bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors contributing to the hybrid dysgenesis syndrome in
Drosophila virilis
Authors: VIEIRA JORGE , VIEIRA CRISTINA P. , HARTL DANIEL L. , LOZOVSKAYA ELENA R.
Published: July 2002

A hybrid dysgenesis syndrome in Drosophila virilis
is associated with the mobilization of at least
four unrelated transposable elements designated Helena, Paris,

Penelope and Ulysses. We carried
out 42 crosses between eight strains differing in transposable element
copy number in order to
assess their contributions to hybrid dysgenesis. Linear regression and

stepwise regression analysis
was performed to estimate the correlation between the difference in euchromatic
transposable
element number between the parental flies of different strains involved
in the crosses and the
percentage, in the progeny of these crosses, of males with atrophic
gonads. Male gonadal atrophy
is a typical manifestation of the D. virilis hybrid dysgenesis

syndrome. About half the variability in
the level of male gonadal atrophy can be attributed to
Penelope and Paris/Helena. Other factors

also seem to play a significant role in hybrid dysgenesis in D. virilis,

including maternally
transmitted host factors and/or uncontrolled environmental variation.

In the course of this work a
novel transposable element named Telemac was found. Telemac

is also mobilized in hybrid
dysgenesis but does not appear to play a major causative role.
Linkage disequilibrium mapping of molecular
polymorphisms at the scabrous locus associated with
naturally occurring variation in bristle number in Drosophila
melanogaster
Authors: LYMAN RICHARD F. , LAI CHAOQIANG , MACKAY TRUDY F. C.
Published: July 2002

We evaluated the hypothesis that the Drosophila melanogaster second chromosome gene scabrous
(sca), a candidate sensory bristle number quantitative trait locus (QTL), contributes to naturally
occurring variation in bristle number. Variation in abdominal and sternopleural bristle number
was quantified for wild-derived sca alleles in seven genetic backgrounds: as homozygous second
chromosomes (C2) in an isogenic background, homozygous lines in which approximately 20 cM
including the sca locus had been introgressed into the isogenic background (sca BC), as C2 and sca
BC heterozygotes and hemizygotes against a P element insertional sca allele and a P-induced sca
deficiency in the same isogenic background, and as sca BC heterozygotes against the wild-type sca
allele of isogenic strain. Molecular restriction map variation was determined for a 45 kb region
including the sca locus, and single-stranded conformational polymorphism (SSCP) was examined
for the third intron and parts of the third and fourth exons. Associations between each of the 27
molecular polymorphisms and bristle number were evaluated within each genotype and on the first
principal component score determined from all seven genotypes, separately for each sex and bristle
trait. Permutation tests were used to assess the empirical significance thresholds, accounting for
multiple, correlated tests, and correlated markers. Three sites in regulatory regions were associated
with female-specific variation in abdominal bristle number, one of which was an SSCP site in the
region of the gene associated with regulation of sca in embryonic abdominal segments.
Stable oxygen and carbon isotopes from brachiopods of
southern England and northwestern Germany: estimation of
Upper Turonian palaeotemperatures
Authors: VOIGT SILKE
Published: July 2002

More than 190 articulate brachiopods from Turonian sections in northwestern Germany
and southern England were studied for their stable carbon and oxygen isotopic composition, and
some of them for their elemental composition. Most of the brachiopod shells are well preserved, and
oxygen isotope composition reflects the temperate conditions of the European epicontinental sea.
Upper Turonian mean δ18O values from Lower Saxony and southern England show bottom-water
temperatures in the range of 14.2 to 18.2 °C (δ18Ow = −1.5‰ SMOW for an ice-free world). The relative
trend of mean brachiopod oxygen and carbon isotopes shows a short-term (200 k.y.) increase in
the mid-Upper Turonian horizons that confirms the climate cooling (∼ 2 °C) observed in bulk-rock
samples at different sites in Europe. Interbasinal comparisons between England and Germany show
similar δ13C values in both basins, whereas oxygen isotopes are heavier in northwestern Germany than
in England, suggesting a cool-water influence from the North Sea basin and temperate conditions in
the Anglo-Paris basin.
‘SCEPTICISM IN EXCESS’: GIBBON AND
EIGHTEENTH-CENTURY CHRISTIANITY
Authors: YOUNG B. W.
Published: July 2002

Since the appearance of volume I of The decline and fall of
the Roman empire
in 1776, the religion of Edward Gibbon has been subject to intense debate.

He has been variously
identified as an atheist, a deist, even as a somewhat detached Christian.

Examination of his relations,
both personal and scholarly, with the varieties of religion and
irreligion current in eighteenth-century
Britain leads to the conclusion that he remained resolutely critical
of all such positions. He did not
share the convictions of dogmatic freethinkers, still less those of
determined atheists. The product of
a nonjuring family, Gibbon benefited from the scholarly legacy of
several high church writers, while
maintaining a critical attitude towards the claims of Anglican orthodoxy.

