bluuebunny/crossref_metadata_2025 huggingface dataset:
A critical appraisal of propensity‐score matching in the medical literature between 1996 and 2003
Authors: Austin Peter C.
Published: November 2007

Propensity‐score methods are increasingly being used to reduce the impact of treatment‐selection bias in the estimation of treatment effects using observational data. Commonly used propensity‐score methods include covariate adjustment using the propensity score, stratification on the propensity score, and propensity‐score matching. Empirical and theoretical research has demonstrated that matching on the propensity score eliminates a greater proportion of baseline differences between treated and untreated subjects than does stratification on the propensity score. However, the analysis of propensity‐score‐matched samples requires statistical methods appropriate for matched‐pairs data. We critically evaluated 47 articles that were published between 1996 and 2003 in the medical literature and that employed propensity‐score matching. We found that only two of the articles reported the balance of baseline characteristics between treated and untreated subjects in the matched sample and used correct statistical methods to assess the degree of imbalance. Thirteen (28 per cent) of the articles explicitly used statistical methods appropriate for the analysis of matched data when estimating the treatment effect and its statistical significance. Common errors included using the log‐rank test to compare Kaplan–Meier survival curves in the matched sample, using Cox regression, logistic regression, chi‐squared tests, t‐tests, and Wilcoxon rank sum tests in the matched sample, thereby failing to account for the matched nature of the data. We provide guidelines for the analysis and reporting of studies that employ propensity‐score matching. Copyright © 2007 John Wiley & Sons, Ltd.
A likelihood reformulation method in non‐normal random effects models
Authors: Liu Lei , Yu Zhangsheng
Published: November 2007

In this paper, we propose a practical computational method to obtain the maximum likelihood estimates (MLE) for mixed models with non‐normal random effects. By simply multiplying and dividing a standard normal density, we reformulate the likelihood conditional on the non‐normal random effects to that conditional on the normal random effects. Gaussian quadrature technique, conveniently implemented in SAS Proc NLMIXED, can then be used to carry out the estimation process. Our method substantially reduces computational time, while yielding similar estimates to the probability integral transformation method (J. Comput. Graphical Stat.2006;15:39–57). Furthermore, our method can be applied to more general situations, e.g. finite mixture random effects or correlated random effects from Clayton copula. Simulations and applications are presented to illustrate our method. Copyright © 2007 John Wiley & Sons, Ltd.
A discrete‐continuous mixture quantile function estimator with a practical application to phase II cancer clinical trials
Authors: Hutson Alan D.
Published: November 2007

Oftentimes in biological and clinical settings an underlying continuous variable or discrete‐continuous mixture is dichotomized in order to interpret the results in a simpler fashion. Tests of interest are then typically based on exact binomial tests. In this article, we illustrate the utility of a new quantile‐based approach towards testing the same basic scientific question in terms of improved relative efficiency and similar ease of interpretation when compared with the binomial test. We illustrate the utility of our approach with an eye towards mixtures of discrete‐continuous data commonly found in phase II cancer clinical trial data. Copyright © 2007 John Wiley & Sons, Ltd.
Coating selection and tribological testing for engineering equipment applications
Authors: Franklin S.E.
Published: November 2007

This paper considers the process of selecting and testing coatings for parts in professional engineering equipment applications in relation to the needs of design engineers in industry and the practical issues encountered. A methodology for pre‐selection of potential coating solutions is discussed and consideration is given to the practical implementation of testing strategies in order to obtain results that are pertinent to the application. Two example case studies are described and the results are discussed in terms of their practical relevance and use. Copyright © 2007 John Wiley & Sons, Ltd.
Neurological implications of urea cycle disorders
Authors: Gropman A. L. , Summar M. , Leonard J. V.
Published: November 2007

The urea cycle disorders constitute a group of rare congenital disorders caused by a deficiency of the enzymes or transport proteins required to remove ammonia from the body. Via a series of biochemical steps, nitrogen, the waste product of protein metabolism, is removed from the blood and converted into urea. A consequence of these disorders is hyperammonaemia, resulting in central nervous system dysfunction with mental status changes, brain oedema, seizures, coma, and potentially death. Both acute and chronic hyperammonaemia result in alterations of neurotransmitter systems. In acute hyperammonaemia, activation of the NMDA receptor leads to excitotoxic cell death, changes in energy metabolism and alterations in protein expression of the astrocyte that affect volume regulation and contribute to oedema. Neuropathological evaluation demonstrates alterations in the astrocyte morphology. Imaging studies, in particular 1H MRS, can reveal markers of impaired metabolism such as elevations of glutamine and reduction of myoinositol. In contrast, chronic hyperammonaemia leads to adaptive responses in the NMDA receptor and impairments in the glutamate–nitric oxide–cGMP pathway, leading to alterations in cognition and learning. Therapy of acute hyperammonaemia has relied on ammonia‐lowering agents but in recent years there has been considerable interest in neuroprotective strategies. Recent studies have suggested restoration of learning abilities by pharmacological manipulation of brain cGMP with phosphodiesterase inhibitors. Thus, both strategies are intriguing areas for potential investigation in human urea cycle disorders.
Pattern of beverage consumption and long-term association with body-weight status in German adolescents – results from the DONALD study
Authors: Libuda Lars , Alexy Ute , Sichert-Hellert Wolfgang , Stehle Peter , Karaolis-Danckert Nadina , Buyken Anette E. , Kersting Mathilde
Published: November 2007

