bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of frequent machine milking and suckling

in early lactation on blood plasma ion homoeostasis

in high-yielding dairy cows
Authors: BAR-PELED U. , MALTZ E. , TAGARI H. , LEHRER A.-R. , ROBINZON B. , VOET H. , FOLMAN Y. , BRUCKENTAL I. , GACITUA H. , SILANIKOVE N.
Published: July 2002

Groups of nine or ten cows were assigned, after calving, to treatments

in which they were (i) machine

milked three times daily (M3), (ii) machine milked six times daily (M6)
or

(iii) suckled three times

daily in addition to being machine milked three times daily (S). Treatments

were administered during

the first 6 weeks postpartum. On one day, at weeks 1 and 6 postpartum,

blood samples were collected

from all cows at 30-min intervals between 06.00 and 13.00 h and these

were analysed for plasma

osmolality and plasma concentrations of Na+, K+

and Cl−. Milk yield was significantly higher in

suckled cows than in cows milked six times daily, but significantly

lower in cows milked three times

daily. In cows milked six times daily, and to a greater extent in suckled

cows, there was a reduction

in plasma osmolality and monovalent ion concentrations (Na+,

K+ and Cl−), which could increase the

susceptibility of the cows to water intoxication. Moreover, suckling or

milking the cows six times

daily was associated with increased fluctuations in plasma osmolality and
plasma

Cl− concentrations.

The decrease in plasma osmolality and ion concentration and the increased

variation in plasma osmolality and Cl−

were probably related to increased water intake and may be indicative of
a severe

challenge to homoeostasis regulation.
A comparison of animal output and nitrogen leaching

losses recorded from drained fertilized grass and

grass/clover pasture
Authors: TYSON K. C. , SCHOLEFIELD D. , JARVIS S. C. , STONE A. C.
Published: July 2002

Annual liveweight gain of beef cattle (steers) grazing grass pasture

fertilized with 200 kg N/ha was

compared over a period of 7 years (1989–95) with that of

steers grazing grass/white clover pasture

given no artificial N fertilizer at North Wyke, Devon, UK. Nitrogen lost

by leaching over the ensuing

winter drainage periods was monitored from both pastures. Nitrogen leaching

loss from the fertilized

pasture over an extended period of 13 years (1983–95) is also reported.

The average annual liveweight gain of the steers grazing the

grass/clover pasture (0·81 t/ha) was

19% lower than that of the steers grazing the N-fertilized

grass pasture (1·00 t/ha). The average

annual loss of nitrate-N by leaching in winter drainage from

the grass/clover pasture (13 kg/ha) was

only 26% of that recorded from the fertilized grass (50 kg/ha).

A possible reason for this difference

may arise from the previous history of the grass/clover

pasture which had been ploughed in 1982,

causing a flush of N mineralization and consequently greater immobilization

of N in the soil in subsequent years.

Losses of N each winter by leaching measured over a 13-year period from

the fertilized grass were

highly correlated (P<0·001) with the preceding

summer's soil moisture deficit, with the highest losses

following dry summers. The nitrate-N concentration in

the drainage water exceeded the European

Union limit in drinking water (11·3 mg/l) in the

initial 25 mm of drainage during 11 of the 13

autumns. The average loss of N each winter (53 kg/ha) was

equivalent to 26% of the fertilizer-N

applied annually. Immediate losses of N by leaching of fertilizer applied

in early spring and

throughout one very wet summer (1993) were minimal.
Yield and partitioning in crops of contrasting cultivars

of winter wheat in response to CO2 and temperature in

field studies using temperature gradient tunnels
Authors: BATTS G. R. , ELLIS R. H. , MORISON J. I. L. , NKEMKA P. N. , GREGORY P. J. , HADLEY P.
Published: July 2002

Diverse cultivars of winter wheat (Triticum

aestivum L.) were grown in the field in 1993/94 and

1994/95 at Reading UK in temperature gradient tunnels

at normal atmospheric (c. 370) or elevated

CO2 concentration (c.

700 μmol CO2 mol−1

air). In 1993/94, grain yield of cv. Avalon was insensitive

to mean temperature (between 8·8 and 10·9°C),

while elevated CO2 increased yield by

1·3 t ha−1

(12·6%). In all other cultivars, warming reduced

grain yield and CO2 increased grain yield. In

1993/94, in cvs Galahad and Mercia the effects of

CO2 and temperature on yield were additive.

However, for cv. Hereward in both years and for cv.

Soissons in 1994/95, there were negative

interactions between the effects of CO2 and

temperature on yield: the maximum benefit of doubling

CO2 to grain yield, 4·5 and

2·7 t ha−1

(65 and 29%) respectively, occurred at cooler temperatures;

there was no benefit from doubling CO2 (i.e. 0%)

once the temperature had increased above the

seasonal mean by 2·2–2·6°C in cv.

