bluuebunny/crossref_metadata_2025 huggingface dataset:
Vorticity transport in solidification boundary layers
Authors: REED BARRY L. , HIRSA AMIR H. , STEEN PAUL H.
Published: July 2002

A solidification boundary layer, where vorticity is concentrated, is shown to scale
as δ ∼ (v/V) sin θ where θ is the angle that the solidification front makes with the
oncoming flow, v is the kinematic viscosity of the melt, and V is the solidification rate.
Key similarities with the suction boundary layer are outlined. Transport of vorticity,
by diffusion and advection, in flows that solidify is discussed in the context of the
planar-flow spin casting process, with special attention paid to how vorticity leaves
the flow. Direct experimental evidence for a solidification layer in that application is
reported.
On the forced oscillations of a small gas bubble in a spherical liquid-filled flask
Authors: NIGMATULIN R. I. , AKHATOV I. Sh. , VAKHITOVA N. K. , LAHEY R. T.
Published: July 2002

A spherically-symmetric problem is considered in which a small gas bubble at the
centre of a spherical flask filled with a compressible liquid is excited by small radial
displacements of the flask wall. The bubble may be compressed, expanded and made
to undergo periodic radial oscillations. Two asymptotic solutions have been found
for the low-Mach-number stage. The first one is an asymptotic solution for the field
far from the bubble, and it corresponds to the linear wave equation. The second
one is an asymptotic solution for the field near the bubble, which corresponds to
the Rayleigh–Plesset equation for an incompressible fluid. For the analytical solution
of the low-Mach-number regime, matching of these asymptotic solutions is done,
yielding a generalization of the Rayleigh–Plesset equation. This generalization takes
into account liquid compressibility and includes ordinary differential equations (one
of which is similar to the well-known Herring equation) and a difference equation
with both lagging and leading time. These asymptotic solutions are used as boundary
conditions for bubble implosion using numerical codes which are based on partial
differential conservation equations. Both inverse and direct problems are considered
in this study. The inverse problem is when the bubble radial motion is given and
the evolution of the flask wall pressure and velocity is to be calculated. The inverse
solution is important if one is to achieve superhigh gas temperatures using non-periodic forcing (Nigmatulin et al. 1996). In contrast, the direct problem is when the
evolution of the flask wall pressure or velocity is given, and one wants to calculate
the evolution of the bubble radius. Linear and nonlinear periodic bubble oscillations
are analysed analytically. Nonlinear resonant and near-resonant periodic solutions
for the bubble non-harmonic oscillations, which are excited by harmonic pressure
oscillations on the flask wall, are obtained. The applicability of this approach bubble
oscillations in experiments on single-bubble sonoluminescence is discussed.
On the orbital response of a rotating cylinder in a current
Authors: STANSBY P. K. , RAINEY R. C. T.
Published: July 2002

A new form of dynamic response has been observed in some simple experiments
with a lightly damped rotating cylinder in a current. The response is orbital with a
period several times the structural natural period and an amplitude ranging up to
many diameters. It is mainly dependent on the ratio of current velocity to cylinder
surface velocity, α, and the reduced velocity, Vr (the ratio of current velocity to the
product of natural frequency in water and diameter). Big orbital responses occur
with 0.25 < α < 0.5 and Vr > 5, and are accompanied by the expected large static
response. To understand the flow mechanisms causing this response computational
simulations have been made for two-dimensional laminar flow and the experimental
response characteristics are qualitatively reproduced. Streamline and vorticity contour
plots are output through a cycle and are related to instantaneous values of lift and
drag coefficients and α (all based on flow relative to the cylinder). The movement of
the stagnation point away from and towards the cylinder surface with intermittent
wake formation in a cycle causes a large lift variation which is mainly responsible for
the dynamic response. The variation of lift coefficient with α (as defined above) shows
a generally negative gradient, and a pronounced hysteresis loop when substantial
response occurs for α [gsim ] 0.25. The computations show that a small-amplitude, high-frequency
response may also be superimposed on the high-amplitude, low-frequency
response, most noticeably for α [lsim ] 0.25. This is consistent with a simple potential-flow
idealization of the lift force. For α ∼ 0.2 a large dynamic response, not observed
in the experiments, was produced in the computations due essentially to attached
boundary-layer behaviour.
Chaotic advection in three-dimensional stationary vortex-breakdown bubbles: šil'nikov's chaos and the devil's staircase
Authors: SOTIROPOULOS FOTIS , VENTIKOS YIANNIS , LACKEY TAHIRIH C.
Published: July 2002