In the present study the relationship between the consumption of different beverage groups and body-weight status in 5 years of study participation in German adolescents was investigated. We used anthropometric and dietary data from 3 d weighed records of 244 subjects between 9 and 18 years of age participating in the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study. Only subjects with at least four out of six possible weighed dietary records were considered. A repeated-measures regression model (PROC MIXED) was used to analyse the effect of beverage consumption on body-weight status. BMI standard deviation scores (BMI-SDS) and body fat percentage (%BF) were chosen as the dependent variables. In boys, energetic beverage consumption was not associated with BMI-SDS or %BF, neither cross-sectionally nor prospectively. In girls, baseline consumption of energetic beverages did not predict baseline BMI-SDS, baseline %BF, or change in either variable over the study period. However, an increase in energetic beverage consumption over the study period was associated with an increase in BMI-SDS (+0.070 SDS/MJ increase in energetic beverage consumption; P = 0·01). Separate consideration of regular soft drinks and fruit juices revealed that, in girls, BMI-SDS increased with increased fruit juice consumption (+0·096 SDS/MJ increase in fruit juice consumption; P = 0·01), and to a lesser extent with regular soft drink consumption (+0·055 SDS/MJ increase in regular soft drink consumption; P = 0·08). In conclusion, these results suggest that an increase in energetic beverage consumption may result in weight gain, at least in adolescent girls.
OBITUARY
Authors: Anderson Ian
Published: November 2007

Daniel Martin B.Sc., M.A., Ph.D., F.R.S.E. was born in Carluke on 16 April 1915, the only child of William and Rose Martin (née Macpherson). The family home in which he was born, Cygnetbank in Clyde Street, had been remodelled and extended by his father, and it was to be Dan's home all his life. His father, who was a carpenter and joiner, had a business based in School Lane, but died as a result of a tragic accident when Dan was only six. Thereafter Dan was brought up single handedly by his mother.

After attending primary school in Carluke from 1920 to 1927, Dan entered the High School of Glasgow. It was during his third year there that he started studying calculus on his own. He became so enthused by the subject that he set his sights on a career teaching mathematics, at university if at all possible. On leaving school in 1932, he embarked on the M.A. honours course in Mathematics and Natural Philosophy at the University of Glasgow. At that time the Mathematics Department was under the leadership of Professor Thomas MacRobert; the honours course in Mathematics consisted mainly of geometry, calculus and analysis, and the combined honours M.A. with Natural Philosophy was the standard course for mathematicians. A highlight of his first session at university was attending a lecture on the origins of the general theory of relativity, given on 20th June 1933 by Albert Einstein. This was the first of a series of occasional lectures on the history of mathematics funded by the George A. Gibson Foundation which had been set up inmemory of the previous head of the Mathematics Department. From then on, relativity was to be one of Dan's great interests, lasting a lifetime; indeed, on holiday in Iona the year before he died, Dan's choice of holiday reading included three of Einstein's papers.
PBW THEOREMS AND FROBENIUS STRUCTURES FOR QUANTUM MATRICES
Authors: GAVARINI FABIO
Published: November 2007

Let $G \in \{{\it Mat}_n(\C), {GL}_n(\C), {SL}_n(\C)\}$, let $\Oqg$ be the quantum function algebra – over $\Z [q,q^{-1}]$ – associated to G, and let $\Oeg$ be the specialisation of the latter at a root of unity ϵ, whose order ℓ is odd. There is a quantum Frobenius morphism that embeds $\Og,$ the function algebra of G, in $\Oeg$ as a central Hopf subalgebra, so that $\Oeg$ is a module over $\Og$. When $G = {SL}_n(\C)$, it is known by [3], [4] that (the complexification of) such a module is free, with rank ℓdim(G). In this note we prove a PBW-like theorem for $\Oqg$, and we show that – when G is Matn or GLn – it yields explicit bases of $\Oeg $ over $ \Og$ over $\Og,$. As a direct application, we prove that $\Oegl$ and $\Oem$ are free Frobenius extensions over $\Ogl$ and $\Om$, thus extending some results of [5].
SPATIALLY NONDECAYING SOLUTIONS OF THE 2D NAVIER-STOKES EQUATION IN A STRIP
Authors: ZELIK SERGEY
Published: November 2007

