bluuebunny/crossref_metadata_2025 huggingface dataset:
DETERMINANTS OF INFANT AND CHILD MORTALITY IN THE WEST BANK AND GAZA STRIP
Authors: PEDERSEN JON
Published: July 2002

Infant and child mortality in the West Bank and Gaza Strip has steadily reduced since 1967, even though fertility has remained extremely high. In this paper the determinants of infant and child mortality are discussed, with particular emphasis on the role of consanguineous marriages, short birth spacing and maternal education. It is shown that short birth spacings and type of marriage are more important determinants of infant mortality than maternal education. Moreover, the relative role of consanguineous marriages appears to increase with time.
CONSISTENCY IN CONDOM USE IN THE CONTEXT OF HIV/AIDS IN ZIMBABWE
Authors: ADETUNJI JACOB , MEEKERS DOMINIQUE
Published: July 2002

Against the backdrop of a high prevalence of the human immunodeficiency virus infection in Zimbabwe, this paper analyses data from the 1997 Zimbabwe Sexual Behaviour and Condom Use Survey to throw light on the degree to which sexually active adults consistently use condoms in high-risk sexual situations. The multivariate results indicate that at the time of the survey, consistent condom use in non-marital relationships is significantly higher for males than females, higher among those who had access to information about condoms from multiple sources than among those with limited access, and higher among those who have positive attitudes to condoms than among those with negative attitudes. Even though consistent condom use with non-marital partners is higher for those who know a source where condoms can be obtained, this effect is due to the fact that these respondents have more positive attitudes towards condoms. Likewise, the higher levels of consistent condom use exhibited by those who are aware of the efficacy of condoms are due to the fact that men have higher awareness of this, and men use condoms more consistently than women. In sum, the results suggest that the effects of the respondents’ sex and their knowledge of the prophylactic importance of condoms and where condoms might be obtained are a function of other socioeconomic advantages they have. It is, therefore, concluded that programmes that use mass media information, education and communication campaigns to reduce shyness, embarrassment and stigma about condom use can help increase consistent use of condoms in non-marital relationships in Zimbabwe.
CHILD IMMUNISATION IN GHANA: THE EFFECTS OF FAMILY, LOCATION AND SOCIAL DISPARITY
Authors: MATTHEWS ZOE , DIAMOND IAN
Published: July 2002

The data from the Demographic and Health Survey conducted in Ghana in 1988 are used to identify determinants of immunisation uptake for children under 5 years. The logistic binomial analysis shows that socioeconomic factors are significant, especially women's education and region, and that the type of prenatal care received by the mother is also important. There is a strong familial correlation of vaccination behaviours, and there is also clustering of data within enumeration areas.
EFFECTS OF THE STATUS OF WOMEN ON THE FIRST-BIRTH INTERVAL IN INDIAN URBAN SOCIETY
Authors: NATH DILIP C. , LAND KENNETH C. , GOSWAMI GITI
Published: July 2002

The status of women, which is relative and multidimensional, has an important bearing on any long-term reduction in fertility. In Indian society, where cohabitation and childbearing are socially sanctioned only after marriage, the length of the first-birth interval affects the completed family size by influencing the spacing and childbearing pattern of a family. This study examines the influence of certain aspects of the status of married women – education, employment, role in family decision making, and age at marriage – along with three socioeconomic variables – per capita income of the family, social position of the household, and the caste system – on the duration of the first-birth interval in an urban Hindu society of the north-east Indian state of Assam. The data were analysed by applying life table and hazard regression techniques. The results indicate that a female's age at marriage, education, current age, role in decision making, and the per capita income of the household are the main covariates that strongly influence the length of the first-birth interval of Hindu females of urban Assam. Of all the covariates studied, a female's education appears to be a key mediating factor, through its influence on her probability of employment outside the home and thereby an earned income and on her role in family decision making. Unlike other Indian communities, the effect of the caste system does not have a significant effect on first-birth timing in this urban Hindu society.
Effects of supplementation of dairy cattle with fish oil on silage
intake, milk yield and milk composition
Authors: KEADY TIMOTHY W. J. , SINCLAIR MAYNE C. , FITZPATRICK DEIRDRE A.
Published: July 2002

The effects of level of fish oil inclusion in the diet on grass silage intake,
and milk yield and composition of dairy cows offered either 5 or 10 kg concentrates/d
were evaluated in a ten treatment, partly balanced, changeover design experiment
involving 50 cows in early lactation. Concentrates were prepared to provide 0, 150,
300 or 450 g fish oil/cow per d or 300 g fish oil/cow per d from a premix when each
animal was offered 5 kg/d. The fish oil was predominantly from herring and mackerel
caught in the North Atlantic while the fish oil premix was obtained from a
commercial source and used palm kernel expeller as a carrier. Increasing fish oil
supplementation decreased silage dry matter intake and the concentrations of milk
fat and protein, and increased milk yield and diet digestibility. There were significant
interactions between concentrate feed level and level of fish oil for silage intake and
milk yield. Other than for the concentrations of milk fat and protein, and 20[ratio ]4n−6
fatty acids, the source of fish oil did not affect forage intake or animal performance.
Fish oil supplementation also decreased the concentrations of milk protein by
0·9 g/kg for each 100 g increase in fish oil supplementation, the depression being
similar at each level of concentrate feeding. Supplementing the feed of dairy cows
with 450 g fish oil/cow per d decreased the concentration of milk fat by 15 g/kg. This
study also showed that feeding dairy cattle with fish oil is an efficient method of
increasing eicosapentaenoic acid in the human diet through transfer into milk.
Performances of falling film evaporators on whole milk and a
comparison with performance on skim milk
Authors: JEBSON R. SELWYN , CHEN HONG
Published: July 2002

