bluuebunny/crossref_metadata_2025 huggingface dataset:
Gravitational settling of particles through density interfaces
Authors: SRDIĆ-MITROVIĆ A. N. , MOHAMED N. A. , FERNANDO H. J. S.
Published: July 2002

Gravitational settling of dense particles through density interfaces
is common in
many environmental and engineering flow situations, yet very little research
has been
done to understand the mechanics of particle–stratification interactions.
To this end,
a detailed experimental study was carried out to investigate the settling
of solid
spherical particles through density interfaces. In these experiments, the
solid particles
first descended through a deep homogeneous layer, entered a thick pycnocline
and then
descended to another denser homogeneous layer. It was found that the stratification

has a significant impact on the settling of particles in the approximate
parameter
range 1.5<Re1<15, where
Re1=U1dp/v

is the Reynolds number based on the
particle entry velocity U1 to the stratified layer,

dp is the particle diameter and v
is
the kinematic viscosity of the fluid. In the above parameter range, the
particles tend
to drag lighter fluid from the upper layer into the stratified region,
thus increasing the drag
on them substantially and decelerating them within the stratified layer.
In the Froude number
Fr1=U1/Ndp
range
investigated, 3<Fr1<10, where N is the

buoyancy frequency of the stratified layer, the drag coefficient was found
to be an
order of magnitude larger than its homogeneous-fluid counterpart. The internal-wave

contribution to the drag was small compared to that of fluid dragged into
the stratified
layer, but substantial internal-wave activity could be detected after the
fluid dragged
from the lighter layer (the caudal fluid) detached from the particle.

The minimum velocity of the solid particle within the stratified layer
was found to be given
by Umin/U1=
5.5×10−2Fr9/101,
occurring on a
time scale tmin/
(d2p/v)=
1.4×102Re−1.71, where

tmin was measured relative to the time of
the particle's
entry into the stratified region. Outside the parameter range
1.5<Re1<15, the drag on the
sphere in the density-stratified layer could be approximated to that in
a homogeneous
fluid, whence the bringing of lighter fluid into the stratified layer as
a tail behind the
descending particle was found to be negligible.
The mechanism of vortex connection at a free surface
Authors: ZHANG CHIONG , SHEN LIAN , YUE DICK K. P.
Published: July 2002

Vortex connections at the surface are fundamental and prominent
features in free-surface vortical flows. To understand the detailed mechanism of such connection,
we
consider, as a canonical problem, the laminar vortex connections at a free
surface when
an oblique vortex ring impinges upon that surface. We perform numerical
simulations
of the Navier–Stokes equations with viscous free-surface boundary
conditions. It is
found that the key to understanding the mechanism of vortex connection
at a free
surface is the surface layers: a viscous layer resulting from the dynamic
zero-stress
boundary conditions at the free surface, and a thicker blockage layer which
is due to
the kinematic boundary condition at the surface. In the blockage layer,
the vertical
vorticity component increases due to vortex stretching and vortex turning
(from the
transverse vorticity component). The vertical vorticity is then transported
to the free
surface through viscous diffusion and vortex stretching in the viscous
layer leading to
increased surface-normal vorticity. These mechanisms take place at the
aft-shoulder
regions of the vortex ring. Connection at the free surface is different
from that at a
free-slip wall owing to the generation of surface secondary vorticity.
We study the
components of this surface vorticity in detail and find that the presence
of a free
surface accelerates the connection process. We investigate the connection
time scale
and its dependence on initial incidence angle, Froude and Reynolds numbers.
It is
found that a criterion based on the streamline topology provides a precise
definition
for connection time, and may be preferred over existing definitions, e.g.
those based
on free-surface elevation or net circulation.
Experimental studies of stability and transition
in high-speed wakes
Authors: LYSENKO V. I.
Published: July 2002

The investigation undertaken deals with the development of disturbances in a supersonic
wake (free viscous layer and regular wake) behind a flat plate both in its linear
and nonlinear stages. The influence of a number of factors (Mach and Reynolds
numbers, temperature factor, thickness of the plate, length of its stern) on the wake
stability and transition was studied. The development of the artificial disturbances in
a wake at Mach number M∞ = 2 was investigated also.

It was found that compressibility of the flow (increasing Mach number) stabilizes
the wake disturbances – their amplification rates decrease, and the transition point
moves away from the model plate. Cooling of the model surface at
M∞ ≈ 7 has a
destabilizing influence on the development of disturbances in the wake. With increase
of unit Reynolds number the beginning of transition in the wake moves forward to
a rear critical point. It was confirmed that a distinctive maximum in the spectral
distribution of fluctuations appears, corresponding to Strouhal number (based on
frequency of this maximum) of 0.3. With the growth of the model thickness the
disturbance amplification rates in the wake increase, which results in earlier transition
of a laminar wake into turbulent one. With the growth of length of the plate stern,
the position of the wake transition moves back accordingly, while the wake stability
increases a little (though very unsignificantly). In the nonlinear stage of development
of disturbances, the occurrence of a triad of waves, satisfying the resonant correlation
of frequencies, and the growth of harmonics are observed. A monochromatic packet
of waves of Tollmien–Schlichting type, rather narrow (in the transversal coordinate)
in the boundary layers on a flat plate with an opposite wedge at the stern, was found
to extend in the wake. The wake disturbances have a complex wave structure. At
the Mach number of free flow 2.0, the three-dimensional disturbances are the most
unstable in the wake.
The flickering candle: transition to a global
oscillation in a thermal plume
Authors: MAXWORTHY T.
Published: July 2002

