bluuebunny/crossref_metadata_2025 huggingface dataset:
The evolution of a uniformly sheared thermally

stratified turbulent flow
Authors: PICCIRILLO PAUL , VAN ATTA CHARLES W.
Published: July 2002

Experiments were carried out in a new type of stratified flow facility

to study the evolution of turbulence in a mean flow possessing both uniform

stable stratification and uniform mean shear.

The new facility is a thermally stratified wind tunnel consisting of ten

independent supply layers, each with its own blower and heaters, and is
capable

of producing arbitrary temperature and velocity profiles in the test section.

In the experiments, four

different sized turbulence-generating grids were used to study the effect
of

different initial conditions. All three components of the velocity were
measured,

along with the temperature. Root-mean-square quantities and correlations
were

measured, along with their corresponding power and cross-spectra.

As the gradient Richardson number Ri = N2/(dU/dz)2 was increased, the downstream spatial evolution of the turbulent kinetic energy changed from increasing, to stationary, to decreasing. The stationary value of the Richardson number, Ricr, was found to be an increasing function of the dimensionless shear parameter Sq2/∈ (where S = dU/dz is the mean velocity shear, q2 is the turbulent kinetic energy, and ∈ is the viscous dissipation).

The turbulence was found to be highly anisotropic, both at the small scales
and at

the large scales, and anisotropy was found to increase with increasing

Ri. The evolution of the velocity power spectra for

Ri [les ] Ricr, in which the

energy of the large scales

increases while the energy in the small scales decreases, suggests that
the

small-scale anisotropy is caused, or at least amplified, by buoyancy forces

which reduce the amount of spectral energy transfer from large to small
scales. For the largest values of Ri, countergradient buoyancy flux occurred for the small scales of the turbulence, an effect noted earlier in the numerical results of Holt et al. (1992), Gerz et al. (1989), and Gerz & Schumann (1991).
A theory of particle deposition in turbulent pipe flow
Authors: YOUNG JOHN , LEEMING ANGUS
Published: July 2002

The paper describes a theory of particle deposition based formally on
the conservation
equations of particle mass and momentum. These equations are formulated in an
Eulerian coordinate system and are then Reynolds averaged, a procedure which
generates a number of turbulence correlations, two of which are of prime importance.
One represents ‘turbulent diffusion’ and the other
‘turbophoresis’, a convective drift
of particles down gradients of mean-square fluctuating velocity. Turbophoresis is
not a small correction; it dominates the particle dynamic behaviour in the
diffusion-impaction and inertia-moderated regimes.

Adopting a simple model for the turbophoretic force, the theory is used to
calculate
deposition from fully developed turbulent pipe flow. Agreement with experimental
measurements is good. It is found that the Saffman lift force plays an important role
in the inertia-moderated regime but that the effect of gravity on deposition from
vertical flows is negligible. The model also predicts an increase in particle
concentration
close to the wall in the diffusion-impaction regime, a result which is partially
corroborated by an independent ‘direct numerical simulation’ study.

The new deposition theory represents a considerable advance in physical
understanding over previous free-flight theories. It also offers many avenues
for future
development, particularly in the simultaneous calculation of laminar (pure inertial)
and turbulent particle transport in more complex two- and three-dimensional
geometries.
The interaction of spatially modulated vortex pairs with free surfaces
Authors: WILLERT CHRISTIAN E. , GHARIB MORTEZA
Published: July 2002

Spatially modulated vortex pairs were generated below a free surface

by two counter-rotating flaps whose edges approximate a sinusoid.

The surface interactions of the

vertically approaching vortex pairs were visualized by the shadowgraph
technique.

Two limiting cases were investigated in detail: the interaction

with a surfactant-rich

(contaminated) surface and with a surfactant-poor (‘clean’)

surface. In the latter

case shadowgraph images showed that the underlying vortex core formed a
line of

circular surface depressions. Subsequent measurements of the temporally
evolving

velocity fields using digital particle image velocimetry (DPIV) of the
vortex pair

cross-sections and the subsurface plane confirmed the connection process
of the main

vortex core with the surface. As a result of the connection the initially
modulated

vortex tube was broken into a line of U-vortices. In the presence of surfactants

this connection could not be observed; rather a Reynolds ridge (or stagnation
line)

was formed and a very weak connection of the secondary separation vortex
could

be seen in the shadowgraphs as well as measured with the time-resolved
DPIV

technique.

A prerequisite for connection of the vortex with the

surface is that the flow's

kinematics force the vortex core, that is, regions of concentrated vorticity,
toward

the surface. The ensuing locally concentrated viscous flux

of surface-parallel vorticity through the surface is balanced by

a local surface deceleration. Surface-normal

vorticity appears on each side of the decelerated region whose gradually

increasing circulation is directly balanced by the loss of

circulation of the surface-parallel

vortex. However, the shear forces caused by small amounts of surface

contamination and its associated subsurface boundary layer inhibit

the connection process by

preventing the essential viscous flux of parallel vorticity through the
surface.

