bluuebunny/crossref_metadata_2025 huggingface dataset:
On the competition between centrifugal and

shear instability in spiral Poiseuille flow
Authors: MESEGUER A. , MARQUES F.
Published: July 2002

A numerical exploration of the linear stability of a fluid confined between two coaxial

cylinders rotating independently and with an imposed axial pressure gradient (spiral

Poiseuille flow) is presented. The investigation covers a wide range of experimental

parameters, being focused on co-rotation situations. The exploration is made for a

wide gap case in order to compare the numerical results with previous experimental

data available. The competition between shear and centrifugal instability mechanisms

affects the topological features of the neutral stability curves and the critical surface

is observed to exhibit zeroth-order discontinuities. These curves may exhibit

disconnected branches which lower the critical values of instability considerably. The same

phenomenon has been reported in similar fluid flows where shear and centrifugal

instability mechanisms compete. The stability analysis of the rigid-body rotation case

is studied in detail and the asymptotic critical values are found to be qualitatively

similar to those obtained in rotating Hagen-Poiseuille and spiral Couette flows. The

results are in good agreement with the previous experimental explorations.
Experimental and theoretical analysis of the wave decay along a long array of vertical cylinders
Authors: KAGEMOTO H. , MURAI M. , SAITO M. , MOLIN B. , MALENICA š.
Published: July 2002

A row of fifty identical, truncated vertical cylinders is submitted to regular head
waves, with wave periods in a narrow range around the period of the so-called
Neumann trapped mode. The free-surface elevation is measured at 14 locations along
the array. Response amplitude operators of the free-surface motion are compared
with numerical predictions from a potential flow model. Resonance effects, at wave
periods equal to or larger than the critical one, are found to be much less than given
by the numerical model. It is advocated that these discrepancies are due to dissipative
effects taking place in the boundary layers at the cylinder walls. An artificial means is
devised to incorporate dissipation in the potential flow model, whereby the cylinder
walls are made slightly porous; the inward normal velocity of the flow is related to the
dynamic pressure. The coefficient of proportionality is based on existing knowledge
for circular cylinders in oscillatory flows. With this modification in the numerical
code, excellent agreement is obtained with the experiments. The numerical model is
further used for the case of a very long array composed of 1000 cylinders; it is found
that with dissipation at the cylinder walls, the wave action steadily decreases along the
array, even for wave periods substantially larger than the critical one. On the other
hand, at wave periods less than the critical one, dissipation plays a negligible role;
the observed decay is solely due to diffraction effects. Implications of these results
for very large structures such as column-supported floating airports are discussed.
In particular, it is concluded that scale effects may be an important issue in the
experimental analysis of such multi-column structures.
The effects of thermal modulation upon the onset of Marangoni–Bénard convection
Authors: OR A. C. , KELLY R. E.
Published: July 2002

The effects of thermal modulation with time on the thermocapillary instability of
a thin horizontal fluid layer with a deformable free surface are investigated on the
basis of linear stability theory. First, a sinusoidal heating with a mean component is
applied at the lower wall, corresponding to boundary conditions either in the form
of prescribed temperature or heat flux. For finite-wavelength convection the thermal
modulation exerts a strong effect, giving rise to a family of looped regions of instability
corresponding to alternating synchronous or subharmonic responses. In the case of
prescribed heat flux, the critical curve consists of significantly fewer loops than in
the case of prescribed temperature. Thermal modulation with moderate modulation
amplitude tends to stabilize the mean basic state, and optimal values of frequency and
amplitude of modulation are determined to yield maximum stabilization. However,
large-amplitude modulation can be destabilizing. A basic state with zero mean is then
considered and the critical Marangoni number is obtained as a function of frequency.
The effects of modulation are also investigated in the long-wavelength limit. For
the case of prescribed temperature, the modulation does not affect the onset of the
long-wavelength mode associated with the mean basic state and a purely oscillating
basic state is always stable with respect to long-wavelength disturbances. For the
case of prescribed heat flux both at the wall and free surface, by contrast, thermal
modulation exerts a significant effect on the onset of convection from a mean basic
state and long-wavelength convection can occur even for a purely oscillating basic
state. The modulation can be stabilizing or destabilizing, depending on the frequency.
Active electrostatic stabilization of liquid bridges in low gravity
Authors: THIESSEN DAVID B. , MARR-LYON MARK J. , MARSTON PHILIP L.
Published: July 2002

In experiments performed aboard NASA's low-gravity KC-135 aircraft, it was found
that rapid active control of radial electrostatic stresses can be used to suppress the
growth of the (2,0) mode on capillary bridges in air. This mode naturally becomes
unstable on a cylindrical bridge when the length exceeds the Rayleigh–Plateau (RP)
limit. Capillary bridges having a small amount of electrical conductivity were deployed
with a ring electrode concentric with each end of the bridge. A signal produced by
optically sensing the shape of the bridge was used to control the electrode potentials
so as to counteract the growth of the (2,0) mode. Occasionally the uncontrolled
growth of the (3,0) mode was observed when the length far exceeded the RP limit.
Rapid breakup from the growth of the (2,0) mode on long bridges was confirmed
following deactivation of the control.
The role of drift mass in the kinetic energy and momentum of
periodic water waves and sound waves
Authors: YIH CHIA-SHUN
Published: July 2002

For two-dimensional periodic water waves or sound waves, the
kinetic energy per wavelength is
½mdc2, and the
momentum per
wavelength is ±mdc, where
c is the
wave velocity, and md is the drift mass per
wavelength. These results also hold for three-dimensional periodic
waves, for which the kinetic energy, momentum, and drift mass are all
for one wave cell, the area of which is the product of the wavelengths
in two perpendicular directions.

