bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent shear flow over active and passive porous surfaces
Authors: JIMÉNEZ JAVIER , UHLMANN MARKUS , PINELLI ALFREDO , KAWAHARA GENTA
Published: July 2002

The behaviour of turbulent shear flow over a mass-neutral permeable wall is studied
numerically. The transpiration is assumed to be proportional to the local pressure
fluctuations. It is first shown that the friction coefficient increases by up to 40% over
passively porous walls, even for relatively small porosities. This is associated with
the presence of large spanwise rollers, originating from a linear instability which is
related both to the Kelvin–Helmholtz instability of shear layers, and to the neutral
inviscid shear waves of the mean turbulent profile. It is shown that the rollers can
be forced by patterned active transpiration through the wall, also leading to a large
increase in friction when the phase velocity of the forcing resonates with the linear
eigenfunctions mentioned above. Phase-lock averaging of the forced solutions is used
to further clarify the flow mechanism. This study is motivated by the control of
separation in boundary layers.
Transition stages of Rayleigh–Taylor instability between miscible fluids
Authors: COOK ANDREW W. , DIMOTAKIS PAUL E.
Published: July 2002

Direct numerical simulations (DNS) are presented of three-dimensional, Rayleigh–Taylor
instability (RTI) between two incompressible, miscible fluids, with a 3:1
density ratio. Periodic boundary conditions are imposed in the horizontal directions
of a rectangular domain, with no-slip top and bottom walls. Solutions are obtained
for the Navier–Stokes equations, augmented by a species transport-diffusion equation,
with various initial perturbations. The DNS achieved outer-scale Reynolds numbers,
based on mixing-zone height and its rate of growth, in excess of 3000. Initial growth is
diffusive and independent of the initial perturbations. The onset of nonlinear growth
is not predicted by available linear-stability theory. Following the diffusive-growth
stage, growth rates are found to depend on the initial perturbations, up to the end of
the simulations. Mixing is found to be even more sensitive to initial conditions than
growth rates. Taylor microscales and Reynolds numbers are anisotropic throughout
the simulations. Improved collapse of many statistics is achieved if the height of the
mixing zone, rather than time, is used as the scaling or progress variable. Mixing has
dynamical consequences for this flow, since it is driven by the action of the imposed
acceleration field on local density differences.
On the crest instabilities of steep surface waves
Authors: LONGUET-HIGGINS MICHAEL , TANAKA MITSUHIRO
Published: July 2002

The forms of the superharmonic instabilities of irrotational surface
waves

on deep water are calculated for wave steepnesses up to 99.9% of the limiting

value. It is found

that as the limiting wave steepness is approached the rates of growth of
the

lowest two

unstable modes (n=1 and 2) increase according to the asymptotic

law suggested by the

theory of the almost-highest wave (Longuet-Higgins & Cleaver 1994;

Longuet-Higgins, Cleaver & Fox 1994; Longuet-Higgins & Dommermuth

1997). Moreover,

each eigenfunction becomes concentrated near the wave crest, with a horizontal
scale

proportional to the local radius of curvature at the crest. These are therefore

‘crest instabilities’ in the original sense.

Similar calculations are carried out for the normal-mode instabilities
of solitary

waves in shallow water, at steepnesses up to 99.99% of the limiting steepness.

Similar conclusions are found to apply, though with greater accuracy.
Coalescence and fragmentation of colliding mercury drops
Authors: MENCHACA-ROCHA A. , HUIDOBRO F. , MARTINEZ-DAVALOS A. , MICHAELIAN K. , PEREZ A. , RODRIGUEZ V. , CÂRJAN N.
Published: July 2002

Coalescence and fragmentation of equal and unequal liquid-drop

pairs are studied

using a new experimental technique in which mercury drops collide while
sliding on

a horizontal glass surface. The limits for coalescence measured as a function
of the

incident relative velocity and impact parameter are found to be similar
to what has

been reported for free-moving drops of other liquids, while new

correlations are found

to occur among the number, size, speed and angular distribution of fragmentation

residues. The predictions of various models, including a dynamic theory
originally

developed for nuclear reactions, and specifically modified by us for macroscopic

applications, are compared with the observations.
On generalized Bragg scattering of surface waves

by bottom ripples
Authors: LIU YUMING , YUE DICK K. P.
Published: July 2002

We study the generalized Bragg scattering of surface

waves over a wavy bottom. We

consider the problem in the general context of nonlinear

wave–wave interactions, and

write down and provide geometric constructions for the

Bragg resonance conditions

for second-order triad (class I) and third-order quartet

(class II and class III) wave–

bottom interactions. Class I resonance involving one bottom

and two surface wave

components is classical. Class II resonance manifests bottom

nonlinearity (it involves

two bottom and two surface wave components), and has been

studied in the laboratory. Class III Bragg resonance is new

and is a result of free-surface nonlinearity

involving resonant interaction among one bottom and three

surface wave components. The amplitude of the resonant wave

is quadratic in the surface wave slope

and linear in the bottom steepness, and, unlike the former

two cases, the resonant

wave may be either reflected or transmitted (relative to the

incident waves) depending

on the wave–bottom geometry. To predict the initial

spatial/temporal growth of the

Bragg resonant wave for these resonances, we also provide

the regular perturbation

solution up to third order. To confirm these predictions

and to obtain an efficient

computational tool for general wave–bottom problems

with resonant interactions,

we extend and develop a powerful high-order spectral

method originally developed

for nonlinear wave–wave and wave–body interactions.