The weighted energy theory for Navier-Stokes equations in 2D strips is developed. Based on this theory, the existence of a solution in the uniformly local phase space (without any spatial decaying assumptions), its uniqueness and the existence of a global attractor are verified. In particular, this phase space contains the 2D Poiseuille flows.
VOLUME INEQUALITIES FOR Lp-JOHN ELLIPSOIDS AND THEIR DUALS
Authors: FENGHONG LU , GANGSONG LENG
Published: November 2007

In this paper, we establish some inequalities among the Lp-centroid body, the Lp-polar projection body, the Lp-John ellipsoid and its dual, which are the strengthened version of known results. We also prove inequalities among the polar of the Lp-centroid body, the Lp-polar projection body, the Lp-John ellipsoid and its dual.
BIHARMONIC LAGRANGIAN SURFACES OF CONSTANT MEAN CURVATURE IN COMPLEX SPACE FORMS
Authors: SASAHARA TORU
Published: November 2007

Biharmonic Lagrangian surfaces of constant mean curvature in complex space forms are classified. A further important point is that new examples of marginally trapped biharmonic Lagrangian surfaces in an indefinite complex Euclidean plane are obtained. This fact suggests that Chen and Ishikawa's classification of marginally trapped biharmonic surfaces [6] is not complete.
Selection of promising genotypes based on path and cluster analyses
Authors: KOZAK M. , BOCIANOWSKI J. , RYBIŃSKI W.
Published: November 2007

The objective of the present paper was to propose a statistical approach to support selection of the most promising genotypes in a breeding programme. The approach is based on applying two state-of-the-art statistical methodologies, likelihood-based path analysis and model-based cluster analysis. The first method is applied to find a causal mechanism lying behind a biological process of development of final crop yield. These results are then used for weighting traits to be used in cluster analysis, which helps select genotypes possessing a desirable level of yield and yield-contributing traits. An application of the approach is presented for a 2-year study on 22 grasspea genotypes, two cultivars (Derek and Krab) and 20 mutants from those cultivars. Seed yield/plant and seven yield-related traits were studied. Among these, plant height, number of branches/plant, pod length and number of seeds/plant determined seed yield; number of pods/plant influenced seed yield only for 2002. These results were used for appropriate weighting in cluster analysis, which indicated that cultivar Krab and its two mutants, K3 and K64, had the best level of the traits and were the most stable genotypes.
The contribution of the gibberellin-insensitive semi-dwarfing (Rht) genes to genetic variation in wheat seedling growth in response to osmotic stress
Authors: LANDJEVA S. , KORZUN V. , STOIMENOVA E. , TRUBERG B. , GANEVA G. , BÖRNER A.
Published: November 2007

The effects of various gibberellin-insensitive semi-dwarfing (Rht) alleles and background genotypes on the growth response of wheat seedlings to simulated low water potential were investigated. Four sets of near-isogenic lines, each consisting of six members (Rht-B1a+Rht-D1a (rht), Rht-B1b, Rht-B1c, Rht-D1b, Rht-B1b+Rht-D1b and Rht-B1c+Rht-D1b), and one set of five members (rht, Rht-B1b, Rht-B1c, Rht-B1d and Rht-D1b) were germinated in the presence of polyethylene glycol (PEG). The growth responses were assessed by measuring the lengths of the longest root, coleoptile and longest leaf (shoot) and calculating the root length:shoot length ratio and a tolerance index (TI). Seedling growth was significantly affected by the allelic status at the Rht loci, background genes and the water potential. The PEG treatment had major effects on root and shoot growth. Coleoptile growth was mainly affected by the Rht alleles. There were significant interactions of the Rht allele and variety on the growth response to low water potential. Genotypes with longer roots, coleoptiles and shoots when grown in water, as determined by the Rht allelic status (rht, Rht-B1b and Rht-D1b) and varietal background, had the highest TI and maintained this advantage under stress, while genotypes with smaller seedlings (Rht-B1c and Rht-B1c+Rht-D1b) when grown in water were more strongly affected.
Transverse-jet shear-layer instabilities. Part 1. Experimental studies
Authors: MEGERIAN S. , DAVITIAN J. , DE B. ALVES L. S. , KARAGOZIAN A. R.
Published: November 2007