The results obtained are rigorous, and not restricted to linear
waves or even to nonlinear symmetric waves. For linear water waves, in
particular, the kinetic energy can be shown to be equal to the sum of
the potential energy and the surface energy (due to surface tension),
so that the total energy E is twice the kinetic energy, and

formula here

McIntyre's (1981) contention that wave momentum is a myth is
discussed at length for both water waves and sound waves.
On the nonlinear stability and detonability limit
of a detonation wave for a model three-step chain-branching reaction
Authors: SHORT MARK , QUIRK JAMES J.
Published: July 2002

The nonlinear stability of a pulsating detonation wave driven by
a three-step chain-branching reaction is studied. The reaction model consists
sequentially of a chain-initiation step and a chain-branching step, both
governed by Arrhenius kinetics,
followed by a temperature-independent chain-termination step. The model mimics
the essential dynamics of a real chain-branching chemical system, but is sufficiently
idealized that a theoretical analysis of the instability is possible. We introduce as
a bifurcation parameter the chain-branching cross-over temperature
(TB), which is
the temperature at which the chain-branching and chain-termination rates are equal.
In the steady detonation structure, this parameter controls the ratio of the
chain-branching induction length to the length of the recombination zone.
When TB
is at the lower end of the range studied, the steady detonation structure, which is
dominated by the temperature-independent recombination zone, is found to be stable.
Increasing TB increases the length of
the chain-branching induction region relative to
the length of the recombination zone, and a critical value of
TB is reached where the
detonation becomes unstable, with the detonation shock pressure evolving as a
single-mode low-frequency pulsating oscillation. This single-mode nonlinear
oscillation
becomes progressively less stable as TB
is increased further, persisting as the
long-term dynamical behaviour for a significant range of
TB before eventually undergoing
a period-doubling bifurcation to a two-mode oscillation. Further increases
in TB
lead to a chaotic behaviour, where the detonation shock pressure
history consists of a
sequence of substantive discontinuous jumps, followed by lower-amplitude continuous
oscillations. Finally, for further increases in TB a detonability
limit is reached, where
during the early onset of the detonation instability, the detonation shock
temperature
drops below the chain-branching cross-over temperature causing
the wave to quench.
Asymptotic defect boundary layer theory applied
to thermochemical non-equilibrium hypersonic flows
Authors: SÉROR S. , ZEITOUN D. E. , BRAZIER J.-Ph. , SCHALL E.
Published: July 2002

Viscous flow computations are required to predict the heat flux or
the viscous
drag on an hypersonic re-entry vehicle. When real gas effects are included,
Navier–Stokes computations are very expensive, whereas the use of standard
boundary layer
approximations does not correctly account for the ‘entropy layer
swallowing’ phenomenon. The purpose of this paper is to present an
extension of a new boundary
layer theory, called the ‘defect approach’, to two-dimensional
hypersonic flows including chemical and vibrational non-equilibrium phenomena.
This method ensures
a smooth matching of the boundary layer with the inviscid solution in hypersonic
flows with strong entropy gradients. A new set of first-order boundary layer
equations has been derived, using a defect formulation in the viscous region together
with a matched asymptotic expansions technique. These equations and the associated
transport coefficient models as well as thermochemical models have been
implemented. The prediction of the flow field around the blunt-cone wind tunnel
model ELECTRE with non-equilibrium free-stream conditions has been done by solving
first the inviscid flow equations and then the first-order defect boundary layer
equations. The numerical simulations of the boundary layer flow were performed with
catalytic and non-catalytic conditions for the chemistry and the vibrational mode.
The comparison with Navier–Stokes computations shows good agreement. The wall
heat flux predictions are compared to experimental measurements carried out during
the MSTP campaign in the ONERA F4 wind tunnel facility. The defect approach
improves the skin friction prediction in comparison with a classical boundary layer
computation.
A method for computing unsteady fully nonlinear interfacial waves
Authors: GRUE JOHN , FRIIS HELMER ANDRÉ , PALM ENOK , RUSÅS PER OLAV
Published: July 2002

We derive a time-stepping method for unsteady fully nonlinear

two-dimensional motion of a two-layer fluid. Essential parts of

the method are: use of Taylor series

expansions of the prognostic equations, application of spatial finite difference

formulae of high order, and application of Cauchy's theorem to

solve the Laplace equation,

where the latter is found to be advantageous in avoiding instability. The
method is

computationally very efficient. The model is applied to investigate unsteady

trans-critical two-layer flow over a bottom topography. We

are able to simulate a set of

laboratory experiments on this problem described by Melville &

Helfrich (1987), finding a very good agreement between the

fully nonlinear model and the experiments,

where they reported bad agreement with weakly nonlinear Korteweg–de

Vries theories

for interfacial waves. The unsteady transcritical regime is identified.

