bluuebunny/crossref_metadata_2025 huggingface dataset:
Instabilities in a high-Reynolds-number

boundary layer on a film-coated surface
Authors: TIMOSHIN S. N.
Published: July 2002

A high-Reynolds-number asymptotic theory is developed for

linear instability waves

in a two-dimensional incompressible boundary layer on a flat surface coated
with

a thin film of a different fluid. The focus in this study is on the influence
of the

film flow on the lower-branch Tollmien–Schlichting waves,

and also on the effect of

boundary-layer/potential flow interaction on interfacial

instabilities. Accordingly, the

film thickness is assumed to be comparable to the thickness of a viscous

sublayer in a

three-tier asymptotic structure of lower-branch Tollmien–Schlichting

disturbances. A

fully nonlinear viscous/inviscid interaction formulation is derived,

and computational and analytical solutions for small disturbances are obtained

for both Tollmien–Schlichting and interfacial instabilities for a
range of

density and viscosity ratios of

the fluids, and for various values of the surface tension coefficient and
the Froude

number. It is shown that the interfacial instability contains

the fastest growing modes

and an upper-branch neutral point within the chosen flow regime if the
film viscosity

is greater than the viscosity of the ambient fluid. For a less viscous

film the theory

predicts a lower neutral branch of shorter-scale interfacial waves. The
film flow is

found to have a strong effect on the Tollmien–Schlichting

instability, the most dramatic

outcome being a powerful destabilization of the flow due to a

linear resonance between

growing Tollmien–Schlichting and decaying capillary modes. Increased

film viscosity also destabilizes Tollmien–Schlichting disturbances,
with the

maximum growth rate

shifted towards shorter waves. Qualitative and quantitative comparisons
are made

with experimental observations by Ludwieg & Hornung (1989).
Local energy flux and subgrid-scale statistics in three-dimensional
turbulence
Authors: BORUE VADIM , ORSZAG STEVEN A.
Published: July 2002

Statistical properties of the subgrid-scale stress tensor, the
local energy flux and
filtered velocity gradients are analysed in numerical simulations of forced

three-dimensional homogeneous turbulence. High Reynolds numbers are achieved
by using
hyperviscous dissipation. It is found that in the inertial range the subgrid-scale
stress
tensor and the local energy flux allow simple parametrization based on
a tensor
eddy viscosity. This parametrization underlines the role that negative
skewness of
filtered velocity gradients plays in the local energy transfer. It is found
that the local
energy flux only weakly correlates with the locally averaged energy dissipation
rate.
This fact reflects basic difficulties of large-eddy simulations of turbulence,
namely
the possibility of predicting the locally averaged energy dissipation rate
through
inertial-range quantities such as the local energy flux is limited. Statistical
properties
of subgrid-scale velocity gradients are systematically studied in an attempt
to reveal
the mechanism of local energy transfer.
Interactions of a horizontal flexible membrane with
oblique incident waves
Authors: CHO I. H. , KIM M. H.
Published: July 2002

The interaction of oblique monochromatic incident waves with a
horizontal flexible
membrane is investigated in the context of two-dimensional linear hydro-elastic
theory.
First, analytic diffraction and radiation solutions for a submerged impermeable

horizontal membrane are obtained using an eigenfunction expansion method.

Secondly, a multi-domain boundary element method (BEM) is developed to
confirm
the analytic solutions. The inner solution based on a discrete membrane
dynamic
model and simple-source distribution over the entire fluid boundaries is
matched to the
outer solution based on an eigenfunction expansion. The numerical solutions
are in
excellent agreement with the analytic solutions. The theoretical prediction
was then
compared to a series of experiments conducted in a two-dimensional wave
tank at
Texas A&M University. The measured reflection and transmission coefficients

reasonably follow the trend of predicted values. Using the computer program

developed, the performance of surface-mounted or submerged horizontal membrane

wave barriers is tested with various system parameters and wave characteristics.
It is
found that the horizontal flexible membrane can be an effective wave barrier
if properly
designed.
An axisymmetric ‘fluidic’ nozzle to generate jet precession
Authors: NATHAN G. J. , HILL S. J. , LUXTON R. E.
Published: July 2002

A continuously unstable precessing flow within a short cylindrical
chamber following
a large sudden expansion is described. The investigation relates to a nozzle
designed
to produce a jet which achieves large-scale mixing in the downstream field.
The inlet
flow in the plane of the sudden expansion is well defined and free from
asymmetry.
Qualitative flow visualization in water and semi-quantitative surface flow
visualization
in air are reported which identify this precession within the chamber.
Quantitative
simultaneous measurements from fast-response pressure transducers at four
tapping
points on the internal walls of the nozzle chamber confirm the presence
of the
precessing field. The investigation focuses on the flow within the nozzle
chamber
rather than that in the emerging jet, although the emerging flow is also
visualized.