The performances of falling film evaporators used in the New Zealand

dairy industry for concentrating whole milk were evaluated by determining
kg steam
used/kg water evaporated, and the heat transfer coefficient of each
pass in the
evaporators. A specially written computer program was used to calculate
the results.
The heat transfer coefficients varied from 0·3 to
3·0 kW/m2K, and the steam
consumption from 0·10 to 0·39 kg steam/kg evaporation,

depending on the number
of effects. The steam consumptions for whole and skim milk were similar.
The
momentum of the vapours passing down the tubes, the temperature difference
across
the tubes, the viscosity of the feed and the liquid loading were
found to be the main
factors controlling the heat transfer coefficient. A correlation between
the heat
transfer coefficient and these factors is presented, and other factors

likely to have an
influence on the performance are discussed. The correlation is compared
with that
obtained for skim milk.
Management practices associated with high mortality among
preweaned dairy heifers
Authors: LOSINGER WILLARD C. , HEINRICHS A. JUD
Published: July 2002

In a national survey of US dairy operations, 1685 dairy operations

reported 47057 new dairy heifers (either births or acquisitions) and 4427
deaths
(9·4%) of preweaned dairy heifer calves over a 3 month
period. Stepwise logistic
regression was used to identify management practices associated with high
mortality
among preweaned heifers in dairy operations where at least three dairy
heifer calves
were born alive or moved on to the operation. Analysis was done twice:
once by
separating all operations by size into high or low mortality; again using
only
operations with <2 and >10% mortality to eliminate dairy operations
with
intermediate levels of mortality from the comparisons. Results were similar.
Dairy
operations in the West were more likely to fall in the high mortality category
than
dairy operations in the rest of the country. In addition, the
following dairy operation
characteristics were associated with high death levels in both models:
rolling herd
average milk production <7710 kg, preweaned heifers placed in groups
of seven or
more, a male having primary responsibility for the care and feeding of
preweaned
heifers, calves not receiving hay or other roughages until >20 d
old, calves fed on
mastitic or antibiotic milk after colostrum and calves not given whole
milk after
colostrum.
Binding of Staphylococcus aureus to milk fat globules increases

resistance to penicillin-G
Authors: ALI-VEHMAS TERHI , WESTPHALEN PETER , MYLLYS VESA , SANDHOLM MARKUS
Published: July 2002

The susceptibility to penicillin-G of Staphylococcus
aureus strains that
cause mastitis was tested in milk and in Iso-sensitest broth (ISB). The
minimal
inhibitory concentrations (MIC) of β-lactamase-positive
strains in milk were 10–100-fold those in ISB, whereas the
MIC of β-lactamase-negative strains in milk were some
10-fold those in ISB; β-lactamase production was induced by
milk in β-lactamase-positive strains. Much of the increase in
resistance to penicillin-G caused by milk can
be attributed to milk fat globules; the increase in resistance was related
to the
binding capacity of the bacteria to milk fat globules as well as to capsule
formation
by the bacteria. It appears that the binding of the staphylococci to the
fat globules
and bacterial capsule formation resulted in a biofilm type of
growth. In this case, the
staphylococci behaved differently from the planktonic type of growth in
artificial
broth medium in which antibiotic susceptibility testing is usually carried
out.
Study of the polymorphism of caprine milk caseins by
capillary electrophoresis
Authors: RECIO ISIDRA , PÉREZ-RODRÍGUEZ MARIA LUISA , AMIGO LOURDES , RAMOS MERCEDES
Published: July 2002

Polymorphism of caprine milk proteins was studied by capillary

electrophoresis. Identification of casein (CN) fractions was effected by

using isolated
fractions from cation-exchange fast protein liquid chromatography. Genetic

polymorphisms in caprine αs2-CN, αs1-CN,

β-CN and κ-CN have been determined. κ-CN A and B,
β-CN A and null, αs2-CN A, B and C,
αs1-CN A, B, C and null, and other
forms with intermediate and low αs1-CN content have been

identified. The capillary
electrophoresis method made it possible to analyse whole caprine milk using
simple
sample preparation and was rapid, automated and suitable for phenotyping
studies.
This method may also permit the quantitative study of different protein
fractions.
Phosphopeptides from Grana Padano cheese: nature, origin
and changes during ripening
Authors: FERRANTI PASQUALE , BARONE FRANCESCA , CHIANESE LINA , ADDEO FRANCESCO , SCALONI ANDREA , PELLEGRINO LUISA , RESMINI PIERPAOLO
Published: July 2002

Casein phosphopeptides (CPP) which develop in Grana Padano cheese
at
different ages were isolated by precipitation with Ba2+
and analysed by HPLC.
Profiles were complex throughout the period between 4 and 38 months. CPP
in a
cheese sample 14 months old were identified by a combination of fast atom

bombardment–mass spectrometry and Edman degradation. They were found
to
consist of a mixture of components derived from three parent peptides,