A number of experiments have been performed on the properties of propane diffusion
flames at relatively low fuel flow rates and using a variety of burner types. Optical
methods were used to observe the flame and plume above it. We have studied the
transition from a steady flame, with a plume exhibiting a helical instability at low
flow rates, to an axisymmetric instability of the whole flame/plume, that grows
from the base of the flame and oscillates at a well-defined and robust frequency, at
higher flow rates. These results and the observation of the effects of various external
modifications, e.g. the generation of an annular counter flow, a pressure perturbation,
etc. are consistent with the view that the transition to the axisymmetric state, at
which the flame flickers, is one to a globally excited oscillation forced by a region of
absolutely unstable flow at or near the base of the burners used in this study.
Evolution of vortex knots
Authors: RICCA RENZO L. , SAMUELS DAVID C. , BARENGHI CARLO F.
Published: July 2002

For the first time since Lord Kelvin's original conjectures of 1875 we address and
study the time evolution of vortex knots in the context of the Euler equations. The
vortex knot is given by a thin vortex filament in the shape of a torus knot
[Tscr ]p,q (p>1, q>1; p, q
co-prime integers). The time evolution is studied numerically by
using the Biot–Savart (BS) induction law and the localized induction approximation
(LIA) equation. Results obtained using the two methods are compared to each other
and to the analytic stability analysis of Ricca (1993, 1995). The most interesting
finding is that thin vortex knots which are unstable under the LIA have a greatly
extended lifetime when the BS law is used. These results provide useful information
for modelling complex structures by using elementary vortex knots.
The dynamics of sedimenting surface gravity currents
Authors: MAXWORTHY T.
Published: July 2002

We have performed a series of experiments on the dynamics of sedimenting, surface
gravity currents. The physical situation concerns a current,
with total density ρC,
evolving at the surface of a fluid of greater density, ρA.
In turn ρC is made up of
interstitial fluid of density ρI and heavy
particles with a concentration by weight c
and a density ρP. Only the case of the release of a constant volume of particles and
interstitial fluid has been considered in detail. It has been found that the sedimentation
of the particles, plus some of the interstitial fluid, through the interface between the
two fluids has a profound effect upon the motion of the current. When the rejected
mixture of particles and upper- and lower-layer fluids reaches the bottom of the
experimental tank it generates a secondary gravity current which in turn interacts
with the primary current to further modify its behaviour. Using simple models we
have been able to rationalize the observations and reveal the dynamical balances
which appear to be important. A subsidiary experiment and analysis on the flux
characteristics of the interface have been performed in order to further clarify the
important effects of the particle motion through that region.
Resonant acoustic frequencies of a tandem
cascade. Part 2. Rotating blade rows
Authors: WOODLEY B. M. , PEAKE N.
Published: July 2002

In Part 1 (Woodley & Peake 1999) we described a method for predicting the occurrence
of resonant states in a system comprising twin cascades in zero relative motion. We
now demonstrate how that work can be extended to account for the case of more
practical interest, in which the upstream cascade (rotor) is rotating in the transverse
direction relative to the downstream cascade (stator). Time periodicity now forces the
temporal frequency of any disturbance to be an integer multiple of the rotor passing
frequency in the stator frame, and vice versa, and this leads to the requirement to
sum over a discrete set of temporal modes, as well as over the spatial modes already
described in Part 1. The mechanisms by which temporal and spatial modes are
scattered by the blade rows is made clear by the analytical approach adopted here;
the scattering of the incident pressure (and, for the stator, vorticity) fields by each row
in its own frame is completed using results similar to those presented in Part 1, and
the fields in the two frames then matched across the inter-row gap to provide a single
matrix equation. Specimen results for the conditioning of this equation are given, and
although it seems more difficult to obtain very strong excitation than it was for zero
rotation, the significance of Parker resonance of the stator is again apparent.
Optimal LES formulations for isotropic turbulence
Authors: LANGFORD JACOB A. , MOSER ROBERT D.
Published: July 2002

It is shown that there is an abstract subgrid model that is in all senses ideal. An
LES using the ideal subgrid model will exactly reproduce all single-time, multi-point
statistics, and at the same time will have minimum possible error in instantaneous
dynamics. The ideal model is written as an average over the real turbulent fields
whose large scales match the current LES field. But this conditional average cannot
be computed directly. Rather, the ideal model is the target for approximation when
developing practical models, though no new practical models are presented here. To
construct such models, the conditional average can be formally approximated using
stochastic estimation. These optimal formulations are presented, and it is shown that a
relatively simple but general class of one-point estimates can be computed from two-point correlation data, and that the estimates retain some of the statistical properties
of the ideal model.

