy and Lorentz forces in the core, together with
the condition that the flow of electric current between core and Hartmann layer is
negligible. A modified Rayleigh number RaG/Ha2,
which is a measure of the ratio of thermal convection to diffusion when there is a balance
between buoyancy and Lorentz forces, is the determining parameter for the flow.
Coalescence of liquid drops
Authors: EGGERS JENS , LISTER JOHN R. , STONE HOWARD A.
Published: July 2002

When two drops of radius R touch, surface tension drives an initially singular motion
which joins them into a bigger drop with smaller surface area. This motion is always
viscously dominated at early times. We focus on the early-time behaviour of the radius
rm of the small bridge between the two drops. The flow is driven by a highly curved
meniscus of length 2πrm and width
Δ[Lt ]rm around the bridge, from which we conclude
that the leading-order problem is asymptotically equivalent to its two-dimensional
counterpart. For the case of inviscid surroundings, an exact two-dimensional solution
(Hopper 1990) shows that Δ∝r3m
and rm∼(tγ/πη) ln
[tγ(ηR)]; and thus the same
is true in three dimensions. We also study the case of coalescence with an external
viscous fluid analytically and, for the case of equal viscosities, in detail numerically.
A significantly different structure is found in which the outer-fluid forms a toroidal
bubble of radius Δ∝r3/2m
at the meniscus and rm∼(tγ/4πη) ln
[tγ/(ηR)]. This basic
difference is due to the presence of the outer-fluid viscosity, however small. With
lengths scaled by R a full description of the asymptotic flow for
rm(t)[Lt ]1 involves matching of lengthscales of order
r2m, r3/2m,
rm, 1 and probably
r7/4m.
Experimental study of the wake behind a surface-piercing cylinder for a clean and
contaminated free surface
Authors: WARNCKE LANG AMY , GHARIB MORTEZA
Published: July 2002

This experimental investigation into the nature of free-surface flows was to study the
effects of surfactants on the wake of a surface-piercing cylinder. A better understanding
of the process of vorticity generation and conversion at a free surface due to the
absence or presence of surfactants has been gained. Surfactants, or surface contaminants,
have the tendency to reduce the surface tension proportionally to the respective
concentration at the free surface. Thus when surfactant concentration varies across
a free surface, surface tension gradients occur and this results in shear stresses, thus
altering the boundary condition at the free surface. A low Reynolds number wake
behind a surface-piercing cylinder was chosen as the field of study, using digital
particle image velocimetry (DPIV) to map the velocity and vorticity field for three
orthogonal cross-sections of the flow. Reynolds numbers ranged from 350 to 460 and
the Froude number was kept below 1.0. In addition, a new technique was used to
simultaneously map the free surface deformation. Shadowgraph imaging of the free
surface was also used to gain a better understanding of the flow. It was found that,
depending on the surface condition, the connection of the shedding vortex filaments
in the wake of the cylinder was greatly altered with the propensity for surface tension
gradients to redirect the vorticity near the free surface to that of the surface-parallel
component. This result has an impact on the understanding of turbulent flows in the
vicinity of a free surface with varying surface conditions.
Steady flow separation patterns in a 45 degree junction
Authors: ETHIER C. ROSS , PRAKASH SUJATA , STEINMAN DAVID A. , LEASK RICHARD L. , COUCH GREGORY G. , OJHA M.
Published: July 2002

Numerical and experimental techniques were used to study the physics of flow
separation for steady internal flow in a 45° junction geometry, such as that observed
between two pipes or between the downstream end of a bypass graft and an artery.
The three-dimensional Navier–Stokes equations were solved using a validated finite
element code, and complementary experiments were performed using the photochromic
dye tracer technique. Inlet Reynolds numbers in the range 250 to 1650 were considered.
An adaptive mesh refinement approach was adopted to ensure grid-independent
solutions. Good agreement was observed between the numerical results and the
experimentally measured velocity fields; however, the wall shear stress agreement was less
satisfactory. Just distal to the ‘toe’ of the junction, axial flow separation was observed
for all Reynolds numbers greater than 250. Further downstream (approximately 1.3
diameters from the toe), the axial flow again separated for Re [ges ] 450. The location and
structure of axial flow separation in this geometry is controlled by secondary flows,
which at sufficiently high Re create free stagnation points on the model symmetry
plane. In fact, separation in this flow is best explained by a secondary flow boundary
layer collision model, analogous to that proposed for flow in the entry region of a
curved tube. Novel features of this flow include axial flow separation at modest Re (as
compared to flow in a curved tube, where separation occurs only at much higher Re),
and the existence and interaction of two distinct three-dimensional separation zones.
Indians, the Military and the Rebellion

of 1932 in El Salvador
Authors: CHING ERIK , TILLEY VIRGINIA
Published: July 2002