We study the motion of non-diffusive, passive particles within steady, three-dimensional
vortex breakdown bubbles in a closed cylindrical container with a rotating
bottom. The velocity fields are obtained by solving numerically the three-dimensional
Navier–Stokes equations. We clarify the relationship between the manifold structure
of axisymmetric (ideal) vortex breakdown bubbles and those of the three-dimensional
real-life (laboratory) flow fields, which exhibit chaotic particle paths. We show that the
upstream and downstream fixed hyperbolic points in the former are transformed into
spiral-out and spiral-in saddles, respectively, in the latter. Material elements passing
repeatedly through the two saddle foci undergo intense stretching and folding, leading
to the growth of infinitely many Smale horseshoes and sensitive dependence on initial
conditions via the mechanism discovered by šil'nikov (1965). Chaotic šil'nikov orbits
spiral upward (from the spiral-in to the spiral-out saddle) around the axis and then
downward near the surface, wrapping around the toroidal region in the interior of the
bubble. Poincaré maps reveal that the dynamics of this region is rich and consistent
with what we would generically anticipate for a mildly perturbed, volume-preserving,
three-dimensional dynamical system (MacKay 1994; Mezić & Wiggins 1994a). Nested
KAM-tori, cantori, and periodic islands are found embedded within stochastic regions.
We calculate residence times of upstream-originating non-diffusive particles and
show that when mapped to initial release locations the resulting maps exhibit fractal
properties. We argue that there exists a Cantor set of initial conditions that leads
to arbitrarily long residence times within the breakdown region. We also show that
the emptying of the bubble does not take place in a continuous manner but rather
in a sequence of discrete bursting events during which clusters of particles exit the
bubble at once. A remarkable finding in this regard is that the rate at which an initial
population of particles exits the breakdown region is described by the devil's staircase
distribution, a fractal curve that has been already shown to describe a number of
other chaotic physical systems.
Reynolds-number dependence of turbulent velocity and pressure increments
Authors: PEARSON B. R. , ANTONIA R. A.
Published: July 2002

The main focus is the Reynolds number dependence of Kolmogorov normalized
low-order moments of longitudinal and transverse velocity increments. The velocity
increments are obtained in a large number of flows and over a wide range (40–4250)
of the Taylor microscale Reynolds number Rλ. The Rλ dependence is examined for
values of the separation, r, in the dissipative range, inertial range and in excess of
the integral length scale. In each range, the Kolmogorov-normalized moments of
longitudinal and transverse velocity increments increase with Rλ. The scaling exponents
of both longitudinal and transverse velocity increments increase with Rλ, the
increase being more significant for the latter than the former. As Rλ increases, the
inequality between scaling exponents of longitudinal and transverse velocity increments
diminishes, reflecting a reduced influence from the large-scale anisotropy or the
mean shear on inertial range scales. At sufficiently large Rλ, inertial range exponents
for the second-order moment of the pressure increment follow more closely those
for the fourth-order moments of transverse velocity increments than the fourth-order
moments of longitudinal velocity increments. Comparison with DNS data indicates
that the magnitude and Rλ dependence of the mean square pressure gradient, based
on the joint-Gaussian approximation, is incorrect. The validity of this approximation
improves as r increases; when r exceeds the integral length scale, the Rλ dependence
of the second-order pressure structure functions is in reasonable agreement with the
result originally given by Batchelor (1951).
Stokes flow in a half-filled annulus between rotating coaxial cylinders
Authors: GASKELL P. H. , SAVAGE M. D. , WILSON M.
Published: July 2002

A model is presented for viscous flow in a cylindrical cavity (a

half-filled annulus

lying between horizontal, infinitely long concentric cylinders of radii

Ri, Ro rotating

with peripheral speeds Ui,

Uo). Stokes' approximation is used to
formulate

a boundary value problem which is solved for the streamfunction, ω,
as a

function of radius ratio R¯=

Ri/Ro and
speed ratio

S=Ui/Uo.

Results show that for S>0 (S<0) the flow domain

consists of two (one) large

eddies (eddy), each having a stagnation point on the centreline and a

potentially rich

substructure with separatrices and sub-eddies. The behaviour of the streamfunction

solution in the neighbourhood of stagnation points on the centreline is
investigated

by means of a truncated Taylor expansion. As R¯ and S

are varied it is shown that a

bifurcation in the flow structure arises in which a centre becomes a

saddle stagnation

point and vice versa. As R¯→1, a sequence of

‘flow bifurcations’ leads to a flow

structure consisting of a set of nested separatrices, and provides the
means by which

the two-dimensional cavity flow approaches quasi-unidirectional flow in
the small gap

limit. Control-space diagrams reveal that speed ratio has little effect
on the flow

structure when S<0 and also when S>0 and aspect
ratios

are small (except near

S=1). For S>0 and moderate to large aspect ratios
the

bifurcation characteristics

of the two large eddies are quite different and depend on both

R¯ and S.
Small-scale characteristics of a turbulent

boundary layer over a rough wall
Authors: SHAFI H. S. , ANTONIA R. A.
Published: July 2002

Measurements of the spanwise and wall-normal components of

vorticity and their

constituent velocity derivative fluctuations have been made in a turbulent
boundary

layer over a mesh-screen rough wall using a four-hot-wire vorticity probe.
The

measured spectra and variances of vorticity and velocity derivatives have

been corrected

for the effect of spatial resolution. The high-wavenumber behaviour of
the spectra

conforms closely with isotropy. Over most of the outer layer, the normalized

magnitudes of the velocity derivative variances differ significantly

from those over a smooth

wall layer. The differences are such that the variances are

much more nearly isotropic

over the rough wall than on the smooth wall. This behaviour is

consistent with earlier

observations that the large-scale structure in this rough wall

layer is more isotropic

than that in a smooth wall layer. Isotropy-based approximations for the
mean energy

dissipation rate and mean enstrophy are consequently more reliable in this
rough

wall layer than in a smooth wall layer. In the outer layer, the

vorticity variances are

slightly larger than those over a smooth wall; reflecting structural

differences between the two flows.
Non-parallel linear stability analysis of the

vertical boundary layer in a differentially heated cavity
Authors: BROOKER A. M. H. , PATTERSON J. C. , ARMFIELD S. W.
Published: July 2002

A non-parallel linear stability analysis which utilizes the assumptions

made in the

parabolized stability equations is applied to the buoyancy-driven flow

in a differentially

heated cavity. Numerical integration of the complete Navier–Stokes
and energy

equations is used to validate the non-parallel theory by introducing an
oscillatory

heat input at the upstream end of the boundary layer. In this way the stability

properties are obtained by analysing the evolution of the resulting

disturbances. The

solutions show that the spatial growth rate and wavenumber are highly dependent

on the transverse location and the disturbance flow quantity under consideration.