Hereward and by 1·3°C in cv. Soissons. The

beneficial effect of doubling CO2 on grain yield

in cvs Galahad, Hereward, Mercia and Soissons was negated by an

increase in mean seasonal temperature of only

0·7–2·0°C. Warming

decreased root dry mass at anthesis in 1994/95 while

it increased at elevated CO2 (49 and 186%,

coolest and warmest regime, respectively). Carbon partitioned

to roots declined progressively with warming, while at

elevated CO2 there was an average of 56% increase

in allocation to roots. The relative impacts of both

CO2 and temperature were greater on root dry

mass than on either grain yield or total above-ground biomass,

while the effects on grain and biomass yield varied

considerably between cultivars, suggesting that the

impact of rising CO2 and temperature are

likely to be dependent on cultivar.
Controlled-temperature effects on cotton growth and development
Authors: ROUSSOPOULOS D. , LIAKATAS A. , WHITTINGTON W. J.
Published: July 2002

The growth and development of cotton was studied on cotton plants

grown in pots in growth rooms
under constant day/night temperature (C) and varying temperature regimes
throughout the day
and/or night (V) The V-treatments had a common mean temperature
of 22°C. The objectives were
to determine the thermal requirements of three cultivars and to observe
the extent of
genotype×thermal environment interactions throughout the entire growth
period.

Vegetative growth was found to be almost exclusively time and
temperature dependent, varietal
differences being largely insignificant. Plant material was found
to accumulate four times faster under
the warmest C-regime, which was 7°C warmer than the coolest. The
C-treatments caused variation
in the number and size of lateral shoots and leaves, causing leaf
area to be larger at the squaring stage
in cool environments but at maturity in warm regimes. Relatively
cool nights lowered the position of
the first floral or fruiting branch, whereas warm days shortened flowering
intervals and thus
promoted earliness. However, the effect of temperature in altering
the position of the first floral
branch seems to be less important than its effect on the shedding of early
squares.

The effects of fluctuating temperature (V) on vegetative growth and

earliness were similar to those
from constant temperature environments. Growth and development rates were
low in the low
minimum V-regimes, especially when the maximum temperature was also low.
Temperature variation
affected vegetative growth to a greater extent in the early than
in the later stages of development. At
squaring, leaf area and dry weight were lowest under the regime with the
highest minimum and
maximum temperatures. Later on, only leaf area at flowering and total dry
weight at maturity
significantly differed between treatments. High maximum or
minimum temperatures produced effects
similar to a higher or lower mean temperature, respectively. The low minimum
raised the node
number of the first floral or fruiting branch, whereas in the
case of boll dry weight it acted in the same
way as a further drop in temperature, decreasing the weight,
regardless of the maximum temperature.
Boll period was affected mainly by the temperature variation itself rather
by than the type of
variation.

The inverse of time to a certain stage and the corresponding mean
temperature were linearly related
and allowed threshold temperatures (T0) and thermal

time requirements to be estimated. T0=12°C,
except for the initial stage, when it was lower. A cotton growing
season cooler on average by only
1°C will considerably delay maturity.
The feeding value of chicory (Cichorium intybus) for
ruminant livestock
Authors: BARRY T. N.
Published: July 2002

Chicory (Cichorium intybus) is perhaps best known
for the extract of its roots used as an ingredient in
‘coffee substitute’ beverages. It is less well known as
a grazed forage for ruminants. Thomas et al. (1952)
reported the high content of some major and minor
trace minerals in chicory grown in the UK, and
commented on its use in pasture mixtures as a source
of these minerals. Chicory was first mentioned in New
Zealand (NZ) literature as an animal forage by
Cockayne (1915), but a long period then elapsed
before Lancashire (1978) reported its excellent value
for forage production under rotational grazing in dry
summer conditions. Plant selection then followed and
the cultivar ‘Grasslands Puna’ was approved for
commercial release as a grazed forage plant in 1985
(Rumball 1986). The use of Puna chicory has now
spread throughout NZ and the variety is also being
used commercially in Australia, North America and
South America and is being evaluated in parts of
Europe and Asia (W. Green, personal communication). Chicory is a herb,
whereas other temperate
forages used for ruminant production are either
grasses or legumes. This paper reviews work on the
chemical composition, nutritive value and feeding
value of chicory relative to perennial ryegrass (Lolium
perenne) and to red clover (Trifolium pratense), a
legume that, like chicory, is used as a forage for dry
summer conditions. Throughout this paper, feeding
value is defined as the animal production response to
grazing a forage under unrestricted conditions (Ulyatt
1973), with its components being voluntary feed
intake (VFI), the digestive process and the efficiency
of utilization of digested nutrients; the latter two
comprise nutritive value/dry matter (DM) eaten.
STABILITY OF MARITAL UNIONS AND FERTILITY IN NIGERIA
Authors: ISIUGO-ABANIHE UCHE C.
Published: July 2002

Using nationally representative data, it is shown that marital unions are relatively stable in Nigeria. Remarriage rates are high so little time is lost between unions. Consequently, the fertility of women who have experienced marital disruption is only slightly lower than for those in stable unions. Their slightly lower parity may be a function of a high incidence of reproductive impairment, which is a major reason for divorce and separation in Nigeria.
Effect of storage at 4 °C on the physicochemical and renneting
properties of milk: a comparison of caprine, ovine and bovine milks
Authors: RAYNAL KETSIA , REMEUF FLORENT
Published: July 2002