To investigate the nature of these models, optimal formulations were applied to
forced isotropic turbulence. A variety of optimal models of increasing complexity were
computed. In all cases, it was found that the errors between the real and estimated
subgrid force were nearly as large as the subgrid force itself. It is suggested that
this may also be characteristic of the ideal model in isotropic turbulence. If this is
the case, then it explains why subgrid models produce reasonable results in actual
LES while performing poorly in a priori tests. Despite the large errors in the optimal
models, one feature of the subgrid interaction that is exactly represented is the energy
transfer to the subgrid scales by each wavenumber.
Dynamical properties of forced shear layers in an annular geometry
Authors: BERGERON K. , COUTSIAS E. A. , LYNOV J. P. , NIELSEN A. H.
Published: July 2002

Results of numerical simulations of a forced shear flow in an annular geometry
are presented. The particular geometry used in this work reduces the effects of
centrifugal and Coriolis forces. However, there are still a large number of system
parameters (shear width, shear profile, radius of curvature, initial conditions, etc.)
to characterize. This set of variables is limited after the code has been validated
with experimental results (Rabaud & Couder 1983; Chomaz et al. 1988) and with
the associated linear stability analysis. As part of the linear stability characterization,
the pseudo-spectrum for the associated Orr–Sommerfeld operator for plane, circular
Couette flow is calculated, and it is found to be insensitive to perturbations.

The numerical simulation code is a highly accurate de-aliased spectral method which
utilizes banded operators to increase the computational efficiency. Viscous dissipation
terms enter the code directly from the equations of motion. The results from the
simulation code at low Reynolds numbers are compared with the results from linear
stability analysis and are used to give predictions for the coefficients of the Landau
equation describing the saturation behaviour near the critical Reynolds number.
Numerical results at higher Reynolds numbers demonstrate the effects of spin-up and
spin-down, including the experimentally observed hysteresis. The properties of two-
dimensional shears at high Reynolds numbers, at which temporal states are formed,
are also addressed.
Nonlinear equilibrium solutions in a three-dimensional boundary layer
and their secondary instability
Authors: KOCH WERNER , BERTOLOTTI FABIO P. , STOLTE ANDREAS , HEIN STEFAN
Published: July 2002

The observed nonlinear saturation of crossflow vortices in the DLR swept-plate transition
experiment, followed by the onset of high-frequency signals, motivated us to
compute nonlinear equilibrium solutions for this flow and investigate their instability
to high-frequency disturbances. The equilibrium solutions are independent of
receptivity, i.e. the way crossflow vortices are generated, and thus provide a unique
characterization of the nonlinear flow prior to turbulence. Comparisons of these
equilibrium solutions with experimental measurements exhibit strong similarities. Additional
comparisons with results from the nonlinear parabolized stability equations
(PSE) and spatial direct numerical simulations (DNS) reveal that the equilibrium
solutions become unstable to steady, spatial oscillations with very long wavelengths
following a bifurcation close to the leading edge. Such spatially oscillating solutions
have been observed also in critical layer theory computations. The nature of the
spatial behaviour is herein clarified and shown to be analogous to that encountered
in temporal direct numerical simulations. We then employ Floquet theory to systematically
study the dependence of the secondary, high-frequency instabilities on
the saturation amplitude of the equilibrium solutions. With increasing amplitude, the
most amplified instability mode can be clearly traced to spanwise inflectional shear
layers that occur in the wake-like portions of the equilibrium solutions (Malik et al.
1994 call it ‘mode I’ instability). Both the frequency range and the eigenfunctions
resemble recent experimental measurements of Kawakami et al. (1999). However,
the lack of an explosive growth leads us to believe that additional self-sustaining
processes are active at transition, including the possibility of an absolute instability
of the high-frequency disturbances.
Feature-marking in the L2 development of deverbal compounds
Authors: LARDIERE DONNA , SCHWARTZ BONNIE D.
Published: July 2002

This study focuses on the development of complex word formation
in

L2 acquisition.

We examine experimentally elicited data on English deverbal synthetic compounding

(such as toe-painter) by native Spanish speakers and conclude

that: (a) development

proceeds in stages which clearly reflect UG-constrained L1 influence; (b)

nontargetlike productions (e.g. painter-toes) show attempts to

spell out the grammatical

features associated with functional categories in deverbal compounding;
though

nontargetlike, they are nonetheless consistent with the compound's
required

feature-marking; (c) such attempts implicate the early existence in the

Interlanguage of those

functional heads and their projections in the (lexical) syntax; i.e., the

absence of the

correct phonological form cannot be taken to imply lack of knowledge of

morphosyntactic features and their corresponding phrase structure.
Informal repression, zero-sum politics and late third wave transitions
Authors: Kirschke Linda
Published: July 2002

Transitions to multiparty politics occurred throughout Sub-Saharan Africa
with remarkable speed in the early 1990s, linking the region to the broader
‘third wave of democratisation’ which, from 1974, progressively marked
many areas of southern Europe, Latin America and post-communist Europe.
Unlike most earlier cases of political reform, however, the changes in Sub-Saharan Africa demonstrated a strong external orientation. A unique combination
of donor pressure, internal opposition and ‘snowballing’ led
regimes to rapidly introduce multiparty politics regardless of whether ruling
elites in fact supported democratisation. The particular constraints
surrounding these transitions place much of Sub-Saharan Africa at high risk
of civil violence. Drawing on the cases of Cameroon, Rwanda and Kenya,
this article argues that, during transitional periods, the greater the conflict
between ruling elites and opposition forces, and the greater the pressure
which regimes face to proceed with reform, the greater the likelihood that
states will sponsor ‘informal repression’, covert violations by third parties, to
regain political control.
Routes: language and the identity
of African literature
Authors: Adejunmobi Moradewun
Published: July 2002