The local solution to the parabolized stability equations

accurately predicts the wave

properties observed in the direct simulation whereas conventional parallel
stability

analysis overpredicts the spatial amplification and the wavenumber.
Eddy formation by dense flows on slopes in a rotating fluid
Authors: LANE-SERFF GREGORY F. , BAINES PETER G.
Published: July 2002

Properties of the flow generated by a continuous source of dense
fluid on a slope in a
rotating system are investigated with a variety of laboratory experiments.
The dense
fluid may initially flow down the slope but it turns (under the influence
of rotation) to
flow along the slope, and initial geostrophic adjustment gives it an anticyclonic
velocity
profile. Some of the dense fluid drains downslope in a viscous Ekman layer,
which may
become unstable to growing waves. Provided that the viscous draining is
not too
strong, cyclonic vortices form periodically in the upper layer and the
dense flow breaks
up into a series of domes. Three processes may contribute to the formation
of these
eddies. First, initial downslope flow of the dense current may stretch
columns of
ambient fluid by the ‘Taylor column’ process (which we
term ‘capture’). Secondly, the
initial geostrophic adjustment implies lower-layer collapse which may stretch
the fluid
column, and thirdly, viscous drainage will progressively stretch and spin
up a captured
water column. Overall this last process may be the most significant, but
viscous
drainage has contradictory effects, in that it progressively removes dense
lower-layer
fluid which terminates the process when the layer thickness approaches
that of the
Ekman layer. The eddies produced propagate along the slope owing to the
combined
effects of buoyancy–Coriolis balance and ‘beta-gyres’.

This removes fluid from the
vicinity of the source and causes the cycle to repeat. The vorticity of
the upper-layer
cyclones increases linearly with Γ=Lα/D

(where L is the Rossby deformation radius,
α the bottom slope and D the total depth), reaching
approximately 2f in the
experiments presented here. The frequency at which the eddy/dome structures
are
produced also increases with Γ, while the speed at
which the structures propagate along
the slope is reduced by viscous effects. The flow of dense fluid on slopes
is a very
important part of the global ocean circulation system and the implications
of the
laboratory experiments for oceanographic flows are discussed.
The impulsive motion of a liquid resulting from a particle collision
Authors: ZENIT R. , HUNT M. L.
Published: July 2002

When two particles collide in a liquid, the impulsive acceleration
due to the rebound
produces a pressure pulse that is transmitted through the fluid. Detailed
measurements
were made of the pressure pulse and the motion of the particles by generating

controlled collisions with an immersed dual pendulum. The experiments were
performed
for a range of impact velocities, angles of incidence, and distances between

the wall and the pairs of particles. The radiated fluid pressure was measured
using
a high-frequency-response pressure transducer, and the motion of the particles
was
recorded using a high-speed digital camera. The magnitude of the impulse
pressure
was found to scale with the particle velocity, the particle diameter and
the density of
the fluid. Additionally, a model is proposed to predict the impulse field
in the fluid
based on the impulse pressure theory. The model agrees well with the experimental

measurements.
Relative dispersion for solute flux in aquifers
Authors: ANDRIČEVIĆ ROKO , CVETKOVIĆ VLADIMIR
Published: July 2002

The relative dispersion framework for the non-reactive and reactive
solute flux in
aquifers is presented in terms of the first two statistical moments. The
solute flux is
described as a space–time process where time refers to the solute
flux breakthrough
and space refers to the transverse displacement distribution at the control
plane. The
statistics of the solute flux breakthrough and transversal displacement
distributions
are derived by analysing the motion of particle pairs. The results indicate
that
the relative dispersion formulation approaches the absolute dispersion
results on
increasing the source size (e.g. >10 heterogeneity scales). The solute
flux statistics,
when sampling volume is accounted for, show a flattened distribution for
the solute
flux variance in the space–time domain. For reactive solutes, the
solute flux shows
a tailing phenomenon in time while solute flux variance exhibits bi-modality
in
transverse distribution during the recession stage of the solute breakthrough.
The
solute flux correlation structure is defined as an integral measure over
space and time,
providing a potentially useful tool for sampling design in the subsurface.
Numerical simulations of large-amplitude internal solitary waves
Authors: TEREZ DMITRY E. , KNIO OMAR M.
Published: July 2002