In this regime,

we find that an upstream undular bore is generated when the speed of the
body is

less than a certain value, which somewhat exceeds the critical speed.

In the remaining

regime, a train of solitary waves is generated upstream. In both

cases a corresponding

constant level of the interface behind the body is developed. We also perform
a

detailed investigation of upstream generation of solitary waves by a moving
body,

finding that wave trains with amplitude comparable to the thickness of
the thinner

layer are generated. The results indicate that weakly nonlinear

theories in many cases

have quite limited applications in modelling unsteady transcritical two-layer
flows,

and that a fully nonlinear method in general is required.
Dynamics of interfaces and layers in a stratified
turbulent fluid
Authors: BALMFORTH N. J. , LLEWELLYN SMITH STEFAN G. , YOUNG W. R.
Published: July 2002

This paper formulates a model of mixing in a stratified
and turbulent fluid. The model
uses the horizontally averaged vertical buoyancy gradient and
the density of turbulent
kinetic energy as variables. Heuristic
‘mixing-length’ arguments lead to a coupled set of
parabolic differential equations. A particular form of
mechanical forcing is proposed;
for certain parameter values the relationship between the
buoyancy flux and the
buoyancy gradient is non-monotonic and this leads to an
instability of equilibria with
linear stratification. The instability results in the formation
of steps and interfaces in
the buoyancy profile. In contrast to previous ones, the model
is mathematically well
posed and the interfaces have an equilibrium thickness that
is much larger than that expected from molecular diffusion.

The turbulent mixing process can take one of three forms
depending on the strength
of the initial stratification. When the stratification
is weak, instability is not present
and mixing smoothly homogenizes the buoyancy. At
intermediate strengths of stratification, layers and
interfaces form rapidly over a substantial interior region bounded
by edge layers associated with the fluxless condition of
the boundaries. The interior
pattern subsequently develops more slowly as interfaces
drift together and merge; simultaneously, the edge layers
advance inexorably into the interior. Eventually the edge
layers meet in the middle and the interior pattern of layers
is erased. Any remaining
structure subsequently decays smoothly to the homogeneous
state. Both the weak and
intermediate stratified cases are in agreement with
experimental phenomenology. The
model predicts a third case, with strong stratification,
not yet found experimentally,
where the central region is linearly stable and no
steps form there. However, the edge
layers are unstable; mixing fronts form and then erode
into the interior.
Mean flow refraction effects on sound radiated
from localized sources in a jet
Authors: TAM CHRISTOPHER K. W. , AURIAULT LAURENT
Published: July 2002

It is well-known that sound generated by localized sources embedded
in a jet undergoes
refraction as the acoustic waves propagate through the jet mean flow. For

isothermal or hot jets, the effect of refraction causes the deflection
of the radiated
sound waves away from the jet flow direction. This gives rise to a cone
of silence
around the jet axis where there is a significant reduction in the radiated
sound intensity.
In this work, the mean flow refraction problem is investigated through
the
use of the reciprocity principle. Instead of the direct source Green's
function, the
adjoint Green's function with the source and observation points interchanged
is used
to quantify the effect of mean flow on sound radiation. One advantage of
the adjoint
Green's function is that the Green's functions
for all the source locations in the jet
radiating to a given direction in the far field can be obtained in a single
calculation.
This provides great savings in computational effort. Another advantage
of the adjoint
Green's function is that there is no singularity in the jet flow so
that the problem can
be solved numerically with axial as well as radial mean flow gradients
included in a
fairly straightforward manner. Extensive numerical computations have been
carried
out for realistic jet flow profiles with and without exercising the locally
parallel flow
approximation. It is concluded that the locally parallel flow approximation
is valid as
long as the direction of radiation is outside the cone of silence.
Complex flow mechanisms in compound
meandering channels with overbank flow
Authors: SHIONO K. , MUTO Y.
Published: July 2002

Turbulence and secondary flow measurements were undertaken using
a two-component
laser-Doppler anemometer in meander channels with straight flood plain

banks. The most interesting feature of the compound meandering channel
flow was
found to be the behaviour of the secondary flow. The difference in direction
of rotation
of the flow before and after inundation at a bend section was confirmed
by the detailed
velocity measurements. In addition, by performing the measurement over
a half
wavelength of meander, the originating and developing processes of the
secondary flow
were also clarified. In contrast to the centrifugal force for inbank flow,
the interaction
between the main channel flow and the flood plain flow in the cross-over
region was
found to play an important role in developing a shear produced secondary
flow in the
overbank cases. New experimental evidence concerning the spatial distribution
of
Reynolds stress −ρuw,
−ρuv and −ρvw are presented for sinuous
compound meander
channels. In such channels, large interfacial shear stresses were induced
at around the
bankfull level, especially in the cross-over region, and were found to
be larger than the
bed shear stress in magnitude. Particular importance is placed
on −ρvw, which is
usually small compared with other stress components, as the cause of the
secondary
flow in the lower layer. The influence of secondary flow on eddy viscosity
was found
also to be significant. These turbulence data are particularly useful in
understanding
the flow mechanisms that occur in meandering channels and in developing
proper
turbulence models for such flows.
Cyclone and anticyclone formation in a rotating
stratified fluid over a sloping bottom
Authors: CENEDESE C. , LINDEN P. F.
Published: July 2002