Two flow modes are identified: a ‘precessing jet’ mode which
is instantaneously
highly asymmetric, and a quasi-symmetric ‘axial jet’ mode.
The precessing jet mode,
on which the investigation concentrates, predominates in the geometric
configuration
investigated here. A topologically consistent flow field, derived from
the visualization
and from the fluctuating pressure data, which describes a three-dimensional
and
time-dependent precessing motion of the jet within the chamber is proposed.
The surface
flow visualization quantifies the axial distances to lines of positive
and negative
bifurcation allowing comparison with related flows involving large-scale
precession
or flapping reported by others. The Strouhal numbers (dimensionless frequencies)
of
these flows are shown to be two orders of magnitude lower than that measured
in the
shear layer of the jet entering the chamber. The phenomenon is demonstrated
to be
unrelated to acoustic coupling.
Post-stall flow control on an airfoil by local unsteady forcing
Authors: WU JIE-ZHI , LU XI-YUN , DENNY ANDREW G. , FAN MENG , WU JAIN-MING
Published: July 2002

By using a Reynolds-averaged two-dimensional computation of a turbulent
flow over
an airfoil at post-stall angles of attack, we show that the massively separated
and
disordered unsteady flow can be effectively controlled by periodic blowing–suction

near the leading edge with low-level power input. This unsteady forcing
can modulate
the evolution of the separated shear layer to promote the formation of
concentrated
lifting vortices, which in turn interact with trailing-edge vortices in
a favourable
manner and thereby alter the global deep-stall flow field. In a certain
range of post-stall
angles of attack and forcing frequencies, the unforced random separated
flow can
become periodic or quasi-periodic, associated with a significant lift enhancement.
This
opens a promising possibility for flight beyond the static stall to a much
higher angle
of attack. The same local control also leads, in some situations, to a
reduction of drag.
On a part of the airfoil the pressure fluctuation is suppressed as well,
which would
be beneficial for high-α buffet control. The computations are in
qualitative agreement
with several recent post-stall flow control experiments. The physical mechanisms

responsible for post-stall flow control, as observed from the numerical
data, are
explored in terms of nonlinear mode competition and resonance, as well
as vortex
dynamics. The leading-edge shear layer and vortex shedding from the trailing
edge
are two basic constituents of unsteady post-stall flow and its control.
Since the former
has a rich spectrum of response to various disturbances, in a quite wide
range the
natural frequency of both constituents can shift and lock-in to the forcing
frequency
or its harmonics. Thus, most of the separated flow becomes resonant, associated
with
much more organized flow patterns. During this nonlinear process the coalescence

of small vortices from the disturbed leading-edge shear layer is enhanced,
causing a
stronger entrainment and hence a stronger lifting vortex. Meanwhile, the
unfavourable
trailing-edge vortex is pushed downstream. The wake pattern also has a
corresponding
change: the shed vortices of alternate signs tend to be aligned, forming
a train of
close vortex couples with stronger downwash, rather than a Kármán
street.
Large-eddy simulations of a round jet in crossflow
Authors: YUAN LESTER L. , STREET ROBERT L. , FERZIGER JOEL H.
Published: July 2002

This paper reports on a series of large-eddy simulations of a round
jet issuing normally
into a crossflow. Simulations were performed at two jet-to-crossflow velocity
ratios,
2.0 and 3.3, and two Reynolds numbers, 1050 and 2100, based on crossflow
velocity
and jet diameter. Mean and turbulent statistics computed from the simulations

match experimental measurements reasonably well. Large-scale coherent structures

observed in experimental flow visualizations are reproduced by the simulations,
and
the mechanisms by which these structures form are described. The effects
of coherent
structures upon the evolution of mean velocities, resolved Reynolds stresses,
and
turbulent kinetic energy along the centreplane are discussed. In this paper,
the
ubiquitous far-field counter-rotating vortex pair is shown to originate
from a pair of
quasi-steady ‘hanging’ vortices. These vortices
form in the skewed mixing layer that
develops between jet and crossflow fluid on the lateral edges of the jet.
Axial flow
through the hanging vortex transports vortical fluid from the near-wall
boundary
layer of the incoming pipe flow to the back side of the jet. There, the
hanging vortex
encounters an adverse pressure gradient and breaks down. As this breakdown
occurs,
the vortex diameter expands dramatically, and a weak counter-rotating vortex
pair is
formed that is aligned with the jet trajectory.
Ocean waves and ice sheets
Authors: BALMFORTH N. J. , CRASTER R. V.
Published: July 2002

A complete analytical study is presented of the reflection and transmission of surface
gravity waves incident on ice-covered ocean. The ice cover is idealized as a plate of
elastic material for which flexural motions are described by the Timoshenko–Mindlin
equation. A suitable non-dimensionalization extracts parameters useful for the characterization
of ocean-wave and ice-sheet interactions, and for scaled laboratory studies.
The scattering problem is simplified using Fourier transforms and the Wiener–Hopf
technique; the solution is eventually written down in terms of some easily evaluated
quadratures. An important feature of this solution is that the physical conditions at
the edge of the ice sheet are explicitly built into the analysis, and power-flow theorems
provide verification of the results. Asymptotic results for large and small values of the
non-dimensional parameters are extracted and approximations are given for general
parameter values.
Contact-line dynamics of a diffuse fluid interface
Authors: JACQMIN DAVID
Published: July 2002

An investigation is made into the moving contact line dynamics of
a Cahn–Hilliard–van der Waals (CHW) diffuse mean-field interface.
The interface separates two incompressible viscous fluids and can evolve
either through convection or through
diffusion driven by chemical potential gradients. The purpose of this paper is to show
how the CHW moving contact line compares to the classical sharp interface contact
line. It therefore discusses the asymptotics of the CHW contact line velocity and
chemical potential fields as the interface thickness ε and the mobility κ both go to
zero. The CHW and classical velocity fields have the same outer behaviour but can
have very different inner behaviours and physics. In the CHW model, wall–liquid
bonds are broken by chemical potential gradients instead of by shear and change of
material at the wall is accomplished by diffusion rather than convection. The result
is, mathematically at least, that the CHW moving contact line can exist even with
no-slip conditions for the velocity. The relevance and realism or lack thereof of this
is considered through the course of the paper.

