bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of sulphur application on the efficiency of
nitrogen use in two contrasting grassland soils
Authors: BROWN L. , SCHOLEFIELD D. , JEWKES E. C. , PREEDY N. , WADGE K. , BUTLER M.
Published: July 2002

The effect of sulphur (S) application on the efficiency of nitrogen (N) use was investigated using cut
plot experiments on two contrasting soil types. Nitrogen was applied at 200 and 450 kg N/ha per
year, with and without 38 kg SO3/ha (15·2 kg S/ha) per cut. Over three conventionally timed silage
cuts for 2 years, measurements were made of herbage dry matter, the yield of N and S in herbage and
losses of N and S by leaching, and N by denitrification.

Herbage dry matter and N yields were significantly increased by the application of S at the high
N level at the sandy loam site (Halse). At the clay loam site (Great Close) the application of S had
no significant effect on herbage dry matter or N yields. At Halse, the pattern of response through the
year was not the same in the 2 years studied, although in both, the effect of S was significant at third
cut at high N. Deficiency was suggested by the N[ratio ]S ratio of herbage on the plots without S, especially
at first cut, and at later cuts at Halse. Nitrate leaching was reduced by S at Halse by 72% and 58%
with high N in 1997 and 1998, respectively, and by 10% and 5% on the low N treatments in 1997
and 1998, respectively. Application of S at high N at Halse reduced the peak concentration of nitrate-N in leachate from 27·3 mg N/l to 9·3 mg N/l. At Great Close, application of S had no significant
effect on the amount or peak concentration of nitrate-N leached. The improvement in efficiency
reported at Halse suggests that on permeable soils receiving high levels of N, the application of S
could have a large effect on nitrate leaching and its associated environmental impact.
Prediction of chemical, nutritive and agronomic
characteristics of wheat by near infrared spectroscopy
Authors: GARNSWORTHY P. C. , WISEMAN J. , FEGEROS K.
Published: July 2002

Near infrared spectroscopy (NIRS) is widely used in the flour milling industry for rapid determination
of moisture and protein in wheat. However, these measurements give little indication of the nutritive
value of wheat when fed to poultry or pigs. Accurate estimates of nutritive value require specialist
facilities and are time-consuming and costly. Accordingly, prediction from chemical or NIRS
measurements would be of some considerable benefit. In the current study 160 samples of wheat,
representing 24 different varieties, were used to generate NIRS calibration equations for chemical,
nutritive and agronomic characteristics. Predictions of chemical constituents in wheat were very
accurate. Coefficients of determination (r2) were 0·94 for dry matter, 0·90 for crude protein, 0·97 for
ash, 0·78 for starch and 0·98 for oil. True metabolizable energy in broiler chickens was predicted more
accurately (r2 = 0·52 for adult birds, 0·74 for young birds) than apparent metabolizable energy (r2 = 0·45). Digestible energy (r2 = 0·17) and nitrogen digestibility (r = 0·22) in pigs were not predicted
very accurately on a smaller subset (n = 33). Agronomic characteristics were predicted very
accurately (r2 = 0·98 hardness, 0·80 bushel weight, 0·99 thousand-grain weight). Predictions of
nutritive value of wheat from chemical or agronomic characteristics are very inaccurate, since
coefficients of determination vary from zero to 0·25. It is concluded that NIRS can accurately estimate
the chemical composition of wheat, but accurate prediction of nutritive value is reduced by animal
variation. Nevertheless, NIRS is potentially more reliable for assessing nutritive value than chemical
composition or agronomic characteristics.
Being Human in the Wor(l)d: Chinese Men and Maxine Hong Kingston's Reworking of Robinson Crusoe
Authors: CHIU MONICA
Published: July 2002

Daniel Defoe's 1719 novel Robinson Crusoe is nothing less than a nationalist
narrative that extols the burgeoning capitalism of eighteenth-century
England. In this moving tale, a ship-wrecked slave trader, stranded on an
island for twenty-four-years, single-handedly consolidates the arduous
and multi-tasked feat of making bread – from planting the wheat to
producing the finished product – into a one-person job. On a smaller but
no less devastating scale, he also succeeds in replicating the process of
colonization through his master–slave relationship with Friday. The novel
thus popularizes the notion of self-sufficiency through the mechanisms of
capitalism, conquest, and the transmission of hegemony.
TEENAGE MOTHERHOOD AND INFANT MORTALITY IN BANGLADESH: MATERNAL AGE-DEPENDENT EFFECT OF PARITY ONE
Authors: ALAM NURUL
Published: July 2002

Nuptiality norms in rural Bangladesh favour birth during the teenage years. An appreciable proportion of teenage births are, in fact, second births. This study examines the relationship between teenage fertility and high infant mortality. It is hypothesized that if physiological immaturity is responsible, then the younger the mother, the higher would be the mortality risk, and the effect of mother's ‘teenage’ on mortality in infancy, particularly in the neonatal period, would be higher for the second than the first births. Vital events recorded by the longitudinal demographic surveillance system in Matlab, Bangladesh, in 1990–92 were used. Logistic regression was used to estimate the effects on early and late neonatal (0–3 days and 4–28 days respectively) and post-neonatal mortality of the following variables: mother's age at birth, parity, education and religion, sex of the child, household economic status and exposure to a health intervention programme.