The debate over the language of African literature has continued to generate
significant interest ever since the emergence of African literary writing in
European languages. Discussions of this debate have in the past often highlighted
the inherently normative character of the idea of an African literature
in African languages. By tracing the history of the debate, this paper seeks
to distinguish between the actual role played by African languages in the
emergence of a literature identified as African by its practitioners, and the
ideological function of the debate for Africans who write in European
languages. From this perspective, appeals for a literature in indigenous
languages appear to serve the purpose of ethnic signification on behalf of a
tradition of writing that continues to rely on European languages at the
levels of both creative practice and theoretical formulation.
States, international organisations
and the refugee: reflections on
the complexity of managing the
refugee crisis in the Horn of
Africa
Authors: Bariagaber Assefaw
Published: July 2002

This article explores the complexity of managing refugee issues, particularly
refugee repatriations, taking the Horn of Africa as a case. I argue that refugee
repatriation endeavours are complex because their success depends on at
least four actors, each with different – indeed often conflicting – interests. I
examine the proposition that as the number of actors involved in a given
issue area increases so does the likelihood of less-than-successful outcomes.
This is particularly true if resource-poor actors are included in the decision-making process, and, because of the need to extract maximum benefits and/or
minimise maximum losses, usually operate under the assumption of zero-sum situations. This assumption narrows their range of responses and
hampers their ability to engage in mutually beneficial exchange
relationships. As a result, repatriations, which are necessarily consensus-based, become more difficult to accomplish successfully as evidenced in the
Horn of Africa.
The stability of charged-particle motion in sheared magnetic reversals
Authors: TSALAS M. , CHAPMAN S. C. , ROWLANDS G.
Published: July 2002

We consider the motion of charged particles in a static magnetic reversal
with a shear component, which has application for the stability of current sheets,
such as in the Earth's geotail and in solar flares. We examine how the topology of
the phase space changes as a function of the shear component by.
At zero by, the
phase space may be characterized by regions of stochastic and regular orbits (KAM
surfaces). Numerically, we find that as we vary by, the position of the periodic orbit
at the centre of the KAM surfaces changes. We use multiple-timescale perturbation
theory to predict this variation analytically. We also find that for some values of
by, all the KAM surfaces are destroyed owing to a resonance effect between two
timescales, making the phase space globally chaotic. By investigating the stability
of the solutions in the vicinity of the fixed point, we are able to predict for what
values of by this happens and when the KAM surfaces reappear.
Magneto-optical Kerr effect for a dissipative plasma
Authors: BUCHERT STEPHAN C.
Published: July 2002

Ion collisions in plasmas cause damping of hydromagnetic modes,
but also a strong Hall effect if the collision time is of the same order as
the gyroperiod.
This is known to be very marked in the E region of the Earth's
ionosphere, but
should also occur in other partially ionized space and laboratory
plasmas. In this work dynamic effects of such Hall currents are investigated
theoretically. The linear modes that are obtained are, for sufficiently
large scales, distinctly
different from ordinary damped Alfvén modes, and similar to
whistler waves even when the dynamic time scale is much longer than the ion
gyroperiod. The
dynamics of the coupling between planetary ionospheres and magnetospheric
plasmas may be viewed as a reflection of Alfvén waves at a
sharp boundary. By
applying the results of the linear mode analysis, it is shown
that the usually employed reflection coefficient needs to be replaced by a
reflection tensor for
large-scale waves due to self-induction of ionospheric Hall currents.
This is similar to the magneto-optical Kerr effect, which is well-known in
solid state physics. In the Earth's ionosphere, variations from
incident torsional modes
over periods as long as several minutes, which have been observed to
occur over scales of a few thousand kilometres, are predicted to cause the
generation of substantial eddy electric fields and compressional flows.
Consequences for the
energy exchange between ionosphere and magnetosphere and possibilities to
observe the effect are discussed.
Some properties of large-amplitude, negative-potential solitary waves

in a three-component plasma
Authors: SHERIDAN T. E.
Published: July 2002

Large-amplitude, negative-potential solitary waves in a plasma
containing
positive and negative, cold, collisionless ions and isothermal electrons
are
studied computationally and analytically. When their amplitude and speed
are
large, both speed and width are proportional to the square root of amplitude.

That is, amplitude is proportional to speed squared, while width increases

directly with speed. Approximate expressions relating these quantities
are
derived.
Dielectric screening and stopping power of a
test charge moving in a plasma
Authors: SHIVAMOGGI B. K. , MULSER P.
Published: July 2002

Investigations are made of the dielectric screening and stopping
power of a test
charge moving in a plasma. Effects of collisions with neutral particles,
if any,
and the effect of an applied magnetic field with and without plasma
inhomogeneity are taken into account and described.
Shipibo
Authors: Valenzuela Pilar M. , Pinedo Luis Márquez , Maddieson Ian
Published: July 2002