Instead, the subsurface boundary layer is associated with

a flux of parallel vorticity

into the surface which then concentrates into the observable secondary
separation

vortex.
The effects of successive distortions on a

turbulent boundary layer in a supersonic flow
Authors: SMITH DOUGLAS R. , SMITS ALEXANDER J.
Published: July 2002

Experiments were conducted to investigate the response of a

high-Reynolds-number

turbulent boundary layer in a supersonic flow to the perturbation presented
by

a forward-facing ramp. Two ramps were used: one with sharp corners, the
other

with rounded corners having radii of curvature equal to 15 initial boundary
layer

thicknesses. The flow was turned through 20° in each of the compressions
and

expansions. Hence, there was no net change in the flow direction over the
ramps

and only a small change in free-stream conditions due to the entropy increase
across

relatively weak shocks. The two experiments gave similar results.

In the middle of the

relaxing boundary layer, the streamwise Reynolds stress undershot the undisturbed

levels and exhibited a response similar to that observed in subsonic boundary
layer

flows recovering from an impulse of streamline curvature (Smits,

Young & Bradshaw

1979b). The turbulent shear stress vanished throughout most of
the

boundary layer,

and an overall destruction of the turbulence production mechanisms was
apparent as

the boundary layer exhibited a slow recovery.
Laboratory measurements of the generation and
evolution of Langmuir circulations
Authors: MELVILLE W. KENDALL , SHEAR ROBERT , VERON FABRICE
Published: July 2002

We present laboratory measurements of the generation and evolution
of Langmuir
circulations as an instability of a wind-driven surface shear layer. The
shear layer,
which is generated by an accelerating wind starting from rest above a quiescent

water surface, both accelerates and deepens monotonically until the inception
of the
Langmuir circulations. The Langmuir circulations closely follow the initial
growth
of the wind waves and rapidly lead to vertical mixing of the horizontal
momentum
and a deceleration of the surface layer. Prior to the appearance of the
Langmuir
circulations, the depth of the shear layer scales with
(vt)1/2 (v is the kinematic
viscosity and t is time), in accordance with molecular
rather than turbulent transport.
For final wind speeds in the range 3 to 5 m s−1, the wavenumber
of the
most unstable Langmuir circulation normalized by the surface wavenumber,

k*lc, is 0.68±0.24, at a reciprocal
Langmuir number,
La−1, of 52±21. The observations are compared
with
available theoretical results, although none are directly applicable to
the conditions
of the experiments. The implications of this work for the generation and
evolution of
Langmuir circulations in the ocean and other natural water bodies are discussed.
Low-frequency unsteadiness in the wake of a normal flat plate
Authors: NAJJAR F. M. , BALACHANDAR S.
Published: July 2002

The separated flow past a zero-thickness flat plate held normal
to a free stream at
Re=250 has been investigated through numerical experiments. The
long-time
signatures of the drag and lift coefficients clearly capture a low-frequency
unsteadiness
with a period of approximately 10 times the primary shedding period. The
amplitude
and frequency of drag and lift variations during the shedding process are
strongly
modulated by the low frequency. A physical interpretation of the low-frequency

behaviour is that the flow gradually varies between two different regimes:
a regime H
of high mean drag and a regime L of low mean drag. It is observed that
in regime H
the shear layer rolls up closer to the plate to form coherent spanwise
vortices, while in
regime L the shear layer extends farther downstream and the rolled-up Kármán

vortices are less coherent. In the high-drag regime three-dimensionality
is characterized
by coherent Kármán vortices and reasonably well-organized
streamwise vortices
connecting the Kármán vortices. With a non-dimensional spanwise
wavelength of
about 1.2, the three-dimensionality in this regime is reminiscent of mode-B

three-dimensionality. It is observed that the high
degree of spanwise coherence that exists in
regime H breaks down in regime L. Based on detailed numerical flow visualization
we
conjecture that the formation of streamwise and spanwise vortices is not
in perfect
synchronization and that the low-frequency unsteadiness is the result of
this imbalance
(or phase mismatch).
Miscible porous media displacements in the quarter five-spot configuration.

Part 2. Effect of heterogeneities
Authors: CHEN CHING-YAO , MEIBURG ECKART
Published: July 2002

Direct numerical simulations are employed to investigate the coupling
between the
viscous fingering instability and permeability heterogeneities for miscible
displacements
in quarter five-spot flows. Even moderate inhomogeneities are seen to have
a strong
effect on the flow, which can result in a complete bypass of the linear
growth phase
of the viscous fingering instability. In contrast to their homogeneous
counterparts
(cf. Part 1, Chen & Meiburg 1998), heterogeneous quarter five-spot
flows are seen
to exhibit a more uniform dominant length scale throughout the entire flow
domain.
In line with earlier findings for unidirectional displacements, an optimal
interaction
of the mobility and permeability related vorticity modes can occur when
the viscous
length scale is of the same order as the correlation length of the heterogeneities.
This
resonance mechanism results in a minimal breakthrough recovery for intermediate

correlation lengths, at fixed dimensionless flow rates in the form of a
Péclet number
Pe. However, for a constant correlation length, the recovery does
not show a minimum
as Pe is varied.