β-CNf(7–28)4P, αs1-CNf(61–79)4P and
αs1-CNf(7–21)4P. In total, 45 phosphopeptides
were identified: 24 from β-CN, 16 from αs1-CN and
5 from
αs2-CN. The presence of
aminopeptidase activity during cheese ripening was deduced from the presence
of a
number of CPP of different lengths with the loss of one or more residues
from
the N-terminus. The longest had C-terminal lysine and seemed to be progressively

hydrolysed by carboxypeptidases A and B to shorter peptides. CPP in cheese

appeared to be shortened plasmin-mediated products. Moreover, those most
resistant
to further hydrolysis contained at least three closely located phosphoserine

residues. The anticariogenic activity of CPP is also discussed.
Effect of altering the daily herbage allowance in mid lactation on
the
composition and processing characteristics of bovine milk
Authors: O'BRIEN BERNADETTE , MURPHY JOHN J. , CONNOLLY JAMES F. , MEHRA RAJ , GUINEE TIMOTHY P. , STAKELUM GEARÓID
Published: July 2002

Milk production in Ireland, New Zealand and Australia is seasonal,
with the
majority of cows calving in spring. This pattern of production makes the
maximum
use of grazed grass, and in Ireland >80% of total milk for manufacturing
is
produced between April and November inclusive. Such a seasonal pattern
of
production results in a large variation in the gross composition of
milk due to stage
of lactation effects (Phelan et al. 1982). Some studies
have investigated the
relationship between milk composition and its processing characteristics

(O'Keeffe et
al. 1982; Grandison et al. 1984); however, in these studies

the effects of diet and
lactation stage were not segregated. Kefford et al. (1995) attempted

to segregate the
effects of diet and stage of lactation and concluded that diet quality
(type and
quantity) had a larger effect on Cheddar cheese quality than
the stage of lactation.

The nutritive value of the diet of cows fed on grazed grass can change
owing to
changes in grass supply or quality. In the current study, changes in
grass supply were
achieved by altering the daily herbage allowance (DHA) to the herds. The
objective
of the current study was to investigate the effect of varying the DHA in
the range
16–24 kg grass dry matter (DM), which is typical of the variation
in pasture
allowance in Ireland in mid lactation, on milk composition and its processing

characteristics.
Sole disorders in conventionally managed and organic dairy herds
using different housing systems
Authors: VAARST METTE , HINDHEDE JENS , ENEVOLDSEN CARSTEN
Published: July 2002

Records of claw trimmings were analysed in seven organic and six

conventional Danish herds (a total of 974 cows). The housing systems represented

were tie stall systems, loose housing system with slatted floor (one organic
herd), and
deep litter systems (deep straw bedding). Occurrence of sole disorders
was analysed
separately for cows in first lactation and for cows in later lactations.
Three different
responses (acute haemorrhage, sole ulcer in one leg and sole ulcer in two
or more legs)
were analysed using three binomial logistic regression analyses for each
group. Herd
analysed as a fixed effect was a strong risk factor for all kinds of sole
ulcer. Lactation
stage was a risk factor for acute haemorrhage in both groups of cows, and
for sole
ulcer in first parity cows. In general, there was a strong positive association
between
the period 61–120 d post partum and the presence of sole disorders.
Breed was
associated with acute haemorrhage in cows in second and later parities,
and sole ulcer
in one leg only in first parity cows in an interaction with lactation stage
in both
conditions. Danish Friesian cows were strongly associated with sole disorder,

although the combination of lactation stage from 61 to 120 d post partum
in cows of
other dual purpose breeds was positively associated with the presence of
sole ulcer in
one leg only in first parity cows. The time of year for claw trimming was
a risk factor
for acute haemorrhage in first parity cows, with the period from December
to
January most strongly associated with acute haemorrhage. Previous disease

treatment was a risk factor for sole ulcer in two or more legs in second
and later
parities. Udder related disorders and disorders other than reproductive
problems
were positively associated with the occurrence of sole ulcer. Body weight
at calving
was associated with acute haemorrhage in cows in second and subsequent
parities.
Body weight lower than the mean herd level by >50 kg was negatively
associated
with acute haemorrhage.
Nutritional value of the non-protein N that accumulates during
growth of proteinase-positive strains of Lactococcus lactis in
milk for
dairy lactococcal and leuconostoc isolates
Authors: FOUCAUD CATHERINE , FURLAN SYLVIANE , BELLENGIER PASCALE , JUILLARD VINCENT , RICHARD JEAN
Published: July 2002

To estimate the suitability of cultured milk for the subsequent
growth of
dairy lactic acid bacteria in cheese manufacturing, control milk was first
cultured
until the end of the exponential phase with one of four proteolytic (Prt+)

strains of Lactococcus lactis differing in their proteolytic enzymes,

and pasteurized after
readjusting the pH to its initial value. Nineteen non-proteolytic (Prt−)

strains of Lc. lactis and nine Leuconostoc mesenteroides

strains of dairy origin were then grown in
the precultured milk until the stationary phase and their growth was compared
with
that in control milk. Despite the accumulation of non-protein N (NPN) during

preculture, the growth of most Prt−
strains of Lc. lactis in precultured milk was either
reduced or unchanged whereas that of Ln. mesenteroides strains
was unchanged or
slightly stimulated. This reduction in growth was reversed by adding an
NPN source
to precultured milk, indicating that it was due to the exhaustion of assimilable
NPN
in precultured milk. Thus, preculturing milk with Prt+
strains of Lc. lactis could not
be recommended for promoting the subsequent growth of starter cultures
in cheese
manufacturing.
ELISA for differential quantitation of plasmin and plasminogen in
cheese
Authors: DUPONT DIDIER , GRAPPIN REMY
Published: July 2002

