bluuebunny/crossref_metadata_2025 huggingface dataset:
The proper orthogonal decomposition of pressure

fluctuations surrounding a turbulent jet
Authors: ARNDT R. E. A. , LONG D. F. , GLAUSER M. N.
Published: July 2002

It is shown that the pressure signal measured at the outer edge
of a

jet mixing layer is

entirely hydrodynamic in nature and provides a good measure of the large-scale

structure of the turbulent flow. Measurement of the pressure signal provides
a unique

opportunity to utilize proper orthogonal decomposition (POD) to deduce
the

streamwise structure. Since pressure is a scalar, a significant reduction

in the numerical

and experimental complexity inherent in the analysis of velocity vector

fields results.

The POD streamwise eigenfunctions show that the structure associated
with any

frequency–azimuthal mode number combination displays the

general characteristics of

amplification–saturation–decay of an instability wave,

all within about three

wavelengths. High-frequency components saturate early in x and
low-frequency

components saturate further downstream, indicative of the inhomogeneous
character

of the flow in the streamwise direction. Application of the POD technique
allows the

phase velocity to be determined taking into account the inhomogeneity of
the flow in

the streamwise direction. The phase velocity of each instability

wave (POD eigenvector)

is constant and equal to 0.58Uj, indicating

that the jet structure is non-dispersive.

Using the shot-noise decomposition, a characteristic event is constructed.

This event

is found to contain evidence of both pairings and triplings of vortex

structures. The

tripling results in a rapid increase in the first asymmetric

(m=1) component. On

average, pairing occurs once every four

Uj/D while tripling occurs

once every 13Uj/D.
Reflection of a high-amplitude solitary wave

at a vertical wall
Authors: COOKER M. J. , WEIDMAN P. D. , BALE D. S.
Published: July 2002

The collision of a solitary wave, travelling over a horizontal
bed,

with a vertical wall

is investigated using a boundary-integral method to compute the potential
fluid flow

described by the Euler equations. We concentrate on reporting new results
for

that part of the motion when the wave is near the wall. The wall residence
time,

i.e. the time the

wave crest remains attached to the wall, is introduced. It is shown that
the wall

residence time provides an unambiguous characterization of the phase shift
incurred

during reflection for waves of both small and large amplitude. Numerically
computed

attachment and detachment times and amplitudes are compared with asymptotic

formulae developed using the perturbation results of Su & Mirie (1980).

Other features

of the flow, including the maximum run-up and the instantaneous wall force,
are also

presented. The numerically determined residence times are in good agreement
with

measurements taken from a cine film of solitary wave reflection

experiments conducted by Maxworthy (1976).
Microstructure of strongly sheared suspensions
and its impact on rheology and diffusion
Authors: BRADY JOHN F. , MORRIS JEFFREY F.
Published: July 2002

The effects of Brownian motion alone and in combination with an
interparticle force
of hard-sphere type upon the particle configuration in a strongly sheared
suspension
are analysed. In the limit Pe→∞ under the influence
of hydrodynamic interactions
alone, the pair-distribution function of a dilute suspension of spheres
has symmetry
properties that yield a Newtonian constitutive behaviour and
a zero self-diffusivity.
Here, Pe=γ˛a2/2D is
the
Péclet number with γ˛ the shear rate, a
the particle radius,
and D the diffusivity of an isolated particle. Brownian
diffusion at large Pe gives rise to an
O(aPe−1) thin boundary layer at contact
in which the effects of Brownian
diffusion and advection balance, and the pair-distribution function is
asymmetric
within the boundary layer with a contact value of
O(Pe0.78) in pure-straining motion;
non-Newtonian effects, which scale as the product of the contact value
and the
O(a3Pe−1) layer
volume,
vanish as Pe−0.22 as Pe→∞.
Transonic flow of dense gases around an airfoil

with a parabolic nose
Authors: RUSAK ZVI , WANG CHUN-WEI
Published: July 2002

Transonic potential flow of dense gases of retrograde type

around the leading edge of

a thin airfoil with a parabolic nose is studied. The analysis follows the
approach of

Rusak (1993) for a perfect gas. Asymptotic expansions of the velocity potential

function are constructed in terms of the airfoil thickness ratio in

an outer region around

the airfoil and in an inner region near the nose. The outer expansion consists
of the

transonic small-disturbance theory for dense gases, where a leading-edge
singularity

appears. Analytical expressions are given for this singularity by

constructing similarity

solutions of the governing nonlinear equation. The inner expansion accounts
for the

flow around the nose, where a stagnation point exists. A boundary value
problem

is formulated in the inner region for the solution of an oncoming uniform
sonic

flow with zero values of the fundamental derivative of gasdynamics

(Γ=0) and the second nonlinearity parameter (Λ=0) around a
parabola

at zero angle of attack. The numerical solution of the inner problem

results in a symmetric flow around

the nose. The outer and inner expansions are matched asymptotically resulting
in a

uniformly valid solution on the entire airfoil surface. In the

leading terms, the flow

around the nose is symmetric and the stagnation point is located at the
leading edge

for every transonic Mach number, and small values of Γ and Λ
of the

oncoming flow and any shape and small angle of attack of the airfoil.

