bluuebunny/crossref_metadata_2025 huggingface dataset:
The analysis of multivariate interval‐censored survival data
Authors: Kim Mimi Y. , Xue Xiaonan
Published: November 2002

This paper considers a marginal approach for the analysis of the effect of covariates on multivariate interval‐censored survival data.Interval censoring of multivariate events can occur when the events are not directly observable but are detected by periodically performing clinical examinations or laboratory tests. The method assumes the marginal distribution for each event is based on a discrete analogue of the proportional hazards model for interval‐censored data. A robust estimator for the covariance matrix is developed that accounts for the correlation between events. A simulation study comparing the performance of this method and a midpoint imputation approach indicates the parameter estimates from the proposed method are less biased. Furthermore, even when the events are only modestly correlated, ignoring the correlation can result in erroneous variance estimators. The method is illustrated using data from an ongoing clinical trial involving subjects with systemic lupus erythematosus. Copyright © 2002 John Wiley & Sons, Ltd.
A hierarchical Poisson mixture regression model to analyse maternity length of hospital stay
Authors: Wang K. , Yau Kelvin K. W. , Lee Andy H.
Published: November 2002

Inpatient length of stay (LOS) is often considered as a proxy of hospital resource consumption. Using statewide obstetrical delivery data, a two‐component Poisson mixture model provides a reasonable fit to the heterogeneous LOS distribution. Adopting the generalized linear mixed model (GLMM) approach, random effects are introduced to the two‐component Poisson mixture regression model to account for the inherent correlation of patients clustered within hospitals. An EM algorithm is developed for the joint estimation of regression coefficients and variance component parameters. Related diagnostic measures for assessing model adequacy are derived. When applying the method to analyse maternity LOS, appropriate risk factors for the short‐stay and long‐stay subgroups can be identified from the respective Poisson components. In addition, predicted random hospital effects enable the comparison of relative efficiencies among hospitals after adjustment for patient case‐mix and health provision characteristics. Copyright © 2002 John Wiley & Sons, Ltd.
Selecting the best method to evaluate bronchodilation when analysing bronchodilator studies
Authors: Goedhart Dick M. , Zanen Pieter
Published: November 2002

Changes in lung function (that is, FEV1) are commonly expressed as a percentage of the predicted value. The question is whether this parameter is best suited for statistical analysis. A total of 2199 bronchodilation tests were selected and pre‐ and post‐dilator FEV1, age, height and sex extracted. Predicted FEV1 values, the difference between pre‐ and post‐dilator FEV1 and the change as percentage of predicted or baseline FEV1 were calculated. The latter parameters were subjected to analysis of variance and pre‐ and post‐dilator FEV1 to analysis of covariance. The statistical power of these four approaches and the residual structure were used to select the best approach. Analysis of variance of the change as percentage of predicted and covariance analysis of pre‐ and post‐dilator FEV1 offers the best performance. The residuals of the analysis of variance showed a funnel shaped structure. The latter causes residual heterogeneity, resulting in a loss of power and deviations between the actual and nominal α‐level. This is not taken into account when calculating sample sizes using the standard equations, which implicitly assume lack of these problems. Analysis of covariance does not suffer from these problems. The best way to evaluate bronchodilation in trials is to use analysis of covariance. Copyright © 2002 John Wiley & Sons, Ltd.
Alternatives to the hazard ratio in summarizing efficacy in time‐to‐event studies: an example from influenza trials
Authors: Keene Oliver N.
Published: November 2002

Estimates of the efficacy of new medicines are key to the investigation of their clinical effectiveness. The most widely recommended approach to summarizing time‐to‐event data from clinical trials is to use a hazard ratio. When the proportional hazards assumption is questionable, a hazard ratio depends on the length of patient follow‐up. Hazard ratios do not directly translate into differences in times to events and therefore can present difficulties in interpretation. This paper describes an area where summary by hazard ratio would seem unsuitable and explores alternative estimates of efficacy. In particular, the difference in median time to event between treatments can provide a useful and consistent measure of efficacy. Methods of calculating confidence intervals for differences in medians for censored time‐to‐event will be described. Accelerated failure time models provide a useful alternative approach to proportional hazards modelling. Estimates of the ratio of the median time to event between treatments are directly available from these models. One of the reasons given for summarizing time‐to‐event studies by a hazard ratio is to facilitate meta‐analyses. The bootstrap estimate of standard error for difference in median in each trial can provide a method for combining results based on summary statistics. Copyright © 2002 John Wiley & Sons, Ltd.
Evaluating mixed stains with contributors of different ethnic groups under the NRC‐II Recommendation 4.1
Authors: Fung Wing K. , Hu Yue‐Qing
Published: November 2002

In countries with multiple racial or ethnic groups, it is not uncommon that contributors to a mixed stain or a DNA mixture belong to different ethnic origins. This paper derives a general formula for evaluating the likelihood ratio in such situations based on the commonly adopted Recommendation 4.1 of the U.S. Second National Research Council Report on the evaluation of DNA evidence. The restrictive Hardy–Weinberg assumption is not taken in this paper. Our formula generalizes the results of Fung and Hu for a single ethnic group, and of Weir et al. under the Hardy–Weinberg law for a single, and Fukshansky and Bär for multiple ethnic groups. The effect of different ethnic groups of contributors to the interpretation of mixtures is illustrated through the analysis of the Simpson case. Copyright © 2002 John Wiley & Sons, Ltd.
The study of long‐term HIV dynamics using semi‐parametric non‐linear mixed‐effects models
Authors: Wu Hulin , Zhang Jin‐Ting
Published: November 2002