A numerical model based on the incompressible two-dimensional Navier–Stokes

equations in the Boussinesq approximation is used to study mode-2 internal
solitary
waves propagating on a pycnocline between two deep layers of different
densities.
Numerical experiments on the collapse of an initially mixed region reveal
a train
of solitary waves with the largest leading wave enclosing an intrusional
‘bulge’.
The waves gradually decay as they propagate along the horizontal direction,
with
a corresponding reduction in the size of the bulge. When the normalized
wave
amplitude, a, falls below the critical value
ac=1.18, the wave is no longer able to
transport mixed fluid as it propagates away from the mixed region, and
a
sharp-nosed intrusion is left behind. The wave structure is studied using
a Lagrangian
particle tracking scheme which shows that for small amplitudes the bulges
have a
well-defined elliptic shape. At larger amplitudes, the bulge entrains and
mixes fluid
from the outside while instabilities develop in the rear part of the bulge.
Results
are obtained for different wave amplitudes ranging from small-amplitude
‘regular’
waves with a=0.7 to highly nonlinear unstable waves with
a=3.8. The dependence
of the wave speed and wavelength on amplitude is measured and compared
with
available experimental data and theoretical predictions. Consistent with
experiments,
the wave speed increases almost linearly with amplitude at small values
of a. As
a becomes large, the wave speed increases with amplitude at a
smaller rate, which
gradually approaches the asymptotic limit for a two-fluid model. Results
show that
in the parameter range considered the wave amplitude decreases linearly
with time
at a rate inversely proportional to the Reynolds number. Numerical experiments
are
also conducted on the head-on collision of solitary waves. The simulations
indicate
that the waves experience a negative phase shift during the collision,
in accordance
with experimental observations. Computations are used to determine the
dependence
of the phase shift on the wave amplitude.
‘Loca’ or ‘Libertadora’?: Manuela Sáenz in the Eyes of History and
Historians, 1900–c.1990
Authors: MURRAY PAMELA S.
Published: July 2002

This article traces the historiography of the romantic yet poorly
understood mistress, friend and political ally of Simón Bolívar: Manuela Sáenz
Aizpuru de Thorne (1797–1856). It highlights two opposing schools of
interpretation on Sáenz: the ‘bad girl’ and ‘heroine’ schools. Nationalism and the
cult of Bolívar (especially among Venezuelan and Ecuadorean authors), have
combined with the later influence of revolutionary socialist and feminist ideas to
ensure the predominance of the latter and, thus, of an heroic-mythic view of
Sáenz. Yet scholars' efforts to recover the historical woman have challenged this
view and, above all, paved the way for a more nuanced, gender-conscious
understanding of Sáenz's role and significance.
Living with Dictator Rosas: Argentina through Scottish Eyes
Authors: STEWART IAIN A. D.
Published: July 2002

Whilst much illuminating research has been conducted into

early British diplomatic and commercial activity in the River Plate,

few scholars have yet focused upon the lives of individual settlers in

any detail. The present article moves some way towards redressing this

imbalance through the study of the Gibsons, a prominent

Argentine-Scottish family with pioneering interests in commerce and

sheep breeding. The analysis gives special weight to letters exchanged

by the brothers Robert and George Gibson during the late 1830s,

casting light upon the incomers' perspective of political

turbulence as dissident forces fought to depose the dictator Juan

Manuel de Rosas.
Editorial note
Authors: Borsley Robert , Fabb Nigel , Tallerman Maggie
Published: July 2002

With this issue of the Journal Ian Roberts steps down from the editorial
team. He has been an editor since 1994 and we are most grateful for all he
has done for the Journal. He becomes a member of the Editorial Board, and
we look forward to receiving his advice. Ian's place as an editor is taken by
Caroline Heycock of the University of Edinburgh. We are very pleased to
welcome her to the editorial team.
A relevance-theoretic account of be going to
Authors: NICOLLE STEVE
Published: July 2002

This paper provides a relevance theoretic account of the semantics

of the be going to

construction in English, based on Klinge's (1993) model for the

semantics of the

modal auxiliaries, and in particular of will. The semantics of

both forms will be

accounted for in terms of the relation between linguistic representations
of

situations

and cognitive domains. Finally the pragmatics of utterances of sentences
containing

will and be going to will be discussed.
Nonlinear and three-wave resonant interactions in magnetohydrodynamics
Authors: WEBB G. M. , ZAKHARIAN A. R. , BRIO M. , ZANK G. P.
Published: July 2002

Hamiltonian and variational formulations of equations describing weakly
nonlinear magnetohydrodynamic (MHD) wave interactions in one Cartesian space
dimension are discussed. For wave propagation in uniform media, the wave interactions
of interest consist of (a) three-wave resonant interactions in which high-frequency waves may evolve on long space and time scales if the wave phases satisfy
the resonance conditions; (b) Burgers self-wave steepening for the magnetoacoustic
waves, and (c) mean wave field effects, in which a particular wave interacts with the
mean wave field of the other waves. The equations describe four types of resonant
triads: slow–fast magnetoacoustic wave interaction, Alfvén–entropy wave interaction,
Alfvén–magnetoacoustic wave interaction, and magnetoacoustic–entropy
wave interaction. The formalism is restricted to coherent wave interactions. The
equations are used to investigate the Alfvén-wave decay instability in which a large-amplitude forward propagating Alfvén wave decays owing to three-wave resonant
interaction with a backward-propagating Alfvén wave and a forward-propagating
slow magnetoacoustic wave. Exact solutions of the equations for Alfvén–entropy
wave interactions are also discussed.
Ion transport in glow discharges with dust
Authors: SUN A. P. , GENG M. , QIU X. M.
Published: July 2002