The two contacting fluids are assumed to be Newtonian and, to a first approximation,
to obey the no-slip condition. The analysis is linear. For simplicity most of
the analysis and results are for a 90° contact angle and for the fluids having equal
dynamic viscosity μ and mobility κ. There are two regions of flow. To leading order
the outer-region velocity field is the same as for sharp interfaces (flow field
independent of r) while the chemical potential behaves like
r−ξ, ξ = π/2/max{θeq,
π − θeq}, θeq being the equilibrium contact
angle. An exception to this occurs for θeq = 90°,
when the chemical potential behaves like ln r/r. The diffusive and viscous contact line
singularities implied by these outer solutions are resolved in the inner region through
chemical diffusion. The length scale of the inner region is about 10√μκ – typically
about 0.5–5 nm. Diffusive fluxes in this region are O(1). These counterbalance the
effects of the velocity, which, because of the assumed no-slip boundary condition,
fluxes material through the interface in a narrow boundary layer next to the wall.

The asymptotic analysis is supplemented by both linearized and nonlinear finite
difference calculations. These are made at two scales, experimental and nanoscale.
The first set is done to show CHW interface behaviour and to test the qualitative
applicability of the CHW model and its asymptotic theory to practical computations
of experimental scale, nonlinear, low capillary number flows. The nanoscale calculations
are carried out with realistic interface thicknesses and diffusivities and with
various assumed levels of shear-induced slip. These are discussed in an attempt to
evaluate the physical relevance of the CHW diffusive model. The various asymptotic
and numerical results together indicate a potential usefullness for the CHW model
for calculating and modelling wetting and dewetting flows.
Direct simulation of weak axisymmetric
fountains in a homogeneous fluid
Authors: LIN WENXIAN , ARMFIELD S. W.
Published: July 2002

The weak axisymmetric fountain that results from the injection of a dense fluid
upwards into a large container of homogeneous fluid of lower density is studied
numerically. Using a time-accurate finite volume code, the behaviour of fountains
with both a uniform and a parabolic profile of the discharge velocity at the source
has been investigated. The evolution of the transient fountain flow has been analysed
and two distinct stages have been identified. The time series of the passage of the
fountain front has been presented and the initial, temporary and final characteristic
fountain heights have been determined and scaled with the Froude number at the
source. At steady state, the final fountain height and the fountain width are found to
be the height and horizontal length scales which provide the full parameterization of
the flow in the fountain core. The vertical velocity and temperature on the symmetry
axis have been scaled with the height scale and an explicit correlation is also obtained
for the former. The radial distributions of both the vertical and horizontal velocities
in the zone of self-similarity in the fountain core at steady state have been scaled with
the two length scales and empirical correlations have been obtained.
An explicit algebraic Reynolds stress model for
incompressible and compressible turbulent flows
Authors: WALLIN STEFAN , JOHANSSON ARNE V.
Published: July 2002

Some new developments of explicit algebraic Reynolds stress turbulence models
(EARSM) are presented. The new developments include a new near-wall treatment
ensuring realizability for the individual stress components, a formulation for
compressible flows, and a suggestion for a possible approximation of diffusion terms in
the anisotropy transport equation. Recent developments in this area are assessed and
collected into a model for both incompressible and compressible three-dimensional
wall-bounded turbulent flows. This model represents a solution of the implicit ARSM
equations, where the production to dissipation ratio is obtained as a solution to a
nonlinear algebraic relation. Three-dimensionality is fully accounted for in the mean
flow description of the stress anisotropy. The resulting EARSM has been found to
be well suited to integration to the wall and all individual Reynolds stresses can be
well predicted by introducing wall damping functions derived from the van Driest
damping function. The platform for the model consists of the transport equations for
the kinetic energy and an auxiliary quantity. The proposed model can be used with
any such platform, and examples are shown for two different choices of the auxiliary
quantity.
Turbulent diffusion near a free surface
Authors: SHEN LIAN , TRIANTAFYLLOU GEORGE S. , YUE DICK K. P.
Published: July 2002