Furthermore, analysis of the

inner region in the immediate neighbourhood of the stagnation point reveals
that the

flow is purely subsonic, approaching critical conditions in the

limit of large (scaled) distances, which excludes the formation of shock

discontinuities in the nose region.
Nonlinear self-excited oscillations of a ducted flame
Authors: DOWLING A. P.
Published: July 2002

Self-excited oscillations of a confined flame, burning in

the wake of a bluff-body flame-holder, are considered. These

oscillations occur due to interaction between unsteady

combustion and acoustic waves. According to linear theory, flow disturbances
grow

exponentially with time. A theory for nonlinear oscillations

is developed, exploiting the

fact that the main nonlinearity is in the heat release rate,

which essentially ‘saturates’.

The amplitudes of the pressure fluctuations are sufficiently

small that the acoustic waves remain linear. The time evolution of the
oscillations

is determined by numerical

integration and inclusion of nonlinear effects is found to lead to

limit cycles of finite

amplitude. The predicted limit cycles are compared with results from experiments

and from linear theory. The amplitudes and spectra of the limit-cycle oscillations

are in reasonable agreement with experiment. Linear theory is found to
predict the

frequency and mode shape of the nonlinear oscillations remarkably well.
Moreover,

we find that, for this type of nonlinearity, describing function

analysis enables a good

estimate of the limit-cycle amplitude to be obtained from linear theory.

Active control has been successfully applied to eliminate these oscillations.
We

demonstrate the same effect by adding a feedback control system to our
nonlinear

model. This theory is used to explain why any linear controller capable

of stabilizing the linear flow disturbances is also able to stabilize

finite-amplitude oscillations in the nonlinear limit cycles.
Direct numerical simulation of forced MHD turbulence at low magnetic
Reynolds number
Authors: ZIKANOV OLEG , THESS ANDRE
Published: July 2002

The transformation of initially isotropic turbulent flow of electrically
conducting
incompressible viscous fluid under the influence of an imposed homogeneous
magnetic
field is investigated using direct numerical simulation. Under the assumption
of large
kinetic and small magnetic Reynolds numbers (magnetic Prandtl number
Pm[Lt ]1) the quasi-static
approximation is applied for the computation of the magnetic
field fluctuations. The flow is assumed to be homogeneous and contained
in a
three-dimensional cubic box with periodic boundary conditions. Large-scale
forcing
is applied to maintain a statistically steady level of the flow energy.
It is found
that the pathway traversed by the flow transformation depends decisively
on the
magnetic interaction parameter (Stuart number). If the magnetic interaction
number
is small the flow remains three-dimensional and turbulent and no detectable
deviation
from isotropy is observed. In the case of a strong magnetic field (large
magnetic
interaction parameter) a rapid transformation to a purely two-dimensional
steady state
is obtained in agreement with earlier analytical and numerical results
for decaying
MHD turbulence. At intermediate values of the magnetic interaction parameter

the system exhibits intermittent behaviour, characterized by organized
quasi-two-dimensional
evolution lasting several eddy-turnover times, which is interrupted by

strong three-dimensional turbulent bursts. This result implies that the
conventional
picture of steady angular energy transfer in MHD turbulence must be refined.
The
spatial structure of the steady two-dimensional final flow obtained in
the case of
large magnetic interaction parameter is examined. It is found that due
to the type of
forcing and boundary conditions applied, this state always occurs in the
form of a
square periodic lattice of alternating vortices occupying the largest possible
scale. The
stability of this flow to three-dimensional perturbations is analysed using
the energy
stability method.
A universal time scale for vortex ring formation
Authors: GHARIB MORTEZA , RAMBOD EDMOND , SHARIFF KARIM
Published: July 2002

The formation of vortex rings generated through impulsively started
jets is studied
experimentally. Utilizing a piston/cylinder arrangement in a water
tank, the velocity
and vorticity fields of vortex rings are obtained using digital particle
image velocimetry
(DPIV) for a wide range of piston stroke to diameter
(L/D) ratios. The results indicate
that the flow field generated by large L/D consists

of a leading vortex ring followed
by a trailing jet. The vorticity field of the leading vortex ring formed
is disconnected
from that of the trailing jet. On the other hand, flow fields generated
by small stroke
ratios show only a single vortex ring. The transition between these two
distinct states
is observed to occur at a stroke ratio of approximately 4, which, in this
paper, is
referred to as the ‘formation number’. In all cases, the maximum
circulation that
a vortex ring can attain during its formation is reached at this non-dimensional

time or formation number. The universality of this number was tested by
generating
vortex rings with different jet exit diameters and boundaries, as well
as with various
non-impulsive piston velocities. It is shown that the ‘formation

number’ lies in the
range of 3.6–4.5 for a broad range of flow conditions. An explanation
is provided
for the existence of the formation number based on the Kelvin–Benjamin
variational
principle for steady axis-touching vortex rings. It is shown that based
on the measured
impulse, circulation and energy of the observed vortex rings, the Kelvin–Benjamin

principle correctly predicts the range of observed formation numbers.
A note on interior vs. boundary-layer damping of surface waves in
a circular cylinder
Authors: MILES J. W. , HENDERSON D. M.
Published: July 2002

Martel et al. (1998) have shown that interior damping
may be comparable with
boundary-layer damping for surface waves in small cylinders and that its
incorporation
yields predictions in agreement with the experimental results of Henderson