The effects of cold storage at 4 °C for 12, 24 and 48 h on the
physicochemical characteristics and renneting properties of ewes', goats' and cows'
milks were compared. The most important changes were observed in cows' milk.
Soluble calcium concentrations were not affected in ewes' milk but were increased by
10% in cows' milk and 7% in goats' milk. More casein was dissociated on cooling
cows' (+300%) than goats' (+100%) milk, and there was no change in soluble
casein in ewes' milk. The coagulation characteristics of cows' milk were more
impaired by cold storage than goats' or ewes' milks. Coagulation times increased by
∼30% and whey draining capacity decreased by 40% after cows' milk was cooled,
but there were no changes with ewes' milk and only a slight decrease in coagulation
time with goats' milk. We propose an interpretation of these results based on the
physicochemical properties of each type of milk.
Application of polymerase chain reaction for detection of goats' milk adulteration by milk of cow
Authors: BANIA JACEK , UGORSKI MACIEJ , POLANOWSKI ANTONI , ADAMCZYK ERYK
Published: July 2002

Numerous methods based on DNA analysis have been employed in the food
industry to monitor adulterations of food products of animal origin. Among them the
most frequently used are: polymerase chain reaction (PCR) amplification of a marker
gene fragment(s) with universal primers, or amplification of DNA with species-specific
primers. PCR-products of different origin can be discriminated by size, restriction
fragment length polymorphism (RFLP) or single stranded conformational polymorphism
(SSCP) analysis. These methods have been used for identification, and
differentiation between, the animal origins of raw or heat-treated meat and meat
products (Chikuni et al. 1994; Meyer et al. 1994, 1995; Zehner et al. 1998; Behrens et
al. 1999; Guoli et al. 1999; Hopwood et al. 1999; Matsunaga et al. 1999; Wolf et al.
1999). These approaches are also applicable to the analysis of dairy products.
However, adulterations of goats' milk and its products are traditionally tested by
immunological and/or electrophoretic methods (Amigo et al. 1992; Levieux &
Venien, 1994; Mimmo & Pagani, 1998). So far, only a few DNA-based techniques
designed to detect the presence of bovine DNA in goats' milk have been described
(Plath et al. 1997; Branciari et al. 2000). This paper presents a one-step PCR
procedure for detection of adulteration of goats' milk with cows' milk. The method,
employing bovine-specific primers for amplification of a 274 bp fragment of
cytochrome b DNA, seems to be simple, fast, specific and sensitive.
Molecular self-assembly of partially hydrolysed α-lactalbumin resulting in strong gels with a novel microstructure
Authors: IPSEN RICHARD , OTTE JEANETTE , B. QVIST KARSTEN
Published: July 2002

Gelation of α-lactalbumin (α-la) incubated with a protease from Bacillus licheniformis (BLP) at 50 °C for 4 h was monitored using small oscillatory shear and the large deformation properties of final gels were characterized by uniaxial compression. Transmission electron microscopy was used to visualize the microstructure. Gels made from α-la (10 g/l) using BLP were almost transparent, although somewhat whitish, and they were more than 20 times stiffer (measured as complex modulus) than equivalent gels made from β-lactoglobulin (β-lg) at the same concentration. The microstructure of the gels consisted of non-branching, apparently hollow strands with a uniform diameter close to 20 nm, similar in overall structure to microtubules. Adding Ca2+ in amounts of 50 or 100 mM changed the spatial distribution of the strands and resulted in a reduction in the failure stress recorded in uniaxial compression. Apart from affecting the microstructure, Ca2+ was shown to be essential for the formation of the gels. It is proposed, that the mechanism behind the self-assembly of the partially hydrolysed α-la into long tubes is a spatially restricted creation of ionic bonds between Ca2+ and carboxyl acid groups on peptide fragments resulting from the action of BLP on α-la. Proteolysis of α-la with BLP in the presence of Ca2+ thus results in formation of a strong gel with a microstructure not previously observed in food protein systems.
Streptococcus thermophilus in Cheddar cheese – production and fate of galactose
Authors: MICHEL VALÉRIE , MARTLEY FRANK G.
Published: July 2002

The behaviour of Streptococcus thermophilus in combination with Lactococcus lactis subsp. cremoris or subsp. lactis mesophilic starters in experimental Cheddar cheese is reported. In a standard manufacturing procedure employing a 38 °C cook temperature, even very low levels (0·007%) of Str. thermophilus combined with normal levels of the mesophilic starter (1·7%) resulted in increased rates of acid production, the formation of significant amounts of galactose (∼ 13 mmol/kg cheese), and populations nearly equivalent to those of the mesophilic lactic starter in the curd before salting. At a 41 °C cook temperature, the Str. thermophilus attained a higher maximum population (∼ log 8·2 colony forming units (cfu)/g) than the Lc. lactis subsp. cremoris (∼ log 6·8 cfu/g) and formed more galactose (∼ 28 mmol/kg). Lactobacillus rhamnosus, deliberately added to a cheese made using Str. thermophilus starter and which contained 24 mmol galactose/kg at day one, utilized all the galactose during the first 3 months of cheese ripening. Adventitious non-starter lactic acid bacteria had the potential to utilize this substrate too, and a close relationship was demonstrated between the increase in this flora and the disappearance of the galactose. Some possible consequences for cheese quality of using Str. thermophilus as a starter component are discussed.
Digestive utilization of goat and cow milk fat in malabsorption syndrome
Authors: ALFÉREZ M. J. M. , BARRIONUEVO M. , LÓPEZ ALIAGA I. , SANZ-SAMPELAYO M. R. , LISBONA F. , ROBLES J. C. , CAMPOS M. S.
Published: July 2002