We discuss laboratory experiments with a continuous source or sink
of fluid in a
two-layer rotating environment which produces anticyclonic and cyclonic
vortices,
respectively. Experiments were carried out with a sloping bottom in order
to simulate
the β-effect and they were conducted for different values for the
source/sink flow rate
Q and the Coriolis parameter f. The Rossby number
Ro of these vortices was small
but finite and the flow was expected to be quasi-geostrophic. The qualitative
behaviour
of the anticyclonic and cyclonic vortices was generally similar, but it
depended on the
flow rate. For low flow rates, a single vortex formed at the source and
extended to the
west. At higher flow rates, the vortex broke free from the source and moved
to the
west; this vortex was then followed sequentially by other vortices behaving
similarly.
The westward velocity U of these vortices was calculated and compared
with the
speed Us of a linear topographic Rossby
wave. For multiple vortices the westward
velocities were greater than Us
while for a single vortex produced by a low flow rate
the velocity was less than Us. Significant

asymmetry between the anticyclonic and
cyclonic vortices was observed in the transition zone from single to multiple
vortices
which implies that ageostrophic effects were still present in the flow.
Turbulent transport in the core of a trailing half-delta-wing vortex
Authors: SHAH P. N. , ATSAVAPRANEE P. , HSU T. Y. , WEI T. , McHUGH J.
Published: July 2002

The development of a turbulent streamwise vortex core in the wake of a half delta
wing has been examined using high-resolution DPIV. The objective of this work was
to gain understanding of the transport processes at work a short distance downstream
of the wing trailing edge as the wake vortex developed. Experiments were conducted
in the Rutgers Free Surface Water Tunnel using an in-house DPIV system. A turbulent
streamwise vortex was generated by a half delta wing, with 44 cm chord length and 60°
sweep angle, mounted at 30° angle of attack. Reynolds number based on chord length
was 65 000. Laser sheets oriented perpendicular to the flow direction were positioned
1, 3.5, and 7 chord lengths downstream of the wing trailing edge. Instantaneous
vortex centres were identified in order to track vortex meandering as well as for
better quantification of turbulence levels in the vortex core. Mean and fluctuating
turbulence terms in the mean streamwise vorticity transport equation along with
turbulent kinetic energy dissipation and production were evaluated relative to an
inertial reference frame as well as relative to a vortex-centred frame. The results of
this analysis highlight the importance of this near-wake region to the downstream
evolution of the trailing vortices. There is a high degree of dissipation as well as
streamwise vorticity convection in the very near wake which decreases rapidly with
increasing distance from the trailing edge.
Stability of non-parabolic flow in a flexible tube
Authors: SHANKAR V. , KUMARAN V.
Published: July 2002

Flows with velocity profiles very different from the parabolic velocity profile can occur
in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the
temporal stability of such ‘non-parabolic’ flows in a
flexible tube in the limit of high
Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible
tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile
contains both axial and radial components, the flow is assumed to be locally parallel
in the stability analysis. The fluid is Newtonian and incompressible, while the flexible
wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis
shows that the non-parabolic velocity profiles can become unstable in the inviscid
limit. This inviscid instability is qualitatively different from that observed in previous
studies on the stability of parabolic flow in a flexible tube, and from the instability of
developing flow in a rigid tube. The results of the asymptotic analysis are extended
numerically to the moderate Reynolds number regime. The numerical results reveal
that the developing flow could be unstable at much lower Reynolds numbers than
the parabolic flow, and hence this instability can be important in destabilizing the
fluid flow through flexible tubes at moderate and high Reynolds number. For flow in
a slightly converging tube, even small deviations from the parabolic profile are found
to be sufficient for the present instability mechanism to be operative. The dominant
non-parallel effects are incorporated using an asymptotic analysis, and this indicates
that non-parallel effects do not significantly affect the neutral stability curves. The
viscosity of the wall medium is found to have a stabilizing effect on this instability.
Mixture segregation within sonoluminescence bubbles
Authors: STOREY BRIAN D. , SZERI ANDREW J.
Published: July 2002

This paper concerns a relaxation of the assumption of uniform mixture composition in
the interior of sonoluminescence bubbles. Intense temperature and pressure gradients
within the bubble drive relative mass diffusion which overwhelms diffusion driven
by concentration gradients. This thermal and pressure diffusion results in a robust
compositional inhomogeneity in the bubble which lasts several orders of magnitude
longer than the temperature peak or light pulse at the main collapse of the bubble.
This effect has important consequences for control of sonoluminescence, gas dynamics,
sonochemistry, and the physics of light production.
Turbulent transport of momentum and heat in magnetohydrodynamic rectangular
duct flow with strong sidewall jets
Authors: BURR ULRICH , BARLEON L. , MÜLLER U. , TSINOBER A.
Published: July 2002