We study numerically and analytically the turbulent diffusion characteristics in a
low-Froude-number turbulent shear flow beneath a free surface. In the numerical
study, the Navier–Stokes equations are solved directly subject to viscous boundary
conditions at the free surface. From an ensemble of such simulations, we find that a
boundary layer develops at the free surface characterized by a fast reduction in the
value of the eddy viscosity. As the free surface is approached, the magnitude of the
mean shear initially increases over the boundary (outer) layer, reaches a maximum and
then drops to zero inside a much thinner inner layer. To understand and model this
behaviour, we derive an analytical similarity solution for the mean flow. This solution
predicts well the shape and the time-scaling behaviour of the mean flow obtained in
the direct simulations. The theoretical solution is then used to derive scaling relations
for the thickness of the inner and outer layers. Based on this similarity solution,
we propose a free-surface function model for large-eddy simulations of free-surface
turbulence. This new model correctly accounts for the variations of the Smagorinsky
coefficient over the free-surface boundary layer and is validated in both a priori and
a posteriori tests.
Multidimensional modal analysis of nonlinear sloshing in a rectangular tank
with finite water depth
Authors: FALTINSEN ODD M. , ROGNEBAKKE OLAV F. , LUKOVSKY IVAN A. , TIMOKHA ALEXANDER N.
Published: July 2002

The discrete infinite-dimensional modal system describing nonlinear sloshing of an
incompressible fluid with irrotational flow partially occupying a tank performing an
arbitrary three-dimensional motion is derived in general form. The tank has vertical
walls near the free surface and overturning waves are excluded. The derivation is based
on the Bateman–Luke variational principle. The free surface motion and velocity
potential are expanded in generalized Fourier series. The derived infinite-dimensional
modal system couples generalized time-dependent coordinates of free surface elevation
and the velocity potential. The procedure is not restricted by any order of smallness.
The general multidimensional structure of the equations is approximated to analyse
sloshing in a rectangular tank with finite water depth. The amplitude–frequency
response is consistent with the fifth-order steady-state solutions by Waterhouse (1994).
The theory is validated by new experimental results. It is shown that transients and
associated nonlinear beating are important. An initial variation of excitation periods
is more important than initial conditions. The theory is invalid when either the water
depth is small or water impacts heavily on the tank ceiling. Alternative expressions for
hydrodynamic loads are presented. The procedure facilitates simulations of a coupled
vehicle–fluid system.
Philip Saffman and viscous flow theory
Authors: STONE H. A.
Published: July 2002

Philip Saffman made valuable theoretical contributions to different areas of low-Reynolds-number hydrodynamics. Three themes are selected for discussion here: (i)
the lift force on a sphere in a shear flow at small, but finite Reynolds number,
(ii) Brownian motion in thin liquid films, and (iii) particle motion in rapidly rotating
flows. In addition, brief descriptions are given of some of Saffman's other contributions
including dispersion in porous media, the average velocity of sedimenting suspensions,
and compressible low-Reynolds-number flows.
Seasons of Rebellion: Nature,

Organisation of Cotton Production

and the Dynamics of Revolution in

La Laguna, Mexico, 1910–1916
Authors: MEYERS WILLIAM K.
Published: July 2002

Throughout the Mexican Revolution, the ebb and flow

of conflict in the

north-central Laguna region (see Map 1) fed directly into

the mainstream of national politics. From 1900, the Laguna's

workers and peasants

expressed economic and social discontent through

insubordination, theft,

banditry and sporadic – sometimes organised –

demands for better wages

and working conditions. Following the lead of a

discontented, highly

competitive and fractious landholding elite, they were

among the first to

revolt against the Porfirio Díaz government and

continued to influence

the direction of the revolution as the region was

alternately fought over

and administered by each of the north's principal

factions. The ultimate

triumph of any faction in the revolution required control

of Mexico's north, and that required controlling the Laguna.
Irruptions of Memory: Expressive
Politics in Chile's Transition to
Democracy
Authors: WILDE ALEXANDER
Published: July 2002

Even before Augusto Pinochet was arrested in London in October 1998,
the past hung heavily over Chile's distinctive transition to democracy.
This was apparent during the previous year in the attention given to its
conflictive recent history in television and radio talk shows and in
newspaper and magazine articles. Since the return to elected rule in 1990,
volumes on the dictatorship and the Popular Unity government were
staples in Santiago bookstores. With the approach of the 25th anniversary
of the 1973 military coup, what had been a steady stream of publication
turned into a torrent of personal and political memoirs, extended essays,
political journalism, and scholarly studies evoking the country's divided
historical memory.
Marriage, Honor, Agency, and Trials by Ordeal: Women's Gender Roles in Candimangal
Authors: CURLEY DAVID L.
Published: July 2002

This essay discusses women's gender roles as they were imagined and debated in a Bengali text written towards the
end of the sixteenth century. Efforts to reexamine precolonial gender roles and debates about them are important for
three reasons. First, that large body of research on gender which begins with the colonial period often has obscured
elements of continuity between colonial and precolonial discourse on gender in South Asia, and often exaggerates or
misstates both the degree of consensus about gender in the precolonial period, and the nature of change in the colonial
period.
Leishmania infantum promastigotes have a poor capacity
for anaerobic functioning and depend mainly on
respiration for their energy generation
Authors: VAN HELLEMOND J. J. , VAN DER MEER P. , TIELENS A. G. M.
Published: July 2002