We studied the effects of goat and cow milk fat on the digestive utilization of this nutrient and on some of the biochemical parameters that are related to the metabolism of lipids, using rats with a resection of 50% of the distal small intestine and control animals (transected). The fat content in all the diets was 10% but the lipid quality was varied: the standard diet was based on olive oil, while the other two diets included fat obtained from lyophilized goat milk and cow milk, respectively. The digestive utilization of the fat was lower in the resected animals than in the transected ones for all three diets studied. In both resected and transected animals, the apparent digestibility coefficient (ADC) of the fat was greater with the standard diet (olive oil) than with diets whose fat content was provided by goat or cow milk. The digestive utilization of the fat was greater in the transected and resected rats receiving a diet of goat's milk (rich in medium-chain triglycerides) than those given a cow-milk-based diet, and more closely approached the values obtained for olive oil. The consumption of goat milk reduced levels of cholesterol while levels of triglycerides, HDL, GOT and GPT remained within the normal ranges, for both transected and resected animals. The advantageous effect of goat milk on the metabolism of lipids with respect to cow milk suggests that the former should be included in the diet in cases of malabsorption syndrome.
Trace elements and their distribution in protein fractions of camel milk in comparison to other commonly consumed milks
Authors: AL-AWADI FARIDA M. , SRIKUMAR T. S.
Published: July 2002

Studies on camels' milk, whether with respect to concentration or bioavailability of trace elements from this milk, are limited and warrant further investigation. The object of this study was to analyse the concentration and distribution of zinc, copper, selenium, manganese and iron in camel milk compared to those in human milk, cows' milk and infant formula under similar experimental conditions. Camels' milk and cows' milk were collected from local farms, human milk samples were obtained from healthy donors in Kuwait and infant formula was purchased locally. Milk fractionation was performed by ultra-centrifugation and gel-column chromatography. The concentration of trace elements was analysed by atomic absorption spectrometry and that of protein was determined spectrophotometrically. The concentration of manganese and iron in camels' milk was remarkably higher (7–20-fold and 4–10-fold, respectively) than in human milk, cows' milk and infant formula. The zinc content of camels' milk was higher than that of human milk but slightly lower than in cows' milk and infant formula. The concentration of copper in camels' milk was similar to that of cows' milk but lower than in human milk and infant formula. The selenium content of camels' milk was comparable to those of other types of milk. Approximately 50–80% of zinc, copper and manganese in camels' milk were associated with the casein fraction, similar to that of cows' milk. The majority of selenium and iron in camels' milk was in association with the low molecular weight fraction. It is recommended that camels' milk be considered as a potential source of manganese, selenium and iron, perhaps not only for infants, but also for other groups suspected of mild deficiency of these elements. Further investigations are required to confirm this proposal.
Characterization of the lactic acid bacteria in artisanal dairy products
Authors: COGAN TIMOTHY M. , BARBOSA MANUELA , BEUVIER ERIC , BIANCHI-SALVADORI BRUNA , COCCONCELLI PIER S. , FERNANDES ISABEL , GOMEZ JESUS , GOMEZ ROSARIO , KALANTZOPOULOS GEORGE , LEDDA ANTONIO , MEDINA MARGARITA , REA MARY C. , RODRIGUEZ EVA
Published: July 2002

In all, 4379 isolates from 35 products, including 24 artisanal cheeses, were
surveyed with a view to identifying strains that could be used as starters in
commercial dairy fermentations. Of the isolates, 38% were classified as
Lactococcus,
17% as Enterococcus, 14% as Streptococcus thermophilus,
12% as mesophilic
Lactobacillus, 10% as Leuconostoc and 9% as thermophilic
Lactobacillus. Acid
production by the isolates varied considerably. Of the 1582 isolates of
Lactococcus
and 482 isolates of mesophilic Lactobacillus tested, only 8 and
2% respectively
produced sufficient acid to lower the pH of milk to <5·3 in 6 h
at 30°C. In contrast,
53, 32 and 13% of Str. thermophilus, thermophilic Lactobacillus
and Enterococcus
isolates respectively reduced the pH to 5·3. These isolates were
found only in some
French, Italian and Greek cheeses. Bacteriocins were produced by 11% of the 2257
isolates tested and 26 of them produced broad-spectrum bacteriocins which inhibited
at least eight of the ten target strains used, which included lactic acid bacteria,
clostridia and Listeria innocua. The most proteolytic of the 2469
isolates tested were
Str. thermophilus from Fontina cheese followed by Enterococcus
from Fiore Sardo and
Toma cheese and thermophilic Lactobacillus from all sources.
Exopolysaccharides
were produced by 5·3% of the 2224 isolates tested.
Effects of white clover content in the diet on herbage intake, milk

production and milk composition of New Zealand dairy cows housed indoors
Authors: HARRIS SHARON L. , AULDIST MARTIN J. , CLARK DAVID A. , JANSEN ERNA B. L.
Published: July 2002

