bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling tooth emergence data based on multivariate interval‐censored data
Authors: Bogaerts K. , Leroy R. , Lesaffre E. , Declerck D.
Published: December 2002

Studies on emergence of (permanent) teeth are published regularly in the dental literature. Besides descriptive statistics (mean or median values) on emergence times, comparisons between boys and girls are of interest. Gender comparisons are intersubject analyses, but also intrasubject questions, like ‘Is there a left–right symmetry with respect to the mean (median) emergence times?’ are of interest. Studies on emergence times most often are faced with interval‐censored data. We will extend a GEE‐type test proposed by Husteret al.for bivariate right‐censored data to the multivariate setting with interval‐censored data. Central to our paper is to provide appropriate statistical models to resolve some dental questions on emergence. The analyses are based on data from the longitudinal Signal‐Tandmobiel study. Copyright © 2002 John Wiley & Sons, Ltd.
Global goodness‐of‐fit tests in logistic regression with sparse data
Authors: Kuss Oliver
Published: December 2002

The logistic regression model has become the standard analysing tool for binary responses in medical statistics. Methods for assessing goodness‐of‐fit, however, are less developed where this problem is especially pronounced in performing global goodness‐of‐fit tests with sparse data, that is, if the data contain only a small numbers of observations for each pattern of covariate values. In this situation it has been known for a long time that the standard goodness‐of‐fit tests (residual deviance and Pearson chi‐square) behave unsatisfactorily ifp‐values are calculated from the χ2‐distribution. As a remedy in this situation the Hosmer–Lemeshow test is frequently recommended; it relies on a new grouping of the observations to avoid sparseness, where this grouping depends on the estimated probabilities from the model. It has been shown, however, that the Hosmer–Lemeshow test also has some deficiencies, for example, it depends heavily on the calculating algorithm and thus different implementations might lead to different conclusions regarding the fit of the model. We present some alternative tests from the statistical literature which should also perform well with sparse data. Results from a simulation study are given which show that there exist some goodness‐of‐fit tests (for example, the Farrington test) that have good properties regarding size and power and that even outperform the Hosmer–Lemeshow test. We illustrate the various tests with an example from dermatology on occupational hand eczema in hairdressers. Copyright © 2002 John Wiley & Sons, Ltd.
Simplifying a prognostic model: a simulation study based on clinical data
Authors: Ambler Gareth , Brady Anthony R. , Royston Patrick
Published: December 2002

Prognostic models are designed to predict a clinical outcome in individuals or groups of individuals with a particular disease or condition. To avoid bias many researchers advocate the use of full models developed by prespecifying predictors. Variable selection is not employed and the resulting models may be large and complicated. In practice more parsimonious models that retain most of the prognostic information may be preferred. We investigate the effect on various performance measures, including mean square error and prognostic classification, of three methods for estimating full models (including penalized estimation and Tibshirani's lasso) and consider two methods (backwards elimination and a new proposal called stepdown) for simplifying full models. Simulation studies based on two medical data sets suggest that simplified models can be found that perform nearly as well as, or sometimes even better than, full models. Optimizing the Akaike information criterion appears to be appropriate for choosing the degree of simplification. Copyright © 2002 John Wiley & Sons, Ltd.
Regional differences in sympathetic purinergic transmission along the length of the mouse vas deferens
Authors: Knight D. , D'Arbe M. , Liang S. , Phillips W.D. , Lavidis N.A.
Published: December 2002

Contraction of the smooth muscle in the mouse vas deferens is elicited by sympathetic nerves releasing at least two neurotransmitters, adenosine triphosphate (ATP) and noradrenaline (NA). Several studies have indicated the presence of regional variation in the purinergic and noradrenergic contributions to sympathetic nerve‐evoked contractions in rodent vasa deferentia. We examined the relative contribution of ATP and NA to neurotransmission and contraction at the prostatic and epididymal ends of the mouse vas deferens. The success rate of recording excitatory junction currents (EJCs, extracellular indication of ATP release) from varicosities at the prostatic end of the vas deferens was eight times greater than for varicosities located at the epididymal end. Both regions of the vas deferens responded similarly to focal application of NA and ATP. Furthermore, the relative density and distribution of P2X1‐receptor mRNA and anti‐P2X1 immunostaining did not differ between the two regions. Our results suggest that most varicosities located at the epididymal end of the vas deferens are releasing an insufficient amount of ATP to evoke detectable EJCs. Synapse 47:225–235, 2003. © 2002 Wiley‐Liss, Inc.
Creation, expression, and characterization of a constitutively active mutant of the human serotonin 5‐HT6 receptor
Authors: Purohit Anil , Herrick‐Davis Katharine , Teitler Milt
Published: December 2002