It was through the deliberate
and ironical adoption of the idiom of via media Anglicanism, represented

by such theologians as the
clerical historian John Jortin, that Gibbon developed a woundingly sceptical

appraisal of the history
of the early church. This stance made it as difficult for his contemporaries

to identify Gibbon's religion
as it has since proved to be for modern historians. Gibbon appreciated
the
central role of religion in
shaping history, but he remained decidedly sceptical as to Christianity's

ultimate status as revealed and unassailable truth.
PARISH ECONOMIES OF WELFARE, 1650–1834
Authors: BROAD JOHN
Published: July 2002

This article argues for a more holistic approach to understanding the Old Poor Law.
Using three detailed case studies from southern England, it focuses on the dynamics of differing social
groups within the parish. It also looks at the role of the law, looking beyond the statutes to the parts
played by King's Bench, Quarter Sessions and individual justices and petty sessions in creating a
diversity of experiences for the poor. However, it also stresses the differential access to charitable funds,
common rights, and poor relief in individual communities, and the ways in which parish elites
attempted to put the total available resources to what they saw as the best uses. From 1650 to 1780
these combined resources allowed a generally humane approach to the treatment of poverty and
misfortune, and maintained the independence of the cottager and labourer in southern England. Only
after 1780 when population rose sharply and rural employment shrank did the flexibility of combined
charitable and rate-based relief founder and more drastic devices were employed to cope with basic
needs. In this process the independence of the labourer and cottager was undermined, charitable sources
were marginalized, and the seeds were sown for the acceptance of the New Poor Law.
THE EVOLUTION OF ‘PORTUGUESE’ IDENTITY:
LUSO-AFRICANS ON THE UPPER GUINEA COAST
FROM THE SIXTEENTH TO THE EARLY
NINETEENTH CENTURY
Authors: MARK PETER
Published: July 2002

During the late fifteenth and early sixteenth century, Portugal established
a trading presence along the Upper Guinea Coast from Senegal to Sierra
Leone. Emigrants from Portugal known as lançados – some of them Jews
seeking to escape religious persecution – settled along the coast, where many
of them married women from local communities. By the early sixteenth
century, Luso-Africans, or ‘Portuguese’ as they called themselves, were
established at trading centers from the Petite Côte in Senegal, south to Sierra
Leone. Descendants of Portuguese immigrants, of Cape Verde islanders, and
of West Africans, the Luso-Africans developed a culture that was itself a
synthesis of African and European elements. Rich historical documentation
allows a case study of the changing ways Luso-Africans identified themselves
over the course of three centuries.

The earliest lançados established themselves along the coast as commercial
middlemen between African and European traders and as coastal traders
between Sierra Leone and Senegambia. Their position was formally
discouraged by the Portuguese Crown until the second decade of the
sixteenth century, but they nevertheless played an important role in trade
with Portugal and the Cape Verde islands. Lançado communities were
permanently settled on the Petite Côte, while in Sierra Leone and Rio Nunez
much early commerce was in the hands of lançados who sailed there regularly
from S. Domingos, north of present day Bissau. The offspring of these
lançados and African women were called filhos de terra and were generally
considered to be ‘Portuguese’.

Throughout the sixteenth century, the descendants of the lançados
maintained close commercial ties with the Cape Verde islands. Cape
Verdeans were themselves the offspring of mixed Portuguese and West
African marriages. Sharing elements of a common culture and united by
marriage and economic ties, mainland Luso-Africans and Cape Verdeans
represented a socially complex and geographically dispersed community.
Cape Verdeans, like mainland Luso-Africans, resolutely maintained that
they were ‘Portuguese’, and both sub-groups employed the same essentially
cultural criteria of group identification.
Development, growth and dry matter partitioning in
bambara groundnut (Vigna subterranea) as influenced
by photoperiod and shading
Authors: BRINK M.
Published: July 2002

A semi-controlled environment study was conducted from May to September 1996 in Wageningen,
The Netherlands, to investigate the interaction between growth and development in bambara
groundnut (Vigna subterranea) and the influence of photoperiod on dry matter partitioning. The
experimental design was a split-plot with four photoperiods (10·5, 11·8, 13·2
and 14·5 h/d) and two
light treatments: unshaded and shaded (42% light reduction). The selection used was ‘DipC94’ from
Botswana. The dates of 50% flowering and 50% podding were determined, and samples of plants
were harvested at 22, 36, 50, 64, 78, 92, 106 and 120 days after sowing. Total dry matter production
was 41% lower in the shaded treatment than in the unshaded treatment, but the rates of progress
from sowing to flowering and flowering to podding decreased by only 3 and 12% respectively. This
suggests that growth and development in bambara groundnut are largely independent. Photoperiod
influenced dry matter partitioning indirectly, through its influence on the onset of podding. There
were, however, no strong direct photoperiod effects on dry matter partitioning, either before or after
the onset of podding.
Influence of additional ammonium supply on some
nutritional aspects in hydroponic rose plants
Authors: LORENZO H. , CID M. C. , SIVERIO J. M. , CABALLERO M.
Published: July 2002

The influence of an additional supply of ammonium to a nitrate containing hydroponic solution on
the mineral nutrition of greenhouse rose plants (Rosa hybrida cv. ‘Lambada’) has been investigated.
The effect on NPK uptake, mineral contents in roots and leaves as well as nitrate reductase (NR) and
glutamine synthetase (GS) activities were examined. The addition of ammonium in a nutrient solution
containing nitrate produced a total nitrogen uptake increase during shoot elongation, while in the
absence of ammonium, nitrate uptake was lower during shoot elongation. Adding ammonium to the
hydroponics solution caused an increase of potassium uptake while ammonium absorption was
constant. Phosphate uptake was always higher in combined nitrate plus ammonium treatment,
likewise in this treatment the most relevant effect on plant mineral content was the increase of P
concentration in the roots. In both treatments with or without NH+4, free nitrate was notably higher
in the roots than in leaves, indicating that nitrate reduction in rose plants takes place mainly in the
leaves. NR activity in the leaves was higher when ammonium was present, whereas the root GS
activity was similar in both treatments. The influence of ammonium on phosphate uptake and the
subsequent effects on transport of other ions and enzymatic activities are discussed.
The n-alkane concentrations in buds and leaves of browsed broadleaf trees
Authors: PIASENTIER E. , BOVOLENTA S. , MALOSSINI F.
Published: July 2002