The effect of the proportion of clover in the diet (200, 500 or
800 g/kg
total dry matter (DM)) on milk production of cows housed indoors and fed
on a
mixture of perennial rye-grass and white clover was measured in mid (Expt
I) and
late (Expt II) lactation. Higher clover contents increased the nutritive
value of the
diets, resulting in increased energy and protein intakes. DM intakes of
cows offered
500 or 800 g clover/kg DM diets ad lib. (Expt I and Expt II,
Period 1) were not
significantly different but were 11–17% greater
(P<0·05) than intakes of cows fed
on 200 g clover/kg total DM diets. Cows offered restricted allowances
(Expt II,
Period 2) had similar intakes irrespective of diet. In Expt I cows fed
on 500 or 800 g
clover/kg DM diets ad lib. produced 30 or 33% respectively
more milk
(P<0·05)
than cows fed on 200 g clover/kg total DM diets. During Expt II, Period
1, cows fed
on 500 or 800 g clover/kg DM diets ad lib. produced 18 or
16% more milk
(P<0·05)
respectively than cows given 200 g clover/kg total DM diets. In both
these
experiments the increased milk yields were due to increased intake and
the higher
nutritive value of the high clover diets. There was no difference in the
feed conversion
efficiencies of cows if maintenance energy requirements were taken into
account.
However, cows on restricted allowances (Expt II, Period 2) showed no significant

difference in milk yield, indicating that the effect of increased nutritive
value was
very slight. There were no consistent effects on milk fat, protein or lactose

concentrations. Concentrations of blood and milk urea increased as the
clover
content of the diet increased (Expt 1 only), and this was associated with
increased
milk non-protein N and a decreased ratio of casein N[ratio ]total N. Both
trials indicated
an optimum clover content in the diet for milk production of 600–700
g/kg total DM.
Kinetics of the renneting reaction followed by measurement of
turbidity as a function of wavelength
Authors: LOMHOLT STIG B. , WORNING PEDER , ØGENDAL LARS , QVIST KARSTEN B. , HYSLOP DOUGLAS B. , BAUER ROGERT
Published: July 2002

In order to describe the kinetics of rennet coagulation, measurements
of
turbidity as a function of wavelength were used to determine the weight-average
degree of polymerization, x¯w,
during renneting of milk at three different concentrations
of enzyme and three concentrations of casein, including the normal casein
concentration of milk. The change of x¯w
as a function of time was described using Von
Smoluchowski's equation, testing a number of expressions for the aggregation
rate
constant, kij. The best description was
achieved when kij was taken as a function
of
an energy barrier against aggregation that was diminished by the proteolysis
of
κ-casein. The initial value of the energy barrier partly depended
on the casein
concentration, and had a value >25 kBT at
normal casein concentration, where kB
is Boltzmann's constant and T the absolute temperature. When
the proteolysis of
κ-casein was complete, the energy barrier was reduced to
11 kBT and was independent of casein concentration.
Production of calcium-reduced milks using an ion-exchange resin
Authors: PREMLAL RANJITH H. M. , LEWIS MIKE J. , MAW DAVID
Published: July 2002

Ion exchange is used commercially in such processes as water softening,
chemical
purification, separation of ionic from non-ionic forms and analytical applications.
Van Kreveld & van Minnen (1955) reported a method for the determination
of
Ca2+ and Mg2+
activity in milk using an ion-exchange resin. From this early work, it
was
established that with suitable resins exchange of salts was possible in
milk, permeate
and whey. This included the exchange of Ca and Mg from micelles by using
Na+ or K+. Cationic resins of the Zerolit
236 type have been used successfully in the
production of Ca-reduced single cream (Anderson et al. 1976).
Such treatment prior
to UHT processing was shown to increase physical stability when it was
used as a
coffee whitener. There is evidence that reduction of Ca2+ would
also reduce the
deposit formation that may occur during storage of UHT milk. Thus there
is a need
to establish commercial techniques to produce Ca-adjusted milks that could
then be
used as raw materials for industrial applications or product development
work.

The present study investigated the use of ion exchange to reduce Ca
in milk with
particular reference to understanding the exchange of salts in Ca-reduced
milk and
the changes to some of its physical properties.
Pressure denaturation and aggregation of β-lactoglobulin studied by
intrinsic fluorescence depolarization, Rayleigh scattering,
radiationless energy transfer and hydrophobic fluoroprobing
Authors: STAPELFELDT HENRIK , SKIBSTED LEIF H.
Published: July 2002

β-Lactoglobulin (β-lg) in aqueous solution under pressure showed a
marked depolarization of intrinsic fluorescence assigned to a gradually increased
rotational diffusion of tryptophyl moieties in pressure-unfolded states. The
corresponding change in anisotropy provided a new and more accurate method for
determining denaturation volume which, for β-lg in neutral aqueous solution with
ionic strength 0·16 (NaCl) at 25 °C, was ΔV°=−73
(SE 3) ml mol−1, corresponding
to half denaturation at 123 MPa. The pressure unfolding led to exposure of
hydrophobic regions to the protein–water interface that could be probed by
fluorescence intensity of a β-lg–1-anilinonaphthalene-8-sulphonic acid (ANS)
complex with 1:1 stoichiometry, as determined by Job's method of continuous
variation. The unfolding of β-lg impaired the binding capacity of the inner calyx,
with a reduction in binding capacity of 50% at 50 MPa, as shown by decreasing cis-
parinaric acid fluorescence, decreasing anisotropy and decreasing radiationless
energy transfer from tryptophans to this probe with increasing pressure. The
pressure-induced reversible exposure of hydrophobic groups to the protein–water
interface may, at least partly, explain the initial aggregation reactions, evident
from increased Rayleigh scattering from ∼50 MPa, prior to irreversible pressure-induced gel formation of β-lg. Using results from this and previous studies, we
propose a three step pressure denaturation model for β-lg for neutral solution at
ambient temperature, including an initial pressure-melted state (up to 50 MPa) with
partial collapse of the inner calyx and solvent exposure of the free thiol group,
followed by a reversible denaturation with exposure of hydrophobic regions (half
denaturation at 123 MPa) and with irreversible denaturation with thiol–disulphide
exchange becoming increasingly important at higher pressures. Effects of pressure on
β-lg, as measured by fluorescence depolarization, were found for the reversible
denaturation steps to be similar to the effects of chemical denaturants but different
with respect to shift in ANS emission maxima.
Vortex organization in the outer region of the turbulent boundary layer
Authors: ADRIAN R. J. , MEINHART C. D. , TOMKINS C. D.
Published: July 2002