In earlier studies on the supposedly anaerobic metabolism of
Leishmania promastigotes it was suggested that the reduction
of fumarate to succinate functions as the main electron sink during anoxia.
Interestingly, however, our preliminary results
demonstrated that rhodoquinone, an essential component for efficient fumarate
reduction in eukaryotes, was absent in
L. infantum promastigotes. Therefore, we re-investigated the energy
metabolism and succinate production of these
promastigotes. Our studies demonstrated that L. infantum promastigotes
could, to a certain extent, survive periods without
respiration but had a low capacity for anaerobic metabolism. When oxygen
could not
be used as terminal electron acceptor,
the degradation of glucose was severely inhibited, forcing the parasite
to
reduce its energy expenditure, which resulted
in inhibited motility and proliferation. In addition, we studied the mechanism
of succinate production under aerobic
conditions and showed that in L. infantum promastigotes this succinate
was mainly produced via an oxidative pathway,
the Krebs cycle, and not significantly via fumarate reduction, which correlated
with the absence of rhodoquinone. Taken
collectively our studies show that L. infantum promastigotes depend
mainly on respiratory chain activity for energy
generation, have a poor capacity for anaerobic functioning, and go into
metabolic arrest during anoxic conditions.
Schistosoma mansoni: anomalous immunogenic properties
of a 27 kDa larval serine protease associated with protective immunity
Authors: DARANI H. Y. , CURTIS R. H. C. , McNEICE C. , PRICE H. P. , SAYERS J. R. , DOENHOFF M. J.
Published: July 2002

A cationic Schistosoma mansoni cercarial antigen was shown
to
be a serine protease as it was capable of hydrolysing
N-acetyl-dl-phenylalanine β-naphthyl ester (NAPBNE)
after precipitation by immunoelectrophoresis, and this reaction was
modulated by the serine protease inhibitors phenylmethanesulfonyl fluoride
(PMSF) and diisopropylfluorophosphate
(DFP). The antigen in the immunoprecipitin arcs could also be radio-isotope
labelled with tritiated DFP. The peptidolytic
enzyme identified in immunoelectrophoresis with polyspecific
sera and radio-isotope labelled with tritiated DFP had a
relative molecular size of approximately 27 kDa in sodium dodecyl
sulphate polyacrylamide gel electrophoresis (SDS–PAGE),
and evidence obtained after partial purification, SDS–PAGE
and immunoblotting supported this size estimate
for the enzyme. A rabbit antiserum raised against the peptidolytic
antigen reacted against a doublet of antigens at
27/28 kDa in immunoelectrophoresis arcs and against an antigen of
60 kDa in Western immunoblots of crude cercarial
homogenate. However, the latter serum precipitated the cationic antigen
in immunoelectrophoresed cercarial homogenates
only after pre-incubation of the homogenates with PMSF. Fractions containing
the partially purified protease also
degraded radio-isotope labelled human IgG. The reactivity of a range of
polyspecific and monospecific rabbit antisera in
Western blots with larval extracts indicated that antibody responses
against the 27/28 kDa doublet may be modulated.
When immunized with material which contained the 27 kDa enzyme as
a major constituent, and which was secreted by
S. mansoni cercariae during transformation, only 5 of 16 mice
produced antibody to this antigen that was detectable in
Western blots. The 5 antibody ‘responder’ mice were significantly
(P<0·001) protected against challenge with a
percutaneous infection of S. mansoni cercariae compared with
a group of mice also immunized with CTF, but which had
not produced antibodies against the 27/28 kDa doublet. The results
indicate that the 27 kDa serine protease of S. mansoni
larvae is a target that is sensitive to immunological attack.
Host searching in Argulus foliaceus L.
(Crustacea: Branchiura): the role of vision and selectivity
Authors: MIKHEEV V. N. , VALTONEN E. T. , RINTAMÄKI-KINNUNEN P.
Published: July 2002

In laboratory experiments, the swimming behaviour of the ectoparasite

Argulus foliaceus and its infection rates on juvenile
perch (Perca fluviatilis) and roach (Rutilus rutilus)

were examined. The highest infection rate and a preference for perch
juveniles were obtained in darkness, the lowest infection rate and a lack
of
preference in the light, when aquaria with glass
walls (high reflectivity) were used. In the light, when aquaria were lined

with black plastic (low reflectivity) an intermediate
level of infection for perch and the highest for roach was recorded. Under

such conditions roach were significantly more
heavily infected than perch; an attack rate 4 times greater was recorded
for
brighter (more reflective) roach juveniles than
for perch. Within the aquaria with a low reflective interior parasites
swam
4·4 times slower and were observed predominantly in the central

area, while in the highly reflective aquaria fast swimming
A. foliaceus were recorded mainly near
the walls. The primary role of visual stimuli for the host search behaviour
of
A. foliaceus in the light is suggested. Parasites
can effectively use such stimuli only in the low reflective surroundings.

Highly reflective glass aquarium walls produce
numerous secondary local light sources, which cause fast, erratic parasite

movements and prevent the efficient location of potential hosts.
Reply to: Models for the in-host dynamics of malaria
revisited: errors in some basic models lead to large over-estimates of growth rates
Authors: GRAVENOR M. B. , LLOYD A. L.
Published: July 2002

In the accompanying manuscript Saul (1998) points
out that a model of within-host malaria population
dynamics (Anderson, May & Gupta, 1989) can
exhibit unrealistically large growth rates. He
suggests that this error can be avoided by replacing
the parameter r, which is the number of merozoites
produced by each parasite at schizogony, with the
value ln (r)+1. This substitution does not, however,
address the true underlying problem with the model,
namely that whilst in reality there is small variation
in the distribution of Plasmodium spp. life-spans, the
use of the constant rate α assumes an exponential,
and hence much more variable, distribution. This
can allow the population to increase, over the time
period of the average life-span (48 h in the case of
Plasmodium falciparum), by factors considerably
larger than r. Saul identifies this assumption as
unrealistic in terms of the biology of malaria, but it
is not remedied in the proposed model.