The efficacy of the method is

illustrated in high-order Bragg resonance computations in two

and three dimensions.

These results compare well with existing experiments and

perturbation theory for the

known class I and class II Bragg resonance cases, and obtain

and elucidate the new

class III resonance. It is shown that under realistic

conditions with moderate to small

surface and bottom steepnesses, the amplitudes of third-order

class II and class III

Bragg resonant waves can be comparable in magnitude to those

resulting from class

I interactions and appreciable relative to the incident wave.
Active control of streamwise vortices and streaks in boundary layers
Authors: JACOBSON STUART A. , REYNOLDS WILLIAM C.
Published: July 2002

Coherent structures play an important role in the dynamics of turbulent
shear flows.
The ability to control coherent structures could have significant technological
benefits
with respect to flow phenomena such as skin friction drag, transition,
mixing, and
separation. This paper describes the development of an actuator concept
that could
be used in large arrays for actively controlling transitional and turbulent
boundary
layers. The actuator consists of a piezoelectrically driven cantilever
mounted flush
with the flow wall. When driven, the resulting flow disturbance over the
actuator is
a quasi-steady pair of counter-rotating streamwise vortices with common-flow
away
from the wall. The vortices decay rapidly downstream of the actuator; however,
they
produce a set of high- and low-speed streaks that persist far downstream
(well over
40 displacement thicknesses). The amplitude of the actuator drive signal
controls the
strength of the generated vortices. The actuator is fast, compact, and
generates a
substantial disturbance in the flow. Its performance has been demonstrated
using a
small array of sensors and actuators in low-speed water laminar boundary
layers
with imposed steady and unsteady disturbances. Experiments are reported
in which
transition from a large disturbance was delayed by 40 displacement thicknesses,
and
in which the mean and spanwise variation of wall shear under an array of
high- and
low-speed streaks was substantially reduced downstream of a single transverse
array
of actuators.
A numerical study of the sedimentation of fibre suspensions
Authors: MACKAPLOW MICHAEL B. , SHAQFEH ERIC S. G.
Published: July 2002

The sedimentation of fibre suspensions at low Reynolds number is
studied using two
different, but complementary, numerical simulation methods: (1) Monte Carlo

simulations, which consider interparticle hydrodynamic interactions at
all orders
within the slender-body theory approximation (Mackaplow & Shaqfeh 1996),
and (ii)
dynamic simulations, which consider point–particle interactions and
are accurate for
suspension concentrations of nl3=1, where n

and l are the number density and
characteristic half-length of the fibres, respectively. For homogeneous,
isotropic
suspensions, the Monte Carlo simulations show that the hindrance of the
mean
sedimentation speed is linear in particle concentration up to at least

nl3=7. The speed
is well predicted by a new dilute theory that includes the effect of two-body

interactions. Our dynamic simulations of dilute suspensions, however, show
that
interfibre hydrodynamic interactions cause the spatial and orientational
distributions
to become inhomogeneous and anisotropic. Most of the fibres migrate into
narrow
streamers aligned in the direction of gravity. This drives a downward convective
flow
within the streamers which serves to increase the mean fibre sedimentation
speed. A
steady-state orientation distribution develops which strongly favours fibre
alignment
with gravity. Although the distribution reaches a steady state, individual
fibres
continue to rotate in a manner that can be qualitatively
described as a flipping between
the two orientations aligned with gravity. The simulation results are in
good agreement
with published experimental data.
Spatio-temporal character of non-wavy and wavy Taylor–Couette
flow
Authors: WERELEY STEVEN T. , LUEPTOW RICHARD M.
Published: July 2002

The stability of supercritical Couette flow has been studied extensively,
but few
measurements of the velocity field of flow have been made. Particle image
velocimetry
(PIV) was used to measure the axial and radial velocities in a meridional
plane for
non-wavy and wavy Taylor–Couette flow in the annulus between a rotating
inner
cylinder and a fixed outer cylinder with fixed end conditions. The experimental
results
for the Taylor vortex flow indicate that as the inner cylinder Reynolds
number
increases, the vortices become stronger and the outflow between pairs of
vortices
becomes increasingly jet-like. Wavy vortex flow is characterized by azimuthally
wavy
deformation of the vortices both axially and radially. The axial motion
of the vortex
centres decreases monotonically with increasing Reynolds number, but the
radial
motion of the vortex centres has a maximum at a moderate Reynolds number
above
that required for transition. Significant transfer of fluid between neighbouring
vortices
occurs in a cyclic fashion at certain points along an azimuthal wave, so
that while one
vortex grows in size, the two adjacent vortices become smaller, and vice
versa. At other
points in the azimuthal wave, there is an azimuthally local net axial flow
in which fluid
winds around the vortices with a sense corresponding to the axial deformation
of the
wavy vortex tube. These measurements also confirm that the shift-and-reflect
symmetry
used in computational studies of wavy vortex flow is a valid approach.
On the self-induced motion of a helical vortex
Authors: BOERSMA J. , WOOD D. H.
Published: July 2002