Confirming earlier observations, the simulations show a more rapid breakthrough

as the variance of the permeability variations increases. However, this
tendency is far
more noticeable in some parameter regimes than in others. It is furthermore
observed
that relatively low variances usually cannot change the tendency for a
dominant finger
to evolve along the inherently preferred diagonal direction, especially
for relatively
small correlation lengths. Only for higher variances, and for larger correlation
lengths,
are situations observed in which an off-diagonal finger can become dominant.
Due to
the nonlinear nature of the selection mechanisms at work, a change in the
variance
of the heterogeneities can result in the formation of dominant fingers
along entirely
different channels.
Low-Reynolds-number flow around an oscillating circular cylinder at
low
Keulegan–Carpenter numbers
Authors: DÜTSCH H. , DURST F. , BECKER S. , LIENHART H.
Published: July 2002

Time-averaged LDA measurements and time-resolved numerical flow
predictions
were performed to investigate the laminar flow induced by the harmonic
in-line
oscillation of a circular cylinder in water at rest. The key parameters,
Reynolds number
Re and Keulegan–Carpenter number KC, were
varied to study three parameter
combinations in detail. Good agreement was observed for Re=100
and KC=5
between measurements and predictions comparing phase-averaged velocity
vectors.
For Re=200 and KC=10 weakly stable and non-periodic flow
patterns occurred,
which made repeatable time-averaged measurements impossible. Nevertheless,
the
experimentally visualized vortex dynamics was reproduced by the two-dimensional

computations. For the third combination, Re=210 and KC=6,
which refers to
a totally different flow regime, the computations again resulted in the
correct fluid
behaviour. Applying the widely used model of Morison et al. (1950)
to the computed
in-line force history, the drag and the added-mass coefficients were calculated
and
compared for different grid levels and time steps. Using these to reproduce
the force
functions revealed deviations from those originally computed as already
noted in
previous studies. They were found to be much higher than the deviations
for the
coarsest computational grid or the largest time step. The comparison of
several
in-line force coefficients with results obtained experimentally by
Kühtz (1996) for β=35
confirmed that force predictions could also be reliably obtained by the
computations.
The surface layer for free-surface turbulent flows
Authors: SHEN LIAN , ZHANG XIANG , YUE DICK K. P. , TRIANTAFYLLOU GEORGE S.
Published: July 2002

Direct numerical simulation (DNS) is used to examine low Froude number free-surface turbulence (FST) over a two-dimensional mean shear flow. The Navier–Stokes
equations are solved using a finite-difference scheme with a grid resolution of 1283.
Twenty separate simulations are conducted to calculate the statistics of the flow.
Based on the velocity deficit and the vertical extent of the shear of the mean flow,
the Reynolds number is 1000 and the Froude number is 0.7. We identify conceptually
and numerically the surface layer, which is a thin region adjacent to the free surface
characterized by fast variations of the horizontal vorticity components. This surface
layer is caused by the dynamic zero-stress boundary conditions at the free surface
and lies inside a thicker blockage (or ‘source’) layer, which is due to the
kinematic boundary condition at the free surface. The importance of the outer blockage layer is
manifested mainly in the redistribution of the turbulence intensity, i.e. in the increase
of the horizontal velocity fluctuations at the expense of the vertical velocity fluctuation.
A prominent feature of FST is vortex connections to the free surface which occur
inside the surface layer. It is found that as hairpin-shaped vortex structures approach
the free surface, their ‘head’ part is dissipated quickly in the surface layer,
while the two ‘legs’ connect almost perpendicularly to the free surface. Analysis
of the evolution of surface-normal vorticity based on vortex surface-inclination angle shows
that both dissipation and stretching decrease dramatically after connection. As a
result, vortex structures connected to the free surface are persistent and decay slowly
relative to non-connected vorticities. The effects of surface and blockage layers on the
turbulence statistics of length scales, Reynolds-stress balance, and enstrophy dynamics
are examined, which elucidate clearly the different turbulence mechanisms operating
in the respective near-surface scales. Finally we investigate the effect of non-zero
Froude number on the turbulence statistics. We show that the most significant effect
of the presence of the free surface is a considerable reduction of the pressure–strain
correlation at this surface, compared to that at a free-slip at plate. This reduction is
finite even for very low values of the Froude number.
Can the atmospheric kinetic energy spectrum
be explained by two-dimensional turbulence?
Authors: LINDBORG ERIK
Published: July 2002

The statistical features of turbulence can be studied either through spectral quantities,
such as the kinetic energy spectrum, or through structure functions, which are statistical
moments of the difference between velocities at two points separated by a variable
distance. In this paper structure function relations for two-dimensional turbulence
are derived and compared with calculations based on wind data from 5754 airplane
flights, reported in the MOZAIC data set. For the third-order structure function
two relations are derived, showing that this function is generally positive in the two-dimensional case, contrary to the three-dimensional case. In the energy inertial range
the third-order structure function grows linearly with separation distance and in the
enstrophy inertial range it grows cubically with separation distance. A Fourier analysis
shows that the linear growth is a reflection of a constant negative spectral energy flux,
and the cubic growth is a reflection of a constant positive spectral enstrophy flux.
Various relations between second-order structure functions and spectral quantities
are also derived. The measured second-order structure functions can be divided into
two different types of terms, one of the form r2/3, giving a
k−5/3-range and another, including a logarithmic dependence,
giving a k−3-range in the energy spectrum. The
structure functions agree better with the two-dimensional isotropic relation for larger
separations than for smaller separations. The flatness factor is found to grow very fast
for separations of the order of some kilometres. The third-order structure function
is accurately measured in the interval [30, 300] km and is found to be positive. The
average enstrophy flux is measured as
Πω≈1.8×10−13 s−3
and the constant in the k−3-law is measured as [Kscr ]≈0.19. It is
argued that the k−3-range can be explained by two-dimensional
turbulence and can be interpreted as an enstrophy inertial range, while the
k−5/3-range can probably not be explained by two-dimensional
turbulence and should not be interpreted as a two-dimensional energy inertial range.
On the collision rate of small particles in turbulent flows
Authors: MEI RENWEI , HU KEVIN C.
Published: July 2002