The serotonin 5‐HT6 receptor, a G‐protein‐coupled receptor, displays high affinity for antipsychotic, antidepressant, and psychotropic drugs. We created a constitutively active form of the human 5‐HT6 receptor in order to probe the molecular domains of receptor activation and to determine if inverse agonist activities of antipsychotic drugs contribute to their clinical profile. Previous studies from our laboratory support a critical role for the c‐terminal region of the third intracellular loop (il3) in the activation of Gq‐coupled serotonin receptors. In the present study, PCR‐based mutagenesis was used to mutate serine 267 (S6.34) in the c‐terminal region of il3 to lysine (S267K). The native and S267K 5‐HT6 receptors were expressed in COS‐7 cells to study the functional effects of the mutation. The S267K receptor shows 10‐fold higher affinity for serotonin than the native receptor and demonstrates agonist‐independent activity. Clozapine decreased the basal activity of the S267K receptor to vector control levels. Therefore, we can conclude that the S267K mutation renders the 5‐HT6 receptor constitutively active and that clozapine is an inverse agonist at the mutant 5‐HT6 receptor. These results indicate that the c‐terminal region of il3 of the Gs‐coupled 5‐HT6 receptor is a key domain for G‐protein coupling, similar to the Gq‐coupled 5‐HT receptors. The inverse agonist action of clozapine indicates that drugs displaying competitive antagonist activity at native 5‐HT6 receptors may display inverse agonist activity at the constitutively activated form of the receptor. Synapse 47:218–224, 2003. © 2002 Wiley‐Liss, Inc.
Regional infusions of serotonin into the striatum and memory consolidation
Authors: Prado‐Alcalá Roberto A. , Ruiloba María Isabel , Rubio Laura , Solana‐Figueroa Rafael , Medina Cristina , Salado‐Castillo Rigoberto , Quirarte Gina L.
Published: December 2002

Lesions, temporal inactivation, electrical stimulation and administration of drugs that antagonize synaptic activity of the striatum lead to significant deficits of memory. Also, it has been shown that interruption of dopaminergic, GABAergic, or cholinergic activity in discrete areas of this structure is sufficient to disrupt cognitive functions. In spite of the known interactions among dopamine, GABA, acetylcholine, and serotonin, there is a notable scarcity of data germane to the participation of striatal serotonin in learning and memory. It was important, therefore, to investigate the possible involvement of serotonin in cognition. In light of the differential distribution of serotonergic elements within the striatum, a prediction was made that focal injections of serotonin into distinctive regions would produce dissimilar effects on memory. Rats were trained in a one‐trial step‐through inhibitory avoidance task and a retention test was carried out 24 h later. Posttraining injections of serotonin into the dorsal and ventral aspects of the posterior region produced strong amnesia compared to similar injections into the dorsal and ventral aspects of the anterior region. The present findings support the hypothesis that striatal serotonergic activity is involved in memory functions and also provide further evidence of neurochemical heterogeneity within the striatum regarding memory consolidation. Synapse 47:169–175, 2003. © 2002 Wiley‐Liss, Inc.
Presynaptic quantal plasticity: Katz's original hypothesis revisited
Authors: Vautrin Jean , Barker Jeffery L.
Published: December 2002

Changes in the amplitudes of signals conveyed at synaptic contacts between neurons underlie many brain functions and pathologies. Here we review the possible determinants of the amplitude and plasticity of the elementary postsynaptic signal, the miniature. In the absence of a definite understanding of the molecular mechanism releasing transmitters, we investigated a possible alternative interpretation. Classically, both the quantal theory and the vesicle theory predict that the amount of transmitter producing a miniature is determined presynaptically prior to release and that rapid changes in miniature amplitude reflect essentially postsynaptic alterations. However, recent data indicates that short‐term and long‐lasting changes in miniature amplitude are in large part due to changes in the amount of transmitter in individual released packets that show no evidence of preformation. Current representations of transmitter release derive from basic properties of neuromuscular transmission and endocrine secretion. Reexamination of overlooked properties of these two systems indicate that the amplitude of miniatures may depend as much, if not more, on the Ca2+ signals in the presynaptic terminal than on the number of postsynaptic receptors available or on vesicle's contents. Rapid recycling of transmitter and its possible adsorption at plasma and vesicle lumenal membrane surfaces suggest that exocytosis may reflect membrane traffic rather than actual transmitter release. This led us to reconsider the disregarded hypothesis introduced by Fatt and Katz (1952; J Physiol 117:109–128) that the excitability of the release site may account for the “quantal effect” in fast synaptic transmission. In this case, changes in excitability of release sites would contribute to the presynaptic quantal plasticity that is often recorded. Synapse 47:184–199, 2003. © 2002 Wiley‐Liss, Inc.
The mGluR5 antagonist MPEP reduces the conditioned rewarding effects of cocaine but not other drugs of abuse
Authors: McGeehan Andrew J. , Olive M. Foster
Published: December 2002

We examined the ability of 2‐methyl‐6‐(phenylethynyl)‐pyridine (MPEP), a selective antagonist of the type 5 metabotropic glutamate receptor (mGluR5), to reduce the rewarding effects of various drugs of abuse in the conditioned place preference (CPP) paradigm. Mice were treated with MPEP (1, 5, and 20 mg/kg i.p.) 10 min prior to cocaine (15 mg/kg i.p.), D‐amphetamine (2 mg/kg i.p.), nicotine (0.5 mg/kg i.p.), morphine (5 mg/kg i.p.), or ethanol (2 g/kg i.p.) on 3 successive days of CPP conditioning trials. MPEP pretreatment dose‐dependently reduced the development of CPP for cocaine only. When tested alone at the doses effective in reducing CPP, MPEP produced neither a place preference nor aversion. These data provide further support for a role of the mGluR5 receptor in the rewarding effects of cocaine. Synapse 47:240–242, 2003. © 2002 Wiley‐Liss, Inc.
Effect of isolation rearing on pre‐ and post‐synaptic serotonergic function in the rat dorsal hippocampus
Authors: Muchimapura Suparporn , Mason Robert , Marsden Charles A.
Published: December 2002