The concentration of n-alkanes in the cuticular wax of plants can be used to estimate the composition
of the diet selected by free-ranging animals. The aims of this study were to characterize the n-alkane
profiles of developing leaves and evaluate the degree of chemical discrimination between six browsed
broadleaf tree species: European ash (Fraxinus excelsior L.), flowering ash (Fraxinus ornus L.),
hornbeam (Carpinus betulus L.), hazel (Corylus avellana L.), mountain ash (Sorbus aucuparia L.) and
beech (Fagus sylvatica L). The effect of the stage of development was examined by considering five
different vegetative stages: dormant bud (DB), late bud (LB), young leaf (YL), mature leaf (ML) and
senescing leaf (SL). Five samples per each vegetative stage and species, gathered in a mixed woodland
of the Italian Eastern Alps between February and October, were analysed for their n-alkane
concentrations (C23–C36).

The residual coefficient of variation was 15·5% on average for the individual n-alkanes considered.
There were noticeable differences in individual and total n-alkanes content between species. In
particular, C27 was the predominant n-alkane in beech and C33 was found in high proportions in the
two species of Fraxinus; hazel and flowering ash had a higher total n-alkanes content than the overall
mean, while the lowest values were found in hornbeam and beech. The n-alkane profile also
underwent important changes during the vegetative development, with different extent and direction
according to the species. In the three successive leaf stages, a tendency for a progressive increase in
the longest chain homologues was observed. In any case, the young leaf stage differed most from the
contiguous stages.

Canonical discriminant analysis indicated that the n-alkane profile of buds and leaves were
mathematically distinguishable and the chemical differences between species were persistent over the
plant vegetative development.
Climate change: a response surface study of the effects
of CO2 and temperature on the growth of French
beans
Authors: WURR D. C. E. , EDMONDSON R. N. , FELLOWS J. R.
Published: July 2002

The possible impact of global rises in atmospheric CO2 concentration and temperature on the growth
and development of French beans (Phaseolus vulgaris) was examined using growth cabinets. Five CO2
concentrations of 350, 450, 550, 650 and 750 vpm and five temperatures of 14·5, 15·5, 16·5, 17·5 and
18·5°C were tested using a fractional factorial design comprising nine treatment combinations of the
two factors. Plants were grown under constant irradiance, common atmospheric humidities (vpd
0·5 kPa) and non-limiting supplies of water and mineral nutrients. The plant growth response was
modelled by fitting polynomial response function curves to the times to first flower opening, first bean
set, 50% maturity and the number and yield of beans. The effects of temperature were large and
positive for most of the measured variables, whereas the effects of CO2 were small and negative or
non-existent. Increased temperature substantially reduced the time to flowering and the time from
bean set to 50% maturity and increased the number and yield of mature beans whereas increased CO2
concentration had little effect on plant growth except that bean yield was very slightly reduced. There
was no significant evidence of interaction between the CO2 concentration effects and the temperature
effects.

The time to maturity and yield of mature beans was simulated for the 2020s (2010 to 2039) and the
2050s (2040 to 2069) using the fitted polynomial models and four climate change scenarios suggested
by the UK Climate Impacts Programme. These simulations showed that, depending upon the assumed
scenario, the 2020s yields could rise by 39–84% and time to maturity reduce by between 6 and 15 days
whereas the 2050s yields could rise by 51–118% and time to maturity reduce by between 9 and
25 days.
Rumen biohydrogenation of n-3 polyunsaturated fatty
acids and their effects on microbial efficiency and
nutrient digestibility in sheep
Authors: WACHIRA A. M. , SINCLAIR L. A. , WILKINSON R. G. , HALLETT K. , ENSER M. , WOOD J. D.
Published: July 2002

The study examined the extent to which n-3 PUFA from different sources were biohydrogenated in
the rumen and their effects on rumen microbial efficiency and whole tract nutrient digestibility. Four
ruminally and duodenally cannulated wether lambs were used in a 4×4 Latin square design. Four
iso-energetic and iso-nitrogenous diets based on dried grass were formulated to provide similar fat
levels (60g/kg DM) from different sources; Megalac (palmitic acid: C16:0; Control), whole linseed
(α-linolenic acid, C18:3n-3 ; Linseed) fish oil (eicosapentaenoic acid, C20:5n-3, EPA and
docosahexaenoic acids C22:6n-3, DHA; Fish oil) and whole linseed plus fish oil providing equal
amounts of oil (LinFish). Diets were offered at a rate of 1·2kg/day in 12 equal portions.