This paper presents an experimental study of the momentum and heat transport in a
turbulent magnetohydrodynamic duct flow with strong wall jets at the walls parallel
to the magnetic field. Local turbulent flow quantities are measured by a traversable
combined temperature-potential-difference probe. The simultaneous measurements of
time-dependent velocity and temperature signals facilitates the evaluation of Reynolds
stresses and turbulent heat fluxes. Integral quantities such as pressure drop and temperature
at the heated wall are evaluated and compared with results from conservative
design correlations. At strong enough magnetic fields the destabilizing effect of strong
shear generated at the sidewalls wins the competition with the damping effect by
Joule's dissipation and turbulent side layers are created. Due to the strong non-isotropic character of the electromagnetic forces, the turbulence structure is characterized
by large-scale two-dimensional vortices with their axis aligned in the direction
of the magnetic field. As most of the turbulent kinetic energy is concentrated in the
near-wall turbulent side layers, the temperatures at the heated wall are governed by
the development of the thermal boundary layer in the turbulent flow.
Flow and reaction in solid oxide fuel cells
Authors: COOPER R. J. , BILLINGHAM J. , KING A. C.
Published: July 2002

A fuel cell is an electrochemical device that converts chemical energy into electrical
energy. The essential difference between a fuel cell and a battery is that the fuel and
oxidant are continually supplied to a fuel cell whereas a battery has a finite amount
of fuel stored within it which eventually becomes exhausted, after which the battery
has to be recharged or replaced. We consider here a tubular cell which is run on
methane. A mathematical model for the reaction and transport processes in the cell
is presented. This takes into account diffusion, advection and reaction as well as the
electrochemical flow of oxygen. When the device is running steadily, we perform an
analysis, using the method of matched asymptotic expansions to find the flow field, the
mass fractions of each chemical species and the electrical power output. These results
are confirmed by a numerical technique and compared with experimental results.
Racial Ideologies and the Quest for National Development: Debating
the
Agrarian Problem in Ecuador (1930–50)
Authors: CLARK A. KIM
Published: July 2002

During an economic crisis in Ecuador, three models of and solutions

to the agrarian problem were proposed. A peasant path of agricultural
development was formulated by peasant leaders and socialist activists.
A large-landholder
model was promoted by modernising large landowners. A medium-landholder

model was advanced by promoters of European immigration and
urban mestizos seeking land through state colonisation projects.
The adherents of
each approach identified certain groups as the cause of low agricultural

productivity and national crisis, articulating racial ideologies by defining
those
groups as inherently ‘traditional’, and thus debating the boundaries
of inclusion
to the national community.
Beyond the development impasse: the role of local economic
development and community self-reliance in rural South Africa
Authors: Binns Tony , Nel Etienne
Published: July 2002

The failure of successive generations of imported, Western development strategies
and projects to deliver meaningful reductions in poverty and achieve
basic needs in Africa, has provoked a deep questioning of Western concepts
and methodologies of development. Non-governmental organisations and development
practitioners are increasingly focusing their attention on strategies
which build upon local knowledge, skills and resources. The concepts of ‘self-
reliance’ and local economic development are examined in the context of
development challenges which face Africa. This is followed by a detailed case
study of local economic development in the rural Mpofu District of the former
Ciskei Homeland, which was incorporated into the Eastern Cape province of South
Africa with the demise of apartheid in 1994.
Charged-particle orbits near a magnetic null point
Authors: JAROENSUTASINEE K. , ROWLANDS G.
Published: July 2002

An approximate analytical expression is obtained for the orbits of a
charged particle moving in a cusp magnetic field. The particle orbits pass close
to or through a region of zero magnetic field before being reflected in regions
where the magnetic field is strong. Comparison with numerically evaluated
orbits shows that the analytical formula is surprisingly good and captures all
the main features of the particle motion. A map describing the long-time
behaviour of such orbits is obtained.
Inelastic Compton scattering of photons by bound atomic electrons in weakly coupled plasmas
Authors: JUNG YOUNG-DAE
Published: July 2002

Plasma screening effects on inelastic Compton scattering of photons
by bound atomic electrons of hydrogenic target ions in weakly coupled plasmas
are investigated. The particle interaction potential in weakly coupled plasmas
is obtained using the Debye–Hückel model. The screened wave functions and
energy eigenvalues for the ground and excited states of the target ion are
obtained using the Ritz variational method. The expression for the lowest-order
transition matrix element is obtained from a two-photon process associated
with terms quadratic in the vector potential A. The inelastic Compton
scattering cross-section from the 1s ground state to the 2p excited state is
obtained as a function of the incident photon energy, including plasma
screening effects. It is found that plasma screening effects significantly reduce
the inelastic Compton scattering cross-section.
Nonlinear waves propagating transverse to the magnetic field
Authors: McKENZIE J. F. , DUBININ E. , SAUER K.
Published: July 2002