& Miles (1994) for non-axisymmetric waves on a clean surface with a
fixed contact
line. In the present note, Henderson & Miles's boundary-layer
calculation is
supplemented by a calculation of interior damping based on Lamb's
dissipation
integral for an irrotational flow. The analysis, which omits second-order
boundary-layer
effects, is simpler than that of Martel et al. (which includes
these effects and
is based on an expansion in an inverse Reynolds number), but yields results
of
comparable accuracy within the parametric domain of the experiments. The
corresponding
calculations for a fully contaminated (inextensible) surface reduce the

discrepancy between calculation and experiment but, in contrast to the
results for
a clean surface, leave a significant residual discrepancy. An unexplained
discrepancy
also remains for axisymmetric waves on either a clean or a contaminated
surface.
Formation of a jump by the dam-break wave over a granular bed
Authors: CAPART H. , YOUNG D. L.
Published: July 2002

A previously unreported shock feature associated with the scouring
of a horizontal
granular bed by a dam-break wave is discussed. Near the wave centre, the
present
study shows, the free surface breaks backward and a hydraulic jump forms.
This behaviour
is described from the standpoint of shallow-water theory, suitably extended

to deal with non-equilibrium sediment transport. The shock formation involves
a
particularly strong coupling between flow free-surface evolution and bed
morphodynamics.
Support for our conclusions is sought through experimental and numerical

approaches. In order to magnify the observed phenomena, measurements were
performed
for the case of light bed particles moving in sheet and debris flow modes.

A detailed picture of the transient two-phase flow is presented, based
on whole
field acquisition of the grain motions by particle tracking techniques.
Corresponding
shallow-water solutions are constructed numerically using a shock capturing
scheme.
Finally, an interpretation of the jump formation is proposed based on the
theory of
characteristics.
Turbulent combined oscillatory flow and current in a pipe
Authors: LODAHL C. R. , SUMER B. M. , FREDSØE J.
Published: July 2002

This work concerns the combined oscillatory flow and current in
a circular, smooth
pipe. The study comprises wall shear stress measurements, and laser-Doppler-anemometer

velocity and turbulence measurements. Three kinds of pipes were used,
with diameters D=19 cm, 9 cm, and 1.1 cm, enabling the influence
of the parameter
R/δ to be studied in the investigation (R/δ
ranging
from about 3 to 53), where R is the
radius of the pipe, and δ is the Stokes layer thickness. The ranges
of the two other
parameters of the combined flow processes, namely the current Reynolds
number,
Rec,
and the oscillatory-flow boundary-layer (i.e. the wave–boundary layer)
Reynolds
number, Rew, are:
Rec=0−1.6×105, and

Rew=0−7×106. The transition
to turbulence
in the combined flow case occurs at a current Reynolds number larger than
the
conventional value, ca. 2×103, depending on
Rew, and R/δ. A turbulent
current can
be laminarized by superimposing an oscillatory flow. The overall average
value of the
wall shear stress (the mean wall shear stress) may retain its steady-current
value, it may
decrease, or it may increase, depending on the flow regime. The increase
(which can be
as much as a factor of 4) occurs when the combined flow is in the wave-dominated

regime, while the oscillatory-flow component of the flow is in the turbulent
regime. The
component of the wall shear stress oscillating around the mean wall shear
stress can
also increase with respect to its oscillatory-flow-alone value. For this
to occur, the
originally laminar oscillatory boundary layer needs to become a fully developed

turbulent boundary layer, when a turbulent current is superimposed. This
increase can
be as much as O(3–4). The velocity profiles across
the cross-section of the pipe change
near the wall when an oscillatory flow is superimposed on a current, in
agreement with
the results of the wall shear stress measurements. The period-averaged
turbulence
profiles across the cross-section of the pipe behave differently for different
flow regimes.
When the two components of the flow are equally significant, the turbulence
profile
appears to be different from those corresponding to the fundamental cases;
the level
of turbulence increases (only slightly) with respect to those experienced
in the
fundamental cases.
Effect of free-stream turbulence and other
vortical disturbances on a laminar boundary layer
Authors: LEIB S. J. , WUNDROW DAVID W. , GOLDSTEIN M. E.
Published: July 2002

This paper is concerned with the effect of free-stream turbulence
on the pretransitional
flat-plate boundary layer. It is assumed that either the turbulent Reynolds

number or the downstream distance (or both) is small enough that the flow
can be linearized.
The dominant disturbances in the boundary layer, which are of the Klebanoff

type, are governed by the linearized unsteady boundary-region equations,
i.e. the
linearized Navier–Stokes equations with the streamwise derivatives
neglected in the
viscous and pressure-gradient terms. The turbulence is represented as a
superposition
of vortical free-stream Fourier modes and the corresponding Fourier component
solutions
to the boundary-region equations are obtained numerically. The results
are then
superposed to compute the root mean square of the fluctuating streamwise
velocity
in the boundary layer produced by the actual free-stream turbulence. It
is found that
the disturbances computed with isotropic free-stream turbulence do not
reach the
levels measured in experiments. However, good quantitative agreement is
obtained
with the relatively low turbulent Reynolds number data of Kendall when
the measured
strong anisotropy of the low-frequency portion of his spectrum is accounted

for. Data at higher turbulent Reynolds numbers are affected by nonlinearity,
which
manifests itself through the generation of small spanwise length scales.
We attempt
to model this within the context of the linear theory by choosing a free-stream
spectrum
whose energy is concentrated at larger transverse wavenumbers and achieve

very good agreement with the data. The results suggest that even small
deviations
from pure isotropy can be an important factor in explaining the large amplitudes

of the Klebanoff modes in the pre-transitional boundary layer, and also
point to
the importance of nonlinear effects. We discuss some additional effects
that may
need to be accounted for in order to obtain a complete description of the
Klebanoff
modes.
Evaporation waves in superheated dodecane
Authors: SIMÕES-MOREIRA J. R. , SHEPHERD J. E.
Published: July 2002