Modelling HIV dynamics has played an important role in understanding the pathogenesis of HIV infection in the past several years. Non‐linear parametric models, derived from the mechanisms of HIV infection and drug action, have been used to fit short‐term clinical data from AIDS clinical trials. However, it is found that the parametric models may not be adequate to fit long‐term HIV dynamic data. To preserve the meaningful interpretation of the short‐term HIV dynamic models as well as to characterize the long‐term dynamics, we introduce a class of semi‐parametric non‐linear mixed‐effects (NLME) models. The models are non‐linear in population characteristics (fixed effects) and individual variations (random effects), both of which are modelled semi‐parametrically. A basis‐based approach is proposed to fit the models, which transforms a general semi‐parametric NLME model into a set of standard parametric NLME models, indexed by the bases used. The bases that we employ are natural cubic splines for easy implementation. The resulting standard NLME models are low‐dimensional and easy to solve. Statistical inferences that include testing parametric against semi‐parametric mixed‐effects are investigated. Innovative bootstrap procedures are developed for simulating the empirical distributions of the test statistics. Small‐scale simulation and bootstrap studies show that our bootstrap procedures work well. The proposed approach and procedures are applied to long‐term HIV dynamic data from an AIDS clinical study. Copyright © 2002 John Wiley & Sons, Ltd.
Optimal designs of two‐stage studies for estimation of sensitivity, specificity and positive predictive value
Authors: McNamee Roseanne
Published: November 2002

The cost efficiency of estimation of sensitivity, specificity and positive predictive value from two‐stage sampling designs is considered, assuming a relatively cheap test classifies first‐stage subjects into several categories and an expensive gold standard is applied at stage two. Simple variance formulae are derived and used to find optimal designs for a given cost ratio. The utility of two‐stage designs is measured by the reduction in variances compared with one‐stage simple random designs. Separate second‐stage design is also compared with proportional allocation (PA). The maximum percentage reductions in variance from two‐stage designs for sensitivity, specificity and positive predictive value estimation arePper cent, (1‐P) per cent andW, respectively, wherePis the population prevalence of disease andWthe population percentage of test negatives. The optimum allocation of stage‐two resources is not obvious: the optimum proportion of true cases at stage two may even be less than under PA. PA is near optimal for sensitivity estimation in most cases when prevalence is low, but inefficient compared with the optimal scheme for specificity. Copyright © 2002 John Wiley & Sons, Ltd.
Adjustment for misclassification in studies of familial aggregation of disease using routine register data
Authors: Andersen Elisabeth Wreford , Andersen Per Kragh
Published: November 2002

This paper discusses the misclassification that occurs when relying solely on routine register data in family studies of disease clustering. A register study of familial aggregation of schizophrenia is used as an example. The familial aggregation is studied using a regression model for the disease in the child including the disease status of the parents as a risk factor. If all the information is found in the routine registers then the disease status of the parents is only known from the time when the register started and if this information is used unquestioningly the parents who have had the disease before this time are misclassified as disease‐free. Two methods are presented to adjust for this misclassification: regression calibration and an EM‐type algorithm. These methods are used in the schizophrenia example where the large effect of having a schizophrenic mother hardly shows any signs of bias due to misclassification. The methods are also studied in simulations showing that the misclassification problem increases with the disease frequency. Copyright © 2002 John Wiley & Sons, Ltd.
Updating of covariates and choice of time origin in survival analysis: problems with vaguely defined disease states
Authors: Liestøl Knut , Andersen Per Kragh
Published: November 2002

This paper discusses survival analysis based on updated covariates with focus on proportional hazard regression in situations where some disease states may be vaguely defined. Analyses of a trial in liver cirrhosis are used to motivate the discussion. We use problems caused by inclusion of recordings from unscheduled follow‐ups to illustrate the importance of appropriate coding of covariates and describe how such problems may be approached using appropriately ‘lagged’ covariates. The choice of time origin is discussed with emphasis on situations where disease initiation is difficult to define. Simulations are used to assess the effect of an erroneously specified time origin. It is argued that age or calendar time may frequently be sensible time variables. Copyright © 2002 John Wiley & Sons, Ltd.
Power and sample size for DNA microarray studies
Authors: Lee Mei‐Ling Ting , Whitmore G. A.
Published: November 2002

A microarray study aims at having a high probability of declaring genes to be differentially expressed if they are truly expressed, while keeping the probability of making false declarations of expression acceptably low. Thus, in formal terms, well‐designed microarray studies will have high power while controlling type I error risk. Achieving this objective is the purpose of this paper. Here, we discuss conceptual issues and present computational methods for statistical power and sample size in microarray studies, taking account of the multiple testing that is generic to these studies. The discussion encompasses choices of experimental design and replication for a study. Practical examples are used to demonstrate the methods. The examples show forcefully that replication of a microarray experiment can yield large increases in statistical power. The paper refers to cDNA arrays in the discussion and illustrations but the proposed methodology is equally applicable to expression data from oligonucleotide arrays. Copyright © 2002 John Wiley & Sons, Ltd.
Positive Political Theory I: Collective Preference. By David Austen-Smith and Jeffrey S. Banks. Ann Arbor: University of Michigan Press, 1999. 208p. $39.50.
Authors: Schofield Norman
Published: November 2002