A Monte Carlo method is used to simulate ion transport in a

radiofrequency parallel-plate glow discharge with a negative-voltage pulse

connected to the electrode. The dust generated during the discharge and a self-consistent electric field are taken into account. Charge exchange and elastic

collisions between ions and neutral atoms and the collection and Coulomb

scattering of ions on the dust particles are examined during the motion of ions

in the sheath. It is found that self-consistent field, neutral gas pressure, and

dust charge, dust concentration and dust size influence, to varying degrees, the

energy distribution and density of ions arriving at the target, and in particular,

the dust charge and concentration have significant influences. As they increase,

the number of ions arriving at the target is greatly reduced. In summary,

although the dust content is very low (of order 10−3) in most plasma processing

devices, its influence cannot be neglected, because of the large dust size and

charge (in particular, the former). Therefore, in order to produce good results

with ion implantation, coating, stripping, and etching, it is necessary to reduce

the dust content and control the size of dust particles.
Theory of nonlinear plasma surface waves
Authors: GRADOV O. M. , STENFLO L.
Published: July 2002

By means of the cold-electron fluid equations, we deduce a new
strongly nonlinear surface solitary-wave solution for a semi-infinite plasma.
Experimental evidence of rapid relaxation to
large-scale structures in turbulent fluids:
selective decay and maximal entropy
Authors: BROWN MICHAEL R.
Published: July 2002

There is abundant experimental, theoretical and computational evidence
that
certain constrained turbulent fluid systems self-organize into large-scale
structures.
Examples include two-dimensional (geostrophic) fluids, guiding-centre plasmas
and
pure-electron plasmas, as well as two- and three-dimensional magnetofluids
such as
reversed-field pinches and spheromaks. The theoretical understanding of
relaxation
phenomena is divided into two quite different constructs: selective decay
and
maximal entropy. Theoretical foundations of both of these principles are
largely due
to Montgomery and his collaborators. In this paper, selective decay and
maximal
entropy theories of turbulent relaxation of fluids are reviewed and experimental
evidence is presented. Experimental evidence from both 2D fluids and from
3D
magnetofluids is consistent with the selective decay hypothesis. However,
high-resolution computational evidence strongly suggests that formation
of
large-scale
structures is dictated by maximal-entropy principles rather than selective
decay.
Nonlinear dispersive instabilities in
Kelvin–Helmholtz MHD flows
Authors: SINGH M. , KHOSLA H. K. , MALIK S. K.
Published: July 2002

The nonlinear evolution of Kelvin–Helmholtz instability
is examined in 2+1
dimensions in the context of magnetohydrodynamics. When the velocity
difference U is less than the critical velocity
Uc, the equation governing the
amplitude evolves into a self-focusing singularity. The self-focusing
of waves
predominates at short wavelengths, is directionally dependent, and also
depends sensitively on the strength of the applied magnetic field.
The minimum
velocity that allows the existence of self-focusing increases
with increasing
magnetic field strength. The explosive instability at the second-harmonic
resonance is also investigated.
Hamiltonian vortices and reconnection in a magnetized plasma
Authors: KUVSHINOV B. N. , LAKHIN V. P. , PEGORARO F. , SCHEP T. J.
Published: July 2002

Hamiltonian vortices and reconnection in magnetized plasmas are
investigated
analytically and numerically using a two-fluid model. The equations are
written in
the Lagrangian form of three fields that are advected with different velocities.
This
system can be considered as a generalization and extension of the two-dimensional

Euler equation for an ordinary fluid. It is pointed out that these equations
allow
solutions in the form of singular current-vortex filaments, drift-Alfvén
vortices and
magnetic islands, and admit collisionless magnetic reconnection where magnetic

flux is converted into electron momentum and ion vorticity.
Exact results for the homogeneous cooling state of an inelastic hard-sphere
gas
Authors: BRENIG L. , SALAZAR J. M.
Published: July 2002

The infinite set of moments of the two-particle distribution function
is found exactly
for the uniform cooling state of a hard-sphere gas with inelastic collisions.
Their
form shows that velocity correlations cannot be neglected, and consequently
the
‘molecular chaos’ hypothesis leading to the inelastic Boltzmann
and Enskog kinetic
equations must be questioned.
A model equation for non-resonant interacting ion acoustic plasma
waves
Authors: MACCARI ATTILIO
Published: July 2002

The interaction among non-resonant ion acoustic plasma waves with
different
group velocities that are not close to each other is studied by an asymptotic

perturbation method, based on Fourier expansion and spatio-temporal
rescaling. It is shown that the nonlinear Schrödinger equation is
not adequate,
and instead a model system of nonlinear evolution equations is necessary
to
describe oscillation amplitudes of Fourier modes. This system is C-integrable,

i.e. it can be linearized through an appropriate transformation of the
dependent
and independent variables. We demonstrate that the subclass of localized

solutions gives rise to a solitonic phenomenology. These solutions propagate

with the relative group velocity and maintain their shape during a collision,
the
only change being a phase shift. Numerical calculations confirm the validity
of
these predictions.
Alfvén-wave dissipation and current in strongly elongated tokamaks
Authors: TSYPIN V. S. , ELFIMOV A. G. , de AZEVEDO C. A. , de ASSIS A. S.
Published: July 2002