Bovine plasmin (PLM) and its precursor plasminogen (PLG) are present
in cheese, in which the proteinase is thought to play a significant role
in proteolysis
during ripening. PLM in cheese is usually assayed by enzymic techniques
and
concentrations are generally expressed as activities. In order to determine
absolute
concentrations of PLM and PLG in cheese, we have applied an ELISA previously
developed for the differential determination of PLM and PLG in milk. The
assay
used two monoclonal antibodies, one specific for PLG and the other cross
reacting
with PLM and PLG. PLM concentration was obtained by subtracting the PLG
concentration from the value for PLM plus PLG. The assay was evaluated
in cheese
by determining the total amount of PLG and PLM in milk used in the manufacture
of eight semi-hard cheeses on a pilot plant scale, and comparing it with
the total
amount of PLG and PLM present in the eight corresponding wheys and unripened
cheeses. Concentrations of PLG and PLM in 19 commercial cheeses were also
determined. It was thus demonstrated that the ELISA made it possible to
quantify
PLM and PLG in milk and cheese and that PLM and PLG concentrations in cheese
were highly dependent on the technology used for cheesemaking.
Desorbed terpenes and sesquiterpenes from forages and cheeses
Authors: VIALLON CHRISTINE , VERDIER-METZ ISABELLE , DENOYER CHRISTIAN , PRADEL PHILIPPE , COULON JEAN-BAPTISTE , BERDAGUÉ JEAN-LOUIS
Published: July 2002

The composition and sensory characteristics of matured cheeses are controlled by
a number of factors, among which the type of feed is important. The influence of
feeding can be reflected by the presence in cheeses of terpenes and sesquiterpenes,
compounds typically indicating their vegetable origin (Mariaca et al. 1997). Indeed,
several investigators have already established that these compounds could
characterize the forage even to a specific geographical location. Dumont & Adda
(1978), Dumont et al. (1981), Guichard et al. (1987),
Bosset et al. (1994) and Moio et
al. (1996) were thus able to distinguish cheeses from lowland and upland regions. In
most of these studies, the conditions under which milk was produced and processed
were not completely controlled. Furthermore, all these studies analysed only the
volatile fraction of cheeses and did not examine the volatile compounds in the forages
used. Recently Bosset et al. (1994), in one part of the project described by Jeangros
et al. (1997), showed that highland grass with a highly diversified botanical
composition produces milk and cheeses with significantly different chemical
compositions from those from lowland grass. To improve our understanding of the
relationship between animal feed and cheese composition, we have investigated
under controlled experimental conditions both the composition of the terpene and
sesquiterpene fractions of four forages with different botanical diversities and the
influence of those forages on the terpene fraction of cheeses.
Crusading as Social Revolt: The
Hungarian Peasant Uprising of 1514
Authors: HOUSLEY NORMAN
Published: July 2002

On 9 April 1514 Tamás Bakócz, archbishop
of Esztergom and cardinal-legate of Pope Leo X,
initiated the preaching of a crusade against the Turks in
Hungary. On 24 April György
Dózsa Székely, a minor nobleman serving with
the garrison of Belgrade
who had experience of fighting the Turks, was appointed as
commander of the crusading army. Dózsa marched
southwards from Pest on 10 May
with the main body of crusaders, some 15,000 strong, for
the most part peasants. Five days later Archbishop Bakócz
and the Hungarian royal council called a halt to the preaching.
Their cancellation was provoked by
the fact that the crusade preaching had generated alarming
social unrest, and on 22 May an encounter occurred at
Várad in which an army of
crusaders defeated a force of nobles. The crusade was now
showing all the features of an uprising, and two days after
the battle of Várad,
coincidentally on the same day that György Dózsa
inflicted another
defeat on the nobles at Nagylak, the king called off the
crusade and
ordered the peasant crusaders to return home. His command
was ignored and attempts to organise local resistance against
the various crusade
armies met with only partial success. It proved necessary
to recall János Zápolyai and the troops who were
engaged against the Turks in the east.
At the end of June Zápolyai marched in relief of
Temesvár (Timisoara),
the fortress which Dózsa was besieging, evidently
with the plan to
establish a strategic base between the Maros and the
Danube. Here, on
15 July, the vojvoda smashed the crusading army and turned
the tide of the revolt, which lasted for just a few more weeks.
Breaking of axisymmetry and onset of unsteadiness in the wake of a sphere
Authors: GHIDERSA BRĂDUŢ , DUšEK JAN
Published: July 2002