Several behavioural, neurochemical, and structural alterations found in isolation‐reared rats are similar to those in human schizophrenia. This study investigated changes in cholinergic and serotonergic function in the hippocampus following isolation rearing. Rats were reared in social isolation from weaning for 6 weeks before study and compared to group‐reared rats. An in vitro electrophysiological study investigated the effect of isolation rearing on postsynaptic 5‐HT1A function on CA1 hippocampal neurones activated with the muscarinic agonist carbachol and found no change in the sensitivity of these postsynaptic receptors between the groups. However, a change in presynaptic function was identified, as there was a significant reduction in the time taken for neuronal firing to recover to 50% of the original rate following 5‐HT (10 μM) application, in isolation compared to group‐reared rats. These data suggest a possible change in reuptake following isolation. Uptake studies using 3[H]5‐HT, however, found no change in the inhibition of uptake produced by either fluoxetine or paroxetine in isolation compared to group‐reared rats. The selective 5‐HT1B antagonist CP‐294253 (1 μM), increased endogenous 5‐HT release from hippocampal slices in vitro and this effect was greater (P < 0.001) in group compared to isolation‐reared rats. These results indicate that the change in presynaptic 5‐HT neuronal function was due to impaired autoreceptor responsiveness. Carbachol (1 μM) increased the firing rate of all neurones recorded but only a proportion of these showed a concentration‐related increase. Isolation rearing increased the sensitivity of neurones, showing a concentration‐related increase in firing in response to carbachol, but had no effect on the other neurones. In summary, the present study showed that isolation rearing alters presynaptic 5‐HT1B but not postsynaptic 5‐HT1A receptor activity in the hippocampus. Isolation rearing in the rat results in hippocampal dysfunction, including reduced serotonergic and enhanced muscarinic activity of some neurones. These effects may in part underlie the behavioural consequences of isolation relevant to human developmental disorders. Synapse 47:209–217, 2003. © 2002 Wiley‐Liss, Inc.
Increased dopamine D3 receptor expression accompanying behavioral sensitization to nicotine in rats
Authors: Le Foll Bernard , Diaz Jorge , Sokoloff Pierre
Published: December 2002

Behavioral sensitization to nicotine, which appears following repeated nicotine administration, has been suggested to take part in the development of smoking habit in humans. The mesolimbic dopaminergic system plays a role in this process and a hypersensitivity of postsynaptic neurons of the nucleus accumbens as been proposed as a mechanism, but changes in dopamine D1 or D2 receptors have not been demonstrated to date. A challenge administration of nicotine (0.5 mg/kg s.c.) produced a strong increase in locomotor activity in rats repeatedly pretreated with nicotine (0.5 mg/kg sc), but not saline, once a day for 5 days. This behavioral sensitization was accompanied by an increase in D3 receptor binding and mRNA in the shell of nucleus accumbens. D3 receptor expression was unchanged in the core of nucleus accumbens and dorsal striatum, as it was in the shell of nucleus accumbens after an acute administration of nicotine to naive rats. In contrast, no changes were noticed in D1 and D2 receptor expressions in any brain region examined after chronic or acute treatment with nicotine. In addition, nicotine challenge decreased preprodynorphin and preprotachykinin mRNA levels in naive rats, but only preprotachykinin mRNA levels in rats pretreated with nicotine. These biochemical changes resemble those occurring during behavioral sensitization to levodopa of dopamine‐denervated rats, which had been causally related to the induction of D3 receptor expression. We propose that a similar mechanism is responsible for behavioral sensitization to nicotine. Synapse 47:176–183, 2003. © 2002 Wiley‐Liss, Inc.
THE PREVALENCE AND CORRELATES OF CONSANGUINEOUS MARRIAGES IN YEMEN: SIMILARITIES AND CONTRASTS WITH OTHER ARAB COUNTRIES
Authors: JURDI ROZZET , SAXENA PREM C.
Published: December 2002

Using data on 9762 women from the 1997 Yemen Demographic and Maternal and Child Health Survey, this paper examines the prevalence and socioeconomic correlates of consanguineous marriages in Yemen. The results indicate that 40% of marriages are consanguineous, over 85% of which are between first cousins. The prevalence of consanguineous marriages appears to have increased over time, particularly for the last marriage cohort. As for socioeconomic correlates, the study confirms the inverse association between consanguineous marriages and women’s education and occupation, age at marriage and economic status. However, no statistically significant difference in the prevalence of consanguinity has been found by place of residence and geographical region. Somewhat unexpected results have been obtained by husband’s background characteristics, with higher educated men and those working in the modern sector of the economy being more likely to be married to cousins.
THE IMPACT OF RURAL–URBAN MIGRATION ON UNDER-TWO MORTALITY IN INDIA
Authors: STEPHENSON ROB , MATTHEWS ZOE , MCDONALD J. W.
Published: December 2002