Total fatty acid intake was similar on all diets whilst duodenal fatty acid flow varied between
101, 94, 87 and 90% of dietary intake for animals fed the Control, Linseed, Fish oil and Linfish diets
respectively. Duodenal flow of C18:3 n-3 in animals fed the Linseed diet was twice that of animals
fed the Control diet (P < 0·01) whilst animals fed the Fish oil diet had a significantly greater flow of
EPA and DHA than those fed any of the other dietary treatments. Duodenal flow of trans C18:1 in
animals fed the Linfish diet was significantly greater than that in animals fed either Linseed, Fish oil
or Control diets (P < 0·001). Biohydrogenation of C18:3n-3 was 80 to 93% in all diets whilst that
of C20:5n-3 and C22:6n-3 was 72 to 79% in diets that contained fish oil or linseed and fish oil.
Apparent fatty acid digestibility (duodenum to rectum) tended to be greater for unsaturated than
saturated fatty acids whilst whole tract fatty acid digestibility (mouth to rectum) was significantly
greater in animals fed diets containing fish oil (P0·05). All dietary n-3 PUFA sources decreased
microbial protein synthesis and efficiency when expressed as either gN/kg organic matter (OM)
apparently or truly degraded in the rumen. Additionally, the inclusion of fish oil increased the
proportion of propionate in the rumen whilst depressing the rumen digestibility of OM and fibre
(P < 0·01), but had no significant effect on whole tract OM or fibre digestibility.
Involvement of a pasteurizer in the contamination of milk by Bacillus cereus in a commercial dairy plant
Authors: SVENSSON BIRGITTA , ENEROTH ÅSA , BRENDEHAUG JOHANNE , MOLIN GÖRAN , CHRISTIANSSON ANDERS
Published: July 2002

Bacillus cereus is a common contaminant in raw milk. The spores survive
pasteurization and psychrotrophic strains of B. cereus often limit the keeping quality
of pasteurized milk stored at > 6 °C (Griffiths, 1992). High numbers of B. cereus in
pasteurized milk are most frequent when the cows are grazing (Slaghuis et al. 1997),
mainly owing to increased levels of spores in raw milk resulting from teat
contamination by soil (Christiansson et al. 1999). However, high numbers can also be
found in pasteurized milk while the cows are housed indoors, and this is probably
caused by additional contamination at the dairy plant (te Giffel et al. 1996; Larsen &
Jørgensen, 1997; Lin et al. 1998). There is little information available about the
sites of recontamination in the dairy. The use of typing techniques capable of
discrimination below the species level, such as fatty acid profiles and random
amplification of polymorphic DNA–polymerase chain reaction (RAPD–PCR), could
be helpful in demonstrating contamination routes (Lin et al. 1998; Nilsson et al.
1998).

Spores of B. cereus are very hydrophobic and readily adhere to surfaces of steel,
glass and rubber (Rönner et al. 1990), and short cleaning-in-place programmes do not
always eliminate all the spores (Rönner & Husmark, 1992). Spores adhering to
surfaces are more difficult to eliminate by disinfectants than spores in solution (te
Giffel et al. 1995). Many B. cereus spores germinate rapidly in milk upon heat
activation and, if allowed to propagate undisturbed on surfaces, may form biofilms
that are extremely difficult to eliminate (Mosteller & Bishop, 1993; Wirtanen et al.
1996; Kumar & Anand, 1998).

This paper describes how we demonstrated the involvement of a pasteurizer in
the contamination of pasteurized milk by B. cereus in a commercial dairy plant using
a combination of classic microbiological analyses and typing of strains by
RAPD–PCR.
Application of capillary electrophoresis to the study of
proteolysis of caseins
Authors: RECIO ISIDRA , AMIGO LOURDES , RAMOS MERCEDES , LOPEZ-FANDIÑO ROSINA
Published: July 2002

Capillary electrophoresis using a hydrophilically coated capillary
and a
low pH buffer containing urea has been used to follow the proteolytic action
of
plasmin and chymosin on isolated casein fractions, whole casein and individual
milk
samples selected on the basis of their genetic variants. Several of the
main casein
breakdown products were identified. These included, among others,
γ1-casein (CN) A1,
γ1-CN A2,
γ1-CN B,
γ1-CN C,
γ2-CN A,
γ1-CN A3,
γ2-CN B,
γ3-CN A and
γ3-CN B, as well as proteose peptones, arising from the

action of plasmin on the
different genetic variants of β-CN. αs1-I-CN and

αs1-CN f(1-23) from αs1-CN, and
para-κ-CN and caseinomacropeptide from κ-CN produced by
chymosin action were
also separated. The knowledge of their migration times provided information
on the
extent and origin of casein hydrolysis in both milk and cheese, as found
in samples
of proteolysed milk or fresh cheese.
Relationship between level of hydrophobic peptides and bitterness
in
cheese made from pasteurized and raw milk
Authors: GOMEZ MARIA J. , GARDE SONIA , GAYA PILAR , MEDINA MARGARITA , NUÑEZ MANUEL
Published: July 2002

Hydrophobic and hydrophilic peptides in the water-soluble fraction
of 20
batches of Hispanico cheese made from pasteurized and raw milk were determined

by reversed-phase HPLC, with detection at 214 and 280 nm. Cheese flavour

characteristics were evaluated by a sensory panel, and
regressions of bitterness scores
on levels of hydrophobic and hydrophilic peptides and their ratio were
calculated.
The best fitting relationship for pasteurized milk cheese was
the linear regression of
mean panel bitterness scores on hydrophobic peptides at 280 nm
(r2=0·791). The
determination coefficient for the regression of hydrophobic peptides at
280 nm on
panellist bitterness scores (r2=0·356)
was lower, owing to individual differences in
the perceived intensity of bitterness. In the case of
raw milk cheese, the respective
determination coefficients were 0·203 for panel scores and
0·034 for individual panellist scores.
Mineral content of camel milk and colostrum
Authors: GORBAN ALI M. S. , IZZELDIN OMAR M.
Published: July 2002

The camel population of Saudi Arabia is ∼607000 out
of a world population of
17 million. All are dromedaries (Camelus dromedarius) of
four major ecotypes (Elamin & Wilcox, 1992), giving daily milk yields of
3·5–35·0 kg/animal (Knoess,
1977). Camel milk is low in lactose compared with cows' milk
(Elamin & Wilcox,
1992). However, levels of potassium, magnesium, iron, copper, manganese, sodium
and zinc are higher than in cows' milk (Sawaya et al. 1984;
Abu-Lehia, 1987). Farah
(1993) found low levels of potassium and phosphorus in Egyptian dromedaries. There
is little difference between the milk of dromedaries and that of bactrian camels
(Kheraskov, 1961).