We have observed propagating adiabatic evaporation waves in superheated
liquid
dodecane, C12H26. Experiments were
performed with a rapid decompression apparatus
at initial temperatures of 180–300°C. Saturated dodecane in a
tube was suddenly
depressurized by rupturing a diaphragm. Motion pictures and still photographic

images, and pressure and temperature data were obtained during the evaporation

event that followed depressurization. Usually, a front or wave of evaporation
started at
the liquid free surface and propagated into the undisturbed regions of
the metastable
liquid. The evaporation wave front moved with a steady mean velocity but
the
front itself was unstable and fluctuating in character. At low superheats,
no waves
were observed until a threshold superheat was exceeded. At moderate superheats,

subsonic downstream states were observed. At higher superheats, the downstream
flow
was choked, corresponding to a Chapman–Jouguet condition. At the
most extreme
superheat tested, a vapour content of over 90% was estimated from the measured

data, indicating a nearly complete evaporation wave. Our results are interpreted
by
modelling the evaporation wave as a discontinuity, or jump, between a superheated

liquid state and a two-phase liquid–vapour downstream state. Reasonable
agreement
is found between the model and observations; however, there is a fundamental

indeterminacy that prevents the prediction of the observed wave speeds.
Time-dependent response of a floating flexible
plate to an impulsively started steadily
moving load
Authors: NUGROHO W. S. , WANG K. , HOSKING R. J. , MILINAZZO F.
Published: July 2002

The time-dependent response of a floating flexible plate to an
impulsively started
steadily moving load defines the time taken to approach a steady-state
deflection
due to the load, or indeed whether such a steady state is achieved at all.
The
asymptotic analysis for large time reported here, for both a concentrated
point load
and a uniformly distributed circular load, confirms that a steady-state
deflection is
achieved at both subcritical and supercritical load speeds. This analysis
also predicts
a logarithmically growing response near the critical speed corresponding
to the
minimum phase speed of the hybrid waves generated, but an eventual steady-state

response when the load speed moves at the shallow water wave speed. These
results
are supported by numerical computation.
Experimental study of the sedimentation of
dilute and semi-dilute suspensions of fibres
Authors: HERZHAFT BENJAMIN , GUAZZELLI ÉLISABETH
Published: July 2002

Steady-state velocity and orientation distributions of sedimenting
fibres were measured
as a function of particle concentration and aspect ratio. Two different
regimes of
sedimentation were clearly identified. For dilute suspensions, the fibres
tend to align
in the direction of gravity with occasional flipping and clump together to
form
packets. In this regime, the vertical mean sedimentation speed is not hindered
and
can be larger than the Stokes' velocity of an isolated vertical fibre.
Its scaling is a
complex function of particle volume fraction and aspect ratio. As the concentration
is
increased, the fibres still tend to orient in the direction of gravity.
The mean velocity
becomes hindered and scales with particle volume fraction. The velocity
fluctuations
were found to be large and anisotropic. They were found to increase with
increasing
volume fraction. A similar substantial anisotropy of the orientation distribution
was
observed for all particle concentrations and aspect ratios studied.
A consistent coupled-mode theory for
the propagation of small-amplitude water waves
over variable bathymetry regions
Authors: ATHANASSOULIS G. A. , BELIBASSAKIS K. A.
Published: July 2002

Extended mild-slope equations for the propagation of small-amplitude water waves
over variable bathymetry regions, recently proposed by Massel (1993) and Porter
& Staziker (1995), are shown to exhibit an inconsistency concerning the sloping-bottom boundary condition, which renders them non-conservative with respect to
wave energy. In the present work, a consistent coupled-mode theory is derived from
a variational formulation of the complete linear problem, by representing the vertical
distribution of the wave potential as a uniformly convergent series of local vertical
modes at each horizontal position. This series consists of the vertical eigenfunctions
associated with the propagating and all evanescent modes and, when the slope of the
bottom is different from zero, an additional mode, carrying information about the
bottom slope. The coupled-mode system obtained in this way contains an additional
equation, as well as additional interaction terms in all other equations, and reduces
to the previous extended mild-slope equations when the additional mode is neglected.
Extensive numerical results demonstrate that the present model leads to the exact
satisfaction of the bottom boundary condition and, thus, it is energy conservative.
Moreover, it is numerically shown that the rate of decay of the modal-amplitude
functions is improved from O(n−2), where n is the
mode number, to O(n−4), when the additional
sloping-bottom mode is included in the representation. This fact substantially accelerates the
convergence of the modal series and ensures the uniform convergence of the velocity field
up to and including the boundaries.
Saline and particle-driven interfacial intrusions
Authors: DE ROOIJ FRANS , LINDEN P. F. , DALZIEL STUART B.
Published: July 2002