The velocity field in the immediate vicinity of a curved vortex
comprises a circulation
around the vortex, a component due to the vortex curvature, and a ‘remainder’
due
to the more distant parts of the vortex. The first two components are relatively
well
understood but the remainder is known only for a few specific vortex geometries,

most notably, the vortex ring. In this paper we derive a closed form for
the remainder
that is valid for all values of the pitch of an infinite helical vortex.
The remainder
is obtained firstly from Hardin's (1982) solution for the flow induced
by a helical
line vortex (of zero thickness). We then use Ricca's (1994) implementation
of the
Moore & Saffman (1972) formulation to obtain the remainder for a helical
vortex
with a finite circular core over which the circulation is distributed uniformly.
It is
shown analytically that the two remainders differ by 1/4 for all values
of the pitch.
This generalizes the results of Kuibin & Okulov (1998) who obtained
the remainders
and their difference asymptotically for small and large pitch. An asymptotic
analysis
of the new closed-form remainders using Mellin transforms provides a complete

representation by a residue series and reveals a minor correction to the
asymptotic
expression of Kuibin & Okulov (1998) for the remainder at small pitch.
Evolution and modelling of subgrid scales during
rapid straining of turbulence
Authors: LIU SHEWEN , KATZ JOSEPH , MENEVEAU CHARLES
Published: July 2002

The response, evolution, and modelling of subgrid-scale (SGS) stresses during rapid
straining of turbulence is studied experimentally. Nearly isotropic turbulence with low
mean velocity and Rλ˜290 is generated in a water tank by means of spinning grids.
Rapid straining (axisymmetric expansion) is achieved with two disks pushed towards
each other at rates that for a while generate a constant strain rate. Time-resolved,
two-dimensional velocity measurements are performed using cinematic PIV. The SGS
stress is subdivided to a stress due to the mean distortion, a cross-term (the interaction
between the mean and turbulence), and the turbulent SGS stress
τ(T)ij. Analysis of the
time evolution of τ(T)ij at various
filter scales shows that all scales are more isotropic
than the prediction of rapid distortion theory, with increasing isotropy as scales
decrease. A priori tests show that rapid straining
does not affect the high correlation
and low square-error exhibited by the similarity model. Analysis of the evolution of
total SGS energy dissipation reveals, surprisingly, that the Smagorinsky model with
a constant coefficient (determined from isotropic turbulence data) underpredicts the
dissipation during rapid straining. While the partial dissipation
−〈τ(T)ijS˜ij〉 (due only to
the turbulent part of the stress) is overpredicted by the Smagorinsky model, addition
of the cross-terms reverses the trend. The similarity model with a constant coefficient
appropriate for isotropic turbulence, on the other hand, overpredicts SGS dissipation.
Owing to these opposite trends a linear combination of both models (mixed model)
provides better prediction of SGS dissipation during rapid straining. However, the
mixed model with coefficients determined from dissipation balance underpredicts the
SGS stress.
Planetary waves in a stratified ocean of variable
depth. Part 1. Two-layer model
Authors: REZNIK G. M. , TSYBANEVA T. B.
Published: July 2002

Linear Rossby waves in a two-layer ocean with a corrugated bottom relief (the isobaths
are straight parallel lines) are investigated. The case of a rough bottom relief (the wave
scale L is much greater than the bottom relief scale
Lb) is studied analytically by the
method of multiple scales. A special numerical technique is developed to investigate
the waves over a periodic bottom relief for arbitrary relationships between
L and Lb.

There are three types of modes in the two-layer case: barotropic, topographic,
and baroclinic. The structure and frequencies of the modes depend substantially on
the ratio Δ =
(Δh/h2)/(L/a) measuring the
relative strength of the topography and β-effect. Here
Δh/h2 is the typical relative height
of topographic inhomogeneity and
a is the Earth's radius. The topographic and barotropic mode frequencies depend
weakly on the stratification for small and large Δ and increase monotonically with
increasing Δ. Both these modes become close to pure topographic modes for
Δ>1.

The dependence of the baroclinic mode on Δ is more non-trivial. The frequency
of this mode is of the order of
f0L2i/aL
(Li is the internal Rossby scale) irrespective
of the magnitude of Δ. At the same time the spatial structure of the mode depends
strongly on Δ. With increasing Δ the relative magnitude of motion in the lower layer
decreases. For Δ>1 the motion in the mode is confined mainly to the upper layer
and is very weak in the lower one. A similar concentration of mesoscale motion in an
upper layer over an abrupt bottom topography has been observed in the real ocean
many times.

Another important physical effect is the so-called ‘screening’.
It implies that for Lb<Li
the small-scale component of the wave with scale
Lb is confined to the lower layer, whereas in the upper layer the scale
of the motion L is always greater than or
of the order of, Li. In other words, the stratification prevents the ingress of motion
with scale smaller than the internal Rossby scale into the main thermocline.
A nonlinear model of flow in meandering submarine and subaerial channels
Authors: IMRAN JASIM , PARKER GARY , PIRMEZ CARLOS
Published: July 2002