This study is intended as the first of a two-volume presenta-
tion of positive political theory. As the authors indicate in the
preface, in this volume they develop what may be termed
Arrovian direct preference aggregation, a theory that exam-
ines the properties of a direct aggregation rule, f, mapping
from a domain of preference profiles on a set, X. For any
profile, , the image of f is a social preference relation
denoted f( ). The social relation may exhibit maximal or
unbeaten outcomes, mf( ), in X itself. Thus, the volume is
concerned with the "classification" of all social rules that map
from preference profiles into X itself.
The Clinton Scandal and the Future of American Government. Edited by Mark J. Rozell and Clyde Wilcox. Washington, DC: Georgetown University Press, 2000. 288p. $55.00 cloth, $18.95 paper.
Authors: Silverstein Mark
Published: November 2002

Ted Lowi once wrote that scandals are a proper subject for
the political scientist because the observer is catching the
country in the act of being itself (Theodore J. Lowi, "Fore-
word," in Andrei S. Markovits and Mark Silverstein, eds., The
Politics of Scandal: Power and Process in Liberal Democracies,
1988, p. xii). Lowi's remark seems particularly apt when
applied to the study of politics in the United States. At the
heart of the American political tradition lies an acute ambiv-
alence concerning the nature and uses of political power.
Paths toward Democracy: The Working Class and Elites in Western Europe and Latin America. By Ruth Berins Collier. Cambridge: Cambridge University Press, 1999. 230p. $49.95 cloth, $17.95 paper.
Authors: Fishman Robert M.
Published: November 2002

Ruth Collier has written an important contribution to the
literatures on democracy and on labor, one that should
reorient much discussion and work on democratization.
Collier makes a powerful case that labor has been a far more
important and decisive actor in redemocratization than con-
ventionally thought, and her reconceptualization of the cases
on this basis yields an important new typology of regime
transitions. The book casts a wide empirical net, examining
the contribution of labor to the emergence of democracy in
numerous countries in both the Americas and Europe.
Exporting Environmentalism: U.S. Multinational Chemical Corporations in Brazil and Mexico. By Ronie Garcia-Johnson. Cambridge, MA: MIT Press, 2000. 282p. $20.00.
Authors: Carruthers David V.
Published: November 2002

As toxic pollutants and hazardous production emerged across
the twentieth century, first-world states came to play a
guardian role, imposing constraints on capital to safeguard
their workers, communities, and environments. As we enter
the new century, vigorous protest and debate over the
character and conditions of neoliberal globalization center on
whether or how to reaffirm or extend such protections in an
era of free trade, capital mobility, privatization, and deregu-
lation. From Rio to Seattle, Kyoto to Prague, controversy
arises over where the locus of authority for codes of corpo-
rate conduct might rest. Can states be redeemed as guardians
and still avert a destructive "race to the bottom"? Can
existing supranational bodies or regimes be charged with
design and enforcement of global standards, or are new
international institutions imperative? Dare we trust multina-
tional corporations (MNCs) to police themselves? What is
the proper role of advocacy networks and civic organiza-
tions?
Bargaining and Learning in Recurring Crises: The Soviet-American, Egyptian-Israeli, and Indo-Pakistani Rivalries. By Russell J. Leng. Ann Arbor: University of Michigan Press, 2000. 336p. $64.50 cloth, $24.95 paper.
Authors: Reiter Dan
Published: November 2002

In the past ten years there has been a burst of theoretical and
empirical research on the topic of learning in international
relations. Russell J. Leng's new book is the latest addition to
this body of scholarship, and it builds on his past research on
learning and crisis bargaining. Leng examines the role of
learning in crisis bargaining strategies within ongoing, inter-
national rivalries. He asks a series of questions, including: Do
patterns of crisis behavior repeat from one crisis to the next?
Presidents and Prime Ministers: Conviction Politics in the Anglo-American Tradition. By Patricia Lee Sykes. Lawrence: University of Kansas Press, 2000. 399p. $45.00.
Authors: Wayne Stephen J.
Published: November 2002

In the Stephen Skowronek tradition of leadership studies
(The Politics Presidents Make, 1993), Patricia Lee Sykes
makes an important substantive and methodological contri-
bution with her cross-national comparison of conviction
politicians in the United States and the United Kingdom. She
begins with a topology that dichotomizes two basic leadership
styles: conviction and consensus. She carefully defines these
on the basis of their goals and strategies and the external
conditions that facilitate them.
Studies of mitochondrial DNA, allozyme and morphometric variation in a house mouse hybrid zone
Authors: HAUFFE HEIDI C. , FRAGUEDAKIS-TSOLIS STELLA , MIROL PATRICIA M. , SEARLE JEREMY B.
Published: November 2002