Within the structure of the original model there
are two ways of addressing the growth rate problem.
Firstly, the ‘growth constant’ r can be replaced by

the value ln (r)+1, so that if all parasites reinvade,
the model increases by a factor r over 1 generation.
As pointed out by Saul, this is an artificial device
since it means that each parasite produces a reduced
number of merozoites. Alternatively, a parasite can
produce the observed number of merozoites, r,
many of which do not reinvade. This is the situation
in the original paper and Gravenor, McLean &
Kwiatkowski (1995). In these papers the model does
grow at a reasonable rate because the parameter β is
estimated directly from observed growth rates.
These points, however, are only an aside. Both the
original and Saul's modified model can grow at the
same rate and they both have the same distributional
assumptions concerning parasite life-span.
Identification of a developmentally regulated Schistosoma
mansoni serine protease homologous to mouse plasma
kallikrein and human factor I
Authors: COCUDE C. , PIERROT C. , CÊTRE C. , FONTAINE J. , GODIN C. , CAPRON A. , KHALIFE J.
Published: July 2002

The isolation of 2 genomic clones has allowed us to further characterize
a Schistosoma mansoni serine protease designated
SmSP1. The deduced amino acid sequence (248aa) considered as a ‘light
chain’ encoding the active site, presents
significant homologies with mouse plasma kallikrein and human factor I
light chain. The secondary structure of SmSP1
‘light chain’ is correctly predicted and may be sufficient
by itself to constitute an active enzyme. The biological function
of SmSP1 is unknown, however, the homology with 2 serine proteases suggests
that SmSP1 may play a role in the evasion
of the host immune response. This is supported by the presence of the native
protein corresponding to SmSP1 particularly
in schistosomula released products (SRP) and in male dorsal spines. The
expression of this enzyme is differentially
regulated throughout the parasite life-cycle. However, infected animals
with S. mansoni did not produce specific antibodies
to recombinant SmSP1. The lack of such response could be advantageous to
the parasite by protecting itself from host
effector mechanisms.
A functional study of auditory verbal imagery
Authors: SHERGILL S. S. , BULLMORE E. T. , BRAMMER M. J. , WILLIAMS S. C. R. , MURRAY R. M. , McGUIRE P. K.
Published: July 2002

Background. We used functional MRI to examine the functional anatomy of inner speech and different forms of auditory verbal imagery (imagining speech) in normal volunteers. We hypothesized that generating inner speech and auditory verbal imagery would be associated with left inferior frontal activation, and that generating auditory verbal imagery would involve additional activation in the lateral temporal cortices.

Methods. Subjects were scanned, while performing inner speech and auditory verbal imagery tasks, using a 1.5 Tesla magnet.

Results. The generation of inner speech was associated with activation in the left inferior frontal/insula region, the left temporo-parietal cortex, right cerebellum and the supplementary motor area. Auditory verbal imagery in general, as indexed by the three imagery tasks combined, was associated with activation in the areas engaged during the inner speech task, plus the left precentral and superior temporal gyri (STG), and the right homologues of all these areas.

Conclusions. These results are consistent with the use of the ‘articulatory loop' during both inner speech and auditory verbal imagery, and the greater engagement of verbal self-monitoring during auditory verbal imagery.
Probabilistic reasoning in deluded, depressed and normal subjects
: effects of task difficulty and meaningful versus
non-meaningful material
Authors: YOUNG HEATHER F. , BENTALL RICHARD P.
Published: July 2002

Background. Research indicates that deluded patients
‘jump to conclusions’ on probabilistic reasoning tasks.
Two experiments were carried out with patients suffering from
persecutory delusions and depressed and normal controls in order to
determine whether this response bias is affected by task difficulty
and the meaningfulness of the materials.

Methods. Tasks were variants of those employed by Huq
et al. (1988) and Garety et al. (1991). In
Experiment 1, subjects judged which of two bags a sequence of coloured
beads had been taken from. Difficulty was manipulated by varying the
ratios of coloured beads in the bags. In Experiment 2, a neutral
condition required judgements about coloured beads drawn whereas, in
meaningful conditions, subjects had to judge whether personality
characteristics described one of two individuals.

Results. In Experiment 1, estimates of certainty varied
with task difficulty, and there was no evidence of ‘jumping to
conclusions’ in the deluded group. In Experiment 2, all groups
reached an initial level of certainty and reduced their estimates of
certainty following disconfirmatory evidence more quickly in the
meaningful conditions. Both clinical groups expressed higher certainty
levels in early trials, and a greater magnitude of reduction in
certainty following disconfirmatory information. These group
differences were more evident in the meaningful conditions than in the
neutral conditions.