This study challenges the widely held belief that

the peasant rebellion

of 1932, and the massive military response to it, marked

the demise of Indian

ethnic identity. Working from documents that have become

available only

recently, we demonstrate that the Indian population was

not decimated by the

military repression. The percentage of Indians in the

population remained steady

and in some regions even increased. We show that the

bedrock of Indian identity,

the cofradías and the communities,

survived the repression as well. We propose

that these survivals are due, ironically, in part to the

military. Despite their

willingness to employ violence on a colossal level,

military leaders believed that

order in the countryside was to be achieved through

reform as well as repression.

The military's reformist ideology and reform

programme worked to defend

individual Indians and Indian communities from ladinos

anxious to avenge their losses in the uprising.
Definiteness in the Hebrew noun phrase
Authors: WINTNER SHULY
Published: July 2002

This paper suggests an analysis of Modern Hebrew noun phrases in the framework
of HPSG. It focuses on the peculiar properties of the definite article, including the
requirement for definiteness agreement among various elements in the noun phrase,
definiteness inheritance in construct-state nominals, the fact that the article does not
combine with constructs and the similarities between construct-state nouns and
adjectives. Central to our analysis is the assumption that the Hebrew definite article
is an affix, rather than a clitic or a stand-alone word. Several arguments, from all
levels of linguistic representation, are provided to justify this claim. Adopting the
lexical hypothesis, we conclude that the article combines with nominals in the lexicon,
and is no longer available for syntactic processes. This leads to an analysis of noun
phrases as NPs, rather than as DPs; we show that such a view is compatible with
accepted criteria for headedness. We provide an HPSG analysis that covers the above
mentioned phenomena, correctly predicting the location of the definite article in
constructs, accounting for definiteness agreement and definiteness inheritance
constraints, and yielding similar structures for the two major ways of expressing
genitive relations in Hebrew.
Spanish imperatives: syntax meets morphology
Authors: HARRIS JAMES
Published: July 2002

Contrary to Rivero & Terzi's (1995) claim that morphological
mood and logical
mood correlate one-to-one in Spanish imperatives, verbs in imperative sentences
in all
dialects of Spanish have obligatory non-imperative morphology more often
than not.
For example, the morphology of the verb in the imperative
hágalo ‘do it’ is not
imperative but subjunctive. A satisfactory account of semantic, syntactic,
and
morphological mismatches in Spanish imperatives must appeal to a Morphology

module of grammar; real explanation is beyond the reach of purely syntactic
analysis.
Taxation, coercion and donors: local government tax enforcement in Tanzania
Authors: Fjeldstad Odd-Helge
Published: July 2002

This paper presents three propositions about tax collection by local authorities in Tanzania. First, revenue performance depends on the degree of coercion involved in tax enforcement. Reciprocity does not seem to be an inherent component of the state–society relationship in connection with local government taxation. Second, the extent of coercion depends on the bargaining powers of the stakeholders involved in the tax enforcement process. In particular, coercive tax enforcement is facilitated when the ‘bargaining powers’ with respect to tax collection favour the council administration, and the elected councillors have no direct influence on collection. Third, the presence of donors in a local authority may be crucial by changing the ‘balance of power’ in favour of the council administration, with implications for accountability, responsiveness and democratic development. These results may explain why widespread differences in revenue performance between local authorities are observed.
Beyond the gold standard?: the
idea of a (post-apartheid) university
Authors: Nolutshungu Sam C.
Published: July 2002

We cannot do better than Marcello Cecco's (1984: 1) concise definition
of an international gold standard: it exists ‘when gold is the effective
numeraire in most countries, and/or when the other means of payment
used as monetary numeraire in those countries are readily redeemable
in gold at their bearers' request’. Such a standard existed from the mid-1890s to 1914, even though Britain went on the gold standard much
earlier than that, in 1816, and Germany a little over a half century
later, in 1871. The Latin Union in Europe (France, Belgium,
Switzerland and Italy) did not join effectively until 1900 (Mertens
1994). Many claims were, and are still made for the system: that it
facilitated international trade by providing a uniform standard of
value; and as an automatic adjustment system, it freed markets from
the (nationalistic) interference of public authorities while it created
price equalisation in traded goods and ensured, over a protracted
period, price stability.