A generalized model of flow in meandering subaqueous and subaerial channels is
developed. The conservation equations of mass and momentum are depth/layer
integrated, normalized, and represented as deviations from a straight base state. This
allows the determination of integrable forms which can be solved at both linear and
nonlinear levels. The effects of various flow and geometric parameters on the flow
dynamics are studied. Although the model is not limited to any specific planform, this
study focuses on sine-generated curves. In analysing the flow patterns, the turbidity
current of the subaqueous case is simplified to a conservative density flow with water
entrainment from above neglected. The subaqueous model thus formally corresponds
to a subcritical or only mildly supercritical mud-rich turbidity current. By extension,
however the analysis can be applied to a depositional or erosional current carrying
sand that is changing only slowly in the streamwise direction. By bringing the
subaqueous and subaerial cases into a common form, flow behaviour in the two
environments can be compared under similar geometric and boundary conditions. A
major difference between the two cases is the degree of superelevation of channel flow
around bends, which is modest in the subaerial case but substantial in the subaqueous
case. Another difference concerns Coriolis effects: some of the largest subaqueous
meandering systems are so large that Coriolis effects can become important. The
model is applied to meander bends on the youngest channel in the mid-fan region of
the Amazon Fan and a mildly sinuous bend of the North-West Atlantic Mid-Ocean
Channel. In the absence of specific data on the turbid flows that created the channel,
the model can be used to make inferences about the flow, and in particular the range
of values of flow velocity and sediment concentration that would allow the growth
and downfan migration of meander bends.
Filtered mass density function for large-eddy
simulation of turbulent reacting flows
Authors: JABERI F. A. , COLUCCI P. J. , JAMES S. , GIVI P. , POPE S. B.
Published: July 2002

A methodology termed the ‘filtered mass density function’ (FMDF) is developed and
implemented for large-eddy simulation (LES) of variable-density chemically reacting
turbulent flows at low Mach numbers. This methodology is based on the extension
of the ‘filtered density function’ (FDF) scheme recently proposed by Colucci et
al. (1998) for LES of constant-density reacting flows. The FMDF represents the
joint probability density function of the subgrid-scale (SGS) scalar quantities and is
obtained by solution of its modelled transport equation. In this equation, the effect
of chemical reactions appears in a closed form and the influences of SGS mixing
and convection are modelled. The stochastic differential equations (SDEs) which yield
statistically equivalent results to those of the FMDF transport equation are derived
and are solved via a Lagrangian Monte Carlo scheme. The consistency, convergence,
and accuracy of the FMDF and the Monte Carlo solution of its equivalent SDEs
are assessed. In non-reacting flows, it is shown that the filtered results via the
FMDF agree well with those obtained by the ‘conventional’ LES in which the finite
difference solution of the transport equations of these filtered quantities is obtained.
The advantage of the FMDF is demonstrated in LES of reacting shear flows with
non-premixed reactants. The FMDF results are appraised by comparisons with data
generated by direct numerical simulation (DNS) and with experimental measurements.
In the absence of a closure for the SGS scalar correlations, the results based on the
conventional LES are significantly different from those obtained by DNS. The FMDF
results show a closer agreement with DNS. These results also agree favourably with
laboratory data of exothermic reacting turbulent shear flows, and portray several of
the features observed experimentally.
The mean velocity profile of turbulent boundary layers with system rotation
Authors: NICKELS T. B. , JOUBERT P. N.
Published: July 2002

This paper examines changes in the mean velocity profiles of turbulent boundary
layers subjected to system rotation. Analysis of the data from several studies conducted
in the large rotating wind tunnel at the University of Melbourne shows the existence
of a universal linear correction to the velocity profile in the logarithmic region.
The appropriate parameters relevant to rotation are derived and correlations are
found between the parameters. Flows with adverse pressure gradients, zero pressure
gradients and secondary flows are examined and all appear to exhibit the universal
linear correction, suggesting that it is robust.
Peronism and Anti-imperialism in the
Argentine Press: ‘Braden or Perón’
Was Also ‘Perón Is Roosevelt’
Authors: JIMÉNEZ LAURA RUIZ
Published: July 2002

An analysis of the seven daily newspapers with the widest circulation

in Argentina, including the Peronist La Epoca, shows the humanisation
of
capitalism and social justice as the main topics of discussion in Argentine
society
between 1930 and 1946. Newspapers and parties debated the foundations of
a
much desired democratic revival and depicted the government of F. D. Roosevelt

as a model to be followed. By 1946 most Argentines supported the implementation

of policies similar to those of Roosevelt.
In the light of this, Perón and the Unión
Democrática competed to present themselves as the Argentine
version of the US
president. The deciding factor in the 1946 elections was not the defence
of
national sovereignty but rather the impression of which candidate would
be
capable of developing a democratic system which included economic and social

concerns.
Role of neutral-particle bombardment in dust–dust interactions in plasmas
Authors: KHODATAEV Ya. K. , MORFILL G. E. , TSYTOVICH V. N.
Published: July 2002

It is shown that the interaction of dust with neutral plasma particles
can lead to attractive forces between dust particles, both in the case where the
distance between dust particles is less than the mean free path of neutral
particles and in the case where it is greater. The expressions for attractive forces
differs in the two limits only by a numerical coefficient. The additional force of
dust interaction is found to be due to the neutrals created by recombination of
charged plasma particles on the surface of dust particles. The influence of
radiative dust cooling on dust–dust interaction is considered.
Three-dimensional deformable-grid
electromagnetic particle-in-cell for parallel
computers
Authors: WANG J. , KONDRASHOV D. , LIEWER P. C. , KARMESIN S. R.
Published: July 2002