This paper examines the impact of rural–urban migration on under-two mortality in India, using data from the 1992/93 Indian National Family Health Survey. Multilevel logistic models are fitted for mortality in three age groups: neonatal, early post-neonatal, and late post-neonatal and toddler. Migration status was not a significant determinant of mortality in any of the three age groups. Further analysis shows that a relationship between migration status and mortality exists when socioeconomic and health utilization variables are omitted from the models. The relationship between migration and mortality is thus explained by differences in socioeconomic status and use of health services between rural–urban migrant and non-migrant groups. The selectivity of rural–urban migrants on socioeconomic characteristics creates mortality differentials between rural–urban migrants and rural non-migrants. Problems faced by migrants in assimilating into urban societies create mortality differentials between rural–urban migrants and urban non-migrants. These results highlight the need to target migrants in the provision of health services, and demonstrate that rural areas continue to have the highest levels of infant–child mortality. Further research is needed to understand the health care needs of rural–urban migrants in order to inform the provision of appropriate health care.
SECULAR GAINS IN FLUID INTELLIGENCE: EVIDENCE FROM THE CULTURE-FAIR INTELLIGENCE TEST
Authors: COLOM ROBERTO , GARCÍA-LÓPEZ OSCAR
Published: December 2002

There is no doubt about the reality of the secular increase in cognitive test scores. However, there is disagreement about a key issue: does the observed increase reflect a genuine upward trend in intelligence? Evidence from the Raven test is clear, although there are some doubts about its adequacy as a fine-grained measure of fluid intelligence. Evidence from the so-called ‘method of correlated vectors’ is much less clear. When a crystallized battery is considered, the results leave little doubt: the increase does not reflect gains in general intelligence. However, when a fluid battery is analysed, the increase does reflect gains in general intelligence. The present study uses one of the best available measures of fluid intelligence (the Culture-Fair intelligence test) to provide new evidence for the secular increase in fluid intelligence, beyond the findings from the Raven test and the method of correlated vectors. A total of 4498 Spanish high school students and high school graduates were tested within a time interval of 20 and 23 years, respectively. The results show that there is a clear upward trend in intelligence. Moreover, students show an average increase equivalent to 6 IQ points, while graduates show an average increase of 4 IQ points. Therefore, more selected people (graduates) show a smaller increase than less selected people (students). Some implications are discussed.
PILLS, INJECTIONS AND AUDIOTAPES: REACHING COUPLES IN PAKISTAN
Authors: COLLUMBIEN MARTINE , DOUTHWAITE MEGAN
Published: December 2002

An innovative social marketing intervention in Pakistan distributes audiocassettes via chemist shops and Lady Health Visitors (LHVs) to reach women in a segregated society with accurate information on hormonal contraceptives. Operations research was done to assess the utility of the cassette in knowledge dissemination and adoption of hormonal use. In total 187 structured questionnaires were completed with couples who had obtained a cassette. Listeners were significantly more knowledgeable than non-listeners about correct use of hormonals (OR=8·6 for women and OR=12·7 for men). Hormonal use increased from 12% to 25%. LHVs also organized discussion groups for women, and attending such a chat group was the strongest predictor for adoption of pills and injectables (OR=4·15). Equivalent male groups are suggested to reach apprehensive men. By providing accurate information to urban couples and by acquiring a knowledgeable critical mass of satisfied users, the cassette could be a powerful catalyst to further contraceptive diffusion.
DETERMINANTS OF WAITING TIME TO THIRD PREGNANCY USING CENSORED LINEAR REGRESSION
Authors: AWANG HALIMAH
Published: December 2002

The intervals between pregnancies have important effects on fertility and maternal and infant health outcomes. This study uses linear regression with censored observation to assess the determinants of the waiting time to third pregnancy. The analysis is applied to data from the Second Malaysian Family Life Survey consisting of 1172 women who had their second delivery ending in a live birth. Contraceptive use, age of the woman, duration of breast-feeding, length of previous pregnancy interval and education of the woman all affect the waiting time to third pregnancy significantly.
ADOLESCENTS’ DECISION-MAKING AND ATTITUDES TOWARDS ABORTION IN NORTH-EAST BRAZIL
Authors: BAILEY PATRICIA E. , BRUNO ZENILDA V. , BEZERRA MARIA F. , QUEIRÓS IVANY , OLIVEIRA CRISTIANA M.
Published: December 2002

Three groups of adolescents are compared with regard to their own considerations of abortion and when they believe abortion is justified. One group of adolescents terminated their pregnancies (n=95), a second became pregnant and carried their pregnancies to term but considered abortion (n=68), and the third also carried their pregnancies to term but did not consider abortion (n=204). The study was carried out between 1995 and 1998 in Fortaleza, Brazil. Adolescents were interviewed at the time of their hospitalization or their first prenatal visit and again at 6 weeks and 1 year post-abortion or postpartum. Friends and family recommended abortion to at least half of the teenagers in each group. Teenagers who aborted were more accepting of abortion than those who did not abort, while those who considered abortion found the practice more justified than those who did not consider abortion. Teenagers who aborted became less accepting a year later, while those who did not consider abortion became more accepting. A better understanding of adolescent attitudes towards abortion and their decision-making process should help adults and professionals meet the needs of adolescents for support in the process and in the reduction of the number of unintended pregnancies in the future.
SEASONALITY OF BIRTHS IS ASSOCIATED WITH SEASONALITY OF MARRIAGES IN MALTA
Authors: GRECH VICTOR , SAVONA-VENTURA CHARLES , AGIUS-MUSCAT HUGO , JANULOVA LINA
Published: December 2002