The general approach to Alfvén-wave current drive and induced
plasma rotation
in tokamaks with strongly elongated transverse cross-sections is considered.
Model
approximations are used to describe the circulating- and trapped-particle
dynamics
in all particle-trapping regions. This approach gives an accuracy of some
percent.
New terms, connected with the wave dissipation on trapped particles in
the second
and third trapped-particle regions for elongated tokamaks, are taken into
account.
The plasma rotation and longitudinal current, depending on the absorbed
power of
kinetic Alfvén waves, are discussed.
Relativistic cross-focusing of two coaxial
Gaussian laser beams in a plasma
Authors: KUMAR RAJ , PANDEY H. D. , SHARMA R. P. , KUMAR M.
Published: July 2002

The paper presents a paraxial theory of the relativistic cross-focusing
of two
coaxial Gaussian laser beams of different frequencies in a homogeneous
plasma.
We discuss the self-focusing of a weaker laser beam in the plasma due to
the
optical inhomogeneities introduced by another stronger copropagating laser

beam. In the presence of the second stronger beam
(Pcr21<P2<Pcr22),
the
plasma behaves as an oscillatory waveguide for the first, weaker, beam

(P1<Pcr11) as it propagates

in the plasma. When both the beams are strong
(Pcr11,21<P1,2<Pcr12,22),

the nonlinearities introduced by the relativistic effect are
additive in nature, such that one beam can undergo oscillatory self-focusing
and
the other simultaneously defocusing, and vice versa. A comparison reveals
that
cross-focusing due to relativistic nonlinearity is possible for a wider
range of
powers of the laser pulses than is cross-focusing due to ponderomotive

nonlinearity. Relativistic cross-focusing is important in plasma beat-wave

excitation and collective laser particle accelerators.
Influence of ion density on electron-beam
propagation from a gas-filled diode
Authors: UHM HAN S. , CHOI E. H. , KO J. J. , SHIN H. M. , CHO G. S.
Published: July 2002

Electron-beam propagation from a gas-filled diode is investigated.
The
beginning portion of the electron beam pulse creates an ion channel not
only
inside the diode but also in the region beyond the anode. A theoretical
model
is developed for the space-charge-limited current of a relativistic electron
beam
propagating through an ion channel. A simple analytical expression for
the
space-charge-limited current is obtained within the context of a thin-beam

approximation, where the conducting-tube radius is much larger than the
beam
radius. The beam current propagating through an ion channel is measured

experimentally for a mildly relativistic electron beam. Whenever the ion

density inside the diode is the same as the beam electron density, the
diode is
short-circuited. The ion-channel density at the short-circuiting time is

calculated numerically and is used to estimate the space-charge-limited
current.
It is shown that the experimental data agree well with the analytical results

predicted by the theoretical model.
Bifurcated equilibria in two-dimensional MHD with diamagnetic effects
Authors: TEBALDI C. , OTTAVIANI M.
Published: July 2002

In this work, we analyse the sequence of bifurcated equilibria in two-dimensional reduced magnetohydrodynamics. Diamagnetic effects are studied under
the assumption of a constant equilibrium pressure gradient, not altered by the
formation of a magnetic island. The formation of an island when the symmetric
equilibrium becomes unstable is studied as a function of the tearing-mode stability
parameter Δ′ and of the diamagnetic frequency, by employing fixed-point numerical
technique and an initial-value code. At larger values of Δ′, a tangent bifurcation
takes place, above which no small-island solutions exist. This bifurcation persists
up to fairly large values of the diamagnetic frequency (of the order of one-tenth of
the Alfvén frequency). The implications of this phenomenology for the intermittent
MHD dynamics observed in tokamaks is discussed.
Identification of Leadership among the KMT Yunnanese Chinese in Northern Thailand
Authors: Chang Wen-Chin
Published: July 2002

The leader-follower relationship among the KMT Yunnanese Chinese in northern Thailand is analyzed through the application of patron-client theories. It is argued that the relationship has been embedded in a particular socio-cultural context, which incorporates both Han Chinese culture and the native ethos of long-distance caravan trade, and that it is characterised by both instrumental and emotional forms.
Ciliate colonization of artificial substrates in the Lagoon of Venice
Authors: Coppellotti Olimpia , Matarazzo Paola
Published: July 2002

In work performed during the period February–October 1996, about 47 species of ciliates were detected in the communities of Aufwuchs, or periphyton, colonizing glass substrates submerged in three sites in the Lagoon of Venice, two in the urban area of Chioggia and one at a mussel-farming site. The ciliate communities were composed of sessile forms of Peritrichia and Suctoria and of motile ciliates, belonging especially to Hypotrichia and Karyorelictea. Four species of the peritrich Zoothamnium and the suctorians Acineta tuberosa and Ephelota gemmipara are reported here for the first time in the Lagoon of Venice. The richest ciliate communities were recovered at 60 cm from the bottom. Processed by multivariate analysis, data of samplings performed up to day ten from the positioning of glass slides indicated significant differences in biotic and physico-chemical parameters, according to season. The first data did not give definite indications on the possibility of using ciliates colonizing solid surfaces to assess the quality of this peculiar environment.
Observations on Morphogenesis in a marine ciliate Tachysoma ovata (Protozoa: Ciliophora: Hypotrichida)
Authors: Song Weibo , Warren Alan
Published: July 2002