An unusual chromosomal hybrid zone of the house mouse, Mus musculus domesticus, exists in Upper Valtellina, Northern Italy, consisting of four Robertsonian (Rb) races and the standard (all-acrocentric, or 2n = 40) race, all hybridizing freely within 10 km2. The hybrid zone in Valtellina provides an excellent opportunity to study the role of Rb fusions in reproductive isolation and speciation. This hybrid zone has already been well studied for the distribution of Rb fusions and the fertility of hybrids, but in order to understand the dynamics of the zone, a basic understanding of the origin and genetic similarity of the chromosomal races is necessary. This paper presents the results of three different methods of measuring genetic differentiation: multivariate analysis of morphological traits and analyses of allozyme variation and mitochondrial DNA sequences. The standard race is clearly distinguishable from the three Rb races by all three methods, but the Rb races are not distinguishable from one another. This provides strong evidence for our previous suggestions that the well-established Rb races in Valtellina are closely related, and that the standard race was introduced into the valley more recently from a distant source. The fact that the Rb races are indistinguishable is also consistent with our hypothesis that a within-village speciation event involving two of the races (Hauffe & Searle, 1992) was a recent occurrence. The low level of allozyme heterozygosity among the Rb races suggests that these populations are the products of at least one bottleneck. The present article substantially extends earlier studies and provides the first detailed morphological and molecular analysis of this complex hybrid zone.
Inbreeding depression and heterosis in a subdivided population: influence of the mating system
Authors: THEODOROU KONSTANTINOS , COUVET DENIS
Published: November 2002

We investigate the joint effects of gene flow and selfing on the level of inbreeding depression, heterosis and genetic load in a subdivided population at equilibrium. Low gene flow reduces inbreeding depression and substantially increases heterosis. However, in highly self-fertilizing populations, inbreeding depression is independent of the amount of gene flow. When migration occurs via pollen, consanguinity of the reproductive system could have a negative influence on subpopulation persistence, in contrast to the case of isolated populations. However, with only seed migration, genetic load and heterosis depend mildly on the mating system. From an evolutionary point of view, we reach two main conclusions: first, outcrossing is selected for if gene flow is low; second, intermediate levels of gene flow could promote mixed mating systems, especially when migration occurs through pollen.
The mutational rate of Drosophila viability decline: tinkering with old data
Authors: GARCÍA-DORADO A. , CABALLERO A.
Published: November 2002

In the first 25 generations of his classical mutation accumulation experiment, T. Mukai estimated a large rate of early linear decay for the relative viability of Drosophila melanogaster chromosome II (ΔMII = 0.004). Mukai forced through zero the regression of viability decline on generation number, but it has recently been shown (Fry, 2001) that a similar decline (ΔMII = 0.006) is obtained from unforced regression even if generation 32 instead of generation 25 (whose validity has been questioned) is included. We show that, from the perspective of the whole long-term experiment, it is hard to decide up to which generation viability can be considered to decline linearly. Depending on this decision, and on whether or not the regression is forced through the origin, very different estimates are obtained. Furthermore, the particular behaviour of the lines used as control suggests that they could have been different from the remaining lines at the beginning of the experiment, and casts doubts on the adequacy of a forced regression. Estimates from the linear unforced regression (ΔMII = 0.011) or from the linear term in a quadratic unforced regression (ΔMII = 0.001) are very different. The data fit both models very well, and the choice between them should be based on biological grounds.
QTL mapping for growth and carcass traits in an Iberian by Landrace pig intercross: additive, dominant and epistatic effects
Authors: VARONA L. , OVILO C. , CLOP A. , NOGUERA J. L. , PÉREZ-ENCISO M. , COLL A. , FOLCH J. M. , BARRAGÁN C. , TORO M. A. , BABOT D. , SÁNCHEZ A.
Published: November 2002

Results from a QTL experiment on growth and carcass traits in an experimental F2 cross between Iberian and Landrace pigs are reported. Phenotypic data for growth, length of carcass and muscle mass, fat deposition and carcass composition traits from 321 individuals corresponding to 58 families were recorded. Animals were genotyped for 92 markers covering the 18 porcine autosomes (SSC). The results from the genomic scan show genomewide significant QTL in SSC2 (longissimus muscle area and backfat thickness), SSC4 (length of carcass, backfat thickness, loin, shoulder and belly bacon weights) and SSC6 (longissimus muscle area, backfat thickness, loin, shoulder and belly bacon weights). Suggestive QTL were also found on SSC1, SSC5, SSC7, SSC8, SSC9, SSC13, SCC14, SSC16 and SSC17. A bidimensional genomic scan every 10 cM was performed to detect interaction between QTL. The joint action of two suggestive QTL in SSC2 and SSC17 led to a genome-wide significant effect in live weight. The results of the bidimensional genomic scan showed that the genetic architecture was mainly additive or the experimental set-up did not have enough power to detect epistatic interactions.
Nucleotide polymorphism at the Atmyb2 locus of the wild plant Arabidopsis thaliana
Authors: KAMIYA TAKU , KAWABE AKIRA , MIYASHITA NAOHIKO T.
Published: November 2002