A theoretical framework is developed to predict the rate of geometric collision and
the collision velocity of small size inertialess particles in general turbulent flows. The
present approach evaluates the collision rate for small size, inertialess particles in
a given instantaneous flow field based on the local eigenvalues of the rate-of-strain
tensor. An ensemble average is then applied to the instantaneous collision rate to
obtain the average collision rate. The collision rates predicted by Smoluchowski
(1917) for laminar shear flow and by Saffman & Turner (1956) for isotropic turbulence
are recovered. The collision velocities presently predicted in both laminar
shear flow and isotropic turbulence agree well with the results from numerical simulations
for particle collision in both flows. The present theory for evaluating the
collision rate and the collision velocity is also applied to a rapidly sheared homogeneous
turbulence to assess the effect of strong anisotropy on the collision rate.
Using (ε/v)1/2, in which ε is the
average turbulence energy dissipation rate and v
is the fluid kinematic viscosity, as the characteristic turbulence shear rate to normalize
the collision rate, the effect of the turbulence structure on the collision rate
and collision velocity can be reliably described. The combined effects of the mean
flow shear and the turbulence shear on the collision rate and collision velocity are
elucidated.
Turbulence modification by particles in
a backward-facing step flow
Authors: FESSLER JOHN R. , EATON JOHN K.
Published: July 2002

The current study investigates turbulence modification by particles in a backward-facing step flow with a fully developed channel flow inlet. This flow provides a
range of flow regimes in which to compare turbulence modification under the same
experimental conditions. Gas-phase velocities in the presence of 3–40% mass loadings
of three different particle classes (90 and 150 μm diameter glass and 70 μm diameter
copper spheres) were measured. Attenuation of the streamwise fluid turbulence of up
to 35% was observed in the channel-flow extension region of the flow for a 40% mass
loading of the largest particles. The level of attenuation decreased with decreasing
particle Stokes number, particle Reynolds number and mass loading. No modification
of the turbulence was found in the separated shear layer or in the redevelopment region
behind the step, although there were significant particle loadings in these regions.
Fully nonlinear internal waves in a two-fluid system
Authors: CHOI WOOYOUNG , CAMASSA ROBERTO
Published: July 2002

Model equations that govern the evolution of internal gravity waves at the interface
of two immiscible inviscid fluids are derived. These models follow from the original
Euler equations under the sole assumption that the waves are long compared to the
undisturbed thickness of one of the fluid layers. No smallness assumption on the
wave amplitude is made. Both shallow and deep water configurations are considered,
depending on whether the waves are assumed to be long with respect to the total
undisturbed thickness of the fluids or long with respect to just one of the two
layers, respectively. The removal of the traditional weak nonlinearity assumption is
aimed at improving the agreement with the dynamics of Euler equations for large-amplitude waves. This is obtained without compromising much of the simplicity
of the previously known weakly nonlinear models. Compared to these, the fully
nonlinear models' most prominent feature is the presence of additional nonlinear
dispersive terms, which coexist with the typical linear dispersive terms of the weakly
nonlinear models. The fully nonlinear models contain the Korteweg–de Vries (KdV)
equation and the Intermediate Long Wave (ILW) equation, for shallow and deep
water configurations respectively, as special cases in the limit of weak nonlinearity
and unidirectional wave propagation. In particular, for a solitary wave of given
amplitude, the new models show that the characteristic wavelength is larger and
the wave speed is smaller than their counterparts for solitary wave solutions of the
weakly nonlinear equations. These features are compared and found in overall good
agreement with available experimental data for solitary waves of large amplitude in
two-fluid systems.
Effect of gravity modulation on
the stability of convection in a vertical slot
Authors: CHEN WEN-YAU , CHEN C. F.
Published: July 2002

The nature of instability occurring in a differentially heated infinite slot under steady
gravity depends only on the Prandtl number of the contained Boussinesq fluid. For
fluids with Pr < 12.5, the instability is shear dominated and onsets in a steady
convection mode; for fluids with Pr > 12.5, the instability is buoyancy dominated
and onsets in an oscillatory mode. In this paper, we examine the effect of gravity
modulation on the stability characteristics of convection in an infinite slot with both
kinds of fluids, in particular, Pr = 1 and Pr = 25.
Using the method of Sinha & Wu
(1991), we are able to obtain accurate results without excessive numerical integration
in the linear stability analysis by Floquet theory. Results show that, for Pr = 1, at
a non-dimensional oscillation frequency ω = 20, the critical state alternates between
the synchronous and subharmonic modes. At higher frequencies, ω > 100, all critical
states occur in the synchronous mode. For Pr = 25, with a modulation amplitude
ratio of 0.5, resonant interaction occurs in the neighbourhood of
ω = 2σc, where σc
is the oscillation frequency of the instability at the critical state under steady gravity.
This resonant interaction is destabilizing, with the critical Grashof number being
reduced by approximately 20% from that at steady gravity. It is due to the presence
of a detached subharmonic branch of the marginal stability curve. In frequency
ranges where the detached subharmonic branch is absent, the critical state is in the
quasi-periodic mode consisting of two waves of different oscillation frequencies whose
sum is the forcing frequency. An analysis of the rate of change of the perturbation
kinetic energy shows that, for Pr = 1, the instability is shear dominated regardless
of the mode of oscillation, synchronous or subharmonic. Similarly, for Pr = 25, the
instability is buoyancy dominated whether it is in the quasi-periodic or subharmonic
mode. The mode switching is a response to the forcing and is independent of the
dominant mechanisms of instability.
A fully nonlinear Boussinesq model for surface
waves. Part 2. Extension to O(kh)4
Authors: GOBBI MAURÍCIO F. , KIRBY JAMES T. , WEI GE
Published: July 2002