This study was carried out to quantify secular trends in seasonal variation in births in Malta, a small Mediterranean country where the vast proportion of births occur in wedlock due to a predominantly Roman Catholic population. It also related such variations to seasonal variation in marriages. Annual seasonal peaks of marriages and births were analysed over the period 1950–1996 by X11 ARIMA. A significant peak in marriages (n=111,932) in the third quarter of the year was found for almost the entire period under study. This was paralleled by a peak in births (n=299,558) for the period 1970–1996, which lagged after the peak in marriages by 13–14 months. For the period 1994–1996, when monthly data for monthly pregnancies were available by pregnancy order, the peak in births was caused by first pregnancies only. Seasonal patterns in births occur almost universally due to cultural and/or biometeorological factors. The best known patterns include those of the southern United States, where births decline in April and May, and in northern Europe, where births peak in March and April. In Malta, the late summer peak in births appears to be due to a practical and planned approach by Maltese couples to contraceptive planning, probably influenced by the Roman Catholic ethos and social pressures, with unprotected intercourse occurring only after marriage. In Malta, birth control, albeit by so-called natural methods, was introduced in the 1960s. Prior to this period, births peaked towards the beginning/end of the year, and this may be the more natural seasonality of births in Malta.
ROLE OF HEALTH-SEEKING BEHAVIOUR IN CHILD MORTALITY IN THE SLUMS OF KARACHI, PAKISTAN
Authors: D’SOUZA RENNIE M.
Published: December 2002

The role of family health-seeking behaviour in under-five-year child mortality was explored through the combined approach of examining health-seeking behaviour regarding treatment generally, and in specific in relation to illness before death. A population-based case control study was carried out during the period 1993–1994 using 222 deaths from diarrhoea and acute respiratory illness (ARI) in children under five years of age in six slums of Karachi as cases, and 419 controls matched on age, disease (diarrhoea and ARI) and slum. Factors significantly associated (p<0·05) with child mortality in the multivariate analysis were: mothers changing healers quickly, using a traditional healer or an unqualified doctor and mothers to whom doctors did not explain the treatment, even when maternal education was controlled for. Seeking effective medical services is highly influential on whether the child survives or succumbs to ARI or diarrhoea. As mothers are the first providers of care, an attempt should be made to try and improve their skills through health education so that they can use simple and effective treatments for minor illnesses. They should also be taught to recognize potentially life-threatening conditions, to seek care early and to persist with treatment.
SEX DIFFERENCES ON THE PROGRESSIVE MATRICES: SOME DATA FROM HONG KONG
Authors: LYNN RICHARD , WAH TSE-CHAN PO
Published: December 2002

There has been a debate between N. J. Mackintosh and the first author of this paper on whether the sex difference on the Progressive Matrices is zero or, at most, 1–2 IQ points in favour of either sex, as maintained by Mackintosh, or whether from the age of 15 years onwards males obtain higher average scores than females by more than 2 IQ points, as maintained by Lynn. New data relevant to this controversy are presented from Hong Kong consisting of sex differences on the standardization sample of the Advanced Progressive Matrices on 15- to 18-year-olds. The results are that males obtained a higher mean score than females of 1·6 raw score points, equivalent to an advantage of 3·2 or 4·1 IQ points, according to two alternative methods of calculation. The results provide further confirmation that in later adolescence and among adults, males obtain significantly higher mean IQs on the Progressive Matrices than females.
GABRIEL WARD LASKER
Authors: Mascie-Taylor C. G. Nicholas
Published: December 2002

Gabriel died on Tuesday 27 August 2002 in his 91st year. He had been a very
committed member of the Editorial Board since January 1991 and he continued to
review papers for the Journal with the same degree of impartiality and care until a
week before he died.
Numerical simulation of the wake of a towed
sphere in a weakly stratified fluid
Authors: DOMMERMUTH DOUGLAS G. , ROTTMAN JAMES W. , INNIS GEORGE E. , NOVIKOV EVGENY A.
Published: December 2002

We present some preliminary results from using large-eddy simulation to compute the
late wake of a sphere towed at constant speed through a non-stratified and a uniformly
stratified fluid. The wake is computed in each case for two values of the Reynolds
number: Re = 104, which is comparable to that used in laboratory experiments, and
Re = 105. An important aspect of the simulation is the use of an iterative procedure
to relax the initial turbulence field so that the normal and shear turbulent stresses are
properly correlated and the turbulent production and dissipation are in equilibrium.
For the lower Reynolds number our results compare well with existing laboratory
experimental results. For the higher Reynolds number we find that even though the
turbulence is more developed and the wake contains finer structure, most of the
similarity properties of the wake are unchanged compared with those observed at the
lower Reynolds number.
Resonance forever: existence of a critical mass
and an infinite regime of resonance in
vortex-induced vibration
Authors: GOVARDHAN R. , WILLIAMSON C. H. K.
Published: December 2002