We describe a new parallel, non-orthogonal-grid, three-dimensional electromagnetic
particle-in-cell (EMPIC) code based on a finite-volume formulation. This code uses
a logically Cartesian grid of deformable hexahedral cells, a discrete surface integral
(DSI) algorithm to calculate the electromagnetic field, and a hybrid logical–physical
space algorithm to push particles. We investigate the numerical instability of the
DSI algorithm for non-orthogonal grids, analyse the accuracy for EMPIC simulations
on non-orthogonal grids, and present performance benchmarks of this code on
a parallel supercomputer. While the hybrid particle push algorithm has a second-order accuracy in space, the accuracy of the DSI field solve algorithm is between
first and second order for non-orthogonal grids. The parallel implementation of this
code, which is almost identical to that of a Cartesian-grid EMPIC code using domain
decomposition, achieved a high parallel efficiency of over 96% for large-scale
simulations.
Nasal airflow in French spontaneous speech
Authors: Basset Patricia , Amelot Angélique , Vaissière Jacqueline , Roubeau Bernard
Published: July 2002

The goal of this paper is to compare the degree of anticipatory and carryover phenomena in the behaviour of the velum during the production of French spontaneous speech, and to compare the data with the same speech material, but read. Airflows through the nose and the mouth were taken as an indirect indication of the velum behaviour. French is a language of special interest because there is a phonological contrast between oral and nasal vowels. The results show a tendency for nasal airflow to start before the nasal and a strong propensity to spread after the nasal. No differences could be established between speaking styles (spontaneous vs. read speech) regarding nasal airflow anticipation and carryover.
Variation in the reproductive cycle of Elminius modestus in southern Ireland
Authors: O'Riordan Ruth M. , Murphy Orla
Published: July 2002

The reproductive cycle of the Australasian barnacle Elminius modestus (Crustacea: Cirripedia) was studied at three sites within Whitegate Bay, Cork, Ireland over 15 months. At all three sites, there were seasonal trends in development of the male and female reproductive organs with, for example, the ovaries regenerating whilst eggs were being brooded. Throughout the year, significantly lower percentages of animals were brooding embryos at the site of a warm-water outfall than at another site nearby. The factors which may affect the reproductive cycle of E. modestus are discussed.
Community structure of bathyal decapod crustaceans off south-west Balearic Islands (western Mediterranean): seasonality and regional patterns in zonation
Authors: Maynou Francesc , Cartes Joan E.
Published: July 2002

The community structure of decapod crustacean assemblages was established and analysed from two experimental trawl samplings. The data were taken in the south-west Balearic Islands (Algerian Basin, western Mediterranean Sea) at depths ranging from ∼200 to 1800 m. The results of multivariate analysis indicate that the community structure remained constant between samplings. The analysis also revealed that there exist differences between bathyal decapod communities at a regional level (<1000 km) when compared with well-studied nearby areas. The differences relate mainly to the relative contribution of different species and feeding guilds, not to the taxonomic composition of the assemblages studied. It is proposed that these differences result from contrasting surface production regimes (coastal vs open sea) and food web organization (relative dependence on mesopelagic or infaunal prey).
Ceratothoa steindachneri (Isopoda: Cymothoidae) new to British waters with a key to north-east Atlantic and Mediterranean Ceratothoa
Authors: Horton T.
Published: July 2002

This paper presents the first record of Ceratothoa steindachneri from Cornwall, making it the first resident species of the fish–parasitic isopod family Cymothoidae in Britain. The host is Echiichthys vipera (Trachinidae) the lesser weever fish, the isopod attaching to the host tongue. A complete redescription and reillustration for C. steindachneri is given, and a neotype is selected for the species Ceratothoa parallela. A key to the north-east Atlantic and Mediterranean species of Ceratothoa is included, with a brief illustrated account for each species.
Life history of Allopetrolisthes spinifrons, a crab associate of the sea anemone Phymactis clematis
Authors: Baeza J.A. , Stotz W. , Thiel M.
Published: July 2002

Allopetrolisthes spinifrons is an ectocommensal crab of the sea anemone Phymactis clematis. The population biology of A. spinifrons in north central Chile was examined between January and December 1996. During 1996, 74% of P. clematis in the rocky intertidal zone hosted at least one commensal crab. In most cases, one sea anemone was inhabited by a single adult crab, either male or female. A few sea anemones hosted two or more crabs, one usually being an adult and the others juveniles or small crabs that just had recruited to the host. The sex ratio of adult crabs was ∼1:1 during most months. Reproduction occurred with similar intensity throughout the year as indicated by the continuous presence of reproductive females. Similarly, recruitment of A. spinifrons occurred throughout the year with the exception of late winter when no megalopae and small juveniles were found on sea anemones. Fecundity of female crabs varied between 121 and 5661 eggs per female (6·9–19·2 mm carapace length) and was significantly higher during the austral winter (July) than during the summer (December). The fact that most sea anemones were inhabited by a single adult crab indicates that hosts may be monopolized by individual crabs. Resource requirements may prohibit adult crabs from sharing a host individual with another large crab, while adult tolerance towards juveniles may facilitate the maintenance of local populations.
Hydroids associated with deep-sea corals in the boreal north-west Atlantic
Authors: Henry Lea-Anne
Published: July 2002

This paper reports on the distribution of epifaunal hydroids associated with deep-sea corals collected from the boreal north-west Atlantic. Thirteen hydroid species were collected from only four coral specimens, suggesting that northern corals support highly diverse epifaunal communities.
Oxygen uptake of developing eggs of Cancer pagurus (Crustacea: Decapoda: Cancridae) and consequent behaviour of the ovigerous females
Authors: Naylor J.K. , Taylor E.W. , Bennett D.B.
Published: July 2002