The Shipibo language is spoken by about 30,000 people in the Ucayali River valley, in the Upper Amazon watershed in the central eastern part of Peru. The language is sometimes also called Shipibo-Conibo after the two main previously distinct ethnic groups which form its speakers. It is a member of the Panoan family and thus is related to such languages as Capanahua, Amahuaca and Chacobo. Panoan languages are principally found in Peru but the family also has members in Bolivia and Brazil. This description is based on the speech of the second author, a 30-year-old male from the village of Dos Unidos de Pachitea. The Río Pachitea flows into the Ucayali, which itself forms one of the major headwaters of the Amazon.
The endostyle and the feeding filter in salps (Tunicata)
Authors: Bone Q. , Carre C. , Ryan K.P.
Published: July 2002

This note examines the way the pharyngeal feeding filter is constructed within the salp endostyle. Three salp species (Pegea confoederata, Thalia democratica and Salpa fusiformis) have been examined: results from each are essentially similar. The endostyle is a deep ventral groove in the pharynx, divided by a line of long basal cilia. These are flanked by gland cells which secrete the ‘mucus” which forms one of the sets of filaments of the filter. Beside the openings of this basal row of gland cells (marked by bumps of curious ‘mucus’ rodlets), there is a fence of two adjacent rows of cilia. The first of these two rows, (nearest the basal mid-line), whose tips lie next to the rodlet bumps, are regularly spaced 1.0 μm apart along the endostyle, whilst the cilia of the second row are at around half this spacing. Passing upwards in the endostylar groove, this first ciliary fence is followed by a ciliated zone, and then a second row of glandular cells is linked to a second ciliary fence with a single row of cilia only.

Filaments derived from the first set of gland cells pass obliquely over the ciliated zone, and continue over the second ciliary fence. The cilia of the second fence are often surrounded by very striking borders or curtains of rodlets which appear to dissolve, run down the cilia and pass off the tips as filaments, when they are joined by the first set of filaments to form a net with an elongate rhomboidal mesh. As this passes upwards, the mesh changes to become more or less square by the time it comes to overlie a striking asymmetrical band of cilia arranged in columns, when it is now composed of two sets of filaments running vertically and horizontally, spaced some 1.3 μm apart.

Various aspects of the formation of this filter net are considered.
Seasonal patterns in the reproductive activity of barnacle-dwelling littorinids
Authors: Johnson Lisa J. , Mill Peter J. , Hull Susan L. , Ducrotoy Paul , Caley Kevin J.
Published: July 2002

The reproductive activity of a population of barnacle-dwelling littorinids at Peak Steel, on the north-east coast of England, was investigated. Variation in the number of mature males and females, expressed as a percentage of the whole population, showed a marked difference among the barnacle-dwelling littorinids. Littorina neglecta displayed a distinct seasonal component to its reproductive activity, with a peak in early summer. Littorina arcana B also displayed a distinct seasonal component, with a lull in the summer months. However, L. saxatilis B maintained its reproductive activity all year, but with an increase in output in the summer. The reproductive activity of both L. arcana B and L. saxatilis B follow similar patterns of reproductive activity as their typical non barnacle-dwelling forms, suggesting that these are true barnacle-dwelling ecotypes. The controversy surrounding the specific status of L. neglecta is also discussed.
Seasonal variations of total mercury in foliar tissues of Posidonia oceanica
Authors: Capiomont Anne , Piazzi Luigi , Pergent Gérard
Published: July 2002

Cold vapour atomic absorption spectrophotometry (CV-AAS) was used to evaluate total mercury concentrations in Posidonia oceanica, after initial mineralization of the samples in a microwave oven. Measurements were taken of three leaf tissue types: the adult leaf blade, the adult leaf sheath, and the intermediate leaf blade. Plants were sampled monthly over a one year period at two sites presenting different degrees of pollution: Rosignano (Tuscany, Italy) and Tonnara (Corsica, France).

The mercury concentrations recorded in the different P. oceanica tissues were systematically higher at the more contaminated of the two sites, thus confirming the value of this plant as a biological indicator. The mercury concentrations observed exhibit seasonal variations, with higher concentrations recorded in winter than in summer. These variations seemed to be negatively correlated to the plant's phenology. Also, the mean mercury concentrations were generally lower in young tissue (intermediate leaf blade) than in the older tissue (adult leaf blade).
Size at maturity of Liocarcinus depurator (Brachyura: Portunidae): a reproductive and morphometric study
Authors: Muiño Rámon , Fernández Luis , González-Gurriarán Eduardo , Freire Juan , Vilar José A.
Published: July 2002

Sexual maturity in brachyurans is often associated with an allometric change in the relative growth of the animal. Maturity of Liocarcinus depurator was examined by analysing the monthly percentages of mature females (determined by the stage of gonad maturation and the presence of brood and sperm plugs) by size-class and the relative growth of different body parts: length and width of the carapace, length, height and width of the cheliped propodus; width of the abdominal segments in females and length of the first pleopod in males. Using the reproductive criteria the size at the onset of sexual maturity (carapace width at which 50% females are mature) in females of L. depurator is around 30–34 mm cephalothorax width. Principal component analysis (PCA) showed that the main source of morphometric variation for both sexes was due to heterochelia and allometric changes in growth. Morphometric variables were fitted using different regression techniques to one and two-phase growth models. The length of the first pleopod and the propodus of the right cheliped in males, and width of abdominal segments in females showed two clearly differentiated phases. Estimated maturity size (carapace width) corresponding to 50% mature animals was greater in males than in females. In males, size at the onset of maturity ranged between 31.4 and 35.7 mm, depending on the methods and variables used. The size at the onset of maturity in females ranged between 25.5 and 31.5 mm. In the Ría de Arousa, the size at maturity in females of L. depurator estimated using reproductive criteria is considerably greater than the size found based on morphometric criteria. The size at maturity based on morphometric criteria is greater in males than in females.
Early postlarval fish in the hyperbenthos of the Dutch Delta (south-west Netherlands)
Authors: Beyst Bregje , Mees Jan , Cattrijsse André
Published: July 2002