In this paper, we study the transverse vortex-induced vibrations of a cylinder with
no structural restoring force (k = 0). In terms of the conventionally used normalized
flow velocity, U*, the present experiments correspond to an infinite value (where
U* = U/fND, fN = natural frequency, D = diameter). A reduction of mass ratios m*
(mass/displaced mass) from the classically studied values of order m* = 100, down to
m* = 1, yields negligible oscillations. However, a further reduction in mass exhibits a
surprising result: large-amplitude vigorous vibrations suddenly appear for values of
mass less than a critical mass ratio, m*crit = 0.54. The classical assumption, since the
work of den Hartog (1934), has been that resonant large-amplitude oscillations exist
only over a narrow range of velocities, around U*∼5, where the vortex shedding
frequency is comparable with the natural frequency. However, in the present study,
we demonstrate that, so long as the body’s mass is below this critical value, the regime
of normalized velocities (U*) for resonant oscillations is infinitely wide, beginning at
around U*∼5 and extending to U*→∞. This result is in precise accordance with
the predictions put forward by Govardhan & Williamson (2000), based on elastically
mounted vibration studies (where k > 0). We deduce a condition under which this
unusual concept of an infinitely wide regime of resonance will occur in any generic
vortex-induced vibration system.
Asymptotic model of the mobile interface
between two liquids in a thin porous stratum
Authors: PANFILOV M. , BUÈS M.
Published: December 2002

We propose a new generalized model to describe deformations of the mobile interface
separating two immiscible liquids in a porous medium. The densities and the viscosities
of the fluids can have any value. The horizontal size of the interface is much
greater than the vertical size of the domain. Unlike the classical theory, the new model
describes gravitational non-equilibrium processes, including the Rayleigh–Taylor
instability which appears in the form of a negative apparent diffusion parameter. Several
flow regimes are established depending on the ratio between gravity and the elastic
fluid/medium forces, and between the vertical and horizontal flow rates. The model is
used to analyse the evolution of the interface during the free spreading of one liquid
over another. This is characterized by the presence of interface degeneration points.
The explicit solution to the problem of oil and water flow towards a well is presented
as an application to oil reservoirs.
Nonlinear stratified spin-up
Authors: THOMAS LEIF N. , RHINES PETER B.
Published: December 2002

Both a weakly nonlinear analytic theory and direct numerical simulation are used to
document processes involved during the spin-up of a rotating stratified fluid driven
by wind-stress forcing for time periods less than a homogeneous spin-up time. The
strength of the wind forcing, characterized by the Rossby number ε, is small enough
(i.e. ε[Lt ]1) that a regular perturbation expansion in ε can be performed yet large
enough (more specifically, ε∝E1/2, where E is the Ekman number) that higher-order
effects of vertical diffusion and horizontal advection of momentum/density are
comparable in magnitude. Cases of strong stratification, where the Burger number S
is equal to one, with zero heat flux at the upper boundary are considered. The Ekman
transport calculated to O(ε) decreases with increasing absolute vorticity. In contrast
to nonlinear barotropic spin-up, vortex stretching in the interior is predominantly
linear, as vertical advection negates stretching of interior relative vorticity, yet is
driven by Ekman pumping modified by nonlinearity. As vertical vorticity is generated
during the spin-up of the fluid, the vertical vorticity feeds back on the Ekman
pumping/suction, enhancing pumping and vortex squashing while reducing suction
and vortex stretching. This feedback mechanism causes anticyclonic vorticity to grow
more rapidly than cyclonic vorticity. Strict application of the zero-heat-flux boundary
condition leads to the growth of a diffusive thermal boundary layer E−1/4 times
thicker than the Ekman layer embedded within it. In the Ekman layer, vertical
diffusion of heat balances horizontal advection of temperature by extracting heat
from the thermal boundary layer beneath. The flux of heat extracted from the top of
the thermal boundary layer by this mechanism is proportional to the product of the
Ekman transport and the horizontal gradient of the temperature at the surface. The
cooling caused by this heat flux generates density inversions and intensifies lateral
density gradients where the wind-stress curl is negative. These thermal gradients make
the potential vorticity strongly negative, conditioning the fluid for ensuing symmetric
instability which greatly modifies the spin-up process.
Formation and propagation of a shock wave in a
gas with temperature gradients
Authors: SOUKHOMLINOV V. S. , KOLOSOV V. Y. , SHEVEREV V. A. , ÖTÜGEN M. V.
Published: December 2002

A theoretical analysis was carried out to study the formation and propagation of
a weak shock wave in a gas with longitudinal temperature gradients. An equation
describing the formation and propagation of a weak shock wave through a non-uniform
medium in the absence of energy dissipation was derived. An approximate
analytical solution to the one-dimensional wave propagation equation is established.
With this, the thermal gradient effects on the shock-wave Mach number and speed
were investigated and the results were compared to earlier experiments. Numerical
solutions for the same problem using Euler’s equations have also been obtained and
compared to the analytical results. The analysis shows that the time of shock-wave
formation from the initial disturbance, for mild temperature gradients, is independent
of the gradient. The shock wave forms at a longer axial distance from the initial
disturbance when the temperature gradient is positive whereas the opposite is true
for a negative temperature gradient.
Bounds on Rayleigh–Bénard convection with an
imposed heat flux
Authors: OTERO JESSE , WITTENBERG RALF W. , WORTHING RODNEY A. , DOERING CHARLES R.
Published: December 2002