DNA variation was studied in a 2.2 kb region of the regulatory gene Atmyb2 using 20 ecotypes of Arabidopsis thaliana and one accession each of Arabis gemmifera and Arabidopsis himalaica. Nucleotide diversity (π) in the region was 0.0027, which was lower than for other loci in A. thaliana. The MYB domain of the Atmyb2 gene (π = 0.0036) had a larger variation than the non-MYB region (π = 0.0013). Tajima's test and Fu and Li's test did not give a significant result. In contrast to the low level of polymorphism, the degree of divergence of the Atmyb2 region was higher between A. thaliana and A. gemmifera (K = 0.0730) than for other loci. The MYB domain (K = 0.0436) had smaller divergence than the non-MYB region (K = 0.0939). The HKA test detected significant discordance in the ratio of polymorphism to divergence in some comparisons. The pattern of low polymorphism and high divergence, which is mainly observed in the non-MYB region of the gene, is inconsistent with the neutral mutation theory. Strong purifying selection after establishment of A. thaliana and a species-specific adaptive process could be invoked to account for this pattern of polymorphism and divergence of Atmyb2.
Male age, host effects and the weak expression or non-expression of cytoplasmic incompatibility in Drosophila strains infected by maternally transmitted Wolbachia
Authors: REYNOLDS K. TRACY , HOFFMANN ARY A.
Published: November 2002

In Drosophila melanogaster, the maternally inherited endocellular microbe Wolbachia causes cytoplasmic incompatibility (CI) in crosses between infected males and uninfected females. CI results in a reduction in the number of eggs that hatch. The level of CI expression in this species has been reported as varying from partial (a few eggs fail to hatch) to nonexistent (all eggs hatch). We show that male age in this host species has a large impact on the level of CI exhibited and explains much of this variability. Strong CI is apparent when young males are used in crosses. CI declines rapidly with male age, particularly when males are repeatedly mated. Wolbachia from a Canton S line that was previously reported as not causing CI does in fact induce CI when young males are used in crosses, albeit at a weaker level than in other D. melanogaster strains. The strain differences in CI expression are due to host background effects rather than differences in Wolbachia strains. These results highlight the importance of undertaking crosses with a range of male ages and nuclear backgrounds before ascribing particular host phenotypes to Wolbachia strains.
Ottoman Guilds as a Setting for Ethno-Religious Conflict: The Case of the Silk-thread Spinners' Guild in Istanbul
Authors: Yildirim Onur
Published: November 2002

I and my son are bakers and barbers, you and your sons are lapidaries and gardeners, but if you bid one of your sons be barber, a second baker, a third lapidary and a fourth gardener, all is confusion, and how can good come out of it? Furthermore he is no barber nor baker who does not belong to the Guild of the Barbers and the Guild of the Bakers. If your son [does not go] to the peshkadim and rank himself among the apprentices; next to the tehaoosh, to bid him inscribe his name on the rolls; then to the kihaya, to pay him toll, how should he be a member of the guild? Ask of the scheikh if I have not spoken well.
Labour Strategies of Families: A Critical Assessment of an Appealing Concept
Authors: Engelen Theo
Published: November 2002

Phyllis Moen and Elaine Wethington were absolutely right when they called family strategies “the intuitively appealing metaphor for family response to structural barriers”. This appeal probably explains the avalanche of studies on the subject since the 1970s and especially since the 1980s. The last contribution, to my knowledge, is a collection of articles edited by Laurence Fontaine and Jurgen Schlumbohm in 2000. I will not even try to outline the vast historiography. This paper focuses on another problem. It is an attempt to show that concepts built on appealing metaphors lose much of their appeal in empirical research for the simple reason that their application tends to be more complicated than expected. In the following pages an example of such an experience is presented. Within the virtual walls of the Dutch National Research Institute for Economic and Social History, the N.W. Posthumus Institute, we have been struggling with family strategies since 1994. Now that we are about to publish the third volume on the subject, it is time to evaluate what we have accomplished.
The Challenge of Strategy: A Comment
Authors: Kok Jan
Published: November 2002

Is “strategy” merely a sympathetic and convenient phrase, on closer scrutiny devoid of explanatory value as a scientific concept? Have we been beguiled by its appeal and should we now, wiser and sadder, return to less pretentious concepts such as tactics or agency? Or do we need more empirical applications and have we just begun to explore strategy's vistas?
An experimental study on
hurricane mesovortices
Authors: MONTGOMERY MICHAEL T. , VLADIMIROV VLADIMIR A. , DENISSENKO PETR. V.
Published: November 2002

Mesovortices in the eyewall region of a hurricane are intriguing elements of the
hurricane engine. In-situ measurements of them are sparse, however, and our understanding of their overall role in the physics of a hurricane is incomplete. To further
understand their dynamics an experimental apparatus using a homogeneous fluid
(water) has been constructed to emulate the lower tropospheric flow of the hurricane
eye/eyewall region.

For experimental configurations possessing a central aspect ratio less than unity, a
primary and secondary circulation similar to the in flow layer of an intense hurricane,
and a similar radius-to-width ratio of the curvilinear shear layer bordering the eye and
eyewall region, the flow supports two primary quasi-steady vortices and secondary
intermittent vortices. The vortices form through Kelvin–Helmholtz instability of the
curvilinear shear layer bordering the slowly upwelling fluid in the centre and the converging fluid from the periphery. The primary vortices are maintained by convergence
of circulation from the periphery and merger of secondary vortices spawned along
the shear layer.