Early (post)larval fish constitute a significant part of the temporary hyperbenthos, i.e. of the fauna living in the lower reaches of the water column close to the substratum. Information on the densities and spatial and temporal variations of these stages, as well as on their lengths at the moment of occurrence, can be an important contribution to the knowledge of their dispersion, migrations and to the identification of possible bottlenecks in their recruitment. Therefore the hyperbenthos of the Voordelta, a shallow coastal zone in front of the Dutch Delta, as well as that of the subtidal channels and the intertidal brackish marsh creeks of the Westerschelde Estuary, was sampled monthly during one year by means of a sledge and a stow net. A total of 37 taxa were recorded from 410 samples. Densities often exceeded 400 ind 1000 m−2 in the Voordelta and 300 ind 1000 m−2 in the Westerschelde, including the tidal marshes of Waarde and Saeftinghe. The dominant taxa were clupeid larvae (predominantly herring Clupea harengus and sprat Sprattus sprattus), Pomatoschistus spp. (a mixture of sand goby P. minutus and Lozano's goby P. lozanoi), common goby Pomatoschistus microps, Syngnathus spp. (probably almost exclusively Nilsson's pipefish S.rostellatus), plaice Pleuronectes platessa, sole Solea solea and flounder Pleuronectes flesus. Most species were found at a larger size in the Westerschelde (and in the tidal marshes) suggesting migration from the shallow coastal area into the estuary. Several species utilize the tidal marshes in the brackish reaches of the Westerschelde. The nursery value of these areas however, is restricted to specific early life history stages of a few species, especially flounder, bass Dicentrarchus labrax and the common goby. The estuary itself seems to function as a nursery for other species like sole and plaice. The hyperbenthic sledge was found to sample specific life history stages of postlarval flatfish (early settlement stages at the onset of asymmetry), which are not easy to sample with other types of sampling gear.
Biomechanics and mass mortality of erect bryozoans on a coral reef
Authors: Barnes David K.A. , Whittington Mark
Published: July 2002

The bryozoan Cigclisula sp., is a heavily calcified erect species which occurs abundantly in the shallow sublittoral coral reef at Quilaluia Island, Quirimba Archipelago, northern Mozambique. It grows in an arborescent bilaminate form termed adeoniform on the undersides of coral heads or other available bioconstructed hard substratum. The geography and bathymetry of the area results in periodic high and complex current regimes often carrying water borne debris. If this periodic force overcomes the structural integrity of Cigclisula sp. either the outermost branches break or the colony topples at the base. The local population was dominated by young individuals: nearly 40% of the sample population had ten branches or fewer and less than 10% had more than 50 branches (these could be ascertained as young due to the lower proportion of damaged colonies with ≤10 branches; Figure 1). The only size group with no damaged specimens (branch breakage) were those with ≤5 branches. The mean proportion of branches broken significantly increased with increasing colony size. After one year a population of Cigclisula sp., initially comprising 30 colonies (encompassing the entire size spectrum of colonies), consisted of just one small specimen.
Sex-biased colour polymorphism in the marine ostracod Paradoxostoma variabile (Crustacea)
Authors: Hull Susan L. , Rollinson Daniel
Published: July 2002

Samples of four species of algae were collected from three mid-shore pools on each of three shores on the north-east coast of England in order to describe colour polymorphism in the common intertidal ostracod Paradoxostoma variabile. Eight different colour morphs were found within the populations. On all shores, male P. variabile occurred in significantly higher densities than did the females, and males exhibited a significantly higher colour morph diversity and colour morph richness than females. On two out of three shores, males showed a significant association in colour morph frequency with algal species (but the pattern was not consistent between shores), but no such association was found in the female populations. In either sex, colour morph diversity did not vary between algal species but samples of male ostracods from the shore at Holbeck contained a significantly higher diversity of colour morphs than samples from the other two shores. In the laboratory, neither sex demonstrated a specific association with algal species suggesting that habitat selection is not an important factor in maintaining colour morph frequencies in this species.
The Schistosoma mansoni host-interactive tegument forms from vesicle eruptions of a cyton network
Authors: SKELLY P. J. , SHOEMAKER C. B.
Published: July 2002