A Boussinesq-type model is derived which is accurate to O(kh)4 and which retains the
full representation of the fluid kinematics in nonlinear surface boundary condition
terms, by not assuming weak nonlinearity. The model is derived for a horizontal bottom,
and is based explicitly on a fourth-order polynomial representation of the vertical
dependence of the velocity potential. In order to achieve a (4,4) Padé representation of
the dispersion relationship, a new dependent variable is defined as a weighted average
of the velocity potential at two distinct water depths. The representation of internal
kinematics is greatly improved over existing O(kh)2 approximations, especially in the
intermediate to deep water range. The model equations are first examined for their
ability to represent weakly nonlinear wave evolution in intermediate depth. Using a
Stokes-like expansion in powers of wave amplitude over water depth, we examine
the bound second harmonics in a random sea as well as nonlinear dispersion and
stability effects in the nonlinear Schrödinger equation for a narrow-banded sea state.
We then examine numerical properties of solitary wave solutions in shallow water,
and compare model performance to the full solution of Tanaka (1986) as well as the
level 1, 2 and 3 solutions of Shields & Webster (1988).
Scaling in thermal convection: a unifying theory
Authors: GROSSMANN SIEGFRIED , LOHSE DETLEF
Published: July 2002

A systematic theory for the scaling of the Nusselt number Nu and of the Reynolds
number Re in strong Rayleigh–Bénard convection is suggested and shown to be
compatible with recent experiments. It assumes a coherent large-scale convection roll
(‘wind of turbulence’) and is based on the dynamical equations both in the bulk and
in the boundary layers. Several regimes are identified in the Rayleigh number Ra
versus Prandtl number Pr phase space, defined by whether the boundary layer or
the bulk dominates the global kinetic and thermal dissipation, respectively, and by
whether the thermal or the kinetic boundary layer is thicker. The crossover between
the regimes is calculated. In the regime which has most frequently been studied in
experiment (Ra [lsim ] 1011) the leading terms are
Nu ∼ Ra1/4Pr1/8,
Re ∼ Ra1/2Pr−3/4
for Pr [lsim ] 1 and
Nu ∼ Ra1/4Pr−1/12,
Re ∼ Ra1/2Pr−5/6 for
Pr [gsim ] 1. In most measurements these laws are modified by additive corrections from
the neighbouring regimes so that the impression of a slightly larger (effective) Nu
vs. Ra scaling exponent can arise. The most important of the neighbouring regimes
towards large Ra are a regime with scaling
Nu ∼ Ra1/2Pr1/2,
Re ∼ Ra1/2Pr−1/2 for
medium Pr (‘Kraichnan regime’), a regime with scaling
Nu ∼ Ra1/5Pr1/5,
Re ∼ Ra2/5Pr−3/5 for small
Pr, a regime with Nu ∼ Ra1/3,
Re ∼ Ra4/9Pr−2/3 for larger
Pr, and a regime with scaling
Nu ∼ Ra3/7Pr−1/7,
Re ∼ Ra4/7Pr−6/7 for even
larger Pr. In particular, a linear combination of the ¼ and the 1/3 power
laws for Nu with Ra,
Nu = 0.27Ra1/4 + 0.038Ra1/3 (the
prefactors follow from experiment), mimics a 2/7 power-law exponent in a regime as large
as ten decades. For very large Ra the laminar shear boundary layer is speculated to
break down through the non-normal-nonlinear transition to turbulence and another regime
emerges. The theory presented is best summarized in the phase diagram figure 2 and in table 2.
Some steady vortex flows past a circular cylinder
Authors: ELCRAT ALAN , FORNBERG BENGT , HORN MARK , MILLER KENNETH
Published: July 2002

Steady vortex flows past a circular cylinder are obtained numerically as solutions
of the partial differential equation Δψ = f(ψ), f(ψ)
= ω(1 − H(ω − α)), where H is the
Heaviside function. Only symmetric solutions are considered so the flow may be
thought of as that past a semicircular bump in a half-plane. The flow is transplanted
by the complex logarithm to a semi-infinite strip. This strip is truncated at a finite
height, a numerical boundary condition is used on the top, and the difference equations
resulting from the five-point discretization for the Laplacian on a uniform grid are
solved using Fourier methods and an iteration for the nonlinear equation. If the area
of the vortex region is prescribed the magnitude of the vorticity ω is adjusted in an
inner iteration to satisfy this area constraint.