The younger the mother, the higher were the odds of her child dying as a neonate, and the odds were higher for second children than first children of teenage mothers. First-born children were at higher odds of dying in infancy than second births if mothers were in their twenties. Unfavourable mother's socioeconomic conditions were weakly, but significantly, associated with higher odds of dying during late neonatal and post-neonatal periods. The results suggest that physical immaturity may be of major importance in determining the relationship between teenage fertility and high neonatal mortality.
INTERACTING FACTORS AFFECTING ILLEGITIMACY IN PREINDUSTRIAL NORTHERN ENGLAND
Authors: SCOTT SUSAN , DUNCAN C. J.
Published: July 2002

Illegitimacy in a historic, single community at Penrith, Cumbria
(1557–1812), has been studied using aggregative analysis, family
reconstitution and time series analysis. This population was living under
extreme conditions of hardship. Long, medium and short wavelength cycles in
the rate of illegitimacy have been identified by time series analysis; each
represents a different response to social and economic pressures. In a complex
interaction of events, the peaks of the cycles in wheat prices were associated
with rises in adult mortality which promoted an influx of migrants and a
concomitant rise in illegitimacy. The association between immigration and
illegitimacy was particularly noticeable after the mortality crises of the
late sixteenth and early seventeenth centuries. Children of immigrant families
also tended to
produce illegitimate offspring.
Native and immigrant families responded
differently to extrinsic fluctuations, and variations in their
reproductive
behaviour were probably related to access to resources.
SEX ON CAMPUS: A PRELIMINARY STUDY OF KNOWLEDGE, ATTITUDES AND BEHAVIOUR OF UNIVERSITY STUDENTS IN DELHI, INDIA
Authors: SACHDEV P.
Published: July 2002

Eight hundred and eighty-seven students from two major universities in Delhi, India, were surveyed, using a self-administered questionnaire, about their sexual knowledge, attitudes and behaviour. The data show that female students seem to be rejecting traditional Indian repressive sexual standards of premarital and non-procreative sex and the gender differences are beginning to narrow. Despite their sexual awareness, the students were highly ignorant of the facts of life. Being male and married did not make them more knowledgeable.
INFANT AND YOUNG CHILD FEEDING PRACTICES AMONG AFRICAN PASTORALISTS: THE DATOGA OF TANZANIA
Authors: SELLEN DANIEL W.
Published: July 2002

Breast-feeding and weaning practices were observed for a cohort of 81 children under 3 years of age in the context of a longitudinal study of social, ecological and nutritional factors affecting growth in a semi-nomadic population of pastoralists in northern Tanzania (WaDatoga of Mbulu District). The adequacy of indigenous infant and young child feeding practices was assessed in relation to current international recommendations. Objectives were to provide baseline data for future investigations of any changes in young child feeding practices which accompany population shifts towards settlement and non-pastoral modes of subsistence, and to improve understanding of the strengths and limitations of indigenous feeding practices in this type of population. It was found that while breast-feeding was universally initiated, other aspects of young child feeding practices do not meet current international recommendations. Prelacteal feeds are commonly used, supplementary feeding with non-human milks usually occurs before 4 months of age, use of solid foods normally begins later than 6 months, and breast-feeding does not continue until 2 years of age for the majority of children. The data have implications for the design of breast-feeding promotion and improved weaning food interventions among African pastoralists.
Composition of the sterol fraction of caprine milk fat by gas chromatography and mass spectrometry
Authors: FRAGA MARÍA J. , FONTECHA JAVIER , LOZADA LUCIDIA , MARTÍNEZ-CASTRO ISABEL , JUÁREZ MANUELA
Published: July 2002

The sterol fraction of milk is of nutritional interest because high levels of
cholesterol in plasma (modulated by the cholesterol ingested) are associated with an
increasing risk of cardiovascular disease. In addition, some sterols (ergosterol and
7-dehydrocholesterol) are provitamins (D2 and D3 respectively). At the same time,
through the study of the sterol fraction, vegetable fats can be detected in milk and
dairy products. Sterols are a minor fraction of total milk fat, the main sterol being
cholesterol (3 mg/g fat, equivalent to 100 mg/l cows' milk). Small quantities of other
sterols (7-dehydrocholesterol, 22-dehydrocholesterol, ergosterol, fucosterol, lanosterol,
lathosterol, 24-methylenecholesterol) and several phytosterols have been
reported in cows' milk (Walstra & Jennes, 1984). International Dairy Federation
(1992) states that in the sterol profile of genuine milk fat there may appear, in
addition to the peak of 7-dehydrocholesterol which ranges from 0·7 to 4% of total
sterols, < 1% of minor sterols with retention times corresponding to phytosterols.

Values for the cholesterol content of goats' milk vary considerably, from
211 mg/l (Pantulu et al. 1975) to 125 mg/l (Lu, 1993), partly owing to the use of
different analysis techniques. Some of these values were obtained using non-specific
colorimetric methods, which are inaccurate in the presence of cholesterol precursors
or phytosterols (Clark et al. 1983; Haugh & Harzer, 1984). Some minor peaks have
been assumed to be sterols but have not been identified (García-Olmedo & Barrera,
1985).

Conventional methods of sample preparation for sterol analysis prior to gas
chromatography (GC), which involve saponification of fat with or without isolation
of the sterol fraction by thin layer chromatography, are tedious and time-consuming.
Transesterification with KOH–methanol has been successfully used as a rapid
alternative for obtaining the unsaponifiable fraction.