During trans-dermal invasion of the vertebrate host, larval schistosomes (cercariae) transform into schistosomula and become enveloped by a double lipid bilayered, tegumental membrane. The glucose transporter protein SGTP4 is found exclusively in these host-interactive tegumental membranes and in membranous vesicles proposed to be their precursor. In this study, we monitored the appearance and migration of this tegumental marker protein during larval transformation to test the current model of tegumental membrane biosynthesis in parasitic blood flukes. Only minutes after transformation was initiated, SGTP4 began accumulating in a previously unrecognized, bilaterally symmetrical, ‘cyton network’ beneath the peripheral muscle. Approximately 30min after the initiation of transformation the marker protein was seen in tubules connecting the network to the surface and erupting onto the surface in discrete patches. After 1h the patches were regularly arrayed over the schistosomula body and began to cover the anterior organ. By 3h the staining has largely resolved into a contiguous layer of fluorescence covering most of the worm surface. These findings confirm earlier suggestions, based on electron microscopy, that the parasite's surface tegumental membranes are derived from the migration of membranous vesicles produced within cytons and reveal a new subtegumental architecture interconnecting the cytons.
The effect of anthelmintic treatment on helminth infection and anaemia
Authors: GILGEN D. , MASCIE-TAYLOR C.G.N.
Published: July 2002

A 24-week randomized double blind intervention trial was conducted on adult female tea pluckers from an estate in Bangladesh to investigate the impact of iron supplementation and anthelmintic treatment on changes in ferritin and haemoglobin levels as well as on prevalence and intensity of helminth infections. A total of 553 women were randomly assigned to 1 of 4 intervention groups: group 1 received iron supplementation on a weekly basis, group 2 received anthelmintic treatment at the beginning and half way through the trial, group 3 received both iron supplementation as group 1 and anthelmintic treatment as group 2, and group 4 was a control group and received placebos for both iron supplementation and anthelmintic treatment. Prevalence and intensity of helminth infections (egg counts/g stool) of Ascaris lumbricoides, Trichuris trichiura and hookworms significantly fell in the 2 groups receiving anthelmintic treatment and there were some reductions in the 2 groups not receiving anthelminthic treatment. Haemoglobin and haematocrit concentrations increased significantly in the iron supplemented groups with smaller increases in the anthelmintic only group. All women showed a decrease in serum ferritin levels post-trial with greater losses in the 2 dewormed groups. Significant negative associations were found between hookworm egg counts and ferritin levels and Trichuris trichiura egg counts and haemoglobin concentration.
Prevalence, transmission and intensity of infection by a microsporidian

sex ratio distorter in natural Gammarus duebeni populations
Authors: DUNN A. M. , HATCHER M. J.
Published: July 2002

This is a report of the prevalence, transmission and intensity

of infection of a microsporidian sex ratio distorter in natural

populations of its crustacean host Gammarus duebeni. Prevalence

in the adult host population reflects differences in the

intensity of infection in transovarially infected embryos and in

adult gonadal tissue. The efficiency of transovarial parasite

transmission to young also differs between populations, but this

alone is insufficient to explain observed patterns of

prevalence. Infection intensity may be important in determining

future infection of target tissue in the adult and

subsequent transmission to future host generations. We consider

patterns of parasite infection in terms of selection on

transmission and virulence.
‘Total evidence’ refutes the inclusion of Perkinsus
species in the phylum Apicomplexa
Authors: SIDDALL M. E. , REECE K. S. , GRAVES J. E. , BURRESON E. M.
Published: July 2002

The phylogenetic affinities of the oyster pathogen Perkinsus
marinus were investigated with morphology, 18S-like rDNA
data and actin sequence data. Morphological investigations revealed that
Perkinsus species do not have a conoid and that
other criteria which have been used to place them in the Apicomplexa are
general to alveolates. When considered separately,
18S-like rDNA and actin data sets each support a closer affinity for
Perkinsus marinus with the dinoflagellates. However,
each of these separate analyses possess their own biases and weaknesses.
Use of the phylogenetic principle of ‘total
evidence’ in which data sets are combined in simultaneous analysis
yielded a more robust hypothesis that is stable both
to character and taxonomic sampling. The resulting cladogram strongly
corroborates the placement of Perkinsus species
with the Dinoflagellida and not with the Apicomplexa.
The influence of dietary supplementation with urea on
resilience and resistance to infection with Haemonchus contortus
Authors: WALLACE D. S. , BAIRDEN K. , DUNCAN J. L. , ECKERSALL P. D. , FISHWICK G. , GILL M. , HOLMES P. H. , McKELLAR Q. A. , MURRAY M. , PARKINS J. J. , STEAR M. J.
Published: July 2002

Previous research has indicated that supplementing an apparently
adequate diet with additional protein improves both
host resistance and resilience in lambs infected with
Haemonchus contortus. The present study tested the influence of
supplementation with non-protein nitrogen (urea). Helminth-naive
Hampshire Down lambs were given an apparently
adequate basal diet or a diet supplemented with urea. The lambs were
then infected with Haemonchus contortus for
10 weeks. Supplementation with urea had no discernible effect on
resistance to infection; faecal egg counts, worm burdens,
worm lengths and mean number of eggs per adult female worm did not
differ between the 2 groups. However, lambs on
the supplemented diet showed better resilience; they had greater
packed red cell volumes, higher plasma albumin
concentrations and increased liveweight gain compared to lambs on
the basal diet. The loss of appetite following infection
was less in lambs fed the urea-supplemented diet. The observed effect
of urea supplementation was seemingly due to
greater food consumption as well as the better diet.
Identification of an Ixodes ricinus salivary gland fraction
through its ability to stimulate CD4 T cells present in
BALB/c mice lymph nodes draining the tick fixation site
Authors: GANAPAMO F. , RUTTI B. , BROSSARD M.
Published: July 2002