In the Gulf region and some southern Mediterranean countries, substantial
amounts of camel milk are consumed by the local people. The investigation reported
here was undertaken to shed more light on the nutritional contribution made by
camel milk.
Effect of stocking density on ewes' milk yield, udder health
and microenvironment
Authors: SEVI AGOSTINO , MASSA SALVATORE , ANNICCHIARICO GIOVANNI , DELL'AQUILA SALVATORE , MUSCIO ANTONIO
Published: July 2002

Three groups of 12 lactating Comisana ewes were housed in separate
rooms of the same building that contained straw-bedded pens with total areas of 12,
18 and 24 m2. The ewes were assigned to groups with different stocking densities:
high (HSD, 1 m2/animal), medium (MSD, 1.5 m2/animal) or low
(LSD, 2 m2/animal).
The LSD treatment resulted in lower air concentrations of total microorganisms and
coliform bacteria than the other two. Ewes in the LSD group gave greater yields of
milk, total protein and fat than those in the other two groups. LSD treatment
increased milk casein content and improved clotting time and clot firmness. LSD also
resulted in ewes giving milk with lower somatic cell counts and smaller concentrations
of mesophiles, psychrotrophs and faecal coliforms than MSD and HSD. Subclinical
mastitis occurred in three ewes of the MSD group and four ewes of the HSD group,
while no cases were recorded in the LSD group. These results indicate that stocking
density is a critical factor in dairy sheep housing and suggest that a space allocation
<2 m2/animal may adversely affect the performance and
health of the lactating ewe.
Miscible rectilinear displacements with gravity
override. Part 2. Heterogeneous porous media
Authors: CAMHI EMMANUEL , MEIBURG ECKART , RUITH MICHAEL
Published: July 2002

The effects of permeability heterogeneities on rectilinear displacements with viscosity contrast and density variations are investigated computationally by means
of direct numerical simulations. Physical interpretations are given in terms of mutual interactions among the three vorticity components related to viscous, density
and permeability effects. In homogeneous environments the combined effect of the
unfavourable viscosity gradient and the potential velocity field generated by the horizontal boundaries was seen to produce a focusing mechanism that resulted in the
formation of a strong vorticity layer and the related growth of a dominant gravity
tongue (Ruith & Meiburg 2000). The more randomly distributed vorticity associated
with the heterogeneities tends to ‘defocus’ this interaction, thereby preventing the
formation of the vorticity layer and the gravity tongue. When compared to neutrally
buoyant flows, the level of heterogeneity affects the breakthrough recovery quite differently. For moderate heterogeneities, a gravity tongue still forms and leads to early
breakthrough, whereas the same result is accomplished for large heterogeneities by
channelling. At intermediate levels of heterogeneity, these tendencies partially cancel
each other, so that the breakthrough recovery reaches a maximum. Similarly, the
dependence of the breakthrough recovery on the correlation length is quite different
in displacements with density contrasts compared to neutrally buoyant flows. For
neutrally buoyant flows the resonant interaction between viscosity and permeability
vorticities typically leads to a minimal recovery at intermediate values of the correlation length. In contrast, displacements with density contrast give rise to a gravity
tongue for both very small and very large values of this length, so that the recovery
reaches a maximum at intermediate values.
Finite-core hetons: stability and interactions
Authors: SOKOLOVSKIY M. A. , VERRON J.
Published: July 2002

The dynamics of vertically compensated two-layer vortices (hetons) with finite cores
are examined within the context of the quasi-geostrophic approximation on the
f-plane. The two-layer version of the contour dynamics method is used, and complemented
by the so-called contour surgery technique. Special attention is paid to
two-heton interactions when the initial locations of the vortex patches are symmetrical.
A classification of the different regimes observed is made according to external
parameters, namely geometrical parameters and stratification. In this parameter space,
novel quasi-stationary states resulting from collisions between two hetons may be observed:
(i) formation of a configuration consisting of two-layer vortices moving in
opposite directions and, as a special case, a configuration analogous to the ‘klapstoss’
billiard shot, (ii) absorption of one heton by the other and subsequent movement of
a new dipole, (iii) formation of two-layer dipoles, larger than the original hetons, associated
with rotating peripheral satellite eddies in their wakes. Some of these results
may have implications for the analysis of mesoscale vortices in the ocean.
The dynamics of a laminar flow in a symmetric channel with a sudden expansion
Authors: HAWA T. , RUSAK Z.
Published: July 2002