This paper presents a theoretical and experimental investigation into saline and
particle-driven intrusions along the interface between two layers of different densities.
The conditions at the nose of an intrusion are described in an analysis similar to that
applied by Benjamin (1968) to boundary gravity currents. Equations for propagation
velocity and front position as functions of relative density are derived. These are used
in an integral model for intrusions, which also includes the effects of sedimentation of
particles and detrainment of interstitial fluid. The model describes the time-evolution
of the length of the intrusion and the sediment distribution it produces. Laboratory
experiments were carried out with lock-releases of a fixed volume of saline or particle-laden fluid into a two-layer stratification. Measurements were taken of the intrusion
propagation, intrusion position and sediment distribution, and are found to be in
good agreement with the solutions of the integral model.
On the suppression of shock-induced separation
in Bethe–Zel'dovich–Thompson fluids
Authors: CRAMER M. S. , PARK S.
Published: July 2002

We consider the reflection of oblique compression waves from a two-dimensional,
steady, laminar boundary layer on a flat, adiabatic plate at free-stream pressures
such that dense-gas effects are non-negligible. The full Navier–Stokes equations are
solved through use of a dense-gas version of the Beam–Warming implicit scheme. The
main fluids studied are Bethe–Zel'dovich–Thompson (BZT) fluids. These are ordinary
gases which have specific heats large enough to cause the fundamental derivative of
gasdynamics to be negative for a range of pressures and temperatures in the single-phase vapour regime. It is demonstrated that the unique dynamics of BZT fluids
can result in a suppression of shock-induced separation. Numerical tests performed
reveal that the physical mechanism leading to this suppression is directly related to
the disintegration of any compression discontinuities originating in the flow. We also
demonstrate numerically that the interaction of expansion shocks with the boundary
layer produces no adverse effects.
A new approach to high-order Boussinesq models
Authors: AGNON Y. , MADSEN P. A. , SCHÄFFER H. A.
Published: July 2002

An infinite-order, Boussinesq-type differential equation for wave shoaling over variable
bathymetry is derived. Defining three scaling parameters – nonlinearity, the dispersion
parameter, and the bottom slope – the system is truncated to a finite order.
Using Padé approximants the order in the dispersion parameter is effectively doubled.
A derivation is made systematic by separately solving the Laplace equation in the
undisturbed fluid domain and then addressing the nonlinear free-surface conditions.
We show that the nonlinear interactions are faithfully captured. The shoaling and
dispersion components are time independent.
A note on the two-phase Hele-Shaw problem
Authors: HOWISON SAM D.
Published: July 2002

We discuss some techniques for finding explicit solutions to immiscible two-phase flow
in a Hele-Shaw cell, exploiting properties of the Schwartz function of the interface
between the fluids. We also discuss the question of the well-posedness of this problem.
Elite Politics and Popular Rebellion in
the Construction of Post-colonial
Order. The case of Maranhão, Brazil
(1820–41)
Authors: ASSUNÇÃO MATTHIAS RÖHRIG
Published: July 2002

This article seeks to explain the breakdown of post-colonial order
in the
northern Brazilian province of Maranhão that culminated in the Balaiada

rebellion (1838–41). Interpretations usually do not take into account
the intense
political agitation of the previous decades, which already involved lower
class
participation, and they fail to recognise the major socio-economic differences

between the areas touched by the revolt. The main arguments are, first,
that the
struggle for Independence in Maranhão, more violent than in most
other
provinces, opened the door to lower class involvement in politics under
liberal
leadership. Secondly, the struggle between local elites for regional power
led to
exclusion of peripheral elites within the province and fuelled lower class
unrest.
Significant moments of rupture between liberal leadership and popular movement

occurred as early as 1823–4 and 1831–2. Thirdly, the main structural
factor
leading to the 1838 outbreak of rebellion was the resistance to military

recruitment by the free lower classes, which provided a unifying slogan
to
otherwise heterogeneous groups of peasants, cowboys, and fishermen. Fourthly,

the differences in social structure between the cattle producing South,
the cotton
plantation belt of the Itapecuru valley and the strong subsistence sector
in Eastern
Maranhão account for substantial differences in terms of support
and leadership
during the Balaiada. Whilst fazendeiros lead the struggle in Southern
Maranhão,
as well as in most of the neighbouring Piauí province, leadership
in Eastern
Maranhão was almost entirely of lower class origin. Finally, the
dynamics of the
movement could lead in Eastern Maranhão to a rupture with elite
liberalism and
envisage the alliance between free rebels and maroons.
China's foreign policy towards Africa in the 1990s
Authors: Taylor Ian
Published: July 2002

The People's Republic of China's (PRC's) policy
towards Africa in the
1990s has its roots in the crisis surrounding the Tiananmen Square
crackdown on 4 June 1989, and the heavy and persistent criticism by
the developed world levelled against Beijing's human rights record

since that date. Previous to this, the importance of the African
continent to China had become less and less important in the 1980s, as

the Cold War underwent a thawing process and China's modernisation

project demanded foreign investment and technological assistance.
Though Chinese officials paid rhetorical lip service to such issues as

South–South co-operation, the reality of the situation was that Beijing

was mainly interested in maintaining intimate relations with those
countries from which it could benefit economically. In stark contrast to

China's position in the 1960s and 1970s, exhortations and propaganda

grounded in Maoist foundations disappeared, for the ‘socialist
modernisation’ project of Deng Xiaoping demanded economic investment

and a non-conflictual approach to international politics. As a
result, non-ideological relations with the United States, Western
Europe and Japan based on expanding trade links and co-operation
took a priority in China's foreign policy formulation.
Propagation of a large-amplitude rarefactive ion acoustic pulse
Authors: SINGH A. K. , SAXENA Y. C.
Published: July 2002

In an experiment carried out in a linear, unmagnetized plasma,
evolution and

propagation of nonlinear, rarefactive ion–acoustic pulses have

been investigated.