The primary and secondary instabilities of the sphere wake are investigated from
the viewpoint of nonlinear dynamical systems theory. For the primary bifurcation,
a theory of axisymmetry breaking by a regular bifurcation is given. The azimuthal
spectral modes are shown to coincide with nonlinear modes of the instability, which
provides a good reason for using the azimuthal expansion as an optimal spectral
method. Thorough numerical testing of the implemented spectral–spectral-element
discretization allows corroboration of existing data concerning the primary and
secondary thresholds and gives their error estimates. The ideal axisymmetry of the
numerical method makes it possible to confirm the theoretical conclusion concerning
the arbitrariness of selection of the symmetry plane that arises. Investigation of
computed azimuthal modes yields a simple explanation of the origin of the so-called
bifid wake and shows at each Reynolds number the coexistence of a simple wake and a
bifid wake zone of the steady non-axisymmetric regime. At the onset of the secondary
instability, basic linear and nonlinear characteristics including the normalized Landau
constant are given. The periodic regime is described as a limit cycle and the power of
the time Fourier expansion is illustrated by reproducing experimental r.m.s. fluctuation
charts of the streamwise velocity with only the fundamental and second harmonic
modes. Each time–azimuthal mode is shown to behave like a propagating wave having
a specific spatial signature. Their asymptotic, far-wake, phase velocities are the same
but the waves keep a fingerprint of their passing through the near-wake region. The
non-dimensionalized asymptotic phase velocity is close to that of an infinite cylinder
wake. A reduced-accuracy discretization is shown to allow qualitatively satisfactory
unsteady simulations at extremely low cost.
Three-dimensional numerical simulation of thermocapillary flows
in cylindrical liquid bridges
Authors: LEYPOLDT JENS , KUHLMANN HENDRIK C. , RATH HANS J.
Published: July 2002

The dynamics of thermocapillary flows in differentially heated cylindrical liquid
bridges is investigated numerically using a mixed finite volume/pseudo-spectral
method to solve the Navier–Stokes equations in the Boussinesq approximation. For
large Prandtl numbers (Pr = 4 and 7) and sufficiently high Reynolds numbers, the
axisymmetric basic flow is unstable to three-dimensional hydrothermal waves. Finite-amplitude azimuthally standing waves are found to decay to travelling waves. Close
to the critical Reynolds number, the former may persist for long times. Representative
results are explained by computing the coefficients in the Ginzburg–Landau equations
for the nonlinear evolution of these waves for a specific set of parameters. We
investigate the nonlinear phenomena characteristic of standing and pure travelling
waves, including azimuthal mean flow and time-dependent convective heat transport.
For Pr [Lt ] 1 the first transition from the two-dimensional basic flow to the three-dimensional stationary flow is inertial in nature. Particular attention is paid to the
secondary transition leading to oscillatory three-dimensional flow, and this mechanism
is likewise independent of Pr. The spatial and temporal structure of the perturbation
flow is analysed in detail and an instability mechanism is proposed based on energy
balance calculations and the vorticity distribution.
Modelling the formation of shoreface-connected sand ridges on storm-dominated inner shelves
Authors: CALVETE D. , FALQUES A. , DE SWART H. E. , WALGREEN M.
Published: July 2002

A morphodynamic model is developed and analysed to gain fundamental understanding
of the basic physical mechanisms responsible for the characteristics of shoreface-connected
sand ridges observed in some coastal seas. These alongshore rhythmic bed
forms have a horizontal lengthscale of order 5 km and are related to the mean current
along the coast: the seaward ends of their crests are shifted upstream with respect to
where they are attached to the shoreface. The model is based on the two-dimensional
shallow water equations and assumes that the sediment transport only takes place
during storms. The flux consists of a suspended-load part and a bed-load part and
accounts for the effects of spatially non-uniform wave stirring as well as for the
preferred downslope movement of sediment. The basic state of this model represents
a steady longshore current, driven by wind and a pressure gradient. The dynamics
of small perturbations to this state are controlled by a physical mechanism which is
related to the transverse bottom slope. This causes a seaward deflection of the current
over the ridges and the loss of sediment carrying capacity of the flow into deeper
water. The orientation, spacing and shape of the modelled ridges agree well with
field observations. Suspended-load transport and spatially non-uniform wave stirring
are necessary in order to obtain correct e-folding timescales and migration speeds.
The ridge growth is only due to suspended-load transport whereas the migration is
controlled by bed-load transport.
Refraction of gravity waves by weak current gradients
Authors: DYSTHE KRISTIAN B.
Published: July 2002

When deep water surface waves cross an area with variable current, refraction takes
place. If the group velocity of the waves is much larger than the current velocity we
show that the curvature of a ray, χ, is given by the simple formula
χ = ζ/vg. Here ζ
is the vertical component of the current vorticity and vg is the group velocity.
Finite-amplitude solitary states in viscoelastic shear flow: computation and mechanism
Authors: KUMAR K. ARUN , GRAHAM MICHAEL D.
Published: July 2002

Starting from stationary bifurcations in Couette–Dean flow, we compute stationary
nontrivial solutions in the circular Couette geometry for an inertialess finitely extensible
nonlinear elastic (FENE-P) dumbbell fluid. These solutions are isolated from
the Couette flow branch arising at finite amplitude in saddle–node bifurcations as
the Weissenberg number increases. Spatially, they are strongly localized axisymmetric
vortex pairs embedded in an arbitrarily long ‘far field’ of pure Couette flow, and are
thus qualitatively, and to some extent quantitatively, similar to the ‘diwhirl’ (Groisman
& Steinberg 1997) and ‘flame’ patterns (Baumert & Muller 1999) observed experimentally.
For computationally accessible parameter values, these solutions appear
only above the linear instability limit of the Couette base flow, in contrast to the
experimental observations. Correspondingly, they are themselves linearly unstable.
Nevertheless, extrapolation of the trend in the bifurcation points with increasing
polymer extensibility suggests that for sufficiently high extensibility the diwhirls will
come into existence before the linear instability, as seen experimentally.