Bifurcation analysis, linear stability study, and direct numerical simulations of the
dynamics of a two-dimensional, incompressible, and laminar flow in a symmetric long
channel with a sudden expansion with right angles and with an expansion ratio D/d
(d is the width of the channel inlet section and D is the width of the outlet section)
are presented. The bifurcation analysis of the steady flow equations concentrates on
the flow states around a critical Reynolds number Rec(D/d)
where asymmetric states appear in addition to the basic symmetric states when
Re [ges ] Rec(D/d). The bifurcation
of asymmetric states at Rec has a pitchfork nature and the asymmetric perturbation
grows like √Re − Rec(D/d). The
stability analysis is based on the linearized equations of motion for the
evolution of infinitesimal two-dimensional disturbances imposed
on the steady symmetric as well as asymmetric states. A neutrally stable asymmetric
mode of disturbance exists at Rec(D/d)
for both the symmetric and the asymmetric equilibrium states. Using asymptotic methods, it is demonstrated that when
Re < Rec(D/d)
the symmetric states have an asymptotically stable mode of disturbance.
However, when Re > Rec(D/d),
the symmetric states are unstable to this mode of asymmetric disturbance. It is also shown that when
Re > Rec(D/d) the asymmetric
states have an asymptotically stable mode of disturbance. The direct numerical
simulations are guided by the theoretical approach. In order to improve the numerical
simulations, a matching with the asymptotic solution of Moffatt (1964) in the regions
around the expansion corners is also included. The dynamics of both small- and large-amplitude disturbances in the flow is described and the transition from symmetric to
asymmetric states is demonstrated. The simulations clarify the relationship between
the linear stability results and the time-asymptotic behaviour of the flow. The current
analyses provide a theoretical foundation for previous experimental and numerical
results and shed more light on the transition from symmetric to asymmetric states of
a viscous flow in an expanding channel. It is an evolution from a symmetric state,
which loses its stability when the Reynolds number of the incoming flow is above
Rec(D/d), to a stable asymmetric
equilibrium state. The loss of stability is a result of
the interaction between the effects of viscous dissipation, the downstream convection
of perturbations by the base symmetric flow, and the upstream convection induced
by two-dimensional asymmetric disturbances.
Examination of large-scale structures in a turbulent plane mixing layer. Part 2. Dynamical systems model
Authors: UKEILEY L. , CORDIER L. , MANCEAU R. , DELVILLE J. , GLAUSER M. , BONNET J. P.
Published: July 2002

The temporal dynamics of large-scale structures in a plane turbulent mixing layer
are studied through the development of a low-order dynamical system of ordinary
differential equations (ODEs). This model is derived by projecting Navier–Stokes
equations onto an empirical basis set from the proper orthogonal decomposition
(POD) using a Galerkin method. To obtain this low-dimensional set of equations, a
truncation is performed that only includes the first POD mode for selected streamwise/spanwise
(k1/k3) modes. The initial truncations
are for k3 = 0; however, once
these truncations are evaluated, non-zero spanwise wavenumbers are added. These
truncated systems of equations are then examined in the pseudo-Fourier space in
which they are solved and by reconstructing the velocity field. Two different methods
for closing the mean streamwise velocity are evaluated that show the importance
of introducing, into the low-order dynamical system, a term allowing feedback between
the turbulent and mean flows. The results of the numerical simulations show a
strongly periodic flow indicative of the spanwise vorticity. The simulated flow had the
correct energy distributions in the cross-stream direction. These models also indicated
that the events associated with the centre of the mixing layer lead the temporal
dynamics. For truncations involving both spanwise and streamwise wavenumbers,
the reconstructed velocity field exhibits the main spanwise and streamwise vortical
structures known to exist in this flow. The streamwise aligned vorticity is shown to
connect spanwise vortex tubes.
Numerical investigations of heat transfer mechanisms in the forced laminar wall jet
Authors: SEIDEL JÜRGEN , FASEL HERMANN F.
Published: July 2002

The effect of high-amplitude forcing on a laminar wall jet over a heated flat plate is
analysed. Highly accurate direct numerical simulations (DNS) are used to investigate
the dominant transport mechanisms. When forcing is applied, the skin friction is
reduced markedly and the wall heat transfer is increased. Detailed examination of
the unsteady flow field showed that the concepts of eddy viscosity and eddy thermal
diffusivity, usually applied to turbulent flows, can be applied to the analysis of
unsteady laminar flows to explain the effect of highly unsteady phenomena.
Transverse jets and jet flames. Part 2. Velocity and OH field imaging
Authors: HASSELBRINK E. F. , MUNGAL M. G.
Published: July 2002

Detailed measurements of the velocity field in the symmetry plane of two jets and two
jet flames in a crossflow are obtained using particle image velocimetry. The jets issue
into a wind tunnel at density-weighted jet-to-crossflow velocity ratios r = 10 and r = 21,
with corresponding Reynolds numbers 6000 and 12 800. Ensemble statistics of the
velocity field are presented, and some interesting features of the entrainment process
in transverse jets are discussed. Deviations from the simple behaviour predicted by
the similarity analysis presented in Part 1 are highlighted. Simultaneous planar laser-induced
fluorescence imaging of the OH radical is performed in selected regions of the
flames. Results suggests that flame/flow interaction is strong near the lifted flamebase,
but increasingly weaker further downstream.
Stability of flow in a wavy channel
Authors: CABAL A. , SZUMBARSKI J. , FLORYAN J. M.
Published: July 2002

Linear stability analysis of flow in a channel bounded by wavy walls is considered. It
is shown that wall waviness gives rise to an instability that manifests itself through
generation of streamwise vortices. The available results suggest that the critical
stability criteria based on the Reynolds number based on the amplitude of the
waviness can be formulated.
Inertial nonlinear equilibration of equatorial flows
Authors: HUA BACH LIEN , MOORE DENNIS W. , GENTIL SYLVIE LE
Published: July 2002