This study investigated factors affecting the metabolic rate of Cancer pagurus eggs. The oxygen uptake of portions of the egg mass and recently hatched zoeae was measured. Oxygen uptake of the eggs of an individual animal was found to vary widely, with measured mean values under normoxic conditions ranging from 38 to 250 μmoles O2 kg−1 min−1. Mean values for the oxygen uptake of zoeae ranged from 958 to 1168 μmoles O2 kg−1 min−1. Mean rates of oxygen uptake of the eggs generally increased with increasing seasonal temperature and advancing developmental stage. Rates of oxygen uptake were maintained over a wide range of ambient oxygen partial pressures. As oxygen partial pressure in the seawater surrounding the eggs fell from a critical value (Pc) of between 60 and 90 mm Hg, the oxygen uptake of the eggs also declined. Mean values for ambient oxygen partial pressures within the egg mass in vivo ranged from 34 to 98 mm Hg. Adult female C. pagurus appear to be able to detect conditions within the egg mass and adjust their egg ventilation behaviour accordingly. Active egg mass ventilation by the adult increased as the eggs became more developed and their oxygen demands increased.
The sizes at settlement in natural populations of the cyprids of Chthamalus montagui and C. stellatus
Authors: O'Riordan Ruth M. , Myers Alan A. , McGrath David , Delany Jane , Power Anne-Marie
Published: July 2002

The lengths of chthamalid cyprids collected during August 1996 on six rocky shores in County Cork, Ireland are reported. The lengths showed a bimodal distribution. The smaller length mode corresponded well with the length range of laboratory-reared cyprids of Chthamalus montagui (Crustacea: Cirripedia), whilst the larger length mode was greater than the length range reported for laboratory-reared C. stellatus. Size may be a useful means to identify Chthamalus cyprids in field investigations.
Eicosanoids are modulators of larval settlement in the barnacle, Balanus amphitrite
Authors: Knight John , Rowley Andrew F. , Yamazaki Mizue , Clare Anthony S.
Published: July 2002

Eicosanoids are oxygenated derivatives of C20 polyunsaturated fatty acids known to play key roles in many physiological events in both invertebrates and vertebrates. The eicosanoid generating capacity of cypris larvae of the barnacle, Balanus amphitrite, was examined using enzyme immunoassay and high-performance liquid chromatography. These larvae generated the lipoxygenase products, 12-hydroxyeicosapentaenoic acid (HEPE), 8-HEPE and 8,15-diHEPE, together with the cyclooxygenase products, prostaglandin (PG) E, PGF and thromboxane (TX) B. Indomethacin, a selective cyclooxygenase inhibitor, caused a dose-dependent inhibition of PGE generation by B. amphitrite larvae, while esculetin and nordihydroguaiaretic acid (lipoxygenase inhibitors) also strongly inhibited the generation of 8-HEPE, 12-HEPE and 8,15-diHEPE. PGE2, PGE3 and 16,16-dimethyl PGE2 caused a dose-dependent inhibition of settlement of B. amphitrite larvae while indomethacin (25–100 μM) stimulated this process. Lipoxygenase products (8-HEPE, 12-HEPE and 8,15-diHEPE) as well as esculetin and nordihydroguaiaretic acid (10–100 μM) had no effect on the attachment of larvae.
Spatial distribution of copepods in the north of the Humboldt Current region off Chile during coastal upwelling
Authors: Escribano Ruben , Hidalgo Pamela
Published: July 2002

During the austral spring (December 1996), numerical abundance of copepod species (Crustacea: Copepoda) was estimated from 53 sampling stations scattered over the coastal waters off Mejillones Peninsula, northern Chile. Samples were obtained from two depth strata; 0-50 m and 50-200 m depth. Oceanographic data over the three-day cruise indicated that coastal upwelling was actively occurring during the survey.

A total of 19 species was identified, of which four of them, Paracalanus parvus, Oncaea conifera, Oithona similis and Calanus chilensis, accounted for more than 80% of the whole copepod assemblage in terms of numerical abundance. Using the K-means exploratory analysis the 53 locations were grouped into two clusters: an upwelling type and a non-upwelling type. The former characterized by locations nearshore, with low temperature (<17°C) and high chorophyll-a (>13.4 mg m−3), while the latter had warmer waters (>18°C) and low chlorophyll-a (<4.8 mg m−3). Chlorophyll-a (chl-a), distance to shoreline and temperature at 10 m depth (T10) were all significant variables ( P<0.05) for clustering analysis. There was a strong negative correlation between T10 and chl-a ( P<0.01). The same clustering technique, based on species abundance, suggested the presence of a unique cluster, whose composition was dominated by P. parvus, O. similis, Acartia tonsa and Centropages brachiatus. Stepwise multiple regression showed that these species were also strongly correlated to chl-a and T10. Together these analyses suggest that water mass circulation during upwelling is the driving force for structuring spatial patterns of copepod distribution. In addition, a vertical distribution parameter suggested that copepods, independently of time of the day, tended to remain in a large proportion in near surface waters, possibly constrained by a shallow oxygen minimum layer. This implies that advection during active upwelling may cause large fractions of populations being transported offshore, allowing zooplankton export to more oceanic waters. Rapid turnover rates of copepods growing continuously year-round, may act as a mechanism to compensate population losses during persistent coastal upwelling.
Distribution of nitric oxide synthase immunoreactivity in the nervous system and peripheral tissues of Schistosoma mansoni
Authors: KOHN A.B. , MOROZ L.L. , LEA J.M. , GREENBERG R.M.
Published: July 2002