This study provides a detailed exploration of the near-field shear-layer instabilities associated with a gaseous jet injected normally into crossflow, also known as the transverse jet. Jet injection from nozzles which are flush as well as elevated with respect to the tunnel wall are explored experimentally in this study, for jet-to-crossflow velocity ratiosRin the range 1 ≲R≤ 10 and with jet Reynolds numbers of 2000 and 3000. The results indicate that the nature of the transverse jet instability is significantly different from that of the free jet, and that the instability changes in character as the crossflow velocity is increased. Dominant instability modes are observed to be strengthened, to move closer to the jet orifice, and to increase in frequency as crossflow velocity increases for the regime 3.5 <R≤ 10. The instabilities also exhibit mode shifting downstream along the jet shear layer for either nozzle configuration at these moderately high values ofR. WhenRis reduced below 3.5 in the flush injection experiments, single-mode instabilities are dramatically strengthened, forming almost immediately within the shear layer in addition to harmonic and subharmonic modes, without any evidence of mode shifting. Under these conditions, the dominant and initial mode frequencies tend to decrease with increasing crossflow. In contrast, the instabilities in the elevated jet experiments are weakened as R is reduced below about 4, probably owing to an increase in the vertical coflow magnitude exterior to the elevated nozzle, untilRfalls below 1.25, at which point the elevated jet instabilities become remarkably similar to those for the flush injected jet. Low-level jet forcing has no appreciable influence on the shear-layer response when these strong modes are present, in contrast to the significant influence of low-level forcing otherwise. These studies suggest profound differences in transverse-jet shear-layer instabilities, depending on the flow regime, and help to explain differences previously observed in transverse jets controlled by strong forcing.
Shear instability and coherent structures in shallow flow adjacent to a porous layer
Authors: WHITE BRIAN L. , NEPF HEIDI M.
Published: November 2007

Results are presented from an experimental study of shallow flow in a channel partially obstructed by an array of circular cylinders. The cylinder array is a model for emergent vegetation in an open channel, but also represents a simple sparse porous medium. A shear layer with regular vortex structures forms at the edge of the array, evolving downstream to an equilibrium width and vortex size. The vortices induce nearly periodic oscillations with a frequency that matches the most unstable linear mode for a parallel shear flow. The shear layer is asymmetric about the array interface and has a two-layer structure. An inner region of maximum shear near the interface contains a velocity inflection point and establishes the penetration of momentum into the array. An outer region, resembling a boundary layer, forms in the main channel, and establishes the scale of the vortices. The vortex structure, educed by conditional sampling, shows strong crossflows with sweeps from the main channel and ejections from the array, which create significant momentum and mass fluxes across the interface. The sweeps maintain the coherent structures by enhancing shear and energy production at the interface. A linear stability analysis is consistent with the experimental results and demonstrates that the instability is excited by the differential drag between the channel and the array.
Interaction of lithotripter shockwaves with single inertial cavitation bubbles
Authors: KLASEBOER EVERT , FONG SIEW WAN , TURANGAN CARY K. , KHOO BOO CHEONG , SZERI ANDREW J. , CALVISI MICHAEL L. , SANKIN GEORGY N. , ZHONG PEI
Published: November 2007

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillatingvs.non-oscillating) on the dynamics of the shockwave-bubble interaction are discussed.
Laminar flow in a two-dimensional plane channel with local pressure-dependent crossflow
Authors: HALDENWANG P.
Published: November 2007

Long ducts (or pipes) composed of transpiring (e.g. porous) walls are at the root of numerous industrial devices for species separation, as tangential filtration or membrane desalination. Similar configurations can also be involved in fluid supply systems, as irrigation or biological fluids in capillaries. A transverse leakage (or permeate flux), the strength of which is assumed to depend linearly on local pressure (as in Starling's law for capillary), takes place through permeable walls. All other dependences, as osmotic pressure or partial fouling due to polarization of species concentration, are neglected. To analyse this open problem we consider the simplest situation: the steady laminar flow in a two-dimensional channel composed of two symmetrical porous walls.

First, dimensional analysis helps us to determine the relevant parameters. We then revisit the Berman problem that considers a uniform crossflow (i.e. pressure-independent leakage). We expand the solution in a series of Rt, the transverse Reynolds number. We note this series has a rapid convergence in the considered range of Rt (i.e. Rt ≤ O(1)). A particular method of variable separation then allows us to derive from the Navier–Stokes equations two new ordinary differential equations (ODE), which correspond to first and second orders in the development in Rt, whereas the zero order recovers the Regirer linear theory. Finally, both new ODEs are used to study the occurrence of two undesirable events in the filtration process: axial flow exhaustion (AFE) and crossflow reversal (CFR). This study is compared with a numerical approach.
On the motion induced in a gas confined in a small-scale gap due to instantaneous boundary heating
Authors: MANELA A. , HADJICONSTANTINOU N. G.
Published: November 2007

We analyse the time response of a gas confined in a small-scale gap (of the order of or smaller than the mean free path) to an instantaneous jump in the temperature of its boundaries. The problem is formulated for a collisionless gas in the case where the relative temperature jump at each wall is small and independent of the other. An analytic solution for the probability density function is obtained and the respective hydrodynamic fields are calculated. It is found that the characteristic time scale for arriving at the new equilibrium state is of the order of several acoustic time scales (the ratio of the gap width to the most probable molecular speed of gas molecules). The results are compared with direct Monte Carlo simulations of the Boltzmann equation and good agreement is found for non-dimensional times (scaled by the acoustic time) not exceeding the system Knudsen number. Thus, the present analysis describes the early-time behaviour of systems of arbitrary size and may be useful for prescribing the initial system behaviour in counterpart continuum-limit analyses.
Contour dynamics in complex domains
Authors: CROWDY DARREN , SURANA AMIT
Published: November 2007

