bluuebunny/crossref_metadata_2025_split huggingface dataset:
Settling of small particles near vortices and in turbulence
Authors: DÁVILA J. , HUNT J. C. R. 
Published: July 2002

The trajectories of small heavy particles in a gravitational field, having fall speed in still
fluid V˜T and moving with velocity V˜ near fixed
line vortices with radius R˜v and circulation Γ˜,
are determined by a balance between the settling process and the centrifugal
effects of the particles' inertia. We show that the main characteristics are determined
by two parameters: the dimensionless ratio VT
= V˜TR˜v/Γ˜
and a new parameter (Fp) given by the ratio between the relaxation time of the particle
(t˜p) and the time
(Γ˜/V˜2T)
for the particle to move around a vortex when VT is of order unity or small.The average time ΔT˜ for particles to settle between two levels a distance
Y˜0 above and below the vortex (where
Y˜0 [Gt ] Γ˜/VT) and the average
vertical velocity of particles 〈Vy〉L along their
trajectories depends on the dimensionless parameters VT and
Fp. The bulk settling velocity
〈Vy〉B
= 2Y˜0/〈ΔT˜〉, where the average value of
〈ΔT˜〉 is taken over all initial particle positions of the upper level, is only equal to
〈V˜y〉L for small values of the effective volume
fraction within which the trajectories of the particles are distorted,
α = (Γ˜/V˜T)2/
Y˜20. It is shown here how
〈Vy〉B is related to
Δ&η;(X˜0), the difference between the vertical settling distances with and
without the vortex for particles starting on
(X˜0, Y˜0) and falling for a fixed period
Δt˜T [Gt ]
&Γtilde;/V˜2T;
〈V˜y〉B
= V˜T[1 − αD], where D
= ∫∞−∞(Δ&η;dX˜0/
(&Γtilde;/V˜T)2)
is the drift integral. The maximum value of 〈V˜〉B for any
constant value of VT occurs when
Fp = FpM ∼ 1
and the minimum when Fp = Fpm
> FpM, where typically
3 < Fpm < 5.Individual trajectories and the bulk quantities D and
〈Vy〉B have been calculated
analytically in two limits, first Fp → 0, finite VT,
and secondly VT [Gt ] 1. They have also been computed for the range
0 < Fp < 102, 0 < VT < 5
in the case of a Rankine vortex. The results of this study are consistent with experimental observations of the
pattern of particle motion and on how the fall speed of inertial particles in turbulent
flows (where the vorticity is concentrated in small regions) is typically up to 80%
greater than in still fluid for inertial particles (Fp ∼ 1) whose terminal velocity is
less than the root mean square of the fluid velocity, ũ′, and typically up to 20% less
for particles with a terminal velocity larger than ũ′.
If V˜T/ũ′ > 4 the differences are negligible.
A global investigation of solitary-wave solutions

to a two-parameter model for water waves
Authors: CHAMPNEYS ALAN R. , GROVES MARK D. 
Published: July 2002

The model equationformula herearises as the equation for solitary-wave solutions to a fifth-order

long-wave equation

for gravity–capillary water waves. Being Hamiltonian, reversible
and depending

upon two parameters, it shares the structure of the full steady water-wave
problem.

Moreover, all known analytical results for local bifurcations of

solitary-wave solutions

to the full water-wave problem have precise counterparts for the model
equation.At the time of writing two major open problems for steady water waves
are

attracting particular attention. The first concerns the possible

existence of solitary

waves of elevation as local bifurcation phenomena in a particular parameter
regime;

the second, larger, issue is the determination of the global bifurcation
picture for

solitary waves. Given that the above equation is a good model for solitary
waves

of depression, it seems natural to study the above issues

for this equation; they are comprehensively treated in this article.The equation is found to have branches of solitary waves of elevation
bifurcating

from the trivial solution in the appropriate parameter regime,

one of which is described

by an explicit solution. Numerical and analytical investigations

reveal a rich global

bifurcation picture including multi-modal solitary waves of elevation

and depression together with interactions between the two types of wave.
There

are also new orbit-flip

bifurcations and associated multi-crested solitary waves with non-oscillatory
tails.
The vorticity jump across a shock in a non-uniform flow
Authors: KEVLAHAN N. K.-R. 
Published: July 2002