We explore the nature of inertial equilibration of equatorial
flows in the presence of mean meridional and vertical shears of the
basic state, with oceanic applications in mind. The study is
motivated by the observational evidence that the subthermocline
equatorial mean circulation displays nearly zero Ertel potential
vorticity away from the equator, when taking into account the
non-traditional horizontal component of the Earth rotation. This
observed state precisely verifies the marginal condition for inertial
instability: a linear analysis for the equatorial β-plane
confirms that the usual condition of instability, namely that Ertel
potential vorticity should be of opposite sign to the vertical
Coriolis parameter, remains valid even when the traditional
approximation is relaxed. Analytical linear normal modes reveal that
a meridional shear of the basic state leads to a vertical stacking of
equatorially-trapped zonal flows of alternate signs, with a new
centre of symmetry located at the dynamical equator. A vertical shear
of the basic state causes a meridional stacking of extra-equatorial
zonal flows.

In an inviscid framework, a two-dimensional formulation is
ill-posed and we resort to non-hydrostatic viscous simulations to
determine the nonlinear normal forms of the system. The influence of
a small-scale eddy diffusivity and a large-scale Rayleigh damping on
the equilibrated vertical scale is determined numerically. The
nonlinear equilibration occurs through a steady-state bifurcation
from a basic state without jets to another steady state with
secondary jets of alternate signs. The final state corresponds to
eastward jets located on the geographic equator, while westward jets
are located near the dynamical equator. These results are consistent
with in situ observations of equatorial deep jets.

The analogy between the equatorial meridional shear flow and the
cylindrical Couette–Taylor flow with an axial density
stratification is detailed. There is a strong similarity in the
general symmetries and nonlinear normal forms of the two problems.
Similarly to the homogeneous Couette–Taylor flow, the gap width
between the two cylinders is important for determining the axial
scale of the secondary flow through the Reynolds number. For the
equatorial problem, an upper bound for the height scale of inertial
jets is such that the corresponding equatorial radius of deformation
times √2 fits between the geographic and dynamic equators.

One of our main conclusions is that the raisond’être of the observed region of zero
Ertel potential vorticity is to facilitate angular momentum exchanges
between the two hemispheres and inertial deep jets are the byproducts
of this angular momentum mixing.
Laboratory study of the interaction between

two internal wave rays
Authors: TEOH S. G. , IVEY G. N. , IMBERGER J.
Published: July 2002

Laboratory experiments were conducted to study the interaction
between two

downward propagating internal wave rays with identical properties but opposite

horizontal phase velocities. The intersection of the rays produced a velocity

field with

stagnation points, and these points propagated vertically upwards within
the

intersection region. Nonlinear non-resonant interactions between the two
rays

produced evanescent modes, with frequencies greater than the ambient buoyancy

frequency, trapped within the intersection region. These evanescent modes
provided a

mechanism whereby energy could accumulate locally and, even though the
vertical

wavelength of the primary resultant wave remained the same, the local isopycnal

displacements increased in time. Eventually, the isopycnals were forced
to

overturn in the region just above the stagnation points by the variation
with

depth in the local horizontal strain rate.

The gravitationally unstable overturning ultimately broke down releasing
its

available potential energy and generating turbulence within the intersection
region.

The results showed that the release of available potential energy was disrupted
by

the wave motions and even the dissipative scales were directly affected
by the

ambient stratification and the background wave motion. The distribution
of the

centred displacement scales was highly skewed towards the Kolmogorov scale
and the

turbulent Reynolds number Ret was low. Thus,
the net

buoyancy flux was very small

and almost all turbulent kinetic energy was dissipated over the parameter
range

investigated. The results also showed that for such dissipative events
the

square of the strain Froude number

(ε/νN20)

and the turbulent Reynolds number Ret can
be less than

one.
Numerical simulation of the evolution of

Tollmien–Schlichting waves over finite compliant panels
Authors: DAVIES CHRISTOPHER , CARPENTER PETER W.
Published: July 2002

The evolution of two-dimensional Tollmien–Schlichting waves
propagating

along a

wall shear layer as it passes over a compliant panel of finite length is

investigated by

means of numerical simulation. It is shown that the interaction of such
waves with

the edges of the panel can lead to complex patterns of behaviour. The behaviour

of the Tollmien–Schlichting waves in this situation, particularly
the effect

on their

growth rate, is pertinent to the practical application of compliant walls
for

the delay

of laminar–turbulent transition. If compliant panels could be made

sufficiently short

whilst retaining the capability to stabilize Tollmien–Schlichting
waves,

there is a good

prospect that multiple-panel compliant walls could be used to maintain
laminar flow

at indefinitely high Reynolds numbers.

We consider a model problem whereby a section of a plane channel is
replaced

with a compliant panel. A growing Tollmien–Schlichting wave is then

introduced into

the plane, rigid-walled, channel flow upstream of the compliant panel.
The results

obtained are very encouraging from the viewpoint of laminar-flow control.
They

indicate that compliant panels as short as a single Tollmien–Schlichting

wavelength

can have a strong stabilizing effect. In some cases the passage of the

Tollmien–Schlichting wave over the panel edges leads to the excitation
of

stable flow-induced

surface waves. The presence of these additional waves does not appear to
be

associated

with any adverse effect on the stability of the Tollmien–Schlichting
waves.