This paper describes the identification of sterols (cholesterol and other minor
sterols) in goats' milk fat using an alkali-catalysed transesterification procedure prior
to GC and GC–mass spectrometry (GC–MS) analysis.
Effect of β-lactoglobulin and precipitation of calcium phosphate on the thermal coagulation of milk
Authors: O'CONNELL JOHN E. , FOX PATRICK F.
Published: July 2002

The effect of β-lactoglobulin and heat-induced precipitation of calcium
phosphate on the pH dependence and mechanism of thermal coagulation of milk
throughout the pH range 6·3–7·3 was studied using serum protein-free milk and
sodium caseinate as models for micellar and non-micellar milk protein systems
respectively. It appears that the specific effect of β-lactoglobulin at the pH of
maximum stability may be related to its ability to chelate calcium. The effect of
β-lactoglobulin at the pH of minimum stability does not appear to be directly related
to heat-induced dissociation of κ-casein or micellar integrity but may be due to its
ability to sensitize casein micelles to heat-induced precipitation of calcium
phosphate, by increasing micellar hydrophobicity. The extent of heat-induced
precipitation of calcium phosphate, as a function of pH, is an inverse reflection of the
pH dependence of heat stability. Micellar integrity appears to play a critical role in
the heat stability of milk but for reasons not previously appreciated.
Influence of growth conditions on heat-stable phospholipase activity in Pseudomonas
Authors: KOKA RAMARATHNA , WEIMER BART C.
Published: July 2002

Many psychrotrophic bacteria contaminating raw milk produce phospholipase
that withstands pasteurization and UHT treatments. This enzyme acts on the
milk fat globule membrane and exposes triacylglycerides to the action of lipase.
Phospholipase production by various isolates of Pseudomonas was investigated. The
isolates were cultured aerobically at 8 °C in nutrient broth, McKellar's minimal salts
medium, Chrisope's medium, and skim milk. Each strain produced phospholipase
during the 50 h incubation. Enzyme production varied significantly (P < 0·001) with
strain and growth medium. Strains varied significantly (P < 0·001) in their enzyme
production in each medium and during the incubation time as well. Strain,
incubation time, and the growth medium significantly influenced (P < 0·001) heat
stability of the enzyme activity. Pasteurization reduced the activity, but did not
eliminate it in skim milk.
Phenotypic and genetic diversity of enterococci isolated from Italian cheeses
Authors: ANDRIGHETTO CHRISTIAN , KNIJFF EDO , LOMBARDI ANGIOLELLA , TORRIANI SANDRA , VANCANNEYT MARC , KERSTERS KAREL , SWINGS JEAN , DELLAGLIO FRANCO
Published: July 2002

In the present study, 124 enterococcal strains, isolated from traditional Italian cow, goat and buffalo cheeses, were characterized using phenotypic features and randomly amplified polymorphic DNA polymerase chain reaction (RAPD–PCR). The RAPD–PCR profiles obtained with four primers and five different amplification conditions were compared by numerical analysis and allowed an inter- and intraspecific differentiation of the isolates. Whole-cell protein analysis by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) was used as a reference method for species identification. The strains were identified as Enterococcus faecalis (82 strains), E. faecium (27 strains), E. durans (nine strains), E. gallinarum (four strains) and E. hirae (two strains). Species recognition by means of RAPD–PCR was in agreement with the SDS–PAGE results except for eight strains of E. faecium that clustered in separated groups. On the other hand, phenotypic identification based on carbohydrate fermentation profiles, using the rapid ID 32 STREP galleries, gave different results from SDS–PAGE in 12·1% of the cases. The majority of the strains had weak acidifying and proteolytic activities in milk. One E. faecium strain showed vanA (vancomycin resistance) genotype while four strains showed a β-haemolytic reaction on human blood. Several strains showed antagonistic activity towards indicator strains of Listeria innocua, Clostridium tyrobutyricum and Propionibacterium freudenreichii subsp. shermanii.
Oxytocin and prolactin suppress cortisol responses to acute stress in
both lactating and non-lactating sheep
Authors: COOK CHRISTIAN J.
Published: July 2002

Cortisol response to stress appears to differ between lactating and non-
lactating animals. Lactating (14 d post partum) and non-lactating sheep were fitted
with probes so that drugs and hormones could be infused directly into the posterior
pituitary and paraventricular nucleus of the hypothalamus. The animals were also
fitted with instruments to allow monitoring of heart rate, body temperature and
blood cortisol levels. Their reactions to a source of acute stress (a barking dog)
were then followed, with or without drug and hormone manipulation. Results in both
lactating and non-lactating animals indicated shortcomings in the use of cortisol as
a stress indicator. Infusing prolactin and oxytocin into either the
posterior pituitary
or the paraventricular nucleus of the hypothalamus suppressed cortisol
responsiveness to stress in both lactating and non-lactating animals (the
latter to a greater
extent). In the absence of drugs, lactating animals had a slightly higher basal level
of cortisol and a lower cortisol response to stress than their non-lactating
counterparts. Despite suppression of cortisol responses, with or without drugs, other
indicators of stress still changed with the presence of a barking dog, suggesting the
complexity of control involved in stress responses.
Effect of various milking machine systems and components on free
fatty acid levels in milk
Authors: O'BRIEN BERNADETTE , O'CALLAGHAN EDMOND , DILLON PATRICK
Published: July 2002

Elevated free fatty acid (FFA) levels in milk can impair the flavour
quality and
shelf life of milk and milk products and thus have implications for the
dairy industry.
An increase in milk FFA is induced when the protective fat globule membrane
is
disrupted and the fat exposed to the action of lipoprotein lipase (EC 3.1.1.34).