The nonlinear rarefactive pulse is observed to undergo fissioning as it
propagates.

Measurements of the ion velocity distribution function within the pulse
indicate

strong modifications of the distribution functions at velocities in the
neighbourhood

of the ion acoustic speed. Wave–particle interaction is thus shown

to play an important role in the observed behaviour. Large-amplitude

rarefactive pulses, while showing multiple fissioning, also exhibit

a large-amplitude, low-frequency (≈30 kHz)

oscillatory tail, downstream of the main pulse. The oscillatory tail is
unlike the

expected Airy function that normally accompanies a weakly nonlinear rarefactive

pulse. The observations suggest the existence of ion-hole-like structures
on the

downstream side. The mechanism of the excitation seems to be through modification

of the ion phase space due to trapping of ions in the negative potential
well of

the rarefactive pulse.
Relaxation of a non-ideal incompressible plasma with mass flow
Authors: CHEREMNYKH O. K. , EDENSTRASSER J. W. , GORIN V. V.
Published: July 2002

The time evolution of an incompressible non-ideal magnetohydrodynamic
(MHD), current-carrying plasma with mass flow is investigated.
An approach for the reduction of the nonlinear vector MHD equations to a set
of scalar partial differential equations is supposed. Analytical time-dependent
solutions of this system are presented. They describe kinetic plasma equilibria
both with well-defined nested-in magnetic and velocity surfaces and in the form
of vortices. The obtained solutions may be called ‘diffusion-like’, since their
temporal structure is very similar to the solutions of the diffusion problem. It
is shown that the magnetic field and the velocity have different dumping rates.
In the asymptotic limit t→∞, the plasma slowly relaxes towards the
hydrostatic equilibrium of gravitating systems.
Reproductive biology of three caridean shrimp, Rimicaris exoculata, Chorocaris chacei and Mirocaris fortunata (Caridea: Decapoda), from hydrothermal vents
Authors: Llodra Eva Ramirez , Tyler Paul A. , Copley Jonathan T.P.
Published: July 2002

The caridean shrimp Rimicaris exoculata, Chorocaris chacei and Mirocaris fortunata, together with bathymodiolid mussels, dominate the vent fauna along the Mid-Atlantic Ridge. Vent shrimp show the characteristic reproductive patterns of caridean decapods. The gonads are paired organs overlying the digestive gland under the carapace. In the ovaries, the oogonia (∼20-30 μm diameter) proliferate in the germinal epithelium at the periphery of the gonad, developing into previtellogenic oocytes. The previtellogenic oocytes grow to 70-100 μm before undergoing vitellogenesis. The maximum size for mature oocytes ranged between 200 and 500 μm depending on the species and the sample. The oocyte size–frequency data show no evidence of synchrony in oogenesis at population level for any of the species studied. Mirocaris fortunata is the only species where gravid females are commonly collected. The brood is carried on the pleopods, and the number of eggs per female ranges from 25 to 503, with a mean egg length of 0.79±0.14 mm. There is a positive correlation between fecundity and body size, characteristic of crustaceans. One ovigerous C. chacei and two R.exoculata have been studied. The former was carrying 2510 eggs and the later 988 small eggs in an early stage of development. The fecundity of M. fortunata, C. chacei and R. exoculata is significantly higher than that of species from the Acanthephyra group collected in the north-east Atlantic.
Observations on the behaviour of the cirrate octopod Opisthoteuthis grimaldii (Cephalopoda)
Authors: Villanueva Roger
Published: July 2002

Specimens of Opisthoteuthis grimaldii were video recorded in a shipboard aquarium and their behavioural traits, such as bottom resting, flat-spreading, web-inversion and ballooning response, were described. Ballooning, as defence response, has been recorded only for cirrate octopod families with an intermediate web (Cirroteuthidae: Stauroteuthidae), and this structure has been supposed to be essential for developing this behaviour. Members of the Opisthoteuthidae family lack an intermediate web, indicating that this is a common defence response in cirrates, expressed in a basic form in the Opisthoteuthidae, offering an illustration of how this behaviour can evolve.
Gametogenesis of the oyster Crassostrea gigas in southern Ireland
Authors: Steele S. , Mulcahy M.F.
Published: July 2002

The Pacific oyster Crassostrea gigas (Mollusca: Bivalvia) was introduced to Ireland in 1965 and is farmed at many sites around the coast. The reproductive biology of 1377 oysters from two sites on the south coast of Ireland was examined from April 1996 until December 1997 for variations in maturation rate and condition indices. Qualitative data were compiled by staging gonadal development using histological sections. Environmental parameters of temperature, dissolved oxygen and chlorophyll-a levels, as well as parasites and pathology were monitored. Unusually high sea temperatures led to oysters in Dungarvan (site 1) spawning in both years of the study. Although sea temperatures were significantly higher, oysters in Cork Harbour (site 2) did not spawn but instead reached ripeness and then started a process of gametic degeneration called resorption. Lack of spawning was not attributed to environmental conditions monitored but was tentatively attributed to levels of pollutants in the water. Oyster condition in Cork Harbour was significantly affected by the presence of blistering due to tributyltin levels in the water and also by Polydora sp. (Polychaete) in the shell. Oyster condition in Dungarvan was not affected by the presence of the exotic species Mytilicola orientalis (Copepoda: Cyclopoida).
Species-specific antigens in salivary glands of phlebotomine sandflies
Authors: VOLF P. , ROHOUšOVÁ I.
Published: July 2002