Based on the computed stress and velocity fields, we propose a fully nonlinear self-sustaining
mechanism for these flows. The mechanism is related to that for viscoelastic
Dean flow vortices and arises from a finite-amplitude perturbation giving rise to a
locally unstable profile of the azimuthal normal stress near the outer cylinder at
the symmetry plane of the vortex pair. The unstable stress profile, in combination
with a ‘tubeless siphon’ effect, nonlinearly sustains the patterns. We propose that
these solitary, strongly nonlinear structures comprise fundamental building blocks for
complex spatiotemporal dynamics in the flow of elastic liquids.
Drag reduction in wall-bounded turbulence via a transverse travelling wave
Authors: DU YIQING , SYMEONIDIS V. , KARNIADAKIS G. E.
Published: July 2002

Computational experiments based on direct numerical simulation of wall-bounded
flow reveal that turbulence production can be suppressed by the action of a transverse
travelling wave. Flow visualizations show that the near-wall flow structure is altered
substantially, compared to other turbulence control techniques, leading to a large
amount of shear stress reduction (i.e., more than 30%). The travelling wave can be
induced by a spanwise force that is confined within the viscous sublayer, it has its
maximum at the wall, and decays exponentially away from it. We demonstrate the
robustness of this approach, and its application in salt water using arrays of electro-magnetic
tiles that can produce the required travelling wave excitation. We also study
corresponding results from spanwise oscillations using a similar force, which also leads
to large drag reduction. Although the turbulence statistics for the two approaches
are similar, the near-wall structures appear to be different: in the spanwise oscillatory
excitation there is a clear presence of wall-streaks whereas in the travelling wave
excitation these streaks have disappeared. From the fundamental point of view, the
new finding of this work is that appropriate enhancement of the streamwise vortices
leads to weakening of the streak intensity, as measured by the normal vorticity
component, and correspondingly substantial suppression of turbulence production.
From the practical point of view, our findings provide guidance for designing different
surface-based actuation techniques including piezoelectric materials, shape memory
alloys, and electro-magnetic tiles.
A two-dimensional model for slow convection at infinite
Marangoni number
Authors: THESS A. , SPIRN D. , JÜTTNER B.
Published: July 2002

The free surface of a viscous fluid is a source of convective
flow (Marangoni convection) if its surface tension is distributed
non-uniformly. Such non-uniformity arises from the dependence of the
surface tension on a scalar quantity, either surfactant concentration
or temperature. The surface-tension-induced velocity redistributes
the scalar forming a closed-loop interaction. It is shown that under
the assumptions of (i) small Reynolds number and (ii) vanishing
diffusivity this nonlinear process is described by a single
self-consistent two-dimensional evolution equation for the scalar
field at the free surface that can be derived from the
three-dimensional basic equations without approximation. The
formulation of this equation for a particular system requires only
the knowledge of the closure law, which expresses the surface
velocity as a linear functional of the active scalar at the free
surface. We explicitly derive these closure laws for various systems
with a planar non-deflecting surface and infinite horizontal extent,
including an infinitely deep fluid, a fluid with finite depth, a
rotating fluid, and an electrically conducting fluid under the
influence of a magnetic field. For the canonical problem of an
infinitely deep layer we demonstrate that the dynamics of singular
(point-like) surfactant or temperature distributions can be further
reduced to a system of ordinary differential equations, equivalent to
point-vortex dynamics in two-dimensional perfect fluids. We further
show, using numerical simulations, that the dynamical evolution of
initially smooth scalar fields leads in general to a finite-time
singularity. The present theory provides a rational framework for a
simplified modelling of strongly nonlinear Marangoni convection in
high-Prandtl-number fluids or systems with high Schmidt
number.
Steady axisymmetric motion of deformable drops

falling or rising through a homoviscous fluid in a

tube at intermediate Reynolds number
Authors: BOZZI LLOYD A. , FENG JAMES Q. , SCOTT TIMOTHY C. , PEARLSTEIN ARNE J.
Published: July 2002

The steady axisymmetric flow in and around a deformable drop moving

under the action of gravity along the axis of a vertical tube at intermediate

Reynolds number is

studied by solving the nonlinear free-boundary problem using a Galerkin

finite-element method. For the case where the drop and suspending liquid
have the

same viscosity, the ratio of the densities is 6/5 or 5/6, and the

radius of the tube is equal to

twice the radius of a sphere having the drop volume, four significant results
are

apparent in the computations. First, we compute drops showing much more

deformation, and in particular the development of considerably more non-convexity,

than those found in previous calculations for non-zero Reynolds number.
The degree

of non-convexity typically grows with the Reynolds number. Secondly, external

recirculation zones can be attached to or disjoint from the drop. We find
when there

is a single external recirculation zone, that is disjoint (as found by
Dandy

& Leal), it

can attach to the drop as the Reynolds number is increased. As the Reynolds
number