Divisional morphogenesis of the marine hypotrichous ciliate, Tachysoma ovata was investigated based on protargol impregnated specimens. Its morphogenesis reveals the following peculiarities: (1) there is a definite period during which the anterior part of the newly formed adoral zone of membranelles (AZM) in the opisthe connects with the parental AZM which remains unchanged during the morphogenesis. (2) The anlagen of left and right marginal rows do not develop simultaneously. (3) The replication processes of macronuclear segments are not recognizable during cell division. It is likely that the replication takes place during the interphase. (4) The origin of the fronto-ventral-transverse (FVT) cirral anlagen in the opisthe is characteristic: in other Tachysoma spp. these primordia are generated either from differentiated parental ciliatures (or are orientated by pre-existent organelles), or by division of the proter's FVT-cirral primordia. (5) The primordium of the undulating membranes in the proter always keeps the form of two streaks (so-called ‘semi-anlagen’). There is no conspicuous dedifferentiation or reorganization of the undulating membranes. A morphogenetic comparison with other species of this genus was carried out.
Beyond Beasts and Bullion: Economic Considerations in Bombay's Military Logistics, 1803
Authors: Cooper Randolf G. S.
Published: July 2002

A previous work on British Indian Army logistics from 1757 to 1857 called into question the accuracy of labeling Arthur Wellesley ‘The Logistical Architect of the British Indian Army’. As the ‘soldier brother’ of India's Governor-General Richard, Marquis Wellesley, Arthur was bound to have drawn some attention while in India; but secondary sources have tended to be too ethnocentric in their interpretation of his South Asian military experience. Arthur Wellesley's successful command-apprenticeship, during the Dhoondiah Waugh Campaign, led him to the promotional track which culminated in his appointment as the Commander of the Southern Theatre in the 1803 Anglo-Maratha War. However, one should not confuse his prominence with precedence and I have argued elsewhere that East India Company (EIC) logistical policy was essentially South Asian in origin.
The Deradicalization of Jesus' Ethical Sayings in 1 Corinthians
Authors: WONG ERIC K. C.
Published: July 2002

The article seeks to provide an answer to the question of why Paul says so little about Jesus in his letters. Paul's relative silence on Jesus' words is dealt with in the light of a socio-historical perspective. The study seeks to elucidate how Paul mitigates Jesus' seemingly radical remarks over ethical issues on marriage and the requirements of inheriting the kingdom of God in 1 Corinthians (6.9–10 and 7.10–11), so that his teaching may fit into the new Sitz im Leben of the Corinthian Christian community.
A role for granulomatous inflammation in the transmission
of infectious disease: schistosomiasis and tuberculosis
Authors: DOENHOFF M. J.
Published: July 2002

The relationship between cell-mediated granulomatous inflammation
and
transmission of disease in schistosomiasis and
tuberculosis has been explored. In 2 experiments involving
Schistosoma mansoni-infected normal and T cell-deprived
mice, and infected deprived mice that had been variously reconstituted
with
immune or normal lymphocytes or immune
serum, there was a significant positive numerical correlation between
mean liver granuloma diameters and faecal egg
counts in individual animals. Lymphocytes from donors with recently patent

infections were more active than cells from
chronically infected or uninfected donors in reconstituting egg excretion

rates in deprived recipients, and mesenteric
lymph node (MLN) cells were more active than spleen cells. Modulation of

granulomatous activity with increasing
chronicity of infection in the donors, resulting in a decrease in granuloma

size around freshly produced tissue-bound eggs,
was paralleled by a waning of the capacity of transferred lymph node cells

to reconstitute egg excretion in the recipients.
Serum taken from chronically infected donor mice over the same period and

transferred to infected deprived recipients
became more active in enhancing egg excretion in the recipients as the

cell-mediated activity declined. A recent study in
Kenya has found that S. mansoni-infected patients with concurrent

human immunodefficiency virus (HIV) infection
excrete fewer eggs than patients exposed to the same levels of schistosome

infection, but who are not HIV-infected, thus
indicating that schistosome egg excretion in humans is also immune-dependent.

Attention is drawn to an apparently
parallel situation in human tuberculosis, another pathogen which induces

a cell-mediated granulomatous immune
response. Several studies have shown that patients with tuberculosis who

are also HIV-seropositive tend to have fewer
tubercle bacilli detectable in their saliva than those with tuberculosis,

but who are HIV-negative. This discrepancy,
associated with differences in lung pathology in HIV-positive patients,

suggests that in tuberculosis immune cell-mediated
granulomatous inflammation causes the destruction of host tissue in a
manner which facilitates onward transmission of the bacterial pathogen.
Seasonal changes in the Plasmodium falciparum population

in individuals and their relationship to clinical malaria:
a longitudinal study in a Sudanese village
Authors: ROPER C. , RICHARDSON W. , ELHASSAN I. M. , GIHA H. , HVIID L. , SATTI G. M. H. , THEANDER T. G. , ARNOT D. E.
Published: July 2002