This paper demonstrates that there is a contour dynamics formulation for the evolution of uniform vortex patches in any finitely connected planar domain bounded by impenetrable walls. A general numerical scheme is presented based on this formulation. The algorithm makes use of conformal mappings and follows the evolution of a conformal pre-image of a given vortex patch in a canonical multiply connected circular pre-image region. The evolution of vortex patches can be computed given just the conformal map from this pre-image region to the physical fluid region. The efficacy of the scheme is demonstrated by illustrative examples.
The surface-tension-driven evolution of a two-dimensional annular viscous tube
Authors: GRIFFITHS I. M. , HOWELL P. D.
Published: November 2007

We consider the evolution of an annular two-dimensional region occupied by viscous fluid driven by surface tension and applied pressure at the free surfaces. We assume that the thickness of the domain is small compared with its circumference, so that it may be described as a thin viscous sheet whose ends are joined to form a closed loop. Analytical and numerical solutions of the resulting model are obtained and we show that it is well posed whether run forwards or backwards in time. This enables us to determine, in many cases explicitly, which initial shapes will evolve into a desired final shape. We also show how the application of an internal pressure may be used to control the evolution.

This work is motivated by the production of non-axisymmetric capillary tubing via the Vello process. Molten glass is fed through a die and drawn off vertically, while the shape of the cross-section evolves under surface tension and any applied pressure as it flows downstream. Here the goal is to determine the die shape required to achieve a given desired final shape, typically square or rectangular. We conclude by discussing the role of our two-dimensional model in describing the three-dimensional tube-drawing process.
Normal modes of a rectangular tank with corrugated bottom
Authors: HOWARD LOUIS N. , YU JIE
Published: November 2007

We study some effects of regular bottom corrugations on water waves in a long rectangular tank with vertical endwalls and open top. In particular, we consider motions which are normal modes of oscillation in such a tank. Attention is focused on the modes whose internodal spacing, in the absence of corrugations, would be near the wavelength of the corrugations. In these cases, the perturbation of the eigenfunctions (though not of their frequencies) can be significant, e.g. the amplitude of the eigenfunction can be greater by a factor of ten or more near one end of the tank than at the other end. This is due to a cooperative effect of the corrugations, called Bragg resonance. We first study these effects using an asymptotic theory, which assumes that the bottom corrugations are of small amplitude and that the motions are slowly varying everywhere. We then present an exact theory, utilizing continued fractions. This allows us to deal with the rapidly varying components of the flow. The exact theory confirms the essential correctness of the asymptotic results for the slowly varying aspects of the motions. The rapidly varying parts (evanescent waves) are, however, needed to satisfy accurately the true boundary conditions, hence of importance to the flow near the endwalls.
Weak compressibility of surface wave turbulence
Authors: VUCELJA MARIJA , FOUXON ITZHAK
Published: November 2007

We study the growth of small-scale inhomogeneities in the density of particles floating in weakly nonlinear small-amplitude surface waves. Despite the small amplitude, the accumulated effect of the long-time evolution may produce a strongly inhomogeneous distribution of the floaters: density fluctuations grow exponentially with a small but finite exponent. We show that the exponent is of sixth or higher order in wave amplitude. As a result, the inhomogeneities do not form within typical time scales of the natural environment. We conclude that the turbulence of surface waves is weakly compressible and alone it cannot be a realistic mechanism of the clustering of matter on liquid surfaces.
Reflecting tidal wave beams and local generation of solitary waves in the ocean thermocline
Authors: AKYLAS T. R. , GRIMSHAW R. H. J. , CLARKE S. R. , TABAEI ALI
Published: November 2007

It is generally accepted that ocean internal solitary waves can arise from the interaction of the barotropic tide with the continental shelf, which generates an internal tide that in turn steepens and forms solitary waves as it propagates shorewards. Some field observations, however, reveal large-amplitude internal solitary waves in deep water, hundreds of kilometres away from the continental shelf, suggesting an alternative generation mechanism: tidal flow over steep topography forces a propagating beam of internal tidal wave energy which impacts the thermocline at a considerable distance from the forcing site and gives rise to internal solitary waves there. Motivated by this possibility, a simple nonlinear long-wave model is proposed for the interaction of a tidal wave beam with the thermocline and the ensuing local generation of solitary waves. The thermocline is modelled as a density jump across the interface of a shallow homogeneous fluid layer on top of a deep uniformly stratified fluid, and a finite-amplitude propagating internal wave beam of tidal frequency in the lower fluid is assumed to be incident and reflected at the interface. The induced weakly nonlinear long-wave disturbance on the interface is governed in the far field by an integral-differential equation which accounts for nonlinear and dispersive effects as well as energy loss owing to radiation into the lower fluid. Depending on the strength of the thermocline and the intensity of the incident beam, nonlinear wave steepening can overcome radiation damping so a series of solitary waves may arise in the thermocline. Sample numerical solutions of the governing evolution equation suggest that this mechanism is quite robust for typical oceanic conditions.
The origin of the stationary frontal wave packet spontaneously generated in rotating stratified vortex dipoles
Authors: VIÚDEZ ÁLVARO
Published: November 2007