Saliva inoculated by sandfly females during feeding stimulated production of high levels of anti-saliva antibodies. To determine whether 3 species of the genus Phlebotomus have species-specific salivary antigens we performed dot-blots and immunoblots using sera from mice, hamsters and rabbits repeatedly bitten by sandflies. Important differences were found in the antigen components of the salivary gland lysates (SGL) of Phlebotomus papatasi, P. perniciosus and P. halepensis. In total 4–9 species-specific antigens were detected in each species by immunoblotting. Cross-reactivity was not detected between P. papatasi and the other species tested; in the SGL of P. papatasi sera from animals bitten by this species recognized 5–7 major antigens while sera from animals bitten by other species did not react. A weak cross-reaction was observed between P. perniciosus and P. halepensis; in SGL from P. perniciosus, the sera from rabbits and hamsters bitten by this species recognized about 8 intense bands while sera from animals bitten by P. halepensis reacted weakly with up to 4 saliva polypeptides.
Schistosoma japonicum cathepsin D aspartic protease cleaves human IgG and other serum components
Authors: VERITY C. K. , LOUKAS A. , McMANUS D. P. , BRINDLEY P. J.
Published: July 2002

Recombinant cathepsin D aspartic protease of Schistosoma japonicum cleaved human IgG in vitro in a time and dose-dependent manner. Optimal cleavage was seen at pH 3·6–4·5; modest cleavage remained at pH 5·0, and no cleavage was detected above pH 5·0. Amino terminal sequencing of the major cleavage fragments of human IgG identified a Fab fragment from the VH1 domain, and 2 cleavage sites in the CH2 domain below the hinge region. The P1 and P1′ residues at the 2 CH2 cleavage sites were Phe254–Leu255 and Leu325–Thr326, indicating a preference by the schistosome protease for bulky hydrophobic residues flanking the scissile bond. No cleavage of the immunoglobulin light chain was detected. In addition, the recombinant schistosome protease indiscriminately degraded the human serum proteins complement C3 and serum albumin into numerous small fragments. These results demonstrate specific cleavage of human IgG by the recombinant schistosome aspartic protease, and highlight the broad range digestive specificity of the enzyme which may play a role in the degradation of host serum proteins ingested as part of the schistosome bloodmeal.
Dactylogyrus (Monogenea) infections on the gills of roach
(Rutilus rutilus L.) experimentally exposed to pulp and
paper mill effluent
Authors: SIDDALL R. , KOSKIVAARA M. , VALTONEN E. T.
Published: July 2002

Experimental exposure to bleached kraft pulp and paper mill effluent
(BKME) at a concentration of 10% significantly
reduced the abundance and mean number of species of Dactylogyrus
on
the gills of naturally infected roach, Rutilus rutilus,
over a 3 week period. Seven Dactylogyrus species were recorded
which
differed widely in their susceptibility to the effluent.
The experiment coincided with a natural spring peak in dactylogyrid infections
on roach. BMKE exposure did not prevent
parasite reproduction but post-larval abundance was significantly higher
on
control than effluent-exposed hosts. There
was no evidence of a BKME-induced shift in microhabitat distribution of
dactylogyrids. Elevated levels of infection with
Dactylogyrus spp. have been recorded on roach from a Finnish lake
containing relatively low concentrations of BMKE.
The high exposure concentration in this experiment produced a similar reduction
in dactylogyrid infections to that
reported in separate studies in close proximity to Swedish pulp and paper
mills. The discrepancy between the results of
the Finnish and Swedish field investigations is therefore considered to
be
due to differences in BKME concentration between the study areas.
Mitochondrial genomic markers confirm the presence of
the camel strain (G6 genotype) of Echinococcus granulosus
in north-western China
Authors: ZHANG L-H. , CHAI J-J. , JIAO W. , OSMAN Y. , McMANUS D. P.
Published: July 2002

Twenty-eight isolates of E. granulosus, collected
from humans at surgery, and a range of intermediate hosts, including
sheep, cattle and camels from abattoirs in North and South Xinjiang
Uygur Autonomous Region, People's Republic of
China, were analysed for DNA sequence variation within regions of
the mitochondrial cytochrome c oxidase I (COI) and
NADH dehydrogenase subunit I (NDI) genes. The isolates were
categorized into 2 distinct and uniform genotypic
groupings, based on the sequences obtained, and the data clearly
indicated that the camel/dog strain (G6 genotype) of
E. granulosus as well as the cosmopolitan, common sheep strain
(G1 genotype) occur in north Xinjiang. The presence of
the camel strain has thus been confirmed in Xinjiang but it is
evident from this and a previous molecular genetic survey
of E. granulosus isolates from north-western China that the
common sheep strain is the most predominant in the region.
From the public health perspective, the majority of infected livestock
will act as reservoirs of human infection there.
During the course of the study, a polymerase chain reaction
(PCR)-restriction fragment length polymorphism (RFLP)
assay, based on the NDI sequence variation, was developed that
allows rapid discrimination of the G1 and G6 genotypes.
Tick salivary gland extracts promote virus growth in vitro
Authors: HAJNICKÁ V. , FUCHSBERGER N. , SLOVÁK M. , KOCAKOVA P. , LABUDA M. , NUTTALL P. A.
Published: July 2002