The distribution of nitric oxide synthase (NOS) immunoreactivity and putative NOS activity in adult Schistosoma mansoni was analysed using 3 different types of NOS antibodies and NADPH-diaphorase histochemistry. Although potential involvement of the gaseous radical nitric oxide (NO) in host response to infection by schistosomes has been suggested, there is little or no information available regarding the role, or even the presence, of the NO pathway in schistosomes themselves. Here, we demonstrate that antibodies against neuronal NOS (nNOS) and inducible NOS (iNOS) isoforms stain adult worms with distinctive patterns; anti-endothelial NOS (eNOS) shows no selective labelling. nNOS-like immunoreactivity is found in the main nerve cords and the peripheral nervous system. Putative sensory neurons with apical neuronal processes leading to the tegument of male worms are also immunoreactive for nNOS. Anti-iNOS labels a variety of predominantly non-neuronal tissues, showing intense labelling at or near the surface of the worm and in components of the gastrointestinal tract. The distribution of NADPH-diaphorase reactivity (a histochemical marker of NOS), is generally similar to the pattern of NOS immunoreactivity, including labelling of neuronal-like cells as well as developing eggs. These results suggest that an NOS-like enzyme is present in S. mansoni, and indicate potential roles for the different NOS isoforms in neuronal signalling, reproduction and development.
The suppressive excretory–secretory product of
Trichobilharzia ocellata: a possible factor for determining
compatibility in parasite–host interactions
Authors: NÚÑEZ P. E. , DE JONG-BRINK M.
Published: July 2002

Factors which may determine trematode–snail interactions
were assessed in the present study. Compatibility was examined
using a bacterial clearance assay to detect the modulatory effects of
both compatible and incompatible trematode infections
on the activity of haemocytes from Lymnaea stagnalis, during the
early stages of infection. Exposure to and injection with
Trichobilharzia ocellata, a compatible trematode, or the incompatible
Schistosoma mansoni, resulted in modulation of
haemocyte activity. However, T. ocellata activated haemocytes
1·5 h post-infection (p.i.) and then suppressed activity
24–72 h p.i. whereas with S. mansoni no suppression, only
activation of haemocytes was observed throughout the test
period (1·5–72 h p.i.). In previous studies, modulation of
the
haemocyte clearance activity by T. ocellata was found to be
mediated by 2 E–S fractions, an activating fraction and a suppressing
one.
Investigations to assess whether the lack of
suppression of haemocyte activity, observed in the S. mansoni–L.
stagnalis incompatible trematode–snail interaction
studied, was due to either the absence or ineffectiveness of the suppressing
E–S fraction, were performed on a second
incompatible combination, T. ocellata–Planorbis corneus.
Using
this combination it was revealed that only the activating
E–S fraction had modulatory effects on P. corneus haemocytes,
indicating that the suppressing E–S fraction, which actively
interferes with the clearance activity of haemocytes from L.
stagnalis, appears to act in a host-specific manner. In
conclusion, the suppressing E–S fraction determines, at least in
part,
compatibility in the trematode–snail association
studied. This is also probably likely in other trematode–snail
combinations.
Cellular distribution of a feminizing microsporidian
parasite: a strategy for transovarial transmission
Authors: TERRY R. S. , DUNN A. M. , SMITH J. E.
Published: July 2002

The cellular distribution of a vertically transmitted, feminizing
microsporidian was followed in its host Gammarus duebeni.
In adult females the parasite was restricted to gonadal tissue, in particular
primary and secondary follicle cells. Spores
were diplokaryotic with a thin spore wall and a short polar filament,
characteristics typical of ‘early’ spores involved in
autoinfection. The diplokaryotic life-cycle, absence of spore groupings
and of a pansporoblast membrane typify the genus
Nosema. However, the unusual globular polaroplast of the spore
and
restriction of this stage to host ovarian tissue have
not previously been described in Nosema. Sporogony occurred only
in
follicle cells adjacent to developing oocytes and was
in synchrony with the process of vitellogenesis. Oocytes were infected
after
formation of intracellular connections with
follicle cells but harboured only vegetative stages of the parasite.
Parasites were associated with the perinuclear cytoplasm
and, in developing embryos, segregated to daughter cells along the axis
of
the spindle. In juvenile animals there was no
evidence of pathology linked with feminization and the parasite was found
at low density in cells under the cuticle. The
parasite is highly adapted to transovarial transmission with an efficient
mechanism of oocyte infection and no evidence of pathology.
Female-specific gene expression in Schistosoma mansoni

is regulated by pairing
Authors: GREVELDING C. G. , SOMMER G. , KUNZ W.
Published: July 2002

Gene expression studies in adult females of Schistosoma mansoni

cultured in vitro revealed that the transcription of female-specifically

expressed genes is influenced by pairing. In contrast, the activity of
genes

that are expressed in both genders

was not affected by contact with the male. The transcription of genes was

monitored in paired, separated and remated

females. The transcript level of female-specifically expressed genes

decreases within a few days following separation from

males. Remating of uncoupled females with males leads to the reinitiation

of transcription. These results provide strong

evidence for the influence of the male on gene transcription in the female

and contribute a molecular basis for the classical

histological observation that the maturation of females is male dependent.