We generalize the classical work of Adlam and Allen [Phil. Mag.3, 448
(1958)] on solitons in a cold plasma propagating perpendicular to the magnetic field
to include the effects of plasma pressure. This is done by making extensive use of
the properties of total momentum conservation (denoted by the term ‘momentum
hodograph’, since it yields a locus in the plane of the electron and proton speeds in
the direction of the wave) and the energy integral of the system as a whole. These relations
elucidate the phase and integral curves of stationary flows, from which soliton
solutions may be constructed. In general, only compressive solitons are permitted,
and we have found an analytical expression for the critical fast Mach number
as a function of the proton acoustic Mach number, which shows that it varies from
its classical value of 2 (at large proton acoustic Mach numbers) to unity, where the
incoming flow is proton-sonic. At the critical fast Mach number, two possible soliton-like
solutions can be constructed. One is the classical compression, in which the magnetic
field develops a cusp in the centre of the wave. The other is a compression in the
magnetic field followed by a deep depression in the centre of the wave, which is completed
by the mirror image of this signature of compression–rarefaction. This structure
involves a smooth supersonic–subsonic transition in the proton flow. For Mach
numbers in excess of the critical one, this kind of structure can also be constructed,
but now the magnetic field is cusp-like at the points of maximum compression.
Microwave coherent backscattering from
acoustic or electronic waves in a magnetized plasma
Authors: PISANI FRANCESCA , PIERRE THIÉRY , BATANI DIMITRI
Published: July 2002

A microwave coherent backscattering experiment has been
carried out on
Mirabelle, a weakly ionized plasma device, with the objective of
measuring the
electron-density fluctuation level. The experiment is a preliminary
step in order
to prepare the detection system for a microwave stimulated-backscattering
experiment. The incident electromagnetic wave is focused in
front of a plane
grid, which excites ion acoustic or electron Bernstein waves and induces
fluctuations in the plasma. The backscattering signal is collected by the
launching circuit and detected by homodyne mixing. The typical ratio of the
scattered power to the incident power is about 10−12
and the relative density fluctuations is of the order of
δne/ne
≈10−3 against a background electron density
ne=(1–5)×109
cm−3. The backscattering measurement is also compared
with Langmuir-probe measurements, and gives good agreement with the
relative density fluctuations. The spectral width of the
backscattered signal has
also been studied, by taking into account effects due to the incident-wave
focusing and plasma-wave damping.
Electrostatic fluctuations in plasmas containing suprathermal particles
Authors: MACE R. L. , HELLBERG M. A. , TREUMANN R. A.
Published: July 2002

The spectral density of electrostatic fluctuations is investigated
in a plasma
containing an excess of suprathermal particles. As a model for the statistical
distribution
of the suprathermal particles, the kappa velocity distribution is used.
It is found
that the Debye length λD for
such a plasma depends strongly on the spectral index
κ of the velocity distribution, and can be much smaller than is commonly
found for
Maxwellian plasmas. Consequently the plasma parameter
g=1/nλ3D can
be larger,
and plasma effects that depend on particle discreteness more important,
than for
a Maxwellian plasma. Consequently, levels of fluctuation are higher, and
their
extent in wavenumber and frequency greater, in plasmas containing suprathermals.

Results for a number of different ‘concentrations’ of suprathermal
particles are
discussed and interpreted in terms of the normal- as well as transient-mode
behaviour
of the plasma. Both the cases
Te[Gt ]Ti and

Te=Ti, as well
as
κe[Lt ]κi and
κe[Gt ]κi, are investigated.
Linear and nonlinear dust-acoustic waves in non-ideal dusty plasmas
Authors: RAO N. N.
Published: July 2002

Linear and nonlinear dust-acoustic wave propagation in a non-ideal
classical dusty
plasma consisting of electrons, ions and dust grains is investigated by
incorporating
the van der Waals equation of state for the dust component. For linear
waves,
it is found from the normal mode dispersion relation that the volume reduction

coefficient enhances the phase speed of the dust-acoustic waves, while
the molecular
cohesive forces lead to a decrease in the phase speed. The relative magnitudes

of the two contributions depend on the specific parameter regimes characterizing

the non-ideal nature of the dust component. In the high-temperature limit,
there
is a net increase in the dust-acoustic phase speed, while near the critical
point
the phase speed is reduced when compared with that for the ideal-gas case.
For
large amplitudes, we discuss the existence of dust-acoustic solitons by
deriving the
exact Sagdeev potential. While supersonic solitons are found to be admissible
in
both the sub- and supercritical parameter regimes, subsonic propagation
near the
dust-acoustic speed is possible only for the supercritical case. For small
but finite
amplitudes, explicit analytical solutions have been obtained. A limiting
case of
these solutions is also discussed.
Intraerythrocytic inclusion bodies in the loggerhead sea turtle Caretta caretta from Madeira
Authors: Eiras J.C. , Dellinger T. , Davies A.J. , Costa G. , Alves de Matos A.P.
Published: July 2002

Intracytoplasmic inclusion bodies were detected in the mature red blood cells of twenty juvenile loggerhead sea turtles, Caretta caretta, captured in Madeira. The bodies were mostly single, round to oval, frequently irregular in outline, and their diameter varied from 0.5 to 2.0 μm. Most bodies were associated with small granular areas, often in the form of a tail or projection. In some cells, only granular areas were apparent. The nuclei of most erythrocytes were irregular in outline but degeneration of red blood cells was not observed. The identity of these intraerythrocytic structures is not clear but they may be viral or rickettsial in nature.
Movements and growth of a female basking shark re-sighted after a three year period
Authors: Sims David W. , Speedie Colin D. , Fox Adrian M.
Published: July 2002