The ‘Gold Standard’ in the title of this talk refers to the ‘academic
gold standard’ invoked by Lord Ashby (1964; see also Austin 1980),
one time Master of Clare College, Cambridge, a British educationist
who was deeply involved with the development of universities in the
later years of colonial rule in British West Africa. Although the
University of the Witwatersrand and the city of Johannesburg owe a
great deal to the gold industry, my talk is not about money or the
metal's place in it. It is about the metaphorical ‘academic gold
standard’.
Growth rate of instability of obliquely propagating ion-acoustic solitons in a magnetized non-thermal plasma
Authors: BANDYOPADHYAY ANUP , DAS K. P.
Published: July 2002

The Korteweg–de Vries–Zakharov–Kuznetsov (KdV–ZK) equation,
governing the behaviour of long-wavelength weakly nonlinear ion-acoustic
waves propagating obliquely to an external uniform magnetic field in a non-thermal
plasma, admits soliton solutions having a sech2 profile. The higher-order growth rates of
instability are obtained using the method developed by
Allen and Rowlands [J. Plasma Phys.50, 413 (1993); 53, 63 (1995)]. The growth
rate of instability is obtained correct to order k2, where k is the wavenumber of
a long-wavelength plane-wave perturbation. The case where the coefficient of
the nonlinear term in the KdV–ZK equation vanishes is also considered.
Geographical variations in carbon and nitrogen stable isotope ratios in squid
Authors: Takai Noriyuki , Onaka Sayaka , Ikeda Yuzuru , Yatsu Akihiko , Kidokoro Hideaki , Sakamoto Wataru
Published: July 2002

The magnitude of geographical variations of stable isotope ratios of carbon and nitrogen was examined in ten squid species captured in seven areas of the world's oceans. The average of all 139 squid was −17.4±1.4‰ for δ13C and 11.6±1.6‰ for δ15N. The δ13C of squid showed a clear-cut negative correlation with the latitude of the sampling locations, reflecting the well-known latitudinal characteristics of phytoplankton δ13C, while squid δ,15N did not correlate with the latitude significantly. The δ15N reflected the regional characteristics of nitrogen metabolism such as denitrification and N2 fixation, and it was conspicuous in the intraspecific variation in Sthenoteuthis oualaniensis ranging from 10.0±1.5‰ off Japan to 16.3±0.6‰ off Peru in the Pacific Ocean. Significant isotopic variations were also found in the local area among the five species off Japan in the Pacific Ocean and among the three species in the Japan Sea. Attention must be paid to the isotopic variations of primary producers as well as those of squid in examining the trophic positions of squid.
All three species of Ptychodactiaria belong to order Actiniaria (Cnidaria: Anthozoa)
Authors: Cappola Valerie A. , Fautin Daphne G.
Published: July 2002

Ptychodactiaria, currently recognized as an order equivalent to Actiniaria (sea anemones sensu stricto) and Scleractinia (‘true’ or hard corals) of cnidarian class Anthozoa, contains three monotypic genera, Dactylanthus, Ptychodactis, and Preactis, in two families, Ptychodactiidae and Preactiidae. Features that had been considered distinctive to the order among hexacorallian anthozoans were that gametes mature in protrusions from the mesenteries, as in octocorallian anthozoans, and that gametes do not mature embedded in mesogloea. However, we found that ptychodactiarian gametes develop in the mesenteries, surrounded by mesogloea, as in other sea anemones. We conclude that the three species constitute a clade, the most distinctive feature of which is medially fused mesenteries at the proximal end of the body. This clade merits subordinal status within order Actiniaria. We redefine Ptychodactiaria and its component taxa, moving Dactylanthus from family Ptychodactiidae to family Preactiidae.
Maturity, fecundity and reproductive potential of the European lobster (Homarus gammarus) in Ireland
Authors: Tully O. , Roantree V. , Robinson M.
Published: July 2002