The data also show that the culture system is

suitable to monitor gene expression and, furthermore, they indicate

de novo RNA synthesis in vitro.
Enhancing antibodies in HIV infection
Authors: FÜST G.
Published: July 2002

The author has summarized the history of discovery, the mechanism
and the
clinical significance of antibody-dependent
enhancement (ADE) of HIV infection. ADE has two major forms: (a)

complement-mediated antibody-dependent
enhancement (C-ADE) and (b) complement-independent Fc receptor-dependent

ADE (FcR-ADE). The most important
epitope responsible for the development of C-ADE-mediating antibodies is

present in the immunodominant region of
gp41 while antibodies mediating FcR-ADE react mainly with V3 loop of gp120.

There are at least three fundamentally
different hypotheses for the explanation of ADE in vitro:
(a) increased adhesion of HIV-antibody-(complement) complexes

to FcR or complement receptor carrying cells; (b) facilitation
of
HIV-target cell fusion by complement fragment deposited
on the HIV-virions and (c) complement activation products may
have
a non-specific stimulatory effect on target cells
resulting in enhanced virus production. FcR-ADE and C-ADE have been measured

in vitro mostly by using FcR-carrying
and complement receptor-carrying cell lines, respectively; no efforts have

been made to standardize these methods. Several
data support the possible clinical significance of FcR-ADE and C-ADE:
(a) Cross-sectional and longitudinal studies
indicate a correlation between the amounts of FcR-ADE and C-ADE-mediating

antibodies and clinical, immunological
and virological progression of the HIV-disease; (b) ADE may
facilitate maternal–infant HIV-1 transmission; (c) According

to experiments in animal models, ADE are present and may modify the course
of
SIV (simian immunodeficiency) infection
as well. The author raises a new hypothesis on the mechanism of the
in vivo effect of C-ADE. According to the hypothesis,
C-ADE-mediating antibodies exert their effect through enhancement of
HIV propagation and consequent facilitation of
the progression of HIV disease. Finally, according to observations from

animal experiments and human clinical trials it
cannot be excluded that ADE-mediating antibodies may develop, diminish
the
beneficial effect or may be harmful in
volunteers vaccinated with HIV-1 candidate vaccines.
Vertical transmission of Toxoplasma gondii from
chronically infected house (Mus musculus) and field
(Apodemus sylvaticus) mice determined by polymerase chain reaction
Authors: OWEN M. R. , TREES A. J.
Published: July 2002

Captive-bred Mus musculus (house mice) and Apodemus

sylvaticus (field mice) were each infected with 50 oocysts of
Toxoplasma gondii M1 strain per os and infection in them

and their offspring was assessed by polymerase chain reaction
(PCR) amplification of the T. gondii B1 gene in brain tissue and

by serology, using the modified agglutination test (MAT).
The chronically infected female A. sylvaticus (n=10)
and
M. musculus (n=23) were mated at least 6 weeks after
infection
(and subsequently to produce up to 6 litters) and their pups examined
3 weeks after weaning at 6 weeks of age. By PCR,
in offspring of A. sylvaticus and M. musculus respectively,

vertical transmission was demonstrated in 82·7% (n=83)
and
85·0% (n=207) of all pups (N.S.,
P>0·05),

95% (n=21) and 100% (n=30) of all litters
(N.S.,

P>0·05), with a mean
(±S.E.) proportion of each litter infected of
0·87 (0·06) and 0·86 (0·04) (N.S.,

P>0·05). There was no change in any of these
variables between first and subsequent litters. By serology, whilst MAT

suggested 100% vertical transmission in A. sylvaticus, it
under-estimated rates of infection in offspring of M. musculus.

A limited series of bioassays from M. musculus
tissues confirmed the good correlation of PCR and the poor correlation
of
MAT with mouse inoculation. These results
indicate that vertical transmission in A. sylvaticus and
M. musculus is extremely efficient and probably endures for the
life
of the breeding female. This mechanism favours parasite transmission and

dispersion by providing a potential reservoir
of infection in hosts predated by the cat.
Toxoplasmosis in rats (Rattus norvegicus): congenital

transmission to first and second generation offspring and

isolation of Toxoplasma gondii from seronegative rats
Authors: DUBEY J. P. , SHEN S. K. , KWOK O. C. H. , THULLIEZ P.
Published: July 2002

To study congenital transmission of Toxoplasma gondii

during acute and chronic infections, 4 pregnant Sprague-Dawley

rats were each fed 10000 oocysts of the VEG strain. Toxoplasma gondii

was recovered from 33, 55, 83 and 57% of rats

(F1) when dams were inoculated at 6, 9, 12 or 15 days of gestation,

respectively. Progeny of 15 congenitally infected female

rats were examined for T. gondii. Toxoplasma gondii was

recovered from tissues of 1 of 155 rats (F2) born to congenitally

infected dams. A total of 4 (F2) females were mated; 0 of 40 (F3) rats
born

to them were infected. None of the acutely

infected 4 dams that had given birth to congenitally infected litters

produced congenitally infected offspring during the

second pregnancy. Thus, unlike mice, evidence for repeated congenital

transmission of T. gondii in the rat was found in

<1% of cases. Of the 16 congenitally T. gondii infected pups

with demonstrable tissue cysts, 5 were seronegative (<1[ratio ]4)

in the Sabin-Feldman dye test and 5 were seronegative (<1[ratio ]20)
in the

modified agglutination test by the use of whole

formalinized tachyzoites and mercaptoethanol.