The horizontal flow field is measured using a particle image velocimeter. Despite
the relatively strong secondary circulation through the parent vortex the horizontal
flow is found to be approximately uniform in the direction parallel to the rotation
axis. The peak tangential velocity is found to occur in the mesovortices and is roughly
50% greater than the parent vortex that supports them. The measurements provide
insight into recent observations of excessive wind damage in landfalling storms and
support the hypothesis that intense storms contain coherent vortex structures in the
eyewall region with higher horizontal wind speeds locally than the parent hurricane.
Stability of thermal convection in two
superimposed miscible viscous fluids
Authors: LE BARS MICHAEL , DAVAILLE ANNE
Published: November 2002

The stability of two-layer thermal convection in high-Prandtl-number fluids is investigated using laboratory experiments and marginal stability analysis. The two fluids
have different densities and viscosities but there is no surface tension and chemical
diffusion at the interface is so slow that it is negligible. The density stratification
is stable. A wide range of viscosity and layer depth ratios is studied. The onset of
convection can be either stationary or oscillatory depending on the buoyancy number
B, the ratio of the stabilizing chemical density anomaly to the destabilizing thermal
density anomaly: when B is lower than a critical value (a function of the viscosity
and layer depth ratios), the oscillatory regime develops, with a deformed interface and
convective patterns oscillating over the whole tank depth; when B is larger than this
critical value, the stratified regime develops, with a flat interface and layers convecting
separately. Experiments agree well with the marginal stability results. At low Rayleigh
number, characteristic time and length scales are well-predicted by the linear theory.
At higher Rayleigh number, the linear theory still determines which convective regime
will start first, using local values of the Rayleigh and buoyancy numbers, and which
regime will persist, using global values of these parameters.
Chaotic dynamics in a strained rotating flow:
a precessing plane fluid layer
Authors: MASON R. M. , KERSWELL R. R.
Published: November 2002

The nonlinear dynamics exhibited by a planar layer of precessing fluid is examined
as a canonical example of a strained rotating flow. The simple basic flow, Ubasic =
−YXˆ+(X−2εZ)Yˆ
in a frame rotating at εXˆ, consists of sheared circular streamlines
(where ε measures the shearing) which are linearly unstable through the pairwise
resonance of two inertial waves in a fashion similar to elliptical flow. Direct numerical
simulation shows that the weakly nonlinear regime is quickly disrupted by further
instabilities which lead to a multitude of co-existing solution branches, some of which
represent chaotic flows. All these solutions remain within O(ε) (in an energy norm) of
Ubasic so that energy is not apparently withdrawn from the fluid's underlying rotation.
Further increases in the precession rate cause the flow to branch-switch randomly
between these now quasi-stable states so that a new form of ‘slow’ dynamics emerges.
The implication of this and the fact that these instabilities can nevertheless be classed
as ‘strong’ is discussed from the perspective of the closely related problem of the
precessing Earth and laboratory models thereof.
Downstream evolution of unconfined vortices:
mechanical and thermal aspects
Authors: PÉREZ-SABORID M. , HERRADA M. A. , GÓMEZ-BAREA A. , BARRERO A.
Published: November 2002

We present a numerical study of the downstream evolution (mechanical and thermal)
of vortex-jet cores whose velocity and temperature fields far from the axis match a
family of inviscid and non-conducting vortices. The far-velocity field is rotational,
except for a particular case which corresponds to the well-known Long's vortex. The
evolution of the vortex core depends on both the conditions at a certain upstream
station, characterized by the dimensionless value of the velocity at the axis, and a
dimensionless swirling parameter L defined as the ratio of the values of the azimuthal
and axial velocities outside the vortex core. This numerical study, based on the
quasi-cylindrical approximation (QC) of the Navier–Stokes equations, determines the
conditions under which the vortex evolution proceeds smoothly, eventually reaching
an asymptotic self-similar behaviour as described in the literature (Fernández-Feria,
Fernández de la Mora & Barrero 1995; Herrada, Pérez-Saborid & Barrero 1999),
or breaks in a non-slender solution (vortex breakdown). In particular, the critical
value L = Lb(a) beyond which vortex breakdown occurs downstream is a function
of a dimensionless parameter a characterizing the axial momentum of the vortex
jet at an initial upstream station. It is found numerically that for very large values
of a this vortex breakdown criterion tends to an asymptote which is precisely the
value L = L* predicted by the self-similar analysis, and beyond which a self-similar
structure of the vortex core does not exist. In addition, the computation of the total
temperature field provides useful information on the physical mechanisms responsible
for the thermal separation phenomenon observed in Ranque–Hilsch tubes and other
swirling jet devices. In particular, the mechanical work of viscous forces which gives
rise to an intense loss of kinetic energy during the initial stages of the evolution has
been identified as the physical mechanism responsible for thermal separation.
Fluid–structure interactions of a torsion spring
pendulum at large initial amplitudes
Authors: DÜTSCH H. , DURST F. , MELLING A.
Published: November 2002