The structure of energy-containing turbulence in the outer region of a zero-pressure-
gradient boundary layer has been studied using particle image velocimetry (PIV) to
measure the instantaneous velocity fields in a streamwise-wall-normal plane. Experiments
performed at three Reynolds numbers in the range 930 < Reθ < 6845 show
that the boundary layer is densely populated by velocity fields associated with hairpin
vortices. (The term ‘hairpin’ is here taken to represent cane, hairpin, horseshoe, or
omega-shaped vortices and deformed versions thereof, recognizing these structures are
variations of a common basic flow structure at different stages of evolution and with
varying size, age, aspect ratio, and symmetry.) The signature pattern of the hairpin
consists of a spanwise vortex core located above a region of strong second-quadrant
fluctuations (u < 0 and v > 0) that occur on a locus
inclined at 30–60° to the wall.

In the outer layer, hairpin vortices occur in streamwise-aligned packets that propagate
with small velocity dispersion. Packets that begin in or slightly above the buffer
layer are very similar to the packets created by the autogeneration mechanism (Zhou,
Adrian & Balachandar 1996). Individual packets grow upwards in the streamwise
direction at a mean angle of approximately 12°, and the hairpins in packets are typically
spaced several hundred viscous lengthscales apart in the streamwise direction.
Within the interior of the envelope the spatial coherence between the velocity fields
induced by the individual vortices leads to strongly retarded streamwise momentum,
explaining the zones of uniform momentum observed by Meinhart & Adrian
(1995). The packets are an important type of organized structure in the wall layer
in which relatively small structural units in the form of three-dimensional vortical
structures are arranged coherently, i.e. with correlated spatial relationships, to form
much longer structures. The formation of packets explains the occurrence of multiple
VITA events in turbulent ‘bursts’, and the creation of Townsend's (1958) large-scale
inactive motions. These packets share many features of the hairpin models proposed
by Smith (1984) and co-workers for the near-wall layer, and by Bandyopadhyay
(1980), but they are shown to occur in a hierarchy of scales across most of the
boundary layer.

In the logarithmic layer, the coherent vortex packets that originate close to the wall
frequently occur within larger, faster moving zones of uniform momentum, which may
extend up to the middle of the boundary layer. These larger zones are the induced
interior flow of older packets of coherent hairpin vortices that originate upstream
and over-run the younger, more recently generated packets. The occurence of small
hairpin packets in the environment of larger hairpin packets is a prominent feature
of the logarithmic layer. With increasing Reynolds number, the number of hairpins
in a packet increases.
Simulations of bypass transition
Authors: JACOBS R. G. , DURBIN P. A.
Published: July 2002

Bypass transition in an initially laminar boundary layer beneath free-stream turbulence
is simulated numerically. New perspectives on this phenomenon are obtained
from the numerical flow fields. Transition precursors consist of long backward jets
contained in the fluctuating u-velocity field; they flow backwards relative to the local
mean velocity. The jets extend into the upper portion of the boundary layer, where
they interact with free-stream eddies. In some locations a free-stream perturbation to
the jet shear layer develops into a patch of irregular motion – a sort of turbulent spot.
The spot spreads longitudinally and laterally, and ultimately merges into the downstream
turbulent boundary layer. Merging spots maintain the upstream edge of the
turbulent region. The jets, themselves, are produced by low-frequency components of
the free-stream turbulence that penetrate into the laminar boundary layer. Backward
jets are a component of laminar region streaks.

A method to construct turbulent inflow from Orr–Sommerfeld continuous modes
is described. The free-stream turbulent intensity was chosen to correspond with the
experiment by Roach & Brierly (1990). Ensemble-averaged numerical data are shown
to be in good agreement with laboratory measurements.
Measurements of the average properties of a suspension of bubbles rising in a vertical channel
Authors: ZENIT ROBERTO , KOCH DONALD L. , SANGANI ASHOK S.
Published: July 2002

Experiments were performed in a vertical channel to study the behaviour of a
monodisperse bubble suspension for which the dual limit of large Reynolds number
and small Weber number was satisfied. Measurements of the liquid-phase velocity
fluctuations were obtained with a hot-wire anemometer. The gas volume fraction,
bubble velocity, bubble velocity fluctuations and bubble collision rate were measured
using a dual impedance probe. Digital image analysis was performed to quantify the
small polydispersity of the bubbles as well as the bubble shape.