Fecundity and size at maturity of the European lobster Homarus gammarus (Crustacea: Decapoda) was estimated in four coastal regions of Ireland. Egg size increased with carapace length (CL) (egg size=0·9939×ln (CL)−3·0809). The size–fecundity relationship for all coasts combined was (fecundity=0·0044×CL3·1554).  Physiological maturity was assessed using ovary colour, ovary factor, ova size, abdomen width/CL ratio, cement gland activity and moult status as criteria. Size at 50% maturity varied from 92·5 to 96  mm depending on region. The size–maturity relationship for all coasts combined was (Maturity= 1/(1+exp(14·595−0·15598×CL))). Over 60% of lobsters in the commercial landings were under the size at 50% maturity.  Relative reproductive potential (RRP) of different size-classes was calculated from the size–fecundity and size–maturity models and the numbers by length in the landings. The modal RRP size-class was 98–100 mm. The commercial landings were dominated by the 86–92  mm size-classes.
The current distribution and abundance
of the Australasian barnacle Elminius modestus in Portugal
Authors: O'Riordan Ruth M. , Ramsay Neil F.
Published: July 2002

The current distribution and abundance of Elminius modestus
(Crustacea: Cirripedia) were examined at 15 sites along the Portuguese coast in
March/April 1998. Elminius modestus was found at two sites only but was
absent from a site where it had previously been recorded. The site at Faro is the
most southerly location on continental Europe where Elminius has yet
been recorded and it is nearly 300 km south of where it was previously found.
Checks in the statolith microstructure of the short-finned squid, Illex coindetii from the Strait of Sicily (central Mediterranean)
Authors: Arkhipkin Alexander , Jereb Patrizia , Ragonese Sergio
Published: July 2002

Microstructural prominent discontinuities (checks) were observed within the statoliths of the short-finned squid Illex coindetii from the Strait of Sicily. Two hundred and forty-two pairs of statoliths were extracted from specimens (52–175 mm of mantle length, ML) sampled during autumn 1995 and analysed. Beside the check delimiting the postnuclear zone, up to four peripheral checks were detected in the peripheral zone. The occurrence of peripheral checks in the statoliths of immature squid was low (5–15%), whereas 80–95% of mature squid had peripheral checks. The mean number of peripheral checks within statoliths of mature males and females did not differ significantly (1.53–1.68 peripheral checks per squid). In mature and spawning females, the number of peripheral checks corresponded well with the number of spermatophoric bundles inside the mantles. Age at peripheral check formation was estimated for each sex, indicating that the first peripheral check formed at a significantly younger age in males than in females. Formation of the first peripheral check coincided with the start of maturation in both sexes, at a wide age range. The number of increments between peripheral checks subsequent to the first one declined sharply and remained similar in the two sexes, with a predominant mode between three and seven increments. A possible relationship between the number of peripheral checks and mating events in I. coindetii is discussed.
Induction of larval metamorphosis in the ascidian, Halocynthia roretzi by excess potassium ion and by reduced calcium ion
Authors: Matsumura Kiyotaka , Mori Sachiko , Fusetani Nobuhiro
Published: July 2002

Effects of external cation concentrations on larval metamorphosis in the ascidian, Halocynthia roretzi were examined. Metamorphosis (tail resorption) was induced by 20 mM and 50 mM K+ but, interestingly, was suppressed by 30 mM K+. Low concentrations of Ca2+ (1–5 mM) induced metamorphosis, while high concentrations did not, in contrast to findings in other invertebrates. Moreover, BAPTA-AM, an intracellular Ca2+ chelator, induced metamorphosis. This suggests that a decrease in intracellular Ca2+ of certain cells initiates larval metamorphosis in H. roretzi.
The White Town of Calcutta Under the Rule of the East India Company
Authors: Marshall P. J.
Published: July 2002

Late eighteenth and early nineteenth-century Calcutta was the setting for the first sustained encounter between Asian intellectuals and the west. An Indian intelligentsia living in Calcutta responded in a most creative way to aspects of European culture that became available to them in the city. Much about this response is now contentious. If the term Bengal Renaissance is still generally applied to it, the implications of that term are disputed. It is no longer necessarily assumed that ‘modern’ India was born in early nineteenth-century Calcutta by a fusing of what was western and what was ‘traditional’. Assumptions that Indian cultures in general and that of Hindu Bengal in particular lacked a capacity to change and to develop on their own internal dynamics, whatever the input from the west, now look more than a little ‘orientalist’. Furthermore, even if the Bengal Renaissance can be shown to have had its roots in its own culture, to some recent critics it was still a movement whose impact was severely limited by the very narrow base on which it rested: an elite group enclosed in a colonial situation. Yet, however the Renaissance may be reassessed, there can still be no doubt that Calcutta under the East India Company contained Indian intellectuals of exceptional talent, who absorbed much from the west. ‘The excitement over the literature, history and philosophy of Europe as well as the less familiar scientific knowledge was deep and abiding’, Professor Raychaudhuri has recently written.