Conclusions. Probabilistic reasoning is affected by task
difficulty and meaningfulness of materials in both deluded and
depressed subjects. Observed reasoning abnormalities were not specific
to the deluded group.
The dimensional structure of first episode psychosis: an exploratory
factor
analysis
Authors: McGORRY P. D. , BELL R. C. , DUDGEON P. L. , JACKSON H. J.
Published: July 2002

Background. Recent research has focused upon the
subdiagnostic level in an effort to derive more
valid domains of psychotic disorder. This has led to the influential
positive–negative dichotomy in
schizophrenia being superseded by a three-syndrome model. The
strategy of looking for syndromes
within poorly validated diagnostic categories, such as schizophrenia,
has limitations, particularly
since it originated in, and has been largely restricted to, the more chronic
subsamples.

Method. A representative sample of first episode psychosis

(N=509), which includes the full
spectrum of functional psychosis, was utilized to re-examine the
dimensional structure of functional
psychosis from first principles. Patients were assessed with the Royal
Park Multidiagnostic
Instrument for Psychosis (MIP), a comprehensive procedure that documents
the psychopathology
of the first episode in a clinically valid manner.

Results. Principal axis factor analysis was carried
out on the tetrachoric correlation matrix of 92
core psychopathological items. A robust and clinically valid four-factor
solution was obtained,
comprising depression, mania and only two other factors. The first was
a Bleulerian blend of
negative symptoms, catatonic/motor symptoms and disorganization. The
second was
a combination of Schneiderian first rank symptoms, and other hallucinations

and delusions. The data thus failed
to support the three-syndrome model for non-affective symptoms in this
population. A six-factor
solution, although partially consistent with other studies, represented
a more complex and
confusing elaboration of the more clinically valid four-factor solution.

Conclusions. The findings have implications for
the conceptualization of early psychosis, which
need to be explored further in validation studies.
The development of the Short Explanatory Model Interview (SEMI)
and its use among primary-care attenders with common mental disorders
Authors: LLOYD K. R. , JACOB K. S. , PATEL V. , St. LOUIS L. , BHUGRA D. , MANN A. H.
Published: July 2002

Background. Recent anthropological studies have
documented the importance of understanding
the relation of culture to the experience of mental illness. The use of
interviews that elicit
explanatory models has facilitated such research, but currently
available interviews are lengthy and
impractical for epidemiological studies. This paper is a
preliminary report on the development of
a brief instrument to elicit explanatory models for use in field work.

Method. The development of the SEMI, a short interview
to elicit explanatory models is described.
The interview explores the subject's cultural background, nature
of presenting problem, help-seeking behaviour, interaction with physician/healer and beliefs related
to mental illness.

Results. The SEMI was employed to study the explanatory
models of subjects with common mental
disorders among Whites, African-Caribbean and Asians living in London and
was also used in
Harare, Zimbabwe. Data from its use in four different ethnic
groups is presented with the aim of
demonstrating its capacity to show up differences in these varied settings.

Conclusions. The simplicity and brevity of the SEMI allow
for its use in field studies in different
cultures, data can be used to provide variables for use in quantitative
analysis and provide
qualitative descriptions.
A population-based twin study of self-esteem and gender
Authors: KENDLER K. S. , GARDNER C. O. , PRESCOTT C. A.
Published: July 2002

Background. Self-esteem (SE), a widely used construct
in the social sciences, is usually conceptualized
as a reflection of socialization and interpersonal experiences that may
differ considerably between
the genders.

Methods. The Rosenberg self-esteem scale was assessed at personal
interview in both members of
3793 unselected twin pairs (1517 male–male, 856 female–female
and 1420 male–female) from the
population-based Virginia Twin Registry. Gender effects on SE were assessed
by both analysis of
variance and biometrical twin modelling.

Results. The mean SE score was slightly but significantly lower
in women v. men, and in women who
grew up with a male v. a female co-twin. Twin modelling suggested
that: (i) individual differences
in self-esteem in both men and women were best explained by genetic and
individual-specific
environment factors; (ii) heritability estimates were similar
in women (32%) and in men (29%); and
(iii) the same genetic factors that influenced SE in women also
influenced SE in men. Analyses
supported the validity of the equal environment assumption for SE. The
heritability of SE cannot
be explained by the moderate correlation between SE and symptoms of depression.

Conclusions. These results are inconsistent with prominent
gender-related aetiological models for
SE, which postulate that individual differences arise from socialization
experiences both within and
outside the home of origin which differ widely for the two genders. Instead,
a significant proportion
of the population variance in SE is due to genetically-influenced temperamental
variables that are
the same in men and women.
Symptoms of depression and anxiety during adult
life: evidence for a decline in prevalence with age
Authors: HENDERSON A. S. , JORM A. F. , KORTEN A. E. , JACOMB P. , CHRISTENSEN H. , RODGERS B.
Published: July 2002

Background. To test the hypothesis that the prevalence,
in the general population, of symptoms of
depression and anxiety declines with age.

Methods. A general population sample of 2725 persons aged 18
to 79 years was administered two
inventories for current symptoms of depression and anxiety, together with
measures of neuroticism
and of exposures that may confer increased risk of such symptoms.

Results. Symptoms of depression showed a decline with age in
both men and women. For anxiety,
the decline was statistically significant for women but not consistently
so for men. For the risk
factors examined, there was a decline with age in the neuroticism score,
the frequency of adverse
life events, being seriously short of money and having had parents who
separated or divorced.
Further analysis showed that the association between age and a declining
symptom score cannot be
entirely attributed to these risk factors, with the single exception of
neuroticism. The latter is itself
likely to be contaminated by current symptoms.