A rapid decrease in bubble velocity with bubble concentration in very dilute
suspensions is attributed to the effects of bubble–wall collisions. The more gradual
subsequent hindering of bubble motion is in qualitative agreement with the predictions
of Spelt & Sangani (1998) for the effects of potential-flow bubble–bubble interactions
on the mean velocity. The ratio of the bubble velocity variance to the square of the
mean is O(0.1). For these conditions Spelt & Sangani predict that the homogeneous
suspension will be unstable and clustering into horizontal rafts will take place.
Evidence for bubble clustering is obtained by analysis of video images. The fluid
velocity variance is larger than would be expected for a homogeneous suspension and
the fluid velocity frequency spectrum indicates the presence of velocity fluctuations
that are slow compared with the time for the passage of an individual bubble. These
observations provide further evidence for bubble clustering.
Stability of thermocapillary flows with inclined temperature gradient
Authors: NEPOMNYASHCHY ALEXANDER A. , SIMANOVSKII ILYA B. , BRAVERMAN LEONID M.
Published: July 2002

The stability of a two-layer return thermocapillary flow in the presence of an inclined
temperature gradient is investigated. Both a linear stability analysis and nonlinear simulations
have been performed for an air–water system. It is found that a rather weak
deviation of the mean temperature gradient from the vertical direction suppresses
Pearson's instability mechanism and leads to the appearance of oblique hydrothermal
waves. In a certain region of parameters, transverse convective rolls drifting with the
mean flow appear.
Surface flow of granular materials: model and experiments in heap formation
Authors: KHAKHAR D. V. , ORPE ASHISH V. , ANDRESÉN PETER , OTTINO J. M.
Published: July 2002

Granular surface flows are important in industrial practice and natural systems, but
the understanding of such flows is at present incomplete. We present a combined theoretical
and experimental study of quasi-two-dimensional heap formation by pouring
particles continuously at a point. Two cases are considered: open systems and closed
systems. Experimental results show that the shear rate in the flowing layer is nearly
independent of the mass flow rate, and the angle of static friction at the bed–layer
interface increases with flow rate. Predictions of the model for the flowing layer
thickness and interface angles are in good agreement with experiments.
An ‘ideal’ form of decaying two-dimensional turbulence
Authors: IWAYAMA TAKAHIRO , SHEPHERD THEODORE G. , WATANABE TAKESHI
Published: July 2002

In decaying two-dimensional Navier–Stokes turbulence, Batchelor's similarity
hypothesis fails due to the existence of coherent vortices. However, it is shown that
decaying two-dimensional turbulence governed by the Charney–Hasegawa–Mima (CHM)
equation

(∂/∂t)(∇2φ−λ2φ)
+J(φ, ∇2φ) = D,

where D is a damping, is described well by Batchelor's similarity hypothesis for wave
numbers k [Lt ] λ (the so-called AM regime). It is argued that CHM turbulence in the
AM regime is a more ‘ideal’ form of two-dimensional turbulence than is Navier–Stokes
turbulence itself.
Direct numerical simulation of turbulent flow over a

backward-facing step
Authors: LE HUNG , MOIN PARVIZ , KIM JOHN
Published: July 2002

Turbulent flow over a backward-facing step is studied by

direct numerical solution of the Navier–Stokes equations. The

simulation was conducted at a Reynolds number of 5100 based on the

step height h and inlet free-stream velocity, and an

expansion ratio of 1.20. Temporal behaviour of spanwise-averaged

pressure fluctuation contours and reattachment length show evidence

of an approximate periodic behaviour of the free shear layer with a

Strouhal number of 0.06. The instantaneous velocity fields indicate

that the reattachment location varies in the spanwise direction, and

oscillates about a mean value of 6.28h. Statistical results

show excellent agreement with experimental data by Jovic & Driver

(1994). Of interest are two observations not previously reported for

the backward-facing step flow: (a) at the relatively low

Reynolds number considered, large negative skin friction is seen in

the recirculation region; the peak

|Cf| is about 2.5 times

the value measured in experiments at high Reynolds numbers;

(b) the velocity profiles in the recovery region fall below

the universal log-law. The deviation of the velocity profile from the

log-law indicates that the turbulent boundary layer is not fully

recovered at 20 step heights behind the separation.

The budgets of all Reynolds stress components have been computed.

The turbulent kinetic energy budget in the recirculation region is

similar to that of a turbulent mixing layer. The turbulent transport

term makes a significant contribution to the budget and the peak

dissipation is about 60% of the peak production. The

velocity–pressure gradient correlation and viscous diffusion

are negligible in the shear layer, but both are significant in the

near-wall region. This trend is seen throughout the recirculation and

reattachment region. In the recovery region, the budgets show that

effects of the free shear layer are still present.
The instability of the shear layer separating from

a bluff body
Authors: PRASAD ANIL , WILLIAMSON CHARLES H. K.
Published: July 2002

Notwithstanding the fact that the instability of the separated
shear

layer in the

cylinder wake has been extensively studied, there remains some

uncertainty regarding not only the critical Reynolds number at which

the instability manifests itself, but also the variation of its

characteristic frequency with Reynolds number (Re). A large

disparity exists in the literature in the precise value of the critical

Reynolds number,

with quoted values ranging from Re = 350 to Re = 3000.

In the present paper, we demonstrate that the spanwise end conditions

which control the primary mode of vortex shedding significantly affect

the shear-layer instability. For parallel shedding conditions, shear-layer

instability manifests itself at Re ≈ 1200, whereas for

oblique shedding conditions it is inhibited until a significantly

higher Re ≈ 2600, implying that even in the absence of a

variation in free-stream turbulence level, the oblique angle of primary

vortex shedding influences the onset of shear-layer instability, and

contributes to the large disparity in quoted values of the critical

Reynolds number. We confirm the existence of intermittency in

shear-layer fluctuations and show that it is not related to the

transverse motion of the shear layers past a fixed probe, as suggested

previously. Such fluctuations are due to an intermittent streamwise

movement of the transition point, or the location at which fluctuations

develop rapidly in the shear layer.