further increases, this is immediately followed by division of the drop
into two

adjacent recirculating regions. Thirdly, we sometimes find two recirculation
zones

in the suspending liquid. Finally, the drag coefficient, axis ratio, and
normalized

interfacial and frontal areas of the drop can vary non-monotonically with
the Weber

number, exhibiting as many as four local extrema. The results are compared
to

previous theoretical and experimental work, and implications for drop motion
and

heat and mass transfer are discussed.
The role of angular momentum in the magnetic

damping of turbulence
Authors: DAVIDSON P. A.
Published: July 2002

Landau & Lifshitz showed that Kolmogorov's

E∼t−10/7 law for the decay of
isotropic

turbulence rests on just two physical ideas: (a) the conservation
of

angular momentum, as expressed by Loitsyansky's integral; and (b)

the removal of energy from the large

scales via the energy cascade. Both Kolmogorov's original analysis
and

Landau &

Lifshitz's reinterpretation in terms of angular momentum are now known
to

be flawed.

The existence of long-range velocity correlations means that Loitsyansky's

integral is

not an exact representation of angular momentum, nor is it strictly conserved.

However, in practice the long-range velocity correlations are weak and

Loitsyansky's

integral is almost constant, so that the Kolmogorov/Landau model provides
a

surprisingly simple and robust description of the decay. In this paper
we redevelop

these ideas in the context of MHD turbulence. We take advantage of the
fact that the

angular momentum of a fluid moving in a uniform magnetic field has particularly

simple properties. Specifically, the component parallel to the magnetic
field is

conserved while the normal components decay exponentially on a time scale
of

τ=ρ/σB2.

We show that the counterpart of Loitsyansky's integral for MHD turbulence
is

∫x2⊥Q⊥dx,

where Qij is the velocity correlation. When
the

long-range correlations

are weak this integral is conserved. This provides an estimate of the rate
of

decay of energy. At low values of magnetic field we recover Kolmogorov's
law.

At high values we find E∼t−1/2,

which is a result derived earlier by Moffatt. We also show that

∫x2⊥Q∥dx

decays exponentially on a time scale of τ. We interpret these results
in terms of

the behaviour of isolated vortices orientated normal and parallel to the

magnetic field.
A study of particle paths in non-axisymmetric Taylor–Couette flows
Authors: ASHWIN P. , KING G. P.
Published: July 2002

We study the paths of fluid particles in velocity fields modelling
rigidly rotating
velocity fields that occur in the concentric Taylor problem. We set up velocity
fields
using the model of Davey, DiPrima & Stuart (1968) based on small-gap
asymptotics.
This allows a numerical study of the Lagrangian properties of steady flow
patterns in
a rotating frame. The spiral and Taylor vortex modes are integrable, implying
that in
these cases almost all particle paths are confined to two-dimensional surfaces
in the
fluid. For the case of Taylor vortices the motion on these surfaces is
quasi-periodic,
whereas for spirals the particles propagate up or down the cylinder on
these surfaces.

The non-axisymmetric modes we consider are wavy vortices, spirals, ribbons and
twisted Taylor vortices. All of these flows have the property that they are
steady flows
when examined in a rotating frame of reference. For all non-axisymmetric modes
with the exception of spirals, we observe the existence of regions of chaotic mixing
within the fluid. We discuss mixing of the fluid by these flows with
reference to the
pattern of stagnation points and some of the periodic trajectories within
the fluid and on the boundary.
Low-frequency two-dimensional linear instability
of plane detonation
Authors: SHORT MARK , STEWART D. SCOTT
Published: July 2002

An analytical dispersion relation describing the linear stability of
a plane detonation
wave to low-frequency two-dimensional disturbances with arbitrary wavenumbers is
derived using a normal mode approach and a combination of high activation energy
and Newtonian limit asymptotics, where the ratio of specific heats
γ→1. The reaction
chemistry is characterized by one-step Arrhenius kinetics. The analysis assumes a
large activation energy in the plane steady-state detonation wave and a
characteristic
linear disturbance wavelength which is longer than the fire-zone thickness.
Newtonian limit asymptotics are employed to obtain a complete analytical
description of the
disturbance behaviour in the induction zone of the detonation wave. The analytical
dispersion relation that is derived depends on the activation energy and exhibits
favourable agreement with numerical solutions of the full linear stability problem
for low-frequency one- and two-dimensional disturbances, even when the activation
energy is only moderate. Moreover, the dispersion relation retains vitally
important characteristics of the full problem such as the one-dimensional
stability of the
detonation wave to low-frequency disturbances for decreasing activation energies or
increasing overdrives. When two-dimensional oscillatory disturbances are considered,
the analytical dispersion relation predicts a monotonic increase in the disturbance
growth rate with increasing wavenumber, until a maximum growth rate is reached at
a finite wavenumber. Subsequently the growth rate decays with further increases in
wavenumber until the detonation becomes stable to the two-dimensional disturbance.
In addition, through a new detailed analysis of the behaviour of the perturbations
near the fire front, the present analysis is found to be equally valid for detonation
waves travelling at the Chapman–Jouguet velocity and for detonation waves which
are overdriven. It is found that in contrast to the standard imposition
of a radiation
or piston condition on acoustic disturbances in the equilibrium zone for overdriven
waves, a compatibility condition on the perturbation jump conditions across the fire
zone must be satisfied for detonation waves propagating at the Chapman–Jouguet
detonation velocity. An insight into the physical mechanisms of the one- and
two-dimensional linear instability is also gained, and is found to involve an
intricate
coupling of acoustic and entropy wave propagation within the detonation wave.
Sinusoidal forcing of a turbulent separation bubble
Authors: KIYA M. , SHIMIZU M. , MOCHIZUKI O.
Published: July 2002