The origin of the stationary frontal wave packet spontaneously generated in rotating and stably stratified vortex dipoles is investigated through high-resolution three-dimensional numerical simulations of non-hydrostatic volume-preserving flow under the f-plane and Boussinesq approximations. The wave packet is rendered better at mid-depths using ageostrophic quantities like the vertical velocity or the vertical shear of the ageostrophic vertical vorticity. The analysis of the origin of vertical velocity anomalies in shallow layers using the generalized omega-equation reveals that these anomalies are related to the material rate of change of the ageostrophic differential vorticity, which in shallow layers are themselves related to the large-scale ageostrophic flow along the dipole axis, and in particular, to the advective acceleration. It is found that on the anticyclonic side of the dipole axis the combined effect of the speed and centripetal accelerations causes an anticyclonic rotation of the horizontal ageostrophic vorticity vector in a time scale of about one inertial period. These facts support the hypothesis that the origin of the stationary and spontaneously generated frontal wave packet at mid-depths is the large acceleration of the fluid particles as they move along the anticyclonic side of the dipole axis in shallow layers.
Aerobreakup in disturbed subsonic and supersonic flow fields
Authors: THEOFANOUS T. G. , LI G. J. , DINH T. N. , CHANG C.-H.
Published: November 2007

This work concerns the breakup of millimetre-scale liquid droplets in gaseous flow fields that are disturbed from free-stream conditions by the presence of solid obstacles or other drops. A broad range of flow conditions is considered – from subsonic to supersonic, from highly rarefied to ambient pressures, and from fixed cylindrical obstacles to free liquid droplets (as obstacles). The liquid is water or tributyl phosphate, a water-like low-viscosity fluid of very low vapour pressure. We present data on deformation and breakup regimes, and, aided by numerical simulations, we discuss governing mechanisms and the time scaling of these events. Thereby a methodology is demonstrated for conveniently forecasting first-order behaviours in disturbed flow fields more generally. The highly resolved images lend themselves to testing/benchmarking numerical simulations of interfacial flows. These results, along with the experimental capability developed, constitute one of the key building blocks for our overall long-term aim towards predicting ultimate particle-size distributions from such intense aerodynamic interactions involving very large quantities of Newtonian and viscoelastic liquids.
The rise of Newtonian drops in a nematic liquid crystal
Authors: ZHOU CHUNFENG , YUE PENGTAO , FENG JAMES J.
Published: November 2007

We simulate the rise of Newtonian drops in a nematic liquid crystal parallel to the far-field molecular orientation. The moving interface is computed in a diffuse-interface framework, and the anisotropic rheology of the liquid crystal is represented by the Leslie–Ericksen theory, regularized to permit topological defects. Results reveal interesting coupling between the flow field and the orientational field surrounding the drop, especially the defect configuration. The flow generally sweeps the point and ring defects downstream, and may transform a ring defect into a point defect. The stability of these defects and their transformation are depicted in a phase diagram in terms of the Ericksen number and the ratio between surface anchoring and bulk elastic energies. The nematic orientation affects the flow field in return. Drops with planar anchoring on the surface rise faster than those with homeotropic anchoring, and the former features a vortex ring in the wake. These are attributed to the viscous anisotropy of the nematic. With homeotropic anchoring, the drop rising velocity experiences an overshoot, owing to the transformation of the initial surface ring defect to a satellite point defect. With both types of anchoring, the drag coefficient of the drop decreases with increasing Ericksen number as the flow-alignment of the nematic orientation reduces the effective viscosity of the liquid crystal.
On the turbulence structure in inert and reacting compressible mixing layers
Authors: MAHLE INGA , FOYSI HOLGER , SARKAR SUTANU , FRIEDRICH RAINER
Published: November 2007

Direct numerical simulation is used to investigate effects of heat release and compressibility on mixing-layer turbulence during a period of self-similarity. Temporally evolving mixing layers are analysed at convective Mach numbers between 0.15 and 1.1 and in a Reynolds number range of 15000 to 35000 based on vorticity thickness. The turbulence inhibiting effects of heat release are traced back to mean density variations using an analysis of the fluctuating pressure field based on a Green's function.
Linear and nonlinear decay of cat's eyes in two-dimensional vortices, and the link to Landau poles
Authors: TURNER M. R. , GILBERT ANDREW D.
Published: November 2007

This paper considers the evolution of smooth, two-dimensional vortices subject to a rotating external strain field, which generates regions of recirculating, cat's eye stream line topology within a vortex. When the external strain field is smoothly switched off, the cat's eyes may persist, or they may disappear as the vortex relaxes back to axisymmetry. A numerical study obtains criteria for the persistence of cat's eyes as a function of the strength and time scale of the imposed strain field, for a Gaussian vortex profile.