Three types of solutions are discussed: vortices attached to the cylinder, vortex
patches standing off from the cylinder and strips of vorticity extending to infinity.
Three families of each type of solution have been found. Equilibrium positions for
point vortices, including the Föppl pair, are related to these families by continuation.
The mixing transition in turbulent flows
Authors: DIMOTAKIS PAUL E.
Published: July 2002

Data on turbulent mixing and other turbulent-flow phenomena suggest that a (mixing)
transition, originally documented to occur in shear layers, also occurs in jets, as well
as in other flows and may be regarded as a universal phenomenon of turbulence. The
resulting fully-developed turbulent flow requires an outer-scale Reynolds number of
Re = Uδ/v [gsim ] 1–2 × 104, or a
Taylor Reynolds number of ReT
= u′ λT/v [gsim ] 100–140,
to be sustained. A proposal based on the relative magnitude of dimensional spatial
scales is offered to explain this behaviour.
Why Rules Matter: Changes in Candidate Selection in Mexico's PRI, 1988–2000
Authors: LANGSTON JOY
Published: July 2002

The traditional literature on Mexico's formerly hegemonic party, the PRI, notes the importance of the ‘informal rules of the game' in determining outcomes, such as who will be the PRI's presidential candidate. This article argues that the onset of electoral competition allowed weaker actors within the party to strengthen their position by reforming the statutes in order to give them decision-making power previously denied them. However, this was a difficult process. President Salinas was able to overturn statutory reforms, while President Zedillo was not. Now that the PRI has lost the presidential elections, internal mechanisms of distributing selective benefits become even more important because of the loss of the omnipotent president who once exacted cooperation from all actors within the party and the regime.
The Alfonsín Administration and the
Promotion of Democratic Values in
the Southern Cone and the Andes
Authors: FOURNIER DOMINIQUE
Published: July 2002

This article seeks to demonstrate the need to incorporate the
international component of political strategy into analysis of the behaviour

of democratising elites, a standpoint that too often has been neglected
in
democratisation theory. It explores a little-known aspect of Argentina's
foreign
policy that took place under the stewardship of the transitional democratic

administration of President Raúl Alfonsín (1983-1989). Specifically,
it reveals
that the first-freely elected administration that followed the Procesco
military
dictatorship articulated and implemented a strategy that aimed at defending
and
promoting democratic values in relation to Argentina's Southern Cone
and
Andean neighbours. Argentine bilateral relations with Brazil, Uruguay,
Paraguay,
Bolivia, and Chile are analysed through this analytical standpoint. It
is argued
that the Alfonsín government pursued such a policy out of a blend
of fear for its
own perpetuation and principled beliefs about the value of democracy as
a mode
of governance.
Minimalist architectures
Authors: CULICOVER PETER W.
Published: July 2002

Ray Jackendoff, The architecture of the language faculty. Cambridge, MA:
MIT Press, 1997. Pp. xiv+262.

In The architecture of the language faculty Jackendoff responds to the
Minimalist Program (MP) of Chomsky (1995). There are three major
themes: the conceptual foundations of MP and its historical antecedents; the
interfaces between syntactic structure, phonetic structure and conceptual
structure, and the nature of the lexicon. The basic approach is that of
Jackendoff (1983, 1990), with roots going back at least as far as Jackendoff
1975. In the first chapter Jackendoff sets out the more or less standard views
about universal grammar and subjects them to a critical analysis. Chapters
2–4 focus on the various ‘interfaces’ between levels of representation,
and on how the interface relations are reified in individual lexical entries. Chapters
5–7 explore the properties of various types of lexical entries and the relations
between them. Chapter 8 concludes with a speculative essay on the relation
between language and thought.

This book is a rich compilation of observations, analyses, suggestions,
perspectives, speculations and proposals. One could easily write a review at
least as long as the book, developing and responding to the many ideas that
it contains. Since space here is limited, I will concentrate on the main
conceptual and foundational issues that are addressed by the book. In many
ways, Jackendoff's work points to significant departures from classical
perspectives on the organization of grammar. I will focus some attention on
those areas where even more radical steps might be worth pursuing.
The politics of autonomy and cooptation in Africa: the case of the Ugandan Women's Movement
Authors: Tripp Aili Mari
Published: July 2002

State responsiveness to pressures from women's movements in Africa has been
limited. However, where inroads have been made, associational autonomy
from the state and dominant party has proved critical. The women's movement
is one of the most coordinated and active social movements in Uganda,
and one of the most effective women's movements in Africa more generally.
An important part of its success comes from the fact that it is relatively
autonomous, unlike women's movements in earlier periods of Uganda's
post-independence history. The women's movement, in spite of enormous
pressures for cooptation, has taken advantage of the political space afforded
by the semi-authoritarian Museveni government, which has promoted
women's leadership to serve its own ends. Leaders and organisations reflect
varying degrees of autonomy and cooptation. Nevertheless the women's
movement has had a visible impact on policy as a result of its capacity to set
its own far-reaching agenda and freely select its own leaders.
Possibility of pulse compression of a short-pulse
laser in a plasma
Authors: SHIBU S. , PARASHAR JETENDRA , PANDEY H. D.
Published: July 2002