The vorticity jump across an unsteady curved shock propagating
into a

two-dimensional non-uniform flow is considered in detail. The exact

general expression for the

vorticity jump across a shock is derived from the gasdynamics equations.
This general

expression is then simplified by writing it entirely in terms of the Mach
number of

the shock MS and the local Mach number of
the

flow ahead of the shock MU.The vorticity jump is very large at places where the curvature of the
shock is

very large, even in the case of weak shocks. Vortex sheets form behind
shock-shocks

(associated with kinks in the shock front).The ratio of vorticity production by shock curvature to vorticity production
by

baroclinic effects is

O(½(γ−1)M2U),

where γ is ratio of specific heats, which is very small if the flow
ahead of

the shock is only weakly compressible. If, however, the

tangential gradient along the shock of M2U

is large then baroclinic production is

significant; this is the case in turbulent flows with large gradients of

turbulent kinetic energy ½M2U.

The vorticity jump across a weak shock decreases in proportion to shock

intensity if the flow ahead of the shock is rotational, rather than in
proportion to

the cube of shock intensity as is often assumed, and thus is not negligible.

It is also

shown that vorticity may be generated across a straight shock even if the
flow ahead

of the shock is irrotational. The importance of the

contribution to the vorticity jump

by non-uniformities in the flow ahead of the shock has not been recognized
in the

past.Examples are given of the vorticity jump across strong and weak

shocks in a variety of flows exhibiting some properties of turbulence.
Subgrid-scale stresses and their modelling in a

turbulent plane wake
Authors: O'NEIL JOHN , MENEVEAU CHARLES 
Published: July 2002

Velocity measurements using hot wires are performed across a

high-Reynolds-number

turbulent plane wake, with the aim of studying the subgrid-scale (SGS)
stress and

its modelling. This quantity is needed to close the filtered

Navier–Stokes equations

used for large-eddy simulation (LES) of turbulent flows. Comparisons of
various

globally time-averaged quantities involving the measured and modelled SGS
stress

are made, with special emphasis on the SGS energy dissipation rate. Experimental

constraints require the analysis of a one-dimensional surrogate

of the SGS dissipation.

Broadly, the globally averaged results show that all models considered,
namely the

Smagorinsky and similarity models, as well as the dynamic Smagorinsky model,

approximately reproduce profiles of the surrogate SGS

dissipation. Some discrepancies

near the outer edge of the wake are observed, where the Smagorinsky model
slightly

overpredicts, and the similarity model underpredicts, energy dissipation
unless the

filtering scale is about two orders of magnitude smaller than the integral

length scale.A more detailed comparison between real and modelled SGS stresses is
achieved

by conditional averaging based on particular physical phenomena: (i) the
outer

intermittency of the wake, and (ii) large-scale coherent structures of
the turbulent

wake. Thus, the interaction of the subgrid scales with the resolved flow
and model

viability can be individually tested in regions where isolated mechanisms

such as outer

intermittency, vortex stretching, rotation, etc., are dominant. Conditioning
on outer

intermittency did not help to clarify observed features of the measurements.
On the

other hand, the large-scale organized structures are found to have a strong
impact

upon the distribution of surrogate SGS energy dissipation, even at filter
scales well

inside the inertial range. The similarity model is able to capture this

result, while the

Smagorinsky model gives a more uniform (i.e. unrealistic) distribution.
Both dynamic

Smagorinsky and similarity models reproduce realistic distributions, but
only if all

filter levels are contained well inside the inertial range.
Observations of shock waves in cloud cavitation
Authors: REISMAN G. E. , WANG Y.-C. , BRENNEN C. E. 
Published: July 2002