Various aspects of FFA development have been reviewed (Deeth & Fitz-Gerald,

1976; Fleming, 1979; International Dairy Federation, 1980). Mechanical
factors that
contribute to FFA development are directly related to poor milking systems
and
procedures (O'Halloran et al. 1975; Judge et al.

1977; Fleming, 1991). Mechanical
abuse of milk in many modern milking systems arises from air admission
to the
milking system, height of milklines and pump operation. Surveys and experience

(Fleming et al. 1996) showed that the quality of the components
used and the overall
maintenance of many milking machines was inadequate. In continental Europe
low-level
milking systems are generally recommended in preference to higher lines.

However, low-level systems are considerably more expensive as units have
to be
doubled up compared with the mid-level system.

Some of the machine factors contributing to excessive FFA development
in milk
can be eliminated by proper design, installation, maintenance and operation;

however, the benefits of design changes remain a source of debate. The
purpose of
this investigation was to determine the relative effects on milk FFA of
various
components of a modern mid-level milking system (a pipeline milking system
with
the milkline 1·2–1·5m above cow standing level)
and then to compare the optimal
mid-level system with direct-to-line and low-level milking systems.
Sequence analysis of Camelus dromedarius milk caseins
Authors: KAPPELER STEFAN , FARAH ZAKARIA , PUHAN ZDENKO
Published: July 2002

αs1-, αs2-, β- and κ-caseins

from Somali camels (Camelus dromedarius) were
purified by acid precipitation at pH 4·4, crudely separated into

an α-CN and a β-CN
fraction and further purified by reversed-phase HPLC. Fragments of tryptic
digests
were sequenced. Amino acid patterns obtained were used to screen a cDNA
library
constructed from mRNA from lactating udder tissue. Full length clones corresponding

to the four caseins were sequenced. The numbers of residues in the
sequences deduced were αs1-CN 207, αs2-CN
178,
β-CN 217, κ-CN 162. Percentage
similarity to bovine proteins was αs1-CN A 39,
αs2-CN 56, β-CN 64, κ-CN 56.
Acid-precipitated casein of pooled milk was separated by reversed-phase
HPLC and
monitored at 220 nm, and its composition, estimated from peak integration,
was
(g/kg total casein) αs1-CN 220, αs2-CN
95,
β-CN 650, κ-CN 35. Degrees of
phosphorylation and glycosylation were determined by laser ionization mass

spectrometry and sequence pattern analysis. Molecular masses determined
were
(kDa) αs1-CN A, 24·755 and 24·668; αs1-CN
B,
25·293; αs2-CN 21·993; β-CN, 24·900;

κ-CN 22·294–22·987. The pH values of the most

probable isoelectric points were: αs1-CN A 6P 4·41,

αs1-CN B 6P 4·40, αs2-CN 9P 4·58,

β-CN 4P 4·66, κ-CN 1P, with ten sialic acid residues
bound, 4·10.
Simple flow injection analysis system for determination of added
sugars in dairy products
Authors: CORTÓN EDUARDO , LOCASCIO GUILLERMO
Published: July 2002

A microbial sensor based on a carbon dioxide electrode coupled
with
immobilized Saccharomyces cerevisiae (baker's yeast) has
been used for the
determination of sucrose in dairy products. The sensor was used as the
detector in a
flow injection analysis system. Calibration curves for sucrose were established
from
1 to 100 g/l. Determinations for several dairy products containing
added sucrose
gave good agreement with the concentrations given by manufacturers. Typically,
the
se of the method was shown to be <5% of the calculated mean.
Protein A gene polymorphism analysis in Staphylococcus aureus
strains isolated from bovine subclinical mastitis
Authors: DALLA POZZA MARIA CRISTINA , RICCI ANTONIA , VICENZONI GADDO
Published: July 2002

Mammary infections caused by Staphylococcus aureus are still one of the most
serious problems in dairy farms all over the world (Sischo et al. 1993), and the
epidemiology of the infection has not yet been completely elucidated (Aarestrup et
al. 1995). Any effective modern approach to this disease must therefore be based on
more comprehensive epidemiological studies, conducted with valid microbiological
typing tools.

A technique for use in epidemiological studies should identify many types, and
should be inexpensive, quick and easy to perform, but above all reproducible. Among
the available methods, phage typing has up to now been widely and successfully used
in differentiating strains of Staph. aureus isolated from cattle with mastitis (Mackie
et al. 1987; Fox et al. 1991), but it has some limitations, being a technically
demanding method subject to considerable experimental as well as biological
variation (Maslow et al. 1993). Moreover, in some studies the number of strains that
could not be typed with available bacteriophage panels has been high (Carroll &
Francis, 1985; Farah et al. 1988).