The motion of a lamina of high aspect ratio suspended in a Newtonian fluid was studied experimentally and numerically. The damped oscillations for one rotational degree
of freedom showed strong nonlinear fluid–structure interactions, mainly caused by
the vortex structures forming at the lamina tips. The numerical results were obtained
by a fully implicit Navier–Stokes solver, using partitioned coupling of the equations
of motion of the fluid and suspended structure. Computations were carried out for
different grid levels and time steps, providing information on the accuracy of the numerical results. For the fluid domain, a Langrangian–Eulerian finite-volume method
was applied in order to solve the two-dimensional Navier–Stokes equation on grids
moving with the oscillating lamina. The elastic motion of the lamina was computed
as that of a torsion spring pendulum. The computed time traces of the angular position are in close agreement with corresponding experimental results. An equivalent
empirical model which accounted for the fluid moments by empirical coefficients was
much less successful in predicting the experimentally observed behaviour.
Slow mixed convection in rectangular containers
Authors: SHANKAR P. N. , MELESHKO V. V. , NIKIFOROVICH E. I.
Published: November 2002

We consider the slow motion of viscous fluid completely filling a rectangular container.
The motion is generated by the combined action of differential wall temperatures and
the linear motion of the lid. If the relevant Reynolds and Péclet numbers and the lid
speed are all small enough, the velocity field will be governed by an inhomogeneous
biharmonic equation. In this approximation the temperature field, unaffected by the
fluid motion, drives, at least in part, the fluid velocity field. Of interest here are
the relative effects of buoyancy and lid motion. It is shown that the field, suitably
scaled, depends on the dimensionless depth and lid speed alone. The mixed convection
problem is solved for two pairs of wall heating protocols by sequentially solving, by
an eigenfunction expansion method, up to four biharmonic problems. We present
streamline patterns and quantitative data on the relative effects of lid motion on the
buoyancy-driven fields in these containers.
The mixing in a room by a localized
finite-mass-flux source of buoyancy
Authors: CAULFIELD C. P. , WOODS ANDREW W.
Published: November 2002

The mixing produced by a turbulent buoyant plume with finite mass flux in a
room is examined analytically and numerically. The entrainment of ambient fluid
into the ascending buoyant plume leads to a return flow in the room which carries
fluid downwards from the top of the room. The cycling of ambient fluid through
the buoyant plume and the return flow causes the density to become uniform and
gradually evolve towards that of the source fluid. As a result the buoyancy flux
associated with the input fluid decreases and the plume motion becomes dominated
by the source momentum flux. We develop an asymptotic model of the mixing using
buoyant plume theory for a momentum-dominated flow. This provides an analytical
description of the evolution of the density in the room which is in excellent accord with
a full numerical simulation, and provides an improved description of the experimental
filling-box data originally presented by Baines & Turner (1969).
Sound generation by a two-dimensional circular
cylinder in a uniform flow
Authors: INOUE OSAMU , HATAKEYAMA NOZOMU
Published: November 2002

The sound generated by a circular cylinder in a flow at low Mach numbers is
investigated by direct solution of the two-dimensional unsteady compressible Navier–Stokes equations. Results show that sound pressure waves are generated primarily
by vortex shedding from the cylinder surface into its wake. When a vortex is shed
from one side of the cylinder, a negative pressure pulse is generated from that side
whereas a positive pressure pulse is generated from the other side; alternate vortex
shedding from the upper and lower sides of the cylinder produces negative and
positive pulses alternately and thus produces sound pressure waves on both sides.
The dipolar nature of the generated sound is confirmed; lift dipole dominates the
sound field. The Doppler effect is shown to play an important role at finite Mach
numbers. The direct solutions are also compared with the solutions obtained by
Curle's acoustic analogy. The results show that Curle's solution describes well not
only the generation mechanism of the sound but also the propagation process if we
take the Doppler effect into consideration.
Magnetohydrodynamic flow in the liquid phase
for a specific pool boiling scenario
Authors: BÜHLER LEO
Published: November 2002

In the EVOLVE concept for a nuclear fusion blanket a pool boiling scenario has been
proposed where a number of permanent vertical vapour channels are formed in a
horizontal layer of liquid lithium. Similar situations occur during laser beam welding
where a relatively long vapour capillary is observed. The present analysis focuses
on the flow of the electrically conducting liquid phase in the presence of a strong
uniform horizontal magnetic field. The cross-section of vapour channels is circular if
surface tension dominates magnetic forces. In the opposite case a stretching of the
liquid–vapour interface along magnetic field lines is observed and contours become
possible where a major part of the interface is straight and aligned with the field. For
strong magnetic fields the liquid flow exhibits several distinct subregions. Most of the
liquid domain is occupied by inviscid cores. These are separated from each other by
parallel layers that spread along the field lines which are tangential to the vapour
channel. In one core, which is located between two parallel layers, the flow direction
is preferentially oriented along magnetic field lines, while in the other cores the flow
is perpendicular to the field.
Nonlinear geostrophic adjustment in the
presence of a boundary
Authors: REZNIK G. M. , GRIMSHAW R.
Published: November 2002

The process of nonlinear geostrophic adjustment in the presence of a boundary (i.e.
in a half-plane bounded by a rigid wall) is examined in the framework of a rotating
shallow water model, using an asymptotic multiple-time-scale theory based on the
assumed smallness of the Rossby number ε. The spatial scale is of the order of the
Rossby scale. Different initial states are considered: periodic, ‘step’-like, and localized.
In all cases the initial perturbation is split in a unique way into slow and fast
components evolving with characteristic time scales f−1 and (εf)−1, respectively. The
slow component is not influenced by the fast one, at least for times t [les ] (fε)−1, and
remains close to geostrophic balance. The fast component consists mainly of linear
inertia–gravity waves rapidly propagating outward from the initial disturbance and
Kelvin waves confined near the boundary.