Except very

near the panel edges the panel response and flow perturbation can be represented
by

a superposition of the Tollmien–Schlichting wave and two other eigenmodes

of the

coupled Orr–Sommerfeld/compliant-wall eigensystem.

The numerical scheme employed for the simulations is derived from a
novel

vorticity–velocity formulation of the linearized Navier–Stokes

equations and uses

a mixed finite-difference/spectral spatial discretization. This approach

facilitated the

development of a highly efficient solution procedure. Problems with numerical

stability were overcome by combining the inertias of the compliant wall
and fluid

when imposing the boundary conditions. This allowed the interactively coupled

fluid and wall motions to be computed without any prior restriction on
the form

taken by the disturbances.
Shear-free turbulence near a wall
Authors: ARONSON DAG , JOHANSSON ARNE V. , LÖFDAHL LENNART
Published: July 2002

The mean shear has a major influence on near-wall turbulence but
there

are also

other important physical processes at work in the turbulence/wall interaction.
In

order to isolate these, a shear-free boundary layer was studied experimentally.
The

desired flow conditions were realized by generating decaying grid turbulence
with a

uniform mean velocity and passing it over a wall moving with the stream
speed. It

is shown that the initial response of the turbulence field can be well
described by

the theory of Hunt & Graham (1978). Later, where this theory ceases
to give an

accurate description, terms of the Reynolds stress transport (RST) equations
were

measured or estimated by balancing the equations. An important finding
is that two

different length scales are associated with the near-wall damping of the
Reynolds

stresses. The wall-normal velocity component is damped over a region extending

roughly one macroscale out from the wall. The pressure–strain

redistribution that

normally would result from the Reynolds stress anisotropy in this region
was found

to be completely inhibited by the near-wall influence. In a thin region
close

to the wall

the pressure–reflection effects were found to give a pressure–strain

that has an effect

opposite to the normally expected isotropization. This behaviour is not
captured by

current models.
Dynamics of a vortex ring moving

perpendicularly to the axis of a rotating fluid
Authors: EISENGA A. H. M. , VERZICCO R. , VAN HEIJST G. J. F.
Published: July 2002

The dynamics of a vortex ring moving orthogonally to the

rotation vector of a uniformly rotating fluid is analysed by

laboratory experiments and numerical simulations.

In the rotating system the vortex ring describes a curved trajectory,

turning in the

opposite sense to the system's anti-clockwise rotation. This

behaviour has been explained by using the analogy with the motion of

a sphere in a rotating fluid for which

Proudman (1916) computed the forces acting on the body surface.

Measurements

have revealed that the angular velocity of the vortex ring in its

curved trajectory is

opposite to the background rotation rate, so that the vortex has a

fixed orientation in

an inertial frame of reference and that the curvature increases

proportionally to the rotation rate.

The dynamics of the vorticity of the vortex ring is affected

by the background

rotation in such a way that the part of the vortex core in

clockwise rotation shrinks

while the anti-clockwise-rotating core part widens. By this

opposite forcing on either

side of the vortex core Kelvin waves are excited, travelling along

the toroidal axis

of the vortex ring, with a net mass flow which is responsible for

the accumulation

of passive scalars on the anti-clockwise-rotating core part. In

addition, the curved

motion of the vortex ring modifies its self-induced strain field,

resulting in stripping

of vorticity filaments at the front of the vortex ring from the

anti-clockwise-rotating

core part and at the rear from the core part in clockwise rotation.

Vortex lines, being

deflected by the main vortex ring due to induction of relative

vorticity, are stretched

by the local straining field and form a horizontally extending

vortex pair behind

the vortex ring. This vortex pair propagates by its self-induced

motion towards the

clockwise-rotating side of the vortex ring and thus contributes to

the deformation of

the ring core. The deflection of vortex lines from the main vortex

ring persists during

the whole motion and is responsible for the gradual erosion of

the coherent toroidal structure of the initial vortex ring.
Oscillatory motions of circular disks and nearly
spherical particles in viscous flows
Authors: ZHANG WENDY , STONE H. A.
Published: July 2002

Oscillatory translational and rotational motions
of small particles in viscous fluids are
studied for two cases: (i) circular disks and (ii) nearly spherical particles.
For circular
disks, four motions are treated: broadside and edgewise oscillatory translations
and
out-of-plane and in-plane oscillatory rotations. In each case the unsteady
Stokes
equations are reduced to dual integral equations and solved exactly for
all frequencies.
Streamline portraits of the flow fields are used to understand the evolution
of the
velocity and pressure fields. The motions of nearly spherical particles
are then studied
using the reciprocal theorem. Asymptotic formulae for the hydrodynamic
resistance
tensors are derived and discussed.
On the persistence of non-axisymmetric vortices
in inviscid two-dimensional flows
Authors: DRITSCHEL DAVID G.
Published: July 2002

Previous research has suggested that isolated, initially non-axisymmetric
vortices in
two-dimensional flows tend to become axisymmetric, in a coarse-grained
sense, by
purely inviscid mechanisms. That research, however, considered only vortices
with
broadly distributed vorticity. In this paper, it is shown that vortices
with sufficiently
steep edge gradients behave in a radically different way; in particular
they can remain
non-axisymmetric, apparently indefinitely. Such vortices, it is argued,
are more typical
in inviscid two-dimensional flows than the broadly distributed vortices
previously
considered, and hence the tendency for vortices to become axisymmetric
is not
generic to these flows.