Alternative methods have been investigated, and of these molecular techniques
have been the most intensely studied (Aarestrup et al. 1995). In studies of human
infections caused by Staph. aureus, analysis of the so-called X region of protein A
gene polymorphism has been a useful epidemiological marker (Frénay et al. 1994).
This gene is ∼2150 bp and harbours some functionally distinct regions: an FC-binding region, the so-called X region and, at the C terminus, a sequence required for
cell wall attachment (Guss et al. 1984; Frénay
et al. 1994). The X region
polymorphism depends on the presence, within the region itself, of a varying number
of 24 bp repeats, highlighted by the amplification of this highly polymorphic DNA
region and its subsequent restriction fragment length polymorphism (RFLP)
analysis (Frénay et al. 1994).

Human epidemic (MRSA) and non-epidemic methicillin-resistant Staph. aureus
(non-MRSA) strains, which both cause infections but have completely different
infection patterns, have been successfully distinguished by analysis of this
polymorphism (Frénay et al. 1994). However, protein A has been identified in only
93% of Staph. aureus strains isolated from bovine intramammary infections
(Poutrel & Ducelliez, 1979; Johne & Jarp, 1988).

The aim of the present study was to determine whether the gene for protein A of
Staph. aureus (Spa) was present in Staph. aureus strains isolated from cases of
subclinical bovine mastitis. This was carried out using the polymerase chain reaction
(PCR), as suggested by Frénay et al. (1994). In addition, we have investigated the
genetic polymorphism related to the X region of the gene, by means of PCR
amplification and subsequent RFLP analysis. Finally we verified the stability of this
region after in vitro subculture.
Effects of sodium fertilizers and supplements on milk production
and mammary gland health
Authors: PHILLIPS CLIVE J. C. , CHIY PAUL C. , ARNEY DAVID R. , KÄRT OLAV
Published: July 2002

A series of experiments was conducted to investigate the effects of sodium
fertilizers and supplements on the milk production and mammary health of dairy
cows. In Expt 1, where sodium fertilizer was applied to productive pastures
consisting mainly of the natrophile perennial rye-grass, the herbage sodium content
and the milk yield of cows was increased and milk somatic cell count (SCC) reduced.
In Expt 2, which used pastures containing less productive, natrophobic grasses and
broad-leaved plants in Estonia, sodium fertilizer did not increase herbage sodium
content and did not affect milk production or composition. In Expt 3 the sodium
content of the diet of individually tethered cows was increased from 1 to either 6 or
11 g/kg dry matter (DM) by adding salt to their restricted feed allowance, and the
cows' milk yield was increased by the high level of sodium supplement and milk SCC
were reduced by both levels of sodium supplement. The calcium and magnesium
status of cows was improved by the sodium supplement. In Expt 4 a low level of
supplementary salt was included in the ration of tethered cows to increase the
sodium content of the diet from 2 to 3·6 g/kg DM. No effects on milk yield or SCC
were found, but the sodium supplement reduced Staphylococcus aureus contamination
of the milk, but not the proportion of milk samples infected with Escherichia coli. It
was concluded that the optimum dietary sodium concentration for maximum milk
yield was greater than the published requirements, and that substantial increases in
sodium intake above current requirements also reduced milk SCC.
Inability of dairy propionibacteria to grow in milk from low inocula
Authors: PIVETEAU PASCAL , CONDON SÉAMUS , COGAN TIMOTHY M.
Published: July 2002

Growth of propionibacteria in complex media was independent of the
initial number of cells; in contrast, growth of propionibacteria in milk and whey did
not occur if the initial level of cells was <106 cfu/ml. Addition of vitamins, minerals
or complex nitrogen sources to the milk or whey, or incubation under anaerobic
conditions had no effect on the lack of growth. Addition of freeze-dried whey,
prepared from skim milk reconstituted from powder, to a complex medium
prevented growth from low inocula in the complex medium, demonstrating the
presence of an inhibitor or inhibitors in the whey. The inhibitor(s) was heat stable,
had a low molecular mass and retained its activity for at least 4 weeks at 20 °C.
Pregrowth of some lactic acid bacteria, used as starter cultures in Swiss-type cheese
manufacture, in milk for 2 weeks at 20 °C removed the inhibition, which explains
how propionibacteria develop in Swiss-type cheese from low numbers even though
they are inhibited in milk.
Drag on a sphere moving horizontally in a stratified fluid
Authors: GREENSLADE M. D.
Published: July 2002

The steady translational motion of a sphere in a Boussinesq stratified fluid, where
the motion is parallel to the stratification surfaces, is studied. A model based on
existing linear gravity wave theory for large Froude numbers and on new theory for
small Froude numbers is presented. The small-Froude-number theory describes wave
generation and the presence of a rectangular-section attached wake whose size and
shape is controlled by the size and shape of the wave generation regions. Existing
laboratory data are used to evaluate the model's prediction for the drag coefficient of
the sphere as a function of Froude number.
The three-dimensional structure of confined swirling flows with vortex breakdown
Authors: SOTIROPOULOS FOTIS , VENTIKOS YIANNIS
Published: July 2002