This paper describes an investigation of the dynamics
and acoustics of cloud cavitation, the structures which are
often formed by the periodic breakup and collapse of a
sheet or vortex cavity. This form of cavitation frequently
causes severe noise and damage, though the precise mechanism
responsible for the enhancement of these adverse
effects is not fully understood. In this paper, we investigate
the large impulsive surface
pressures generated by this type of cavitation and correlate
these with the images
from high-speed motion pictures. This reveals that several
types of propagating structures (shock waves) are formed in
a collapsing cloud and dictate the dynamics and
acoustics of collapse. One type of shock wave structure is
associated with the coherent
collapse of a well-defined and separate cloud when it is
convected into a region of
higher pressure. This type of global structure causes the
largest impulsive pressures
and radiated noise. But two other types of structure,
termed ‘crescent-shaped regions’
and ‘leading-edge structures’ occur during
the less-coherent collapse of clouds. These
local events are smaller and therefore produce less
radiated noise but the interior
pressure pulse magnitudes are almost as large as those
produced by the global events.The ubiquity and severity of these propagating shock
wave structures provides a
new perspective on the mechanisms reponsible for noise
and damage in cavitating
flows involving clouds of bubbles. It would appear that
shock wave dynamics rather
than the collapse dynamics of single bubbles determine the
damage and noise in many cavitating flows.
Particle motion in resonance tubes
Authors: GOLDSHTEIN A. , SHUSTER K. , VAINSHTEIN P. , FICHMAN M. , GUTFINGER C. 
Published: July 2002

Small particle motions in standing or travelling acoustic waves
are well known and
extensively studied. Particle motion in weak shock waves has been studied
much less,
especially particle motion in periodic weak shock waves which as yet has
not been dealt
with.The present study considers small particle motions caused by weak periodic
shock
waves in resonance tubes filled with air. A simple mathematical model is
developed for
resonance gas oscillations under the influence of a vibrating piston with
a finite
amplitude at the first acoustic resonance frequency. It is shown that a
symmetrical
sinusoidal piston motion generates non-symmetric periodic shock waves.
A model of
particle motion in such a flow field is suggested. It is found that non-symmetric
shock
waves cause particle drift from the middle cross-section toward the ends
of the
resonance tube. The velocity of particle drift is found to be of the order
of
Dpρp/
Trρg,
where Dp is the particle diameter,
Tr the period of
the resonance oscillation, ρp and
ρg are the particle and gas density, respectively.

At the same time, the velocity drift
strongly depends on the ratio τ/Tr,
where
τ is the particle relaxation time. Particle drift
is vigorous when τ/Tr∼1 and
insignificant when τ/Tr 1. Theoretical
predictions of
particle drift in resonance tubes are verified numerically as well as experimentally.When the particle relaxation time is much smaller than period of the
resonance
oscillations particles perform oscillations around their equilibrium positions
with
amplitude of the order of
Dpρp/ρg.

It is shown that the difference in oscillation
amplitude of particle of difference sizes explains coalescence of aerosol
droplets
observed in experiments of Temkin (1970).The importance of the phenomena for particle separation, coagulation
and transport
processes is discussed.
Laminar–turbulent transition in pipe flow for
Newtonian and non-Newtonian fluids
Authors: DRAAD A. A. , KUIKEN G. D. C. , NIEUWSTADT F. T. M. 
Published: July 2002

A cylindrical pipe facility with a length of 32 m and a diameter
of 40 mm has been designed. The natural transition Reynolds number, i.e. the Reynolds number at which transition occurs as a result of non-forced, natural disturbances, is approximately