Residents of Daraweesh village in Sudan were monitored for
Plasmodium falciparum infection and malaria morbidity in
3 malaria seasons from 1993 to 1996. Malaria parasites were detected
microscopically and by polymerase chain reaction
(PCR) in a series of cross-sectional surveys. PCR revealed submicroscopical

infections during the dry season, particularly
among individuals who had recovered from a malaria episode following
successful drug treatment. Clinical and subclinical
infections were contrasted by assaying for allelic polymorphism at 2 gene

loci, MSP-1 and GLURP and 2 hypotheses
examined with reference to these data: that clinical malaria is
associated with infection with novel parasite genotypes not
previously detected in that host, or alternatively, that clinical
malaria episodes are associated with an increased number
of clones in an infection. We detected more mixed infections among
clinical isolates, but people carrying parasites during
the dry season were not found to have an increased risk of disease in
the following malaria season. There was a clear
association of disease with the appearance of novel parasite genotypes.
Within-host transmission strategies of transovarial, feminizing parasites
of
Gammarus duebeni
Authors: DUNN A. M. , TERRY R. S. , TANEYHILL D. E.
Published: July 2002

The amphipod Gammarus duebeni harbours several species

of vertically transmitted, feminizing microsporidian parasites.
G. duebeni were collected from 3 localities in the UK. Animals
from
Budle Bay, Northumberland, were infected with
Octosporea effeminans, and those from Millport, Isle of Cumbrae
and
Fenham Flats, Northumberland were infected with
microsporidia of the genus Nosema. We derived expected distributions

of parasites per host embryonic cell by modelling
parasite transmission as a multitype, Galton–Watson branching
process. Parasite prevalence (proportion of females
infected) was significantly heterogeneous among localities. Parasite burden

in zygotes was much higher for females infected
with Nosema than in animals infected with O. effeminans.

There was no significant difference between localities in the
number of Nosema in the zygotes. Comparison of models and data
from
64-cell host embryos showed that the distributions
of parasites per cell were consistent with the hypothesis that sorting
of
parasites into daughter cells is biased for at least
1 cell lineage. Host embryos infected with O. effeminans could

expect to contain a growing number of parasites in each
cell generation within such biased cell lineages; similar estimates for

Nosema predict a decline in the number of parasites
per cell within a biased lineage. We discuss the possibility that the
2 species of parasite may be employing different
strategies in order to ensure transmission to the next host generation.
Psychiatrists' diagnoses of subthreshold depression in old age: frequency and correlates
Authors: GEISELMANN B. , LINDEN M. , HELMCHEN H.
Published: July 2002

Background. Depressive syndromes not fulfilling the criteria for specified disorders (subthreshold
depression, SD) may be clinically important. We aimed to study SD in old and very old age, in
comparison with subjects with no depressive symptoms (NDS) and subjects with major depression
(MD).

Methods. A community-based random sample of 516 subjects, age 70 to 100 years and over,
stratified by age and sex, was examined. All participants were investigated by psychiatrists and by
geriatricians independently.

Results. In 16·5% (N = 85) of the study subjects SD was identified. Study subjects with SD had,
similarly to the subjects with MD, significantly more somatic diagnoses and used more somatic as
well as psychotropic medications than the subjects with NDS. Self-ratings and observer ratings of
depression indicated that SD was a milder depressive state than MD.

Conclusions. Compared with MD, SD is probably a milder form of depression. The increased use
of psychotropic medications indicates that at least a portion of these individuals have a disorder
requiring treatment. One of the characteristics of SD is co-morbidity with somatic illnesses and
physical disability.
The Autonomy and Explanation of Mystical Perception
Authors: EBERLE CHRISTOPHER J.
Published: July 2002

William Alston has articulated a powerful defence of the claim
that
mystical perception generates prima facie justified beliefs about God.
At the heart
of his defence is the claim that mystical perception is
‘innocent until proven guilty’;
that is, Alston claims that the practice of forming beliefs on the basis
of putative
perceptions of God should be accorded the same presumptive innocence we
accord
to other standard ways of forming beliefs like sense perception, memory
and introspection.
But Alston employs a strategy for defending mystical perception that
seems to obviate the possibility of criticizing mystical perception and
thus that
renders otiose Alston's claim that that practice is innocent only
until proven guilty.
I argue that this appearance is deceptive; Alston's strategy does
not render effective
criticism of mystical perception unreasonably difficult. I further argue
that granting
the legitimacy of Alston's strategy is essential to a fair, measured
criticism of mystical
perception.
Interfering with divinely imposed suffering
Authors: LERNER BEREL DOV
Published: July 2002

In the course of presenting his celebrated ‘vale of soul-making’ theodicy,
John Hick claims that in a world where all human suffering is either justly deserved
divine punishment or imposed by God for the spiritual growth of the sufferer,
people would lack opportunity to be involved in genuine acts of deep compassion. I
argue that the relief of divinely imposed suffering can be a morally valuable and
spiritually beneficial activity, and mention ideas from the Jewish tradition which
suggest that it is right for people to ameliorate suffering even when that suffering
constitutes a just punishment from God.
Rodolfo Jacobson (ed.), Codeswitching worldwide.
(Trends in linguistics: Studies and monographs, 106.) Berlin:
Mouton de Gruyter, 1998. Pp. vi, 267. Hb DM 218.00.
Authors: Clyne Michael
Published: July 2002

The past decade has seen a healthy increase in
the number of studies in the areas constituting language
contact research. Prominent among these have been investigations
into grammatical aspects of “code-switching,”
often covering pairs of languages not previously investigated.
Many of the chapters in the book under review are based
on papers read at a conference in Bielefeld, Germany, in
1994. While this gives the papers coherence, it means that
some of the points made have already been left behind in
later publications by the same and other authors.