In a recent experimental study, Spohn, Mory & Hopfinger (1998) investigated in
detail the flow in a closed cylindrical container with a rotating bottom for Reynolds
numbers in the steady and unsteady regimes. Their visualization photographs revealed
that the stationary vortex breakdown bubbles, which form along the container axis
within a range of governing parameters, are open, with inflow and outflow, and
asymmetric at their downstream end. For Reynolds numbers within the unsteady
regime, visualizations of the limiting streamlines on the cylindrical wall showed that
the Stewartson layer separates asymmetrically along stationary spiral convergence
lines that form below the top cover. We study numerically the container flow, by
solving the unsteady, three-dimensional Navier–Stokes equations, in order to clarify
the origin and elucidate the underlying physics of these complex, three-dimensional
flow features. The stationary vortex breakdown bubbles we simulate exhibit all the
asymmetries observed in the laboratory. By analysing the Lagrangian characteristics
of the calculated flow fields, we explain the origin of these asymmetries, clarify the
experimentally documented filling and emptying mechanisms, and show that the
flow in the interior of stationary vortex breakdown bubbles exhibits chaotic particle
paths. We also show that the spiral separation lines observed by Spohn et al. (1998)
inside the Stewartson layer at high Reynolds numbers are due to the growth of
pairs of counter-rotating, spiral vortices and the interaction of these vortices with the
stationary-cover boundary layer.
Splash formation by spherical drops
Authors: LENG LIOW JONG
Published: July 2002

The impact of a spherical water drop onto a water surface has been studied experimentally
with the aid of a 35 mm drum camera giving high-resolution images that
provided qualitative and quantitative data on the phenomena. Scaling laws for the
time to reach maximum cavity sizes have been derived and provide a good fit to
the experimental results. Transitions between the regimes for coalescence-only, the
formation of a high-speed jet and bubble entrapment have been delineated. The
high-speed jet was found to occur without bubble entrapment. This was caused by
the rapid retraction of the trough formed by a capillary wave converging to the centre
of the cavity base. The converging capillary wave has a profile similar to a Crapper
wave. A plot showing the different regimes of cavity and impact drop behaviour in
the Weber–Froude number-plane has been constructed for Fr and We less than 1000.
On the preferential concentration of solid particles in turbulent channel flow
Authors: ROUSON DAMIAN W. I. , EATON JOHN K.
Published: July 2002

We present results from a direct numerical simulation of the passive transport of
solid particles by a fully developed turbulent channel flow with a Reynolds number
of 180 based on the friction velocity and the channel half-width. Three particle
sets are studied, ranging in diameter from 0.5 to 1.4 viscous wall units and in
aerodynamic time constant from 0.6 to 56 centreline Kolmogorov time scales. We
use particle number density histograms and fractal dimensions to show that the level
of order in the particle spatial distribution peaks near a Stokes number of unity
based on the Kolmogorov time scale. We then quantify the relationship between this
spatial distribution and the instantaneous flow topology. The results indicate that the
previously reported preferential concentration of particles in low-speed streaks leads
to a suppression of particle velocities in the viscous sublayer and buffer region even
in the presence of streamwise gravitational acceleration. In other regions of the flow,
the particles' non-random spatial distribution is shown to be uncorrelated with the
local flow topology. We compare our results with the experimental data of Kulick et
al. (1994) and Fessler et al. (1994) and confirm that the latter authors' results were
not influenced by turbulence modification.
Modelling the two-phase flow and current distribution along a vertical gas-evolving electrode
Authors: DAHLKILD ANDERS A.
Published: July 2002

The bubbly two-phase flow and electric current density distribution along a single,
vertical, gas-evolving electrode are modelled and the results of a boundary layer
analysis are presented. Existing empirical models for particle transport in sheared and
sedimenting suspensions are adopted for the bubble mixture to close the two-phase
model. Ionic species concentrations are shown to be essentially homogeneous as
the mixing effect of the bubble suspension usually is much larger than dispersion by
molecular diffusion even at laminar flow conditions. The non-uniformity of the bubble
distribution along the electrode results in a non-uniform current density distribution,
which agrees well with existing experimental findings in the literature.
Convection in directionally solidifying alloys under inclined rotation
Authors: CHUNG C. A. , CHEN FALIN
Published: July 2002

In an experiment on binary alloys directionally solidifying from below, Sample &
Hellawell (1984) showed that the plume convection can be successfully prohibited by
rotating the cooling tank around an inclined axis. In the present paper we interpret
their experimental observation by an analytical approach. Results show that there is a
flow induced by the inclination. The induced flow in the fluid layer is a parallel shear
flow consisting of three parts: the thermal boundary-layer flow, the solute boundary-
layer flow, and the Ekman-layer flow. In the mush, the induced flow is also a parallel
flow but of much smaller velocity, consisting of two flows of opposite directions. The
induced velocity in the fluid layer increases with inclination angle and decreases with
the effective Taylor number Te. The induced velocity in the mush also increases with
inclination angle but remains virtually the same on varying the speed of rotation. The
linear stability analysis of the mushy layer shows that, due mostly to the reduction
of buoyancy, the mush becomes more stable as the inclination angle increases. In the
precession-only case, the most-unstable mode of instability is the longitudinal mode,
which propagates in a direction perpendicular to the induced flow. In the spin (with
or without precession) case, the instability modes propagating in different directions
are of equal stability. Because the induced flow changes direction with a frequency
equal to the spin angular velocity, the flow scans over all the directions of the system
and stabilizes equally the modes in different directions. We conclude on the basis of
the present results and from the practical point of view that spin-only rotation is
more effective than the precession-only rotation in stabilizing the convection during
solidification.
Normal stresses and microstructure in bounded
sheared suspensions via Stokesian Dynamics simulations
Authors: SINGH ANUGRAH , NOTT PRABHU R.
Published: July 2002