Basking shark (Cetorhinus maximus) movement patterns and growth rates over annual cycles remain entirely unknown. Here the re-sighting of a female identified by a highly distinctive first dorsal fin, after a 3·1 year period is described. Our results show this individual foraged at the surface in coastal areas off south-west England in at least two of four summer seasons and increased in total length by 2·4 m over this period. The growth increment observed was similar to that predicted from the growth model for this species.
Comparative study of the covering reaction of the purple sea urchin, Paracentrotus lividus, under laboratory and field conditions
Authors: Crook Anne C. , Verling Emma , Barnes David K.A.
Published: July 2002

Abiotic and biotic aspects of the covering behaviour of the purple sea urchin, Paracentrotus lividus (Echinodermata: Echinoidea) were systematically examined in situ and in the laboratory to analyse potential intra-population differences in the nature of this behaviour. In the field, significant differences in the occurrence of covering behaviour were found between age groups. Smaller P. lividus covered at higher frequencies than larger individuals. Higher proportions of individuals were also observed to cover during afternoon sampling periods. Significant differences in the types of covering material used were found between P. lividus observed in the laboratory and in the field. These findings suggest that the benefits and/or opportunities of covering behaviour may change with size and habitat.
The Authority of the Voice: A Theological Reading of 1 Cor 11.2–16
Authors: WATSON FRANCIS
Published: July 2002

The polarity between ‘hierarchical’ and ‘egalitarian’ perspectives on the relationship of male and female is not the best way to approach this passage (1 Cor 11.2–16), which interprets this relationship as one of interdependence. This interdependence is expressed in the shared practices of prophecy and prayer, in which the dialogue between God and the congregation is articulated. In Paul's proposed modification to these practices, female head-covering – probably a veil – serves as a symbol of women's freedom from an erotic basis for the relationship of male and female derived from creation.
The Geography of Restoration: Galilee–Jerusalem Relations in Early Jewish and Christian Experience
Authors: FREYNE SEAN
Published: July 2002

This paper discusses Galilee–Jerusalem relations in the context of the ‘geography of restoration’ as this is represented in various Jewish writings of the Second Temple period. The literary and archaeological records for the Jewish presence in Galilee in the Hasmonean and Herodian periods are examined against this ideology of a greater Israel. Finally, the alleged opposition in early Christianity between Galilee and Jerusalem is judged to be poorly grounded when various NT documents are read within this larger horizon of meaning.
JAMES AND SCRIPTURE: AN EXERCISE IN INTERTEXTUALITY
Authors: POPKES WIARD
Published: July 2002

The epistle contains three OT quotations as well as several biblical allusions and examples; other sources (such as Ben Sira) are not discernible. James collected excerpt-material from a wide background, not just by oral tradition – hence ‘intertextuality’. In a similar way the OT quotations, all combative in nature, seem to have been taken from secondary sources, viz. from Pauline (ch. 2) and ‘Petrine’ (ch. 4) traditions. Probably James had no direct access to a full OT text or longer parts of it. Nevertheless he uses ‘scripture’ as an authority and may have had a concept of canon.
Transformation ofLeishmania mexicanametacyclic promastigotes to amastigote-like forms mediated by binding of human C-reactive protein
Authors: BEE A. , CULLEY F. J. , ALKHALIFE I. S. , BODMAN-SMITH K. B. , RAYNES J. G. , BATES P. A.
Published: July 2002

Infective metacyclic promastigote forms ofLeishmania mexicanaare introduced by the bite of sandfly vectors into their human hosts where they transform into the amastigote form. The kinetics of this process was examinedin vitroin response to different combinations of temperature (26 °C or 32 °C), pH (7.2 or 5.5), and exposure to human serum. Little transformation occurred at 26 °C/pH 7.2, intermediate levels at 26 °C/pH 5.5 and 32 °C/ pH 7.2, and the greatest response at 32 °C/pH 5.5. Transformation was stimulated by exposure to normal human serum, but was markedly reduced when serum previously incubated at 56 °C for 1 h was used (complement heat-inactivated). This stimulatory effect was reproduced by exposure to a single purified component of human serum, C-reactive protein (CRP). Binding of CRP to the whole surface ofL. mexicanametacyclic promastigotes, including the flagella, was demonstrated by an indirect fluorescent antibody test. The effect of purified CRP was dose dependent and occurred using normal serum concentrations. The stimulatory effect of whole serum was oblated by CRP depletion and restored by addition of purified CRP. The effects of cAMP analogues indicated that transformation could be mediated via an adenylate cyclase cascade.
Paramyosin from the parasitic miteSarcoptes scabiei: cDNA cloning and heterologous expression
Authors: MATTSSON J. G. , LJUNGGREN E. L. , BERGSTRÖM K.
Published: July 2002