On account of nonlinear refraction, arising through the
relativistic mass effect,
a short intense laser pulse tends to accumulate its energy around
the intensity maximum, leading to pulse compression over a length
Zc≈
τ0c2ω2/
ω2pv, where
τ0 and ω are the pulse duration and frequency of
the laser, v is the oscillatory
electron velocity and ωp is the plasma
frequency. When the transverse extent
of the laser is finite, nonlinear self-focusing interferes strongly
with this process. The self-focusing occurs in a periodic manner on a
shorter scale length.
However, over long lengths of pulse propagation, pulse compression could be
significant.
Ionizing drift-wave instability in a low-temperature plasma
Authors: VLADIMIROV S. V. , I LIN
Published: July 2002

The dissipative drift-wave instability is considered in a non-uniform
weakly
ionized magnetoplasma when additional ionization is caused by electrons

moving in the field of the wave. It is demonstrated that the instability
can be
considerably enhanced due to the wave-induced perturbations of the
ionization/recombination balance and may therefore strongly affect
transport properties
of the plasma.
Solar damage to the solitary ascidian, Corella inflata
Authors: Bingham B.L. , Reitzel A.M.
Published: July 2002

The ascidian Corella inflata (Chordata, Ascidiacea) is common in many areas of Puget Sound, Washington, USA. However, it occurs only in habitats where it is protected from direct sunlight. Previous experiments with artificial lights showed that UV irradiation kills all life stages of this animal. The effects of natural sunlight exposure (measuring survival of adults, juveniles, larvae, and embryos) were compared. We partitioned the light spectrum to separate the effects of UVB, UVA, and visible light (PAR). Natural sunlight severely damaged C. inflata. Adults and juveniles died after 2-5 d. Exposed embryos failed to develop normally and larvae did not settle. As expected, UVB had significant effects, but pronounced effects were also seen when the animals were exposed to longer wavelengths alone (UVA and PAR). Thus, the distribution of C. inflata may be determined largely by exposure to light. Understanding the basic ecology of this species requires consideration of its vulnerability to sunlight damage and the effects of UVB, UVA, and PAR.
Contribution to the knowledge of growth and postmarsupial development of Natatolana borealis (Crustacea: Isopoda)
Authors: Johansen Per-Otto
Published: July 2002

Postmarsupial development and growth of Natatolana borealis were studied from Skogsvåg and Raknesvåg on the western coast of Norway. Growth was determined from size and instar stage distributions. Growth was also examined in laboratory kept isopods that were collected from Skogsvåg. The postmarsupial instar stages were identified using the number of articles and the position of setae on the flagellum of the first antenna and other morphological features. The mean size of isopods in instar stages 1—3 did not show any significant seasonal variation in Raknesvåg. The estimated growth and mortality rates of males and females were not significantly different. Nine and 11 postmarsupial instar stages were found in material from Skogsvåg and Raknesvåg, respectively. The life span from instar stage 1 to 9 of male and female N. borealis from western Norway was estimated to be 3—4 y. Mortality rate increased significantly from instar stage 9 to 10 of both sexes. Isopods that attained instar stage 10 and instar stage 11 in Raknesvåg, may have lived 4—5 y. The mean size of instar stages 8 and 9 and the size-to-weight relationships were significantly higher in material from Raknesvåg relative to that from Skogsvåg and may have been caused by differences in food access and predation pressure at the two study sites. Specimens sampled from the Bay of Monaco attained smaller adult size than the isopods from the Norwegian population.
Some physical factors affecting the accumulation of biofouling
Authors: Kerr A. , Beveridge C.M. , Cowling M.J. , Hodgkiess T. , Parr A.C.S. , Smith M.J.
Published: July 2002

The effects of surface roughness and microsolubility on fouling levels are examined using glass and acrylic samples. It is found that both of these, often overlooked, physical characteristics have a noticeable effect on the rate of fouling. The microsolubility of acrylic results in lower fouling than found on glass despite the higher hydrophobicity of acrylic and the resultant increase in initial attraction for fouling organisms. Fouling levels were found to increase with increasing surface roughness and therefore studies on the fouling susceptibility of different materials should report the roughness values of the samples examined.
Influence of sublethal long-term UV irradiation on body mass, reproduction and behaviour of north European Actinia equina
Authors: Westholt Rainer , Kestler Paul , Sicken Olaf , Westheide Wilfried
Published: July 2002

Two strains of 6–8-y old Actinia equina (Anthozoa: Actiniaria) asexually derived from two individuals collected on the coast of Brittany were artificially UV irradiated in long-term experiments in the laboratory. After the animals had been allowed to adjust to the test aquaria for 15 months, a programme of UV irradiation and multiparameter analysis continued for 24 months. Ultraviolet irradiated sea anemones obtained in addition a quasi-solar UV irradiation at intensities representing the daily and annual cycles. Of the three modes of UV irradiation tested (1X, 2X and 4X), the one with the lowest intensity and duration (1X) corresponded approximately to the irradiation to which sea anemones are exposed in their natural habitat in the tidal zone of the southern North Sea. In all three modes all the actinians showed a similar, highly significant quasi-exponential weight loss immediately after the onset of UV irradiation. The more the animals were irradiated, the later juveniles were released from the gastrovascular cavity. At 2X the number of active animals gradually decreased after 18 months, whereas with the 4X irradiation mode the amount of activity fell abruptly and significantly after only eight months and remained at a very low level. Detachment from the substrate was also induced by UV irradiation. The experiments showed genotype-specific differences in body mass and migration. The crucial findings were that A. equina individuals that had adjusted to the laboratory for a long time did give clear responses to UV doses and intensities corresponding approximately to the irradiation in their natural intertidal environment or by radiation increased severalfold. The responses were immediate and sometimes irreversible to UV even in naturally occurring intensities and doses. The genotype specificity of some responses provides evidence that the stressor UV could induce genetic modifications of the population.
Three newly recognized cheilostomate bryozoans from the British sea area
Authors: Hayward P.J. , Hansen K.B.
Published: July 2002