Following the original suggestion of Bloor (1964), it has generally

been assumed in previous studies that the shear-layer frequency

(normalized by the primary vortex shedding frequency) scales with

Re1/2, although a careful examination of the

actual data points from these studies does not support such a

variation. We have reanalysed all of the actual data points from

previous investigations and include our own measurements, to find

that none of these studies yields a relationship which is

close to Re1/2. A least-squares analysis which

includes all of the previously available data produces a variation

of the form Re0·67. Based on simple physical

arguments that account for the variation of the characteristic

velocity and length scales of the shear layer, we predict a variation

for the normalized shear-layer frequency of the form

Re0·7, which is in good agreement with the

experimental measurements.
Analysis and modelling of anisotropies in the dissipation rate of
turbulence
Authors: SPEZIALE CHARLES G. , GATSKI THOMAS B.
Published: July 2002

The modelling of anisotropies in the dissipation rate of

turbulence is considered based

on an analysis of the exact transport equation for the dissipation rate
tensor. An

algebraic model is systematically derived using integrity bases methods
and tensor

symmetry properties. The new model differs notably from all previously
proposed

models in that it depends nonlinearly on the mean velocity gradients. This
gives rise

to a transport equation for the scalar dissipation rate that is of the
same general

form as the commonly used model with one major exception: the coefficient
of the

production term is dependent on the invariants of both the

rotational and irrotational

strain rates. The relationship between the new model and other recently
proposed

models is examined in detail. Some basic tests and applications

of the model are also

provided along with a discussion of the implications for turbulence modelling.
Wave propagation in porous media containing

a dilute gas–liquid mixture: theory and experiments
Authors: SMEULDERS D. M. J. , VAN DONGEN M. E. H.
Published: July 2002

The influence of a small amount of gas within the saturating

liquid of a porous

medium on acoustic wave propagation is investigated. It is assumed that
the gas

volumes are spherical, homogeneously distributed, and that they are within
a very

narrow range of bubble sizes. It is shown that the compressibility of the
saturating

fluid is determined by viscous, thermal, and a newly introduced Biot-type
damping of

the oscillating gas bubbles, with mean gas bubble size and concentration
as important

parameters. Using a super-saturation technique, a homogeneous

gas–liquid mixture

within a porous test column is obtained. Gas bubble size and concentration
are

measured by means of compressibility experiments. Wave reflection and propagation

experiments carried out in a vertical shock tube show pore pressure

oscillations, which

can be explained by incorporating a dynamic gas bubble behaviour in the
linear Biot

theory for plane wave propagation.
Nonlinear diffusive surface waves in porous media
Authors: LIU PHILIP L.-F. , WEN JIANGANG
Published: July 2002

A fully nonlinear, diffusive, and weakly dispersive wave

equation is derived for

describing gravity surface wave propagation in a shallow porous

medium. Darcy's flow

is assumed in a homogeneous and isotropic porous medium. In deriving the
general

equation, the depth of the porous medium is assumed to be small in comparison

with the horizontal length scale, i.e. O(μ2)

=O(h0/L)2[Lt ]1.

The order of magnitude

of accuracy of the general equation is O(μ4).

Simplified governing equations are also

obtained for the situation where the magnitude of the free-surface fluctuations
is

also small,

O(ε)=O(a/h0)[Lt ]1,

and is of the same order of magnitude as O(μ2).

The resulting equation is of O(μ4, ε2)

and is equivalent to the Boussinesq equations

for water waves. Because of the dissipative nature of the porous medium
flow, the

damping rate of the surface wave is of the same order magnitude as the
wavenumber.

The tide-induced groundwater fluctuations are investigated by

using the newly derived

equation. Perturbation solutions as well as numerical solutions are obtained.
These

solutions compare very well with experimental data. The interactions between
a

solitary wave and a rectangular porous breakwater are then examined by
solving the

Boussinesq equations and the newly derived equations together. Numerical
solutions

for transmitted waves for different porous breakwaters are obtained and
compared

with experimental data. Excellent agreement is observed.
The effect of the induced mean flow on solitary
waves in deep water
Authors: AKYLAS T. R. , DIAS F. , GRIMSHAW R. H. J.
Published: July 2002

Two branches of gravity–capillary solitary
water waves are known to bifurcate from
a train of infinitesimal periodic waves at the
minimum value of the phase speed.
In general, these solitary waves feature oscillatory
tails with exponentially decaying
amplitude and, in the small-amplitude limit, they may be
interpreted as envelope-soliton solutions of the nonlinear
Schrödinger (NLS) equation such that the envelope
travels at the same speed as the carrier oscillations. On
water of infinite depth,
however, based on the fourth-order envelope equation derived
by Hogan (1985), it
is shown that the profile of these gravity–capillary
solitary waves actually decays
algebraically (like 1/x2) at
infinity owing to the induced mean flow that is not
accounted for in the NLS equation. The algebraic decay
of the solitary-wave tails
in deep water is confirmed by numerical computations
based on the full water-wave equations. Moreover, the
same behaviour is found at the tails of solitary-wave
solutions of the model equation proposed by Benjamin (1992)
for interfacial waves in a two-fluid system.