We report the normal stresses in a non-Brownian suspension in plane Couette flow
determined from Stokesian Dynamics simulations. The presence of normal stresses
that are linear in the shear rate in a viscometric flow indicates a non-Newtonian
character of the suspension, which is otherwise Newtonian. While in itself of interest,
this phenomenon is also important because it is believed that normal stresses
determine the migration of particles in flows with inhomogeneous shear fields. We
simulate plane Couette flow by placing a layer of clear fluid adjacent to one wall
in the master cell, which is then replicated periodically. From a combination of
the traceless hydrodynamic stresslet on the suspended particles, the stresslet due to
(non-hydrodynamic) inter-particle forces, and the total normal force on the walls, we
determine the hydrodynamic and inter-particle force contributions to the isotropic
‘particle pressure’ and the first normal stress difference. We determine the stresses
for a range of the particle concentration and the Couette gap. The particle pressure
and the first normal stress difference exhibit a monotonic increase with the mean
particle volume fraction ϕ. The ratio of normal to shear stresses on the walls also
increases with ϕ, substantiating the result of Nott & Brady (1994) that this condition
is required for stability to concentration fluctuations. We also study the microstructure
by extracting the pair distribution function from our simulations; our results are in
agreement with previous studies showing anisotropy in the pair distribution, which is
the cause of normal stresses.
The normal field instability in ferrofluids: hexagon–square transition mechanism and wavenumber selection
Authors: ABOU BÉRENGÈRE , WESFREID JOSÉ-EDUARDO , ROUX STÉPHANE
Published: July 2002

When a ferrofluid layer is subjected to a uniform and vertically oriented magnetic
field, an interfacial instability occurs, above a critical value of the magnetic field,
giving rise to a hexagonal array of peaks. On increasing the magnetic field, a smooth
morphological transition from the hexagonal array to a square array was observed
above a second threshold. The hexagon–square transition phenomenology, in addition
to the role of penta–hepta defects initially present in the hexagonal pattern, was
investigated. Furthermore, the pattern and wavenumber selection was studied by two
different procedures: first by imposing jumps in field intensity and second by varying
the magnetic field in a quasi-static way. The results obtained were very different
for the two procedures. They indicated that the square pattern was a metastable
state induced by the compression of the hexagonal pattern on increasing the control
parameter. This hypothesis was confirmed by performing an additional experiment
where the pattern was isotropically compressed. In this experiment, the transition was
induced at a constant magnetic field lower than the transition onset value. However,
the theoretical values for stability domains of hexagons and squares proposed in the
literature were found to not agree with the experimental values.
Spatio-temporal behaviour in an enclosed corotating disk pair
Authors: RANDRIAMAMPIANINA ANTHONY , SCHIESTEL ROLAND , WILSON MICHAEL
Published: July 2002

We present a numerical investigation of the flow between corotating disks with a
stationary outer casing – the enclosed corotating disk pair configuration. It is known
that in such a geometry, axisymmetric and three-dimensional flow regimes develop
depending on the value of the rotation rate. The three-dimensional flow is always
unsteady flowing to its wavy structure in the radial-tangential plane. Axisymmetric
regimes exhibit first a pitchfork bifurcation, characterized by a symmetry breaking
with respect to the inter-disk midplane, before a Hopf bifurcation is established.
The regime diagrams for these bifurcations are given in the (Re, G)-plane, where
Re(= Ωb2/ν) is the rotational Reynolds number
and G(= s/(b−a)) is the gap ratio. For values of G
smaller than a critical limit Gc ∼ 0.26, there exists a range of rotation rates
where the motion becomes time-dependent before bifurcating to a steady symmetry
breaking regime. It is shown that for G [ges ] Gc the transition to
unsteady three-dimensional flow occurs after the pitchfork bifurcation, and the flow structure is
characterized by a shift-and-reflect symmetry. The transition to three-dimensional
flow is consistent with experimental observations made by Abrahamson et al. (1989)
where multiple solutions develop (known as the intransitivity phenomenon) with the
presence of quasi-periodic behaviour resulting from successive vortex pairings. On
the other hand, for smaller values of gap ratio, the three-dimensional flow shows
a symmetry breaking. Finally, it is found that the variation of torque coefficient as
a function of the rotation rate is the same for both the axisymmetric and three-dimensional solutions.
Mass flow and tangential momentum accommodation in silicon micromachined channels
Authors: ARKILIC ERROL B. , BREUER KENNETH S. , SCHMIDT MARTIN A.
Published: July 2002

High-precision experimental results are reported showing the tangential momentum
accommodation coefficient (TMAC) for several gases in contact with single-crystal
silicon to be less than unity. A precise and robust experimental platform is demonstrated
for measurement of mass flows through silicon micromachined channels due
to an imposed pressure gradient. Analytic expressions for isothermal Maxwellian slip
flows through long channels are used to determine the TMAC at a variety of Knudsen
numbers. Results from experiments using nitrogen, argon and carbon dioxide are
presented. For all three gases the TMAC is found to be lower than one, ranging from
0.75 to 0.85.
Magnetohydrodynamic turbulent flow in a channel at low magnetic Reynolds number
Authors: LEE DONGHOON , CHOI HAECHEON
Published: July 2002