60 000. In this facility we have studied the stability of cylindrical pipe
flow to imposed disturbances. The disturbance consists of periodic suction and injection of fluid from a slit over the whole circumference in the pipe wall. The injection and suction are equal in magnitude and each distributed over half the circumference so
that the disturbance is divergence free. The amplitude and frequency can be varied
over a wide range.First, we consider a Newtonian fluid, water in our case. From the observations we compute the critical disturbance velocity, which is the smallest disturbance
at a given Reynolds number for which transition occurs. For large wavenumbers, i.e.
large frequencies, the dimensionless critical disturbance velocity scales according to
Re−1, while for small wavenumbers, i.e. small frequencies, it scales as Re−2/3. The latter is in agreement with weak nonlinear stability theory. For Reynolds numbers
above 30 000 multiple transition points are found which means that increasing the
disturbance velocity at constant dimensionless wavenumber leads to the following
course of events. First, the flow changes from laminar to turbulent at the critical
disturbance velocity; subsequently at a higher value of the disturbance it returns back
to laminar and at still larger disturbance velocities the flow again becomes turbulent.Secondly, we have carried out stability measurements for (non-Newtonian)
dilute polymer solutions. The results show that the polymers reduce in general the natural transition Reynolds number. The cause of this reduction remains unclear, but a possible explanation may be related to a destabilizing effect of the elasticity on the
developing boundary layers in the entry region of the flow. At the same time the
polymers have a stabilizing effect with respect to the forced disturbances, namely
the critical disturbance velocity for the polymer solutions is larger than for water. The stabilization is stronger for fresh polymer solutions and it is also larger when the polymers adopt a more extended conformation. A delay in transition has been only found for extended fresh polymers where delay means an increase of the critical Reynolds number, i.e. the number below which the flow remains laminar at any imposed disturbance.
Beyond the gold standard?: the
idea of a (post-apartheid) university
Authors: Nolutshungu Sam C. 
Published: July 2002

We cannot do better than Marcello Cecco's (1984: 1) concise definition
of an international gold standard: it exists ‘when gold is the effective
numeraire in most countries, and/or when the other means of payment
used as monetary numeraire in those countries are readily redeemable
in gold at their bearers' request’. Such a standard existed from the mid-1890s to 1914, even though Britain went on the gold standard much
earlier than that, in 1816, and Germany a little over a half century
later, in 1871. The Latin Union in Europe (France, Belgium,
Switzerland and Italy) did not join effectively until 1900 (Mertens
1994). Many claims were, and are still made for the system: that it
facilitated international trade by providing a uniform standard of
value; and as an automatic adjustment system, it freed markets from
the (nationalistic) interference of public authorities while it created
price equalisation in traded goods and ensured, over a protracted
period, price stability.The ‘Gold Standard’ in the title of this talk refers to the ‘academic
gold standard’ invoked by Lord Ashby (1964; see also Austin 1980),
one time Master of Clare College, Cambridge, a British educationist
who was deeply involved with the development of universities in the
later years of colonial rule in British West Africa. Although the
University of the Witwatersrand and the city of Johannesburg owe a
great deal to the gold industry, my talk is not about money or the
metal's place in it. It is about the metaphorical ‘academic gold
standard’.
The Technology of Sanitation in Colonial Delhi
Authors: PRASHAD VIJAY 
Published: July 2002

I. Sewage Under CapitalismThe preservation of the wealth and welfare of nations, and advances in
culture and civilisation depend on how the
sewage question is resolved.(von Liebig, 1850s).Delhi is a very suggestive and moralising place—such stupendous
remains of power and wealth passed and passing away—and somehow I feel
that we horrid English have just ‘gone and done it’,
merchandised it, revenue it, and spoiled it all. (Emily Eden, 1838).Veena Oldenburg argues that after the Rebellion of 1857 British colonial
officials inaugurated a process of urban reconstruction following three
imperatives: safety, sanitation and loyalty. To make the cities of India
safe, clean and loyal, the colonial regime exerted a measure of
‘social control . . . In an era when tinkering with the structure of
society had been officially and unambiguously forsworn.’. If the highest offices
of the colonial regime proclaimed its remove from society, she argues, the
‘lowest levels of decision making and action’, intruded effectively to
reconstruct the social fabric of urban life. In this essay, we will examine this lowest level
of the colonial regime in the local government of Delhi (the Delhi Municipal
Corporation [DMC], the commissioner's office, the army, the Public Works
Department [PWD], the railway officials) and its relations with the local nobility
(the rais and amirs), the merchants, and working people.
Is ‘What is Time?’ a Good Question to Ask?
Authors: Read Rupert 
Published: July 2002