Three species of cheilostomate Bryozoa are described, and illustrated by scanning electron micrographs. One was previously poorly characterized and is here stabilized by the selection of a neotype; a second is recognized as distinct from an Arctic congener while the third is entirely new to science and represents the first record of the genus Codonellina from the north-east Atlantic.
DIE KULTISCHE BZW. AGRARTECHNISCH-BIOLOGISCHE LOGIK DER GLEICHNISSE VON DER TEIGHEBE UND VOM ÖLBAUM IN RÖM 11.16–24 UND DIE SICH DARAUS ERGEBENDEN THEOLOGISCHEN KONSEQUENZEN
Authors: HARTUNG MATTHIAS
Published: July 2002

Das Verhältnis Kirche/Israel beschreibt Paulus in Röm 11.16–24 mittels zweier Gleichnisse. Das Gleichnis von der Teighebe legt Paulus entgegen dem traditionell jüdischen Verständnis aus, um den kultischen Begriff ‘Heiligkeit’ in seine Darstellung einzuführen: So wie im Kult ein Teil das Ganze heiligen könnte, so heiligt im Gleichnis vom Ölbaum die Wurzel (Abraham) die Zweige (Juden).
PCR-based diagnosis for Chagas' disease in Bolivian
children living in an active transmission area: comparison
with conventional serological and parasitological diagnosis
Authors: WINCKER P. , TELLERIA J. , BOSSENO M. F. , CARDOSO M. A. , MARQUES P. , YAKSIC N. , AZNAR C. , LIEGEARD P. , HONTEBEYRIE M. , NOIREAU F. , MOREL C. M. , BRENIERE S. F.
Published: July 2002

A large field study has been performed in the Cochabamba region
of
Bolivia with the aim of comparing the polymerase chain
reaction (PCR) with other diagnostic methods for Chagas' disease.
The
amplification of Trypanosoma cruzi-specific
kinetoplast DNA sequences in blood samples was compared with classical
serological methods, specific IgM detection and
direct parasite visualization for 268 school children in a single village
where
Chagas' disease transmission is active. Of 113
children positive by classical serology or buffy coat examination, 106
were
detected by PCR (sensitivity: 93·8%). We did
not observe any significant difference of PCR sensitivity between initial
(IgM
and/or buffy coat positive) and indeterminate
stage (only IgG positive) patients. Among the remaining 155 children unconfirmed
as chagasic (who were either only IgM
positive, IgG-, IgM-, and buffy coat-negative) only 1 case was PCR positive.
This
case may be due to DNA contamination,
or to a very recent infection not detected otherwise, or to specific immune
depression. These results show that PCR is a
very sensitive parasitological test for Chagas' disease in active
transmission regions. The future follow-up of the possibly
infected patients who were only IgM-positive should clarify the interest
of
PCR and IgM tests in the detection of starting infections.
Effect of praziquantel and liposome-incorporated
praziquantel on peritoneal macrophage activation in mice
infected with Mesocestoides corti tetrathyridia (Cestoda)
Authors: HRČKOVA G. , VELEBNY S.
Published: July 2002

The activation of peritoneal macrophage effector functions after
therapy
with free PZQ and PZQ incorporated in
liposomes (lip.PZQ) was studied in the Mesocestoides corti–mouse
model system. Each drug formulation was administered
to an infected group of mice in 6 daily doses from day 14 p.i. Phagocytic
activity
of macrophages increased significantly
after the administration of both drug formulations, more after lip.PZQ
with
an earlier peak observed for PZQ (day 3) than
for lip.PZQ (day 6). Empty liposomes had no significant effect. The average
counts of ingested particles in phagocytosing
cells were significantly higher only after lip.PZQ administration. The
pattern
of changes in phagocytic activity correlated
with the reduction of parasite numbers in the peritoneal cavity, with the
highest observed on day 6 after therapy with
lip.PZQ. Phagocytosis of lip.PZQ in vivo stimulated significantly
the
respiratory burst in peritoneal macrophages, with
the highest concentration of superoxide anions recorded on day 1 after
the last
dose, whereas therapy with PZQ itself did
not increase this process significantly. The capacity for the respiratory
burst declined in all groups with progressing
infection. It is proposed that the phagocytic activity of peritoneal
macrophages after therapy was stimulated indirectly as
a consequence of activation of the specific immune response. The larvicidal
effect of lip.PZQ on the tetrathyridia in the
peritoneal cavity was synergistic with the phagocytic activity and might
be
the result of double action of drug and
superoxide anions generated during the respiratory burst stimulated by
this
drug formulation.