A turbulent separation bubble is forced by single- and double-frequency

sinusoidal

disturbances, with the emphasis placed on the reattachment length as a

function of the

forcing amplitude and frequency. The separation bubble is that

formed along the side

of a blunt circular cylinder with a square leading edge. In

single-frequency forcing, the

reattachment length attains a minimum at a particular forcing frequency,

F, which

scales with the frequency of shedding of vortices from the

reattachment region of the

separated shear layer. A flow model is presented to interpret the

frequency F. Forcing

of sufficiently high amplitude eliminates the recirculating region in a
range of the

forcing frequency. Flow visualization and a survey of the mean flow and
turbulence

properties demonstrate how the flow in the separated shear layer is modified
by the

forcing. In double-frequency forcing, the superposition of the

F-component on its

higher or subharmonic components is considered. A non-resonant combination
of the

two frequencies is also considered.
Visco-resistive magnetic reconnection due to
steady inertialess flows.
Part 1. Exact analytical solutions
Authors: TITOV VYACHESLAV S. , PRIEST E. R.
Published: July 2002

Magnetic reconnection at an X-type neutral point of
a two-dimensional magnetic
field is studied in an incompressible viscous resistive fluid whose flow
is assumed
to be slow enough that its inertia is negligible. In both the ideal and
resistive
magnetohydrodynamic approximations current singularities appear at the
X-point
and along the separatrices. It is shown here analytically that the combined
effect
of viscosity and resistivity can resolve these singularities with the
flow crossing the
separatrices. A wide class of exact solutions describing the
structure of the flow and
current density distribution is found. The results suggest that
reconnection may occur
with localized distributions of strong current density restricted to finite
regions.
Instability and transient growth for two trailing-vortex pairs
Authors: CROUCH J. D.
Published: July 2002

The stability of two vortex pairs is analysed as a model for

the vortex system generated

by an aircraft in flaps-down configuration. The co-rotating

vortices on the starboard

and port sides tumble about one another as they propagate downward. This
results in

a time-periodic basic state for the stability analysis. The

dynamics and instability of

the trailing vortices are modelled using thin vortex filaments.

Stability equations are

derived by matching the induced velocities from Biot–Savart

integrals with kinematic

equations obtained by temporal differentiation of the vortex position vectors.
The

stability equations are solved analytically as an eigenvalue problem, using
Floquet

theory, and numerically as an initial value problem. The instabilities
are periodic

along the axes of the vortices with wavelengths that are large compared
to the

size of the vortex cores. The results show symmetric instabilities that
are linked to

the long-wavelength Crow instability. In addition, new symmetric and antisymmetric

instabilities are observed at shorter wavelengths. These

instabilities have growth rates

60–100% greater than the Crow instability. The system of two vortex
pairs also

exhibits transient growth which can lead to growth factors of

10 or 15 in one-fifth of

the time required for the same growth due to instability.
Stratification effects on the stability of columnar
vortices on the f-plane
Authors: POTYLITSIN P. G. , PELTIER W. R.
Published: July 2002

We consider the stability with respect to
three-dimensional perturbations of columnar
vortices on the f-plane and as a function of the
strength of a stabilizing density
stratification parallel to the axis of the vortex. We seek to
understand the dynamics
of the processes through which such a vertically oriented
barotropic vortex may be
destabilized. As models of the basic vorticity distribution
we consider both Kelvin–Helmholtz vortices in
shear and ‘Kida-like’ vortices in
strain. In the case of rotating
unstratified flow, an isolated anticyclonic vortex column is
shown to be strongly
destabilized to three-dimensional perturbations by small
values of the background rotation, while rapid rotation
strongly stabilizes both anticyclonic and cyclonic columns,
as expected on the basis of the Taylor–Proudman
theorem. The dominant instability mechanism which drives the
destruction of anticyclonic vortices in the presence
of slow background rotation may be understood to constitute
a three-dimensional
inertial (centrifugal) instability. Through explicit analysis
we show that sufficiently
strong density stratification stabilizes the two-dimensional
columnar structures to disruption by this and additional
modes of instability that exist even in the absence of
rotation. We furthermore demonstrate that there exists a
second fundamental mode
of instability in the presense of background rotation which
affects only anticyclonic
vortex columns whose cross-sections are elliptical. Only
when the ellipticity of the
vortex is sufficiently high does this mode dominate the
centrifugal mode. The process
whereby anticyclonic vortices may be selectively destroyed
appears to provide a possible explanation of an asymmetry that
is sometimes observed to be characteristic of
the atmospheric von Kármán vortex streets that
are observed in the lee of oceanic
islands. The anticyclonic branch of the street often seems
to be absent. More generally, the centrifugal mechanism for
the selective destruction of anticyclones discussed
herein very clearly explains a number of recent results
obtained from both laboratory
experiments and numerical simulations.