Dummett in his recent paper in Philosophy replies in the negative to the question, “Is time a continuum of instants?” But Dummett seems to think that this negative reply entails giving an alternative theoretical account; he nowhere canvasses the possibility that there is something amiss with the question. In other words, Dummett thinks that he still has to reply to the question, “What (then) is time?”
I offer no answer whatsover to such ‘questions’. Rather, I ask what it could possibly mean to say that time is (e.g.) a continuum of instants (and by extension, whether it can mean anything at all to assert that it isn't).
In the course of doing so, I suggest that Dummett's ‘Anti-Realism’ is invariably a form of Realism, just a subtly inconsistent form. Anti-Realism keeps the fundamental metaphysical picture of Realism intact. Anti-Realism still thinks that there is a Reality...settling whether Realism or Anti-Realism is correct!
‘Anti-Realism’ is never anti-Realist enough.
The course of depression in the elderly: a
longitudinal community-based study in Australia
Authors: HENDERSON A. S. , KORTEN A. E. , JACOMB P. A. , MACKINNON A. J. , JORM A. F. , CHRISTENSEN H. , RODGERS B. 
Published: July 2002

Background. We report the outcome of
depressive states after 3-4 years in a community sample
of the elderly.Methods. A sample of 1045 persons aged 70+ years in 1990–1
was re-interviewed after 3·6
years.Results. Mortality (21·7%) and refusal or non-availability (10·4%) were higher in those who
initially had had a diagnosis or symptoms of depression. Of those with an ICD-10 depressive
episode in 1990–1, 13% retained that diagnosis. Of those who were not depressed initially only
2·5% had become cases. Depression was unrelated to age or apolipoprotein E genotype. The best
predictors of the number of depressive symptoms at follow-up was the number at Wave 1,
followed by deterioration in health and in activities of daily living, high neuroticism, poor
current health, poor social support, low current activity levels and high service use. Depressive
symptoms at Wave 1 did not predict subsequent cognitive decline or dementia.Conclusions. Non-random sample attrition is unavoidable. ICD-10 criteria yield more cases than
other systems, while continuous measures of symptoms confer analytical advantages. Risk
factors for depressive states in the elderly have been further identified. The prognosis for these
states is favourable. At the community level, depressive symptoms do not seem to predict cognitive decline,
as they do in referred series.
Clinical factors associated with short-term changes in
outcome of patients with somatized mental disorder in primary care
Authors: DOWNES-GRAINGER E. , MORRISS R. , GASK L. , FARAGHER B. 
Published: July 2002

Background. There is little research that examines demographic,

clinical and treatment factors
associated with changes in physical symptoms, psychiatric symptoms and
functional outcome in
patients with somatized depression or anxiety in primary care.Method. Factors associated with the outcome of psychologized
or
somatized depression or anxiety
were derived from the literature. These factors were tested individually
for
their effects on changes
in physical symptoms, psychiatric symptoms and functional outcome between
baseline consultation
with the general practitioner and 1 or 3 months later in 215 patients
with somatized depression or
anxiety. Individual factors associated with a particular outcome, demographic,

DSM-IV diagnosis and treatment variables were entered into a multiple regression
analysis.Results. Factors associated with a better outcome on all
three types of outcome measure were the
absence of generalized anxiety disorder and/or simple or social
phobias, absence of physical
pathology, and the prescription of fewer drugs, especially hypnotics or
benzodiazepines. In
addition, a better psychiatric symptom outcome was associated with the
patients' perceived
satisfaction with the general practitioner's understanding or
explanation of the patient's problems.
A better functional outcome was associated with having a job, less
distress over physical symptoms,
not receiving invalidity benefit and no referral to hospital.Conclusion. There are clinical and demographic factors associated

with all types of short-term
outcome in patients with somatized depression or anxiety but there
are additional factors that are
associated only with either psychiatric or functional outcome.