In the limit of a weak external strain field and high Reynolds number, the disturbance decays exponentially, with a rate that is linked to a Landau pole of the linear inviscid problem. For stronger strain fields, but not strong enough to give persistent cat's eyes, the exponential decay of the disturbance varies: as time increases the decay slows down, because of the nonlinear feedback on the mean profile of the vortex. This is confirmed by determining the decay rate given by the Landau pole for these modified profiles. For strain fields strong enough to generate persistent cat's eyes, their location and rotation rate are determined for a range of angular velocities of the external strain field, and are again linked to Landau poles of the mean profiles, modified through nonlinear effects.
Spontaneous cervical surgical emphysema following childbirth
Authors: Mylvaganam S , Hobbs C G L
Published: November 2007

Objective:

We report a case of post-partum surgical cervical emphysema, which is a rare but well recognised complication of labour. By reporting the first case in the ENT literature, we aim to raise awareness of this complication, particularly amongst trainees, to ensure that patients are managed most appropriately.

Case report:

A 36-year-old, primigravida woman developed neck swelling and odynophagia post-partum. Surgical cervical emphysema was palpated, with further examination excluding pneumomediastinum and pneumothorax. The patient was managed conservatively, with complete resolution of symptoms within a week.

Conclusions:

Surgical cervical emphysema, pneumothorax and pneumomediastinum are all well recognised post-partum complications. The vast majority of cases do not present with respiratory or cardiac compromise and can be appropriately managed conservatively, with expectation of resolution in a fortnight. There is no evidence that such patients are at increased risk during subsequent pregnancies.
Public disclosure of industrial pollution: the PROPER approach for Indonesia?
Authors: GARCÍA JORGE H. , STERNER THOMAS , AFSAH SHAKEB
Published: November 2007

This paper evaluates the effectiveness of the Program for Pollution Control Evaluation and Rating (PROPER) in Indonesia. PROPER, the first major public disclosure program in the developing world, was launched in June 1995; though it collapsed in 1998 with the Asian financial crisis, it is currently being revived. There have been claims of success for this pioneering scheme, yet little formal and conclusive analysis has been undertaken. We analyze changes in emissions concentrations (mg/L) using panel data techniques with plant-level data for participating firms and a control group. The results show that there was indeed a positive response to PROPER, especially among firms with poor environmental compliance records. The response was immediate, and firms pursued further emissions reductions in the following months. The total estimated reductions in biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were approximately 32 per cent.
Fuel choices in urban Indian households
Authors: FARSI MEHDI , FILIPPINI MASSIMO , PACHAURI SHONALI
Published: November 2007

This paper applies an ordered discrete choice framework to model fuel choices and patterns of cooking fuel use in urban Indian households. The choices considered are for three main cooking fuels: firewood, kerosene, and LPG (liquid petroleum gas). The models, estimated using a large microeconomic dataset, show a reasonably good performance in the prediction of households’ primary and secondary fuel choices. This suggests that ordered models can be used to analyze multiple fuel use patterns in the Indian context. The results show that lack of sufficient income is one of the main factors that retard households from using cleaner fuels, which usually also require the purchase of relatively expensive equipments. The results also indicate that households are sensitive to LPG prices. In addition to income and price, several socio-demographic factors such as education and sex of the head of the household are also found to be important in determining household fuel choice.
Farmer willingness to pay for seed-related information: rice varieties in Nigeria and Benin
Authors: HORNA J. DANIELA , SMALE MELINDA , OPPEN MATTHIAS VON
Published: November 2007

This study examines farmers’ preferences for seed of new rice varieties (improved and NERICA) and their willingness to pay (WTP) for information embodied in the seed, in villages of Nigeria and Benin. Information might not generate rivalry among its users but excludability is certainly a characteristic of information and its delivery can generate incentives for private participation. Conjoint utility analysis is used to estimate the structure of farmers’ preferences for rice seed. Farmers prefer one variety based on the utility they obtain from its attributes, which depends on their own social and economic characteristics. Contingent methods are used to elicit preferences and rice seed price. The marginal values of attributes are estimated with an ordered probit regression. The WTP for seed-related information is derived from the utility model. The results have implications for the best way to finance extension services in the areas of intervention, particularly for new rice varieties.
Optimal time for investment to regulate emissions of particulate matter in Indian thermal power plants
Authors: SENGUPTA ISHITA
Published: November 2007

This study aims to find the optimal switching point for the Indian coal-based power plants to switch to a cost-effective technology and reduce particulate emissions. Regulation in the form of an emission standard, an emissions tax, an ash tax, or a coal tax provides an incentive for the power plants to abate. We have taken a period of 40 years to show the pattern of abatement in a sample of 40 power plants. Linear programming using GAMS has been used for the analysis to determine when the plants will shift to cost-efficient technology. We have first done the analysis on a firm-to-firm basis and then we have aggregated to show the variability of our results.
Teleseismic P wave imaging of the 26 December 2004 Sumatra‐Andaman and 28 March 2005 Sumatra earthquake ruptures using the Hi‐net array
Authors: Ishii Miaki , Shearer Peter M. , Houston Heidi , Vidale John E.
Published: November 2007