The burrowing miteSarcoptes scabieiis the causative agent of the highly contagious disease sarcoptic mange or scabies. So far, there is noin vitropropagation system forS. scabieiavailable, and mites used for various purposes must be isolated from infected hosts. Lack of parasite-derived material has limited the possibilities to study several aspects of scabies, including pathogenesis and immunity. It has also hampered the development of high performance serological assays. We have now constructed anS. scabieicDNA expression library with mRNA purified from mites isolated from red foxes. Immunoscreening of the library enabled us to clone a full-length cDNA coding for a 102.5 kDa protein. Sequence similarity searches identified the protein as a paramyosin. RecombinantS. scabieiparamyosin expressed inEscherichia coliwas recognized by sera from dogs and swine infected withS. scabiei. We also designed a small paramyosin construct of about 17 kDa that included the N-terminal part, an evolutionary variable part of the helical core, and the C-terminal part of the molecule. The miniaturized protein was efficiently expressed inE. coliand was recognized by sera from immunized rabbits. These data demonstrate that the cDNA library can assist in the isolation of importantS. scabieiantigens and that recombinant proteins can be useful for the study of scabies.
Production of an interferon-gamma homologue by an
intestinal nematode: functionally significant or interesting artefact?
Authors: GRENCIS R. K. , ENTWISTLE G. M.
Published: July 2002

Chronic infection is a prominent feature of many intestinal nematode

infections in man and animals. It is also clear that
in such situations host immunity is activated but is unable to induce a

protective response. A great deal of work has shown
that genetic control of host immunity contributes to the variation in worm

burdens often observed in the field. There is
increasing appreciation, however, of the capability of infectious agents

themselves to modulate the host immune response
and potentiate their own survival. Using an immunologically well defined

model of intestinal nematode infection in mice
(Trichuris muris) we have shown that parasite derived molecules

share cross reactive epitopes with the host cytokine
interferon-γ using cytokine specific monoclonal antibodies in ELISA,

Western blotting and immunoprecipitation assays.
Furthermore, the parasite molecules can be shown to bind to the
interferon-γ receptor and induce change in lymphoid
cells similar to those induced by murine interferon-γ. The functional

activity of the molecule in vivo remains to be
determined. Previous studies have established that interferon-γ is

critical for progression to chronic T. muris infection in
mice and, therefore, it raises the distinct possibility that the production

of an interferon-γ homologue by the worm may
be one mechanism whereby the parasite is able to interfere with the regulation

of the host immune response and potentiate its own survival.
Induction of immunity to Schistosoma mansoni: interaction

of schistosomula with accessory leucocytes in murine skin
and draining lymph nodes
Authors: RIENGROJPITAK S. , ANDERSON S. , WILSON R. A.
Published: July 2002

A single exposure to radiation-attenuated cercariae of
Schistosoma mansoni induces a high level of protective immunity
in
C57BL/6 mice, which is mediated by Th1 responses. Events in the
skin and/or draining lymph nodes early after exposure
are crucial for the induction of protection, and we have investigated
the interactions of vaccinating parasites with host
leucocytes in these 2 locations. We observed extensive lateral
spreading of cercarial secretions along layers of the stratum
corneum but not between keratinocytes. There was little direct contact

with host leucocytes during the first 1–2 days when
the parasites lay at the base of the epidermis, but cells accumulated
in the underlying dermis. In contrast to normal
parasites, attenuated larvae persisted in the dermis for >10 days,
often surrounded by aggregates of macrophages/dendritic cells.
Whilst cells bearing MHC II, CD11b or CD11c markers were present
in the lymph nodes, particularly
in the periphery and paracortical areas, no obvious redistribution
was seen as a result of parasite residence there for 5–15
days. However, ultrastructural observations revealed numerous cells
with macrophage/dendritic morphology in the
vicinity of parasites, in some instances closely adherent to the
tegument. The observations strongly suggest that the
tegument is a potent source of the antigens which prime the immune
system in the lymph nodes of vaccinated mice for a protective response.
Parasitology and immunology of mice vaccinated with
irradiated Litomosoides sigmodontis larvae
Authors: LE GOFF L. , MARTIN C. , OSWALD I. P. , VUONG P. N. , PETIT G. , UNGEHEUER M. N. , BAIN O.
Published: July 2002

This study was performed with Litomosoides sigmodontis, the only filarial species which can develop from the infective
larvae to the patent phase in immunocompetent laboratory BALB/c mice. Parasitological features and immune responses
were analysed up to 3 months before and after challenge inoculation, by comparing 4 groups of mice: vaccinated
challenged, challenged only, vaccinated only, and naive mice. Male larvae were very susceptible to irradiation and only
female irradiated larvae survived in vivo. Protection, assessed by a lower recovery rate, was confirmed and was established
within the first 2 days of challenge. This early reduction of the recovery rate in vaccinated challenged mice was determined
by their immune status prior to the challenge inoculation. This was characterized by high specific IgM and IgG subclass
(IgG1, IgG2a and IgG3) levels, high specific IL-5 secretion from spleen cells in vitro and a high density of eosinophils
in the subcutaneous connective tissue. Six h after the challenge inoculation, most tissue eosinophils were degranulated in
vaccinated challenged mice. Thus, in the protocol of vaccination described, protection appeared mainly to result from the
stimulation of a Th2 type response and eosinophils seemed to be the main effectors for the increased killing of infective
larvae in vaccinated challenged mice. Two months after challenge inoculation, the percentage of microfilaraemic mice was
lower in vaccinated challenged mice as a consequence of this overall reduction in the worm load. In both vaccinated
challenged and challenged only groups, the in vitro splenocyte proliferative capacity was reduced in microfilaraemic mice.