BALB/c mice infested with larvae or nymphs of Ixodes
ricinus develop in their lymph nodes a T cell-specific immune
response triggered by salivary gland soluble antigens (SGA). SGA are
apparently conserved in the 3 biological stages of
I. ricinus ticks and are species specific. SGA derived from
partially fed females I. ricinus stimulate lymph node T cells from
mice infested with I. ricinus larvae or nymphs. In contrast,
lymph node cells from mice infested with Amblyomma hebraeum
nymphs do not respond. A chromatographic fraction enriched with a
65 kDa protein (IrSG65) isolated from salivary
glands of I. ricinus partially fed females induces in vitro
a specific T cell proliferation of lymph node cells from mice
infested with I. ricinus nymphs. The depletion of CD4+ T
cells drastically reduces the ability of lymphocytes from infested
mice to proliferate after IrSG65 stimulation.
Isolation of an aspartic proteinase precursor from the egg
of a hard tick, Boophilus microplus
Authors: LOGULLO C. , DA SILVA VAZ I. , SORGINE M. H. F. , PAIVA-SILVA G. O. , FARIA F. S. , ZINGALI R. B. , DE LIMA M. F. R. , ABREU L. , OLIVEIRA E. FIALHO , ALVES E. W. , MASUDA H. , GONZALES J. C. , MASUDA A. , OLIVEIRA P. L.
Published: July 2002

An aspartic proteinase precursor, herein named BYC
(Boophilus Yolk pro-Cathepsin) was isolated from eggs of the hard

tick, Boophilus microplus. As judged by electrophoresis on sodium

dodecyl sulfate polyacrylamide slab gel (SDS–PAGE),
purified BYC presented 2 bands of 54 and 49 kDa, bearing the same
NH2-terminal amino acid sequence. By Western blot
analysis, BYC was also found in the haemolymph, indicating an extraovarian

site of synthesis. Several organs were incubated in culture medium with

[35S] methionine, and only the gut and fat body
showed synthesis of BYC polypeptides.
Protein sequencing of both the NH2-terminal and an internal

sequence obtained after cyanogen bromide (CNBr) cleavage
of BYC revealed homology with several aspartic proteinase precursors.
Incubation at pH 3·5 resulted in autoproteolysis of
BYC, which produced the mature form of the enzyme, that displayed
pepstatin-sensitive hydrolytic activity against
haemoglobin. Western blot analysis using anti-BYC monoclonal antibodies

showed proteolytic processing of BYC during
embryogenesis and suggested activation of the enzyme during development.
A
role of BYC in degradation of vitellin, the
major yolk protein of tick eggs, is discussed.
Polymerase chain reaction–restriction fragment length
polymorphism (PCR–RFLP) for the identification of
Trichinella isolates
Authors: WU Z. , NAGANO I. , POZIO E. , TAKAHASHI Y.
Published: July 2002

In the present study, polymerase chain reaction–restriction
fragment length polymorphism (PCR–RFLP) analysis was
developed to identify 5 species (Trichinella spiralis, Trichinella
britovi, Trichinella nativa, Trichinella nelsoni
and Trichinella
pseudospiralis) and 3 phenotypes of uncertain taxonomic status (Trichinella
T5, T6, and T8). Eleven restriction endonucleases
were used to restrict 3 DNA fragments (1) a 2800 bp fragment of the 43
kDa excretory–secretory (E–S) protein
gene, (2) a 1250 bp fragment amplified with the primer pair SB147A and
(3) a 372 bp fragment amplified with the primer
pair SB372A. This RFLP method allows the identification of the 8 Trichinella
phenotypes as follows: T. spiralis by the
HinfI or DdeI endonuclease restriction of the 2800 bp
fragment; T. nativa by the RsaI restriction of the 2800
bp fragment,
or by the AluI restriction of the 1250 bp fragment; T. britovi
and Trichinella T8 by the AluI restriction of the 1250
bp
fragments, and can be discriminated between them by the SspI restriction
of the 2800 bp fragment; T. pseudospiralis by
the MspI restriction of the 372 bp fragment; T. nelsoni
by the HhaI or AluI restriction of the 2800 bp fragment;
Trichinella
T5 by the HhaI restriction of the 2800 bp fragment; Trichinella
T6 by the AluI restriction of the 1250 bp fragment; and
Trichinella T8 by the SspI or RsaI restriction
of the 2800 bp fragment. This study reveals also an intraspecifies polymorphism

in the 2800 bp and 1250 bp fragments for T. britovi, Trichinella
T5 and T6.
Normative and Natural Laws
Authors: Mumford Stephen
Published: July 2002

A theory of laws is developed that takes from E. J. Lowe the claim of natural laws being consistent with certain classes of exceptions. Neither abnormal cases, such as albino ravens, nor miracles falsify covering laws. This suggests that law statements cannot have the form of a universally quantified conditional. Lowe takes it that this is best explained by natural laws having normative force in the same way as moral laws and laws of the land. I argue that there is a non-normative, descriptivist account that also explains the exception cases and which is preferable, given our reservations about normative laws of nature. I also suggest an improved account of miracles within the descriptivist account.