The theory provides simple formulae allowing us to construct the initial profile of
the Kelvin wave, given arbitrary initial conditions. With increasing time, the Kelvin
wave profile gradually distorts due to nonlinear-wave self-interaction, the distortion
being described by the equation of a simple wave. The presence of Kelvin waves
does not prevent the fast–slow splitting, in spite of the fact that the frequency
gap between the Kelvin waves and slow motion is absent. The possibility of such
splitting is explained by the special structure of the Kelvin waves in each case
considered.

The slow motion on time scales t [les ] (εf)−1
is governed by the well-known quasigeostrophic potential vorticity equation for the elevation. The theory provides an
algorithm to determine initial slow and fast fields, and the boundary conditions to
any order in ε. For the periodic and step-like initial conditions, the slow component
behaves in the usual way, conserving mass, energy and enstrophy. In the case of a
localized initial disturbance the total mass of the lowest-order slow component is
not conserved, and conservation of the total mass is provided by the first-order slow
correction and the Kelvin wave.

On longer time scales t [les ] (ε2f)−1
the slow motion obeys the so-called modified
quasi-geostrophic potential vorticity (QGPV) equation. The theory provides initial
and boundary conditions for this equation. This modified equation coincides exactly
with the ‘improved’ QGPV equation, derived by Reznik, Zeitlin & Ben Jelloul (2001),
in the step-like and localized cases. In the periodic case this equation contains an
additional term due to the Kelvin-wave self-interaction, this term depending on the
initial Kelvin wave profile.
On the persistence of trailing vortices
Authors: JACQUIN LAURENT , PANTANO CARLOS
Published: November 2002

The short-wave stability properties of a Batchelor vortex are used to explain the intrinsic resistance of vortices to turbulent diffusion. We show that turbulence produced
within the vortex core has to overcome a stabilizing ‘dispersion buffer’, where energy
of the perturbations is dispersed by inertial waves without interfering with the mean
flow, before they can reach the periphery of the vortex. While angular momentum
is maintained by this mechanism, the difference in energy extraction by turbulence
from the axial and tangential velocity fields due to a lack of alignment between the
mean and turbulent strain tensors, a typical effect of flow rotation or curvature, leads
to stabilization through a progressive damping of the axial shear in the vortex core.
We show that the efficiency of these stabilizing mechanisms depends on the swirl
number, the ratio between the maximum tangential velocity and the axial velocity
difference. If the swirl parameter is low enough, turbulence is able to reach the vortex
periphery and a small circulation overshoot develops, leading to weak diffusion of
angular momentum outward.
Direct numerical simulation of a separated
turbulent boundary layer
Authors: SKOTE MARTIN , HENNINGSON DAN S.
Published: November 2002

Direct numerical simulation of two turbulent boundary layer flows has been performed. The boundary layers are both subject to a strong adverse pressure gradient.
In one case a separation bubble is created while in the other the boundary layer is
everywhere attached. The data from the simulations are used to investigate scaling
laws near the wall, a crucial concept in turbulence models. Theoretical work concerning the inner region in a boundary layer under an adverse pressure gradient is
reviewed and extended to the case of separation. Excellent agreement between theory
and data from the direct numerical simulation is found in the viscous sub-layer, while
a qualitative agreement is obtained for the overlap region.
Theoretical predictions for the elliptical
instability in a two-vortex flow
Authors: LE DIZÈS STÉPHANE , LAPORTE FLORENT
Published: November 2002

Two parallel Gaussian vortices of circulations Γ1 and Γ2
radii a1 and a2, separated
by a distance b may become unstable by the elliptical instability due the elliptic
deformation of their cores. The goal of the paper is to analyse this occurrence
theoretically in a general framework. An explicit formula for the temporal growth
rate of the elliptical instability in each vortex is obtained as a function of the
above global parameters of the system, the Reynolds number Γ1/v
and the non-dimensionalized axial wavenumber kzb of the perturbation. This formula is based on
a known asymptotic expression for the local instability growth rate at an elliptical
stagnation point which depends on the local characteristics of the elliptical flow and
the inclination angle of the local perturbation wavevector at this point. The elliptical
flow characteristics are estimated by considering each Gaussian vortex alone in a
weak uniform external strain field whose properties are provided by a point vortex
modelling of the vortex pair. The inclination angle is obtained from the dispersion
relation for the Gaussian vortex normal modes and the local expression near each
vortex centre for the two helical modes of azimuthal wavenumber m = 1 and m = −1
which constitute the elliptical instability global mode. Both the final formula and
the hypotheses made for its derivation are tested and validated by direct numerical
simulations and large-eddy simulations.