Conclusion. Unless these findings are due to bias in the sample
of those who agreed to participate,
they add to the evidence that symptoms of depression and to a lesser extent
of anxiety decline in
prevalence with age. Some risk factors also decline with age. It now has
to be determined if these
cross-sectional observations are also to be found in longitudinal data;
and what process may
underlie this striking change in mental health during adulthood.
Symptoms of depression among community-dwelling
elderly African-American and White older adults
Authors: BLAZER D. G. , LANDERMAN L. R. , HAYS J. C. , SIMONSICK E. M. , SAUNDERS W. B.
Published: July 2002

Background. Few studies have explored the variance in
individual symptoms by race in older
adults.

Methods. Data were analysed from the Duke site of the Established
Populations for Epidemiologic
Studies of the Elderly (EPESE), a community sample of persons 65 years-of-age
and older, 54% of
whom were African-Americans. Of the 3401 subjects with adequate data on
depressive
symptomatology, confirmatory factor analysis and LISREL were first used
to confirm the presence
of the factor structure previously reported for the CES-D. Next, bivariate
analysis was performed
to determine the prevalence of individual symptoms by race. Finally, LISREL
analysis was
performed to control for potential confounding variables.

Results. When bivariate comparisons of specific symptoms by
race were explored, African-Americans
were more likely to report less hope about the future, poor appetite, difficulty

concentrating, requiring more effort for usual activities, less talking,
feeling people were unfriendly,
feeling disliked by others and being more ‘bothered’ than usual.
When LISREL analyses were
applied to these data (controlling for education, income, cognitive impairment,
chronic health
problems and disability and other factors) racial differences in somatic
complaints and life
satisfaction disappeared, yet differences in interpersonal relations persisted.

Conclusions. This study confirms earlier findings of minimal
overall differences in symptom
frequency between African-American and non-African-American community-dwelling
older adults
in controlled studies.
Childhood attention deficit/hyperactivity disorder in
adults with anxiety disorders
Authors: MANCINI C. , VAN AMERINGEN M. , OAKMAN J. M. , FIGUEIREDO D.
Published: July 2002

Background. Previous research has reported co-morbidity between attention deficit hyperactivity
disorder (ADHD) and anxiety disorders. Interpretation of these findings is complicated by
symptom overlap in the clinical presentation of the disorders. We estimate the prevalence of ADHD
in both the current and childhood histories of adults with anxiety disorders, while taking symptom
overlap into account. We also evaluate the utility of the Wender Utah Rating Scale (WURS) for
retrospective reporting of ADHD.

Methods. Consecutive admissions (N=149) to an anxiety disorders clinic were given a diagnostic
and psychometric assessment. The WURS was administered to obtain a retrospective diagnosis of
childhood ADHD. Twenty-nine of the 35 people surpassing the cut-off score on the WURS were
given a structured interview of adult ADHD symptoms.

Results. The WURS contains many ‘internalizing’ items that may inflate retrospective accounts of
ADHD. After taking this into account, there is still a significantly higher prevalence of ADHD in
the retrospective reports of adults with anxiety disorders (15%) than would be expected by chance
(4%). Furthermore, of those who meet retrospective criteria for ADHD, 45% (13 of 29) continue
to meet diagnostic criteria for ADHD as adults.

Conclusions. The WURS may require considerable revision for use with clinical populations. In
spite of these difficulties with retrospective assessment, available evidence indicates that ADHD is
more prevalent in the histories of anxiety disordered patients than would be expected from base
rates.
Conditions not attributable to a mental disorder in
Dutch psychiatric out-patients
Authors: SPINHOVEN P. , VAN DER DOES A. J. W.
Published: July 2002

Background. According to DSM-III-R V-code conditions refer
to marital relationships, family
circumstances, interpersonal relationships, or stressful life events that
are not attributable to a
mental disorder but that are the focus of treatment. The purpose of the
present study was to assess
the prevalence and patient and treatment characteristics of adult psychiatric
out-patients diagnosed
with V-code conditions.

Methods. The records of all 5660 consecutive admissions to
a psychiatric out-patient clinic over a
12-year period were studied retrospectively. On the basis of both primary
and secondary
DSM-III-R diagnoses on Axis I, two subgroups of patients were compared:
(1) patients with V-code
conditions; and (2) patients with mental disorders.

Results. Fourteen per cent of the patients had a V-code condition
and no mental disorder, while the
remaining patients were diagnosed with mental disorder (with or without
an additional V-code
condition). Comparisons of sociodemographic and clinical severity characteristics
of the two groups
indicated that patients with V-code conditions tended to have a higher
socio-economic status and
to present with less severe problems as assessed both by the primary therapist
and the
Symptom-Checklist-90. With respect to service use and treatment outcome
variables, it appeared that V-code
patients tended to be more frequently treated by couple/family therapy
and to receive a slightly
lower number of treatment sessions.

Conclusions. The pattern of results in The Netherlands seems
comparable to results of previous
North American studies. Implications of these findings for future studies
and for use of mental
health services are discussed.