We formulate a bounding principle for the heat transport in Rayleigh–Bénard
convection with fixed heat flux through the boundaries. The heat transport, as measured
by a conventional Nusselt number, is inversely proportional to the temperature drop
across the layer and is bounded above according to Nu [les ] cRˆ1/3, where c < 0.42 is
an absolute constant and Rˆ = αγβh4/(νκ) is the ‘effective’ Rayleigh number, the
non-dimensional forcing scale set by the imposed heat flux κβ. The relation among the
parameter Rˆ, the Nusselt number, and the conventional Rayleigh number defined in
terms of the temperature drop across the layer, is NuRa = Rˆ, yielding the bound
Nu [les ] c3/2Ra1/2.
Energy propagation of long extratropical Rossby
waves over slowly varying zonal topography
Authors: TAILLEUX RÉMI , McWILLIAMS JAMES C.
Published: December 2002

In classical WKB theory the only way wave energy density, as a surrogate for
wave action density, can increase or decrease along a ray is as a result of the ray
focusing or widening. This occurs when the group velocity is divergent. There are
particular regions, however, where the wave can resonantly exchange action with
another wave mode with approximately the same wavenumbers; a situation known
as Landau–Zener transition, mode conversion, linear (adiabatic) resonance, etc. This
effect invalidates locally the underlying assumption of WKB theory that no scattering
of energy occurs between WKB wave modes. In this paper this effect is investigated
theoretically for free long baroclinic Rossby waves in a two-layer planetary geostrophic
model of the ocean with a purely zonal topography, here taken as a Gaussian ridge.
The waves are excited along the east coast by an unspecified wavemaker at a fixed
frequency ω. In the computation considered, mode conversion is found to occur
principally near the ridge’s top and on the eastern flank. The predictions of mode
conversion theory are tested against the results of direct numerical simulations. This
shows excellent agreement, both for the locations of mode conversion points, and for
the amplitude of the transmitted and converted WKB wave modes.
On the influence of coherent structures upon
interscale interactions in turbulent plane jets
Authors: da SILVA C. B. , MÉTAIS O.
Published: December 2002

The influence of the coherent structures on grid/subgrid-scale (GS/SGS) interactions
in free shear layers is analysed through the application of a top-hat filter to several
plane jet direct numerical simulations (DNS). The Reynolds number based on the
plane jet inlet slot width is Reh = 3000. The study deals with energy containing
(Kelvin–Helmholtz) and inertial range (streamwise) vortices, from the far field of
the turbulent plane jet. The most intense kinetic energy exchanges between GS and
SGS occur near these structures and not randomly in the space. The GS kinetic
energy is dominated by GS advection and GS pressure/velocity interactions which
appear located next to the Kelvin–Helmholtz rollers. Surprisingly, GS/SGS transfer
is not very well correlated with the coherent vortices and GS/SGS diffusion plays
an important role in the local dynamics of both GS and SGS kinetic energy. The
so-called ‘local equilibrium assumption’ holds globally but not locally as most viscous
dissipation of SGS kinetic energy takes place within the vortex cores whereas forward
and backward GS/SGS transfer occurs at quite different locations. Finally, it was
shown that SGS kinetic energy advection may be locally large as compared to the
other terms of the SGS kinetic energy transport equation.
Liquid-fuel thermocapillary flow induced by
a spreading flame
Authors: HIGUERA F. J.
Published: December 2002

An analysis is presented of the flow in a layer of liquid whose surface tension varies
under the action of a moving surface heat flux distribution chosen to model the
spread of a flame over the liquid. Subject to this heat flux, the surface temperature
increases from the ambient temperature of the liquid, far upstream, to its vaporization
temperature at a moving vaporization front, and stays constant at this value
downstream of the vaporization front. The speed of the front is determined by a
condition of regularity of the temperature. Three different regimes are found which
correspond to the uniform, pulsating and pseudo-uniform regimes of flame spread
observed experimentally when the ambient temperature of the liquid, or the strength
of the surface heat flux, is decreased. The first and third of these are stationary
regimes of high and low front speed, and the second is an oscillatory regime featuring
long phases of low speed and short pulses of high speed. An asymptotic description
is given of the flow relative to the moving vaporization front in the stationary regime
of low speed, which includes a long recirculation eddy ahead of the front and a small
region around the front that controls its speed. An explanation of the mechanism of
oscillation is proposed based on the interplay between the quasi-steady response of
this small controlling region and the delay introduced by the recirculating flow.
On the capillary interaction between solid plates
forming menisci on the surface of a liquid
Authors: SAIF TAHER A.
Published: December 2002