Effects of the Lorentz force on near-wall turbulence structures are investigated using
the direct numerical simulation technique with the assumption of no induced magnetic
field at low magnetic Reynolds number. A uniform magnetic field is applied in the
streamwise (x), wall-normal (y) or spanwise (z) direction to turbulent flow in an
infinitely long channel with non-conducting walls. The Lorentz force induced from
the magnetic field suppresses the dynamically significant coherent structures near the
wall. The skin friction decreases with increasing streamwise and spanwise magnetic
fields, whereas it increases owing to the Hartmann effect when the strength of the
wall-normal magnetic field exceeds a certain value. All the turbulence intensities and
the Reynolds shear stress decrease with the wall-normal and spanwise magnetic fields,
but the streamwise velocity fluctuations increase with the streamwise magnetic field
although all other turbulence intensities decrease. It is also shown that the wall-normal
magnetic field is much more effective than the streamwise and spanwise magnetic fields
in reducing turbulent fluctuations and suppressing the near-wall streamwise vorticity,
even though the wall-normal magnetic field interacts directly with the mean flow
and results in drag increase at strong magnetic fields. In the channel with a strong
streamwise magnetic field, two-dimensional streamwise velocity fluctuations u(y, z)
exist, even after other components of the velocity fluctuations nearly vanish. In the
cases of strong wall-normal and spanwise magnetic fields, all turbulence intensities,
the Reynolds shear stress and vorticity fluctuations decrease rapidly and become
zero. The turbulence structures are markedly elongated in the direction of the applied
magnetic field when it is strong enough. It is shown that this elongation of the
structures is associated with a rapid decrease of the Joule dissipation in time.
On buoyancy-driven natural ventilation of a room with a heated floor
Authors: GLADSTONE CHARLOTTE , WOODS ANDREW W.
Published: July 2002

The natural ventilation of a room, both with a heated floor and connected to a
cold exterior through two openings, is investigated by combining quantitative models
with analogue laboratory experiments. The heated floor generates an areal source
of buoyancy while the openings allow displacement ventilation to operate. When
combined, these produce a steady state in which the air in the room is well-mixed,
and the heat provided by the floor equals the heat lost by displacement. We develop
a quantitative model describing this process, in which the advective heat transfer
through the openings is balanced with the heat flux supplied at the floor. This
model is successfully tested with observations from small-scale analogue laboratory
experiments. We compare our results with the steady-state flow associated with a
point source of buoyancy: for a given applied heat flux, an areal source produces
heated air of lower temperature but a greater volume flux of air circulates through
the room. We generalize the model to account for the effects of (i) a cooled roof
as well as a heated floor, and (ii) an external wind or temperature gradient. In
the former case, the direction of the flow through the openings depends on the
temperature of the exterior air relative to an averaged roof and floor temperature. In
the latter case, the flow is either buoyancy dominated or wind dominated depending
on the strength of the pressure associated with the wind. Furthermore, there is an
intermediate multiple-solution regime in which either flow regime may develop.
Computation of jet mixing noise due to coherent

structures: the plane jet case
Authors: BASTIN F. , LAFON P. , CANDEL S.
Published: July 2002

A computational approach to the prediction of jet mixing noise
is

described. It is based

on Lighthill's analogy, used together with a semi-deterministic modelling

of turbulence

(SDM), where only the large-scale coherent motion is evaluated. The features
of SDM

are briefly illustrated in the case of shear layers, showing that suitable

descriptions

of the mean flow and of the large-scale fluctuations are obtained. Aerodynamic

calculations of two cold fully expanded plane jets at Mach numbers 0.50
and 1.33 are

then carried out. The numerical implementation of Lighthill's analogy
is

described and

different integral formulations are compared for the two jets. It is shown
that

the one

expressed in a space–time conjugate (κ, ω)-plane is particularly

convenient and allows

a simple geometrical interpretation of the computations. Acoustic results
obtained

with this formulation are compared to relevant experimental data. It is
concluded

that the radiation of subsonic jets cannot be explained only by the contribution

of the turbulent coherent motion. In this case, directivity effects are
well

recovered but the

acoustic spectra are too narrow and limited to the low-frequency range.
In contrast

at Mach number 1.33, especially in the forward quadrant, results are satisfactory,

showing that coherent structures indeed provide the main source of supersonic
jet

mixing noise.
The effects of surfactant on the dynamics of bubble snap-off
Authors: TSAI T. M. , MIKSIS MICHAEL J.
Published: July 2002

The effects of an insoluble surfactant on the motion of a drop
or

bubble as it is

driven by a pressure gradient through a capillary tube is investigated
numerically.

We find that a drop in a straight capillary tube can either approach a
steady-state

shape or develop a re-entrant cavity at its rear. For a gas bubble moving
through a

constricted capillary tube, we find that snap-off can occur and surfactants
enhance

the snap-off process. The effects of the parameters on the dynamics of
bubble

snap-off are illustrated and discussed.
Two-dimensional long waves in turbulent flow
over a sloping bottom
Authors: GWINN ALLAN W.
Published: July 2002

We investigate weakly two-dimensional weakly nonlinear weakly
dispersive surface
waves propagating in a turbulent flow over a gradually sloping bottom. The waves
are shown to be governed by a turbulently damped variable-coefficient
Kadomtsev–Petviashvili equation with periodic boundary conditions.
Equations governing the
lowest-order mean currents in both directions as well as the equation describing the
lowest-order mean surface elevation are also derived. Solutions for the wave equation
are found numerically using a Fourier pseudospectral technique in space and finite
differencing in the time-like variable.