Saliva of blood-feeding arthropods promotes infection by the
vector-borne pathogens they transmit. To investigate this
phenomenon in vitro, cultures of mouse L cells were treated with

a salivary gland extract (SGE) prepared from feeding
ticks and then infected with vesicular stomatitis virus (VSV). At low
input doses of VSV, viral yield was increased 100-fold to 10000-fold by

16–23 h post-infection compared with untreated cultures, and
depending on the SGE concentration.
SGE-mediated acceleration of viral yield corresponded with the earlier

appearance of VSV nucleocapsid protein as
detected by 2-dimensional electrophoresis of infected cells. The
observation that physiological doses of virus (i.e. doses
likely to be inoculated by an infected arthropod vector into its
vertebrate host during blood-feeding) respond to SGE
treatment in vitro provides a new opportunity for identifying

the factors in tick saliva that promote virus transmission in vivo.
Effects of an anti-exospore monoclonal antibody on
microsporidial development in vitro
Authors: ENRIQUEZ F. J. , WAGNER G. , FRAGOSO M. , DITRICH O.
Published: July 2002

In this study we evaluated the effects of the anti-microsporidial
exospore monoclonal antibody 3B6, recognizing 3
Encephalitozoon species, Encephalitozoon intestinalis
(Syn. Septata intestinalis), Encephalitozoon cuniculi,

and Encephalitozoon hellem on microsporidial growth in vitro.
Pre-treatment of spores for 24 h with mAb 3B6 resulted in 21–29%

fewer infected host cells 4 days after inoculation of the cultures compared
to cultures pre-treated with medium or an
irrelevant isotype control mAb (P<0·001). Fewer intracellular
spores (1·2±0·2) in infected cells were found when

mAb 3B6 was present in cultures compared to cultures with medium alone
(4·3±0·8) or an irrelevant isotype control mAb
(4·2±0·9; P<0·001). This decrease
appeared not to be dependent on time of exposure, mAb concentration, or
presence
of complement. It is concluded that antibodies, particularly those directed
to potential neutralizing-sensitive epitopes on
spores, may have a role in the control of microsporidial growth in
vitro.
Richness and diversity of parasite communities in
European eels Anguilla anguilla of the River Rhine,
Germany, with special reference to helminth parasites
Authors: SURES B. , KNOPF K. , WÜRTZ J. , HIRT J.
Published: July 2002

A total of 121 European eels (Anguilla anguilla) from 2 sampling sites on the River Rhine were investigated in respect of
their parasite communities. Special attention was given to the swim bladders, intestines, gills and fins of the fish. Twelve
different parasite species were found to live in and on the eels. Data from each sampling site were kept separate. Parasites
found in descending order of prevalence were: Anguillicola crassus, Trypanosoma granulosum, Myxobolus sp., Paratenuisentis
ambiguus, Pseudodactylogyrus sp., Bothriocephalus claviceps, Myxidium giardi, Pomphorhynchus laevis, Trichodina
sp., Raphidascaris acus, Acanthocephalus lucii and Acanthocephalus anguillae. Significantly different prevalences were
reported for L3 larvae of A. crassus, adult P. ambiguus, B. claviceps and Myxobolus sp. at the 2 sampling sites. The highest
number of parasite species was recorded from the intestine, which contained up to 6 different helminths. The coexistence
of the acanthocephalans P. laevis and P. ambiguus, which showed clear patterns of distribution within the intestine of the
respective hosts, was reported for the first time. Up to 3 different helminth species were found in the intestine of individual
fish. Among those, acanthocephalans were the most prevalent worms with the eel-specific parasite P. ambiguus as the
dominant species not only of the intestinal but also of the total component communities. Both infra and component
communities exhibited low diversity and were dominated by this single species. The evenness reached only approximately
50% or less and it remained unclear why the helminth communities of the eels from the River Rhine with its huge
catchment area exhibit such a low parasite diversity and high dominance.
Trichobilharzia regenti, a pathogen of the avian and
mammalian central nervous systems
Authors: HORÁK P. , DVOŘÁK J. , KOLÁŘOVÁ L. , TREFIL L.
Published: July 2002

The development of nasal avian schistosomes of the genus Trichobilharzia in their final host is poorly known. Therefore,
an experimental infection of ducklings (Anas platyrhynchos f. dom.) by T. regenti was performed. The infection resulted
in leg paralysis and orientation/balance disorders of birds. The examination of the duck's spinal cord and brain confirmed
the presence of developing parasites in pre-patent as well as patent periods. The absence of the worms in other tissues
strongly supports our hypothesis that the parasite migrates through the central nervous system (CNS) to its final location
in bird nasal mucosa. The injury level is probably dependent on number of parasites as well as yet unknown host factors.
The affinity to the CNS seems to be high; also by exposure of experimental animals to low cercarial doses the growing
worms in the CNS were found. In addition to the generally accepted view that bird schistosomes may cause cercarial
dermatitis of mammals (including man), there is evidence of a partial development of T. regenti in mouse CNS; in certain
cases leg paralysis was also recorded. Therefore, the pathogenesis spectrum caused by bird schistosomes in birds/mammals
needs to be reconsidered.