A hydrophilic or a hydrophobic long rigid solid plate of finite width, forming a
meniscus with a liquid in a uniform gravitational field is considered. The one-dimensional
meniscus with prescribed heights of the triple point from the far-field
liquid surface is investigated analytically using the Young–Laplace equation. It is
found that for a hydrophilic plate, the vertical force necessary to break the meniscus
during removal of the plate from the liquid is larger than the force necessary to break
the meniscus during submersion of the plate into the liquid. Furthermore, the capillary
force on the plate reaches a maximum before the meniscus collapses during removal,
but no maximum exists before collapse during submersion. The reverse is true when
the plate is hydrophobic. The study is then extended to investigate the interaction
force between two plates, each forming a meniscus with the liquid. The elevations of
the plates from the far-field liquid surface are prescribed, in contrast to earlier studies
where interaction between long cylinders floating under self weight was considered.
Here, the menisci are determined exactly using the Young–Laplace equation. It is
shown that for prescribed plate elevations, there can be at most two possible pairs
of menisci between them. Each pair bifurcates from a meniscus that is determined by
the elevations of the plates and the gap between them. Furthermore, as known for
solids floating under self-weight, the horizontal component of the interaction force
is attractive for similar menisci (e.g. when the two plates are equally displaced in or
out of the liquid), and repulsive when they form opposite menisci. It is shown that
if the two menisci are of the same type, but not similar (e.g. one plate is pushed
more into the liquid than the other), then the force is attractive at long distances, and
may be repulsive at shorter distances with a stable equilibrium at a finite distance
between the plates, depending on the elevations of the plates. Such interaction can be
between two hydrophilic or two hydrophobic plates or between a hydrophilic and a
hydrophobic plate.
Sidewall finite-conductivity effects in confined
turbulent thermal convection
Authors: VERZICCO ROBERTO
Published: December 2002

The effects of a sidewall with finite thermal conductivity on confined turbulent
thermal convection has been investigated using direct numerical simulation. The
study is motivated by the observation that the heat flowing through the lateral wall is
not always negligible in the low-aspect-ratio cells of several recent experiments. The
extra heat flux modifies the temperature boundary conditions of the flow and therefore
the convective heat transfer. It has been found that, for usual sidewall thicknesses,
the heat travelling from the hot to the cold plates directly through the sidewall is
negligible owing to the additional heat exchanged at the lateral fluid/wall interface. In
contrast, the modified temperature boundary conditions alter the mean flow yielding
significant Nusselt number corrections which, in the low Rayleigh number range, can
change the exponent of the Nu vs. Ra power law by 10%.
Instabilities in the flow between co- and
counter-rotating disks
Authors: GAUTHIER G. , GONDRET P. , MOISY F. , RABAUD M.
Published: December 2002

The flow between two rotating disks (radius to heigh ratio of 20.9), enclosed by a
rotating cylinder, is investigated experimentally in the cases of both co- and
counter-rotation. This flow gives rise to a large gallery of instability patterns. A regime
diagram of these patterns is presented in the (Reb,Ret)-plane, where Reb,t is the
Reynolds number associated with each disk. The co-rotation case and the weak
counter-rotation case are very similar to the rotor–stator case, both for the basic flow
and the instability patterns: the basic flow consists of two boundary layers near each
disk and the instability patterns are the axisymmetric vortices and the positive spirals
described in the rotor–stator experiments of Gauthier, Gondret & Rabaud (1999),
Schouveiler, Le Gal & Chauve (2001), and the numerical study of Serre, Crespo del
Arco & Bontoux (2001). The counter-rotation case with higher rotation ratio is more
complex: above a given rotation ratio, the recirculation flow becomes organized into
a two-cell structure with the appearance of a stagnation circle on the slower disk. A
new kind of instability pattern is observed, called negative spirals. Measurements of
the main characteristics of this pattern are presented, including growth times, critical
modes and phase velocities.
On sediment transport under dam-break flow
Authors: PRITCHARD DAVID , HOGG ANDREW J.
Published: December 2002

We present exact solutions for suspended sediment transport under one-dimensional
dam-break flow, both over a dry bed and into a small depth of tail water. We explicitly
calculate the suspended sediment concentration, including erosion and deposition, and
investigate the effect of varying the erosional and depositional models employed. These
solutions order insight into sediment transport processes under floods or sheet flow
events, and we also discuss their application as test-bed solutions for the validation
of numerical models.
The stability of a slowly diverging swirling jet
Authors: COOPER A. J. , PEAKE N.
Published: December 2002

The spatial evolution of small-amplitude unsteady disturbances of an axisymmetric
swirling jet is examined theoretically. The slow axial divergence of the jet mean flow
is accounted for by using the method of multiple scales and a consistent solution
for both the mean flow and unsteady disturbance is derived. Previous work by Lu &
Lele (1999) has considered the leading-order analysis, in which the modal eigenvalues
are determined from locally parallel theory, but the key feature of our analysis is
the solution of the next-order secularity condition for the axial variation of the
wave-envelope amplitude.

The swirling jet profile sustains two types of instability waves: the Kelvin–Helmholtz
instability associated with axial shear, and a centrifugal instability which arises due
to a decrease in circulation with radial distance. The evolution of the disturbance
axial wavenumber and envelope amplitude with downstream distance is calculated.
Numerical results show that the growth of the centrifugal mode is significantly
curtailed as a result of a rapidly decaying envelope amplitude. The shear instability
is significantly more amplified by the addition of swirl.

The general solution for the disturbance envelope amplitude breaks down at so-called
turning points. This is found to occur for a series of neutral propagating modes.
A rescaling in the vicinity of the turning point shows that the amplitude in this region
is governed by a parabolic cylinder equation. The modal amplitude is seen to decay
very significantly through this turning point, even though the mode is neutral to
leading order.