Seismograms from a dense, high‐quality seismic network in Japan are used to investigate the characteristics of the 26 December 2004 Sumatra‐Andaman and the 28 March 2005 Sumatran earthquakes. The onset of the P waveforms are aligned through cross correlation, and a simple concept of back‐projecting seismic energy to a grid of potential source locations is applied. The waveform alignment removes the effects due to lateral variations in wave speed between the hypocenter and each station. To better approximate the effects of three‐dimensional heterogeneity for paths originating from grid points away from the hypocenter, cross‐correlation results of the P waveforms from aftershocks are introduced. This additional information leads to improved resolution of smaller‐scale features near many of the aftershocks by reducing wavefront distortion. The back‐projection analysis provides a quick assessment of the spatiotemporal extent and variability of relative high‐frequency energy release, which can be translated into an estimate of the moment magnitude, as well as an unparalleled view of high‐frequency rupture propagation. The results are, in general, consistent with those obtained from more involved source inversion methods. The 2004 Sumatra‐Andaman earthquake released most energy in a region northwest of the Sumatra island and the rupture extended to the northern Andaman islands, about 1300 km from the epicenter. This northern portion of the rupture radiated a considerable amount of energy, but there is little evidence of slow slip. The 2005 event is imaged to have bilateral rupture with northwestern slip occurring for about 50 s before it moved to the southeast of the epicenter.
Warm intrusions in the intermediate layer (150–500 m) of the Black Sea eastern gyre interior
Authors: Falina Anastasia , Sarafanov Artem , Volkov Igor
Published: November 2007

The new CTD data from the R/V Akvanavt 2002 cruise presented and discussed in this study, show that lateral limits of the Bosphorus lens penetration into the Black Sea interior are substantially wider than the earlier observed ones. The data reveal unexpectedly thick warm lenses in the 150–500 m depth range within the eastern gyre of the Black Sea. Thus, we provide observational evidence that the Bosphorus warm water penetration into the sea interior is not a local phenomenon confined to the southwestern and central parts of the western gyre (the intrusions have been previously observed only there), but rather a fundamental basin‐wide process determining the intermediate layer structure in the Black Sea, as was recently assumed on the basis of the numerical modeling results.
Dissolved methane distributions and air‐sea flux in the plume of a massive seep field, Coal Oil Point, California
Authors: Mau Susan , Valentine David L. , Clark Jordan F. , Reed Justin , Camilli Richard , Washburn Libe
Published: November 2007

Large quantities of natural gas are emitted from the seafloor into the stratified coastal ocean near Coal Oil Point, Santa Barbara Channel, California. Methane was quantified in the down current surface water at 79 stations in a 280 km2 study area. The methane plume spread over an area of ∼70 km2 and emitted on the order of 5 × 104 mol d−1 to the atmosphere. A monthly time series at 14 stations showed variable methane concentrations which were correlated with changing sub‐mesoscale surface currents. Air‐sea fluxes estimated from the time series indicate that the air‐sea flux derived for the 280 km2 area is representative of the daily mean flux from this area. Only 1% of the dissolved methane originating from Coal Oil Point enters the atmosphere within the study area. Most of it appears to be transported below the surface and oxidized by microbial activity.
Preliminary evaluation of the European Centre for Medium‐Range Weather Forecasts' (ECMWF) Nature Run over the tropical Atlantic and African monsoon region
Authors: Reale O. , Terry J. , Masutani M. , Andersson E. , Riishojgaard L. P. , Jusem J. C.
Published: November 2007

Meteorological observing systems are continuously being developed to improve our knowledge of the atmosphere and our forecasting capabilities. Observing System Simulation Experiments (OSSEs) are a general technique to assess a priori the potential impact of future instruments, which is particularly important in the case of spaceborne systems. One crucial component of OSSEs is the Nature Run (NR), representing a virtual atmosphere from which observations can be simulated so that the impact of future instruments can be assessed. A community‐based, 13‐month T511 NR was designed in an international collaborative effort and was produced by the European Centre for Medium‐Range Weather Forecasts (ECMWF) to build a next‐generation OSSE capability. This new Joint OSSE NR is being analyzed with emphasis on tropical development over the western African monsoon region and the tropical Atlantic. The NR representation of the African Easterly Jet and the characteristics of African Easterly Waves including their propagation and development in tropical‐cyclone like vortices are investigated. This is the first NR that encompasses one entire Atlantic tropical cyclone season producing realistic tropical cyclone activity. As such it is a valuable tool to perform OSSEs to assess the possible impact of future instruments targeting hurricanes.